Expansion Coating and Its Manufacturing Method, Application, and Permanent Magnet Containing the Expansion Coating

Abstract

To provide an expansion coating and a manufacturing method and application of the same, and a permanent magnet including the expansion coating.SOLUTION: An expansion coating includes pores, and further includes a filler resin between the pores, wherein the pores include at least an oval structure pore, the cross section of the oval structure pore includes a major axis and a minor axis, in the cross section of the expansion coating, the area of the oval structure pole occupies 50% to 60% of the cross-sectional area of the expansion coating. A permanent magnet includes an expansion coating, wherein the expansion coating has high strength, can exhibit excellent mechanical characteristics and corrosion resistance at high temperature (for example, 170°C), and has shear strength at 170°C larger than 2 MPa, tensile strength larger than 2 MPa, oil resistance performance larger than 1,800 h and neutral salt spray larger than 288 h.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] This application claims the priority of a prior application filed with the China National Intellectual Property Administration on September 27, 2022, with the application number 202211185592.X and the invention title "Expansion Coating and Its Manufacturing Method and Application, Permanent Magnet Containing the Expansion Coating". The prior application is incorporated herein by reference in its entirety.

[0002] The present invention relates to an expansion coating and its manufacturing method and application, and a permanent magnet containing the expansion coating, and particularly relates to a permanent magnet containing an expansion coating with a specific microstructure and its manufacturing method and application.

Background Art

[0003] With the rapid progress of the new energy vehicle industry, rare earth permanent magnet synchronous motors are widely used due to their advantages such as low loss, high efficiency, and obvious power-saving effect. At the same time, as one of the main production processes of the motor, the assembly process of the magnetic steel for rare earth permanent magnet synchronous motors has also attracted more and more attention from major automobile manufacturers in terms of issues such as environmental friendliness, convenience, and assembly accuracy.

[0004] In recent years, in addition to the currently mainstream injection molding and adhesive injection processes, the expansion type coating has been increasingly used in the assembly process of magnetic steel due to its advantages such as safety, environmental friendliness, simple operation, and high assembly accuracy. After heating and expanding the expansion type coating, it fills the magnetic steel groove and plays a role in fixing the magnetic steel.

[0005] Patent Document with the publication number CN112774959A discloses a process of applying expandable powder to a magnet. The expandable powder includes a prepolymer, a curing agent, at least one functional filler, and a foaming agent, and the foaming agent is a chemical foaming agent. Since the foaming agent does not react quickly with the coating substrate, the magnet coated with the coating can maintain its structural stability during the transportation and storage processes.

[0006] The patent document with the publication number CN113593817A discloses a method for manufacturing a magnet base material and a magnet assembly. The base material includes a magnet and an expandable layer on its surface. The expandable layer contains ammonium polyphosphate, polyol, epoxy resin, carbodiimide, N-hydroxysuccinimide, etc. After expansion, the expandable layer has a relatively high bonding force between the magnet and the substrate at room temperature and neutral salt spray resistance.

Summary of the Invention

Problems to be Solved by the Invention

[0007] However, for automotive motors, the maximum temperature during operation may exceed 150°C. If the high-temperature stability of the expansion coating is relatively poor, due to the action of centrifugal force, the product may shear along the magnetic steel groove and the coating may be damaged. Therefore, the mechanical properties and corrosion resistance of the expansion coating at high temperatures (>150°C) need to be further improved.

Means for Solving the Problems

[0008] To solve the above technical problems, the present invention provides the following technical solutions. An expansion coating including pores and further including a filling resin between the pores, wherein the pores include at least quasi-elliptical structure pores, and a cross-section of the quasi-elliptical structure pores includes a major axis and a minor axis, and an expansion coating is provided. In the present invention, the cross-section of the quasi-elliptical structure pores refers to any cross-section passing through the center point of the pores, the major axis refers to the longest distance passing through the center point in the cross-section of the quasi-elliptical shape, denoted as R1, and the minor axis refers to the shortest distance passing through the center point in the cross-section of the quasi-elliptical shape, denoted as R2.

[0009] According to an embodiment of the present invention, in the cross-section of the expansion coating, the area of the quasi-elliptical structure pores accounts for 50% - 60%, preferably 53% - 57%, for example 56%, 57%, 60%, 68%, 70% of the cross-sectional area of the expansion coating.

