Brief analysis of the exposure time of the PS version
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Generally speaking, there are three main factors that determine the quality of the PS plate: the quality of the plate, the exposure time, and the quality of the development. Correct and reasonable exposure time is a very important step to ensure the quality of the printing. Correct control of the exposure time, in order to ensure that the printing plate outlets are smooth, well-defined, accurate image reproduction, but also to avoid the "hollow", "burr", "virtual edge" and other key problems. If the exposure time is short, it will cause the loss of the dark level, the white point in the dark tone, etc.; if the exposure time is too long, it will lead to the lack of small dots, the thin lines of the text are missing, the overall picture Light. In addition, reasonable control of the exposure time can also make up for some of the deficiencies in the original version and improve the quality of the printing plate. This article will analyze the exposure time setting of PS plate printing through several different methods: PS version of different brands and models have different requirements on exposure time, even the same type of plate of the same brand. There will be differences due to different storage times. For the PS version just purchased, it is best to use the test strip to test the standard exposure, and then determine the different exposure times according to different prints to achieve standardized printing.
There are many ways to test the exposure time. The following two commonly used methods are introduced: 1. Continuous step rule test method: Attach a continuous step to the PS test strip for staged exposure (starting from 80s, each time) Add 20S, divided into five times, until 160s), after normal normal development, find the number of exposure levels specified on the test strip and the PS version of the manual, that is, the correct exposure of the version. Second, the network point ladder test method: the print version of the test strip attached to the PS version of the small test strip, for graded exposure, normal development, to find out the bright and dark with the network point is relatively complete, the first exposure time is the best Exposure time. Under normal circumstances, the positive PS version should be able to restore 2% -97% of the network points, if the bright point is less lost, the dark white point is more dead, indicating that the exposure time is insufficient; if the small black point is lost, And the little white spots are less dead, indicating overexposure.
Different printing time is determined according to different printings (assuming the standard exposure time is lOOs). In the daily printing work, the more common original plates are sulfuric acid paper based and polyester based; if according to the text Types can be divided into text line version, solid color block version, and network cable version, while network cable version also has different types, such as flat screen version, gradient version, layered version, etc.; some plates will be in the same block. At the same time, several kinds of pictures and texts are mixed on the printing plate, and the mastery of the exposure time is relatively more complicated.
First, the large version of the sulphuric acid paper and the polyester text base lined up by the computer. The exposure time is 120S. This exposure not only ensures that the lines of the text are intact, but also develops thoroughly, but the edges of the base and the traces of the tape will remain on the plate, so be sure to remove the dirt carefully. Some original text lines are not black enough, especially the horizontal strokes of the Song characters are relatively thin. If the printing time is too long, the drawing will be short-term; the pattern is not black enough, the printing time is long, the PS plate is developed, the gloss is lost, and the printing performance is poor, which affects the printing quality.
Second, the large version of the lined text version photographed or copied. The exposure time is approximately 250S. Because, these original graphics density can reach 4.0, very dark. The exposure time increases, and there is no obvious influence on the line text, but the original film edge and the tape paper trace can be fully exposed. After the development, the printing plate is very clean, and basically no need to remove the dirt, which can improve the work efficiency of the printing plate.
Third, the monochrome layer dot version printing time is about 120s. This type of printing time can not be too much, especially to prevent 3% of small outlets from disappearing due to too much printing time.
Fourth, the color layer version with flat screen printing, 10% flat screen version, more time for printing, there will be rotten net; more than 30% of the flat screen version, the version of the time will not appear bad . 1. In the color layered version, there is a large version of the collage of 10-20% flat net, and the exposure time is about 120S; 2. The color version has a collage version with more than 30% flat net, and the exposure time is about 140S.
5. In the color layered version, there is no flat net, but there is a larger title word or pattern on the ground. In this type of printing, this often happens: the ink color of the printed dots is enough, but the color of the solid parts is not enough, and the ink layer is not thick enough. If the ink volume is increased, the color of the solid part is enough, but the color of the dot is partially Not enough. If the printing time is properly increased, the outlets are reduced, that is, the printing plate is lightened, and some gaps due to the large amount of ink in the field are caused, and the printing time is about 160S.