EXPANDED COATING, PREPARATION METHOD AND USE THEREOF, AND PERMANENT MAGNET COMPRISING SAME

Abstract

The present disclosure provides an expanded coating, a preparation method and use thereof, and a permanent magnet comprising same. The expanded coating described herein comprises pores and a filler resin arranged among the pores; the pores comprise at least a spheroid pore having a cross section with a long diameter and a short diameter; in the cross section of the expanded coating, the area of the spheroid pores accounts for 50%-60% of the cross-sectional area of the expanded coating. The permanent magnet of the present disclosure comprises the expanded coating. The expanded coating has high strength and can exhibit excellent mechanical properties and corrosion resistance at high temperatures (such as 170? C.), with a shear strength greater than 2 MPa, a tensile strength greater than 2 MPa, an oil resistance greater than 1800 h and a neutral salt spray performance greater than 288 h at 170? C.

Claims

1. An expanded coating, wherein the expanded coating comprises pores and a filler resin arranged among the pores; the pores comprise at least a spheroid pore having a cross section with a long diameter and a short diameter; in the cross section of the expanded coating, the area of the spheroid pores accounts for 50% -60% of the cross-sectional area of the expanded coating.

2. The expanded coating according to claim 1, wherein in a cross section of the expanded coating, the area of the spheroid pores accounts for 53%-57% of the cross-sectional area of the expanded coating; preferably, the short diameter to the long diameter is denoted as R2/R1, and based on the total amount of the spheroid pores, the percentage proportion of spheroid pores having a ratio of 0.7<R2/R1?1 is 60%-80%, preferably 70%-78%; the percentage proportion of the spheroid pores having a ratio of R2/R1?0.5 is less than 8%, preferably less than or equal to 5%; preferably, the percentage proportion of spheroid pores having a ratio of 0.8<R2/R1?1 is 40%-55%, preferably 50%-53%; furthermore, the percentage proportion of spheroid pores having a ratio of 0.9<R2/R1?1 is 25%-30%, preferably 26%-28%.

3. The expanded coating according to claim 1, wherein based on the total amount of the spheroid pores: the percentage proportion of spheroid pores having a diameter of R1>60 ?m is less than 12%, preferably less than or equal to 10%; the percentage proportion of spheroid pores having a diameter of 30 ?m<R1?50 ?m is 50%-60%, preferably 55%-60%; the percentage proportion of spheroid pores having a diameter of 20 ?m<R1?30 ?m is 15%-20%, preferably 16%-20%; the percentage proportion of spheroid pores having a diameter of R1?20 ?m is less than 10%, preferably less than 7%; preferably, the percentage proportion of spheroid pores having a diameter of R1>80 ?m is less than 5%, preferably less than 3%.

4. The expanded coating according to claim 1, wherein the filler resin is provided by a thermosetting resin; preferably, the expanded coating has a neutral salt spray performance greater than 288 h; preferably, the expanded coating has an oil resistance greater than 1800 h at 170? C.; preferably, the expanded coating has a shear strength greater than 2 MPa at 170? C.; preferably, the expanded coating has a tensile strength greater than 2 MPa at 170? C.

5. A preparation method for the expanded coating according to claim 1, wherein the preparation method comprises applying a coating on a surface of a magnet substrate, pre-curing the coating, and expanding and curing the coating to obtain the expanded coating; preferably, the coating is provided by an expandable coating material; preferably, based on the part by weight, the expandable coating material comprises at least 50-80 parts of a thermosetting resin, 5-20 parts of an expandable microsphere, 0.2-1.5 parts of a chemical foaming agent, 0.3-2 parts of a curing agent, and 15-30 parts of a pigment and filler; preferably, based on the part by weight, the expandable coating material comprises 60-70 parts of the thermosetting resin, 8-15 parts of the expandable microsphere, 0.5-1.5 parts of the chemical foaming agent, 0.8-1.5 parts of the curing agent, and 17-25 parts of the pigment and filler; preferably, the amount ratio of the expandable microsphere to the chemical foaming agent is (5-20):(0.1-1.5), preferably (10-18):(0.3-1.1).

