CA2047592C - Bonded rare earth magnet and a process for manufacturing the same - Google Patents
Bonded rare earth magnet and a process for manufacturing the sameInfo
- Publication number
- CA2047592C CA2047592C CA 2047592 CA2047592A CA2047592C CA 2047592 C CA2047592 C CA 2047592C CA 2047592 CA2047592 CA 2047592 CA 2047592 A CA2047592 A CA 2047592A CA 2047592 C CA2047592 C CA 2047592C
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- Prior art keywords
- resin
- powder
- coating
- magnet
- high molecular
- Prior art date
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Classifications
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- H01F1/00—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties
- H01F1/01—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials
- H01F1/03—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity
- H01F1/032—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials
- H01F1/04—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials metals or alloys
- H01F1/047—Alloys characterised by their composition
- H01F1/053—Alloys characterised by their composition containing rare earth metals
- H01F1/055—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5
- H01F1/057—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B
- H01F1/0571—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B in the form of particles, e.g. rapid quenched powders or ribbon flakes
- H01F1/0575—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B in the form of particles, e.g. rapid quenched powders or ribbon flakes pressed, sintered or bonded together
- H01F1/0578—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B in the form of particles, e.g. rapid quenched powders or ribbon flakes pressed, sintered or bonded together bonded together
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- Chemical & Material Sciences (AREA)
- Crystallography & Structural Chemistry (AREA)
- Inorganic Chemistry (AREA)
- Engineering & Computer Science (AREA)
- Power Engineering (AREA)
- Hard Magnetic Materials (AREA)
Abstract
A highly rustproof resin-bonded magnet made by using a specific rustproofing resin for coating the particles of a magnetic powder, bonding them to form a molded body, or coating its surface, or for two or all of those purposes. The specific resin is selected from ones containing groups of atoms having a power of forming a coordinate bond and a reducing action. More specifically, it is (a) a high molecular compound produced by reacting with an epoxy resin one or more of a polyhydric phenol having adjacent hydroxyls, a polyhydric phenolic carboxylic acid having adjacent hydroxyls, an ester of a polyhydric phenol and a polyhydric alcohol having adjacent hydroxyls, and a polycyclic and polyhydric phenol having adjacent hydroxyls, (b) a redox resin as a reduction agent, or (c) a high molecular compound produced by curing a mixture of ascorbic acid, or a derivative thereof, and an epoxy resin.
Description
BONDED RAP~E E~RTH MACNE;T ANI:~ A PROC-ESS FOR MANU~P.CTURIN~ T~IE SAME
BACK~ROU~D O~ THE INVENTIO~ 2 0 4 7 5 9 2 1, Field of the Invention:
This invention relates to a resin-bonded magnet having consisting ~ainly o iron and~an improved level o~ rust-proofne~s, and a proce~s fo~ m~king the ~am~. More par-ticularly, it i8 conce~ned with a re~in-bonded rare earth-iron-~oron (hereinafter referred to as RE-Fe-B) ~agnet and a process for making the ~ame.
BACK~ROU~D O~ THE INVENTIO~ 2 0 4 7 5 9 2 1, Field of the Invention:
This invention relates to a resin-bonded magnet having consisting ~ainly o iron and~an improved level o~ rust-proofne~s, and a proce~s fo~ m~king the ~am~. More par-ticularly, it i8 conce~ned with a re~in-bonded rare earth-iron-~oron (hereinafter referred to as RE-Fe-B) ~agnet and a process for making the ~ame.
2. Description o~ the Prior Art:
It has long been known ~hat there are alloy~ or compound~ con~i~ting mainly o~ iron (l,e " containin~ at least 50 atom ~ o~ iron), and having very hlgh magnetic propertie~, ~in~e i~on is an elemen~ having a higher satur~-tion magnetic flux density ~ room temperature than any other elemen~ does, a~d ~ha~ those Alloys or compound~ can be used for making resin-bonded magnets having very high magnetic properties. Specific example~ of those a~loys or compound~ are Nd2Fel4~, SmFel2 and ~el6N2 w all been ~ecently developed. All of these ~lloys or com-pounds have, however, the drawback of being easily oxidized and getting ru~ty, a~ they contain a high propor~ion of iron. This i~ part~ul~ly the case with RE-Fe-B magne~s for which there ha~ recently been an increasing de~and.
They easily get rusted in a highly humid environment.
Various m~aæures have, therefore, been proposcd for making those m~gnets rustproof, and in~lude the coating of the surface of a resin-~onded RE-Fe-B magnet with an acrylic or epoxy resin (Japanese Patent Applica~ions Laid-Open No~. ~44710/1988 and ~44711/~9~8), and the ~oa~ing thereof with a fluorine-con~Aining resin (Japanese Patent Applica-~ion Laid-~pen No. 1~8221/lg86). ~hey also include electro-deposition on the maynet surface, ~nd the platin~ of th~
magnet surface with ni~kel, or other metal.
All of these mcthodæ are~ howev~r, unsatisf~c~ory from the standpoint of e~onomy o~ corrosion resistance, or both. The ~oatin~ of the magnet surfa~e with a resin ~an be done a~ ~ low cost, but i~ incomplet~ as a rustproof-ing method, sin~e it i~ difficult for any re~in to ~hut offoxygen and water completely. Ele~trodepositi~n is costly.
Metal plating is also costl~, and ~oreover involv~s ever~
likelihood that even a small amount of coating ~olution remaining on the magne~ ~urface may cause corro~ion to propagate over an enlarg~d area~
The u~e of a reducing resin has also ~een proposed.
For example, Japanes~ Patent Appli~ation Laid-Op~n No, 290209/1989 discloæes a ~are earth alloy maynet coated wi~h a film containing an al~ylphenol, or alkyl-polyhydri~ p~enol resin. Thc resin is, however, used only for coat~ng the 2047~92 surface of a ~intered magnet, and c~nnot always be said to be effec~ive as a bondin~ ~e~in or a bonded magnet.
We, the inven~ors o~ this invention, ~ound that a ~pecial re~in which was obtained by polycondensation reaction from ~anni~ acid, phenol and formaldehyde (here-inafter referred to as a "poly~annin resin") was very effective for rustproofing a bonded Nd-Fe-B ~agnet.
As a ~esult of further research, however, ~e have found that bonded magne~s ~ade by using this re~in ~s a binder are not al~ays satisf~ctory in strength, apparently becau~e it is a res~n intended primarily for coating a surface.
Thi~ i~ pa~ticularly the case with a cylindrical magnet having a ~mall wall thicknes~ and a larye bore diameter.
It cracks or chips during handli~g, and hardly can withstand any pra~tical u~c. Thus, we have reached the conclu~ion that this reæin is not suitable a~ a binder, despite l~s excellent ru~tproofing powor.
~ he known ~ethods for improving the corrosion r~sistance o a bonded magnet inciude not only the use of a ruætproofing ~ynthe~ic resin ~s a binder, but also the coatin~ of a ma~ne~ic powder, or the ~urface of a magn~t with a rustproofing synthetic resin. A combination of the~e method:3 Inay be employed for achieving a still hi~her level of rustproofness. However, insofar as none of the 25 resin~ as hereina~ove men~ioned i ~uitable as a binder, 20g7~92 but all of them are used only for ~oating a magnet to render it rustproof, it has b~en necessar~ to employ another resin as a binder. This has been an obstacle to the rea~ization of a simplified manuf~cturing proeess.
SUMMARY O~ T~E INVENTION
U~der these circwms~ances, it is an object of this invention to develop a resin ~hich is very effective for ru~tproofing purposes.and can al80 be used as a binder to make a satisfactorily s~rong bonded ma~net, or a re-Qin which is useful no~ only ~ a binder, ~ut also for coating the powder of ~ magn~t material, or the surfa~e of a magnet, and there~y to provide a bonded ma~n~t w~lich i~ easy to manufacture and yet is excellent in ~orrosion resistance and is ~ufficiently strong fox practical use.
lS It i8 another object of thi~ invention to provide a sim~le proces~ for manufactu.~ing a rustproo~ an~ strong bonded magnet.
A rus~proofing resin i~ used as a binder for making a magnet intended for uso in an environment which i~ not very co~rosive. The magnet is not given any ~ustprooEing surface treatment, but oan be manu~actured at a corr~s~ond-ingly lower cost. On the other hand, a magnet which is intended for use in a corrosive en~;ronment is made from a powde~ coated with a ru~tproofing resin, and bonded with a r~tproofing resin, and is coatcd with a rustproofing re~in to acqui.re a ~till h~gher level of corrosion resistance.
It has occ~rred to us th~t a resin containing a gro~p of atoms having a power of ~o~min~ a ~oordin~tion ~nd a reducing action bond ~or chela~e)~,as a polytannin resin dos~, can probab~y bo used for the purpoæ~ of this in~ention. As a ~esult of further rescar~h, we hav~ found that the hi~h molccular compounds as identif~ed at (a) to (~) below are, ~mong other~, useful for the purpose of this invention:
(a) A high molecular compound produ~ed by reacting with an epoxy re8in one or more of a polyhydric phenol containing adjacent hydroxyl~, a polyhydric phenolic carboxylic acid containin~ ad;a~ent h~droxyls, an ester of a polyhydric phenol and a po}yhydric alcohol containin~ adiacent hydro~yls, and ~ poly-cycli~ a~d polyhydric phenol containing adja~ent hydroxyls (hereinafter referred to a# an ~epoxy resin modified with a polyhydric phenol");
(b) A redox re~ln as ~ r~duc~ion a~ent; ~nd ~c) A hi~h molecula~ compound produced by curing a mixture of ascorbic acid, or a de~ivative thereof, and an epox~ resin.
- In the foregoing and throughout this specification, the term "high molecular" is synonymous with "high molecular weight".
According to a first aspe~t of ~hi~ invention, there is provided a ma~net compos¢d mainly of a powd~r of a magnetic material containing at least 50~ of iron, ~nd .
an epoxy resin modified with polyhydric phenol, or composed mainly of such a powder, such an epoxy resin, and another ordinary resin.
According to a second aspect of this invention, there is provided a process for manufacturing a magnet which comprises coating a powder of a magnetic material containing at least 50~ of iron with an epoxy resin modified with polyhydric phenol, or coating it with a mixture of an epoxy resin modified with polyhydric phenol and another ordinary resin, or coating it with an epoxy resin modified with polyhydric phenol, and thereafter with another ordinary resin to thereby form a doublc resin coating on the magnetic powder surface, and bonding the powder with a synthetic resin as a binder.
According to a third aspect of this invention, there is prouided a process for manufacturing a magnet which comprises bonding a powder of a magnetic material containing at least 5~ of iron with a binder selected from an epoxy resin modified with polylhydric phenol, and a mixture thereof with another ordinary resin.
According to a fourth aspect of this invention, there is provided a process for manufacturing a magnet which comprises bonding a powder of a magnetic material containing at least 50~ of iron with an ordinary resin as a binder to form a body, and coating surface of the body with an epoxy resin modified with polyhydric phenol, or coating it with a mixture thereof with another synthetic X
20~7592 resin, or coating it with an epox~ resin modified with polyhydric phenol, and thereafter wi~h another ordinary rQsin to thereby form a double resin .coating on the body sur~ace~
A~cordin~ to a fi~th aspect of thi~ invention, there is provided a bonded rare earth ~agnet oomp~isin~
a body made ~y bondin~ a powder of a magnetic mate~ial containing at l~ast 50% of iron ~i~h a reducing redox resin used a~ a bindex.
According to a sixth aspec~ o.E thi~ invention, there i6 provided a ~onded rare earth ma~net comp~ising a body made by bonding a powder of a magnetic materlal containing at least 5~% of iron wi~h a binder resin o~tained by c~ring a mixture of a~corbic acid, or a derivative there-of, and an ~poxy resin.
The ~oating of a magneti~ powder wi~h an epoxy resin modifie~ wi~h a polyhydric phenol, or with su~h an epoxy resin and another resin enables the ma~u ~acture of a magnet whi~h is wholly resistant to oxidation and corrosion. The u~e, as ~ binder, of such an epoxy resin, or both ~uch an epoxy resin And another ordina~y resin make~ it possi~le to manufact~re ~ magnet having oxidation and corrosion resi~ance at a low co~t without ~allin~ for any addi~ional ~tep ~ver any relevant p~oces~ known in the art. The use of s~h a binde~ is ~l~o effe~tive ~or making up any defect 2oq7592 . tha~ may exi~t in a film ~ormed on the surface of a bonded or molded body to impart oxid~tion and ~OrroBiOn resistance to it, if any~
~he for~ation of a layer of ~uch an epo~y reæin, or of guch an epox~ ~esin and ano~her resin on the surrace of a molded body i~ an eco~omical way o~ i~parting h~gh oxida~ion and ~orrosion resi~tance to it. The formation of such a ~ayer i~ also effective for mak~ng up any defe~t that may d~velop in a film covering the parti~les of the ~a~netic powder, if any.
Still higher oxi~ation and corrosion resi~tance can be achieved by combining in differen~ ways the coating of ~he magnetic powd~r with such an epoxy re~inj or with such an epoxy xesin and another rcsin, the u~e of su~h an epoxy resin, or s~ch ~n epoxy resin and another resin, as the binder, and ~he coating of the ~olded body with ~u~h an epoxy resin, o~ with such an epoxy resin and another resin.
The ~ame compoun~ can be u~ed for coating ~he ~o magnetic powder, as the binder, and for ~oating the molded body. This enables a grea~ly s~plified manufac~uring proce5s.
Spraying or dipping can, for example, be used for coatin~ the ~urfac:e of ~he molded body ~ith a modified epoxy resin, or a ~ixture thereof with another resin, or for coat- ;
~ ing a film of a modified epoxy resin with another resin.
