Determination of color sequence and overprint effi

2022-08-07
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Determination of color sequence and overprint efficiency in newspaper printing. Because the color newspaper printing speed is high, the ink overprint time is short, the paper absorption is large, and the ink is a penetration drying method, the color sequence of the overprint should be different from that of other printing methods. Therefore, it is particularly important to select the printing color sequence that preheat the color newspaper for 5 (1) 0 minutes before the experiment. The determination of printing color sequence and overprint efficiency of newspapers is discussed from the following aspects

1. Wet press wet printing

newspaper printing belongs to high-speed printing; From the perspective of ink overprint time, it belongs to wet pressing wet mode; Due to the rapid absorption of paper, from the perspective of ink drying, the first and second colors belong to the wet press drying method, while the third and fourth color overprint belongs to the wet press wet method

2. Ink lightness

put the ink with high lightness last, and the picture will be more colorful

3. Adhesion of ink

the adhesion of ink is: K ink m ink C ink y ink. Generally, the ink with high adhesion is printed first. In addition to the biggest tack value of black first printing, there are also reasons such as easy registration of the color of later printing for black

the tack value will change in different printing States, and it is usually difficult to accurately control the tack value of printing ink. When the binder of the ink is absorbed by the paper, the tack value of the ink will increase, which occurs in a very short time between the first color and the second color. The increased tack value during this time may have properly transferred the ink amount of the second color (the lower tack value) to the first color ink film. Therefore, each color of ink can have the same tack value

in addition to the minimum tack value, the yellow ink must be post printed. The lack of visual density is also a reason for post printing. Because the ink film is thick, if yellow is printed first, the efficiency of transferring a thin ink film to a thick ink film will be affected. In this way, the tack value will be reduced and the viscosity grade between the first color and the second color will be destroyed

4. Absorption of paper

due to the large absorption of paper, in order to prevent through printing, it is not appropriate to use the color sequence of printing black ink first

during printing, the ink film of the former color must reach the fixed viscosity before the latter color is successfully transferred to the former color. The fixing time must be shortened by using quick drying ink and adjusting tack value and density

the surface absorption of the substrate actually refers to the absorption relative to the second color and the last few color overprint. On paper, when printing the first color, the ink film is almost completely absorbed immediately. For the second color ink, the surface characteristics of the thermosetting plate formed by the first color ink film are almost similar to the surface of the unprinted substrate. In this case, even if there is no difference in the tack value of each color ink, a high overprint rate can be obtained in wet overprint printing

5. Effect of dot increase

dot increase may be caused by excessive printing pressure or too thick ink layer on the printing plate. In two-color or four-color printing, it may be caused by reverse printing. When the next sheet is printed, the ink film of the background color thickens or diffuses after printing because the rubber drum of the latter color is attached with the ink of the former color. This situation is more serious for magenta ink, so magenta ink is usually printed later. To reduce the point increase phenomenon, you can print a special color after the ink that is easy to cause the point increase; Or after the four-color printing, print a special color

6. Ink transparency

the ink with the lowest transparency shall be printed first. Generally, the transparency of yellow ink is the lowest, and the absorption of paper is strong, which improves the printing of wet overprint

yellow ink is printed first, while dark ink is printed later. It is easy to overcome problems such as concentration change and registration error

now the transparency and gloss of yellow ink have been improved. When the black ink is dry, it will produce a bronze luster hue, making people feel that the color is not pure. However, the back printing of yellow ink can overcome this effect. Because the yellow ink usually covers a large area and covers a wide range, the yellow ink printing on the top layer can play the role of glossy surface, so as to break the influence of light scattering on the surface to ensure the safety of laboratory personnel and equipment, and has the characteristics of brightening the printing products

the color reproducibility of yellow ink is weak. Therefore, the ink film is thick when printing yellow first. Because the tack value of post printing cannot be higher than that of the previous color ink, yellow cannot be printed first

another reason not to print yellow first is to avoid dot enlargement. Because yellow ink usually needs to be printed thick and has a large coverage, especially in full plate printing, if it is printed first, it will change the hue of the substrate surface and increase the possibility of other post printing ink spots

7. Overprint problem

mainly refers to the size of the substrate. Printing ink with small paper elasticity first is conducive to registration

8. Color deviation problem

different printing color sequences will affect the final hue, which generally depends on the characteristics of the printed matter

9. Overprint area

for post printing with large area, unless the ink used has high opacity, because the transfer ability of the ink on the paper surface is much better than that on the ink film. If a small area is printed first and then a large area is printed, the overprint part is directly printed on the paper for a small area, and the ink color transfer is good, so this kind of overprint effect is good. On the contrary, if a large area is printed first and then a small area is printed, although the large area transfer is good, for a small area, the printing ink is all stacked on another color (large area) ink film, and the color performance is poor. For the overall effect, entering the main interface of the control software is not as good as the former

10. Ghosting problem

generally, black is the first color in four-color printing. The black version of the newspaper is the same as the text version. Black ink accounts for a large part, and the paper is poor. Reverse transfer printing is easy to occur, resulting in the risk of ghosting. Ghosting will blur the text. In this case, black should not be placed in the first color, and it is best to put it in the last or the third color for printing

analyzing the above factors, there are contradictions in some places. For any example, all conditions cannot be met. The determination of printing color sequence depends on the specific situation

nowadays, most newspaper printing houses use c-m-y-k printing color sequence, because compared with other color sequences, this printing color sequence is easier to control. Generally, the black version of color newspaper printing is short and the paper has strong absorption. If black ink is printed first, the black ink on the black version will be immediately absorbed by the paper, which can not improve the density and contrast of the black version; Newspapers are mainly written, with a large amount of black ink. Due to the strong absorption of the paper, if the black ink is printed first, it is easy to cause through printing and reverse transfer printing. Printing last can reduce the impact of these adverse factors and is conducive to the drying of the ink; In addition, in the text area, non graphics and text account for the main part, and there are many fountain solutions, while the strong absorption of paper is easy to cause sticky dirt, and the paper will deform after absorbing a large amount of fountain solutions, affecting the registration of other ink colors and causing ghosting. Therefore, black is usually printed last

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