JP2005116789A - Rare earth injection molding bonded magnet and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rare earth injection molding bonded magnet which has a nylon film on its surface, thereby having excellent rust resistance for salt and water, and to provide its manufacturing method. <P>SOLUTION: In the rare earth injection molding bonded magnet on a surface of the rare earth injection molding bonded magnet, containing a magnetic powder (A) and a thermoplastic resin binder (B), a nylon film (C) having a film thickness of 2 to 20 μm is coated. In the method of manufacturing the rare earth injection molding bonded magnet, after the rare earth injection molding bonded magnet has been formed from a compound containing the magnetic powder (A) and the thermoplastic resin binder (B), the rare earth injection molding bonded magnet is dipped in a nylon coating agent, or is coated with the coating agent by any of spraying, spin coating or brush coating. Thereafter, a solvent is evaporated to form the nylon film on the surface. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a rare earth injection molded bonded magnet and a method for producing the same, and more particularly to a rare earth injection molded bonded magnet having a nylon film on the surface and excellent in rust resistance against salt water and the like, and a method for producing the same. .

  Conventionally, rare earth magnets and the like have been used for various applications including motors. However, since these magnets are mainly produced by a sintering method, they are generally fragile and have a drawback that it is difficult to obtain a thin or complicated shape. In addition, since the shrinkage during sintering is as large as 15 to 20%, a product with high dimensional accuracy cannot be obtained, and post-processing such as polishing is necessary to improve accuracy. .

Bond magnets, on the other hand, have been developed in recent years to solve the above-mentioned drawbacks and to pioneer new applications, but usually use thermoplastic resins such as polyamide resins and polyphenylene sulfide resins as binders. This is filled with magnetic powder and manufactured by injection molding or extrusion molding. Also, thermosetting resin such as epoxy resin or phenol resin is used as a binder, and this is filled with magnetic powder by compression molding. It is manufactured. Of these, injection moldings using thermoplastic resins have expanded their applications for higher functionality because they can be integrally molded with magnets and motor cores and shafts using complex shapes and insert molding. ing.
However, bond magnets using rare earth elements include, for example, NdFeB-based magnet alloys, SmFeN-based magnet alloys, and the like, and these magnet alloys have a drawback of being easily rusted because they mainly use Fe as a transition metal.

In order to improve the corrosion resistance, means for providing an oxidation resistant coating layer on the surface of the main body of the permanent magnet has been taken. As the surface coating method, various methods such as an electroplating method and an electrodeposition coating method are known. Among them, the resin coating method is simple and has been actively used because of its high anticorrosion properties.
As a magnet using a resin-coated rare earth element, a permanent magnet having a resin layer such as an epoxy resin, a thermosetting acrylic resin, an alkyd resin, a melamine resin, or a silicon resin has been proposed (see Patent Document 1). There has also been proposed a permanent magnet in which an oxidation-resistant chemical conversion film and a resin layer such as an epoxy resin are sequentially laminated and coated (see Patent Document 2). Further, a permanent magnet in which a corrosion-resistant resin layer such as polyester or epoxy is formed by electrodeposition coating (see Patent Document 3), and a permanent magnet coated with a fluororesin by a thin film coating method has been proposed (see Patent Document 4). ).

However, in the resin-coated permanent magnet as described above, it is difficult to precisely control the thickness of the film, and since the material is porous, the hole is not coated with a coating film and a void (pinhole) is generated. As a result, sufficient corrosion resistance could not be obtained. When precise control of the film thickness was poor or when there was a pinhole, the penetration of moisture from the thin film thickness portion and the pinhole was accelerated, resulting in a decrease in corrosion resistance.
In addition, if a film is formed from a polyimide resin, it is expected that precise control of the film thickness is good and pinholes can be eliminated. However, in the case of R-TM-B permanent magnets, there is no oxide on the surface. In a high humidity environment, the adhesion strength with the magnet body is poor and the corrosion resistance is also poor.

On the other hand, in the case of a bonded magnet using a rare earth element, a compression-molded bonded magnet using an Nd-Fe-B based magnet alloy is generally electrodeposited, electrostatically coated, sprayed or immersed on the magnet surface. Rust-proof resin coating such as painting is applied.
In addition, injection-molded type bonded magnets often do not require rust-proof coating compared to compression-molded bonded magnets due to the presence of a resin film on the surface of the molded magnet. In a rough environment, rust occurred and became a problem. In order to solve this problem, when an anti-corrosion resin coating is applied to an injection-molded bonded magnet, the adhesion between the thermoplastic resin serving as the binder and the coating material for the resin coating is poor, and the coating film is easily peeled off. There was also a disadvantage that a portion where no was generated occurred.

  For this reason, a highly corrosion-resistant permanent magnet in which a chromate film and a polyimide resin film are laminated on the surface of an R-TM-B permanent magnet has been proposed (see Patent Document 5). According to this, even in the case of a bonded magnet, by depositing a chromate film or a silane coupling agent at the interface between the resin film and the magnet body, the polyimide resin vapor-deposited film and the magnet body have a uniform film thickness and no pinholes. The adhesion strength is improved and the corrosion resistance is improved. However, since the process is complicated and an expensive apparatus is required, there is a problem that the cost is increased.

Under such circumstances, the emergence of a method that can efficiently apply a coating to an injection-molded bonded magnet without using an expensive apparatus with simple means and impart excellent rust prevention performance is desired. It was.
JP-A-60-63901 JP 60-63902 A Japanese Patent Laid-Open No. 61-130453 JP-A 61-168221 JP-A-8-22910

  An object of the present invention is to provide a bonded magnet that has a nylon film on the surface of a rare earth injection molded bonded magnet and is excellent in rust prevention against salt water and the like, and a method for manufacturing the bonded magnet.

  In light of the above-mentioned problems in the rare earth injection molded bond magnet, the present inventors have conducted extensive research and as a result, applied a nylon coating on the surface of the rare earth injection molded bond magnet and vaporized the solvent to achieve a specific film thickness. It has been found that a rare earth injection-bonded magnet having excellent antirust properties can be obtained, and the present invention has been completed.

