Silicone rubber refers to a kind of elastomer whose molecular main chain is -Si-O-inorganic structure and side chain is organic group. Its high and low temperature resistance is good, and its use range is about -100℃ ~ 300℃. Its high temperature resistance is similar to fluorine rubber, and its low temperature resistance is the best among the rubber materials used. Excellent weathering resistance; With excellent biomedical properties and moisture resistance; With excellent electrical insulation performance, can be used as high insulation products. However, the mechanical properties of silicone rubber, especially the tear strength, are low due to the weak interaction between molecular chains, as shown in the figure below. In automotive, consumer goods, electronics, aviation, medical and other fields, a large number of silicone rubber products are small parts with complex structures, requiring high tear resistance. Therefore, how to effectively improve the tearing strength of silicone rubber, so that its physical and mechanical properties meet the requirements of use.

How can the tearing strength of silicone rubber be improved? The tearing strength of silicone rubber is mainly affected by raw rubber, reinforcing agent and curing agent.

Raw rubber

When the vinyl mole fraction of the silicone rubber is lower than 0.15 %, the tear resistance of the silicone rubber can be improved by selecting the appropriate ratio. When the vinyl mole fraction of silicone rubber is 0.15 % and the vinyl mole fraction of silicone rubber is 0. 06 %, the vinyl mole fraction of silicone rubber is 0. 105 %, and the tear strength is the highest, reaching 45.8 kN/m. When the vinyl mole fraction of silicone rubber exceeds 0.15 %, the ratio of silicone rubber has little effect on the tearing performance of vulcanized rubber.

Reinforcing agent

The most important factor affecting tear strength is reinforcement system. Commonly used reinforcement agents are gas phase silica and precipitated silica, among which the reinforcing effect of gas phase silica is better than precipitated silica. According to the influence of silica particle size on the reinforcing effect, the smaller the particle size, the larger the specific surface area, the stronger the adsorption capacity of rubber molecules on silica surface, the better the reinforcing effect. According to this principle, gas phase silica with smaller particle size should be selected as far as possible. Therefore, silica modification is also the main way to improve the tearing strength of silicone rubber.

Vulcanizing agent

The vulcanizing agent commonly used for silicone rubber is peroxide, double 24 for molding and double 25 for extrusion. Taking Elkem silicone HCR 9170 UE as an example, the tear strength of the first section after adding platinum vulcanization agent reaches 47.8kN /m, which is higher than that of peroxide vulcanization. Therefore, the tearing requirements of high products can be considered platinum vulcanizing agent.

Application of high tear resistance silicone rubber

1. Car lifting lug;

2, mobile wire, scratch resistant cable sheath;

3, alloy mold;

4, baby pacifier;

5, complex products, demoulding easy to tear products, such as automobile dust cover;

6, mixed with other rubber to prepare cots (improve tearing, prolong service life).