AU617620B2

AU617620B2 - Composition for producing bonded magnet

Info

Publication number: AU617620B2
Application number: AU57933/90A
Authority: AU
Inventors: James Hugh Raistrick; Masaaki Sakata; Tatsuya Shimoda
Original assignee: Imperial Chemical Industries Ltd
Current assignee: Imperial Chemical Industries Ltd; Seiko Epson Corp
Priority date: 1987-03-03
Filing date: 1990-06-27
Publication date: 1991-11-28
Anticipated expiration: 2008-02-24
Also published as: GB8804062D0; JPH11150012A; JPS63289807A; AU1213088A; JP2867140B2; AU601815B2; EP0281295A3; EP0281295A2; AU5793390A; JP3229948B2

Description

AUSTRALIA

Patent Act C7 COMPLETE SPECIFICATIO N

(ORIGINAL)

Class Int. Class Application Number: Lodged: Complete Specification Lodged: Accepted: Published: Priority: Related Art: Name(s) of Applicant(s): IMPERIAL CHEMICAL INDUSTRIES PLC SEIKO EPSON CORPORATION Address(es) of Applicant(s): Imperial Chemical House Millbank, London SW1P 3t

ENGLAND

Our Address for service is: 4-1 Nishinshinjuku2-chome Shinjuku-ku JF Tokyo Japan PHILLIPS ORMONDE FITZPATRICK Patent and Trade Mark Attorneys 367 Collins Street MELBOURNE, Australia 3000 Complete Specification for the invention entitled: COMPOSITION FOR PRODUCING BONDED MAGNET The following statement is a full description of this invention, including the best method of performing it known to applicant(s): 1 0804N I A -la- Composition For Producing Bonded Magnet This application is a divisional application from parent Australian application 12130/88, the entire disclosure of which is incorporated herein by reference.

The invention provides a composition from which a shaped article having magnetic properties may be produced.

Specifically, the present invention resides in a composition, suitable for use in the production of a shaped article having magnetic properties, which composition comprises a mixture of a solid melt-processable and cross-linkable organic material, a particulate magnetic material, and a polymeric material which is soluble in or, dispersable in the organic material when the organic material is in a liquid state.

The composition may also contain an additive which is S capable of effecting or assisting cross-linking of the organic material to produce a cross-link material.

Bonded magnets which are produced from a composition comprising an organic material e.g. an organic polymeric material, and a particulate magnetic material, are well-known. Most commonly such magnets are produced commercially from a composition comprising a mixture of a thermopl stic organic polymeric material and particulate magnetic material. For example, a composition comprising a S mixture of a thermoplastic organic polymeric material and particulate magnetic material may be shaped in plastics processing equipment, e.g. in an injection moulder or in an extruder, or the composition may be processed by compression moulding.

The composition is shaped whilst the thermoplastic organic polymeric material is in a fluid state and the composition is then cooled to a tolid state. Optionally, whilst the organic polymeric material is in a fluid state, the composition may be subjected to the influence of a magnetic field in order to align the articles of magnetic material to the- direction of easy magnetisation and thus enhance the performance of the magnet. The magnetic field is maintained whilst the organic polymeric material is cooled to a solid state, and thereafter the thus shaped composition is removed from the influence of the magne ic field as, when the organic polymeric material is in a solid state, the magnetic: field is no longer needed in order to maintain the alignment of the particles of magnetic material. The thus produced shaped article is then removed from the plastics processing equipment.

The organic polymeric material in the composition used in the production of the bonded magnet may be a polyolefCn, for example, polyethylene or polypropylene, but a particularly favoured material for use in such a composition is a polyamide, that is one of the nylons. A particularly favoured nylon is nylon-6. For example, Japanese Patent Publication No. 59 094406 describes a composition of a synthetic resin and a powdered magnetic material whose surface has been treated with a coupling agent. The magnetic material may be a ferrite or a rare-earth/cobalt intermetallic compound, and the synthetic resin may be polypropylene, polyvinyl chloride or a polyamide, e.g. nylon nylon -11 or nylon -12. The use of polyamides, e.g.

nylon -6 and nylon in such compositions is also described in Japanese Patent Publication No. 60 216524 and in Japanese Patent Publication No. 61 059705.

