What is modified silica gel? For example, SEP rubber is a variety of EPDM modified with silicone to improve the weather resistance and low temperature characteristics of EPDM. The performance is between silicone rubber and EPDM, and it has brand-new excellent performance in chlorine resistance and sponge foaming. In terms of mechanical strength in a high-temperature environment, especially tear strength, it is better than EPDM at temperatures above 100°C and comparable to high-strength silicone rubber. In addition, it has superior durability to silicone rubber in terms of steam resistance, hot water resistance, acid resistance and alkali resistance.

      Silicone rubber is a linear polysiloxane with high molecular weight. It has good flexibility and outstanding heat resistance. It is widely used as the basic polymer of coatings, but its mechanical strength is poor. Generally, it needs to be reinforced with reinforcing fillers before it can be used. . With the enhancement of people's awareness of environmental protection, water-based silicone rubber coating has become a development trend. White carbon black is often used as a reinforcing filler for liquid silicone rubber, but it has poor compatibility with water systems and cannot play a good reinforcing role in water-based silicone rubber coating systems. Silica sol is a silica colloid in the form of an aqueous dispersion. There are a large number of hydroxyl groups on the surface, which has good compatibility with aqueous systems, and the silicon hydroxyl groups on the surface of the silica particles can form a hydrogen bond with silicone rubber, thereby To a very good reinforcement effect.

      Silica sol needs a charge or other stabilizers to assist dispersion. It is a thermodynamically unstable system. During storage, it is easy to change from sol to gel due to changes in environmental conditions, and gelation, flocculation, or agglomeration occurs. Even at room temperature, high-purity silica sol can easily coalesce and cause agglomeration. At low temperatures, the silica sol will irreversibly precipitate and become invalid. In order to improve its stability and its dispersion uniformity with other components, it is usually necessary to modify its surface, through various organic functional groups to establish a covalent bond with the surface of the silica particles, so that it has a special surface activity And spatial stability. The most commonly used surface modifier is a silane coupling agent, the molecular structure is generally R′—Si—(OR)3, the R′ group is organophilic, and can be vinyl, alkylamino, alkylepoxy, etc. It can strengthen the affinity with silicone rubber; OR groups can be alkoxy, acetoxy, etc., can hydrolyze and react with silicon hydroxyl groups on the surface of silica.

      Taking the modification of KH560 as an example, the storage stability after modification of silica sol is significantly improved compared with that before modification. It can still recover the colloidal state quickly after undergoing multiple freeze-thaw cycles. Using methyl silicone rubber emulsion as the matrix and modified silica sol as the reinforcing filler, water-based silicone rubber coatings are prepared. With the increase of KH-560 concentration, the interaction between silica sol and methyl silicone rubber is enhanced. The mechanical properties are improved; as the amount of modified silica sol added increases, the cross-linking density of the aqueous silicone rubber coating increases and the mechanical strength increases.