阅读说明：本技术 磁体预制件、磁体组件及其制备方法 (Magnet preform, magnet assembly and method for manufacturing the same ) 是由 张明鑫 刘延斌 曾庆业 王宏雪 董义 袁易 陈雅 袁文杰 于 2021-08-03 设计创作，主要内容包括：本发明公开了一种磁体预制件、磁体组件及其制备方法。该磁体预制件包括磁体本体和附着在所述磁体本体的表面的可膨胀层；所述可膨胀层由包括(1)10～25wt％聚磷酸铵、(2)5～20wt％脂肪族多元醇、(3)20～50wt％环氧树脂、(4)2～10wt％水溶性碳二亚胺或其盐和(5)2～10wt％的N-羟基琥珀酰亚胺或其衍生物的可膨胀组合物形成。该磁体预制件可以提高磁体本体与基体的结合力。(The invention discloses a magnet prefabricated part, a magnet assembly and a preparation method thereof. The magnet preform comprises a magnet body and an expandable layer attached to a surface of the magnet body; the expandable layer is formed by an expandable composition comprising (1) 10-25 wt% of ammonium polyphosphate, (2) 5-20 wt% of aliphatic polyol, (3) 20-50 wt% of epoxy resin, (4) 2-10 wt% of water-soluble carbodiimide or salt thereof, and (5) 2-10 wt% of N-hydroxysuccinimide or derivative thereof. The magnet prefabricated member can improve the bonding force between the magnet body and the substrate.)

1. A magnet pre-form, characterized in that the magnet pre-form comprises a magnet body and an expandable layer attached to a surface of the magnet body; the expandable layer is formed by an expandable composition comprising (1) 10-25 wt% of ammonium polyphosphate, (2) 5-20 wt% of aliphatic polyol, (3) 20-50 wt% of epoxy resin, (4) 2-10 wt% of water-soluble carbodiimide or salt thereof and (5) 2-10 wt% of N-hydroxysuccinimide or derivative thereof;

wherein the structure of the N-hydroxysuccinimide or the derivative thereof is shown as the formula (1):

wherein R is₁And R₂Each independently selected from H, containingAn alkyl group having 1 to 6 carbon atoms.

2. The magnet preform of claim 1, wherein the salt of a water-soluble carbodiimide is selected from one or more of a hydrochloride salt of a water-soluble carbodiimide, a sulfate salt of a water-soluble carbodiimide, a phosphate salt of a water-soluble carbodiimide, a nitrate salt of a water-soluble carbodiimide.

3. The magnet preform of claim 1, wherein the water-soluble carbodiimide is selected from compounds represented by formula (2):

wherein R is₄、R₅、R₆Each independently selected from alkyl groups having 1 to 6 carbon atoms, R₃Selected from alkylene groups having 1 to 6 carbon atoms.

4. The magnet preform according to claim 1, wherein the aliphatic polyhydric alcohol is one or more selected from the group consisting of a dihydric alcohol having 2 to 20 carbon atoms, a trihydric alcohol having 3 to 20 carbon atoms, a tetrahydric alcohol having 4 to 20 carbon atoms, and a pentahydric alcohol having 5 to 20 carbon atoms.

5. The magnet preform of claim 1, wherein the expandable composition further comprises 20 to 50 wt% of a solvent; the solvent comprises saturated cyclic ketone and a compound shown as a formula (3):

wherein n is a positive integer greater than or equal to 1.

6. A magnet assembly, characterized in that the magnet assembly comprises a base body and a magnet preform according to any one of claims 1 to 5; the base body is provided with a groove for accommodating the magnet prefabricated part; at least a portion of the expandable layer is disposed between the magnet body and an inner wall of the recess.

7. The method of manufacturing a magnet assembly of claim 6, comprising the steps of:

1) spraying the expandable composition onto the surface of the magnet body;

2) precuring the magnet prefabricated part to obtain a magnet prefabricated part;

3) and placing the magnet prefabricated member in the groove, then solidifying, and expanding the expandable layer so as to tightly combine the magnet body with the inner wall of the groove to obtain the magnet assembly.

