Functions of major compounding agents commonly used in rubber products
Raw rubber
Raw rubber is a kind of polymer material with high elasticity, and it is the parent material for manufacturing rubber products, generally referring to unvulcanized rubber compound.
Raw rubber includes natural rubber and synthetic rubber, the main varieties are as follows: commonly used natural rubber has smoke sheet rubber, standard rubber; commonly used synthetic rubber has styrene butadiene rubber, parabutylene rubber, butyl rubber. There are also a small number of special rubber using chloroprene rubber, nitrile rubber.
Application of carbon black in rubber
Carbon black is mainly used in rubber industry, and tires are the main products. The carbon black used in the tire industry accounts for more than 80% of the carbon black needed in the whole rubber industry. Generally, rubber products other than tires of various motor vehicles (including motorcycles) are collectively referred to as "rubber products". The carbon black consumed by rubber products accounts for about 20% of the carbon black used for rubber every year.
There are many kinds of rubber products, with different conditions of use and performance requirements. According to the main functions, the products include several categories of products, such as adhesive tape, hose, rubber sheet, rubber damping products, rubber sealing products, cots, conductive or antistatic rubber products, hard rubber and rubber shoes, and each category of rubber products is refined into several categories according to the purposes and conditions of use. In order to meet the performance and use requirements of different products, rubber formulators comprehensively consider the selection of reasonable formulas, various additives and processing conditions from the aspects of rubber use, vulcanization system, reinforcing and filling system, softening system, anti-aging system and 3252 processing system to meet the use performance requirements of products.
Carbon black is an important reinforcing filler in the reinforcing filling system, which has an important influence on the physical and mechanical properties and processing technology of rubber compound, but its influence on the heat resistance, oil resistance and corrosion resistance of rubber compound is far less direct than that of rubber, vulcanization system and protection system. For this reason, general rubber formulators pay less attention to the specific performance indicators of a certain carbon black than carbon black technicians, and often only pay attention to the selection of a certain type of carbon black, without detailed investigation of the specific indicators of using carbon black, or through the combination of different varieties of carbon black, carbon black and inorganic fillers can meet the use requirements of products. Therefore, it is difficult to quantify the impact of specific physical and chemical indicators of carbon black.
Vulcanizing agent
Chemicals that can cross-link rubber molecular chains are called vulcanizing agents. In the early days, sulfur was added to raw rubber, and under the action of heat, linear rubber molecules were cross-linked into a network structure, thus increasing the strength, elasticity and solvent resistance of rubber. People usually call this process vulcanization. Vulcanization is an important link to improve the quality of rubber products in rubber processing. Sulfur is the most widely used vulcanizing agent. Some sulfur-containing organic substances, peroxides and metal oxides can also be used as vulcanizing agents. These non-sulfur compounds are also called vulcanizing agents.
Vulcanization accelerator
When heated, the vulcanization accelerator can be decomposed into active molecules, which promotes sulfur to cross-link with rubber molecules quickly at a lower temperature, enhances the vulcanization of rubber, shortens the vulcanization time, reduces the amount of sulfur, and is beneficial to improving the physical and mechanical properties of rubber. Inorganic vulcanization accelerators include calcium oxide and magnesium oxide, and organic accelerators include D (diphenylguanidine), DM (disulfide dibenzothiazole) and TMTD (tetramethyltetramethyltetramethyltetramethyl disulfide). Organic accelerators are commonly used. The mixed use of several accelerators is better than the single use.
Promotional aids
Promotional aids are also called active agents. It can enhance the activation of vulcanization accelerator and improve the vulcanization effect of rubber. Commonly used accelerating agents include zinc oxide and stearic acid.
