12. Production of flat offset printing forms (features of the process, analog and digital technologies for manufacturing printing plates for flat offset printing).
13. Production of letterpress printing plates (process features, zincography, stages of manufacturing photopolymer printing plates).
This made it possible to isolate a whole group of diazoresins sensitive to the ultraviolet part of the spectrum. Layers based on diazoresin could be both positive and negative. Currently widely used in the manufacture of flat molds offset printing. One of the most common substances is orthonaphthoquinone diazide (OHCD).
e) A layer based on photopolymers. Layers based on photopolymers are widely used in the manufacture of letterpress printing plates, in particular flexo printing, as well as in computer technologies for the manufacture of printing plates. Polymers are sensitive to the ultraviolet part of the spectrum in the wavelength range of more than 320 nm. Glass and other materials, as a rule, do not transmit these wavelengths, so polymers have to be photoinitiated, i.e., their spectral sensitivity must be changed to another region of the spectrum. Modern photopolymers can be sensitive not only to the ultraviolet spectrum, but also to daylight, as well as to IR spectra.
The production of flat offset printing forms is carried out using analog and digital technologies. In analog technology, ready-made plates with a copy layer based on ONCD are used. The plate thickness is 0.3 mm. The thickness of the copy layer is 1.5–2 microns. The spectral sensitivity of the plate lies in the range of 320–450 nm, i.e., it covers, in addition to UV, also the visible part of the spectrum. Therefore, in the departments where the production of printing forms takes place, yellow lighting is mandatory.
A feature of the flat offset printing process is the use of mirror photoforms. Since the copying process is positive, mirror transparencies are used as photoforms. The mounting form is also made mirror.
The printable contains an image of the printed sheet. On the printed sheet, the stripes must be arranged in a certain sequence, and this sequence is determined by the imposition.
Imposition - the placement of strips on a printed sheet so that, as a result of printing and the subsequent operation of folding and collating the block, the correct page numbering in the publication is obtained.
After the assembly of photoforms is made, in accordance with the imposition and installation plan, technological holes (pin holes) are punched in the plate, then the plate is combined with the mounting of photoforms along the pins, and the exposure operation is performed in the copy frame.
After the production of the printed form, its quality control is carried out. Using a densitometer, the relative area of the raster elements on the printing plate is estimated. If there are foreign elements on the form (traces of dust, lint), they are removed using “-” pencils. If the amount of proofreading is significant, additional processing of the printing plate is carried out, starting from the washing stage. To increase the circulation resistance of finished forms, they are heat treated at a temperature of 180–210°C for 5 minutes in special ovens.
Historically, woodcut printing was the first technology for making letterpress plates. It was replaced in the 19th century by zincography, which lasted until the 1950s. 20th century Zincography is based on zinc plate plates, on which a layer based on chromic acid salts was deposited. As a result of exposure, a basis for printing elements was formed under the negative; after removing the rest of the layer, the form was subject to etching with HNO 3, i.e., metal sections were etched off, which served as gap elements. After stopping the etching process, the tanned areas of the copy layer were removed from the surface, freeing the printing elements of the form. One of the disadvantages of the method was the etching of zinc not only deep, but also lateral etching.
Zinc printing was replaced by photopolymer layers, which made it possible to produce letterpress forms without harmful chemical effects, and also led to the emergence of flexography. Currently, zinc plate manufacturing technologies are used only in finishing processes (foil stamping), since they allow printing runs of up to 1 million copies at high pressure. Classic letterpress printing has not been preserved almost anywhere at the present time, it has been replaced by flexo printing.
Flexo printing forms are made as follows:
Pre-exposure - allows you to form the level of whitespace elements.
Basic exposure - forms the image on the printed form.
Substrate exposure - allows you to form the basis of the printed form.
Processing - carried out with water, the remains of the photopolymer composition are removed from the surface of the blank elements.
Finishing - is done either mechanically or with a weak solution of perchloric acid to eliminate the stickiness of the printing plate.
Final exposure - allows you to significantly increase the circulation stability of the printing form.
Ministry of Education Russian Federation
Moscow State University printing
Specialty - Technology of printing production
Form of education - part-time
COURSE PROJECT
in the discipline "Technology of Form Processes"
the theme of the project is “Development of manufacturing technology
flat offset printing plates according to the scheme computer-printing form on photosensitive plates"
Student Molchanova Zh.M.
Course 4 group ZTpp 4-1 code pz004
Moscow 2014
Keywords Keywords: plate, printing plate, exposure, exposure device, recorder, laser, developing solution, polymerization, ablation, lineature, gradation characteristic.
Abstract text: in this course project, the choice of CtP technology for the manufacture of offset printing plates for the projected publication is carried out. The use of CtP technology makes it possible to significantly simplify the production process, reduce the production time for a set of printing plates, and significantly reduce the amount of equipment and material consumption.
Introduction
Technical characteristics and design indicators of the publication
Possible variant technological scheme edition
General information about flat offset printing forms
2 Varieties of Flat Offset Printing Forms
4 Plate classification for Computer-to-Plate technology
The choice of the designed technological mold process
The choice of the used form equipment and control and measuring equipment
Selection of the main materials of the plate process
Map of the designed mold process
Conclusion
Bibliography
Introduction
For the choice of printing plate technology, the main starting point is the characteristics of publications produced by a given printing house. I will consider a printing house that produces magazine products.
Recently, a new technology has been actively introduced into the printing industry, called computer-printing form (STR-technology). Its main feature is the receipt of ready-made printed forms without intermediate operations. The designer, having finished the layout, directs the image from the computer to the output device, which can be a printer, phototypesetter or a specialized device, and immediately receives a printed form.
Computer-to-Plate technology has been known to printers for about 30 years, but it began to develop actively only in recent years, due to the development of software, the creation of new plate materials on which direct laser writing is possible.
offset printing plate
1. Specifications of the selected edition
For the choice of printing plate technology, the main starting point is the characteristics of the publication being prepared for printing. In this term paper considers the development of technology for manufacturing printing plates for publication with the following characteristics:
Table 1 Characteristics of the planned edition
Index namePublication accepted for designingPublication typePublication format Edition format after trimming (mm)Format of stripes (square)9 1/3 × 1 3 1/4Volume of the publication in printed and accounting sheets, paper sheets, pages, Circulation, pp. ind.Colorfulness of the constituent elements of the edition of cover notebooks 4+4 4+4Nature of inline images raster (screen line 62 lines / cm) four-color Area of inline illustrations as a percentage of the entire volume60%Size of the main text 12 pTypeface of the main textPalladiumPrinting methodflat offsetType of paper used for printingcoatedType of printing inks for printingEuropean triadNumber of notebooks5Number of pages in one notebook16Method of folding in mutually perpendicular Way of stacking blocksselectionType of coversolid, glued to the block in a seamless adhesive way
2. Possible variant of the technological scheme for the production of the publication
3. General information about flat offset printing forms
1 Basic concepts of flat offset printing
Flat offset printing is the most widespread and progressive printing method. It's kind flat print, in which the ink from the printing plate is transferred first to an elastic intermediate carrier - a rubber-fabric cloth, and then to the printed material.
Flat offset printing forms differ from letterpress and gravure printing forms in two main ways:
- there is no geometric difference in height between printing and white space elements
- there is a fundamental difference physical and chemical properties surfaces of printing and blanking elements
The printing elements of the flat offset printing form have pronounced hydrophobic properties. Gap elements, on the contrary, are well wetted by water and are able to retain a certain amount of it on their surface; they have pronounced hydrophilic properties.
In the process of flat offset printing, successive wetting of the printing plate with a water-alcohol solution and ink is carried out. In this case, water is retained on the gap elements of the form due to their hydrophilicity, forming a thin film on their surface. The ink is retained only on the printing elements of the form, which it wets well. Therefore, it is customary to say that the process of flat offset printing is based on the selective wetting of blank and printing elements with water and ink.
3.2 Varieties of flat offset printing forms
To obtain forms of flat offset printing, it is necessary to create stable hydrophobic printing and hydrophilic blank elements on the surface of the plate material. In order to achieve the effect of ink repulsion on the printing plate, two methods are used, based on the different interaction of the surface of the printing plate and ink:
· in traditional offset, the printing plate is moistened with a dampening solution. The solution is applied in a very thin layer with the help of rollers on the form. The non-image-bearing portions of the form are hydrophilic, i.e. perceive water, and the areas that carry paint are oleophilic (perceive paint). A film of dampening solution prevents the transfer of paint to blank areas of the form;
· in dry offset, the surface of the plate material is ink-repellent, which is caused by the application of a silicone layer. By specially targeted removal of it (layer thickness of approx. 2 µm), the ink-receiving surface of the printing plate is exposed. This method is called offset without moisture, and often also "dry offset".
The share of "dry" offset does not exceed 5%, which is mainly due to the following reasons:
-higher cost of form plates;
-the reduced stickiness and viscosity of the inks places higher demands on the quality of the paper, since no moisturizing solution is applied to the offset rubber during printing. It quickly becomes dirty due to the accumulation of paper dust and plucking of fibers. As a result, print quality is reduced, and the machine has to be stopped for service;
-more stringent requirements for temperature stability during printing;
-low circulation resistance and resistance to mechanical damage.
Currently, the most widely used printing plates for flat offset printing with moistening of blank elements. They, like forms without moisture, have their drawbacks and advantages. Consider the main and most important of them:
The main disadvantages of OSU:
-the difficulty of maintaining the balance of paint-water;
-the impossibility of obtaining exactly the same size of raster dots when printing a run, which increases the amount of loss of materials and time;
-low environmental performance.
The main advantages of OSS:
-the presence of a large number of consumables for the manufacture of forms of this type and equipment for printing from them;
-the printing process does not require the maintenance of strictly defined climatic conditions (for example, temperature), as well as the purity of the preparation of the printing machine;
-lower cost of consumables.
Printing plates for offset printing are thin (up to 0.3 mm), well stretched on the plate cylinder, mostly monometallic or, less often, polymetallic plates. Forms on a polymer or paper basis are also used. Among the materials for printing plates on a metal basis, aluminum has gained significant popularity (compared to zinc and steel).
Paper-based offset printing forms can withstand print runs of up to 5,000 copies, however, due to the plastic deformation of the moistened paper base in the zone of contact between the plate and offset cylinders, the line elements and raster dots of the plot are greatly distorted, so paper forms can only be used for single-color printing products. High Quality. Polymer-based molds have a maximum circulation capacity of up to 20,000 copies. The disadvantages of metal molds include their high cost.
From the analysis of the advantages and disadvantages of the forms under consideration, it can be concluded that monometallic forms with moistening of blank elements are a suitable type of forms for printing the circulation of the edition selected in this work.
3 Introduction to Computer-to-Plate Technology
Computer-to-Plate technology is a method of manufacturing printing plates, in which the image on the plate is created in one way or another based on digital data received directly from a computer. At the same time, any intermediate material semi-finished products are completely absent: photoforms, reproduced originals-layouts, etc.
There are various variants of CtP technologies. Many of them are already firmly entrenched in the technological process of Russian and foreign printing enterprises, not representing competition from classical technology, but only being one of the options for manufacturing printing plates for certain circulations and product quality requirements.
Devices "Computer - printing form" register the image on the plate by element-by-element recording. Plates with the image are further developed in the traditional way. Then, for printing a circulation, they are installed in sheet or roll printing machines.
Form plates are fed into the recording device, which are in light-protective cassettes. The form plate is attached to the drum and is written with a laser beam. Further, the exposed plate is fed through the conveyor from the exposure plate to the developing device. The system is fully automated.
The main advantages of CtP technologies:
-a significant reduction in the duration of the process of making printing plates (due to the absence of a process for making photo plates)
-high quality of finished printing plates due to the reduction of distortions that occur during the manufacture of photo plates
-equipment reduction
-less need for staff
-saving photographic materials and processing solutions
-environmental friendliness of the process.
