Today I will introduce to you the key points of operation in the process of polyurethane elastomer processing
1. Temperature control
When synthesizing the prepolymer, the temperature is controlled between 75-82°C. If it is too high, the performance of the synthesized prepolymer will decrease, and if it is too low, the polymerization time will be prolonged. The temperature of the prepolymer when mixed with MOCA is controlled between 90-110°C. If it is too high, it will reduce the hardness and strength of the product, and if it is too low, it will increase the viscosity of the polymer, which is not conducive to the pouring operation. For polyurethane elastomer equipment, the vulcanization time is controlled at 130°C. If it is too high, it will decompose MOCA, which is not conducive to cross-linking reaction, and will increase other side reactions; if it is too low, it will prolong the molding time. The melting temperature of MOCA should be controlled as soon as it melts into a liquid, and the heating cannot be continued, otherwise the color of the liquid MOCA will become darker and decompose, which will affect the performance of the product.
2. Time control
Synthesis reaction 2h, intermittent vacuuming 2h. Then seal it and store it at room temperature. The prepolymer synthesis should not exceed 4 hours at 75 ° C, let alone 2 hours at a high temperature of 100 ° C, otherwise the performance of the product will be reduced. The pouring should be completed within 1-2 minutes, because the stability period of the prepolymer and MOCA is very short after mixing, generally only 4-5 minutes, otherwise the mixture will solidify and cannot be poured. Molding vulcanization time depends on the shape and size of the product, generally between 15-30 minutes, to ensure that the product is molded. For large products, it takes longer, 2-3 hours.
3. Degassing of prepolymer
The quality of degassing is the key to the failure of casting polyurethane elastomer. Generally, two steps need to be controlled. After the prepolymer is synthesized, when it is standing still, vacuum degassing at 75°C to remove most of the gas in the prepolymer; before the prepolymer is mixed with MOCA, it needs to be heated to 100-110°C, high temperature Degassing; at the same time, vacuum (-0.095mpa) degassing for 10 minutes, then take it out and stir to turn the bottom air bubbles to the top, then vacuum and degass for 10 minutes, and then discharge the gas in the prepolymer before mixing it with the vulcanizing agent to cast the product.
