Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
  • H01F7/00—Magnets
• • 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
  • H01F1/0555—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 pressed, sintered or bonded together
  • H01F1/0558—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 pressed, sintered or bonded together bonded together

Definitions

• the present invention relates to a flame retardant bond magnet formed of rare earth-­cobalt base alloy magnet powders and more particu­larly provides a highly flame retardant bond magnet which will find wide uses in electric equipment as sensor field magnet, various drive magnet, convergence correction magnet, etc., and which is produced by coating said alloy magnet powders with an oxidation resistant inorganic substance.
• rare earth magnets Alloy magnets of rare earth metals and transition metals as their main components (here­inafter referred to as rare earth magnets) are finding uses as high performance magnets, because of their high energy products and small magnetic flux density temperature coefficients, but they have a drawback on account of low mechanical strength and to remedy this situation, bond magnets have been put on the market. These rare earth magnet powders are susceptible to oxidation. Thus well-known rare earth bond magnets are liable to combustion.
• rare earth magnet powders represented by a general formula RM5 where R stands for a rare earth metal element, and M a transition metal element
• the object of this invention is to provide a bond magnet excellent in flame retardancy.
• the present inventors as a result of repetitive assiduous studies with a view to attainment of the aforementioned object, have realized a bond magnet excellent in combustion resistance (flame retardancy) even by using rare earth magnet powders with mean grain size less than 10 ⁇ m, which has led to this invention.
• the present invention covers flame retardant bond magnet comprising alloy magnet powders with mean grain size not greater than 10 ⁇ m represented by a general formula RM5 (where R designates a rare earth metal element, and M a transition metal element), which is coated on their surfaces with an oxidation resistant inorganic substance, a flame retarder and an organic binder.
• RM5 where R designates a rare earth metal element, and M a transition metal element
• the rare earth magnet powders used according to this invention are represented by a general formula RM5.
• R denotes samarium, prace­odymium, cerium, neodymium, yttrium and other rare earth metal elements, including mixtures of samarium with other rare earth metal elements and misch metal, etc.
• M designates cobalt and other transition metal elements; as these elements, mixtures of cobalt/iron or these with copper, zirconium, etc., added may be preferably utilized.
• Particularly useful in industrial applications are samarium - cobalt alloy magnet powders. Said rare earth magnet powders normally need to be reduced in their mean grain size to 10 ⁇ m or less in order to achieve magnetic characteristic.
• a first of such methods is a method comprising coating the powder surfaces with organic compounds having affinity with said magnet powder surfaces. This method is scarcely effective for imparting flame retardancy, as above described.
• a second method comprises exposing alloy magnet powders to air under a high temperature condition, thereby forming an oxide layer on the powder surfaces. By this method, the magnetic characteristic of the bond magnet thus obtained is impaired and, moreover, dispersion in the oxide layer thickness is large. Thus this method can hardly be said advantageous.
• a third method involves this invention.
• This method comprises coating the surfaces of said alloy magnet powders with a fine grained inorganic substance which has high oxidation resistance.
• a fine grained inorganic substance which has high oxidation resistance.
• Various materials may be utilized as the coating layer to be formed on magnet powders.
• Such materials may include, for example, chrome, nickel, copper, zinc, silver, tin, gold and other metals; nickel - chrome alloy, nickel - copper alloy and other alloys, silicates, borates, phosphates, borophosphates and other inorganics represented by inorganic glass. More particularly, lithium, sodium, potassium and ammonium silicates may be illustrated as silicates.
• Such metal film forming techniques as electroless plating, vapor deposition, spattering, etc., may be utilized.
• electroless plating Magnetic powders are dispersed in an electroless plating solution which is commercially available, which violently stirring them; the stirring is continued until the color peculiar to the metal ion in the plating solution disappears; thereafter, the powders are filtered and cleaned, yielding the intended treated magnet powders.
• the most representative is nickel plating.
• Such a metal coating layer's structure is particularly fine grained and even a relatively small amount of coating has a satisfactory specified effect, but on industrial scale, the treating facility price and the required treating time is relatively large, with a result that the manufacturing cost tends to be high.