3.4 Plate classification for Computer-to-Plate technology
Scheme 3.1. Classification of CtP technology according to the type of mold materials used
Scheme 3.2. Classification of methods for manufacturing offset printing plates using CtP technology
4. The choice of the developed technological form process
Production of printing plates based on digital data received directly from a computer can be carried out both offline (exposure device for CtP technology) and directly in the printing machine. It is impossible to say unequivocally that the quality of printed forms obtained offline is lower compared to those obtained in a printing machine. The determining factor is the selection and selection of mold material and equipment. In terms of the duration and energy intensity of the process, the level of mechanization and automation, the consumption of plate material and processing solutions, the technology for making printing plates in an offline mode is inferior to the technology for making plates in a printing machine. However, the technology for making printing plates in a printing machine is very expensive and can often be unjustified in the manufacture of a particular product, since it does not involve the use of different plate materials. Therefore, for the projected publication, we will make printing plates in an autonomous exposure device in the following sequence: element-by-element recording of information (exposure), preheating, development, washing, gumming and drying (justification see section 6).
5. Choice of used plate equipment and instrumentation
When choosing plate equipment, it is necessary to pay attention not only to such characteristics as format, power consumption, dimensions, degree of automation, etc., but also to the fundamental structure of the exposure system (drum, flatbed), which determines technological capabilities equipment (resolution, laser spot size, repeatability, productivity), as well as service difficulties and service life.
In CtP systems focused on the production of offset printing plates, laser exposure devices - recorders - of three main types are used:
ü drum, made according to the "external drum" technology, when the mold is located on the outer surface of the rotating cylinder;
ü drum, made according to the "inner drum" technology, when the mold is located on the inner surface of a stationary cylinder;
ü flatbed, when the form is located in a horizontal plane motionless or moves in a direction perpendicular to the direction of image recording.
Tablet recorders are characterized by low recording speed, low recording accuracy, and the impossibility of exposing large formats. These properties are usually not typical for drum recorders. But the intra-drum and external-drum principles for constructing devices also have their drawbacks and advantages.
In systems with plate positioning, 1-2 radiation sources are installed on the inner surface of the cylinder. During exposure, the plate is stationary. The main advantages of such devices are: ease of mounting the plate; the sufficiency of one radiation source, due to which high recording accuracy is achieved; mechanical stability of the system due to the absence of large dynamic loads; ease of focusing and no need to align laser beams; easy replacement of radiation sources and the ability to smoothly change the recording resolution; large optical depth of field; ease of installation of the punching device for pin registration of forms.
The main disadvantages are the large distance from the radiation source to the plate, which increases the likelihood of interference, as well as the downtime of systems with one laser in case of its failure.
External drum devices have such advantages as: low drum rotation frequency due to the presence of numerous laser diodes; durability of laser diodes; low cost of spare radiation sources; the possibility of exhibiting large formats.
Their disadvantages include: the use of a significant number of laser diodes; the need for laborious adjustment; low depth of field; the complexity of installing devices for punching forms; during exposure, the drum rotates, which leads to the need to use automatic balancing systems and complicates plate mounting designs.
Companies producing devices with external and internal drums note that with the same format and approximately equal performance, the former are 20-30% more expensive than the latter (differences in the price of high-performance systems, due to the high cost of multi-beam exposure heads for external drum devices, can be even greater ).
The size of the laser beam spot and the possibility of its variation is an essential indicator in the choice of equipment. Another important characteristic is the multifunctionality of the equipment, i.e. the possibility of exhibiting various uniform materials.
According to the above reasoning and table. 2 is advisable to use the following equipment: Escher-Grad Cobalt 8 - device with an internal drum, suitable for the format of the product, has a sufficiently high resolution, the laser used is a violet laser diode 410 nm, the minimum spot size is 6 microns. Image quality is achieved using a micron-precision carriage movement system, high-frequency electronics and a 60-milliwatt violet laser with a thermal control system.
The FlightCheck 3.79 program is used to control output files. This is a program for checking the presence and compliance with the PrePress requirements of the files that make up the layout file, the availability of fonts used in the layout file, as well as for collecting and preparing all the necessary files for output. To control the production of offset printing plates using CtP technology, it is necessary to use a densitometer for measuring in reflected light and having the function of measuring printing plates (for example, ICPlate II from GretagMacbeth) and a multifunctional test object - the Ugra/Fogra Digital Plate Control Wedge for CtP scale.
For all the above exposure devices, the possible thickness of the exposed plate material is 0.15-0.4 mm.
The Glunz&Jensen Interplater 135HD Polymer plate processor is recommended for Escher-Grad Cobalt 8 equipment for photopolymer plates.
Table 2 Comparative characteristics of mold equipment
Types of possible equipment design used laser laser spot size resolution, dpimax. plate format, mm productivity, forms/exposed plate plates Polaris 100 + Pre-loader manufacturer Agfa planar FD-YAG 532 nm10 µm1000-2540914x650120 format 570x360 mm at 1016 dpi Agfa N90A, N91, Lithostar UltraGalileo S manufacturer Agfa int. Drum ND-YAG 532 nm10 µm 1200-36001130x82017 full format at 2400 dpiAgfa N90A, N91, Lithostar UltraPanther Fastrack Manufacturer Prepress Solutions Planar Ar 488 nm FD-YAG 532 nm Variable from 14 µm 1016-2540625x91463 format 500x7016 N91star LithopidA, 9140625x91463 format 500x7016 mm; FujiCTP 075x manufacturer Krauseex. drum ND-YAG 532 n10 microns 1270-3810625x76020 at 1270 dpi all photopolymer or silver plates Agfa, Mitsubishi; film Fuji, Polaroid, KPG; materials MatchprintEscher-Grad Cobalt 8int. drum violet laser diode 410 nm6 µm 1000-36001050х810105 at 1000 dpiSilver-containing and photopolymer plates sensitive to violet radiation Xpos 80e manufacturer Luscherint. drum 830 nm 32 diodes 10 µm 2400800х65010all thermoplates
Table 3 Characteristics of &Jensen Interplater 135HD Polymer Processor
Speed40-150 cm/min Plate width, max1350 mm Plate thickness 0.15-0.4 mm Preheat temperature 70-140 ° Drying temperature 30-55 ° Developer temperature20-40 ° C, cooler recommended Included Pre-heat and wash sections, full plate immersion, developer filter, automatic solution replenishment system, brushes, circulation in wash and post-wash sections, automatic section of the gumming section, cooling device
6. Selection of the main materials of the mold process
Table 4 Comparative characteristics of the main types of plates for CtP technology
Principle of layer construction Exposure wavelength (nm) Gradation characteristic and reproducible raster lineature Circulation stability without firing (thousand copies) Type of processing Advantages Disadvantages can be exposed with cheap low power argon lasers; use standard chemistry for processing; can be exhibited both traditionally and digitally Insufficient wear resistance for large runs; tendency to increase the cost of printing plates due to the use of silver; expensive development, regeneration and disposal of chemical solutions; need to work with non-actinic red radiation Hybrid technology488-6702-99%150developing/fixing for the silver layer; UV light through the mask; manifestation, washing; gumming plates can be exposed to almost all lasers used in the printing industry; can be exposed both traditionally and digitally due to double exposure loss in resolution; a bulky and expensive processing machine is required, capable of controlling two separate chemical processes; need to work under red non-actinic radiation Light-sensitive photopolymerizable 488-5412-98% 70 lin/cm100-250 preheating, developing, rinsing, gumming, depending on the plate coating used, can be processed in a normal standard aqueous solution, pre-firing is required before processing; depending on the spectral sensitivity, it may be necessary to work with red non-actinic radiation. allow you to get a sharp raster dot; do not require processing in chemical solutions use of an expensive high-power laser Technology of three-dimensional structuring830, 10641-99 % 80 lin/cm250-1000 plates cannot be overexposed, as they can only have two states (exposed or not); allow to obtain a sharper halftone dot and, accordingly, a higher lineature, while pre-firing is still required before processing
From Table 4 we can draw the following conclusions: almost all heat-sensitive printing plates (regardless of what technology they implement) have the highest possible parameters today, which subsequently determine the technological process and quality printed matter. These include: reproduction and graphic indicators (gradation characteristic, resolution and highlighting ability) and printing and technical (print resistance, perception of printing ink, resistance to solvents of printing inks, molecular surface properties). Thermal sensitive plates are more user friendly than their photosensitive counterparts. They allow you to work in normal working conditions, do not require safe lighting, heat-sensitive coatings practically do not need protective films, have a high, stable print run and other printing and technical properties.
On the other hand, since the energy sensitivity of these plates is much lower than that of light-sensitive plates, the manufacture of molds on thermosensitive plates requires not only an increase in the power of the IR laser during exposure, but also, as a rule, it is necessary to supply large amounts of mechanical and chemical energy at the stages of additional processing when developing or cleaning ready-made forms.
However, the determining factor limiting their widespread use is their high cost. Therefore, it is expedient to use them for highly artistic multicolor products.
In our case, since silver-containing form materials and solutions for their processing tend to become more expensive, and due to a number of environmental and technological reasons (high labor intensity, low productivity, etc., see Table 4), we use a negative light-sensitive photopolymer Ozasol N91V from Agfa. Its characteristics: sensitized to the radiation of a violet laser diode with a wavelength of 400-410 nm; material thickness 0.15-0.40 mm; layer color red, photosensitivity 120 µJ/cm 2; the resolution of the N91V plates depends on the type of exposure device used and provides raster reproduction with lineature up to 180-200 lines/cm; coverage of raster gradations from 3-97 to 1-99%; circulation resistance reaches 400 thousand copies.
Figure 5.1 shows the fundamental structure of the selected material.
Fig.5.1. Scheme of the structure of light-sensitive photopolymer plates: 1 - protective layer; 2 - photopolymerizing layer; 3 - oxide film; 4 - aluminum base
The main advantages of photopolymer technology are the speed of printing plate production and its high circulation stability, which is very important both for newspaper enterprises and for printing houses that have a large load of small-circulation products. In addition, if properly stored, these forms can be reused.
The selected plate material can be exposed on the previously selected CtP device - Escher-Grad Cobalt 8, because it can be supplied in any format. This allows you to print the publication on printing machines with a maximum paper size of 720x1020 mm. Printing can be done on a sheet-fed four-section duplex offset press such as the SpeedMaster SM 102.
The thickness of the photopolymerizing layer of the N91V plate is small, which makes it possible to carry out exposure in one stage. During the exposure process, the printing elements of the form are formed. Under the action of laser radiation, layer-by-layer photopolymerization of the composition occurs according to the radical mechanism, and an insoluble three-dimensional structure is formed, the spatial cross-linking of which ends during subsequent heat treatment at a temperature of 110 - 120 ° C. Additional heating of the plate with IR lamps also makes it possible to reduce internal stresses in the printing elements and increase their adhesion to the substrate before development. After heat treatment, the plate undergoes a preliminary wash, during which the protective layer is removed, which avoids contamination of the developer and speeds up the development process. As a result of development, the unexposed areas of the original coating dissolve and gap elements are formed on the aluminum substrate. The finished forms are washed, gummed and dried.