  That is, according to the first aspect of the present invention, a nylon film (C) having a film thickness of 2 to 20 μm is formed on the surface of a rare earth injection molded bond magnet containing the magnetic powder (A) and the thermoplastic resin binder (B). And a rare earth injection-bonded bonded magnet.

  According to a second aspect of the present invention, there is provided a rare earth injection-bonded magnet according to the first aspect, wherein the magnetic powder (A) is an alloy powder containing a rare earth and a transition metal. The

  According to the third invention of the present invention, in the second invention, the magnetic powder (A) further contains at least one element selected from B, Si, N, Zr, Al, or Ti. A rare earth injection molded bonded magnet is provided.

  According to a fourth aspect of the present invention, in the first aspect, the magnetic powder (A) has a surface coated with a phosphate film of a water-soluble phosphate compound. An injection molded bonded magnet is provided.

  Furthermore, according to the fifth invention of the present invention, in the first invention, the thermoplastic resin binder (B) is at least one polyamide resin selected from nylon, modified nylon, or nylon elastomer. A rare earth injection molded bonded magnet is provided.

  On the other hand, according to the sixth invention of the present invention, in any one of the first to fifth inventions, a rare earth injection molded bond magnet is molded from a compound containing the magnetic powder (A) and the thermoplastic resin binder (B). Then, the rare earth is characterized in that it is immersed in a nylon coating agent or applied by spraying, spin coating or brush coating, and then the solvent is evaporated to form a nylon film on the surface. A method of manufacturing an injection molded bonded magnet is provided.

  According to a seventh aspect of the present invention, there is provided the method for producing a rare earth injection molded bonded magnet according to the sixth aspect, wherein the solvent used in the nylon coating agent is an alcohol solvent. .

  The rare earth injection molded bonded magnet of the present invention has a nylon film formed on the surface of the molded body. Therefore, the film thickness variation and the occurrence of pinholes, which have been a problem in conventional bonded magnets with resin coating, It is possible to provide a rare earth injection-molded bonded magnet which is dense even though it is a relatively thin film and excellent in rust prevention.

  Hereinafter, the rare earth injection molded bonded magnet of the present invention and the manufacturing method thereof will be described in more detail.

1. Rare Earth Injection Molded Bond Magnet The rare earth injection molded bond magnet of the present invention has a nylon film (C) having a specific thickness on the surface of a rare earth injection molded bond magnet containing magnetic powder (A) and a thermoplastic resin binder (B). ).

(A) Rare earth magnet powder The rare earth magnet powder used in the present invention is usually a magnetic powder used in a bond magnet, and if it is a magnetic powder containing a rare earth element and a transition metal element in its constituent elements, There is no particular limitation.

  The rare earth elements include lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy). , Holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu).

  On the other hand, examples of the transition metal element include iron (Fe), cobalt (Co), nickel (Ni), and manganese (Mn), and one or more kinds are selected from these groups. In addition to this, in transition metal element, you may contain either Cr, V, or Cu.

  In addition to the main component of the magnetic powder, those containing at least one element selected from B, Si, N, Zr, Al, or Ti are preferable. In addition, C, P, Ca, Zn, Ga, Nb, Mo, Ag, In, Sn, Hf, Ta, W, Re, Os, Ir, Pt, or Au can be included. One or more selected from C, Al, Si, P, Ca, Ti, Zn, Ga, Zr, Nb, Mo, Ag, In, Sn, Hf, Ta, W, Re, Os, Ir, Pt, or Au When the content is 7% by weight or less, the heat resistance of the magnetic powder can be improved.

  A particularly preferred rare earth element is either Nd or Sm, and the transition metal element is at least one selected from Fe or Co. Specific magnetic powders include, for example, rare earth-iron-boron and rare earth-iron-nitrogen based magnetic powders, which are magnetic powders having an anisotropic magnetic field (HA) of 4000 kA / m or more. Examples include powder.

  The inventors of the present invention used a fine Sm—Fe—N alloy powder obtained by nitriding and pulverizing SmFe alloy coarse powder obtained by the reduction diffusion method as the magnetic powder of the present invention, and an Nd—Fe—B based powder. Using an alloy powder obtained by the liquid quenching method or an anisotropic Nd-Fe-B alloy powder obtained by the HDDR (Hydrogenation-Depositionation-Recombination-Recombination) method, a nylon film is formed by the method described later. It has been confirmed that an injection-molded bonded magnet having a remarkable rust prevention effect can be obtained by forming.

In the above-described resin bond magnet using the Sm-Fe-N magnetic powder, if the magnetic powder is a resin bond magnet of 92.5%, the composition of the magnetic powder is, for example, approximately 23 wt% of Sm (samarium), N (nitrogen) is 3.5 wt%, and the remainder is Fe (iron). The magnetic powder has a volume content of 59.7% and a maximum energy product (BHmax) of 116 kJ / m ³ . Incidentally, the maximum energy product (BHmax) of a resin-bonded magnet whose SmCo (samarium cobalt) magnetic powder is 93 wt% is about 80 kJ / m ³ .
An Nd-Fe-B magnet is a rare earth magnet powder containing Nd, Fe, and B as main components and the Nd ₂ Fe ₁₄ B phase as a main phase, approximately 26 wt% Nd (neodymium), Fe (iron) ) Is 68 wt%, B (boron) is 1.2 wt%, and the remainder is Co (cobalt). The volume content of the magnetic powder of this magnet is about 58%, and the maximum energy product (BH) max is 64 kJ / m ³ .

  The physical properties of the rare earth-transition metal magnetic powder are not particularly limited, but from the viewpoint of the melt flowability of the obtained bonded magnet compound, the orientation of the magnetic powder, the filling rate, etc., the average particle size of the magnetic powder is 1 to 100 μm. The average particle size is preferably 1 to 50 μm, and more preferably 1 to 10 μm.

In the present invention, one or more magnetic powders of ferrite magnetic powders such as Sr ferrite and Ba ferrite and metal magnetic material powders such as alnico and iron chromium cobalt are used in accordance with the required magnetic properties. A powder mixed with the powder can be used.
The mixing ratio of the ferrite magnetic powder to the rare earth-iron-based magnetic powder can be arbitrarily set. However, if the rare earth magnetic powder is set to be larger than the target magnetic characteristics, the total amount of the rare earth magnetic powder and the ferrite magnetic powder is set. Since it can be reduced, a bonded magnet compound having a low melt viscosity can be obtained. Conversely, if a larger amount of ferrite is set, the cost performance of the magnet compound can be improved.

