Spot color ink preparation method

Keywords: spot color experience color matching instrument color matching computer color matching ink transfer

In the color printing of packaging products, advertisements, book covers, etc., the colors used are mostly spot-painted in spot colors. The spot color in these designs cannot be overprinted on the printing machine through the four colors of cyan (C), magenta (M), yellow (Y), and black (BK). In the printing industry, the original ink is often not found directly. use. The spot color inks of different colors must be selected and applied by the operator according to the actual production conditions of the enterprise, and appropriate color matching methods should be adopted to obtain different proportions of the original ink.

First, the experience of color matching

Many small and medium-sized printing companies, including some large printing companies, still generally adopt an empirical color matching method. That is, using long-term accumulation of practical experience, according to the law of color changes and the principle of mixing out a variety of colors of ink, printing out in accordance with the requirements of the original print.

The empirical coloring method can be divided into three steps:

1. Analyzing color manuscripts

The color composition and characteristics of the manuscript are analyzed to determine which kind of complex color tone the original color belongs to in order to determine the hue, proportion, and the type and ratio of the diluting agent to be used.

The use of print chromatography to determine the ratio of three primary color inks is a simple, practical method of color matching. The ink color matching has a similar rule to the dot area of ​​the three primary colors. Each color block in the chromatogram is marked with the percentage of the area of ​​the primary color dots. The ratio of the three primary colors in the original color sample can be determined based on these values. When calculating, it should be noted that in the unit area of ​​the printing chromatogram, the content of the three primary colors is removed, and the remaining area percentage of white paper is the white ink content.

For example, the original color sample is the same as the pink color formed by the 40% magenta dot. The calculation method is as follows:
M:W=40%:(100%-40%)=40%:60%=4:6=2:3
That is, according to the proportion of 2 parts of the original ink of magenta and 3 parts of white ink, the light red color can be obtained.
Another example: the original color sample is similar to the light green color consisting of 50% yellow dots and 50% blue dots. The calculation method is as follows:
Y:C:W=50%:50%:[(100%-50%)ten (100%-50%)]=50%:50%:100%=b:b:10=1:1:2

That is, it is formulated according to the ratio of 1 part of yellow original ink, 1 part of cyan original ink, and 2 parts of white ink. However, due to the equal proportion of yellow ink mixed with blue ink, green ink can be obtained, according to subtractive color theory, the type of primary ink should be used as little as possible when adjusting the ink, otherwise it will reduce the brightness of the matching ink, affect the color saturation, To make the dark gray ink is not clear. That is to say, the color that can be tuned out with two kinds of original ink, it is better not to use three kinds of primary color ink to adjust. Therefore, in this case, when the ink is actually dispensed, the proportion of 1 part of the green original ink plus 2 parts of the white ink is allotted.

2. Ink transfer

According to the calculated ratio, a small amount of primary color ink is used for debugging, and at the same time, a small portion of the uniform ink is diluted to the extent required by the printing, and two small pieces of paper are used to make a small color sample (must be used for printing ink. Uniform, and the thinner the ink layer, the better.) Contrast to the original. In order to ensure the accuracy of the excellent hue, you should pay attention when you look at the color sample by hand: it is best to use the same paper as the paper used for printing; to watch the thinnest and lightest ink of the color ink : It is advisable to look at a standard light source or with sufficient natural light to keep it in line with the process color. After the ink to be dispensed reaches the requirements of the original, the weight of the formulated ink is determined according to the amount of printing, and the ink is transferred in large quantities.

3. recording

Mix the proportion of various inks used in ink transfer, ink transfer, dry oil, ink type, quantity, and manufacturer information to register in detail, which is convenient for future reference.
In addition, the following points should also be noted in the actual transfer of ink:

(1) Deployment of grey ink

Theoretically speaking, gray series inks can be tuned with the same amount of three primary color inks, but this will waste a lot of color inks, and it is difficult to achieve a correct gray. Therefore, in practice, according to the requirements of the manuscript, different levels of black ink and white ink are used to generate gray levels.

(2) Blending dark ink

Dark ink refers to the ink that is formulated with different proportions of the three primary inks without adding any diluting agent. Before the ink transfer, first put the main ink into the ink tray or the ink tank, and then add the auxiliary color ink to harmonize evenly. Use the comparison method to view the difference from the original hue and use the complementary color theory to adjust the color characteristics until the hue conforms to the original color. until. For example, when a hue of red color is heavy, a certain amount of blue ink may be used to correct; when the green taste is heavy, a small amount of magenta ink may be added to correct; when the hue is heavy, yellow ink may be added to correct it. However, it should be noted that this will increase neutral gray and reduce lightness. In addition, black ink is generally not used to lower the brightness of black when adjusting ink, but some special colors can also be added with a little black ink. For example, the dark brown color is dominated by yellowish red; suitable amount of black ink may also be added.

(3) Blending light color ink

Any ink added with dilute agent, white ink, and Weili oil is collectively referred to as light ink. When the ink is transferred, the primary color ink must be added gradually and gradually in the diluting agent, and the diluting agent must not be added in the primary color ink, because the primary color ink has a strong color developing ability in the diluting agent, and the original ink concentration is not well understood, thus wasting. Ink, but also not easy to adjust the ink.