7. Map of the designed mold process
Table 5 Form Process Map
Name of the operation Purpose of the operation Applied equipment, fixtures, instruments and tools Applied materials and working solutions Modes for performing the operation Input control of files intended for output and plate plates Determination of their suitability for use in accordance with the technological instructions for offset printing processes FlightCheck 3.79 program, ruler, thickness gauge, lupaform plates -Preparation of equipment, turning on the equipment, checking the availability of solutions for processing in containers, setting the required modes of Escher-Grad Cobalt 8; developing processor Glunz&Jensen Interplater 135HD Polymerdeveloping solutions Ozasol EP 371 replenisher, MX 1710-2; distilled water; gumming solutions Spectrum Gum 6060, HX-148 -Exposure Preheating Developing Washing Gumming Drying Transferring file information to the plate (formation of a cross-linked three-dimensional structure) Ensuring the required run resistance (increasing the stability of printed elements) Removing the non-polymerized layer Removing residual developer solution Protection against dirt, oxidation and damage Removing excess moisture Escher-Grad Cobalt 8; processor Glunz&Jensen Interplater 135HD Polymer processor Glunz&Jensen Interplater 135HD Polymer see p. preheat see p. preheat see p. preheat see p. preheat plates Ozasol N91; - developing solutions Ozasol EP 371 replenisher, MX 1710-2; distilled water gumming solutions Spectrum Gum 6060, HX-148T=3 min t=70-140 ° C copy speed 40-150 cm/min - - t=30-55 ° Control of the printing form, determination of their suitability for use in accordance with the technological instructions for offset printing processes, ICPlate II densitometer from GretagMacbeth, magnifying glass -
The descent of the strips of the first and second notebooks (“turnover is a foreign form”)
I side
II side
Conclusion
I must say that no one buys, as a rule, just equipment - they buy a solution. And this decision should meet certain tasks. This can be, for example, a reduction in production costs, an increase in product quality, an increase in productivity, etc. In this case, of course, the specifics of a particular printing house should be taken into account - the circulation, the required quality, the colors used, etc. On the other side of the scale is the price of this decision.
Theoretically, there is no doubt that CtP is the future. The development of any technology, and printing is no exception, inevitably leads to its automation, minimizing manual labor. In the future, any technology tends to reduce the production cycle to one step. However, until printing technology has reached such a level of development, potential consumers You have to weigh the many pros and cons.
Used Books
1. Kartashova O.A. Fundamentals of the technology of form processes. Lectures read for students. FPT. 2004.
Amangeldyev A. Direct exposure of plates: we say one thing, we mean another, we do the third. Journal. "Kursiv", 1998. No. 5 (13). pp. 8 - 15.
Bityurina T., Filin V. Form materials for CTP-technologies. Journal. "Polygraphy", 1999. No. 1. pp. 32-35.
Samarin Yu.N., Saposhnikov N.P., Sinyak M.A. Printing systems from Heidelberg. Prepress equipment. M: MGUP, 2000. S. 128-146.
Burnt V. Modern systems CTP. Journal. CompuPrint, 2000. No. 5. pp. 18 - 29.
Legion group of companies. Catalog of prepress printing equipment: autumn 2004 - winter 2005.
7. Encyclopedia of printed media. G. Kipphan. MGUP, 2003.
8. Offset printing processes. Technological instructions. M: Book, 1982. S.154-166.
Polyansky N.N. Methodical manual for the design of course projects and final works. M: MGUP, 2000.
Polyansky N.N., Kartashova O.A., Busheva E.V., Nadirova E.B. Form process technology. Laboratory works. Part 1. M: MGUP, 2004.
Goodilin, D. "Frequently Asked Questions About CtP." Journal. CompuArt, 2004, No. 9. pp. 35-39.
Zharova A. «CTP plates - experience in mastering technologies». Journal. Polygraphy, 2004. No. 2. pp. 58-59.
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Varieties of digital technologies for the manufacture of flat offset printing forms. The last decade has been marked by the rapid development of digital technologies for the manufacture of flat offset printing plates and the use of various types of plate equipment and plates in these technologies. There are no scientifically based recommendations for their use, so there is no generally accepted classification. For the purpose of a more competent methodological consideration of the educational material, an approximate classification of digital technologies for offset printing processes is given (Fig. 10.1 
) according to the following main features:
Type of radiation source;
Method of technology implementation;
Form material type;
Processes occurring in the receiving layers.
In publishing and printing practice and technical literature, depending on the method of implementing technologies, it is customary to distinguish three of their options:
CTP and CTPress digital technologies use lasers as radiation sources. Therefore, these technologies are called laser. UV lamp radiation is used only in CTSR technology. Element-by-element recording of information using the STR and CTsP technology is carried out on an independent exposure device, and using the CTPress technology directly in the printing machine. In essence, the technology implemented according to the CTPress scheme, (also known as DI technology, from English - Direct Imaging) is a kind of digital technology CTP, while the printed form can be obtained by writing information either on a form material (plate or roll), or formed on a thermographic sleeve placed on a plate cylinder.
In contrast to the STR and CTPress mold technologies, which are used both in the OSU and in the OBU, the technology for making molds according to the CTSR scheme is used in the OSU.
There is no single generally accepted classification of digital flat offset printing forms. However, they can be classified according to the same criteria as digital technologies (see Figure 10.1). In addition, the classification can be extended by such features as the type of substrate, the structure of the molds, and the area of use (for OSU and OBU).
The processes occurring in the receiving layers of the plates as a result of laser exposure or exposure to a UV lamp provide information recording. After processing the exposed plates (if necessary), printing and blanking elements can be formed in the areas of the layer that were either exposed to radiation or, conversely, not exposed to it. The structure of the form depends on the type and structure of the plate, and in some cases on the method of exposure and processing of forms.
On fig. 10.2 
shows in a simplified way the structures of the forms of flat offset printing with the moistening of blank elements, obtained by the most widely used digital technologies:
The printing element can be an exposed photosensitive or thermally sensitive layer, a layer of deposited silver on unexposed areas of silver-containing plates, and also an unexposed photosensitive layer; a blank element is a hydrophilic film located, for example, on an aluminum substrate (Fig. 10.2, but);
The printing element has a two-layer structure and consists of an unexposed thermosensitive layer located on the surface of the hydrophobic layer, the gap element is a hydrophilic film on the surface of the aluminum substrate (Fig. 10.2, b);
The printing element is an unexposed thermosensitive layer located on the surface of the hydrophilic layer, and the hydrophilic layer acts as a gap element (Fig. 10.2, c);
The printing element can be an oleophilic (polymeric) substrate, which is exposed under the exposed areas of the thermally sensitive layer, the gap element is an unexposed thermally sensitive layer (Fig. 10.2, d);
The printing element is an oleophilic (polymer) substrate, the gap element has a two-layer structure and consists of a hydrophilic layer located on an unexposed thermosensitive layer (Fig. 10.2, e);
The printing element may be, for example, an unexposed thermosensitive layer having oleophilic properties; gap element - an exposed thermosensitive layer that has changed its properties to hydrophilic (Fig. 10.2, e).
A comparison of these structures with the structures of flat offset printing forms made using analog technology shows that the structure of some of them is similar (see Fig. 10.2, a and 6.1, c 
), others differ in the structure of printing and space elements.
Schemes for the manufacture of flat offset printing forms using digital technologies. Digital technologies for manufacturing forms of flat offset printing with moistening of blank elements, the most widely used at present, can be represented as a general scheme (Fig. 10.3 
). Depending on the processes occurring in the receiving layers under the action of laser radiation, mold manufacturing technologies can be presented in five versions. The mold making stages are shown in fig. 10.4-10.8, starting with the plate and ending with the printing plate.
In the first version of the technology (Fig. 10.4 
) a photosensitive plate with a photopolymerizable layer is exposed (Fig. 10.4, b). After heating the plate (Fig. 10.4, c), the protective layer is removed from it (Fig. 10.4, d) and development is carried out (Fig. 10.4, e).
In the second option (Fig. 10.5 
) a plate with a thermally structured layer is exposed (Fig. 10.5, b). After heating (Fig. 10.5, b), development is performed (Fig. 10.5, d).
On certain types of printing plates used for these two technologies, preheating (before development) is required to enhance the effect of laser radiation (stage c in Fig. 10.4 and 10.5).
In the third version of the technology (Fig. 10.6 
) a light-sensitive silver-containing plate is exposed (Fig. 10.6, b). After development (Fig. 10.6, c), washing is carried out (Fig. 10.6, d). The form obtained using this technology differs from the form made using analog technology (see Fig. 6.2, e 
).
Making a mold according to the fourth option (Fig. 10.7 
) on a heat-sensitive plate by thermal destruction consists of exposure (Fig. 10.7, b) and development (Fig. 10.7, c).
Fifth option (Fig. 10.8 
) technology for making molds on heat-sensitive plates by changing the state of aggregation, includes carrying out a single stage of the process - exposure (Fig. 10.8, b). Chemical processing in aqueous solutions (in practice called "wet processing") is not required in this technology.
Final operations production of printing plates for various technology options (see Fig. 10.3) may differ.
So, printing plates made according to options 1, 2, 4 can, if necessary, be subjected to heat treatment to increase their circulation resistance.
Printing plates manufactured according to option 3 after washing require special treatment to form a hydrophilic film on the surface of the substrate and improve the oleophilicity of the printing elements. Such printing forms are not subjected to heat treatment.
Printing plates made on various types of plates according to option 5 after exposure require complete removal of the heat-sensitive layer from the exposed areas or additional processing, for example, washing in water, or suction of gaseous reaction products, or treatment with a moisturizing solution directly in the printing machine. Heat treatment of such printed forms is not provided.
The process of manufacturing printing plates may include such operations as gumming and technical proofreading, if they are provided by the technology. Form control is the final stage of the process.
Analog technologies of element-by-element recording. In the plate processes of flat offset printing, the recording of information on plate plates using a laser has been used since the mid-60s. of the last century, when almost simultaneously in a number of countries, including the USSR, various options for manufacturing technologies for offset printing plates were implemented. In these technologies, a real information carrier was used as the original, which was a photomontage of a strip or a newspaper print. Several types of LU have been created for scanning and transferring information to a plate.
In the mid 70s. A thermographic method for manufacturing flat offset printing forms was developed, based on the transfer of a heat-sensitive layer from a film thermographic material to the surface of a plate using laser radiation. In the future, this method was apparently used in DICO technology (see § 10.3.9). The development of element-by-element recording technologies was carried out in the direction of improving the already known models of laser exposure devices that differ in purpose, type of laser used and performance. As a result, several dozens of such devices were created.
Digital technologies. These technologies have replaced the analog ones. The emergence of real developments in the field of digital technologies of form processes was explained by the creation of multifunctional devices for element-by-element processing and recording of information. The first variants of digital technologies for recording information on form plates were focused on the use of photo output devices, in which form plates were used instead of film, mainly on paper or polymer substrates. In terms of their sensitometric properties, the receiving layers of such plates were similar to the silver halide layers of photographic films. The first CTP technologies were also developing, in which the production of forms was carried out on laser printers. Form plates intended for these purposes are often called "polyester" plates in practice.
The beginning of the widespread use of digital technologies in plate offset printing processes was laid in the mid-90s, when industrial models of specialized electronic devices were introduced on the market, capable of recording information on plate plates on a metal substrate. Form plates with receiving layers sensitive in the visible and IR regions of the spectrum, necessary for this purpose, had already been produced by this time.
In parallel with the development of CTP technologies, the digital technology CTPress began to develop, focused on the production of small-circulation and small-format printed products. In 1991, the “spark” technology for manufacturing printing plates for OBU was implemented for the first time in a GTO-DI printing machine from Heidelberg (Germany). "Spark" technology was based on the phenomenon of surface erosion (from the Latin erosio - destruction of the surface) under the influence of electrical discharges. As a result of the action of a spark discharge created by the electrodes when a high voltage was applied to them, the areas of the anti-adhesion coating (see § 7.2.2) of the plate were removed and the oleophilic surface that perceived the ink was exposed - printing elements were formed.
The insufficiently high quality of the resulting image elements, which differed in uneven edges, did not allow the reproduction of high-line images on such forms. In 1993, this technology was improved: information recording began to be carried out using IR laser diodes. For such a record, special form materials were developed, which were made in two modifications: for OSU and OBU.
Along with these technologies, the CTcP technology developed by Basys Print GmbH (Germany) began to develop in the same period of time. The advantage of this technology was the ability to record information on monometallic plates, and the recording technology itself in the device and its design features were as close as possible to the traditional technology of exposure on a copier.
The last five years of the 20th century are considered to be the period of formation of digital technologies, when digital methods for manufacturing offset printing plates began to be introduced everywhere at printing enterprises around the world.
