2. two component condensation type RTV silicone rubber

Two-component condensation RTV silicone rubber is the most common type of RTV silicone rubber. Its raw rubber is usually polysiloxane at the hydroxyl end, which is combined with other compounds and catalysts to form a rubber. The viscosity of this rubber can range from 100 centistokes to one million centistokes. The vulcanization reaction of two-component RTV silicone rubber is not triggered by moisture in the air, but by catalyst. Usually, silicone rubber, filler, crosslinking agent is packaged as one component, catalyst is packaged as another component, or other combination methods, but the catalyst and crosslinking agent must be packaged separately. No matter what packaging method is used, curing begins only when the two components are completely mixed together. The crosslinking agent is ethyl orthosilicate and the catalyst is tin dibutyl dilaurate. Appropriate fillers and additives are added according to the nature of the desired final product. In recent years, because dibutyl tin dilaurate belongs to the medium toxic level of substances in many countries, in food bags and plasma bags are prohibited to add dibutyl tin, basically has been replaced by low toxic octyl tin.

The curing time of two-component condensation RTV silicone rubber mainly depends on the type, amount and temperature of catalyst. The more the catalyst dosage, the faster the vulcanization, and the shorter the shelving time. At room temperature, the shelving time is generally a few hours, if you want to prolong the shelving time of the glue, the cooling method can be used. The two-component condensation RTV silicone RTV rubber takes about a day to achieve complete curing at room temperature, but only 1 hour at 150℃. The curing rate of γ -aminopropyl triethoxysilane can be significantly increased by the synergistic effect. Two-component RTV silicone rubber can maintain elasticity in the temperature range of 65 ~ 250℃ for a long time, and has excellent electrical properties and chemical stability, water resistance, ozone resistance, weather aging resistance, in addition to simple usage, strong applicability of the process, so it is widely used as sealing and molding materials. All kinds of electronic and electrical components are coated and sealed with RTV silicone rubber, which can protect against moisture (anti-corrosion, shock and so on. Can improve performance and stability parameters. Two-component RTV silicone rubber is particularly suitable for deep encapsulation material and has a faster curing time, which is better than single-component RTV silicone rubber.

Two-component RTV silicone rubber has excellent anti-viscosity after vulcanization, and the shrinkage rate is very small when vulcanization, so it is suitable for manufacturing soft molds, used for casting molds of epoxy resin, polyester resin, polystyrene, polyurethane, vinyl plastics, paraffin wax, low melting point alloy and so on. In addition, the high simulation performance of two component RTV silicone rubber can be used to replicate all kinds of exquisite patterns. For example, it can be used to copy ancient bronze ware in the replication of cultural relics, and can be used to copy the skin patterns of animals such as snakes, pythons, crocodiles and pangolins in the production of artificial leather to distinguish the fake from the real.
The use of two-component RTV silicone rubber should pay attention to several specific problems: first of all, the base material, crosslinking agent and catalyst were weighed, and then mixed in proportion. In general, the two components should be provided in different colors so that the mixing of the two components can be visually observed, and the mixing process should be carefully handled to minimize the amount of gas attached. After the rubber material is mixed (uniform color), the bubbles can be removed by standing or decompressing (vacuum degree 700 mm hg). After all the bubbles are discharged, the rubber can be vulcanized into silicon rubber at room temperature or placed for a certain time at the specified temperature.

In addition to methyl, the side groups on the main chain of the two-component RTV silicone rubber can be replaced by other groups such as phenyl, trifluoropropyl, cyanoethyl, etc., in order to improve its low temperature resistance, heat resistance, radiation resistance or solvent resistance. At the same time, according to the need to add heat resistance, flame retardant, thermal conductivity, electrical conductivity additives, to prepare with ablative resistance, flame retardant, thermal conductivity and electrical properties of silicone rubber.