Spraying, dipping or kneading can, for example, be used for coating the particles of the magnetic powder with an epoxy resin modified with polyhydric phenol, or a mixture thereof with another resin, or for coating a film of an epoxy resin modified with polyhydric phenol on the particles with another resin.
There are two modes when both a modified epoxy resin and another resin are employed:
(I)A mixture of the two resins is used as the binder, or for coating the magnetic powder, or the molded body; and (II)The epoxy resin modified with polyhydric phenol is first used for coating the magnetic powder, or the molded body, and is overcoated with the other resin, whereby a double-layer coating is formed.
When the mode (I) is employed, it is preferable to use the epoxy resin modified with polyhydric phenol in a proportion which is equal to at least 10~ by volume of the other resin. If its proportion is less than lO~ by volume, it is difficult to achieve a satisfactorily high level of oxidation and corrosion resistance. When the mode (II) is employed, it is preferable to form a film of the epoxy resin modified with polyhydric phenol having a thickness of 0.1 to 100 microns. If its thickness is smaller than 0.1 micron, it is impossible to achieve any satisfactory oxidation and corrosion resistance, and if it exceeds 100 microns, ~ the surface of the magnet proper is spaced apart from the outer surface of the film by so large a distance that a reduction in effective magnetic force results in the failure to achieve any satisfactory magnetic properties.
The amount, or total amount of the epoxy resin modified with polyhydric phenol, or the modified epoxy resin and the other resin used for coating the particles of the magnetic powder, or as the binder, is preferably equal to at least 5%
by volume of the magnetic powder. If it is less than 5% by volume it is difficult to obtain any satisfactory oxidation and corrosion resistance, or any practically acceptable magnet strength.
It is possible without departing from the scope of this invention to use a mixture of the epoxy resin modified with polyhydric phenol and another resin having a high film-forming power, high adhesive strength and high mechanical strength as the binder, or for coating the magnetic powder, or the molded body.
Compression, injection, extrusion, or calender molding can, for example, be used for making a molded body from a mixture of the magnetic powder and the binder.
The ordinary resin which may be used for the purpose of this invention in addition to the specific resin having a rustproofing action is selected from among common thermo-plastic or thermosetting resins1or rubbers, depending on the molding and film-forming methods which will be employed.
Specific examples of the thermosetting resins which can be used include phenolic, epoxy, and melamine resins. Examples of the thermoplastic resins include polyamides such as nylon 6 and nylon 12, polyolefins such as polyethylene and polypropylene, polyvinyl chloride, polyesters, and polyphenylene sulfide. It is also possible to use with those resins any ordinary additives including a plasticizer, a lubricant, a heat stabilizer, a flame retardant, and any other modifier.
The following is probably a proper explanation of the reason for the rustproofing action which is exhibited by a high molecular compound produced by reacting with an epoxy resin a polyhydric phenol compound (or a polyhydric phenol) containing a group of atoms having a power of forming a coordinate bond and a reducing action, like a poly- tannin resin.
When an epoxy resin modified with a polyhydric phenol (sometimes referred to simply as a "modified epoxy resin~
which contains a group of atoms having a power of forming a coordinate bond and a reducing action, is used as a binder for a bonded magnet, the hydroxyl groups which it contains react with oxide or oxyhydroxide existing on the surface of the rare earch magnetic material and form a water-insoluble complex compound which covers the surfaces of the magnetic particles and isolates them from my oxygen and water penetrating the binder resin. When a polyhydric phenol compound contain-ing at le~st two adjacent hydroxyl groups is employed,at least two oxygen atoms are a~ailabl~ for bonding th~
compound to ~he su~face o~ the magnetic materldl apparently more strongly than any compound not containin~ ad3acent hydroxyl group~ i~ bonded to it~
It i~ also ~on~idered that by virtue of i~s high reduction action, the polyhydric ~henol com~ound can reduce to stable blac~ ru~t, ~e3O4, a part o~ FeOO}I of which, for example, the red rust o~ iron consist~ malnly, and thercby 1nhih~t ~he spreading of rust~
It is also possible that, in~o~ar ~ a polyhydric phenol compound acts as a radical scavenge~, and as an oxygen molçc~le i8 a kind of radical (or triplet radical), the polyhydric phenol remaining wi~hout formin~ any complex compound as herein~bove men~ioned may scaveng~ any oxygen mol~cule invading the magnet of ~hi~ invention before it reache~ t~e mayncti~ particles. This mech~nis~ delay~
th~ oxidation o~ the ~ac~netlc particles and thcreby prolongs th~ life of the ~onded maynet aocording to this inve~tio~.
Th~ polyhydric phenol compound can be consider~ to exhibit æuch an action, whe~her it may be u~ed for coating the magne~ic powder, as ~he binder, or for coatiny the ~olded body.
~ oreover, as ~he compound has a very high moleo~lar wei~h~, it can bond the magnstic powder so ~trongly a8 ~0 -2047~92 over~ome ~he p~oblem o~ brittlcness which i~ encounter~d when a polytannin r~sin is used, and can thereby make a bond~d magnet h~ving a satisfac~orily high str~ngth for practi~al use.
D~s~ription will now be made of the ~a~e in whi~h (b) a redox resin, or ~c) a high ~olecular compo~nd produced by curing a mixture o~ ascorbic acid, or a deriva~ive there-o~, and an epoxy ~esin i~ used as the ~esin cont~ining a group of a~oms having a power of forming a coo~dinate bond (o~ chelate) ~nd a ~eduolng action.
(b) A redox rnsin a~ a red~ation ~p,~nt:
Exa~ples of the red~ing redox resin~ are polyvinyl polyhydric phenol (where the polyhydric phenol i~ ~ compound having a plurality of hydroxyl gxoups bonded to the benzene lS ring, ~uch as hydroguinone, ~ate~hol, or pyrogallol), a polyhydric phenol-formaldehyde resin, and a polyvinyl thiokol res~n~
(c) ~ high molecular compound produced by curing a mix-ture of ascorbic acid, o~ a derivative thereof, and an epoxy resin:
There i~ no particular limi~tion to the epoxy re~in whi~h ~an be used. ~ is po~ible to Use any known epoxy resin ormed from, fo~ example, bisphenol, phenol, ester, or N-glycidylamine. The mlxing ra~io of the epoxy resin and ascorbic ~id o~ a derivative thereof depends on the Z047~92 epoxy equivalent of the resin and the number of the hydroxyl (-OH) groups which the acid or its derivative contains.
The following is believed to be a proper explanation of the mechanism which causes the redox resin as a reduction agent (b) or the high molecular compound (c) to exhibit a rustproofing action.
The hydroxyl group which the redox resin as a reduction agent contains can form a coordinate bond with a metal ion, and is, therefore, considered to react with a metal oxide or oxyhydroxide (e.g. FeOOH) on the surfaces of the magnetic particles and form a complex (or chelate) compound which is chemically adsorbed to the particle surfaces, whereby the resin is strongly bonded to the magnetic particles. The redox resin as a reduction agent is also considered to inhibit by its reduction nature the oxidation of the magnetic material (i.e. its chemical reaction forming rust). Moreover, as the redox resin as a reduction agent has also a radical scavenging action, and as the oxygen molecule is a kind of radical (or triplet radical), it is considered that the residual hydroxyl or SH
group (which remains without forming any complex compound) scavenges any invading oxygen molecule before it reaches the magnetic particles.
Ascorbic acid has a hydroxyl group capable of forming a complex compound with a metal ion and is reducing, as any reducing redox resin does and is. Therefore, it is 20~7592 ~ assumed that the binder for a bonded magnet which is prepared from a mixture of ascorbic acid and an epoxy resin has the same rustproofing action as that of the redox resin which has hereinabove been described.
DETAILED DESCRIPTION OF THE INVENTION
This invention consists essentially in the use of a specific resin for one or more of the purposes of coating the particles of a magnetic powder, bonding them to make a molded body, and coating the surface of the molded body. The specific resin contains a group of atoms having a power of forming a coordinate bond and a reducing action, like a polytannin resin, and is also useful as a binder for making a bonded magnet which is sufficiently strong for practical use.
According to the first to fourth aspects of the invention, the specific resin is a high molecular compound produced by reacting a polyhydric phenol compound and an epoxy resin. According to the fifth aspect thereof the specific resin is a redox resin as a reduction agent.
According to the sixth aspect thereof, the specific resin is a high molecular compound produced from a mixture of ascorbic acid or a derivative thereof, and an epoxy resin. Each aspect of the invention will now be described in further detail.
The First to Fourth AsPects of the Invention:
According to the first to fourth aspects of this X
204759~`
invention, a high molecular compound which is produccd by reacting an epoxy re~;in wi~h a polyhydric phenol com-pound or compounds i~ used ~or one or more of the purpos~s of coating the pa~ticles of a ma~ne~ic powder, bonding them ~o makc a molded ~ody, and coating the ~rface of the molded body. The polyhydric ph~nol co~pound or com-pounds are selec~e~ from a~ong a ~olyhydric phenol having aai~cen~ hydroxyl group6, polyhydric phenolic carboxylia acid having adjacent hydroxyl groups, an ester of a poly-hydric phenol and a polyhydric alcohol having ad~acent hydroxyl groups, ~nd a polycyclic and pol~hyd.ric ph~nol h~vin~ adjacent hydroxyl groups, and are similar to a poly-tannin re~in, insoFar as they contain groups havin~ a power of forming a coordina~e bond and a r~duc~ng action.
The following are specific example~ of the poly-hydric phenols and compounds which can be employed;
(1) Pol~hydric Phenol~:
Cstechol, pyrogallol, a~d hydroxyhydroquinone:
(2) Polyhydric Phenolic Carboxylic Acids:
G~llic acid, cate~hol-3- carboxylic acid, catechol-4-carboxyl.ic acid, m-digallic acid, pyrogallol-4-carboxy~ic acid, pyrogallol-4 6-dicarboxylic acid, and tannic acidt (3) Esters of Polyhydri¢ Phenols and Pol~hyd~ic Alcohol~:
E~ters for~ed f~o~ any ¢o~binat~on of the p~lyhydric 204~9~
phenolic ~arboxylic acids as listed ~t (2) above, and the al~ohol-~ as listed below;
Ethylene glycol, propyle~e glycol, butylene glycol, 1.6-hexanediol, glycerol, trinlethylo}propane, pen~aerythritol, sor~ltol, and glucose~
It has long been known ~hat there are alloy~ or compound~ con~i~ting mainly o~ iron (l,e " containin~ at least 50 atom ~ o~ iron), and having very hlgh magnetic propertie~, ~in~e i~on is an elemen~ having a higher satur~-tion magnetic flux density ~ room temperature than any other elemen~ does, a~d ~ha~ those Alloys or compound~ can be used for making resin-bonded magnets having very high magnetic properties. Specific example~ of those a~loys or compound~ are Nd2Fel4~, SmFel2 and ~el6N2 w all been ~ecently developed. All of these ~lloys or com-pounds have, however, the drawback of being easily oxidized and getting ru~ty, a~ they contain a high propor~ion of iron. This i~ part~ul~ly the case with RE-Fe-B magne~s for which there ha~ recently been an increasing de~and.
They easily get rusted in a highly humid environment.
Various m~aæures have, therefore, been proposcd for making those m~gnets rustproof, and in~lude the coating of the surface of a resin-~onded RE-Fe-B magnet with an acrylic or epoxy resin (Japanese Patent Applica~ions Laid-Open No~. ~44710/1988 and ~44711/~9~8), and the ~oa~ing thereof with a fluorine-con~Aining resin (Japanese Patent Applica-~ion Laid-~pen No. 1~8221/lg86). ~hey also include electro-deposition on the maynet surface, ~nd the platin~ of th~
magnet surface with ni~kel, or other metal.
All of these mcthodæ are~ howev~r, unsatisf~c~ory from the standpoint of e~onomy o~ corrosion resistance, or both. The ~oatin~ of the magnet surfa~e with a resin ~an be done a~ ~ low cost, but i~ incomplet~ as a rustproof-ing method, sin~e it i~ difficult for any re~in to ~hut offoxygen and water completely. Ele~trodepositi~n is costly.
Metal plating is also costl~, and ~oreover involv~s ever~
likelihood that even a small amount of coating ~olution remaining on the magne~ ~urface may cause corro~ion to propagate over an enlarg~d area~
The u~e of a reducing resin has also ~een proposed.
For example, Japanes~ Patent Appli~ation Laid-Op~n No, 290209/1989 discloæes a ~are earth alloy maynet coated wi~h a film containing an al~ylphenol, or alkyl-polyhydri~ p~enol resin. Thc resin is, however, used only for coat~ng the 2047~92 surface of a ~intered magnet, and c~nnot always be said to be effec~ive as a bondin~ ~e~in or a bonded magnet.
We, the inven~ors o~ this invention, ~ound that a ~pecial re~in which was obtained by polycondensation reaction from ~anni~ acid, phenol and formaldehyde (here-inafter referred to as a "poly~annin resin") was very effective for rustproofing a bonded Nd-Fe-B ~agnet.
As a ~esult of further research, however, ~e have found that bonded magne~s ~ade by using this re~in ~s a binder are not al~ays satisf~ctory in strength, apparently becau~e it is a res~n intended primarily for coating a surface.
Thi~ i~ pa~ticularly the case with a cylindrical magnet having a ~mall wall thicknes~ and a larye bore diameter.
It cracks or chips during handli~g, and hardly can withstand any pra~tical u~c. Thus, we have reached the conclu~ion that this reæin is not suitable a~ a binder, despite l~s excellent ru~tproofing powor.
~ he known ~ethods for improving the corrosion r~sistance o a bonded magnet inciude not only the use of a ruætproofing ~ynthe~ic resin ~s a binder, but also the coatin~ of a ma~ne~ic powder, or the ~urface of a magn~t with a rustproofing synthetic resin. A combination of the~e method:3 Inay be employed for achieving a still hi~her level of rustproofness. However, insofar as none of the 25 resin~ as hereina~ove men~ioned i ~uitable as a binder, 20g7~92 but all of them are used only for ~oating a magnet to render it rustproof, it has b~en necessar~ to employ another resin as a binder. This has been an obstacle to the rea~ization of a simplified manuf~cturing proeess.
