Platemaking Technology and Attention Problems

The flexographic printing platemaking process is generally as follows: preparation is like a negative film → cutting plate → back exposure → main exposure → developing and rinsing → drying → post-processing → post-exposure → anti-sticking → inspection. In the operation of each process, the main problems to be noted and the techniques emphasized are as follows. (1) Just like a negative film preparation. Prepare graphic and copy the size of the image to meet the requirements of the positive image, in order to close the exposure in the negative and the layout close, generally use matte film. Negative film is the premise of ensuring the quality of the plate. It controls the quality of the picture and text on the plate, so it is very important to check the quality of the negative film. Check whether the negative film is positive, that is, film film surface facing upward, film density generally requires> 3.5 (transparent part <0.06), to ensure that the negative film graphic clear, negative film formation, no distortion of the picture and text neat, layout crease-free , scratches, burrs, dirt, etc., the image network points are clear and strong, high light dark tone network points meet the requirements of plate making, conditional available density meter measurement, if the use of visual inspection, the film can be directed towards the sun or fluorescent lamps, film opaque place Light passes through to be qualified. If the density of negative pictures does not meet the requirements of plate making, the pictures on the system will be unclear, the pictures on the system will not reach a sufficient depth, and even the pictures will not be printed on the surface; if the shade is cloudy or dirty Point, will cause the thin line to bend, the lack of writing broken pen and other problems.

(2) Cutting board. According to the negative film size cut the corresponding plate. In order to avoid the waste of media, the size of the negative film should be measured before cutting. Then put the plate on the cutting table (face down). Cut the appropriate size according to the size of the negative film, but pay attention to the layout. Four weeks should be slightly larger than the size of the negative film, which is generally reserved 12mm clamping margin, mainly for the printing after the printing plate, to prevent the ink solvent immersed in double-sided adhesive and make the plate off the plate roller (that is, as the edge) effect.

(3) Back exposure. The function of the back exposure is mainly to increase the thickness of the substrate, form a uniform thickness and can support the entire layout of the floor, and ensure that the relief of the layout has a certain depth, and improve the printing rate. The method is to put the cut plate material into the exposure device, and place the photosensitive film face down on the printing plate rack to suck tightly, without using film and vacuum, turn on the light source, and perform the exposure after preheating for about 5 minutes. The amount of exposure should be controlled according to the amount of embossed depth required by the model of the media, the strength of the light source, the thickness of the text, and the complexity of the image. The more exposure, the longer the exposure time, the thicker the plate base, the shallower the relief on the layout, and the greater the plate thickness. Because the sensitivity of different plates and the newness of the exposure light source will affect the exposure, prediction tests must be done before batch exposure. Especially when the plate thickness changes, test exposure must be performed. The test exposure may take a small length of plate material, first block exposure for 10 seconds, and then divided into 1 to 5 sections, make a mark, use a piece of black paper to cover 2 to 5 sections, then exposure for 10 seconds, then cover 3 to 5 segments, then exposed for 10 seconds, followed by implementation, and then the first 1 to 5 segments exposure time 50,40,30,20,10 seconds. After this version has been developed and dried, it can be used to determine the exposure according to the different thicknesses of the 1 to 5 sections of the thickness gauge.

