Discussion on the arrangement of color sequence in color printing
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Lithography is a monochrome version of a halftone that is decomposed into a series of continuous-tone originals, and then color-reproduced by halftone monochrome overprinting. In practice, we found that different inks have different properties such as transparency, hiding power, viscosity, and brightness. Therefore, we need to arrange the order of overprinting in color printing. Scientifically and rationally arranging the order of overprinting is extremely important for obtaining correct, soft, rich layers and correct color reproductions to meet the needs of customers. Below we analyze how to perform overprinting in production.
First, the overprinting theory of ink in multi-color printing.
In the multi-color machine, the inks of the various color plates are overprinted in less than a fraction of a second, and the interval between the colors is extremely short, and the post-printing color cannot be printed on the ink layer of the oxidized conjunctiva. The species is called wet pressure. When the multi-color printing machine prints the ink of the first color on the substrate, the amount of ink transferred is about 1/2 of that of the ink on the blanket, and then the ink changes from liquid to semi-solid in a very short time. The process (ink is initially fixed), and then the substrate is printed with the semi-liquid ink film which is not completely dried, entering the second color and starting the printing of the second color. At this time, the amount of ink transferred is smaller than the ratio of the first color, because the first color is not completely dried, and the splitting of the ink film is inevitably affected by the first color dry film. As shown, Figure A is a superimposed overprint of a monochrome machine that is almost unaffected by the pre-color, and Figure B is a wet-pressed ink overprint of a multi-color press that is affected by the pre-drying ink.
It is precisely because of the characteristics of multi-color printing wet and wet, we need to consider more factors than the use of monochrome printing when determining the color sequence in printing.
In the color sequence arrangement of multicolor machines, we must consider the following factors and try to reduce this effect by reasonable color sequence arrangement:
First of all: try to ensure that the adhesion of the second color ink is less than the first color, if the adhesion of the back color is greater than the front color, not only will the amount of transfer be significantly reduced, or even the reverse printing of the ink (ie, the ink of the front color) Sticked to the back color).
Generally 4 color ink adhesion relationship: T black ≥ T blue = T magenta > T yellow, T represents the ink adhesion value.
In addition: the viscosity of the post-printing ink must be less than the viscosity of the pre-color. The high viscosity of the ink indicates that the cohesive force of the ink is large. If the ink having a large cohesive force is overprinted as the back color in the front color, the back color ink relies on its own cohesive force to peel off the first printed ink from the surface of the substrate.
Taking Shanghai Peony offset printing ink as an example, the order of viscosity of four-color offset printing inks is from black to green, magenta and yellow.
Secondly, the thickness of the ink layer will also significantly affect the transfer of the back color ink. In the printing, the ink with a thick ink layer should be placed in the back color as much as possible, and the thin color of the ink layer should be placed in the front color, so that the ink can reach a relatively large transfer amount during the printing process. If the back ink layer is smaller than the front color, then the ink film will be closer to the front color during the transfer process, even in the middle of the front ink film.
China's industry standard CY/Y5-91 stipulates that the density range of fine products printed on copperplate paper is: yellow 0.85~1.15; magenta 1.25~1.55; cyan 1.30~1.60; black 1.40~1.80. Experiments have shown that the yellow ink layer thickness should be 1.5 μm if the maximum density is to be achieved; magenta is 1.0 μm; cyan is 0.85 μm; black is 0.75 μm. According to the distribution from thin to thick printing color, it should be black-green-magenta-yellow.
Through the above analysis, we found that whether it is from the viscosity of the ink, the viscosity or the thickness of the ink film from which the ink can achieve the desired density, the black-cyan-magenta-yellow order is used for printing, which is a comparison for general prints. Reasonable color sequence. Moreover, since the properties of magenta and cyan ink are close, the color sequence is often changed as needed in printing. In addition, in printing, we also need to adjust some color sequence to meet certain needs, but generally need to be based on the above principles (can be added in the ink in the appropriate amount of additives). Below we discuss further the other factors we need to consider about the color sequence during the printing process.
Second, arrange the printing color sequence according to the printed matter.