• a simple and easy method as forming a fine grained coating of said inorganic salt on the magnet powder surfaces by adding a hardener, while dispersing magnet powders in an aqueous medium in which the inorganic salt is dissolved beforehand. This method is quite pre­ferable in industrial applications, involving only a simple process and requiring short treating time.
• the hardeners silicofluorides; mineral acids; oxides or salts of zinc, magnesium, zirconium, potassium, aluminum and other polyvalent metals and organic solvents, etc., may be illustrated.
• the intended flame retard­ancy of the bond magnets will vary depending on the content and grain size of magnet powders, material of the magnet powder coating layer, type of binder, type and amount of flame retarder used. Accordingly, the amount of the coating layer in the treated magnet powders required can not be unconditionally defined, varying depending on the flame retardancy level of the bond magnet, type of the coating layer, binder and flame retarder, and the content and grain size of the magnet powders, but generally, at least 0.5% by volume of this layer in the treated magnet powders is necessary.
• the volume proportion of the coating layer should desirably be limited to the minimum where the desired flame retardancy should be 1 - 40% by volume of the treated magnet powders, more preferably, 2 - 15% by volume.
• the organic binder used according to this invention shall be arbitrarily selected from universally used thermoplastic resins or thermo­setting resins or rubber.
• resins mainly composed of polyolefin or polyalkyl methacrylate or dienic synthetic rubbers which require very large amounts of flame retarders for attaining high flame retardancy are not recommendable.
• organic binders used according to this invention polyvinyl chloride, vinyl chloride/vinyl acetate copolymer, polystyrene, acrylonitrile/styrene copolymer, 6-polyamide, 11-polyamide, 12-polyamide, polyethylene terephthalate, polybutylene tere­phthalate, polyphenylene oxide, polystyrene denatured polyphenylene oxide, polycarbonate, polysufone, polyphenylene sulfide, polyallylate, thermoplastic polyimide, chlorinated polyethylene, chloroprene rubbers, phenol resins, unsaturated polyester resins and epoxy resins, etc., may be illustrated.
• the amount of treated magnetic powders used in the bond magnet of this invention may be varied over a wide ranges depending on the objects.
• a commercially effectively utilizable range of the powders should ultimately be 15 - 85% by volume of the formulation used for molding the magnet, the balance to be composed of the organic binder and the flame retarder. If their amount exceeds 85% by volume, the product can not be put to practical use because of very small mechanical strength, even when molded by any commercially applicable method, while under 15% by volume, practically useful magnetic characteristic can not be achieved.
• the amount of the treated magnetic powders used exceeds about 70% by volume, the compression molding method should be used. When it is below 70% by volume, almost all molding methods including injection, extrusion and compression molding, etc., may be utilized.
• a minimal amount of treated magnet powders should desirably be used, so long as the ultimately required magnetic characteristic can be met therewith.
• the amount of the treated magnet powders used providing the product in the form of an anisotropic magnet is effective.
• the amount of the treated magnetic powders may be reduced to 30% by volume or less. In that way, not only the flame retardancy may be imparted as intended by this invention, but excellent mechanical strength and favorable moldability may be provided as well.
• a flame retarder is used in the bond magnet of this invention. If any flame retarder is not used, even if the treated magnet powders used are improved in oxidation resistance, they are normally liable to combustion, providing only inadequate flame retardancy.
• bond magnets have large specific gravities and also high thermal conductivities and, moreover, contain large amounts of magnet powders and treated magnet powders which have small specific heats; therefore, unburnt parts tend to be heated to above the softening and decomposing temperature of the organic binder by the combustion heat at the time of initial ignition and combustion; then, the bond magnet drips, causing surrounding combustibles to catch fire, or the glowing after extinguishment to continue.
• a halogen containing flame retarder may be used in combination with a flame retarder aid and antiglowing agent, as required.
• a preferred flame retarder may be formulated by combination of aromatic bromine compound or chlorinated poly­cyclic or alicyclic compound and antimony trioxide. If the molding temperature of bond magnet is low, so that the halogen containing flame retarder will not decompose, of course, chlorinated or brominated aliphatic hydrocarbon compounds may be used.
• halogen containing flame retarders decabromodiphenyl ether, polybromostyrene tetra­bromobisphenol A, tetrabromobisphenol S, "DECHLORANE 604", “DECHLORANE PLUS” ("DECHLORANE” is a Hooker Chemical's trade name), etc.
