Epoxy resins have excellent dielectric properties, mechanical properties, adhesive properties, corrosion resistance, small curing shrinkage and linear expansion coefficient, good dimensional stability, good processability and excellent overall performance. What’s more, due to the flexibility and diversity of epoxy material formulation design, it is possible to obtain epoxy materials that can adapt to almost all kinds of specialized performance requirements, thus making it widely used in the field of electronics and electrical appliances. And its growth momentum is very strong, especially in Japan. In 1998, the proportion of epoxy resin used in the field of electronic and electrical appliances to the total consumption of epoxy resin in each country or region was 40% in Japan, 24% in Western Europe, 19% in the United States, and only 13% in China. With the rapid development of electronic industry, one of the four pillar industries in China, it is expected that the application of epoxy resin in this field will have a substantial growth.
Epoxy resins are mainly used in the field of electronics and electrical appliances: casting materials for electrical appliances such as power transformers, transformers and insulators, potting materials for electronic devices, plastic sealing materials for integrated circuits and semiconductor components, circuit boards and copper-clad boards, insulating coatings for electronic appliances, insulating adhesives, insulating structural materials such as high-voltage insulator mandrels and insulating parts in high-voltage and high-current switches. The last three types of epoxy materials will be introduced one by one in the following chapters.
The development direction of epoxy resin electronic and electrical packaging and insulation materials is mainly: to improve the heat resistance, dielectric properties and flame retardancy of the material, reduce the water absorption rate, shrinkage rate and internal stress. The main ways of improvement are: synthesis of new epoxy resin and curing agent; high purity of raw materials; modification of epoxy resin, including toughening, flexibility, filling, reinforcement, blending, etc.; development of bromine-free flame retardant system; improvement of molding process methods, equipment and technology.
1. Epoxy resin pouring and pouring material
Epoxy resin casting is the process of pouring epoxy resin, curing agent and other matching materials into the set mold and cross-linking and curing from thermoplastic fluid into hot lying products. Because of the excellent electrical and mechanical properties of epoxy resin casting products, epoxy resin casting has been widely used and developed rapidly in the electrical industry.
The process method of epoxy resin casting has different differentiation methods from different process conditions to understand. From the way of material entering the mold, it can be divided into pouring and pressure injection. Pouring refers to the self-flow of material into the mold, and it is divided into normal pressure pouring and vacuum pouring. Pressure injection refers to the material entering the mold under external pressure, and in order to force the shrinkage, the material curing process, but still maintain a certain external pressure, it is developed from the past simple pressure gel method to the current mature automatic pressure gel method.
From the material curing temperature to distinguish can be divided into normal temperature pouring method and high temperature pouring method. The choice of normal temperature or high temperature casting method is determined by the nature of the casting material itself, the fundamental difference is the temperature conditions necessary for the curing process of the casting material.
From the speed of material curing, it can be divided into normal curing method and fast curing method. The time required from the entry of the material into the mold to the removal of the mold is the initial curing time, which takes several hours or even a dozen hours for the ordinary curing method, but only ten minutes to a few minutes for the rapid curing method.
The modern casting process, the application of more mature casting process method is mainly vacuum casting method and automatic pressure gel method.
(1)Vacuum casting process
Vacuum casting process is the most widely used and most mature method in epoxy resin casting.
For an electrical insulation product casted with epoxy resin, it requires perfect appearance, stable size, mechanical and electrical properties. These properties depend on the design of the part itself, the quality of the mold, the selection of the casting material and the control of the casting process. The technical point of epoxy resin vacuum casting is to reduce the air gap and air bubbles in the cast product as much as possible. In order to achieve this goal, it is necessary to control the vacuum skin, temperature and process time in each process such as raw material pretreatment, mixing and casting.
