1 Eraser
Due to different production processes, it can be divided into the following three methods:
1) Manual carving method. It is often used for corrugated carton printing. The screen is generally based on thick lines, large and small color blocks and bold text. The content is simple and the printing requirements are not too high.
Production process:
Depict the original image → Reverse image rubbing on the rubber plate → Engraved version
Paste the transparent original image on the surface of a certain standard, flat rubber plate, the text image must be clear. The operator uses engraving knives of different shapes and sizes, purely by hand skills, according to the outline of the text image to remove the rubber of the non-printed part, forming a depression, the text image is retained and becomes a printing plate.
2) Molded rubber plate (this process is more complicated. First make a metal plate (copper plate or zinc plate), and then press the phenolic resin plate (paper-like plate similar to letterpress), also known as the master plate. Then cover the master plate with a rubber plate, Using special equipment, after high temperature and high pressure treatment, the rubber is vulcanized and cooled in the master mold, and then smoothed and smoothed, which becomes the rubber printing plate.
The production process of the molded rubber plate:
Manuscript → negative film negative film → metal plate printing → pressed phenolic resin plate → high temperature and high pressure to produce rubber plate → thickness measurement → grinding the back of the rubber plate.
3) Laser engraving method adopts photoelectric scanning, analog-to-digital conversion, and automatic engraving of rubber plates by laser engraving head. When engraving, according to the graphic data engraved on the rubber plate into different depth layout, become a printing plate. This method can be used to make a screen version, especially for seamless sleeve printing plates.
2 photosensitive resin version
Can be divided into two kinds of solid photosensitive resin plate and liquid photosensitive resin plate. The two plate materials have different compositions, different production processes, and some performance differences, but the scope of application is the same.
l) Liquid photosensitive resin version. When making a plate, photosensitive resin should be pre-coated on a specific exposure device. The exposure device is composed of upper and lower precision glass plates and upper and lower ultraviolet light sources, so that the printing plate can be exposed to the front and back.
※ Liquid resin coating, main exposure and back exposure.
As shown in Figure 1, when applying liquid resin, place the emulsion of the negative picture face up, place it on the lower glass, and cover it with a layer of film. Distribute the photosensitive resin solution and put the substrate on the resin layer. Put the upper glass down so that the photosensitive resin layer is sandwiched between the two glass plates. Figure 2 shows the back exposure and main exposure device. The back exposure makes the substrate and the resin adhere Strong; during the main exposure, light shines on the photosensitive resin layer through the negative picture, the light-receiving part of the resin hardens and becomes solid, and the photosensitive resin in the unreceived area is still in a liquid state. Therefore, the exposed printing plate can be placed at an angle In a recovery tank, the unexposed excess resin on the plate is recovered.
Figure 1 Coating liquid photosensitive resin
Figure 2 Exposure device
※ Rinse (develop).
For the printing plate that has been exposed, use a special brush to remove the photosensitive resin solution remaining on the plate surface in the machine tank, as shown in Figure 3. The developed printing plate is placed in an oven to dry, and then post-exposure treatment is performed to completely harden the resin on the printing plate.
Figure 3 Rinse and develop
The domestic flexo printing industry does not use many liquid plates, and only applies to corrugated box plate making. It has problems such as limited plate size, low resolution, and poor hand feel, and is not suitable for making fine image printing plates.
2) Solid photosensitive resin plate. This is a pre-coated version, just like the PS version used in lithography. It should be stored in a cardboard box protected from light. When using, it is very convenient to take out and cut out from the box according to the size of the plate making.
At present, the commonly used flexible solid photosensitive resin plates in China are DuPont's Cyrel version, German BASF version, China's GS version, American Poly version, Japan's co-prosperity version, etc. These plates have a series of products, with different specifications, thickness and hardness. They have the same characteristics: a. The plate structure is the same; b. The exposure machine and the plate washing machine are the same; c. The plate washing solution is the same, all are organic solvents such as trichloroethylene and tetrachloroethylene; d. The operation process is the same, Have to go through the same process.
The following mainly describes the operation experience of the solid resin plate for reference.
Figure 4 is a schematic diagram of the plate structure. Main functions: ①The protective layer is a matte film base. The function is to prevent the photosensitive resin layer from being damaged, and to block the light from irradiating the resin layer to cause a photochemical reaction, resulting in a waste version. ② The adhesive layer is coated between the protective layer and the photosensitive resin layer, but it cannot be excessively firmly bonded. ③The photosensitive resin layer is the main body of the plate material, and its photosensitive performance should be stable and reliable, with uniform coating, uniform thickness, and good flatness. ④There is an adhesive between the bottom of the resin layer and the plate base, so that the two are firmly bonded and difficult to tear. ⑤ The plate base is the basis of the solid plate. It is very important to keep the plate size stable and free of elasticity, including the flatness and thickness consistency of the plate base itself.
