The research on injection molding technology of liquid silicone rubber began in the 1970s. The initial purpose was to prepare products with complex shapes, such as aerospace sealing parts. In the 1980s, liquid silicone rubber began to get the attention of all countries, and the demand increased sharply. Liquid silicone rubber injection molding not only has the advantages of low cost, low energy consumption, high production efficiency and automatic production, but also has good adaptability to temperature and can maintain good elasticity in a wide temperature range, so its application range is more and more extensive.

Addition molded liquid silicone rubber (LSR) is a kind of high-grade silicone rubber. Compared with condensed liquid silicone rubber, LSR has the advantages of no by-products in vulcanization process, minimal shrinkage, deep vulcanization, and better sealing at high temperature than condensed liquid silicone rubber. In addition, addition molded liquid silicone rubber (LSR) also has the advantages of simple process and low cost. This is because the liquid silicone rubber has small relative molecular weight, low viscosity and convenient processing and molding. It can save the processes such as mixing, preforming and finishing, easy to realize automation, save energy and labor, short production cycle and high efficiency. Although the raw material price of LSR is slightly higher than that of ordinary silicone rubber, the total cost is lower than that of ordinary silicone rubber, especially when manufacturing small products.

Process characteristics

Addition liquid silicone rubber (LSR) is usually composed of base rubber - polymethylvinyl siloxane raw rubber, crosslinking agent - polymethylhydrosiloxane, catalyst - complex of transition metals (such as platinum, nickel, rhodium, etc.), and other fillers can be added according to different uses, such as fumed or precipitated silica, iron oxide, titanium dioxide and carbon black. In order to prepare transparent addition liquid silicone rubber (LSR), silicone resin can also be added as filler. Addition molded liquid silicone rubber (LSR) is a kind of silicone rubber elastomer formed by bridging between SIH group in crosslinking agent and si-ch-ch2 group in base rubber.

The mixing and processing of rubber compound takes a certain time. If the reactant is cured in advance, the required shape and properties will not be obtained. This is more required for addition molded liquid silicone rubber (LSR). Therefore, it is required that there is almost no catalytic reaction before the vulcanization temperature, and the catalytic reaction can be carried out quickly after reaching the vulcanization temperature. The method of inhibiting the reaction is usually the addition of inhibitors.

The inhibitor can form a certain form of complex with platinum catalyst and affect the movement of reaction equilibrium. The effective inhibitor can be stored together with the compound for a long time and decomposes only when heated to the vulcanization temperature. There are two kinds of inhibitors: one is added to the compound as an additive to block its activity with platinum; The other is to prepare complexes (composite catalysts) with inhibitory ligands in advance to inhibit the catalytic activity of platinum. Alkynol compounds, nitrogen-containing compounds and organic peroxides with good compatibility are widely used.