Although rubber has many excellent properties, there are still many shortcomings in raw rubber itself. Simply using raw rubber cannot produce rubber products that meet various usage requirements. All kinds of rubber must be added with appropriate amount of relevant compounding agents to make rubber products with practical value. This is not only a technical requirement, but also because adding a compounding agent can improve the performance of the rubber, make it meet the corresponding use requirements, and reduce the cost of rubber products.
There are many types of rubber compounding materials, and their role in rubber is also very complex. According to the main function of compounding agent in rubber, it can be divided into vulcanizing agent, vulcanization accelerator, antioxidant, softener, reinforcing agent, filler, colorant and compounding agent for special purposes. Vulcanizing agent is one of the most important compounding agents. Now we will focus on the commonly used vulcanizing agents in the market.
The vulcanizing agent can vulcanize the rubber under certain conditions. The substances are collectively referred to as vulcanizing agents. The so-called vulcanization is to make the linear molecular structure of the rubber become a three-dimensional network structure through the 'bridge' of the vulcanizing agent, so that the mechanical and physical properties of the rubber can be obtained. Significant improvement.
1. Sulfur: yellow solid substance, widely used in natural rubber and some synthetic rubber. Commonly used sulfur is sulfur powder, sublimated sulfur (also known as sulfur bloom) and precipitated sulfur. Sulfur is insoluble in water, slightly soluble in ethanol and ether, soluble in carbon disulfide and carbon tetrachloride. It is characterized by vulcanized rubber with low heat resistance, high strength, and corrosive effect on copper wires, and is suitable for natural rubber and some synthetic rubbers. In the formula of wire and cable rubber, the amount of sulfur is about 0.2 to 5 parts, but due to the addition of accelerators, the amount of sulfur can be reduced accordingly.
2. Metal oxides: Metal oxides are mainly used as vulcanizing agents for neoprene, chlorosulfonated polyethylene, etc. Commonly used are zinc oxide, magnesium oxide, lead oxide, lead tetroxide and so on. Zinc oxide has a specific gravity of 5.6 and is a white powder, non-toxic and odorless. Zinc oxide is widely used in rubber, and is often used together with magnesium oxide as the main vulcanizing agent in general-purpose neoprene. It can be used as an activator for accelerators in natural rubber and other olefin rubbers. In addition, it also has a reinforcing effect. It plays the role of shielding ultraviolet rays in the sun-resistant rubber. The dosage of zinc oxide in natural rubber and butyl rubber is 5 to 10 parts, and the general dosage of zinc oxide and magnesium oxide in neoprene rubber is 5 parts. Magnesium oxide Magnesium oxide is used as a secondary vulcanizing agent in neoprene, which can prevent pre-vulcanization of neoprene during mixing. This product can improve the tensile strength, tensile strength and hardness of neoprene. It can neutralize small amounts of hydrogen sulfide generated during vulcanization, such as halogenated rubber, or under other oxidative conditions. The chlorosulfonated polyethylene rubber can give it good physical and mechanical properties, especially the permanent deformation is relatively small. But the water resistance is poor. The general dosage is 3 to 7 parts. Magnesium oxide is a white loose powder with a specific gravity of 3.2. It can gradually absorb moisture and carbon dioxide in the air to become alkali or magnesium carbonate and reduce its activity, so it should be strictly sealed and stored.
3. Resin vulcanizing agent: Resin vulcanizing agent is mainly some thermosetting alkyl phenolic resin and epoxy resin. Vulcanization of unsaturated carbon chain rubber and butyl rubber with alkylphenolic resin can significantly improve the heat resistance of the vulcanizate. The main varieties commonly used are phenol formaldehyde resins, such as tert-butyl phenol formaldehyde resin and tert-octyl phenol formaldehyde resin. Epoxy resin has good vulcanization effect on carboxyl rubber and chloroprene rubber, and its vulcanized rubber has good flex resistance.