Composition and four technical indicators of water-based ink - Industry news - Zhangjiagang Free Trade Zone Covord Chemical Technology Co., Ltd.

Position:

Composition and four technical indicators of water-based ink

2022-07-26 13:37:00

main ingredient

Water-based ink is a uniform paste-like substance composed of binders, pigments, additives and other substances. The vehicle provides the necessary transfer properties for the ink, and the pigment imparts color to the ink. The binders of water-based inks are mainly divided into two types: water-dilutable and water-dispersed. There are many types of resins that can be used in the former, such as maleic acid resin, shellac, maleic acid resin modified shellac, urethane, water-soluble acrylic resin and water-based amino resin. The water-dispersed binder is obtained by the polymerization of emulsified monomers in water. It is a two-phase system, in which the oil phase is dispersed in the water phase in the form of particles. Although it cannot be dissolved by water, it can be diluted by water. It can be considered as an oil-in-water emulsion type.

Viscosity

Viscosity is a property that prevents fluid flow, and is a measure of the ability of fluid molecules to interact with each other to hinder the relative movement of their molecules, that is, the resistance of fluid flow.

Viscosity is the most important control index in ink application, which directly affects the transfer performance of ink and the quality of flexographic printing. In addition to the viscosity and density of the resin in the binder, the viscosity is also related to the type and particle size of the pigment. In printing, low viscosity ink transfers quickly, which will cause light color, large dot expansion, high gloss dot deformation, uneven ink transfer, etc.; high viscosity, slow ink transfer, will affect the transfer performance of the anilox roller, resulting in ink color Unevenness, sometimes not deep color printing, dirty version, paste version and other drawbacks.

If the viscosity is low, it can be adjusted by mixing it with new ink; if the viscosity is high, it can be diluted with water or water and ethanol (50% each), and it can also be adjusted with an ink stabilizer. In addition, in the printing process, the temperature also has a great influence on the viscosity of the ink. Usually, the viscosity decreases when the temperature increases, and vice versa, the viscosity increases. Therefore, in the printing process, in order to keep the density of the printed products consistent, the temperature of the printing workshop should be kept constant.

pH value

The binder used in ink is mainly alkali-soluble acid resin, so the control of PH value is very important. Usually the PH value should be controlled between 8.5 and 9.5. At this time, the printing performance of the ink is the best, and the quality of the printed product is the most stable.

Since the amine is constantly volatilizing during the printing process, the operator has to add new ink and various additives from time to time, so the PH value of the ink is changing at any time. When the pH value of the ink is higher than 9.5, the alkalinity is too strong, and the viscosity of the ink will decrease, resulting in slower drying speed and poorer water resistance; when the pH value is lower than 8.5, the alkalinity is too weak, and the viscosity of the ink will increase. High, resulting in faster drying speed, easy to block the printing plate and anilox roller, cause the layout to be dirty, and will generate air bubbles.

Since the influence of PH value is directly related to viscosity, it is recommended to control the two in actual printing, especially in the process of register printing, this problem should be paid more attention. Usually in addition to the viscosity cup, a simple pH indicator should be prepared for testing at any time. When the pH value of the ink is low, a pH stabilizer or a small amount of alkaline substances can be added; when the pH value is high, a solvent or diluent can be added for dilution.

Thickness

The so-called thickness of the ink refers to the degree to which the solid powder substances such as pigments and fillers mixed in the linkage are dispersed.

The thickness of the ink is also a very important quality indicator, because it is not only related to the application properties of the ink (including tinting strength, hue, stability, etc.), but also to the rheological properties and economic benefits of the ink. If the ink is too thick, it will cause problems such as accumulation of ink and paste, and the tinting strength and hue of the ink will also deteriorate; if the ink is too fine, the fluidity will be great, and it will flow after printing. This flow will cause the dot to expand and affect print quality. In addition, the thickness of the ink will also affect its dispersion. When the dispersibility of the ink is not ideal, its printing performance will not be satisfactory, and the surface of the printed matter is not smooth, smooth and soft, and it will produce a "block" feeling, thus greatly reducing the printing effect.

In actual printing, inks of different thicknesses can be selected according to specific requirements. When printing the prints with finer screen lines and higher precision, the fineness of the ink is higher; when printing the prints or solid prints that do not require very high precision, the thickness of the ink can be appropriately reduced, which is also for the purpose of Reduce costs and improve economic efficiency.

dryness

The drying speed of the ink is not only related to the performance of the ink itself, but also related to the printing speed, the drying capacity of the drying equipment and the performance of the printing material. This article only considers the factors of the ink itself. The general principle for selecting ink dryness is that the ink should be able to dry sufficiently before the next print and before rewinding or stacking under the existing conditions of the printing press, but not on the printing plate.

Ink uses water as the solvent and alkali-soluble acid resin as the binder, which is mostly used for the printing of corrugated boxes and paper bags. Therefore, the drying forms are mainly infiltration drying and a small amount of volatilization drying. Since water is used as a solvent, its volatilization speed is lower than that of other solvents, so the drying of ink is slower than that of solvent-based ink. Therefore, a small amount of alcohol is usually added to the solvent to improve the drying speed of ink. In addition, under the condition that the solvent is determined, the selection of different types of resins also affects the drying properties of the ink. Because different resins have different curing speeds on the substrate and different release characteristics of the solvent, the drying properties of the ink are also different.

In practical applications, the dryness of the ink is also related to its viscosity and PH value. The ink is dry but the viscosity may be too high, which can be solved by further dilution; the ink dries quickly, and the pH value may be lower than 8.5, which can be adjusted by adding a stabilizer.

Previous: The difference between UV varnish and ordinary varnish

Next: no more

Back