Explain the specific application of color science in printing from many aspects
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This article will explain the application of color science in printing from the aspects of printing chromatographic production, printing hue measurement and spot color ink blending.
1. Using color science to produce printing chromatography
Throughout the color reproduction process, it has undergone three processes of color analysis, color transfer, and color combination. The correctness of the color change control in each process is directly related to the final quality of the printed matter, so a color standard, ie, printing chromatography, is required to regulate the various hue in the printing process. Printing chromatography is the use of three primary colors of yellow, magenta, cyan and black, mixed in different proportions or dots, stacked to form a book of various color patterns for people in design, original copy, ink blending, etc. Check it out.
Four-color chromatography uses four colors of yellow, magenta, cyan, and black inks, with different dot area percentages (usually only 0, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100% eleven dot grades, or 5% of the dot grade) overlay overlay, and arranged in a certain order, it has the same process for electronic color separation, proofing and printing Important reference and guidance. The spot color in printing is a color ink that has been mixed, and the color is not directly related to Y, M, C, and K. Therefore, a set of standard primary color inks is first defined, and various kinds of mixing colors are produced according to different mixing ratios. The color swatches are marked with a scalar indicating the mixing ratio of the primary colors, so that people can use the three primary colors to blend the spot colors of the various colors. This is the spot color chromatography.
At present, Pantone color matching chromatography of American PANTONE is widely used in the world. However, printing chromatography uses color to indicate color. Its production is usually affected by many factors such as ink, paper, printing process and equipment. Therefore, the printing unit should make its own special according to the raw materials, production process and equipment conditions used by the factory. Printed chromatography.
2. Using color to measure color and color difference
The color measurement in color printing can be roughly divided into three types: contrast visual method, density measurement method and color measurement method.
The color measurement is measured by the contrast visual method in the printing process, mainly by an experienced operator who evaluates the color of the original, the signal strip, and the printed sheet by a standard visual method with reference to the standard color ratio. Due to the influence of the observer's own physiological and psychological factors, the accuracy of the comparison visual method is relatively poor. However, because it does not need to be equipped with fine measuring instruments, it is widely used in general copying work.
Densitometry is a method of measuring the tone and color of a color using optical density values. In the color printing process, the density value can well reflect the proportional relationship and superposition performance of the three primary color inks, and the detection equipment is simple, so it is widely used. However, using optical density as a means of monitoring and measuring the printing process, the amount of each monochromatic ink can only be obtained from the control strip, and the information of the color error cannot be directly obtained from the image, so that it is difficult to communicate with the printing customer, which is inconvenient. Density measurement is precisely controlled, so density measurement is just an indirect method of color measurement.
Chroma measurement method is based on the principle of colorimetry, using the color of the important part of the printed image as the monitoring point, directly measuring the tristimulus value of the color, and obtaining the color measurement method of the color chromaticity information. The method can accurately express the color difference of the standard proof and the sample to be tested and the required proximity, without additional check or control strip. However, it has not been promoted and popularized at present, mainly because the instrument is expensive and has high color theory requirements for users. As a large-scale cigarette printing company, most of our products involve spot color printing. Due to the good use of color measurement to control chromatic aberration, we have rarely complained about customers in color for several years.
In the color printing copy work, not only to understand the three attributes of the color, but also to understand the difference between the colors, in order to compare and distinguish the color, which is the color difference. The unit of color difference is NBS, which is an abbreviation of the US National Bureau of Standards. At present, the color measurement standard commonly used in the world is CIE1976Lab uniform color space, which was proposed by Canadian Weizesky at the 18th CIE Conference in 1975. Where L is the psychological brightness, a and b are the psychological chromaticity, and the color difference is represented by △E. When a is positive, it means reddish, when it is negative, it means greenish; when b is positive, when b is positive, it means Yellowish, when it is negative, it means bluish; when L is positive, it means light color, otherwise it is darker. The color difference ΔE is generally less than 3, and the chromatic aberration is not very large, but it is also affected by the deep, light color and the printing material.