  In the rare earth injection-bonded bonded magnet of the present invention, the magnetic powder preferably contains a water-soluble phosphate compound. Although the detailed mechanism is not clear, in a high-humidity environment, the contained water-soluble phosphate compound dissolves into a water film formed on the surface of the magnetic powder and liberates phosphate ions. This phosphate ion reacts immediately with Fe ions and the like eluted from the magnetic powder into the water film, and precipitates as water-insoluble phosphate in the part lacking the phosphate film. It is estimated that the progress is suppressed.

  Furthermore, the magnetic powder obtained as described above is preferably subjected to a heat treatment in an inert gas or in a vacuum at a temperature range of 100 to 400 ° C. When the heat treatment is performed at a temperature lower than 100 ° C., the magnetic powder does not sufficiently dry. On the other hand, if the heat treatment is performed at a temperature higher than 400 ° C., the magnetic powder is thermally damaged or the coercive force is lowered. It is not preferable.

(B) Thermoplastic resin binder The thermoplastic resin binder used in the rare earth injection molded bonded magnet of the present invention is not particularly limited as long as it functions as a binder for magnetic powder.

  For example, 6 nylon, 66 nylon, 11 nylon, 12 nylon, 612 nylon, aromatic nylon, polymerized fatty acid polyamide block copolymer, or polymerized fatty acid polyetheresteramide block copolymer, some of these molecules Modified or copolymerized polyamide resin such as modified nylon, linear polyphenylene sulfide resin, crosslinked polyphenylene sulfide resin, semi-crosslinked polyphenylene sulfide resin, low density polyethylene, linear low density polyethylene resin, high density polyethylene resin, Ultra high molecular weight polyethylene resin, polypropylene resin, ethylene-vinyl acetate copolymer resin, ethylene-ethyl acrylate copolymer resin, ionomer resin, polymethylpentene resin, polystyrene resin, acrylonitrile-butadiene -Styrene copolymer resin, acrylonitrile-styrene copolymer resin, polyvinyl chloride resin, polyvinylidene chloride resin, polyvinyl acetate resin, polyvinyl alcohol resin, polyvinyl butyral resin, polyvinyl formal resin, methacrylic resin, polyvinylidene fluoride resin, poly III Fluorinated chloroethylene resin, tetrafluoroethylene-hexafluoropropylene copolymer resin, ethylene-tetrafluoroethylene copolymer resin, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer resin, polytetrafluoroethylene resin, polycarbonate resin , Polyacetal resin, polyethylene terephthalate resin, polybutylene terephthalate resin, polyphenylene oxide resin, polyallyl ether allyl sulfone resin, polyether sulfone resin, polyether Examples include rutheketone resins, polyarylate resins, aromatic polyester resins, cellulose acetate resins, and the above-mentioned resin-based elastomers. Random copolymers, block copolymers, and grafts with these monopolymers and other monomers. Examples thereof include copolymers and end group-modified products with other substances. Among these, 11 nylon, 12 nylon and their modified nylon, nylon elastomer, polymerized fatty acid based polyamide block copolymer, or polymerized fatty acid based polypolymer are used because of various properties of the obtained molded product and ease of production thereof. The use of an ether ester amide block copolymer is preferred. It is naturally possible to blend two or more of these thermoplastic resins.

  The melt viscosity and molecular weight of these thermoplastic resins are desirably lower within a range where desired mechanical strength can be obtained, and although depending on other conditions, the molecular weight is preferably 50000 or less. Although the shape as a raw material is not particularly limited, such as powder, beads, pellets, etc., powder form is desirable in view of uniform mixing with magnetic powder.

  Next, modified nylon, which is a preferable polyamide resin in the present invention, that is, a polyamide resin in which a terminal amino group is modified with a carboxyl group-containing hydrocarbon will be described.

  For example, modified nylon is modified by random copolymerization, block copolymerization, or graft copolymerization of monopolymers such as 6 nylon, 66 nylon, 11 nylon, 12 nylon, 612 nylon, and aromatic nylon with other monomers. And end-group-modified products.

  Among these polyamide resins, those obtained by modifying 11 nylon or 12 nylon as a base polymer from the viewpoints of moldability and water absorption are preferable. Polyamide resin having an amino group at the end impairs moldability if the composition melt viscosity changes significantly during heating kneading or injection molding due to special reactivity with non-oxidized iron element contained in the magnetic powder to be mixed. In some cases, the modified terminal amino group can greatly improve these problems.

  The residual amount of the terminal amino group after this modification is preferably 20 mmol / kg or less, more preferably 15 mmol / kg or less. When the residual terminal amino group content is increased from 20 mmol / kg, the reaction with the magnetic powder, particularly the magnetic powder containing the non-oxidized iron element, becomes remarkable, leading to an increase in melt viscosity and a decrease in fluidity.

  The carboxyl group-containing hydrocarbons used for modification include acetic acid, propionic acid, butyric acid, phacolic acid, lauric acid, palmitic acid, stearic acid, behenic acid and other monocarboxyl saturated fatty acids, oxalic acid, malonic acid, succinic acid Dicarboxylic saturated fatty acids such as glutaric acid and adipic acid, monocarboxylic unsaturated fatty acids such as acrylic acid, linoleic acid and oleic acid, dicarboxyl unsaturated fatty acids such as maleic acid and fumaric acid, and fragrances such as benzoic acid Aromatic monocarboxyl hydrocarbons, aromatic dicarboxyl hydrocarbons such as phthalic acid and naphthalenedicarboxylic acid.

  Among these, a monocarboxyl group-containing hydrocarbon is preferable, and further, this hydrocarbon is preferably a fatty acid. Further, the number of carbon atoms in one molecule of the hydrocarbon is desirably 10 or more and 30 or less. If the carbon number is less than 10, no improvement effect on moldability is observed, and if it exceeds 30, the melt viscosity increases. The average molecular weight of these modified nylons is preferably from 5,000 to 15,000. If it is less than 5,000, the strength of the molded product is significantly lowered and lacks practicality, and if it exceeds 15,000, the moldability is deteriorated due to an increase in melt viscosity.

