JP2008166523A - Bonded-magnet composition and bonded magnet using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a bonded-magnet composition that has excellent fluidity and includes rare earth-iron-nitrogen based magnetic powder, ferrite magnetic powder, and a resin binder, and a bonded magnet using the same. <P>SOLUTION: The bonded-magnet composition includes rare earth-iron-nitrogen based magnetic powder with a Th<SB>2</SB>Zn<SB>17</SB>-type crystal structure, ferrite magnetic powder, and a resin binder. The circularity coefficient of the rare earth-iron-nitrogen based magnetic powder is ≥0.6. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a bonded magnet composition including a rare earth-iron-nitrogen based magnetic powder, a ferrite magnetic powder, and a resin binder, and a bonded magnet using the same.

  Magnets are roughly classified into sintered magnets and bonded magnets. Sintered magnets have high magnetic properties, but have disadvantages such as low degree of freedom in molding and low mechanical strength. On the other hand, a bond magnet made of magnetic powder and a resin ibander has a resin bond as a component, so that the magnetic properties are weak, but it is excellent in molding flexibility and mechanical strength. For example, bond magnets are used in fields where impact resistance or corrosion resistance is required, such as rotors of small motors and small sensors. Furthermore, depending on the field to which the bonded magnet is applied, a relatively small molded product in which the weight of the bonded magnet is less than 10 g may be required. In such a molded product, it is common to have a thin portion as a part of a thickness of 1 mm or less, and not only a sintered magnet but also a bonded magnet, Depending on the type of resin binder, molding may not be possible.

  As a method for manufacturing the bonded magnet, calender rolls and extrusion molding are mainly applied when a rubber-based material is used as a resin binder, and press molding is mainly applied when a thermosetting resin is used. And in the case of a thermoplastic resin, injection molding is applied. This injection molding is suitable for manufacturing a molded product with high dimensional accuracy or a molded product having a special shape, and is an especially important technique among the processing methods for bonded magnets.

  Magnetic powders used for bonded magnets and sintered magnets are roughly classified into ferrite magnetic powders and rare earth magnetic powders. Ferrite magnetic powders include barium ferrite and strontium ferrite. The rare earth magnetic powder includes Sm—Co, Nd—Fe—B, and Sm—Fe—N. Magnetic powder includes an anisotropic material having anisotropy and an isotropic material having no magnetic anisotropy. An anisotropic material needs to rotate and fix particles in the direction of easy magnetization in a mold at the time of manufacturing a magnet, but the obtained magnetic properties are relatively high. The isotropic material does not need to rotate and fix the particles in the mold, but has a relatively low magnetic property.

  On the other hand, in order to adjust the magnetic properties of the bonded magnet, a so-called hybrid magnet in which a plurality of the above magnetic powders are mixed has been proposed.

  For example, in Japanese Patent Application Laid-Open No. 55-99703 (Patent Document 1) and Japanese Patent Application Laid-Open No. 57-39102 (Patent Document 2), a hybrid magnet using ferrite magnetic powder and Sm—Co magnetic powder is disclosed. Japanese Patent Application Laid-Open No. 61-284906 (Patent Document 3) and Japanese Patent Application Laid-Open No. 62-257703 (Patent Document 4) propose a hybrid magnet using ferrite magnetic powder and Nd—Fe—B based magnetic powder. Has been. Further, in Japanese Patent Laid-Open No. 05-144621 (Patent Document 5), a hybrid magnet using Sm—Co based magnetic powder and Sm—Fe—N based magnetic powder is disclosed in Japanese Patent Laid-Open No. 05-152116 (Patent Document 6). Proposes a hybrid magnet using Nd—Fe—B based magnetic powder and Sm—Fe—N based magnetic powder.

  However, since the above-described hybrid magnet uses Sm—Co based magnetic powder or Nd—Fe—B based magnetic powder having a relatively large particle size, the magnetic powder can be applied only to a molded product having a relatively large size. There was a problem.

  On the other hand, a hybrid magnet of ferrite magnetic powder and R (rare earth) -Fe-N magnetic powder, which is a combination of magnetic powders having a small particle size, is disclosed in JP-A-2002-33205 (Patent Document 7). This is proposed in Japanese Unexamined Patent Application Publication No. 2004-266151 (Patent Document 8). This hybrid magnet has the advantage that the degree of freedom of molding is high and high magnetic properties can be obtained as compared with a hybrid magnet using Sm—Co based magnetic powder or Nd—Fe—B based magnetic powder.

