1.raw glue:
Silicone rubber raw rubber types are: 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) and fluorine silicon, nitrile silicone rubber. Most of the hot vulcanized silicone rubber is methyl vinyl silicone rubber, especially the vinyl dimethylsiloxane (vinyl double head) chain end sealing type is the main product type in the market.

Commercially available vinyl rubber is generally 110 methyl vinyl silicone rubber, according to its vinyl content is divided into 110-1,110-2 and 110-3 three models. Each model is divided into A and B grades according to molecular weight size.

The viscosity of raw rubber has a certain impact on the performance of vulcanized silicone rubber, the smaller the viscosity of raw rubber, the smaller the molecular weight, the higher the vinyl content (end). Low viscosity vinyl silicone oil has higher vinyl content and increased crosslinking points, which makes the crosslinking density large, so that the hardness of silicone rubber can be improved; With the increase of raw adhesive viscosity, the vinyl content decreased, the cross-linking point density decreased, and the rubber hardness decreased after vulcanization, but the trend slowed down.

At the beginning, with the increase of raw adhesive viscosity, the molecular weight of silicone rubber increases, the molecular chain increases, the molecular chain entanglement degree increases, the tear strength and elongation of vulcanized silicone rubber increase to the peak; At the same time, the possibility of sliding to each other is reduced with the increase of molecular chain entanglement, and the tear strength and permanent deformation of vulcanized silicone rubber are reduced after a small increase. However, when the raw adhesive viscosity continues to increase, the vinyl content is reduced, the crosslinking point is reduced, and the density of the crosslinking is reduced, which leads to the tear strength, elongation and tensile strength of the vulcanized silicone rubber is reduced, and finally tends to a stable value.


2, stuffing:
Adding filler can improve the mechanical properties of silicone rubber, and the amount of filler has great influence on the electrical and mechanical properties of silicone rubber. The fillers are generally inorganic substances, mainly white carbon black, titanium dioxide, quartz powder, kaolin, micronized talc and precipitated calcium carbonate. The reinforcement filler used in silicone rubber is mainly white carbon black, including vapor phase and precipitation method white carbon black. Silicone rubber raw rubber due to the low intermolecular cohesion energy density, the tensile strength of vulcanized rubber is only about 0.35MPa, almost no use value, it is necessary to use gas phase method or precipitation method of white carbon black reinforcement to improve the mechanical properties of vulcanized silicone rubber. With the increase of the amount of white carbon black, the tear and tensile strength of vulcanized silicone rubber increased, the hardness gradually increased and then decreased, and the volume resistivity gradually decreased.

Because the silicone compound itself has good insulation, the addition of filler will affect the molecular chain, making the resistivity of the vulcanized silicone rubber decrease. However, because the filler has a reinforcing effect, it can improve the mechanical properties of silicone rubber, making the hardness of silicone rubber increase, but if the filler is added too much, it will affect the cross-linking between the polymer molecular chains, making the hardness of silicone rubber reduced.


3, structure control agent
The silicone rubber material reinforced with gas phase white hair and black will harden during storage, reduce plasticity, and gradually lose the processing performance, which is called the "structuring" effect. The results show that the hardening degree of the compound is related to the specific surface area of silica and the isolated hydroxyl group on the surface of silica.

The reason: Due to the large specific surface area of white carbon black particles and the large amount of Si-OH group on the surface (the cohesion between particles is quite strong, and it is easy to agglomerate, which makes it difficult to disperse in silicone rubber rubber, which is not conducive to reinforcement), the active Si-OH group and its adsorbed water react with the silicone hydroxyl group and the residual alkoxy group at the end of the rubber molecule at room temperature. Some active hydroxyl groups can also form hydrogen bond chemisorption with silicone rubber molecular chains to form a three-dimensional network structure.

The compounding agents added to prevent and weaken this tendency to "structure" are called "structure control agents". The structure control agent can prevent or delay the structuring effect, because the active groups of these substances and the active hydroxyl group on the surface of silica condensation reaction, thereby preventing the interaction between silica and raw rubber.

Generally, two methods can be adopted: treatment of reinforced silica filler and addition of structural chemical control agents during mixing. However, the cost of dealing with white carbon black is too high, and most of them now use the method of adding structural chemical control agents to deal with white carbon black in situ when mixing. The addition of appropriate structural chemical control agents not only solves the processability and storage stability of silicone rubber rubber, but also significantly improves the comprehensive properties of tear resistance, elongation, rheology, etc., and can increase the amount of filler to reduce the cost while ensuring the performance of vulcanized rubber.


4. Release agent
Internal and external release agent. Most of the internal release agents will reduce the transparency of the compound, and can be added during the return process.