3. Methods of controlling printing color quality
In the printing industry, the quality constraints of printed images such as paper, ink and printing plates. When these factors have been determined, how to control the color quality of the printed image when the image is reproduced on the printing machine?
1. Adjust printing pressure according to upper body production
Adjust the printing pressure according to the print image copy quality requirements, paper thickness, printing plate and other conditions, so that the image dots can be best reproduced.
2. Reasonably arrange the color sequence
Currently, multicolor printing generally uses ink, cyan, magenta, and yellow sequences or cyan, magenta, yellow, and black sequences. This color sequence makes color reproduction easier and more accurate. The thickness of the ink layer is arranged from small to large. For example, when black, cyan, magenta and yellow are used in offset printing, the thickness of the ink layer is: 0.8 μm for black ink, 0.9 μm for cyan ink, and 1. 0μm, yellow ink is 1.1μm; ink viscosity is arranged from large to small, such as black ink 1188Pa, cyan ink 488Pa, magenta ink 477Pa, yellow ink 147Pa. When the ink viscosity cannot meet the arrangement requirements, the ink viscosity can be adjusted in advance.
3. Calibrate the printing press
Adjust the printing machine according to the proof sheet and the predetermined printing conditions to make the printed image effect consistent with the printed sheet.
4. During the printing process of the printing press, control the color reproduction quality
In the printing process, there are many variables that affect the quality of the printed image. In order to compensate for the adverse effects of these variables, currently more advanced printing machines such as those produced by Heidelberg, Roland, and Mitsubishi in Japan mainly adjust three parameters: Temperature, ink supply and water supply.
1. Inking device temperature control
Some printing presses are equipped with or optionally equipped with temperature control devices for inking devices. In the process of inking, the ink roller rotates and moves at the same time, so its temperature rises the most. When the temperature is controlled, cooling water is generally passed through the shaft core of the ink roller to reduce the temperature, so that the surface temperature of the ink roller remains stable , So as to ensure a stable ink supply. In some printing machines, in addition to the ink channeling roller, cooling water is passed through the ink fountain roller to lower the temperature.
2. Ink supply control
The solid ink density on the surface of the printed image directly affects the color quality of the copy. The solid ink density is affected by the amount of ink supplied (the thickness of the ink layer on the surface of the printed image). As the thickness of the ink layer increases, the solid density also increases. After reaching a certain point, the solid density will not increase with the thickness of the ink layer. The amount of ink supply (ink layer thickness) can be adjusted according to the quality information of the control strip on the surface of the printed image.
At present, the automatic adjustment of the ink volume of the printing press mainly includes two parts, namely, the overall ink volume of the ink fountain roller and the adjustment of the ink volume of each local area of ​​the ink roller. The overall ink volume adjustment ensures the correct reproduction of the tone and tone of the entire screen of the printed image. Due to the different distribution of the printed image on the entire layout, the demand for ink volume in each area is also different. Therefore, the ink fountain roller is divided into several along the axis direction of the ink roller In the small ink area, different ink areas send different amounts of ink to meet the different requirements for the amount of ink in each local area of ​​the image.
3. Water supply control
The amount of water in offset printing plates must be controlled. The amount of water should be different according to the printing speed and ink supply of the printing press to ensure the balance of water and ink, so that the printed image does not bloom, the color saturation is good, and it does not paste. The water volume is adjusted by changing the rotation speed of the water bucket roller.
V. Conclusion
In order to meet the quality requirements of color image printing and copying, the printed image must be detected and controlled. Modern printing presses make the quality of printed images meet the requirements by controlling the ink temperature, ink supply and water supply.
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