During the plate making process, different printing time needs to be determined according to different prints (assuming the standard exposure time is 100s). In the daily printing work, the more common originals are sulfuric acid paper-based and polyester-based; if divided according to the type of graphics, they can be divided into text line version, solid color block version, screen version, and screen There are also different types of plates, such as flat screen version, gradient version, layered version, etc .; some printing plates will mix several graphics and text on the same printing plate at the same time, relatively speaking, the master of exposure time will be More complicated.
1. A large-scale version made up of the line text version of sulfuric acid paper and polyester film base directly from the computer phototypesetting. The exposure time is 120S. This exposure not only ensures that the lines of the text are intact, but also can be developed thoroughly, but the edges of the film base and the marks of the adhesive tape will still be left on the printing plate, and it must be carefully removed. Some original text lines are not dark enough, especially the horizontal strokes of the Song typeface are relatively thin. If the printing time is too long, there will be short lines and lack of drawing; but the pattern is not black enough and the printing time is long. After the PS plate is developed, it will lose its gloss and the ink performance will be poor during printing, which will affect the printing quality.
Second, the large-scale version made up of photographs or copied line text editions. The exposure time is about 250S. Because the density of these original graphics can reach 4.0, very dark. Increased exposure time has no obvious effect on line text, but the original film edges and tape paper traces can be fully exposed. After development, the printing plate is very clean, basically without removing dirt, and can improve the efficiency of printing.
3. The printing time of the monochrome level dot version 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.
4. Prints with flat screens in the color gradation version, 10% flat screen version, the rotten screen will appear when the printing time is longer; more than 30% flat screen version, the rotten screen will not appear a little more .
1. A large collage version with a flat screen of 10 to 20% in the color gradation version, the exposure time is about 120S;
2. The large-scale collage version with more than 30% flat screen in the color gradation version, the exposure time is about 140S.
5. In the color gradation version, there is no flat screen, but there is a large headline or pattern on the ground. This type of printing plate often has this situation: the dot ink color of the printed part is enough, but the color of the solid part is not enough, and the ink layer is not thick enough. If the amount of ink is increased, the color of the solid part is enough, but the color of the dot part is again Not enough. If the printing time is properly increased, the dots are reduced, that is, the printing plate is lightened, and the gap between dots increased due to the large amount of ink in the field is compensated. The printing time is about 160S.
Generally speaking, there are three main factors that determine the quality of PS plate printing: the quality of the plate material, the exposure time, and the development quality. Correctly and reasonably controlling the exposure time is a very critical step to ensure the quality of the printing. Correct control of the exposure time can ensure that the printing plate dots are smooth, clear, and the graphics and text are copied accurately. It is also the key to avoiding "hollow", "burr", "virtual edge" and other printing faults. If the exposure time is short, it will cause the loss of the dark tone level, and the small white dots in the dark tone will die and other failures; if the exposure time is too long, it will lead to the loss of small dots, the lack of fine lines of text, the overall picture and text Lightly. 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. This article will analyze the setting of the exposure time when the PS version is printed through several different methods: the PS version of different brands and models has different requirements on the exposure time, and even the same brand and the same model version of the material There will be differences due to different storage times. For the newly purchased PS version, it is best to be able to use the test strip to test the standard exposure, and then, according to different prints to determine the different exposure time, to achieve standardized printing.
There are many ways to test the exposure time. The following introduces two more commonly used methods: First, the continuous ladder test method: use the continuous ladder to be closely attached to the PS version test strip for graded exposure (you can start from 80s, each time Add 20S, divided into five times, until 160s), after unified normal development, find out the exposure level specified in the PS version manual on the test strip, which is the correct exposure of the version. Second, the dot ladder test method: attach the printing test strip to the PS version of the small test strip, perform graded exposure, normal development, and find the level of exposure with the bright tone and dark dots is complete. The optimal exposure time is the best. Exposure time. In general, the PS version of Yangtu should be able to restore 2% to 97% of the dots. If the bright dots lose less and the dark dots lose more, it means that the exposure time is insufficient; if the small black dots lose more, The little white dots are less dead, indicating overexposure.
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