Magnets produced from compositions in which the organic polymeric material is a thermoplastic such as a nylon or a polyolefin do, however, suffer from disadvantages, as do the processes used in production of the magnets. Thus, the glass transition temperatures of polyolefins and of the nylons may be relatively low such that at relatively low temperatures magnets made from compositions comprising polyolefins and ,he nylons may tend to distort and become

I--

-3misshapen, particularly under the influence of a strot.g magnetic field or as a result of repulsion between the aligned particles of magnetic material, with possible serious consequences for the equipment in which the magnet is installed. For example, the glass transition temperatures of nylon nylon -11 and nylon -12 are respectively 62.5 0 ,4 0

°C

and 37 0 C. Thus, the effective upper limit of operation of such a magnet may be at a relatively low temperature, and in particular it may be at a temperature which is not as high as might be desired. Furthermore, it is necessary to process the composition at a temperature at which the organic polymeric material is in a fluid state, and the latter material may melt at a temperature which is so high that during the processing there is an adverse effect on the properties of the particles of magnetic material, e.g. ,s a result of oxidation.

Also, in order to produce a bonded magnet having a high magnetic performance it is necessary to use a composition containing a high proportion of particles of magnetic material. Such a composition may have a high viscosity when it is subjected to plastics processing, and it may be difficult if not impossible to shape a comnposition containing the desired high proportion of particulate magnetic material. Excessively high temperatures may also be needed in order that the organic polymeric material shall be in a sufficiently *fluid state that the composition can be shaped, with possible adverse effect on the properties of the particles of magnetic material.

m r ~1 -4- By "magnetic material" we mean a material which is magnetic or which is capable of being magnetised. Thus, the magnetic material may not itself be magnetic but it may be magnetized under the influence of the magnetic field when the composition is processed.

Whilst there is no particular limit on the maximum size of the particles of magnetic material the particles suitably have a size in the range of 0.5 micron to 200 microns.

Examples of suitable magnetic materials include ferrite materials, eg barium hexaferrite (Ba 0 6 Fe 2 0 3 and strontium hexaferrite (Sr 0 6 Fe 2 0 3 Other magnetic materials which may be used in the process of the invention and from which bonded magnets having high magnetic performance may be produced include intermetallic compounds formed from at S least one rare earth metal and at least one transition metal.

Rare earth metals from which such a magnetic material may be formed include Sm, Ce, La, Y, Nd, Pr and Gd, and suitable transition metals include Fe, Co, Ni, Zr, Hf, Cu and Ti. The intermetallic compound may, for example, having an empirical formula which may be generally referred to as RCo 5 or RCo 1 7 where R is at least one rare earth metal. An example of a rare earth metal from which the intermetallic compound may be produced is Sm, for example as in the S intermetallic compounds which are generally referred to by the empirical formulae SmCo 5 and Sm 2 Col 7 These latter empirical formulae are not intended to represent exact chemical formulae for the intermetallic rare earth transition metal S compounds as elements other than Sm and Co maybe present in the intermetallic compounds. By way of example, Japanese Patent Publication No 60 227408 refers to a rare earth-transition metal intermetallic compound having the formula Sm(Co C 0 672 Fe 022 Zr0*028)5*3 and Japanese Patent Publication No 220905 to rare earth-transition metal compounds having L' formulae Sm (Co 0 672 Cu0.6 Fe022 Zr 0 "0 28 )8' 35 Sm0' 75

Y

0 2 (Co0' 65 -Cu0 05 Fe028 Zr 0 02 7 .8' and Sm Ce (Co Cu and Sm0'81 Ce0.19 (Co0' 61 Cu0'06 Fe0' 31 Zr0' 0 2 7 Other examples of magnetic materials which are intermetallic compounds of at least one rare earth metal and at least one transition metal include those based as Nd Fe B, for example, Nd (Fe 0 905 B 0095)567 which is also described in Japanese Patent Publication No. 60 220905.

Other examples of such intermetallic compound magnetic materials include SM(Co Cu008Fe022 Zr 0 03 7 Sm(Co 0 0 74 Cu0'10 Fe 1 5 Ti 1 )72 Sm(Co 0 15T O 01 72' O'69 Cu Fe Hf CU O 0 0'20H 001)7'0' Sm 0 5 Pr 0 5 Co 5 Ce(Co Cu 0 0*5 0*5 5' 0'69 0*12 Fe Zr0 Sm05Nd0.4 0*18 0'01)6'01 S 0-5 0-4 Ce 0 1 (Co 0 6 7 2 Cu 0 0 8 Fe 022 Zr 003)8*35' and Nd 1 4 Fe 8 1

B

5 The composition may of course contain more than one organic material, more than one particulate magnetic material, and/or more than one additive capable of effectiing or assisting cross-linking of the organic materia.

