Optimum operational testing of coated cardboard on corrugating machines

At present, color printing is usually performed by using yellow, magenta, cyan, and black four-color plates and superimposing them in a certain order. Theoretically speaking, four-color printing can have twenty-four different printing color sequences. The use of yellow, magenta, cyan, and black four-color plates regardless of the type of printing color sequence used should achieve satisfactory results. However, there are many factors that affect the color of printed materials, such as the printing area, ink performance, texture of the substrate, human visual effects, overprinting requirements, manuscript type, and so on, which will affect the quality of printed matter from different degrees. Printing color sequence is different, and the color effect of printed materials is not the same. Reasonable printing color sequence will make the picture color closer to the original, and even strengthen the atmosphere of a certain color, adjust the level of the picture, make the round corridor clear, distinct or soft. In addition, it can also protect the paper surface, increase the gloss of the product, and facilitate overprinting. Therefore, in the case of color printing, especially packaging printing, more than four colors or spot colors, and a full version, attention should be paid to the arrangement of the printing color sequence.
For the arrangement of four-color printing color sequence, the following aspects can be considered as a priority factor:
First, the color shift in the product design process, should be based on the main color of the original to determine the 45 ° color version, and then determine the other color version of the cable angle, and to specify the four-color machine printing color order. For example, for landscapes with blue and green main colors, the cyan cable is set to 45°, the black cable is set to 15°, the magenta cable is set to 75°, the yellow cable is set to 90°, and the color sequence is determined to be : Black → Magenta → Blue → Yellow. Different printing color sequences will affect the color tone of the final prints. For example, yellow, magenta, and blue colors will be printed in magenta, cyan, and yellow colors. A slight greenish color will be formed; if the color sequence is blue→magenta→ Yellow, it will form a slight reddish. The following table shows the effect of changes in the printing sequence on the color rendering effect, which does not include black. For color deviation after overprinting, it can be corrected when making plates. At the same time, in order to emphasize the main colors of print screens, we must also take full advantage of the special effects of the color deviations produced by different printing sequences.
Second, reverse printing phenomenon For four-color offset printing press this wet printing method, to make the latter color ink can be better transferred to the previous color substrate ink layer, ink sequence printing ink sequence should be followed by reduction Small, otherwise it will produce reverse printing phenomenon.
Group-type lithographic printing machine (such as domestic four-color machine, Heidelberg four-color machine, etc.), the ink on each color group is directly transferred to the surface of the paper at the time of printing, and the low-viscosity component and the solvent in the ink are fast and instantaneously penetrated in large quantities. Into the gaps in the paper, leaving a high viscosity component and synthetic grease enveloping the pigments in a gelled state on the surface of the paper, the viscosity of the ink in the process rises sharply, so that the viscosity of the latter color ink is even with the viscosity of the previous color ink The same or slightly greater than the viscosity of the previous color ink does not produce the phenomenon of reverse overprinting. However, the viscosity of the ink is also affected by many factors, such as the thickness of the printed ink layer, the printing speed, the temperature, the degree of ink emulsification, the amount of ink accessories added, etc., which are likely to break the original normal ink transfer relationship. In order to ensure the normal transfer of ink, following the printing sequence, the viscosity of the ink should be reduced in turn. For a satellite lithographic printing machine, since each color of ink is transferred to the blanket cylinder after printing, the ink is transferred to the paper, and the color ink of the preceding color does not increase in viscosity. This type of printing machine has a structural deficiency. Easy to produce anti-stack phenomenon. Therefore, for this type of printing press, printing must be strictly followed in accordance with the principle of decreasing ink viscosity in the printing sequence, and between the front and rear colors, the tack value of the ink should be significantly different.
In addition, when printing smooth, low-absorbency paper, consider the effect of ink stickiness on ink transfer. For the ink viscosity control, generally speaking, the single-long offset press has a speed of 7 to 13 at a speed of about 5000 to 10000 rph. The stickiness is 4 to 5 per hour when the speed is around 20000rph, and the stickiness is 3 to 5 when the speed of the web offset printing machine is over 2000rph. After testing, the general order of the stickiness of four-color printing inks is from black to blue to magenta to yellow.