[0010] According to an embodiment of the present invention, the cross-section of the oval-shaped pores basically has the shape shown in FIG. 1.

[0011] According to an embodiment of the present invention, the major axis and the minor axis are preferably perpendicular.

[0012] According to an embodiment of the present invention, taking the ratio of the minor axis to the major axis as R2 / R1, for the total number of the oval-shaped pores, the content rate of the oval-shaped pores with 0.7 < R2 / R1 ≤ 1 is 60% - 80%, preferably 70% - 78%, such as 65%, 68%, 72%, 74%, 77%; the content rate of the oval-shaped pores with R2 / R1 ≤ 0.5 is less than 8%, preferably 5% or less, such as 2%, 3%, 4%, 5%, 6%, 7%.

[0013] Preferably, the content rate of the oval-shaped pores with 0.8 < R2 / R1 ≤ 1 is 40% - 55%, preferably 50% - 53%, such as 33%, 47%, 48%, 52%, 55%. Further, the content rate of the oval-shaped pores with 0.9 < R2 / R1 ≤ 1 is 25% - 30%, preferably 26% - 28%, such as 25%, 28%, 29%, 30%.

[0014] According to an embodiment of the present invention, among the total number of the oval-shaped pores, the content rate of the oval-shaped pores with R1 > 60 μm is less than 12%, preferably 10% or less, such as 7%, 8%, 9%, 10%; the content rate of the oval-shaped pores with 30 μm < R1 ≤ 50 μm is 50% - 60%, preferably 55% - 60%, such as 50%, 53%, 54%, 55%, 59%; the content rate of the oval-shaped pores with 20 μm < R1 ≤ 30 μm is 15% - 20%, preferably 16% - 20%, such as 16%, 17%, 18%, 19%; the content rate of the oval-shaped pores with R1 ≤ 20 μm is less than 10%, preferably less than 7%, such as 0%, 4%, 5%, 6%.

[0015] Preferably, the content of oval-shaped structural pores with R1 > 80 μm is less than 5%, preferably less than 3%, for example, 0%, 1%, 2%, 3%.

[0016] According to an embodiment of the present invention, the filled resin is provided by a thermosetting resin.

[0017] According to an embodiment of the present invention, the neutral salt spray performance of the expansion coating is greater than 288 h, illustratively 312 h, 336 h, 360 h.

[0018] According to an embodiment of the present invention, the oil resistance performance of the expansion coating at 170 °C is greater than 1800 h, illustratively 1920 h, 2016 h, 2112 h.

[0019] According to an embodiment of the present invention, the shear strength of the expansion coating at 170 °C is greater than 2 MPa, illustratively 2.1 MPa, 2.3 MPa, 2.5 MPa.

[0020] According to an embodiment of the present invention, the tensile strength of the expansion coating at 170 °C is greater than 2 MPa, illustratively 2.1 MPa, 2.2 MPa, 2.3 MPa.

[0021] The present invention further provides a method for manufacturing the above expansion coating, the manufacturing method including applying a coating on the surface of a magnet substrate and pre-curing the coating, and obtaining the expansion coating by expanding and curing the coating.

[0022] According to an embodiment of the present invention, the coating is provided by an expansion-type paint.

[0023] According to an embodiment of the present invention, based on parts by weight, the expansion-type paint includes at least 50 - 80 parts by weight of thermosetting resin, 5 - 20 parts by weight of expandable microspheres, 0.2 - 1.5 parts by weight of chemical blowing agent, 0.3 - 2 parts by weight of curing agent, and 15 - 30 parts by weight of pigment filler.

[0024] Preferably, based on parts by weight, the intumescent paint comprises 60 to 70 parts by weight of a thermosetting resin, 8 to 15 parts by weight of intumescent microspheres, 0.5 to 1.5 parts by weight of a chemical blowing agent, 0.8 to 1.5 parts by weight of a curing agent, and 17 to 25 parts by weight of a pigment filler.

