Gravure ink color method

First, the principle of color

Each color has three characteristics of hue, lightness, and saturation. Therefore, the above three factors must be considered in the color adjustment process. Although black is theoretically the complete absorption of light, black is still glossy. The ink is "submerged by pigment (toner) and resin binder." The pigment particles are surrounded by a layer of nearly transparent resin oil that refracts and reflects light. So we can feel black ink printed on the substrate, still has a certain degree of gloss. Pigments often account for 8% to 35% of the ink composition. Its amount determines the concentration of the ink, and has a great influence on the ink. Such as: the relative density of ink, transparency, heat resistance, light resistance and resistance to chemicals. In the ink coloring process, the ink to be used is determined according to the actual printing process, the ink layer thickness, the printing substrate, and the like. When selecting the ink, the gloss, hue, tinting strength, hiding power and the like of the ink itself must be considered. Gloss - Gloss can be measured either with the instrument or with the naked eye. It is usually observed with the naked eye only during the color adjustment process. Of course, for special situations, it must be measured with instruments, chromatographs, etc. Gloss is actually the extent of the ability of an ink print to reflect light in the same direction after being exposed to light. Its direct influence on the appearance of printing is a very important indicator. At the same time, when selecting the ink, it is necessary to distinguish whether the ink itself is a bright, semi-glossy or matte type ink, and it should also be considered whether the same type of ink is used. If the printing ink is printed in India (chlorinated polypropylene resin type) or table printing (polyamide resin) ink, it must be prepared for the same ink to avoid mixing errors and cause unnecessary losses. Hue - the basic characteristics of the color, due to qualitative differences, when toning, we must first consider whether the hue is the same, the detection method is usually observed through the scraping comparison. The specific way to observe hue is:

1 On a flat glass color viewing platform, take the standard and the tone pattern at a distance of 1 to 2 cm.

2 Take a scraping paper to flatten the glass stand, and then take the color ink. Use a glass tamper to scrape and compare the results.

There are two important factors in the comparison of the color palette results:

1 hiding power - the degree of ink cover the background color, the better the hiding power, the worse the transparency. The level of transparency affects the efficiency of ink trapping and the extent to which it is affected by the printed substrate. Such as the blue light yellow is better, and the ink hiding power is good, but also has a close relationship with the ink itself. Such as the thickness factor, under normal conditions, the hiding power of white ink is related to the thickness of titanium dioxide particles. The coarse particles have poor hiding power. The printing is easy to agglomerate; the particles are fine, the hiding power is good, the surface is uniform, smooth and delicate. The white ink generally requires a diameter of no more than 15 μm, and other colors of ink cannot exceed 12 μm.

2 coloring power - a method that represents the level of ink concentration. The determination is based on a certain amount of color ink, and then a certain amount of standard white ink is added. After mixing and comparing with the standard sample, the strength of coloring reflects the mixed color of the ink. Through the color identification (scratch paper coloring experiment) can be compared, ink samples and standards of the gloss, hue, hiding power of the three differences. The specific method is as follows: Put the standard ink in the upper left corner of the fixed paper, and put the color ink in the upper right corner. Using a spatula at a nearly vertical angle to the scraping paper, lightly force the standard and color inks to be contrasted. After the ink surface is dry, under a certain light source, determine the difference in gloss between the two and observe the appearance of the entire color. Normally black and color inks use white scratch paper, while white ink uses black scratch paper. When observing the color sample, it is better to compare it with the indirect light source during the daytime and it is not easy to be exposed to direct sunlight. It is recommended to use at night observation: “Color price fluorescent tubes and color temperature 5000±200°K, can also use self-made hybrid light source. 2 blue fluorescent tubes, 3 6500K400W fluorescent tubes, 6 100W tungsten filament lamps are fixed on the dedicated Inside the hood, it is easy to observe color samples."

Second, the attention of color

1 Carefully observe the color samples, pay particular attention to the printed substrate, and select the ink from the rough and smooth reflectance of the substrate. For example, inks are printed on aluminum plates or cans that are highly reflective and highly transparent. This will help greatly enhance the metallic luster of inks.

