Composition and properties of the most popular gra

2022-08-03
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Gravure printing ink raw material composition and performance - the development of social economy and the increasing improvement of people's living standards make gravure printing more prominent in various printing methods. The research on gravure printing technology has very important practical significance. Here, the composition principle and performance of gravure printing ink are briefly discussed. Please correct the mistakes

like other printing inks, gravure printing inks are mainly composed of colored substances (pigments) and binders. Among them, colored substances play a role in color development, and display images on the substrate by forming a contrast with the color of the substrate. Only when the proportion of each component of the ink is well adjusted, can the printing suitability and use performance of the ink be achieved, and the printing ink can be well coordinated with the printing plate, printing machine and substrate materials, so that the printing process can be carried out smoothly

I. raw materials

gravure printing inks are mostly volatile solvent inks, which are composed of pigments, solid resins, volatile solvents, fillers and additives

1. pigment. Pigments are divided into inorganic pigments and organic pigments. Most of the inorganic pigments are hard and dense crystal materials. These crystals are difficult to grind into fine particles without special treatment, and cannot be well dispersed into the binder. Therefore, the printing suitability of the ink made of inorganic pigments is often not ideal, and it is easy to wear the printing plate. However, most organic pigments can be artificially modified to be easily dispersed in binders. The ink made of them has great advantages in printability, but the price is often high. The pigment components of gravure printing ink are mostly organic pigments, which is determined by the printing characteristics of gravure printing and the quality requirements of printing products

the influence of pigments on the printability in oil is mainly determined by the properties of pigments, such as dispersion, hiding power, apparent volume, resistance, etc

① dispersion refers to the size of pigment particles. The pigment particles in the ink must be completely immersed in the binder in the ink film. The size of the pigment particles cannot exceed the thickness of the ink film, which is generally 5 μ M, otherwise it will affect the gloss of the printed matter. The smaller the particle, the higher the dispersion, the greater the hue saturation of the ink. Gravure printing is hole transfer printing, which requires high pigment dispersion

② tinting power refers to the ability of a pigment to affect the color of mixed pigments after mixing with other pigments. All pigments that are easily diluted due to mixing with white substances have weak colouring power. The pigments with strong colouring power should be selected for ink preparation. When used for printing, the effect of less ink consumption and faster drying can be achieved. For high-speed gravure printing with high requirements for ink dryness, this is very important

③ hiding power refers to the ability of pigments to cover the background color. Whether the ink has hiding power depends on the ratio of the refractive index of the pigment to the refractive index of the binder. When the ratio is 1, the pigment is transparent; When the ratio is greater than 1, the pigment is opaque, that is, it has hiding power. Different prints have different requirements for the hiding power of pigments. For example, iron printing ink requires that the pigments have strong hiding power to prevent the exposure of the background color, while four-color overprint ink requires that the pigments have high transparency, so that the stacked inks can achieve better color reduction effect

④ apparent specific volume refers to the volume per gram of pigment, expressed in cubic centimeter. The apparent specific volume of the same pigment with different particles is different. The larger the apparent volume of the pigment, the smaller its specific gravity. It is not easy to precipitate in the binder, and the stability of the ink is good

2. binder. Binder is the dispersing medium in ink and the carrier of pigment particles. The printability of ink is closely related to the properties of binder. The composition of binder is complex, mainly including oil binder, resin binder and organic solvent

① oil type binder is made by heating the dry vegetable oil to a certain temperature and keeping it warm at this temperature. The dry vegetable oil is a mixture of unsaturated fatty acid glyceride. Polymerization occurs during heating to form dimer and trimer. The longer the heating and holding time, the greater the viscosity. The oil binder contains a small amount of free fatty acids, which acts as a surfactant and is conducive to the mixing of pigments and binder; The oily binder has good adhesion and certain water resistance, and can form a glossy ink film, but the fixing speed is slow and the drying time is long

② resin type binder is made by dissolving in mineral oil, vegetable oil or volatile solvent the in-process synthetic resin or modified resin. It can also be divided into four types of resin binder: dissolved, dispersed, colloidal and volatile. Commonly used synthetic resins include pentaerythritol rosin, alkyd resin, rosin modified phenolic resin, polyacid resin, maleic acid resin, petroleum, asphalt, etc. because the density of titanium alloy is much smaller than that of steel

③ organic solvent is also the main component of ink binder. It enables the ink to have a certain fluidity. When the ink is transferred to the paper, the solvent with high volatility volatilizes rapidly, and the solvent with low volatility penetrates into the paper by capillary action. In this way, the resin binder left at the bottom of the paper that will slightly adhere to the surface of the printer platform is fixed on the paper surface and dried. Commonly used solvents include ethyl acetate, butyl acetate, isopropanol, etc

3. auxiliary. Additives, also known as additives, are the auxiliary components of the ink. Their role is to adjust the printability of the ink. For different purposes, different types and quantities of additives should be added to the ink preparation to adjust the fluidity, dryness, hue, etc. There are mainly plasticizers, slow drying agents, desiccants, etc

① plasticizer is a solvent with high boiling point and low volatility or a solid with low melting point, which is used to increase the plasticity of polymer materials. Adding plasticizer to the ink can make the original brittle ink layer have better toughness, and make the ink layer have better adhesion with the substrate. In order for the plasticizer to better complete these functions, the molecules of the plasticizer must penetrate into the long molecules of the binder to play a certain lubricating role, so that the long chain of the binder can move freely, and the polymer will become soft and elastic

② desiccant. For dry oil, the oxidation reaction can be greatly accelerated if there is a small amount of metal salts. The commonly used metal salts include cobalt, manganese and lead salts, which are desiccants. Desiccant in the ink drying process can accelerate the drying of the ink without any change

in addition, in order to improve the printability and other indicators of the ink, there are other additives in the ink, such as wax, antioxidant, anti smudge agent, surfactant, preservative, adhesive remover, defoaming agent during the whole mold opening process during mold installation, etc

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