Silicone rubber is classified into high temperature vulcanized silicone rubber (HTV) and room temperature vulcanized silicone rubber (RTV) according to its curing method. Due to the low bonding strength of high temperature vulcanized silicone rubber adhesives and the complexity of processing equipment, its application is greatly limited.

Since the advent of room temperature vulcanized silicone rubber in the early 1960s, it has grown faster and faster. The room temperature vulcanized silicone rubber has the advantages of oxidation resistance, high and low temperature resistance, cold resistance, ozone resistance, excellent electrical insulation and moisture resistance. At present, most of the basic compounds of silicone room temperature vulcanized silicone rubber are still hydroxyl terminated PDMS. According to its product packaging form, it can be divided into one-component and two-component room temperature vulcanized silicone rubber.

The one-component room temperature vulcanized silicone rubber is a cross-linking curing of the polyfunctional silicone after contact with moisture in the air, and forms a small molecule upon curing, thereby having a deacidification type, a dehydration type, a dealcoholization type, a deamination type, and a deketone. Type, deamidation type, etc. The crosslinking agent is a silane having two or more functional groups per molecule. Silane coupling agents are also commonly used as crosslinking agents.

The order of bonding performance of different cross-linking types is: deacetic acid type > amine type > ketone oxime type > amide type > alcohol type. The acetic acid type is low in cost and has good bonding strength to most materials. Neutral room temperature vulcanized silicone rubber develops rapidly due to its non-corrosive properties. Ketone type RTV has good adhesion and heat resistance and storage stability, and is odorless and non-corrosive. It does not use an organic carboxylic acid metal salt as a catalyst, and the vulcanized rubber is non-toxic. The use of a mixed crosslinking agent also contributes to an increase in the bonding strength. Commonly used catalysts are organic compounds such as tin, titanium, and platinum, amines, and carboxylates of organic lead, zinc, zirconium, iron, cadmium, barium, and manganese. The titanium complex catalyst can improve the bonding strength of the alcohol type RTV. The curing time can be controlled by adjusting the type and amount of the catalyst. Stannous octoate can gel the sealant in a few minutes, and tin dibutyl dilaurate can be geled within a few hours.

The cross-linking reaction of the one-component RTV starts with vulcanization by the surface of the rubber material contacting the moisture in the atmosphere and further diffuses inward, so the thickness of the rubber layer is limited. Two-component RTV is divided into two types: condensation type and addition type. The condensation type is carried out by the condensation of the hydroxyl group at the end of the silicone polymer with the hydrolyzable group in the crosslinking agent under the action of the catalyst organotin, lead, etc., and the condensation reaction is mainly There are two major types of dealcoholization and dehydrogenation, and the amount of catalyst is generally from 0% to 5%.

The addition reaction type RTV is obtained by hydrosilylation of a vinyl group-containing siloxane with a hydrogen-containing siloxane by a catalyst such as platinum or ruthenium, and the catalyst is effective at several ×10^6. The biggest advantage of two-component RTV is uniform vulcanization on the surface and inside, which can be deep vulcanized. However, the two-component RTV has poor bonding properties, and a silane coupling agent is often used as a primer or a tackifier to increase the bonding strength. The RTV polysiloxane molecules are spirally curled, the polarities of the silicon-hydrogen bonds cancel each other out, and the non-polar groups attached to the silicon atoms are arranged outside the helical silicon-oxygen backbone. Therefore, the strength and pair of the RTV itself The adhesion strength of various materials is relatively low. It is common to add reinforcing fillers such as fumed silica to increase the RTV strength. It is also possible to blend silicone rubber with other organic polymers or to change the silicone rubber main chain structure to increase its strength.