[0025] According to an embodiment of the present invention, the ratio of the usage amounts of the intumescent microspheres and the chemical blowing agent is (5 to 20):(0.1 to 1.5), preferably (10 to 18):(0.3 to 1.1), for example, 10:0.3, 10:0.8, 16:0.9, 18:1.

[0026] According to an embodiment of the present invention, the thermosetting resin is at least one selected from bisphenol A type epoxy resins, preferably a bisphenol A type epoxy resin having a softening point between 50 and 95 °C.

[0027] According to an embodiment of the present invention, the intumescent microspheres are selected from those having an average particle diameter of the expandable microspheres of 5 to 50 μm, preferably 5 to 20 μm, more preferably 10 to 15 μm. Exemplarily, the intumescent microspheres are at least one selected from 920DU80, 920DU40, and 920DU20 in the Expancel series of AKZO-Nobel. Exemplarily, the intumescent microspheres are selected from a mixture of 920DU40 and 920DU20, and the weight ratio of the two is (1 to 10):(1 to 10).

[0028] According to an embodiment of the present invention, the chemical blowing agent is at least one selected from azodicarbonamide, azobisisobutyronitrile, and paratoluenesulfonyl hydrazide, for example, azodicarbonamide.

[0029] According to an embodiment of the present invention, the curing agent is at least one selected from latent amine curing agents.

[0030] Preferably, the latent amine curing agent is at least one selected from imidazole, an epoxy resin adduct of imidazole, or an epoxy resin adduct of polyamine, for example, dicyandiamide.

[0031] According to an embodiment of the present invention, the pigment filler is at least one selected from insulating carbon black, mica powder, calcium carbonate, and nanoaluminum silicate fiber, for example, insulating carbon black.

[0032] According to an embodiment of the present invention, applying the coating includes applying the intumescent paint to the surface of the magnet substrate to form a coating. Preferably, the application can select a coating method known in the art such as electrostatic spraying.

[0033] According to an embodiment of the present invention, the conditions for pre-curing include that the pre-curing temperature is 90 to 130 °C, preferably 95 °C to 110 °C, for example, 95 °C, 100 °C, 105 °C, 110 °C, and the pre-curing time is 5 to 20 min, preferably 8 to 18 min, for example, 8 min, 10 min, 12 min, 14 min, 16 min, 18 min.

[0034] According to an embodiment of the present invention, after pre-curing, the thickness of the coating is 50 to 200 μm, preferably 80 to 150 μm, for example, 80 μm, 90 μm, 100 μm, 110 μm, 120 μm, 130 μm, 140 μm, 150 μm.

[0035] According to an embodiment of the present invention, the intumescent curing includes placing the magnet substrate coated with the coating in a groove body, and obtaining an expanded coating after curing at a high temperature.

[0036] Preferably, the temperature for high-temperature curing is 190 °C to 230 °C, preferably 200 °C to 220 °C, for example, 200 °C, 205 °C, 210 °C, 215 °C, 220 °C.

[0037] Preferably, the high-temperature curing time is 15 to 40 min, preferably 20 to 30 min, for example 20 min, 25 min, 30 min.

[0038] Exemplarily, it is preferable that the groove body is provided on the rotor.

[0039] The present invention further provides an expanded coating manufactured by the above manufacturing method, and the expanded coating has the above-mentioned meaning.

[0040] The present invention further provides an application of the above expanded coating, preferably used for a permanent magnet.

[0041] The present invention further provides a permanent magnet, the permanent magnet includes the above expanded coating and a magnet substrate, and the expanded coating is located on the surface of the magnet substrate.

[0042] According to an embodiment of the present invention, for the magnet substrate, as long as the permanent magnet can be obtained, a magnet substrate known in the art may be selected.

[0043] Exemplarily, the shape of the magnet substrate is selected from a square magnet.

[0044] According to an embodiment of the present invention, the expanded coating is obtained by manufacturing by the above manufacturing method.

[0045] The present invention further provides an application of the above permanent magnet, preferably used for a rotor.

Effects of the Invention

[0046] Beneficial effects 1. The permanent magnet of the present invention includes an expansion coating. The uniformity of the pore size in the expansion coating is relatively good. It includes oval-shaped pores with a specific shape, no through holes, and the pores are filled with resin. The expansion coating of the present invention has high strength and can exhibit excellent mechanical properties and corrosion resistance even at high temperatures (e.g., 170 °C). The shear strength at 170 °C is greater than 2 MPa, the tensile strength is greater than 2 MPa, the oil resistance performance is greater than 1800 h, and the neutral salt spray is greater than 288 h.