SUMMARY O~ T~E INVENTION
U~der these circwms~ances, it is an object of this invention to develop a resin ~hich is very effective for ru~tproofing purposes.and can al80 be used as a binder to make a satisfactorily s~rong bonded ma~net, or a re-Qin which is useful no~ only ~ a binder, ~ut also for coating the powder of ~ magn~t material, or the surfa~e of a magnet, and there~y to provide a bonded ma~n~t w~lich i~ easy to manufacture and yet is excellent in ~orrosion resistance and is ~ufficiently strong fox practical use.
lS It i8 another object of thi~ invention to provide a sim~le proces~ for manufactu.~ing a rustproo~ an~ strong bonded magnet.
A rus~proofing resin i~ used as a binder for making a magnet intended for uso in an environment which i~ not very co~rosive. The magnet is not given any ~ustprooEing surface treatment, but oan be manu~actured at a corr~s~ond-ingly lower cost. On the other hand, a magnet which is intended for use in a corrosive en~;ronment is made from a powde~ coated with a ru~tproofing resin, and bonded with a r~tproofing resin, and is coatcd with a rustproofing re~in to acqui.re a ~till h~gher level of corrosion resistance.
It has occ~rred to us th~t a resin containing a gro~p of atoms having a power of ~o~min~ a ~oordin~tion ~nd a reducing action bond ~or chela~e)~,as a polytannin resin dos~, can probab~y bo used for the purpoæ~ of this in~ention. As a ~esult of further rescar~h, we hav~ found that the hi~h molccular compounds as identif~ed at (a) to (~) below are, ~mong other~, useful for the purpose of this invention:
(a) A high molecular compound produ~ed by reacting with an epoxy re8in one or more of a polyhydric phenol containing adjacent hydroxyl~, a polyhydric phenolic carboxylic acid containin~ ad;a~ent h~droxyls, an ester of a polyhydric phenol and a po}yhydric alcohol containin~ adiacent hydro~yls, and ~ poly-cycli~ a~d polyhydric phenol containing adja~ent hydroxyls (hereinafter referred to a# an ~epoxy resin modified with a polyhydric phenol");
(b) A redox re~ln as ~ r~duc~ion a~ent; ~nd ~c) A hi~h molecula~ compound produced by curing a mixture of ascorbic acid, or a de~ivative thereof, and an epox~ resin.
- In the foregoing and throughout this specification, the term "high molecular" is synonymous with "high molecular weight".
According to a first aspe~t of ~hi~ invention, there is provided a ma~net compos¢d mainly of a powd~r of a magnetic material containing at least 50~ of iron, ~nd .
an epoxy resin modified with polyhydric phenol, or composed mainly of such a powder, such an epoxy resin, and another ordinary resin.
According to a second aspect of this invention, there is provided a process for manufacturing a magnet which comprises coating a powder of a magnetic material containing at least 50~ of iron with an epoxy resin modified with polyhydric phenol, or coating it with a mixture of an epoxy resin modified with polyhydric phenol and another ordinary resin, or coating it with an epoxy resin modified with polyhydric phenol, and thereafter with another ordinary resin to thereby form a doublc resin coating on the magnetic powder surface, and bonding the powder with a synthetic resin as a binder.
According to a third aspect of this invention, there is prouided a process for manufacturing a magnet which comprises bonding a powder of a magnetic material containing at least 5~ of iron with a binder selected from an epoxy resin modified with polylhydric phenol, and a mixture thereof with another ordinary resin.
According to a fourth aspect of this invention, there is provided a process for manufacturing a magnet which comprises bonding a powder of a magnetic material containing at least 50~ of iron with an ordinary resin as a binder to form a body, and coating surface of the body with an epoxy resin modified with polyhydric phenol, or coating it with a mixture thereof with another synthetic X
20~7592 resin, or coating it with an epox~ resin modified with polyhydric phenol, and thereafter wi~h another ordinary rQsin to thereby form a double resin .coating on the body sur~ace~
A~cordin~ to a fi~th aspect of thi~ invention, there is provided a bonded rare earth ~agnet oomp~isin~
a body made ~y bondin~ a powder of a magnetic mate~ial containing at l~ast 50% of iron ~i~h a reducing redox resin used a~ a bindex.
According to a sixth aspec~ o.E thi~ invention, there i6 provided a ~onded rare earth ma~net comp~ising a body made by bonding a powder of a magnetic materlal containing at least 5~% of iron wi~h a binder resin o~tained by c~ring a mixture of a~corbic acid, or a derivative there-of, and an ~poxy resin.
The ~oating of a magneti~ powder wi~h an epoxy resin modifie~ wi~h a polyhydric phenol, or with su~h an epoxy resin and another resin enables the ma~u ~acture of a magnet whi~h is wholly resistant to oxidation and corrosion. The u~e, as ~ binder, of such an epoxy resin, or both ~uch an epoxy resin And another ordina~y resin make~ it possi~le to manufact~re ~ magnet having oxidation and corrosion resi~ance at a low co~t without ~allin~ for any addi~ional ~tep ~ver any relevant p~oces~ known in the art. The use of s~h a binde~ is ~l~o effe~tive ~or making up any defect 2oq7592 . tha~ may exi~t in a film ~ormed on the surface of a bonded or molded body to impart oxid~tion and ~OrroBiOn resistance to it, if any~
~he for~ation of a layer of ~uch an epo~y reæin, or of guch an epox~ ~esin and ano~her resin on the surrace of a molded body i~ an eco~omical way o~ i~parting h~gh oxida~ion and ~orrosion resi~tance to it. The formation of such a ~ayer i~ also effective for mak~ng up any defe~t that may d~velop in a film covering the parti~les of the ~a~netic powder, if any.
Still higher oxi~ation and corrosion resi~tance can be achieved by combining in differen~ ways the coating of ~he magnetic powd~r with such an epoxy re~inj or with such an epoxy xesin and another rcsin, the u~e of su~h an epoxy resin, or s~ch ~n epoxy resin and another resin, as the binder, and ~he coating of the ~olded body with ~u~h an epoxy resin, o~ with such an epoxy resin and another resin.
The ~ame compoun~ can be u~ed for coating ~he ~o magnetic powder, as the binder, and for ~oating the molded body. This enables a grea~ly s~plified manufac~uring proce5s.
Spraying or dipping can, for example, be used for coatin~ the ~urfac:e of ~he molded body ~ith a modified epoxy resin, or a ~ixture thereof with another resin, or for coat- ;
~ ing a film of a modified epoxy resin with another resin.
Spraying, dipping or kneading can, for example, be used for coating the particles of the magnetic powder with an epoxy resin modified with polyhydric phenol, or a mixture thereof with another resin, or for coating a film of an epoxy resin modified with polyhydric phenol on the particles with another resin.
There are two modes when both a modified epoxy resin and another resin are employed:
(I)A mixture of the two resins is used as the binder, or for coating the magnetic powder, or the molded body; and (II)The epoxy resin modified with polyhydric phenol is first used for coating the magnetic powder, or the molded body, and is overcoated with the other resin, whereby a double-layer coating is formed.
When the mode (I) is employed, it is preferable to use the epoxy resin modified with polyhydric phenol in a proportion which is equal to at least 10~ by volume of the other resin. If its proportion is less than lO~ by volume, it is difficult to achieve a satisfactorily high level of oxidation and corrosion resistance. When the mode (II) is employed, it is preferable to form a film of the epoxy resin modified with polyhydric phenol having a thickness of 0.1 to 100 microns. If its thickness is smaller than 0.1 micron, it is impossible to achieve any satisfactory oxidation and corrosion resistance, and if it exceeds 100 microns, ~ the surface of the magnet proper is spaced apart from the outer surface of the film by so large a distance that a reduction in effective magnetic force results in the failure to achieve any satisfactory magnetic properties.
The amount, or total amount of the epoxy resin modified with polyhydric phenol, or the modified epoxy resin and the other resin used for coating the particles of the magnetic powder, or as the binder, is preferably equal to at least 5%
by volume of the magnetic powder. If it is less than 5% by volume it is difficult to obtain any satisfactory oxidation and corrosion resistance, or any practically acceptable magnet strength.
It is possible without departing from the scope of this invention to use a mixture of the epoxy resin modified with polyhydric phenol and another resin having a high film-forming power, high adhesive strength and high mechanical strength as the binder, or for coating the magnetic powder, or the molded body.
Compression, injection, extrusion, or calender molding can, for example, be used for making a molded body from a mixture of the magnetic powder and the binder.
The ordinary resin which may be used for the purpose of this invention in addition to the specific resin having a rustproofing action is selected from among common thermo-plastic or thermosetting resins1or rubbers, depending on the molding and film-forming methods which will be employed.
Specific examples of the thermosetting resins which can be used include phenolic, epoxy, and melamine resins. Examples of the thermoplastic resins include polyamides such as nylon 6 and nylon 12, polyolefins such as polyethylene and polypropylene, polyvinyl chloride, polyesters, and polyphenylene sulfide. It is also possible to use with those resins any ordinary additives including a plasticizer, a lubricant, a heat stabilizer, a flame retardant, and any other modifier.
The following is probably a proper explanation of the reason for the rustproofing action which is exhibited by a high molecular compound produced by reacting with an epoxy resin a polyhydric phenol compound (or a polyhydric phenol) containing a group of atoms having a power of forming a coordinate bond and a reducing action, like a poly- tannin resin.
When an epoxy resin modified with a polyhydric phenol (sometimes referred to simply as a "modified epoxy resin~
which contains a group of atoms having a power of forming a coordinate bond and a reducing action, is used as a binder for a bonded magnet, the hydroxyl groups which it contains react with oxide or oxyhydroxide existing on the surface of the rare earch magnetic material and form a water-insoluble complex compound which covers the surfaces of the magnetic particles and isolates them from my oxygen and water penetrating the binder resin. When a polyhydric phenol compound contain-ing at le~st two adjacent hydroxyl groups is employed,at least two oxygen atoms are a~ailabl~ for bonding th~
compound to ~he su~face o~ the magnetic materldl apparently more strongly than any compound not containin~ ad3acent hydroxyl group~ i~ bonded to it~
It i~ also ~on~idered that by virtue of i~s high reduction action, the polyhydric ~henol com~ound can reduce to stable blac~ ru~t, ~e3O4, a part o~ FeOO}I of which, for example, the red rust o~ iron consist~ malnly, and thercby 1nhih~t ~he spreading of rust~
It is also possible that, in~o~ar ~ a polyhydric phenol compound acts as a radical scavenge~, and as an oxygen molçc~le i8 a kind of radical (or triplet radical), the polyhydric phenol remaining wi~hout formin~ any complex compound as herein~bove men~ioned may scaveng~ any oxygen mol~cule invading the magnet of ~hi~ invention before it reache~ t~e mayncti~ particles. This mech~nis~ delay~
th~ oxidation o~ the ~ac~netlc particles and thcreby prolongs th~ life of the ~onded maynet aocording to this inve~tio~.
Th~ polyhydric phenol compound can be consider~ to exhibit æuch an action, whe~her it may be u~ed for coating the magne~ic powder, as ~he binder, or for coatiny the ~olded body.
~ oreover, as ~he compound has a very high moleo~lar wei~h~, it can bond the magnstic powder so ~trongly a8 ~0 -2047~92 over~ome ~he p~oblem o~ brittlcness which i~ encounter~d when a polytannin r~sin is used, and can thereby make a bond~d magnet h~ving a satisfac~orily high str~ngth for practi~al use.
D~s~ription will now be made of the ~a~e in whi~h (b) a redox resin, or ~c) a high ~olecular compo~nd produced by curing a mixture o~ ascorbic acid, or a deriva~ive there-o~, and an epoxy ~esin i~ used as the ~esin cont~ining a group of a~oms having a power of forming a coo~dinate bond (o~ chelate) ~nd a ~eduolng action.
(b) A redox rnsin a~ a red~ation ~p,~nt:
Exa~ples of the red~ing redox resin~ are polyvinyl polyhydric phenol (where the polyhydric phenol i~ ~ compound having a plurality of hydroxyl gxoups bonded to the benzene lS ring, ~uch as hydroguinone, ~ate~hol, or pyrogallol), a polyhydric phenol-formaldehyde resin, and a polyvinyl thiokol res~n~
(c) ~ high molecular compound produced by curing a mix-ture of ascorbic acid, o~ a derivative thereof, and an epoxy resin:
There i~ no particular limi~tion to the epoxy re~in whi~h ~an be used. ~ is po~ible to Use any known epoxy resin ormed from, fo~ example, bisphenol, phenol, ester, or N-glycidylamine. The mlxing ra~io of the epoxy resin and ascorbic ~id o~ a derivative thereof depends on the Z047~92 epoxy equivalent of the resin and the number of the hydroxyl (-OH) groups which the acid or its derivative contains.
The following is believed to be a proper explanation of the mechanism which causes the redox resin as a reduction agent (b) or the high molecular compound (c) to exhibit a rustproofing action.
The hydroxyl group which the redox resin as a reduction agent contains can form a coordinate bond with a metal ion, and is, therefore, considered to react with a metal oxide or oxyhydroxide (e.g. FeOOH) on the surfaces of the magnetic particles and form a complex (or chelate) compound which is chemically adsorbed to the particle surfaces, whereby the resin is strongly bonded to the magnetic particles. The redox resin as a reduction agent is also considered to inhibit by its reduction nature the oxidation of the magnetic material (i.e. its chemical reaction forming rust). Moreover, as the redox resin as a reduction agent has also a radical scavenging action, and as the oxygen molecule is a kind of radical (or triplet radical), it is considered that the residual hydroxyl or SH
group (which remains without forming any complex compound) scavenges any invading oxygen molecule before it reaches the magnetic particles.
