1. Classification of CTP
At present, according to different classification methods, the CTP system has different classifications.
(1) According to the working mode of computer direct plate-making system, CTP direct plate-making machine mainly has four categories: inner drum type, outer drum type, platform type and curve type, and curve type is rarely used. The characteristics of the first three CTP systems are briefly introduced below.
The outer drum CTP system is suitable for thermal plates, and is more suitable for large format. Because the energy required for the thermal printing plate is large, the light source must have a large power, and a multi-beam laser head is used at the same time. However, the specifications of the plate materials suitable for this CTP system are few, the rotation speed of the drum is not high, and the plate changing speed is relatively slow. Kodak and Screen have launched products with this exposure method.
The inner drum CTP system is not suitable for large format output printing plates. However, the scanning speed of this type of CTP system is relatively fast and the accuracy is relatively high. At the same time, due to the use of a single-beam laser head, the price is relatively cheap, and the version change is also simpler and more convenient than the outer drum CTP system. It can support multiple punching specifications at the same time. Both Agfa and ECRM have mature products that use such exposure methods .
The platform CTP system also uses a single beam laser head, which has a relatively cheap price. At the same time, this type of system has a simple mechanical structure, stable operation, and a high scanning speed, but it covers a large area and is not suitable for large-format printing plate output. Such representatives mainly include Barco's CTP system.
(2) According to the exposure light source, the main light sources used in the CTP system include gas lasers, solid-state lasers and semiconductor lasers. The two main types of CTP systems currently on the market are violet laser CTP and thermal CTP.
The imaging technology of the purple laser plate-making system is recognized as a technology with good durability and high reliability. The CTP equipment made by combining the imaging technology and the purple laser technology has gradually gained market recognition in the past few years. Its characteristics are: Low purchase cost, low operating cost and high operating speed.
The advantage of thermal technology is that the imaging quality is good, and the image hierarchy can be restored for both the negative and positive images. However, the cost of thermal CTP for small format printing is relatively high, and it is not competitive in the field of thermal newspapers, but there is a relatively large market in the field of commercial printing where there is a demand for high-precision reproduction.
(3) According to the degree of automation, the CTP system can be divided into: manual stand-alone, semi-automatic, fully automatic and hybrid (CTF-computer to film and CTP-computer to plate).
(4) In terms of the fixing method of the printing plate on the drum, it can be divided into: full adsorption type and middle adsorption, and two kinds of fixing with a clip at the beginning and the end. The full-adsorption type has no restrictions on the size of the plate, and the plate format used by the clip-type must have a fixed size.
(5) From the aspect of application, it can be divided into: commercial CTP system and report CTP system.
2. Classification of CTP plates
For now, there are three main types of CTP plates in the market: silver salt type, photopolymerization type, and thermal type (thermographic type). Below we mainly look at the characteristics and advantages and disadvantages of these types of plates.
Performance comparison of three major types of plates
Types of
Silver salt
Light gathering
Heat sensitive
Laser wavelength:
532nm
405nm
830nm
Light source energy:
<5mw
> 30mw
40w
Plate sensitivity:
μJ / cm2
mJ / cm2
J / cm2
Plate making speed:
> 180 sheets / h
<80 sheets / h
<30 sheets / h
Reproduction of outlets:
2% -98%
2% -98%
1% -99%
Adaptation:
Newspaper
Business, newspaper
business
1. Silver salt CTP plate
Silver salt type CTP plate material mainly includes two types of silver salt diffusion transfer plate and silver salt and PS plate composite plate material.
The silver salt diffusion transfer plate is mainly composed of a plate base, a silver salt emulsion layer and a physical development core layer. It uses diffusion transfer imaging technology, the principle is the silver salt plate exposed by laser scanning, in the developer containing silver halide solvent, Ag + and silver halide solvent complex and diffuse to the image receiving layer, in the physical development of the nuclear catalysis Reduced to metallic silver under the action of
Deposited on the body surface to form a silver image. After the development is completed, the silver halide emulsion layer on the surface is removed by water washing, exposing the hydrophilic sands and image areas of the non-image area. In the lipid-sensing liquid, the organic molecules of the long fat chain with mercapto groups are selectively adsorbed on the surface of the deposited silver Make the image area oleophobic. As a result, the deposited silver image began to accept ink and repel water, while the non-image part (without silver deposition) still repels ink, thereby achieving the goal of computer-to-plate.