JP-A-55-99703 JP-A-57-39102 Japanese Patent Laid-Open No. 61-284906 JP 62-257703 A JP 05-144621 A Japanese Patent Laid-Open No. 05-152116 JP 2002-33205 A JP 2004-266151 A

  However, although the hybrid magnet of R-Fe-N magnetic powder and ferrite magnetic powder described in Patent Documents 7 to 8 has a high degree of freedom in molding, it is formed with a thin thickness of, for example, 1 mm or less. In the production of products, there is a further improvement in the fluidity of the compound comprising a resin binder and magnetic powder. This is because, when a molded product having a small thickness is produced, it is necessary to feed the compound into a gate or a mold having a width equal to or smaller than the thickness of the molded product at the time of injection molding.

  Originally, forming a thin region of 1 mm or less is not easy even when a single magnetic material is used. This is because the frictional effect on the inner surface of the mold is prominent. Further, since the anisotropic direction is the thickness direction of the molded product, a magnetic brake is applied together with the friction effect. As a matter of course, molding while making anisotropy is very difficult compared to the case without it. Therefore, in the hybrid material of R-Fe-N magnetic powder and ferrite magnetic powder, there has been a situation in which development of resins and additives that dramatically improve fluidity has not been achieved, and thin molded products of 1 mm or less The formation of is in a very difficult situation.

  The particle size of the ferrite magnetic powder is as small as about 1/3 to 1/5 of the R—Fe—N magnetic powder. As small particles increase in the compound, the fluidity will naturally worsen. Therefore, in the bonded magnet containing the R—Fe—N magnetic powder and the ferrite magnetic powder, how to suppress the deterioration of the fluidity due to the ferrite magnetic powder becomes a problem.

  Accordingly, an object of the present invention is to provide a bonded magnet composition having good fluidity and a bonded magnet using the composition.

  In order to solve the above-mentioned problems, the present inventors have intensively studied and as a result, the present invention has been completed.

The present invention provides a bonded magnet composition comprising a rare earth-iron-nitrogen based magnetic powder having a Th ₂ Zn ₁₇ type crystal structure, a ferrite magnetic powder, and a resin binder. It is related with the composition for bonded magnets characterized by circularity coefficient being 0.6 or more.

  The plate ratio of the ferrite magnetic powder is preferably 1.5 or more.

  Furthermore, it is preferable to use a coprecipitate of rare earth metal ions and iron ions as a raw material for the rare earth-iron-nitrogen based magnetic powder.

Here, in determining the circularity coefficient in the rare earth-iron-nitrogen based magnetic powder, the definition formula used in Japanese Patent Application Laid-Open No. 2004-115921 filed earlier by the present applicant: circularity coefficient = (4πS / L ² ) Is used. Where S is the two-dimensional projection area of the particle, and L is the two-dimensional projection perimeter. If the particles are spherical, the circularity coefficient is 1 at the maximum. In the case of a square, the value is 0.785, and when the bump is formed on the surface and the peripheral length L becomes longer, the numerical value becomes smaller. For the measurement, a scanning electron microscope was used, and particle analysis Ver. 3 is used as image analysis software. An SEM image taken at 3000 times is binarized by image processing, and a circularity coefficient is obtained for each particle. The circularity coefficient defined in the present invention means an average value of circularity coefficients obtained by measuring about 1000 to 10000 particles.

  Next, the plate ratio of the ferrite magnetic powder will be described. Ferrite magnetic powder having a hexagonal crystal form generally has hexagonal faces on the c-plane of the crystal and has a particle thickness in the c-axis direction, in other words, hexagonal plate-like grains. is there. In the measurement of the ferrite magnetic powder, for example, in order to make the thickness side of the particles in the c-axis direction the viewing surface, the measurement is performed with the magnetic powder oriented and fixed, for example, using a resin or the like. The plate ratio is a value obtained by dividing the maximum diameter in the direction perpendicular to the easy magnetization direction by the thickness in the easy magnetization direction. The thickness in the easy magnetization direction has the same meaning as the thickness of the particles in the c-axis direction. For example, if the thickness is the same as the maximum diameter of the medium-high (intermediate) particles with the c-axis extended, the plate ratio is 1. A scanning electron microscope is used for the measurement. From the SEM image taken at a magnification of 5000 times, the maximum diameter and thickness are obtained for each particle, and this operation is performed for about 1000 to 10,000 particles. The plate ratio defined in the present invention is a value obtained by measuring the above number of particles and dividing the total maximum diameter by the total thickness.

