1. Flexible plate-making process
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: manuscript → electronic color separation or photography → positive negative image → back exposure → main exposure → development and processing → Drying → Post-processing → Post-exposure → Plate. Compared with offset printing plate, there are the following differences: 1. Reproducible color value range. Offset printing is 1% to 99% (or 2% to 98%), flexo printing is 3% to 95%. 2. Expansion of outlets (at 50%). 15% ～ 20% for offset printing, 30% ～ 40% for flexographic printing Offset printing generally has a maximum of 175 lines / inch, and the number of flexo and screen lines generally does not exceed 150 lines / inch.
Second, the dimensional deformation of the color separation film
The most obvious feature of the flexographic plate is its elasticity. When the flexographic plate is installed on the cylindrical cylinder, the printing plate is bent and deformed along the surface of the cylinder. The text could not be reproduced correctly, or even deformed seriously. In order to compensate for the distortion of the printed image, it is necessary to reduce the size of the corresponding graphic on the negative film. When designing the original or color separation before plate making, the elongation of the printing plate should be considered, and the corresponding value should be subtracted from the circumferential length of the original to compensate, so that the printed product will meet the size requirements.
Third, the transmission rule of the flexible version of the dot
1. Reasons for dot expansion The dot expansion in printing is inevitable. There are two main reasons for the dot expansion: one is the physical reason. At the moment of imprinting, the ink on the dots of the printing plate has a certain effect due to the squeezing effect. The deformation causes the dots to expand; another reason is optical, and the light is scattered at the edge of the dot ink film, resulting in a considerable dot expansion visually. Optical dot expansion depends on the transparency of the ink and the smoothness and absorption properties of the paper.
2. Flexographic dot transmission law In flexographic printing, due to the relatively high elasticity of the photosensitive resin plate used, a certain printing pressure needs to be applied during the printing process, which will cause the expansion of the image dots on the printed matter and the extension 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 expansion in the flexographic printing process is very serious, and the dots below 10% are difficult to control. Therefore, special treatment should be done for the highlight area. Flat net.
3. Influencing factors (1) The number of screens added, the higher the number of screens added, the more serious the network expansion. (2) The size of the printing pressure, the greater the printing pressure, the more serious the dot expansion, and the "zero pressure" should be kept as much as possible in flexographic printing. (3) Dot shape. Circular dots, square dots, chain dots and elliptical dots have different expansions at different levels. Chain-shaped dots are commonly used in flexographic printing; for small dots in high-gloss areas, FM dots (FM) are the best.
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