[0047] 2. The present invention combines a chemical blowing agent and a physical blowing agent (expanded microspheres) in a specific ratio to improve the expansion rate of the coating, having both the stability of the expanded microspheres and the flexibility of the chemical blowing agent, with high controllability, relatively uniform expansion, strong supporting force. The chemical blowing agent can achieve a higher expansion rate. The combination of the two enables the expanded coating after expansion to have a high expansion rate, a stable coating structure, high strength, light weight, good adhesiveness, difficulty in delamination and splitting, and the advantages of strong shock resistance and supporting force.

[0048] 3. The present invention adopts a method of combining a chemical blowing agent and a physical blowing agent (expanded microspheres) in a specific ratio, which can achieve a relatively good foaming effect and reduce the environmental problems caused by the chemical blowing agent. Also, the reaction of the chemical blowing agent is rapid, it is difficult to accurately control the expansion ratio, the requirements for the foaming gap are high. If the amount of the chemical blowing agent is too large, furthermore, the microspheres will be penetrated, the stability will deteriorate, and the thrust, adhesive force, etc. may become poor, and furthermore, the bonding force will be low, and the coating will be prone to falling off.

Brief Description of the Drawings

[0049]

Figure 1

[0050] In the figure, R1 is the major axis of the pore, and R2 is the minor axis of the pore.

Figure 2

[0051] In the figure, 1: magnetic steel groove hole of the rotor core, 2: magnet substrate, 3: expansion coating.

Embodiment for Carrying Out the Invention

[0052] Hereinafter, in accordance with specific embodiments, the technical solution of the present invention will be further described in detail. It should be understood that the following embodiments are merely illustrative explanations and interpretations of the present invention and should not be construed as limiting the scope of the claims of the present invention. Any technology realized based on the above content of the present invention is included within the scope of the claims of the present invention.

[0053] Unless otherwise specified, all raw materials and reagents used in the following embodiments are commercially available products or can be manufactured by known methods.

[0054] In the following examples and comparative examples, in each case, a neodymium iron boron product having a size of 20 mm × 10 mm × 3.5 mm was selected as the magnet substrate.

[0055] Example 1 The manufacturing method of the permanent magnet is as follows: 1) Applying the coating An expansion-type paint was applied to the surface of the magnet substrate by an electrostatic spraying method. The expansion-type paint is composed of components with a mass ratio of 68% epoxy resin, 4% Expancel (registered trademark) 920DU40 expansion microspheres, 6% 920DU20, 0.8% azodicarbonamide, 1.2% curing agent dicyandiamide (alazine, 98%), and 20% pigment filler insulating carbon black (Tianjin Yibo Rui). It was pre-cured at 90°C for 20 minutes to form a film, and a permanent magnet with a coating thickness of 100 μm and a coating on the surface was obtained.

[0056] 2) Foaming and expansion treatment The permanent magnet in step 1) was placed in an oven with magnetic steel and cured at 210 °C for 30 min to obtain a permanent magnet with an expansion coating on the surface.

[0057] Comparative Example 1 The method for manufacturing the permanent magnet is basically the same as that of Example 1, except that the expansion-type paint consists of components with a mass ratio of 68% epoxy resin, 12% Expancel® 920DU40, 14% Expancel® 920DU20, 0.8% azodicarbonamide, 1.2% curing agent dicyandiamide (arazine, 98%), and 4% pigment filler insulating carbon black (Tianjin Yiborui).

[0058] Example 2 The method for manufacturing the permanent magnet is as follows: 1) Applying the coating The expansion-type paint was applied to the surface of the magnet by an electrostatic spraying method. The expansion-type paint consists of components with a mass ratio of 56% epoxy resin, 8% Expancel® 920DU40, 8% Expancel® 920DU20, 0.9% azodicarbonamide, 0.7% curing agent dicyandiamide (arazine, 98%), and 26.4% pigment filler insulating carbon black (Tianjin Yiborui). It was pre-cured at 90 °C for 20 min to form a film, and a permanent magnet with a coating thickness of 160 μm and a coating applied on the surface was obtained.

