Plate back exposure test

We can first determine the back exposure time for different etching depth by doing back exposure test on the plate making machine. For comparison, we use multiple exposures with different exposure times for the same plate. Take a piece of media about 320 mm long and 100 mm wide. When performing back exposure on a platemaking machine, we use red cover strips to partially cover the plate, and the platesetter makes multiple exposures, resulting in five different back exposure times. Regional plate. In addition, about 20 mm of blank space is left at the end of the plate for the plate washer. Suppose we choose a flexographic plate with a thickness of 1.70 mm produced by the Dutch AV-500 combined platemaking machine and the GRACE company. After partial coverage and multiple exposures, we have exposure times of 0 on the same plate. The five parts of 15, 20, 25, and 30 seconds were exposed and placed on the drum of the printing plate for washing, about 7 minutes. Then dry in a drying oven at a temperature of 50. c, the time is 1.5 hours. Finally, the printing plate is taken out, and four different plate thickness values ​​on the printing plate can be measured by using a caliper, while the unexposed portion of the printing plate remains only the hard polyester plate base.

Through the above test, the platemaking machine can be quickly familiar with, and its test results also have guiding significance for adjusting the corrosion depth of the printing plate. From the above experiments, it can be seen that the length of the back exposure time will affect the thickness of the substrate. Therefore, different back-exposure times should be used for plate making for different printing images. Still using a 1.70 mm thick flexographic plate as an example, the anti-white and large-size solids on the plate will have a deeper etching depth (ie, a thinner base plate) up to 1.0 mm, and the back exposure time will be the shortest. The general picture and text part has a medium depth of corrosion, about 0.85 mm, and the back exposure time is moderate. As for the fine lines and dots, the corrosion depth should be the shallowest, about 0.63 mm, so the back exposure time should be the longest. .

In addition, there are two other points worth noting: When the printer changes to a flexible plate of another thickness or another brand of flexographic plate, the back exposure test must be performed again. With the extension of UV lamp usage time, its light intensity will be reduced. At this time, the back exposure time should be adjusted accordingly.

Source: "The Graphic Arts Society Monthly"