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You need to pay attention to three times
Determination of back exposure time
The back exposure time is determined according to the thickness of the desired plate base. As shown in the figure below, if the required thickness is C, the corresponding back exposure time is 12 seconds. We can divide a plate into a number of pieces and then use different exposure times to achieve different thicknesses. A comparison table is created based on the thickness of the test plate after exposure. With the beta version, it is possible to produce a printed version that meets the requirements very accurately when the official version is made.
Determination of the main exposure time
The main exposure time can also be determined by the test version. For example, we take four plates and use different time to expose. After the completion, the percentage of the negative image is measured, and the negative control image is selected. If the dot is larger than the negative image, reduce the exposure time; if the dot is small relative to the negative image, increase the exposure time so that the optimal main exposure time can be determined.
Plate elongation compensation
In the process of making plates, pay attention to the compensation of the elongation of the plate. As shown below, the normal pattern (lithographic) is a circle. However, the printing plate is wrapped on the printing roller. Since the radius of the printing roller is different, its arc will be different, so that the dot will become elliptical and the ellipticity will be different. Therefore, the plate should be corrected for the different radius of the roller.
Compensation for the elongation of the photosensitive resin plate
How to correct the plate, there is a correction formula can refer to:
In the formula,
R is the plate roll radius
a is the thickness of the paper
b is the thickness of double-sided tape
c is the plate thickness
This formula can be used to calculate the compensation for the elongation dimension, which will make our printing more accurate. Therefore, when making a printed version, it is necessary to be very clear about the elongation of the plate.
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