In the composition the proportions of organic material, or additive capable of effecting or assisting S cross-linking, if present, and of particulate magnetic material, may be varied between wide limits. In -eneral, the proportion of magnetic material will be as hicm possible, consistent with the composition being melt-prucessable on S plastics processing equipment, in order that the magnetic performance of the bonded magnet which is produced may be as high as possible. In general, the proportion of magnetic material in the composition will be at least 50% by weight of the composition, preferably at least 80% by weight of the composition. A suitable range for the proportion of the magnetic material is 80 to 95% by weight of the composition.

The amount of organic material in the composition should be such as to result in a composition which is -1

L

-6melt-processable on plastics processing equipment, and in general the composition will contain at least 5% of organic material by weight of the composition. A suitable proportion of organic material is in the range 5 to 20% by weight of the composition.

The amount of additive which is capable of effecting or assisting cross-linking will depend to someextent at least: on the nature of the additive and on the nature of the organic material but an amount of additive in the range of 0.01% to 5% by weight of the composition will generally suffice. Where the organic material contains ethylenically unsaturated groups, as in a polyester resin or in an acrylic material, and the additive is a free-radical generator, an amount of additive in the range 0.01% to 2% by weight of the 99 composition will generally suffice. Where the organic.material is an epoxy resin the amount of additive will generally also be in the range 0.01% to 2% by weight of the composition.

The greater is the amount of such additive in the composition the faster will be the cross-linking of the organic material.

The components of the composition may be mixed by any gag• convenient means. For example, the components when in particulate form may be mixed in any suitable equipment for blending particulate material. A preferred manner of forming a particularly homogenous composition of the organic material and the particulate magnetic material is to mix the composition under conditions of high shear, for example, on a twin roll mill at an elevated temperature at which the organic material is heat-softened. The mixture may be passed repeatedly throught the nip between the rolls of the mill, and finally, and if desired, the additive which is capable of effecting or assisting cross-linking may be added to the mixture on the mill. This is a particularly convenient means of mixing the components of the composition when the additive itself is liquid. The mixiLg of the additive should be effected relatively rapidly so that little if any cross-linking of the organic material is effected during the mixing, and for this reason the additive is preferably added at the end of the mixing process.

I

-7- In an alternative method the components of the composition may be mixed in the presence of a liquid diluent which is subsequently removed from the composition. The liquid diluent assists in producing a homogenous mixture of the components of the composition and it may be removed from the composition, for example by evaporation, particularly when the diluent is a low boiling liquid.

Where the organic material in the composition is a monomeric material, and even where it is a polymeric material, mixing of the components of the composition under conditions of high shear and in particular the formation of a homogenous mixture, and the subsequent melt-processing of the composition, may be assisted by including in the composition S. a proportion of, and generally a small proportion of, a polyneric material which is soluble in or dispersible in the S organic material when the organic material is in a fluid, or liquid state. The presence of a small proportion of such a S polymeric material also assists in the formation of a composition which contains a high proportion of particulate magnetic material and which is also melt-processable on plastic processing equipment.

The polymeric material will generally be a co-polymer -ontaining some functional groups which have an affinity for the magnetic particles. The polymeric material may promote the wetting of the particles by the organic material.

Suitable polymeric materials include polyvinyl butyral/polyvinyl alcohol co-polymer, polyvinyl chloride/polyvinyl acetate/polyvinyl alcohol co-polymer, polyvinyl acetate/polycrotonic acid co-polymer, and polyvinylidene chloride/polyacrylonitrile co-polymer. The composition suitably contains from 0.5 to 5% by weight of such polymeric material. The composition may contain more than one such polymeric material.

The composition may be melt-processed and shaped on suitable plastic processing equipment, for example in an oxtruder, in an injection moulder, or by compression moulding, as is described in more detail in parent application 12130/88.

r I I 1 i 8 The composition of the present invention is illustrated by the followine examoles in which all parts are expressed as parts by weight. Comparison of the advantages of the composition when used in the process of the parent application are referred to in greater detail in the specification of the parent application.

Example 1 A compostion of Magnetic particles: Organic material: C. *9 S. 4e

C

9 9* 9**9 eq.

