Styrene butadiene rubber
Styrene butadiene rubber is a copolymer of styrene and butadiene. According to the polymerization methods, styrene butadiene rubber can be divided into emulsion polymerization and solution polymerization. Because this kind of rubber has low rolling resistance, high wet skid resistance and better comprehensive performance, so the development is fast. Styrene butadiene rubber is one of the largest production of synthetic rubber, according to statistics, in 1991 the total production of 7.55 million tons in the world, accounting for about 55% of synthetic rubber, accounting for 34% of all rubber, about 70% of which are used in the tire industry. Among all kinds of styrene butadiene rubber, low temperature emulsion polystyrene butadiene rubber has the largest yield.
Nitrile butadiene rubber
Nitrile butadiene rubber is a polymer made of butadiene and acrylonitrile copolymerized by emulsion. Nitrile rubber has excellent oil resistance and yarrow says that its oil resistance is second only to polysulfide rubber, acrylic rubber and fluorine rubber. In addition, nitrile rubber also has good wear resistance, aging resistance and air tightness, but ozone resistance, electrical insulation and cold resistance are poor, and electrical conductivity is better. Therefore, it is widely used in rubber industry. The use of nitrile rubber is mainly used in oil resistant products, such as various sealing products. Other as PVC modifier and PVC and used as flame retardant products, and phenolic and used as structural adhesive, do antistatic good rubber products, etc.
Basic knowledge of rubber
First, the formation of raw glue:
Raw rubber can be divided into natural rubber and synthetic rubber two categories:
1. Natural rubber: The raw rubber material is formed by the cutting mouth of the rubber trunk and the collecting of the outgoing glue pulp. It is processed by removing impurities, solidifying, smoking and drying.
2. Synthetic rubber: a by-product produced by the petrochemical industry, according to different needs, synthetic rubber material with different physical properties. Commonly used such as :SBR, NBR, EPDM, BR, IIR, CR, Q, FKM and so on. However, due to the differences in the synthesis method, the same kind of rubber can be divided into several different kinds of raw rubber, and through the formulation, any type of rubber, can change hundreds of raw rubber in line with the needs of products.
Two, the preparation of rubber raw materials:
The preparation of rubber raw materials can be divided into three basic processes:
1. Plasticizing: Plasticizing is to cut the raw glue and plasticize and homogenize the raw glue to help the mixing operation of the compound. Its effect is to improve the dispersion of drugs, prevent friction heat in the operation, and cause the burning of rubber phenomenon, and then change the processing property of rubber.
2. Mixing: mixing is to mix the drug evenly into the raw rubber completed by plasticizing, and the quality of mixing directly affects the good or bad of the product. Drug dispersion is not uniform, molecular structure can not be fully crosslinked, rubber can not achieve the ideal physical properties.
3. Pressing out: After pressing out operation, the excess air contained in the rubber material will be pressed out and the required thickness will be completed to facilitate the molding operation in the mold.
Three, rubber forming:
The molecular structure of raw rubber is an elastomer with unsaturated long bonds, so in the forming elements, appropriate drug additives and external environmental factors (such as time, temperature, pressure, etc.) are required to destroy its unsaturated bonds, and then recombine into saturated bonds, and with vacuum assistance, the contained air is completely forced out. In this way, the rubber can be formed to play its due characteristics. If there is any missing in the molding process (such as wrong formula, insufficient time, improper temperature, etc.), it can cause loss of physical properties, release of excess drugs, deformation, accelerated aging, and a variety of serious adverse phenomena.
Four, the aging phenomenon of rubber:
According to the environmental conditions of rubber products, with the passage of time, causing cracking or hardening, rubber physical degradation and other phenomena, called aging phenomenon. The causes of aging include external factors and internal factors:
1. External factors: external factors such as aerobic, oxide, ozone, heat, light, radiation, mechanical fatigue, loss of processing, etc.
2. Internal factors: internal factors include the type of rubber, the way of forming, the degree of bonding, the type of matching drugs, the factors in processing engineering, etc.
To prevent the aging phenomenon, the emphasis is on the correct rubber selection and formula design, plus strict production concept. In this way, the life of rubber products can be increased and the special function can be played.
Five, the basic characteristics of rubber products:
1. When rubber products are formed, after large pressure compression, the cohesion of the elastomer can not be eliminated. When forming the mold, it often produces extremely unstable shrinkage (the shrinkage rate of rubber, because of different rubber types and differences), it must be after a period of time, in order to be gentle and stable. Therefore, at the beginning of the design of rubber products, no matter the formula or mold, it is necessary to carefully calculate and cooperate, if not, it is easy to produce product size instability, resulting in low product quality.
2. Rubber is a hot-soluble and hot-setting elastomer, and plastics are hot-soluble and cold-solid. Rubber due to the sulfide type of the main body is different, its forming curing temperature range, there is also a considerable gap, even because of climate change, indoor temperature and humidity. Therefore, the production conditions of rubber products need to be adjusted moderately at any time. If not, it may produce differences in product quality.
