Shaiban is the link between the prepress process and proofing, printing process, on the one hand, it should completely and faithfully transfer the original graphic information to the PS plate; on the other hand, it should make the graphic part of the ink affinity The blank part is hydrophilic and allows the printing plate to withstand the enormous long-term pressure between the rollers without changing its hydrophilic properties.
When we manufacture the PS version, we always hope that the sun-dried outlets will be strong and smooth; because the printing plate outlets are actually bright and clean, the edges of the outlets will withstand long-term erosion of water and ink and will not easily shrink or expand. In order to ensure the relative stability of the printing plate dot size in printing. Otherwise, if the printing plate outlets are fragile and hairy, the small changes in the balance of ink and water in the printing, the ink reprint of the printing plate outlets will occur at any time, or affect the stability of ink dot transfer data. In addition, we also hope that the blank part of the printing plate will be clean and free of dirt, and the graphics and text will have good lipophilicity; So, what are the factors that determine the quality of printing? We summarize the following points:
(1) The appropriate original. For the original, it has an important influence on the quality of the printing. First of all, we usually use a violet light source or ultraviolet light source with a wavelength of 400 μm. The penetrating power is strong. In order to transfer the original film web site to the printing plate completely, it does not allow the future to express the image part. The photochemical reaction of the adhesive layer requires the on-site density of the original negative film to reach 3.3 or more, otherwise, it is difficult to achieve the desired effect; secondly, the original fog level is lower, otherwise it will affect the density contrast on the plate; The original should be clean and dirty, otherwise it will give the printing plate dirty; finally, the original plate is preferably a piece of film without a knife edge and collage tape, so that it can better ensure that the film is tightly integrated with the PS plate and avoid the scattering of light. The dots in the network are virtual, and even if they must be tiled, the distance between the tape and the dots representing the image information should be too flat or equal to 7mm.
(2) The glass of the printing plate is required to be clean. Otherwise, dust on the glass can easily make the PS plate dirty. Because our current working conditions are difficult to achieve absolute cleanliness of the printing workshop, we must use alcohol to wipe the printing plate rack before printing.
(3) Suitable light forms. We should reduce as much as possible the phenomenon of light penetration caused by the light and the phenomenon caused by light penetration.
(4) Resolution of PS version. The most important factor affecting the virtual reality of printing plates is the resolution of printing plates. So how do we test the resolution of the printing plate? UGRA1982 measurement and control bar has provided us with great help.
UGRA1982 measurement and control bar consists of five parts:
1. High-light and dark-sounding control area, usually when printed on the printing machine: To ensure that 98% of the outlets are not smeared and 2% of the outlets are to be preserved: In the case of printing the prototype: to ensure that 98% outlets are not pasted, and 3% outlets are required. Reservations.
2, test ghost area.
3, used to measure dot gain and print contrast area.
4, 12 4.5mm diameter Yin Yang pattern area, line width between 4μm and 70μm, this section can be used to determine the correct exposure time and PS version resolution;
5. The gray scale section used to test whether the development is normal.
Under the guidance of Mr. Schmitz, a professional education professional who has a reputation in the printing industry in Germany, we have put UGRA control strips on a Fujitsu version for use on the GTO printing plate, using 2T. , 4T, 8T, 16T, 32T, 40T Beat grading the PS version of the exposure, and under normal development conditions after the development, observe the UGRA control strip yin and yang loop shape of the yin and Yang line reproduction (at least 50% can be clearly reproduced quasi).
According to the regulations of the UGRA 1982 measurement and control strip, at a certain exposure time, the same level of the Yin and Yang lines in the yin and yang circle area can be clearly observed at the same time. This level is the resolution of the printing plate, so the PS version we tested is resolved. The rate is 6 μm.
(5) Appropriate suction time; because the degree of contact between the original film and the plate adhesive layer is changed at any time during printing. Such as: uneven printing plate glass and blanket, dust clip pad, film pads and dirt on the pads, as well as the vacuum pumping vacuum, etc., will cause the negative and the plate material adhesive layer of poor adhesion, The appearance of voids causes serious damage to the light, which changes the size of the screen dot transfer. Therefore, we can closely match the PS plate and the original plate by searching for the proper pumping, so that the correct exposure can be achieved.
(6) Appropriate exposure time. If we only have a high-resolution PS version, good exposure conditions are not enough, but there must be sufficient and not excessive exposure time to produce a good PS version.
The following table is a list of parameters recommended by UGRA manufacturers for finding the right exposure time: (The thick area in the table is what we can use in real production.)
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