(4) The main exposure. The frontal exposure is the key to plate making. Expose the light-backed plate, turn it over, and place the plate upside down on the vacuum platen to remove the plate protection film. Be careful not to bend the plate to avoid the appearance of a large printing plate. In the skin-like phenomenon, on the stencil of the vacuum plate, the emulsion surface of the positive picture is closely attached to the photosensitive layer of the plate, and the plate and the negative film are cleaned with an antistatic brush to form a band-shaped polyester (or Cellulose Acetate Film) Placed on a negative plate (mainly to prevent the top layer from sticking to the sticky plate and creating aeration conditions for vacuuming), covered with a transparent matte suction film , adjust the timer, vacuum the main exposure. The length of the main exposure time should be determined according to the type of the material, light source strength, negative film density, graphic thickness and other factors, such as thin lines and dot exposure than the field text, the general thickness of 2 ~ 4mm version The exposure time is within 20 minutes. Mastering the main exposure time is the key to ensuring the quality of plate making. The length of the main exposure is related to the depth of the relief on the layout and the size of the side slope of the font. Excessive light exposure will cause large trapezoidal slopes on the sides of large and small sides due to scattering of light, shallower embossed depths, and smaller voids between words and diagrams, resulting in pastes during printing or anti-white characters, hollow lines, etc. Failure, in addition, overexposure will also make the hardness of the plate too large, bending and graphics will be broken when the field phenomenon; lack of exposure, the bottom of the photosensitive layer can not be fully cross-linked curing, will make the layout relief too deep, while not passing light Scattered to form a large and small trapezoid, when developing and flushing, this small trapezoidal fine text, lines, dots, etc. on the big bottom is difficult to stop, it will produce a word off, the line is wave (plate material or water temperature The cause of this phenomenon is that it takes a long time to wash the plate, and it may also cause this problem, etc., or it may cause problems such as slag, pinholes, and pits on the solid floor. In addition, due to different types of plates, their performance (especially the exposure time tolerance) there are differences, as well as the use of aging of the light source, etc. Therefore, the main exposure time for different media to be tested, available exposure test or film Set the thickness of the yin and yang figure lines or text on the film to determine the appropriate main exposure time. In addition, to ensure that the film meets the requirements and make the film and the layout close, but also pay attention to the choice of light source, the general resin plate photosensitive wavelength region 300 ~ 400 nm, to choose the emission wavelength in this area of ​​the light source. If the bottom plate is reversed and the quality is poor, it will expand between the image dots and the text lines, will not be washed out, and will not even develop. If the light source is not properly selected, even if the exposure time is very large, it will still result in word drop, line bending, and word line “shoulder” phenomenon due to underexposure and paste. These must pay great attention to platemaking.

(5) Developing rinse. After the plate is exposed, the light-receiving portion hardens, leaving a latent image on the plate, which undergoes a developing rinse and removes the unexposed and hardened portion. The developer solution is brushed and brushed with a special brush, and the photo-hardened photosensitive resin layer is washed away, and the photosensitive resin layer of the light-receiving portion is polymerized and hardened, and is not dissolved by the organic solvent, so that the plate surface has a concave-convex shape and becomes a printing plate. . During operation, first remove the negative film, check the printing plate, put it in the washing machine, avoid the image and clip the plate, add the appropriate developer, adjust the brush pressure and rinse timer. In developing and rinsing, it is necessary to pay attention to the factors such as developer formula, temperature, and time. Commonly used chlorinated hydrocarbon solvents (trichloroethylene, tetrachloroethylene, and trichloroethane) as the main agent, plus n-butanol, etc. According to the recipe and development temperature provided by the manufacturer of the plate, it is necessary to pay attention to the prompt replacement of the fresh solvent, so as to avoid the decline in the developing power of the old solvent and the adhesion of the mono-base polymer and other contaminants to the plate, so that the water pattern appears during printing. The defects affect the printing quality. The development time is generally controlled within 20 minutes. The development time is too short. There will be problems such as shallow embossing, uneven bottom surface, and scum on the surface. If the development time is too long, graphic damage, surface bulging, and layout will not occur. Equity problems. The flushing time is proportional to the depth of relief on the layout. Long time, deep relief, on the contrary, shallow relief. The length of the flushing time is also directly related to the developer's oldness and developing temperature, the pressure of the brush, etc., which must be flexibly controlled according to various relevant factors. During the rinsing process, the lid can be opened for inspection. If the time is insufficient, rinsing can continue. For the exposed plate, rinse it in time to avoid corrosion of solvent or solvent vapor before flushing, resulting in a large area of ​​white spots in the field.

