One
Acrylonitrile butadiene rubber (NBR)
It is an irregular copolymer synthesized by emulsion polymerization of butadiene and acrylonitrile monomer. Its molecular structure is: - (CH2-CH=CH) m- (CH2-CH2- CH) n- CN. Nitrile rubber was first developed in Germany in 1930, and is a copolymer of butadiene and 25% acrylonitrile. Its aging resistance, heat resistance and wear resistance are better than natural rubber. Therefore, rubber industry attaches great importance to rubber industry. During the Second World War, with the rapid development of weapons and equipment, the demand for heat-resistant and oil-resistant NBR as war preparedness materials increased dramatically. So far, more than 20 countries have produced NBR, with an annual output of 560,000 tons, accounting for 4.1% of the world's total synthetic rubber.

Because of its excellent heat resistance, oil resistance and mechanical properties, it has become the main product of oil-resistant rubber, accounting for about 80% of all oil-resistant rubber demand. Nitrile-butadiene rubber (NBR) has made great progress in the 1950s. Up to now, there are more than 300 brands. According to the content of acrylonitrile, it can be divided into 18%-50% acrylonitrile content range: acrylonitrile content > 42% is very high grade, 36%-41% is high grade, 31%-35% is medium and high grade, 25%-30% is medium grade, and below 24%. For low nitrile grade. The most widely used in industry are nitrile-18 of low nitrile grade (17%-20% combined with acrylonitrile), nitrile-26 of medium nitrile grade (27%-30% combined with acrylonitrile), and cyanide-40 of high nitrile grade (36%-40% combined with acrylonitrile). The increase of acrylonitrile content can significantly improve the oil and heat resistance of NBR, but not more, because the increase of acrylonitrile content will reduce the low temperature performance of rubber.

Nitrile-butadiene rubber is mainly used in the manufacture of petroleum-based hydraulic oil, lubricating oil, kerosene and gasoline rubber products working temperature is - 50 - 100 degrees; short-term work can be used for 150 degrees, in the air and ethanol glycerol antifreeze working temperature is - 45 - 100 degrees. Nitrile-butadiene has poor ageing resistance. When ozone concentration is high, it will crack rapidly. It is not suitable to work in high temperature air for a long time or in phosphate fire-resistant hydraulic oil.
The general physical properties of NBR:
(1) Nitrile-butadiene rubber is generally black, the color can be adjusted according to customer needs, but it needs to increase some costs, and may affect the use of rubber effect.

(2) acrylonitrile butadiene rubber has a slight smell of rotten eggs.

(3) According to the oil-resistant characteristics of NBR and the temperature range of use to determine whether the sealing material is NBR.

Two
Silicone rubber (Si or VMQ)
It is a linear polymer based on a silicon oxygen bond (-si-o-si) chain and an organic group as a side group. Due to the development of aerospace and other advanced industries, the rubber sealing materials with high temperature and low temperature resistance are urgently needed. Early use of natural, cyanide-butadiene, chloroprene and other general-purpose rubber can not meet the needs of industrial development, so in the early 1940s the United States two companies began to produce dimethyl silicone rubber, is the earliest silicone rubber. China was also successful in the early 1960s and put into production. After decades of development, the variety, performance and yield of silica gel have been greatly developed.
The main characteristics of silica gel are:
(1) high temperature stability of heat resistant silica gel. It can be used for a long time at 150 C without obvious change in performance; it can work continuously for more than 10,000 hours at 200 C, even for a short time at 350 C.

(2) Low-phenyl silica gel and medium-phenyl silica gel have good low-temperature elasticity when their cold-resistance coefficients are above 0.65 at - 60 and - 70%. The average temperature of silica gel is -50 C.

(3) Oil-resistant and chemical-resistant properties Silica gel has a good tolerance to polar solvents such as ethanol, acetone and food oil, only causes a small expansion, and the mechanical properties will not be reduced basically; Silica gel has a good tolerance to low concentration of acid, alkali, salt, and placed in 10% sulfuric acid solution for 7 days, the volume change rate is less than 1%, the force. The basic performance is basically unchanged. However, silica gel is not resistant to non-polar solvents such as concentrated sulfuric acid, strong alkali, carbon tetrachloride and toluene.

(4) Silica gel has a strong anti-aging property, which is incomparable with ordinary rubber in ozone resistance and radiation resistance.

(5) The dielectric properties of silica gel have high volume resistivity (1014-1016_ cm) and its resistance value is stable in a wide range. It is suitable for insulating materials under high pressure.

(6) Flame retardant properties of silica gel will not be immediately burned, and its combustion produces less toxic gases, the burned products will form insulating ceramics have been, so silica gel is still a good flame retardant material.

In view of the above characteristics, silica gel is widely used in household electrical appliances industry for sealing parts or rubber parts, such as electric kettle, iron bucket, microwave oven rubber parts; electronic industry seals or rubber parts, such as mobile phone keys, DVD shock absorber, cable connector seals; and human contact. All kinds of seals, such as kettle, water dispenser, etc.

Three
Fluorine glue (FKM or Vtion)
It is also called fluoro elastomer, which is a high molecular polymer containing fluorine atoms on the main chain and side chain carbon atoms. In the early 1950s, the development of fluorinated elastomers began in the United States and the former Soviet Union. DuPont and 3M's VtionA and Kel-F were first put into production after half a century of development. Fluoroelastomers have made rapid progress in heat resistance, medium resistance, low temperature resistance and process, and formed a series of products.

Fluoroadhesive has excellent heat resistance, ozone resistance and various hydraulic properties. Its working temperature in the air ranges from -40 to 250 degrees.