Discussion on the Suitability of Flexographic Letterpress and Lithographic Printing Ink

2020-08-20 04:12:26

When we study the printability, there are many aspects that need to be studied from the nature of the ink, that is, the printability of the ink. Because China's printing industry and ink industry are managed by different departments, the relationship is relatively estranged. Ink workers rarely clarify the nature of ink with printers, resulting in many inadequate research on printing suitability. Now briefly introduce the composition of ink, and then discuss the relationship between the various properties of ink and printing. For everyone to study the suitability of certain printing, please forgive me if the content cannot be exhaustive.

Composition of ink

The pigment (coloring material), filler, connecting material and auxiliary agent are mixed and ground to make the pigment, filler and auxiliary agent uniformly and finely distributed in the connecting material, becoming a colloidal dispersion system, the appearance is a uniform and delicate fluid Or paste, this is the ink.

Due to the different printing processes, inks are required to have different properties. For example, the gravure ink is very thin, and the viscosity is also very small, otherwise it cannot be filled into the recess of the plate. It can't be cleaned by a scraper. The printing ink is mostly used by letterpress transfer printing machine. The printing speed is up to 10,000 printings per hour or more. The paper used is newsprint with good absorption, so the printing ink is only thicker than gravure ink , And penetration drying is very good. Otherwise, it will not meet the requirements of high-speed printing and rapid drying. The letterpress rotary machine for printing books is slow, the paper used is firm, and the absorption is poor. Therefore, the printed ink is thicker and more sticky than the newspaper ink, and the penetration and drying property is a little slower, and even some have the property of a part of the oxidation and conjunctiva drying. It can make the writing of books and periodicals more clear and hard to wipe off after drying. Color relief printing is mostly used for printing trademarks, packaging and other printings, the printing speed is slower, the paper used is from relief paper, offset paper, coated paper to glass powder coated paper. The printed materials are required to have bright colors and clear graphics. The general letterpress ink, or color lead ink, and other ink (including copper-zinc ink) are much thicker and more sticky than printed ink, otherwise the dot printing is not clear. Because the printing speed is slower, and the paper has poor absorbability, the oxidative polymerization conjugate needs to be dried. In addition, it must be colorful and have a certain gloss. As for printed paper such as coated paper, coated paper, etc., offset ink with higher color density is generally used, and even the offset ink is fastened with bright light, in order to achieve bright colors and excellent gloss. Because offset printing uses the principle of mutual exclusion between oil and water, offset ink must have a certain water resistance, and should not be seriously emulsified on the printing machine and bleed in the liquid medicine. Because offset printing speed is now faster than relief printing, and after rubber transfer, the viscosity of the ink must not be too high, so its thickness is less than the color lead ink, and the viscosity is also small. The paper used is offset paper and copperplate paper, so it is also dried by oxidative polymerization film. In some cases, the back is not stained, so it is necessary to use fast fixing ink. If the gloss is good, it is necessary to fix the ink quickly with bright light.

The nature of the ink is actually determined by its composition, such as ink color, tinting strength, light resistance, acid resistance, alkali resistance, soap resistance, heat resistance, resistance to various solvents and water resistance, mainly determined by the pigment. The dryness, fast fixability, gloss, friction resistance, flex resistance and other properties of the ink are mainly determined by the binder. The viscosity, viscosity, fluidity and other properties of the ink are largely related to the binder, but also related to the nature and amount of the pigment and filler used. Therefore, the ink worker should understand the printing process and the nature of the substrate before designing, in order to design and manufacture the ink that meets the requirements. And printing workers should also have a certain degree of understanding of the nature of ink, in order to use ink reasonably.

The relationship between various properties of ink and printing

1. Color tinting power and transparency

The color of the ink, especially the color of the three primary colors, is often measured by density, color difference, gray scale and actual color efficiency in printing. It is generally measured and calculated by a color density meter on the solid or color scale part of the print or proof Get. But to measure from the quality of ink, you must take a certain amount of ink according to the international standard method, use an IGT suitability testing machine to print a color block on a specified coated paper with a certain pressure and printing area, and then use a color density meter Make measurements and calculations. Otherwise, these valid data will not be standardized and comparative.

For tri-primary inks, the color density should be within a certain range, usually yellow 1.00 Â± 0.05, magenta 1.45 Â± 0.05, cyan 1.55 Â± 0.05. However, due to the different requirements of the original tone, it may be slightly different. When the density of the three primary colors is within the above range, it is generally possible to achieve gray balance, and the color difference, gray scale and actual color efficiency calculated from this are also of practical significance. There is no standard color ink that meets the ideals of the three primary colors in the world. But the color difference should be as small as possible, the more conducive to the gray balance and reproduction of the original color. Small gray scale means high brightness. When the color of the original is very bright, the three primary colors with large gray scale cannot reproduce the bright original color. As for pictures or some manuscripts with darker tones themselves, it is not necessarily required that the gray of the three primary colors is small when printing. Sometimes, it is necessary to increase the gray scale or add the background color or spot color. The actual color efficiency refers to the purity of the main hue. The higher the color efficiency, the greater the range of matching with the other two primary color inks to form a pure color. Generally speaking, the actual color efficiency of ink with small color and small gray scale is greater. To measure the color quality of tri-primary inks, it should generally be small color, small gray scale, and the actual color efficiency is better.

The coloring power of the ink is also known as the color density. Ink with a large coloring power, a smaller amount of ink can make the printed matter reach a certain color density, and ink with a small coloring power requires a larger amount of ink. Bring disadvantages to the printing process, such as dot expansion, paste and even dirty. However, it should be noted that inks with large coloring power also have large gray levels, which affects the vividness of colors. Therefore, the coloring power of the three primary color inks should be equivalent to the three. When the coloring power of one color is too large or too small, it will affect the gray balance and color reproduction.

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