Flexographic printing dot transmission law
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From the perspective of manuscript design and plate making process, the flexographic printing process is self-contained and has its own unique features. The plate making process is basically as follows: original → electronic color separation or photography → positive negative image → back exposure → main exposure → development rinsing → Dry → Post-treatment → Post-exposure → Paste. Compared with offset printing, there are the following differences:
1. A range of color values that can be reproduced. Offset printing is 1% to 99% (or 2% to 98%), and flexo printing is 3% to 95%.
2. The outlet is expanded (50%). Offset printing is 15% to 20%, flexo printing is 30% to 40%
3. Number of screen lines. Offset printing is generally up to 175 lines/inch, and the number of flexo screens is generally no more than 150 lines/inch.
Dimensional deformation of the color separation sheet
The most obvious feature of the flexographic plate is its elasticity. When the flexographic plate is mounted on the cylindrical drum, the printing plate produces a bending deformation along the surface of the roller. This deformation affects the pattern and text on the surface of the printing plate, so that the printed image is printed. The text cannot be reproduced correctly, or even severely deformed. In order to compensate for the deformation of the printed image, it is necessary to reduce the size of the corresponding image on the negative film. The design of the original or color separation before the plate making should take into account the elongation of the printing plate, and subtract the corresponding value from the circumferential length dimension in the original to compensate, so that the printed product will meet the size requirements.
Flexible version of dot transmission
1. Reasons for the expansion of outlets
The expansion of dot in printing is inevitable, and there are two main reasons for the expansion of the dot: one is the physical reason. At the moment of imprinting, the ink on the plate dot is deformed by the pressing action, causing the dot to expand; Another reason is that optical causes the light to scatter at the edge portion of the dot ink film, thereby visually creating a considerable dot gain. The expansion of the optical dot depends on the transparency of the ink, the smoothness of the paper, the absorption properties, and the like.
2. Flexible version of dot transmission
In flexographic printing, since the photosensitive resin plate used is relatively elastic, it is necessary to apply a certain printing pressure in the printing process, which leads to enlargement of the image dot on the printed matter and elongation of the image, causing changes in color and layer reproduction. In practice, by measuring and drawing the corresponding flexographic printing characteristic curve, it can be seen that the dot enlargement in the flexographic printing process is very serious, and the dot below 10% is difficult to control. Therefore, special treatment should be made for the highlight zone, and as far as possible Flat net.
3. Influencing factors
(1) The number of screen lines is increased. The higher the number of screen lines, the more serious the network expansion.
(2) The size of the printing pressure, the greater the printing pressure, the more serious the dot enlargement, and the “zero pressure” should be kept as much as possible in flexographic printing.