Ascorbic acid has a hydroxyl group capable of forming a complex compound with a metal ion and is reducing, as any reducing redox resin does and is. Therefore, it is 20~7592 ~ assumed that the binder for a bonded magnet which is prepared from a mixture of ascorbic acid and an epoxy resin has the same rustproofing action as that of the redox resin which has hereinabove been described.
DETAILED DESCRIPTION OF THE INVENTION
This invention consists essentially in the use of a specific resin for one or more of the purposes of coating the particles of a magnetic powder, bonding them to make a molded body, and coating the surface of the molded body. The specific resin contains a group of atoms having a power of forming a coordinate bond and a reducing action, like a polytannin resin, and is also useful as a binder for making a bonded magnet which is sufficiently strong for practical use.
According to the first to fourth aspects of the invention, the specific resin is a high molecular compound produced by reacting a polyhydric phenol compound and an epoxy resin. According to the fifth aspect thereof the specific resin is a redox resin as a reduction agent.
According to the sixth aspect thereof, the specific resin is a high molecular compound produced from a mixture of ascorbic acid or a derivative thereof, and an epoxy resin. Each aspect of the invention will now be described in further detail.
The First to Fourth AsPects of the Invention:
According to the first to fourth aspects of this X
204759~`
invention, a high molecular compound which is produccd by reacting an epoxy re~;in wi~h a polyhydric phenol com-pound or compounds i~ used ~or one or more of the purpos~s of coating the pa~ticles of a ma~ne~ic powder, bonding them ~o makc a molded ~ody, and coating the ~rface of the molded body. The polyhydric ph~nol co~pound or com-pounds are selec~e~ from a~ong a ~olyhydric phenol having aai~cen~ hydroxyl group6, polyhydric phenolic carboxylia acid having adjacent hydroxyl groups, an ester of a poly-hydric phenol and a polyhydric alcohol having ad~acent hydroxyl groups, ~nd a polycyclic and pol~hyd.ric ph~nol h~vin~ adjacent hydroxyl groups, and are similar to a poly-tannin re~in, insoFar as they contain groups havin~ a power of forming a coordina~e bond and a r~duc~ng action.
The following are specific example~ of the poly-hydric phenols and compounds which can be employed;
(1) Pol~hydric Phenol~:
Cstechol, pyrogallol, a~d hydroxyhydroquinone:
(2) Polyhydric Phenolic Carboxylic Acids:
G~llic acid, cate~hol-3- carboxylic acid, catechol-4-carboxyl.ic acid, m-digallic acid, pyrogallol-4-carboxy~ic acid, pyrogallol-4 6-dicarboxylic acid, and tannic acidt (3) Esters of Polyhydri¢ Phenols and Pol~hyd~ic Alcohol~:
E~ters for~ed f~o~ any ¢o~binat~on of the p~lyhydric 204~9~
phenolic ~arboxylic acids as listed ~t (2) above, and the al~ohol-~ as listed below;
Ethylene glycol, propyle~e glycol, butylene glycol, 1.6-hexanediol, glycerol, trinlethylo}propane, pen~aerythritol, sor~ltol, and glucose~
(4) Poly~ycli~ and Polyhydric ~henols:
Product~ fo~med by condensation reac~ions fro~
aldehydes and ~ompounds ~s listed below:
Catechol, catechol-3 (o~ 4 ) -carboxylia acid (or an ester thereof), pyrogallol, hydroxyhydroquinone, pyrogallol-4-carboxylic acid ~or an ester the~eof), pyr~gallol-4.~-dicarboxylic acid (or an estex the~e-of), 3~4~5-trioxybe~oic acid (or An e~ter ther2- .
of ~, tannic acid ~or an eæ~er thereof), ~nd urushiol, Specific exa~ples o~ the polyhydric phenol com-pound~ as mentioned at ~4) above include ~he condensation produc~ of pyrogallol or hydroxyhydro~uinone, and aro~atic aldeh~des, as dls~losed in ~apanese Pa~ent Appli~ation L~id-Open No. 54317/1980, and the ~ondensation p~oducts of pyro-gallol and aldehydes ~formaldehyde, d~cylaldehyde, benz-aldehyde, etc.), as disclosed i~ Ja~ancse Pa~ent Appl~catlon Laid-Open No. 130642/1978.
There i~ no particular li~ita~ion ~o the epoxy resin wh.ich can be used for the purpose of t~is invention.
I~ is possl~le ~o ~se any kno~n epoxy resin formed ~rom 20~7~92 bisphenol, pheno~, ester, N~glycidyl~mine, or the like.
The mixing ratio of the epoxy resin and th~ polyhydri~
phenol compound ~or compound~) depends on the epoxy equiva-len~ oE the resin and the number of hydroxyl groups ~hlch the polyhy~rlc phenol compound contains.
A magnetic powder containing at leas~ S0 atom ~
of iron is used for th~ purpose o~ this invention. More specifically, it is, for example, a powder of an alloy which is generally callcd a Nd-~e-B alloy, ~uch ~s RE 2Fel4~, ox another alloy ~urther containing a~other element ~e.~., another rare earth elelnent such as Pr or Dy, another 3d t~ansition element such as Co o~ v, or Al, Ga, or Nb), a powdcr of a compound obtained by adding anothcr element or elements (e.g., Al, Si, Ti, Co, V, Cr and Mo) to SmFe12 1~ having a crystal str~ctu~e of the ThMnl~ type, or a powder of ~el6~2 consisting of needle crystals providing anisotropy.
The powder of a N~-~e-B ~lloy is, ~nong other~, preferred f~om a practical standpoint, as i~ exhi~its higher magnetic proper~ies ~han any other presen~ly known maynetic material does.
The bonded magnet o~ this invention preferably ct~ntain~ 70~h to 95% by volumc o~ ma~netiC powdc~. A magnet containing less th~n 70~ by volume of magnetic pow~er has too low magnetic properties to be useful for a wide range 2S o~ purposes. A magne~ containing over 95~ by volume of 20~75g2 ma~netic po~dcr ~ontains too small a propoxtion of binder, and is, therefore, too brittlc to wi~hstand practical u~e.
The invention ~ill now b~ described more speci-~ically wit:h rereren¢e to ex~mples. Althou~h ~11 of these examples are dir¢c:ted ~o bondcd RE-Fe-s alloy ma~net~ whi~h theoretically con~ain 80% by volume o~ magnetic powder, it i~ to be understood that they ~re merely illustra~ive of this invention, and are not intended for limiting the ~copc of thi 8 inven~ion .
1~ EXAMPLI~ 1 A hi~h mol~cula~ compound produced ~y reac~ing tannic acid and an epoxy resin was used a~ a binder ~
A ~ethanol~ golution contain.ing 1.0Q g of ~annic acid, C6H2(OH)3-CO-O-C~(OII)2COOH, which is a polyhydri¢
phenolic carboxylic a~id having a molecular ~cight of 306, was mi~ed with ~ ~e~hyl-ethyl-ketone (MEK) sol~tion contain-ing 9.S3 g of "~pikotc 1007", which i~ a ~olit~ epoxy rc~in of Yuka-Shell Company h~ving a molecular weight of about 2~00 and.an epoxy e~uivalent of 160~ to l~00, and prod~ced by using bisphenol, 2~7 g of a NdFeB powder prepared by ultrarapid quonching tGeneral ~otors ' product, MQ-B) was put in the mixed ~olution, and was mixed wi~h i~ careful~y.
Substanti~lly all of the solvent~ wcrc rcmovcd by vaporiza-tion to yield a substantially dry compound. Th~ compound `~ 2047~92 was put in a mold, and pre~s molded at a pressure of 6 tjcm2 to form a green molded ~ody. The molded body wa~ cured in an oven having a temperature o~ 160C for ~hree hour~ to yield a bonded magnet approximately meaæur-ing 10 mm in diame~er by 10 mm long, and s~ill remaining unmagn~tized .
Ten ma~net~ wcre prepa~ed. They w~r~ put ir an en~iron~ental tester havin~ a temperature of 60C ~nd a humidi~y of ~0%. After e~ery 100 ho~s, they were taken ou~ of the ~e~ter and the surrac~ of each ~ample was examined with tho naked eye and th~ough an optical ~icroscope having a magniflcation of 30. The s~mple~ were p~t back in the te~t~r immediately after examination. This test wa~ con-tinued untll ~he samples had been left to stand in the te~er lS for a total period of 500 hourq.
EXA~PLE 2 A ~igh molecula~ co~pound produ~ed by reactin~
g~llic acid and an epox~ r~sln was u:3ed a~ a binder.
A methanol ~olution containing 1~00 g of gallic a~id, ~H2~OH)3COOH, which i~ a polyhydric phenolic ~arboxylic acid having a molecular wei~ht of 170, was mixed with a MEK
solu~ion containing ~ . 5~ g of "Epikote 1007 " under ~tirring, and 248 g of M~-B w~ put in the mixed solution, and mix~d with i~ carQf~lly. Thereafter, EXAM~LE 1 was repea~ed for 20~7592 preparing magnets each mcrsuring 10 mm in diamcter by 10 mm long, and conducting 500 ~ours of an environmental test.
EXA~PLE 3 S A high mole~lar compound produced ~y reac~ing a polycyclic and polyhydric phenol And an epoxy resin was used as a binder.
~ compo~nd having the $tructural formula ~hown below, which is a poly~ycli¢ and polyhydric phenol having a molecular wcight of ~40, was synthesized by the process of Exam~le 4 in Japanese Patent Application Laid-Open No.
30642/lg78 OH
HO~CH ~
HO~ CgH19 ~OII
An ac~tone solution ¢on~ainin~ 1.00 g of the above compound ~as mixed wi~h a ME~ solution containing 8.50 g o~ "Epikote 1007", and 240 g of M~-B wa~ put in the mixed solution, and mixed with it carefully. Thereaftex, EX~MPLE
1 was repeated for preparing magnets each measuxing 10 ~m in diameter by 10 mm long, and conducting S00 hours of an environmental test.
20~7592 EX~M~LE 4 A h~gh molecul~r compoun~ produced by reacting a polycy~lic and polyhydric phenol and an epoxy resin was used as a binder.
S ~ compound ha~ing the ~truct~ral formula shown below, ~ ich i s a polycyc:lic and polyhydric phenol having a molecular weight of 340, ~s syn~hesized ~y the process of Example ~ ln J~panese Patent ~pplication Laid-O~en No.
54317/19~0; OH o~ HO OH
0 HO~/ H \~OH
An acetone ~olution ~ontaining 1. ~ ~ of the abo~le co~pound was mixed with a ME~ solu~ion ~ontainin~ 8.50 g of "Epi~co~e 10û7", and 240 q oE MQ-B wa~ put in the mixed solution, and mixed with it carefully. The~eaf~er, EXAM~IIE
~0 1 ~as repe~ted for preparing magnets each mea~uring 10 mm in diameter by 10 ~m long, and conducting 5~0 hou~ of an en~ironmen~al test.
~OMPARAT~VE EXAMPLE 1 An ~rdinary resin was used as a binde~. !
A me~hanol and toluene solution ~ontaining 0.50 g of dicyandia~nide, which i~ a common curing agent, w~s mixed i- 2047~92 with a ME~ solut~on containing 9.50 ~ of "Epikote 1007", and 253 g of MQ-B was put in the mixed solution, and ~ixed uniformly with i~. Thereafter, EXAMPLE 1 w~s rep~ated for pre~aring magn¢ts each m~asuring 10 mm in diameter by S 10 mm long, and condu~ting 500 ho~rs of an en~ironmental test.
An ordinary resin was u~ed as a binder ~or ~kiny molded bodies, ~nd their surf~ces wer~ ~oated with a polytannin resin.
COM~ARATIVE EXAM~LE 1 was repeated for ~oldiny magnet~. They wore dipped in a MEK solu~ion cont~in~ nq lS~ b~ weight of a polytannin re~in. Then, the solvent was removed by ~aporization, and the resin w~s cured by lS heating at lS0~ for }5 minutes, whereby thc surface of each ma~nQt wa~ coa~ed with a film of the polytannln re~in.
ThQ magnets were dippcd in a lN ~ol~tion of sulfuri~ acid, and left to st~nd for a period of about 30 seconds, but only a trac~ of hydrogen gas was produ~ed. Thus, it was con-finmed that the film ~.~ith which each magnet had been coated was su~stantially frec of any pinhole defect. Thereafter, EXAMPLE 1 was repeated for conducting 500 hours of an en-v~ron~en~l test to see if any ~us~ would form on the mag-nets.
TABLE 1 3hows the resu~t~ of the tests whlch were obtained in EXA~IPLES 1 tt: 4 and ~OMPA~ATIVE EXA~LES 1 and 2, Each syrnbol ha~ the rneaning as defined below.
TABLE 1 ~e~ults of the environmental te8ts at 60C and 9096 humidity.
Tes~ period (hours) Samples 100 200 300 400 5~0 EXA~qPLE 1 EXAMP~E 2 EXAMPLE 3 ~ ~ ~ O
lo EXAMPLE 4 ~ ~ ~ O A
CO~PARATIVE O ~ x x x x x EX~MPLE 1 COMPARAT~VE
(~) : No ru~ting was found to have o~c~lrred;
o : ~ots of ruæt were detec~ed:
~: A medium dcgrec of r-~sting was found to ha~e rred:
x: ~Ie~vy xusting: :
xx: very heavy ru~ing (rust wa~ found to cover the whole ~urEac~ of the sample, and was ~learly visible to the na3ced eye).
