Insulating powder coating as well as preparation method and application thereof

Abstract

The invention discloses an insulating powder coating as well as a preparation method and application thereof. The insulating powder coating comprises a heat-conducting filler, the heat-conducting filler is composed of heat-conducting filler powder with three particle size grades, and the ratio of D50 of the powder with two adjacent particle size grades is 4-10. According to the insulating powder coating disclosed by the invention, a motion mode among particles tends to a rolling state through a proper particle size ratio, sliding among the particles is reduced as much as possible, and the viscosity of the heat-conducting filler is reduced, so that the viscosity of the coating in a molten state is reduced under the condition that the ratio of the filler is not reduced; therefore, a compact and complete protective layer with good heat-conducting property can be obtained under the condition of not containing the flatting agent, and the protective layer is free of pinholes, good in adhesiveness, excellent in insulativity, anti-creeping property, flame retardance and mechanical property and capable of timely conducting and releasing heat generated during operation of a stator and a rotor of a motor. Permanent insulation protection can be provided for the exterior of the motor stator and rotor, and the running reliability of the motor is improved.

Description

Technical Field

[0001] This invention belongs to the field of powder coating production technology, specifically relating to a thermally conductive and insulating powder coating for insulating the stator and rotor of a rotating motor, particularly one with a rated voltage of at least 12V to 1200V, as well as its preparation method and application. Background Technology

[0002] Due to the ever-increasing power density requirements of developing technologies, motors with increasingly higher performance are being developed, such as external rotor motors, axial flux motors, and high-speed generators. High-power-density motors and generators, such as those used in turbine air compressors, particularly include stators and rotors with stator laminations and multiple generator slots, where insulation material is typically in sheet form within the motor slots. In principle, wound insulation is used from a rated voltage of 1000V onwards; for motors below 1000V, such as automotive drive motors, pre-formed insulating slot paper insert insulation is used.

[0003] Besides pre-formed insulating groove paper, known resin-based materials used in the manufacture of insulating materials often include epoxy-impregnated mica tape and other resin-based insulating materials with high specific surface area fillers. Depending on the application, other additives may be added, such as initiators or accelerators that initiate the curing of the applied impregnation or powder coating into a solid insulating material. Impregnating agents are generally in the form of low-viscosity liquids, while powder coating formulations are mixtures of solid powders and are usually present as solid mixtures. In both cases, magnesium oxide and fumed silica are used as fillers according to existing technology because, as particulate, especially flake-like, inorganic inert materials, they can effectively and reliably suppress electrolytic corrosion under partial discharge throughout the entire service life of the motor or generator and have good chemical stability and thermal stability.

[0004] However, known fillers significantly increase the viscosity of powder coatings. But high-viscosity powders used in the manufacture of insulating materials, whether applied by electrostatic spraying, immersion in a fluidized bed, coating, or liquid impregnation, are prone to poor degassing problems, which can lead to the formation of pores, especially air-filled pores, in the cured insulating coating. Clearly, a non-porous insulating coating is important for the electrical life of motors. Air has a relatively low dielectric strength, which can cause partial discharge and creepage even at relatively low electric fields. Therefore, inclusions such as air must be avoided in the resin portion of insulating materials. High viscosity also results in poor leveling of the powder coating's surface quality, which is also defective. Summary of the Invention

[0005] To overcome the above-mentioned defects, the present invention provides an insulating powder coating with high thermal conductivity, its preparation method and application.

[0006] The first aspect of the present invention provides an insulating powder coating, comprising a thermally conductive filler, wherein the thermally conductive filler is composed of thermally conductive filler powder of three particle size grades, and the ratio of D50 of two adjacent particle size grades is 4-10.

[0007] According to one embodiment of the present invention, the thermally conductive filler is cubic boron nitride and / or aluminum oxide.

[0008] According to another embodiment of the present invention, the insulating powder coating comprises, by weight, 100 parts of solid epoxy resin, 1 to 60 parts of latent curing agent, 10 to 100 parts of flame retardant, 10 to 100 parts of the thermally conductive filler, and 0.1 to 10 parts of accelerator.

[0009] According to another embodiment of the present invention, the epoxy resin is a solid bisphenol A type epoxy resin; the latent curing agent is selected from one or more of dicyandiamide and its derivatives, melamine and its derivatives, organic acid hydrazide, boron trifluoride-amine complex and diaminomaleonitrile and its derivatives; the flame retardant is a halogen-free phosphate ester; and the accelerator is an organic urea.

