Specific application of epoxy resin

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Specific application of epoxy resin

[Source: Electronic Design Technology] [Author: admin] [Time: 2006-1-7 9:45:27] [Clicks: 585]

Epoxy resin has excellent dielectric properties, mechanical properties, bonding properties, and corrosion resistance, small curing shrinkage and linear expansion coefficient, good dimensional stability, good processability, and excellent comprehensive performance. Due to the flexibility and diversity of epoxy material formula design, epoxy materials that can almost meet various special performance requirements can be obtained, so that it is widely used in the field of electronic appliances. And its growth momentum is very strong. Especially in Japan, it is developing very fast. In 1998 , the proportion of epoxy resin used in the field of electronic appliances in the world's major epoxy resin consumption countries and regions was 40 % in Japan, 24 % in Western Europe, and 19 % in the United States . China only accounted for 13% . With the rapid development of the electronics industry , one of China's four pillar industries , it is expected that the application of epoxy resin in this field will increase significantly. The main applications of epoxy resin in the field of electronic and electrical appliances include: casting materials for electrical appliances such as power transformers, transformers, insulators, potting materials for electronic devices, plastic sealing materials for integrated circuits and semiconductor components, circuit board and copper clad laminate materials, insulating coatings for electronic appliances, insulating adhesives, high-voltage insulator core rods, insulating components in high-voltage and high-current switches, and other insulating structural materials. The development direction of epoxy resin electronic and electrical packaging and insulation materials is mainly to improve the heat resistance, dielectricity and flame retardancy of materials, and reduce water absorption, shrinkage and internal stress. The main ways to improve are: synthesizing new epoxy resins and curing agents; high purity of raw materials; modification of epoxy resins, including toughening, flexibilization, filling, reinforcement, blending, etc.; developing bromine-free flame retardant systems; and improving molding process methods, equipment and technologies. 1Epoxy resin casting and casting materials Epoxy resin casting is the process of pouring epoxy resin, curing agent and other ingredients into a set mold, and curing the thermoplastic fluid into a hot-rolled product through cross-linking. Since epoxy resin casting products combine excellent electrical and mechanical properties, epoxy resin casting has been widely used and developed rapidly in the electrical industry. The process of epoxy resin casting has different ways of distinguishing from different process conditions. It can be divided into pouring and pressure casting based on the way the material enters the mold. Pouring refers to the material flowing into the mold by itself. It is divided into normal pressure casting and vacuum casting. Pressure casting refers to the material entering the mold under external pressure, and in order to force shrinkage compensation, a certain external pressure is still maintained during the material curing process. It has developed from the simple pressurized gel method in the past to the mature automatic pressure gel method now. From the perspective of the curing temperature of the material, it can be divided into normal temperature casting method and high temperature casting method. The choice of normal temperature or high temperature casting method is determined by the properties of the casting material itself. The fundamental difference is the temperature conditions required for the curing process of the casting material. From the perspective of the curing speed of the material, it can be divided into ordinary curing method and rapid curing method. The time required from the material entering the mold to demolding is the initial curing time. The ordinary curing method takes several or even more than ten hours, while the rapid curing method only takes more than ten minutes to dozens of minutes. In modern casting technology, the relatively mature casting process methods are mainly vacuum casting method and automatic pressure gelation method. (1) Vacuum casting process Vacuum casting process is currently the most widely used and most mature process method in epoxy resin casting. For an electrical insulation product cast by epoxy resin, it requires perfect appearance, stable dimensions, and qualified mechanical and electrical properties. These properties depend on various aspects such as the design of the part itself, the quality of the mold, the selection of casting materials, and the control of casting process conditions. The technical key point of epoxy resin vacuum casting is to minimize the air gaps and bubbles in the cast product. In order to achieve this goal, the vacuum skin, temperature and process time need to be controlled in each process of raw material pretreatment, mixing, pouring, etc. (2) Automatic pressure gelation process The automatic pressure gelation process is a technology developed by Swiss CIB Ctigy in the early 1970s . Because this process is similar to the process method of thermoplastic injection molding, it is also called pressure injection process. Its most significant advantage is that it greatly improves the pouring efficiency. It can be said that the successful development of automatic pressure gelation technology and its large-scale application in industry are a revolution in the development of vacuum pouring from intermittent and manual operation to automated production. The main differences between it and vacuum pouring are: 1) The pouring material is injected into the mold through the pipe from the injection port under external pressure. 