Initiate the printing work (2)

Second, seriously implement the exposure process

Under the premise of doing a good job of preparation, we must strictly control the spectrum of the light source, luminous efficiency, uniformity and stability of the illumination, the amount of exhaust gas, and the amount of exposure.

1. The choice of light source spectrum. At present, China's printing industry is mainly using a photo-decomposition type positive PS plate. The energy distribution of the light source spectrum should be matched with the sensitivity sensitivity of the PS plate. The sensitizer (215 type) currently used has a photodecomposition wavelength of less than 460 nm (nanometer), and the absorption wavelength of the exposure glass is less than 320 nm. Therefore, a light source having a main spectrum in the range of 320 nm to 460 nm is preferred. Iodine deuterium lamp (metal halogen lamp) is a kind of gas discharge type light source. It has high luminous efficiency, relatively stable performance, and the spectrum is concentrated in the range of 350nm to 450nm. It is the most widely used light source for printing.

2. High luminous efficiency and power matching. Due to the low sensitivity of the positive PS version, light sources with higher light energy are required. In this regard, iodine lamps are ideal. According to the printing plate with different power sources, the general open printing machine with 5kW ~ 8kW, open with 3kW ~ 5kW, four open and the following with 1kW ~ 3kW, to meet the needs of printing brightness and uniformity.

3. The light source illumination should be stable. Iodine lamps are an important basis for printing quality. Under the premise that the original version meets the requirements, there must be standards-compliant media. First, the basic layout should be smooth, there should be no scratches, horseshoe pits, layout can not have any dirt, sand specifications, preferably multi-layer, so that the plate has a good hydrophilic properties. In recent years, there have been corresponding increases in the processing of copyright bases or prints of 250 lines/inch or more. If the foundation is not flat, or the grain is not treated in accordance with the requirements of the specification, or if there is a scratch, the problem of Figure 2 will be affected and the quality of the printing plate will be affected. The performance of the photosensitive coating shall be stable, the particles shall be moderate, and the coating shall be uniform and sufficient. Sensitivity and resolution, the photosensitive layer has a good lipophilic properties.

Second, we must pay attention to procurement. Market economy is not to not plan. The procurement of plate materials shall be procured according to the consumption of the enterprise according to the plan; the quality and reputation of the supplier shall be known and the supplier shall be stabilized; the relevant standards and qualification certificates shall be obtained when purchasing, and the purchase of counterfeit, inferior or expired products shall be prevented; The plate material must come under the premise of ensuring quality, ensure supply, reduce inventory, prevent light decay, and affect the use.

The third is to strengthen the storage of plates. Plate is a kind of photochemical material, should be stored at low temperature, low humidity, dark light, to prevent the occurrence of dark decay or light failure, affect the quality of printing plate. At present, there are many unsatisfactory places in this area: Some purchased plates are placed in a room with strong light, and some even have window glass. The indoor temperature is as high as 40°C or more; the storage is not marked, and some are expired; Multi-channel supply, ask its related personnel, also lack the necessary knowledge. These tend to cause instability in the properties of the plate.

The fourth must be strictly used. Should be used for quotas, the best plate and flushing liquids are used for collection and use; strict process specifications must be followed to properly prepare rinsing fluid. If self-purchased drugs are self-manufactured, ensure the quality of the drugs and the order of the formulas; if it is purchased solid washing powder to be dissolved according to regulations; if it is purchased liquid washing fluid, it should be diluted according to the specified proportion, it is best to use distilled or demineralized water Dissolve or dilute. In this way, the performance of the rinsing liquid is stable and the service life is prolonged, and the quality of the printing plate can be improved. Strictly follow the document requirements to overcome arbitrariness and blindness in the implementation process. At present, printing companies mainly have problems with the use of materials, lack of plans, and rinsing fluids are not formulated according to regulations (the author sees that a certain unit does not use cups for the preparation of flushing fluids, and only adds tap water based on experience). There is no uniform requirement for the operating fluid, so it is not possible to print a good plate. Therefore, we must raise awareness, strengthen management, and standardize operations.