[0059] 2) Foaming expansion treatment The permanent magnet in step 1) was placed in an oven and cured at 230 °C for 40 min to obtain a permanent magnet with an expansion coating on the surface.

[0060] Comparative Example 2 The method for manufacturing the permanent magnet is the same as that of Example 2, except that the expansion-type paint consists of components with a mass ratio of 56% epoxy resin, 12% Expancel® 920DU40, 10% Expancel® 920DU20, 1.8% azodicarbonamide, and 20.2% pigment filler insulating carbon black (Tianjin Yiborui).

[0061] Example 3 The manufacturing method of the permanent magnet is as follows: 1) Applying a coating An expandable paint is applied to the surface of the magnet by an electrostatic spraying method. The expandable paint consists of components with a mass ratio of 65% epoxy resin, 6% Expancel® 920DU40, 3% Expancel® 920DU20, 1.2% azodicarbonamide, 0.8% hardener dicyandiamide (Araldite, 98%), and 24% pigment filler insulating carbon black (Tianjin Yibo Rui). It is pre-cured at 100 °C for 15 min to form a film, with a coating thickness of 100 μm, and a permanent magnet with a coating on its surface is obtained.

[0062] 2) Foaming expansion treatment The permanent magnet obtained in step 1) is placed in an oven and cured at 190 °C for 30 min to obtain a permanent magnet containing an expanded coating on its surface.

[0063] Comparative Example 3 The manufacturing method of the permanent magnet is as follows: 1) Applying a coating An expandable paint is applied to the surface of the magnet by an electrostatic spraying method. The expandable paint consists of components with a mass ratio of 60% epoxy resin, 6% Expancel® 920DU40, 10% Expancel® 920DU20, 1.0% azobisisobutyronitrile, 0.5% azodicarbonamide, 0.6% hardener dicyandiamide (Araldite, 98%), and 21.9% pigment filler insulating carbon black (Tianjin Yibo Rui). It is pre-cured at 100 °C for 15 min to form a film, with a coating thickness of 100 μm, and a permanent magnet with a coating on its surface is obtained.

[0064] 2) Foaming expansion treatment The permanent magnet obtained in step 1) is placed in an oven and cured at 210 °C for 30 min to obtain a permanent magnet containing an expanded coating on its surface.

[0065] Example 4 The manufacturing method of the permanent magnet is as follows: 1) Applying a coating The intumescent paint was applied to the surface of the magnet by an electrostatic spraying method. The intumescent paint consisted of components with a mass ratio of 66% epoxy resin, 6% Expancel® 920DU40, 8% Expancel® 920DU20, 0.8% azobisisobutyronitrile, 1.2% curing agent dicyandiamide (araldite, 98%), and 18% pigment filler insulating carbon black (Tianjin Yiborui). It was pre-cured at 100 °C for 15 min to form a film, with a coating thickness of 100 μm, and a permanent magnet with a coating applied to its surface was obtained.

[0066] 2) Foaming expansion treatment The permanent magnet obtained in step 1) was placed in an oven and cured at 230 °C for 35 min to obtain a permanent magnet with an expanded coating on its surface.

[0067] The data of the oval-shaped pores in the cross-section of the expanded coating on the surface of the permanent magnets in the examples and comparative examples are shown in Table 1.

[0068] Test example The following tests were performed on the expanded coatings on the surfaces of the permanent magnets in the above examples and comparative examples, and the test results are shown in Table 2.

[0069] (1) Test conditions for shear strength at 170 °C The test was carried out at an environmental temperature of 170 °C with reference to GB / T 7124-2008.

[0070] (2) Test conditions for tensile strength at 170 °C The test was carried out at an environmental temperature of 170 °C with reference to GB / T 6329-1996.

[0071] (3) Corrosion resistance (a) Test conditions for SST experiment (neutral salt spray performance) At 35 °C, the concentration of the NaCl aqueous solution was 50 g / L ± 5 g / L, the pH was from 6.5 to 7.2, and the NaCl aqueous solution was formed into salt spray by spraying method and deposited on the neodymium iron boron magnet product to be measured, and the time when rust began to occur on the magnet surface was recorded.