  On the other hand, the present invention is a bonded magnet obtained by injection molding the bonded magnet composition, and the filling rate of both magnetic powders comprising the rare earth-iron-nitrogen based magnetic powder and the ferrite magnetic powder is: The present invention relates to a bonded magnet having a volume ratio of 50% or more.

  Moreover, it is preferable that the said bonded magnet has the thickness which is 1 mm or less at least in part.

  The present invention provides a bonded magnet composition and a bonded magnet having excellent magnetic properties and fluidity that have not been obtained in the past by appropriately adjusting the circularity coefficient of the rare earth-iron-nitrogen based magnetic powder. be able to.

Hereinafter, although an embodiment concerning the present invention is explained in full detail, it is an example for materializing the technical idea of the present invention, and the present invention is not limited to this embodiment and an example.
(Magnetic powder)
The rare earth-iron-nitrogen based magnetic powder (hereinafter abbreviated as R—Fe—N based magnetic powder) and ferrite magnetic powder used in the present invention are both anisotropic magnetic powders.

The composition formula of the R—Fe—N-based magnetic powder used in the present invention is R _x Fe _(100-xy) N _y (where R is at least one of lanthanoid elements including Y, and x is 3 ≦ x ≦ 30, y satisfies 5 ≦ y ≦ 15.), And the crystal form belongs to hexagonal crystal.

Here, R is defined as 3 atomic% or more and 30 atomic% or less, and if it is less than 3 atomic%, the unreacted portion (α-Fe phase) of the iron component is separated and the coercive force of the nitride is reduced, This is because when it exceeds 30 atomic%, the lanthanoid element containing Y is precipitated, the magnetic powder becomes unstable in the atmosphere, and the residual magnetization decreases. Nitrogen is defined as 5 atomic% or more and 15 atomic% or less, and if it is less than 5 atomic%, almost no coercive force can be expressed, and if it exceeds 15 atomic%, lanthanoid elements including Y, iron and alkali metals themselves This is because nitride is formed. The most preferred composition is a composition that can be represented by Sm ₂ Fe ₁₇ N ₃ . Although it is possible to substitute R and Fe in the composition formula with other rare earth elements, the substitution amount is about 20 atomic%. Moreover, the mixing of oxygen as an impurity is 2% by weight or less, preferably 1.4% by weight or less.

  The average particle size of the R—Fe—N magnetic powder is preferably 2.0 μm or more and 5.0 μm or less, and more preferably 2.5 μm or more and 4.0 μm or less. The reason why the average particle size is 5.0 μm or less is to produce an effective coercive force, and the reason why the particle size is 2.0 μm or more is to reduce the risk of ignition and the like. In order to obtain a target particle size, pulverization may be performed. The crusher includes a jaw crusher, a brown mill, an attritor, and a jet mill. In order to obtain an R—Fe—N magnetic powder having a circularity coefficient defined in the present invention, an attritor or jet Means such as a mill that destroy the particles themselves should be avoided.

  The most important aspect of the present invention is the particle shape of the R—Fe—N magnetic powder. This will deteriorate the fluidity of the compound by mixing ferrite magnetic powder having a smaller particle diameter than R-Fe-N magnetic powder, but use R-Fe-N magnetic powder with high circularity. This is because the deterioration can be suppressed. There is simply a bearing effect of the R—Fe—N magnetic powder as a background to obtain good fluidity in the combination of the R—Fe—N magnetic powder having high circularity and the ferrite particles. It is an image in which particles of relatively large and round R—Fe—N magnetic powder roll while rolling up the particles of terrible ferrite magnetic powder.

