When designing the formula of extrusion compound, emphasis should be placed on reducing the elastic recovery of the compound and reducing the expansion rate of the mouth during extrusion.
(1)The rubber content should be low, the rubber content of 30% to 50%, the extrusion performance is good, and the extrusion surface is smooth. The addition of filler can reduce the glue content and reduce the elastic deformation of the glue. Among them, the most suitable fillers are high structure and high wear resistance furnace black, fast pressure oven black, semi-reinforced furnace black, calcium carbonate, magnesium carbonate, clay and so on.
(2) The use of recycled rubber: the use of recycled rubber has the tendency to reduce extrusion deformation, accelerate extrusion speed, reduce extrusion temperature and reduce scorch.
(3) With lubricating softener: with grease, mineral oil, stearic acid, paraffin, paraffin oil and other lubricating softener, has the effect of reducing mouth resistance, improving the extrusion speed, making the surface of semi-finished products smooth. On the contrary, if the addition of rosin, asphalt, etc., which has a large viscosity increasing effect, it will reduce the extrusion speed and cause the phenomenon of glue flow congestion.
When designing a good adhesive formula, the following points should be paid attention to：
(1)The selection of good self-adhesive rubber: the molecular chain activity is large, the rubber with high rubber strength has good self-adhesive. Among the commonly used raw rubber varieties, the best self-adhesive is natural rubber, followed by neoprene rubber, followed by butadiene rubber, styrene butadiene rubber, nitrile rubber and so on.
(2) The selection of plasticizer with large viscosity increasing effect: the addition of plasticizer with large viscosity increasing effect can increase the activity of rubber molecular chain and improve the adhesive property.
(3) The selection of filler with large reinforcement: adding active filler with large reinforcement can increase the strength of the adhesive, thus improving the self-adhesive force of the adhesive. Among them, carbon black with small particles and high activity has the most significant effect. In the white filler, white carbon black with strong reinforcing effect is the best, followed by magnesium oxide, zinc oxide and so on.
(4) Compounding agents that are easy to spray, such as wax, sulfur, accelerator TMTD, etc., should be used as little as possible to avoid contaminating the surface of the rubber.
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