1. Arrange the color sequence according to the content and characteristics of the original.
Printing is a means of expressing graphic design, and the emotional components of various colors are different. Therefore, the arrangement of the color sequence must first consider the content and characteristics of the original. When designing graphic layouts, customers often have chosen the tone of the layout color. This main color is the overall feeling of the entire tone, becoming the dominant color in printing. In terms of color properties, red, orange, and yellow are called warm colors; green, green, and blue are called cool colors. Because the ink has hiding power, it is generally printed with black and green, and then printed with magenta and yellow. The first color is mainly printed with cool color, followed by cyan. For example, anyone wants a pink and healthy color on the child's face in print. I don't want to see the result of printing being purple or green. The color sequence is different, and the effect of the color shift is of course different. Therefore, the color of the screen atmosphere needs to be strengthened, and the final color printing can obtain a better effect.
<Generally, the landscape-based picture is mainly based on cold tone. Generally, it is recommended to print after cyan. Generally, the picture is mainly based on characters. We arrange the magenta to print behind the cyan, and it can achieve the effect of emphasizing the main color. >
* Arrange the color sequence method: The principle of highlighting the main color of the screen should be followed to prevent the main color from being covered.
2. Arrange the color sequence to facilitate overprinting.
Due to defects such as paper deformation and expansion, we can arrange the main colors of the printing products with higher overprinting requirements in the adjacent two color groups. If it is a two-color machine, it can be arranged in the same unit for one printing to avoid The problem of overprinting is too large due to the expansion and contraction of the paper caused by paper storage.
3. On a large area, you can arrange post-printing to avoid problems such as smudging during paper transfer. For a picture with a small four-color overprinting area, the color registration sequence can generally be printed with a large color version of the graphic area. When the replica has a flat net and a solid, in order to obtain good printing quality, the ground is flat and the ink color is bright and thick. Generally, the flat net graphic is printed first, and the solid structure is printed.
4. About the printing of gold and silver ink.
Gold and silver products, because 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. Under normal circumstances, it is not suitable to use three-fold ink printing.
5. Products with text and black solids are generally in the order of cyan, magenta, yellow and black, but black text and patterns cannot be printed on the yellow ground. Otherwise, due to the small viscosity of yellow ink and the high viscosity of black, reverse overprinting occurs. Causes black to be printed or untrue.
Third, according to the nature of the printed materials to consider the arrangement of printing color
1. Arrange the color sequence according to the transparency of the ink.
The transparency and hiding power of the ink depends on the difference in refractive index between the pigment and the binder. A good transparency ink, after the two-color phase is overprinted, the color of the ink layer below can pass through the upper ink layer to achieve a better color mixing effect and present a correct color. Generally speaking, the transparency order of the ink is yellow > magenta > cyan > black, and the principle of color sequence distribution is the first print with poor transparency and the good print with good transparency.
2. Arrange the color order according to the brightness of the three primary colors.
The brightness of the three primary color inks is reflected on the spectrophotometric curve of the three primary color inks, and the higher the reflectance, the higher the brightness of the ink. Therefore, the brightness of the three primary colors ink is: yellow > green > magenta > black. The ink with high brightness is bright in color, so the ink with high brightness is placed in the back color printing, which makes the whole picture bright and bright. The ink with a lower brightness as the outline of the picture should be considered to be printed in the first color.
3. Arrange the color order by considering the nature of the paper.
Paper of poor quality, considering its whiteness and poor smoothness, loose fibers, poor ink absorption, easy to remove powder, can be printed with yellow ink to make up for the lack of paper. In the case of poor lighting, we generally put the strong color of the ink on the front.
Fourth, the long-order black version of the color sequence in the printing
In recent years, the use of background removal processes in printing has continued to rise. At this time, the black plate in printing not only compensates for black, but also improves the reproducibility of the image. From the auxiliary plate to the main version for image reproduction, the amount of black ink is greatly improved compared with the conventional process. Considering the thickness of the ink layer, in order to prevent reverse overprinting, black should be placed in the last color, but the viscosity and viscosity of the black ink are significantly higher than the other three colors. In this case, we need to add it appropriately in the ink. An additive that adjusts the adhesion and viscosity of the ink so that the overprint can be carried out smoothly when the black color is placed in the last color.
Speaking of this, we will find that reasonable arrangement of printing color sequence requires comprehensive consideration, not only considering the viscosity, viscosity, transparency, film gloss, printing thickness, etc. of various inks, but also considering the main color and print of the printed matter. Overprinting, and even considering the nature of the substrate. Comprehensive consideration and flexible mastery will be more convenient in the printing process.