Six, rubber laminating with double-sided adhesive distinguish:
General industrial double-sided adhesive can be divided into two categories: acrylic adhesive and rubber adhesive. And these two categories, and can be divided into two types of substrate and no substrate (substrate: add a layer of cotton in the glue, strengthen the double-sided adhesive itself, no substrate: pure gum, to ensure the transparency of double-sided adhesive). Because the main body of rubber rubber system is CR, used in rubber products, easy to react with rubber vulcanization system, and yellow. Therefore, the lighter color of rubber products, are made of acrylic rubber system with double-sided adhesive substrate (the same kind of double-sided adhesive, whether there is a substrate or no substrate, are differentiated by its own gum thickness.
Classification of synthetic rubber
1. Styrene butadiene rubber
Styrene butadiene rubber is made by copolymerization of butadiene and styrene. The English abbreviation is SBR. Is the largest production of general synthetic rubber, milk polystyrene butadiene rubber, polystyrene butadiene rubber dissolved.
About 87% of the world's styrene butadiene rubber production capacity using emulsion polymerization, commonly referred to as styrene butadiene rubber mainly refers to emulsion styrene butadiene rubber. Emulsion polystyrene butadiene rubber includes hot butadiene and cold butadiene. The former was industrialised in 1942 and is still produced in small quantities, mainly for cement, adhesives, chewing gum, as well as certain fabric covering and moulding products and machinery. Commonly referred to as styrene butadiene rubber mainly refers to the low temperature emulsion polymerization of styrene butadiene rubber production, industrialization in 1947, it has higher wear resistance and high tensile strength, good processing performance, and other comprehensive properties, is the largest output, the most widely used synthetic rubber variety.
Dissolved polystyrene butadiene rubber (SSBR) is prepared by polymerization of butadiene and styrene in hydrocarbon solvent in the presence of butyl lithium catalyst. The rolling resistance of the second generation of dissolved polystyrene butadiene rubber produced in the late 1980s is better than that of latex polystyrene butadiene rubber and natural rubber, the wet skid resistance is better than that of butadiene rubber, and the wear resistance is good. It can meet the requirements of high speed, safety, energy saving and comfort of tires.
Butadiene gum is a light yellow brown elastic solid, the density increases with the increase of styrene content, the oil resistance is poor, but the dielectric property is good; Raw rubber tensile strength is only 20-35 kg force/cm 2, adding carbon black reinforcement, tensile strength can reach 250-280 kg force/cm 2; Its adhesion, elasticity and calorific value of deformation are not as good as natural rubber, but its wear resistance, natural aging resistance, water resistance and air tightness are better than natural rubber, so it is a kind of rubber with good comprehensive performance.
Styrene butadiene rubber is the backbone of rubber industry products, it is the largest variety of synthetic rubber, comprehensive performance is good, low price, in most occasions can replace natural rubber used, mainly used in the tire industry, automobile parts, rubber hose, tape, rubber shoes, wire and cable and other rubber products.
Two, butadiene rubber \\ polybutadiene rubber (BR)
The polymerization of butadiene can produce different types of polymers due to different conditions. High-order polybutadiene rubber was formally put into industry abroad in 1960, and our country's industry was produced in 1967. This rubber is conventionally called butadiene rubber. It is a large variety of synthetic rubber, mainly used in the tire industry. Because of its superior performance and low cost, butadiene rubber has always played an important role in rubber production.
(1) Classification of polybutadiene rubber polybutadiene rubber is mainly classified by manufacturing method:
Dissolved poly ---- 1. High sequence polybutadiene rubber (ciliform 96-98%, nickel, cobalt, rare earth catalyst)
2. Low cis-polybutadiene rubber (Cis-35%-40%, lithium catalyst)
3. Ultra-high cis-polybutadiene rubber (cis-98% or more)
4. Low vinyl polybutadiene rubber (vinyl 8%, cis-91%)
5. Medium vinyl polybutadiene rubber (vinyl 35%-55%)
6. High vinyl polybutadiene rubber (vinyl 70% or more)
7. Low trans polybutadiene rubber (trans 9%, cis 90%)
8. Trans-polybutadiene rubber (trans-95% or more, non-rubber at room temperature)
Emulsion ---- emulsion polybutadiene rubber
Bulk polymerization ---- sodium butadiene rubber (obsolete)
(2) The structure of butadiene rubber butadiene rubber contains homeopathic 1, 4-structure of 96%~98%, trans 1, 4- structure of 1%~2%, 1, 2- structure of 1%~2%. Butadiene rubber is crystalline rubber, but the crystallization ability is not strong, so the self-reinforcing ability is small. In addition, the crystalline correspondence of butadiene rubber becomes less sensitive, which is one of the reasons that the self-reinforcing property of butadiene rubber is much lower than that of natural rubber.
(3) Properties of butadiene rubber Because the molecular structure of butadiene rubber is mainly cis-1, 4-structure, the molecular arrangement is regular, so its elasticity is better than natural rubber. The glass transition temperature of butadiene rubber is Tg=-105℃, so its low temperature physical performance is very good, and the cold resistance temperature is lower than -55℃. Elasticity is the best kind of universal rubber. The heat resistance is the same as that of natural rubber, which is 120℃, but the heat resistance aging performance is better than that of natural rubber. The tensile strength is lower than that of natural rubber and styrene butadiene rubber, so carbon black and other reinforcing agents must be added. Tear strength is also lower than natural rubber, anti-skid performance is not good, for tire tread, sole, easy to slip on the wet road. Butadiene rubber has excellent wear resistance, small hysteresis loss and low heat generation, which is very favorable for reducing heat generation and permanent deformation of products under multiple deformation.
