Analysis of Features and Difficulties of Pre-press Processing in Flexible Plates (Part 2)

Flexographic prepress processing and features and difficulties

After understanding the characteristics of flexographic printing, it is easy to grasp the features and difficulties of prepress processing. As mentioned above, changes in pressure will lead to changes in the printing effect. Moreover, different presses have different pressure, tension, and other characteristics, and the technical level of the printing workers will also have certain differences, and the impact on the printing effect will be different. Therefore, the flexographic plate maker must first make a test version for the customer before making the plate, and the test version should be printed under the same process environment (such as ink, pressure, printing speed, etc.), otherwise the test sample reflects the information Will not be referenced.

By testing test coupons, plate makers can get a lot of information on printing pressure, ink, and equipment. For example, the thin line through which the flexo printing machine can print can be tested by the line box, the smallest text that can be printed by the flexographic printing press can be detected by the text block, and the ability to express the dot by the flexographic printing press can be measured by the dot step. Increase the value. After the plate maker knows this information, it will make corresponding compensation when performing color separation processing before printing.

Specifically, when the prepress is processed, the manuscript can be divided into two types according to the situation: the line script and the mesh rephrasing, and the emphasis of the prepress processing is not the same. Stroke drafts, also known as outline drafts, contain text, lines, and field information. Modifications are relatively easy, but pay attention to the smallest and finest thread sizes in a test print, and do not exceed this size during processing. In addition, due to the effect of pressure during printing, the lines may become thicker, and a certain amount of compensation may be required during the production, in particular, the bar code day WR (bar width reduction rate) value is measured. Individual thin lines and a set of thin lines (such as text) have different pressure tolerances. A single thin line will bend when the pressure is too high, so try to ensure that its width is not less than 0.1 m. The mesh remastering is an image or a pattern containing a hierarchy, and many factors need to be taken into consideration during production. The processing of reprofiling is the core part of prepress processing, and the issue of increasing the number of printing outlets must be fully taken into account when making the layout.

Dot gain is divided into two types: optical dot gain and mechanical dot gain (Figure 2). The optical dot gain refers to the decrease of reflected light due to the thickness of the ink layer after the dots are printed on the substrate, so that the dot measurement value is larger than the original value. Optical dot gain is an optical phenomenon that cannot be changed. The increase in mechanical network points means that the printing dot diameter (circular dot) caused by the printing pressure is larger than the original value. The increase in the mechanical dot size is related to the performance of the printing press and the operation level of the printing worker. One of the test versions is to increase the number of test machine outlets, and adjust the production of the screens based on the increase in the test sample. Table 1 shows the dot gain value measured when a printing factory prints 149 lines/in., and Figure 3 shows the corresponding dot gain curve. From Table 1, it can be seen that 2% of the dots are increased to 10% after printing, and 50% of the dots are increased to 79%. Therefore, 10% of the dots on the printed proof sheet must be designed to be 2% before the prepress processing. (to be continued)