8. The preparation method according to claim 7, wherein the pre-curing temperature is 80-150 ℃ and the pre-curing time is 10-40 min; the curing temperature is 200-280 ℃, and the curing time is 15-50 min.

9. The method of claim 7, further comprising the step of preparing an expandable composition:

(a) reacting (1) ammonium polyphosphate, (2) aliphatic polyol and (3) epoxy resin, and cooling to obtain a first reactant;

(b) reacting the first reactant, (4) a water-soluble carbodiimide or a salt thereof, and (5) N-hydroxysuccinimide or a derivative thereof to obtain a composition.

10. The method of claim 9, wherein:

in the step (a), firstly reacting (1) ammonium polyphosphate, (2) aliphatic polyhydric alcohol and (3) epoxy resin at 30-60 ℃ for 2-6 h, and then reacting at 70-90 ℃ for 1-4 h;

in the step (b), the first reactant and (4) water-soluble carbodiimide or salt thereof react for 1.5-5 h at the temperature of 20-35 ℃ to obtain a pre-reactant; reacting the pre-reactant with (5) N-hydroxysuccinimide or a derivative thereof at 20-35 ℃ for 2-6 h.

Technical Field

The invention relates to a magnet prefabricated part, a magnet assembly and a preparation method thereof.

Background

A magnet refers to a substance or material capable of generating a magnetic field, which can attract and repel some substances, and is generally classified into a permanent magnet and a soft magnet. The magnetic embodiment is widely applied to the aspects of generators, motors, compasses and the like. In some applications, it is desirable to firmly bond the magnet to the substrate for stable operation. For example, in an ac motor, it is necessary to embed a permanent magnet in a rotor core, and to rotate a rotor more efficiently by using torque of the permanent magnet and reluctance torque of the rotor core. In general, permanent magnets are inserted into magnet insertion holes formed in a rotor core and fixed to the rotor core with an adhesive. Permanent magnets are typically bonded to the rotor core using epoxy. The epoxy resin has the advantages of high strength, low shrinkage, high heat resistance, etc., but the bonding force between the magnet and the substrate needs to be increased. For example, CN102832729A discloses a rotor of a permanent magnet synchronous motor, which includes a rotor core, a rotor shaft, and permanent magnets embedded in the rotor core, wherein epoxy resin is disposed in gaps between the rotor core and the permanent magnets.

In addition, the corrosion resistance of the permanent magnet in the above prior art is yet to be enhanced. CN110136946A discloses a preparation method of a corrosion-resistant neodymium iron boron magnet, wherein an anticorrosive coating is sprayed on a sintered neodymium iron boron magnet, and the anticorrosive coating is obtained by mixing epoxy resin, carbon black, titanium dioxide, silicon carbide, sodium tripolyphosphate, graphene and epoxy resin diluent. Although the coating has certain corrosion resistance, the adhesion performance of the epoxy resin is greatly reduced due to excessive added components.

Disclosure of Invention

In one aspect, the present invention provides a magnet preform. The magnet prefabricated member can improve the bonding force between the magnet body and the substrate. Further, the magnet preform has high corrosion resistance.

In another aspect, the present invention provides a magnet assembly. In the magnet assembly, the bonding force between the magnet body and the base body is high. Further, the magnet assembly has high corrosion resistance.

In another aspect, the present invention provides a method for manufacturing a magnet assembly, which is simple and easy to operate.

In one aspect, the present invention provides a magnet preform comprising a magnet body and an expandable layer attached to a surface of the magnet body; the expandable layer is formed by an expandable composition comprising (1) 10-25 wt% of ammonium polyphosphate, (2) 5-20 wt% of aliphatic polyol, (3) 20-50 wt% of epoxy resin, (4) 2-10 wt% of water-soluble carbodiimide or salt thereof and (5) 2-10 wt% of N-hydroxysuccinimide or derivative thereof;

wherein the structure of the N-hydroxysuccinimide or the derivative thereof is shown as the formula (1):

wherein R is₁And R₂Each independently selected from H and alkyl containing 1-6 carbon atoms.

