In the various processes of dyeing and dyeing, foaming is a difficult problem in the process of refining, bleaching, dyeing and finishing. The reasons for foaming are manifold. In the process of dyeing and dyeing the knitted fabric, there are different degrees of active substances, and the surface-acting gas is dispersed in the liquid to form a gas-liquid dispersion system. The gas in the liquid is continuously and sufficiently in contact with the liquid, the gas is the dispersed phase (discontinuous phase), the liquid is the dispersion medium (continuous phase), the density of the gas and the liquid differ greatly, and the foam quickly rises to the surface of the liquid, at this time The surface tension of the liquid is small, and the gas in the liquid breaks through the liquid surface and accumulates into the foam.
Destruction of harmful foam can be carried out by standing, decompressing (vacuum), warming or pressurizing, but when it is necessary to quickly and effectively eliminate the foam in a short time, it is necessary to add an antifoaming agent. Silicone defoamers are widely used in the textile industry because of their characteristics.
1) poorly soluble
Silicone oil has a special chemical structure and is a non-polar compound, so it is insoluble in water and polar compounds, and is incompatible with hydrocarbons or hydrocarbon-containing substances in the molecule, and thus is insoluble in the dyeing liquid.
2) low surface tension
Medium viscosity dimethyl silicone oil with a surface tension of 20-21mN/m2 and a water tension of 76mN/m2. The surface tension of silicone oil is much lower than that of dyeing and finishing solution. This is a strong silicone defoaming agent and widely used. One of the main reasons.
3) good thermal stability
Silicone antifoam can withstand temperatures of 150 ° C for a long time, can withstand high temperatures above 300 ° C for a short time, and its Si-O-Si main chain will not decompose, thus ensuring the silicone defoamer in the dyeing and finishing process. The operating temperature range does not fail within 0-100 °C.
4) Chemical and physiological inertiaThe silicone antifoaming agent does not chemically react with the dye and the finishing agent, does not affect the chemical properties of the dye and its aqueous solution, and is not damaged by the organism.