Fluorine rubber has the characteristics of high temperature resistance, oil resistance and corrosion resistance of many chemicals, and is an indispensable material for modern aviation, missiles, rockets, aerospace and other cutting-edge technologies. In recent years, with the continuous improvement of reliability and safety requirements in the automobile industry, the amount of fluororubber in automobiles has also increased rapidly.
Fluorine rubber refers to a synthetic polymer elastomer with fluorine atoms in the carbon atoms in the main chain or side chain. The earliest fluororubber was poly 2- fluoro-1.3- butadiene and its * * * polymer with styrene and propylene. , trial-produced by DuPont Company in the United States on 1948. However, its performance is not better than that of chloroprene rubber and cis-butadiene rubber, and it is expensive and has no practical industrial value. At the end of 1950s, Thiokol Company of the United States developed a binary nitroso fluororubber with good low temperature and strong oxidant (N2O4) resistance, and fluororubber began to enter practical industrial applications. Since then, with the progress of technology, various new fluororubbers have been continuously developed.
China has also developed a variety of fluororubbers from 1958, mainly polyolefin fluororubbers, such as 23, 26, 246 and nitrosfluororubbers; Later, newer tetrapropyl fluororubber, perfluoroether rubber and phosphorus fluoride rubber were developed. These fluororubber varieties are first popularized and applied in the field of civil industry to meet the needs of national defense and military industries such as aviation and aerospace.
main performance
Good chemical stability
Fluorine rubber has a high degree of chemical stability, which is the best medium resistance of all elastomers at present. Type 26 fluororubber is resistant to petroleum-based oil, diester oil, silicone oil, silicic acid oil, inorganic acid, most organic and inorganic solvents and drugs. , but excluding low molecular weight ketones, ethers, esters, amines, ammonia, hydrofluoric acid, chlorosulfonic acid and phosphoric acid hydraulic oil. The dielectric properties of 23-type fluoroadhesive are similar to those of 26-type fluoroadhesive, which is more unique. Its resistance to fuming nitric acid, concentrated sulfuric acid and other strong oxidizing inorganic acids is better than that of 26-type fluoroadhesive. After soaking in 98% HNO3 for 27 days at room temperature, its volume expansion is only 13%~ 15%.
Excellent high temperature resistance
Like silicone rubber, fluororubber is the best elastomer at present. 26-4 1 fluororubber can be used for a long time at 250℃ and for a short time at 300℃; The heat resistance of 246 fluororubber is better than that of 26-4 1. The physical properties of 26-4 1 after air thermal aging at 300℃× 100 hour are equivalent to those of 246 after air thermal aging at 300℃× 100 hour, and its elongation at break can be kept at about 100%, and its hardness is 90~95 degrees. Model 246 still maintains good elasticity after hot air aging at 350℃ 16 hours and hot air aging at 400℃ 1 10 minutes. After hot air aging at 400℃ for 1 10 minutes, the elongation of the compound containing spray carbon black, thermal cracking carbon black or carbon fiber increased by about 65438. 23- 1 1 fluororubber can be used at 200℃ for a long time and at 250℃ for a short time.
Good anti-aging performance
Fluorine rubber has excellent weather resistance and ozone resistance. It is reported that after ten years of natural storage, the performance of VitonA developed by DuPont is still satisfactory, and there is no obvious crack in the air with ozone concentration of 0.0 1% for 45 days. Type 23 fluororubber has excellent weather resistance and ozone resistance.
Excellent vacuum performance
Type 26 fluororubber has excellent vacuum performance. The vacuum deflation rate of vulcanizate with the basic formula of 246 fluororubber is only 37× 10-6 Torr/s. Square centimeters. 246 fluororubber has been successfully applied in the vacuum condition of 10-9 torr.
Excellent mechanical properties
Fluorine rubber has excellent physical and mechanical properties. Generally, the strength of type 26 fluororubber is 10~20MPa, the elongation at break is 150~350%, and the tear strength is 3 ~ 4kn/m ... The strength of type 23 fluororubber is 15.0~25MPa, and the elongation is 200%~600%. The compression set of fluororubber is generally large at high temperature, but if compared under the same conditions, such as compression set at 150℃ for the same time, both butadiene and chloroprene rubber are larger than 26-type fluororubber, and the compression set of 26-type fluororubber at 200℃×24 hours is equivalent to that of cis-butadiene rubber at 150℃×24 hours.