C

Sm(CoO*572 Fe Cuo*.o Zro.

0 oa 8 35 powder 91.47 parts Oligomerised and epoxidised bisphenol A powder 4.13 parts Phenol-formaldehye novolak powder 2.29 parts Epoxidised phenol-formaldehyde novolak powder 0.33 parts A powder of a copolymer containing units of vinyl butyral and vinyl alcohol Pioloform BN 18, Wacker Chemie GmbH 1.26 parts Polymeric material: Silica powder (Aerosil OX 50) Calcium stearate Bleached Monton wax Diuron 0.2 parts 0.17 parts 0.17 parts 0.05 parts was mixed by hand to form a reasonably homogenous mixture of the powders and the mixture was then charged to a twin-roll mill, the rolls of which were at temperature of 90CC, and the composition was passed -9repeatedly through the nip between the rolls of the mill to form a plastic sheet. The presence of the organic polymer in the composition assisted in the production of a sheet. The sheet was then callendered on the twin-roll mill at 800°C to a thickness of 0.7 mm and the sheet was placed in a mould at 1100°C and pressed to reduce the thickness of the sheet to 0.5 mm. The sheet was then divided into six equal-sized smaller sheets.

One of the smaller sheets was placed in a mould positioned between the poles of a 23.5 kG electromagnet and the sheet was heated rapidly to 140°C and thereafter I immediately cooled to ambient temperature. At 1400C the o 'organic material in the composition melted and the magnetic particles became aligned under the influence of the magnetic field. It was possible to remelt a part of the sheet thus demonstrating that the extent of cross-linking which had taken place, if any, was not such as to prevent reprocessing of the sheet. The sheet was then placed between the poles of an electromagnet and a series of decreasing alternating magnetic fields ~I .were applied in order to demagnetise the magnetic particles. The sheet was then heated in the mould at :170°C for 30 minutes in order to cross-link the organic material, and finally the sheet was subjected to magnetisation between the poles of a 23.5 kG electromagnet and the sheet was found to have a (BH) max Q of 4.5 MG Oe.

10 10 Example 2 A composition of Magnetic particles: as used in Exam.le 1 187 parts, Organic material: a powder of an adduct of 4:4' diphenyl methane diisocyanate and hydroxy ethyl methacrylate 18.7 parts, Polymeric material: a powder of a copolymer containing units of vinyl butyral and vinyl alcohol Pioloform BS 18, Wacker Chemie GmbH.

3.1 parts was mixed by hand to form a reasonably homogenous mixture of the powders and the mixture was then charged to a twin-roll mill, the rolls of which were at temperature of 80 0 C, and the composition was passed repeatedly through the nip between the rolls of the mill to form a plastic sheet. The presence of the organic polymer in the composition assisted in the production of a sheet. 0.2 part of 1,1' azo bis (cyclohexanecarbonitrile) free radical generator was then added and milling was continued for 1 minute and the plastic sheet was removed from the mill and cooled to ambient temperature. The sheet was then callendered on the twin-roll mill at 60 0 C to a thickness of 0.7 mm and the sheet was placed in a mould at 80 0 C and pressed to reduce the thickness of the sheet to 0.5 mm. The sheet was then divided into five equal sized smaller sheets.

One of the smaller sheets was placed in a mould positioned between the poles of a 23.5 kG electromagnet and the sheet was heated rapidly to 100 0 C and thereafter immediately cooled to ambient temperature. At 100 0 C the 4 rr a

B)

'4, 4 4B bE 11 organic.material in the composition melted and the particles of magnetic material became aligned under the influence of the magnetic field. It was possible to remelt a part of the cooled sheet thus indicating that the extent of cross-linking which had taken place, if any, was not such as to prevent reprocessing of the sheet.

The sheet was then irradiated with Co 60 y-rays at ambient temperature in order to cross-link the organic material when the latter material was in a solid state.

The irradiation was continued for a time sufficient to result in a cross-linked resin having a glass transition temperature of 60 0 C. The sheet was then heated to at which temperature the sheet softened slightly but not to an extent which allowed the sheet to distort nor which allowed the particles of magnetic material in the sheet to become misaligned. Heating at 120 0 C was continued for 5 minutes to effect more cross-linking, and the sheet was then found to have a glass-transition temperature of 100 0 C. The (BH) max value for the sheet was 5.0 MG Oe.

a I iS 4

C

'4 a E 1 r I 1 I rT 12 EXAMPLE 3 A composition of Magnetic particles: Organic material: 64 aJ *4 a) a a' a. d Se Polymeric material: Nd,,Fe,,B, 93.30 parts Oligomerised and epoxidised bisphenol A powder 4.13 parts Phenol-formaldehye novolak powder:.

