How to prevent color deviation in printed matter
Any kind of color printed matter is overprinted by four color inks of yellow, magenta, cyan and black according to a certain plate-making process and printing color sequence. How to prevent the color deviation of the printed matter and accurately reproduce the color and gradation is a problem that should be noted in the printing process. If these aspects are ignored, the quality of the printing will be affected and the color and gradation of the printed matter will be biased.
Color deviation: refers to the difference in color between the printed product and the original or proof.
There are two reasons for preventing color shift in the process technology. ⑴Arrangement of plate-making network angle. ⑵ Arrangement of printing color sequence.
One: Arrangement of screen angle during color plate making
In the process of color plate making, if the arrangement of the screen angle is not correct, it will affect the printing color effect, and in severe cases will also produce moire.
The current four-color plate-making printing is mainly based on the three primary colors of yellow, magenta, and cyan, and expresses the ever-changing colors in the picture. The black version only emphasizes the dark tone part and plays the role of a skeleton. In terms of color rendering performance: among the four colors of yellow, magenta, cyan and black, yellow has the weakest visual sense, followed by magenta and cyan, and black has the strongest sense. Since the person's line of sight is particularly sensitive to the dots at an angle of 45 °, it feels poor for the dots at 0 degrees or 90 degrees, and the human eye feels average for the dots at 15 degrees or 75 degrees.
In view of the above factors, the screen angle of each color version should be determined according to the main color of the original when making a plate. Therefore, the main color printing plate of the original should be made 45 °, other colors 15 °, 75 °, 90 °.
For monochromatic mesh tone prints, we should choose a 45-degree dot.
However, for multi-color mesh-adjusted prints, the dot angles of the various color plates must be staggered. The angles of the color screens usually used are as follows:
1. For two-color printing, the primary color version or dark version uses a 45 ° screen angle, and the secondary color version or light color version uses a 15 ° screen angle.
2. For three-color printing, the main color version or dark version uses a 45 ° screen angle, and the other two-color version uses 15 ° and 75 ° screen angles.
3. For four-color printing, the main color version uses a 45 ° screen angle, the yellow version uses a 90 ° screen angle, and the other two colors use 15 ° and 75 ° screen angles, respectively.
According to the main color of the screen, the angle of the network line is arranged as follows:
⑴If the main color of the picture is warm red, it can be set as follows: magenta version 45 °, black version 15 °, cyan version 75 °, yellow version 90 °.
⑵ If the main color of the screen is a cool color of cyan, then: cyan version 45 °, black version 75 °, magenta version 15 °, yellow version 90 °.
⑶ If the main color of the picture is a black Chinese painting, then: black version 45 °, cyan version 75 °, magenta version 15 °, yellow version 90 °.
Under normal printing conditions, arrange the screen angle according to the above method, and then arrange the color sequence correctly, which can effectively prevent the color deviation of the printed matter. Make the prints colorful and clear.
Two: Arrangement of printing color sequence.
Color printing, whether it is a single-color machine or a multi-color machine, regardless of the type of ink used, will face a color sequence problem. Only by arranging the printing color sequence reasonably can we achieve the gray balance, fully reproduce the color and gradation of the original, and achieve the ideal printing effect.
In multi-color printing, the color sequence in which the color separation plates are sequentially overprinted on the substrate in a certain color sequence is called the printing color sequence.
The arrangement of printing color sequence is very important, and its main role has three aspects:
â‘´ Correct color cast
The printing inks of the three primary colors of yellow, magenta, and cyan have certain gray components, and some have more or less color cast. The whiteness of the paper we use, the accuracy of the printing press, and the process operation will also have some deficiencies. This will cause color cast. Choosing a reasonable printing color sequence can make up for these deficiencies to a certain extent and play a role in correcting color deviation.
⑵Display colors correctly
The combination of three primary color inks in different proportions will show ten million new colors. Different printing color sequences will show different color effects. If the same printing plate is used, the same operation process is used to superimpose magenta on yellow, or superimpose yellow on magenta, the color effect they present is different. In four-color screen printing, the dots of the dark tone part are superimposed on the dots, and the dots of the highlight part are printed on the blank part of the paper. Due to the difference in the cover of the ink and the thickness of the ink layer, the role of the displayed color is also different. .
In four-color printing, yellow, magenta, cyan, and black can have 24 different printing color sequences according to the arrangement and combination. The printing color sequence is good, there are no specific regulations, and appropriate arrangements must be made according to the specific situation.
⑶Reflect the status of overprint
If the selected printing color sequence does not match the performance of the ink, there will be problems such as color mixing, ghosting, and unprintable.
This shows that choosing the correct printing color sequence is one of the important measures to ensure normal printing and obtain the best printing effect.
The selection of printing color sequence generally follows the following principles: 1. Arrange the color sequence according to the brightness of the three primary colors: the brightness of the three primary colors ink is reflected on the spectrophotometric curve of the three primary colors ink, the higher the reflectivity, the higher the brightness of the ink. Therefore, the brightness of the three primary inks is yellow> cyan> magenta> black. The first printing with small brightness and the second printing with large brightness.
2. Arrange the color sequence according to the transparency and hiding power of the three primary colors ink: the transparency and hiding power of the ink depends on the difference between the refractive index of the pigment and the connecting material. The ink with strong covering effect has a great influence on the color after over-coloring. As the post-printing color over-printing, it is not easy to show the correct color, and a good color mixing effect cannot be achieved. Therefore, the ink with poor transparency is printed first, and the strong transparency is printed afterwards.
