1、 Raw rubber:
The types of silicone rubber raw rubber include: dimethyl silicone rubber (referred to as methyl silicone rubber), methyl vinyl silicone rubber (referred to as vinyl silicone rubber), methyl phenyl vinyl silicone rubber (referred to as phenyl silicone rubber), fluorosilicone, nitrile silicone rubber, etc. The vast majority of hot vulcanized silicone rubber is made of methyl vinyl silicone rubber, especially the type of raw rubber with vinyl dimethyl siloxane (vinyl double head) chain segment sealing at the end of the molecular chain is the main product type in the market.

The commercially available vinyl rubber is generally 110 methyl vinyl silicone rubber, which can be divided into three types based on its vinyl content: 110-1110-2 and 110-3. Each model is further divided into two grades based on its molecular weight: A and B.

The viscosity of raw rubber has a certain impact on the properties of vulcanized silicone rubber. The lower the viscosity of raw rubber, the smaller the molecular weight, and the higher the (end) vinyl content. Low viscosity vinyl silicone oil has a higher vinyl content and an increase in crosslinking point, resulting in a higher density of crosslinking and an increase in the hardness of silicone rubber; As the viscosity of the raw rubber increases, the vinyl content decreases, the crosslinking point density decreases, and the hardness of the vulcanized rubber decreases, but the trend gradually slows down.

At the beginning, as the viscosity of the raw rubber increases, the molecular weight of the silicone rubber increases, its molecular chain grows, and the degree of molecular chain entanglement increases. After vulcanization, the tear strength and elongation of the silicone rubber increase and reach the peak; At the same time, the increase in molecular chain entanglement reduces the possibility of mutual sliding, and the tear strength and permanent deformation of vulcanized silicone rubber decrease after a small increase. But as the viscosity of the raw rubber continues to increase, the vinyl content decreases and the crosslinking point decreases, resulting in a decrease in the density of the crosslinking, resulting in a decrease in the tear strength, elongation, and tensile strength of the vulcanized silicone rubber, ultimately tending to a stable value.

2. Filler:
Adding fillers can improve the mechanical properties of silicone rubber, and the amount of fillers has a significant impact on the electrical and mechanical properties of silicone rubber. Fillers are generally inorganic substances, mainly including white carbon black, titanium dioxide, quartz powder, kaolin, micronized talc, and precipitated calcium carbonate. The reinforcing filler used in silicone rubber is mainly white carbon black, including gas phase method and precipitation method white carbon black. Due to the low intermolecular energy density of silicone rubber raw rubber, the tensile strength of vulcanized rubber is only about 0.35MPa, which has almost no practical value. It is necessary to use gas phase or precipitation method of white carbon black for reinforcement to improve the mechanical properties of vulcanized silicone rubber. As the amount of white carbon black increases, the tear and tensile strength of the vulcanized silicone rubber increases, the hardness gradually increases and then decreases, and the volume resistivity gradually decreases.

Due to the excellent insulation properties of organic silicon compounds themselves, the addition of fillers can affect the molecular chains, resulting in a decrease in the electrical resistivity of vulcanized silicone rubber. However, due to the reinforcing effect of fillers, the mechanical properties of silicone rubber can be improved, resulting in an increase in the hardness of silicone rubber. However, if too much filler is added, it will affect the cross-linking between polymer molecular chains, resulting in a decrease in the hardness of silicone rubber.

3. Structure control agent
Silicone rubber material reinforced with vapor phase white hair and black hair will harden during storage, reduce plasticity, and gradually lose processing performance, which is called the "structured" effect. The experiment shows that the degree of hardening of the adhesive is related to the specific surface area of silica and the isolated hydroxyl groups on the surface of silica.

The reason: due to the large specific surface area of the silica particles and the large amount of Si-OH groups on the surface (the cohesion between particles is quite strong, which is easy to agglomerate, making it difficult to disperse in the silicone rubber raw rubber, which is not conducive to reinforcement), the active Si-OH groups and their adsorbed water Condensation reaction with the silicone hydroxyl group at the end of the rubber molecule and the residual alkoxy group at room temperature, some active hydroxyl groups can also form hydrogen bonded chemical adsorption with the silicone rubber molecular chain, And form a three-dimensional network structure.

The complex agent added to prevent and weaken this "structural" tendency is called a "structural control agent". The structure control agent can prevent or delay the structural action because the active groups of these substances and the active hydroxyl groups on the surface of silica undergo Condensation reaction, thus preventing the action between silica and raw rubber.

Usually, two methods can be used: processing reinforced filler white carbon black and adding structured control agents during mixing. But the cost of treating white carbon black is too high, and now most methods use adding structured control agents during mixing to treat white carbon black on-site. The addition of appropriate structured control agents not only solves the processability and storage stability of silicone rubber blends, but also significantly improves the comprehensive properties such as tear resistance, elongation, and rheological properties of the blends. It can also increase the amount of fillers while ensuring the performance of the vulcanized rubber, thereby reducing costs.

4. Release agent
Separate internal and external release agents. Most of the internal release agents will reduce the transparency of the mixed rubber and can be added during the return refining process.