JPS6241759A - Manufacture of ferrite base permanent magnet - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for efficiently manufacturing a ferrite permanent magnet having excellent magnetic properties.

(Prior Art) In recent years, a large amount of ferrite resin magnets have been manufactured by mixing ferrite magnetic powder with a resin such as polyamide or polyolefin and injection molding the mixture while orienting the magnetic powder in a magnetic field.

Compared to the press molding method, the injection molding method makes it easier to orient the magnetic powder in the direction of the magnetic field, and it is also possible to produce magnets with high dimensional accuracy even with complex shapes. It has the advantage of being able to be mass-produced efficiently.

(Problem to be solved by the invention) However, the magnetic properties of ferrite resin magnets obtained by injection molding depend on the content of ferrite magnetic powder in the magnet, and in general, the higher the content, the more magnetic. Although the properties tend to improve, if the content is too high (too much), the injection moldability will decrease, and the magnetic powder will also become difficult to orient, resulting in a decrease in magnetic properties, so there is a limit to how well the magnetic properties can be improved. It has the disadvantage of inferior magnetic properties compared to conventional sintered magnets made by molding.

(Means for solving the problem) As a result of intensive research in view of the above situation, the present inventors have found that
By demagnetizing a ferrite resin magnet, sintering it, and then magnetizing it, a ferrite permanent magnet with much better magnetic properties than conventional ferrite resin magnets can be created, even if it has a relatively complex shape. It was discovered that the dimensional accuracy is good and mass production can be carried out efficiently, leading to the completion of the present invention.

That is, in the present invention, a magnetic material containing a ferritic fn powder and an organic binder is injection molded while applying a magnetic field, then demagnetized, the binder removed, and then sintered. The present invention provides a method for manufacturing a ferrite permanent magnet, which is characterized by magnetization.

As the ferrite magnetic powder used in the present invention, any known ferrite magnetic powder can be used, and is not particularly limited. For example, it has the general formula MO'6FezOs (where M is Ba, Sr, or Ca.

Examples include ferrite-based magnetic powders represented by (representing Pb).

Among them, those having an average particle diameter of 0.05 to 5 μm are preferable,
Particularly preferred is a thickness of 0.2 to 2 μm. Moreover, it is preferable that M in the general formula J- is Ba or SrO in terms of excellent magnetic properties.

Examples of the organic binder used in the present invention include thermoplastic resins and thermosetting resins that are known as binders for resin magnets, and are not particularly limited, such as polystyrene, styrene-acrylic nitrile copolymer, styrene-acrylic Styrenic resins such as di-butadiene copolymer; polyvinyl chloride, polyvinyl alcohol, polyvinyl acetate, vinyl chloride-vinyl acetate copolymer, ethylene-
Vinyl resins such as vinyl acetate copolymer; vinylidene resins such as vinylidene chloride; polymethyl (meth)acrylate, polyethyl methacrylate, poly-n-butyl (meth)acrylate, methacrylate-acrylate copolymer, ethylene-methyl acrylate Polyacrylic acid resins such as copolymers and ethylene-ethyl acrylate copolymers; Olefin resins such as polyethylene and polypropylene; Unsaturated polyester resins, furanol resins,
There are amino resins 1, epoxy resins, diallyl phthalate resins, thermosetting acrylic resins, urethane resins, etc., and each can be used alone or in combination of two or more.

The mixture consisting of the ferrite magnetic powder and the organic binder used in the present invention has properties such as dispersibility, lubricity, flexibility, mold releasability, adjustment of melt viscosity, pore shape, etc. without departing from the purpose of the present invention. It can contain various additives that have the following characteristic effects.

Examples of such additives include waxes such as paraffin wax, microcrystalline wax, liquid paraffin, polyethylene wax, polypropylene wax, and low molecular weight polystyrene; stearic acid, lauric acid,
Fatty acids such as myristic acid, hydroxystearic acid, and hydrogenated oils; partial esters of fatty acid amides, fatty acid ketones, fatty alcohols, and polyhydric alcohols; fats and oils such as vegetable oils and light oils; glycerin, ethylene glycol, isopropyl alcohol, cellosolve acetate, and park Solvents such as chloroethylene; phthalate esters, adipate esters, higher fats fd! Plasticizers such as esters, phosphoric acid esters, and polyester plasticizers; dimethylpolysiloxane, etc., may be used singly or in combination of two or more.

