Magnetic material with expansion coating and preparation method thereof

Abstract

The invention provides a magnetic material with an expansion coating and a preparation method thereof, and the preparation method comprises the following steps: S1, preparing photocuring foaming glue which contains foaming microbeads; and S2, printing the photocuring foaming glue on the surface of the permanent magnet by adopting a silk-screen printing process, and obtaining the magnetic material with the expansion coating after photocuring. According to the preparation method, the photocuring foaming glue is printed on the surface of the permanent magnet through a simple silk-screen printing technology, the magnetic material with the expansion coating is obtained after photocuring, and the related preparation method not only can be used for fixing the magnetic steel, but also has the advantages that the technology is simple, the production efficiency is high, and the commercialization requirement can be well met.

Description

Technical Field

[0001] The present invention relates to the technical field of special functional magnets, and more particularly, to a magnetic material with an expansion coating and a preparation method thereof. Background Art

[0002] With the rapid development and wide promotion of new energy vehicles, permanent magnet drive motors have become one of the key research and development directions. Currently, permanent magnet drive motors mainly use adhesives to fix magnets, which require special adhesive / potting equipment and have relatively high process costs. In order to improve the magnet fixing method, people are constantly seeking new solutions. Using an expansion coating can not only fix the magnet, but also absorb impact, provide insulation and heat insulation, which is one of the ideal technologies to replace adhesives / potting.

[0003] Patent application CN113881294A discloses a coating, a neodymium iron boron magnet, and a preparation method and application thereof. First, the magnet is phosphated, then an expandable powder is prepared, and the powder is coated on the surface of the magnet by electrostatic spraying, and finally cured. Patent CN 113764150 A discloses an expandable sintered neodymium iron boron magnet and a preparation method thereof, and its solution uses compressed air spraying of an expansion coating to apply the expansion coating. Both of them have a common drawback: the coating area is uncontrollable. Electrostatic spraying and air spraying will spray the expansion coating onto the tooling and hanging fixtures, causing pollution and waste.

[0004] Based on this, how to overcome the problem of uncontrollable coating area during the coating process of the existing magnet with an expansion coating is a major problem to be solved in this field. Summary of the Invention

[0005] The main object of the present invention is to provide a magnetic material with an expansion coating and a preparation method thereof to solve the problem of uncontrollable coating area during the coating process of the existing magnet with an expansion coating.

[0006] To achieve the above object, on the one hand, the present invention provides a preparation method of a magnetic material with an expansion coating, the preparation method comprising:

[0007] Step S1, preparing a photocurable foaming glue containing foaming microspheres;

[0008] Step S2, printing the photocurable foaming glue on the surface of the permanent magnet by screen printing, and obtaining a magnetic material with an expansion coating after photocuring.

[0009] Further, the photocurable foaming glue comprises foaming microspheres and a photocurable binder.

[0010] Further, the photocuring binder includes initiator A, catalyst B, additive C, and main glue D; preferably, initiator A is selected from one or more of 2-hydroxy-2-methyl-1-phenyl-1-propanone, 1-hydroxycyclohexyl phenyl ketone, 2-methyl-1-[4-(methylthio)phenyl]-2-(4-morpholinyl)-1-propanone, and benzophenone; preferably, catalyst B is selected from one or more of epoxy acrylate, polyurethane acrylate, polyether acrylate, polyester acrylate, and acrylic resin; preferably, additive C is selected from one or more of polyurethane resin, bismaleimide resin, silicone-modified epoxy resin, PVA, PVB, PVC, and nylon 66; preferably, main glue D is selected from one or more of isobornyl acrylate, isobornyl methacrylate, 2-hydroxyethyl methacrylate, trimethylolpropane triacrylate, hexanediol diacrylate, diethylene glycol diacrylate, neopentyl glycol diacrylate, trimethylolpropane triacrylate, and pentaerythritol triacrylate; preferably, the weight ratio of initiator A, catalyst B, additive C, and main glue D is (0.002-0.1):(0.2-0.5):(0-0.02):(0.8-1.2).