  These polyamide resins have a large molecular weight distribution (weight average molecular weight / number average molecular weight), and are preferably 2.8 or more and 10 or less. The molecular weight distribution is preferably 2.8 or more and 6 or less, more preferably 2.8 or more and 4.2 or less. When this molecular weight distribution is less than 2.8, the mechanical strength around about 100 ° C., which is about the temperature in the mold at the time of molding, is low and cannot be practically used. On the other hand, if it exceeds 10, the amount of unmelted material at the molding temperature increases and the fluidity is lowered.

  The molecular weight and molecular weight distribution of the polyamide resin can be determined by conventional methods such as gel permeation chromatography (GPC). The polyamide resin may be a mixture of two or more having different average molecular weights and molecular weight distributions.

  Further, a polymerized fatty acid-based polyamide block copolymer preferable as the polyamide resin of the present invention is obtained by mixing and polymerizing a polymerized fatty acid (ii), dicarboxylic acid (b), and diamine (c), and polymerized fatty acid-based The polyether ester amide block copolymer is produced by reacting an oligomer of this polymerized fatty acid-based polyamide block copolymer with polyoxyalkylene glycol (d) or dihydroxy hydrocarbon.

  As the polymerized fatty acid (a), a polymerized fatty acid obtained by polymerizing an unsaturated fatty acid having 20 to 48 carbon atoms, for example, a monobasic fatty acid having one or more double bonds or triple bonds having 10 to 24 carbon atoms is used. Used. Specific examples include natural animal and vegetable oil fatty acids such as soybean oil fatty acid, tall oil fatty acid, and rapeseed oil fatty acid, polymerized fatty acids obtained by purifying these from oleic acid, linoleic acid, erucic acid, and the like, and ester derivatives thereof.

  Commercially available polymerized fatty acids usually contain dimer acid (dimerized fatty acid) as the main component, but also contain fatty acids as raw materials and fatty acids higher than trimer, but dimer acid (dimerized fatty acid). It is desirable that the content is 70% or more, preferably 95% or more, and the degree of unsaturation is reduced by hydrogenation. In particular, commercially available products such as “Prepole 1004”, “Prepole 1009”, “Prepole 1010” (manufactured by Unikema) and “Enpole 1008” (manufactured by Cognis) are preferred. Of course, mixtures and ester derivatives thereof can also be used.

As the dicarboxylic acid (b), aliphatic or aromatic dicarboxylic acids having 6 to 22 carbon atoms and ester derivatives thereof are used. For example, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, dodecanedioic acid, hexadecanedioic acid, eicosandioic acid, eicosadiene dienedioic acid, diglycolic acid, 2,2,4-trimethyladipic acid Xylene dicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, terephthalic acid, isophthalic acid, and ester derivatives thereof may be used.
In particular, azelaic acid, sebacic acid, dodecanedioic acid, and a mixture thereof are preferable from the viewpoint of (co) polymerization and physical properties of the obtained polyamide copolymer.

  The diamine (c) is preferably a diamine having 2 to 20 carbon atoms, and specifically includes ethylenediamine, 1,4-diaminobutane, tetramethylenediamine, methylpentamethylenediamine, hexamethylenediamine, nonamethylenediamine, unamethylene. Decamethylenediamine, dodecamethylenediamine, 2,2,4-trimethylhexamethylenediamine, 2,4,4-trimethylhexamethylenediamine, bis- (4,4'-aminocyclohexyl) methane, metaxylylenediamine, paraxylylene Examples thereof include alicyclic diamines such as range amine, isophorone diamine and norbornane diamine, and aliphatic diamines such as dimer diamine derived from a polymerized fatty acid having 20 to 48 carbon atoms.

  Polyoxyalkylene glycol (d) includes polyoxyethylene glycol, polyoxypropylene glycol, polyoxytetramethylene glycol, block or random copolymer of ethylene oxide and propylene oxide, block or random copolymer of ethylene oxide and tetrahydrofuran. Examples include polymers and mixtures thereof.

The polymerized fatty acid-based polyamide block copolymer includes “PA-30R”, “PA-30M”, “PA-30”, “PA-40M”, “PA-50R”, “PA-50R” manufactured by Fuji Chemical Industry Co., Ltd. −50M ”,“ PA-60 ”,“ PA-160M ”,“ PA-160 ”,“ PA-260R ”,“ PA-260M ”,“ PA-260 ”,“ PA-270M ”,“ PA-280R ” ”,“ PA-280M ”,“ PA-280 ”and the like.
Examples of the polymerized fatty acid-based polyetheresteramide block copolymer include “TPAE8”, “TPAE10 · C”, “TPAE10 · HP”, and “TPAE12” manufactured by Fuji Kasei Kogyo Co., Ltd.

  These polymerized fatty acid-based poly (ether ester) amide block copolymers preferably have a number average molecular weight of 1000 to 50000, more preferably 5000 to 25000. When the number average molecular weight is less than 1000, the melt viscosity is remarkably reduced, and may be separated from the magnetic powder during the molding process, or the strength of the bond magnet formed from the composition may be significantly reduced. If it exceeds 50,000, sufficient melt fluidity cannot be obtained during molding.

(C) Nylon film The nylon film is coated on the surface of the bonded magnet using a nylon coating agent containing solvent-soluble nylon, and the film thickness is in the range of 2 to 20 μm.

  Here, examples of the solvent-soluble nylon include 6 nylon, 66 nylon, 11 nylon, 12 nylon, 610 nylon and copolymers thereof (copolymer nylon), or polyamide resins obtained by modifying a part of functional groups of these polyamides. Any nylon that is included and soluble in the solvent can be used. Two or more kinds of these polyamide resins can be blended and used.

Nylon 12-based copolymer nylon has lauric lactam as a copolymerization component, and caprolactam, pyrrolidone, caprin lactam, ω-aminoheptanoic acid, or various raw material monomers such as nylon 66 and nylon 610 as required. There are those copolymerized at a ratio of Further, there are ε-caprolactam / adipic acid / hexamethylenediamine / bis (ρ-aminocyclohexyl) methane copolymer, and when these are used, easy solubility and weather resistance of the coating are expected.
Examples of commercially available products include “CM4000”, “CM4001”, “CM8000” manufactured by Toray, and “Nycote MT-25” manufactured by Hakuyosha.