Butadiene rubber does not need to be plasticized before mixing. The extrusion performance of the compound is good, suitable for injection molding, but the adhesion is poor. Butadiene rubber is sensitive to the change of processing temperature. When the roller temperature of the mill is above 60℃, the rubber material is easy to roll off, which brings certain difficulties to the processing. Generally, it is necessary to use with natural rubber or styrene butadiene rubber to improve the processing property.
The cold flow property of butadiene rubber is large, which requires the packaging, storage and storage of semi-finished products of raw rubber.
(4) The use of butadiene rubber is mainly used in the manufacture of tires, but also can be used in the manufacture of wear-resistant products (such as rubber shoes, cots), cold resistant products and shock-proof products, can be used as a modifier of plastics. Butadiene rubber can be used with many kinds of rubber. It can be used with styrene butadiene rubber in the manufacture of passenger wheels, and the dosage is 35%~50%. When the tread of truck tire is manufactured, it is often used with natural rubber, and the dosage is 25%~50%. For heavy off-road vehicle tire tread, natural rubber 75, butadiene rubber 25 is better. When it is used for adhesive cloth, it is generally used with styrene butadiene rubber, and the dosage is 15%~30%. It can be used with neoprene rubber to improve the low temperature resistance when it is used to manufacture the tire side. Butadiene rubber can also be used with chlorosulfonated polyethylene.
Classification of synthetic rubber
Iii. Polyisoprene rubber (IR)
Polyisoprene rubber is referred to as isoprene rubber, its structural unit is isoprene. Like natural rubber, industrial production began in 1954. On the whole, the processing, performance and application of isoamyl rubber is similar to that of natural rubber, suitable for making light-colored products. But because of the difference in structure and composition with natural rubber, there are some differences in performance.
The microstructure of polyisoprene is lower than that of natural rubber in cis-content, that is, the molecular regularity is lower than that of natural rubber, so the crystallization capacity of isoprene rubber is worse than that of natural rubber, the molecular weight distribution is narrower, and the distribution curve is unimodal. It does not contain as many non-rubber hydrocarbon components as natural rubber, such as protein and acetone extract.
Compared with natural rubber, the quality and appearance of isoamyl rubber are more uniform, the color is lighter, and the plasticizing is fast. Unvulcanized rubber fluidity is better than natural rubber, raw rubber has a cold flow tendency, green strength is low, vulcanization rate is slow, so when matching the amount of sulfur should be 10%~15% less than natural rubber, promote the amount of 10%~20% more than natural rubber. The shrinkage rate of isoprene rubber is lower when rolled and pressed out, and its adhesion is no less than that of natural rubber. Compared with vulcanized natural rubber, the hardness, constant elongation stress and tensile strength of isoamyl rubber vulcanized rubber are lower, and the elongation at break is slightly higher. Compared with natural rubber, the resilience of isoamyl rubber vulcanized rubber is slightly higher at high temperature, and the thermal generation, compressive permanent deformation and tensile permanent deformation are lower than that of natural rubber. The aging resistance of isoamyl rubber is slightly inferior to that of natural rubber.
Four, ethylene propylene rubber
Ethylene propylene rubber is synthesized with ethylene and propylene as the main raw materials. It has excellent aging resistance, electrical insulation and ozone resistance. Ethylene propylene rubber can be filled with oil and carbon black, the product price is low, ethylene propylene rubber chemical stability is good, wear resistance, elasticity, oil resistance and styrene butadiene rubber close. Ethylene propylene rubber has a wide range of uses, can be used as tire side, rubber strip and inner tube and automobile parts, but also can be used as wire, cable coating and high voltage, ultra-high voltage insulation material. Also can manufacture rubber shoes, sanitary products and other light products.
Five, nitrile rubber
Nitrile butadiene rubber is made of butadiene and acrylonitrile by emulsion polymerization. Nitrile butadiene rubber is mainly produced by low temperature emulsion polymerization. It has excellent oil resistance, high wear resistance, good heat resistance and strong adhesion. Its disadvantages are poor low temperature resistance, poor ozone resistance, poor electrical performance, slightly lower elasticity. Nitrile butadiene rubber is mainly used in the manufacture of oil resistant rubber products.
Six, butyl rubber
Butyl rubber is made by copolymerization of isobutene and a small amount of isopentadiene, which is mainly produced by slurry method. Low permeability, excellent air tightness, good heat resistance, ozone resistance, aging resistance, its chemical stability, electrical insulation is also very good. The disadvantages of butyl rubber are slow curing speed, poor elasticity, strength and adhesion. The main use of butyl rubber is to manufacture a variety of vehicle inner tubes, used for manufacturing wire and cable coating, heat resistant conveyor belt, steam hose, etc.