  In the present invention, the average value of the circularity coefficient is preferably 0.60 or more, and more preferably 0.65 or more. When the circularity coefficient is less than 0.60, the fluidity of the compound deteriorates. For example, when the width of the gate or mold used for injection molding is as thin as 1 mm or 2 mm, the moldability is excellent. A bonded magnet cannot be obtained. Moreover, when the fluidity | liquidity of a compound is bad, stress will be applied between particle | grains at the time of magnetic field shaping | molding, and the magnetic characteristic of the resultant bonded magnet will deteriorate.

  Examples of the method for producing the R—Fe—N magnetic powder used in the present invention include a metal dissolution solidification method, a reduction diffusion method, and a melt spinning method. Among these, the reduction diffusion method is a method suitable for synthesizing fine particles, and is therefore used as a suitable method in the present invention. In order to obtain an R—Fe—N-based magnetic powder having a circularity coefficient of 0.60 or more, for example, a substance that forms a cation and an insoluble salt described in JP-A-11-189811 It is possible to suitably apply a production method having a step of causing a precipitate to react in a solution, a step of firing the precipitate to obtain a metal oxide, and a step of heating the metal oxide in a reducing atmosphere. . By using a coprecipitate of rare earth metal ions and iron ions as a raw material, an R—Fe—N magnetic powder having a desired circularity coefficient can be obtained.

  Next, the ferrite magnetic powder used in the present invention is strontium ferrite, barium ferrite, or a mixture or solid solution thereof. For the purpose of improving performance, a part of alkaline earth metal is replaced with zinc, or iron It is also possible to partially replace some with cobalt. The average particle diameter of the ferrite is preferably 0.8 μm or more and 1.5 μm or less.

  Here, the shape of the ferrite particles used for the bonded magnet and the manufacturing method of the bonded magnet using the ferrite will be described. In order to produce an excellent bonded magnet, it is required that the shape of the ferrite particles be a flat hexagonal plate as much as possible (for example, Japanese Patent Publication No. 58). -27212). On the other hand, the shape of the ferrite particles is preferably the same hexagonal plate shape, which is a medium-high with the c-axis extended, or the plate-like ratio is as small as possible. -22744). In other words, both the flat hexagonal plate shape and the medium and high hexagonal plate shape are said to be suitable for the bonded magnet. At first glance, it seems contradictory, but with the current state of the art, there is an appropriate separation. That is, the flat hexagonal plate shape is mainly used when kneaded into rubber and further mechanically oriented by a roll (for example, JP-A-7-240309). On the other hand, a medium-high hexagonal plate shape is often kneaded into a thermoplastic resin and further used for injection molding in a magnetic field (for example, JP-A-2005-268729).

  Regarding the cost of ferrite particles, the flat hexagonal plate shape is synthesized by a relatively simple method, and rubber magnets are produced in large quantities. Compared to the medium and high hexagonal plate shape for injection molding. It is said that it is inexpensive. In addition, the medium and high hexagonal plate shape is complicated because the compounding components are complicated, and the post-treatment including the pulverization process is complicated.

  In the present invention, either ferrite can be used depending on the required magnetic properties, but the plate ratio is more preferably 1.5 or more, and even more preferably 1.9 or more. It is a flat hexagonal plate. In the flat hexagonal plate-like ferrite particles, the thickness of the particles (thickness in the c-axis direction of the crystal) is the direction of easy magnetization, so the ferrite particles are within the anisotropic bonded magnet and in the thickness direction of the bonded magnet. In addition, the thickness direction of the particles is arranged in an orderly manner so as to be folded. This results in an improvement in the surface magnetic flux of the bonded magnet.

In addition to excellent magnetic properties typified by surface magnetic flux, good fluidity is obtained when the R-Fe-N magnetic powder having the circularity coefficient defined in the present invention and the ferrite magnetic powder are mixed. A compound having This is a peculiar phenomenon in the present invention, contrary to the current state of the art in which a medium-high hexagonal plate shape for injection molding is generally used. Furthermore, the ability to use a flat hexagonal plate-like ferrite magnetic powder, which is relatively inexpensive, is preferable in terms of cost.
(Bonded magnet)
In the present invention, as magnetic characteristics, aims at maximum energy product (BHmax) is to provide a bonded magnet which is ^{20kJ / m 3 ~70kJ / m 3} . Therefore, a bonded magnet is produced by adjusting the blending amount of the R—Fe—N-based magnetic powder and the ferrite magnetic powder as appropriate so as to have the above magnetic characteristics.

