JPS6167203A - Non-vulcanized type rubber magnet - Google Patents

Abstract

PURPOSE:To obtain a rubber magnet of high mechanical strength by using a uniform mixture in a specific ratio of a metal oxide magnetic power, EPM or EPDM containing a specific quantity of ethylene, and fatty acid or metal salt. CONSTITUTION:Uniform mixture of one or more kinds of 62-68vol% metal oxide magnetic powders such as barium ferrite and strontium ferrite magnetic powders, an ethylene propylene rubber base composed of EPM or EPDM containing 60wt% or more ethylene, and fatty acid or metal salt thereof corre sponding to 5-15wt% or more of the rubber base is used. For instance, a com pound of a 63.8vol% strontium ferrite magnetic powder, EPDM containing 75wt% ethylene whose Mooney viscosity (ML1+4 100 deg.C) is 90, and 3-15phr stearic acid zinc is mixed and kneaded in a kneader for about 10min. This mixed and kneaded material is passed through two rolls about 10 times, then it is elongated so that it has a thickness of about 3mm, whereby a steet rubber magnet is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a rubber magnet, and particularly to an unvulcanized rubber magnet.

[Prior art]

Various natural and synthetic rubbers are used in the production of rubber magnets, and when powdered hard magnetic materials such as barium ferrite and strontium 7-elite are mixed into the rubber base, vulcanization is used as one of the additives. After adding the additive and uniformly mixing it and molding it into a predetermined shape, it is vulcanized at a high temperature of around 150° C. for several tens of minutes to several hours to obtain an excellent rubber magnet with high mechanical strength.

Although such a vulcanization process is desirable for manufacturing rubber magnets, it requires a heating device for the vulcanization process, consumes a large amount of energy, and has the disadvantage that the vulcanization process takes a long time. Furthermore, once the vulcanization process is completed, the rubber molecules are crosslinked, so if a rubber magnet is chipped or cracked during the manufacturing process, it is no longer possible to recycle it and it must be discarded as a defective product. There were also problems in terms of resource utilization. There are also resin magnets based on thermoplastic resins such as vinyl chloride, polyethylene, etc., but their properties at high temperatures cannot be said to be good.

[Purpose of the invention]

Therefore, an object of the present invention is to provide a rubber magnet that does not require a vulcanization process.

Another object of the present invention is to provide a rubber magnet with high mechanical strength, although it is an unvulcanized rubber magnet that does not require a vulcanization process.

[Summary of the invention]

The above purpose is to use 62-68 vol% of one or more types of metal oxide magnetic powder, such as barium ferrite and strontium ferrite magnetic powder, as the magnetic powder, and EPM with an ethylene content of 6 owts or more as the rubber base. (Saturated ethylene propylene elastomer) or tiEPDM (unafLfffi ethylene propylene elastomer) is used as the remainder, and s-1s phr (wt% based on the rubber content) of fatty acid or its metal salt is added to the rubber magnet to form a homogeneous mixture. This is achieved by

The rubber base preferably has a Mooney viscosity (ML1+410
0°C) is 60 or higher.

The greatest advantage of the rubber magnet of the present invention is that although it is an unvulcanized type, it has mechanical strength equivalent to that of a vulcanized rubber magnet over a fairly wide temperature range. According to the present invention, manufacturing costs are reduced because there is no vulcanization treatment. As well,
Even if defective products occur on the production line, they can be crushed and recycled as raw materials for rubber magnets.

[Detailed description of the invention]

The magnetic powder for magnets used in the present invention is a metal oxide magnetic powder with an average particle size of around 1 μm, particularly 1 μm or less having a single magnetic domain structure.
For example, barium ferrite, strontium ferrite magnetic powder, etc. These ferrite powders are used in a proportion of 62-68 molar % based on the total amount including the rubber content. If this amount is less than 62 vol %, the residual magnetic flux density of the rubber magnet will not be sufficient. On the other hand, this amount is 68
If it exceeds vol %, it becomes difficult to mix with the rubber component, making it impossible to manufacture a rubber magnet with high mechanical strength.

The EPM or EPDM used in the present invention is 60wt9
It is necessary to contain an ethylene content of 6 or more. Such an ethylene propylene elastomer provides extremely excellent physical properties as a base for a rubber magnet, and can provide a rubber magnet with high mechanical strength without vulcanization. When the ethylene content is 60 wt% or less,
The mechanical strength of the rubber magnet decreases.

Desirably, the EPM or EPDM has a Mooney viscosity of 60 or higher. Mooney viscosity is related to the chain length of rubber molecules, and when this viscosity is 60 or more, the strength of the rubber magnet can be sufficiently increased.

It is difficult to mix and disperse ferrite magnetic powder directly into the above-mentioned EPM or EPDM. Therefore, stearic acid, zinc stearate, lauric acid, deficient zinc phosphate, other fatty acids or gold salts thereof are used as the third component. The fatty acid or its metal salt improves the dispersibility of the magnetic powder, allowing the magnetic powder to be well dispersed even at a high content, thereby increasing mechanical strength. Moreover, the coercive force, which is one of the important properties of a rubber magnet, can be increased by improving the monodispersity.