[0072] (b) Oil immersion test conditions Immerse the neodymium iron boron magnet product completely in transmission oil at 150°C, observe the conditions such as rust, bubbling, and peeling on the surface of the magnet, record the time when the coating on the surface of the magnet begins to change, and re-detect the performance of the magnet coating. If it has no impact, this time is regarded as the oil immersion resistance time.

[0073]

Table 1

[0074]

Table 2

[0075] As can be seen from the results of Table 1 and Table 2, 1. From the comparison results between Example 1 and Comparative Example 1, the ratio of expanded microspheres to chemical blowing agent is 26:0.8. The number of microspheres increases, the chemical blowing agent is too little, the total amount of blowing agent increases, the expansion rate is too high, and the ratio of pores in the coating reaches 74%. Therefore, the pores of the expanded coating become sparse, excessive pores occur, the stability, thrust, adhesion, etc. deteriorate, and furthermore, the bonding force becomes low, indicating that the coating is prone to peeling.

[0076] 2. From the comparison results between Example 2 and Comparative Example 2, in Comparative Example 2, the ratio of expanded microspheres to chemical blowing agent is 22:1.8. The expanded microspheres and chemical blowing agent are too much, exceeding the range. After expansion, the ratio of oval-shaped structure pores in the coating is 70%. Similarly, it shows that there is a problem that the expansion rate is too high, the pores of the expanded coating become sparse, the pores are too large, and the stability deteriorates. The permanent magnet of Example 2 has a higher shear strength at 170°C than that of Comparative Example 2, and the shear and tensile strengths are significantly higher than those of Comparative Example 2, and the corrosion resistance is also better.

[0077] 3. From the comparison results between Example 3 and Comparative Example 3, although the ratios of the expanded microspheres to the chemical blowing agent in both Example 3 and Comparative Example 3 are within the range of (5 - 20):(0.1 - 1.5), the ratio of the oval-shaped structure pores in the coating of the product of Comparative Example 3 is 68% (higher than 60%). Similarly, the expansion rate is too high, the pores of the expanded coating are sparse and large, resulting in poor stability, and it is shown that the shear and tensile strengths are significantly higher than those of Example 3.

[0078] 4. From the comparison results between Example 3 and Comparative Example 2, it is shown that the shear strength of the permanent magnet of Example 3 at 170°C is higher than that of Comparative Example 2, the tensile strength is significantly higher than that of Comparative Example 2, and the corrosion resistance is superior to that of Comparative Example 2. From this, the ratio of 30 μm < R1 ≤ 50 μm in Example 3 is 35% (outside the range of 50 - 60%), the ratio of R2 / R1 is less than 8%, and the ratio of the oval-shaped pores in the coating is 50% - 60%. Therefore, it can be seen that both the shear force and tensile strength of the permanent magnet expanded coating of Example 3 are relatively good.

[0079] 5. From the comparison results between Example 4 and Example 1, since the content of the oval-shaped structure pores with 0.8 < R2 / R1 ≤ 1 in the permanent magnet expanded coating of Example 4 is 33% (outside the range of 40% - 55%), it is shown that both the shear force and tensile strength of the permanent magnet expanded coating of Example 4 are slightly inferior to those of Example 1.

[0080] 6. From the comparison results between Example 3 and Comparative Example 3, although the ratios of the amounts of the expanded microspheres and the chemical blowing agent used in both Example 3 and Comparative Example 3 are within the range of (5 - 20):(0.1 - 1.5), since the area of the oval-shaped structure pores in the coating of the product of Comparative Example 3 occupies 68% (exceeding the range of 50% - 60%) of the cross-sectional area of the expanded coating, it is shown that the shear and tensile strengths of the product of Comparative Example 3 at 170°C are slightly lower than those of Example 3, and the corrosion resistance is comparable.

[0081] 7. From the comparison results between Example 1 and Example 2, if the ratio of R2 / R1 is less than 8%, both the R1 value and the ratio of pores in the coating are within the preferred ranges. It is shown that the shear and tensile strengths at 170°C of the permanent magnet expansion coating in Example 1 are slightly higher and the corrosion resistance is comparable.