  In order to obtain the bonded magnet of the present invention, the above-described R-Fe-N magnetic powder, ferrite magnetic powder, and resin binder, preferably a coupling agent, antioxidant, and lubricant are mixed. The coupling agent is added for the purpose of improving the wettability between the R-Fe-N magnetic powder and ferrite magnetic powder and the resin binder and the strength of the bonded magnet. The antioxidant is added for the purpose of preventing deterioration of the resin binder due to heat history during kneading and molding in the manufacturing process. The lubricant is added for the purpose of reducing the melt viscosity of the compound and improving the injection moldability.

  In the case of a thermoplastic resin, the resin binder used is 12-nylon, 6 nylon, 6, 6 nylon, 11 nylon, 6,12-nylon, 4,6-nylon, 6,10-nylon, nylon 6T, nylon MXD6, Polyamide resins such as aromatic nylon, 11-nylon, amorphous nylon and copolymer nylon, olefin resins such as polyethylene, high density polyethylene, low density polyethylene and polypropylene, ionomer resins such as ethylene ionomer resins, ethylene acrylic EEA resin such as ethyl acid copolymer, acrylonitrile / acrylic rubber / styrene copolymer resin, acrylonitrile / styrene copolymer resin, acrylonitrile / butadiene / styrene copolymer, acrylonitrile / acrylonitrile / chlorinated polyethylene / styrene copolymer, etc. Resins, ethylene-vinyl acetate copolymers, polyvinyl resins such as ethylene-vinyl alcohol copolymer resins, acetate fiber resins, polytetrafluoroethylene, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymers, tetrafluoroethylene-hexylo-propylene Copolymers, fluoropolymers such as tetrafluoroethylene / ethylene polymer, polyvinylidene fluoride and polyvinyl fluoride, acrylic resins such as polymethyl methacrylate and ethylene / ethyl acrylate resins, polyurethane resins, aromatic polyester resins, Polyacetal, polycarbonate, polysulfone, polybutylene terephthalate, polyethylene terephthalate, polyarylate, polyphenylene oxide, polyphenyl sulfide, polyo Engineering such as liquid crystalline resins such as cypendylene, polyether ketone, polyether sulfone, polyether imide, polyamide imide, polyimide, polyallyl ether nitrile, polybenzimidazole, polyaramid, polyester amide, wholly aromatic amide, semi-aromatic amide At least one or more of plastics, super engineering plastics and the like can be used.

  For thermoplastic elastomers, ester-based, special ester-based ethers, caprolactone-based, adipate-based, carbonate-based, lactone-based thermoplastic urethane elastomers, olefin-based thermoplastic elastomers, styrene-based thermoplastic elastomers, styrene-butadiene-based At least one or more of thermoplastic elastomers such as thermoplastic elastomers, polyamide-based thermoplastic elastomers, polyester-based thermoplastic elastomers, nitrile-based thermoplastic elastomers, hydrogenated SBS-based thermoplastic elastomers, and fluorine-based thermoplastic elastomers can be used. .

  Although it does not specifically limit as a coupling agent, antioxidant, and a lubrication agent, The well-known thing described in Unexamined-Japanese-Patent No. 2004-266151 can be used.

  Examples of the present invention will be described below, but the present invention is not limited thereto.