  These polyamide resins preferably have a low melt viscosity and molecular weight within a range in which a desired film can be obtained, and depending on other conditions, the molecular weight is preferably 5000 or less, particularly 3000 or less, and more preferably 2500 or less. . The shape may be a dry solid, but it must be liquid when a uniform coating film is formed on the magnetic powder.

  As the solvent used for the nylon coating agent, for example, alcohol solvents such as methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, butyl alcohol, benzyl alcohol, furfuryl alcohol, and other solvents are used. May be added.

  When the polyamide resin (nylon) is dissolved in these solvents, the concentration is selected according to the required film thickness of the nylon film, but the amount of nylon is 0.1 to 30% by weight, preferably 0. It is preferable to set it as 3 to 15 weight%. If the concentration is less than 0.1% by weight, the film becomes thin and the weather resistance is lowered. If the concentration is more than 30% by weight, the film thickness varies greatly and the dimensional accuracy of the magnet compact decreases.

  In addition to the solvent, a plasticizer, a colorant, a crosslinking agent, and the like can be added to the nylon coating agent as necessary. Here, as the crosslinking agent, saturated monocarboxylic acid such as octanoic acid and lauric acid, saturated dicarboxylic acid such as oxalic acid and adipic acid, unsaturated fatty acid such as crotonic acid and maleic acid, carbon such as phthalic acid and benzoic acid, etc. Among hydroxy acids such as cyclic carboxylic acid, lactic acid and tartaric acid, any one or two or more compounds can be used.

  By the way, since rare earth injection molded bond magnets have a larger amount of binder resin than rare earth magnet powder compared to compression molded bond magnets, there are many resin films on the surface of injection molded bond magnets, and compression with less resin content. Although it is said that rust prevention is better than a molded bond magnet, a part of the molded body cannot be prevented in molding, and there is a portion where the resin layer does not exist on the surface. Further, when the amount of magnetic powder increases, there is a portion where there is no surface resin layer and the magnetic powder is exposed.

  The present invention provides a halogen film that promotes corrosion by forming a nylon film having excellent resistance to various organic solvents and aqueous alkali solutions on the magnet surface and having a dense structure and low gas permeability. It is to protect the magnet powder from ions and the like. In general, a paint is sometimes applied to improve the corrosion resistance of an injection-molded magnet having a thermoplastic resin as a binder, but the cost is high and the adhesion to the paint is poor, resulting in peeling.

  In the present invention, by applying a solution of a nylon coating agent to a bonded magnet and evaporating the solvent, the nylon film, which is a thermoplastic resin, is coated to have a thickness of 2 to 20 μm, thereby achieving high adhesion. It is characterized by being able to obtain.

  In conventional coating, corrosion resistance cannot be obtained without a film thickness of 10 μm or more, whereas a liquid nylon coating agent exhibits good corrosion resistance if the film after drying is 2 μm or more. The reason why the film thickness is set to 20 μm or less is that a dimensional defect of the magnet occurs due to variations in the film thickness, and when the film is thick, the gap between the magnet surface and the coil or the detection element increases, and the magnetic flux density on the detection side decreases. It is.

2. Manufacturing method of rare earth injection molded bonded magnet The present invention is (1) surface treatment of magnetic powder as a raw material with a water-soluble phosphoric acid compound, if necessary, and (2) mixing a thermoplastic resin binder and necessary additives. A resin compound for a bonded magnet, (3) injection molding of the compound, and (4) a method for producing a rare earth injection molded bond magnet comprising coating the resulting molded body with a nylon coating solution. It is.

(1) Surface treatment of magnetic powder In the present invention, the magnetic powder as a raw material can be surface treated with a water-soluble phosphoric acid compound as necessary.

(Phosphate compound)
The phosphoric acid compound should be capable of forming a phosphate salt after the reaction itself or unreacted and covering the surface of the rare earth-transition metal magnetic powder.

  As a phosphoric acid compound capable of satisfying these conditions, a commercially available water-soluble phosphoric acid compound and phosphoric acid solution can be used. The phosphoric acid compound includes phosphoric acid, phosphorous acid, hypophosphorous acid, pyrophosphoric acid, linear polyphosphoric acid, and cyclic metaphosphoric acid. Particularly preferred is phosphoric acid. These phosphoric acid compounds can be used alone or in combination of two or more, and are usually mixed with a chelating agent, a neutralizing agent and the like to form a treating agent.

  Examples of the water-soluble phosphate compound include alkali metal, alkaline earth metal, ammonium phosphate, and the like in addition to the above. These may be used alone or in combination of two or more. When only orthophosphoric acid is added as the water-soluble phosphoric acid compound, orthophosphoric acid reacts with the magnetic powder to form a water-insoluble phosphate film, and the water-soluble phosphoric acid compound to be left is insufficient. Therefore, it is necessary to carefully consider the amount and timing of addition. It is also possible to add a phosphate of iron, which is the main metal constituting the magnetic powder, as a water-soluble phosphate, but it is insoluble in water from a water-soluble primary salt due to a change in pH or the like. Since it easily changes to a second salt or a third salt, attention must be paid to changes in pH when this is used.

  The content of the water-soluble phosphate compound in the magnetic powder is determined by the amount of the water-soluble phosphate compound to be left in the compound depending on the aggregation state of the magnetic powder or the coating state of the surface of the magnetic powder with an oxidation resistant film. Since it changes, it cannot be generally stated, but the water-soluble phosphate compound is preferably contained in the magnetic powder in a proportion of 0.002 to 0.2% by weight as a phosphate group. If the content is less than 0.002% by weight, sufficient weather resistance cannot be obtained. On the other hand, if the content exceeds 0.2% by weight, it is sufficient from the viewpoint of weather resistance, but the magnetic properties deteriorate. It is not preferable.