According to the magnet preform of the present invention, preferably, the salt of water-soluble carbodiimide is selected from one or more of a hydrochloride of water-soluble carbodiimide, a sulfate of water-soluble carbodiimide, a phosphate of water-soluble carbodiimide, and a nitrate of water-soluble carbodiimide.

According to the magnet preform of the present invention, preferably, the water-soluble carbodiimide is selected from compounds represented by the formula (2):

wherein R is₄、R₅、R₆Each independently selected from alkyl groups having 1 to 6 carbon atoms, R₃Selected from alkylene groups having 1 to 6 carbon atoms.

According to the magnet preform of the present invention, preferably, the aliphatic polyhydric alcohol is one or more selected from a dihydric alcohol having 2 to 20 carbon atoms, a trihydric alcohol having 3 to 20 carbon atoms, a tetrahydric alcohol having 4 to 20 carbon atoms, and a pentahydric alcohol having 5 to 20 carbon atoms.

According to the magnet preform of the present invention, preferably, the expandable composition further comprises 20 to 50 wt% of a solvent; the solvent comprises saturated cyclic ketone and a compound shown as a formula (3):

wherein n is a positive integer greater than or equal to 1.

In another aspect, the present invention provides a magnet assembly comprising a base and a magnet preform as described above; the base body is provided with a groove for accommodating the magnet prefabricated part; at least a portion of the expandable layer is disposed between the magnet body and an inner wall of the recess.

In another aspect, the present invention provides a method for preparing the above magnet assembly, comprising the steps of:

1) spraying the expandable composition onto the surface of the magnet body;

2) precuring the magnet prefabricated part to obtain a magnet prefabricated part;

3) and placing the magnet prefabricated member in the groove, then solidifying, and expanding the expandable layer so as to tightly combine the magnet body with the inner wall of the groove to obtain the magnet assembly.

According to the preparation method, preferably, the pre-curing temperature is 80-150 ℃, and the pre-curing time is 10-40 min; the curing temperature is 200-280 ℃, and the curing time is 15-50 min.

According to the preparation method of the present invention, preferably, the preparation method further comprises the steps of:

(a) reacting (1) ammonium polyphosphate, (2) aliphatic polyol and (3) epoxy resin, and cooling to obtain a first reactant;

(b) reacting the first reactant, (4) a water-soluble carbodiimide or a salt thereof, and (5) N-hydroxysuccinimide or a derivative thereof to obtain a composition.

According to the production method of the present invention, preferably,

in the step (a), firstly reacting (1) ammonium polyphosphate, (2) aliphatic polyhydric alcohol and (3) epoxy resin at 30-60 ℃ for 2-6 h, and then reacting at 70-90 ℃ for 1-4 h;

in the step (b), the first reactant reacts with the water-soluble carbodiimide or the salt thereof in the step (4) for 1.5 to 5 hours at the temperature of 20 to 35 ℃ to obtain a pre-reactant; reacting the pre-reactant with (5) N-hydroxysuccinimide or a derivative thereof at 20-35 ℃ for 2-6 h.

The magnet preform of the present invention has an expandable layer. The expandable layer expands in situ to bring the magnet body into close engagement with the inner wall of the recess. Therefore, the magnet preform of the present invention can improve the bonding force of the magnet body and the base. Further, the expandable layer of the present invention covers the surface of the magnet body, and thus corrosion resistance can be improved.

Detailed Description

The present invention will be further described with reference to the following specific examples, but the scope of the present invention is not limited thereto.

< magnet preform >

The magnet preform of the present invention comprises a magnet body and an expandable layer attached to a surface of the magnet body. The magnet preform is placed in a groove formed in the base body and then cured, and the expandable layer is expanded in situ to tightly bond the magnet body to the inner wall of the groove, so that the magnet body and the base body are firmly bonded. The expandable composition has higher binding force, and further improves the binding force between the magnet body and the matrix.

