GB2035344A - Magnetodielectric material - Google Patents

Abstract

A magnetodielectric material comprises iron and from 8 to 25% wt. of a thermosetting phenol-formaldehyde resin binder, from 5 to 20% wt. of a fibrous filler previously impregnated with a phenol-formaldehyde resin, and from 0.5 to 1.5% wt. of a lubricant. The filler may be asbestos powder, glass fibre or a synthetic resin fibre, e.g. polyethylene terephthalate. The binder may be modified with a polyolefin, a polyvinylacetal or colophony.

Description

SPECIFICATION Magnetodielectric material The present invention relates to a magnetodielectric material and to a process for producing such material.

This material is useful in electrical engineering, electronics, radio engineering and other industries.

A magnetodielectric material is known (see for example USSR copyright no. 169706 of 1965) which is iron-based and contains a thermosetting resin produced from furane and epoxy resins. Such a material has the following composition: Furano-epoxy resin 100 parts by weight Iron powder 250 parts by weight Hardeners (hexamethylenediamine or polyethylenepolyamine ) 15 parts by weight Glass fibre additive 1 - 1.5 parts by weight.

A magnetodielectric material which is iron-based and contains a filler in addition to a thermosetting resin is also known (see for example USSR copyright no. 524232 of 1976). In this case the material contains an epoxy-novolac block copolymer and has the following composition: Epoxy-novolac block-copolymer 30 - 35 parts by weight Urotropine 3 - 4 parts by weight Phthalic anhydride 2 - 3 parts by weight Filler 5 - 6 parts by weight Iron the balance.

Known magnetodielectric materials have been found to have insufficiently good physical and mechanical properties, such as inadequate resistance to vibrational loads. This is because the properties of a magnetodielectric material are determined by the properties of the binder, and known binders are not sufficiently resilient.

We have now discovered a magnetodielectric material which has good physical, mechanical and magnetodielectrical properties, and the desired magnetic permeability. These good performance characteristics are due to the particular thermosetting resin used and to the interaction between the various components.

Thus, the present invention consists in a magnetodielectric material comprising iron and from 8 to 25% by weight of a thermosetting phenol formaldehyde binder, from 5 to 20% by weight of fibrous filler impregnated with a phenol formaldehyde resin, and from 0.5 to 1.5% by weight of a lubricant.

We prefer that the binder is a modified phenol formaldehyde resin, and suitable modifiers include: polyolefins; polyolefin derivatives; polyvinyl acetal; and calophony. The amount of modifier is preferably from 10 to 30% by weight based on the weight of the resin.

Any filler suitable for a phenol formaldehyde resin may be used, but we prefer asbestos powder, glass fibre or synthetic fibre.

Convenient lubricants include fatty acids and salts of fatty acids, and of these we prefer oleic acid, stearic acid and calcium stearate.

The present invention further consists in a process for producing a magnetodielectric material, which comprises compounding athermosetting phenol formaldehyde binderwith powdered iron to form a substantially homogeneous powdered substance, and mixing this substance in the presence of a lubricant with a fibrous filler impregnated with a phenol formaldehyde resin.

This material can then be compression moulded to form any suitable moulded article.

Variation of the composition of the components (especially of the binder) and preliminary impregnation of the filler mean that improved physical and mechanical properties, magnetic permittivity and performance characteristics can be achieved.

The thermosetting binder may comprise a modified and/or non-modified novolac and/or resol type phenol formaldehyde resin. Where a novolac type resin is used a hardener should be employed, for example, hexamethylenetetramine. Any suitable modifier may be used, but we prefer polyolefins, polyolefin derivatives, polyvinylacetals and calophony. The preferred weight of modifier is from 10 to 30% based on the weight of the resin. Suitable fillers include asbestos fibre, glass fibre and synthetic fibres such as polyethylene terephthalate. Fibrous filler is impregnated with phenol formaldehyde resin (preferably using a 20 - 60% solution) and the impregnated filler is then mixed with the remainder of the components.The resin used to impregnate the filler may be, but need not be, the same type of resin as that with which the impregnated filler is mixed.

The preferred techniques for making the magnetodielectric material are similar two conventional methods of manufacturing phenol plastics. Two such techniques are as follows.

The first technique uses a dry resin. A thermosetting binder plus lubricant is compounded with iron powder to mechanically disperse the components. The resultant composition is homogenised using rollers, and then powdered. This powder together with a fibrous filler previously impregnated with the same binder are then fed to a mixer. Articles may be produced from the product by compression moulding. This technique is suitable when the filler is a glass fibre filler.

The second technique uses an emulsified resin. A mixer is charged with a lubricant, iron powder, and a thermosetting binder in the form of a 40 - 90% alcoholic solution. After compounding the iron powder and the binder, fibrous filler impregnated with the same binder is added to the mixer. The resulting composition is then homogenized using water-cooled non-friction rollers, and dried at 60 - 90"C to the desired fluidity.

The invention is further illustrated by the following examples. Unless otherwise stated all amounts are given as percent by weight.

Example I A novolac phenol formaldehyde resin (15.5), hexamethylenetetramine (3), calcium stearate (0.7) and iron powder (66.8) were charged into a mixer. The components were stirred for 60 minutes, and the resulting mixture was homogenized for from 6 to 10 minutes using friction rolls at a working roll temperature of from 70 to 1000C and an idle roll temperature of from 105 to 140on. The rolled mass was then cooled and comminuted. The resulting composition was mixed with chopped glass fibre (14) which had been previously impregnated with resol phenol formaldehyde resin. The magnetodielectric material thus produced was processed into articles using a conventional method for processing phenol plastics.

