(1) Moisture
     The moisture content of precipitation silica includes: free water and bound water. Free water on the surface of white carbon black is easily removed under heat. Too little free water indicates that there is not much light base on the surface of white carbon black, which reduces the activity of white carbon black, and promotes the white carbon black to aggregate during mixing, which is difficult to distribute in the rubber compound. Less surface water not only affects the vulcanization speed, but also reduces the reinforcement effect accordingly. The free water is slightly higher, the mixing rubber has good operation performance, the powder is eaten fast, the dust is less flying, the roll performance is also good, and the vulcanization speed is slightly faster. However, the water content is too high, the heat generation is large, it is easy to scorch, agglomerate, uneven dispersion, the surface of the vulcanizate is prone to air bubbles, and the physical and mechanical properties are correspondingly reduced. In general, the surface water at 6 to 8% can provide the best isolation for the silica molecules, thereby preventing the particles from re-aggregating, and being evenly distributed in the rubber compound during mixing, which is beneficial to the improvement of performance and the speed of vulcanization. Binding water is "internal" of white carbon black, which is relatively stable and can only be removed above 400 ° C. The general content is 4.0-7.0%. If the combined water is too much, it indicates that the gel content generated during the reaction is high, the activity of the finished product after drying is small, and the reinforcing effect on the rubber is also small. Too little combined water indicates that the dehydration is too heavy and the tendency of sanding is large, which is also not conducive to reinforcement.

(2) PH value
      The acidity and alkalinity of white carbon black have a greater effect on the vulcanization of rubber compounds. Acidic white carbon black latex compounds are vulcanized, and alkalinity promotes vulcanization. However, too high alkalinity is not conducive to reinforcement. White carbon black with a slightly acidic pH is beneficial to the tensile strength and abrasion resistance of rubber materials and products. Therefore, the precipitation value of white carbon black for rubber is generally 6-8, which is close to neutral.

(3) Surface modification
     The surface modification treatment of white carbon black refers to adding a coupling agent to the white carbon black to achieve the purpose of hydrophobicity. After the coupling agent is added, one end of the coupling agent, CH 3 O- (methoxy), easily reacts with the silanol group on the surface layer of silica, and the other end reacts with the gel molecule, that is, the coupling agent is in silica. "Bridge" between black and rubber. There are many ways to modify the surface of white carbon black. At present, the most common treatment is to use a silane coupling agent (such as Si-69).

(4) Influence of impurities
        Precipitation white carbon black is easy to bring in impurities such as Cu, Fe, and Mn during the preparation process. Although these trace impurities have little effect on the physical properties of the rubber compound, in order to make rubber products have excellent oxidation and aging resistance, Cu is still required , Fe, Mn content dropped to a certain limit. For this, GB 10517 stipulates the precipitation method of white carbon: Cu ≤ 30 mg / kg, Mn ≤ 50 mg / kg, Fe ≤ 1000 mg / kg.

     The sodium salt in the production of precipitation white silica is unavoidable in production, but the sodium content is too high to be used as a reinforcing filler for natural or synthetic rubber, and the transparency of the rubber is obviously not good. However, in the production process, the reaction synthesis process is controlled to prevent the formation of gels with too much Na + and strengthen the rinsing of the semi-finished slurry.The sodium salt content can be reduced to less than 0.5%. Such precipitation method has no effect on the rubber performance. Very influence,

in conclusion
1.The physical and chemical indexes of precipitation method of white carbon black directly affect various properties of rubber compounds, and the reinforcement depends on it

Particle size, structure, surface properties and types and content of impurities.

2. G B 10517 The specific surface area and particle size index of the precipitated hydrated silica (silica) for rubber are not specified in the technical conditions, which significantly affect the physical properties of the rubber. Manufacturers should strictly stabilize production operations and gradually improve the measurement and control measures.

3. Special attention should be paid to "anti-gelation" during the production of precipitation white silica. Only silica with extremely low "gel" content can have good activity and satisfactory physical and chemical indicators.