Development and application of special epoxy curing agent for potting (I)

Abstract : A new type of aliphatic amine TAB was prepared by chemical modification. And epoxy resin, flame retardant, toughening agent, etc. formulated into an epoxy potting material, discussed its formulation and preparation process and performance.

Keywords: potting special epoxy curing agent; flame retardant; toughening agent; epoxy potting compound

Epoxy resin is an excellent thermosetting resin with a wide range of applications. The conversion from a linear oligomer to a bulk structure must be accomplished by a curing agent.

The excellent curing agent can give epoxy resin cured products excellent physical and mechanical properties, adhesive properties, heat resistance, chemical resistance, and electrical insulation properties, and is thus widely used in various fields of the national economy.

In recent years, with the continuous development of the electronic and electrical industry, epoxy resin is also the most widely used in electrical and electronic fields. In the packaging of electronic components, transformers, current transformers, motors, and so on, the packaged electronic products play a role in supporting and dielectric insulation, and they also function as heat transfer, heat dissipation, moisture resistance, and flame retardancy for the sealed components.

At present, the performance requirements for cured epoxy resins are getting higher and higher. Many potting materials and encapsulants for electrical insulating materials, castings, and electrical components require flexibility and flame retardant properties, while common types of epoxy potting are required. Seals, the epoxy resin cured material has a high elastic modulus, low impact resistance, brittle and easy to produce cracks, does not have flame retardant properties. Therefore, we selected the fat of (2,3 dimethyl) dibutylene triamine (TAB) with four methyl branches for how to change the brittleness of the epoxy potting material and increase the flame retardancy. Group polyamines, they have synthesized a modified amine curing agent, and epoxy resin, reactive flame retardant, toughening agent, diluent, curing promotion prepared as a room temperature curing, with a certain degree of flexibility and resistance Burnable epoxy potting compound.

1 Experimental section

1.1 Raw materials and instruments

1.1.1 Raw materials: (2,3 dimethyl) dibutylene triamine (TAB), Henan Tianze Industrial Co., Ltd.; Acrylonitrile, Daqing Petrochemical; Epoxy resin E-44, Langfang Nuoxin Chemical Limited; brominated epoxy resin EX-40 (Chenguang Chemical Research Institute); small molecule epoxy and reactive diluent (import); curing agent (homemade); accelerator (commercially available), the above raw materials are industrial grade .

1.1.2 Apparatus: Four-necked flask; reflux condenser; electric stirrer; thermometer. NDJ-1 rotary viscometer; Bunsen burner (tube length 100mm, internal diameter 9.5±0.5mm); simple beam impact tester (40kg rammer); LJ 5000A tensile machine, reverser; ZC 36 high resistance meter ; QM Model 102B Q; high voltage test transformer (5kVA), JC 4 dielectric breakdown device (1kVA).

1. 2 Preparation of curing agent

1.2.1 Reaction mechanism

In this experiment, cyanoethylation was carried out by utilizing the active hydrogen on the amine group in the TAB structure to partially alkylate with a small molecule epoxy group for hydroxyalkylation and partial double bond addition with acrylonitrile. (reaction mode omitted)
Hydroxyalkylation and cyanoethylation reduce the toxicity of fatty polyamines, lower the melting point, and improve the color effect. Hydroxyalkylation due to the introduction of hydroxyl group also promote the role of curing, cyanoethylation has reduced the reactivity, so hydroxyalkylation and cyanoethylation have their own advantages and complement each other, in order to achieve low melting point, low toxicity , And there is a comprehensive effect of flexibility.

1.2.2 Preparation Process

A four-necked flask was charged with an appropriate amount of (2,3-dimethyl)dibutylenetriamine (TAB). The bath was heated to 70-80° C., and a small amount of a small molecule epoxy was dropped and reacted for 1 to 2 hours. The reaction solution was cooled down to 60-70°C, and the metered acrylonitrile was added dropwise. After completion of the dropwise addition, the reaction was continued at a constant temperature and stirred for 1 to 2 hours. The reaction was stopped, and the product was discharged. Its technical indicators are shown in Table 1.

