Lithography is the decomposition of a series of successively tuned originals into a half-tone monochromatic version, followed by halftone monochromatic printing to achieve color reproduction. In practice, we have found that different inks have different properties such as transparency, hiding power, stickiness and lightness. Therefore, we decided that we need to arrange the order of overprinting in color printing. Scientifically and rationally arranging the overprinting sequence is extremely crucial for obtaining the correct, gentle, richly-graded, and correctly printed copies of the colors to meet the needs of customers. Here we analyze how overprinting occurs in production.
First, the overprint theory of ink in multicolor printing.

Multi-color printing machine at the time of printing each color version of the ink in a fraction of a second instant superimposed together, the interval between the colors is very short, the latter printing color is impossible to print on the oxidized conjunctiva ink layer The species is called wet wet. When a multicolor printer prints ink of the first color on a substrate, the amount of ink transferred is approximately 1/2 of the ink on the blanket, and then the ink completes a change from liquid to semi-solid within a very short period of time. The process (the initial fixation of the ink), followed by the substrate with a semi-liquid ink film that is not completely dry, enters the second color and begins the second color printing. At this time, the amount of ink transferred is less than the proportion of the first color. Since the first color is not completely dried, the separation of the ink film is inevitably affected by the dry ink film of the first color. As shown in the figure, Figure A is a multicolor overlay of a monochromator that is virtually unaffected by the pre-color, and Figure B is a wet-pigment wet-ink overprint for a multicolor printer that is affected by the pre-colored dry ink.

It is precisely because of the characteristics of multi-color printing wet-pressing that we determine the color sequence in printing, we need to consider more factors than using a monochrome machine.
In the color-sequencing arrangement of multicolor machines, we must consider the following factors and try to reduce this effect through reasonable color-sequencing arrangements:

First of all: try to ensure that the stickiness of the second color ink is less than the first color. If the stickiness of the back color is greater than the front color, not only will the amount of transfer be significantly reduced, it will even cause reverse printing of the ink (ie, the ink of the front color After the color is sticky).
The general four-color ink adhesion relationship: T black ≥ T green = T magenta> T yellow, T represents the ink stickiness value.
In addition: the viscosity of the post-printing ink must be less than the viscosity of the previous color. The large viscosity of the ink indicates that the cohesive force of the ink is large. If a cohesive ink is superimposed on the front color as a rear color, the rear ink peels the previously printed ink from the surface of the substrate depending on its cohesive force.
Taking Shanghai peony offset printing ink as an example, the order of viscosity of four-color offset printing inks is black, blue, magenta, and yellow.
Second: The thickness of the ink layer will also significantly affect the transfer of the ink after the color. In the printing, the ink with thick ink layer should be placed in the back color as much as possible. 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 rear color ink layer is smaller than the front color, the ink film will be closer to the front color in the transfer process, even in the middle of the front color ink film.
China's industry standard CY/Y5-91 stipulates that the density range of fine products printed using copperplate paper is: 0.85 to 1.15 for yellow, 1.25 to 1.55 for magenta, 1.30 to 1.60 for cyan, and 1.40 to 1.80 for black. Experiments have shown that if the maximum density is to be achieved, the yellow ink layer thickness should be 1.5 μm; the magenta color is 1.0 μm; the cyan is 0.85 μm; and the black color is 0.75 μm. According to the thin to thick printing sequence, it should be black-cyan-magenta-yellow.

From the above analysis, we found that printing from the order of black-cyan-magenta-yellow is a comparison for general prints, regardless of the viscosity or viscosity of the ink or the ink film thickness at which the ink can achieve an ideal density. Reasonable color sequence. Because the properties of the magenta and cyan inks are close to each other, the color sequence is often changed as needed during printing. In addition, in the printing, we also need to meet some needs to carry out some adjustment of the color sequence, but generally need to meet the above principles on the basis of the (by adding an appropriate amount of additives in the ink). Below we discuss further about other factors that we need to consider about the color sequence during the printing process.
Second, according to print to arrange the printing sequence.
1. Arrange the color sequence according to the content and characteristics of the original.

