Nowadays, multi-color printing has occupied the dominant position in the printing industry. When we use the four-color printing press for production, how should we arrange the printing color sequence? The author combines his practical experience and summarizes it as follows.
1, ink factor
Four-color machines generally use a printing color sequence in which ink film thickness gradually increases. For example, the C ink density is 1.6, the ink film thickness on paper is about 0.85 μm, the M ink density is 1.4, the ink film thickness is about 0.9 μm, the Y ink density is 1.0, and the ink film thickness is about 1.3 μm. If you print by CMY color sequence, overprinting works well. If the printing color sequence is changed to CYM, the ink film thickness is 0.85 μm, 1.3 μm, and 0.9 μm, respectively, resulting in a poor M-color overprinting effect. Although the thickness of the ink film can be increased and the overprint effect can be improved by increasing the amount of ink in the ink, when the thickness of the ink film exceeds 1.2 μm, the dots increase, resulting in color shift.
When the density of C ink is 1.6, the thickness of the ink film is 0.85 μm. If the density is reduced to 1.5, the thickness of the ink film is about 0.7 μm. This is the lowest value that the ink can cover the paper when the coated paper is printed, and is lower than this density value. Printing will be poor in the field. Therefore, in order to encounter this problem, it is preferable to dilute the ink so that the thickness of the printing ink film reaches 0.7 μm or more. Of course, when the thickness of the ink film exceeds 1.4 μm, in addition to the dot gain, defects such as back-scratching or reverse-printing are liable to occur. It can be seen that the ink density is of great importance. It is necessary to fully understand the relationship between ink film thickness and ink density when printing.
Four-color printing belongs to the wet-wet printing process, and the printing ink is easy to be anti-adhesive. Therefore, considering the viscosity of the ink, it is preferable to perform the printing in the descending order of the ink viscosity. In addition, in terms of the transparency of the ink, the printing color sequence with increasing transparency is preferred.
If the four-color printing is based on the K version, the background color removal is done deeper. From the perspective of reverse printing, the best printing color sequence is CMYK. However, if the K version is a complementary version, KCMY can be selected for the printing color sequence, which can also save costs from another perspective. However, if the K version of ink is used excessively, it will cause ink-printing in the latter-color printing and must attract attention.
2, product features
There are many types of color printing and each has its own characteristics. Therefore, we must arrange the printing sequence according to the characteristics of the products themselves.
For newspaper printing, color newspapers are printed using newsprint paper that is porous, easily deformed, and has low whiteness. It is difficult to overprint on high-speed web offset presses, and the color reproduction capability is inferior to that of offset and coated paper. The national standard "Quality Requirements and Inspection Methods for Newspaper Prints" states: The print quality of color pictures basically conforms to the natural tone, and the four-color overprint is accurate. Therefore, in addition to considering the overprinting effect of ink, the printing color sequence of color newspapers also meets the requirements for overprinting and color reproduction of newspaper color pictures in the national standard. For example: The newspaper of the city published the "Zhoukou Daily" of the party newspaper of the city, and one of the editions featured mostly people's pictures. Therefore, after comprehensive consideration of various factors, we adopted the CMYK printing color sequence, which not only ensures a good overprinting effect, but also does not produce ink stringing phenomenon in high-speed printing.
When copying a print or high-grade artwork, it should be printed in strict accordance with the color sequence of the original in order to faithfully copy the original. When the ticket is printed, it is necessary to print the background and print the border first. In the printing of certain packaged prints, the main text or picture should be kept clear and not covered by other inks. Therefore, the main color sequence of the main character or the main body of the print should be adopted.
3, overprint accuracy
In the printing process, through the pressure of the roller and the action of the fountain solution, it will produce a certain degree of deformation and extension, which will inevitably affect the overlay accuracy of the printed product. From the analysis of overprinting accuracy, how should we choose the printing color sequence in order to better guarantee the printing product registration?
First of all, it is necessary to print the ink with the low printing accuracy and the ink with the high precision after the printing. This will gradually stabilize the paper after printing with the first two colors, which can reduce the situation of overprinting and inaccurate printing. Second, it should first print a smaller area of ​​the color or dark version, and then print a larger area of ​​the color or light-colored version, so that even if the paper has a certain degree of deformation at the beginning, but the impact of the printing of the product is relatively small.
The color sequence arrangement of the four-color printing shall be analyzed in detail according to specific conditions, and the printing color sequence shall be adjusted at any time according to the actual situation so as to achieve the best combination of printing quality, printing cost and printing operation.