The proportion of one or more of these additives used is generally 0 to 300 parts by weight, preferably 2 to 100 parts by weight, per 1 part of 100fi of the organic binder.

The magnetic material used in the present invention is obtained by mixing the above-described ferrite-based magnetic material, an organic binder, and optionally added additives. As the mixing method, any known method can be applied, and there is no particular limitation, but among them, mixing can be performed using a heating vacuum extruder, vacuum mixing agitator, kneader, roll, high-speed mixer, or a -shaft or multi-shaft kneader. It is preferable to do so.

The content of ferrite-based magnetic powder in the magnetic material is usually in the range of 45 to 70% by volume, and the moldability of the magnetic material and the magnetic properties of the resulting magnet are excellent, and there is no temporary deformation, blistering, or swelling during binder removal. The content is preferably 50 to 65% by volume since insufficient shrinkage during sintering can be prevented and a magnet with particularly excellent dimensional accuracy and magnetic properties can be obtained.

The magnetic material obtained in this way is heated above its softening point to at least 1000 oersted (Oe) or more.
The injection molding is performed using an injection molding machine, preferably an in-line screw set injection molding machine, while applying a DC magnetic field of preferably 4,000 to 20,000 oersteds to produce a molded product with high dimensional accuracy and uniform composition, and then molded in or outside the mold. Demagnetization is performed by applying a DC reversal magnetic field and a DC pulse attenuating repetitive magnetic field.

The presence or absence of demagnetization is an important point in the first step of demagnetizing the binder.If there is residual magnetism in the molded product, when the temperature of the mixture reaches the softening point or higher in the first step of removing the binder, magnetic force will be generated between the oriented magnetic powder particles. Repulsion occurs, causing deformation, cracking, cracking, etc. of the molded product, making it impossible to obtain a satisfactory binder-free product or fired crystal.

In order to prevent this phenomenon, the residual magnetic flux density Br of the molded product must be
100 Gauss or less, preferably 10
Must be less than Gauss.

The molded article demagnetized as described above is then sintered after removing the binder. Binder removal is performed at a temperature increase rate appropriate for the thickness of the molded article and the organic binder used. Generally, this is carried out by raising the temperature from room temperature to a temperature of 1 to 600°C (300 to 600'C). During this time, it is also possible to change the temperature increase rate in multiple stages depending on the degree of thermal decomposition of the organic matter.

Sintering is usually done by a known and commonly used method suitable for each magnetic powder.
0'' is achieved by holding in a sintering furnace at 0-1300°C for 0.5-3 hours.

The sintered magnet is then magnetized to obtain the permanent magnet of the present invention. Normally, magnetization is performed by applying a magnet with a coercive force greater than or equal to the coercive force of the magnet in any magnetization direction according to the magnetic properties of each obtained magnet. This is done by applying a magnetic field.

(Effects of the Invention) According to the manufacturing method of the present invention, since the magnetic material is formed into a desired shape by injection molding while applying a magnetic field, it is easy to blend the magnetic powder, and moreover, it is possible to form a magnetic material into a desired shape by injection molding while applying a magnetic field. It can be mass-produced with high dimensional accuracy even when using magnets, and is then magnetized after demagnetization, debinding, and sintering, making it easy to obtain ferrite permanent magnets with significantly improved magnetic properties compared to conventional ferrite resin magnets. .

(Example) The present invention will be specifically described below with reference to Examples and Comparative Examples.

Example 1 Strontium ferrite powder 8 with an average particle size of 0.5 μm
8% by weight, 7.5% by weight of n-butyl methacrylate, 2% by weight of polystyrene, 3% by weight of dioctyl phthalate, and 1.2% by weight of calcium stearate were uniformly heated and kneaded in a pressurized double-arm kneader, and then coarsely kneaded. This was ground to obtain a uniform magnetic material for molding containing 61.5% by volume of strontium ferrite powder.

