(1) Silicone rubber products are generally used at high temperatures, and their compounding agents should be stable at high temperatures. For this reason, inorganic oxides are usually used as reinforcing agents.
(2) The silicone rubber sheet is a raw rubber with high saturation, and usually cannot be vulcanized with sulfur, but hot vulcanized. Thermal vulcanization uses organic peroxide as a vulcanizing agent, so the silicone rubber sheet compound must not contain active substances that can interact with peroxide decomposition products, otherwise it will affect the vulcanization.
(3) Silicone rubber sheets are prone to cleavage and rearrangement of siloxane bonds under the action of a small amount of polar chemical reagents such as acids or bases, resulting in a decrease in heat resistance of the silicone rubber sheets.
Therefore, when selecting the compounding agent, the acidity and alkalinity of the silicone rubber sheet must be considered, and the acidity of the peroxide decomposition product should also be considered, so as not to affect the performance of the vulcanizate.
(1) Selection of raw rubber
When designing the formula, raw rubber with different characteristics should be selected according to the performance and use conditions of the product. For general silicone rubber products, vinyl silicone rubber can be used when the operating temperature is within the range of -70°C to 250°C;
When the use temperature of the product is required to be high, low phenyl silicone rubber can be used; when the product requires high and low temperature resistance and resistance to fuel or solvent, fluorosilicone rubber should be used.
(2) Vulcanizing agent
The vulcanizing agents used for heating and vulcanizing silicone rubber sheets mainly include organic peroxides, aliphatic azo compounds, inorganic compounds, high-energy rays, etc., among which organic peroxides are the most commonly used.
This is because organic peroxides are generally stable at room temperature, but can be rapidly decomposed and produce dissociation at higher vulcanization temperatures.
(3) Reinforcing agent
The strength of the unreinforced silicone rubber sheet vulcanizate is very low, only about 0.3MPa, and has no actual use value.
The strength of the vulcanizate of the silicone rubber sheet can reach 3.9-9.8MPa by using the appropriate reinforcing agent, which is extremely important to improve the performance of the silicone rubber sheet and prolong the service life of the product.
The selection of reinforcing fillers for silicone rubber sheets should take into account the high temperature use of silicone rubber and the use of peroxide vulcanization, especially the adverse effects of acidic and alkaline substances on silicone rubber.
Reinforcing fillers for silicone rubber sheets can be divided into reinforcing fillers and non-reinforcing fillers according to their reinforcing effects. The diameter of the former is 10 ~ 50nm, the specific surface area is 70 ~ 400m2 / g, and the reinforcement effect is good; The latter is 300 ~ 10000 nm, the specific surface area is less than 30m2 / g, and the reinforcement effect is poor.