JP2004035939A - Spindle-shaped alloy magnetic particle powder for magnetic recording, and its manufacturing process - Google Patents
Spindle-shaped alloy magnetic particle powder for magnetic recording, and its manufacturing process Download PDFInfo
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- JP2004035939A JP2004035939A JP2002193546A JP2002193546A JP2004035939A JP 2004035939 A JP2004035939 A JP 2004035939A JP 2002193546 A JP2002193546 A JP 2002193546A JP 2002193546 A JP2002193546 A JP 2002193546A JP 2004035939 A JP2004035939 A JP 2004035939A
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- spindle
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- particle powder
- goethite
- shaped alloy
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- 239000006249 magnetic particle Substances 0.000 title claims abstract description 162
- 239000000843 powder Substances 0.000 title claims abstract description 149
- 229910045601 alloy Inorganic materials 0.000 title claims abstract description 108
- 239000000956 alloy Substances 0.000 title claims abstract description 108
- 230000005291 magnetic effect Effects 0.000 title claims abstract description 90
- 238000004519 manufacturing process Methods 0.000 title claims description 23
- 230000005415 magnetization Effects 0.000 claims abstract description 78
- 239000011248 coating agent Substances 0.000 claims abstract description 37
- 238000000576 coating method Methods 0.000 claims abstract description 37
- 229910052742 iron Inorganic materials 0.000 claims abstract description 35
- 229910017052 cobalt Inorganic materials 0.000 claims abstract description 31
- 239000010941 cobalt Substances 0.000 claims abstract description 31
- GUTLYIVDDKVIGB-UHFFFAOYSA-N cobalt atom Chemical compound [Co] GUTLYIVDDKVIGB-UHFFFAOYSA-N 0.000 claims abstract description 31
- 239000002245 particle Substances 0.000 claims description 239
- 229910052598 goethite Inorganic materials 0.000 claims description 142
- AEIXRCIKZIZYPM-UHFFFAOYSA-M hydroxy(oxo)iron Chemical compound [O][Fe]O AEIXRCIKZIZYPM-UHFFFAOYSA-M 0.000 claims description 142
- 230000009467 reduction Effects 0.000 claims description 53
- 239000007864 aqueous solution Substances 0.000 claims description 49
- 239000007789 gas Substances 0.000 claims description 40
- 238000007254 oxidation reaction Methods 0.000 claims description 39
- 229910052761 rare earth metal Inorganic materials 0.000 claims description 36
- 239000000243 solution Substances 0.000 claims description 34
- 239000007900 aqueous suspension Substances 0.000 claims description 31
- VHUUQVKOLVNVRT-UHFFFAOYSA-N Ammonium hydroxide Chemical compound [NH4+].[OH-] VHUUQVKOLVNVRT-UHFFFAOYSA-N 0.000 claims description 30
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Chemical compound O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 30
- 230000003647 oxidation Effects 0.000 claims description 27
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 claims description 26
- 150000001875 compounds Chemical class 0.000 claims description 26
- 229910052760 oxygen Inorganic materials 0.000 claims description 26
- 239000001301 oxygen Substances 0.000 claims description 26
- 239000013078 crystal Substances 0.000 claims description 25
- 239000011019 hematite Substances 0.000 claims description 25
- 229910052595 hematite Inorganic materials 0.000 claims description 25
- LIKBJVNGSGBSGK-UHFFFAOYSA-N iron(3+);oxygen(2-) Chemical compound [O-2].[O-2].[O-2].[Fe+3].[Fe+3] LIKBJVNGSGBSGK-UHFFFAOYSA-N 0.000 claims description 25
- 229910021446 cobalt carbonate Inorganic materials 0.000 claims description 24
- ZOTKGJBKKKVBJZ-UHFFFAOYSA-L cobalt(2+);carbonate Chemical compound [Co+2].[O-]C([O-])=O ZOTKGJBKKKVBJZ-UHFFFAOYSA-L 0.000 claims description 24