[0011] Further, the foamed microspheres are expandable polymer microspheres, and the expandable polymer microspheres are thermoplastic hollow polymer microspheres, including a thermoplastic polymer shell and a liquid alkane encapsulated therein, wherein the thermoplastic polymer shell material is selected from one or more of thermoplastic polyurethane, copolymer of vinylidene chloride and acrylonitrile, polyvinyl alcohol, polyvinyl butyral, polymethyl methacrylate, polyacrylonitrile, polyvinylidene chloride, polysulfone, homopolymer of vinylidene chloride, random terpolymer of vinylidene chloride, acrylonitrile, and divinylbenzene, polystyrene, and polyvinyl chloride; the liquid alkane is selected from one or more of ethane, propane, isobutane, n-pentane, and isopentane; preferably, the size of the foamed microspheres before expansion is 5-50 μm; preferably, the size of the foamed microspheres before expansion is 5-35 μm; more preferably, the foamed microspheres are selected from any two or three combinations of foamed microspheres with a size before expansion of 5-15 μm, 15-25 μm, and 25-35 μm.

[0012] Further, by weight, the photocuring foaming glue includes 0.8-1.5 parts of foamed microspheres and 0.9-1.1 parts of photocuring binder, wherein the photocuring binder includes 0.05-0.1 part of initiator A, 0.2-0.4 part of catalyst B, 0-0.02 part of additive C, and 0.8-1.2 parts of main glue D.

[0013] Further, the printing method used in step S2 is selective printing, and selective printing is to print the photocuring foaming glue on a partial area of the surface of the permanent magnet; preferably, the area of the selective printing accounts for 5-90% of the total area of the surface of the permanent magnet.

[0014] Further, the way of selective area printing is one or more nested hollow rectangles; the printing line width of each hollow rectangle is 0.5 - 2 mm, the interval width between two adjacent hollow rectangles is 1 - 5 mm, and the outermost hollow rectangle is 1 - 5 mm away from the outer edge of the surface of the permanent magnet; or the way of selective area printing is a grid structure, the photocuring foaming glue is printed at the grid lines of the grid structure, the grid structure is 1 - 3 mm away from the outer edge of the surface of the permanent magnet, the width of the grid lines is 1 - 3 mm, and the width of each grid in the grid structure is 0.5 - 5 mm; or the photocuring foaming glue is printed inside the grids of the grid structure, the width of each grid in the grid structure is 1 - 3 mm, and the width of the grid lines is 0.5 - 5 mm; preferably, the grid structure is a rectangular grid, a rhombic grid or a circular grid.

[0015] Even further, the printing thickness of the glue for selective area printing is 0.05 - 0.08 mm.

[0016] Further, the photocuring in step S2 is ultraviolet photocuring; preferably, the wavelength of the ultraviolet photocuring is 10 - 400 nm, and the light energy density is 3.1 eV - 124 eV; more preferably, the time of the ultraviolet photocuring is 1 - 20 s.

[0017] On the other hand, the present invention provides a magnetic material with an expansion coating, and the magnetic material with an expansion coating is prepared by the above preparation method.

[0018] Applying the technical solution of the present invention, the photocuring foaming glue is printed on the surface of the permanent magnet through a simple screen printing process, and after photocuring, a magnetic material with an expansion coating is obtained. Compared with the traditional glue filling process, the preparation method provided by the present invention can not only firmly fix the magnetic steel, but also has the advantages of simple process, high production efficiency, and can well meet the commercial requirements. At the same time, the formed expansion coating has the advantages of heat insulation and impact absorption; the magnetic material with an expansion coating prepared thereby has good impact resistance, thickness consistency and high push-out strength as a whole. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The specification drawings forming a part of this application are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation to the present invention. In the drawings:

[0020] Figure 1 It is a schematic diagram of the printing method adopted in Example 1;

[0021] Figure 2 It is a schematic diagram of the printing method adopted in Example 2;

[0022] Figure 3Schematic diagram of the printing method adopted in Embodiment 3.

[0023] Among them, the above-mentioned drawings include the following reference numerals:

[0024] 10. Permanent magnet; 20. Photo-curing adhesive layer. Detailed implementation manners

[0025] It should be noted that, without conflict, the embodiments in the present application and the features in the embodiments can be combined with each other. The present invention will be described in detail below in conjunction with the embodiments.