6. The preparation method according to claim 5, wherein the thermosetting resin is at least one selected from bisphenol A-based epoxy resins, preferably a bisphenol A-based epoxy resin with a softening point between 50? C. to 95? C.; preferably, the expandable microsphere is selected from an expandable microsphere with an average particle size of 5-50 ?m, preferably 5-20 ?m, more preferably 10-15 ?m; for example, the expandable microsphere is at least one selected from 920DU80, 920DU40 and 920DU20 in the Expancel series from AKZO-Nobel; for example, the expandable microsphere is selected from a mixture of 920DU40 and 920DU20 in a weight ratio of (1-10):(1-10); preferably, the chemical foaming agent is at least one selected from azodicarbonamide, azobisisobutyronitrile, and p-toluenesulfonyl hydrazide; preferably, the curing agent is at least one selected from latent amine curing agents; preferably, the latent amine curing agent is at least one selected from imidazole, an epoxy resin adduct of imidazole, and an epoxy resin adduct of polyamine; preferably, the pigment and filler is at least one selected from insulating carbon black, mica powder, calcium carbonate, and a nano-aluminosilicate fiber; preferably, the applying a coating comprises coating the expandable coating material on the surface of the magnet substrate to form the coating.

7. The preparation method according to claim 5, wherein the pre-curing can be performed under a temperature selected from 90-130? C.; preferably, the pre-curing can be performed for 5-20 min; preferably, after the pre-curing, the coating has a thickness of 50-200 ?m; preferably, the expanding and curing comprise: subjecting the magnet substrate to thermal curing in a groove to obtain the expanded coating; preferably, the thermal curing can be performed under a temperature selected from 190? C. to 230? C.; preferably, the thermal curing can be performed for 15-40 min.

8. Use of the expanded coating according to claim 1 in a permanent magnet.

9. A permanent magnet, comprising the expandable coating according to claim 1 and a magnet substrate, wherein the expandable coating is located on a surface of the magnet substrate.

10. Use of the permanent magnet according to claim 9 in a rotor.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0054] FIG. 1 is a diagram illustrating the cross-sectional microstructure of the expanded coating after expansion; [0055] in the diagram, R1 is a long diameter of pores, and R2 is a short diameter of the pores.

[0056] FIG. 2 is a schematic diagram of a permanent magnet coated with the expanded coating fixed in a magnet steel groove of a rotor; [0057] in the diagram, {circle around (1)}: magnetic steel groove hole of iron-core rotor; {circle around (2)}: magnet substrate; {circle around (3)}: expanded coating.

DETAILED DESCRIPTION

[0058] The embodiments of the present disclosure will be further illustrated in detail with reference to the following specific examples. It will be appreciated that the following examples are merely exemplary illustrations and explanations of the present disclosure, and should not be construed as limiting the protection scope of the present disclosure. All techniques implemented based on the content of the present disclosure described above are included within the protection scope of the present disclosure. Unless otherwise stated, the starting materials and reagents used in the following examples are all commercially available products or can be prepared using known methods.

[0059] In the following examples and comparative examples, a cubic neodymium-iron-boron product with dimensions of 20 mm?10 mm?3.5 mm is used as the magnet substrate.

Example 1

[0060] The preparation method of the permanent magnet are as follows: [0061] 1) Preparation of coating: An expandable coating material was applied to the surface of a magnet substrate by electrostatic spraying. The expandable coating material consisted of components in the following weight proportions: 68% of an epoxy resin, 4% of expandable microsphere Expancel? 920DU40 and 6% of 920DU20, 0.8% of azodicarbonamide, 1.2% of curing agent dicyandiamide (Aladdin, 98%), and 20% of pigment and filler insulating carbon black (Tianjin Ebory Chemical Co., Ltd.). The material was pre-cured at 90? C. for 20 min to form a film, with a coating thickness of 100 ?m, so as to give a permanent magnet coated with the coating on the surface. [0062] 2) Foaming and expanding treatment: The permanent magnet obtained in step 1) was placed in an oven as a magnetic steel piece, and subjected to curing at 210? C. for 30 min to give a permanent magnet comprising an expanded coating on the surface.