Using an injection molding machine with a set of inline screws,
Molding temperature 160 in a unidirectional magnetic field of 000 oersted
℃, injection pressure 600-8001ur/cd, mold temperature 4
It was molded at 0°C to obtain a cylindrical molded body with a diameter of 25+n and a height of 10 m.

After demagnetizing this cylindrical compact using a DC pulse-attenuating repetitive magnetic field (residual magnetic flux density 2 Gauss), the temperature was raised from room temperature to 80°C at a rate of 40°C per hour, and then from 80°C to 500°C at a rate of 5°C per hour. After increasing the temperature to remove organic components,
Sintered at 1150℃, then 60℃ in the vertical direction of the cylinder.
A strontium ferrite permanent magnet with good appearance and magnetic anisotropy was obtained by applying a magnetic field of 0.00 oersted to obtain a magnetically anisotropic strontium ferrite permanent magnet.

The magnetic properties of the obtained magnet are as follows: residual magnetic flux density Br=3900
Gauss, coercive force Hc = 2500 Oersteds, maximum energy product (BH) wax -3.4 mega Gauss Oersteds (MG Oe), which were excellent.

Example 2 Strontium ferrite powder 9 with an average particle size of 1°0 μm
0% by weight, acrylic copolymer (consisting of a weight ratio of n-butyl methacrylate/methyl methacrylate/styrene/butyl acrylate = 40/30/20/10, weight average molecular weight 20000) 5.5% by weight, ethylene-ethyl acrylate (Contains ethyl acrylate: 123% by weight)
, weight average molecular weight M60000) 2.0% by weight, dioctyl adipate 1.5% by weight, stearic acid 1.0% by weight
The mixture was heated and kneaded using a twin-screw extruder to form pellets into a uniform moldable magnetic material containing 64.5% by volume of strontium ferrite powder. This is molded using an injection molding machine with a set of inline screws in a unidirectional magnetic field of 10,000 oersted at a molding temperature of 170°C and an injection pressure of 800 to 100°C.
A cylindrical molded body having a diameter of 25 m and a height of 101 m was obtained by molding under the conditions of +r/-1 mold temperature change of 35°C.

After demagnetizing this cylindrical compact using a DC pulse-attenuating repetitive magnetic field (residual magnetic flux density of 5 Gauss), the temperature was raised at a rate of 50°C per hour from room temperature to 80°C, and then at a rate of 12°C per hour from 80°C to 400°C. After heating to remove organic components,
Sintered at 00℃, then 6000℃ in the vertical direction of the cylinder.
A strontium ferrite permanent magnet with good external appearance and magnetic anisotropy was obtained by applying an Oersted magnetic field and magnetizing it.

The magnetic properties of the obtained magnet were as follows: residual magnetic flux density Br-3800
Gauss, coercive force 1 (c = 2700 oersteds, maximum energy product (BH) max = 3.3 megagauss oersteds, which were excellent.

Example 3 90% by weight of barium ferrite powder with an average particle size of 1.4 μm, 4.0% by weight of polyethylene, 4% by weight of paraffin wax
．． 0% by weight of dibutyl phthalate, 1.0% by weight of dibutyl phthalate, and 1.0% by weight of stearic acid amide were uniformly heated and kneaded in a pressurized double-arm kneader, and then coarsely ground to obtain a homogeneous product containing 60.5% by volume of barium ferrite powder. This is a magnetic material for molding. This is made using an injection molding machine with a set of inline screws.
Molding temperature 140 in a unidirectional magnetic field of 000 oersted
℃, injection pressure 600-800kg/-1 mold temperature 30℃
A cylindrical molded body having a diameter of 25 mm and a height of 100 mm was obtained by molding under the following conditions.

After demagnetizing this cylindrical molded body in a mold using a DC pulse-attenuated repetitive magnetic field (residual magnetic flux density: 15 Gauss), the temperature was raised from room temperature to 500°C at a rate of 8°C per hour to remove residual components. Sintered at 1200°C, then magnetized by applying a magnetic field of 6000 oersted in the vertical direction of the cylinder,
A barium ferrite permanent magnet with good appearance and magnetic anisotropy was obtained.