[0026] As described in the background art, there is a problem of uncontrollable coating area during the coating process of the existing magnet with an expansion coating. To solve the above technical problem, on the one hand, the present application provides a preparation method of a magnetic material with an expansion coating, and the preparation method includes: Step S1, preparing a photo-curing foaming glue, and the photo-curing foaming glue contains foaming microspheres; Step S2, using a screen printing process to print the photo-curing foaming glue on the surface of the permanent magnet, and after photo-curing, a magnetic material with an expansion coating is obtained.

[0027] In the above preparation method provided by the present invention, the photo-curing foaming glue is printed on the surface of the permanent magnet through a simple screen printing process, and after photo-curing, a magnetic material with an expansion coating is obtained. Compared with the traditional potting process, the involved preparation method can not only firmly fix the magnet steel, but also has the advantages of simple process, high production efficiency, and can well meet the commercial requirements. At the same time, the formed expansion coating has the advantages of heat insulation and impact absorption. Moreover, compared with the thermo-curing glue, the photo-curing and its related photo-curing foaming glue adopted in the present invention show a faster curing speed, so as to achieve more efficient production, and the photo-curing process is also beneficial to maintaining the stability of the glue layer, and problems such as glue layer deformation that are easily caused during the thermo-curing process will not occur. Therefore, it is more beneficial to ensure the overall uniformity of the expansion coating; and the screen printing process also has the advantages of simple process and convenient batch production compared with other printing processes, so as to further improve the product efficiency of the magnetic material with an expansion coating.

[0028] In a preferred embodiment, the photo-curing foaming glue includes foaming microspheres and a photo-curing binder. The foaming microspheres and the photo-curing binder cooperate with each other when forming the coating structure, and can obtain a more suitable expansion rate and high-temperature thrust during application, so that the finally obtained magnetic material with an expansion coating not only shows better impact resistance, but also is easier to assemble, so as to achieve high compatibility with a variety of devices.

[0029] In several typical implementation manners, the magnetic material selected in the present invention is a permanent magnet commonly used in the art, that is, permanent magnets such as sintered neodymium iron boron, samarium cobalt, and ferrite with specific specifications.

[0030] Since the physical and chemical properties of the final obtained magnetic material with the expansion coating and the synergistic cooperation between the expansion coating and the magnetic material are closely related to the formulation of the photocurable foaming glue, and thus are finally presented in the overall performance of the magnetic material with the expansion coating, in a typical embodiment, the photocurable binder includes initiator A, catalyst B, additive C, and main glue D.

[0031] Among them, for the magnetic material used in the present invention, preferably, the main glue D is selected from one or more of isobornyl acrylate, isobornyl methacrylate, 2-hydroxyethyl methacrylate, trimethylolpropane trimethacrylate, hexanediol diacrylate, diethylene glycol diacrylate, neopentyl glycol diacrylate, trimethylolpropane triacrylate, pentaerythritol triacrylate. In principle, the main glue D can be selected from various polymers commonly used in the art. However, the inventor found through a large number of experiments that the above one or more ester compounds have better adhesion to the permanent magnet after polymerization, thus showing higher overall consistency. Preferably, the initiator A is one or more of 2-hydroxy-2-methyl-1-phenyl-1-propanone, 1-hydroxycyclohexyl phenyl ketone, 2-methyl-1-[4-(methylthio)phenyl]-2-(4-morpholinyl)-1-propanone, benzophenone, so that the polymerization reaction can proceed smoothly, obtaining a coating with more uniform structure and performance, and thus showing better impact resistance during application. In several typical embodiments, in order to increase the speed of the polymerization reaction, shorten the experimental period for printing the expansion coating, thereby shortening the production cycle of the overall magnetic material with the expansion coating and improving its product efficiency, the catalyst B is selected from one or more of epoxy acrylate, polyurethane acrylate, polyether acrylate, polyester acrylate, acrylic resin. On this basis, in order to further improve the compatibility between the photocurable binder and the foaming microspheres, thereby enhancing the high-temperature thrust of the obtained expansion coating, preferably, the additive C is selected from one or more of polyurethane resin, bismaleimide resin, silicone-modified epoxy resin, PVA, PVB, PVC, nylon 66.

[0032] In a typical embodiment, the weight ratio of initiator A, catalyst B, additive C, and main glue D is (0.002 - 0.1):(0.2 - 0.5):(0 - 0.02):(0.8 - 1.2). The photocurable binder formulated with this formulation can better bond with the permanent magnet while cooperating with the foaming microspheres, thereby forming an expansion coating with a more uniform structure and improving its impact resistance.

