Some Discussion on Arrangement of Color Order in Multicolor Printing
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Lithography is the decomposition of a continuous tone original with rich layers into a half-tone monochrome version, which is then overprinted with a half-tone monochrome version to achieve color reproduction. In practice, we have found that different inks have different characteristics such as transparency, hiding power, viscosity, lightness, etc., which also determines that we need to arrange the order of overprinting reasonably in color printing. Scientifically and reasonably arranging the overprinting sequence is extremely critical for obtaining correct, soft, rich layers and correct color tones to meet the needs of customers. Below we analyze how to overprint in production.
When the multi-color machine is printing, the ink of each color version is overprinted in less than a fraction of a second, and the interval between the colors is extremely short. It is impossible for the post-printing color to be printed on the ink layer of the oxidized conjunctiva. This species is called wet pressing wet. When the multi-color printing machine prints the ink of the first color on the substrate, the transfer amount of ink is about 1/2 of the ink on the blanket, and then the ink completes a change from liquid to semi-solid in a very short time. The process (the initial fixation of the ink), and then the substrate carries the semi-liquid ink film that has not been completely dried into the second color to start the printing of the second color. At this time, the transfer amount of the ink is less than the ratio of the first color, because the first color is not completely dried, the split of the ink film must be affected by the undried ink film of the first color. As shown in the figure, Figure A is the overprinting of a monochromatic machine that is hardly affected by the front color, and Figure B is the wet press wet ink overprinting of a multi-color printer affected by the ink of the previous color.
It is precisely because of the characteristics of multi-color printing wet press wet, when we determine the color sequence in printing, we need to consider more factors than printing with a monochrome machine.
In the color sequence arrangement of multi-color machines, we must consider the following factors, and try to reduce this effect through a reasonable color sequence arrangement:
First: 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 transfer amount be significantly reduced, but even the ink will be reversed (that is, the ink of the front color) Was sticking away after the color).
The general four-color ink adhesion relationship: T black ≥ T cyan = 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 front color. The high viscosity of the ink indicates that the cohesive force of the ink is large. If the cohesive ink is overprinted on the front color as the post-color, the post-color ink relies on its cohesion to peel the pre-printed ink from the surface of the substrate.
Taking Shanghai Peony offset printing ink as an example, the viscosity order of four-color offset printing ink is from large to small: black, cyan, magenta, and yellow.
Secondly: the thickness of the ink layer will also obviously affect the transfer of the post-color ink. In printing, try to put ink with a thick ink layer in the back color, and put a thin ink layer in the front color, so that the ink can achieve a relatively large transfer during the printing process. If the back color ink layer is smaller than the front color, the splitting of the ink film during the transfer process will be closer to the front color, even in the middle of the front color ink film.
China's industry standard CY / Y5-91 stipulates: the density range of fine products printed with copperplate paper is: yellow 0.85 to 1.15; magenta 1.25 to 1.55; cyan 1.30 to 1.60; black 1.40 to 1.80. Experiments show that if the maximum density is to be achieved, the yellow ink layer thickness should be 1.5 μm; magenta is 1.0 μm; cyan is 0.85 μm; black is 0.75 μm. According to the printing color sequence from thin to thick, it should be black-cyan-magenta-yellow.
Through the above analysis, we find that whether it is considered from the viscosity of the ink, the viscosity, or the thickness of the ink film that the ink can achieve the ideal density, the order of black-cyan-magenta-yellow is used for printing, which is a comparison for general prints. Reasonable color order. Since the properties of magenta and cyan inks are similar, the color sequence is often changed as needed during printing. In addition, in printing, we also need to meet some needs to make some color sequence adjustments, but generally need to be based on meeting the above principles (you can add appropriate additives in the ink). In the following, we will further discuss the other factors that we need to consider in the printing process.
