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 methyltriacetoxysilane. Its Si-O-C bond is easily hydrolyzed. The acetoxy group combines with the hydrogen group in the water to form acetic acid, and the hydroxyl group in the water is moved to the original acetoxy group. position, it becomes tri-hydroxymethylsilane. Tri-hydroxymethylsilane is extremely unstable and easily condenses with linear silicone with hydroxyl end groups to form a cross-linked structure. Usually, the organic silicone rubber containing silanol end groups and various compounding agents such as fillers, catalysts, and cross-linking agents are put into a sealed hose. When used, it is extruded from the container and vulcanized with the help of moisture in the air. Elastomers also release low molecular weight substances. In addition to methyl triacetoxysilane, the cross-linking agent can also be a silane containing an alkoxy group, an oxime group, an amine group, an amide group, or a ketone group. When it is cross-linked with an alkoxy group and releases alcohol, it is called a dealcoholized one-component room temperature vulcanized silicone rubber. When it is cross-linked with an oxime group, an oxime is generated, which is called a deoxime type room temperature vulcanized silicone rubber. Therefore, with the cross-linking Depending on the agent, single-component room temperature vulcanized silicone rubber can be of many varieties such as deacidification type, deoxime type, dealcoholization type, deamination type, deamidation type and deketone type, but the deacidification type is currently the most widely used. A sort of.
The vulcanization time of one-component room temperature vulcanized silicone rubber depends on the vulcanization system, temperature, humidity and thickness of the silicone rubber layer. Increasing the temperature and humidity of the environment can speed up the vulcanization process. Under typical environmental conditions, generally after 15 to 30 minutes, the surface of the silicone rubber can become non-sticky, and a 0.3 cm thick adhesive layer can be cured within one day. The depth and strength of the cure gradually builds up over about three weeks.
One-component room temperature vulcanized silicone rubber has excellent electrical properties and chemical inertness, as well as heat resistance, natural aging resistance, flame resistance, moisture resistance, breathability and other properties. They can maintain elasticity for a long time in the range of -60~200℃. It does not absorb or release heat when curing, has a small shrinkage after curing, and has good adhesion to materials. Therefore, it is mainly used as adhesives and sealants, but other applications include form-in-place gaskets, protective coatings and caulking materials. Many one-component silicone rubber adhesives are formulated to exhibit self-bonding properties on a variety of materials such as most metals, glass, ceramics and concrete. When bonding is difficult, a primer can be applied on the base material to improve the bonding strength. The primer can be a reactive silane monomer or resin. When they are cured on the base material, a layer of modified suitable on silicone bonded surfaces.
Although one-component room temperature vulcanized silicone rubber is easy to use, its vulcanization depends on moisture in the atmosphere, so the thickness of the vulcanized rubber is limited and can only be used in situations requiring a thickness of less than 6 mm.
The vulcanization reaction of one-component room temperature vulcanized silicone rubber proceeds gradually from the surface to the depth. The thicker the rubber layer, the slower the curing. When the deep part needs to be cured quickly, the layered pouring and gradual vulcanization method can be used. Some rubber can be added each time and then added after vulcanization, which can reduce the total vulcanization time. Adding magnesium oxide can accelerate the vulcanization of deep glue.