Fatty acids or their metal salts are known as lubricants for rubber and plastics, and the amount added is generally Q, 3 to 0.
It is only about 5 phr. In the present invention, 5-15 phr
In other words, 5-15wt based on the rubber content must be used. If this amount is less than 5 phr, the dispersion effect is low;
Rubber magnets with high mechanical strength cannot be obtained. On the other hand, if this amount exceeds 15 phr, the dispersion effect not only becomes saturated but also causes blooming, which is not desirable.

Although the present invention does not require any other ingredients, small amounts of other organic or inorganic additives may be added if necessary.

A remarkable feature of the present invention is the use of EPM or EPDM having an ethylene content of 60 wt % or more, preferably a rubber base having a Mooney viscosity of 60 or more. This rubber base potentially has excellent mechanical properties and dispersibility, but its superior effects can only be achieved by co-using fatty acids or fatty acid salts such as stearic acid or zinc stearate. This is possible.

The rubber magnet of the present invention can be used, for example, as a motor magnet, and its strength from room temperature to about 60° C. is no different from that of a vulcanized rubber magnet.

Examples of the present invention will be described in detail below.

Example.

Strontium ferrite magnetic powder 618 vol1%,
Mooney viscosity (ML 1+4100℃) 90
A blend of EPDM with +4 tyrene content of 7 s wt % and 5-15 phr zinc stearate was kneaded in a kneader for about 10 minutes. No solvents were used. Next, this kneaded material was placed on two rolls with a diameter of 15 cIIL for about 1 hour.
It was passed 0 times and then rolled out to a thickness of about 3 nm to obtain a sheet-like rubber magnet. This was cut into predetermined dimensions and tested. All of the above manufacturing steps were performed in an environment at room temperature.

Comparative Example Instead of EPDM in Example, the ethylene content was 55w1
% EPDM and 10 phr zinc stearate.
A rubber magnet was manufactured using the same method as in the example.

[Consideration of results]

The relationship between zinc stearate content, castability, and coercive force (iHc) of various rubber magnets obtained in Examples was investigated, and the results shown in FIG. 1 were obtained. In other words, the minimum bending radius represents the limit radius at which no cracks will occur even if the material is bent at that radius. As is clear from the figure, when the zinc stearate content is less than about 5%, the rubber magnet becomes brittle and has low flexibility. Therefore, it can be seen that this amount is required to be 5% or more. Pluming was observed at 15 inches. On the other hand, it can be seen that the coercive force increases in proportion to the amount of zinc stearate. Therefore, it can be seen that this amount of 5 or more is necessary from the viewpoint of both magnetic properties and mechanical properties.

Next, the temperature dependence of the tensile strength of the example sample and the comparative example sample with zinc stearate of 10 phr was determined by J
When the test was carried out according to the method specified in 56301, the results shown in FIG. 2 were obtained. As can be seen from this result, it can be seen that EPDM with a high ethylene content provides high strength. As shown in FIG. 2, the tensile strength at temperatures below 60° C. is superior to that of vulcanized EPDM.

Next, when we measured the hardness (Shore D hardness) of the samples used to measure the characteristics shown in Figure 2, the hardness of the example was 38, which was 9, while the comparative example was 28. . A rubber magnet with a hardness of 28 has some flexibility. A hardness of 38 is a good hardness. Generally hardness 20-5
A material with a diameter of about 0 is suitable because it allows bending to a certain extent and has considerable rigidity.

In addition, all samples have a residual magnetic flux density Br = 240
0 (Q), and coercive force 1Hc = 3500 (Oe).

[Effect]

As described above, the present invention utilizes EPM with a high ethylene content.
Or, by using EPDM and a fatty acid or its metal salt, the dispersibility is improved and the bending strength and tensile strength are high.
A rubber magnet with a large coercive force was obtained. Although the magnet of the present invention is a non-vulcanized type, it has sufficiently high mechanical strength at a temperature of 60° C. or lower, and is advantageous in terms of manufacturing process, manufacturing time, and raw material cost.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the relationship between fatty acid metal salt, bending strength and coercive force in the rubber magnet of the present invention, and FIG. 2 is a graph showing the temperature dependence of ethylene content and tensile strength.

Claims (1)

[Claims] 1. Ethylene consisting of one or more metal oxide magnetic powders such as barium ferrite and strontium ferrite magnetic powder of 62-68 vol% and EPM or EPDM with an ethylene content of 60 wt% or more. An unvulcanized rubber magnet made of a homogeneous mixture of a propylene rubber base and 5 to 15 wt% of a fatty acid or a metal salt thereof corresponding to the rubber base. 2. Mooney viscosity of ethylene propylene rubber (ML_1
_+_4100°C) is 60 or more.