~ is obvious ~rom TABI,~ 1, no ru$~in~ occurred for a total of 300 hours to any of the bonded magnet~ accoxding to EX~P~F,S 1 to 4 that had b~cn madQ by u~ing a modified epoxy resin a5 the binder, and it was only when they were 20~7592 exa~ined a~ter a total of 400 hours that so~e spots of rust w~r~ detected on the magnets. Thes~ rs~ults ~on-firm ~he excellen~ ru~tprooness of the ~agne~s accordiny to thig invention. ~he ma~nets of thi~ inven~ion were by far superior in oxidation ~esistance to the conventional magnets according to COMrA~ATIVE EXA~PLE 1 whi~h had been made by ~sing an ordinary resin a~ the binder, tho~t3h they were inferior to the product~ of COMPARATIV~ EXA~PLE 2 having a surface coated with a pol~tannin r~sin. It is, there~ore, obvious that the magnet of this lnvention made by ~æing a modified epoxy re~in as the binder i8 very effective for u5e in any of a wide variety of usual cases in which no extremely high level of ru~tproofnes~ is required o~ the magnet. Moreover, the use of a rustproofing resin as the binder enables a reduc~ion in t~e cost of man~fac-turing the ma(~net of this invcntion, since the molded body docs not call ~or any ru~tproofin~ ~urfa~e treatment ~uch as coating with a ru~ inhibi~ive a~ent.
EXAMP~E g A modified epoxy resin was u~ed ~s a ~inder to form molded bodies, and their surfaces we~e coated with a polytannin re~in.
EXAMPLES 1 to 4 were repe~ted for making bonded magnets and COMPARATIVE EXAMPLE ~ was repea~ed for coating each ~a~net with a polytannin ~esin. ~hese ~a~ne~s will 2047~92 herein~tcr be r~fer~ed to as Samples S-l, 5-~, 5-3 and 5-4, respec~ively. Sam~les 5-l mean th~ magnets which were mad~ by repeating EX~PLE l, and coa~ed with the polytannin reæin, and so on. CO~lPARATIV~ EXA~P~ 2 was also repe~ted ~or makin~ samples coated with the polytannin resin. ~11 of these ~amples we~e lef~ to stand in ~
seve~er environmen~ having a ~emperature of 60C and a hunidity o 95% for a ~o~al of 600 hours. ~h~ results of ~bis environmental t~st are sho~n in ~ABLE 2, i~ which each ~ymbol me~ns wha~ ~he cor~espond~ng s~mbol in TABLE
1 does, as deined above.
TABLE 2 ~esul~s o~ the environmeta~ test a~ 60~C ~nd 95~ humidi~y.
T~st p~riod (hours) ~5 Samples 100 ~00 400 500 600 5~ O
5-Z ~ ~ ~ ~ O
5-3 ~ O
5-4 ~ O
20 CO~PAR~TIVE ~ ~ O ~ X
:EX~MPLE ~
~ s is obvious f~om TAB~E 2, all of Samples 5-l to 5-4 of ~his i~ve~tion could wi~h~tand exposure to the oorrosive en~ir~nment without getting rusted for a total period of 500 hours, while rust wa~ detected on the s~mples ~f C:OMPARATIVE EXAMPLE 2 when they wc~e ex~mined after a 21~47~92 total of ~00 ~OUrB. These results conrirm that the bonded magnet of thi~ invention made by u~ing a modified epoxy re~in as the binder, and having $t~ surface ~oated with a polyt~nnin ~esin can stand use ~ven in a vc~y severc or ~orrosive environment, and exhibit a high level of r~stproofness which has b~en difficult ~o achieve by any conventional bonded magnet. It i~, ho~ever, to be noted that it is not always necessary to ~sc a polytannin r~sin for coating the magnet of th~s invention, ~ut that i~ is, of course, po~ible to u~c for ~he same purpose any other resin emplo~ed usually as a rust inhibi~ive ag~nt, and also any modified epoxy resin as herei~ disclo~ed.
~XAMPLF. 6 Compa~ison was made in ~echanical strength between magnot~ ~ade by u~ng a modified epoxy resin as a binde~ and maynets made by u~ing a poly~annin resin ag a binder.
Cylindriaal ma~nets each having a large bore dia-meter, i,e~ having an outside diameter of 32 mm, an inside dia~ter of 30 m~ and a length o~ 10 mm, were pres~ molded from the same ~ixtures of material~ as thos~ employed in ~XAMPLES 1 to 4, re~pectively. An identically sized and shaped ma~lnet containing 80~ by volume of MQ-B (magnetic powder) a~ a cal~lated value was al~ made by ~ing a poly-2~ tannin resin as a binder. ~hese magnet~ were compared in 20~7~92 strength. T~e comparison ~as made by allowing each magnet to drop onto a concrete floor fro~n a height of 50 c~ so that i~s cylindrical poripheral surfa~e might strike against the floor s~l~f~ce~ The magnet containing the polytannin re~in as the binde~ broke into ~everal piece ~3, bu~ no breakaye occurred to any of the m~ynets which had becn madc by following EXAM~LES 1 to 4. More-ov~r, none of the magne~s according to thi~ invention had broken during any p~rt of its manufact-lring pro~ess in~ludlng the steps of press molding and curing, while cracking and chippi~g had often occurred to the comparative magnct during the manufacture ~hereof. Thcsc r~sult~
confirm ~hat the ma~et of th~ invent~ on h~s a suffi~iently high mechanical strength for p~cti~al use which i8 higher than that of ~ny bonde~ magnet made by using a polytannin resin as the binder.
~!hus, the bonded ma~net of this invention has not only a high level of rus~proofness, but also a hig~ level of strenqth, and can, therefore, be used for a variety of purposcs for which no convcntional bond~d magnet has been suitable. The applic~tion of a rust inhibitive agent to the s~rface of the molded body imparts to the bonded magnet of this inven~ion a s~ill hi~her level of rustproofness which enables it ~o wi~hs~and a lon~ time of ~se even in a very severe or corrosive environment.
20~ 7592 COMPARATIYE F.XAMPLE 3 AND EXAM~LE~ 7 TO 13 A modified epoxy resin was u~ed for one or mo~e o~ th~ purposes of coating a mag~etic po~der, bonding it, and coatin~ a molded body.
A comparati~e samplc ~COMPARATI~ EXA~L~ 3~ and ~even sa~ple~ o this invention (EXAMPLES 7 to 13) were prepared by using the materials shown in ~AB~E 3 below. In TABLE 3, "none" means that no such film was fo.rmed, and "modified epoxy" means ~e ~ixture of a meth~nol solu~ion of tannic acid, C6H~(OH)3-CO-O-C~H2(OH)2COOH, ~hich is a polyhydria-phenoli~ ~arboxylic acid ha~ing a molec~lar weight of 306, and a MEK solution of "Epikote 1007", which i~ a solid bi~phenol type epo~y resin produced by Yuka-S~ell Company, and having a ~olecular weight o~ about 2~00 and an epoxy equiv~lent of 1600 to 1900. The mixture was ob-tAined by employing tann$~ aoid and thc epoxy resin in a weight ratio of 1 ~o 9.53. l'Phenol" mean~ a resol type phenoli~ resin.
The following iæ a descrip~ion o~ the methods which were employed for "forming a re~in film on the ~urface~ of maynetic particles", "mixing the magnetic powder and a binder resin, and mo}din~ their mixture", and "fo~ming a ~esin film on th~ ~urface of a ~olded ~ody":
~o.rm~ng a resin film on th~ surfaces of magnetlc particles:
ThC maynetic powder was dipped in the above mixture - 2~ --20~7~92 of the solutions, was allowed to dry to the tou~h, and wa3 hcated at 180C for an hour in a ~itroyen atmosphere.
Mixing the ma~netic powder and a binder resin, and ~olding their mixture:
The powder and the resin were mixcd to form a mix-ture cons~tin~ of 80~ by volume of powder and 20~ by vol~me of re~in, and the mixture was molded unde~ a pro6-sure of 6 tons/cm2 at ordinary temperature. Then, the binde~ resin was cured in a nitrogen atmo~phere by hcating at 180C for an hour if it was the above mixture of the solutions, or by hQating at 190C for t~o hours if it wa~
thc phenolic resin, ~hereby each molded body measuring approxima~ely 10 mm in diameter by 10 mm long was obtained.
Forming ~ resin film on the surface o~ a molded body:
Each mold¢d body was dipped in the above mixture of the solution~, and was allowed to dry to the touch.
Then, tho resin covering th~ molded body was ~ured by hea~-ing at 180C for an hour in a nitrogen atmosphere.
-:~0~7592 TABI,l; 3 Resin ~ilm orl the magnetic R~sin film on particle sur- the molded body Sample face~ B~nder surface COMPARATIVE None Phenol None EXAr~IPLE 3 EXA~PI,E 7 Modified n epoxy EXAMPLE 8 . NModifi~d n epoxy EXAM~LE g n Phenol Modified epoxy 13XAMPLE 10 ~Modlfied ~' epoxy EXAMP~E 11 None " Nonc EXAMP~E 12 n "Modified epoxy EXAMPLE 13 " Phenol n Th~ ma~ne~ samples which had been made as hexein-above de~cri~ed were tested ~or rustproofne~s in an environ-ment having a tempe~ature of 60C ~nd a humidi~y of 95% ~s hereinabove described. The tes~ results are shown in TABLE
4, in whiah ea~h ~ymbol ~an~ ~hat ~he correspondlng symbol in TABLE 1 ~eans, aq defined before.
20~7S92 TABLE 4 Re~ults of the environmetal tests at ~0C and 95~ humidity.
Test p~riod (hour) Sample 100 200 300 4~0 bOO 800 COMPARATIVE
EXAMPLE 3 ~ x X X x x x x x x EXA MPLE 7 0 69 0 0 ~ X
EXAMPLE 8 0 ~ ~ O ~ X
EXAMPl,E 10 0 0 0 0 ~ ~
EX)~MPLE 11 0 g~ Q X X X
EXAI~PLE 12 0 ~ D ~
EXAMPLE 13 l~ x Th~ results ~hown in ~A~LE 4 confirm ~ha~ the modified epoxy resin used for ~oating the magneti~ par-ticle~, bonding them, or coating the surface of the molded body can improve the ru~tproofness of the ma~nct, though to a v~rying degr~c, and ~hat its use for two o~ all ot those purpo~es yields a m~gnet having ~ s~ill high~r le~el of rustproofness, As is obvious f om ~he foregoing de~cription, the us¢ as a binder of a modified epoxy resin, or a mixture thereof wit~ a~other ordinary resin, enAbles the realiz~-tion of a bonded mag~et having a very high level of rust-p~oofness whi~h eliminate~ the necessity for the usc o~
any additional rus~ inhibiti~e a~en~, and th~ magnet of this invention can, therefore, be ~anufactured at a lower ~5 cost by a simpler process. Moreove~, it can be molded with a complic~ed ~hape or a small wall thickness and yet ~s so ~trong that it~ handling doe~ not call for any fipecial pre~aution.
Moreover, it i8 possi~le to coat the particles of a ma~netic powder and~or the surface of ~ molded ~ody with a rustproofin~ compound to make a bonded ma~net intended for use in a particularly ~evere or corros~ve environment.
Thi~ magnet has a by far highe~ leveI of ru~tproofne~ than that o~ any product coated wi~h a polytannin re~in.
Thus, the bond~d ~a~ne~ of this invention is subs~an-- 33 _ tially free from the problem of rusting which has been unavoidable by any known bonded magnet formed from a magnetic powder consisting mainly of iron. It has both a very high level of oxidation and corrosion resistance and a sufficiently high level of strength for practical use.
The Fifth and Sixth Aspects of the Invention:
The fifth and sixth aspects of this invention will now be described more specifically with reference to a few examples. According to the fifth aspect of this invention, a redox resin as a reduction agent is used as the binder, and according the sixth aspect thereof, the binder is a high molecular compound produced by curing a mixture of ascorbic acid or a derivative thereof, and an epoxy resin.
A redox resin as a reduction agent was used as the binder for molding a bonded magnet.
277 g of MQ-B (the tradename of General Motors for a Nd-Fe-B alloy powder produced by ultrarapid quenching) was put in a MBK (methyl ethyl ketone) solution containing 10 g of polyvinylhydroquinone resin having the structural formula shown below, and was thoroughly mixed with it:
.--C~--C~2--~0~
X
where n i~ an integQr.
Substantially all of the solven~ was rcmoved by vaporization, where~y a su~stantially dry ~ompound was obtained. ~t was put in a m~ld, and pre~s molded at pressure of 6 ton~/cm to form a green molded body. The molded body was cured by heating in an o~en having a tem-pe~a~ure of 16b~C for three hours to yield a bonded magnet ~easuring approximately 10 mm in diameter ~y 10 mm long, and still remaining un~agnetizcd. ~he magnet ~as pu~ in an environmental tester having a tempera~ure of 60C and a hu~idit~ of 90%. After e~ery 100 hour~, it wag takcn out and it~ ~urface was examined with the n~ked eye and through an optical microscope having a ma~nifica~ion of 30. The sample wa~ put back in the tester immediately after exa~i~ation. Thi~ test was continued fox a total of 500 hour~.
A high molecula~ compound produced by mixlng a~corbic acid and an epoxy resin was used a~ the binder for molding a bonded magnet, A ~ethanol ~olution containing 0.50 g of L-a~corbic acid ~vitamin C) was mixed with a M~:K ~olution con~aininy 8.25 g of "Epikote 1007" (the tradename of Yuka-Shell ~O.
~or a solid epoxy re~in having a mole~ular weight of about 2900)- 222 g of MQ-I~ wa~ put in ~he mixed solution, and 2047~92 mixed unlformly with it~ The~e~fter, EXAMPL~ 14 wa~
~ollowed ~or ~aking ~ bond~d magnet m~asuring lO mm in diam~t~r by lO ~m long, and ~ndu~ting 500 hours of an environmental test, except ~hat the molded body ~as ~ured in an argon gas atmosphere. ~he argon gas, which ix an inext g~s, was ~sed for p~eVenting the decompo~tion by oxidation of ~ny ~nre~cted as~orbic a~id.
