Effect of Hanging Agent and Leveling Agent on Ink Properties (I)

The quality of packaging and printing ink film determines the quality of printed products, so the surface state of the ink film is one of the main performance indicators of ink. The ink film of the printing ink is often caused by the appearance of orange peel, floating color, hair, air bubbles, shrinkage, pinholes, sagging, water lines, and frost defects, resulting in poor packaging products. In order to prevent the surface failure of the ink film, it is necessary to use a leveling agent, an anti-floating agent, an anti-foaming agent, an anti-sagging agent, and a frost-controlling agent. This article will focus on the sagging and leveling of printing ink graphic ink film.

The ink sagging is also called sinking. Only the p refers to the sagging of the ink when printing on the vertical surface. In the sag region, the thickness of the ink film becomes non-uniform and a stacking phenomenon occurs. We know that the shapes of the sag are various, some are larger in the form of curtains, and some are in the form of water lines, water columns, corrugations, swirls, and so on.

The occurrence of ink sagging failure is often directly related to the rheological properties such as the solid content, viscosity, thickness of the printed picture film, and the yield value of the ink in the printing ink system. The low viscosity of the packaging printing ink and the thick film of the ink contribute to the leveling and sagging. The ink system has many solid contents and high viscosity. The thin ink film is printed, which helps to prevent sagging, but it is not easy to level out. . Sagging and leveling are often contradictory, and the preventive agent for preventing sagging is the ability to form a net structure by printing a secondary bond in the printing ink, so that the printing ink obtains a structural viscosity and becomes a thixotropic fluid. Conflicting effective additives.

The leveling of the ink film is a process in which, after the printing ink is printed and even after the film is coated, the ink film has not yet dried to a solid state, the surface tension gradually shrinks to a minimum area. Ink is affected by certain factors,. When the surface tension is poor, the ink film cannot reach a smooth and smooth surface state, and uneven flow occurs. This phenomenon is called ink leveling defects or uneven failure. After the ink film is dried, the surface may have irregular surface conditions such as orange peel, scratches, corrugations (water marks), shrinkage, and pinholes. The ink film leveling requires time, increases with increasing ink viscosity, scratches, and wavelength, and decreases with increasing surface tension and ink film thickness. For this reason, it is necessary to add a leveling agent to solve the problem of preventing the occurrence of the above-mentioned trouble in the printing ink film. The additive is an additive added to the ink to make the ink form a smooth and smooth ink film after printing. The additive only seeks results and does not look at the leveling process.

Factors affecting the sagging and leveling of the ink film The ink viscosity, ink film thickness, width and depth of the print, and the interfacial tension between the ink and the substrate of the substrate directly affect the sagging and leveling of the graphic ink film.

Practice has already told us that the thicker the ink film, the higher the peak, the greater the surface tension of the ink, and the longer the wavelength (watermark) of the print when printing the package, indicating that the time for leveling will be longer. For this reason, it is necessary to introduce anti-sag agents and leveling agents into the ink system. Because of the increasing demand for pollution-free, energy-saving, and resource-saving technologies, solvent-based inks are gradually being developed for high-solids, water-soluble, powder, solvent-free, and radiation-curable printing inks. In the ascendant packaging printing ink auxiliaries is in the "import, screening, imitation, innovation" eight-character principle, the thixotropy anti-settling additives for ink, ink leveling and bright additives put forward new requirements to adapt to these novel inks. The ink additives needed for the variety will be improved and improved in practical applications.

Anti-sagging agent

It is mainly a thixotropic agent. Its function and mechanism are auxiliaries that can increase the viscosity of liquid inks and make them thixotropic, which are collectively referred to as thixotropic agents. Organic bentonite, hydrogenated castor oil, polyvinyl alcohol, fumed silica, metal soap, etc. are thickening thixotropic agents for organic systems; cellulose derivatives such as hydroxyethyl cellulose, polyvinyl alcohol are used in aqueous ink systems. Water-soluble resins such as polyacrylic acid are thickeners; thixotropic agents are used in packaging printing inks to make them thixotropic and thixotropic, also known as false thickening, that is, high-speed operation of inks in ink dispersion machines or printing machinery. When the shear force acts (such as when stirring or printing), the viscosity temporarily decreases. Without shear force, it gradually returns to its original viscosity. This feature can make the ink in the storage, to prevent the precipitation of pigments, fillers, in the printing process to prevent the ink sag caused by water lines, scratches and other defects - that is, in the packaging printing can make the ink thicker without transfer Hangs, and prevents ink penetration or dirtying when porous web materials are printed. Although increasing the resin content can also eliminate watermarks and scratches, the addition of trace additives is convenient and economical for inks that have been stored for use.

Ink thixotropes on the market are often divided into: inorganic (that is, additives that can form a colloidal dispersion structure in the ink, synthetic ultra fine silica bentonite, organic modified bentonite, surface-treated ultrafine calcium carbonate, etc.) Organic compounds (ie, additives that can form a swelling dispersion structure in the ink and enable the pigment to form a flocculation structure. The former include hydrogenated castor oil wax, metallic soap, benzylidene sorbitol, and vegetable oil-based polymeric oil. For surfactants).

Inorganic is dispersed in the ink in a colloidal state, relying on the dispersed colloid to form a network structure to achieve the purpose of anti-settling and thixotropic. The ink industry mostly chooses polyethylene wax (the product is produced by free radical polymerization of ethylene and other monomers under high pressure, and also produced by high molecular polyethylene degradation reaction). Because the additive functions as a protective colloid, it forms a stable colloidal structure together with the pigment, which constitutes a thixotropy that acts as an anti-sinking effect, and at the same time it also has a slightly anti-sagging effect. In recent years, polytetrafluoromethane has quietly introduced the ink system with its own characteristics of almost no matting and direct addition, and has a tendency to replace polyethylene wax.

Ultra-fine silica (which belongs to colloidal particles with silanol groups on the surface, but the ultra-fine silica surface produced by the wet and thermal methods of production contains different amounts of silanol groups, usually more wet than hot ). As we all know, due to the small content of silanol groups and the large space, it can not be used as an anti-settling agent because it cannot form hydrogen bonds. The silanol groups are mostly due to the small distance between the hydroxyl groups, and they easily form hydrogen bonds. That is, the more hydrogen bonds, the stronger the gelation effect. After adding the ink system, the three-dimensional network structure can be destroyed under the shear force of printing. , thereby reducing the viscosity of the ink. When stationary, the viscosity of the ink can be restored. Although the speed of viscosity recovery in different polar media is different, for example, in non-polar ink solvents such as hydrocarbons, halogenated hydrocarbons and the like, the viscosity recovery is even a fraction of a second. Aerosilcok 84 is available on the market in general non-polar solvent inks with mild thixotropic properties, and Aerosil 300 is a familiar thixotropic anti-settling additive. Usually depending on the type of ink and the solvent used, the amount of addition is controlled between 0.5% and 3%. Tianyang Chemical Factory's TM-27 coupling agent can effectively prevent floating color and hair growth.

(to be continued)