Analysis of Exposure Time Setting for PS Plate Printing

Generally speaking, there are mainly three factors that determine the quality of the PS printing plate, the quality of the PS plate, the exposure time, and the development quality. 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 defects such as “hollow”, “glitch” and “virtual edge”. 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.

Different brands and models of PS version, there are differences in the exposure time requirements, and even the same type of brand with the same type of material will be due to different storage time, resulting in differences. 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 scale attached to the PS version of the strip, the classification of exposure (starting from 80s, each adding 20S, five times, until 160s), unified normal development, in the test Finding the number of sun exposure levels specified in the instruction manual for the PS version on the bar is the correct exposure for that version.

Second, the network ladder 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 tone network is relatively complete that level of exposure time is the best Exposure time. Under normal circumstances the positive PS version should be able to restore 2% -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 different prints to determine the different printing time (assuming the standard exposure time is 100s)

In our day-to-day printing work, the more common originals are paper-based and polyester-based. If they are classified according to the type of graphic, they can be divided into text line version, field color version, and cable version. There are different types of cable screen editions, such as flat screen, gradient, and layered versions; some printing plates will be mixed with several types of graphics on the same plate, relatively speaking, the exposure time It will be more complicated.

First, the large version of the line text version of sulfuric acid paper and polyester film base lined out by computer. Exposure time is 120S. This amount of exposure not only ensures that the text lines are in good condition, but also develops thoroughly. However, the edges of the film base and the marks of the tape are still left on the 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 short and lack of painting; the pattern is not black enough, and the printing time is long. After the PS plate is developed, it loses its luster and the printing performance is poor.

Second, the large version of the text version of the line by photography or copy. 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, color level version with flat net prints, 10% flat screen version, print more time, there will be a bad network; more than 30% of the flat screen version, print a little more time will not appear rotten network.

1. The color version of the collage with a 10-20% flat net large version, exposure time is about 120S.
2. The color version contains a large collage of 30% or more flat screens with an exposure time of approximately 140 seconds.

5. In the color gradation version, there is no flat screen, but there are larger headlines or patterns in the field. In this type of printing, this is often the case: the dots of the prints have enough ink, but the solid parts are not of sufficient color, and the ink layer is not thick enough. If the ink volume is increased, the solid part color is enough, but the dots are partially colored. Not enough. If the printing time is appropriately increased, the outlets will be shrunk, that is, the printed edition will be sun-dried, which will make up for the increase in outlets caused by the large amount of ink on the actual site. The printing time is about 160S.

Sixth, color level version, that is, flat net, and there are on-site prints, this type of print, mainly as the middle part of the flat screen to determine the print time, if only consider the real part, print time will inevitably increase a lot, and A dot network of less than 10% will have a bad network, which will result in no printing.
1. With 10-20% flat screen, printing time is about 120S.
2. With more than 30% flat screen, printing time is about 140S.

Seventh, the original version of the monochrome large field version with flat screen. The main flat screen section determines the exposure time.

1. With 10-20% flat screen, printing time is about 120S.
2. With 30-40% flat screen, printing time is 150S.
3. With 50-60% flat screen, printing time is 250S.
4. With more than 60% flat screen, printing time is about 300S.

Eight, a large field, but the text line of the anti-white original, because it is a large field, the amount of ink is certainly large when printing, can ensure that the large field of ink is sufficient, but the increase in the amount of ink after the text lines against white parts, it is easy to paste Version. This kind of original version mainly depends on the thickness of the lines of the white parts, the size of the text and the thickness of the lines. The smaller the text, the finer the lines, the more exposure time, and even the pad printing imprints in the middle of the original version of PS, in order to fine lines, fine text, strokes thicker, it is not easy to print when printing.

1. 0.1mm lines or 5th (15th grade) text on the reversed part, first pad a 0.1mm thick imposition film between the PS plate and the original plate, and then vacuum the plate, the printing time is about 300s.
2. The anti-white part is 0.2mm line, or No. 2 (32 levels) text, printing time is 400s.
3. The anti-white part is 0.3mm line or small initial (50) text, and the printing time is about 300s.
4. The inverting part is a 0.4mm line or larger than the initial number and the printing time is about 250s.

Dual Exposure Time Setting by Diffusion Film Removal

If the original or printing glass has many scratches or small spots (including tape marks) that are difficult to remove, you can use a diffusion film on the printing plate to make a double exposure, using a diffusion film for light. Scattering principle, the direct light into scattered light, so that the original scratches or dirty spots covered by the unexposed part of the re-exposure exposure, to achieve the purpose of removing dirty. This is actually the PS version of the two exposure. The first time is the normal exposure, we call it the main exposure, and its time should be 4/5 of the standard exposure time; the second exposure is the exposure under the cover film, also called the sub-exposure, the sub-exposure. The time should be half the time of the main exposure. Although this method can effectively remove the dirty spots, we also need to note that this double exposure will also cause the dots to be reduced or even missing, so this method should be used with caution.

Monitoring and calculation of exposure (time)
It is a relatively simple and reliable method to quantitatively detect the exposure amount by using the continuous adjustment transmission scale and the unequal transmittance of light at each level. During the printing process, only a 10-step continuous projection ladder ruler with a step difference of 0.15 was printed on the outer side of the original plate core. After developing, it appeared completely white, completely black, and 1-2 intermediate overstage segments. Exposure state, comparing this state with the reference exposure state: when the number of sunning stages is less than the reference level, it indicates overexposure; when the number of sunning stages is more than the reference level, it indicates underexposure; when both are consistent, it indicates that the exposure is appropriate. .


When an overexposure or underexposure occurs and the exposure latitude exceeds the allowable range of the platelet requirement, the correct exposure time can be calculated by the following formula:

t - Adjusted exposure time t1 - Preset exposure time for debugging n0 - Number of exposure series for standard exposure time n1 - Number of printing steps for test exposure time ΔD - Step difference density &