Talking about the quality and color sequence of lithographic offset printing
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Lithographic offset printing is a halftone monochrome version that is decomposed into a series of continuous tone originals, and then color-reduced by halftone monochrome overprinting. By selecting the appropriate color sequence under the guidance of the color-matching rule, it is possible to overprint a colorful and richly-printed print to ensure the correct printing ash balance. Due to the difference in the transparency, hiding power, brightness and other properties of the ink and its own defects, what color is printed first and then printed, will affect the color mixing effect. Therefore, scientifically and rationally arrange the color sequence to obtain a high-quality replica of correct, soft, rich layers and correct color to meet the needs of customers. Summarize my more than ten years of printing professional teaching theory research and guide the printing students' training experience. Now I will talk about some of my views on the relationship between lithographic offset quality and color sequence.
First, the arrangement of printing color sequence
In multi-color printing, in the process of monochromatic printing in the order of overlapping imprinting of originals in a certain order, the order of ink overprinting is called color order. In four-color printing, yellow, magenta, cyan, and black can have 24 different printing color sequences according to the arrangement.
Second, determine the principle of printing color sequence
Printing color sequence will directly affect the quality of printed products. In order to obtain good copying results, the following principles must be observed:
1. Arrange the color sequence according to the brightness of the three primary colors: the brightness of the three primary colors is reflected on the spectrophotometric curve of the three primary colors. The higher the reflectivity, the higher the brightness of the ink. Therefore, the brightness of the three primary colors of ink is: yellow > green > magenta > black.
2. Arrange the color sequence according to the transparency and hiding power of the three primary inks: the transparency and hiding power of the ink depends on the difference between the refractive index of the pigment and the binder. The ink with strong opacity has a great influence on the color after the color combination, and it is not easy to display the correct color as the post-printing overprint, and the good color mixing effect is not achieved. Therefore, the ink with poor transparency is printed first, and the ink with strong transparency is printed.
3. Arrange the color order according to the size of the dot area: in general, the area of the dot is small and the back of the dot is large.
4. Arrange the color sequence according to the characteristics of the original: Each original has different characteristics, some are warm and some are cold. In the arrangement of the color sequence, the first black and the green are printed in black, the red is printed in red, and the yellow is printed in the first place.
5. According to the different arrangement of the color sequence of the device: under normal circumstances, the printing color sequence of the monochrome or two-color machine alternates with light and dark colors; the four-color printing machine generally prints dark colors first, then prints bright colors.
6. Arrange the color sequence according to the nature of the paper: the smoothness, whiteness, tightness and surface strength of the paper are different. The flat and tight paper is printed first with dark color and the later printed with bright color. The thick and loose paper is printed with bright yellow. Ink, the latter is dark, because yellow ink can cover paper defects such as paper and powder.
7. Arrange the color sequence according to the drying performance of the ink: It has been proved that the yellow ink is nearly twice as fast as the magenta ink, the magenta ink is twice as fast as the green ink, and the black ink is the slowest. Slow drying inks should be printed first, and fast drying inks should be printed. The monochromator is anti-vitrification, and the yellow is usually printed at the end to facilitate rapid conjunctival drying.
8. Arrange the color sequence according to the flat net and the field: When the replica has the flat net and the ground, 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 later.
9. Arrange the color order according to light and dark colors: In order to make the print have a certain luster, print a light color, first print dark, then print light color.
10. The green version of the landscape products is much larger than the magenta version. According to the principle of large prints, the black, magenta, cyan, and yellow sequences should be used.
11. Products based on text and black solid are generally in the order of cyan, magenta, yellow and black, but black text and pattern cannot be printed on the yellow solid. Otherwise, due to the small viscosity of yellow ink and the high viscosity of black, reverse overprinting occurs. Causes black not to print or print.
12. For a picture with a small four-color overprint area, the color registration sequence can generally be applied to the principle of large-format color printing.
13. 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-layer ink printing.
14. The color sequence of the print should be as close as possible to the color sequence when proofing, otherwise it will not catch up with the proofing effect.
The superiority of yellow ink to the last color in three-color printing
1. Since the yellow ink has good transparency, the last color is good for enough white light to enter the upper and lower ink layers to obtain bright and vivid colors.
2. Yellow ink has a fast drying performance and a large printing area. The yellow ink is listed in the last color, which not only prevents the vitrification caused by the excessive drying speed of the yellow ink, but also utilizes the characteristics that the printing area is large and the conjunctiva is quickly oxidized, and the cover is covered on the surface of other ink layers. The print has a certain degree of gloss.
3. The yellow color is in the last color, which is convenient for controlling the amount of ink used in yellow. It can be adjusted at any time according to the original.
4. Yellow ink is expensive, and the last color can save the amount of yellow ink and reduce the cost.
In short, in the specific printing process, according to the quality requirements of the product, the best printing color sequence is selected according to the flexibility of the color mixing law, so that it can print the most ideal product.