Form plates for digital technologies. prototype for photosensitive plate plates were used for direct photography (see § 6.1.2), but unlike the latter, they must be sensitive to the radiation of the laser sources used at that time. These were silver-containing plates: with internal diffusion transfer of silver complexes and plates of a hybrid structure, as well as plates with a photopolymerizable layer. Plates of a hybrid structure are currently of limited use due to the multi-stage process of obtaining a printing form on them.
The first mention of development thermosensitive plates date back to the mid-1980s. last century. They were used in the first EU, equipped with a laser on carbon dioxide, for recording information on which the process of thermal destruction of the layer was implemented. They were developed both for OSU and for OBU. Later, other types of heat-sensitive plates appeared - mainly on an aluminum substrate.
Depending on the type of receiving layers of plate plates, the processes of laser light exposure are accompanied by:
photopolymerization;
Reduction of silver and internal diffusion of silver complexes;
change in photoconductivity.
Recovery of silver and internal diffusion of silver complexes. The process of manufacturing a printing plate on a silver-containing plate, accompanied by the reduction of silver, the formation and diffusion transfer of silver complexes, is based on the ability of silver halide to be reduced under the action of radiation, while the silver complexes formed during development (in unexposed areas of the layer) acquire the ability to diffuse (see §§ 6.2.2 and 6.2.3). Differences in the structure of plate plates (see Fig. 6.2 and 10.6) do not change the essence of the ongoing processes. Under the action of laser radiation (see Fig. 10.6, b) a latent image is formed in the silver halide emulsion layer 4. In the process of chemical development (see Fig. 10.6, c) in these areas, silver is reduced from halide to metal, while silver forms stable bonds with the gelatin of the emulsion layer. At the same time, in areas that were not exposed to radiation, the silver halide is converted (with the help of a complexing agent) into water-soluble complexes. These complexes are mobile and diffusible, so they diffuse to the surface of the substrate through the barrier layer 3 into layer 2, where, as a result of physical development, printing elements in the form of deposited silver are formed on the development centers. In contrast to the process described in § 6.2.3, gap elements are formed on the surface of the hydrophilic substrate after removal of gelatin and a barrier layer from its surface, which are dissolved in water during washing.
Compared to the above process of obtaining printing elements on plate plates with FPS, on silver-containing plates, these elements are formed not as a result of radiation, but in the process of development and subsequent washing in areas that were not exposed to radiation.
Change in photoconductivity, which is the basis of the electrophotographic platemaking process, is discussed in § 6.1.2. Currently, such forms are not widely used due to the low quality of the image obtained on them.
The thermal effect implemented on plate plates with heat-sensitive layers leads to the formation of printing plates as a result of the following processes:
Thermostructuring;
Thermal destruction;
Changes in the state of aggregation;
Wettability inversions.
Varieties of form plates. The variety of printing plates used in digital laser technologies requires their systematization. However, there is no generally accepted classification yet. The most widely used plates at present can be classified according to the following criteria (Fig. 10.9 
):
When classifying platens depending on the mechanism for obtaining an image, it should be borne in mind that the concepts of “negative” and “positive” plates are interpreted in the same way as in the analog technology for manufacturing flat offset printing plates: positive plates are those on the exposed areas of which blank elements, negative - printing elements are formed on the exposed areas.
In addition to those shown in Fig. 10.9 features, printing plates can also be classified according to a number of particular features: the geometric dimensions of the plates (formats, thicknesses of substrates and receiving layers), methods of preparing the substrate, its microgeometry, the color of the layer dyed with dye, etc.
The main characteristics of form plates. The main characteristics of plate plates used in digital laser mold manufacturing technologies include the following: energy and spectral sensitivity of the receiving layers, reproducible gradation interval, run resistance.
energy sensitivity. It is determined through the amount of energy per unit surface required for the processes to occur in the receiving layers of the plate. Plates with a photopolymerizable layer require 0.05-0.2 mJ / formula" src="http://hi-edu.ru/e-books/xbook609/files/sm2.gif" border="0" align="absmiddle "alt="(!LANG:, thermally sensitive - 50-200 mJ / selection "> Spectral sensitivity. Different types of plate plates can have spectral sensitivity in different wavelength ranges: UV, visible and IR spectral regions. Plates whose receiving layers are sensitive in the UV and visible wavelength ranges waves are called photosensitive, form plates with receiving layers sensitive in the IR wavelength range, - heat sensitive.
Interval of reproduced gradations. In the practice of working with plate plates, their reproduction and graphic properties are evaluated by the interval of gradations, the formula "alt="(!LANG:from 1 to 99% (with a maximum rasterization line equal to 200-300 lpi). The interval of reproducible gradations on heat-sensitive plates that do not use such processing is less - from 2 to 98% (at 200 lpi )..gif" border="0" align="absmiddle" alt="(!LANG:equal to 2-98% at 200 lpi (or 1-99% at 175 lpi ), example ">lpi .
Theoretical prerequisites for achieving certain values \u200b\u200bselection "> Run resistance. Printing plates made on light-sensitive and heat-sensitive plate plates on a metal substrate have a print run from 100 to 400 thousand otts. It can be further increased by heat treatment on some types of forms (see § 10.1.1) up to 1 mln.
Application of various types of plates for specific conditions. When choosing the type of plates for the manufacture of various publications, one should first of all focus on the characteristics of the plates, which allow achieving the required quality of printing plates. The length of the mold making process is also important. It consists of the exposure time, the duration and the number of stages of plate processing after exposure. The absence of chemical treatment in the manufacture of forms on certain types of form plates also ensures the simplicity and convenience of their use. Also important is the cost of the plates and their availability.
So, for newspaper products, for which the duration of the process of making forms is decisive, it is advisable to use light-sensitive plates, which, having a high sensitivity, provide a reduction in the exposure time. If the determining parameter is the quality of the image on the form, which is necessary for reproducing, for example, magazine products, then preference should be given to heat-sensitive plates that have higher reproduction and graphic performance (according to some researchers, the same quality of reproduction of image elements on the form can be achieved with the use of silver-containing plates). For the rapid production of forms for publications containing low-line images, polyester plates can be used, for example.
The number of editions also influences the choice of plate type, since the run-time stability of not all types of printing plates can be increased by heat treatment (see § 10.1.1).
Types of exposure devices. LEU for recording information on offset plates are designed to expose the receiving layer of the plate to laser radiation. They can be made either in the form of a separate module, or in the form of a production line with devices for performing plate processing operations after exposure.
LEU can be classified according to a number of features: the type of plate used to record information, the type of laser source, design (construction scheme), purpose, degree of automation, format (Fig. 10.10 
). They may also differ in size and design, cost and other parameters.
Various types of LEAs can be designed for exposure to light- and temperature-sensitive layers of printing plates. For this purpose, they are equipped with various lasers. At present, devices with laser diodes that emit radiation with an example "> thermal" are widely used for exposing light-sensitive plates. The lasers used in them (with a power of the order of 10 W) make it possible to record information on heat-sensitive plate plates.
One of the main features by which these laser systems are classified as one type or another is their construction scheme, they are built according to one of the three main schemes (Fig. 10.11 
).
Main technical characteristics of devices. The main characteristics determine the technological capabilities of the LEU.
As in analog technologies, digital technologies for recording information on plates require quality control:
Recorder testing and calibration;
Control of the recording process itself;
Evaluation of indicators of the finished printed form.
Each stage of control is important, and the first two stages are considered fundamental, since setting up the ED and setting the required power of the laser source inevitably affects the entire subsequent technological process, and ultimately, the quality of the molds. Means for quality control of forms are control test objects. They are presented in digital form and contain a number of fragments for various purposes for visual and instrumental control:
An information fragment with constant information about the test object itself and variable information with current data about specific recording modes;
Fragments containing pixel art objects for visual control reproduction of image elements;
Fragments that allow you to evaluate the technological capabilities of the recording device and the raster processor, as well as the reproduction and graphic performance of printing forms.
One of the first test objects that began to be used in digital technologies was the UGRA / FOGRA POST SCRIPT object, which appeared in 1990. Currently, several test objects are used and among them the most popular UGRA/FOGRA DIGITAL PLATE CONTROL WEDGE. Also known are similar control test objects of EC manufacturers recommended by them for use in recording and adapted to a certain type of plate.
Test object UGRA/FOGRA DIGITAL PLATE CONTROL WEDGE (UGRA/FOGRA DIGITAL) supplied in in electronic format in several versions, serves to set up devices for optimal recording modes and subsequent control of these modes, as well as to evaluate the gradation and graphic fidelity of image elements. It consists of four files, each of which is designed to control the process of making printing plates for yellow, cyan, magenta and black inks. On fig. 10.12 shows its structure.
There are six fragments in the test object:
Selection "> Test object DIGI CONTROL WEDGE (Fig. 10.13), developed by Agfa, performs almost the same functions as discussed above. It can be presented both in negative and positive versions and is also assembled from a number of fragments, which are similar in many respects to the fragments of UGRA/FOGRA DIGITAL , although they are technically solved differently.The test object contains:
Define "> Determination of exposure modes and quality of forms using test objects. The test objects used for control allow you to visually evaluate the result of exposure to radiation. For this, fragment 5 of the UGRA / FOGRA DIGITAL test object is used (see Fig. 10.12) or fragment 2 of the DIGI CONTROL WEDGE test object (Fig. 10.14 
).
So, on the image of the UGRA / FOGRA DIGITAL test object obtained on the form on fragment 5, the field with the example "> DIGI CONTROL WEDGE" should merge with the background, all raster fields with a "checkerboard" filling (Fig. 10.14, c).
For some types positive plates it is recommended to slightly increase the exposure in order to get rid of the “shadowing” on whitespace elements (Fig. 10.14, d).
In practice, exposure control is carried out on other fragments of the considered test objects: on UGRA / FOGRA DIGITAL on fragment 4 containing fields of “chess” filling (Fig. 10.15 
) or fragment 3 (Fig. 10.16 
). On DIGI CONTROL WEDGE - fragment 3 (Fig. 10.17 
). This is possible, since these image elements are especially sensitive to changes in laser power, and with a correctly selected exposure (the rule is valid only for positive plates) the width of the strokes should correspond to the width of the gaps (Fig. 10.17, b). To assess their correspondence, the dashed elements on this fragment are located opposite each other. Control of the reproduction of line elements also allows you to evaluate the operation of the device in the selected exposure modes, since other factors, such as beam focusing, optics pollution, etc., can also affect the change in the size of these elements.
Digital test objects are used not only to control the exposure, but also allow you to evaluate the quality of the forms, including the reproduction of raster images on them. In the entire gradation interval, selection "> 6 of the UGRA / FOGRA DIGITAL test object, gradation interval - according to fragment 4 of the DIGI CONTROL WEDGE test object. Reproduction of dashed elements, including those located in mutually perpendicular directions, - according to fragment 3 of the considered test objects objects.
When choosing modes on negative plates it must be taken into account that the exposure (or exposure and additional heating) should be sufficient to completely structure the layer on future printing elements. That's why right choice exposure to control elements of test objects is an important component of the mold making process. To assess the effect of radiation on the negative layer of the plate, an analog tone scale is often used, for example, fragment 1 UGRA-82 (see Fig. 6.7), which is used in conjunction with a digital test object.
Initially, before outputting a digital test object to the plate (for example, DIGI CONTROL WEDGE ), you must select the exposure using an analog gray scale. For this purpose, an analog test object is glued onto the plate and exposure is carried out, after which the plate is developed. The exposure is estimated by the number of the field under which the layer was preserved after development. Subsequently, the digital test object is displayed on the plate with the same exposure. With this exposure, one of the fields of fragment 2 of the image of the DIGI CONTROL WEDGE test object on the form (the so-called operating point for a given device and type of plate) will coincide with the background, determining the recording modes.