In the present invention, the expandable layer may be attached to multiple surfaces of the magnet body. The description will be given taking a block magnet body as an example. In certain embodiments, the expandable layer may be attached to four surfaces of the bulk magnet body, namely the front surface, the back surface, the left surface, and the right surface. This is advantageous for cost reduction. In other embodiments, the expandable layer may be attached to five surfaces of the bulk magnet body, namely, the front surface, the back surface, the left surface, the right surface, and the upper surface. This can improve corrosion resistance and bonding force of the magnet. In still other embodiments, the expandable layer may be attached to six surfaces of the bulk magnet body, namely, the front surface, the back surface, the left surface, the right surface, the upper surface, and the lower surface. This can further improve the corrosion resistance of the magnet and further improve the bonding force.

The magnet body of the present invention may be a soft magnet or a permanent magnet. Types of magnets include, but are not limited to, samarium cobalt magnets or neodymium iron boron magnets. Preferably, the magnet body is a sintered neodymium iron boron magnet.

The expandable layer of the present invention is formed from an expandable composition. The expandable composition comprises (1) ammonium polyphosphate, (2) an aliphatic polyol, (3) an epoxy resin, (4) a water-soluble carbodiimide or a salt thereof, and (5) N-hydroxysuccinimide or a derivative thereof. In certain embodiments, the expandable composition further comprises a solvent. According to one embodiment of the invention, the expandable composition consists of ammonium polyphosphate, an aliphatic polyol, an epoxy resin, a water-soluble carbodiimide or a salt thereof and an N-hydroxysuccinimide or a derivative thereof and a solvent. The composition expands in the high-temperature curing process, and can be coated on the surface of a magnet body, so that the magnet body and a substrate have high bonding force; and the composition can also improve the corrosion resistance of the magnet.

The amount of ammonium polyphosphate may be 10 to 25 wt% based on the total weight of the expandable composition; preferably 12 to 20 wt%; more preferably 14 to 17 wt%. This enables the composition to achieve an appropriate expansion ratio, and improves the bonding force between the magnet body and the substrate and the corrosion resistance.

The ammonium polyphosphate is a mixture of ammonium orthophosphate and a plurality of ammonium polyphosphates, and the ammonium polyphosphates contained in the ammonium polyphosphate mainly comprise ammonium pyrophosphate, ammonium tripolyphosphate and ammonium tetrapolyphosphate. Ammonium polyphosphate is produced by the reaction of superphosphoric acid and ammonia or by the dehydration of ammonium orthophosphate.

The aliphatic polyol may be used in an amount of 5 to 20 wt% based on the total weight of the expandable composition; preferably 6 to 15 wt%; more preferably 8 to 12 wt%. This enables the composition to achieve an appropriate expansion ratio, and improves the bonding force between the magnet body and the substrate and the corrosion resistance.

The aliphatic polyhydric alcohol can be one or more of dihydric alcohol, trihydric alcohol, tetrahydric alcohol and pentahydric alcohol; preferably, the aliphatic polyol is a tetrahydric alcohol. The aliphatic polyol can be a saturated aliphatic polyol or an unsaturated aliphatic polyol; preferably, the aliphatic polyol is a saturated aliphatic polyol. The aliphatic polyhydric alcohol may contain 2 to 20 carbon atoms; preferably, the carbon atoms are 2 to 10; more preferably, it contains 4 to 7 carbon atoms. According to one embodiment of the present invention, the aliphatic polyhydric alcohol is a saturated aliphatic tetrahydric alcohol having 4 to 7 carbon atoms; preferably, the aliphatic polyol is pentaerythritol. This enables the composition to expand better at high temperatures, improving the bonding force and corrosion resistance of the magnet body and the substrate.

