Plate positive exposure test

Plate positive exposure test

The frontal exposure is also called the main exposure, which forms the graphic printing part of the flexo version. Proper exposure and back exposure work together to produce high-quality printing plates that meet the requirements of various graphic types. In general, underexposure will cause the bottom of the shoulder around the graphic to be washed away, which will affect the life of the printing plate. Excessive positive exposure will result in insufficient corrosion, which can easily cause stencil printing and cause waste during printing.

Before conducting the front exposure test, we recommend that the operator prepare a test “special sample” dedicated to the production of flexible plates. The “samples” should include small anti-white, normal anti-white and field, common graphic, and small The basic printing and graphic types of lines and characters, dots, etc., and reflecting a certain number of lines (eg, 150 lpi) from 10% to 100% on the ground are all reflected in “samples”.

The positive exposure test can be performed using a "swatch" on the platesetter with partial coverage and multiple exposures. In the early stage, it is also possible to start from the less difficult business, from easy to difficult, to accumulate experience, and to fully master the technology of making flexible versions. In theory, the longer the positive exposure time required for finer graphics, the more important it is to remember the combined effect of back exposure. If the anti-white characters need less back exposure and positive exposure, and the fine dots need a shallower depth of corrosion, their back exposure and positive exposure time will be longer.

Through common time exploration and practice, platemaking operators need to understand the limits of their own plate making, such as whether the finest lines, the smallest characters, the densest dots, and 3% of the dots can be “stopped”, and whether 50% of the dots are highlighted. "Open up" and so on.

Source: "The Graphic Arts Society Monthly"

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