[0033] Further, the foaming microbeads are expandable polymer microspheres, and the expandable polymer microspheres are thermoplastic hollow polymer microspheres, including a thermoplastic polymer shell and a liquid alkane enclosed therein. The thermoplastic polymer shell material is selected from one or more of thermoplastic polyurethane, copolymer of vinylidene chloride and acrylonitrile, polyvinyl alcohol, polyvinyl butyral, polymethyl methacrylate, polyacrylonitrile, polyvinylidene chloride, polysulfone, homopolymer of vinylidene chloride, random terpolymer of vinylidene chloride, acrylonitrile and divinylbenzene, polystyrene and polyvinyl chloride; the liquid alkane is selected from one or more of ethane, propane, isobutane, n-pentane and isopentane. When heated, the thermoplastic shell softens and the liquid alkane gasifies, so as to expand. When cooled, its shell hardens and the volume is fixed, thus forming a stable structure. Preferably, the size of the foaming microbeads before expansion is 5-50 μm; more preferably, the size of the foaming microbeads before expansion is 5-35 μm. In a typical embodiment, the foaming microspheres are selected from any two or three combinations of foaming microbeads with sizes of 5-15 μm, 15-25 μm and 25-35 μm before expansion. Foaming microbeads with different size distributions are selected to obtain a more suitable expansion rate, which is more conducive to improving the impact resistance of the magnetic material with an expansion coating. The foaming microbeads used in the present invention can be prepared by oneself or directly purchase existing products on the market. Exemplarily, foaming microbeads 920DU40 in the Expancel Microspheres product of AkzoNobel Company are preferably used.

[0034] In a preferred embodiment, by weight, the photocurable foaming glue comprises 0.8-1.5 parts of foaming microbeads and 0.9-1.1 parts of photocurable binder. The photocurable binder comprises 0.05-0.1 part of initiator A, 0.2-0.4 part of catalyst B, 0-0.02 part of additive C and 0.8-1.2 parts of main glue D. Through a large number of experiments, the inventor found that the expansion coating obtained after printing and curing the photocurable foaming glue prepared with the above formula has a structure with loose pores and good toughness, which helps to improve the impact resistance of the obtained magnetic material with an expansion coating; at the same time, its roughness is significantly improved, which is beneficial to the fixation of the finally obtained magnetic material with an expansion coating in the magnetic steel groove, so that it can be applied to various fields of magnetic steel assembly.

[0035] Further, the printing method adopted in step S2 is selective printing. Selective printing is to print the photocurable foaming glue on some areas of the surface of the permanent magnet, so as to avoid the occurrence of "glue overflow" after expansion, better meet the customized requirements of downstream customers; and avoid coating on the tooling. The utilization rate of the photocurable foaming glue is close to 100%, efficiently utilizing resources, having higher environmental friendliness while improving economic benefits, and being more able to meet the industrialization requirements; on this basis, the area of selective printing is selected to account for 5-90% of the total surface area of the permanent magnet, and more preferably 20-60%, so as to further balance economic benefits and the functionality of the product.

[0036] In several typical implementation manners, the selective printing method is one or more nested hollow rectangles; the printing line width of each hollow rectangle is 0.5-2 mm, the interval width between two adjacent hollow rectangles is 1-5 mm, and the outermost hollow rectangle is 1-5 mm away from the outer edge of the surface of the permanent magnet; or the selective printing method is a grid structure, and the photocurable foaming glue is printed at the grid lines of the grid structure. The grid structure is 1-3 mm away from the outer edge of the surface of the permanent magnet, the width of the grid lines is 1-3 mm, and the width of each grid in the grid structure is 0.5-5 mm; or the photocurable foaming glue is printed inside the grids of the grid structure, and the width of each grid in the grid structure is 1-3 mm, and the width of the grid lines is 0.5-5 mm; preferably, the grid structure is a rectangular grid, a rhombic grid or a circular grid. The above several selective printing methods can be printed on the permanent magnet independently in a double-sided printing or single-sided printing manner. Among them, double-sided printing can obtain a better shock absorption effect and the permanent magnet is more firm; single-sided printing can make the air gap of the working surface small, thereby increasing the effective magnetic flux and simplifying the process. Different from the conventional double-sided full coating and single-sided full coating, the above several selective printing methods disclosed in the present invention rely on the flexibility and selectivity of the screen printing process during printing, and can freely select the printed area, so that when heated and expanded, more expansion space is provided for the expanded coating to avoid the problem of the expanded layer overflowing from the slot holes; and the above several specific printing methods disclosed in the present invention can optimize the stress of the expanded layer on the basis of the above content, so as to improve the overall impact resistance of the finally obtained magnetic material with an expanded coating under the condition of controlling the cost.