The surface treatment method of the magnetic powder is not particularly limited. For example, an ammonium compound such as phosphoric acid, ammonium phosphate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate is added to the magnetic powder during or after pulverization. A predetermined amount of a water-soluble phosphate compound such as phosphate or magnesium phosphate may be added and mixed. The magnetic powder thus surface-treated is preferably subjected to a heat treatment in an inert gas or vacuum in a temperature range of 100 to less than 400 ° C. When heat treatment is performed at a temperature lower than 100 ° C., the drying of the magnetic powder does not proceed sufficiently. On the other hand, if the heat treatment is performed at 400 ° C. or higher, the magnetic powder may be thermally damaged or the coercive force is lowered. There is.
The obtained magnetic powder exhibits high weather resistance, and the compound for bonded magnets and bond magnets obtained therefrom also exhibit extremely high weather resistance because the water-soluble phosphate compound added together with the magnetic powder remains.

The formation of the oxidation-resistant film on the magnetic powder is also performed by a known method using a silane coupling agent, an aluminum coupling agent, a titanate coupling agent, etc. in addition to the phosphoric acid compound. Can do.
In the present invention, it is preferable to provide a surface treatment step with a phosphoric acid compound in advance as necessary to coat the magnetic powder, then treat the magnetic powder with a coupling agent, and then mix the resin binder. However, the magnetic powder, the resin binder, and the coupling agent may be mixed together. However, in order to obtain a more reliable surface-treated film, it is desirable that the magnetic powder is previously treated with a phosphoric acid compound or a coupling agent and then mixed with a resin binder.

(2) Mixing of thermoplastic resin binder Next, a thermoplastic resin binder is mixed with the rare earth magnet powder. The blending amount of the thermoplastic resin binder is not particularly limited, but is 1 to 50 parts by weight, preferably 3 to 50 parts by weight with respect to 100 parts by weight of the bonded magnet compound. Furthermore, 5 to 30 parts by weight, particularly 7 to 20 parts by weight is more preferable. If the resin binder is less than 1 part by weight, not only will the kneading torque increase and fluidity will be lowered, making the molding difficult, but the magnetic properties will be insufficient. Since characteristics cannot be obtained, it is not preferable.

  The bonded magnet compound may be blended with the following additives and fillers if necessary, and then the bonded magnet compound may be melt-kneaded. For kneading, for example, a Banbury mixer, kneader, roll, kneader ruder, A kneader such as a screw extruder or a twin screw extruder is used.

(Additive)
In the compound for the bond magnet, a reactive diluent, an unreactive diluent, a thickener, a lubricant, a mold release agent, an ultraviolet absorber, a flame retardant, various stabilizers, etc., as long as the object of the present invention is not impaired. Can be blended.

Examples of the reactive diluent include styrene, fatty acid diglycidyl ether, ethylene glycol glycidyl ether, phenyl glycidyl ether, and glycerin polyglycidyl ether.
Examples of the unreactive diluent include alcohols such as ethanol and isopropanol.

Examples of the thickener include beryllium oxide, magnesium oxide, magnesium hydroxide, calcium oxide, calcium hydroxide, and zinc oxide.
Examples of the lubricant include waxes such as paraffin wax, liquid paraffin, polyethylene wax, polypropylene wax, ester wax, carnauba, and micro wax, stearic acid, 1,2-oxystearic acid, lauric acid, palmitic acid, oleic acid, and the like. Fatty acid salts such as fatty acids, calcium stearate, barium stearate, magnesium stearate, lithium stearate, zinc stearate, aluminum stearate, calcium laurate, zinc linoleate, calcium ricinoleate, zinc 2-ethylhexoate (metal soaps) ), Stearic acid amide, oleic acid amide, erucic acid amide, behenic acid amide, palmitic acid amide, lauric acid amide, hydroxystearic acid amide, methylene bis-stear Fatty acid amides such as acid amide, ethylene bis stearic acid amide, ethylene bis lauric acid amide, distearyl adipic acid amide, ethylene bis oleic acid amide, dioleyl adipic acid amide, N-stearyl stearic acid amide, butyl stearate, etc. Fatty acid esters, alcohols such as ethylene glycol and stearyl alcohol, polyethylene glycol, polypropylene glycol, polytetramethylene glycol, and polyethers made from these modified products, polysiloxanes such as dimethylpolysiloxane and silicon grease, fluorine-based oils Fluorine compounds such as fluorine-based grease and fluorine-containing resin powder, and inorganic compound powders such as silicon nitride, silicon carbide, magnesium oxide, alumina, silicon dioxide, and molybdenum disulfide.
The blending amount of the lubricant is usually 0.01 to 20 parts by weight, preferably 0.1 to 10 parts by weight with respect to 100 parts by weight of the magnetic powder.
Examples of the mold release agent include zinc stearate and a system in which this is mixed with other metal stearates.

Examples of the ultraviolet absorber include benzophenone series such as phenyl salicylate, p-tert-butylphenyl salicylate, 2,4-dihydroxybenzophenone, 2-hydroxy-4-methoxybenzophenone, 3-2′-dihydroxy-4-methoxybenzophenone; 2 Benzotriazoles such as-(2'-hydroxy-5'-methylphenyl) benzotriazole and 2- (2'-hydroxy-3 ', 5'-ditert-butylphenyl) benzotriazole; oxalic anilide derivatives and the like It is done.
Examples of the flame retardant include antimony trioxide, sodium antimonate, organic bromine compounds, chlorinated paraffin, and chlorinated polyethylene.

As stabilizers, bis (2,2,6,6-tetramethyl-4-piperidyl) sebacate, bis (1,2,2,6,6-pentamethyl-4-piperidyl) sebacate, 1- [2 -{3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionyloxy} ethyl] -4- {3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionyloxy} -2,2,6,6-tetramethylpiperidine, 8-benzyl-7,7,9,9-tetramethyl-3-octyl-1,2,3-triazaspiro [4,5] undecane-2,4- Dione, 4-benzoyloxy-2,2,6,6-tetramethylpiperidine, dimethyl-1- (2-hydroxyethyl) -4-hydroxy-2,2,6,6-tetramethylpiperidine polycondensate Poly [[6- (1,1,3,3-tetramethylbutyl) imino-1,3,5-triazine-2,4-diyl] [(2,2,6,6-tetramethyl-4-piperidyl ) Imino] hexamethylene [[2,2,6,6-tetramethyl-4-piperidyl] imino]], 2- (3,5-di-tert-butyl-4-hydroxybenzyl) -2-n-butyl In addition to hindered amine stabilizers such as bis (1,2,2,6,6-pentamethyl-4-piperidyl) malonate, phenolic, phosphite, thioether antioxidants, etc. One or more of these can be used.
The compounding amount of the stabilizer is usually 0.01 to 5 parts by weight, preferably 0.05 to 3 parts by weight with respect to the total amount of the magnetic powder.

