One-component room temperature vulcanized silicone rubber

The vulcanization reaction of one-component room temperature vulcanized silicone rubber is initiated by moisture in the air. The commonly used cross-linking agent is methyl triacetoxysilane, whose Si-O-C bond is easily hydrolyzed. Acetoxy and hydrogen groups in water are combined to form acetic acid, and hydroxyl groups in water are moved to the original acetoxy position to become trihydroxymethyl silane. Trihydroxymethylsilane is extremely unstable and easy to condense with linear organosilicon with hydroxyl end group to form cross-chain structure. Ordinarily, organosilicon raw rubber containing terminal group of silanol, fillers, catalysts, cross-linking agents and other complexes are put into sealed hoses. When used, they are extruded from containers, vulcanized into elastomers by means of moisture in the air, and low molecular weight substances are released at the same time. In addition to methyl triacetoxysilane, cross-linking agent can also be silane containing alkoxy, oxime, amino, amide and ketone groups. When crosslinking with alkoxy group, alcohol is released, which is called dealcoholic one-component room temperature vulcanized silicone rubber. When crosslinking with oxime group, oxime is formed, which is called deoxime room temperature vulcanized silicone rubber. Therefore, with the different crosslinking agents, one-component room temperature vulcanized silicone rubber can be deacid, deoxime, dealcoholic, deaminated, deamidated and deketone. Type A and many other varieties, but deacidification type is currently the most widely used one.

The curing time of one-component room temperature vulcanized silicone rubber depends on the curing system, temperature, humidity and the thickness of silicone rubber layer. Increasing the temperature and humidity of the environment can accelerate the curing process.  Under typical environmental conditions, the surface of silicone rubber can be non-sticky after 15-30 minutes, and the rubber layer with thickness of 0.3 cm can be cured in one day. The curing depth and strength will gradually increase in about three weeks.

One-component room temperature vulcanized silicone rubber has excellent electrical properties and chemical inertia, as well as heat resistance, natural aging resistance, flame resistance, moisture resistance, air permeability and other properties. They can keep elasticity for a long time in the range of - 60 - 200 C. It does not absorb heat and exothermic when curing, and has small shrinkage rate after curing, and good adhesion to materials. Therefore, it is mainly used as adhesives and sealants. Other applications include in-situ forming gaskets, protective coatings and seam materials. Many single-component silicone rubber adhesives exhibit automatic bonding properties to many materials such as most metals, glass, ceramics and coagulation. For bare aluminium, for example, the shear strength can reach 200 pounds/inch 2, and the tear strength can reach 20 pounds/inch 2 (0.35 joule/centimeter 2). When bonding is difficult, the bonding strength can be improved by undercoating on the substrates. The undercoating can be reactive silane monomers or resins. When they are cured on the substrates, a modified surface suitable for silicone bonding is formed.

One-component room temperature vulcanized silicone rubber is easy to use, but because its vulcanization is the moisture in the lazy atmosphere, the thickness of vulcanizate is limited, so it can only be used when the thickness of vulcanizate is less than 6 mm.

The vulcanization reaction of one-component RTV silicone rubber proceeds from the surface to the depth gradually. The thicker the rubber layer, the slower the curing. When the deep part also needs to be cured rapidly, the gradual vulcanization method of layered irrigation can be adopted, and some rubber can be added at a time, etc. after vulcanization, the total vulcanization time can be reduced. Magnesium oxide can accelerate the vulcanization of deep rubber.

Two-component RTV silicone rubber can be divided into condensation type and addition type.