[0037] For the schematic diagrams of the above several printing methods, see Figures 1 to 3 , in each figure, the permanent magnet 10 and the photocurable glue layer 20 obtained by selective printing on its surface are shown.

[0038] Since the expansion rate of the obtained expansion coating is roughly positively correlated with the printed thickness, in a preferred embodiment, the printed thickness of the glue for selective area printing is 0.05 - 0.08 mm. As the inventor found that as the printed thickness increases, the growth rate of the expansion rate gradually slows down, so choosing this printed thickness can not only more effectively improve the expansion rate of the expansion coating, but also better balance the cost consumption.

[0039] Furthermore, for the photocurable foaming glue provided in the present invention, the photocuring method selected in step S2 is ultraviolet curing. To better adapt to the photocurable foaming glue in the present invention, preferably, the wavelength of the ultraviolet curing is 10 - 400 nm, and the light energy density is 3.1 eV - 124 eV to obtain a better curing effect and obtain an expansion soil layer coating with a more uniform and continuous structure, thereby improving the overall performance of the magnetic material with the expansion coating; on this basis, more preferably, the ultraviolet curing time is 1 - 20 s to achieve a faster curing, thereby shortening the production cycle to a greater extent and improving the production efficiency.

[0040] Another aspect of the present invention provides a magnetic material with an expansion coating, and the magnetic material with the expansion coating is prepared by the above preparation method. The obtained magnetic material with the expansion coating as a whole has good impact resistance, thickness consistency, and high ejection strength, and is expected to achieve large-scale industrial production and be widely used in various magnetic steel assembly processes.

[0041] The following further describes the present application in detail with specific embodiments, and these embodiments should not be construed as limiting the scope claimed by the present application.

[0042] Unless otherwise defined, all professional terms used hereinafter have the same meaning as commonly understood by those skilled in the art. The professional terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the protection scope of the present invention.

[0043] Example 1

[0044] A preparation method of a magnetic material with an expansion coating:

[0045] Prepare 12 sintered neodymium iron boron magnets, with the magnet size of 30 ± 0.05 mm × 15 ± 0.05 mm × 3 ± 0.03 mm. After pretreatment such as degreasing, derusting, and cleaning to remove surface oil stains and rust stains, and clean them for standby;

[0046] Prepare a 12-hole silicon steel sheet rotor, with the slot hole size of 30.3 ± 0.05 mm × 15.3 ± 0.05 mm × 3.5 ± 0.03 mm;

[0047] Select 920DU40 from the Expancel Microspheres products of AkzoNobel as the foaming microspheres;

[0048] By weight, take 12 parts of the foaming microspheres 920DU40 and 10 parts of the photocurable binder, and mix and stir evenly to obtain the photocurable foaming glue. The photocurable binder is composed of 0.438 parts of 2-hydroxy-2-methyl-1-phenyl-1-propanone, 2.189 parts of epoxy acrylate, 0.073 parts of silicone-modified epoxy resin, and 7.300 parts of isobornyl acrylate;

[0049] Use the screen printing process to print the above-mentioned photocurable foaming glue on both sides of the 30mm×15mm surface of the magnet steel. Adopt the selective printing method to form multiple nested hollow rectangles on the surface of the permanent magnet, as Figure 1 shown. The printing line width of each hollow rectangle on it is 1.5mm, the interval width between two adjacent hollow rectangles is 1.5mm, and the outermost hollow rectangle is 2mm away from the outer edge of the surface of the permanent magnet. The printing thickness is 0.08mm, and the area of the selective printing accounts for about 40% of the total surface area of the permanent magnet;

[0050] Use ultraviolet light with a wavelength of 365nm and a light energy density of 3.42eV to irradiate the printing surface to cure it. The curing time is 15s to obtain the magnetic material with an expansion coating.

