The latest technology application of different types of CTP plates

Compared with the traditional plate-making process, the processing of the CTP plate is somewhat tedious, but its remarkable printability is unmatched by traditional plates, such as the quality of the dots. This article mainly introduces five different types of CTP plates. The performances among them are very different, and each plate has its own characteristics.

Requirements for CTP plates

The plate must be economical and practical to complete the laser exposure process in a short time. The photosensitive wavelength must be shifted from the UV region of the conventional PS plate to the visible or infrared region. And the exposure speed is nearly 100 times that of the conventional PS version, and the exposure energy should be less than 100 UJ/cm2. The plate used for high-quality color printing must have high sensitivity, good resolution, strong dot reproduction capability, and high printing durability. Easy to handle, high contrast requirements.

For a 175 lpi color printed CTP system, the output scanning resolution of the plate making machine should be greater than 2000 dpi, the tone range of the image should be between 2% and 98%, and the plate material is suitable for printing plate suitability and printing capacity. There are also comprehensive practical considerations in terms of costs.

Currently used CTP plates include: heat-sensitive plates, silver salt diffusion transfer plates, silver salt emulsions and polymer compounds, photopolymerization, electrostatic, and spray masks.

Silver salt diffusion transfer

The silver salt diffusion transfer version uses a diffusion transfer imaging technology, and the sensitivity is adapted to a variety of lasers, such as argon blue laser, yttrium aluminum laser, and ruby ​​laser.

Composition: A roughened aluminum plate, a silver salt emulsion layer, and a physical developer layer.

Principle: The blank part sees light. When developing, the light part is dissolved by the developer. The graphic part of the light does not form a conjugate on the core layer. The residue of the blank part is rinsed with warm water, and then the graphic part is subjected to lipophilic treatment. .

Features: Similar to silver halide film, good sensitivity, fast exposure, moderate contrast, light source is low intensity, low energy consumption laser, different manufacturers of CTP plate is compatible with chemical solution formulations.

Photopolymerization type

Photopolymerization CTP plate, printability and the traditional PS version is very close.

Composition: Coarse aluminum plate, polymer compound layer, PVA layer. (PVA not only prevents oxygen from entering the polymer layer and reacts with the photoactive group, but also plays a catalytic role in exposure.) The polymer compound layer includes: a photosensitizer, a polymerization monomer, a polymerization initiator, and a binder.

Principle: When exposed, the sensitizer absorbs the energy of the laser and produces a polymeric group together with the initiator. Prior to development, the PVA layer of the non-visible part is washed away, and the high-sensitivity polymer layer is dissolved with an alkaline developer. After the development is completed, the PVA is completely removed with a brush. Finally, the plate is washed with a synthetic resin solution. The synthetic resin can not only improve the hydrophilicity of the blank part, but also enhance the lipophilicity of the graphic part, and can be printed after drying. It is worth noting that, after the exposure is over, the polymerization reaction continues for several hours. At this time, the defects on the plate are generally removed by the infrared aging effect.

Features: Printability is good, the process is relatively clean, after the baking version, the printing rate is considerable, the printing plate can withstand scratching and brushing.

Silver salt emulsion and polymer compound type

Composition: Coarse aluminum plate, PS photosensitive layer, adhesion layer, silver salt emulsion layer.

Principle: The first exposure, the formation of silver salt latent image, development, washing, producing a protective layer of masking, followed by a second exposure (UV light source), so that the polymer layer to see the light, washed with a brush to remove the layer of polymer The layer is developed with an aqueous solution, rinsed with water, dried on a sizing machine and printed on the machine.

Features: The process is complex, adding chemical scum, but the advantages are obvious. The energy of the light source is lower than that of the single polymer type, which improves the stability of the latent image and the printability of the printing film is good; the printing rate after the baking version is large.

Spray mask type

It utilizes spray or spray technology.

Composition: Conventional PS plate plus a thin layer of soluble or waxy melt.

Principle: The ink jet head of the CTP system is used to inject ink on the plate, expose, wash the mask layer, and the subsequent processing is the same as the conventional PS plate.

Features: Due to the use of the regular PS version, no additional equipment is required, making it the most economical CTP plate.

Thermal type

The choice of heat-sensitive CTP is very large. There are hot-melt type, thermal-etch type, photo-etch type, thermal cross-link type, degradable type, and other thermal-sensitive type printing plates, both direct and indirect. Imagery.

Hot melt type

Composition: smooth, aluminum plate without roughening, ink-receptive layer, PVA layer (in conventional offset printing), silicone (when waterless offset printing).

Principle: Using semiconductor laser diodes, melt the graphic part to expose the following oleophilic layer, except the residue on the support plate, you can prepare to print on the machine.

Features: Non-chemical treatment process, from the environmental point of view, especially worth promoting. Second, you can work under the bright room.

Cross-linked type

Composition: Coarse aluminum plate, single layer PS photosensitive layer.

Principle: After a certain temperature is reached by the heat of infrared rays instead of the spectrum, some of the polymers in the photosensitive layer undergo thermal crosslinking reaction to form a latent image; and then, the polymer compounds in the graphic part are further cross-linked by heating. The purpose is to make the graphic part not dissolved in the alkaline developer. It is worth mentioning that a part of the reaction occurred in the blank part during preheating, so the image of the blank part was removed during development. If the temperature is too high, a hot mist will form on the plate; if the temperature is too low, the graphic part will be weakened or weakened.

Features: There is almost no relationship between exposure time and exposure energy. In other words, below the energy adjustment threshold, the external conditions will not affect the quality of the plate; beyond the energy threshold, the dot size and clarity will not be affected. Therefore, there is no such thing as underexposure and overexposure; the nature of the graphic part is very stable, and the plate is still usable even after six months of exposure; in addition, the thermal crosslinked plate has a low sensitivity to natural light. Therefore, it is possible to work under the bright room, and the processing only requires conventional plate-making equipment.

The thermal plate can be operated in daylight without the use of a safety light, and there are no problems with underexposure or exposure speed. However, the plate material is generally wet-processed. Thermal plates are the direction of development and use, and the silver salt format is only in a transitional period. The heat sensitive CTP plate is one of the most potential plates in the future. It has high energy efficiency, saves precious metals, and meets environmental requirements.

Plate cost analysis

The CTP plate making form is superior to other plate making forms, but relatively speaking, the cost of the plate material is too high. In February 1997, a 1030*770mm plate was sold in the United States at a price of $10, but shipments to the country would require a 25% increase in customs duties, 17% of VAT and freight. So when it comes to Chinese users, it is already ¥120/Zhang. This is equivalent to 4 times the PS version (30 yuan for a PS version and 35 yuan for a split film). But in the United States, the price of the two plates is about 1:1.2. So, after using CTP, the cost will drop accordingly.

The solution to this problem is to look forward to the reduction of the overseas price, or to use the domestic scientific and technological forces to jointly develop and produce self-produced plates. The current domestic scientific research forces have this ability, and there is a certain basis for the research on silver salt photosensitive materials. Therefore, this may reduce the plate price by half. This will promote the popularization and development of CTP technology in China.