The overprinting efficiency of the ink is closely related to the printing color sequence. Due to the high printing speed of the newspapers, the short ink overprinting time, the large paper absorption, and the penetrative drying of the ink, the color sequence of the overprinting should be different from that of other printing methods. Therefore, it is particularly important to select the color sequence suitable for color newspapers. The determination of the printing color sequence and the overprinting efficiency of newspapers is preliminary discussed from the following aspects.
1. Wet and wet printing
Newspaper printing is a high-speed printing; from the point of view of ink overprinting time, it is a wet-pressing-wet method; due to the rapid absorption of newsprint, from the perspective of ink drying: the first two colors are wet and dry, and the third and fourth color are overprinting. Wet pressure wet method.
2. The brightness of the ink
The brightest ink is at the end and the picture is more colorful.
3. Adhesion of ink
The ink's adhesiveness size is: K ink> M ink> C ink> Y ink, generally has a large adhesive preprint. Black print, in addition to the reason for the largest TACK value, there are other reasons for the color of the post-print for easy black registration.
The TACK value will change in different printing states, and it is usually difficult to accurately control the TACK value of the ink. When the ink binder is absorbed by the paper, the TACK value of the ink rises, and this occurs within a very short time between the print and the next color. During this time, the added TACK value may be The two-color (lower TACK value) ink amount is appropriately transferred to the first color ink film. Therefore, each color ink may have the same TACK value.
In addition to the minimum TACK value must be printed after the yellow ink, the lack of visual density is also a cause of post-printing. Because of the thicker ink film thickness, if yellow is printed first, the efficiency problem of transferring a thin ink film to a thick ink film will occur. In this way, the TACK value is reduced and the viscosity level between the first and second colors is destroyed.
4. Absorption of Newsprint
Due to the high absorptivity of newsprint, it is not appropriate to use the color sequence of black ink first in order to prevent print penetration.
During printing, the previous color ink film must reach a fixed viscosity before the succeeding color is successfully transferred to the previous color. Fixing time must be shortened by the use of quick-drying ink and adjusting the TACK value and density.
Substrate surface absorption, in fact, refers to the absorption condition with respect to the overprinting of the second color and the last few colors. On newsprint, when the first color is printed, the ink film is almost completely absorbed. For the second color ink, the surface characteristics of the first color ink film are almost similar to the unprinted substrate surface. In this case, even if there is no difference in the TACK values ​​of the respective color inks, a very high trap rate can be obtained in wet type overprinting.
5. Influence of Dot Increase
The increase in dot formation may be caused by excessive printing pressure or due to over-inking of 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 of the previous color is attached to the latter color rubber roller, so that the ink film of the background color thickens or spreads after printing. This situation is more serious for magenta ink, so magenta ink is usually printed on the back. To reduce dot gain, a special color can be printed after the ink that is more likely to cause dot gain, or a special color can be printed after the four colors are printed.
6. Ink transparency
The ink with the lowest transparency is printed first. Generally, the yellow ink has the lowest transparency, and the newsprint paper has strong absorption, which improves the wet overprint printing.
Yellow ink is first printed, and dark ink is printed. It is easier to overcome problems such as concentration changes and misregistration.
Now the yellow ink has improved transparency and gloss. When the black ink dries, it will produce a bronze luster hue that makes people feel that the color is not pure, and that the yellow ink can overcome this effect. Because the yellow ink is usually larger in area and covers a wider area, yellow ink can act as a glossy surface in the uppermost layer to destroy the effects of light scattering from the surface, and has the feature of brightening the print.
The color reproduction of yellow ink is weak. Therefore, yellow is first printed, and the ink film is thicker. Because the TACK value after the print cannot be higher than the previous color ink, yellow cannot be printed first.
Another reason for not printing yellow first is to avoid dot gains. Because yellow ink is usually required to be printed thicker, and the coverage is larger, especially when it is full of printing, such as printing first, it will change the hue of the surface of the substrate, and increase the possibility of the increase of other after-printing ink outlets.
