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Improving Printing Quality

       Some operating specifications for improving printing quality.Improving Printing Quality

Improving Printing Quality

         Exposure determines the quality of PS plate, which is the main factor affecting the change of printing plate dot and the depth of printing plate.Improving Printing Quality

        The exposure is too large. Due to the diffraction of light, the photosensitive adhesive layer of the image and text without light can also be decomposed by light, resulting in the loss of small dots, the lack of pen and broken lines of fine lines, the overall image and text is shallow, affecting the printing effect, and it is easy to lose the version, and even waste the version in serious cases;Improving Printing Quality

         If the exposure of the printing plate is too small, the photosensitive adhesive layer in the blank part will be decomposed incompletely, and there will be resin residue after development processing, resulting in the expansion of the dot, resulting in the paste of dark tone small white spots, and it is very easy to get dirty for machine printing, which will also indirectly affect the printing resistance.Improving Printing Quality

          Since the light source is relatively fixed, the exposure is mainly controlled by adjusting the exposure time. The exposure time must be determined according to the printing suitability conditions of the unit. The exposure time of PS plates of different types and manufacturers is different, and is also affected by various factors such as different originals, light source aging, film quality and so on. Improving Printing Quality

         Specifically, it should be obtained through the actual test with the printing test strip or gray ladder. Generally, the exposure of 21 gray ladder without inking at the third level and 2% and 98% black-and-white small dots can correspond to the same time is the best.

        But the exposure time of text and line version can be slightly longer than that of fine dot image version. In order to ensure the stability of exposure quality, pay attention to the following points:Improving Printing Quality

           The light source for plate printing shall be standard. The spectral characteristics and illuminance of the light source shall meet the requirements for plate printing. A correct and reasonable light source can not only shorten the exposure time, but also improve the resolution of plate and reduce the change of dot. Improving Printing Quality

          The ideal plate printing light source is iodine gallium lamp (metal halogen lamp), it has a strong ultraviolet spectrum, the spectrum range is 320nm-450nm in the blue purple light area, which matches the spectral sensitivity of PS plate, and the illumination of the lamp tube is uniform, the light has no scattering and less heating, does not produce harmful gas, and has the advantages of cleanness, safety, stability and high efficiency. It is an ideal light source for drying PS plate.Improving Printing Quality

        The printing light source will age, so that the spectral radiation and illuminance will change, and the uniformity of illumination will be affected. If the exposure time is more than 20% longer than normal, it is best to replace it in time.Improving Printing Quality

        When vacuumizing the printing plate, the film and PS plate must be compacted, and there must be no residual air in the middle. In order to ensure the vacuumizing effect, the vacuum degree should be maintained above 20KPa.Improving Printing Quality

        The fluctuation of power supply voltage in the printing workshop should be small to ensure the stable light intensity of printing exposure.Improving Printing Quality

4) Development control

         Development is to dissolve the photosensitive adhesive layer of the light decomposition part of the printing plate under the action of alkaline developer to expose the hydrophilic sand mesh of the aluminum plate base, and the unexposed part is retained to become the image part of the printing plate, which is lipophilic. 

         Correct exposure should be matched by correct development, so development also has a great impact on the quality of PS plate. The main influencing factors are developer concentration, development temperature, development time, etc.Improving Printing Quality

(1) Accurately control developer concentration

          Developer concentration refers to the developer (the main developer is generally NaOH, Na2SiO3 and other strong alkaline substances). On the premise that other conditions remain unchanged, the higher the developer concentration, the faster the development speed. Improving Printing Quality

          However, if the developer concentration is too high, the corrosivity to the graphic foundation is too strong, which is easy to reduce the dot, damage, reduce the brightness, lose the dot, thin the photosensitive adhesive layer and reduce the strength, resulting in printing and inking The performance is reduced and the printing resistance is reduced. Improving Printing Quality

           At the same time, it will corrode and destroy the oxide film and hole sealing layer at the blank part, resulting in the whitening of the layout and the deterioration of the hydrophilicity and wear resistance of the printing plate; Improving Printing Quality

       If the concentration of the developer is too low and the alkalinity is too weak, the development speed will be too slow, which is prone to incomplete development, dirty layout and dead dark white spots.Improving Printing Quality

