Selection and application of silicone release agent (III)


3. Application in Rubber Forming Processing:






In rubber molding, the emulsion type release agent is the most widely used variety, and the solution product is used only when the drying time is fast and the production cycle is short. At present, the tire demoulding accounts for about 85% of all kinds of rubber products, and the air bag forming method is widely used in tire (outer tire) production. The latter is mainly composed of elastic rubber bag (with hot air nozzle) and steel mould. This method transfers pressure to the inner wall of tire through rubber elastic bag (capsule). The pressure of rubber bag always acts on the surface of pressed parts vertically, but has nothing to do with the surface finish of the latter. Because the outer wall of the tire is close to the steel mould, the tire will be formed after curing under heating and pressure. Finally, the tire will be removed by unloading the mould.


In the process of air bag forming, two kinds of release agents can be used: one is between the outer wall of tire and the steel mould, which is usually sprayed on the surface of the steel mould; the other is between the capsule (rubber bag) and the inner wall of tire, which is usually sprayed on the capsule or on the inner wall of tire. The latter requires more stringent release agents.


In general, the emulsion release agent made of high viscosity two methyl silicone oil can be used as a release agent for steel mold and capsule. However, during tire vulcanization, with the decomposition of vulcanizing agent, the residue will deposit on the surface of rubber bag, which makes the demoulding effect worse. Therefore, inorganic powder such as mica powder, talcum powder and calcium carbonate should be added to silicone oil demoulding agent to effectively improve the demoulding effect and the fluidity under extrusion, making the rubber bag easier to move from inside of tire. Peel off and take out, thereby effectively prolonging the service life of rubber bags. However, the addition of inorganic powder such as mica will also bring the defect of tread whitening.


At present, capsule isolators based on modified silicone oil have been developed in China. Different types of release agents with two and one components can be selected according to different production processes of tire factories.


In addition to emulsion release agents, solution type, especially room temperature vulcanized silicone rubber products, have also been widely applied. Various rubber products treated with siloxane release agent can also effectively improve the surface gloss and wear resistance.