Water-based inks, which can be diluted with water or ethanol, can be rinsed with tap water, but are capable of forming a water-resistant film after drying on the substrate. The biggest advantage of water-based ink is that it significantly reduces the emission of VOCs (organic volatiles) into the atmosphere, which can effectively reduce the harm of harmful solvents to the human body and the pollution of packaging products, especially suitable for food, beverages, medicines Packaging and printing of products with strict hygiene requirements, such as cigarettes. However, determined by the nature of its components, water-based inks have a notable feature - easy blistering. Foam can affect the smooth running of the printing process and the quality of the print.

Foams are dispersion systems in which gas is dispersed in a liquid. Foam is formed by the formation of agglomerated gas surrounded by a liquid film, and the process of foam destruction is the process of the liquid film separating the gas from thick to thin until it bursts. The factors affecting the stability of the foam mainly depend on the liquid film. The rate of thinning (ie the rate at which liquid is lost from the liquid layer) and the strength of the liquid film.

When the foam is formed, the surface area of the liquid increases, and the energy of the system increases; when the foam is destroyed, the surface area of the liquid decreases and the energy of the system decreases. Liquids are not prone to foam formation. However, low surface tension does not necessarily contribute to foam stabilization. Low surface tension can help stabilize the foam only if the liquid film is strong enough to form polyhedral bubbles.

Water-based inks are liquid inks, which are much thinner than offset printing inks, and are easily mixed with gas during the ink printing transfer process to generate foam. The vehicle of water-based ink is made of solution or emulsion resin, water and a small amount of ethanol and additives. The resin needs to undergo an ammoniation reaction to dissolve in water. This type of water-soluble resin has a soap-like structure and is prone to bubbles. In addition, in order to improve the adhesion of the water-based ink to the printing material, it is necessary to add some surfactants to reduce the system's

Surface tension, and lower surface tension will promote the formation of bubbles. Therefore, it is often necessary to add a defoamer when printing with water-based inks.

The use of antifoams is in conflict with measures to improve foam stability. Some defoamers achieve the purpose of defoaming through chemical reactions (for example, acids or calcium salts can destroy the soap film), while most defoamers further reduce the surface tension of the system, making it easy to spread and adsorb on the liquid surface. , thereby reducing the strength of the liquid surface film to achieve the purpose of defoaming. There are various types of defoaming agents. In addition to alcohols, fatty acids, phosphate esters, amides, etc., silicone oil is also a commonly used and excellent defoaming agent. It can be used in both aqueous and non-aqueous systems. The surface tension of silicone oil is extremely low. When added to an aqueous system, it will be preferentially adsorbed on the liquid film, so that the formed film has a lower surface tension than the surface of the original bubble-forming film. Reasonably, it is easier to generate bubbles, but because silicone oil defoamer is a short-chain hydrocarbon, although it has a lower surface tension, it can make the formed surface film very low in strength, which can promote bubbles to burst, thereby effectively eliminating Purpose of bubbles.