COMPARATIV~ EXA~PLES 1 and 2 ~e~e repe~ted for p~eparing ~o~pa~ati~e s~mples.
10TABLE 5 sho~s the result~ of tne tes~s which were conducted on the produc~s of EXAMP~E6 14 and 15, and COM-PARAT~V~ EXAMPLES 1 and 2. Each ~ymbol ~eans ~hat the CO~rçsp~nding symbol in T~BLE 1 has here~nbefore been defined as meaning.
lS~AB~F. 5 Result~ of the environmental tests 60~C and 90% humidity.
Test Period (hours) 5amPlc lQQ 200 300 40Q 500 EXAMPLE 14 0 0 ~
EXAMPLE 15 0 ~
CO~PARATIVF., O A X X X
EXAMPE~ 1 CO~PARATIVE O O O ~ 0 EXAMPI..~. ~
EXAMpLE 16 2 0 ~ 7 S 9 2 A redox resin as a reduction agent, or a high molecular compound produced by mixing ascorbic acid and an epoxy resin was used as the binder for molding a bonded magnet, and its surface was coated with a polytannin resin.
EXAMPLES 14 and 15 were repeated for making magnets, and COMPARATIVE EXAMPLE 2 for coating their surfaces.
These magnets will be referred to as Samples 16-14 and 16-15. Sample 16-14, for example, means that EXAMPLE 14 was repeated for making the magnet. COMPARATIVE EXAMPLE 2 was also repeated for making a comparative sample. These samples were left to stand in a severer environment having a temperature of 90-C and a humidity of 95~ for a total of 800 hours. The results are shown in TABLE 6.
TABLE 6 Results of the environmental tests at 80-C and 95~ humidity.
Test Period (hours) Sample 100 200400 600 800 16-15 ~
COMPARATIVE o ~ ~ o x g -2~4 7592 - --EXAME'LE 1 7 Comparison was made in mechanical ~trength between ma~nets em~odying ~his invention and a m~net made by using a po~ytannin resin as th~ binder.
Cylindri¢al ~agnet~ each having a larye bo~e dia-meter, i.e. having an outside diam~ter of 32 mm, an in~ide diameter of 30 m~ ~nd a length of lO mm were made by press molding from th~ same mixture~ of materials as those ~mployed in EXAMPL~S 1~ and lS, xe~pectlvely, An iden~ically sized and shape magnet containing 80% by volume of MQ-B a~
a calculated value was like~i~e m~de ~y u~ing a polytannln re~in as the binder. They were compared in mechani~al ~tr~ngth, ~he compa~i~on wag m~de by allowing each ma~net to drop onto a ~oncrete f~oor from a he~ght of 50 cm so that its cylindrical peripheral ~ur~ace might ~trike against the floor su~face. The magnet cont~n~ng the polytannin resin ~s the binder broke in several pie~es, but no breakage oc~urred to any of the ~agne~s embodying thi~ invention.
Moreover, none of the mag~ets embodying this invention had broken during any part of thelr manufactu~ing process in-~luding ~he steps of molding and cu~ing, while ~racking or chipping had often o~curred ~o the comparative magnet.
Aæ i~ obvious from the foregoing, the magnetæ ac~o~d-~5 ing to t~e fifth ~nd ~ixth aspQcts of this in~ention are by 2047~92 f~r s~perior in corros~on resistance to the magnet made by using an ordinary resin as the ~inder, though they are inferior to the ma~ne~ having ~ts whole surface coated with a polyt~nnin resin (C~OMPARATIVE EX~MPL~ There-fore, those magnets ac~o~ding to thi~ inve~tion are quitesatlsfactory for use in a varie~y of common case~ in which no extremely high level of rustproofness will be re~uired, Moreover, the m~gnet o~ this in~en~ion does not necessarily need to ~e coated with a r~st inhibit~e a~en~, ~nd can, therefor~, be manufactur~d at a ~ery low oost. It i~, however, possible to use a rust inhi~itive agent to ~ake a magnet having a higher le~el of rustproofness if it i8 intended for use in a more corrosive environment. The m~gnets according to the ~ifth and sixt~ aspects o~ thi~
lS invention are al$o so strong that no cracking ox chipping occur~ during their manufacture, or their ~Se.
Product~ fo~med by condensation reac~ions fro~
aldehydes and ~ompounds ~s listed below:
Catechol, catechol-3 (o~ 4 ) -carboxylia acid (or an ester thereof), pyrogallol, hydroxyhydroquinone, pyrogallol-4-carboxylic acid ~or an ester the~eof), pyr~gallol-4.~-dicarboxylic acid (or an estex the~e-of), 3~4~5-trioxybe~oic acid (or An e~ter ther2- .
of ~, tannic acid ~or an eæ~er thereof), ~nd urushiol, Specific exa~ples o~ the polyhydric phenol com-pound~ as mentioned at ~4) above include ~he condensation produc~ of pyrogallol or hydroxyhydro~uinone, and aro~atic aldeh~des, as dls~losed in ~apanese Pa~ent Appli~ation L~id-Open No. 54317/1980, and the ~ondensation p~oducts of pyro-gallol and aldehydes ~formaldehyde, d~cylaldehyde, benz-aldehyde, etc.), as disclosed i~ Ja~ancse Pa~ent Appl~catlon Laid-Open No. 130642/1978.
There i~ no particular li~ita~ion ~o the epoxy resin wh.ich can be used for the purpose of t~is invention.
I~ is possl~le ~o ~se any kno~n epoxy resin formed ~rom 20~7~92 bisphenol, pheno~, ester, N~glycidyl~mine, or the like.
The mixing ratio of the epoxy resin and th~ polyhydri~
phenol compound ~or compound~) depends on the epoxy equiva-len~ oE the resin and the number of hydroxyl groups ~hlch the polyhy~rlc phenol compound contains.
A magnetic powder containing at leas~ S0 atom ~
of iron is used for th~ purpose o~ this invention. More specifically, it is, for example, a powder of an alloy which is generally callcd a Nd-~e-B alloy, ~uch ~s RE 2Fel4~, ox another alloy ~urther containing a~other element ~e.~., another rare earth elelnent such as Pr or Dy, another 3d t~ansition element such as Co o~ v, or Al, Ga, or Nb), a powdcr of a compound obtained by adding anothcr element or elements (e.g., Al, Si, Ti, Co, V, Cr and Mo) to SmFe12 1~ having a crystal str~ctu~e of the ThMnl~ type, or a powder of ~el6~2 consisting of needle crystals providing anisotropy.
The powder of a N~-~e-B ~lloy is, ~nong other~, preferred f~om a practical standpoint, as i~ exhi~its higher magnetic proper~ies ~han any other presen~ly known maynetic material does.
The bonded magnet o~ this invention preferably ct~ntain~ 70~h to 95% by volumc o~ ma~netiC powdc~. A magnet containing less th~n 70~ by volume of magnetic pow~er has too low magnetic properties to be useful for a wide range 2S o~ purposes. A magne~ containing over 95~ by volume of 20~75g2 ma~netic po~dcr ~ontains too small a propoxtion of binder, and is, therefore, too brittlc to wi~hstand practical u~e.
The invention ~ill now b~ described more speci-~ically wit:h rereren¢e to ex~mples. Althou~h ~11 of these examples are dir¢c:ted ~o bondcd RE-Fe-s alloy ma~net~ whi~h theoretically con~ain 80% by volume o~ magnetic powder, it i~ to be understood that they ~re merely illustra~ive of this invention, and are not intended for limiting the ~copc of thi 8 inven~ion .
1~ EXAMPLI~ 1 A hi~h mol~cula~ compound produced ~y reac~ing tannic acid and an epoxy resin was used a~ a binder ~
A ~ethanol~ golution contain.ing 1.0Q g of ~annic acid, C6H2(OH)3-CO-O-C~(OII)2COOH, which is a polyhydri¢
phenolic carboxylic a~id having a molecular ~cight of 306, was mi~ed with ~ ~e~hyl-ethyl-ketone (MEK) sol~tion contain-ing 9.S3 g of "~pikotc 1007", which i~ a ~olit~ epoxy rc~in of Yuka-Shell Company h~ving a molecular weight of about 2~00 and.an epoxy e~uivalent of 160~ to l~00, and prod~ced by using bisphenol, 2~7 g of a NdFeB powder prepared by ultrarapid quonching tGeneral ~otors ' product, MQ-B) was put in the mixed ~olution, and was mixed wi~h i~ careful~y.
Substanti~lly all of the solvent~ wcrc rcmovcd by vaporiza-tion to yield a substantially dry compound. Th~ compound `~ 2047~92 was put in a mold, and pre~s molded at a pressure of 6 tjcm2 to form a green molded ~ody. The molded body wa~ cured in an oven having a temperature o~ 160C for ~hree hour~ to yield a bonded magnet approximately meaæur-ing 10 mm in diame~er by 10 mm long, and s~ill remaining unmagn~tized .
Ten ma~net~ wcre prepa~ed. They w~r~ put ir an en~iron~ental tester havin~ a temperature of 60C ~nd a humidi~y of ~0%. After e~ery 100 ho~s, they were taken ou~ of the ~e~ter and the surrac~ of each ~ample was examined with tho naked eye and th~ough an optical ~icroscope having a magniflcation of 30. The s~mple~ were p~t back in the te~t~r immediately after examination. This test wa~ con-tinued untll ~he samples had been left to stand in the te~er lS for a total period of 500 hourq.
EXA~PLE 2 A ~igh molecula~ co~pound produ~ed by reactin~
g~llic acid and an epox~ r~sln was u:3ed a~ a binder.
A methanol ~olution containing 1~00 g of gallic a~id, ~H2~OH)3COOH, which i~ a polyhydric phenolic ~arboxylic acid having a molecular wei~ht of 170, was mixed with a MEK
solu~ion containing ~ . 5~ g of "Epikote 1007 " under ~tirring, and 248 g of M~-B w~ put in the mixed solution, and mix~d with i~ carQf~lly. Thereafter, EXAM~LE 1 was repea~ed for 20~7592 preparing magnets each mcrsuring 10 mm in diamcter by 10 mm long, and conducting 500 ~ours of an environmental test.
EXA~PLE 3 S A high mole~lar compound produced ~y reac~ing a polycyclic and polyhydric phenol And an epoxy resin was used as a binder.
~ compo~nd having the $tructural formula ~hown below, which is a poly~ycli¢ and polyhydric phenol having a molecular wcight of ~40, was synthesized by the process of Exam~le 4 in Japanese Patent Application Laid-Open No.
30642/lg78 OH
HO~CH ~
HO~ CgH19 ~OII
An ac~tone solution ¢on~ainin~ 1.00 g of the above compound ~as mixed wi~h a ME~ solution containing 8.50 g o~ "Epikote 1007", and 240 g of M~-B wa~ put in the mixed solution, and mixed with it carefully. Thereaftex, EX~MPLE
1 was repeated for preparing magnets each measuxing 10 ~m in diameter by 10 mm long, and conducting S00 hours of an environmental test.
20~7592 EX~M~LE 4 A h~gh molecul~r compoun~ produced by reacting a polycy~lic and polyhydric phenol and an epoxy resin was used as a binder.
S ~ compound ha~ing the ~truct~ral formula shown below, ~ ich i s a polycyc:lic and polyhydric phenol having a molecular weight of 340, ~s syn~hesized ~y the process of Example ~ ln J~panese Patent ~pplication Laid-O~en No.
54317/19~0; OH o~ HO OH
0 HO~/ H \~OH
An acetone ~olution ~ontaining 1. ~ ~ of the abo~le co~pound was mixed with a ME~ solu~ion ~ontainin~ 8.50 g of "Epi~co~e 10û7", and 240 q oE MQ-B wa~ put in the mixed solution, and mixed with it carefully. The~eaf~er, EXAM~IIE
~0 1 ~as repe~ted for preparing magnets each mea~uring 10 mm in diameter by 10 ~m long, and conducting 5~0 hou~ of an en~ironmen~al test.
~OMPARAT~VE EXAMPLE 1 An ~rdinary resin was used as a binde~. !
A me~hanol and toluene solution ~ontaining 0.50 g of dicyandia~nide, which i~ a common curing agent, w~s mixed i- 2047~92 with a ME~ solut~on containing 9.50 ~ of "Epikote 1007", and 253 g of MQ-B was put in the mixed solution, and ~ixed uniformly with i~. Thereafter, EXAMPLE 1 w~s rep~ated for pre~aring magn¢ts each m~asuring 10 mm in diameter by S 10 mm long, and condu~ting 500 ho~rs of an en~ironmental test.
An ordinary resin was u~ed as a binder ~or ~kiny molded bodies, ~nd their surf~ces wer~ ~oated with a polytannin resin.
COM~ARATIVE EXAM~LE 1 was repeated for ~oldiny magnet~. They wore dipped in a MEK solu~ion cont~in~ nq lS~ b~ weight of a polytannin re~in. Then, the solvent was removed by ~aporization, and the resin w~s cured by lS heating at lS0~ for }5 minutes, whereby thc surface of each ma~nQt wa~ coa~ed with a film of the polytannln re~in.
ThQ magnets were dippcd in a lN ~ol~tion of sulfuri~ acid, and left to st~nd for a period of about 30 seconds, but only a trac~ of hydrogen gas was produ~ed. Thus, it was con-finmed that the film ~.~ith which each magnet had been coated was su~stantially frec of any pinhole defect. Thereafter, EXAMPLE 1 was repeated for conducting 500 hours of an en-v~ron~en~l test to see if any ~us~ would form on the mag-nets.