Comparative Example 1

[0063] The preparation method of the permanent magnet are substantially the same as those in Example 1, except that the expandable coating material consisted of components in the following weight proportions: 68% of an epoxy resin, 12% of expandable microsphere Expancel? 920DU40 and 14% of 920DU20, 0.8% of azodicarbonamide, 1.2% of curing agent dicyandiamide (Aladdin, 98%), and 4% of pigment and filler insulating carbon black (Tianjin Ebory Chemical Co., Ltd.).

Example 2

[0064] The preparation method of the permanent magnet are as follows: [0065] 1) Application of coating: An expandable coating material was applied to the surface of a magnet by electrostatic spraying. The expandable coating material consisted of components in the following weight proportions: 56% of an epoxy resin, 8% of expandable microsphere Expancel? 920DU40 and 8% of 920DU20, 0.9% of azodicarbonamide, 0.7% of curing agent dicyandiamide (Aladdin, 98%), and 26.4% of pigment and filler insulating carbon black (Tianjin Ebory Chemical Co., Ltd.). The material was pre-cured at 90? C. for 20 min to form a film, with a coating thickness of 160 ?m, so as to give a permanent magnet coated with the coating on the surface. [0066] 2) Foaming and expanding treatment: The permanent magnet obtained in step 1) was placed in an oven, and subjected to curing at 230? C. for 40 min to give a permanent magnet comprising an expanded coating on the surface.

Comparative Example 2

[0067] The preparation method of the permanent magnet are substantially the same as those in Example 2, except that the expandable coating material consisted of components in the following weight proportions: 56% of an epoxy resin, 12% of expandable microsphere Expancel? 920DU40 and 10% of 920DU20, 1.8% of azodicarbonamide, and 20.2% of pigment and filler insulating carbon black (Tianjin Ebory Chemical Co., Ltd.).

Example 3

[0068] The preparation method of the permanent magnet are as follows: [0069] 1) Application of coating: An expandable coating material was applied to the surface of a magnet by electrostatic spraying. The expandable coating material consisted of components in the following weight proportions: 65% of an epoxy resin, 6% of expandable microsphere Expancel? 920DU40 and 3% of 920DU20, 1.2% of azodicarbonamide, 0.8% of curing agent dicyandiamide (Aladdin, 98%), and 24% of pigment and filler insulating carbon black (Tianjin Ebory Chemical Co., Ltd.). The material was pre-cured at 100? C. for 15 min to form a film, with a coating thickness of 100 ?m, so as to give a permanent magnet coated with the coating on the surface. [0070] 2) Foaming and expanding treatment: The permanent magnet obtained in step 1) was placed in an oven, and subjected to curing at 190? C. for 30 min to give a permanent magnet comprising an expanded coating on the surface.

Comparative Example 3

[0071] The preparation method of the permanent magnet are as follows: [0072] 1) Application of coating: An expandable coating material was applied to the surface of a magnet by electrostatic spraying. The expandable coating material consisted of components in the following weight proportions: 60% of an epoxy resin, 6% of expandable microsphere Expancel? 920DU40 and 10% of 920DU20, 1.0% of azobisisobutyronitrile, 0.5% of azodicarbonamide, 0.6% of curing agent dicyandiamide (Aladdin, 98%), and 21.9% of pigment and filler insulating carbon black (Tianjin Ebory Chemical Co., Ltd.). The material was pre-cured at 100? C. for 15 min to form a film, with a coating thickness of 100 ?m, so as to give a permanent magnet coated with the coating on the surface. [0073] 2) Foaming and expanding treatment: The permanent magnet obtained in step 1) was placed in an oven, and subjected to curing at 210? C. for 30 min to give a permanent magnet comprising an expanded coating on the surface.