[0051] Example 2

[0052] A preparation method of a magnetic material with an expansion coating:

[0053] The difference between this example and Example 1 is the different selective printing methods. Specifically:

[0054] Adopt the selective printing method for grid printing, and print the photocurable foaming glue at the grid lines of the grid structure to form a grid structure as shown in Figure 2 shown on the surface of the permanent magnet. The grid structure on it is 2mm away from the outer edge of the surface of the permanent magnet. The width of the grid line is 1.5mm, the width of each grid in the grid structure is 1.5mm, and the area of the selective printing accounts for about 45% of the total surface area of the permanent magnet.

[0055] Example 3

[0056] A preparation method of a magnetic material with an expansion coating:

[0057] The difference between this example and Example 1 is the different selective printing methods. Specifically:

[0058] Adopt the selective printing method for grid printing, and print the photocurable foaming glue inside the grid of the grid structure to form a structure as shown inFigure 3 The grid structure shown. Each grid in the grid structure thereon is a rectangular grid, with a length of 1.4 mm, a width of 1.4 mm, the width of the grid lines is 0.6 mm, and the area of the selected area printing accounts for about 45% of the total surface area of the permanent magnet.

[0059] Example 4

[0060] A preparation method of a magnetic material with an expansion coating:

[0061] The difference between this example and Example 1 lies in the formula of the photocurable foaming glue and the printing method. Specifically:

[0062] By weight, take 8 parts of foaming microbeads 920DU40 and 11 parts of photocurable binder, and mix and stir evenly to obtain the photocurable foaming glue. The photocurable binder is composed of 0.482 parts of 2-hydroxy-2-methyl-1-phenyl-1-propanone, 2.408 parts of epoxy acrylate, 0.080 parts of organosilicon-modified epoxy resin, and 8.030 parts of isobornyl acrylate;

[0063] The printing line width of each hollow rectangle obtained by printing is 2 mm, the spacing width between two adjacent hollow rectangles is 1 mm, and the outermost hollow rectangle is 1 mm away from the outer edge of the surface of the permanent magnet. The area of the selected area printing accounts for about 60% of the total surface area of the permanent magnet.

[0064] Example 5

[0065] A preparation method of a magnetic material with an expansion coating:

[0066] The difference between this example and Example 1 lies in the formula of the photocurable foaming glue and the printing method. Specifically:

[0067] By weight, take 15 parts of foaming microbeads 920DU40 and 9 parts of photocurable binder, and mix and stir evenly to obtain the photocurable foaming glue. The photocurable binder is composed of 0.394 parts of 2-hydroxy-2-methyl-1-phenyl-1-propanone, 1.970 parts of epoxy acrylate, 0.066 parts of organosilicon-modified epoxy resin, and 6.570 parts of isobornyl acrylate;

[0068] The printing line width of each hollow rectangle obtained by printing is 0.6 mm, the spacing width between two adjacent hollow rectangles is 5 mm, and the outermost hollow rectangle is 5 mm away from the outer edge of the surface of the permanent magnet. The area of the selected area printing accounts for about 30% of the total surface area of the permanent magnet.

[0069] Example 6

[0070] A preparation method of a magnetic material with an expansion coating:

[0071] The difference between this embodiment and Embodiment 1 lies in the formulation of the photocurable foaming glue and the printing method. Specifically:

[0072] By weight, take 6 parts of foaming microspheres 920DU40 and 15 parts of photocurable binder, and mix and stir evenly to obtain the photocurable foaming glue. The photocurable binder is composed of 0.657 parts of 2-hydroxy-2-methyl-1-phenyl-1-propanone, 3.284 parts of epoxy acrylate, 0.109 parts of silicone-modified epoxy resin, and 10.950 parts of isobornyl acrylate.

[0073] The printed line width of each hollow rectangle is 0.4 mm, the spacing width between two adjacent hollow rectangles is 6 mm, and the outermost hollow rectangle is 6 mm away from the outer edge of the surface of the permanent magnet. The area of the selected-area printing accounts for about 20% of the total surface area of the permanent magnet.

[0074] Embodiment 7

[0075] A preparation method of a magnetic material with an expansion coating:

[0076] The difference between this embodiment and Embodiment 1 lies in the components and proportions of the photocurable binder in the photocurable foaming glue:

[0077] By weight, the photocurable binder is composed of 1.053 parts of 1-hydroxycyclohexyl phenyl ketone, 0.530 parts of polyurethane acrylate, and 8.417 parts of isobornyl methacrylate.