Table 1: Specifications of Curing Agents Technical Specifications Reference Standards
Appearance Colorless or light yellow transparent liquid
Viscosity, mPa·s ≤ 1000 Q/HTZ031-2002
Amine value, mgKOH/g 400-450 Ibid

1.3 Preparation of potting compound

1.3.1 Formulation Design The potting material is divided into two components: A and B. The A component is 100 parts of E-44 epoxy resin, 0-100 parts of brominated epoxy resin, and toughening agent 0-20. Reactive diluent 0 to 30 parts; B component for the homemade curing agent 50 to 100 parts, curing accelerator 0 to 5 parts.

1.3.2 Preparation

1.3.2.1 In the preparation container, according to the ratio of group A distribution, E-44, brominated epoxy resin, toughening agent and reactive diluent are added in turn and stirred evenly to obtain a light yellow viscous liquid group A. Minute.

1.3.2.2 In the preparation container, according to the ratio of group B, the self-made curing agent and curing accelerator are added in turn and mixed uniformly to obtain the light yellow viscous liquid B component.

1.3.2.3 In the preparation container, mix the A component and B component in the ratio of A:B=100:30 to 80 in order, add and mix evenly, remove the bubbles, and then use them for casting and potting. The initial curing at room temperature 24h, 7d completely cured, can also be cured by heating, 40 ~ 60 °C, 7 ~ 9h curing.

1.3.3 Performance Test of Encapsulant

A variety of performance tests were performed on the potting material, and the test results are shown in Table 2 after curing at room temperature for 7 days.
Project Specifications Test Standards
Impact strength kg/cm2 91 GB 1043-79
Flexural strength kg/cm2 792 GB 1042-79
Flame Retardant Level UL94 V-0 GB 4068-84
Volume resistance s-1·cm-1 9.5×1015 GB 1010-78
Surface resistance s-1 7.5×1017 GB 1410-78
Dielectric loss 25°C, 30khz 2.6×10-2 GB 1040-70
Dielectric constant 25°C, 30khz 3.2 GB 1040-70
Breakdown voltage kv/m 23 GB 1048-78

2 Results and Discussion

2.1 Selection of synthesis conditions

2.1.1 Reaction temperature

The reaction temperature is higher than the melting point of the reactant (TAB melting point 40.8° C.), so that the reaction system maintains a liquid homogeneous reaction; however, the reaction temperature is too high, and the oxidation of the amine compound darkens the color. Experiments show that the reaction temperature is controlled at 70-80°C in the early stage and 60-70°C in the later stage. Since the modification reaction of TAB is an exothermic reaction, in order to make the reaction proceed uniformly, the dropwise addition method should be adopted. The temperature of the reaction system is kept within the required temperature range by controlling the dropping rate, and the dropping time is about 1.0 hour.

2.1.2 Reaction time

After the addition of the reactants is completed, the reaction is continued to be stirred to complete. From Table 3, after 2.0 hours of reaction, the amine value remained basically unchanged, and the reaction was almost completed.

Response time h 0.5 1.0 1.5 2.0 2.5
Amine value mgKOH/g 474 458 440 442 445

2.1.3 Selection of Modification Ratio

The TAB modified curing agent is a ternary adduct, and an appropriate modification ratio is selected according to specific application requirements. Due to the introduction of small-molecule epoxies, the vapor pressure and toxicity are significantly reduced. Choosing an appropriate modification ratio will keep the curing agent at a lower viscosity. Experimentally, the equivalent ratio of small molecule epoxy to TAB is 0.8 to 1.2:1. Appropriate, acrylonitrile and cyanoethylation reaction, too low modification ratio is not enough to reduce the irritation of the modified skin to the skin. However, too high a loss of the ability to cure at room temperature, experiments that the acrylonitrile and TAB molar ratio is best in the range of 0.5 to 1.5.