  These additives are appropriately selected according to the type of the thermoplastic resin binder and the type of the magnetic powder, and the addition amount is not particularly limited, but is usually 100 parts by weight of the compound for the bonded magnet. The total amount is preferably 0.1 to 20 parts by weight, particularly 0.1 to 3 parts by weight.

(filler)
In the present invention, a filler having a large reinforcing effect such as mica, whisker, talc, carbon fiber, or glass fiber can be appropriately added to the bonded magnet compound as long as the object of the present invention is not hindered. That is, when the magnetic properties required for the bonded magnet are relatively low and the amount of magnetic powder filled is relatively small, the mechanical strength of the bonded magnet tends to be low. In such a case, in order to supplement the mechanical strength Fillers such as mica and whiskers can be added.
The type and blending amount of these fillers are not particularly limited and may be appropriately selected according to the required properties of the bond magnet.

  After adding 7.5 to 11 wt% of the thermoplastic resin as a binder to the rare earth magnet powder 89.0 to 92.5 wt%, the mixture is kneaded at 200 to 250 ° C. using a biaxial kneader or the like. Thereafter, a compound (pellet) for a rare earth injection molded bond magnet having a diameter of about 5 mm × 5 mm, for example, suitable for injection molding is produced by a hot cut pelletizer or the like.

(3) Injection molding The rare earth injection molded bonded magnet compound is injection molded into a desired mold using an injection molding machine. The injection molding is performed under the condition that the maximum history temperature is 265 ° C. or lower, preferably 260 ° C. or lower, more preferably 250 ° C. or lower. When the maximum history temperature exceeds 265 ° C., there is a problem in that the magnetic characteristics are deteriorated, which is not preferable.

  If the bonded magnet compound contains anisotropic magnetic powder, it is anisotropic if a magnetic circuit is incorporated in the mold of the molding machine and an orientation magnetic field is applied to the molding space (mold cavity) of the compound. Can be manufactured. At this time, by setting the orientation magnetic field to 400 kA / m or more, preferably 800 kA / m or more, a bonded magnet having high magnetic properties can be obtained. When the compound for bond magnet contains isotropic magnetic powder, it is performed without applying an orientation magnetic field to the molding space (mold cavity) of the compound.

  The rare earth injection molded bond magnet (molded body) obtained in this way has a resin amount of about 40% by volume with respect to the magnetic powder, so there is a thin binder resin layer on the magnet surface, so a compression molded bond magnet with a small amount of resin. It is said that the rust prevention property is better than the part where there is no resin layer locally on the flat or curved surface of the molded body, the edge of the molded body and the space (cavity) for forming the molded body in the mold There is a portion where it is difficult to form the resin layer or there is no resin layer, such as a portion (gate) connecting the inlets of the melted kneaded material, and it is necessary to form a film at this portion.

(4) Nylon film formation So, by using a nylon coating agent in which solvent-soluble nylon is dissolved in a solvent, a nylon film is formed on the surface of the bonded magnet molding by dipping, spray coating, spin coating, brush coating, etc. . A preferable coating method is dipping or spray coating.

  In the case of the dipping method, the nylon coating solution is taken in a container such as polyethylene or polypropylene that is insoluble in an alcohol solvent, and the magnet molded body is dipped in this solution. At this time, the concentration of the treatment liquid is preferably 0.3 to 8% by weight. The coating film thickness can be controlled by dipping a plurality of times. The treatment environment is preferably a room of 30 ° C. or less, preferably 25 ° C. or less, and in an environment exceeding 30 ° C., the volatilization of the solvent is quick and the concentration of the nylon coating solution tends to change.

  Moreover, when forming a nylon membrane | film | coat on a molded object by the spray coat method, the density | concentration of a process liquid has preferable 3 to 15 weight%. If the concentration is less than 3% by weight, the film is thin and the weather resistance is a problem. If it exceeds 15% by weight, sagging, unevenness, and pinholes occur in the film, resulting in large variations in the film thickness and The dimensional accuracy is lowered and the weather resistance due to pinholes is lowered. Spray coating can be performed using either an automatic coating apparatus using a pneumatic spray gun, a manual coating machine or a tumbling spray coating apparatus.

  After the bonded magnet molded body is treated with the nylon coating agent, the solvent is vaporized to form a nylon film on the surface of the magnet molded body. At this time, vaporization of the solvent may be allowed to stand at room temperature, but it is preferable to carry out means such as heating or decompression alone or in combination. If the molded body is dried at a temperature of 60 ° C. to 90 ° C. for about 1 hour, the solvent can be efficiently vaporized.

  When a heat-crosslinking type or UV-crosslinking type cross-linking agent is added to a solution containing a solvent-soluble nylon having a crosslinkable functional group, in the former case, the temperature is increased following the vaporization stage or vaporization. Thus, the latter can be crosslinked by irradiating with ultraviolet rays during or after film formation.

  According to the present invention, since high corrosion resistance can be obtained with a thinner film thickness than conventional resin coating, the amount of nylon coating agent used can be reduced, and an inexpensive and simple coating method can be adopted. There is also an advantage that high corrosion resistance can be obtained regardless of the shape.

  Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples. In addition, although the detail of each component used for the Example and the comparative example, the test method, the evaluation method, and the obtained result are illustrated, it is not limited to these, unless it deviates from the meaning of this invention.