[0078] Embodiment 8

[0079] A preparation method of a magnetic material with an expansion coating:

[0080] The difference between this embodiment and Embodiment 1 lies in the components and proportions of the photocurable binder in the photocurable foaming glue:

[0081] By weight, the photocurable binder is composed of 0.015 parts of 2-methyl-1-[4-(methylthio)phenyl]-2-(4-morpholinyl)-1-propanone, 1.406 parts of acrylic resin, 0.141 parts of bismaleimide resin, and 8.438 parts of 2-hydroxyethyl methacrylate.

[0082] Embodiment 9

[0083] A preparation method of a magnetic material with an expansion coating:

[0084] The difference between this embodiment and Embodiment 1 is that the printing thickness is 0.05 mm.

[0085] Embodiment 10

[0086] Preparation method of a magnetic material with an expansion coating:

[0087] The difference between this example and Example 1 is that the printing thickness is 0.03 mm.

[0088] Example 11

[0089] Preparation method of a magnetic material with an expansion coating:

[0090] The difference between this example and Example 1 is that the printing thickness is 0.12 mm.

[0091] Example 12

[0092] Preparation method of a magnetic material with an expansion coating:

[0093] The difference between this example and Example 1 is that the printing thickness is 0.015 mm.

[0094] Comparative Example 1

[0095] Preparation method of a magnetic material with an expansion coating:

[0096] The difference between this example and Example 1 is that thermal curing is adopted, that is, the curing method is different. Specifically, the curing temperature is 75 °C and the time is 20 min.

[0097] Performance test:

[0098] Push-out strength test: Place the silicon steel sheet rotor horizontally on the test bench of the mechanical testing machine, with a hollow below the corresponding magnet. Use a push rod to push out the magnet and measure the maximum force. Divide the maximum push-out force by the contact area between the magnet and the silicon steel sheet rotor.

[0099] Drop test: Drop the rotor with the attached magnet freely from a height of 2 meters onto the cement floor 20 times, and check and record the percentage of the number of broken magnets.

[0100] The performance test results of the above examples and the comparative example are shown in Table 1.

[0101] Table 1

[0102] Number Pushing-out strength (MPa) Drop test (%) Whether there is glue overflow at the edge Example 1 783 0 No Example 2 915 0 No Example 3 897 0 No Example 4 936 0 No Example 5 741 0 No Example 6 732 0 No Example 7 828 0 No Example 8 885 0 No Example 9 756 0 No Example 10 728 0 No Example 11 917 0 Slight glue overflow Example 12 682 0 No Comparative example 1 666 16.67 Serious glue overflow

[0103] From the above description, it can be seen that the above embodiments of the present invention have achieved a significant improvement in the push-out strength of the magnet and the impact resistance under the conditions of simple operation and low cost, which is convenient for large-scale popularization and application.

[0104] It should be noted that the terms "first", "second", etc. in the description and claims of this application are used to distinguish similar objects and do not necessarily describe a specific order or sequence. It should be understood that such terms can be interchanged under appropriate circumstances so that the embodiments of this application described here can be implemented in an order other than those described here, for example.

[0105] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A preparation method of a magnetic material with an expandable coating, characterized in that, the preparation method of the magnetic material with an expandable coating comprises: Step S1, preparing a photocurable foaming glue, wherein the photocurable foaming glue contains foaming microspheres; Step S2, printing the photocurable foaming glue on the surface of a permanent magnet by a screen printing process, and obtaining the magnetic material with an expandable coating after photocuring.

2. The preparation method of the magnetic material with an expandable coating according to claim 1, characterized in that, the photocurable foaming glue comprises the foaming microspheres and a photocurable binder.

