In general, there are three main factors that determine the quality of the print version of a PS plate: the quality of the plate, the exposure time, and the quality of the development. Correctly and reasonably grasping the exposure time is a crucial step to ensure the quality of printing. Correctly controlling the exposure time can ensure that the dried printing plate dots are smooth, clear-cut, and accurate in copying images and texts. It is also the key to avoiding printing failures such as “hollowâ€, “glitch†and “virtual edgeâ€. If the exposure time is short, it will result in the loss of dark tone levels, the dark spots in the dark tone, and other defects; if the exposure time is too long, it will lead to the loss of small dots, thin lines of text lack of painting, the overall picture and text Shallow. Another reasonable control of the exposure time can also make up for some deficiencies in the original version and improve the print quality.
This article will analyze the setting of the exposure time of the PS printing plate by several different methods: The PS plates of different brands and models have different requirements for the exposure time, even the same type of plate with the same brand. Differences will occur 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 determine the different exposure times according to different prints to achieve a standardized print. There are many ways to test the exposure time. Here are two more commonly used methods:
First, a continuous ladder test method: using a continuous ladder attached to the PS version of the test strip, the classification of exposure (starting from 80s, each plus 20S, five times, until 160s), unified normal after the test Find out the number of sun exposure levels specified in the instruction manual of the PS version on the article, which is the correct exposure of the edition.
Second, the network ladder ruler test method: the print test strip attached to the PS version of the small test strip, the classification of exposure, normal development, to find the highlights and dark withered dot more complete exposure time is the best Exposure time. Under normal circumstances the positive PS version should be able to restore 2% to 97% of the outlets, if the loss of bright spots is less, dark tone white paste more dead, indicating that the exposure time is insufficient; if the small black point is lost more, However, there is less dead white paste, indicating overexposure.
According to the different prints to determine the different printing time (assuming the standard exposure time is lOOs). In the daily printing work, the more common original sulfuric acid paper base and polyester film base; if according to the graphic The category can be divided into text line version, field block version, and cable version, and the cable version also has different types, such as flat screen version, gradient version, layered version, etc.; some printing plates will be in the same block. Several kinds of graphics are mixed on the plate at the same time, so it is relatively more complicated to grasp the exposure time.
1. The large version of the text version of the line of sulfate paper and polyester film directly from the computer photo line. Exposure time is 120S. This amount of exposure not only ensures that the text lines are in good condition, but also develops completely. However, the edges of the film base and the marks of the tape are still left on the printing plate, and must be carefully removed. Some of the original text lines are not black enough, especially the horizontal strokes of the Chinese characters.
The printing time will be shorter and the picture will be short; the pattern will not be black enough and the printing time will be long. After the PS plate is developed, it will lose its luster and the printing performance will be poor when printing.
Second, the large version of the collage of the line text format photographed or copied. The exposure time is about 250S. Because the original graphic density can reach 4.0, it is very dark. Exposure time increases, there is no obvious effect on the line text, but the original film edge, tape paper traces can be fully exposed, after the development of the printing plate is very clean, basically do not have to remove dirty, can improve the efficiency of the printing plate.
Third, the monochrome version of the dot version of the network version is about 120s. This version of the print version can not be too much time, especially to prevent the 3% of the small outlets disappear because of too much time.
Fourth, the color level version with flat screen printing, 10% flat screen version, copying time is more, there will be a bad network; more than 30% of the flat screen version, a little more time will not appear bad network .
1. The color version contains a collage of 10?20% flat screens with an exposure time of approximately 120 seconds;
2. The color version contains a collage of 30% or more flat screens with an exposure time of approximately 140 seconds. 5. In the color level version, there is no flat screen, but there is a larger title word or pattern in the field. This type of printing is often seen in prints:
The dots of the prints are full of ink, but the solid parts are not of sufficient color and the ink layer is not thick enough. If the amount of ink is increased, the solid parts will have enough color, but the halftone dots will be insufficient. If the printing time is properly increased, the outlets will be shrunk, that is, the printing plate will be sun-dried, making up for some gaps caused by the large amount of ink on the actual site, and the printing time will be about 160 seconds.