JPS5853492B2 - Rubber magnet manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a rubber magnet, and more particularly to a method for manufacturing a rubber magnet that has a high residual magnetic flux density and in which magnetic powder is sufficiently uniformly filled in the rubber material.

In recent years, rubber magnets have been widely used for gaskets, belts, packing materials, etc. due to their flexibility and machinability, and they have also been used as magnets, such as the rods of electromagnetic plungers, which generate loud noises when activated. It is used in various electronic and other devices, such as in easy-to-use parts or on the inner peripheral surface of the turntable of a player.

Conventional rubber magnets of this type are formed by masticating hard permanent magnet powder into natural rubber, filling the mixture, and sulfurizing the rubber to υ0.

In this case, the powder of the above-mentioned permanent magnet, that is, the ferromagnetic particles, is, for example, barium ferrite, manganese,
Bismuth or fine iron powder is available, and barium ferrite is mainly used.

By the way, depending on the purpose of use of such comb magnets, for example, in recording and reproducing signals, the residual magnetic flux density B may be higher than that of rubber magnets up to C.
It is required that r is large and that the individual ferromagnetic particles do not aggregate and are uniformly dispersed in the rubber material.

Also. For example, for magnetization or signal recording, the coercive force Hc of magnetic particles is preferably on the order of several 100 to 1000 oersteds.

Therefore, when considering such conditions, it can be said that ferroalloy powder is the most suitable magnetic material for the ferromagnetic particles.

However, alloy powders such as Fe-Co-Ni, Fe-Co, or Fe-Ni are easily oxidized not only in the air but also during η0 heat mixing with binder rubber, and furthermore, due to oxidation, the alloy powder It has been extremely difficult to handle it because it loses its characteristic of high residual magnetic flux density.

That is, as an example, it is similar to the manufacturing method of ordinary rubber magnets.

NR rubber ・・・・・・・・・ 100 parts Fe−
Co alloy powder ・・・・・・・・・ 300 parts Dragon
・・・・・・・・・ 2.5 parts stearic acid ・・・
...... A rubber magnet obtained by kneading in a roll mill with a material composition of 3.0 parts and heat forming under η pressure at 150°C for 30 minutes contains almost no alloy powder filled therein. It was oxidized and decomposed to such an extent that it no longer exhibited magnetism, and the rubber itself deteriorated significantly, becoming brittle and losing its rubber-like properties.

This is an essential drawback that cannot be avoided as long as the above-mentioned alloy powder is used and the rubber manufacturing method is conventional or a binder material is used.

Therefore, the present invention focuses on the excellent properties of alloy powder as described above, and in view of the drawbacks that occur when using conventional rubber manufacturing methods and binder materials, the present invention aims to prevent the reactivity of alloy powder and create an alloy. The purpose of this invention is to enable the rubber magnet to sufficiently reflect the high residual magnetic flux density that powder inherently has.

In the present invention, thermosetting urethane resin is selected as the binder, and 770
It is mixed with alloy powder having a high magnetic flux density without heating, and then molded and hardened at a relatively low temperature.

To obtain the rubber magnet according to the invention, the alloy powder is mixed with a surfactant in an organic solvent such as methyl ethyl ketone in a ball mill.

In this case, the amount of solvent, amount of dispersant, or mixing time varies depending on the size of the alloy powder particles and the sintering state in the magnetic powder manufacturing process, but approximately the amount of solvent is 1 to 2 times the amount of magnetic powder, and the amount of dispersant is 1%. The mixing time may be about 2 days and nights.

Next, after filtering this suspension, it is transferred to a kneader such as a kneader, and a liquid thermosetting resin mainly composed of polyurethane and a curing agent, for example, one part A of a two-component urethane resin, that is, a polyol Add 711]L and mix for about 1 hour while cooling under reduced pressure.

This step removes the remaining organic solvent and at the same time ensures good mixing with the binder.

Further, the viscosity of the polyol is relatively low. Furthermore, since water cooling was performed, no decomposition of the alloy powder or binder as described above was observed.

Then, in the alloy powder paste obtained in this way, 2
The other B liquid, that is, isocyanate, is added to the liquid type urethane resin, and the mixture is further stirred for 30 minutes to obtain an alloy powder paste for molding.

Through this step, the magnetic particles are completely dispersed and aggregates of several microns or larger are removed.

Examples will be described below.

Example 1 Alloy powder (Fe-Co) 0.3 x 0.05 micron (Hc980 Oersted binder (curing polyurethane, made by Bayer) 100 parts (Liquid A Desmofene 170 ([75 Section B liquid Desmodur L) 25%...300 parts Dispersant (rettin)...3 parts The alloy powder paste produced as described above with the above composition was pressed into a sheet with a thickness of 2 mrtt by 8 mouths, and heated at 770°C and 60°C. Cure for 48 hours to produce a rubber magnet.

The rubber magnet obtained in this way has a high Br of 2400 Gauss (1800 Gauss in an example of a conventional product), and has a ratio of rubber to magnetic powder of 1:3 (1:8 in an example of a conventional product).
), it has high mechanical strength and can withstand sharp bending of the sheet.

Example 2 A rubber magnet obtained by curing for 5 hours using the same composition, η0 pressure, and heating conditions as in Example 1 was uniaxially stretched to 1.5 times, then pressurized, and further cured for 2 days and nights to produce a rubber magnet.

The rubber magnet thus obtained has Br in the stretching direction.
= 2800 Gauss.

Example 3 Alloy powder (Fe-Co granules) 800
Part (1 micron Hc400 Oersted binder (2-component polyurethane)...100 parts Ai
Deismofen 1100 (manufactured by Bayer) (B liquid Urethane prepolymer (Coronate 4046 manufactured by Nippon Polytale 50 Co., Ltd.) 50% Dispersant (Retsutin) 8 parts Comb magnet as a sheet in the same manner as in Example 1 with the above composition was generated.

The rubber magnet thus obtained had an extremely high residual magnetic flux density of Br=4000 Gauss.

In addition, although the flexibility was inferior to that of Example 1, it was more rubbery and stronger than conventional products.

Example 4 Alloy powder (Fe-Co-Ni acicular)...400
Part 0, 5
0 parts A liquid Desmofene 1700-II-50% (B liquid Desmodur L 25% Epicor) 828 (manufactured by Shell) 25% Dispersant (Retstin) 4 parts Same as Example 1 with the above composition A rubber magnet was produced in the form of a sheet.

The rubber magnet thus obtained had a Br-3000 Gauss, and had mechanical strength and flexibility comparable to conventional products, but a significantly high breaking strength.

As is clear from the above, in the present invention, by using a thermosetting urethane resin as a binder, the high residual magnetic flux density characteristic of alloy powders such as alloy iron powders, which were conventionally extremely difficult to handle, can be sufficiently achieved in rubber magnets. Moreover, the rubber magnet according to the present invention is evenly filled with magnetic powder and has high mechanical strength.

Claims (1)

[Claims] 1 The alloy magnetic powder is kneaded with a liquid thermosetting resin mainly composed of polyurethane and a hardening agent, and then molded,
A method for producing a comb magnet, comprising curing the thermosetting resin at a temperature of 60° C. or lower.