Example 4

[0074] The preparation method of the permanent magnet are as follows: [0075] 1) Application of coating: An expandable coating material was applied to the surface of a magnet by electrostatic spraying. The expandable coating material consisted of components in the following weight proportions: 66% of an epoxy resin, 6% of expandable microsphere Expancel? 920DU40 and 8% of 920DU20, 0.8% of azobisisobutyronitrile, 1.2% of curing agent dicyandiamide (Aladdin, 98%), and 18% of pigment and filler insulating carbon black (Tianjin Ebory Chemical Co., Ltd.). The material was pre-cured at 100? C. for 15 min to form a film, with a coating thickness of 100 ?m, so as to give a permanent magnet coated with the coating on the surface. [0076] 2) Foaming and expanding treatment: The permanent magnet obtained in step 1) was placed in an oven, and subjected to curing at 230? C. for 35 min to give a permanent magnet comprising an expanded coating on the surface.

[0077] Data of spheroid pores in the cross section of the expandable coating on the surface of the permanent magnets of the examples and comparative examples are shown in Table 1.

Test Example

[0078] The expandable coatings on the surface of the permanent magnets of the examples and comparative examples described above were subjected to the following tests, and test results are shown in Table 2.

[0079] (1) The condition of the shear strength test at 170? C. is as follows: at an environmental temperature of 170? C. according to GB/T 7124-2008.

[0080] (2) The condition of the tensile strength test at 170? C. is as follows: at an environmental temperature of 170? C. according to GB/T 6329-1996.

[0081] (3) Corrosion resistance: [0082] (a) The condition and procedures of the neutral salt spray test (SST) are as follows: a temperature of 35? C.; an aqueous NaCl solution with a concentration of 50 g/L?5 g/L; pH 6.5-7.2; the aqueous NaCl solution was atomized and deposited on a neodymium-iron-boron magnet product to be tested; the time to the appearance of rust on the surface of the magnet was recorded; [0083] (b) The procedures of the oil immersion test are as follows: the neodymium-iron-boron magnet product was completely soaked in a transmission fluid at 150? C.; the corrosion, bubbling, peeling and other situations on the surface of the magnet were observed; the time to such changes of the coating on the surface of the magnet was recorded and the performance of the coating of the magnet was determined again; if the performance was not affected, the time was recorded as the time for oil immersion resistance.

TABLE-US-00001 TABLE 1 Summary of microstructural data of the spheroid pores in the expanded coatings Example Comparative Example Comparative Example Comparative Example 1 Example 1 2 Example 2 3 Example 3 4 0.9 < R2/R1 ? 1 28.50% 18.20% 29.00% 15.00% 28.00% 25.00% 20.00% 0.8 < R2/R1 ? 1 52.00% 38.00% 47.00% 35.00% 55.00% 48.00% 33.00% 0.7 < R2/R1 ? 1 77.00% 66.00% 68.00% 56.00% 74.00% 72.00% 55.00% R2/R1 ? 0.5 4.00% 3.30% 6.50% 9.00% 4.00% 5.00% 12.00% R1 < 80 ?m 2.00% 1.20% 4.00% 16.10% 12.00% 3.00% 4.00% R1 < 60 ?m 9.30% 14.20% 11.00% 33.30% 25.00% 10.00% 9.00% 30 ?m < R1 ? 50 ?m 55.50% 50.10% 54.00% 42.90% 35.00% 59.00% 53.00% 20 ?m < R1 ? 30 ?m 19.00% 23.00% 14.50% 17.50% 9.00% 16.00% 15.00% R1 ? 20 ?m 6.00% 5.20% 8.00% 0.00% 0.00% 5.00% 4.00% Proportion of 56.50% 74.00% 60.00% 70.00% 57.00% 68.00% 56.00% spheroid pores

TABLE-US-00002 TABLE 2 Performance test results of the expanded coatings Push-out Shear Tensile strength at strength at strength at Oil 170? C./ 170? C./ 170? C./ immer- MPa MPa MPa SST sion Example 1 3.23 2.74 2.37 336 h 2112 h Comparative 0.85 0.69 0.56 312 h 1920 h Example 1 Example 2 3.01 2.53 2.19 336 h 2112 h Comparative 0.98 0.75 0.69 312 h 1920 h Example 2 Example 3 2.58 2.26 1.97 336 h 2112 h Comparative 1.52 1.46 1.03 312 h 2112 h Example 3 Example 4 2.71 2.33 2.04 336 h 2112 h

