Types of rubber additives: vulcanizing agent
There are many types of rubber additives with complex functions. Currently, there are more than 3,000 types used internationally. According to their functional properties, they can be classified into the following categories: vulcanizing agents, accelerators, active agents, reinforcing fillers, plasticizers, antioxidants, colorants, as well as latex-specific additives and other special-purpose additives.
The main vulcanizing agents are as follows.
(1) Elemental sulfur vulcanizing agent
The typical representative is sulfur, which is the most basic and important vulcanizing agent in the rubber industry. Using ordinary sulfur-accelerator-activator system, the vulcanizing agent obtained has the advantages of good comprehensive performance and low cost.
(2) Sulfur donor
Sulfur donors refer to compounds that can release sulfur during vulcanization, so no additional sulfur or less sulfur can be added.
(3) Peroxide vulcanizing agent
Including three categories: inorganic peroxides, silicon organic peroxides and organic peroxides.
(4) Quinone derivatives
Typical varieties include p-quinonedioxime, ditolyl-p-quinonedioxime, etc., which are mostly used as vulcanizing agents for butyl rubber.
(5) Polyfunctional amine compounds
Mainly used for cross-linking special synthetic rubber, such as acrylic rubber and fluorine rubber.
(6) Resin vulcanizing agent
Mainly used for vulcanization of butyl rubber to make it have excellent heat resistance and high temperature resistance. It has been widely used in industry.
Commonly used vulcanizing agents for rubber: Classification of sulfur
(1) Powder sulfur
Sulfur powder can be obtained by crushing and deacidifying the lump sulfur. The fineness of powdered sulfur used in the rubber industry is below 200 mesh, and in special circumstances, about 600 mesh is also useful.
(2) Precipitated sulfur
Heating sulfur and calcium hydroxide together produces calcium polysulfide compounds, and then adding dilute sulfuric acid to precipitate the sulfur.
(3) Colloidal sulfur (highly dispersible sulfur)
In the presence of a dispersant, grind powdered sulfur or settled sulfur in a ball mill or colloid mill to form a viscous substance, which is then dried and crushed to produce colloidal sulfur with a particle size of 1 to 3 microns.
(4) Surface treatment sulfur
A layer of oil or polyisobutylene is coated on the surface of the sulfur particles to prevent the sulfur particles from being surrounded by other compounding agents, which is beneficial to dispersion.
(5)Insoluble sulfur
Crystalline sulfur is heated to a molten state at 200~250°C and rapidly cooled at a low temperature of 20°C to obtain a transparent elastomer.
Various sulfur vulcanization systems
1. Ordinary sulfur vulcanization system
Conventional Vulcanization (CV) refers to a vulcanization system within the usual sulfur dosage range of diene rubber, which can produce soft and highly elastic vulcanized rubber.
2. Effective vulcanization and semi-vulcanization system
The so-called effective vulcanization system (Efficient Vulcaniztion) is referred to as EV, and the semi-effective vulcanization system (Semi-Efficient Vulcaniztion) is referred to as Semi-EV (SEV). They actually refer to the effective degree of cross-linking of sulfur in the vulcanization reaction.
3. High temperature vulcanization system
In order to improve production efficiency, automation linkage in the rubber industry has become an inevitable trend, so high-temperature rapid vulcanization is also widely used.
4. Balanced vulcanization system
Unsaturated diene rubber, especially the ordinary sulfur vulcanization system vulcanized rubber of natural rubber, is not resistant to heat and oxygen aging and will produce severe vulcanization reversion, resulting in a sharp decline in the dynamic performance of the product and affecting the service life of tires and other products. . Although effective vulcanization systems can overcome some of the shortcomings of ordinary vulcanization systems, they cannot eliminate the vulcanization reversion of vulcanized rubber.
The rubber compound of the balanced vulcanization system has the advantages of high strength, high tear resistance, resistance to hot oxygen, resistance to vulcanization reversion, resistance to dynamic fatigue and low heat generation. Therefore, it is used in long-life dynamic fatigue products and giant engineering tires, large thick It has important applications in product manufacturing and other aspects.