- 239000003513 alkali Substances 0.000 claims description 23
- 239000002244 precipitate Substances 0.000 claims description 23
- QGZKDVFQNNGYKY-UHFFFAOYSA-N ammonia Natural products N QGZKDVFQNNGYKY-UHFFFAOYSA-N 0.000 claims description 22
- BAUYGSIQEAFULO-UHFFFAOYSA-L iron(2+) sulfate (anhydrous) Chemical compound [Fe+2].[O-]S([O-])(=O)=O BAUYGSIQEAFULO-UHFFFAOYSA-L 0.000 claims description 21
- 229910052782 aluminium Inorganic materials 0.000 claims description 20
- -1 rare earth compound Chemical class 0.000 claims description 19
- ATRRKUHOCOJYRX-UHFFFAOYSA-N Ammonium bicarbonate Chemical compound [NH4+].OC([O-])=O ATRRKUHOCOJYRX-UHFFFAOYSA-N 0.000 claims description 16
- CWYNVVGOOAEACU-UHFFFAOYSA-N Fe2+ Chemical compound [Fe+2] CWYNVVGOOAEACU-UHFFFAOYSA-N 0.000 claims description 16
- 239000001099 ammonium carbonate Substances 0.000 claims description 16
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 claims description 15
- 239000011790 ferrous sulphate Substances 0.000 claims description 15
- 235000003891 ferrous sulphate Nutrition 0.000 claims description 15
- 229910000359 iron(II) sulfate Inorganic materials 0.000 claims description 15
- 239000011261 inert gas Substances 0.000 claims description 14
- 238000000034 method Methods 0.000 claims description 14
- BVKZGUZCCUSVTD-UHFFFAOYSA-L Carbonate Chemical compound [O-]C([O-])=O BVKZGUZCCUSVTD-UHFFFAOYSA-L 0.000 claims description 13
- 230000001590 oxidative effect Effects 0.000 claims description 13
- 239000000908 ammonium hydroxide Substances 0.000 claims description 12
- 150000001869 cobalt compounds Chemical class 0.000 claims description 11
- 229910000013 Ammonium bicarbonate Inorganic materials 0.000 claims description 9
- 230000032683 aging Effects 0.000 claims description 9
- 235000012538 ammonium bicarbonate Nutrition 0.000 claims description 9
- 238000010301 surface-oxidation reaction Methods 0.000 claims description 9
- 239000000203 mixture Substances 0.000 claims description 6
- 238000001914 filtration Methods 0.000 claims description 5
- 238000002360 preparation method Methods 0.000 claims description 2
- 238000009826 distribution Methods 0.000 abstract description 30
- 239000010419 fine particle Substances 0.000 abstract description 19
- 239000000696 magnetic material Substances 0.000 abstract description 6
- XEEYBQQBJWHFJM-UHFFFAOYSA-N iron Substances [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 79
- 229910052751 metal Inorganic materials 0.000 description 55
- 239000002184 metal Substances 0.000 description 54
- 238000006722 reduction reaction Methods 0.000 description 54
- 239000010410 layer Substances 0.000 description 30
- 235000011114 ammonium hydroxide Nutrition 0.000 description 27
- 238000006243 chemical reaction Methods 0.000 description 27
- 230000001965 increasing effect Effects 0.000 description 20
- 150000003839 salts Chemical class 0.000 description 20
- 229910052783 alkali metal Inorganic materials 0.000 description 17
- 150000001340 alkali metals Chemical class 0.000 description 17
- 238000005406 washing Methods 0.000 description 17
- 238000010438 heat treatment Methods 0.000 description 16
- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 description 15
- 230000007423 decrease Effects 0.000 description 15
- 238000005245 sintering Methods 0.000 description 15
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 13
- 229910001873 dinitrogen Inorganic materials 0.000 description 13
- 230000000694 effects Effects 0.000 description 11
- 239000000047 product Substances 0.000 description 11
- 230000001976 improved effect Effects 0.000 description 9