[0082] 8. From the comparison results between the Examples and the Comparative Examples, it is shown that for the shear and tensile strengths and the corrosion resistance at 170°C, the order of the influence on the performance of the permanent magnet in the microstructure of the expansion coating is: the ratio of oval-shaped structure pores > the R1 value range > the range of the ratio of R2 / R1.

[0083] As described above, the exemplary embodiments of the present invention have been explained. However, the scope of the claims of this application is not limited to the above embodiments. Any modifications, equivalent substitutions, improvements, etc. made by those skilled in the art without departing from the spirit and principles of the present invention should all be included within the scope of the claims of the present invention.

Claims

1. The expansion coating contains pores and further contains a filling resin between the pores. The filling resin is provided by a thermosetting resin. The pores include at least oval-structured pores. The cross-section of the oval-structured pores includes a major axis and a minor axis. Taking the ratio of the minor axis to the major axis as R2 / R1, for the total number of the oval-structured pores, the content rate of the oval-structured pores with 0.7 < R2 / R1 ≤ 1 is 60% - 80%, the content rate of the oval-structured pores with R2 / R1 ≤ 0.5 is less than 8%, and the content rate of the oval-structured pores with 0.9 < R2 / R1 ≤ 1 is 25% - 30%. The content rate of the oval-structured pores with 20μm < R1 ≤ 30μm is 15% - 20%, and the content rate of the oval-structured pores with R1 > 80μm is less than 5%. In the cross-section of the expansion coating, the area of the oval-structured pores occupies 50% - 60% of the cross-sectional area of the expansion coating. The cross-section of the oval-structured pores refers to any cross-section passing through the center point of the pores. The major axis refers to the longest distance passing through the center point in the oval cross-section, denoted as R1, and the minor axis refers to the shortest distance passing through the center point in the oval cross-section, denoted as R2. The manufacturing method of the expansion coating includes applying a coating on the surface of a magnet substrate and pre-curing the coating, and then expanding and curing the coating to obtain the expansion coating. The coating is provided by an expandable paint. Based on parts by weight, the expandable paint includes at least 50 - 80 parts by weight of thermosetting resin, 5 - 20 parts by weight of expandable microspheres, 0.2 - 1.5 parts by weight of chemical blowing agent, 0.3 - 2 parts by weight of curing agent, and 15 - 30 parts by weight of pigment filler. The ratio of the usage amounts of the expandable microspheres to the chemical blowing agent is (5 - 20) : (0.1 - 1.5). The thermosetting resin is at least one selected from bisphenol A type epoxy resins. The expandable microspheres are selected from those with an average particle size of expandable microspheres being 5 - 50μm. The chemical blowing agent is at least one selected from azodicarbonamide, azobisisobutyronitrile, and paratoluenesulfonyl hydrazide. The curing agent is at least one selected from latent amine curing agents. The latent amine curing agent is at least one selected from imidazole, epoxy resin adducts of imidazole, or epoxy resin adducts of polyamines. The pigment filler is at least one selected from insulating carbon black, mica powder, calcium carbonate, and nanoaluminum silicate fiber, and the intumescent coating is characterized by this.

2. In the cross-section of the intumescent coating, the area of the oval-shaped structure pores occupies 53% to 57% of the cross-sectional area of the intumescent coating. Regarding the total number of the oval-shaped structure pores, the content rate of the oval-shaped structure pores with 0.7 < R2 / R1 ≤ 1 is 70% to 78%, the content rate of the oval-shaped structure pores with R2 / R1 ≤ 0.5 is 5% or less, and the content rate of the oval-shaped structure pores with 0.9 < R2 / R1 ≤ 1 is 26% to 28%. The content rate of the oval-shaped structure pores with 20 μm < R1 ≤ 30 μm is 16% to 20%. The intumescent coating according to claim 1, characterized in that the content rate of the oval-shaped structure pores with R1 ≤ 20 μm is less than 10%.

3. Regarding the total number of the oval-shaped structure pores, among them, the content rate of the oval-shaped structure pores with 30 μm < R1 ≤ 50 μm is 50% to 60%. the content rate of the oval-shaped structure pores with R1 > 60 μm is less than 12%. the content rate of the oval-shaped structure pores with 0.8 < R2 / R1 ≤ 1 is 40% to 55%. The intumescent coating according to claim 1, characterized in that the content rate of the oval-shaped structure pores with R1 ≤ 20 μm is less than 7%.

