Compression set is the ability to characterize the rebound of rubber after compression. It is an index to measure the elasticity of rubber. The use of nitrile rubber or nitrile reclaimed rubber to produce oil-resistant rubber products, especially for oil-resistant sealing products, directly affects the compression resistance of rubber. The use performance of rubber products; the nitrile rubber vulcanization process not only affects the physical and mechanical strength of the rubber compound, but also affects the compression and permanent deformation of the rubber compound; strict control of the vulcanization process can reduce the compression permanent deformation of the rubber compound and improve the synthesis of nitrile rubber products. index.
Theoretically, the compression set resistance of nitrile rubber has a great relationship with the type of vulcanization system. Usually, the peroxide-cured nitrile vulcanizate has the smallest compression set and is vulcanized after using ordinary sulfur vulcanization system and cadmium magnesium vulcanization system. The compression set of the rubber material is the largest, and the compression set of the nitrile rubber after vulcanization of the semi-effective vulcanization system and the sulfur vulcanization system is small. Therefore, when using a nitrile rubber or a nitrile reclaimed rubber to produce a low compression and permanent deformation rubber product, the peroxide vulcanization system is mostly selected, or a peroxide is mainly used, and a small amount of sulfur is added.
However, in actual production, the compression set of nitrile rubber is not only related to its vulcanization system, but also the nitrile rubber vulcanizate, the nitrile reclaimed rubber vulcanizate or the nitrile rubber/recycled rubber blend compound in different vulcanization systems. The compression set resistance will decrease as the vulcanization time increases, the vulcanization temperature increases, and the crosslink density increases.
Therefore, when using a nitrile rubber/recycled rubber to prepare a low-compression permanent-setting compound, the rubber must be sufficiently vulcanized and, if necessary, subjected to secondary vulcanization to ensure that the nitrile vulcanizate has the lowest compression set value. Taking flat vulcanization as an example: Generally, the flat vulcanization temperature is appropriately increased, and the vulcanization time is reasonably prolonged, which can reduce the compression set permanent deformation value of the rubber compound.
When nitrile vulcanizate needs secondary vulcanization, rubber products manufacturers need to pay attention to the following problems: increasing the secondary vulcanization temperature and prolonging the vulcanization time will force the rubber to increase in hardness and decrease in tensile elongation. Therefore, secondary vulcanization must be cautious. The vulcanization conditions must be selected from the aspects of physical and mechanical properties, oil resistance, heat resistance and compression set resistance of the nitrile vulcanizate.
At present, many manufacturers of nitrile rubber products use a certain proportion of nitrile reclaimed rubber in the production to reduce the production cost. It is worth mentioning that the nitrile reclaimed rubber itself is fully smelted in the production process, and its expansion and contraction is small. Used in rubber products, the shape and size of the finished rubber products are easier to control, and the compression-resistant permanent deformation of the nitrile rubber can be improved to some extent.