Printing color bias and color mixing failures can be roughly summarized into four reasons:
1. The dots of yellow, magenta and cyan printing plates caused by non-standard plate-making operation are too deep or too shallow.
2. Ink color mismatching or three primary color ink mismatching;
3. The arrangement of printing color sequence is unreasonable.
Fourth, printing paper itself has a serious color bias phenomenon.
1. Color Bias Caused by the Fault of Screen Point Depth in Printing Plate
In the process of plate drying, the intensity and spectrum of plate light source do not match the photosensitive characteristics of plate photosensitive adhesive, or the exposure time is inappropriate; the pH value of developing solution and the improper control of developing time may cause the screen dots to be too deep or too shallow. Such a printing plate on the computer printing, the picture color deviation can not be avoided.
Therefore, the quality of the printing plate must be identified before boarding the machine. The identification of the printing plate network can be controlled by the magnifying glass. The original film of yellow, magenta, green and black is controlled by the magnifying glass. The situation of the bright spot, middle tone and dark area of the same plate should be carefully observed. That is to say, the small dot of the bright spot is 2%, the printing plate should be able to get the same sunlight, and 3% of the printed matter is printed. It should be printed. If 2% of the small dots on the plate can not be exposed, it means that the plate is shallow and not applicable. Using the method of identifying 2% small dots on the bright spot of the plate and the film, 97% dots on the plate with the same dark spot of the original film were identified. If the dots on the plate are pasted, it means that the plate has been sunburned deeply; if the area of the blank area between dots is enlarged, it means that the plate has been sunburned shallowly, it should be re-sunned.
Of course, under certain conditions, using Brunel signal bar to control the quality of printing plate can be accurate and easy to operate. The identification method is to observe 12 Yin and Yang dots in each of the fifth 50% fine screen test block of Brunel signal bar on the plate with the help of a high magnifying glass. The area of Yin and Yang dots should be 6 in order from large to small. 2% of the small dots in the six small grids of block 6 should be exposed. If 3% of the dots of the printed plate exist and 2% of the dots disappear, the printed plate is shallow. Conversely, not only 2% of the dots exist, but also 1% of the small dots exist, which means that the printing plate is too deep.
2. Color Bias Caused by Ink Problem
In the printing process, the color deviation fault caused by ink is mostly due to the existence of different degrees of color deviation in the three primary color inks produced in different places, such as Peony brand 05-24 medium yellow (red 0.16), 05-32 sky blue (red 0.35), which will have different degrees of color deviation impact on the whole picture, especially in the middle tone. But a small amount of color deviation can be corrected from the compatibility of ink. For example, for a long time, a group of three primary color inks used in East China, such as 05-28 transparent yellow, 05-14 magenta, 05-32 sky blue produced by Shanghai Ink Factory and GS-135 magenta, GS-425 sky blue and GS-236 yellow ink produced by Tianjin Ink Factory, all have the characteristics of fast drying, fast fixing, bright color, less color, strong hydrophobicity and good printing adaptability. They are used in high-speed and multi-color printing machine for paint paper printing essence. Fine products play a better role.
3. Color Bias Caused by Colour Order Arrangement
Comparing offset prints with proofing sheets, sometimes even though the density of ink and paper used is the same as that of the sample sheets, the offset prints still have yellowish, reddish or bluish or overlay ink mixing phenomenon.
What is the reason for this? First, the proofing machine is generally single-color wet press dry printing, the ink adsorption and transfer rate is appropriate; second, the machine structure, pressure and speed are different from the actual printing; third, the color sequence arrangement of high-speed multi-color printing is unreasonable. The author believes that the unreasonable arrangement of color sequence will not only cause color skewness failure, but also result in color mixing of printed pattern color due to wet press and overlay printing.
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