Introduction to Room Temperature Vulcanized Liquid Silicone Rubber RTV

1. Classification of Room Temperature Vulcanized Liquid Silicone Rubber

Room Temperature Vulcanized Silicone Rubber (RTV) has one or two functional groups at both ends of the molecular chain (sometimes in the middle). Under certain conditions (moisture in the air or appropriate catalysts), these functional groups can react to form a high molecular weight cross-linked structure. According to its vulcanization mechanism, it can be divided into condensation type and addition type; according to its packaging method, it can be divided into two types: two-component and one-component.

2. Room Temperature Vulcanized Liquid Silicone Rubber

It is the most common type of room temperature vulcanized silicone rubber. Its raw rubber is usually hydroxyl-terminated polysilane, which is combined with other compounding agents and catalysts to form a rubber compound. The viscosity of this rubber compound can range from 100 centistokes to 1 million centistokes.

3. Vulcanization method of room temperature vulcanized liquid silicone rubber

The vulcanization reaction of condensation-type two-component room temperature vulcanized rubber is not initiated by moisture in the air, but by a catalyst. Usually, silicone rubber, filler, and crosslinking agent are packaged as one component, and the catalyst is packaged as another component alone, or other combinations are used, but the catalyst and crosslinking agent must be packaged separately. Regardless of the packaging method used, curing will only begin when the two components are completely mixed together. The vulcanization reaction of the addition-type two-component room temperature vulcanized rubber is completed by the addition reaction of silicon-hydrogen bonds and silicon-vinyl groups in the presence of platinum metal catalysts.

4. Room temperature vulcanized liquid silicone rubber crosslinker

Condensation type silicone rubber The commonly used crosslinking agent is ethyl orthosilicate, and the catalyst is dibutyltin dilaurate. And add appropriate fillers and additives according to the properties of the desired final product. In recent years, many countries have banned the addition of dibutyltin in food bags and plasma bags because dibutyltin dilaurate is a medium-toxic substance, and it has basically been replaced by low-toxic octyltin.

The crosslinking agent of addition-type silicone rubber is generally an oligomeric silicon hydrogen compound. Catalyzed by Custer catalyst or aminoplatinic acid.

5. Curing time of room temperature vulcanized liquid silicone rubber

The curing time of two-component condensation-type room temperature vulcanized silicone rubber mainly depends on the type, dosage and temperature of the catalyst. The more catalyst is used, the faster the vulcanization and the shorter the shelf time. At room temperature, the shelf time is generally a few hours. If you want to extend the shelf time of the rubber, you can use the cooling method. It takes about a day for two-component condensation-type room temperature vulcanized silicone rubber to reach full curing at room temperature, but it only takes 1 hour at a temperature of 150°C. The curing speed can be significantly improved by using the accelerator y-aminopropyl triethoxyethane for synergistic effect.

6. Performance and application of room temperature vulcanized liquid silicone rubber

Two-component room temperature vulcanized silicone rubber can maintain elasticity for a long time in the temperature range of 65~250°C, and has excellent electrical properties and chemical stability. It is resistant to water, ozone and weathering. In addition, it is simple to use and has strong process applicability. Therefore, it is widely used as a potting and molding material. After various electronic and electrical components are coated and potted with room temperature vulcanized silicone rubber, they can play a protective role such as moisture-proof (corrosion-proof, shock-proof, etc.). It can improve performance and stability parameters. Two-component room temperature vulcanized silicone rubber is particularly suitable for deep potting materials and has a faster vulcanization time, which is superior to single-component room temperature vulcanized silicone rubber.

Two-component room temperature vulcanized silicone rubber has excellent anti-sticking properties after vulcanization, and the shrinkage rate during vulcanization is extremely small. Therefore, it is suitable for making soft molds for casting molds of epoxy resin, polyester resin, polyurethane, vinyl plastic, paraffin, low melting point alloy, etc. In addition, the performance of two-component room temperature vulcanized silicone rubber can be used to replicate various exquisite patterns. For example, it can be used to replicate ancient bronze artifacts in the reproduction of cultural relics, and it can be used to replicate the skin patterns of snakes, pythons, crocodiles and other animals in the production of artificial leather, which can make the fake look real.

7. Precautions for use

First weigh the base material, crosslinking agent and catalyst separately, and then mix them in proportion.

Usually the two components should be provided in different colors so that the mixing of the two components can be observed intuitively. The mixing process should be carefully operated to minimize the amount of entrained gas. After the rubber is mixed (uniform color), the bubbles can be removed by standing or decompressing (vacuum degree 700 meters column). After all the bubbles are discharged, it is placed at a certain time at a low temperature or at a specified temperature to vulcanize into silicone rubber.

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