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Defoamer is a material with low surface tension and high surface activity, which can inhibit and eliminate foam in liquid. That is, defoaming agent can reduce the surface tension of water, solution, suspension and so on, prevent bubbles from forming or remove the original foam. Long time antifoaming is also called antifoaming. The length of antifoaming time is the main sign of the quality of antifoaming agent. In most cases, the antifoaming agent is to use its antifoaming performance, rather than the initial antifoaming performance. Defoaming and antifoaming are relative, and products with good defoaming performance will have poor relative antifoaming performance. In practical application, it depends on the specific situation. So defoamers, including defoamers, antifoamers and defoamers, are generally called defoamers.
Some components of water-based adhesives are easy to produce bubbles, and tend to be stable and durable. In addition, the rapid mixing in production and the high speed brushing construction during use will also lead to foam production, which can not produce normal production and affect the quality of products. The formation of foam brings great difficulties to production and gluing, and causes porosity in the adhesive layer, which affects the external and adhesive properties of the product. Therefore, we must try to destroy the foam or prevent foam generation. The most effective way is to use defoamer.
There are many kinds of defoamers used in water-based adhesive industry, but they are mainly divided into two categories: polysiloxane defoamers and non siloxane defoamers.
Polysiloxane defoamers have strong defoaming and antifoaming ability and are widely used in coating industry. In the water-based adhesives industry, especially the emulsion type low viscosity system, such as film adhesive and pressure sensitive adhesive, it is easy to cause shrinkage holes and fish eyes. In addition, after the emulsion is film-forming, the surface migration of silane will cause the decrease of adhesive strength in the later stage, which will affect the bonding effect, so it is seldom used.
The defoamer of mineral oil is generally used in the industry of water-based pressure-sensitive adhesive and laminating adhesive. It is mainly composed of mineral oil, hydrophobic particles, low-carbon alcohol, emulsifier, etc. The quality of such products is easily affected by the differences in grades and batches of mineral oils. As the whole system is a thermodynamically unstable system, it is easy to stratification. It is mainly dispersed by emulsion in the emulsion to provide defoaming action. Affected by small molecular additives and surfactants in the emulsion, mineral oil defoamer is easy to float in these systems. Heavy, the uneven distribution of mineral oil will also affect the coating effect, which brings great trouble to our production and application.
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