4. The content rate of the oval-shaped structure pores with 0.8 < R2 / R1 ≤ 1 is 50% to 53%. the content rate of the oval-shaped structure pores with R1 > 60 μm is 10% or less. the content rate of the oval-shaped structure pores with 30 μm < R1 ≤ 50 μm is 55% to 60%. The intumescent coating according to claim 1, characterized in that the content rate of the oval-shaped structure pores with R1 > 80 μm is less than 3%.

5. The neutral salt spray performance of the intumescent coating is greater than 288 h. The oil resistance performance of the intumescent coating at 170°C is greater than 1800 h. The shear strength of the intumescent coating at 170°C is greater than 2 MPa. The intumescent coating according to claim 1, characterized in that the tensile strength of the intumescent coating at 170°C is greater than 2 MPa.

6. A method for manufacturing an expanded coating according to claim 1, wherein the manufacturing method includes applying a coating to the surface of a magnet substrate and pre-curing the coating, and expanding and curing the coating to obtain the expanded coating. The coating is provided by an expandable paint. Based on parts by weight, the expandable paint includes at least 50 to 80 parts by weight of a thermosetting resin, 5 to 20 parts by weight of expandable microspheres, 0.2 to 1.5 parts by weight of a chemical blowing agent, 0.3 to 2 parts by weight of a curing agent, and 15 to 30 parts by weight of a pigment filler. The ratio of the usage amounts of the expandable microspheres to the chemical blowing agent is (5 to 20):(0.1 to 1.5). The thermosetting resin is at least one selected from bisphenol A type epoxy resins. The expandable microspheres are selected from those having an average particle diameter of expandable microspheres of 5 to 50 μm. The chemical blowing agent is at least one selected from azodicarbonamide, azobisisobutyronitrile, and paratoluenesulfonyl hydrazide. The curing agent is at least one selected from latent amine curing agents. The latent amine curing agent is at least one selected from imidazole, an epoxy resin adduct of imidazole, or an epoxy resin adduct of polyamine. The pigment filler is at least one selected from insulating carbon black, mica powder, calcium carbonate, and nanoaluminum silicate fiber, and the manufacturing method is characterized by this.

7. Based on parts by weight, the expandable paint includes 60 to 70 parts by weight of a thermosetting resin, 8 to 15 parts by weight of expandable microspheres, 0.5 to 1.5 parts by weight of a chemical blowing agent, 0.8 to 1.5 parts by weight of a curing agent, and 17 to 25 parts by weight of a pigment filler, and the manufacturing method according to claim 6 is characterized by this.

8. The ratio of the usage amounts of the expandable microspheres to the chemical blowing agent is (10 to 18):(0.3 to 1.1), and the manufacturing method according to claim 6 is characterized by this.

9. The softening point of the bisphenol A type epoxy resin is between 50 and 95 °C, and / or the expandable microspheres have an average particle diameter of expandable microspheres of 5 to 20 μm, and the manufacturing method according to claim 8 is characterized by this.

10. The expandable microspheres have an average particle diameter of expandable microspheres of 10 to 15 μm, and the manufacturing method according to claim 8.

11. Applying the coating includes applying the expandable paint onto the surface of the magnet substrate to form a coating. And / or, the conditions for the temporary curing include that the temporary curing temperature is 90 to 130 °C. The temporary curing time is 5 to 20 min. And / or, after the temporary curing, the thickness of the coating is 50 to 200 μm. The expansion curing includes placing the magnet substrate coated with the coating in a groove body, and obtaining an expanded coating after curing at a high temperature. The manufacturing method according to claim 8 is characterized in that.

12. The conditions for the temporary curing include that the temperature for the high-temperature curing is 190 °C to 230 °C. And / or, the time for the high-temperature curing is 15 to 40 min. The manufacturing method according to claim 11 is characterized in that.

13. The expandable coating according to claim 1 for use in a permanent magnet.

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

15. A rotor including the permanent magnet according to claim 14.

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