2. Arrange 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 also different. Therefore, the arrangement of the color sequence must first consider the content and characteristics of the original. When customers design graphic layouts, they often have chosen the tone of layout colors. This main hue represents the overall feeling of the entire hue and becomes the dominant color in printing. From the perspective of color attributes, those with red, orange, and yellow as the main tone are called warm colors; those with cyan, green, and blue as the main colors are called cool colors. Due to the hiding power of ink, black and cyan are printed first mainly in warm tone, and magenta and yellow are printed later in cold tone; For example, everyone hopes that the child's face on the print is pink and healthy, and he does not want to see the result of the print being more purple or green. The color sequence is different, and the effect of color deviation is of course different. Therefore, the color that needs to be strengthened in the picture atmosphere can be better printed in the last color printing.
<Generally landscape-based pictures are mainly based on cold tone, and cyan post-printing is generally advocated. Character-based pictures are generally used. We arrange magenta to be printed behind cyan to better emphasize the main color. >
* Arrange the color sequence method: follow the principle of highlighting the main color of the picture to prevent the main color from being covered.
2. Arrange the color sequence to facilitate overprinting.
Due to defects in objective reasons such as paper deformation and expansion, we can arrange the main colors of printing products with high register requirements to be printed in two adjacent color groups. If it is a two-color machine, it can be arranged to print in the same unit at one time to avoid Due to the expansion and contraction of the paper caused by the storage of the paper, the overprint difference is too large.
3. Large-area field, post-printing can be arranged to avoid problems such as smudging during paper handover. For pictures with a small four-color overprinting area, the color sequence can generally be printed with a color plate with a large graphic area. When the reproduction has flat screen and solid ground, in order to obtain good printing quality, make the plain cloth and the ink color bright and thick. Generally, the flat screen graphics and text are printed first, and then the solid ground structure is printed.
4. About the printing of gold and silver ink.
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.
5. The products mainly based on text and black solids generally use cyan, magenta, yellow, and black sequences, but black texts and patterns cannot be printed on the yellow solids, otherwise reverse printing 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.
Third, consider arranging the printing color sequence according to the nature of the printing material 1. Arrange the color sequence according to the transparency of the ink.
The transparency and hiding power of the ink depends on the difference between the refractive index of the pigment and the binder. Ink with good transparency, after the two colors are overprinted, the color of the lower ink layer can pass through the upper ink layer to achieve a better color mixing effect and present the correct color. Generally speaking, the order of transparency of the ink is yellow> magenta> cyan> black. The principle of color sequence distribution is to print first with poor transparency and then print with good transparency.
2. Arrange the color sequence according to the brightness of the three primary colors.
The brightness of the three-primary-color ink is reflected on the spectrophotometric curve of the three-primary-color 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 high-intensity ink is bright in color, so putting the high-intensity ink in the back color printing can make the whole picture bright and bright. The lightness is lower, and the ink with a thicker color as the outline of the screen should be considered for printing in the first color.
3. Consider the nature of the paper to arrange the color sequence.
For poor quality paper, considering its poor whiteness and smoothness, loose fibers and poor ink absorption, it is easy to remove powder and fluff. You can print the yellow ink primer 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 for printing.
Fourth, the color sequence arrangement of the long-tone black plate in printing In recent years, the use of the background color removal process in printing has been on the rise. At this time, the black plate in printing not only plays a role in making up the black color, but also improves the reproducibility of the outline of the image. From the auxiliary plate to the main version of the image copy, the amount of black ink is greatly increased compared with the traditional process. Considering the thickness of the ink layer of the ink, in order to prevent reverse overprinting, black should be placed in the last color, but the viscosity and viscosity of the black ink is significantly higher than the other three colors, in this case, we must add in the ink appropriately Auxiliary agent to adjust the adhesion and viscosity of the ink, so that overprinting can be carried out smoothly when black is placed in the last color.
Speaking of this, we will find that a reasonable arrangement of printing color sequence requires comprehensive consideration, not only to consider the viscosity, viscosity, transparency, film forming gloss, printing thickness, etc. of each color ink, but also to express the main color of the printed matter, the printed matter Overprinting, and even consider the nature of the printing material. Comprehensive consideration and flexible control will make the printing process easier.
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