             The developer shall be the matching developer or recommended formula provided by the PS version manufacturer, Refer to the concentration range instructed by the manufacturer (recommended ratio) is prepared and determined through the test strip test. Improving Printing Quality

             Generally, when developing for 30-100s under normal exposure conditions, if the hollow points are clear and the corresponding small dots are firm, it indicates that the developer concentration is appropriate. If the small dots are lost too much, it indicates that the concentration is too high, and if the hollow dots are pasted too much, it indicates that the concentration is too low.Improving Printing Quality

             It should be used as a basis for developing Accurately adjust the shadow solution concentration. At the same time, pay attention to the fatigue and supplement of developer.Improving Printing Quality

         The developer will gradually fatigue and age with the development and due to the absorption of carbon dioxide in the air or the reaction with calcium and magnesium plasma in water, the concentration will decrease, the development performance will deteriorate and the development ability will be weakened. Improving Printing Quality

               Therefore, the developer should be supplemented and replaced in time, so as to maintain the continuity of the development effect of the developer and ensure the development quality.Improving Printing Quality

(2) The development temperature should be constant

           The developer temperature shall be controlled within a certain range. If the developer temperature is low, the chemical activity of the developer decreases, the ability to dissolve the photosensitive adhesive layer decreases, the development is insufficient, the dot percentage of the graphic part is larger than normal, and the blank part is dirty; Improving Printing Quality

          Too high temperature will also dissolve the exposed picture and text, deteriorate the dot reduction, and reduce the printing resistance. The suitable developing temperature range is 20-25 ℃.Improving Printing Quality

(3) Development time

             The development time has a direct impact on the development quality of PS plate. If the development time is insufficient, the photosensitive layer of non image part cannot be completely dissolved, which will cause the plate to get dirty. The longer the development time is, the more thorough the development will be. 

           However, the longer the development time is, the deeper the erosion effect on the virtual edge transition of the online point exposure of the printing plate is, and the small dots on the printing plate are easy to be lost. Therefore, it should be adjusted according to different developer and development temperature. For example, with the fatigue aging of developer, the development time should be appropriately extended. Improving Printing Quality

           It is best to determine through the print gray scale test, especially when the developer is changed and the temperature changes greatly, the corresponding test and adjustment shall be carried out. It is required that the print gray scale is transparent, the third level is transparent and not inked, the oxidation film layer of the blank part of the printing plate is not corroded, Improving Printing Quality

        The photosensitive layer of the graphic part is not thinned, and the small dot is not lost, so as to ensure the reproduction of the fine level and printing resistance of the printing plate. The development time is generally controlled at about 1 min.Improving Printing Quality

(4) The developer shall be maintained regularly

          The development is completed through the contact and dissolution between the developer and the photosensitive adhesive layer of PS plate. Therefore, the circulation pump and brush roller device should be used to speed up the flow and circulation of the developer, so as to improve the development speed and development uniformity.Improving Printing Quality

            In order to ensure the normal development, the developer shall be maintained regularly, especially the inspection and cleaning work shall be done well, the crystals in the tank and on the pipe wall shall be cleaned regularly, and the driving roller and brush roller shall be kept clean. If the brush roller is seriously worn, it shall be replaced in time.Improving Printing Quality

5) Baking plate

         Baking plate can improve the printing resistance of printing plate, reduce material consumption and improve production efficiency. Therefore, many printing plants use baking plate for long plate live printing plate before machine printing, but the baked PS plate is easy to get dirty. Note when baking:Improving Printing Quality

      Before baking the plate, the printing plate must be carefully cleaned and thoroughly cleaned, because if there are dust, impurities, scratches, etc. left on the plate, these dirt are firmly adsorbed on the plate after baking at high temperature and cannot be easily removed, resulting in dirty printing plate.Improving Printing Quality

        To select the baking glue, the concentration of baking glue should be appropriate, not too thick and too thin, otherwise the baking effect and inking effect are not good, or the baked version is easy to get dirty. If there are impurities in the baking glue, it should be filtered and reused.Improving Printing Quality

      When applying baking glue, shake it well before using it. Be sure to wipe it evenly and wipe it flat. Don’t be thick or thin, especially to avoid glue leakage.Improving Printing Quality