The color of plastic flexible packaging printed matter requires strong physical sense and high accuracy of color. Therefore, the selection and deployment of ink color is very important. In printing, gravure printing belongs to direct printing. Its color restoration and level reproduction are realized by the depth and size of the screen hole on the printing plate. The ink amount per unit area of field printing of flexible packaging is mostly between 3-5 g / m2.
Due to the high cost of gravure cylinder and the restriction of process conditions, the color matching process of plastic gravure ink is more important. Of course, the actual color matching technology is dominated by experience and intuition. With the development of inking technology, automatic color matching has become an important development trend. But before it became popular, manual color matching was still very important.
The color matching of plastic gravure printing ink can be divided into two processes. First, manual scraping and color mixing are used, such as ink scraping stick, scraper or color wheel. When the color is close to the original or customer's requirements, fine adjustment can be carried out on the printing machine.
At present, in addition to spot color ink, the color matching process of gravure printing is basically started after low-speed registration. It is based on the standard sample sheet provided by the customer and the ink color guide provided by the ink manufacturer. After analyzing the color of the original, determine the type of the original ink, and then use the determined original ink for a small amount of blending. After each boot, check and identify with the standard sample under the standard light source. If there is any difference, adjust it again until the color is the same as the standard sample. This requires the color matching personnel to be familiar with gravure printing process and have strong color discrimination ability, and master the color matching rules of three primary color inks based on subtraction principle. It is very practical to establish color matching files in the process of color matching, which can simplify many color matching work.
The following problems should be paid attention to in color matching
1) In the specific color matching, we should first distinguish the main color and the secondary color composition ratio. Different proportion of primary color ink can be mixed to produce different ink color effect. It should be pointed out here that the color of some special color inks is determined by the color itself, which is difficult to adjust with the primary color ink, such as ultramarine, golden red, etc.
2) When the two colors are mixed into the desired color, only the colors with similar color ring positions can get bright colors. For example, to get a bright grass green, you should mix Turquoise with turquoise. When the bright yellow and blue are mixed, the dark grass green is obtained. When you need to darken the ink, you can add complementary ink or directly add black ink.
3) When mixing spot color ink, the color closest to the color code sample is selected as the base color, and then mixed with a small amount of other colors. If several kinds of inks are used for color matching, the color matching should be mainly based on the set ink with similar color, and the color ink with more amount should be mixed first. In order to get the required color, the ideal is to mix as few inks as possible in the necessary range to get the desired color. The more color ink is used in color matching, the worse the brightness and purity of the prepared ink are.
In addition, attention should be paid to: (a) the color of ink film is different before and after drying, and the test result is accurate only after the ink film is dried. (b) The film used in the preparation of spot color ink should be consistent with that of printing film to avoid color error caused by different substrate materials. (c) We should pay attention to the influence of its viscosity on the color.
4) In the deployment of ink, the correct use of complementary colors. In the deployment of intermediate ink or dilute the primary color ink, should avoid the mixing of complementary ink, so as to avoid the ink color darkening. And in the deployment of ink color deviation or need to change from one color deviation to another, you can use its complementary color to correct. For example: if the Yellow flavor of the prepared ink is too heavy, you can add a little purple and blue ink to correct; if the blue flavor is too heavy, you can add a small amount of orange yellow ink to correct. When the red flavor is too heavy, a small amount of blue ink can be added to correct. In addition, if the black is impure, a small amount of cyan ink can be added; if the silver ink becomes dark and black after a long time, a small amount of white ink can be added to correct the problem; a small amount of yellow or magenta ink can be added to the green gold to present the golden and golden red effect; if the cyan is too light, a small amount of magenta ink can be added.
5) When preparing light color ink, white ink or diluent should be added gradually, and the basic proportion of white ink or toner oil (diluent) should be judged from the transmittance of ink film.
6) Adjust the working viscosity and drying performance of the ink after adjusting the ink that meets the color requirements, and then go to the machine for printing and color tracing. In the process of color tracing, gradually adjust and determine the proportion of each color ink in the ink formula.
7) Pay special attention to the coloring power of the ink. If the concentration of the ink used is not enough, no matter how the deployment, it is difficult to achieve the standard color concentration. The following methods can be used to reduce the ink concentration in the printing process:
(1) In the ink mixed with the agent, it has a certain degree of transparency, suitable for ink multi-color overprint.
(2) In the ink mixed with white ink, has a strong covering power, printed patterns bright, plump and bright. Commonly used for field printing.
(3) When diluting solvent is added into the ink, the viscosity of the ink decreases, and the concentration of the ink also decreases.