Printing is a means of expressing graphic design. Moreover, the emotional components of various colors are also different. Therefore, the arrangement of color sequence must first consider the content and characteristics of the manuscript. When designing graphic layouts, customers often have chosen the tone of layout color. This main tone represents the overall feeling of the entire tone and becomes the dominant color of printing. From the perspective of color properties, the red, orange, and yellow tones are called warm colors; the blue, green, and blue tones are called cold tones. Due to the hiding power of the ink, generally the first printing of the warm tone is the printing of black and blue, and the latter of the printing of the magenta and the yellow; the printing of the magenta is the first printing of the magenta, and the printing of the cyan. For example, everybody hopes that the prints on the child's face are pink and healthy. They don't want to see the result of the printing is purple or green. Different color sequences, the effect of color cast is of course not the same, so the color of the screen atmosphere needs to be enhanced in the last color printing can get better results.

Generally speaking, landscape-based images are mainly cold-tone. Generally, green-colored posters are generally advocated. Generally, people-oriented screens are arranged. We arrange magenta printing behind the blue, which can better emphasize the role of the main color. >
* Arrange color order methods: The principle of highlighting the main colors should be followed to prevent the main colors from being covered.
2. Arrange the color sequence to facilitate overprinting.

Due to the defects of objective factors such as paper deformation and stretching, we can arrange the main colors of printing products with higher printing requirements to be printed in the adjacent two color groups. If it is a two-color machine, we can arrange to complete the printing in the same unit and avoid Due to the paper stretching caused by paper storage, the problem of overprinting is too great.
3. A large area of ​​the field can be arranged after the printing, to avoid problems such as filth in the paper transfer process. For a picture with a small four-color overprint area, the color registration sequence can generally use a large-format color plate after printing. When replicas have flat screens and on the spot, in order to obtain good print quality, the plain clothes and the bright and thick ink are used in the field. Generally, they are printed on flat web and printed on the ground.
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 on the last color as much as possible. Under normal circumstances, it is not appropriate to adopt triple ink printing.
5. Text-based and black solid-based products generally use cyan, magenta, yellow and black sequences, but can not print black text and patterns in the yellow field, otherwise due to the small yellow ink viscosity, black viscosity and reverse printing Black or black prints are not true.
Third, according to the nature of printed materials to consider the arrangement of printing color sequence 1. According to the transparency of the ink to arrange the color sequence.
The transparency and hiding power of the ink depends on the difference in the refractive index of the pigment and the binder. Good ink with good transparency, after the two colors are superimposed, the color light of the ink layer below can pass through the ink layer above to achieve a better color mixing effect and present the correct color. Generally speaking, the order of the ink's transparency is yellow> magenta> cyan> black. The principle of color sequence distribution is the first printing with poor transparency and good transparency after printing.
2. According to the brightness of the three primary colors arranged color sequence.

The brightness of the three primary colors of ink is reflected on the spectrophotometric curve of the three primary color inks. The higher the reflectance, the higher the brightness of the ink. Therefore, the brightness of three primary colors of ink is: yellow> cyan> magenta> black. Brightness of the ink color is bright, so the high brightness of the ink in the post-color printing, can make the entire picture colorful and bright. The lower brightness, as the screen outline more concentrated color ink should be considered in the first color printing.
3. Consider the nature of the paper to arrange the color sequence.

Poor quality paper, taking into account its whiteness, poor smoothness, fiber loose, poor ink absorption, easy to remove powder off hair, you can print yellow ink to make the bottom, in order to make up for the lack of paper. In the case of poor light, we generally print the strong color of ink on the front.
Fourth, the long tone black version of the color order arrangement in the printing
Over the past few years, the use of undercuts in printing has continued to increase. At this time, the black edition in the printing will not only make up for the black color and improve the reproducibility of the image outline. From the auxiliary printing plate to the main version of the image reproduction, the amount of black ink is greatly improved compared to the traditional process. Considering the ink layer thickness of the ink, in order to prevent reverse printing, black should be placed in the last color, but the black ink has a significantly higher viscosity and viscosity than the other three colors. In this case, we must add the appropriate ink in the ink. Auxiliaries adjust the tackiness and viscosity of the ink so that the superimposition of black on the last color can be performed smoothly.

When we talk about this, we will find that reasonable arrangements for printing color sequences require comprehensive consideration. We must not only consider the viscosity, viscosity, transparency, film-forming glossiness, print thickness, etc. of various inks, but also the main colors and prints of printed products. Overprinting, and even consider the nature of printing materials. Synthesis