Most flexographic preprint products are converted from offset printing . The offset printing has the advantages of small dot expansion, high registration accuracy, bright and bright printing colors (wide color gamut), and text lines that can be overprinted. Currently, flexographic preprinting cannot be achieved temporarily. In addition, for the highlight dots appearing in the gradation, there are great challenges to the pre-printing and plate making of the flexographic version. Therefore, it is necessary to consider these factors in the production of documents and adapt the documents in advance to achieve the desired printing effect.
The factors to be considered comprehensively in prepress production are roughly divided into the following aspects:
1. Establish color separation scheme
Most offset printing products are mostly CMYK four-color printing, while flexographic pre-printing is mostly CMYK plus 2 to 4 spot color printing. The following points should be paid attention to in flexo preprint color separation:
â‘ CMYK four-color superimposed text is usually replaced with spot color text to reduce the difficulty of registration.
â‘¡ Large-area solid color, flexographic printing does not have the complex ink transfer structure of offset printing and the ink transfer principle of water and ink balance. The ink is transferred directly through the anilox roller, which can ensure the stability of the color well. In order to ensure that the solid color of a large area is not limited by the ink amount of the high-line-number anilox roller during the printing of the screen portion of the screen area, a plate separation process is usually performed.
â‘¢ Replace the four colors with spot colors or participate in color separation to expand the color gamut to achieve the printing effect we want. Flexographic water-based inks have a narrower color gamut than offset inks with higher transparency. You can use the seven primary color printing technology similar to flexo printing to expand the color gamut of flexo printing by means of spot color overprinting.
2. Production information
Including the number of screen lines, the angle of the dots, the reduction rate, horizontal stretching, etc.
a. Number of screens
The number of screen lines determines the fineness of the product, but it is not that the higher the line number of the printing plate, the more beautiful the printed product. It also depends on the quality of the printing plate, the control of the printing press pressure, and the configuration of the printing machine anilox roller . At present, the number of plate lines for general orders is 110LPI, and for special customer orders will increase to 133LPI.
b. Dot angle
The screen angle of flexo printing is usually: 37.5 ° for cyan, 67.5 ° for magenta, 82.5 ° for yellow, and 7.5 ° for black. This setting ensures that the screen angle difference between the three main colors of CMK is 30 °, while the weak colors Y and MK The visual effect of the net-shattering phenomenon with a difference of 15 ° is not obvious. If the angle of the dots of the overprinted color forms an angle less than 30 ° or coincides, moire or bumps will appear. In the event of screen screening problems, the production staff is required to adjust the dot angle in advance in pre-press production software (such as PackEdge).
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