Prepress testing and pre-compensation processing of flexo printing
No matter what kind of printing form, pre-press and pre-press testing are the basis for ensuring stable printing quality. Because there are many unstable factors in the printing process, if there is no systematic data file as a standard to control, the quality of the printed product cannot be guaranteed. We know that in the actual printing process, each ink manufacturer's primary color ink cannot be absolutely pure, and the color of the printing substrate also has certain differences, so it is very necessary to perform pre-press testing in flexo printing .
1. Main features of flexo printing
In terms of pre-press processing and printing principles, flexo printing has the following characteristics:
1) Pre-press processing, flexo printing has its particularity. If pre-press processing is performed as offset or gravure printing, the following faults will occur: â‘ The color becomes lighter, which affects the reproduction of colors; â‘¡The dots in the highlight area are lost, and it cannot express subtle levels; Reappear.
2) The basic principle of flexographic printing is to use a flexographic printing plate to transfer ink through an anilox roller to apply an ink layer of a certain thickness evenly to the graphic part of the printing plate. Then, under the pressure of the impression cylinder, The ink layer of the graphic part is transferred to the surface of the substrate to form a clear printed graphic. Therefore, flexo printing belongs to the category of relief printing in the final analysis, but its printing plate performance and ink transfer process have its own particularity. Especially the flexographic printing plate production process is many, the plate mounting process is poor, and the error is large. Control the different heart degrees of the plate cylinder at 0.015mm, and the thickness error of the double-sided tape is ± 0.015mm. The sum of the above three errors will significantly reduce the overall accuracy of the plate cylinder components. To achieve a good transfer of ink, Increase printing pressure. The increase of the printing pressure will increase the deformation of the flexographic elastic printing plate, resulting in the increase of the dot increase. In order to solve the above-mentioned problems, the necessary compensation must be made through pre-press testing.
2. Prepress test
1) Make and use a beta version
The test version is also called the test version, that is, before the official plate making, the flexographic plate maker first produces a set of test plates for the customer to test on the machine. By testing the test samples, the plate maker can get such Reproducibility, the main performance parameters of the ink, and equipment and many other process information, these reference information is an important basis for plate making.
The test version generally includes the following content: â‘ line frame, test the thinnest line that the printing machine can print; â‘¡text block, detect the smallest text size that the printing machine can print; The capacity of the dot and the increase value of the dot.
After obtaining this information before plate making, targeted compensation can be made in the color separation process, and the emphasis on pre-press processing for line drafts and screen adjustment drafts is also different. Specifically, as far as the processing of line drafts is concerned, it is only necessary to pay attention to the smallest text and the thinnest line range that can be printed in the test print sample. It is necessary to take appropriate compensation (reduction) for the thickening of the lines caused by the printing pressure, and especially pay attention to the measurement of the bar code BWR (reduction rate of bar width) value. Individual thin lines and a group of thin lines (such as text) have different pressure-bearing capabilities. Individual thin lines will bend when the pressure is too large, so try to ensure that the width is not less than 0.1mm.
Editor in charge: Liu Qingqing
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