3. Equipment preparation. The functions of the plate-making and processing machines used should be studied, their functions should be mastered, and the maintenance and testing work should be strengthened. The illuminance, uniformity, and light energy attenuation of the light source are often tested, the washing machine is cleaned, the equipment is kept clean, the function of the device is in a good state, and the equipment integrity rate is improved. Objectively speaking, at present, maintenance and related testing work of most companies is not in place. There is no test on uniformity of illumination of the light source, attenuation of illuminance, etc. The pipelines and tanks of the rinsing machine cannot be cleaned as required. Control instruments (vacuum gauges, temperature indicators, etc.) ) Also lacking inspections, there are varying degrees of inaccuracy.

The gas discharge type light source has a process from start-up to stable light emission, so it is better to use a continuous printing plate after stabilization. Most of the current plate-making machines have regulated power supplies, which are controlled by a light quantity accumulator, that is, the illuminance and time product number to control the illuminance and obtain a stable exposure amount.

4. The illumination of the light source should be uniform. The uniformity of illuminance is related to the area of ​​the illuminant and the distance to the subject. In order to make full use of the light source, the platen is equipped with a back light cover to help ensure the uniformity of illumination. The uniformity of illuminance is determined by the maximum size of the printing plate, the more uniform the better, the minimum required uniformity should be greater than 85%, and the illuminance meter can be used to compare multiple measurements. Shaiban should use parallel light, if the light beam is not parallel, or there is a blue and blue stray light injection, there will be the phenomenon as shown in Figure 3, likely to cause the dot network to reduce the effective area, affecting the dot or solid lipophilic; with vertical printing plate The machine must be equipped with a shade to prevent the operator from being burned by UV light, or other stray light entering the original affects the quality of the graphic.

5. Use positioning plate. This is conducive to standardized printing operation, is conducive to proofing or printing multi-color registration, saving adjustment time.

6. The printing plate suction should be uniform. There is an automatic control device for the pumping volume of the new printing machine. When the pumping reaches a level of compliance, the light source is automatically started and the exposure is started after the output illuminance is stable. This process requires

The air intake can not be blocked, the ambient temperature can not be too high, there can be no dust between the plate and the original (a minimum dust at least affect the actuality of the four outlets), the humidity can not be too low (when the volume is too low, The original is prone to generate static electricity or interference fringes, resulting in local misfiring of the printing plate, uneven flat cable, affecting the overall quality, as shown in Figure 4, so must pay attention when operating).

7. Determine the correct exposure. The other variables of the printing process can be adjusted in advance and considered as quantitative. The most important thing is to study the correct exposure. Taking the positive version of the PS version as an example, the correct amount of exposure is completely decomposed after the exposure of the non-graphical parts. After washing, sand spots are exposed and good hydrophilicity is maintained; the influence of graphic parts is very small, and good lipophilicity is maintained. Under the premise of exposure and rinsing conditions, use the corresponding measurement and control strips (the strips should have network ladder, continuous adjustment ruler, and other fine measurements), or use a dot ladder (0-100%), continuous Adjusting ruler (14 steps of differential 0.15 density, or 21 steps of 0.10 density) and a normal set of original, binned exposure, and simultaneous inspection after flushing: 2% dots on the bright tone, 50% on the middle tone The outlets are not distorted, and dark spots can be seen in the blanks of 97 to 98% of the outlets. The scales of 3 to 4 of the continuous adjustment ladder are completely decomposed, that is, the density of 0.50 to 0.65 is completely decomposed. The exposure of this file is the correct exposure. If the network is rigid, the 4 to 5 levels of continuous adjustment ruler are completely decomposed, that is, the density is completely decomposed from 0.65 to 0.80. This corresponds to a complete decomposition of the density of the virtual edge below 0.80. In this case, the printing plate is not easy to get dirty; if the network point is Soft, in order to prevent the network from shrinking too much, the exposure can be reduced as appropriate. The correct amount of exposure is the key to printing, exposure is too much, has a greater impact on small dots or small strokes, relatively favorable for dark tone; underexposure, is beneficial to keep small outlets, and the middle tone is easy to dark, dark tone is easy to paste version

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