The particle size of precipitation method is divided into primary particle size and secondary structure particle size. Generally speaking, the secondary structure of silica is broken during the compounding process of the rubber, so the most important factor affecting the performance of the rubber compound is the original particle size. The original particle size of the precipitation method is 8-110nm. If the particle size is small, the dispersion performance is good, and the effective area in contact with the rubber is also large, which is obviously beneficial to rubber reinforcement. From the rubber reinforcement mechanism, the amount of OH in the surface layer of silica is directly related to the reinforcement effect.

The American chemist R · K · ILer summarized the following rules in the study of the relationship between the size of the primary particles of hydrogel and the number of hydroxyl groups. This law revealed the effect of the particle size of silica on the strength of rubber compounds (see Table 1). It can be seen that the smaller d, the more active groups, the stronger the interaction between particles and rubber, and the stronger the strength.

The structure of white carbon black is similar to carbon black. It is spherical. Individual particles are in surface contact with each other and are connected in branches and chains. This structure is called "secondary structure". The chain structure also acts with hydrogen bonding forces to form clusters of aggregates. This structure is reversible when damaged by external forces. Its structural size is reflected by the oil absorption value (oil absorption value refers to the adsorption of 1 g of white carbon Dibutyl phthalate (DBP) in milliliters). The larger the oil absorption value, the higher the structure. The larger the structure, the more the branched structure of silica in aggregate state, and the better the reinforcing effect on rubber. However, the precipitation method white carbon black with high oil absorption value needs to consume more work and energy to break the branch structure when mixing in the rubber compound, which makes it evenly dispersed in the rubber. This obviously requires extending the rubber compounding. Refining time. White carbon black oil absorption value of 2.0-3.5cm3 / g can meet the requirements of tires.

The specific surface area of precipitation method white carbon black is also an important indicator reflecting the structure of the product. Although the current national standards take into account that the test conditions of various manufacturers do not compare the surface area with specific indicators, they are only divided into six categories: A, B, C, D, E, and F according to the value. According to the national quality survey of hydrated silica (silica) used in the precipitation of rubber over the years, the comprehensive physical properties of the rubber compound are classified as type B (161-190m 2 / g) silica, but only "reinforcing" ", Class A (≥190m2 / g) with a higher specific surface area is better. However, in the practice of production and use, self-carbon black with high specific surface area often encounters poor physical properties, which is caused by the production of many silicon gels during the production of white carbon black.

The influence of the specific surface area of precipitation method on the physical properties of rubber compounds. In terms of mechanism, a large specific surface area can allow rubber materials and accelerators to obtain better penetration opportunities, thereby performing a series of physical and chemical reactions to obtain better Transparency and physical properties. However, white carbon black with a large specific surface area has a very high adsorption rate and high activity. It can adsorb more accelerators and accelerate the decomposition of the accelerators. Therefore, it has a strong retarding effect on the vulcanization of the rubber compound, which needs to be appropriately increased Accelerator dosage to increase vulcanization speed. In actual production, it is often used to increase the active agent to reduce the strong adsorption of an OH group on the surface layer of silica to the accelerator molecules. In addition, the precipitation method white carbon black with too large specific surface area generates high heat during rubber processing, and the rubber tends to be sticky.