A bonded magnet compound and a bonded magnet were manufactured and evaluated using the following materials.
1) Material A Magnetic powder ・ Magnetic powder 1: SmFeN magnetic powder
(Product name: SmFeN alloy powder, manufactured by Sumitomo Metal Mining Co., Ltd.)
・ Magnetic powder 2: NdFeB-based isotropic magnetic powder
(Product name: MQpowder, manufactured by Magnequench International)
B Resin binder-Thermoplastic resin (nylon 12)
(Product name: Daiamide A-1709P, manufactured by Daicel Huls Co., Ltd.)
-Thermosetting resin (phenol resin, PM-8200, manufactured by Sumitomo Bakelite)
C Solvent-soluble nylon (ε-caprolactam / adipic acid / hexamethylenediamine / bis (ρ-aminocyclohexyl) methane copolymer, manufactured by GENERAL TRADERS, LTD.)

2) Evaluation method-Weather resistance: The molded product obtained by injection molding the compound for bonded magnet was sprayed with a 5 wt% sodium chloride solution at 35 ° C in a salt spray device (manufactured by Suga Test Instruments Co., Ltd.) Treated for 24 hours. After drying, the rusting state of the surface of the molded body, the edge portion, and the gate portion (melt compound inflow portion when forming the molded body in the mold) was visually evaluated.

(Examples 1-18)
The rare earth injection molded bonded magnet of the present invention was manufactured in the following manner.
1) Mixing of rare earth magnet and resin binder and compound preparation Add the thermoplastic resin binder in the ratio shown in Table 1 to each magnetic powder (each part by weight) and mix and stir well in a planetary mixer (Dalton). To obtain a mixture.
The mixture obtained here was extruded with a twin-screw kneading extruder (rotation speed: 30 rpm, 5 mmφ strand die, cylinder temperature: 200-250 ° C.), and a compound for rare earth injection molded bond magnet of φ5 mm × 5 mm with a hot cut pelletizer. (Pellet) was produced.

2) Injection molding The obtained kneaded material (pellet) was injected under the conditions shown in Table 2 using an injection molding machine (manufactured by Nippon Steel Works, J85ELIII type), and a 10 mm × 15 mm × 5 mm prismatic shape test A magnet compact was obtained.

3) Treatment with Nylon Coating Agent Using a nylon coating agent (treatment liquid) shown in Table 3, a molded article obtained by injection molding was coated. The concentration of the treatment liquid was adjusted with isopropyl alcohol. The processed molded bodies were each dried at 60 ° C. for 1 hour to prepare samples. The obtained magnet compacts were evaluated by the methods described above, and the results are shown in Table 4.

(Comparative Examples 1-10)
Under the same conditions as in the Examples, a thermoplastic resin was added to the magnetic powder in the ratio shown in Table 1 (parts by weight), and sufficiently mixed and stirred in a planetary mixer (Dalton) to obtain a mixture. This mixture was kneaded at 200 ° C. with a twin-screw kneading extruder (manufactured by Nakatani Co., Ltd.), and injection molding was performed using the resulting mixture (rare earth injection molding pellet compound). Next, this molded body was not subjected to a coating treatment with a nylon coating solution (treatment liquid), or was immersed once in the treatment liquid to obtain a comparative rare earth injection molded bonded magnet having a thin film. This was evaluated under the same conditions as in Examples, and the results are shown in Table 4.

(Comparative Example 11)
A bonded magnet was produced using a phenol resin, which is a thermosetting resin, as a binder, and a coating treatment was performed using a nylon coating solution in the same manner as in the examples.
The conditions for compound preparation and injection molding were as shown in Table 1. With respect to the amount of magnetic powder of 2, 9.5 wt% phenol resin was pressurized and mixed at room temperature (pressure kneader manufactured by Moriyama Co., Ltd.) to obtain a mixture for injection molding. Using this mixture, a 10 mm × 15 mm × 5 mm prismatic test magnet was injection molded under the conditions of an injection pressure of 150 MPa, an injection speed of 30 mm / sec, a nozzle temperature of 30 ° C., and a mold temperature of 150 ° C. The coating treatment liquid C was used, and the bonded magnet was coated twice by spraying, but the nylon film thickness was as thin as 1 μm. The results are shown in Table 4.

In Examples 1 to 6, a relatively thick nylon film could be formed on the surface of the bonded magnet by spray coating, and there was no rusting from any part of the molded article in the salt spray test. The same was true for the spray coats of Examples 7-10. Furthermore, even when a relatively thin film was formed by the dipping method as in Examples 11 to 18, no rusting was observed.
However, in Comparative Examples 1 to 6 in which the nylon film was not coated with the nylon coating solution, rusting was observed in many parts of the molded body when the salt spray test was performed. Moreover, in Comparative Examples 7-10, although the amount of rusting differed somewhat by the difference in compound composition, since the nylon membrane | film | coat was too thin, spot rust generate | occur | produced partially. It was found that the film thickness is required to be 2 μm or more.
In Comparative Example 11, since a thermosetting resin was used as the binder resin, the adhesion with the solvent-soluble nylon was poor, and a desired nylon film could not be formed on the surface of the bond magnet.

Claims (7)

  A rare earth injection molded bonded magnet having a nylon film (C) with a film thickness of 2 to 20 μm on the surface of a rare earth injection molded bonded magnet containing a magnetic powder (A) and a thermoplastic resin binder (B). .   The rare earth injection-bonded magnet according to claim 1, wherein the magnetic powder (A) is an alloy powder containing a rare earth and a transition metal.   The rare earth injection-bonded magnet according to claim 2, wherein the magnetic powder (A) further contains at least one element selected from B, Si, N, Zr, Al, or Ti.   The rare earth injection-bonded magnet according to claim 1, wherein the surface of the magnetic powder (A) is coated with a phosphate film of a water-soluble phosphate compound.   The rare earth injection-bonded magnet according to claim 1, wherein the thermoplastic resin binder (B) is at least one polyamide resin selected from nylon, modified nylon, or nylon elastomer.   After molding a rare earth injection-molded bonded magnet from a compound containing magnetic powder (A) and thermoplastic resin binder (B), it is immersed in a nylon coating agent, or the coating agent is sprayed, spin coated or brushed. The method for producing a rare earth injection molded bonded magnet according to any one of claims 1 to 5, wherein the solvent is vaporized to form a nylon film on the surface of the bonded magnet.   The method for producing a rare earth injection molded bonded magnet according to claim 6, wherein the solvent used in the nylon coating agent is an alcohol solvent.