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Production of compounded silica gel

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Hot vulcanized silicone rubber is a kind of silicone product with large output and wide application. Silicone rubber has excellent high and low temperature resistance, can be used for a long time in the range of -60 ~ 250 ℃, and also has excellent electrical insulation properties, ozone resistance, weather resistance, water repellency, moisture resistance, and good physiological inertia. 
Adding reinforcing filler, vulcanizing agent (or not adding first) and other auxiliaries to the hot vulcanized silicone rubber raw rubber, and mixing it into a mixed rubber, which can be processed into various silicone rubber by general rubber processing methods such as molding and extrusion. rubber products. 
Mixing silicone rubber can generally be prepared on a general-purpose rubber mill, and large-scale production is carried out in a kneader or closed mixing equipment. The following is the basic coordination process:

1. Mixing:  
When using an open mill for mixing, it is best to equip a dust-proof or ventilation device above the roll of the open mill to reduce the flying of silica. No other impurities or rubber particles should be mixed in during the mixing process, the temperature should be controlled below 40°C, and the cooling water should be fully opened. The open mill is slow to mix and eat powder, and the mixing time of each batch of rubber compound is about 20 to 40 minutes. Mixing with an internal mixer can not only improve production efficiency and reduce labor intensity, but also reduce the flying of silica and improve the operating environment. 
The mixing operation sequence of the internal mixer is basically similar to that of the open mixer, but the requirements for the interval time are not strict. The mixing time of each batch of rubber compound is about 8 to 18 minutes, and the filling factor of the internal mixer should be controlled within the range of 0.7 to 0.75. The degumming temperature is related to the type of filler, and should usually be controlled within the range of 50°C to 70°C. 

2. Heat treatment:  
When using fumed silica without surface modification as a reinforcing agent, a structure control agent must be added to the compound. Therefore, the heat treatment of the rubber compound has become a necessary process. The main purpose of heat treatment is to further combine the structure control agent with the silica surface (Si-OH) and eliminate low molecular volatiles in the glue. The general heat treatment conditions are: under nitrogen protection or in a kneader under reduced pressure at 160°C to 200°C for 1 to 1.5 hours. 

3. Filter: 
For extruded products, calendered products, glued products, and film products, mechanical impurities and undispersed compounding particles are one of the main factors that cause product quality problems. Therefore, the sizing materials used in the above-mentioned products must be filtered. A glue filter machine can be used for filtration, or an ordinary extruder can be used instead. The temperature of the barrel and screw should be controlled to the lowest level, and the size of the filter screen should be 120-200 mesh. 

4. Refinement:  
After the rubber compound is parked, because the gel content increases and the plasticity decreases, it must be re-melted during use. The back-melting of the rubber compound should be done in moderation, if the back-melting is insufficient, the flexibility of the rubber compound is poor, and the surface is not smooth; if the back-melting is excessive, the surface of the rubber compound will be sticky, which is not conducive to the operation.

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