(Adjustment of Sm-Fe-N magnetic powder A)
[1. Precipitation reaction] 513.4 g of anhydrous samarium chloride SmCl ₃ and 2757.6 g of anhydrous iron chloride FeCl ₃ were weighed and simultaneously poured into 10 liters of ion-exchanged water, and completely dissolved while stirring in the reactor. And While continuing to stir the reactor, 5.1 kg of a 15 wt% sodium hydroxide solution is gently put into it. After confirming that the pH of the solution is 10 or more, when the stirring is stopped and the mixture is allowed to stand, the product precipitates at the bottom of the container.
[2. Filtration and washing] The precipitated product is put on a filter paper and sucked while supplying ion exchange water from above. This decantation is continued until the electrical conductivity of the filtrate falls below 50 μS / m. The precipitate cake obtained after washing and suction filtration is dried in an oven at 80 ° C.
[3. Atmospheric calcination] The dried cake is placed in an alumina crucible and baked for 5 hours while oxygen is passed through at 1000 ° C.
[4. Particle size adjustment] The fired product is loosened by hand and then pulverized with a hammer mill. The average particle diameter of this powder measured by a Fisher sub-sieve sizer (FSSS) was 1.2 μm.
[5. Hydrogen reduction] The pulverized powder is filled in a steel tray, placed in a tube furnace, and subjected to heat treatment at 700 ° C. for 10 hours while flowing 100% pure hydrogen at 20 liters / minute. The resulting black powder had an oxygen concentration of 7.0 wt%.
[6. Reduction diffusion reaction] 1000 g of the black powder obtained in the previous step and 350.7 g of granular Ca are mixed, put in a steel tray, and set in an argon gas atmosphere furnace. After evacuating the inside of the furnace, it is heated at 1050 ° C. for 0.5 hour while passing argon gas. The heating is then stopped and subsequently cooled to 450 ° C. in argon gas and thereafter kept constant at this temperature. Then, after evacuating the inside of the furnace again, nitrogen gas is introduced. After heating for 5 hours while passing nitrogen gas at a pressure higher than atmospheric pressure, the heating is stopped and the mixture is allowed to cool.
[7. Washing with water] The obtained reaction product is put into 5 liters of ion-exchanged water, whereby the reaction product immediately disintegrates and separation of the alloy powder and the Ca component starts. Stirring in water, standing still, and removal of the supernatant liquid are repeated 5 times, and finally, it is washed in 5 liters of a 2 wt% acetic acid aqueous solution to complete the separation of the Ca component. This is vacuum dried to obtain about 700 g of Sm ₂ Fe ₁₇ N ₃ alloy powder. Further, the above operation is repeated 10 times to obtain 7 kg of Sm—Fe—N magnetic powder.
[8. Characteristics Evaluation] The obtained powder has a good dispersibility and has a spherical shape even when observed with a scanning electron microscope. The average particle size of the powder was 2.5 μm as measured with a Fisher sub-sieve sizer (FSSS). The magnetic properties of the powder were Br1.3T and iHc 1080 kA / m. The concentration of oxygen contained in the powder was 0.2 wt%, and segregation of Sm and Fe could not be confirmed by cross-sectional observation with EPMA. Further, according to X-ray diffraction using Cu—Kα as a radiation source, nothing was observed besides the hexagonal crystal which is the main phase, and in particular α-Fe which is a pure iron component could not be found. As a result of performing two-dimensional image analysis on the SEM image, the circularity coefficient of this powder was 0.67. The obtained powder is designated as magnetic powder A.

(Adjustment of Sm—Fe—N magnetic powder B)
About 7 kg of Sm—Fe—N magnetic powder is prepared under the same conditions except that the temperature of hydrogen reduction is 750 ° C. and the reduction time is 5 hours in the preparation of the Sm—Fe—N magnetic powder A. The average particle size of the powder at this time was 2.4 μm as measured by a Fischer sub-sieve sizer (FSSS). The magnetic properties of the powder were Br1.33T and iHc950 kA / m. The concentration of oxygen contained in the powder was 0.2 wt%, and segregation of Sm and Fe could not be confirmed by cross-sectional observation with EPMA. Further, according to the X-ray diffraction using Cu—Kα as a radiation source, nothing was observed besides the hexagonal crystal which is the main phase, and in particular α-Fe which is a pure iron component could not be found. As a result of performing two-dimensional image analysis on the SEM image, the circularity coefficient of this powder was 0.60. The obtained powder is designated as magnetic powder B.