Examples of diols include, but are not limited to, ethylene glycol, 1, 2-propylene glycol, 1, 3-propylene glycol, 1, 2-butylene glycol, 1, 3-butylene glycol, 1, 4-butylene glycol, 2, 3-butylene glycol, 1, 2-pentanediol, 1, 3-pentanediol, 1, 4-pentanediol, 1, 5-pentanediol, 2, 3-pentanediol, 2, 4-pentanediol, 2, 5-pentanediol, 1, 2-hexanediol, 1, 3-hexanediol, 1, 4-hexanediol, 1, 5-hexanediol, 1, 6-hexanediol, 2, 3-hexanediol, 2, 4-hexanediol, 2, 5-hexanediol, 2, 6-hexanediol, 3, 4-hexanediol, 3, 5-hexanediol, 3, 6-hexanediol. Examples of triols include, but are not limited to, glycerol, 1,2, 3-butanetriol, 1,2, 4-butanetriol, 1,2, 5-pentanetriol, 1,2, 3-hexanetriol, 1,2, 6-hexanetriol, 1,2, 7-heptanetriol, 1,2, 3-heptanetriol. Examples of tetrahydric alcohols include, but are not limited to, erythritol, pentaerythritol. Examples of pentahydric alcohols include, but are not limited to, pentahydric alcohol.

The epoxy resin may be used in an amount of 20 to 50 wt% based on the total weight of the expandable composition; preferably 25 to 45 wt%; more preferably 30 to 40 wt%. Thus, the composition has excellent film forming property and the bonding force between the magnet body and the substrate is improved.

The epoxy resin is a high molecular polymer, and is a polycondensation product obtained by reacting epichlorohydrin with bisphenol A or polyhydric alcohol. The epoxy resin is selected from one of glycidyl ether epoxy resin, glycidyl ester epoxy resin, glycidyl amine epoxy resin, linear aliphatic epoxy resin and alicyclic epoxy resin.

The water-soluble carbodiimide or salt thereof may be used in an amount of 2 to 10 wt% based on the total weight of the expandable composition; preferably 3-8 wt%; more preferably 4 to 6 wt%. This enables the composition to expand more uniformly and improves the bonding force between the magnet body and the substrate.

The water-soluble carbodiimide or a salt thereof may be selected from one or more of water-soluble carbodiimide, a hydrochloride of water-soluble carbodiimide, a sulfate of water-soluble carbodiimide, a phosphate of water-soluble carbodiimide, a nitrate of water-soluble carbodiimide; preferably the hydrochloride salt of a water-soluble carbodiimide. The water-soluble carbodiimide may be selected from compounds represented by the formula (2):

in the formula (2), R₄、R₅、R₆Are respectively provided withIndependently selected from alkyl groups containing 1 to 6 carbon atoms; preferably, R₄、R₅、R₆Each independently selected from alkyl groups having 1 to 3 carbon atoms. Examples of the alkyl group of 1 to 6 carbon atoms include, but are not limited to, methyl, ethyl, n-propyl, isopropyl, n-butyl, 1-methylpropyl, 2-methylpropyl, 1-dimethylethyl, pentyl, 1-methylbutyl, 2-methylbutyl, 3-methylbutyl, 1-ethylpropyl, 2-ethylpropyl, 1-dimethylpropyl, 2-dimethylpropyl, 1, 2-dimethylpropyl, hexyl, 1-methylpentyl, 2-methylpentyl, 3-methylpentyl, 4-methylpentyl, 1-ethylbutyl, 2-ethylbutyl, 3-ethylbutyl, 1-dimethylbutyl, 1, 2-dimethylbutyl, 1, 3-dimethylbutyl, 2, 2-dimethylbutyl, 2, 3-dimethylbutyl, 3-dimethylbutyl. Examples of alkyl groups of 1 to 3 carbon atoms include, but are not limited to, methyl, ethyl, n-propyl, isopropyl.

R₃Selected from alkylene groups having 1 to 6 carbon atoms; preferably, R₃Selected from alkylene groups having 2 to 4 carbon atoms. Examples of alkylene groups include, but are not limited to, methylene, ethylene, n-propylene, n-butylene, 1-methylethylene.

In certain embodiments, the water-soluble carbodiimide is 1- (3-dimethylaminopropyl) -3-ethylcarbodiimide. According to one embodiment of the invention, the water-soluble carbodiimide or salt thereof is 1- (3-dimethylaminopropyl) -3-ethylcarbodiimide hydrochloride. This enables a higher binding capacity of the composition.