TABLE 1 3hows the resu~t~ of the tests whlch were obtained in EXA~IPLES 1 tt: 4 and ~OMPA~ATIVE EXA~LES 1 and 2, Each syrnbol ha~ the rneaning as defined below.
TABLE 1 ~e~ults of the environmental te8ts at 60C and 9096 humidity.
Tes~ period (hours) Samples 100 200 300 400 5~0 EXA~qPLE 1 EXAMP~E 2 EXAMPLE 3 ~ ~ ~ O
lo EXAMPLE 4 ~ ~ ~ O A
CO~PARATIVE O ~ x x x x x EX~MPLE 1 COMPARAT~VE
(~) : No ru~ting was found to have o~c~lrred;
o : ~ots of ruæt were detec~ed:
~: A medium dcgrec of r-~sting was found to ha~e rred:
x: ~Ie~vy xusting: :
xx: very heavy ru~ing (rust wa~ found to cover the whole ~urEac~ of the sample, and was ~learly visible to the na3ced eye).
~ is obvious ~rom TABI,~ 1, no ru$~in~ occurred for a total of 300 hours to any of the bonded magnet~ accoxding to EX~P~F,S 1 to 4 that had b~cn madQ by u~ing a modified epoxy resin a5 the binder, and it was only when they were 20~7592 exa~ined a~ter a total of 400 hours that so~e spots of rust w~r~ detected on the magnets. Thes~ rs~ults ~on-firm ~he excellen~ ru~tprooness of the ~agne~s accordiny to thig invention. ~he ma~nets of thi~ inven~ion were by far superior in oxidation ~esistance to the conventional magnets according to COMrA~ATIVE EXA~PLE 1 whi~h had been made by ~sing an ordinary resin a~ the binder, tho~t3h they were inferior to the product~ of COMPARATIV~ EXA~PLE 2 having a surface coated with a pol~tannin r~sin. It is, there~ore, obvious that the magnet of this lnvention made by ~æing a modified epoxy re~in as the binder i8 very effective for u5e in any of a wide variety of usual cases in which no extremely high level of ru~tproofnes~ is required o~ the magnet. Moreover, the use of a rustproofing resin as the binder enables a reduc~ion in t~e cost of man~fac-turing the ma(~net of this invcntion, since the molded body docs not call ~or any ru~tproofin~ ~urfa~e treatment ~uch as coating with a ru~ inhibi~ive a~ent.
EXAMP~E g A modified epoxy resin was u~ed ~s a ~inder to form molded bodies, and their surfaces we~e coated with a polytannin re~in.
EXAMPLES 1 to 4 were repe~ted for making bonded magnets and COMPARATIVE EXAMPLE ~ was repea~ed for coating each ~a~net with a polytannin ~esin. ~hese ~a~ne~s will 2047~92 herein~tcr be r~fer~ed to as Samples S-l, 5-~, 5-3 and 5-4, respec~ively. Sam~les 5-l mean th~ magnets which were mad~ by repeating EX~PLE l, and coa~ed with the polytannin reæin, and so on. CO~lPARATIV~ EXA~P~ 2 was also repe~ted ~or makin~ samples coated with the polytannin resin. ~11 of these ~amples we~e lef~ to stand in ~
seve~er environmen~ having a ~emperature of 60C and a hunidity o 95% for a ~o~al of 600 hours. ~h~ results of ~bis environmental t~st are sho~n in ~ABLE 2, i~ which each ~ymbol me~ns wha~ ~he cor~espond~ng s~mbol in TABLE
1 does, as deined above.
TABLE 2 ~esul~s o~ the environmeta~ test a~ 60~C ~nd 95~ humidi~y.
T~st p~riod (hours) ~5 Samples 100 ~00 400 500 600 5~ O
5-Z ~ ~ ~ ~ O
5-3 ~ O
5-4 ~ O
20 CO~PAR~TIVE ~ ~ O ~ X
:EX~MPLE ~
~ s is obvious f~om TAB~E 2, all of Samples 5-l to 5-4 of ~his i~ve~tion could wi~h~tand exposure to the oorrosive en~ir~nment without getting rusted for a total period of 500 hours, while rust wa~ detected on the s~mples ~f C:OMPARATIVE EXAMPLE 2 when they wc~e ex~mined after a 21~47~92 total of ~00 ~OUrB. These results conrirm that the bonded magnet of thi~ invention made by u~ing a modified epoxy re~in as the binder, and having $t~ surface ~oated with a polyt~nnin ~esin can stand use ~ven in a vc~y severc or ~orrosive environment, and exhibit a high level of r~stproofness which has b~en difficult ~o achieve by any conventional bonded magnet. It i~, ho~ever, to be noted that it is not always necessary to ~sc a polytannin r~sin for coating the magnet of th~s invention, ~ut that i~ is, of course, po~ible to u~c for ~he same purpose any other resin emplo~ed usually as a rust inhibi~ive ag~nt, and also any modified epoxy resin as herei~ disclo~ed.
~XAMPLF. 6 Compa~ison was made in ~echanical strength between magnot~ ~ade by u~ng a modified epoxy resin as a binde~ and maynets made by u~ing a poly~annin resin ag a binder.
Cylindriaal ma~nets each having a large bore dia-meter, i,e~ having an outside diameter of 32 mm, an inside dia~ter of 30 m~ and a length o~ 10 mm, were pres~ molded from the same ~ixtures of material~ as thos~ employed in ~XAMPLES 1 to 4, re~pectively. An identically sized and shaped ma~lnet containing 80~ by volume of MQ-B (magnetic powder) a~ a cal~lated value was al~ made by ~ing a poly-2~ tannin resin as a binder. ~hese magnet~ were compared in 20~7~92 strength. T~e comparison ~as made by allowing each magnet to drop onto a concrete floor fro~n a height of 50 c~ so that i~s cylindrical poripheral surfa~e might strike against the floor s~l~f~ce~ The magnet containing the polytannin re~in as the binde~ broke into ~everal piece ~3, bu~ no breakaye occurred to any of the m~ynets which had becn madc by following EXAM~LES 1 to 4. More-ov~r, none of the magne~s according to thi~ invention had broken during any p~rt of its manufact-lring pro~ess in~ludlng the steps of press molding and curing, while cracking and chippi~g had often occurred to the comparative magnct during the manufacture ~hereof. Thcsc r~sult~
confirm ~hat the ma~et of th~ invent~ on h~s a suffi~iently high mechanical strength for p~cti~al use which i8 higher than that of ~ny bonde~ magnet made by using a polytannin resin as the binder.
~!hus, the bonded ma~net of this invention has not only a high level of rus~proofness, but also a hig~ level of strenqth, and can, therefore, be used for a variety of purposcs for which no convcntional bond~d magnet has been suitable. The applic~tion of a rust inhibitive agent to the s~rface of the molded body imparts to the bonded magnet of this inven~ion a s~ill hi~her level of rustproofness which enables it ~o wi~hs~and a lon~ time of ~se even in a very severe or corrosive environment.
20~ 7592 COMPARATIYE F.XAMPLE 3 AND EXAM~LE~ 7 TO 13 A modified epoxy resin was u~ed for one or mo~e o~ th~ purposes of coating a mag~etic po~der, bonding it, and coatin~ a molded body.
A comparati~e samplc ~COMPARATI~ EXA~L~ 3~ and ~even sa~ple~ o this invention (EXAMPLES 7 to 13) were prepared by using the materials shown in ~AB~E 3 below. In TABLE 3, "none" means that no such film was fo.rmed, and "modified epoxy" means ~e ~ixture of a meth~nol solu~ion of tannic acid, C6H~(OH)3-CO-O-C~H2(OH)2COOH, ~hich is a polyhydria-phenoli~ ~arboxylic acid ha~ing a molec~lar weight of 306, and a MEK solution of "Epikote 1007", which i~ a solid bi~phenol type epo~y resin produced by Yuka-S~ell Company, and having a ~olecular weight o~ about 2~00 and an epoxy equiv~lent of 1600 to 1900. The mixture was ob-tAined by employing tann$~ aoid and thc epoxy resin in a weight ratio of 1 ~o 9.53. l'Phenol" mean~ a resol type phenoli~ resin.
The following iæ a descrip~ion o~ the methods which were employed for "forming a re~in film on the ~urface~ of maynetic particles", "mixing the magnetic powder and a binder resin, and mo}din~ their mixture", and "fo~ming a ~esin film on th~ ~urface of a ~olded ~ody":
~o.rm~ng a resin film on th~ surfaces of magnetlc particles:
ThC maynetic powder was dipped in the above mixture - 2~ --20~7~92 of the solutions, was allowed to dry to the tou~h, and wa3 hcated at 180C for an hour in a ~itroyen atmosphere.
Mixing the ma~netic powder and a binder resin, and ~olding their mixture:
The powder and the resin were mixcd to form a mix-ture cons~tin~ of 80~ by volume of powder and 20~ by vol~me of re~in, and the mixture was molded unde~ a pro6-sure of 6 tons/cm2 at ordinary temperature. Then, the binde~ resin was cured in a nitrogen atmo~phere by hcating at 180C for an hour if it was the above mixture of the solutions, or by hQating at 190C for t~o hours if it wa~
thc phenolic resin, ~hereby each molded body measuring approxima~ely 10 mm in diameter by 10 mm long was obtained.
Forming ~ resin film on the surface o~ a molded body:
Each mold¢d body was dipped in the above mixture of the solution~, and was allowed to dry to the touch.
Then, tho resin covering th~ molded body was ~ured by hea~-ing at 180C for an hour in a nitrogen atmosphere.
-:~0~7592 TABI,l; 3 Resin ~ilm orl the magnetic R~sin film on particle sur- the molded body Sample face~ B~nder surface COMPARATIVE None Phenol None EXAr~IPLE 3 EXA~PI,E 7 Modified n epoxy EXAMPLE 8 . NModifi~d n epoxy EXAM~LE g n Phenol Modified epoxy 13XAMPLE 10 ~Modlfied ~' epoxy EXAMP~E 11 None " Nonc EXAMP~E 12 n "Modified epoxy EXAMPLE 13 " Phenol n Th~ ma~ne~ samples which had been made as hexein-above de~cri~ed were tested ~or rustproofne~s in an environ-ment having a tempe~ature of 60C ~nd a humidi~y of 95% ~s hereinabove described. The tes~ results are shown in TABLE
4, in whiah ea~h ~ymbol ~an~ ~hat ~he correspondlng symbol in TABLE 1 ~eans, aq defined before.
20~7S92 TABLE 4 Re~ults of the environmetal tests at ~0C and 95~ humidity.
Test p~riod (hour) Sample 100 200 300 4~0 bOO 800 COMPARATIVE
EXAMPLE 3 ~ x X X x x x x x x EXA MPLE 7 0 69 0 0 ~ X
EXAMPLE 8 0 ~ ~ O ~ X
EXAMPl,E 10 0 0 0 0 ~ ~
EX)~MPLE 11 0 g~ Q X X X
EXAI~PLE 12 0 ~ D ~
EXAMPLE 13 l~ x Th~ results ~hown in ~A~LE 4 confirm ~ha~ the modified epoxy resin used for ~oating the magneti~ par-ticle~, bonding them, or coating the surface of the molded body can improve the ru~tproofness of the ma~nct, though to a v~rying degr~c, and ~hat its use for two o~ all ot those purpo~es yields a m~gnet having ~ s~ill high~r le~el of rustproofness, As is obvious f om ~he foregoing de~cription, the us¢ as a binder of a modified epoxy resin, or a mixture thereof wit~ a~other ordinary resin, enAbles the realiz~-tion of a bonded mag~et having a very high level of rust-p~oofness whi~h eliminate~ the necessity for the usc o~
any additional rus~ inhibiti~e a~en~, and th~ magnet of this invention can, therefore, be ~anufactured at a lower ~5 cost by a simpler process. Moreove~, it can be molded with a complic~ed ~hape or a small wall thickness and yet ~s so ~trong that it~ handling doe~ not call for any fipecial pre~aution.
Moreover, it i8 possi~le to coat the particles of a ma~netic powder and~or the surface of ~ molded ~ody with a rustproofin~ compound to make a bonded ma~net intended for use in a particularly ~evere or corros~ve environment.
Thi~ magnet has a by far highe~ leveI of ru~tproofne~ than that o~ any product coated wi~h a polytannin re~in.
Thus, the bond~d ~a~ne~ of this invention is subs~an-- 33 _ tially free from the problem of rusting which has been unavoidable by any known bonded magnet formed from a magnetic powder consisting mainly of iron. It has both a very high level of oxidation and corrosion resistance and a sufficiently high level of strength for practical use.
The Fifth and Sixth Aspects of the Invention:
The fifth and sixth aspects of this invention will now be described more specifically with reference to a few examples. According to the fifth aspect of this invention, a redox resin as a reduction agent is used as the binder, and according the sixth aspect thereof, the binder is a high molecular compound produced by curing a mixture of ascorbic acid or a derivative thereof, and an epoxy resin.
A redox resin as a reduction agent was used as the binder for molding a bonded magnet.
277 g of MQ-B (the tradename of General Motors for a Nd-Fe-B alloy powder produced by ultrarapid quenching) was put in a MBK (methyl ethyl ketone) solution containing 10 g of polyvinylhydroquinone resin having the structural formula shown below, and was thoroughly mixed with it:
.--C~--C~2--~0~
X
where n i~ an integQr.
Substantially all of the solven~ was rcmoved by vaporization, where~y a su~stantially dry ~ompound was obtained. ~t was put in a m~ld, and pre~s molded at pressure of 6 ton~/cm to form a green molded body. The molded body was cured by heating in an o~en having a tem-pe~a~ure of 16b~C for three hours to yield a bonded magnet ~easuring approximately 10 mm in diameter ~y 10 mm long, and still remaining un~agnetizcd. ~he magnet ~as pu~ in an environmental tester having a tempera~ure of 60C and a hu~idit~ of 90%. After e~ery 100 hour~, it wag takcn out and it~ ~urface was examined with the n~ked eye and through an optical microscope having a ma~nifica~ion of 30. The sample wa~ put back in the tester immediately after exa~i~ation. Thi~ test was continued fox a total of 500 hour~.