[0010] According to another embodiment of the present invention, the insulating powder coating is composed of powder of three particle size grades, wherein the D50 ratio of two adjacent particle size grades is 4-10.

[0011] The second aspect of the present invention provides a method for preparing an insulating powder coating, comprising: mixing three thermally conductive filler powders of different particle size grades in a certain proportion, mixing them with other components of the insulating powder coating, heating and melting them, extruding them into thin sheets, and then pulverizing them.

[0012] According to one embodiment of the present invention, the pulverized powder is sieved to obtain powder of three particle size grades, and then the powder of the three particle size grades is mixed in proportion to obtain the insulating powder coating.

[0013] A third aspect of the present invention provides a motor stator and rotor coated with the above-mentioned insulating powder coating.

[0014] According to one embodiment of the present invention, the motor stator and rotor are rotary motor stators and rotors with a rated voltage of 12V to 1200V.

[0015] The insulating powder coating of this invention, through a suitable particle size distribution, makes the movement mode between particles tend towards a "rolling state," minimizing "slippage" between particles and reducing the viscosity of the thermally conductive filler. This reduces the viscosity of the coating in the molten state without reducing the filler ratio. Therefore, a dense and complete protective layer with good thermal conductivity can be obtained without the presence of leveling agents. This protective layer is pinhole-free, has good adhesion, and possesses excellent insulation, leakage prevention, flame retardancy, and mechanical properties. It can effectively conduct and release the heat generated by the motor stator and rotor during operation. It can provide permanent insulation protection for the external structure of the motor stator and rotor, improving the reliability of motor operation. Detailed Implementation

[0016] The present invention will be described in detail below with reference to specific embodiments.

[0017] The insulating powder coating of this invention includes a thermally conductive filler composed of three particle size grades of thermally conductive filler powder, with the D50 ratio of two adjacent particle size grades being 4-10. To improve the final leveling properties of the product, the viscosity of the thermally conductive filler needs to be reduced without decreasing the filler ratio. The filler ratio (solid content) is the packing characteristic (static characteristic) of the filler, while viscosity is the dynamic characteristic of the filler; traditional grading methods can usually only consider either static or dynamic characteristics. The insulating powder coating of this invention adopts a rolling grading method, which can simultaneously consider both static and dynamic characteristics. The rolling grading method is a grading method derived from the theory of particle rolling. The core objective of this method is to make the movement mode between particles tend towards a "rolling state" through a suitable particle size ratio, minimizing the "slippage" between particles. This invention employs a compound of three thermally conductive fillers of three particle size grades, resulting in a D50 ratio of 4-10 between adjacent particle size grades. This reduces the viscosity of the coating in the molten state, allowing for the formation of a dense, complete protective layer without leveling agents, without reducing the content of the thermally conductive filler in the insulating powder. This layer is free of pinholes, exhibits good adhesion, and possesses excellent insulation, leakage prevention, flame retardancy, and mechanical properties, while also maintaining good thermal conductivity. Those skilled in the art can select the D50 ratio between 4-10 for adjacent particle size grades, for example, 4, 5, 6, 7, 8, 9, and 10. The median particle size (D50) of the three thermally conductive fillers falls within the conventional median particle size range for thermally conductive fillers in insulating powder coatings, for example, it can be set between 1 and 200 μm as needed. Other feasible numerical ranges are also possible.

[0018] In an optional embodiment, the thermally conductive filler is cubic boron nitride and / or aluminum oxide.

[0019] In an optional embodiment, the insulating powder coating comprises, by weight, 100 parts of solid epoxy resin, 1 to 60 parts of latent curing agent, 10 to 100 parts of flame retardant, 10 to 100 parts of thermally conductive filler, and 0.1 to 10 parts of accelerator.

[0020] In an optional embodiment, the epoxy resin is a solid bisphenol A type epoxy resin; the latent curing agent is selected from one or more of dicyandiamide and its derivatives, melamine and its derivatives, organic acid hydrazide, boron trifluoride-amine complex and diaminomaleonitrile (DAMN) and its derivatives; the flame retardant is a halogen-free phosphate ester; and the accelerator is an organic urea.

[0021] In an optional embodiment, the insulating powder coating consists of powders of three particle size grades, with the D50 ratio of two adjacent particle size grades being 4-10. The median particle size D50 of the three particle size grades constituting the powder coating is within the conventional median particle size range of powder coatings, for example, it can be set between 1 and 500 μm as needed. Of course, other feasible numerical ranges are also possible.

