Effect of Additives on Ink Properties

Whether the quality of the printing ink is good or bad depends on the quality of the packaging and printing ink. Therefore, the surface state of the ink film is one of the main performance indicators of the ink. The ink film of printing ink is often caused by the appearance of orange peel, floating color, hair, air bubbles, shrinkage, pinholes, sag, water lines, and frost defects, resulting in poor quality packaging products. In order to prevent the surface failure of the ink film, additives such as leveling agents, anti-floating agents, defoamers, sag prevention agents, and white frost control agents are used.

The ink sagging is also called sinking, which means that the ink droops when printing on a vertical surface. In the sagging area, the thickness of the ink film becomes non-uniform, and a stacking phenomenon occurs. 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 the like.

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. After the ink is affected by certain factors, there is a difference in surface tension, and the ink film cannot reach a smooth and flat surface state, and unevenness 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 ink viscosity, ink film thickness, the 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. 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. They 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 been quietly introduced to the ink system with its own characteristics of almost no matting and direct addition, and it 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 ink viscosity 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. There are also treated ultra-fine calcium carbonate (mostly particle size 21μm-60μm, surface treated with fatty acids and resins, etc.) used in long oil alkyd inks, vinyl printing inks, the amount is too large, often affect the ink Water resistance of the membrane.

The organic system is swell-dispersed in the ink to form a network structure, giving the structural viscosity of the printing ink, making it thixotropic. In recent years, these additives have been used in a slightly smaller range than inorganic ones. The organic additives have little effect on the properties of the printing ink, and have good anti-subsidence properties, and can keep the ink in a good storage stable state. However, depending on the type of binder and the operating temperature of the ink system, the effect and stability will not be the same. For example, castor oil derivatives are often divided into two major categories: aliphatic and aromatic solvent inks and aliphatic oils. Coupled with the different manufacturers of the brand, the use of temperature is not the same. Its greatest feature is that if the temperature is too high, the additive dissolves and the operation can be stopped to allow the swelled particles to precipitate. After heating under shear to the desired temperature, it can be restored to a fully activated state, and a stable ink thixotropic agent can still be prepared.

Organically modified bentonite (containing more than 85% montmorillonite, with high-quality clay for various purposes), it is a layered clay with 2:1, the upper and lower layers are silica tetrahedron, and the middle layer is octahedron. Aluminum or magnesium is coordinated with six oxygen atoms or hydroxide radicals and is salty. The hydrogen bond structure is easily destroyed, resulting in a drop in viscosity; when the shear is removed, the hydrogen bond is restored and the viscosity is increased again. This is the basic principle that the organically modified bentonite can make the printing ink form a thixotropic fluid, and the bentonite has an anti-sinking effect. The reason for the effect. Metal soaps, which are organic thixotropes, have a large swelling gelling ability and exhibit a thickening effect even at a relatively low temperature. In non-polar solvents, metal soap thixotropes can form micelles due to coordination bonds, and these micelles can form a network structure, resulting in increased viscosity of the ink. However, a common disadvantage of this type of thixotropic agent is that the temperature and the solvent are different, the swelling effect is different, and the resulting gel structure is unstable. Especially when water and a polar solvent are mixed in, precipitation or precipitation of particles tends to occur. The advantage of this additive is that it can be used under weak shear force and temperatures of 40°C to 60°C.

To prevent poor scrapping of packaging and printing products, not only anti-settling and anti-sagging auxiliaries should be added, but also necessary leveling aids should be added to prevent the ink from shrinking, pinholes, bubbles, floating color, and white when printing. Frost failure.

Printing ink leveling agent: A general-purpose leveling agent for improving the leveling of the printing ink film (increasing the gloss and improving the film and compound flatness). After different printing inks are printed by different printing methods, there is a flow and dry film formation process, and finally a smooth, uniform ink film is gradually formed. Whether the printing ink film can achieve smooth and smooth characteristics is called leveling. In the actual packaging and printing process, we often have poor leveling properties, such as scratches, orange peel, and water marks during printing. Condensation, shrinkage, pinholes, and other phenomena that accompany the drying process are called poor leveling. These failures are related to the quality of the printing ink, the printing environment and the process. The general leveling agents are high boiling point aromatics, esters, ketones, ether alcohols and other solvents and mixtures thereof with excellent dissolving power, or a silicone resin that is miscible with the ink, such as polyurethane ink, etc. . Because its components do not use solvent or use less solvent, it is easier to produce faults with poor leveling. Therefore, polymer-type leveling agents such as cellulose acetate monobutyrate and polyacrylic acid are often used to improve ink performance. Its purpose is to reduce the viscosity of the ink and improve the leveling of the ink film.

Adding leveling agents tends to produce sagging as the flow increases, so an optimal range should be found between adjusting sagging and leveling.

The use of leveling agents will reduce the solid content of the ink, which is inconsistent with the development trend of today's development of high solids inks that save energy and reduce pollution. Therefore, the use of the additive, the design of mixed solvent-based inks, the appropriate amount of coupling agent to form a gradient, is a major trend in today's ink formulations. This not only overcomes the reduction of solids content, but also avoids the defect of dry film formation when a portion of slow-drying solvent with low volatility flows.

The role of induction leveling agent is to: reduce the interfacial tension between the ink and the substrate, improve the wettability of the ink on the substrate, and reduce the phenomenon of shrinkage, poor adhesion and other failure phenomena caused by the substrate. In addition, it has the property of migrating to the surface of the ink film, which can form a monolayer on the surface of the ink film, lower the surface tension, and balance the surface tension, thereby reducing various surface failure phenomena caused by the surface tension gradient difference. The third is to adjust the volatilization rate of the solvent in the ink, especially to design the gradient balance of the mixed solvent in the system.

Source: China Printing Packaging Network