Talking about the control and detection method of printed image color Ⅱ
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Third, the method of controlling the quality of printing color
Constraints on the quality of printed images such as paper, ink and plates during printing. When these factors have been determined, how to control the color quality of printed images when performing image reproduction on a printing press?
1. Adjust printing pressure according to upper body production
The printing pressure is adjusted according to the quality requirements of the printed image reproduction, the thickness of the paper, the printing plate, etc., so that the image dot is optimally reproduced.
2. Reasonable arrangement of color sequence
Currently, multicolor printing generally uses ink, cyan, magenta, and yellow 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 the black, cyan, magenta and yellow sequences are used in the offset printing, the thickness of the ink layer is 0.8 μm for black ink, 0.9 μm for cyan ink, and 1. 0 μm, yellow ink is 1.1 μm; ink viscosity is arranged from large to small, such as black ink 1188Pa, blue ink 488Pa, magenta ink is 477Pa, yellow ink is 147Pa. When the viscosity of the ink does not meet the alignment requirements, the viscosity of the ink can be adjusted in advance.
3. Calibration press
The press is adjusted according to the proof sheet and the predetermined printing conditions to make the printed image effect consistent with the printed sheet.
Fourth, control the color reproduction quality during the printing process of the printing press
In the printing process, there are many variables affecting the quality of printed images. In order to compensate for the adverse effects of these variables, the printing presses produced by more advanced printing machines such as Heidelberg, Roland and Mitsubishi of Germany mainly adjust three parameters: the inking unit Temperature, ink supply and water supply.
1. Ink unit temperature control
Some presses are equipped with or with optional inking unit temperature control. In the process of inking, the ink roller rotates and sways, so its temperature rises most. When the temperature is controlled, the cooling core is introduced into the core of the ink roller to lower the temperature, so that the surface temperature of the ink roller remains stable. To ensure a stable supply of ink. In some printing machines, in addition to the ink roller, the ink fountain roller is cooled by cooling water.
2. Ink supply control
The density of the ink on the surface of the printed image directly affects the quality of the reproduced color. The density of the ink in the field is affected by the amount of ink supplied (the thickness of the ink layer on the surface of the printed image). The solid density also increases as the thickness of the ink layer increases. After reaching a certain point, the solid density will not increase as the thickness of the ink layer increases. The amount of ink supply (thickness of the ink layer) can be adjusted in accordance with the quality information of the surface of the printed image control strip.
At present, the automatic adjustment of the ink volume of the printing machine mainly includes two parts, namely, the total ink discharge amount of the ink fountain roller and the adjustment of the ink amount in each partial region of the ink roller. The overall ink amount adjustment ensures the correct reproduction of the tone and tone of the entire image of the printed image. Since the printed image is distributed throughout the layout, the demand for the amount of ink varies from area to region. Therefore, the ink fountain roller is divided into several sections along the axial direction of the ink roller. In the small ink zone, the amount of ink sent by different ink zones is different to meet the different requirements of the ink volume in each partial region of the image.
3. Water supply control
The amount of offset printing plate water must be controlled. The amount of water should vary with the printing speed and ink supply of the printing machine to ensure the balance of ink and water, so that the printed image is not smudged, the color saturation is good, and the paste is not paste. Adjusting the amount of water is achieved by changing the speed of the bucket roller.
Fifth, conclusion
In order to meet the quality requirements of color image printing, it is necessary to detect and control the printed image. The modern printing press meets the requirements of the printed image quality by controlling the ink temperature, the amount of ink supplied, and the amount of water supplied.