The characteristics of the lithography are the low pressure, the small amount of ink that can be transferred, and the ink-water balance. Because of this, the color density that can be printed by the lithography is smaller. For example, the highest printing density of the yellow version can only be 1.15, the magenta version is 1.5, the cyan version is 1.6, the black version is 1.8, and the total synthesis density of the Y, M, C, and K blocks is 2.0. It is much lower than 2.6-3.0 of the color reversal film, so when copying high saturation and dark color, the distortion is large. For manuscripts with high contrast and a large range of gradation (more than 2.0), it is necessary to perform gradation compression and copying. Especially at the dark tone, the dark color beyond the reproduction density can be basically compressed at the time of plate making. This determines the contrast of the lithographic products is relatively small, the picture is flat. However, due to the short printing cycle of plate printing, the operation is simple, the modification is relatively easy, and the development is rapid, accounting for the giant of the printing industry. In order to adapt to the characteristics of modern printing, flat printing plate using the GCR and UCA process principles. When copying a color image, a black version was introduced in the flat plate. The introduction of the black edition has greatly improved the defects of the plain printing, and further improved and improved the quality of the plain printing. It has the following benefits:
1. The cost of color ink is higher than that of black ink. Black ink is used to reduce the printing cost.
2. Since YMC three-color inks have color casts, such as Y's color shift is 10%, M's 31%, C's 19%, and K's color shift amount is the smallest, and the control of the gray balance is more complicated. After UCR, the amount of variables affecting the gray balance is reduced, and the entire printing process is controlled at the time of prepress, thus making the process easier;
3. If the black text is reproduced by the YMC, since the printing process cannot completely overprint accurately, there will always be slight deviations, and black text will be used to print black text, completely avoiding overprinting problems caused by printing black text. , Reduced the difficulty of process operation and reduced the scrap rate;
4. In the offset printing, modern high-speed printing is basically wet and wet-wet printing. Due to this feature, the ink layer on each blanket of the printing process must be thicker than the existing ink layer on the printing sheet. Its viscosity is also less than the viscosity of the previous color ink, otherwise it will not be able to superimpose normally. However, if the amount of ink is increased, it will also increase the expansion value of the dot. Thus, using a black plate instead of YMC's overprint ash clearly improves the printing of the overprinting process.
Fifth, gravure (here mainly refers to the plastic film as a printed substrate gravure)
The characteristics of gravure printing are different from those of plain printing. The advantages of gravure printing are often the defects of gravure printing, and the disadvantages of gravure printing are the advantages of gravure printing.
1. The gravure is made of aluminum-plated printing roller, which has a very high printing rate and can reach more than 1 million impressions. However, the gravure platemaking cycle is long, the cost is extremely high, and the control is difficult.
2. Gravure uses a recessed cell to carry the transferred ink. The amount of ink transferred is much larger than that of plain printing. Therefore, gravure prints are very vivid in color and can reproduce highly saturated colors and dark colors with a density of 2.6. However, the dot enlargement value of the gravure printing is much larger than that of the plain printing, and the difference between the regularity of the dot enlargement and the printing of the dot is basically a linear law.
3. The gravure is printed in one color to enter into the dry state, so the printing is wet and dry, and the gravure ink has a viscosity between O.1 and 0.05 Pa·S, which is much less than the viscosity of the offset ink. Therefore, There is no reverse printing in gravure.
This shows that the gravure can reproduce the color, the print color gamut is larger than the color gamut of the print. Because of this, gravure printing can reproduce high contrast, manuscripts with a density range of 2.6 or more without having to compress the tone level of the original.
Sixth, the advantages of not using black version when making plate
1. The gravure printing (referring to plastic gravure printing) consumes a lot of energy. Because of the use of hot air drying ink, the power consumption of each printing unit is more than 2OkW (such as Toshiba GS12O/6, and the power consumption of a single drying oven is about 30kw at the speed of 1O0m/min).
2. In the printing process, printing failures may occur at any time. If one plate is omitted, the probability of printing failures is reduced, thereby reducing the number of abnormal shutdowns and improving work efficiency.
3. Less one plate, you can save a lot of preparation time before printing, the above version, adjust the squeegee, ink, printing and other versions, and improve work efficiency.
4. Less one plate can reduce scrap rate. For example, the phenomenon of dirty prints on the knife line due to inaccurate overprinting of the black version and the fact that the ink is not scratched due to the scraper can be fundamentally solved.
Seven conclusions
After comparing and understanding the basic related theory, the following conclusions can be drawn:
In the gravure platemaking process, we should selectively make specific selections of specific manuscripts. Whether to use YMC three-color platemaking or Y, M, C, K platemaking (hereinafter referred to as non-spot color printing) should be specific to the manuscript. Based on the analysis, make a choice:
1. For manuscripts and layouts with black text, especially small black texts, four-color plate making must be adopted.
2. For originals and layouts without black text, there are several situations:
1 For prints with color photographs as originals, it is entirely possible to adopt Y, M, C, three primary color platemaking methods, that is, no black version;
2 For prints with a color reversal film as the original, the quality of the original document (mainly the gradation level of the original document and the keynote to be expressed by the original document) should be determined. There are two kinds of situations: First, the key tone of the manuscript is dark and dark, and the color of the picture is darker, so four-color plate making must be used. Second, the key tone of the manuscript is adjusted in high light, middle tone, and high school. There are fewer dark holes, and most of the colors in the picture are neutral gray components, bright colors, you can not only use the black version but only the three primary color plate method.