Research and development and application of TMOV epoxy powder coatings

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There are two types of manufacturing methods for powder coatings: dry and wet.
Dry method includes dry mixing method and melt mixing method.
The main manufacturing process flow is shown in Figure 1.
The wet method includes evaporation method, spray drying method and precipitation method.
The main manufacturing process flow is shown in Figure 2.

At present, the manufacturing process widely used in powder coatings at home and abroad is the melt extrusion mixing method.
Including pre-mixing, melting, extrusion, mixing, cooling, crushing, smashing, grading, and sieving.

Among them, melt extrusion mixing and fine pulverization are the key, and melt extrusion mixing uses a damping (kneading) single-screw extruder or twin-screw extruder.

With the development of powder coatings toward thin coatings, which require small particle size and narrow distribution, the widely used ACM pulverizer needs to be further improved.

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2 Epoxy resin for powder coating

Epoxy resin is a compound with more than two active epoxy groups in one molecule.
The most typical material currently used in large quantities is a material with bisphenol A as the skeleton.

This resin is essentially composed of low molecular weight diglycidyl ether and bisphenol A together with some high molecular weight polymers.

Experiments have found that when the amount ratio of epichlorohydrin: bisphenol A is 1:2, the yield of diglycidyl ether is less than 10%, so the actual amount of epichlorohydrin is 2 to stoichiometric.
3 times.
Figure 3 shows the change and reaction of the ratio of the amount of epichlorohydrin to bisphenol A.

Figure 3 shows the one-step method for producing epoxy resin, which is used for the synthesis of low-molecular-weight epoxy resin.
There are many synthetic methods for high-molecular-weight epoxy resin, and one-step or two-step methods can be used.

The two-step method means that the low molecular weight resin continues to react with bisphenol A.
The development of the electronics industry puts forward higher and higher requirements for epoxy powder coatings.

Epoxy coating solder cracking is one of the factors that restrict the performance of electronic products.
The development of epoxy compounds with high heat resistance, low water absorption, low expansion coefficient, and low curing shrinkage has become a research goal.

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This method usually adopts the chemical blending method of the addition grafting of the epoxy compound with the hydroxyl group and the polyurethane prepolymer or the physical blending method of adding the hydroxyl-terminated polyurethane to the epoxy resin.
There is phase separation during curing, but no network interaction.
wear.

It can be made into an IPN polymer.
At the same time as the epoxy group is cured, the isocyanate group reacts with the hydroxyl group newly generated by the epoxy curing or polymerizes with the polyol added to form an interpenetrating network or a semi-interpenetrating network structure, which has excellent The mechanical properties and damping characteristics of the

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Multifunctional acrylate is added to epoxy resin, and acrylate plays a dual role of toughening and diluting, which improves the process performance of epoxy resin.

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Cyanate resin cured products have very excellent dielectric properties, heat resistance and very low water absorption.
Adding cyanate ester to the resin can reduce the hydroxyl concentration, increase the crosslinking density, reduce the water absorption, and improve the electrical properties.

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Liquid crystal thermosetting polymer (LCT) combines the properties of liquid crystal polymer and thermosetting polymer, and at the same time improves the strength, modulus, toughness and glass transition temperature of epoxy resin.
The epoxy/dicyandiamide curing system is designed to replace urea as a synthetic accelerator to enhance the toughening effect.

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3 Curing of epoxy resin

Epoxy resin is a thermoplastic material and needs to undergo a curing reaction with a curing agent to transform it into a thermosetting material.
Curing agents are mainly compounds or resins containing active hydrogen atoms, such as polyamines, polyacids, amino resins, and phenolic resins.

In general, epoxy resin and curing agent contain at least 2 active centers per molecule.
The curing reaction produces a three-dimensional network structure, making the epoxy resin a thermosetting polymer coating film.

Condition of curing agent:

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Compatible with epoxy resin; 

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It is latent at room temperature, and the made powder coating has stable performance at room temperature;

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During melt mixing, the curing agent can still maintain latency, and the curing reaction starts only when the temperature reaches a certain value and the resin is melted and leveled and wets the workpiece;

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It is solid at room temperature and can be pulverized into fine powder for uniform mixing; 5.
It is non-volatile when solidified and is environmentally friendly and safe.

2 Application of epoxy powder coating

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1 Application of epoxy powder coatings in electrical products

Epoxy powder coatings are widely used in the welding and insulation of motors, electrical appliances and radio devices.
At present, the application range of epoxy resin powder coating in electrical insulation mainly includes: 

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Iron core insulation: slot insulation of the stator and rotor of the micro motor and the magnetic pole core insulation; 

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Conductor insulation: high-voltage electrical appliance busbars, rotor copper bar coils, magnetic pole coils, transformer coils, magnet wire coating and other insulation, DC motor commutator commutator risers, etc.
; 

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Coated insulation layer with insulated coils, such as coating insulation of motor coil ends, washing machine inlet valve coils, etc.

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Encapsulation of electronic components, such as capacitors, resistance components, printed circuit board coatings, etc.

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2 Application of epoxy powder coatings in the automotive industry

With the improvement of the technical level of epoxy powder coatings, as well as the development of new applications and construction technologies, the application of epoxy powder coatings in the automotive and other industries has become increasingly widespread.

The amount of powder coatings is the largest in car topcoats and car body primers, and the powder primers used in cars have a good effect.

In recent years, powder coating manufacturers are developing wood powder coatings and automotive topcoats that have a smooth film, good durability, and meet the existing requirements of customers.
The powder coatings for car covers, and the powder coatings for wood and plastics are all epoxy powder coatings.

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The service life of the pipeline depends to a large extent on the anti-corrosion ability of the steel pipe.

Before the 1950s, the materials used for anti-corrosion coatings were mainly coal tar enamel, but these materials had many shortcomings and their use range had certain limitations.

The birth of epoxy powder coating made a leap in pipeline protection technology.
At present, the single-layer heavy-duty epoxy powder coating and the heavy-duty epoxy powder coating are combined as the three-layer anti-corrosion structure of the bottom layer, which can protect the pipeline to the maximum extent and prevent the pipeline from being corroded.

3 concluding remarks

Epoxy powder coatings have been widely used in many fields such as the electronics industry and the automotive industry.
Compared with traditional coatings, epoxy powder coatings have many advantages.
Among them, the biggest advantage is environmental protection and pollution-free, which can ensure people's health.

In the research of epoxy powder coatings, the modification of epoxy resin is one of the current research directions.
Through modification, the coating can have different properties and meet different requirements.