Figure 4 Schematic diagram of the solid version
Production process of solid resin plate:
Manuscript → Make positive image negative image → Opening and cutting → Pre-exposure → Main exposure → Rinse (development) → Drying → Post-processing → Post-exposure → Correction.
Matters needing attention in each process:
a. First check the quality of the negative film. Check content: ①Copy the correct size of the text. ② The picture and text must be positive, with the film face up. ③The reading range of film on the density meter should be about 0.06--3.5. ④The picture and text are clear, and there are no creases or burrs on the layout. ⑤ The dots are strong, and the high-gloss and dark-tone dots meet the requirements of plate-making. If the unit does not have a measuring instrument, the film can be visually inspected towards the sunlight or fluorescent lamp. No light is transmitted through the opaque part of the film to be qualified.
Cutting (cutting): The periphery of the plate should be slightly larger than the size of the negative picture. It is mainly used to prevent the ink solvent from immersing in the double-sided adhesive and printing plate from the plate roller when printing after the plate is installed.
Pre-exposure on the back of the printing plate. Put the cut plate into the exposure device with the photosensitive film face down, without film, without vacuum, turn on the light source and perform exposure, see Figure 5.
Figure 5 Pre-exposure on the back of the flexo
The length of the pre-exposure time is determined by the model of the plate, the strength of the light source, the thickness of the text, and the complexity of the image. Its function is to increase the thickness of the plate base, ensure that the plate relief has a certain depth, and improve the printing durability. The pre-exposure time is proportional to the thickness of the substrate. Long time and thick base; short time and thin base. In fact, for various types of plates, the relief depth of their layouts has certain standards. For example, DuPont Saili 2.28mm plate material, after removing the protective layer, the standard relief depth is l.lmm, how to achieve it? It can be determined by the following method. As shown in Figure 6, use a long and narrow resin plate (length 10cm, width 5cm), firstly expose the entire plate for 10s, then divide the plate into five sections, mark it well, and then use a piece of black paper. Cover the 2 to 5 parts and expose for 10s. At this time, the light in one segment is 20s. Then it is exposed sequentially from 2 to 5 segments, each time exposed for 10 seconds. Then the light receiving time of the first section is 50s, and the second, third, fourth and fifth sections are exposed for 40s, 30s, 20s and 10s respectively. After the plate is developed and dried, it is measured with a thickness gauge, and the thickness of the plate is significantly different (Figure 6). Therefore, the test results can be used as the basis for determining the thickness of the plate base.
Figure 6 The test experiment of the correspondence between the pre-exposure time and the thickness of the substrate
Front exposure (ie main exposure), as shown in Figure 7. The exposed material on the back is turned over to tear off the protective layer to expose the photosensitive resin layer. On the vacuum plate-making machine, closely fit the emulsion side of the negative image and the photosensitive layer. Cover with a suction film (special frosted transparent material) to draw a vacuum.
Figure 7 Front exposure of the flexographic version
The determination of the main exposure time should be based on factors such as the type of the plate material, the intensity of the light, the density of the negative film, and the thickness of the text. The length of the main exposure time is related to the depth of the relief of the layout and the size of the side slope of the font. Excessive exposure time will cause the depth of the relief of the layout to become shallow; while the slope of the side becomes larger, the pores between the characters and graphics will become smaller, and it is easy to produce paste and other defects during printing; on the contrary, insufficient exposure time will make the relief of the layout too deep and small text 2. The lines are easy to bend, the small dots are difficult to stand on, and it is easy to cause waste edition.
It is especially important to master the main exposure time. Generally speaking, for each batch of plates purchased, the main exposure time needs to be re-tested as the light source ages. Can choose to use exposure test or film on the film to set the thickness of the yin and yang drawing lines or text to select the appropriate main exposure time.
Different types of plate materials have different performances, especially in the tolerance of exposure time. Judging from the experience of the DuPont Saili version, the German BASF version, the domestic GS version, and the American Poly release version, I feel that the exposure time of the Saili version and the BASF moderator is easy to master, its tolerance is large, and more exposure and less exposure 15s time has little effect. The Poly version issued by the United States has a small tolerance. If the exposure time is more than 15 seconds, the printing plate will cause problems. Therefore, mastering the main exposure time is the key to ensuring the quality of plate making. (To be continued)
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