The magnetic properties of the obtained magnet are as follows: residual magnetic flux density Br=3700
Gauss, coercive force tlc = 2000 oersted, maximum energy product (Bll) max = 3.0 megagauss
It was as good as Ørsted.

Example 4 Strontium ferrite 85% by weight with an average particle size of 0.8 μm, unsaturated polyester (propylene glycol/isophthalic acid/fumaric acid-1,0/0.5/0.5
A resin prepared by dehydration and condensation using a conventional method with a molar ratio of .2% by weight was uniformly heated and kneaded in a pressurized double-arm kneader and then coarsely ground to obtain a uniform magnetic material for molding containing 58.0% by volume of strontium ferrite powder. This was molded using an injection molding machine with a set of inline screws in a unidirectional magnetic field of 100,000 e at a molding temperature of 95°C and an injection pressure of 800 to 1,000.
kg/cffl and a mold temperature of 25°C to obtain a cylindrical molded body with a diameter of 20 m and a height of 8 m.

This cylindrical molded body was demagnetized by a DC pulse-attenuated repetitive magnetic field (residual magnetic flux density 30 Gauss), and then heated from room temperature to 500°C.
The temperature was raised at a rate of 10°C per hour to remove organic components, and then sintered at 1200°C.
A strontium ferrite permanent magnet with good appearance and magnetic anisotropy was obtained by applying a magnetic field of 0.00 oersted to obtain a magnetically anisotropic strontium ferrite permanent magnet.

The magnetic properties of the obtained magnet are as follows: residual magnetic flux density Br=3900
Gauss, coercive force Hc = 3000 Oersteds, and maximum energy product (BH) max = 3.5 mega Gauss Oersteds.

Comparative Example 1 Strontium ferrite powder 8 with an average particle size of 1.0 μm
8mt%, 11.5% by weight of 6-nylon, and 0.5% by weight of calcium stearate were heated and kneaded using a single-screw extruder, and then shaped into a pellet shape, for uniform molding containing 61.5% by volume of strontium ferrite powder. Made of magnetic material. This was molded using an injection molding machine with a set of inline screws in a unidirectional magnetic field of 10,000 oersted at a molding temperature of 2.
Molding was carried out under the conditions of 90°C, injection pressure of 800 to 1000 kg/4, and mold temperature of 100°C to obtain a cylindrical strontium ferrite permanent resin magnet with a diameter of 20 u and a height of 8 cranes.

The magnetic properties of the obtained magnet are as follows: residual magnetic flux density Br=2750
Gauss, coercive force Hc = 2300 Oersteds, maximum energy product (BH) max -1.8 megagauss Oersteds, and the magnetic properties were lower than that of the permanent magnet of the present invention.

Comparative Example 2 88% by weight of barium ferrite powder with an average particle size of 1.2 μm, 11.5% by weight of 6-nylon, and 0.5% by weight of calcium stearate were heated and kneaded in a pressurized double-arm Nigu, and then coarsely pulverized to form barium ferrite powder. A uniform magnetic material for molding containing 60.5% by volume of ferrite powder was prepared. This was molded using an in-line scrier injection molding machine in a unidirectional magnetic field of 10,000 oersted (Oe) at a molding temperature of 290°C and an injection pressure of 800 to 1,000 kg/-2 at a mold temperature of 100°C.
A cylindrical barium ferrite permanent resin magnet having a diameter of 25 mm and a height of 1 ion was obtained by molding under the following conditions.

The magnetic properties of the obtained magnet were as follows: residual magnetic flux density Br-2100
Gauss, coercive force Hc = 1450 Oersteds, maximum energy product CBH) max = 1.0 megagauss Oersteds, and the magnetic properties were lower than that of the permanent magnet of the present invention.

Claims (1)

[Claims] A magnetic material containing a ferrite magnetic powder and an organic binder is injection molded while applying a magnetic field, then demagnetized, the binder is removed, and then sintered,
A method for manufacturing a ferrite permanent magnet, which comprises then magnetizing it.