(Adjustment of Sm—Fe—N magnetic powder C)
Sm ₂ Fe ₁₇ alloy is produced by high-frequency melting 99.9% purity metal samarium and 99.9% purity metal iron and pouring them into a water-cooled copper mold. After the alloy lump is crushed to about 500 μm with a jaw crusher, heat treatment is performed at 1100 ° C. for 20 hours in an argon stream for the purpose of homogenizing the alloy composition. Further, this is finely pulverized to a mean particle size of 2.1 μm by a jet mill in a nitrogen stream, and then subjected to nitriding treatment at 450 ° C. for 15 hours in a nitrogen stream. The magnetic properties of the powder were Br1.39T and iHc750 kA / m. The concentration of oxygen contained in the powder was 0.2 wt%, and segregation of Sm and Fe could not be confirmed by cross-sectional observation with EPMA. Further, according to X-ray diffraction using Cu—Kα as a radiation source, nothing was observed besides the hexagonal crystal which is the main phase. As a result of performing two-dimensional image analysis on the SEM image, the circularity coefficient of this powder was 0.35, and its appearance was a terrible shape and was indefinite. The obtained powder is designated as magnetic powder C.

(Preparation of ferrite magnetic powder a)
Commercially available strontium ferrite is used. The average particle size of the powder was 1.23 μm as measured with a Fischer sub-sieve sizer (FSSS). The magnetic properties of the powder were Br0.40T and iHc282 kA / m. Further, the plate ratio obtained from the SEM image was 3.1. Let the obtained powder be the magnetic powder a.

(Preparation of ferrite magnetic powder b)
Commercially available strontium ferrite is used. The average particle size of the powder was 0.99 μm as measured by a Fisher sub-sieve sizer (FSSS). The magnetic properties of the powder were Br0.38T and iHc374kA / m. Further, the plate ratio obtained from the SEM image was 1.9. Let the obtained powder be the magnetic powder b.

(Preparation of ferrite magnetic powder c)
Commercially available strontium ferrite is used. The average particle size of the powder was 0.93 μm as measured with a Fisher sub-sieve sizer (FSSS). The magnetic properties of the powder were Br0.38T and iHc422kA / m. Further, the plate ratio obtained from the SEM image was 1.0. Let the obtained powder be the magnetic powder c.

  Table 1 shows the magnetic properties and particle shapes of the Sm—Fe—N-based magnetic powders A to C and the ferrite magnetic powders a to c obtained as described above.

<Example 1, Reference Example 1>
As a resin binder, 5.5 kg of Sm—Fe—N magnetic powder A, 3.7 kg of ferrite magnetic powder a, and 12 kg of nylon are mixed to obtain a composition for a bonded magnet. By this blending, the volume-based blending ratio of the Sm—Fe—N magnetic powder and the ferrite magnetic powder becomes 1: 1, and the filling rate of both magnetic powders in the bonded magnet can be 65 volume%.

  What knead | mixed the said composition for bonded magnets at 200 degreeC is cut | disconnected after cooling, and it is set as the compound for bonded magnets. This compound is injection molded with a bar flow mold. Two types of mold cavities are prepared: a width of 10 mm, a maximum length of 100 mm, and a height of 1 mm and 5 mm. In either case, the gate shape is a 1-point side gate of 1 mm × 0.5 mm. A bonded magnet manufactured using a mold cavity having a height of 1 mm is referred to as Example 1, and a bonded magnet manufactured using a mold cavity having a height of 5 mm is referred to as Reference Example 1.

  The injection molding conditions are as follows: cylinder temperature is 200 ° C-250 ° C, mold temperature is 90 ° C, orientation magnetic field is 720 kA / m applied in the thickness direction, injection pressure is 150 MPa, injection time is 5 seconds, and cooling time is 10 seconds. . Thereby, an anisotropic plate-like bonded magnet is obtained. The fluidity is evaluated by the length (= flow length) of the obtained bonded magnet.

  Further, the obtained plate-like bonded magnet is cut out at 10 mm from the end face on the gate side to produce a molded product of 10 mm × 10 mm × height (1 mm or 5 mm) and magnetized with a magnetic field of 4800 kA / m by a magnetizer. . This surface magnetic flux is measured with a gauss meter to evaluate the magnetic characteristics.

  The results of fluidity and magnetic properties are shown in Tables 2 and 3. Table 2 shows the results when using a mold cavity having a height of 1 mm, and Table 3 shows the results when using a mold cavity having a height of 5 mm.

