Control of plate making quality and color before t

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Prepress plate making quality and color control

at present, the most important part of the quality control of color offset printing is color control. The quality of color reproduction directly affects the quality of printed matter

The printing and reproduction process of color originals can usually be described as a combination of color decomposition and color restoration of image information. In practice, due to various conditions are not ideal, color difference is inevitable. Color difference mainly comes from three aspects. First, the color deviation caused by the shooting process and materials of the original, as well as the color deviation caused by the color of the color medium (color attenuation); Second, the color difference in the process of color decomposition, mainly the errors of light source, lens, color filter, photomultiplier tube and photosensitive materials; Third, the color difference in the process of color reduction, mainly paper. Welcome to consult Zhang, ink and printing process errors

the quality of prepress plate making also directly affects the quality of printed matter. In the process of plate making, there are many reasons for color difference. Here is only an introduction to several factors that affect color quality when offset printing is used as a means of color reduction

point change

color prints are overprinted with three printing plates with different point angles, yellow, green, and then polyurethane reinforced coiled material composite insulation board. Since it entered the market, it shows the color and tone of the original, and a black plate should be added to make up for the lack of dark tone. In offset printing, dot enlargement is inevitable for various reasons

the change of dot size will cause the change of the color depth of the printed matter, and the color depth of the printed matter is not always linear with the dot percentage. At the end where the optical density is small, the influence of the increase of the dot area on the tone density is much smaller than that at the end where the optical density is large. In order to make the difference between two brighter hues, it is necessary to make the point area coverage change greatly; On the contrary, in order to distinguish two darker tones, the point area coverage can be achieved with only a small change. In the bright tone area, the small change of dot percentage has little influence on the tone, which is difficult for the eyes to detect; In dark areas, subtle changes in dot percentage will cause significant changes in hue. Therefore, the influence of the change of point size on the color of image reproduction is complex. In practice, the control of some dark points is particularly important


the structure, properties and other characteristics of the ink itself have a direct impact on the reproduction of color

in color printing, the quality of printed matter is often measured by parameters such as ink field density, dot increase, printing contrast and overprint rate. These parameters are closely related to the thickness of ink film on the printing sheet. The ink layer is too thin, and the ink cannot completely cover the printing area of the substrate. The color must be light, and the gloss is not enough. Generally, the thickness of the ink film is about 1.0um, and then increase the thickness of the ink film, the density will not increase. On the contrary, because the ink layer is too thick, the dots will increase, the layers will be merged, and the tone and color will change significantly due to being buried as garbage, resulting in color deviation. Therefore, controlling the thickness of the ink film is an important means of color restoration. The thickness of ink film is not only restricted by the properties of ink and paper, but also affected by printing conditions and environmental factors. Different inks have different ink film thickness in order to achieve a certain density value due to their own performance differences, such as different coloring power

controlling the ink film thickness is the key, and the defects of Tongjin ink itself should also be understood. The ideal tri primary ink can produce neutral gray by mixing in equal proportion, while the actually used tri primary ink can only produce dark color after mixing in equal proportion. The correct reproduction of gray balance is the basis of color printing. The unsatisfactory ink itself obviously brings some difficulties to the correct reproduction of color

the color range (gamut) that can be reproduced by ink overprint will play an indispensable role, which is the smallest of all gamuts. The range of colors that can be reproduced by overprinting inks produced by different manufacturers and different types of inks produced by the same manufacturer is different. When printing, it is necessary to choose an ink with a large color gamut. The larger the color gamut, the smaller the loss of color information and the higher the fidelity of color reproduction


different printing materials have different printability. The smoothness, ink absorption, surface strength, whiteness, sizing and flexibility of paper are closely related to the quality of printed matter

the smoothness of the paper determines the close contact between the paper and the printing plate. The smoothness of paper is in direct proportion to the ink transfer rate within a certain range. When the smoothness is high, even if the ink layer of the printing plate is very thin, the connecting material of the ink will quickly form a fixed ink layer on the paper, which is conducive to the overprint of the next printing color, but when the ink layer increases to a certain thickness and changes slightly, the printed matter with uniform color can be obtained; Offset paper is poor, low transfer rate, which is not conducive to color restoration

the whiteness of paper, that is, the whiteness of paper, is the ability of paper to reflect visible light of various wavelengths in equal proportion. Except for a few colored papers, most of the printing papers are white, and the whiteness of different papers is different. For printing, the higher the whiteness of the paper, the better. Only paper that is almost pure white and can reflect all the visible light can give full play to the color characteristics of the ink. If the color of the paper is more common, blue or red, it will make the printing produce color deviation, which will affect the hue, lightness and saturation of the printing. The whiteness of the paper will also affect the contrast of the picture level. The whiteness of the paper is good, and the hierarchy and clarity of the picture are correspondingly improved; On the contrary, the color of prints is gray and the contrast is poor

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