JPS5923086B2 - Manufacturing method of anisotropic resin magnet - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a manufacturing method for preventing deterioration of magnetism during molding of anisotropic resin magnets mass-produced by injection molding.

The present inventors have developed magnet powders with large magnetic anisotropy constants such as barium ferrite magnets, strontium ferrite magnets, and rare earth cobalt magnets, ethylene vinyl acetate copolymers, ethylene-ethyl acrylate copolymers, and α-olefin-unsaturated monomers. Excellent permanent magnets are produced by injection molding a mixture of ethylene copolymer resins such as , dicarboxylic acid copolymer metal crosslinked resin, and saponified ethylene vinyl acetate copolymer resin by applying a magnetic field while heating them. They found that it could be obtained and filed patent applications as JP-A-49-120196, JP-A-50-139995, and JP-A-51-21199.

However, when mass-producing the above-mentioned anisotropic resin magnets, the number of injection moldings is limited, especially when the molded product is small compared to the injection capacity of the molding machine, or when the molding temperature is set to a high temperature of around 3000°C to improve fluidity. It has been found that as the amount increases, magnets with lower magnetic properties are produced.

Subsequent investigation revealed that this was because the mixture of resin and magnet powder remained in the injection molding machine in a molten state at high temperature for a long time. Generally, the temperature inside the injection molding machine is 200-300℃ to melt the resin and obtain high magnetic properties.
The temperature is maintained at 00°C.

In addition, since one cycle time of injection molding is about 1 minute, for example, when molding 100 resin magnets in succession,
A part of the raw material of the resin magnet that is finally molded is at least 10
It was confirmed that the resin was exposed to high temperatures for 0 minutes and the resin deteriorated at high temperatures, resulting in a decrease in the magnetic properties of the molded product. Therefore, the present inventors conducted various studies to prevent the deterioration of magnetic properties due to high-temperature deterioration of the resin in anisotropic resin magnets.As a result, by adding an appropriate amount of the antioxidant shown below, the above problem can be significantly alleviated. I found something that could be improved.

That is, the present invention provides a method for manufacturing an anisotropic resin magnet by injection molding a molten mixture of a ferromagnetic powder with a large specific number of magnetic anisotropy and an ethylene copolymer resin while applying a magnetic field. ) 2.6-di-tert-butyl-4-methylphenol(0) 2.1-methylenebis(4-methyl-
6-tert-butylphenol) (c) 4.4'-thiobis(3-methyl-6-tert-butylphenol) (d)
4.4! -Butylidenebis(3-methyl-6-tert-butylphenol) (e) 1.3.5-trimethyl-2.
4.6-tris(3.5-di-tert-butyl-4-hydroxybenzyl)benzene(he)tetra-wound [3-(3.
5-di-tert-butyl-4-hydroxyphenyl)propionyloxymethyl]methane(t)tetra-scratch[methylene-(3.5-di-tert-butyl-4-hydroxyhydrosinmenite)]methane 1) dilaurylthiodipro The total amount of one or more antioxidants selected from pionate(ri), tris(nonylphenyno(c)phosphite) is 0.
．． A method characterized by adding 02 to 1.0% by weight,
Even in the mass production of anisotropic resin magnets, resin magnets having stable magnetic properties with less high-temperature deterioration of the resin raw material can be obtained.

The required amount of the antioxidant to be added is 0.02% by weight or more, and if it is less than this, high temperature deterioration of the resin cannot be improved.

Further, if added in a large amount, it will precipitate on the surface of the molded product and have an adverse effect on the magnetic properties and appearance, so it is preferably 1.0% by weight or less. Next, the features of the method of the present invention will be explained using examples. Example 89% by weight of barium ferrite magnet powder and 11% by weight of Na crosslinked resin of ethylene-methacrylic acid copolymer were mixed, and tetra-scratch [methylene-(3.5-di-tarsiallybutyl)] was added as an antioxidant. -4-hydroxyhydrosinmenite)]methane, 4-4
'-Thiobis(3-methyl-6-tert-butylphenol and dilaurylthiodipropionate were added in weight percentages of 0.1%, 0.04%, and 0.8%, respectively).
A large number of anisotropic resin magnets having an outer diameter of 3,311 mm, an inner diameter of 28 nm, and a thickness of 2,511 mm were continuously molded using different types of magnet raw materials while applying a magnetic field using an injection molding machine.

For comparison, an anisotropic resin magnet to which no antioxidant was added and an anisotropic resin magnet to which 0.3% by weight of the conventionally used oxidizing agent, dodecyl mercaptan, was added were also continuously molded. In order to investigate the deterioration of magnetic properties of these anisotropic resin magnets during continuous molding,
Those in the early, middle, and late stages of molding were randomly selected and their magnetic properties were investigated. Among the results, BHMax was organized by the number of molding shots (elapsed time in the injection molding machine), and the results were as shown in FIG. Anisotropic resin magnets without antioxidants and conventionally used anisotropic resin magnets with antioxidants added are molded more easily as the number of molding shots increases, even if anisotropic resin magnets with the same composition are used. The later the time, the lower the magnetic properties, and especially when the number of molding shots exceeds 40, there is a tendency for the magnetic properties to deteriorate rapidly.

On the other hand, in the anisotropic resin magnet of the present invention in which an appropriate amount of antioxidant was added, the number of molding shots was 10.
Even if the anisotropic resin magnet is molded after more than 0 cycles, its magnetic properties are almost the same as those of the initial molding, indicating that stable magnetic properties can be obtained even during continuous molding. In addition, several kinds of antioxidants listed in the claims were also investigated, and similar effects were obtained. As described above, the present invention is a manufacturing method that can solve all the problems associated with mass production of anisotropic resin magnets manufactured by injection molding, and has great industrial value.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the relationship between the rate of decrease in magnetism and the number of molding shots.

Claims (1)

[Claims] 1. In manufacturing an anisotropic resin magnet by injection molding a molten mixture of ferromagnetic powder with a large magnetic anisotropy constant and ethylene copolymer resin while applying a magnetic field. (a) 2,6-di-tert-butyl-4-methylphenol (b) 2,2'-methylenebis(4-methyl-
6-tert-butylphenol) (c) 4.4'-thiobis(3-methyl-6-tert-butylphenol) (d) 4.
4'-Butylidenebis(3-methyl-6-tert-butylphenol)(e)1.3.5-trimethyl-2.4.6
-Tris(3.5-di-tert-butyl-4-hydroxybenzyl)benzene(h)tetrakis[3-(3.5-di-tert-butyl-4-hydroxyphenyl)propionyloxymethyl]methane(t) Tetrakis [methylene-(
One or two antioxidants selected from 3.5-di-tert-butyl-4-hydroxyhydrosinmenite) methane(thi)dilaurylthiodipropionate(li)tris(nonylphenyl)phosphite The total amount of the above is 0.02
A method for producing an anisotropic resin magnet, characterized by adding ~1.0% by weight.