Good electrical performance.
Type 23 fluororubber has good electrical properties and lower hygroscopicity than other elastomers, so it can be used as a good electrical insulation material. Type 26 rubber can be used at low frequency and low pressure.
Low air permeability
The solubility of fluororubber in gas is large, but the diffusion speed is relatively small, so the overall permeability is also small. It is reported that the permeability of 26-type fluororubber to oxygen, nitrogen, helium and carbon dioxide at 30℃ is equivalent to that of butyl rubber and cis-butadiene rubber, but better than that of chloroprene rubber and natural rubber.
Poor low temperature performance
The poor low-temperature performance of fluororubber is due to its own chemical structure, such as TG of 23- 1 1 type > 0℃. The low temperature performance of fluororubber used in practice is usually expressed by brittleness temperature and compression cold resistance coefficient. The formula of rubber compound and the shape of product (such as thickness) have great influence on brittleness temperature. With the increase of filler content in the formula, the brittleness temperature sensitivity deteriorates, the product thickness increases and the brittleness miscibility increases.
Poor radiation resistance
The radiation resistance of fluororubber is one of the poor elastomers. After radiation, 26-type rubber showed crosslinking effect, and 23-type fluororubber showed cracking effect. When 246 fluororubber was irradiated in room temperature air at a dose of 5× 107, its properties changed significantly. Under the condition of 1× 107, the hardness increases by 1~3 degrees, the strength decreases by less than 20%, and the elongation decreases by 30%~50%, so it is generally considered that 246 fluororubber can withstand 65438.
Key application
Because fluororubber has the characteristics of high temperature resistance, oil resistance, high vacuum resistance, acid and alkali resistance and various chemicals resistance, it has been used in modern aviation, missiles, rockets, aerospace, ships, atomic energy and other cutting-edge technologies and industrial fields such as automobiles, shipbuilding, chemistry, petroleum, telecommunications, instruments and machinery.
Typical application
The fluororubber seal can work at 200℃~250℃ for a long time and 300℃ for a short time, and its service life can be the same as that of engine repair, reaching 1000~5000 flight hours (time 5~ 10 year); When used in chemical industry, it can seal inorganic acids (such as 67% sulfuric acid at 140℃, concentrated hydrochloric acid at 70℃ and 30% nitric acid), organic solvents (such as chlorinated hydrocarbons, benzene and high aromatic gasoline) and other organic substances (such as butadiene, styrene, propylene, phenol and fatty acids at 275℃). When used in deep well oil production, it can withstand the harsh working conditions of 149℃ and 420 atmospheric pressure; When used for superheated steam sealing, it can work in the steam medium of 160~ 170℃ for a long time. In the production of monocrystalline silicon, fluororubber seals are often used to seal special media at high temperature (300℃)-trichlorosilane, silicon tetrachloride, gallium arsenide, phosphorus trichloride, trichloroethylene and 120℃ hydrochloric acid.
In the application of high vacuum, the air pressure is133x10-6pa (10-6mmhg) at the flying altitude of 200~300Km, and neoprene, cis-butadiene rubber and butyl rubber can be used. When the flying altitude exceeds 643Km, the air pressure will drop below133 x10-7pa (10-7mmhg), and only fluororubber can be used in this high vacuum. Usually, high vacuum or ultra-high vacuum equipment systems need high temperature baking treatment. Type 26 and 246 fluororubbers can withstand high temperature aging at 200℃~250℃, so they become the most important rubber materials in high vacuum equipment and spacecraft.
The hose made of fluororubber is suitable for conveying and guiding high temperature, oil and special media, such as aircraft fuel, hydraulic oil, synthetic diester oil, high temperature hot air, hot inorganic and other special media (such as chlorinated hydrocarbons and other chlorides). Wires and cables made of fluororubber have good flexibility and good insulation. Glass fiber adhesive tape made of fluororubber is resistant to high temperature of 300℃ and chemical corrosion. After being coated with fluorine glue, aramid cloth can be used to manufacture telescopic pipes (both ends can be connected with metal flanges) between high-temperature and acid-base storage tanks in petrochemical plants, which can withstand high pressure, high temperature and medium corrosion, and play a role in buffering and damping the deformation and expansion of the two storage tanks. The adhesive tape sealing bag made of nylon cloth coated with fluorine rubber is used as the soft seal of floating roof storage tank in refinery, which plays a role in sealing and reducing the volatile loss of oil level.