7. Overprint problems
Mainly for the size of the substrate, printing ink with small stretchability is printed first, which is advantageous for registering.
8. Color shift problem
Different print sequences affect the final tone, depending on the characteristics of the print.
9. Overprint area
A large area of ​​post-printing, unless the ink used has a high degree of opacity, because the ability of the ink to transfer on the surface of the paper is much better than the transfer on the ink film. If a small area is printed first and then a large area is printed, the overprint portion is directly printed on the paper for a small area, and the ink color is transferred well, so this overprinting effect is good. On the contrary, if a large area is printed first and then a small area is printed, although the large area is well transferred, for a small area, the ink is all stacked on another color (large area) of the ink film, and the color performance is poor. The overall effect is inferior to the former.
10. The problem of ghosting
Usually in the four-color printing, black is the first color printing. In the black version of the newspaper and the text version, black ink accounts for a large part, and the newsprint paper is poor, and it is prone to reverse-transfer, causing the danger of ghosting. Ghosting can make text blurry. In this case, black should not be placed in the first color. It is better to place it in the last or third color.
In analyzing the above factors, some areas are self-contradictory. For any of the examples, all conditions cannot be satisfied. The determination of printing color sequence depends on the specific circumstances.
Today, newspaper printing houses mostly use the C-M-Y-K printing color sequence, because this printing color sequence is easier to control than other color sequences. In general, the black version of printing is shorter and the paper absorbs more. If black ink is printed first, the black ink on the black version will be immediately absorbed by the paper, which will not increase the density and increase the contrast of the black version. Newspapers mainly use Text-based, black ink is relatively large, and the strong absorption of newsprint results in black ink that is liable to cause print-through, and is prone to reverse transfer. On the final print, the influence of these adverse factors can be reduced, and it is beneficial to the drying of the ink. In addition, in the text area, non-graphics account for a major part of the fountain solution, and the strong absorptivity of newsprint may cause stickiness, and the paper may absorb a large amount of dampening fluid and cause paper deformation, affecting the registration of other inks. , produces ghosting. So, black is usually printed last.
Source: Printing Technology
1. Wet and wet printing
Newspaper printing is a high-speed printing; from the point of view of ink overprinting time, it is a wet-pressing-wet method; due to the rapid absorption of newsprint, from the perspective of ink drying: the first two colors are wet and dry, and the third and fourth color are overprinting. Wet pressure wet method.
2. The brightness of the ink
The brightest ink is at the end and the picture is more colorful.
3. Adhesion of ink
The ink's adhesiveness size is: K ink> M ink> C ink> Y ink, generally has a large adhesive preprint. Black print, in addition to the reason for the largest TACK value, there are other reasons for the color of the post-print for easy black registration.
The TACK value will change in different printing states, and it is usually difficult to accurately control the TACK value of the ink. When the ink binder is absorbed by the paper, the TACK value of the ink rises, and this occurs within a very short time between the print and the next color. During this time, the added TACK value may be The two-color (lower TACK value) ink amount is appropriately transferred to the first color ink film. Therefore, each color ink may have the same TACK value.
In addition to the minimum TACK value must be printed after the yellow ink, the lack of visual density is also a cause of post-printing. Because of the thicker ink film thickness, if yellow is printed first, the efficiency problem of transferring a thin ink film to a thick ink film will occur. In this way, the TACK value is reduced and the viscosity level between the first and second colors is destroyed.
4. Absorption of Newsprint
Due to the high absorptivity of newsprint, it is not appropriate to use the color sequence of black ink first in order to prevent print penetration.
During printing, the previous color ink film must reach a fixed viscosity before the succeeding color is successfully transferred to the previous color. Fixing time must be shortened by the use of quick-drying ink and adjusting the TACK value and density.