In the first modifications of UV-Setter devices used to record information using digital CTSR technology, a multichannel liquid crystal shutter was used to modulate the light flux. Liquid crystals, having the ability to change their orientation in space under the action of an electric current, are able to influence the polarization of radiation. Therefore, if a matrix consisting of cells with liquid crystals is placed between polarizing filters, then a radiation modulator can be obtained, which, depending on the control voltage applied to it, will either transmit or delay radiation. Thus, it is possible to divide the light flux into beams, modulating each of them in accordance with the information being recorded. The disadvantage of such devices is the very strong heating of the polarizing filters. This requires limiting the power of the UV lamp used in the device and affects the intensity of the light flux, and, ultimately, the quality of the printing plates.
In later models of UV-Setter devices that implement the DSI process (from English - direct screen imaging - direct raster exposure), information is recorded using DLP technology (from English - digital light processing - digital light modulation). The main element of such a recording device (Fig. 10.18 
) is a DMD micromirror device (from English - digital micromirror device - digital micromirror device) - a chip on which a large number (more than a million) of separately controlled micromirrors are located, each of which is capable of directing a beam reflected from it or into a focusing lens (see Fig. Fig. 10.18), or past it.
When controlling the rotation of the micromirrors, image elements are projected onto the copy layer of the plate. Reflective micromirrors are more efficient than previously used modulators. However, the number of micromirrors in the chip is not enough to simultaneously expose the entire surface of the plate, so the recording is carried out sequentially, with start-stop standing of the recording head. This affects the performance of the device. To increase it, the UV-Setter is also equipped with two recording heads. The performance improvement in the latest UV-Setter models is achieved by using the scrolling method, i.e. recording information without standing the recording head, but in the process of moving it.
Devices operating on this opto-mechanical principle with certain resolution limitations allow you to reproduce images of 10-28 microns in size (the size depends on the recording resolution). The raster image obtained on printing forms (Fig. 10.19 
) is characterized by high edge sharpness.
Processing plates after exposure includes a set of operations, the presence and sequence of which depends not only on the type of plates, but also on their properties. The modes of carrying out the processing process and the compositions of the processing solutions used are determined by the developers. Exposed form plates are processed on installations that provide the possibility of carrying out all the necessary stages of the process. For plates of different types (see fig. 10.4-10.8), these can be step-by-step installations similar to those shown in fig. 5.13 
, or production lines, as well as installations, completed with sections for additional operations. Plates with a copy layer, exposed using the digital technology CTSR, are processed on the same equipment and under the same modes as in the analog technology for making plates for flat offset printing (see § 6.3.4).
Manifestation. If the development is provided for by the printing plate manufacturing technology, then it should be carried out in installations at a temperature of 22-25 ° C at a consumption of the corresponding developer from 50 to 150 g / example "> on-line with an exposure device, in which case the exposed plates are automatically loaded into installation, and after processing they go to the output table or to the drive (staker).
Heat treatment to increase print run resistance is carried out in the manufacture of printing plates obtained on plates with a photopolymerizable layer and heat-sensitive (negative and positive) plates (see § 10.1.1). It is carried out either in vertical ovens, into which printing plates are loaded manually, or in horizontal conveyor ovens, which are often connected in line with the power plant and processing unit.
The processing temperature of various types of printing forms is 200-280°C, the duration of its implementation is 6-8 minutes in vertical ovens and 4-6 minutes in conveyor ovens. The protective solution applied before heat treatment can be the same as in analog technology, or a special solution designed for a particular type of plates is used.
Final operations. The process of making molds does not end with the stages discussed above. Before placing the plate in the printing press, pin holes must be punched in it (if they were not made in the plate before exposure) and the edges bent in order to accurately and quickly fix it on the plate cylinder of the printing press. Sometimes there is a need for trimming forms. For this, a set of additional equipment is used: from manual devices for trimming, perforating and folding to production lines that carry out these operations in automatic mode. In addition to the devices themselves and transport conveyors for moving printing plates between sections, such lines can be equipped with by special means, controlling the quality of operations performed on the received forms.
The most simple handheld devices for these operations are usually supplied with the printing machine. Fully automated devices connected in line, allow you to get ready-made printing forms, on which high precision final operations are carried out. This significantly improves the subsequent registration of forms in the printing press. Various variants of such devices are possible, capable of only bending forms or bending and perforating at the same time. In the first case, already punched forms fall into the device and are positioned along the pins, and then they are bent. The productivity of such a device is 240-300 forms per hour. The position of the form in another type of device is controlled electronic system, after which the fold and perforation are performed simultaneously. Productivity of the device makes 120 forms an hour.
Low contrast of the image on some types of forms does not allow to accurately recognize the border between printing and white space elements;
Different amount of light scattering due to the unevenness of the layer and the rough surface of the substrate on the forms made on plates of different types and different manufacturers;
The problem of taking into account the color of the layer in densitometric analysis;
The need to exclude from the calculation the amount of blur, taken into account by the Sheberstov-Murray-Davis formula, when using embedded software in the densitometer.
Difficulties encountered in evaluating the example">Gretag Macbeth Spectro Eye , Models X-Rite 528, 530, 938, Techkon SD 620 and others that support color filter standards (European DIN 16536 or various variants of the American ANSI).
To evaluate raster images on printing plates made using digital technologies, it is advisable to use dotmeters. These include the Centurfax CCDot 4 and Poly Dot (for inspecting printing plates on polymer substrates), FAG Vipcam 116, Gretag Macbeth ICPlate, Techkon DMS 910, X-Rite PAGE II, which allow you to determine the resolution, measure the lineature of the estimated structure and other parameters on various types of controlled plates. The operation of most of these devices is based on projecting a part of a raster image onto a CCD matrix, and the output digital data about the raster image is recorded using a mini-camera. Based on the information received, the internal software device allows you to display the raster structure, and then calculate the definition "\u003e"\u003e Possible defects in printing plates and their causes. Unlike analog, digital technologies require full control throughout the entire form process, only then can the causes of possible The stability of the performance of each printing plate must be guaranteed by the adjustment of the EM. It is carried out regularly, and the most difficult part of it - the adjustment during installation is usually carried out by specialists who mount and install this device. Regular adjustment includes checking the effective power of the radiation source and its focusing, as well as calibration, control of processing modes and their compliance with the recommendations of the supplier.Visual assessment of the cleanliness of the surface of the form plate before recording information is also mandatory.This is due to the fact that problems during recording and processing can lead to significant material sweat ryam.
The main reasons that lead to the appearance of defects on the forms are:
Incorrect calibration of the raster processor;
Violation (failure) of installations in the EU, associated with changes in external conditions (temperature and humidity);
Change in radiation intensity during exposure due to the depletion of the laser resource, contamination of the optics in the device, etc.;
Changing modes during the development process, associated with overheating of the developer, its replacement or depletion;
A combination of the above factors.
Defects that occur on printing plates due to these factors are:
Distortion of raster and line elements of the image, up to the loss of small details;
The presence of layer residues (exposed and unexposed) on blank elements, leading to shadowing and the formation of a torn contour at the edges of the printing elements.
Defects are eliminated by varying the effective laser power and changing modes of manifestation. You can evaluate the change in these parameters according to the readings of the corresponding fragments of test objects, for example, fragments 1 and 2 of the DIGI CONTROL WEDGE scale. Thus, if the central area on fragment 1 on printing plates made on negative plates becomes larger and at the same time merges with the background, the field on fragment 2, located closer to field A, then the reason for this change is either an increase in power or the use of a plate with a higher sensitivity, or depletion of the developer. Similarly, the influence of these parameters can be assessed using fragment 5 of the UGRA/FOGRA DIGITAL test object (see Fig. 10.12).
The influence of the development modes also affects the quality of the reproduction of the edges of the image elements. At high temperatures, as well as the use of an aggressive developer of high concentration, the edges of the elements have a torn contour. The low temperature of the development leads to the preservation of the remnants of the layer on the blank elements of the form.
Varieties of printing forms and their structure. Printed forms for OBU can be classified according to such criteria as:
Method of technology implementation: there are molds made using CTP and CTPress technologies;
Substrate type (polymer or aluminum).
Simplified structures of printed forms for OBU are shown in fig. 10.20 
. Printing elements on these forms are formed on exposed areas: either on an oleophilic polymer substrate (Fig. 10.20, a), or on an oleophilic layer 2located on an aluminum substrate (Fig. 10.20, b). Gap elements are formed on the anti-adhesive (silicone) layer (see § 7.2.2), previously deposited on the heat-sensitive layer 3 at the stage of plate manufacturing.
Schemes for the manufacture of molds for OBU. Printing plates for OBU are made mainly in one stage: the thermosensitive layer is exposed, further processing (development) in chemical solutions is not required, but thermal decomposition products must be removed. To remove them, the EU is equipped with special vacuum suction. According to this scheme, molds are made for technologies according to the scheme STR and STRress.
The manufacture of molds for OBU is also carried out according to a different scheme: after exposure, development is carried out, as a result of which the anti-adhesive and heat-sensitive layers are removed from the exposed areas. Such printing forms are used only in digital technology CTP.
Formation of printing and space elements on forms for OBU. On form plates for OBU on polymer (Fig. 10.21, a) and aluminum (Fig. 10.21, b) substrates, as a result of thermal destruction of the thermally sensitive layer absorbing IR radiation, are formed printing elements.
This happens in this way: laser infrared radiation passes through the anti-adhesion layer 3 that transmits radiation and is absorbed by the layer 2 that is sensitive to this radiation. There is a change in the aggregate state of layer 2, for example, by sublimation, and the anti-adhesion layer is simultaneously removed. As suggested by a number of researchers, its removal is associated with the elimination of methyl groups from silicon atoms in polysiloxane compounds. As a result, the polymer substrate 1 is exposed (see Fig. 10.21, a), which has oleophilic properties, or the oleophilic layer 4 (see Fig. 10.21, b). Printing elements on printing plates, the thermally sensitive layer of which contains an IR absorbent, are also formed on the oleophilic layer after exposure and development of other types of printing plates.
Functions whitespace elements performs the initial anti-adhesive layer 3 on the forms (see fig. 10.21). This layer can be additionally strengthened during exposure in the version of the technology, which is focused on the use of printing plates containing a heat-sensitive metal layer, for example, titanium. This layer absorbs radiation and heats up above the melting point, and the resulting melt contributes to the hardening of the release layer.
CTPress is used to make molds for OBU and OSU. Her distinctive feature is the possibility of making a printing plate (with subsequent printing) in a machine that is equipped with an electronic device for recording information. The main advantage of CTPress technology is that it allows you to link prepress and press processes, while also reducing the production time of multi-color printed products. The exposure time of the plates of the minimum format (with a width of 33 cm, averages 4 minutes). The technology is focused on printing runs starting from 300 sheets, the maximum run is determined by the print run of the forms (see § 10.3.8). Recording resolution ranges from 1200 to 3556 dpi, while the minimum size of image elements is 10-11 microns.
The scheme for writing a printed form using CTPress technology is shown in fig. 10.22 
.
The process of manufacturing printing plates is carried out as follows: after processing, information is recorded in a buffer memory device (in a printing machine) and preparation for printing begins. At the same time, the plate material is updated, which is located on the outer surface of the plate cylinder, and information is recorded: image data is converted into control signals for the laser ED, laser beams are directed to the optical system, where they are focused. In the future, all color-separated printing plates are recorded simultaneously.
Structurally, different types of printing machines that implement CTPress technology can differ significantly. Existing printing machines have a planetary or sectional construction, some models are designed in such a way that they contain only two plate cylinders (each of them records two color-separated printing plates). Printing machines are used most often for four-color printing, there are also models designed for two-color double-sided printing.
Technical solutions for the design of printing sections and inking machines, cylinder sizes, the construction of EC (they can be stationary or located on a special bar that is brought to the plate cylinder before recording) and devices for loading and unloading plate material expand the range of equipment of this type. Printing machines have AZ+ and A2+ formats, and sheet paper can be fed either long or short sides. Printing on such machines of various manufacturers is carried out at speeds from 7 to 15 thousand otts. in hour.