The N-hydroxysuccinimide or a derivative thereof may be used in an amount of 2 to 10 wt% based on the total weight of the expandable composition; preferably 3-8 wt%; more preferably 4 to 6 wt%. This enables the composition to expand more uniformly and improves the bonding force between the magnet body and the substrate.

The structure of the N-hydroxysuccinimide or the derivative thereof is shown as the formula (1):

in the formula (1), the reaction mixture is,R₁and R₂Each independently selected from H, alkyl containing 1-6 carbon atoms; preferably, R₁And R₂Each independently selected from H, alkyl containing 1-3 carbon atoms; more preferably, R₁And R₂Are all H. Examples of the alkyl group having 1 to 6 carbon atoms include, but are not limited to, methyl, ethyl, n-propyl, isopropyl, n-butyl, 1-methylpropyl, 2-methylpropyl, 1-dimethylethyl, pentyl, 1-methylbutyl, 2-methylbutyl, 3-methylbutyl, 1-ethylpropyl, 2-ethylpropyl, 1-dimethylpropyl, 2-dimethylpropyl, 1, 2-dimethylpropyl, hexyl, 1-methylpentyl, 2-methylpentyl, 3-methylpentyl, 4-methylpentyl, 1-ethylbutyl, 2-ethylbutyl, 3-ethylbutyl, 1-dimethylbutyl, 1, 2-dimethylbutyl, 1, 3-dimethylbutyl, 1-methylbutyl, 1-methylpropyl, 2-methylpropyl, 3-ethylpropyl, 2-ethylpropyl, 1-ethylpropyl, 2-ethylbutyl, 1, 3-dimethylbutyl, and the like, 2, 2-dimethylbutyl, 2, 3-dimethylbutyl, 3-dimethylbutyl. Examples of alkyl groups having 1 to 3 carbon atoms include, but are not limited to, methyl, ethyl, n-propyl, isopropyl. This enables the composition to expand more uniformly and improves the bonding force between the magnet body and the substrate.

The solvent may be used in an amount of 20 to 50 wt% based on the total weight of the expandable composition; preferably 25 to 40 wt%; more preferably 27 to 35 wt%. The solvent may include a saturated cyclic ketone and a compound represented by the formula (3):

wherein n is a positive integer greater than or equal to 1. According to one embodiment of the present invention, the solvent is composed of a saturated cyclic ketone and a compound represented by formula (3). This contributes to the uniform dispersion of the respective raw materials, and contributes to the improvement of the bonding force between the magnet body and the base and the corrosion resistance of the magnet.

In the invention, the mass ratio of the saturated cyclic ketone to the compound shown in the formula (3) can be 1: 0.5-2; preferably 1: 0.5-1.5; more preferably 1:0.7 to 1.2. This contributes to uniformity of film formation, and thus contributes to improvement of the bonding force of the magnet body to the substrate and the corrosion resistance of the magnet.

The saturated cyclic ketone can be selected from one or more of the group consisting of cyclic acetone, cyclobutanone, cyclopentanone, cyclohexanone, cycloheptanone and cyclooctanone; preferably, one or more selected from cyclopentanone, cyclohexanone, cycloheptanone; more preferably cyclohexanone.

In the formula (3), n is a positive integer greater than or equal to 1; preferably, n is a positive integer of 1 or more and 5 or less; more preferably, n is a positive integer of 1 or more and 3 or less. In certain embodiments of the present invention, the compound represented by formula (3) is selected from one or more of triethylene tetramine or diethylene triamine. According to one embodiment of the present invention, the compound represented by formula (3) is triethylene tetramine. This contributes to uniform dispersion of the raw material, and contributes to the adhesion between the high magnetic body and the base and the corrosion resistance of the magnet.

< magnet Assembly >

The magnet assembly of the present invention comprises a base and a magnet preform as described above. The base body is provided with a groove for accommodating the magnet prefabricated member. At least a portion of the expandable layer on the magnet preform is disposed between the magnet body and the inner wall of the recess. The magnet preform is placed in the recess of the base. The gap between the magnet body and the recess is filled with an expandable composition.

