This article will explain the application of color science in printing from the aspects of production of printing chromatogram, measurement of printing hue, and deployment of spot color ink.
1. Use color technology to produce printing chromatography
Throughout the entire color reproduction process, it experienced three processes: 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, a chromatogram, 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, according to different proportions or dots mixed, stacked together to form a variety of color patterns of the atlas for people in the design, copying, ink deployment and other aspects Check it out.
Four-color chromatography uses yellow, magenta, cyan and black four-color inks with different dot area percentages (usually only 0, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, and 100% of the 11 outlets can also be overlaid at the 5% equally divided outlet level, and arranged in a certain order. It has the advantages of electronic color separation, proofing, and printing processes. Important reference and guidance. The spot color in printing is a color ink that has already been mixed and has no direct relationship with Y, M, C, and K. Therefore, a set of standard primary color inks are first defined, and various types of mixing ratios are used to produce various colors. Color color samples, each color sample is marked with a scalar that represents the mixing ratio of the primary colors, so that people can use the three primary color inks to blend out the spot colors of various colors. This is spot color chromatography.
At present, Pantone color chromatography is widely used in the United States. However, chromatograms are used to represent colors in the printing chromatograph. Its production is usually affected by many factors such as ink, paper, printing process, and equipment. Therefore, printing units should make their own products according to the raw materials, production processes, and equipment conditions used by the factory. Printing chromatography.
2. Using colorimetry to measure color and color difference
The color measurement in color printing can be roughly divided into three methods: visual comparison, density measurement and colorimetry.
During the printing process, the contrast visual measurement method is used to measure the color, and the main operator is to evaluate the color of the original document, the signal strip, and the printed sheet with reference to the standard color rate by means of comparative visual inspection. Due to the observer's own physiological and psychological factors, the accuracy of comparative visual inspection is relatively poor. However, because it does not need to be equipped with sophisticated measuring instruments, it is still widely used in the general print reproduction work.
Densitometry is a method of measuring the tone and color values ​​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 inks, and the detection equipment is simple, so it is widely used. However, using optical density as a monitoring and measurement method for the printing process, the size of each single-color ink can only be obtained from the control strip, and the color error information cannot be directly obtained from the image, which makes it difficult to communicate with the printing customer. Precise control of color reproduction, so density measurement is only an indirect method of color measurement.
Colorimetry is based on the principle of colorimetry, using the color of the important part of the printed image as a monitoring point, to directly measure the tristimulus value of the color, and obtain the colorimetric method of the colorimetric information. The method can accurately express the color difference between the standard proof sheet and the tested sample sheet and the required closeness, without additional inspection or control strips. However, it has not been popularized and popularized at present because of the high price of the instrument and the high color theory requirement for the users. As a large-scale tobacco label printing company, most of our products involve spot color printing. Due to the good use of colorimetric measurements to control color differences, we have rarely been complained by customers in color for several years.
In the work of color printing and copying, we must not only understand the three attributes of color, but also understand the difference between colors in order to compare and distinguish colors, which is the color difference. The unit of color difference is NBS, which is an abbreviation for the National Bureau of Standards. At present, the universal color measurement standard in the world is CIE1976Lab uniform color space, which was put forward by Canadian Wizsky at the 18th CIE Conference in 1975. Where L denotes the psychological brightness, a, b denote the mental chromaticity, and the color difference is denoted by ΔE. When a is positive, it means reddish, and when it is negative, it means green; when b is positive, it means that Yellowish, negative when the value is blue; L is positive when the color is light, and vice versa. The color difference ΔE is generally less than 3, and the color difference does not give a great impression, but it is also affected by the deep and light colors and the printing materials.
3. Use color to match spot color ink
Ink is the coloring matter of printed matter. It is a mixture of colorants, binders, fillers, and co-solvents. It is a complex colloidal structure. Ink formulation refers to the process of blending one or more inks together and adding certain auxiliary materials to meet the printing and color requirements. Any color can be obtained by mixing three different primary colors.
3.1 Ink color deployment should follow the rules
(1) The deployment of spot color ink should be performed under the standard light source D65. If it is daytime, it can be done in a sunny north window.
(2) The three primary color inks are mixed in equal amounts to obtain approximately black color. If you add different proportions of white ink or thinner, you will get gray ink with different tones.
(3) The three primary color inks are mixed in different proportions to obtain inter-color or double-color of different hues.
(4) Two kinds of primary color inks are mixed in equal amounts to obtain inter-color; in different proportions, inter-colors of different colors can be obtained.
(5) The more types of color hue used in color matching, the worse the brightness is. When black ink is added to any hue ink, the lightness value decreases. When white ink is added, the lightness increases.
(6) Pay attention to the influence of the used paper, overprinting sequence, lighting source color on the ink, and the color change before and after the drying of the print.
(7) Color correction can be used to correct color cast, but only when the brightness of the ink is high.
(8) Minimize the use of different types of original ink to reduce the effect of complementary colors.
(9) Note the effect of ink viscosity on hue.
(10) Before a more complex spot color ink is dispensed, a small amount of trial mix may be used to determine the ratio, and then the ink volume used may be proportionate to avoid wastage.
3.2 Dark ink deployment
Only three primary colors or the original color ink, without any diluting agent for ink formulation, collectively referred to as the deployment of dark ink. The dark ink is equipped with the following steps:
(1) Determine which primary colors are contained in the original color sample and discharge the main color, the auxiliary color sequence, and the approximate proportion of each color ink.
(2) Determine the amount of dispensing based on factors such as the inked area of ​​the print, the tinting strength of the ink, the depth of the printing plate, the properties of the paper, the viscosity of the ink, and the number of prints.
(3) According to the proportion of deployment, add ink in descending order. Firstly, the main color with the highest content is weighed, then the auxiliary color with less content is weighed, and then the auxiliary color ink is added into the main color ink several times and uniformly adjusted.
(4) After adjusting the proportions of the three primary colors by comparison and color matching, the printability is adjusted by the printing aids.
(5) Record the proportions of the components used in each primary color to ensure the consistency of the reconstructed ink color when it is reprinted or ink is insufficient.
3.3 Light ink preparation
All the spot inks that are formulated with white ink, white ink, diluting agent, bright light paste, and other dilute inks in the original ink are called light inks. The deployment of pale-colored inks is dominated by diluting inks, and primary inks are supplemented. According to the requirements of the transparency of the color sample, choose the appropriate diluent. The pale color ink that is generally used for dot printing should use transparent thinner. White ink can be used as a light-colored ink diluting agent for field printing. The deployment process is as follows:
(1) Determine the relationship between the type of primary ink used and the ratio of the diluting agent based on the primary color sample contrast chromatography.
(2) According to the required amount of ink, the diluent agent is first weighed according to the proportion, and then the selected primary color ink is gradually added. If the primary color ink is more than one kind, the first larger amount is added, and the smaller amount is added later.
(3) The small color sample is checked against the original sample, and the amount of raw ink is constantly adjusted. After the original color is satisfied, the printability is adjusted by the printing aid.
(4) Record the proportions of raw materials used.
The deployment of light-colored inks to master the degree of ink dilution is a key. If the ink is too dark, the printing ink layer will be thinner, which will cause the “flower pattern†or the field color to be not bright. If the ink color is too light, the thicker ink layer will be needed to achieve the color requirement. This is easy. Causes "sticking" and incomplete drying, sticky back, and other issues.
The above is just a few aspects of the application of color science in the printing industry. In addition, printing color science also plays an important role in the dot fineness, printing materials, and printing processes. This article is just for everyone to play a role in attracting attention, improper pointing out the omission.