Antioxidants
Rubber molecules react with oxygen and ozone, and the structure of rubber is destroyed, which reduces the mechanical properties of products and shortens the service life. This phenomenon is called rubber aging. Light and heat promote oxidation, thus accelerating aging. Adding substances to rubber that can resist and slow down the aging of rubber products is called antioxidant. Antioxidants are divided into physical antioxidants and chemical antioxidants. Physical antioxidants include paraffin, wax, beeswax and stearic acid. This kind of substance can form a thin film on the surface of rubber products, prevent oxygen from oxidizing with rubber molecules, and block the irradiation of light. Chemical antioxidants react with oxygen more easily than rubber. Adding a chemical antioxidant into the rubber compound can make the oxygen entering the rubber react with the antioxidant first, and reduce the contact between oxygen and rubber, which can effectively delay aging. Chemical antioxidants are classified into amines, ketoe amines, aldehydes and amines, phenols and others according to their molecular structures. It has antioxidant A(N- phenyl-α-naphthylamine) and antioxidant D(N- phenyl-β-naphthylamine).
Reinforcing and filling agent
Reinforcing filler is used to improve the strength of vulcanized rubber and enhance the wear resistance, tear resistance and elasticity of rubber. The reinforcing filler is mainly carbon black. There are 52 kinds of carbon black used in rubber industry, which is an important raw material in rubber industry.
Refers to a substance that can add a large amount of rubber, improve some properties of rubber compound and reduce volume cost.According to the efficiency, it can be divided into reinforcing fillers and non-reinforcing fillers, or active fillers and inactive fillers (inert fillers).
According to chemical composition, it can be divided into organic fillers and inorganic fillers.
Softening agent and plasticizer
The main function of softener is to make all kinds of compounding ingredients evenly dispersed in rubber, so as to reduce the energy consumption and shorten the processing time of rubber compound. For example, it can enhance the viscosity of rubber compound before vulcanization and enhance the adhesion after vulcanization, which is beneficial to calendering and extrusion molding. Some softeners can also give vulcanized rubber special functions, such as dibutyl phthalate, which can improve the cold resistance of rubber. Commonly used softeners are machine oil, vaseline, paraffin, asphalt, coal tar, stearic acid and rosin.
Plasticization of rubber refers to adding some substances into rubber, which can reduce the intermolecular force of rubber, thus reducing the glass transition temperature of rubber, making rubber plastic and fluid, facilitating molding operations such as calendering and extrusion, and improving some physical and mechanical properties of vulcanized rubber, such as reducing hardness and tensile stress, endowing it with higher elasticity and lower heat generation, and improving cold resistance.
Rubber flame retardant
There are many kinds of flame retardants, which can be divided into organic flame retardants and inorganic flame retardants. Representative flame retardants are chlorine, bromine, phosphorus, aluminum hydroxide, magnesium hydroxide and so on. There are three kinds of organic flame retardants.
Rubber is conductive and antistatic
Conductive rubber is that conductive particles such as conductive carbon black, glass silver plating, aluminum silver plating and silver are evenly distributed in silicone rubber, and the conductive particles are contacted by pressure to achieve good conductivity.
Rubber products have been widely used in industry, agriculture, national defense and daily life because of their own advantages (neat appearance, easy molding, good insulation, etc.). However, when people enjoy the benefits of rubber products, they find that rubber products have high insulation, and electrostatic accumulation on their surfaces will produce many bad phenomena. Rubber special antistatic agent is a new type of antistatic agent successfully developed at the request of users. The product added to rubber products can make rubber products have good antistatic performance.
Coloring agent
Colorants are substances that color rubber products. Inorganic colorants are inorganic pigments, with titanium dioxide as the best white, iron oxide, iron red and antimony red in red, chrome yellow in yellow, ultramarine in blue, chrome oxide in green and oily black in black. Organic colorants are organic pigments and some dyes. Most of these colorants are barium salts or calcium salts of organic compounds, such as Lysol Red in red, Hansa Yellow G in yellow, green with phthalocyanine green, blue with phthalocyanine blue.
Vesicant
Foaming agent is a necessary compounding agent for manufacturing sponge rubber or microcellular rubber. The foaming agent is decomposed by heat during the vulcanization of rubber, and gas is released, so that micropores are generated inside the rubber. The foaming agent used to make sponge rubber is mainly sodium bicarbonate. Foaming agents used for manufacturing microcellular rubber include foaming agent D, foaming agent P or foaming agent T.