Under normal circumstances, for the printing of colorful packaging and decoration on the ground, in order to achieve the requirements of gloss, so that the product is uniform and thick ink, you can use white ink and Weili oil as a dilute. The choice of white ink depends on the printing plate, the color, the structure and smoothness of the paper surface. For example, if the surface of the paper has dark spots or the paper does not meet the specified requirements, the background color of the paper must be printed with opacity. Light color ink, then opaque white ink should be used. In addition, the need for color in the field, you can add light in the dilute agent to deploy, so as not to affect the color effect of the former color.

(4) The amount of dry oil

The temperature and humidity of the environment, the ink absorption of the paper, the thickness of the ink layer, the auxiliary materials, the nature of the ink, and the number of prints are all factors that affect the amount of dry oil added. The amount of red, white dry oil added can not exceed 5% of the amount of ink, dry oil add more will appear crystallization phenomenon, so that the ink is dull; dry oil added less, so that the ink drying speed is reduced, there will be back dirty phenomenon. Therefore, the amount of dry oil added should be appropriate, must not be too much or too little.

The amount of dry oil can be determined according to the following principles:
1 Coated paper prints are more than offset paper prints, winter is more than summer, dark ink is more, post-color is more than the former color, and the number of prints is less than the number of prints.
2 Light-colored inks, mainly white ink, can be added in proportion to the white ink.
3 Light-colored inks mainly based on bright syrup are generally added with red dry oil, and some are added with a certain amount of white dry oil, and at about 0°C: red/white = 3%; at about 35°C: red/white =1%.
(4) Since the auxiliary materials in the ink are added too much, and the drying speed of the ink is affected, the amount of dry oil added can be increased in an appropriate amount and adjusted according to the specific conditions.

In addition, in addition to the preparation of ink in order to make the hue accurate, the printability of the ink is also equally important, the deployment of the ink is too thin or too thick is not appropriate, should make the ink has a certain viscosity and fluidity. After the ink is transferred out, if it is found that there is an error between the color sample and the original printed on the machine, it shall be promptly corrected. The ink fountain and the ink roller should be cleaned when changing color to avoid unclean cleaning and color cast. The remaining spot ink after printing can still be prepared according to the hue of the new manuscript, but often the saturation is grayish, especially the remaining ink retrieved from the ink fountain, which may have been emulsified or the printability has changed. It is best to mix it into black ink or gray ink. In addition, to select an ink with excellent texture, the nature and hue of the original ink produced by different ink factories are not the same, and it is better to select the ink product of the same manufacturer.

Second, the instrument color method

With the further development of science and technology, ink color matching also has corresponding color matching instruments, so that the color matching work is carried out within a certain range of accuracy, and the color matching speed and correction times are reduced. The color matching of the instrument is based on various instruments, and after the precise determination of various color matching results, the color matching rule is found out, and a series of curve charts are drawn as the reference for the color matching. When measuring colors, you only need to determine certain features, you can find the proportion of the original color ink from various types of charts, or you can know the color matching components through simple calculations. Instrument coloring includes color measurement, batching, blending, ink scraping, comparison, and evaluation.

First, the spectrophotometer, colorimeter, and color analyzer are used to analyze and compare the measured spot colors, and the color parameters are measured. Color parameters can be represented by X, Y, Z, or L*a*b* (a color system, where L* is the psychometric brightness; a*b* is the psychometric color). Then, according to the characteristics of the color, the constituent ratios of the primary colors and the auxiliary materials are preliminarily determined, and then the primary color ink and auxiliary materials are mixed evenly with a stirring machine. In the assessment, the original and the color of the prepared spot color ink are quantitatively tested (usually only the color difference meter or the colorimeter can finish the job), and the color difference or other indexes are calculated, and the formula is further revised until it is satisfied.

Third, computer color matching

With the development of computers and color measuring instruments, color matching software is gradually improving. The purpose of the computer color matching method is to equalize the tristimulus value of the mixed color with the tristimulus value of the color to be matched, and the tristimulus value can establish a mathematical relationship with the concentration of each primary color ink. Based on this principle, after many After the calculation, you can get the formula of the primary ink that meets the requirements.

The electronic color matching system consists of hardware and software. The hardware part mainly includes colorimeters, microcomputers, spectrophotometers, printers, etc. The software part includes function modules such as color measurement, basic database, prediction prescription, correction calculation, and prescription management. The color matching program can provide multiple prediction prescriptions and quantitative indicators such as color difference, whiteness, yellowness, metachromatic index, and color depth. When a given color sample needs to be color matched, the reflectance value and observation conditions (standard light source, observer) measured by the color sample are input into the computer, and the computer will perform a series of calculations according to a pre-programmed program. Comparing with the color difference, the computer finally outputs the color prescription. According to the formula of the output for color matching and proofing, the reflectance of the actual color sample is measured again and input into the computer. After the color calculation is performed again, the final optimal correction formula is obtained. Although this method is more complicated in calculation, it is easy to use a computer.

Computer color matching is faster, more accurate and more effective than empirical color matching and instrument color matching. At present, this technology has been widely used in many industries related to the use of color in foreign countries. In China, only a few powerful printing companies adopt this color matching technology. This is mainly due to the high price of taking into account the purchase of computerized color matching systems.

(Luo Guanglin Liu Junjie)