2.29 parts Epoxidised .phenol-formaldehyde novolak powder 0.33 parts A powder of a copolymer containing units of vinyl butyral and vinyl alcohol Pioloform BN 18- Wacker Chemie GmbH 1.26 parts 0.2 parts 0.17 parts 0.17 Darts 0.05 parts 5 4r q *r I Silica powder (Aerosil OX 50) Calcium stearate Bleached Monton wax Diuron was mixed by hand to form a reasonably homogenous mixture of the powders and the mixture was then charged to a twin-roll mill, the rolls of which were at temperature of 900C, and the composition was passed repeatedly through the nip between the rolls of the mill to form a plastic sheet. The presence of the organic polymer in the composition assisted in the production of a sheet. The sheet was then callendered on the -13 twin-roll mill at 80 0 C to a thickness of 0.7 mm and the slieet was placed in a mould at 110 0 C and pressed to reduce the thickness of the sheet to 0.5 mm.

The sheet was placed in a mould and heated rapidly at 140 0 C and thereafter immediately cooled to ambient temperature. I~t was possible to remelt a part of the sheet thus demonstrating that the extent of cross-linking which had taken p.L-ce, if any, was not such as to prevent reprocessing of the sheet. The sheet was then heated in the mould at 170 0 C for 30 minutes in 6000 order -o cross-link the organic material. The sheet was found to have a (BH) max of 5,.5 MG~e.

Examples 4t 3 weghtIn four separate examples solid compositions (in per cent) as shown in Ta!7te 1 were mixed by hand .0 to form reasonably homogeneous mixtures of powders and each mixture was then separately charged to a twin-rol) mill and 'passed repeatedly through the nip betweent the rolls of the mill. The compositions of Examples 6 and 7 were heated at 95 0 C on the mill and the compositions of Examples 8 and 9 at 100 0 C. Each of the compositions was '1 formed into a sheet and removed from the mill. The compositions were then pulverised to particles and -!acb.

composition was charged to a screw extruder and extruded through a cylindrical die. The temperature of the *'*barrel of the extruder was 120 0 C and that of the die was 130 0 C, and the extrusion speed was 1 mm sec- 1 During the extrusion the die of the extruder was subjected to a radip-l magnetic field of 15 KOe in order to align the particles of magnetic material in the compositions. The end of the di-: was at ambient temperature in order to s,-lidify the *,xtruded compositions. The cylindrical extruded compositions had an external diameter 30 mm and an internal diameter of 26 mm. The magnetic particles in each of the cylinders were then deiragnetised T j 14 following the procedure described in Example 1 and each of the cylinders was then heated at 200 0 C for 30 minutes in order to cross-link Example Magnetic particles* Oligomerised and epoxidised bisphenol A powder Phenol-formaldehyde novolak powder Epoxidised phenolformaldehyde novolak powder Polymeric material** Silica powder (Aerosil 0 x Calcium Stearate Bleached Montan wax 20 Diuron the resin Table 1 4 91.50 4.09 in the compositions.

5 93.00 3.37 6 94.40 2.70 7 95.60 2.12

S

*q.

4 505 S...1 9 0e 2.25 0.31 1.26 0.20 0.17 0.17 0.05 1.85 0.26 0.18 0.16 1.49 1.16 1.04 0.16 0.14 0.14 0.04 0.84 0.14 0.11 0.11 0.03 0.65 0.10 0.09 0.09 0.03 *Sm (Coo.' 2Cu0.0 Fe0.22 Zro*o2)a .3 0.5 to 100 microns diameter **As lsed in Example 1.

By way of comparison, in three separate 25 comparative examples, Comparative Examples 1, 2 and 3 compositions as shown in Table 2 (in weight per cent) were mixed to form reasonably homogeneous mixtures and charged separately to twin-roll mills and mixed on the mill at a temperature of either 250 0 C (Comparative examples 1 and 2 or 2600C (Comparative example 3) The mixtures removed from the mill were extruded from a screw extruder through a cylindrical die at a speed of mm sec- 1 at a barrel temperature of 2401C and a die temperature of 220 0 C. The die was subjected to a radial

I'-

'1 magnetic field of 15 KOe and the end of the die was at ambient temperature in order to solidify the extruded compositions. The cylindrical extruded composition had an external diameter of 30 mm and an internal diameter of 26 mm.

