Introduction of epoxy resin

Epoxy resin is a kind of organic macromolecule compound with two or more epoxy groups in its molecule Except for some, its relative molecular weight is not high The molecular structure of epoxy resin is characterized by the active epoxy group in the molecular chain, which can be located at the end, middle or ring-like structure of the molecular chain Because of the active epoxy group in the molecular structure, they can react with many kinds of curing agents to form insoluble and immiscible polymer with three-way network structure ★ performance and characteristics of epoxy resin 1 Various forms All kinds of resin, curing agent and modifier systems can almost meet the requirements of various applications Their range can be from very low viscosity to high melting point solid 2 Easy to cure With different curing agents, the epoxy resin system can be cured in the temperature range of 0 ~ 180 ℃ 3 Strong adhesion The existence of polar hydroxyl and ether bond in the molecular chain of epoxy resin makes it have high adhesion to various substances The shrinkage of epoxy resin is low and the internal stress is small, which also helps to improve the adhesion strength 4 Low contractility The reaction between epoxy resin and curing agent is carried out by direct addition reaction or ring opening polymerization of epoxides in resin molecules, without water or other volatile by-products Compared with unsaturated polyester resin and phenolic resin, they show very low shrinkage (less than 2%) during curing 5 Mechanical properties The cured epoxy resin system has excellent mechanical properties 6 Electrical performance The cured epoxy resin system is a kind of excellent insulating material with high dielectric property, surface leakage resistance and arc resistance 7 Chemical stability Generally, cured epoxy resin system has excellent alkali resistance, acid resistance and solvent resistance As with other properties of cured epoxy systems, chemical stability depends on the resin and curing agent selected Proper selection of epoxy resin and curing agent can make it have special chemical stability 8 Dimensional stability The synthesis of the above properties makes the epoxy resin system have outstanding dimensional stability and durability 9 Mildew resistance The cured epoxy system is resistant to most molds and can be used in harsh tropical conditions ★ classification according to molecular structure, epoxy resins can be generally divided into five categories: 1 Glycidyl ether epoxy resin 2 Glycidyl ester epoxy resin 3 Glycidyl amine epoxy resin 4 Linear aliphatic epoxy resin 5 Aliphatic epoxy resin The most widely used type of epoxy resin in the composite industry is the first type of glycidyl ether epoxy resin mentioned above, among which the bisphenol propane type epoxy resin (bisphenol a type epoxy resin for short) is the main one The next is glycidyl amine epoxy resin 1 Glycidyl ether epoxy resin glycidyl ether epoxy resin is formed by polycondensation of phenol or alcohol containing active hydrogen with epichlorohydrin (1) diphenylpropane type epoxy resin diphenylpropane type epoxy resin is formed by condensation of diphenylpropane and epichlorohydrin Industrial diphenylpropane epoxy resin is actually a mixture of molecules with different degrees of polymerization Most of them are linear structures with two epoxy ends A few molecules may be branched, and a few terminated by chlorohydrin group rather than epoxy group Therefore, the epoxy content and chlorine content of the epoxy resin have a great influence on the curing of the resin and the properties of the cured products The industrial control indexes of the resin are as follows: ① epoxy value Epoxy value is the most important index to identify the properties of epoxy resin The type of industrial epoxy resin is differentiated according to different epoxy values Epoxy value refers to the quantity of epoxy group substance per 100g resin The reciprocal of epoxy value multiplied by 100 is called epoxy equivalent The meaning of epoxy equivalent is: grams of epoxy resin containing 1mol epoxy group ② inorganic chlorine content The chloride ion in the resin can be used together with amine curing agent to affect the curing of the resin and the electrical properties of the cured resin Therefore, the chlorine content is also an important index of the epoxy resin ③ organic chlorine content The content of organochlorine in the resin indicates the content of the chlorohydrin group in the molecule which does not react in a closed loop It should be reduced as much as possible, otherwise it will also affect the curing of the resin and the properties of the cured products ④ volatile matter ⑤ viscosity or softening point (2) phenolic polyepoxy resin phenolic polyepoxy resin includes phenol formaldehyde type and o-cresol formaldehyde type polyepoxy resin Compared with diphenylpropane type epoxy resin, there are more than two epoxy groups in the online type molecule Therefore, the cured product has high crosslinking density, excellent thermal stability, mechanical properties, electrical insulation, water resistance and corrosion resistance They are formed by condensation of phenolic resin and epichlorohydrin (3) other Polyhydroxyphenol glycidyl ether type epoxy resins have practical representatives: resorcinol type epoxy resin, resorcinol formaldehyde type epoxy resin, tetrahydroxyethane type epoxy resin and trihydroxyphenylmethane type epoxy resin These polyfunctional glycidyl ether resins have high thermal deformation temperature and rigidity after curing, which can be used alone Or it can be blended with E-type resin for high performance composite (ACM), printed circuit board and other matrix materials (4) aliphatic polyol glycidyl ether type epoxy resin aliphatic polyol glycidyl ether contains two or more epoxy groups, most of which have low viscosity; most of them are long-chain linear molecules, so they are flexible 2 Other types of epoxy resin (1) glycidyl ester epoxy resin Compared with diphenylpropane epoxide resin, glycidyl ester epoxy resin has the advantages of low viscosity, good usability, high reactivity, high adhesion, good mechanical properties of solidified products, good electrical insulation, good weather resistance, and good ultra-low temperature resistance Under ultra-low temperature conditions, it still has higher bonding strength than other types of epoxy resin 。 It has good surface glossiness, light transmittance and weather resistance (2) glycidyl amine epoxy resin has the advantages of multifunction, high epoxy equivalent, high cross-linking density and significantly improved heat resistance In the past, the superior adhesion and heat resistance of glycidyl amine epoxy resin have been used to manufacture carbon fiber reinforced composite (CFRP) for aircraft secondary structure materials at home and abroad (3) alicyclic epoxies are made by epoxidation of the double bonds of alicyclic alkenes Their molecular structure is quite different from that of diphenylpropane epoxies and other epoxies The former epoxy group is directly connected to the alicyclic ring, and the latter epoxy group is connected to the benzene nucleus or aliphatic hydrocarbon with epoxy propyl ether The curing products of alicyclic epoxy resin have the following characteristics: ① high compression and tensile strength; ② long-term exposure at high temperature can still maintain good mechanical properties; ③ good arc resistance, UV aging resistance and weather resistance (4) aliphatic epoxy resin has no benzene nucleus or alicyclic structure in its molecular structure There are only fat chains, and the epoxy group is linked to the fat chain The cured epoxy polybutadiene resin has good strength, toughness, adhesion and temperature resistance.