Different rubbers have different performance characteristics, and different vulcanization systems are used. When choosing different types of accelerators for different vulcanization systems, the matching between them should be considered.
(2) Accelerator quality
Quality is one of the key considerations for formulators when selecting accelerators. In the current market, there are still many phenomena of fake and shoddy, so we must be careful when selecting them, otherwise it will directly affect the performance of rubber vulcanization or anti-aging.
(3) Influence on the properties of compound rubber and vulcanizate
The accelerator participates in the formation of the rubber space network structure during vulcanization, which is directly related to the structure of the vulcanizate, that is, its physical and mechanical properties and aging properties. The accelerator has a softening effect on the rubber compound, which increases the plasticity of the rubber compound and changes the processing performance of the rubber compound.
(4) Scorch performance
The accelerator has a decisive influence on the scorch time of the compound, that is, the time elapsed before the hot vulcanization of the compound begins. Therefore, the selected accelerator should make the rubber compound have a considerable scorch time, which is very important for the operation safety of the rubber compound in the process of mixing, calendering, extrusion or injection, the fluidity of the rubber compound at the initial stage of vulcanization and the adhesion to the fabric. Efforts are important. Especially in recent years, in order to improve production efficiency, the processing conditions have become more and more strict, and the requirements for the scorch resistance of the rubber compound have become higher and higher. But too long scorch time will lead to the increase of total vulcanization time, which is not only not conducive to the improvement of labor efficiency, but also adversely affects the deformation of moldless vulcanized products during the vulcanization process.
(5) Vulcanization flatness
The accelerator should make the compound have a broad vulcanization flat curve during the optimum vulcanization period. In other words, the properties of the vulcanizate should not show significant changes during this period, which is especially important for thick rubber products and solid products. Rubber is a poor conductor of heat, and the surface and interior of the vulcanized compound are not uniformly heated. The broad vulcanization flatness is the guarantee to avoid over-vulcanization and to make all parts of the product vulcanized evenly.
(6) Dispersion
Accelerators with poor dispersion properties in the rubber compound not only require a long mixing time, increase the power consumption of the equipment, but also often cause uneven vulcanization of the product due to uneven mixing. Generally, low melting point accelerators are easy to melt and diffuse in the compound, so they have good dispersibility; for high melting point accelerators, it is best to use powder products with small particle size; for some accelerators that are difficult to disperse, they can be used as masterbatches glue to use.
(7) Frosting
The frosting of the rubber compound will cause poor adhesion in the subsequent process and reduce the appearance quality of the final product, so it should be avoided. The blooming of the accelerator is related to the compatibility of the accelerator with the rubber. Generally, non-polar EPDM rubber is easy to bloom, while polar nitrile rubber and neoprene rubber are difficult to bloom. Among the accelerators, especially the accelerators TMTD and ZDMC have poor compatibility with rubber, which may cause blooming. Accelerators with large alkyl groups EZ and BZ have better compatibility with rubber than TMTD and PZ, and the blooming phenomenon is reduced.
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