Substrate surface absorption, in fact, refers to the absorption condition with respect to the overprinting of the second color and the last few colors. On newsprint, when the first color is printed, the ink film is almost completely absorbed. For the second color ink, the surface characteristics of the first color ink film are almost similar to the unprinted substrate surface. In this case, even if there is no difference in the TACK values ​​of the respective color inks, a very high trap rate can be obtained in wet type overprinting.
5. Influence of Dot Increase
The increase in dot formation may be caused by excessive printing pressure or due to over-inking of 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 of the previous color is attached to the latter color rubber roller, so that the ink film of the background color thickens or spreads after printing. This situation is more serious for magenta ink, so magenta ink is usually printed on the back. To reduce dot gain, a special color can be printed after the ink that is more likely to cause dot gain, or a special color can be printed after the four colors are printed.
6. Ink transparency
The ink with the lowest transparency is printed first. Generally, the yellow ink has the lowest transparency, and the newsprint paper has strong absorption, which improves the wet overprint printing.
Yellow ink is first printed, and dark ink is printed. It is easier to overcome problems such as concentration changes and misregistration.
Now the yellow ink has improved transparency and gloss. When the black ink dries, it will produce a bronze luster hue that makes people feel that the color is not pure, and that the yellow ink can overcome this effect. Because the yellow ink is usually larger in area and covers a wider area, yellow ink can act as a glossy surface in the uppermost layer to destroy the effects of light scattering from the surface, and has the feature of brightening the print.
The color reproduction of yellow ink is weak. Therefore, yellow is first printed, and the ink film is thicker. Because the TACK value after the print cannot be higher than the previous color ink, yellow cannot be printed first.
Another reason for not printing yellow first is to avoid dot gains. Because yellow ink is usually required to be printed thicker, and the coverage is larger, especially when it is full of printing, such as printing first, it will change the hue of the surface of the substrate, and increase the possibility of the increase of other after-printing ink outlets.
7. Overprint problems
Mainly for the size of the substrate, printing ink with small stretchability is printed first, which is advantageous for registering.
8. Color shift problem
Different print sequences affect the final tone, depending on the characteristics of the print.
9. Overprint area
A large area of ​​post-printing, unless the ink used has a high degree of opacity, because the ability of the ink to transfer on the surface of the paper is much better than the transfer on the ink film. If a small area is printed first and then a large area is printed, the overprint portion is directly printed on the paper for a small area, and the ink color is transferred well, so this overprinting effect is good. On the contrary, if a large area is printed first and then a small area is printed, although the large area is well transferred, for a small area, the ink is all stacked on another color (large area) of the ink film, and the color performance is poor. The overall effect is inferior to the former.
10. The problem of ghosting
Usually in the four-color printing, black is the first color printing. In the black version of the newspaper and the text version, black ink accounts for a large part, and the newsprint paper is poor, and it is prone to reverse-transfer, causing the danger of ghosting. Ghosting can make text blurry. In this case, black should not be placed in the first color. It is better to place it in the last or third color.
In analyzing the above factors, some areas are self-contradictory. For any of the examples, all conditions cannot be satisfied. The determination of printing color sequence depends on the specific circumstances.
Today, newspaper printing houses mostly use the C-M-Y-K printing color sequence, because this printing color sequence is easier to control than other color sequences. In general, the black version of printing is shorter and the paper absorbs more. If black ink is printed first, the black ink on the black version will be immediately absorbed by the paper, which will not increase the density and increase the contrast of the black version. Newspapers mainly use Text-based, black ink is relatively large, and the strong absorption of newsprint results in black ink that is liable to cause print-through, and is prone to reverse transfer. On the final print, the influence of these adverse factors can be reduced, and it is beneficial to the drying of the ink. In addition, in the text area, non-graphics account for a major part of the fountain solution, and the strong absorptivity of newsprint may cause stickiness, and the paper may absorb a large amount of dampening fluid and cause paper deformation, affecting the registration of other inks. , produces ghosting. So, black is usually printed last.
Source: Printing Technology
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