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Basic knowledge of epoxy resin

May 22, 2020

Basic knowledge of epoxy resin and epoxy resin adhesive

 (1) The concept of epoxy resin Epoxy resin refers to the general name of polymer compounds containing more than two epoxy groups in the polymer chain structure. It is a thermosetting resin. The representative resin is bisphenol A epoxy resin.

(2) Characteristics of epoxy resin (usually refers to bisphenol A epoxy resin)

 1. The application value of epoxy resin alone is very low, it needs to be used with curing agent to have practical value.

 2. High bonding strength: The bonding strength of epoxy resin glue is in the forefront among synthetic adhesives.

 3. The curing shrinkage rate is small, and the shrinkage rate of epoxy resin adhesive is the smallest among adhesives, which is also one of the reasons for the high curing adhesiveness of epoxy resin adhesive. For example: phenolic resin glue: 8-10%; silicone resin glue: 6-8% polyester resin glue: 4-8%; epoxy resin glue: 1-3% if modified epoxy resin glue The shrinkage can be reduced to 0.1-0.3%, and the thermal expansion coefficient is 6.0 × 10-5 / ℃

4. Good chemical resistance: the ether group, benzene ring and fatty hydroxyl group in the curing system are not easy to be corroded by acid and alkali. It can be used for two years in seawater, petroleum, kerosene, 10% H2SO4, 10% HCl, 10% HAc, 10% NH3, 10% H3PO4 and 30% Na2CO3; and soaked in 50% H2SO4 and 10% HNO3 at room temperature for half a year % NaOH (100 ℃) immersed for one month, the performance remains unchanged.

  5. Excellent electrical insulation: the breakdown voltage of epoxy resin can be greater than 35kv / mm6. Good process performance, stable product size, good resistance and low water absorption. The advantages of bisphenol A epoxy resin are good, but there are also its disadvantages: ①. The operation viscosity is large, which seems a little inconvenient in construction ②. The cured material is brittle and has low elongation. ③. Low peel strength. ④. Poor resistance to mechanical shock and thermal shock


 (3) Application and development of epoxy resin

1. The development history of epoxy resin: epoxy resin was applied for Swiss patent by P. Castam in 1938, the first epoxy adhesive was developed by Ciba in 1946, and epoxy resin was developed by SOCreentee in 1949 in the United States. Paint, China began industrial production of epoxy resin in 1958.

 2. Application of epoxy resin: ① coating industry: epoxy resin has the largest demand in the coating industry, and currently widely used are water-based coatings, powder coatings and high-solids coatings. It can be widely used in industries such as pipeline containers, automobiles, ships, aerospace, electronics, toys, crafts, etc. ②Electronics industry: Epoxy resin can be used for electrical insulation materials, such as rectifiers, transformers, sealing and pouring; sealing and protection of electronic components; insulation treatment and bonding of electromechanical products; sealing and bonding of batteries; capacitors, resistance, inductance The surface of the device is covered. ③ Hardware accessories, handicrafts, sports goods industry: can be used on signs, accessories, trademarks, hardware, rackets, fishing tackle, sporting goods, handicrafts and other products. ④Photoelectric industry: It can be used for packaging, pouring and bonding of light-emitting diode (LED), digital tube, pixel tube, electronic display screen, LED lighting and other products. ⑤Construction industry: It is also widely used in industries such as roads, bridges, floors, steel structures, construction, wall coatings, dams, engineering construction, and repair of cultural relics. ⑥Adhesives, sealants and composite materials: such as the bonding of various materials such as wind turbine blades, crafts, ceramics, glass, etc., the composite of carbon fiber plates, the sealing of microelectronic materials, etc.

     (4) Characteristics of epoxy resin adhesive

 1. Epoxy resin is to reprocess or modify its characteristics on the basis of epoxy resin, so that its performance parameters and other meet specific requirements. Generally, epoxy resin adhesive also needs to be used with curing agent to match, and needs It can be fully cured after mixing evenly. Generally, epoxy resin glue is called A glue or main agent, and curing agent is called B glue or curing agent (hardener).

 2. The main characteristics of epoxy resin before curing are: color, viscosity, specific gravity, ratio, gel time, usable time, curing time, thixotropy (flow stop), hardness, surface tension, etc. Viscosity: refers to the internal frictional resistance generated by the colloid in the flow, and its value is determined by factors such as substance type, temperature, and concentration. Gel time: The curing of glue is the process of conversion from liquid to curing. The time from the start of the glue to the critical state when the colloid tends to solid is the gel time, which is determined by the mixing amount of epoxy resin, temperature and other factors Thixotropy: This property refers to the phenomenon that when the colloid is touched by external force (shaking, stirring, vibration, ultrasonic wave, etc.), the colloid becomes thinner with the external force. When the external factors stop acting, the colloid returns to its original consistency. Hardness): refers to the resistance of the material to external forces such as imprinting and scratching. According to different test methods, there are Shore hardness, Brinell hardness, Rockwell hardness, Mohs hardness, Barcol hardness, Vichers hardness and so on. The hardness value is related to the type of hardness tester. Among the commonly used hardness testers, the Shore hardness tester has a simple structure and is suitable for production inspection. The Shore hardness tester can be divided into A type, C type, and D type. A type is used to measure softness. Colloids, C and D types are used to measure semi-hard and hard colloids. Surface tension: The attraction of molecules inside a liquid puts the molecules on the surface under an inward force. This force causes the liquid to shrink its surface area as much as possible to form a force parallel to the surface, called surface tension. In other words, the mutual traction force per unit length between two adjacent parts of the liquid surface is a manifestation of molecular force. The unit of surface tension is N / m. The surface tension is related to the nature, purity and temperature of the liquid