1. Additives for vulcanization system

The vulcanization system additives are mainly composed of vulcanizing agents, accelerators and active agents, and their dosage accounts for about 10% of the raw rubber dosage. Depending on the degree of saturation of the synthetic rubber, various vulcanization systems such as sulfur, metal oxides, peroxides and amine compounds can be used.

1.1 Vulcanizing agent

Different vulcanization systems such as sulfur, peroxide, quinone oxime, resin, metal oxide, etc. Among them, the sulfur vulcanization system is further divided into ordinary vulcanization system, effective vulcanization system and semi-effective vulcanization system.

The sulfur vulcanization system is mostly used in general-purpose synthetic rubber and semi-universal synthetic rubber. The metal oxide vulcanization system is mainly used for neoprene (CR), and the quinone oxime and resin vulcanization system is mainly used for butyl rubber (IIR). Compound and resin vulcanization systems are mainly used for ethylene-propylene rubber (EPR), natural rubber (NR) and styrene-butadiene rubber (SBR). Special rubber [such as polysulfide rubber (LP), chlorosulfonated polyethylene rubber (CSM), chlorinated polyethylene rubber (CM), fluororubber (FKM), silicone rubber (MVQ), fluorosilicone rubber (FVMQ), etc.] They are basically saturated rubbers without double bonds, and sulfur does not cross-link them, so it is necessary to use non-sulfur vulcanization systems, such as metal oxides, peroxides, organic amine salt vulcanization systems, etc. In recent years, acrylate rubber (ACM) has basically adopted the sulfur vulcanization system.

(1) Sulfur. Ordinary powdered sulfur is the most commonly used vulcanizing agent in the rubber industry. With the development of radial tires and colored rubber products, insoluble sulfur (IS) that does not bloom, does not affect adhesion properties and product appearance is widely used. IS is mostly used in NR tire compounds, which can improve the adhesive performance of compound-frame material, avoid blooming, and prolong the storage time of the compound. IS is also used in a small amount of BR tire compound.

(2) Peroxide. In addition to IIR and halogenated butyl rubber (XIIR), the rest of the rubber especially MVQ, EPDM rubber (EPDM), nitrile rubber (NBR), hydrogenated nitrile rubber (HNBR), CM, CR and thermoplastic elastomers Almost all of them can be cured with peroxide. The crosslinking bond of peroxide vulcanized compound is C—C bond, and its bond energy is larger than that of single sulfur bond, disulfide bond and polysulfide bond energy of sulfur vulcanized compound, so the heat resistance of peroxide vulcanized compound is higher. It has excellent oxygen aging properties, small compression set, not easy to bloom, and no vulcanization reversion, but its tensile properties, strain properties and fatigue resistance are poor.

(3) Resin. In order to improve the heat resistance and aging resistance of the rubber compound, many types of rubber (IIR, NR, SBR and NBR, etc.) have been widely used resins (such as alkyl phenolic resins, etc.) as crosslinking agents. The resin-vulcanized IIR compound has good heat resistance and small compression set, and has become the most important compound for the manufacture of vulcanized bladders. Resin is used as a vulcanizing agent for IIR, with slow vulcanization speed and high vulcanization temperature. Phenolic resin vulcanization system is also commonly used in the preparation of rubber-plastic blend materials such as EPDM/PP.

(4) Metal oxides. Halogen-containing or carboxyl-containing rubbers such as CR, CM and XIIR require metal oxides as vulcanizing agents. Common metal oxides are zinc oxide and magnesium oxide, with active zinc oxide and light magnesium oxide being the best.

(5) Sulphur donor. The sulfur donor is a vulcanizing agent that can decompose sulfur during the vulcanization of rubber. The rubber compound is characterized by better heat resistance than sulfur compound, excellent compression deformation resistance, good scorch resistance, and not easy to spray frost. However, due to the toxicity of most sulfur donors, they are included in the ranks of restricted use, such as morpholine-containing vulcanizing agents DTDM and TMTD.

(6) Amine compounds. FKM and ACM often use amine compounds as vulcanizing agents, mainly methylene amines, aniline compounds, etc.