Both ends of the main chain of RTV silicone rubber contain active functional groups such as hydroxyl or acetoxy groups. Under certain conditions, these functional groups undergo condensation reaction to form cross-linking structure. According to the curing mechanism, it can be divided into one component RTV silicone rubber and two-component RTV silicone rubber.

a. One component room temperature vulcanized silicone rubber vulcanization system with hydroxyl terminated silicone rubber can use silane containing hydrolyzable group as crosslinking agent. In the presence of condensation catalyst, the condensation reaction occurs and Si-O bond crosslinking is formed.

Flow chart of silicone rubber condensation reaction.

Types and characteristics of crosslinking agents for one component systems.

In addition to the type of crosslinking agent, the curing rate of one component system is greatly affected by air humidity and ambient temperature.

The vulcanization of one component system starts from the surface layer contacted by air, and gradually goes to the deep layer. Generally, the thickness of vulcanization layer is less than 1cm. In order to accelerate vulcanization and prepare thick layer products, magnesium oxide or layered construction can be added.

b. The vulcanization system of two-component RTV silicone rubber consists of crosslinking agent and catalyst. In the presence of catalyst, the hydroxyl groups of the silicone rubber react with the functional groups of the crosslinking agent to form a silicon oxygen bond.

The commonly used crosslinking agents are ethyl orthosilicate (propyl ester), n-butyl titanate, methyltriethoxysilane or their partial hydrolytic condensates. Commonly used crosslinking catalysts include organometallic salts, such as dibutyldilaurate, dibutyldiacetic acid, octanoate, isooctanoate, lead octanoate, etc., and their sulfurization process (165 ~ 166 pages).

In the preparation of rubber compound, part of raw rubber, crosslinking agent and filler are usually mixed into one component, while the remaining rubber, filler and catalyst are mixed into another component. When used, the two components are mixed according to the calculation regulations, so it is called two-component room temperature vulcanized silicone rubber.

The dosage of crosslinking agent is generally 2 ~ 10 phr; The amount of catalyst is 0.1 ~ 5 phr. Examples of curing system formula: room temperature vulcanized silicone rubber 100 phr, dibutyl tin dilaurate 0.4 phr; 0 phr.

The sulfurization rate of the two-component system mainly depends on the type and amount of catalyst, and is also affected by air temperature and ambient temperature. In addition, amine accelerant can also be used as cocatalyst to accelerate its vulcanization.