3. Use color science to match spot color ink
Ink is a coloring substance for printed matter. It is a mixture of coloring materials, binders, fillers and cosolvents. It is a complex colloid. Ink blending refers to the process of blending one or more inks together with a certain auxiliary material to meet the printing and color requirements. Any color can be obtained by mixing different primary colors in different proportions.
3.1 The law of ink color matching should follow
(1) The deployment of the spot color ink should be carried out under the standard light source D65. If it is during the day, it can be carried out in the sunny north window.
(2) The three primary color inks are mixed in equal amounts to approximate black. If you add different proportions of white ink or thinner, you will get different grades of gray ink.
(3) The three primary color inks are mixed in different ratios to obtain inter-color or complex color of different hue.
(4) The two primary colors of the ink are mixed in equal amounts to obtain the inter-color; when mixed in different proportions, the inter-colors of different hue can be obtained.
(5) The more color hue used in color matching, the worse the brightness is. The black ink is added to any hue ink, and the brightness value is reduced. When white ink is added, the brightness is increased.
(6) Pay attention to the influence of the paper used, the color sequence of the printing, the color of the illumination source on the ink color and the color before and after the drying of the blot.
(7) The complementary color can be used to correct the color shift, but it can only be performed when the brightness value of the ink is too high.
(8) Try to use less original inks of different varieties to reduce the complementary color.
(9) Pay attention to the influence of ink viscosity on hue.
(10) Before the more complex spot color is mixed with ink, a small amount of test can be firstly determined to determine the ratio, and then the amount of ink used can be proportioned to avoid waste.
3.2 Dark ink blending
Only three primary colors or intermediate color inks are used, and no thinner is used for ink blending, which is collectively referred to as dark ink blending. There are several steps in the preparation of dark inks:
(1) Determine which primary colors are included in the original color sample and discharge the primary color, the auxiliary color sequence, and the approximate proportion of each color ink.
(2) According to the ink area of the printed matter, ink tinting strength, plate depth, paper properties, ink viscosity, printing quantity and other factors, determine the number of blending.
(3) According to the proportion of blending, add ink in the order of large to small. Weigh the main primary color with the highest content, then weigh the auxiliary color with less content, then add the secondary color ink to the main color ink several times, and mix it evenly.
(4) After comparing the colorimetric and adjusting the proportional relationship of the three primary colors, after conforming to the original condition, the printing suitability is adjusted by the printing aid.
(5) Record the proportional relationship of the primary color components used in order to ensure the consistency of the ink color when the reprinting or the amount of ink is insufficient.
3.3 Light color ink blending
The spot color inks which are blended with white ink, white ink, thinner, bright varnish and other dilute inks are called light-colored inks. The blending of light-colored inks is mainly based on dilute inks, and primary color inks are supplemented. According to the requirements of the transparent condition of the color sample, choose a suitable thinner. The light color ink generally used for dot printing should use a transparent thinner. As a light-colored ink thinner for solid printing, white ink can be used. The mixing process is as follows:
(1) Determine the relationship between the type of primary color ink used and the ratio of the diluent based on the primary color sample.
(2) According to the required amount of ink, the dilution agent is first weighed proportionally, and then the selected primary color ink is gradually added. If the primary color ink is more than one type, the amount is first increased, and the amount added is small.
(3) Scratch the small color sample and check the original sample, continuously adjust the amount of the original ink, and conform to the original sample, then adjust the printing suitability through the printing aid.
(4) Record the proportional relationship of the raw materials used.
Matching light-colored inks, mastering the degree of ink dilution is a key. If the ink color is too deep, the printing ink layer is required to be thin, which will cause the "flower plate" or the solid color to be not bright. If the ink color is too light, a thicker ink layer is required for printing to achieve the color requirement. Causes "paste" and dryness is not complete, the back is dirty and so on.
The above is just a few aspects of the application of color science in the printing industry. In addition, printing colorology also plays an important guiding role in dot coloring, printing materials, and printing processes. This article is just for everyone to play a role in inducing jade, and ignore the omissions.