The composite type of silver salt and PS plate is mainly composed of a silver salt emulsion layer with high sensitivity and a PS plate with a wide color range. A pre-sensitized photosensitive polymer layer, an adhesive layer and a silver halide emulsion layer are sequentially coated on the roughened and anodized aluminum substrate. The imaging principle is that the silver salt layer is first exposed with a laser to form a graphic silver image on the resin layer, so that the secondary photosensitive layer can be protected from light during the second exposure. After the primary development, the emulsion layer in the non-exposed area is dissolved and then subjected to secondary exposure, that is, the entire plate surface is exposed with UV light. Since the graphic image layer blocks the light, the UV light only exposes the photodegradable photosensitive resin layer in the non-graphical part, and the resin layer after secondary development and secondary exposure is dissolved to expose the alumina plate Finally, the silver image layer can be fat-sensitized with solid-plate solution.
Characteristics of Silver Salt CTP Plate
(1) Silver salt type CTP plate has high sensitivity, which can reach 1 ~ 3μJ / cm2, even using low output power, low energy, low intensity laser? Can also achieve high-speed plate output. Moreover, the silver salt type CTP plate has a fast photosensitive speed, which is the fastest photosensitive plate among the CTP plates at present.
(2) The silver salt type CTP plate has a wide range of applications. Red laser, green laser, and purple laser systems can be used. The rinsing method and post-processing process are the same as the traditional method, and different manufacturers of CTP plates have a chemical solution The formula is compatible.
(3) The silver salt type CTP plate has the characteristics of high resolution, wide spectral response and good dot reproducibility. The number of screen lines can reach 300 lines / inch, the dot coverage rate can reach 1% to 99%, and the quality of the printing plate Excellent, with a durability of more than 250,000 prints, it is more suitable for printing with large volume and high quality.
(4) Since the silver salt type CTP plate uses expensive silver as a raw material, the production cost is increased to a certain extent, and the silver salt type CTP plate cannot be operated in the bright room, which brings a certain degree to the preservation of the plate Limitations. [next]
2. Photopolymerization CTP plate
The photopolymerizable CTP plate is mainly composed of three parts: aluminum mesh base, photosensitive layer and protective layer. The photosensitive layer is mainly composed of film-forming resin, sensitizing dye, photoinitiator, monomer or oligomer, stable Agent and other additives. The protective layer is a polyvinyl alcohol oxygen barrier layer, which is mainly used to block the inhibitory effect of oxygen on monomers or oligomers. The imaging principle is that after the plate is scanned by the laser light source, the sensitizing dye in the photosensitive layer of the light-seeking portion first absorbs the photon energy to become an excited state, and then transfers the energy to the photoinitiator, which decomposes to form free radicals, free The base initiates the polymerization of the monomer or oligomer and solidifies, forming a graphic part. The part where no light is seen is removed by development to form a blank part. It should be noted that before development, the protective layer of the unexposed part should be washed away, and then the high-sensitivity polymer layer should be dissolved with an alkaline developer. After the development, the protective layer should be completely removed with a brush. Finally, rinse the layout with a synthetic resin solution. The synthetic resin not only improves the hydrophilicity of the blank part, but also enhances the lipophilicity of the graphic part. It can be printed after drying.
Characteristics of photopolymerization CTP plate
(1) The photosensitive layer of the photopolymerizable CTP plate is very thin, the graphic part and the blank part are basically on the same plane, which belongs to the traditional offset printing type, and has a high sensitivity and fast plate making speed.