Ink is a special fluid. Because the same kind of color printing inks use the same kind of linking material, the dispersion state of each color pigment in the linking material is extremely similar. In the case of the ink ink property unchanged, it can be roughly assumed that the ink viscosity increases with the increase of the ink viscosity. (Actually, the viscosity and viscosity of an ink are two different physical quantities of the ink and cannot be mistaken for two different ways of expressing the same property of the ink). Therefore, in actual printing, the printing color sequence is often determined according to the size of the ink viscosity. For example, the viscosity of the Shanghai Mudan brand four-color version 05 ink is:
BK118.82Pa·SC 48,85Pa·SM 47.71Pa·S Y14.70Pa·S
Third, when the overprinting ability determines the printing color sequence, the overprinting ability of the ink is an important consideration factor. Because the transfer of ink on the surface of the paper is much better than the transfer of ink on another color ink film layer. Although the area of ​​the overprint is the same, if the small area is printed first and then the large area is overprinted, the overprinted part is good for the small area because it is directly printed on the paper, and the whole ink color transfer is very good. For a large area, although there is a small area, The part is overprinted on another color (small area) ink film layer, but the effect on the large area as a whole is not large, so the effect is better. On the contrary, if a large area is printed on a small area, the large area of ​​ink is transferred well, but for a small area, the ink is all overprinted on another color (large area) ink film layer, and the performance is poor, and the entire color is displayed. In terms of effect, it is inferior to the former. It can be seen from here that when the area of ​​the plate on the printing plate is large, especially the full plate, it is usually left behind or printed at the end. Some people have done experiments on the color gradation and inversion order of the four-color machine. The results show that the average color gradation of the four-color machine using the inverted color sequence is better than that of the color sequence in the wet and wet conditions. The amount of overlapping color is reduced by 11.7%, and the amount of overlapping of secondary and tertiary colors is lower, which objectively affects the saturation of the color.... The ideal ink, itself, should be absolutely transparent; otherwise, the light will be printed in multi-color printing. It is impossible to reach the lower ink layer through the upper ink layer, so that the overprinting cannot show the effect of mixing. The hue, saturation, and lightness of the composite color are severely affected.
From the perspective of the transparency of the four-color printing inks used today, the black ink is the worst, the clear yellow ink is the best, and the magenta ink and the cyan ink are determined by the pigment and the connecting material used. The general situation is the blue ink. Red ink is poorly transparent. When printing, inks with poor transparency are generally printed first, and inks with good transparency have to be printed. Of course, the four-color printing sequence currently used usually puts the yellow ink on the last color printing. Besides the reason that the yellow ink has a high transparency, there are also the following reasons:
1. Widely use the low-absorption coated paper and the practical needs of the four-color machine for rapid printing, which overcomes the wet overprint problem that is caused by the large area of ​​the yellow printing.
2, to avoid the blue ink and black ink after printing dry and produce a bronze luster tendency, there is no longer a sense of color is not pure.
3, to avoid the excessive expansion of the yellow dot. V. Overprinting Problems When there are certain print process designs, the overprinting problem may be a determinant factor in the multi-color machine printing color sequence. This factor is mainly for the dimensional stability of paper. For example, when the middle of an image is an inverted white text with a black box, and the surrounding is a full-color version, the black box is just in contact with the full version. At this time, if the paper is very stretched during printing, it may cause overprinting difficulties. Therefore, when arranging the printing color sequence, the black frame should be printed first, and then the printing ink should be full. This is because the contraction of the paper produced by the first printing of the black frame is smaller, and the full version is more easily printed on black.
Sixth, double shadow situation Under normal circumstances, the first color of four-color machine printing color sequence is often black. However, some prints, such as catalogues, often have most of the textual descriptions in the blackboard. If the substrate is a coated paper with poor texture during printing, the retractability of each paper is likely to be different, so the first color of black ink will be partially transferred to different positions on the surface of the second color of the rubber cylinder. There is a danger of double shadows. Double images can make the text blurry and affect product quality. In this case, black should not be placed in the first color, but it should be more appropriate to put it in the third color or the final printing.
VII. Proofing and proofing is not only the final process of plate making, but also the “first mover” of printing. Proofing plays a role in the quality of plate making and also provides a reliable basis for the printing process. At present, the platform-type monochrome proofer is widely used in the proofing. The machine structure, the printing method, the printing pressure, and the operating speed differ greatly from the printing machine. Therefore, it is difficult to make the quality of printed matter exactly the same as proofs. But as long as we can properly handle the relationship between the proofing and printing process, especially the printing sequence, we can completely reduce the gap between print quality and proofs.
Monochromator printing and four-color printing, the print quality judgment process is consistent. For a monochrome machine, the printing effect can be judged according to the single pattern or the overlapping proofs for each color printed, and the printing method of the monochrome machine is the same as the printing method of the proofer, which belongs to the wet-dry printing method. As long as the same print sequence is used, the print quality is easier to control. The four-color printing adopts the wet and wet printing method, and the print is formed once, so the printing effect is far from the proofs. In order to make proofing more reliable for four-color printing, and to narrow the gap between proofing and printing, the following aspects should be emphasized when proofing:
1. The color sequence of proofing is exactly the same as the color sequence of printing.
2, using four-color proofer proofing.
3, using the same printing plate, paper, ink proofing.
VIII. Printing, Printing, Printing, Printing, Printing, Printing, Printing, Printing, Printing, and Printing Silver printing is generally performed on the ground. The ink layer is thick and the process requires high quality. They are usually printed at the end of the printing.
In summary, there are many factors affecting the printing sequence of four-color machines, and even some factors are in conflict with each other. Therefore, we can only take a compromise when determining the printing color sequence.
At present, many printing plants generally use the four-color machine to print black, blue, magenta, and yellow, or black, magenta, and yellow. The two kinds of printing color sequences are determined after combining various factors. They are the two basic color sequences of the four-color machine, and the black, blue, magenta, and yellow color printing sequences are used more often. Called the standard color sequence of a four-color machine. However, this is not the only one. It should be determined according to the specific circumstances when printing. It must not be copied. Once the printing color sequence is determined, it should not be arbitrarily changed during printing so as not to affect the stability of the color balance reproduction of the screen.