Form materials for CTPress technology. For CTPress technology, heat-sensitive roll materials on polymer or plate plates on aluminum substrates are used. Recording forms on these materials is carried out by the method of thermal action of IR laser sources (see § 10.3.8). Form materials, with which the manufacturers of such equipment associate further prospects for the development of CTPress technology, are focused on the use of new generation heat-sensitive materials that do not require any processing after recording.
Thermographic recording on sleeves. Along with the methods discussed above for element-by-element recording of offset printing plates, digital technology is also known DICO, (from English - Digital Change-over) - it allows multiple recording of information by creating a "temporary" printing plate. In this case, replaceable form plates are not used, and the printing form is formed directly in the machine itself. The printing elements of the form (Fig. 10.23, b 
). The functions of the gap elements are performed by the hydrophilic layer. The circulation stability of this form is several tens of thousands of prints. After the printing process is completed, the image is erased with a cleaning solution (Fig. 10.23, c) and information is recorded again.
Other recording options. Very promising, according to a number of experts, is another version of digital technology, which also allows you to create a printing plate directly in the printing press. The process of forming a printing plate using this technology consists of applying (most often by spraying) a liquid hydrophobic layer (of the LiteSpeed type, developed by Agfa) onto a hydrophilic surface.
Printing elements are formed on the exposed areas as a result of laser exposure: the layer is heated and melted, while chemical bonds between the molecules in the layer are not formed. Unexposed areas of the layer are removed with a moisturizing solution for several revolutions of the plate cylinder in the printing machine and on the exposed hydrophilic surface are formed whitespace elements. Similar versions of digital technologies, also implemented according to the CTPress scheme, involve the formation of a printing plate on a plate cylinder using an inkjet method, for example, using ink, which is subsequently removed after printing.
Introduction
1. The main types of printing plates for offset printing
1.1 Offset printing method
1.2 Methods for obtaining printing forms and types of printing plates
2. Analog Form Materials
2.1. Form materials for the production of printing forms by contact copying
2.1.1 Bimetal plates
2.1.2 Monometallic plates
2.2
3. Digital plate materials
3.1 paper plates
3.2 Polyester printing plates
3.3 metal plates
3.3.1 Silver-containing plates
3.3.2 photopolymer plates
3.3.3 Thermal plates
3.3.4 Processless Plates
3.3.5 Hybrid plates
4. Plates for offset without moisture
4.1 Dry offset plates
4.2 Pros and cons of "waterless" plates
Conclusion
Bibliography
Applications
Attachment 1
Appendix 2
Annex 3
Appendix 4
Annex 5
Introduction
Today, despite the variety of ways to obtain printed products, the method of flat offset printing remains dominant. This is due, first of all, to the high quality of obtaining prints due to the possibility of reproducing an image with high resolution and the identity of the quality of any parts of the image; with the comparative simplicity of obtaining printing forms, which makes it possible to automate the process of their manufacture; with ease of proofreading, with the possibility of obtaining prints of large sizes; with a small mass of printed forms; with a relatively inexpensive cost forms. 2010 will be the year of offset printing, with a market share of 40 per cent, surpassing all other printing processes, according to PIRA, the UK Printing Information Research Association.
In the field of prepress offset production processes, rationalization continues, with the aim of reducing production times and merging with printing processes. Reproduction companies are increasingly preparing digital data that is transferred to a printing plate or directly to printing. Technologies for direct exposure to form materials are actively developing, while information processing formats are increasing.
The most important element of offset printing technology is the printing plate, which in recent years has undergone significant changes. The idea of recording information on form material not by copying, but by line-by-line recording, first from the material original, and then from digital data arrays, was already known thirty years ago, but its intensive technical implementation began relatively recently. And although it is impossible to switch to this process immediately, gradually such a transition occurs. However, there are enterprises (and not only in our country) that still work in the old fashioned way, and are suspicious of modern materials, despite the fact that these plates are made with the highest specified quality and have all the manufacturer's warranties. Therefore, along with a wide range of offset printing plates for laser writing, there are also conventional copying plates, which in many cases are recommended by manufacturers at the same time for recording by laser scanning or laser diode.
This paper discusses the main types of plates for the traditional technology of manufacturing offset printing plates, which involves copying an image from a photoform to a plate in a copy frame and subsequent development of an offset copy manually or using a processor, and then for the "computer-printing plate" technology ( Computer-to-Plate (Computer-to-Plate)), let's call it CtP for short. The latter allows you to expose the image directly on the plate without the use of photoforms. The focus will be on CtP wafers.
The main terms of printing production, mentioned in the work, are given in the appendix (see appendix 1).
1. The main types of printing plates for offset printing
1. 1 Offset printing method
The offset printing method has existed for more than a hundred years and today is perfect. technological process, giving the highest quality of printed products among all industrial ways print.
Offset printing(from the English offset) is a kind of flat printing, in which the ink from the printing plate is transferred to the rubber surface of the main offset cylinder, and from there it is transferred to paper (or other material); this allows thin layers of ink to be printed on rough papers. Printing is done from specially prepared offset forms, which are loaded into the printing machine. Currently, two methods of flat printing are used: offset with moisture and offset without moisture (“dry offset”).
In wet offset printing, the printing and blank elements of the printing plate lie in the same plane. Printing elements have hydrophobic properties, i.e. the ability to repel water, and at the same time oleophilic properties that allow them to perceive paint. At the same time, blank (non-printing) elements of the printed form, on the contrary, have hydrophilic and oleophobic properties, due to which they perceive water and repel ink. The printing plate used in offset printing is a ready-to-print plate that is mounted on a printing press. The offset printing machine has groups of rollers and cylinders. One group of rollers and cylinders provides for the application of a water-based moisturizing solution to the printing plate, and the other for the application of oil-based ink (Fig. 1). The printing plate, placed on the surface of the cylinder, is in contact with the roller systems.
Rice. 1. The main components of the offset printing unit
Water or a moisturizing solution is perceived only by blank elements of the form, and oil-based ink is perceived by printing ones. The ink image is then transferred to an intermediate cylinder (called the offset cylinder). The transfer of the image from the offset cylinder to the paper is achieved by creating a certain pressure between the printing and offset cylinders. Thus, flat offset printing is a printing process based solely on the principle that water and printing ink, due to their physical and chemical differences, repel each other.
Offsetwithout moisture uses the same principle, but with different combinations of surfaces and materials. So, an offset printing plate without moisture has gaps that strongly repel ink due to the silicone layer. The ink is perceived only in those areas of the printing form from which it is removed.
1. 2 Ways receiving printed forms and kinds form plates
Today, for the manufacture of printing plates for flat offset printing, a large number of different plate materials are used, which differ from each other in terms of manufacturing method, quality and cost. They can be obtained in two ways - this is a format and element-by-element notation. format notation- this is a recording of an image over the entire area at the same time (photographing, copying), the so-called traditional technology. Printing forms can be made by copying from photo forms - transparencies - in a positive way to copy or the negatives negative way of copying. In this case, plates with a positive or negative copy layer are used.
At element-by-element notation the image area is divided into some discrete elements, which are recorded gradually element by element (recording using laser radiation). The last way to obtain printing forms is called "digital", it involves the use of laser exposure. Printing plates are made in systems of direct production of printing plates or directly in a printing press (Computer-to-Plate, Computer-to-Press (Computer-to-Press)).
So, CtP is a computer-controlled process for making a printing plate by directly writing an image onto a plate material. At the same time, any intermediate material semi-finished products are completely absent: photoforms, reproduced original layouts, montages, etc.
Each printed form recorded from digital data is the first original copy, which provides the following indicators:
greater sharpness of points;
more accurate register;
more accurate reproduction of the gradation range of the original image;
less dot gain when printing;
reduction of time for preparatory and adjustment work on the printing press.
The main problems of using CtP technology are problems with the initial investment, increased requirements for the operator's qualifications (in particular, retraining), organizational problems (for example, the need to display ready-made descents) .
So, depending on the method of making printing plates, there are analaboutnew and digital plates.
There are also plates such as Waterless (Waterless - dry offset), which will be mentioned in my work.
Let us consider in more detail the main types of offset printing plates and their technical characteristics.
2. Analog Form Materials
2. 1 Uniform mate R ials for making printing plates contact copying
Contact copying is understood as a method of manufacturing printing plates, in which the image on the form is obtained as a result of contact exposure of the plate through a solid positive or negative photoform, or through the installation of photoforms. The exposure device, called a contact-copy frame (Fig. 2), consists of a folding glass frame and a table on which a plate and a photoform are placed.
Rice. 2. Contact-copy frame
The contact copy frame table is equipped with a powerful vacuum system, which ensures tight contact between the photoform and the printing plate "layer by layer". The exposure itself is carried out by a high-intensity radiation source, while the plate material and mounting are tightly pressed against each other.
Currently, the largest manufacturers of offset plates are Agfa, Fujifilm, Lastra (owned by Agfa), Ipagsa, Horsell Capiration, Kodak Polychrome Graphics (Kodak Polychrome Graphics). ) and others. Domestic plate manufacturers: Dozakl, Zaraisky Offset, Offset-Siberia [3, 12]. Regardless of the manufacturer, all plate plates are made using approximately the same technology, with the exception of certain nuances, the so-called "know-how".
Today, the most applicable in the printing industry metalplates. They are available in a very wide range of formats for both small and large format presses. Metal plates are divided into monometallic and bimetallic.
2.1.1 Bimetal plates
Main difference monometallic forms from bimetallic in that the printing and blanking elements of monometallic forms are on the same metal surface. On the bimetallic forms the printing elements are located on one metal (usually copper), and the space elements are on the second metal (chromium, less often nickel). That is bimetallicplates consist of two metal layers successively deposited on a metal or polyester substrate and a light-sensitive layer (Fig. 3) .
Rice. 3. The structure of the bimetallic plate
Such plates are used only for making forms by negative copying. Bimetallic forms accurately reproduce high-quality images and maintain up to 3-5 million prints. The best known is a form made on a plate having a steel base coated with a thin layer of copper, chromium and a light-sensitive composition. After copying positive editing, developing, removing copper from blank elements and chromium from printed elements, a purely metallic form is obtained, on which copper areas perceive paint, and chromium areas perceive water. In book production, such forms are used very rarely, since the forms themselves are expensive, and the processes, both for the manufacture of plates and for the forms themselves, require great efforts to protect against environmental pollution.
Today, domestic printers most often use pre-sensitized monometallic plates as an offset form for a small-format printing machine.
2.1.2 Monometallic plates
Pre-sensitized monometallic plates consist of four layers (Fig. 4), each of which performs certain functions:
Substrate (form plate base): paper, plastic (polyester) or metal (aluminum) with a thickness of approximately 0.15 to 0.40 mm;
anode film (provides wear resistance of gap elements);
hydrophilic sublayer (serves to ensure the hydrophilicity of gap elements);
copy layer (forms printing elements).
Rice. 4. The structure of a monometallic plate
Pre-felt offset plates are manufactured by specialized companies on high-performance automated production lines with strict adherence to rules. These plates have a thin aluminum base with a rough surface called grain.
The production of offset printing plates is carried out in several stages:
1. Pre-treatment of aluminum sheets
2. Surface granulation.
3. Anodizing (anodic oxidation).
4. Application of a photosensitive copy layer.
Pre-treatment of aluminum includes cleaning the plate from dirt and degreasing.
After that follows electrochemical granulation(using alternating current), which creates a highly developed surface structure that provides the adsorption properties of the substrate, and also allows you to hold a larger amount of dampening solution and easier to achieve ink-water balance when printing. As a rule, graining proceeds in three stages, as a result of which three types of microroughnesses are created on the surface of the plate: coarse, medium and fine grains. Large grain provides high-quality reproduction of halftones and good perception of the dampening solution. The medium grain is responsible for the print runs. Fine grain allows to achieve the balance "ink - water" and increases the wear resistance of the mold surface.