• the flame retarder aids antimony trioxide, antimony pentoxide, etc., may be illustrated.
• anti-glowing agents zinc borate, phosphoric acid esters, etc.
• the amount of the flame retarder used can not be unconditionally determined, greatly varying with types and proportions of other components of the bond magnet.
• the lower limit for its using amount should be arbitrarily set with the amenability of the organic binder to the process of making it flame retardant as the major index.
• the upper using amount limit may be set in terms of the mold­ability and mechanical strength of the bond magnet, because from further increase in its amount, further effect of flame retardancy improve­ment is not much expectable.
• proper amount of the flame retarder used according to this invention may fall in the range of 20 - 200 parts by weight of the amount of the organic binder as 100 parts by weight, 40 - 170 parts by weight being more preferable.
• Preferable ratio of the amount of the flame retarder used to that of the flame retarder aid is from 3 : 2 to 4 : 1.
• the anti-glowing agent should normally be used at a proportion of 0 - 50 parts by weight of the amount of the aforementioned flame retarder, depending on the amount of the treated magnet powders used, this effect being prominent, when more than 5 parts by weight of it is used.
• bond magnets of this invention with the aim at achieving improvement in the modability characteristic, mechanical porperties or thermal stability, plasticizer, lubricant, surface modifier for treated magnet powders, filler, stabilizer and other modifying additives may be jointly used, so long as they do not interfere with their flame retardancy.
• proper method is selected from among various molding methods universally employed for molding bond magnets, taking account of the type of organic binder, content of treated magnet powders or the end to serve. They include, for example, injection, extrusion, compression and rolling.
• molding methods including, for example, injection, extrusion, compression and rolling.
• the bond magnets of this invention obtained in this way have both the excellent magnetic char­acteristic and flame retardancy which the rare earth/transition metal alloy magnets have. They are valuable as magnet parts for use in the perimeter of live parts in electric and electronic equipment.
• treated magnet powders B and treated magnet powders C were obtained similarly as above-descirbed, except that the amounts of sodium silicate used were set at 2.2g and 8.5g respectively.
• the coating thickness of sodium silicate film of the treated magnet powders A may be determined as 0.22 ⁇ m on the average.
• the treated magnet powders each of A - D obtained in Reference examples 1 and 2 and the organic binder, flame retarder and additives in the component ratio shown in Table 1 were respectively mixed with stirring and the mixture was melted by heating and kneaded for 10 min in a kneader type mixer. A lumpy kneaded product was taken out of the kneader and pulverized; thereafter, the powders obtained were molded in a heating press into a 0.8mm thick plate shape molding. From this plate shape molding, a test piece with 12.7mm width and 127mm length was prepared and with it vertical combustion test was conducted in accordance with the UL (Under­writers' Laboratories) Standard. The results given under the bottom column of Table 1 were obtained.
• UL Under­writers' Laboratories
• a test piece was prepared exactly just as in Example 1, except that the same magnet powders provided for preparation of the treated magnet powders in Reference example 1 were used as they were, and it was put to a combustion test. The sample dripped at the first flame approach of the combustion test and, subsequently, it burned, while dripping, causing ignition of cotton placed downward thereof.
• test piece was prepared exactly just as in Example 1, except that no flame retarder was used, and it was put to a combustion test. This test piece violently dripped already at the first flame approach; the dripping on the burner put out the burner flame, thus making it impossible to conduct the combustion test. The dripped matter quickly taken off above the burner con­tinued glowing for more than 60 sec.
• the bond magnets of this invention obtained from a com­position prepared using specified treated magnet powders and a flame retarder give excellent flame retardancy and attain levels of V-2 or higher in the vertical combustion test according to the UL Standard.
• the flame retardant bond magnets of this invention are finding wide ranges of uses in the fields of electric and electronic equipment, etc., where flame retardancy is required.

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Citations (3)

• 1986
  • 1986-07-25 JP JP61176330A patent/JPS6332903A/ja active Pending
• 1987
  • 1987-07-23 EP EP87110693A patent/EP0255051A1/de not_active Withdrawn
  • 1987-07-25 KR KR1019870008103A patent/KR890002911A/ko not_active IP Right Cessation

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