Water-based inks are prone to blistering, defoamer in water-based inks
Water-based ink, can be diluted with water or ethanol, can be rinsed with tap water, but printed on the substrate after drying but can form a water-resistant film layer. The biggest advantage of water-based inks is the obvious reduction of VOC (Volatile Organic Compounds) emissions into the atmosphere, which can effectively reduce the harmful effects of harmful solvents on humans and pollution of packaging products, especially suitable for packaging printing of food, beverages, pharmaceuticals, cigarettes and other products with strict hygiene requirements. However, due to the nature of its components, water-based inks have a distinctive feature – they are prone to foaming. Foaming affects the smooth running of the printing process and the quality of the printed product.
Foam belongs to the dispersion system of gas dispersed in liquid. Foam is the formation of a mass of gas surrounded by a liquid film, and the process of foam destruction is to separate the gas from the liquid film from thick to thin, until the rupture of the process, the factors affecting the stability of the foam, mainly depends on the speed of thinning of the liquid film (that is, the rate of liquid loss in the liquid layer) and the strength of the liquid film.
In the foam generation, the surface area of the liquid increases, the system energy increases; foam destruction, the surface area of the liquid shrinks, the system energy decreases, from the energy point of view, reduce the surface tension of the liquid is conducive to the formation of foam, and has a high surface tension of the liquid is not easy to form foam. However, the low surface tension does not necessarily contribute to the stability of the foam. Only when the liquid film has a certain strength, can form polyhedral bubbles, low surface tension to help the stability of the foam.
Water-based ink is a liquid ink, much thinner than offset ink, in the ink printing transfer process is easy to mix into the gas and generate foam. Water-based ink linkage material by the solution or emulsion type resin, water and a small amount of ethanol and additives made. Resin needs to be dissolved in water by ammonia reaction, such water-soluble resin has a soap-like structure, easy to produce bubbles. In addition, in order to improve the adhesion of water-based inks to the substrate, it is necessary to add some surfactants to reduce the surface tension of the system, and the lower surface tension will promote the generation of bubbles. Therefore, it is often necessary to add defoamers when printing with water-based inks.
The application of defoamers is in conflict with measures to improve foam stability. Some defoamers are chemical reactions to achieve the purpose of defoaming (such as acid or calcium salts can destroy the soap film), while most defoamers are by further reducing the system surface tension, so that they are easy to spread and adsorption on the surface of the liquid, thereby reducing the strength of the liquid surface film to achieve the purpose of defoaming. Defoamer types are diverse, in addition to alcohols, fatty acids, phosphate, amides, etc., silicone oil is also a commonly used excellent defoamer.
It can be used in both aqueous and non-aqueous systems. The surface tension of silicone oil is extremely low, and when added to aqueous systems, it will be preferentially adsorbed on the liquid film, so that the film formed has a lower surface tension than the original bubble-forming film surface. As a rule, this is more likely to produce bubbles, but because silicone oil defoamer is a short-chain hydrocarbon, although it has a lower surface tension, but can make the formed surface film strength is very low, and thus can promote the rupture of bubbles, so as to effectively achieve the purpose of eliminating bubbles.