There is no significant difference between the injection molding formula and the molding formula. Most of the molding compound can be used for injection. However, since the injection method uses rapid temperature vulcanization, the rubber compound formulation should be adjusted. It is required that the Mooney viscosity before the injection of the rubber compound should be higher than the viscosity of the rubber material of the general method. In addition, the scorch time of the rubber compound should be extended, but the vulcanization speed should meet the requirements of rapid vulcanization.
The Mooney scorch time of the general vulcanization method at 120 ° C is about the weight of the injection compound to be injection molded vulcanized. An important point of injection molding is that it can pass through the nozzle smoothly at high temperatures, that is, it has a certain fluidity. Secondly, it should have enough scorch time and should be vulcanized quickly after entering the cavity. Therefore, it is required to balance the fluidity, scorch and vulcanization speed of the rubber compound.
1 vulcanization system
The injection molding vulcanization system should have sufficient amounts of zinc oxide and stearic acid. It is generally considered that a sulfur carrier accelerator such as DTDM (morphine sulfonate disulfide) 1 to 2 parts, a sulfenamide accelerator 1 to 2 parts, and a small amount of TMTD (TT) are used, and such an effective vulcanization system is preferably used for injection molding. By adjusting the amount of the three, the scorch time, vulcanization rate and degree of vulcanization can be adjusted. The injection molding conditions and ideal vulcanization systems for various rubbers are shown in Table 1-12.
The filler has an influence on the strength, hardness and wear resistance of the vulcanized rubber, and affects the heat build-up, viscosity, fluidity, scorch and vulcanization rate of the rubber compound in the process. It is generally believed that the use of clay, semi-reinforcing furnace black and precipitated calcium carbonate generates less heat; the use of semi-reinforcing furnace black and medium-particle thermal cracking carbon black is the best.
The filler can greatly improve the fluidity of the rubber mixture and shorten the injection time, but because the heat generation is reduced, the injection temperature is also lowered accordingly, thereby prolonging the vulcanization. The softener should have a higher decomposition temperature, and paraffin wax can help improve the fluidity of the rubber compound. Butadiene styrene rubber containing 10 parts of vulcanized grease, Ding Yueqing rubber and neoprene rubber compound, injected by reciprocating screw injection machine, can reduce the injection cycle by 40% compared with no grease, because the grease can soften the rubber compound. The mold filling time is shortened, and the grease has an activation effect on the vulcanization, thereby accelerating the vulcanization rate.
4 anti-aging agent
The use of an effective vulcanization system, which acts similarly to an anti-aging agent, improves aging resistance. In the injection, the thin glue on the side of the model, especially the white rubber or the poorly protective rubber compound, is easy to stick at high temperature due to the air incorporation, and the solution is to add a heat-resistant anti-aging agent such as RD or 246, etc. One part of TMTD (TT) and one part of antioxidant 4010 were added to the vulcanization system.