23-type and 4-type propylene fluororubber are mainly used for sealing occasions with acid resistance and corrosion resistance of special chemicals. Hydroxynitroso fluororubber is mainly used as protective products and sealing products, and as a non-combustible coating in solution form, it is applied to fire-proof electronic components working in pure oxygen. Its solution and liquid rubber can be sprayed and poured into many products, such as spacesuits, gloves, pipe belts, balls and so on. It can also be used as an adhesive for glass, metal and fabric, and can be used to make sponges, gaskets, O-rings, capsules, valve seals and so on. Contact with rocket propellant (N2O4).
The seals made of G series fluororubber have the properties of high temperature steam resistance, methanol resistance or gasoline with high aromatic hydrocarbon content, which can not be achieved by using VitonA, B, E and other fluororubbers. GLT fluororubber, phosphorus chloride rubber, perfluoroether rubber, etc. It has the characteristics of wide temperature range, low temperature flexibility and elastic sealing. Perfluoroether rubber also has outstanding medium corrosion resistance and is widely used in cutting-edge technology of military industry.
Putty is a sealant made of fluororubber, which has outstanding fuel resistance. It can be used in oil at about 200℃ and used as a sealing material for the whole fuel tank of aircraft. The closed-cell sponge made of fluororubber has the advantages of acid resistance, oil resistance, wide temperature range and good insulation. It can be used as sealing material for rocket fuel, solvent, hydraulic oil, lubricating oil and ointment, and can also be used as damping material for rockets and missiles. The temperature resistance can reach 204℃, and the asbestos fiber cloth impregnated with fluororubber emulsion can be made into asbestos rubber board, which can be used in high temperature, combustion and chemical corrosion resistance occasions.
automotive industry
In recent years, with the rapid development of automobile industry, the temperature of automobile engine room has increased, and the use of modified fuel and highly corrosive engine fuel has become increasingly common. Fluorocarbon compounds are widely used as automobile sealing materials.
In order to improve the power of automobile engine, save fuel and ensure the safety of automobile driving, a new fuel injection system has appeared. In this system, the car flows from the fuel tank into the engine and then returns to the fuel tank for circulation, and the mixture of gasoline and oxygen will produce hydroperoxide. Gasoline containing hydrogen peroxide is called "acid gasoline", which can soften or harden various hydrocarbon rubbers. However, fluororubber will not deteriorate due to contact with acidic gasoline.
Every country in the world formulates new environmental protection laws and regulations every year. The total hydrocarbon emission of automobiles is increasingly restricted, and it is increasingly difficult for the automobile industry to meet this requirement. In America, cars must pass the shed test. Fluorine rubber has excellent barrier performance to hydrocarbon permeation (Table 1). If the fuel hose structure is covered with a fluororubber layer, the penetration of hydrocarbons can be reduced.
Automobile fuel system products must work normally in the temperature range of -40℃~ 150℃. However, with the increase of fluorine content, the low temperature resistance of fluororubber becomes worse (the glass transition temperature increases). In order to make products with normal performance at -40℃, it is necessary to improve fluororubber products with poor cold resistance. Nowadays, perfluoroether rubber has been developed and marketed, which effectively improves the low temperature performance of fluororubber, but it is still difficult to popularize it in large quantities because of the price problem.
The automobile industry is very concerned about the fuel methanol, and is eager to carry out the research on FFV (Flexible Fuel Vehicle) which can adapt to any fuel, especially the FFV of rubber parts. When methanol is mixed with gasoline, the volume expansion of fluororubber is about 10%. However, as far as methanol is concerned, the volume swelling of fluororubber varies greatly due to the different fluorine content. When the fluorine content is high, it hardly swells, but with the decrease of fluorine content, the swelling in the low temperature area becomes larger, especially when the fluorine content is 66%, the volume swelling will increase significantly. It can be considered that the SP value of methanol conjugate generated by hydrogen bonding at low temperature is close to that of polymer with fluorine content of 66%.
In a sense, fluororubber is also the product of growth with the progress and development of the times. Although these materials are expensive, they have high practical value because of their excellent wear resistance, oil resistance and reliability. Therefore, it is not surprising that their doses are gradually increasing. The development of fluoride still has great potential and possibility, and it is expected that fluoropolymers with higher use value will be developed in the future.