In the process of intaglio printing copperplate, color separation is one of the processes of printing plate making. Color separation refers to the process of dissolving color manuscripts and making several basic monochrome printing plates. After the disintegrated monochrome printing plate is overprinted with the corresponding color ink, the printed matter that matches the color of the original can be reproduced.
There are three color separation methods, manual color separation, photographic color separation, and electronic color separation. The following mainly introduces electronic color separation.
Electronic color separation: It is a plate-making method of color separation film made by photoelectric scanning color separation through electronic color separation machine.
1. Electronic color separation machine The full name of the electronic color separation machine is called the electronic scanning color separation machine. It adopts photoelectric scanning method and electronic computer technology to separate color and color correction and other corrections of black and white or color, reflective or transmissive manuscripts; it can directly make color separation film from color manuscripts to transfer image information scanning records device.
2. The composition of the electronic color separation machine The basic components of the electronic color separation machine are divided into:
â‘ Original lighting optical system;
â‘¡, image information color separation and photoelectric conversion system;
â‘¢ Image color information processing system;
â‘£, image information output system;
⑤ Image zoom system;
â‘¥, correction and mask system.
3. The basic principle of electronic color separation:
The original is attached to the surface of the scanning drum, and the light source emits a tiny scanning spot on the order of micrometers. The original is scanned helically point by point to analyze the original image into many tiny pixels. It is split into four beams by the beam splitter, and the three beams are received by three photomultiplier tubes after passing through blue, green, and red color filters, respectively, thereby generating the main signals of the yellow, magenta, and cyan channels. The fourth beam is also received by a photomultiplier tube, which generates a filtered signal. The main signals of the yellow, magenta, and cyan channels are amplified by the photomultiplier tubes, converted into electrical signals of different strengths, entered the color correction circuit, sent to video lights and other devices, converted into different amounts of light, or screened by laser The device exposes and records on the photosensitive film to make a color separation film.
4. Copperplate production requirements 1. The plastic film is stretched due to the influence of heat and traction during the gravure printing process. If the gravure plate roller does not have an incremental diameter value, it will affect the accuracy of overprinting. Therefore, it is generally made as a diameter step gravure cylinder. In plastic printing, the diameter of the plate roller is required to increase by about + 0.03mm in each subsequent color. .
2. Quality standard of gravure cylinder:
a. The allowable deviation of coaxiality is ≤0.03mm.
b. The thickness of chromium layer ≥0.07mm, hardness Vickers 750-900HV.
c. Surface roughness ≤ Ra0.16.
d. The dynamic balance test does not appear to jump up and down.
e. The chrome-plated surface is bright and smooth, with blue light and silver-white color.
Fifth, plate-making design requirements During plate-making, it is necessary to continue to modify the original design according to the characteristics of gravure printing, so that it can be more suitable for printing needs.
1. For the purpose of overprinting, such as thin lines and text, multi-color overprinting is not allowed, and there should be no small reverse text on the pattern, and other small text should not be on the pattern. , The black, blue, red, and yellow plates should not be separated by other color plates.
2. For printing needs, the bar code should be arranged so that the line direction is consistent with the circumferential direction of the plate cylinder.
3. In terms of color guarantee, if conditions permit, it is better to make plates separately from the gradation pattern plate, and use the special plate as much as possible for the background color of the large field.
4. The screen-hanging version must fully consider the two color jump areas of 80% and 5%. When the screen is gradually hanging, the dot limit should be above 10%.
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