Sponge rubber made from EPDM/recycled rubber has light texture, low density, good elasticity and high softness. It not only has excellent shock absorption, sound insulation and thermal insulation properties, but also has light, heat, ozone and climate change. Good resistance, among which the sponge rubber produced with EPDM reclaimed rubber as the main raw material has lower production cost and higher cost performance; when EPDM reclaimed rubber produces sponge compound, the vulcanization speed and foaming speed are very important.
Studies have shown that: when the vulcanization rate of EPDM sponge rubber is faster than the foaming speed, the viscosity of the rubber compound increases, and the foaming is difficult; when the foaming speed is faster than the vulcanization speed, the gas easily runs away, and the foaming efficiency is lowered, resulting in a sponge. The rubber is insufficiently foamed and the surface of the crust is not smooth. Therefore, when rubber products manufacturers choose EPDM reclaimed rubber to produce sponge foam rubber, it is necessary to select a suitable blowing agent according to the molding process to ensure that the decomposition of the foaming agent is carried out within a temperature range that can be controlled by the vulcanization temperature. The vulcanization rate and foaming speed of the EPDM sponge rubber are adjusted by adjusting the foaming agent system and the vulcanization system setting.
1. Foaming agent system
In actual production, since the decomposition speed of the foaming agent is greatly affected by the compounding agent used in the rubber compound, it is more difficult to adjust than the vulcanization speed. Generally, after the completion of the foaming agent matching system, the EPDM sponge rubber compound is adjusted. The vulcanization system adjusts the vulcanization rate to suit its foaming speed. For example, when using EPDM reclaimed rubber to produce sponge foam hose, when the compound chemical foaming agent HCB is selected as the EPDM sponge, it is necessary to adjust the type and amount of various compounding agents in the vulcanization system to adapt to the foaming speed.
2. Vulcanization system
The commonly used vulcanization system for EPDM rubber products includes sulfur vulcanization system and peroxide vulcanization system. In the sponge rubber compound with EPDM reclaimed rubber as the main raw material, in order to better adjust the vulcanization speed and foaming speed. Manufacturers of rubber products can use DCP as the main vulcanizing agent and sulfur as the auxiliary vulcanizing agent, and cooperate with the accelerator TT and the accelerator DM to match the foaming speed of HCB. For example, in the EPDM foaming hose, 3 DCP can be used. 0.3 parts of sulfur, 0.5 part of accelerator TT, 0.15 parts of accelerator DM to mix 10 parts of foaming agent HCB, where the amount of raw rubber is calculated as 100 parts). It is worth mentioning that the EPDM reclaimed rubber processed from the waste ethylene propylene diene rubber product itself contains a small amount of a vulcanizing agent, a promoter and the like, and the effective rubber content is different from the raw rubber. Manufacturers need to adjust the amount of compounding agent according to the actual situation.
The EPDM sponge rubber for different use occasions has great differences in the performance requirements of the rubber compound. Therefore, there is a certain difference between the selection and dosage of EPDM reclaimed rubber products. The rubber product manufacturers must “depend on the needs” and choose the most. A suitable EPDM reclaimed rubber, determine the reasonable dosage, adjust the foaming agent system and the vulcanization system to match the foaming speed and vulcanization speed.