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1. Various forms. Various resins, curing agents, and modifier systems can almost meet the requirements of various applications on the form, and their range can range from extremely low viscosity to high melting point solids.
2. Easy curing. Using various 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 bonds inherent in the epoxy resin molecular chain makes it highly adhesive to various substances. Epoxy resins have low shrinkage when cured, and the generated internal stress is small, which also helps to improve the adhesion strength.
4. Low shrinkage. The reaction of the epoxy resin and the curing agent used is carried out by direct addition reaction or ring-opening polymerization reaction of epoxy groups in the resin molecule, and no water or other volatile by-products are released. Compared with unsaturated polyester resins and phenolic resins, 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 an excellent insulating material with high dielectric properties, resistance to surface leakage, and arc resistance.
7. Chemical stability. Generally, the cured epoxy resin system has excellent alkali resistance, acid resistance, and solvent resistance. Like other properties of cured epoxy systems, chemical stability also depends on the resin and curing agent chosen. Proper selection of epoxy resin and curing agent can make it have special chemical stability.
8. Dimensional stability. The combination of many of the above properties gives the epoxy resin system outstanding dimensional stability and durability.
9. Resistant to mold. The cured epoxy resin system is resistant to most molds and can be used under harsh tropical conditions.
According to the molecular structure, epoxy resin can be roughly divided into five categories:
1. Glycidyl ether epoxy resin
2. Glycidyl ester epoxy resin
3. Glycidylamine epoxy resin
4. Linear aliphatic epoxy resin
5. Alicyclic epoxy resin
The most widely used epoxy resins in the composite industry are the above-mentioned first-type glycidyl ether-based epoxy resins, and among them, diphenol-based propane type epoxy resins (referred to as bisphenol-A type epoxy resins) are the main ones. The second is glycidyl amine epoxy resin.
1. Glycidyl ether epoxy resin
The glycidyl ether epoxy resin is formed by polycondensation of phenols or alcohols containing active hydrogen and epichlorohydrin.
(1) Diphenol-based propane epoxy resin
Diphenol-based propane type epoxy resin is formed by polycondensation of diphenol-based propane and epichlorohydrin.
The industrial control indexes as resins are as follows:
① Epoxy value. Epoxy value is the most important indicator to identify the properties of epoxy resin. Industrial epoxy resin models are distinguished according to different epoxy values. Epoxy value refers to the amount of epoxy-containing substance per 100 g of resin. The reciprocal of the epoxy value multiplied by 100 is called the epoxy equivalent. The meaning of epoxy equivalent is grams of epoxy resin containing 1 mol of the epoxy group.
②Inorganic chlorine content. The chloride ion in the resin can complex with the amine curing agent to affect the curing of the resin, and also affect the electrical properties of the cured resin, so the chlorine content is also an important indicator of epoxy resins.
③Organic chlorine content. The organic chlorine content in the resin indicates the content of the part of the chlorohydrin group in the molecule that has not undergone the ring-closing reaction. Its content should be reduced as much as possible, otherwise, it will also affect the curing of the resin and the performance of the cured product.
④ Volatile matter.
⑤Viscosity or softening point.
(2) Phenolic poly epoxy resins include the phenol-formaldehyde type and o-cresol formaldehyde type poly epoxy resins. Compared with diphenol-based propane type epoxy resins, they contain more than two in linear molecules The epoxy group, so the cured product has a large cross-link density, has excellent thermal stability, mechanical properties, electrical insulation, water resistance, and corrosion resistance. They are formed by polycondensation of novolak resin and epichlorohydrin.
(3) Other polyhydroxyphenol glycidyl ether type epoxy resins such as resins with practicality are: resorcinol type epoxy resin, resorcinol-formaldehyde type epoxy resin, tetraphenyl-based epoxy resin Alkane epoxy resin, and tri hydroxyphenyl methane epoxy resin, these multifunctional glycidyl ether resins have high heat distortion temperature and rigidity after curing and can be blended alone or with general E-type resin for high-performance compounding Materials (ACM), printed circuit boards and other substrate materials.
(4) Aliphatic polyol glycidyl ether type epoxy resin The aliphatic polyol glycidyl ether molecule contains two or more epoxy groups, most of these resins have very low viscosity; most are long-chain Linear molecules are therefore flexible.
2. Other types of epoxy resin
(1) Compared with glycidyl ester epoxy resins, glycidyl ester epoxy resins and diphenol-based propane epoxidized resins have low viscosity, good processability, high reactivity, and higher adhesion than general-purpose epoxy resins. High, good mechanical properties of cured products; good electrical insulation; good weather resistance, and good ultra-low temperature resistance, under ultra-low temperature conditions, it still has a higher bonding strength than other types of epoxy resin. It has good surface gloss, good light transmittance, and weather resistance.
(2) Glycidylamine epoxy resin The advantages of this type of resin are multi-functionality, high epoxy equivalent, high crosslinking density, and significantly improved heat resistance. Previously, at home and abroad, glycidyl amine epoxy resin has been used to make carbon fiber-reinforced composite materials (CFRP) for secondary structural materials of airplanes by using the superior adhesion and heat resistance.
(3) Alicyclic epoxy resins These epoxy resins are made by epoxidation of the double bonds of alicyclic olefins, their molecular structure, and diphenol-based propane epoxy resins and other epoxy resins There is a big difference. The former epoxy groups are directly connected to the alicyclic ring, while the latter epoxy groups are all connected to the benzene core or aliphatic hydrocarbon with epoxypropyl ether. The cured products of alicyclic epoxy resins have the following characteristics: ①high compression and tensile strength; ②long-term exposure to high-temperature conditions can still maintain good mechanical properties; ③arc resistance, ultraviolet aging resistance, and Good weather resistance.
(4) Aliphatic epoxy resin The molecular structure of this type of epoxy resin not only has no benzene core but also has no alicyclic structure. There is only a fatty chain, and the epoxy group is connected to the fatty chain. After curing, the epoxidized polybutadiene resin has good strength, toughness, adhesion, and resistance to positive and negative temperatures.