Table 2 Example Comparative Comparative Comparative 1 2 3 Magnetic 91.8 93.2 94.4 Particles* Nylon-12 powder 8.1 6.7 5.6 Zinc stearate 0.1 0.1 0.1 *As used in Examples 4 to 7 i (A composition comprising, in weight per cent, magnetic 15 particles 95.6, nylon-12 powder 4.3, zinc stearate 0.1, could nriot be compounded satisfactorily on the twin-roll mill nor could it be extruded satisfactorily.) 1 The magnetic performances of the cylindrical magnets produced in Examples 4 to 7 and in Comparative Examples 1 to 3 is shown in Table 3.

Table 3 Example Magnetic performance Br (Kg) bHc (KOe) (BH) max (MGOe) 25 4 5.95 4.35 7.8 6.33 4.52 8.9 S6 6.80 4.69 10.2 7 7.18 4.88 12.4 S. Comparative 1 5.83 4.32 7.3 30 Comparative 2 6.22 4.47 8.1 Comparative 3 6.50 4.60 Br remanence bHc coercivity Examples 4 to 7 and Comparative Examples 1 to 3 demonstrate that it is possible to extrude a composition T1 _J I 2 16 of the invention comprising more than 95 weight per cent of magnetic particles whereas this is not possible with a composition containing a conventional thermoplastic resin and comprising more than 95 weight per cent of magnetic particles. Furthermore, the composition of the present invention, when moulded, has a superior magnetic performance indicating better alignment of the magnetic particles in the composition and that the magnetic particles are easier to align in the composition.

Examples 8 to 11 In four separate examples the procedure of Examples 4 to 7 was repeated to produce cylindrical shaped compositions except that the magnetic particles.

were 1 to 200 microns in diameter and had the 15 composition Nd14 (Fe 0 Co 0 0 ;)8.o5 the temperature of the twin-roll mill was 950C and the extrusion speed was 2 mm sec- 1 The compositions in weight per cent are as shown in Table 4.

a

*W

.9 .a a *9 Example Magnetic particles Oligomerised and epoxidised bisphenol A 25 powder Phenol-formaldehyde novolak powder Epoxidised phenolformaldehyde novolak powder Polymeric material* Silica powder (Aerosil 0 x Calcium Stearate Bleached Montan wax Diuron *As used in Example 1.

Table 4 8 9 10 90.30 4.67 92.2 3.76 93.7 3.03 11 95.0 2.41 2.56 2.06 1.66 1.32 0.34 0.27 0.22 0.18 1.43 0.28 0.18 0.18 0.06 1.15 0.23 0.14 0.14 0.05 0.93 0.18 0.12 0.12 0.04 0.74 0.14 0.09 0.09 0.03 17 In two comparative examples, Comparative Examples 4 and 5 compositions comprising, respectively, 90.4 and 91.7 weight per cent of magnetic particles as used in Examples 8 to 11 9.5 and 8.2 weight per cent of nylon-12 powder, and 0.1 and 0.1 weight per cent of zinc stearate, were shaped into cylindrical magnets following the procedure of Comparative Examples 8 to except that the temperature of the twin-roll mill was 250 0 C, the temperature of the barrel of the extruder was 230 0 C, the temperature of the die of the extruder was 205 0 C, and the extrusion speed was 1 mm sec-.

(A composition containing 92 weight per cent or more of magnetic particles could not be milled satisfactorily-on the twin-roll mill nor could the composition be 15 extruded.) os The magnetic performances of the cylindrical magnets are shown in Table Table Example Magnetic performance 20 Br (Kg) bHc (KOe) (BH) max (MGOe) 0**4 *9 8 5.01 3.96 5.2 9 5.60 4.42 1 6.05 4.78 7.6 6.51 5.14 8.7 I Comparative 4 4.90 3.87 4.9 Comparative 5 5.15 4.07 It can be seen that by using a composition of the invention which comprises a solid melt-processable and cross-linkable organic material it is possible to obtain high isotropic performance of the resultant magnets. It is believed that the relatively low isotropic performance of a magnet produced from a composition containing a conventional thermoplastic polymer, e.g.

nylon-12, is due in part to oxidative deterioration of the magnetic particles at the high processing 18 temperatures which it is necessary to use in the production of the magnets.