Example 2 Resol phenol formaldehyde resin (8), calcium stearate (0.5) and iron powder (71.5) were charged into a mixer, and stirred for 40 - 50 minutes. The resulting mixture was rolled and comminuted. The comminuted composition was then mixed with chopped glass fibre (20) which had been previously impregnated with phenol formaldehyde resin.

Example 3 Resol phenol formaldehyde resin (25) modified with chlorosulphonated polyethylene, calcium stearate (1) and iron powder (69) were charged into a mixer and stirred until a homogenous mixture was obtained. The resulting mixture was rolled, comminuted and then mixed with glass fibre (5) impregnated with a resol phenol formaldehyde resin.

Example 4 Emulsified phenol formaldehyde resin (9) modified with polyvinylbutyral, oleic acid (1.5) and hexamethylenetetramine (1.5) were charged into a mixer and stirred for 20 - 30 minutes. Iron powder (79) was then introduced into the mixer and stirring was continued for a further 30 - 40 minutes. The resulting mixture was rolled at room temperature without friction in water-cooled rolls, and then dried and comminuted. The composition that resulted was mixed with glass fibre (9) which had previously been impregnated with a resol phenol formaldehyde resin.

Example 5 Emulsified phenol formaldehyde resin (10) modified with calophony, oleicacid (0.5) and asbestos fibre (10) were charged into a mixer. Mixing was continued until the fibre was completely impregnated. Then, the same resin (10) arid iron powder (69.5) were introduced into the mixer, and stirring was continued for 40 - 50 minutes. The resulting mixture was homogenized in rolls without friction, and subsequently dried and comminuted.

Example 6 Emulsified phenol formaldehyde resin (8) and iron powder (71.3) were charged into a mixer, stirred for 30 minutes, and then discharged, dried and comminuted. Then the same resin (8), stearic acid (0.7) and polyethylene terephthalate fibre (12) were charged into a mixer causing the fibre to be impregnated. Then, the compounded and dried iron powder was introduced into the mixer, and all of the components were stirred for 20 - 30 minutes. The resulting mixture was rolled and dried.

Such magnetodielectric moulding material may be used in the manufacture of components of electrical machines, for example magnetic slot wedges. Typical magnetodielectric material according to the invention has the following properties: Density 3.5 - 4.5 g/cm3 Impact viscosity 10 - 30 kgf cm/cm2 ultimate bending strength 600 - 1,000 kgf/cm2 compression strength 1,300 - 2,000 kgf/cm2 Martens thermal staility 120 - 200or Brinell hardness, 4,000 - 7,500 kgf/cm2 permittivity at H=3,000 3.0 - 8.0 A/cm shrinkage 0.2 - 0.5% operating time under extreme condition 50,000 - 60,000 h.

The magnetodielectric material was found to be stable to heat: the properties of the material did not change after heating at 200"C for 14 days.

The efficiency of slot wedges for electrical machines can be improved by 1 - 2% by using the material of the invention. The material of the invention also reduces over heating, reduces vibroacoustic noises and improves the reliability of the machines.

Claims (18)

1. A magnetodielectric material comprising iron and from 8 to 25% by weight of a thermosetting phenol formaldehyde binder, from 5 to 20% by weight of a fibre filler impregnated with a phenol formaldehyde resin, and from 0.5 to 1.5% by weight of a lubricant.

2. A material according to claim 1, in which the binder is a modified phenol formaldehyde resin.

3. A material according to claim 2, in which the modifier is a polyolefin, a polyolefin derivative, a polyvinylacetal or calophony.

4. A material according to claim 2 or claim 3, in which the amount of modifier is from 10 to 30% by weight based on the weight of the resin.

5. A material according to any one of the preceding claims, in which the filler is asbestos powder, glass fibre our a syntheticfibre.

6. A material according to any one of the preceding claims, in which the lubricant is a fatty acid or a salt of a fatty acid.

7. A material according to claim 6, in which the lubricant is oleic acid, stearic acid or calcium stearate.

8. A material according to claim 1, substantially as herein described with reference to any one of the foregoing examples.

9. A process for producing a magnetodielectric material, which comprises compounding a thermosetting phenol formaldehyde binder with powdered iron to form a substantially homogeneous powdered substance, and mixing this substance in the presence of a lubricant with a fibrous filler impregnated with a phenol formaldehyde resin.

10. A process according to claim 9, in which the binder is a modified phenol formaldehyde resin.

11. A process according to claim 10, in which the modifier is a polyolefin, a polyolefin derivative, a polyvinylacetal or calophony

12. A process according to claim 10 or claim 11, in which the amount of modifier is from 10 to 30% by weight based on the weight of resin.

13. A process according to any one of claims 9 to 12, in which the filler is asbestos powder, glass fibre or a synthetic fibre.

14. A process according to any one of claims 9 to 13, in which the lubricant is a fatty acid or a salt of a fatty acid.

15. A process according to claim 14, in which the lubricant is oleic acid, stearic acid or calcium stearate.

16. A process according to claim 9, substantially as herein described with reference to any one of the foregoing examples.

17. A magnetodielectric material when produced by a process according to any one of claims 9 to 16.

18. A process for producing a moulded article, in which a magnetodielectric material according to any one of claims 1 to 8 and 17 is compression moulded.