Anode oxidation consists in converting the aluminum surface into alumina by electrochemical treatment. Aluminum oxide (A19 O3) is a very strong element, with a very high chemical inertness, which can only be affected by alkaline melting (fusion) at temperatures of about 1000 ° C. Surface transformation produces a layer of aluminum oxide; its weight can vary from 2 to 4 grams of oxide per square meter. As a result of anodizing, the hardness of aluminum increases, the resistance of the plates to mechanical and chemical influences increases, and the circulation resistance of printing plates also increases. After graining and anodic oxidation, the surface of aluminum becomes rough and covered with a strong porous oxide film, which, after being filled with a hydrophilic colloid, acquires stable hydrophilic properties. Then a copy layer is applied to the prepared aluminum base. Its thickness on the plate should be numbered (2-4 microns), since the copy layer is responsible for many indicators of the plate. Copy layers are divided into positive and negative. After exposure, the positive layers become soluble, while the negative ones lose their ability to dissolve.
General requirements for copy layers:
the ability to form a thin, uniform, non-porous film when applied;
good adhesion to the substrate;
change in solubility in the corresponding solvent as a result of exposure to radiation;
sufficient resolution;
high selectivity of manifestation, i.e. lack of solubility of future printing elements;
resistance to aggressive environments.
The properties of the copy layer and the base determine the characteristics of the future printing form.
1) photosensitivity;
2) resolution;
3) gradational transfer;
4) roughness;
5) circulation resistance.
Light sensitivity determines the exposure time of the plate. The higher the sensitivity, the less time it takes to expose. The difference between a negative and a positive plate is that they react differently to light: the negative photosensitive material polymerizes and becomes insoluble when exposed to light. When developed, the unexposed "lacquer" dissolves; thus, a plate is obtained, the values of which are opposite to the values of the original installation. The sensitivity spectrum of the negative plate is similar to that of the positive plate, but absolute values above (Fig.5, 6).
Fig.5. Spectral negative plate
Fig.6. Spectral sensitivity positive plate sensitivity
Spectral sensitivity determines the sensitivity of the copy layer to the effects of radiation at different wavelengths. For copy layers based on orthonaphthofinonediazides, ultraviolet radiation with a wavelength of 330-450 nm is actinic.
The integral light sensitivity determines the exposure time of the plates in the copy frame.
Factors affecting photosensitivity:
chemical composition of the copy layer;
physical parameters of the copy layer and substrate (reflection coefficient, adhesion of the copy layer and substrate, thickness of the copy layer);
exposure conditions (spectral composition of radiation, exposure);
Conditions for processing the copy layer. Light scattering degrades the quality. To reduce light scattering, it is required to expose less time, which requires the use of very powerful radiation sources. The smaller the thickness of the copy layer of the oven mold, the higher the light sensitivity, therefore, the thicker the copy layer is, the greater the exposure should be.
Resolution defines the percentage of the reproduced half-dot and the minimum possible stroke width.
Resolution is affected by:
the thickness of the copy layer (the larger it is, the lower the resolution);
development mode and composition of the processing solution;
dimensions of the radiation source and its distance from the copy layer.
gradation transfer depends on the possibility of transmitting halftone dots. On the forms of flat offset printing, obtained by the method of format recording, the minimum raster dot can be 3 percent, the maximum - 98 percent. The control is carried out both visually and with the help of a densitometer, which makes it possible to measure the relative size of the raster dot on the printing plate.
Roughness the base surface is characterized by three parameters: arithmetic mean deviation of the profile; microroughness height; roughness factor. The adhesion of the copy layer to the substrate and, accordingly, its resistance to mechanical stress, the required amount of moisturizing solution, and the stability of the image quality during printing depend on the roughness. The roughness is determined by the arithmetic mean profile deviation - Ra (µm).
Circulation resistance determined by the resistance of the copy layer to abrasion. After heat treatment (firing), it usually increases by two to three times.
The following factors influence the durability:
violation of the technology and modes of the copying process (for example, overexposure, overdevelopment, etc.);
properties of printing inks;
paper grade;
characteristics of moisturizing solutions, etc. .
Experts ranked the influence of the properties of the copy layer on the characteristics of the future printing form, namely:
1. photosensitivity;
2. resolution;
3. gradation transfer;
4. roughness;
5. circulation resistance.
The ranking method consists in the fact that the expert is invited to assign numerical ranks to each of the factors given in the questionnaire. A rank of 1 is assigned to the most important factor, a rank of 2 to the next most important factor, and so on. The ranking matrix obtained as a result of the survey is shown in Table 1.
Table 1Ranking matrix obtained as a result of a survey of five experts| Feature number printed form | Expert assessment | Sum | Deviation from the mean | Square deviations | |||||
Currently, printing houses mainly use light-sensitive aluminum plates with a pre-applied photopolymerizable composition based on diazo compounds. At the same time, plates for positive and negative copying methods differ in principle only in the composition of the copy layer: in the first case, diazo compounds are used, for example, orthonaphthoquinone diazides (OHCD), in the second, photopolymerizable layers.
Monometallic forms have a number of advantages. For example, if they are copied from high-quality photoforms, they are able to give the best quality level possible today: resolution up to 10 microns, reproduce a 2% half-dot with a lineature of 175 lpi. The grained aluminum surface has a high water holding capacity, so that the gap elements are stable and the machine quickly reaches the paint-water balance. Monometallic plates perform satisfactorily even when humidification is used with significant deviations from the standards. Their circulation resistance is high and reaches 100-250 thousand prints, after firing it can double. Modern monometallic plates have high performance in many ways:
The roughness (Ra from 0.4 µm) ensures that there are no “non-pressures” of the photoform, minimizes distortion during the copying process and keeps the hydrophilic film on white space elements in the printing process. The result is a high ink density on the print, a stable ink-water balance and reduced consumption of a moisturizing solution;
The thickness of the anodized layer is 3.0 g/m2;
Resolution (the minimum width of a reproduced stroke on a copy is 6-12 microns), clear reproduction of the solution (from 2 to 99% with a lineature of 150-175 lpi);
The light sensitivity level allows you to reduce the exposure time when copying, avoid unwanted light scattering and ensure accurate reproduction of small elements;
The color contrast of the image on the form after processing facilitates quality control and, if necessary, the proofreading process;
Circulation resistance - 150 thousand and more (depending on printing conditions); 300 thousand and more (depending on the brand of plates and printing conditions) - after heat treatment.
These plates can be used in a number of industries: commercial sheetfed printing, magazine production, packaging, small offset and even newspaper printing. Storage conditions for plates at temperatures not exceeding 32°C and relative humidity up to 70%.
Comparative characteristics of this form material are presented in Table 1 of Appendix 3.
2. 2 Electrostatic mold materials
The electrostatic platemaking process is based on the principles of electrophotography, which consists in using a photoconductive surface to form a latent electrostatic image, which is subsequently developed.
A special paper substrate with a photoconductive coating applied to it (zinc oxide) is used as a form material. Form material, depending on the type of processing device, can be sheet and roll.
The circulation stability of such printing forms is 1-10 thousand prints, depending on the brand of the plate material. Resolution - 33 lines / cm.
Scope - small-circulation text and line products (textbooks, instructions, etc.), as well as operational display products that do not require high quality (forms, envelopes, folders).
Advantages of technology:
Efficiency of production of a printed form (less than 1 minute);
Ease of use;
the possibility of direct use of non-transparent originals, paper pastings and montages;
low cost of consumables;
High reliability.
Flaws:
low lineature, limited by the capabilities of laser printers;
maximum format -- A2;
Low print runs.
3. Digital plate materials
For a whole century, and even longer, images were fixed on photographic film and transferred to a printing plate by exposing photographic plates to a plate coated with a photosensitive emulsion. Over the past twenty years - and finally in the last five years - film has been pushed out of the prepress process, and the image is recorded on the plate directly from the digital file. As a result, we get a first generation image, much clearer than traditional plate production can give. When transferring an image, the dot gain on the printed plate is negligible or absent, image details are not lost or distorted.
Forecasters say that within five to ten years, film will completely disappear from the printing industry, with the possible exception of very small enterprises. Let's take a closer look at Computer-To-Plate technology.
So, with the traditional way of creating an offset printing plate, the final product that the image recorder (imagesetter) produces is film. Form plate with photosensitive polymer coated placed in a copy frame with a high intensity UV source. UV rays shine through the film and expose the plate. After that, the plate passes through a developing processor with a three-stage processing, where the polymer layer is removed from the gaps. The finished printing plate is dried before being used in the printing press. AT manufacturing process based on CtP technology, the image recording on the plate is performed by lasers based on digital data. If the machine is fully automated, the exposure device picks up the plate and delivers it to the image registration area. The plate can then be punched with registration pin holes in the press (there are exposure systems that can punch both before and after exposure). The finished printing plate during manufacture goes through the same development and drying stages as with traditional technology, but in CtP systems, development can be automated.
The CtP system includes three main components (Fig. 7):
computers that process digital data and manage their flows;
devices for recording on form plates (exposure devices, form output devices);
form material (form plates with various copy layers sensitive to certain wavelengths).
Rice. 7. Computer-to-Plate system
There are many different types of lasers used for printing plates, they operate in different frequency ranges and have different imaging performance. All lasers can be divided into two main categories: near-infrared thermal lasers and visible lasers. Thermal lasers expose the printing plate to heat, while visible plates record to light. It is necessary to use plates specially designed for a particular type of laser, otherwise the image will not be correctly registered; this applies equally to processors.
Plate types
The main types of printing plates for CtP are paper, polyester and metal plates.
3. 1 paper plates
These are the cheapest inserts for CtP. You can see them in small commercial print shops, in fast print shops, for low resolution, "dirty" jobs where register is not important. Circulation stability, or circulation stability of such forms is low, usually less than 10,000 prints. Resolution most often does not exceed 133 lpi.
3. 2 Polyester printing plates
These plates have a higher resolution than paper plates, but at the same time they are cheaper than metal ones. They are used for medium-quality jobs for printing in one and two colors - as well as for four-color orders - in the event that color reproduction, register and image clarity are not critical.
Form material is a polyester film with a thickness of about 0.15 mm, one of the sides of which has hydrophilic properties. This side accepts toner applied by a laser printer or copier. The untoned areas hold onto the dampening solution film during printing and repel ink, while the printed areas, on the contrary, accept it. Since these are photosensitive plates, they are loaded into the exposure device in a room with special lighting, the so-called "dark" or "yellow" room. These plates are available in sizes up to 40 inches, or 1000 mm, and thicknesses of 0.15 and 0.3 mm. The 0.3 mm thick plates are already the third generation of this type of material, having a thickness similar to that of plates on a metal base for four and eight-color machines.
When mounted on a plate cylinder and the tension is exceeded, the polyester printing plate may be stretched. Also, form stretching is often observed on full-format machines. It is currently possible to use polyester printing plates for full color printing. In 2- and 4-color printing, paper stretch is more common than forms. The circulation resistance of polyester forms is 20-25 thousand prints. Maximum lineature 150-175 lpi.
However, the main attention today is focused on the production of metal CtP-plates. In fact, such a printed form has now become the standard.
3. 3 metal plates
Metal plates have an aluminum base; they are able to maintain the sharpest point and the highest level of registration. There are four main types of metal plates: silver halide plates, photopolymer plates, thermal plates, and hybrid plates.
Digitalmetalplates.
photopolymer
thermal
hybrid
The main plate manufacturers for CtP technology are FujiFilm, Agfa, DuPont, Kodak Polychrome Graphics, Presstek, Lastra, Mitsubishi, Creo.
3.3.1 Silver plates
The plates are coated with a photosensitive emulsion containing silver halides. They consist of three layers: barrier, emulsion and anti-stress, deposited on an aluminum base, subjected to preliminary electro-chemical graining, anodizing and special treatment to catalyze the migration of silver and ensure the strength of its fixation on the plate (Fig. 8). Directly on the aluminum base are also the smallest nuclei of colloidal silver, which are reduced to metallic in the course of subsequent processing.
