Fourth, the relationship between the dark line of the black version and the amount of background color removal
The depth of the black version is closely related to the amount of background color removal. The amount of background color removal is large, and the black version should be dark; otherwise, the amount of background color removal is small, and the black version should be shallow. At the same time, the length of the black tone should be based on the length of the dark tone density range of the original. Dark tone density range is long, black version should be long, dark tone density range is short, black version should be short. Neutral gray balance is an important condition for the original copy to be reproduced in color. It is also a technology that is difficult to master in plate making and printing, because the three-color inks of Y, M, and C have certain difficulties in reproducing neutral gray balance.
V. Control of neutral gray balance The main factors affecting neutral gray balance:
â‘ Ink color characteristics.
â‘¡The proportion of the three primary colors.
â‘¢The color sequence of printing.
â‘£ Paper performance.
⑤ Process operation, etc.
1. The color characteristics and changes of ink, the control of neutral gray balance, and the factors affecting neutral gray balance, we must first understand the color change law. â‘ The three primary colors ink can be mixed into black according to a certain proportion. â‘¡ After mixing the three primary colors, the ink will be almost black, and with different proportion of diluent, then different colors of neutral gray will be obtained. â‘¢ The three primary colors can be mixed in different proportions to obtain intermediate or multiple colors of different hue, and the hue is biased to the hue with a large proportion. â‘£ Two primary colors of ink are mixed in equal amounts to obtain standard intermediate colors.
2. The requirements of neutral gray balance on the ink, ①high transparency: when the ink is coated into a uniform film, the degree of color development of the background color of the material that bears the ink film, the more clearly the background color is displayed, the higher the transparency of the ink. ② Fine pigment particles: fine pigment particles are required for printing high-end and exquisite products. ③ Strong coloring power: The coloring power of the ink is a quantity indicating the color intensity or concentration of the ink. For inks of the same hue, the coloring power depends on the dispersion of the pigment on the binder. The higher the dispersion, the stronger the coloring power; It also depends on the content of the pigment, the higher the content, the stronger the coloring power. ④Light resistance: Under the effect of light, the color of the pigment will change and fade to different degrees, which is light resistance. ⑤High color efficiency: Color efficiency is a comprehensive indicator of ink color difference and gray scale. ⑥Good chemical stability: The color of the ink will change under the action of some chemical substances. Therefore, the ink needs to have good chemical stability, water resistance, acid and alkali resistance, ethanol resistance and other properties.
3. The relationship between the performance of the paper and the neutral gray balance, the product quality of the printing company is greatly affected by the raw material paper, the ideal paper whiteness is 100% reflectivity, and the total reflection is 380-700nm. In the process of plate making and printing, it is necessary to consider "different from paper", and adopt appropriate process content to adapt to the paper used, especially in terms of dot thickness, color registration, and contrast of the layout.
The papers for high-end and exquisite offset printing products include domestic coated paper, offset paper, painted newspaper and imported coated paper, egg-textured paper, cloth-textured paper, etc. Due to the difference in paper tightness, whiteness, paper absorbency, smoothness, stretchability, etc. , And the curve that reproduces the reproduction tone is also different. The tone level of printing with coated paper is very rich, while the tone level of printing with offset paper is relatively dull. The same is for 157g / m 2 of coated paper. Due to different places of production, domestic paper or imported paper also has a certain gap.
The high-quality paper with low absorption, high whiteness and high smoothness of the paper has an ideal reproduction curve, the amount of ink is thin, and the color is still bright.
4. The relationship between printing color sequence and neutral gray. Monochromatic offset presses use the sequential color sequence of Y, M, C, and K. First, it is considered that the ink with the lowest transparency is printed in the first color, and then the ink with high transparency is printed. The color sequence is arranged according to the transparency of the ink. At the same time, the viscosity of the ink is also considered. Because the viscosity of the Y ink is small, the backside of the printed matter can be avoided; the light color is placed on the front and the ink roller is easy to clean; it is also convenient for four-color overprint accuracy. Multi-color offset presses use the inverted color sequence K, C, M, Y. Because the multi-color presses are wet stacked wet, the printing ink is overprinted again without the oxidation conjunctiva drying. The viscosity of the four-color ink is K> C> M> Y, which meets the requirements of the four-color machine. The color sequence of the multi-color machine is gradually reduced from high to low according to the viscosity of the ink. The high viscosity is placed in front. Imprint, overprint fastness is better.
In addition, the color sequence arrangement of the multi-color machine takes into consideration that the lowest transparency is printed first, and the black ink has the lowest transparency, that is, the darkest. As the outline of the screen, the color is denser, so it should be printed in front, so that the transparency is high. The C color is printed on the back, which can make the whole picture bright and eye-catching.
Different color sequence arrangements have a greater impact on the neutral gray balance. Different color sequences will directly affect the quality of the printed products and the hue of the colors. In the actual production, a comprehensive analysis should be carried out. Considering the variable factors a little more, the color sequence should be arranged according to the effects of different types of originals and customer requirements in order to achieve the perfect reproduction of the printed matter.
In general, the color cast of several inks should also be considered after overprinting: M, C, and Y are easy to turn green after overprinting, C, M, and Y are reddish after printing, and C, Y, and M are easy to reddish, M, Y, C is brownish green after overprinting, Y, C, M is light purple after overprinting, Y, M, C is bluish green after overprinting.
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