3. The preparation method of the magnetic material with an expandable coating according to claim 2, characterized in that, the photocurable binder comprises an initiator A, a catalyst B, an additive C and a main glue D; preferably, the initiator A is selected from one or more of 2-hydroxy-2-methyl-1-phenyl-1-propanone, 1-hydroxycyclohexyl phenyl ketone, 2-methyl-1-[4-(methylthio)phenyl]-2-(4-morpholinyl)-1-propanone, benzophenone; preferably, the catalyst B is selected from one or more of epoxy acrylate, polyurethane acrylate, polyether acrylate, polyester acrylate, acrylic resin; preferably, the additive C is selected from one or more of polyurethane resin, bismaleimide resin, silicone-modified epoxy resin, PVA, PVB, PVC, nylon 66; preferably, the main glue D is selected from one or more of isobornyl acrylate, isobornyl methacrylate, 2-hydroxyethyl methacrylate, trimethylolpropane triacrylate, hexanediol diacrylate, diethylene glycol diacrylate, neopentyl glycol diacrylate, trimethylolpropane triacrylate, pentaerythritol triacrylate; preferably, the weight ratio of the initiator A, the catalyst B, the additive C and the main glue D is (0.002-0.1):(0.2-0.5):(0-0.02):(0.8-1.2).

4. The preparation method of the magnetic material with an expandable coating according to any one of claims 1 to 3, characterized in that, The foamed microspheres are expandable polymer microspheres, and the expandable polymer microspheres are thermoplastic hollow polymer microspheres, including a thermoplastic polymer shell and a liquid alkane encapsulated therein. The thermoplastic polymer shell material is selected from one or more of thermoplastic polyurethane, a copolymer of vinylidene chloride and acrylonitrile, polyvinyl alcohol, polyvinyl butyral, polymethyl methacrylate, polyacrylonitrile, polyvinylidene chloride, polysulfone, a homopolymer of vinylidene chloride, a random terpolymer of vinylidene chloride, acrylonitrile and divinylbenzene, polystyrene and polyvinyl chloride; the liquid alkane is selected from one or more of ethane, propane, isobutane, n-pentane and isopentane; preferably, the size of the foamed microspheres before expansion is 5-50 μm; preferably, the size of the foamed microspheres before expansion is 5-35 μm; more preferably, the foamed microspheres are selected from any two or three combinations of foamed microspheres with a size before expansion of 5-15 μm, 15-25 μm and 25-35 μm.

5. The method for preparing a magnetic material with an expansion coating according to claim 3, characterized in that by weight, the photocurable foaming glue comprises 0.8-1.5 parts of the foamed microspheres and 0.9-1.1 parts of the photocurable binder, wherein the photocurable binder comprises 0.05-0.1 part of the initiator A, 0.2-0.4 part of the catalyst B, 0-0.02 part of the additive C and 0.8-1.2 parts of the main glue D.

6. The method for preparing a magnetic material with an expansion coating according to any one of claims 1 to 5, characterized in that the printing method used in step S2 is selective printing, and the selective printing is to print the photocurable foaming glue on a partial area of the surface of the permanent magnet; preferably, the area of the selective printing accounts for 5-90% of the total area of the surface of the permanent magnet.

7. The method for preparing a magnetic material with an expansion coating according to claim 6, characterized in that the selective printing method is one or more nested hollow rectangles; the printing line width of each hollow rectangle is 0.5-2 mm, the interval width between two adjacent hollow rectangles is 1-5 mm, and the outermost hollow rectangle is 1-5 mm away from the outer edge of the surface of the permanent magnet; or, the selective printing method is a grid structure, the photocurable foaming glue is printed at the grid lines of the grid structure, the grid structure is 1-3 mm away from the outer edge of the surface of the permanent magnet, the width of the grid lines is 1-3 mm, and the width of each grid in the grid structure is 0.5-5 mm; or, the photocurable foaming glue is printed inside the grid of the grid structure, the width of each grid in the grid structure is 1-3 mm, and the width of the grid lines is 0.5-5 mm; preferably, the grid structure is a rectangular grid, a rhombic grid or a circular grid.

8. The method for preparing a magnetic material with an expansion coating according to claim 6, characterized in that the printing thickness of the glue for selective printing is 0.05-0.08 mm.

9. The preparation method of the magnetic material with an expansion coating according to any one of claims 1 to 8, characterized in that, the photocuring in step S2 is ultraviolet photocuring; preferably, the wavelength of the ultraviolet photocuring is 10 - 400 nm, and the light energy density is 3.1 eV - 124 eV; more preferably, the time of the ultraviolet photocuring is 1 - 20 s.

10. A magnetic material with an expansion coating, characterized in that, the magnetic material with an expansion coating is prepared by the preparation method according to any one of claims 1 to 9.

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