Epoxy resin, phenolic resin and unsaturated polyester resin are called three general-purpose thermosetting resins. They are the most widely used and most widely used thermosetting resins. Epoxy resins contain unique epoxy groups, as well as active groups and polar groups such as light groups and ether bonds, and thus have many excellent properties. Compared with other thermosetting resins, epoxy resins have the most types and grades with different performances. There are more types of epoxy resin curing agents, plus a large number of accelerators, modifiers, additives, etc., can be a variety of combinations and combinations. Thus, various epoxy curing systems and cured products with excellent properties and various characteristics can be obtained. It can almost meet and meet the requirements of various performance and process performance. This is unmatched by other thermosetting resins.
1. Performance characteristics of epoxy resin and its cured products
(1) High mechanical properties. Epoxy resin has strong cohesion and dense molecular structure, so its mechanical properties are higher than general-purpose thermosetting resins such as phenolic resin and unsaturated polyester.
(2) Excellent adhesion performance. The extremely active epoxy groups, hydroxyl groups, ether bonds, amine bonds, ester bonds and other polar groups in the epoxy resin curing system give epoxy cured products with extremely high adhesive strength. Coupled with its high cohesive strength and other mechanical properties, it has particularly strong adhesive properties and can be used as a structural adhesive.
(3) The curing shrinkage rate is small. Generally 1%～2%. It is one of the varieties with the smallest curing shrinkage rate among thermosetting resins (phenolic resin 8%-10%; unsaturated polyester resin 4%-6%; silicone resin 4%-8%). The linear expansion coefficient is also very small, generally 6×10-5/℃. Therefore, the size of the product is stable, the internal stress is small and it is not easy to crack.
(4) Good manufacturability. Epoxy resin basically does not produce low molecular volatiles, so it can be molded under low pressure or contact compression molding. The flexibility of formula design is great, and a formula suitable for various technological requirements can be designed.
(5) Good electrical performance. It is one of the best dielectric properties among thermosetting resins.
(6) Good stability. Epoxy resins without impurities such as alkalis and salts are not easily deteriorated. As long as it is stored properly (sealed, protected from moisture, not exposed to high temperatures), its storage period is 1 year. It can still be used if the inspection passes after the expiration date. The epoxy cured product has excellent chemical stability. Its corrosion resistance to alkali, acid, salt and other media is better than that of unsaturated polyester resin, phenolic resin and other thermosetting resins.
(7) The heat resistance of the epoxy cured product is generally 80 to 100°C. The heat-resistant varieties of epoxy resin can reach 200 ℃ or higher.
(8) Among the thermal resins, epoxy resin and its cured products have the best comprehensive performance.
2. Application characteristics of epoxy resin
(1) has great flexibility and diversity in formula design. According to different performance and process performance requirements, we can design the best targeted formula. This is a major feature and advantage in epoxy resin applications. However, each optimal formula has a certain scope of application (conditions), and it should not be used under any process conditions and any conditions of use. In other words, there is no "universal" best formula. Different optimal formulas must be designed according to different conditions. The curing principles of epoxy resin curing systems with different formulations are not exactly the same, so the curing process of epoxy resin, that is, the curing process conditions, has a great influence on the structure and performance of epoxy cured products. The performance of the product obtained by the same formula under different curing process conditions will be very different. Therefore, making the best material formulation design and process design is the key to epoxy resin application technology, and it is also the technical secret. In order to be able to produce and develop the epoxy materials with the required performance, it is necessary to design the corresponding special formula and the molding process conditions. Therefore, it is necessary to deeply understand and master the structure and performance of epoxy resin and its curing agent, modifier, etc., the reaction mechanism between them and the influence on the structure and performance of epoxy cured product. Only in this way can the material formulation design and process design be handy, use freely, obtain the best plan, produce and develop the best performance and lowest cost epoxy materials and products.
(2) Different epoxy resin curing systems can be cured at low temperature, room temperature, medium temperature or high temperature, can be cured on a wet surface or even in water, can be cured quickly, and can also be cured slowly, so it adapts to the requirements of construction and manufacturing processes Very strong. Epoxy resin can be molded by low pressure or contact pressure molding, so it can reduce the requirements for molding equipment and molds, reduce investment and reduce costs.
(3) Among the three general-purpose thermosetting resins, the price of epoxy resin is relatively high, thus being affected to a certain extent in application. However, because of its excellent performance, it is mainly used in applications requiring high performance, especially in areas requiring high comprehensive performance.