(2) The developing solution used for the photopolymerizable CTP plate is alkaline, and the film-forming resin and monomer or oligomer in the photosensitive layer have a certain acidity, which can be dissolved in an alkaline solution and removed by development, and the alkali The contamination of the developer is small, which is beneficial to environmental protection.
(3) The photopolymerizable CTP plate can use different laser light sources such as violet laser diode (410nm), argon ion laser (488nm), FDYAG laser (532nm), infrared laser diode (830nm) And the photopolymerization type CTP plate can be printed with a printing resistance of over 1 million after baking.
3. Thermal CTP plate
There are many types of heat-sensitive CTP plates, but there are two main types that are relatively mature at present, namely, thermal melting type and thermal cross-linking type.
The hot-melt CTP plate is mainly composed of aluminum plate, ink-receptive layer and PVA layer (for conventional offset printing) or silica gel (for waterless offset printing) without roughening. The imaging principle is to use semiconductor laser diode exposure. The heat-sensitive coating on the plate base (that is, the ink-attractive layer) is ink-friendly and insoluble in alkaline syrup. After exposure, the coating absorbs energy and improves solubility, and can be dissolved in alkaline syrup. During development, the exposed part is dissolved in the alkaline solution, forming a blank part of the printing plate. The unexposed part does not dissolve, forming the graphic part of the printing plate. After development, it usually needs to be cleaned and glued before it can be printed on the machine.
The thermal cross-linking CTP plate is mainly composed of a roughened aluminum plate and a single-layer PS photosensitive layer. The imaging principle is through infrared exposure. During exposure, the photothermal conversion substance converts the light energy of the infrared laser into heat energy, so that some polymers in the photosensitive layer undergo thermal crosslinking reaction to form a latent image; reheating causes the molecular compounds in the graphic part to further undergo crosslinking reaction , So that the graphic part will not be dissolved in the alkaline developer. It should be noted that during preheating, the blank portion also partially reacts, so the image of the blank portion should be removed during development. If the temperature is too high, a hot mist will form on the printing plate; if the temperature is too low, it will fade or weaken the graphic part.
Characteristics of thermal CTP plate
(1) The thermal CTP plate has very low sensitivity to natural light, and it is exposed by infrared laser, so it can be operated in bright room conditions.
(2) To generate images for thermal plates, the initial thermal energy threshold must be reached, and thermal energy above the initial threshold will not change the shape of the dots. It is the only technology that can control the predictable results, the quality is easy to control, the publishing quality is stable, and after exposure The printing plate can be extended to 6 months and then developed, without affecting the quality of the plate.
(3) The dots of the thermal CTP plate have good reproducibility and high resolution, and the edges of the dots are sharp and clear. It is easy to achieve water-ink balance during printing, and has good printing suitability. The plate resistance after baking is up to More than 1 million seals.
In addition to the three dominant CTP plates introduced above, the CTP-free plate has become a hot topic for discussion in recent years.
4. Free processing CTP plate
The processing-free CTP plate was first introduced by Asahi Kasei Corporation of Japan. Broadly speaking, it means that the plate can be printed on the machine without any subsequent processing steps after exposure and imaging on the direct plate-making equipment. Of course, it does not require chemical development and rinsing. It is a true processing-free plate; from In a narrow sense, it means that the plates do not require chemical development after exposure and imaging on the direct plate-making machine, but there will still be individual non-chemical processing steps, such as removal of plate ablation waste, coating protective glue and other processing work. In terms of plate-making methods, processing-free plates can be divided into two categories: processing-free plates for DI (direct imaging on printing press) presses and plates exposed for imaging on CTP direct plate-making machines.
Features of processing-free plates
(1) Compared with the traditional CTP plate, the processing-free plate eliminates the steps of development, fixing, cleaning, gluing, and drying. , Which improves production efficiency and simplifies the production process.
(2) Since the process-free plate does not require chemical development, rinsing, etc., the process-free plate-making process will not produce environmentally harmful chemical waste liquid, exhaust gas, and waste residue, which reduces environmental pollution and is more convenient for printing operators Is beneficial.