A high molecula~ compound produced by mixlng a~corbic acid and an epoxy resin was used a~ the binder for molding a bonded magnet, A ~ethanol ~olution containing 0.50 g of L-a~corbic acid ~vitamin C) was mixed with a M~:K ~olution con~aininy 8.25 g of "Epikote 1007" (the tradename of Yuka-Shell ~O.
~or a solid epoxy re~in having a mole~ular weight of about 2900)- 222 g of MQ-I~ wa~ put in ~he mixed solution, and 2047~92 mixed unlformly with it~ The~e~fter, EXAMPL~ 14 wa~
~ollowed ~or ~aking ~ bond~d magnet m~asuring lO mm in diam~t~r by lO ~m long, and ~ndu~ting 500 hours of an environmental test, except ~hat the molded body ~as ~ured in an argon gas atmosphere. ~he argon gas, which ix an inext g~s, was ~sed for p~eVenting the decompo~tion by oxidation of ~ny ~nre~cted as~orbic a~id.
COMPARATIV~ EXA~PLES 1 and 2 ~e~e repe~ted for p~eparing ~o~pa~ati~e s~mples.
10TABLE 5 sho~s the result~ of tne tes~s which were conducted on the produc~s of EXAMP~E6 14 and 15, and COM-PARAT~V~ EXAMPLES 1 and 2. Each ~ymbol ~eans ~hat the CO~rçsp~nding symbol in T~BLE 1 has here~nbefore been defined as meaning.
lS~AB~F. 5 Result~ of the environmental tests 60~C and 90% humidity.
Test Period (hours) 5amPlc lQQ 200 300 40Q 500 EXAMPLE 14 0 0 ~
EXAMPLE 15 0 ~
CO~PARATIVF., O A X X X
EXAMPE~ 1 CO~PARATIVE O O O ~ 0 EXAMPI..~. ~
EXAMpLE 16 2 0 ~ 7 S 9 2 A redox resin as a reduction agent, or a high molecular compound produced by mixing ascorbic acid and an epoxy resin was used as the binder for molding a bonded magnet, and its surface was coated with a polytannin resin.
EXAMPLES 14 and 15 were repeated for making magnets, and COMPARATIVE EXAMPLE 2 for coating their surfaces.
These magnets will be referred to as Samples 16-14 and 16-15. Sample 16-14, for example, means that EXAMPLE 14 was repeated for making the magnet. COMPARATIVE EXAMPLE 2 was also repeated for making a comparative sample. These samples were left to stand in a severer environment having a temperature of 90-C and a humidity of 95~ for a total of 800 hours. The results are shown in TABLE 6.
TABLE 6 Results of the environmental tests at 80-C and 95~ humidity.
Test Period (hours) Sample 100 200400 600 800 16-15 ~
COMPARATIVE o ~ ~ o x g -2~4 7592 - --EXAME'LE 1 7 Comparison was made in mechanical ~trength between ma~nets em~odying ~his invention and a m~net made by using a po~ytannin resin as th~ binder.
Cylindri¢al ~agnet~ each having a larye bo~e dia-meter, i.e. having an outside diam~ter of 32 mm, an in~ide diameter of 30 m~ ~nd a length of lO mm were made by press molding from th~ same mixture~ of materials as those ~mployed in EXAMPL~S 1~ and lS, xe~pectlvely, An iden~ically sized and shape magnet containing 80% by volume of MQ-B a~
a calculated value was like~i~e m~de ~y u~ing a polytannln re~in as the binder. They were compared in mechani~al ~tr~ngth, ~he compa~i~on wag m~de by allowing each ma~net to drop onto a ~oncrete f~oor from a he~ght of 50 cm so that its cylindrical peripheral ~ur~ace might ~trike against the floor su~face. The magnet cont~n~ng the polytannin resin ~s the binder broke in several pie~es, but no breakage oc~urred to any of the ~agne~s embodying thi~ invention.
Moreover, none of the mag~ets embodying this invention had broken during any part of thelr manufactu~ing process in-~luding ~he steps of molding and cu~ing, while ~racking or chipping had often o~curred ~o the comparative magnet.
Aæ i~ obvious from the foregoing, the magnetæ ac~o~d-~5 ing to t~e fifth ~nd ~ixth aspQcts of this in~ention are by 2047~92 f~r s~perior in corros~on resistance to the magnet made by using an ordinary resin as the ~inder, though they are inferior to the ma~ne~ having ~ts whole surface coated with a polyt~nnin resin (C~OMPARATIVE EX~MPL~ There-fore, those magnets ac~o~ding to thi~ inve~tion are quitesatlsfactory for use in a varie~y of common case~ in which no extremely high level of rustproofness will be re~uired, Moreover, the m~gnet o~ this in~en~ion does not necessarily need to ~e coated with a r~st inhibit~e a~en~, ~nd can, therefor~, be manufactur~d at a ~ery low oost. It i~, however, possible to use a rust inhi~itive agent to ~ake a magnet having a higher le~el of rustproofness if it i8 intended for use in a more corrosive environment. The m~gnets according to the ~ifth and sixt~ aspects o~ thi~
lS invention are al$o so strong that no cracking ox chipping occur~ during their manufacture, or their ~Se.
Claims (20)
1. A bonded rare earth magnet composed mainly of a powder of a magnetic material containing at least 50 atom % of iron, and a high molecular compound produced by reacting with an epoxy resin one or more of a polyhydric phenol having adjacent hydroxyls, a polyhydric phenolic carboxylic acid having adjacent hydroxyls, an ester of a polyhydric phenol and a polyhydric alcohol having adjacent hydroxyls, and a polycyclic and polyhydric phenol having adjacent hydroxyls, or composed mainly of said powder, said compound and a resin.
2. A magnet as set forth in claim 1, wherein said powder is of Nd2Fe14B, an alloy of SmFe12 or an alloy of Fe16N2.
3. A bonded rare earth magnet made by molding a powder of a magnetic material containing at least 50 atoms % of iron with a binder of a redox resin as a reduction agent.
4. A bonded rare earth magnet made by molding a powder of a magnetic material containing at least 50 atom % of iron with a binder of a high molecular weight compound produced by curing a mixture of ascorbic acid, or a derivative thereof, and an epoxy resin.
5. A magnet as set forth in claim 3 or 4, wherein said powder is of Nd2Fe14B, an alloy of SmFe12 or an alloy of Fe16N2.
6. A magnet as set forth in claim 2, wherein said alloy is of Nd2Fe14B containing another element, said element being selected from the group consisting of rare earth elements, Co, V, Al, Ga and Nb.
7. A magnet as set forth in claim 1, wherein said powder is of a compound obtained by adding at least one element selected from the group consisting of Al, Si, Ti, Co, V, Cr and Mo, to SmFe12 having the ThMn12 crystal structure.
8. A magnet as set forth in claim 1, wherein said powder is of Fe16N2 consisting of needle crystals providing anisotropy.
9. A magnet as set forth in claim 5, wherein said alloy is of Nd2Fe14B containing another element, said element being selected from the group consisting of rare earth elements, Co, V, Al, Ga and Nb.
10. A magnet as set forth in claim 3 or 4, wherein said powder is of a compound obtained by adding at least one element selected from the group consisting of Al, Si, Ti, Co, V, Cr and Mo, to SmFe12 having the ThMn12 crystal structure.
11. A magnet as set forth in claim 3 or 4, wherein said powder is of Fe16N2 consisting of needle crystals providing anisotropy.
12. A process for manufacturing a bonded rare earth magnet comprising coating the particles of a powder of a magnetic material containing at least 50 atom ~ of iron by a method selected from (a) coating with a high molecular weight compound produced by reacting with an epoxy resin one or more of a polyhydric phenol having adjacent hydroxyls, a polyhydric phenolic carboxylic acid having adjacent hydroxyls, an ester of a polyhydric phenol and a polyhydric alcohol having adjacent hydroxyls, and a polycyclic and polyhydric phenol having adjacent hydroxyls; (b) coating with a mixture of said high molecular weight compound and another resin; and (c) coating with said high molecular weight compound followed by further coating with said another resin to form a double resin coating on the surfaces of said particles;
and molding said powder by using as a binder a synthetic resin which may or may not be said high molecular weight compound or said mixture.
and molding said powder by using as a binder a synthetic resin which may or may not be said high molecular weight compound or said mixture.
13. A process as set forth in claim 12, wherein said binder is said high molecular weight compound or said mixture.
14. A process as set forth in claim 12, further including coating the surface of a molded product of said powder with said high weight molecular compound or said mixture or said high molecular weight compound and said another resin forming a double resin coating on said surface.
15. A process as set forth in any of claims 12, 13 or 14, wherein said powder is of Nd2Fe14B, an alloy of SmFe12 or an alloy of Fe16N2.
16. A process for manufacturing a bonded rare earth magnet comprising molding a powder of a magnetic material containing at least 50 atom % of iron by using as a binder a high molecular weight compound produced by reacting with an epoxy resin one or more of a polyhydric phenol having adjacent hydroxyls, a polyhydric phenolic carboxylic acid having adjacent hydroxyls, an ester of a polyhydric phenol and a polyhydric alcohol having adjacent hydroxyls, and a polycyclic and polyhydric phenol having adjacent hydroxyls, or a mixture of said compound and another resin.
17. A process as set forth in claim 16, further including coating the surface of a molded product of said powder with said high molecular weight compound, or said mixture, or coating said surface with said high molecular weight compound and then with said another resin to form a double resin coating on said surface.
18. A process as set forth in claim 16 or 17, wherein said powder is of Nd2Fe14B, an alloy of SmFe12 or an alloy of Fe16N2.
19. A process for manufacturing a bonded rare earth magnet comprising forming a molded product of a powder of a magnetic material containing at least 50 atom % of iron by using a resin as a binder, and coating the surface of said product with a high molecular compound produced by reacting with an epoxy resin one or more of a polyhydric phenol having adjacent hydroxyls, a polyhydric phenolic carboxylic acid having adjacent hydroxyls, an ester of a polyhydric phenol and polyhydric alcohol having adjacent hydroxyls, and a polycyclic and polyhydric phenol having adjacent hydroxyls, or coating said surface with a mixture of said compound and another resin, or coating said surface with said compound and then with said another resin to form a double resin coating on said surface.
20. A process as set forth in claim 19, wherein said powder is of Nd2Fe14B, an alloy of SmFe12 or an alloy of Fe16N2.
Applications Claiming Priority (6)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2(1990)-195958 | 1990-07-24 | ||
| JP19595890 | 1990-07-24 | ||
| JP2213110A JPH0494501A (en) | 1990-08-11 | 1990-08-11 | Bond magnet and its production method |
| JP2(1990)-213110 | 1990-08-11 | ||
| JP2309199A JPH04174502A (en) | 1990-07-24 | 1990-11-14 | Rare earth bonded magnet and its manufacture |
| JP2(1990)-309199 | 1990-11-14 |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2047592A1 CA2047592A1 (en) | 1992-01-25 |
| CA2047592C true CA2047592C (en) | 1996-10-15 |
Family
ID=27327168
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2047592 Expired - Fee Related CA2047592C (en) | 1990-07-24 | 1991-07-23 | Bonded rare earth magnet and a process for manufacturing the same |
Country Status (3)
| Country | Link |
|---|---|
| EP (1) | EP0468449B1 (en) |
| CA (1) | CA2047592C (en) |
| DE (1) | DE69101413T2 (en) |
Families Citing this family (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5272008A (en) * | 1992-03-16 | 1993-12-21 | General Motors Corporation | Encapsulated oxidation-resistant iron-neodymium-boron permanent magnet |
| JP3645197B2 (en) * | 2001-06-12 | 2005-05-11 | 日東電工株式会社 | Semiconductor device and epoxy resin composition for semiconductor encapsulation used therefor |
| CN102598168B (en) | 2009-08-25 | 2015-06-17 | 捷通国际有限公司 | Flux concentrator and method of making a magnetic flux concentrator |
Family Cites Families (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH0789521B2 (en) * | 1985-03-28 | 1995-09-27 | 株式会社東芝 | Rare earth iron permanent magnet |
| EP0261579B1 (en) * | 1986-09-16 | 1993-01-07 | Tokin Corporation | A method for producing a rare earth metal-iron-boron permanent magnet by use of a rapidly-quenched alloy powder |
| US4881986A (en) * | 1986-11-26 | 1989-11-21 | Tokin Corporation | Method for producing a rare earth metal-iron-boron anisotropic sintered magnet from rapidly-quenched rare earth metal-iron-boron alloy ribbon-like flakes |
| EP0277416A3 (en) * | 1987-02-04 | 1990-05-16 | Crucible Materials Corporation | Permanent magnet alloy for elevated temperature applications |
| NL8800740A (en) * | 1987-12-11 | 1989-07-03 | Philips Nv | HARD-MAGNETIC MATERIAL FROM A RARE NATURAL METAL, IRON AND CARBON. |
-
1991
- 1991-07-23 DE DE1991601413 patent/DE69101413T2/en not_active Expired - Fee Related
- 1991-07-23 CA CA 2047592 patent/CA2047592C/en not_active Expired - Fee Related
- 1991-07-23 EP EP19910112333 patent/EP0468449B1/en not_active Expired - Lifetime
Also Published As
| Publication number | Publication date |
|---|---|
| EP0468449A1 (en) | 1992-01-29 |
| CA2047592A1 (en) | 1992-01-25 |
| DE69101413T2 (en) | 1994-07-07 |
| DE69101413D1 (en) | 1994-04-21 |
| EP0468449B1 (en) | 1994-03-16 |
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