Development and Application of Special Epoxy Curing Agent for Potting (II)

2.2 The choice of potting material

2.2.1 Selection of Reactive Flame Retardant Resins

Epoxy resin has excellent electrical properties and various mechanical and physical properties. However, the common bisphenol A epoxy resin does not have flame retardancy, and its oxygen index is only about 19.8, which is a more flammable one among thermosetting resins. There are many ways to make epoxy resin flame retardant. We synthesize various factors and use synthetic flame retardants, ie, brominated epoxy resins as the matrix flame retardants. The bromine content is in the range of 16% to 50%. The flame retardancy is related to the bromine content of the resin. Bromine 13% to 15% of the cured resin can achieve the self-extinguishing requirements. The higher the bromine content, the better the flame retardancy. However, although the brominated epoxy resin solves the flame-retardant problem, the chemical resistance, heat resistance, electrical and mechanical properties of the product will be reduced, and the softening point of the brominated epoxy resin will be higher. When used alone, the fluidity is poor. Potting difficult. Therefore, generally used in conjunction with general-purpose epoxy resins. The flame retardancy of cured resin is also related to the amount of brominated epoxy resin. If the bisphenol A type resin is blended with a certain proportion, its fluidity is improved, and the flame retardancy and other various properties are not excessively decreased. Here we use domestically produced EX-40 brominated epoxy resin. Its appearance is a pale yellow viscous liquid with an epoxy value of 0.32 to 0.45 eq/100 g and a bromine content of 19% to 23%.

2.2.2 Selection of toughener

Toughening agents play an important role in potting materials. Toughening modification of epoxy resins is mainly achieved by adding tougheners, plasticizers, etc. to improve its toughness. Toughening agents are mainly active and inert, and their activity is increased. The toughener can participate in the reaction with the epoxy resin to increase the number of chain segments of the reactants, thereby increasing the toughness of the cured product. Experiments suggest that the choice of low molecular liquid rubber-26 is appropriate.

2.2.3 Selection of reactive diluents

Epoxy resins and brominated epoxy resins are used singly because of their high viscosity. A certain amount of diluent is often added to increase their fluidity and permeability, and the service life is prolonged. Diluent is divided into active and inert diluents. . Reactive diluents participate in the curing reaction and increase the number of chain segments of the reactants, which has little effect on the properties of the cured product. Therefore, we have screened a reactive diluent with a flame-retardant effect, which is matched with epoxy resin and brominated epoxy resin, which not only plays a dilution effect, but also improves the flame-retardant properties of the cured product. It is considered that due to the low viscosity of the self-made curing agent, it is preferable that the diluent comprises 0 to 15 parts in the A component. Its appearance is a brown-yellow clear liquid with an epoxy value of 0.27 to 0.32 eq/100 g and a bromine content of >47%.

2.2.4 Selection of Curing Agent

Curing agent is an important component in the formulation of epoxy potting materials, and the properties of cured products depend largely on the structure of the curing agent. To cure at room temperature, aliphatic polyamines are generally used as curing agents, but such curing agents are highly toxic, irritating, and exothermic, and are easily oxidized during curing and use. Therefore, in general, through the modification of polyamines, such as the use of active hydrogen on polyamine amine groups, partial addition of epoxy groups into hydroxyalkylation and partial modification with acrylonitrile into cyanoethylation, The curing agent can achieve a comprehensive effect of low viscosity, low toxicity, low melting point, room temperature curing and a certain toughness. The use of more, toughness, impact performance is good; use less, heat resistance, good hardness. In the formula, it usually takes 30 to 70 parts. After compounding with the A component, it is generally hardened at room temperature (25°C) for 24 hours, fully cured after 7 days, and cured by heating at 40-60°C for 6-8
h. 2.2.5 Selection of curing accelerators

If the accelerator is not added with this formula, the complete curing time is relatively long. To shorten the curing time, a small amount of accelerator may be added. We use a phenolic accelerator with 0 to 5 parts of the hardener and A group. After mixing, the room temperature 6h is initially hardened, and can be fully cured in 24h. The amount of it can not be too much, otherwise it is easy to affect the pot life of the potting material, and has certain influence on the toughness.

3. in conclusion

According to the infrared spectrum of the special curing agent for synthetic potting (not shown in the figure), the epoxy-based absorption peak (910 cm-1) and the acrylonitrile double bond absorption peak (1620 cm-1) (3100 cm- 1) Disappeared, indicating that all the epoxy groups have been opened and the hydroxyalkylation has been achieved. All the acrylonitriles have participated in the addition reaction of the double bonds, achieving the purpose of cyanoethylation.

Using aliphatic polyamines with (2,3-dimethyl)di-butylenetriamine (TAB) with four methyl branches, a modified amine-encapsulating curing agent and epoxy resin were synthesized. Flame-retardant epoxy resin, reactive diluent, and curing accelerator can be used together to obtain a potting material that can be cured at room temperature and has good flame retardancy and flexibility. The potting material can be widely used for insulation and moisture-proof of electronic and electrical components. , shockproof potting, etc., is a new type of potting material with excellent performance.

Source: China Adhesive Network