[0084] As seen from the results of Tables 1 and 2: [0085] 1. The comparison results of Example 1 with Comparative Example 1 indicate that: the 26:0.8 ratio of the expandable microsphere to the chemical foaming agent, i.e., an increased amount of the microsphere and an excessively low amount of the chemical foaming agent, resulted in an increased total amount of the expanding agent along with an excessive expansion rate; the proportion of pores in the coating reached 74%, which resulted in loose pore gaps in the expandable coating, excessive pore gaps, and poor stability, thrust, adhesive force and the like, thereby further causing low binding force and ease to peeling off the coating. [0086] 2. The comparison results of Example 2 with Comparative Example 2 indicate that: the 22:1.8 ratio of the expandable microsphere to the chemical foaming agent used in Example 2, excessive amounts of both the microsphere and the chemical foaming agent exceeding the range resulted in a proportion of the spheroid pores in the coating reaching 70% after expansion, which also led to the problems of an excessive expansion rate, loose pore gaps in the expandable coating, excessive pore gaps, and poor stability. The permanent magnet of Example 2 exhibited a higher shear strength than Comparative Example 2, significantly higher shear and tensile strengths than Comparative Example 2, and superior corrosion resistance at 170? C. [0087] 3. The comparison results of Example 3 with Comparative Example 3 indicate that: Although both ratios of the expandable microsphere to the chemical foaming agent in Example 3 and Comparative Example 3 were in the range of (5-20):(0.1-1.5), the proportion of the spheroid pores in the coating of the product of Comparative Example 3 reached 68% (higher than 60%), which also led to poor stability and significantly higher shear and tensile strengths than those of Example 3, due to an excessive expansion rate, loosen pore gaps in the expandable coating, and large pore gaps. [0088] 4. The comparison results of Example 3 with Comparative Example 2 indicate that the permanent magnet of Example 3 had a higher shear strength than Comparative Example 2, a significantly higher tensile strength than Comparative Example 2, and a superior corrosion resistance to Comparative Example 2 at 170? C. It can be seen that although the proportion of pores with a long diameter of 30 ?m<R1?50 ?m in Example 3 was 35% (not in the range of 50-60%), the ratio of R2/R1 was less than 8% and the proportion of the spheroid pores in the coating was 50-60%, such that the expandable coating of the permanent magnet of Example 3 had relatively better shear strength and tensile strength. [0089] 5. The comparison results of Example 4 with Example 1 indicate that since the percentage proportion of spheroid pores having a ratio of 0.8<R2/R1?1 in the expandable coating of the permanent magnet of Example 4 was 33% (not in the range of 40-55%), the expandable coating of the permanent magnet of Example 4 had relatively worse shear strength and tensile strength than those of Example 1. [0090] 6. The comparison results of Example 3 with Comparative Example 3 indicate that: although both amount ratios of the expandable microsphere to the chemical foaming agent in Example 3 and Comparative Example 3 were in the range of (5-20):(0.1-1.5), the area of the spheroid pores in the coating of the product of Comparative Example 3 accounted for 68% of the cross-sectional area of the expandable coating (exceeding the range of 50% to 60%), such that the product of Comparative Example 3 had slightly lower shear and tensile strengths than those of Example 3 at 170? C. [0091] 7. The comparison results of Example 1 with Example 2 indicate that when the ratio of R2/R1 was less than 8%, and R1 value and the proportion of the pores in the coating were both in preferred ranges, the expandable coating of the permanent magnet of Example 1 exhibited slightly higher shear and tensile strengths and equivalent corrosion resistance at 170? C. [0092] 8. The comparison results of the examples with the comparative examples indicate that, for the performances of the permanent magnet in shear and tensile strengths and corrosion resistance at 170? C., a microstructure of the expandable coating affects the above performances of the permanent magnet in the following order: the proportion of the spheroid pores>the range of R1 value>the range of ratio R2/R1.

[0093] The exemplary embodiments of the present disclosure have been described above. However, the protection scope of the present application is not limited to the above embodiments. Any modification, equivalent, improvement, and the like made by those skilled in the art without departing from the spirit and principle of the present disclosure shall fall within the protection scope of the present disclosure.