(2) Automatic pressure gelation process
The automatic pressure gelation process is a technology developed by CIB into Ctigy in Switzerland in the early 1970s. Because this process is similar to the thermoplastic injection molding process, it is also called the pressure injection process. Its most significant advantage is that it greatly improves the efficiency of the pouring process. It can be said that the successful development and industrial application of automatic pressure gelation technology is a revolution in the development of vacuum casting from intermittent, manual operation to automated production, and the main differences between it and vacuum casting are
1) The casting material is injected into the mold by the injection port through the pipe under external pressure.
2) The mixing temperature of the material is low and the temperature of the mold is high.
3) After the material is injected into the mold, the curing speed is fast, usually from ten minutes to several minutes.
4)The mold is fixed on the hydraulic press, and the mold heating is provided by the electric heater on the mold or mold fixing plate.
5) The closing and dismantling of the mold is done by the movement of the mold fixing plate on the hydraulic press.
Features of automatic pressure gel process: high mold utilization, short production cycle, high labor efficiency; low degree of damage during mold loading and unloading, long mold service life; high degree of automation, light labor intensity of operators; good product formability and improved product quality.
2. Epoxy resin potting and potting materials
(1)The use of potting material
Potting is an important application area of epoxy resin. It has been widely used in electronic device manufacturing industry, and is an important insulation material indispensable for electronic industry.
Potting is to put the liquid epoxy resin compound into the device with electronic components and circuits by mechanical or manual means, and then curing under normal temperature or heating conditions to become a thermal polymer insulating material with excellent performance. Its role is to: strengthen the integrity of electronic devices, improve the resistance to external shocks and vibrations; improve the internal components, lines between insulation, conducive to device miniaturization, lightweight; avoid direct exposure of components, lines, improve the device’s waterproof, moisture-proof performance.
(2)Classification of potting compounds
Epoxy potting compounds are widely used, with many different technical requirements and a wide variety. From the curing conditions, there are two types of room temperature curing and heating curing. From the dosage form, there are two-component and one-component two categories. Multi-component dosage form, due to the use of inconvenient, do not see as a commodity.
Room temperature curing epoxy potting material is generally two-component, potting can be cured without heating, the equipment requirements are not high, easy to use. The disadvantage is that the compound work teaching degree is large, poor permeability, short applicable period, difficult to achieve automated production, and the cured material heat resistance and electrical properties are not very high. Generally used for low-pressure electronic devices potting or not suitable for heating curing occasions.
(3) Potting material requirements
Heating curing two-component epoxy potting compound, is the largest amount, the most widely used varieties. It is characterized by small teaching degree of compound work, good technology, long application period, good permeability, excellent overall performance of cured products, suitable for automatic production line of high-voltage electronic devices.
One-component epoxy potting material, is a new variety developed abroad in recent years, need to be heated and cured. Compared with two-component heating and curing potting materials, the outstanding advantage is that the required potting equipment is simple, easy to use, the quality of potting products on the equipment and process dependence is small. The disadvantage is that the cost is higher, the material storage conditions require strict, the epoxy potting material used should meet the following requirements:
1) Good performance, long application period, suitable for large-volume automatic production line operation.
2) Small teaching degree, strong permeability, can be filled with components and between lines.
3) Filling and curing process, filler and other powder components sink small, no delamination.
4) Low curing exothermic peak, curing shrinkage is small.
5) Excellent electrical and mechanical properties of cured products, good heat resistance, good adhesion to a variety of materials, water absorption and small coefficient of linear expansion.
6) Some occasions also require potting compounds with flame retardant, weathering, thermal conductivity, resistance to high and low temperature alternation and other properties. In recent years, with the rapid development of the electronics industry, China has an excellent epoxy potting compound research and development team. Professional manufacturers continue to grow in scale, the degree of commercialization of products has increased significantly, the initial formation of a complete range of new industries.
More information or free samples or price quotations, please contact us via email: sales@yqxpolymer.com, or voice to us at: +86-28-8411-1861.
Some pictures and texts are reproduced from the Internet, and the copyright belongs to the original author. If there is any infringement, please contact us to delete.