3. Arrange the color sequence according to the size of the dot area: in general, the small dot area is printed first, and the large dot area is printed later.
4. Arrange the color sequence according to the characteristics of the originals: each original has different characteristics, some of them are warm colors, and some are cool colors. In the arrangement of color sequence, the color sequence mainly based on warm colors is black, cyan, magenta, and yellow; the color sequence mainly based on cool colors is black, magenta, cyan, and yellow.
5. Arrange the color sequence according to different printing equipment
(1) Color sequence of monochromatic machine: When printing monochromatic products with monochromatic machine, the transfer of ink belongs to wet stacking. When considering the color sequence, the viscosity of ink can be put in a less important position.
Under the conditions of good paper and ink quality, the general printing color sequence is black, cyan, magenta, and yellow. When the quality of the paper is poor, the surface is rough, the tightness is low, and the ink absorption is strong, the color sequence can be selected as yellow, magenta, cyan, and black. Due to the large area of ​​the yellow plate, it can make up for the defects of the paper. Make the printing effect better. In addition, the order of yellow, magenta, cyan and black is adopted, which is conducive to color change and easy to clean the ink roller and ink tank. Another reason why the monochrome offset press prints the yellow version first is that human vision is not sensitive to the yellow dots. When printing the light color yellow version, even if there is a slight overprinting phenomenon, it is not easy to observe with the naked eye, so Conducive to the effect of four-color overprint.
⑵The second color and the third color in the printing of the two-color machine are wet stack dry overprint. The printing of 1-2 colors and 3 to 4 colors is wet stacked wet overprinting. The color sequence of the two-color machine is preferably alternating between light and dark colors. The large amount of ink is placed in the second color group, so the following are generally used in printing Printing color sequence: 1-2 colors magenta-cyan or cyan-magenta; 3-4 colors black-yellow or yellow-black, but also according to need. To highlight a certain heavy color, such as green, it should be printed in the magenta-yellow, cyan-black overprint color sequence, so as to obtain a more ideal printing effect. The color sequence can also be black-yellow, magenta-cyan, which is easier to control. (3) Four-color machine printing is a wet press wet printing method. If the ink of the latter color can be transferred to the ink layer of the substrate of the previous color, the adhesion of the ink in the printing color sequence should be reduced in sequence, otherwise it will cause reverse stacking Printing phenomenon. Generally, the dark color with large ink viscosity is printed first, and the bright color with low ink viscosity is printed later. Commonly used color sequence is black, cyan, magenta, yellow, or black, magenta, cyan, yellow. While changing the color sequence, the viscosity of the ink should be adjusted accordingly.
In the four-color machine printing, the yellow ink is discharged to the last color printing. There are three main advantages. Due to the good transparency of the yellow ink, the last color is good for enough light to enter the upper and lower ink layers, making the printed products more vivid. ⑵The drying performance of yellow ink is faster and the printing area is larger. Arranging the last color of yellow ink can not only prevent the crystallization caused by the drying speed of the yellow ink is too fast, but also use its large printing area and can quickly oxidize the conjunctiva. Cover the surface of other ink layers. Improve the gloss of printed matter. ⑶ The yellow color is arranged in the last color, which is convenient for controlling the yellow ink consumption, and can be adjusted at any time according to the sample.
6. Arrange the color sequence according to the nature of the paper: the smoothness, whiteness, tightness and surface strength of the paper are different. Flat and tight paper is printed with dark color first, and then printed with bright color; coarse and loose paper is printed with bright yellow color first. Ink, after printing dark, because yellow ink can cover paper defects such as paper wool and powder.
7. Arrange the color sequence according to the drying performance of the ink: Practice has proved that yellow ink dries nearly twice faster than magenta ink, magenta ink doubles faster than cyan ink, and black ink has the slowest fixation. Ink with slow drying performance should be printed first, and ink with fast drying performance should be printed later. Monochrome machine is to prevent the crystallization of the ink surface, usually printed yellow at the end to facilitate rapid conjunctiva drying.
8. Arrange the color sequence according to the flat screen and the field: when the printed matter has the flat screen and the field, in order to obtain good printing quality, the field is printed flat, the ink color is thick, and the color is bright. Generally, the flat screen is printed first, and then the solid screen.
9. Arrange the color sequence according to the light color and the dark color: In order to make the printed matter have a certain gloss, the light color is printed, the dark color is printed first, and then the light color is printed.
10. Products based on text and black version generally adopt cyan, magenta, yellow, and black sequences, but black text and patterns cannot be printed on the yellow field, otherwise reverse overprinting will occur due to the low viscosity of yellow ink and the large black viscosity. The phenomenon that the black is not printed or is not true is printed.
11. For pictures with a small four-color overprint area, the color registration sequence can generally adopt the principle of post-printing with a large color area.
12. For gold and silver products, since the adhesion of gold ink and silver ink is very small, gold and silver ink should be placed in the last color as much as possible. In general, it is not suitable to use three-fold ink printing.
13. The color sequence of the printing should be as consistent as possible during the proofing, otherwise it will not be able to catch up with the effect of the proofing.
14. When printing, the angles of adjacent two color sequences should be separated by 30 °. If black, cyan, magenta, and yellow sequences are used, the corresponding network cable angles are black 75 °, cyan 15 °, magenta 45 °, and yellow 90 °. In summary, in the actual printing production, according to the quality requirements of the printed matter, the performance of the paper and ink, the accuracy of the printing press, etc., the printing color sequence is flexibly arranged to achieve the best printing effect.
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