- 239000011734 sodium Substances 0.000 description 9
- 239000011575 calcium Substances 0.000 description 8
- SZVJSHCCFOBDDC-UHFFFAOYSA-N iron(II,III) oxide Inorganic materials O=[Fe]O[Fe]O[Fe]=O SZVJSHCCFOBDDC-UHFFFAOYSA-N 0.000 description 8
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 7
- 235000012501 ammonium carbonate Nutrition 0.000 description 7
- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 description 6
- QAOWNCQODCNURD-UHFFFAOYSA-L Sulfate Chemical compound [O-]S([O-])(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-L 0.000 description 6
- YXFVVABEGXRONW-UHFFFAOYSA-N Toluene Chemical compound CC1=CC=CC=C1 YXFVVABEGXRONW-UHFFFAOYSA-N 0.000 description 6
- 238000005755 formation reaction Methods 0.000 description 6
- 239000012535 impurity Substances 0.000 description 6
- 238000002156 mixing Methods 0.000 description 6
- CDBYLPFSWZWCQE-UHFFFAOYSA-L sodium carbonate Substances [Na+].[Na+].[O-]C([O-])=O CDBYLPFSWZWCQE-UHFFFAOYSA-L 0.000 description 6
- 239000007858 starting material Substances 0.000 description 6
- 238000005275 alloying Methods 0.000 description 5
- 239000003973 paint Substances 0.000 description 5
- 238000003860 storage Methods 0.000 description 5
- 229910052717 sulfur Inorganic materials 0.000 description 5
- UQSXHKLRYXJYBZ-UHFFFAOYSA-N Iron oxide Chemical compound [Fe]=O UQSXHKLRYXJYBZ-UHFFFAOYSA-N 0.000 description 4
- NINIDFKCEFEMDL-UHFFFAOYSA-N Sulfur Chemical compound [S] NINIDFKCEFEMDL-UHFFFAOYSA-N 0.000 description 4
- 229910021529 ammonia Inorganic materials 0.000 description 4
- 229910052791 calcium Inorganic materials 0.000 description 4
- 238000005259 measurement Methods 0.000 description 4
- 239000012266 salt solution Substances 0.000 description 4
- 229910052708 sodium Inorganic materials 0.000 description 4
- 238000003756 stirring Methods 0.000 description 4
- 239000011593 sulfur Substances 0.000 description 4
- ZWEHNKRNPOVVGH-UHFFFAOYSA-N 2-Butanone Chemical compound CCC(C)=O ZWEHNKRNPOVVGH-UHFFFAOYSA-N 0.000 description 3
- CUPCBVUMRUSXIU-UHFFFAOYSA-N [Fe].OOO Chemical compound [Fe].OOO CUPCBVUMRUSXIU-UHFFFAOYSA-N 0.000 description 3
- 229910052786 argon Inorganic materials 0.000 description 3
- 230000015572 biosynthetic process Effects 0.000 description 3
- 239000000460 chlorine Substances 0.000 description 3
- 230000004907 flux Effects 0.000 description 3
- 239000001307 helium Substances 0.000 description 3
- 229910052734 helium Inorganic materials 0.000 description 3
- SWQJXJOGLNCZEY-UHFFFAOYSA-N helium atom Chemical compound [He] SWQJXJOGLNCZEY-UHFFFAOYSA-N 0.000 description 3
- 239000001257 hydrogen Substances 0.000 description 3
- 229910052739 hydrogen Inorganic materials 0.000 description 3
- 229910021519 iron(III) oxide-hydroxide Inorganic materials 0.000 description 3
- 239000007788 liquid Substances 0.000 description 3
- 239000002923 metal particle Substances 0.000 description 3
- 230000002265 prevention Effects 0.000 description 3
- 230000005070 ripening Effects 0.000 description 3
- 229910000029 sodium carbonate Inorganic materials 0.000 description 3
- 238000012360 testing method Methods 0.000 description 3
- 229910052727 yttrium Inorganic materials 0.000 description 3
- 208000005156 Dehydration Diseases 0.000 description 2
- 229910017061 Fe Co Inorganic materials 0.000 description 2
- DGAQECJNVWCQMB-PUAWFVPOSA-M Ilexoside XXIX Chemical compound C[C@@H]1CC[C@@]2(CC[C@@]3(C(=CC[C@H]4[C@]3(CC[C@@H]5[C@@]4(CC[C@@H](C5(C)C)OS(=O)(=O)[O-])C)C)[C@@H]2[C@]1(C)O)C)C(=O)O[C@H]6[C@@H]([C@H]([C@@H]([C@H](O6)CO)O)O)O.[Na+] DGAQECJNVWCQMB-PUAWFVPOSA-M 0.000 description 2
- 230000003679 aging effect Effects 0.000 description 2