(3) Changes in plate processing conditions, changes in laser energy, concentration, temperature, and speed of processing chemicals all affect the accuracy of dot reproduction, and processing-free plates that do not require processing can make them higher Quality stability.
(4) The processing-free plate does not require a chemical development processing device, which saves plant space, which is a major advantage for small companies, but the processing-free plate is more expensive than conventional CTP plates.
The main evaluation index of CTP plate
In view of so many CTP plates in the current market, from what aspects should we evaluate CTP plates? What kind of plate material meets our printing quality requirements?
(1) Reproduction of outlets. The dots are the basis for printing and copying graphic information. The quality of the printing plate dots will directly affect the quality of the printed dots, which in turn affects the copying of the entire printing process. Therefore, it is important to choose a plate with good dot reproducibility.
The outlets of CTP plates are the same as the traditional PS plates, which are also composed of sand. For the CTP plate material to achieve 1% to 99% dot reproduction, the mesh of the base must be fine enough, because the finer the mesh, the more meshes that support the highlight part of the mesh, the stronger the mesh, which occurs during printing The less likely to be out of version. However, the mesh size of the dots cannot be too fine, and the plate material with too fine mesh size has less tolerance for water-ink balance in printing, which is not conducive to the control of printing quality.
(2) Line reproduction. The reproducibility of the lines of the plate material usually includes two aspects, the reproduction of extremely thin lines and the size of the Yin and Yang lines. The reproduction of extremely fine lines is closely related to the size of the sand mesh of the plate material, especially the uniformity of the sand mesh, because only the edges of the lines of the evenly distributed sand mesh can be smooth. The size of the yin and yang lines is mainly determined by the coating thickness of the plate. We can compare the changes of lines by printing adjacent Yin and Yang lines on the printing plate.
(3) Ink affinity. The ink affinity of the plate material refers to a characteristic that the graphic part of the plate is selectively inked by the ink transfer roller. The thickness of the ink on the plate will directly affect the thickness of the ink on the blanket and the paper, and the amount of ink transferred to the plate It also depends on the ink affinity of the printing plate. If the ink affinity of the graphic part of the printing plate is low, the smaller the range of ink control in the entire printing, the more unfavorable to product quality. Moreover, with a poor ink affinity printing plate, the remaining ink will accumulate on the ink transfer roller, thickening the ink film of the ink transfer roller, and excessive ink accumulation at both ends, resulting in ink splashing, while reducing the hiding power of the ink . Therefore, CTP plates with good ink affinity are very important.
In order to improve the ink affinity of CTP plates, the photosensitive material in the graphic part of the printing plate should have similar chemical characteristics as the pigments, resins and solvents in the ink.
(4) Hydrophilicity. The hydrophilicity of the plate material refers to the characteristic of selectively retaining water on the non-graphic part of the printing plate. The amount of water in printing cannot be too much or too little. Too little, the parts without imprinting are easy to get dirty; too much, it is easy to appear dull and dull imprinting, uneven paper collection, paper deformation, overprinting and other conditions. At present, the main substrate of the CTP plate is aluminum, which is hydrophilic in itself, and the surface is subjected to grinding treatment, and then anodized coating treatment to form a porous surface, which enhances the total surface area and ultimately improves the hydrophilic characteristics.
In addition, the factors that affect the performance of CTP plate materials are also the resolution, printing resistance, degree, sensitivity, size specifications, and coating uniformity of the printing plate.
All in all, with the continuous advancement of CTP plate-making technology and the continuous improvement of CTP plate material performance, the advantages of CTP plate material continue to emerge, the continuous improvement of digital workflow, the continuous improvement of print quality requirements, we have reason to believe that CTP plate material will inevitably There are broader development prospects.
4 burners gas grill, Home Gas Grill, Propane Outdoor Grills, Barbeque Outdoor Grill, Barbecue Grill
JIANGMEN XINXIN METAL PRODUCTS CO., LTD. , https://www.bbqoutdoorgrill.com