The base body may be provided with at least one recess. The number of the grooves is larger than or equal to the number of the magnet bodies. According to one embodiment of the invention, the number of grooves is equal to the number of magnet bodies.

The magnet preform of the present invention is as described above and will not be described in detail here. According to one embodiment of the invention, the magnet body of the magnet preform is a sintered neodymium iron boron magnet.

< method for producing magnet Assembly >

The magnet assembly of the present invention is obtained by spraying, pre-curing and curing. The expandable composition for spraying on the surface of the magnet body can be prepared by the following method. The following is described.

(a) Reacting ammonium polyphosphate, aliphatic polyol and epoxy resin, and cooling to obtain a first reactant; preferably, the ammonium polyphosphate, the aliphatic polyol and the epoxy resin are reacted in the presence of a solvent.

(b) Reacting the first reactant with a water-soluble carbodiimide or a salt thereof and N-hydroxysuccinimide or a derivative thereof to obtain a composition.

According to one embodiment of the invention, the expandable composition is prepared by the following method:

(a) in the presence of a solvent, firstly reacting ammonium polyphosphate, aliphatic polyol and epoxy resin at a low temperature, then reacting at a high temperature, and cooling to room temperature (20-35 ℃) to obtain a first reactant;

(b) reacting the first reactant with water-soluble carbodiimide or salt thereof to obtain a pre-reactant; reacting the pre-reactant with N-hydroxysuccinimide or a derivative thereof to obtain the composition.

In the step (a), the low-temperature reaction temperature can be 30-60 ℃; preferably, the temperature is 40-55 ℃; more preferably 45 to 53 ℃. The low-temperature reaction time can be 2-6 h; preferably 3-5.5 h; more preferably 3.5 to 5 hours. The high-temperature reaction temperature can be 70-90 ℃; preferably 75-85 ℃; more preferably 77 to 83 ℃. The high-temperature reaction time can be 1-4 h; preferably 1.5-3 h; more preferably 1.5 to 2.5 hours.

In the step (b), the reaction temperature of the first reactant and the water-soluble carbodiimide or the salt thereof can be 20-35 ℃; preferably 20-30 ℃; more preferably 22 to 27 ℃. The reaction time of the first reactant and the water-soluble carbodiimide or the salt thereof can be 1.5-5 h; preferably 2-4 h; more preferably 2.5 to 3.5 hours. The reaction temperature of the pre-reactant and the N-hydroxysuccinimide or the derivative thereof can be 20-35 ℃; preferably 20-30 ℃; more preferably 22 to 27 ℃. The reaction time of the pre-reactant and the N-hydroxysuccinimide or the derivative thereof can be 2-6 h; preferably 3-5 h; more preferably 3.5 to 4.5 hours.

In the spraying step, the expandable composition is sprayed on the surface of the magnet body. The expandable composition is first placed in a spray device and preheated. The preheating temperature can be 40-70 ℃; preferably 45-60 ℃; more preferably 47 to 55 ℃. The preheating time can be 2-10 min; preferably 3-8 min; more preferably 4-6 min. The oil amount of the spraying equipment is 10-50 ml; preferably 20-40 ml; more preferably 25 to 35 ml. The pressure of the spraying equipment is 0.1-0.5 MPa; preferably 0.2 to 0.4 MPa; more preferably 0.25 to 0.35 MPa. The step diameter of the spraying equipment can be 1-10 cm; preferably 2-7 cm; more preferably 3 to 5 cm. The step of leveling may also be included after spraying. Leveling is carried out at the temperature of 20-35 ℃; preferably at 20-30 ℃; more preferably at 22 to 27 ℃. The leveling time can be 5-40 min; preferably 10-30 min; more preferably 15 to 25 min. This contributes to uniformity of film formation.

In the precuring step, the magnet preform is precured to obtain a magnet preform. The expandable composition in the magnet preform is pre-cured to form an expandable layer. The pre-curing temperature can be 80-150 ℃; preferably 90-120 ℃; more preferably 95 to 110 ℃. The pre-curing time can be 10-40 min; preferably 15-30 min; more preferably 17 to 25 min.