<Examples 2-18, Comparative Examples 1-6>
A bonded magnet composition is obtained in the same manner as in Example 1 except that the combination of both magnetic powders and the filling rate of both magnetic powders in the bonded magnet are changed as shown in Table 2. The Sm—Fe—N magnetic powder and the ferrite magnetic powder are mixed at a mixing ratio of 1: 1 on a volume basis so that the desired filling rate is obtained. The mixing amount of 12 nylon is appropriately adjusted. Then, a bonded magnet is manufactured using a mold cavity having a height of 1 mm. The results of fluidity and magnetic properties are shown in Table 2. The results when the filling rate is 60% are shown in FIG.

<Reference Examples 2 to 16>
A bonded magnet composition is obtained in the same manner as in Reference Example 1 except that the combination of both magnetic powders and the filling rate of both magnetic powders in the bonded magnet are changed as shown in Table 3. The Sm—Fe—N magnetic powder and the ferrite magnetic powder are mixed at a mixing ratio of 1: 1 on a volume basis so that the desired filling rate is obtained. The mixing amount of 12 nylon is appropriately adjusted. Then, a bonded magnet is manufactured using a mold cavity having a height of 5 mm. The results of fluidity and magnetic properties are shown in Table 3.

  According to the reference example, when the thickness of the molded product is 5 mm, the flow length is as good as 100 mm in any combination with the Sm—Fe—N based magnetic powder having a high circularity coefficient. . In addition, the fluidity when using a combination of Sm-Fe-N magnetic powders having a low circularity coefficient is slightly lower than that having a high circularity coefficient, but the filling rate of both magnetic powders is low. Even if it is as high as 60% by volume, it is about 20% reduction. As for the surface magnetic flux, if the filling rate is the same, the surface magnetic flux is almost the same regardless of the circularity coefficient of the Sm—Fe—N magnetic powder. From this, it can be seen that when the thickness of the molded product is 5 mm or more, almost all of the magnetic powder is oriented 100% regardless of the type of the Sm—Fe—N magnetic powder.

  On the other hand, in the example, when the thickness of the molded product is 1 mm, even if the Sm-Fe-N magnetic powder having a high circularity coefficient is used, the fluidity decreases as the filling rate increases. The decrease in the circularity coefficient is remarkable. Further, in the surface magnetic flux, the combination of the Sm—Fe—N magnetic powder having a high circularity coefficient is excellent, and the difference is particularly remarkable when the filling rate is 50% by volume or more. From this, it can be seen that when the thickness of the molded product is 1 mm or less, the shape of the Sm-Fe-N magnetic powder greatly affects the fluidity and the orientation of the magnetic powder.

  Further, according to the reference example, when the Sm—Fe—N based magnetic powder having a high circularity coefficient is used, there is no significant difference in fluidity even if the type of ferrite is changed.

  In contrast, in the examples, when Sm—Fe—N magnetic powder having a high circularity coefficient is used, higher fluidity is obtained by combining so-called flat ferrite magnetic powder having a higher plate ratio. can get. This effect becomes more prominent as the filling rate increases.

  The present invention can be used as a permanent magnet material for a rotor and a small sensor of a small motor.

It is a figure which shows the difference in the flow length and surface magnetic flux by the combination of magnetic powder, when a molded article is produced using the mold cavity whose filling rate of both magnetic powder is 60 volume% and 1 mm in height.

Claims (5)

In a composition for a bonded magnet comprising a rare earth-iron-nitrogen based magnetic powder having a Th ₂ Zn ₁₇ type crystal structure, a ferrite magnetic powder, and a resin binder,
The composition for bonded magnets, wherein the rare earth-iron-nitrogen based magnetic powder has a circularity coefficient of 0.6 or more.   2. The bond magnet composition according to claim 1, wherein the ferrite magnetic powder has a plate ratio of 1.5 or more.   3. The bonded magnet composition according to claim 1, wherein a coprecipitate of rare earth metal ions and iron ions is used as a raw material for the rare earth-iron-nitrogen based magnetic powder. A bonded magnet obtained by injection molding the bonded magnet composition according to claim 1,
A bonded magnet characterized in that a filling ratio of both magnetic powders comprising the rare earth-iron-nitrogen based magnetic powder and the ferrite magnetic powder is 50% or more by volume ratio.   The bonded magnet according to claim 4, wherein at least a part thereof has a thickness of 1 mm or less.

Images