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The way to increase the hardness of rubber
Source:iotachem.com
PostTime:2023-01-06 13:11:48
The way to increase the hardness of rubber

1. Raw rubber

High-hardness rubber formulations often require a large amount of filler and reinforcing agent, and the raw rubber should choose a grade with a high Mooney viscosity. For example, EPDM should use grades with high Mooney and high ethylene content; NBR can choose grades with high Mooney and high acrylonitrile content. Sometimes according to the needs of other properties, you can choose the combination of high Mooney and low Mooney glue, and low Mooney glue is not conducive to large filling.

2. Reinforcing filler

Reinforcement with carbon black and white carbon black is the best choice. The comprehensive performance of the two is good, and the ability to increase hardness is strong. Among them, carbon black with fine particle size has the best effect, but high hardness rubber requires a large amount of filling. If fine particle size carbon black is used alone, serious problems will occur in rubber refining, vulcanization and other processes, so the combination of fine particle size carbon black and large particle size carbon black is the best, such as N330/N550. Other weak reinforcing fillers should not be used as much as possible. Because these fillers have weak ability to increase hardness, a larger amount of filling is required than carbon black and white carbon black to achieve the target hardness, resulting in a decrease in the overall performance of the rubber compound and the reduction in process performance.

3. Plasticizer

High-hardness rubber materials require a large amount of filling and reinforcing agents, which will cause technical problems such as rubber mixing and vulcanization. An appropriate amount of plasticizer should be added, although plasticizers will reduce the hardness of the rubber material. The choice of plasticizer is preferably solid plasticizer, such as solid coumarone and the like.

4. Vulcanizing agent

Increasing the cross-linking density of the rubber is beneficial to increase the hardness of the rubber. For sulfur vulcanization systems, increasing the amount of accelerators, especially TMTD accelerators, is beneficial to increase hardness. An increase in the amount of vulcanization can also increase the crosslinking density and increase the hardness of the rubber compound. For example, when the amount of sulfur reaches 30-50 parts by mass, hard rubber can be prepared, but when the amount of sulfur and the amount of accelerator are increased, it is easy to produce blooming Phenomena, dosage needs to be balanced. In addition, for the sulfur vulcanization system, due to the high filling of high-hardness rubber materials, the heat generation of mixing and vulcanization processing increases, which is likely to cause scorching. Therefore, it is also beneficial to use an anti-scorch agent for insurance purposes, such as CTP Wait.

For the peroxide vulcanization system, increasing the amount of peroxide can increase the hardness, but it should not be too high. You can choose a variety of peroxide vulcanizing agents and use them together. In addition, adding a crosslinking assistant can significantly increase the crosslinking density of the rubber compound. For example, for DCP vulcanizing agent, TAIC, PDM (HVA-2), TAC, PL-400 (TMPTMA) can be added, and of course sulfur can also be used as auxiliary crosslinking agent.
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