2) The mixing temperature of the material is low and the mold temperature is high. 3) After the material enters the mold, the curing speed is fast, usually from more than ten minutes to dozens of minutes. 4) The mold is fixed on the hydraulic press, and the mold heating is provided by the electric heater on the mold or the mold fixing plate. 5) The assembly and disassembly of the mold is completed by moving the mold fixing plate on the hydraulic press. The characteristics of the automatic pressure gel process are: high mold utilization, short production cycle, high labor efficiency; low degree of damage during mold loading and unloading, and long mold service life; high degree of automation and low labor intensity for operators; good product formability and improved product quality. 2. Potting of epoxy resin and potting materials (1) Application of potting materials Potting is an important application field of epoxy resin. It has been widely used in the electronic device manufacturing industry and is an important insulating material that is indispensable to the electronic industry. Potting is to mechanically or manually pour liquid epoxy resin compound into devices equipped with electronic components and circuits, and solidify it under normal temperature or heating conditions to become a thermally resistant polymer insulating material with excellent performance. Its functions are: to strengthen the integrity of electronic devices and improve their resistance to external impact and vibration; to improve the insulation between internal components and circuits, which is conducive to the miniaturization and lightweight of devices; to avoid direct exposure of components and circuits, and to improve the waterproof and moisture-proof performance of devices. (2) Classification of potting materials Epoxy potting materials have a wide range of applications, with very different technical requirements and a wide variety of varieties. From the perspective of curing conditions, there are two types: room temperature curing and heating curing. From the perspective of dosage form, there are two types: two-component and single-component. Multi-component dosage forms are not common as commodities due to their inconvenience in use. Room temperature curing epoxy potting materials are generally two-component. They can be cured without heating after potting. They have low requirements on equipment and are easy to use. The disadvantages are that the composite material has high working temperature, poor impregnation, short working period, and is difficult to achieve automated production. In addition, the heat resistance and electrical properties of the cured material are not very high. It is generally used for potting low-voltage electronic devices or in places where heating and curing are not suitable. (3) Technical requirements for potting materials Heat-curing two-component epoxy potting materials are the most widely used and widely used variety. Its characteristics are low working temperature of the composite material, good processability, long working period, good impregnation, excellent comprehensive performance of the cured material, and are suitable for use in automatic production lines of high-voltage electronic devices. Single-component epoxy potting materials are new varieties developed abroad in recent years and require heating and curing. Compared with two-component heat-curing potting materials, the outstanding advantages are that the required potting equipment is simple, easy to use, and the quality of the potting product is less dependent on the equipment and process. In addition to the disadvantages, the cost is relatively high and the material storage conditions are strictly required. The epoxy potting material used should meet the following requirements: 1) Good performance, long application period, suitable for large-scale automatic production line operation. 2) Small degree of penetration, strong permeability, can fill components and lines. 3) During the potting and curing process, the powder components such as fillers have little sedimentation and no stratification. 4) The curing exothermic peak is low and the curing shrinkage is small. 5) The cured product has excellent electrical and mechanical properties, good heat resistance, good adhesion to a variety of materials, small water absorption and linear expansion coefficient. 6) In some occasions, the potting material is also required to have flame retardancy, weather resistance, thermal conductivity, high and low temperature alternation resistance and other properties. In recent years, with the rapid development of the electronics industry, China has an excellent epoxy potting material research and development team, the scale of professional manufacturers has continued to grow, the degree of product commercialization has been significantly improved, and a relatively complete range of emerging industries has been initially formed.