In the traditional printing production process, PS plate making is a very important process and plays a role in the entire printing process. PS plate making refers to the application of contact exposure method to transfer the graphic information on the film to the photosensitive plate. After a certain processing process to make the plate, the quality of the PS plate directly affects the final printing quality.
PS plate quality control points PS plate plate control elements mainly in the following aspects.
1. Film is one of the raw materials used in the printing. The film is the object to be copied by the PS plate making. The quality of the film has a decisive effect on the quality of the printing plate. Therefore, the film must be inspected before PS plate making to ensure the PS. Plate making quality. The inspection of the film mainly includes the following aspects.
(1) Density check. It mainly includes two aspects: the density of the film on the ground and the density of the blank part. In general, in order to ensure the quality of PS plate-making, the density of the film on-site is 3.9±0.4, and the blank density is ≤0.05. Otherwise, the density contrast on the plate will be affected.
(2) Inspection of outlets. Before printing, use a transmission densitometer to check whether the dot size of the graduated ruler on the film is true or not. 5% dot error is ±1%, 50% dot error is ±2%, and 95% dot error is ±1%. .
(3) Inspection of appearances. It mainly includes two aspects: layout and graphics. Among them, the inspection of the film layout mainly includes the finished product size and the bleeding size, the imposition method, various types of marks, control strips, front and back register, various color printing, and whether the layout is dry. The examination of the film and graphics mainly includes checking whether the font, the font size and the position are correct, whether there is a lack of strokes, and whether the size, resolution, color number, etc. of the picture meet the requirements.
2. The plate PS plate is another important raw material used as a printing plate, and its quality is also of paramount importance to the quality of PS plates.
(1) Edition base processing. The base plate of the PS plate is to be clean, uniform in thickness, evenly distributed in the grains, and with appropriate thickness and depth. General requirements, the average depth of sand between 5 ~ 7.5μm, the average roughness of about 0.6μm.
(2) Photosensitive adhesive coating. Photosensitive adhesive coating should be uniform, thickness is moderate (thickness difference of each point should be less than 0.04mm), general PS plate coating thickness is about 1.8g/m2, and the printing plate surface is free from bubbles and scratches.
(3) It is required that the printing plate of the PS plate has good printing performance, good dot reducibility, high resistance to printing force, difficulty in smudging, good processing and affinity properties, appropriate tensile strength, and stable chemical properties.
3. Shaiban printing process is the most important part of each process of PS plate making. Therefore, on the basis of good raw materials, the operation of each part of the printing process must be carried out according to the following process instructions.
(1) Check the status of the printer. Mainly refers to the factors associated with the printing plate itself, to a certain extent, can affect the quality of the printing plate. Among them, the uniformity and stability of the light source such as the printing machine, the flatness of the drying surface, the cleanliness of the reflector of the lamp tube, and the cleanness of the drying rack glass are all factors influencing the quality of the printing plate, requiring more inspection and maintenance. When necessary, it needs to be replaced. If the exposure time is longer than the normal exposure time by more than 20%, it is best to replace the copying light source in time. We will not repeat them here.
(2) Loading. The film and printing plate must be closely packed, and the plate is generally required to be placed in the center, and in a special case, it can be biased to a certain extent. If the width of the paper is slightly less than the minimum print size of the machine design, the above position can be slightly shifted to the side where the side rule is located to ensure that the side rule can be pulled to the paper when printing. The position in the cornice is generally determined by the corresponding printer.
(3) Setting of printing parameters. The setting of the printing parameters mainly includes two aspects: vacuuming time and exposure time.
The vacuum pumping time should be reasonably set according to the type of equipment, the specifications of the plate, and the distribution of the graphic and text. Under normal circumstances, in the case of the same type of equipment, and similar distribution of graphics and text, the vacuum drawing time of a large-format medium is longer than that of a small-sized printing plate; the same type of device and the same type of media are used. Under the circumstances, according to the difference in the distribution of photos and texts, the vacuum time of shallow webs is relatively longer.
The setting of the exposure time determines the restoration of the printing plate's internet point. The specific settings should be made according to the type of the original. Under normal circumstances, the exposure time of large-area shallow webs and imposition (with film base) films is longer than that of ordinary graphics; the exposure time for large-area solids is shorter than that of ordinary graphics.
The specific setting methods of the above two printing parameters will be described later in detail.
4. Although the development process of the developing PS plate is simple, it requires strict requirements on the developer and the developing process in order to obtain a truly qualified plate.
(1) Developer concentration. The preferred developer or recommended formula provided by the manufacturer of the PS version should be the first choice, and be formulated with reference to the manufacturer's recommended ratio, and determined by the actual test strip test. Generally under normal exposure conditions when developing 30 ~ 100s, using a magnifying glass to observe the print control strip, if the hollow point is relatively clear, the corresponding small dot is relatively solid, indicating that the developer concentration is more appropriate; if the small dot loss is too much, indicating the concentration Excessively high; if the hollow spots are more dead, the concentration is too low.
(2) Development time. It is best to determine through the printing ash ladder rule, especially when the temperature change is large or when the developer is changed, the corresponding test and adjustment should be carried out. It is required that the printing grey grading scale should penetrate the third level, and the blank of the printing plate is oxidized. The film layer is not corroded, and the photosensitive layer of the graphic part is not thinned and the small dots are not lost. This ensures the fine-grained reproduction and resistance of the printing plate, and the developing time is generally controlled at about 60 seconds.
(3) Development temperature. Usually 18 ~ 25 °C is appropriate, too high or too low will affect the development quality.
Determination of the best printing parameters Due to the aging of the printing plate and the rubber band, it is necessary to re-set the printing parameters in time to meet the requirements of the printing process without affecting the printing quality.
1. Determination of the vacuum pumping time The most simple way to test the vacuum pumping time in the actual production is to use the largest format flat screen film allowed by the printing machine for vacuuming. Observe that as the vacuum time passes, the flat screen film The Newton ring appears until the Newton ring on the flat screen film completely disappears. At this time, the vacuum pumping time is the best vacuuming time for this printing machine.
2. The determination of the exposure time The appropriate exposure time is an important condition for the correct transmission of the dots on the entire tone. The method commonly used for testing exposure time in production is to use a printing plate. Here mainly introduces the UGRA1982 measurement and control bar.
UGRA 1982 measurement and control bar is mainly composed of 5 parts: the first part is used to test whether the normal development of the 13 gray ladder section; the second part is 12 diameter 4.5mm yin and yang circular area, line width between 4 ~ 70μm , used to determine the correct exposure time and PS version resolution; the third part is used to test dot gain and print dot contrast area; the fourth part is used to test the ghost area; the fifth part is the highlight and dark tone Control area, usually in the print to ensure that 98% of the network is not ambiguous, 2% of the network to retain; in the pattern of printing to ensure that 97% of the network does not paste, 3% of the network to retain.
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