Example 12 A composition as used in Example 5 was mixed on a twin roll-mill and extruded following the procedure described in Examples 4 dnd 7 except that the cylindrical shaped magnet which was produced had an external diameter of 16 mm and an internal diameter of 14 mm, and the cylinder was cut into 15 mm lengths.

In a Comparative Example 6 a composition as used in Comparative Example"l was charged to a twin-roll mill b. .f and mixed on the mill at a temperature of 250 0 C. The composition was removed from the mill in the form of a A sheet and the sheet was pulverised to small particles' 15 which were charged to an injection moulding machine.

The die of the injection moulding machine was subjected to a radial magnetic field of 6KOe and the composition was injected into the die to form a cylindrical magnet having a length of 15 mm and external and internal diameters of respectively, 16 mm and 14 mm. The magnetic performance of the magnets was as shown in Table 6.

Table 6 S, Example Magnetic performance Br (Kg) bHc (KOe) (BH) max (MGOe) o 12 6.28 4.49 8.9 Comparative 6 3.34 2.35 2.8 As can be seer from Table 6 the magnet of Comparative Example-'6 had substantially isotropic properties caused, it is believed, by the difficulty of subjecting the composition to a sufficient magnetic field for alignment of the particles when the composition is in the die of the injection moulding machine.

Claims

1. A composition, suitable for use in the production of a shaped article having magnetic properties, which composition comprises a mixture of a solid melt-processable and cross-linkable organic material, a particulate magnetic material, and a polymeric material which is soluble in or dispersable in the organic material when the organic material is in a liquid state.

2. A composition as claimed in claim 1 in which the organic material has a melting point above 25 0 C.

3. A composition as claimed in claim 1 or claim 2 in which the organic material comprises a monomeric material. "t

4. A composition as claimed in claim 1 or claim 2 in which the organic material comprises an organic polymeric material.

A composition as claim 3 in the monomeric material comprises one or more ethylenically unsaturated groups.

6. A composition as claimed ia claim 3 or 5 in which the monomeric material is an adduct of 4, 4' diphenyl methane diisocyanate and hydroxyethyl methacrylate.

7. A composition as claimed in claim 4 in which the polymeric material comprises an epoxy resin.

8. A composition as claimed in claim 4 or 7 in which the epoxy resin comprises epoxidised bisphenol formaldehyde novolak, and phenol formaldehyde novolak as hardener.

9. A composition as claimed in any one of claims 1 to 8 which comprises an additive capable of effecting or assisting cross-linking of the organic material.

A composiktion as claimed in claim 9 in which the organic material comprises one or more ethylenically unsaturated groups and in which the additive is a free-radical generator.

11. A composition as claimed in any one of claims 1 to in which the magnetic material has a particle size in the range 0.5 to 200 microns. ii I 4t ,t 20

12. A composition as claimed in any one of claims 1 to 11 in which the particulate magnetic material comprises an intermetallic compound of at least one rare earth metal and at least one transition metal.

13. A process as claimed in claim 12 in which the transition metal is or comprises Co.

14. A composition as claimed in claim 13 in which the magnetic material has an approximate empirical formula RCo or R 2 Co 17 where R is at least one rare earth metal.

A composition as claimed in any one of claims 12 to 14 in which the rare earth metal is or comprises Sm.

16. A composition as claimed in claim 12 in which the particulate magnetic material comprises an intermetallic compound comprising Nd-B-Fe.

S17. A composition as claimed in any one of claims 1 to 16 which contains at least 80% by weight of particulate magnetic S material.

18. A composition as claimed in any one of claims 1 to 17 in which the composition contains at least 5% by weight of organic material.

19. A composition as claimed in any one of claims 9 to 17 which contains from 0.01 to 2% by weight of additive.

20. A composition as claimed in any one of claims 1 to 19 which contains a polymeric material which is soluble in or dispersible in the organic material when the organic material is in a liquid state.

21. A composition claimed in claim 20 which contain' from 0.5 to 5% by weight of polymeric material. j

22. A composition as claimed in claim 1, substantially as S hereinbefore described with reference to any one of the examples. DATED: 21 June, 1990 PHILLIPS ORMONDE FIZPATRICK Attorneys for: ,1 IMPERIAL CHEMICAL INDUSTR T ES PLC and SEIKO EPSON CORPORATION WDP 4412N