Rice. 8. The structure of the silver plate
All three water-soluble layers are applied in one cycle. This multilayer coating technology is very similar to that used in the production of photographic films, and allows you to optimize the properties of the plate by giving each layer specific characteristics. Thus, the barrier layer is made of a gelatin-free polymer, contains particles that contribute to the most complete removal of the remnants of all layers of the unexposed area during the development of the plates, which stabilizes its printing properties. In addition, the layer contains light-absorbing components to minimize reflection from the aluminum base. The emulsion layer of these plates consists of light-sensitive silver halides, which provide high spectral sensitivity of the material and exposure speed. The top anti-stress layer serves to protect the emulsion layer. It also contains special polymer compounds to facilitate the removal of release paper in automatic systems, and light-absorbing components in a certain part of the spectrum to optimize resolution and working conditions with safe lighting.
The technical characteristics of this form material are presented in Table 2 of Appendix 3.
3.3.2 Photopolymer plates
These are plates with an aluminum base and a polymer coating (Fig. 9), which gives them exceptional circulation stability - 200,000 or more prints. Additional firing of printing plates before the print run can increase the life of the printing plate to 400,000 - 1,000,000 prints. The resolution of the printed form allows you to work with a raster lineature of 200 lpi and a “stochastic” of 20 microns, it withstands very high speeds print. These plates are designed to be exposed in devices with a visible light laser - green or violet.
Rice. 9. The structure of the photopolymer plate
Photopolymer exposure technology involves a negative process, that is, future printed elements are exposed to laser illumination. The plates are intermediate in sensitivity between thermal and silver-containing .
This material was shown in 1993 on Gerber Crescent/42 and Scitex Doplate devices. The disadvantage of the photopolymer is the occurrence of foam in the processing reagents during development. In addition, these plates need to be heated after exposure. They may not be the most sensitive, but they have very high run-time and printability.
The technical characteristics of this form material are presented in Table 3 of Appendix 4.
3.3.3 Thermal plates
They consist of three layers: an aluminum substrate, a printed layer and a heat-sensitive layer, which has a thickness of less than 1 micron, i.e. 100 times thinner than a human hair (Fig. 10).
Rice. 10. The structure of the thermal plate
Registration of the image on these plates is carried out by radiation of the invisible spectrum, close to infrared. When IR energy is absorbed, the surface of the plate heats up and forms image areas from which the protective layer is removed - the process of ablation, blurring occurs; it is an "ablative" technology. The high sensitivity of the top layer to IR radiation provides unsurpassed imaging speed, since it takes a short time to expose the plate to the laser. During exposure, the properties of the upper layer are transformed under the action of induced heat, since during laser irradiation the temperature of the layer rises to 400 ° C, which makes it possible to call the process thermoforming of the image.
Plates are divided into three groups (generations):
Heat sensitive plates with preheating;
Heat-sensitive plates that do not require preheating;
Heat-sensitive plates that do not require additional processing after exposure.
Thermal plates are characterized by high resolution, run resistance is usually specified by manufacturers at the level of 200,000 or more prints. With additional firing, some plates are able to withstand a million copies. Some types of thermal plates are designed for three-part development, others are subjected to preliminary firing, which completes the image recording process. Since the exposure is made with lasers outside the visible spectrum, there is no need for darkening or special protective lighting. When processing heat-sensitive plates of the second generation, the laborious preheating stage, which requires time and energy costs, is eliminated. Due to the fact that the plates have printing elements resistant to various kinds of chemicals, they can be used with a wide variety of auxiliary materials and inks, for example, in printing machines with an alcohol dampening system and when printing with UV-curable inks. The plates provide dot reproduction in the range of 1 - 99% with lineature up to 200 lpi, which allows them to be used for printing jobs that require the highest quality.
- 185.00 KbMoscow State University of Printing. I. Fedorova
Department "Technology of prepress processes"
Test
discipline: "Technology of Form Processes"
Moscow, 2011
Digital technology: CTP and CTcP flat offset printing
CTP
Digital technologies for the production of offset printing plates according to the scheme "Computer - printing plate" is carried out by element-by-element recording of the image on the plate. Image formation occurs as a result of laser exposure to radiation.
The CtP system includes three main components:
- computers that process digital data and manage their flows;
- devices for recording on form plates (exposure devices, form output devices);
- form material (form plates with different copy layers sensitive to certain wavelengths).
There are many different types of lasers used for printing plates, they operate in different frequency ranges and have different imaging performance. All lasers can be divided into two main categories: near-infrared thermal lasers and visible lasers. Thermal lasers expose the printing plate to heat, while visible plates record to light. It is necessary to use plates specially designed for a particular type of laser, otherwise the image will not be correctly registered; this applies equally to processors.
Plate types
The main types of printing plates for CtP are paper, polyester and metal plates.
paper plates
These are the cheapest inserts for CtP. You can see them in small commercial print shops, in fast print shops, for low resolution, "dirty" jobs where register is not important. Circulation stability, or runtime, of such forms is low, usually less than 10,000 prints. Resolution most often does not exceed 133 lpi.
Polyester printing plates
These plates have a higher resolution than paper plates, but at the same time they are cheaper than metal ones. They are used for medium-quality jobs for printing in one and two colors - as well as for four-color orders - in the event that color reproduction, register and image clarity are not critical.
Form material is a polyester film with a thickness of about 0.15 mm, one of the sides of which has hydrophilic properties. This side accepts toner applied by a laser printer or copier. The untoned areas hold onto the dampening solution film during printing and repel ink, while the printed areas, on the contrary, accept it. Since these are photosensitive plates, they are loaded into the exposure device in a room with special lighting, the so-called "dark" or "yellow" room. These plates are available in sizes up to 40 inches, or 1000 mm, and thicknesses of 0.15 and 0.3 mm. The 0.3 mm thick plates are already the third generation of this type of material, having a thickness similar to that of plates on a metal base for four and eight-color machines.
When mounted on a plate cylinder and the tension is exceeded, the polyester printing plate may be stretched. Also, form stretching is often observed on full-format machines. It is currently possible to use polyester printing plates for full color printing. In 2- and 4-color printing, paper stretch is more common than forms. The circulation resistance of polyester forms is 20-25 thousand prints. Maximum lineature 150–175 lpi.
metal plates
Metal plates have an aluminum base; they are able to maintain the sharpest point and the highest level of registration. There are four main types of metal plates: silver halide plates, photopolymer plates, thermal plates, and hybrid plates.
Silver-containing plates
The plates are coated with a photosensitive emulsion containing silver halides. They consist of three layers: barrier, emulsion and anti-stress, deposited on an aluminum base, subjected to preliminary electro-chemical graining, anodizing and special treatment to catalyze the migration of silver and ensure the strength of its fixation on the plate (Fig. 8). Directly on the aluminum base are also the smallest nuclei of colloidal silver, which are reduced to metallic in the course of subsequent processing.
The structure of the silver plate
All three water-soluble layers are applied in one cycle. This multilayer coating technology is very similar to that used in the production of photographic films, and allows you to optimize the properties of the plate by giving each layer specific characteristics. Thus, the barrier layer is made of a gelatin-free polymer, contains particles that contribute to the most complete removal of the remnants of all layers of the unexposed area during the development of the plates, which stabilizes its printing properties. In addition, the layer contains light-absorbing components to minimize reflection from the aluminum base. The emulsion layer of these plates consists of light-sensitive silver halides, which provide high spectral sensitivity of the material and exposure speed. The top anti-stress layer serves to protect the emulsion layer. It also contains special polymer compounds to facilitate the removal of release paper in automatic systems, and light-absorbing components in a certain part of the spectrum to optimize resolution and working conditions with safe lighting.
Silver-containing plates are very sensitive to radiation and easy to use, but they have the disadvantage of low print run up to 350,000 prints and, in addition, according to the law on environmental protection, they require a silver regeneration procedure after their use.
3.3.2 Photopolymer plates
These are plates with an aluminum base and a polymer coating that gives them exceptional circulation stability - 200,000 or more prints. Additional plate firing prior to printing can increase plate life to 400,000 to 1,000,000 prints. The resolution of the printed form allows you to work with a screen lineature of 200 lpi and a "stochastic" of 20 microns, it can withstand very high printing speeds. These plates are designed to be exposed in devices with a visible laser - green or violet.
The structure of the photopolymer plate
Photopolymer exposure technology involves a negative process, that is, future printed elements are exposed to laser illumination. The plates are intermediate in sensitivity between thermal and silver-containing .
Thermal plates
They consist of three layers: an aluminum substrate, a printed layer and a heat-sensitive layer, which has a thickness of less than 1 micron, i.e. 100 times thinner than a human hair.
The structure of the thermal plate
Registration of the image on these plates is carried out by radiation of the invisible spectrum, close to infrared. When IR energy is absorbed, the surface of the plate heats up and forms image areas from which the protective layer is removed - the process of ablation, blurring occurs; it is an "ablative" technology. The high sensitivity of the top layer to IR radiation provides unsurpassed imaging speed, since it takes a short time to expose the plate to the laser. During exposure, the properties of the upper layer are transformed by the induced heat, since the temperature of the layer rises to 400 ° C during laser irradiation, which makes it possible to call the process thermoforming of the image.
Plates are divided into three groups (generations):
Heat-sensitive plates with preheating;
Heat-sensitive plates that do not require preheating;
Heat-sensitive plates that do not require additional processing after exposure.
Thermal plates are characterized by high resolution, run resistance is usually specified by manufacturers at the level of 200,000 or more prints. With additional firing, some plates are able to withstand a million copies. Some types of thermal plates are designed for three-part development, others are subjected to preliminary firing, which completes the image recording process. Since the exposure is made with lasers outside the visible spectrum, there is no need for darkening or special protective lighting. When processing heat-sensitive plates of the second generation, the laborious preheating stage, which requires time and energy costs, is eliminated. Due to the fact that the plates have printing elements resistant to various kinds of chemicals, they can be used with a wide variety of auxiliary materials and inks, for example, in printing machines with an alcohol dampening system and when printing with UV-curable inks. The plates provide dot reproduction in the range of 1 - 99% with lineature up to 200 lpi, which allows them to be used for printing jobs that require the highest quality.
But, despite these advantages, the weakness of this technology is the higher total cost of thermal plates and the high cost of thermal exposure devices compared to photosensitive systems. Such plates require the CtP device to be equipped with a vacuum unit for waste removal.
CTcP
Digital technologies for the production of offset printing plates are implemented not only by recording an image on form output devices using CTP technology, but also with the help of UV radiation in a UV-Setter device from Basys Print. This technology, known as "computer-traditional printing form" - CTcP, is carried out by writing an image on a plate with a copy layer.
The image recording method in this technology is based on digital radiation modulation using a micromirror device - a chip, each mirror of which is controlled in such a way that, in the on position, a single micromirror directs the light signal coming to it through a focusing lens onto a form plate; in the off state, the light reflected from the micromirror does not hit the plate and, therefore, is not recorded on it.
Thus, the image is recorded on the form plate, while each micromirror (and there are about 1.3 million of them) forms a square image subelement with sharp edges (Fig. 1).
Since the UV-Setter currently uses sources that emit radiation in the UV range of the spectrum, plates with a copy layer, both positive and negative, find practical use. At the same time, the use of plates with a negative copy layer allows you to increase productivity due to the fact that recording on them (taking into account the principle of obtaining image details during exposure) requires less time.
Rice. one. An enlarged fragment of the structure of the surface of the printing form I
And the configuration of the raster dots obtained on it II
So far, there is only one group of mass-produced CTcP devices on the market - these are UV-Setter mold makers from bassysPrint (Germany). basysPrint was founded in 1995 by German engineer Friedrich Lüllau to commercialize his DSI (Digital Screen Imaging) technology.
Work description
Digital technologies for the production of offset printing plates according to the scheme "Computer - printing plate" is carried out by element-by-element recording of the image on the plate. Image formation occurs as a result of laser exposure to radiation.