(6) Drying (drying). As the photosensitive resin layer is washed after immersing the organic solvent, the resin absorbs the solvent and expands and softens, so that the graphic text produces normal twist and deformation, and the drying mainly causes the solvent absorbed by the photosensitive resin layer to evaporate, so that the photosensitive resin layer is restored to the original. Thickness and guarantee the truth of the picture, guarantee the printing quality. Drying will remove most of the solvent and the residue will evaporate over a few hours of standing time (stabilization process). Drying is carried out in a constant warm air oven. The drying temperature and time must be strictly controlled to ensure the quality of the printing plate. If it is not completely dry and stable, the platen also has uneven expansion, which not only makes the printing plate uneven, and the printing plate There are pits on the surface, and the hardness can not reach, can not withstand the normal friction in the printing process, and soon will be ground down, so that graphics, strokes, etc. gain weight, reduce the printing quality and print rate, but also make the resin The performance of the adhesive layer between the layer and the substrate is reduced, and the phenomenon of word drop during normal printing occurs, and the moisture is left as a small molecule in the resin, and the plate becomes very crisp, and a slight pressure causes troubles such as cracking. Drying too high a temperature can cause cracks in the layout and change the size of the printing plate graphic, while too low a temperature will make the plate too sticky, which will affect the printing quality. In general, the temperature should be controlled at 50 ~ 80 °C, drying time is generally about 40 minutes.

(7) Post-processing. After the plate is dry, the single substrate left on the surface of the plate is wiped off, wiped with a clean organic solvent before and after, cleaned and dried for about 5 minutes.

(8) After exposure. Its role is to fully harden the monomers on the plate. During operation, put the printing plate upside down on the vacuum plate holder, fully expose the plate surface with UV, put the plate after de-bonding into the exposure device, face up, do not use vacuum, directly start the light source, perform short Exposure of time causes the upper, middle, and lower resin layers of the plate to harden completely. Its role is to increase the hardness of the layout, increase the printing rate of the printing plate; the second is to improve the corrosion resistance of the ink solvent. Pay attention to control the exposure time, usually a few minutes. After overexposure, it will cause the plate surface to be too brittle to reduce the elasticity of the plate, and even cause cracks in the layout. Underexposure will make the plate too sticky.

(9) Anti-sticking treatment. After the post-exposure, in order to remove the tackiness of the printing plate, the printing plate needs to be dirty and anti-sticking treatment. The dirt can be irradiated with short-wave UV light for a short period of time, in addition to the layout of dirty spots. Anti-sticking treatment There are three main methods: 1 chlorite soaked anti-sticking. This is the most common method. This method is generally used for plates that need to be stored for a long period of time. The specific operation can be carried out only for 0.5 to 1 minute in a chlorine solution such as bleach. 2 powder anti-adhesion. It is to use fine corn flour or talc powder to spray the layout, but it should be noted that since the dusting will cause the layout to be inked, it is not suitable for anti-adhesion of halftone, complex or thin line originals. 3 fluorine plastic sticky. It is to use fluorine plastic spray method to spray the layout, the sprayed version should be washed with solvent, so as not to affect the printing ink transfer. However, this method is not suitable for subtle layers, and silicone spray is generally used for this version. For the de-bonding process, it is necessary to pay attention to the sufficient time for sticking, so as to avoid the problem of over-gluing, which affects the printing.

(10) Plate quality inspection. Plate quality is the life of print quality for any printing process and is the key to flexographic printing. Flexographic printing can't make up for and rectify the problematic plate. This is its biggest shortcoming. Therefore, we must strictly inspect the quality of the printing. We must master the following quality standards: 1 The plate must have a certain hardness. According to different printing processes, the hardness of the surface of the printing plate is also required to be different. The soft surface of the printed corrugated box has a Shore hardness of 30 to 35 degrees. The printing plate of the printed plastic film or paper has a Shore hardness of about 50 to 55 degrees. 2 The plate is evenly distributed in four corners and the thickness is the same. The relief depth of the plate should be about 1/2 of the thickness of the printing plate. Fine text and small gaps have a certain depth. 3 text, line edge must have a certain degree of slope, layout is not sticky. 4 text, lines, field version, lack of pen strokes, broken lines, trachoma, dirty spots and so on. 5 The dimensional accuracy of the printing plate graphic is correct, the color separation is correct, and the concave part is flat. 6 textured version, high and low tone network can not afford to come together, the network is smooth, low-key part of the network has a little depth.