Key points in the production of waterless offset CTP plate

Waterless offset printing has attracted more and more attention from the industry due to its excellent environmental protection and good printing results. Special plates, inks, and press refrigerating devices are three conditions for achieving waterless offset printing. Among them, the waterless offset CTP plate eliminates the error caused by the transmission of the dots due to the elimination of the film link during the plate making process, and can effectively improve the printing precision. Moreover, since the waterless offset CTP plate does not use film during the plate making process, it has good environmental protection. This article will introduce the three aspects of plate making, printing and preservation of waterless offset CTP plate.

Waterless offset CTP plate making

1. Structure of waterless offset printing plate

Waterless offset printing plates use silica gel instead of dampening solution to repel the ink with its low surface energy. The waterless offset printing plate (including the waterless offset CTP plate) is composed of an aluminum plate base layer, an undercoat layer, a photosensitive layer, a silica gel layer and a surface film layer.

(1) Aluminum plate base layer

The aluminum base layer mainly serves to support the printing plate.

(2) Undercoat

The undercoat layer is mainly used to enhance the adhesion between the photosensitive layer and the aluminum base layer to prevent the photosensitive layer from falling off.

3) Photosensitive layer

After the printing plate is photosensitive, a chemical reaction occurs, and the bonding force with the silica gel layer becomes small. After development, the weak bonding portion of the silica gel layer is brushed off to expose the photosensitive layer. The exposed photosensitive layer adsorbs ink during printing to form a graphic portion.

4) Silicone layer

The silica gel layer is used in the same manner as the fountain solution, i.e., the ink is repelled during the printing process to form a non-image portion.

(5) Surface film layer

The surface film layer serves primarily to protect the printing plate from scratches during transport during transport and during transport in the platesetter.

It can be seen that the conventional offset printing plate belongs to a plano-convex structure, and the waterless offset printing plate belongs to a plano-concave structure.

2. Waterless offset CTP plate making process

The traditional plate printing process of the water offset printing CTP plate is: exposure, development, water washing, upper protective glue, drying.

(1) Exposure

The exposure of the waterless offset CTP plate is directly exposed in a conventional CTP platesetter. It should be noted that the exposure time should be properly controlled during exposure.

(2) Uncovering the film

In order to prevent the printing plate from scratching, the protective film should be retained on the surface of the printing plate during exposure. However, it is necessary to completely remove the protective film before development. If the film is not completely removed, the development may be incomplete, and even the remaining protective film may fall off during the development process to block the water jet pump.

(3) redemption

The plate after uncovering should be placed in a special waterless automatic plate processor for printing. The process of the plate is divided into pre-treatment, water washing, post-treatment and re-washing.

(4) drying

After washing, the waterless offset CTP version cannot be dried by heating like the traditional water offset CTP plate, but must be dried by cold air.

Waterless offset CTP printing

Due to the special requirements of waterless offset printing, special waterless offset inks must be used for printing, and the printing press should be adjusted accordingly during the printing process.

1. Waterless offset ink

Waterless offset inks are similar to those used in conventional offset inks, and the binders and solvents used are also generally similar. The difference between the traditional offset printing ink and the traditional offset printing ink is as follows: 1 Since the non-image portion of the waterless offset printing CTP plate relies on the silica gel layer to repell the ink, the waterless offset printing ink should have a high cohesive force, and the viscosity is also higher than that of the conventional offset printing ink. In order to achieve good transferability, the waterless offset ink must also have low viscosity and large thixotropic properties; 3 because the waterless offset CTP plate is easily scratched, the pigment particles of the waterless offset ink cannot Too big, the gloss is high; 4 Since the waterless offset printing does not use dampening solution, the waterless offset printing ink does not need to have water resistance.

2. Paper

Paper used for waterless offset printing should have high surface strength. This is because the viscosity of waterless offset printing ink is higher than that of traditional offset printing ink. If the surface strength of the paper is not enough, it will cause powder falling and linting, which will affect printing. The smooth progress of the process will ultimately affect the quality of the print.

3. Printing process

The waterless offset CTP plate must pay attention to the following points during the printing process.

(1) Revision

If the plate layout is scratched or dirty during the printing process, it is necessary to use the water-repellent offset CTP plate-specific trimming solution for revision.

(2) Cleaning of the ink roller and blanket

The ink roller and blanket can be cleaned using the same car wash water and blanket cleaner as water offset. Among them, the cleaning agent used should have good volatility, otherwise the cleaning agent will remain in the ink due to slow evaporation, causing the ink to soften and cause dirt.

(3) Adjustment of the printing press

The adjustment of the printing machine will directly affect the quality of the printed matter. Therefore, we should carefully adjust the printing machine from the following aspects: 1 adjust the ink fountain, control the ink volume, avoid excessive ink volume, to shorten the preparation time and improve work efficiency; 2 reasonable Control the pressure of the ink roller. If the pressure of the ink roller is too large, the friction and heat will be severe, which will cause the viscosity of the ink to drop, causing the dirty phenomenon. If the pressure of the ink roller is too small or the ink roller is seriously worn, the ink will accumulate in the ink roller. It is easy to produce a gray bottom fault after friction and heat generation.

(4) Selection of blanket

It is recommended to use an air cushion blanket and use paper as a liner. Pay attention to the flatness of the pad. Try not to add padding midway to prevent the blanket from bulging and crushing the plate.

(5) Control of temperature and humidity

The waterless printing press must be equipped with a special refrigeration device to control the temperature of the plate and the surface of the drum. The surface temperature of the printing plate is generally controlled at 27 to 30 °C.

Waterless offset CTP version preservation

When removing the plate after printing, pay attention to avoid scratching the waterless offset CTP plate. When the plate is stacked, the paper must be placed between the two plates. Before unloading, dozens of sheets of paper can be pressed together with the inking roller raised to remove the ink on the surface of the printing plate, so that the removed plate is easier to clean. Usually, the printing company will use the printed waste sheets to remove the ink from the printing plates. At this time, pay special attention to the cleaning of the surface of the printed sheets to avoid scratching the plates.

Traditionally, there is a water offset printing CTP version. The waterless offset CTP version can also be retained after use, and will be used for the next printing. The retention plate can be completed by the automatic plate-holding machine. The difference is that the water-repellent CTP plate needs to be protected by the cleaning agent after cleaning with the cleaning agent to prevent the plate from aging, and the water-free offset CTP plate cannot be cleaned after cleaning with the cleaning agent. The upper protective glue can be directly dried by cold air; since the waterless offset CTP version is easy to scratch, a soft brush should be used when leaving the plate to prevent the plate layout from being scratched; the waterless offset CTP plate should be in the proper Store at temperature to avoid high temperatures.

At present, the water-repellent offset CTP version used in China mainly comes from the US 3M company and the Japanese Toray company. Compared with the traditional water-based offset CTP version, the price is relatively high. Therefore, it is difficult to popularize in China. However, waterless offset printing has broad development space due to its excellent environmental performance and printing quality, and will gain wide attention and application in the future.

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