Talking about common treatment methods of trapping
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Trap is also called trapping, also known as expansion and contraction, mainly to compensate for the whitening between two adjacent different colors due to inaccurate printing overprinting.
When people face the printed matter, they always feel that the dark color is close to the human eye, and the light color is far from the human eye. Therefore, when trapping the original, it is always trying to prevent the light color under the dark color from being exposed. The dark color above remains the same to ensure that it does not affect the visual effect.
Principle of trapping processing
The implementation of trapping processing must also follow certain principles. Under normal circumstances, the color is not expanded, the color is not expanded, and the color is expanded without expanding the ground. Sometimes, mutual expansion is also possible. In special cases, reverse trapping is required, and even a gap is added between the two adjacent colors to compensate for the overprinting error, so that the printed matter is beautiful.
The amount of trapping depends on the characteristics of the substrate and the overprinting accuracy of the printing system. Generally, the amount of trapping of offset printing is smaller, and the amount of trapping of gravure and flexo printing is larger, generally 0.2-0.3 mm, which can be determined according to customer's printing accuracy or requirements.
Common trapping method
There are four main types of trapping methods.
(1) Monochrome line overprinting method: add a light color line on the edge of the color block, and select the line attribute as overprint.
(2) Synthetic line method: add a synthetic line on the side of the color block. Line attributes are not selected for overprinting.
(3) Layering method: trapping is achieved by retracting or expanding elements on different layers.
(4) Shift method: The inward or outer expansion is realized by moving the position of the inflection point in the color block, and is generally used in the trapping related to the gradation.
White trapping
In plastic printing, white ink applications are quite extensive. Generally, in transparent or translucent plastics, it is necessary to use white as a support, and sometimes to carry two layers of white. In order to prevent the white under the color block from being exposed due to inaccurate overprinting, white retraction should be considered before printing.
1. The white retraction can be carried out according to the depth of the color or the requirements of the customer, and the retraction amount is generally 0.2-0.3 mm.
2. If the color block is white and the side is transparent, the white can be retracted by 0.3 mm into the color block.
3. When black and gold are placed under white, white can be retracted to black and gold by 0.5-1 mm.
4. If the color block is lighter or flat, the amount of white retraction is small or not retracted. For example, when the dot percentage of the color patch is between 30% and 50%, the white retraction amount may be 0.15 mm; and when the dot percentage of the color patch is less than 30%, the white color may not be retracted.
5. When whitening under a gradual pattern, white should be considered for oblique retraction. The cyan gradient is white, the cyan is dark and the white is 0.2mm, and the cyan is white. The white is 0.1mm, which can be shifted by the inflection point.
6. If the transparent color (not white under the ink) is adjacent to other colors, the white under other colors should be retracted by 0.2 mm; if the transparent color is directly adjacent to white, the white should be enlarged by 0.2 mm into the transparent color to avoid smearing.