[0022] The preparation method of the insulating powder coating of the present invention may include: mixing three thermally conductive filler powders of different particle size grades in a certain proportion, mixing them with other components of the insulating powder coating, heating and melting them, extruding them into thin sheets, and then pulverizing them.

[0023] The pulverized powder is sieved to obtain three particle size grades, and then the three particle size grades are mixed in proportion to obtain an insulating powder coating.

[0024] The insulating powder coating of the present invention can be used on the stator and rotor of an electric motor, forming a non-porous insulating coating on the surface of the stator and rotor, thereby improving the service life of the stator and rotor. Preferably, the stator and rotor are rotating electric motor stator and rotor with a rated voltage of 12V to 1200V. The insulating powder coating of the present invention can be applied to the surface of the stator and rotor of the electric motor by any suitable method, such as, but not limited to, electrostatic spraying, immersion in a fluidized bed, coating, or liquid impregnation.

[0025] The present invention is further described below through specific examples. However, these examples are merely exemplary and do not constitute any limitation on the scope of protection of the present invention. Unless otherwise specified, the reagents, materials, and instruments used in the following embodiments and comparative examples are commercially available.

[0026] Example 1

[0027] Alumina was selected as the thermally conductive filler. The filler consisted of powders of three particle size grades. The first grade had a D50 of 5 μm, the second grade had a D50 of 25 μm, and the third grade had a D50 of 125 μm. The volume ratio of the three particle size grades was 1:2:5. The three particle size grades of thermally conductive filler powder were premixed in a ball mill according to the above ratio.

[0028] 100 parts of solid bisphenol A epoxy resin, 7 parts of latent curing agent, 10 parts of flame retardant, 100 parts of premixed thermally conductive filler, and 0.2 parts of accelerator are added to a mixer, heated and melted, and stirred and mixed.

[0029] Molten raw material is extruded through an extruder and then pressed and cooled into hard, brittle sheets using a tablet press. The pressed sheets are then mechanically cut into fine flakes using a slicing machine. These fine flakes are then ground into powder using a cryogenic airflow mill. The powder is sieved into three particle size grades: grade 1 with a D50 of 8 μm, grade 2 with a D50 of 50 μm, and grade 3 with a D50 of 250 μm. The powders of these three particle size grades are mixed in a volume ratio of 1:2.5:5 to obtain an insulating powder coating.

[0030] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. An insulating powder coating, characterized in that, It includes a thermally conductive filler, which is composed of thermally conductive filler powder of three particle size grades, and the ratio of D50 of two adjacent particle size grades is 4-10.

2. The insulating powder coating according to claim 1, characterized in that, The thermally conductive filler is cubic boron nitride and / or aluminum oxide.

3. The insulating powder coating according to claim 1, characterized in that, The insulating powder coating comprises, by weight, 100 parts of solid epoxy resin, 1-60 parts of latent curing agent, 10-100 parts of flame retardant, 10-100 parts of thermally conductive filler, and 0.1-10 parts of accelerator.

4. The insulating powder coating according to claim 3, characterized in that, The epoxy resin is a solid bisphenol A type epoxy resin; The latent curing agent is selected from one or more of dicyandiamide and its derivatives, melamine and its derivatives, organic acid hydrazide, boron trifluoride-amine complex, and diaminomaleonitrile and its derivatives; The flame retardant is a halogen-free phosphate ester; The accelerator is an organic urea.

5. The insulating powder coating according to claim 3, characterized in that, The insulating powder coating consists of powder of three particle size grades, with the D50 ratio of two adjacent particle size grades being 4-10.

6. A method for preparing an insulating powder coating according to any one of claims 1-5, characterized in that, include: Three thermally conductive filler powders of different particle size grades are mixed in proportion, then mixed with other components of the insulating powder coating, heated and melted, extruded into thin sheets, and then crushed.

7. The method for preparing the insulating powder coating according to claim 6, characterized in that, The pulverized powder is sieved to obtain three particle size grades, and then the three particle size grades are mixed in proportion to obtain the insulating powder coating.

8. A stator and rotor for an electric motor, characterized in that, The coating is made of insulating powder coating as described in any one of claims 1-5.

9. The motor stator and rotor according to claim 8, characterized in that, The stator and rotor of the motor are rotating motor stators and rotors with a rated voltage of 12V to 1200V.