2 When selecting the ink required for color correction, avoid mixing too much ink as much as possible. Use inks that are close to standard colors and made from a single pigment. Toners use too much color, and the farther away from the standard color, the worse the brightness. The higher the degree of matteness of the mixed colors, the impossible to modulate the primary colors by color toning. Therefore, when two kinds of mixes are used in color adjustment, there are no three kinds of them. The less, the better.

3 Pay special attention to the tinting strength of the ink. If the selected ink concentration is not high enough, the standard color density cannot be achieved regardless of how the ink is blended.

4 When it is necessary to add black ink, special attention should be paid to the accuracy of the added weight and weight. In all types of inks, the hiding power of white ink is particularly strong. Adding too much will not only dilute the color, but it will also prevent the reflection of the substrate. However, for the printing uneven substrate such as nylon cloth, cardboard, in order to ensure the appearance of the print, it is best to print a white layer as the background color. Due to the strong coloring power of black ink, adding too much ink to the ink requires adding a considerable amount of other color ink to adjust the color to cause waste. Therefore, special attention is required.

5 When making light color inks, the degree of light transmission from the ink film should be judged, and how much white ink or adjusting ink (dilute agent) should be added for color adjustment. Never use solvents (diluents) for light colors. Excessive solvent addition will not only affect the printing performance, but will also destroy the ink structure, resulting in separation of the pigment and the resin oil. Precipitation or greatly reduces the gloss and brightness of the ink.

Third, the deployment of dark and light ink

The deployment of ink can be divided into dark ink and light ink deployment. The so-called dark ink means that only the primary ink is used for preparation without any diluting agent. According to the amount of ink consumed during printing, the main color ink and the auxiliary color ink determined by the color analysis and their proportions, the main color ink and the auxiliary color ink are uniformly adjusted together. There are three types of dark ink: monochrome, inter-color, and poly-color. Monochromatic refers to the deployment of a primary color ink. Inter-color refers to the deployment of two primary inks. Complex color refers to the mixture of three inks. Any ink that has been formulated with a diluting agent is called light-colored ink. Note the following three points when deploying:

1 Use white ink without thinner; 2 Use white ink as the main color, and add a little color ink to white ink;

3 color selection should be accurate.

Fourth, how to improve the luster of ink film

1 Add appropriate amount of varnish within the allowable range of color density.

2 coating the surface of the printing film varnish or varnish. 3 increase the transparency of ink, use high transparency of the ink or add the right amount of varnish, the use of smooth, reflective base material printing surface smooth degree.

4 to prevent the substrate surface adsorption, and reasonably improve the smoothness of the substrate printing surface.

5 Pay attention to the temperature and humidity of the printing environment. When the plastic gravure printing is performed under high humidity and low temperature, the solvent volatilizes quickly and the heat around the ink film is absorbed, which causes the water vapor in the air to condense abruptly to form a mist on the surface of the printing ink film, resulting in the loss of the ink layer. luster. During the mildew season, special attention must be given to controlling the temperature and humidity of the printing environment to ensure good printing results. Usually room temperature is 21-23°C, and humidity is 40%, which is helpful for real reproduction of color.

Fifth, the production of special colors

1 gold, silver ink production: the use of adjustable oil to add appropriate amount of gold powder, silver powder can be mixed evenly. It is necessary to pay attention to the appropriate fineness of gold powder and silver powder. At the same time, it is also necessary to choose a varnish that is compatible with the printed substrate. It must be prepared during printing to prevent precipitation and delamination of the ink due to long rotation time. The gold ink can also be mixed using silver powder, transparent yellow, and varnish.

2 pearlescent ink: pearlescent pigments and a suitable proportion of high transparency ink or varnish mixed evenly. The hiding power of the ink is strong and the pearlescent effect of the application may be lost.

3 Luminous ink: The ink has the effect of absorbing light energy and then re-lighting for a certain period of time. Therefore, they often emit light at night, so they are called luminous inks or phosphorescent inks. Luminous pigments are usually dispersed in a highly transparent varnish and can be mixed well. All of the above inks cannot be ground. Grinding with gold ink and silver ink will damage the grinding equipment. Pearlescent and luminous ink grinding will damage the surface or crystal structure and lose the effect of hue.

Source: 21st Century Fine Chemicals Network