In the curing step, the magnet preform is placed in the groove, and then cured, and the expandable layer expands to tightly bond the magnet body with the inner wall of the groove, so that the magnet assembly is obtained. The curing temperature can be 200-280 ℃; preferably 210-250 ℃; more preferably 215 to 230 ℃. The curing time can be 15-50 min; preferably 20-40 min; more preferably 25 to 35 min.

The test methods of the examples and comparative examples are described below:

(1) the high-temperature expansion rate of the expandable layer is calculated by adopting the following formula:

k＝H/h×100％；

wherein k is the high temperature expansion ratio;

h, the thickness of the expandable layer after curing;

h-thickness of expandable layer after precuring.

(2) And (3) neutral salt spray test: the test was carried out as specified in GB/T10125-2012.

(3) And (3) testing the binding force: the test was carried out according to the provisions of chapter 4 pull-open section of GB/T39494-2020.

The following raw materials are introduced:

epoxy resin: bisphenol A epoxy resin (E-51) was purchased from Cincho Dry chemical Co., Ltd. free of tin

Ammonium polyphosphate: purchased from Shouguepu chemical Co Ltd

Example 1 and comparative examples 1 to 3

According to the formula shown in Table 1, ammonium polyphosphate, pentaerythritol, epoxy resin, triethylene tetramine and cyclohexanone are reacted for 4 hours at 50 ℃, then heated to 80 ℃ for reaction for 2 hours, and cooled to room temperature to obtain a first reactant.

Reacting the first reactant with 1- (3-dimethylaminopropyl) -3-ethylcarbodiimide hydrochloride (EDC) at 25 ℃ for 3h to obtain a pre-reactant; the pre-reactant was then reacted with N-hydroxysuccinimide (NHS) at 25 ℃ for 4h to give expandable compositions (examples 1 and 3) or unexpanded compositions (comparative examples 1-2).

TABLE 1

Numbering

Ammonium polyphosphate

Pentaerythritol

Epoxy resin

Triethylene tetramine

Cyclohexanone

EDC

NHS

Practice ofExample 1

15wt％

10wt％

35wt％

15wt％

15wt％

5wt％

5wt％

Comparative example 1

—

—

35wt％

32.5wt％

32.5wt％

—

—

Comparative example 2

—

—

35wt％

27.5wt％

27.5wt％

5wt％

5wt％

Comparative example 3

15wt％

10wt％

35wt％

20wt％

20wt％

—

—

The expandable composition (examples 1 and 3) or the unexpanded composition (comparative examples 1 to 2) was placed in a spray apparatus and preheated at 50 ℃ for 5min, and then six surfaces (front surface, rear surface, left surface, right surface, lower surface and upper surface) of the bulk sintered ndfeb magnet were sprayed (parameters of the spray apparatus were set to oil amount: 30ml, pressure: 0.3MPa, step diameter: 4cm) to form a pre-sprayed body. The pre-spray was leveled for 20min at 25 ℃. Then precured at 100 ℃ for 20min to obtain a magnet preform. The magnet preform includes a magnet body and an expandable layer (examples 1 and comparative examples 3) or a non-expandable layer (comparative examples 1 to 2) attached to a surface of the magnet body.

And inserting the magnet prefabricated part into the groove of the base body, wherein a part of the surface of the magnet prefabricated part is exposed out of the base body. Then, cured at 220 ℃ for 30min, the expandable layers of example 1 and comparative example 3 were expanded to tightly bond the magnet body to the inner wall of the groove, to obtain a magnet assembly. The unexpanded layer of comparative examples 1-2 did not expand, and a magnet assembly was obtained. The properties are shown in Table 2.

TABLE 2

Serial number	Expansion ratio	Bonding force between magnet body and substrate	Neutral salt spray
				Example 1	＞300％	＞20MPa	＞500h
Comparative example 1	60％	11MPa	24h
				Comparative example 2	60％	10MPa	100h
Comparative example 3	200％	15MPa	24h

The present invention is not limited to the above-described embodiments, and any variations, modifications, and substitutions which may occur to those skilled in the art may be made without departing from the spirit of the invention.