Exposure time setting for PS version
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The setting of the exposure time of the PS version is generally three factors that determine the quality of the PS plate. The quality, exposure time and development quality of the ps plate. 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.
Different brands and models of PS version, there are differences in exposure time requirements, even the same brand of the same type of plate will be different due to different storage time. 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. Here are two more common ways to do this:
First, the continuous ladder test method: with a continuous ladder attached to the PS version of the test strip, for the staged exposure (can start from 80s, each add 20S, five times, until 160s), unified normal development, after the test Find out the number of exposure levels specified in the PS version of the instruction manual, which is the correct exposure of the version.
Second, the network point ladder test method: the print plate test strip is attached to the PS version of the small test strip, for graded exposure, normal development, to find out the bright and dark tone outlets are 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 dot, if the small dot loss is less, the dark white dot is more dead, indicating that the exposure time is insufficient; if the small black dot is lost, And the little white spots are less dead, indicating overexposure.
Different printing times are determined according to different prints (assuming the standard exposure time is 100s)
In our daily printing work, the more common original version has sulfuric acid paper base and polyester base; if according to the type of graphic, it can be divided into text line version, solid color block version, network line version, and There are also different types of network cable versions, such as flat screen, gradient version, layered version, etc. Some plates will mix several pictures on the same plate at the same time, relatively speaking, the exposure time is mastered. It will be more complicated.
1. A large version of a series of textbooks of sulfuric acid paper and polyester base that are straight out of 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.
2. 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.
3. 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.
4. 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 printing time will not appear bad network.
(1). The color version has a large version of the 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 in the field. In this type of printing, this often happens: the ink color of the printed matter 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 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. The printing time is about 160S.
6. in the color layer version, there are flat nets and solid prints. This type of printing plate mainly depends on the middle part of the flat net to determine the printing time. If only the solid part is considered, the printing time will inevitably increase a lot. Under 10% of the outlets will have a bad net, which will make it impossible to print.
(1) .With 10-20% flat screen, the printing time is about 120S.
(2). With more than 30% of the flat net, the printing time is about 140S.
7. monochrome large version with the original version of the flat net. The exposure time is mainly determined by the flat screen portion.
(1). With 10-20% flat screen, the printing time is about 120S.
(2).With 30-40% flat screen, the printing time is 150S.
(3). With 50-60% flat screen, the printing time is 250S.
(4). With more than 60% flat net, the printing time is about 300S.
8. monochrome original but there are text lines of the anti-white original, because it is a large field, the amount of ink is definitely large when printing, can ensure that the large solid color is enough, but the amount of ink is increased, the text lines are white, it is easy to paste Version. This kind of original version mainly depends on the thickness of the anti-white parts, the size of the text, and the thickness of the lines. The smaller the text, the thinner the line, the more exposure time, even in the middle of the PS version of the original version of the imposition of the imprinted film, in order to find the thin lines, small text anti-white strokes become thicker, it is not easy to print off the printing.
(1). The 0.1mm line or the fifth (15th grade) text of the anti-white part, first pad a 0.1mm 0.1mm thick imposition film between the PS version and the original version, and then vacuum-pressing the plate, the printing time is about 300s.
(2).The reverse part is 0.2mm line, or the second (32 level) text, and the printing time is 400s.
(3).The reverse part is a 0.3mm line or a small initial number (50 level) text, and the printing time is about 300s.
(4). The reverse part is 0.4mm line or larger than the initial number, and the printing time is about 250s.
Setting of secondary exposure time for removing dirt by using a scattering film
If there are many scratches or small dirty spots (including tape marks) that are difficult to remove on the original or the printing glass, you can place a scattering film on the printing glass for double exposure, and use the scattering film to light the light. The scattering principle converts the direct light into scattered light, so that the unexposed parts of the original scratches or dirty spots are re-decomposed and exposed to achieve the purpose of removing dirt.
This is actually a double exposure of the PS version. The first time is the normal exposure, we call it the main exposure, its time should be 4/5 of the standard exposure time; the second exposure is the exposure under the cover scattering film, also called the sub-exposure, the sub-exposure The time should be half of the time of the main exposure.
Although this method can effectively remove the dirty spots, we should also note that this double exposure will also lead to the reduction or even the lack of dots, so this method should be used with caution.
Monitoring and calculation of exposure (time)
It is a relatively simple and reliable way to quantitatively detect the exposure amount by using the continuously adjustable transmission ruler and using the unequal amount of light transmission at all levels. At the time of printing, only a 10-level continuous projection ladder with a step difference of 0.15 is required to be sun-dried to the outside of the original core. After development, there are three completely white, completely black and 1-2 intermediate transitions on the scale. Exposure state, compare this state with the reference exposure state: when the number of drying cycles is less than the reference level, it indicates overexposure; when the number of drying cycles is more than the reference level, it indicates that the exposure is insufficient; when the two are consistent, the exposure is suitable . (as shown)
When there is an overexposure or underexposure that exceeds the range of exposure latitude (tolerance of the print requirements), the correct exposure time can be calculated as follows:
t - adjusted exposure time
T1 - the scheduled exposure time during commissioning
N0 - the number of exposure times for the standard exposure time
N1 - test the number of exposure times of the exposure time
ΔD - scale difference density
That is to say, when using a step scale of 0.15 grade density, if the number of drying passes is one level difference, the exposure time differs by about 1.4 times. If there is a difference of two levels, the exposure time will be different by two times.
Different photosensitive plates have different exposure states under the same exposure conditions, and the number of sun-through stages on the scale is high, indicating that the sensitivity is high; the number of drying cycles is small, indicating that the sensitivity is low. In the actual production operation, it is necessary to make appropriate adjustments to the exposure time based on the results of the inspection and calculation.