- DIZPMCHEQGEION-UHFFFAOYSA-H aluminium sulfate (anhydrous) Chemical compound [Al+3].[Al+3].[O-]S([O-])(=O)=O.[O-]S([O-])(=O)=O.[O-]S([O-])(=O)=O DIZPMCHEQGEION-UHFFFAOYSA-H 0.000 description 2
- 229910052801 chlorine Inorganic materials 0.000 description 2
- 229940011182 cobalt acetate Drugs 0.000 description 2
- UFMZWBIQTDUYBN-UHFFFAOYSA-N cobalt dinitrate Chemical compound [Co+2].[O-][N+]([O-])=O.[O-][N+]([O-])=O UFMZWBIQTDUYBN-UHFFFAOYSA-N 0.000 description 2
- 229910001981 cobalt nitrate Inorganic materials 0.000 description 2
- 229940044175 cobalt sulfate Drugs 0.000 description 2
- 229910000361 cobalt sulfate Inorganic materials 0.000 description 2
- KTVIXTQDYHMGHF-UHFFFAOYSA-L cobalt(2+) sulfate Chemical compound [Co+2].[O-]S([O-])(=O)=O KTVIXTQDYHMGHF-UHFFFAOYSA-L 0.000 description 2
- QAHREYKOYSIQPH-UHFFFAOYSA-L cobalt(II) acetate Chemical compound [Co+2].CC([O-])=O.CC([O-])=O QAHREYKOYSIQPH-UHFFFAOYSA-L 0.000 description 2
- 230000000052 comparative effect Effects 0.000 description 2
- 238000007796 conventional method Methods 0.000 description 2
- 238000001816 cooling Methods 0.000 description 2
- JHIVVAPYMSGYDF-UHFFFAOYSA-N cyclohexanone Chemical compound O=C1CCCCC1 JHIVVAPYMSGYDF-UHFFFAOYSA-N 0.000 description 2
- 230000018044 dehydration Effects 0.000 description 2
- 238000006297 dehydration reaction Methods 0.000 description 2
- 238000010828 elution Methods 0.000 description 2
- 238000005516 engineering process Methods 0.000 description 2
- 229960002089 ferrous chloride Drugs 0.000 description 2
- 230000006698 induction Effects 0.000 description 2
- 230000001939 inductive effect Effects 0.000 description 2
- 150000002500 ions Chemical class 0.000 description 2
- NMCUIPGRVMDVDB-UHFFFAOYSA-L iron dichloride Chemical compound Cl[Fe]Cl NMCUIPGRVMDVDB-UHFFFAOYSA-L 0.000 description 2
- 239000006247 magnetic powder Substances 0.000 description 2
- 239000002994 raw material Substances 0.000 description 2
- 238000011946 reduction process Methods 0.000 description 2
- 229920006395 saturated elastomer Polymers 0.000 description 2
- 238000004904 shortening Methods 0.000 description 2
- 229910052710 silicon Inorganic materials 0.000 description 2
- BNGXYYYYKUGPPF-UHFFFAOYSA-M (3-methylphenyl)methyl-triphenylphosphanium;chloride Chemical compound [Cl-].CC1=CC=CC(C[P+](C=2C=CC=CC=2)(C=2C=CC=CC=2)C=2C=CC=CC=2)=C1 BNGXYYYYKUGPPF-UHFFFAOYSA-M 0.000 description 1
- NGDQQLAVJWUYSF-UHFFFAOYSA-N 4-methyl-2-phenyl-1,3-thiazole-5-sulfonyl chloride Chemical compound S1C(S(Cl)(=O)=O)=C(C)N=C1C1=CC=CC=C1 NGDQQLAVJWUYSF-UHFFFAOYSA-N 0.000 description 1
- NLXLAEXVIDQMFP-UHFFFAOYSA-N Ammonium chloride Substances [NH4+].[Cl-] NLXLAEXVIDQMFP-UHFFFAOYSA-N 0.000 description 1
- 238000004438 BET method Methods 0.000 description 1
- OYPRJOBELJOOCE-UHFFFAOYSA-N Calcium Chemical compound [Ca] OYPRJOBELJOOCE-UHFFFAOYSA-N 0.000 description 1
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 1
- 229910052684 Cerium Inorganic materials 0.000 description 1
- ZAMOUSCENKQFHK-UHFFFAOYSA-N Chlorine atom Chemical compound [Cl] ZAMOUSCENKQFHK-UHFFFAOYSA-N 0.000 description 1
- 229910021503 Cobalt(II) hydroxide Inorganic materials 0.000 description 1
- MYMOFIZGZYHOMD-UHFFFAOYSA-N Dioxygen Chemical compound O=O MYMOFIZGZYHOMD-UHFFFAOYSA-N 0.000 description 1
- 229910001111 Fine metal Inorganic materials 0.000 description 1
- 229910052779 Neodymium Inorganic materials 0.000 description 1
- 229910052777 Praseodymium Inorganic materials 0.000 description 1
- 229910052772 Samarium Inorganic materials 0.000 description 1
- 229910000831 Steel Inorganic materials 0.000 description 1
- 238000002441 X-ray diffraction Methods 0.000 description 1
- 239000002253 acid Chemical class 0.000 description 1
- 230000009471 action Effects 0.000 description 1
- 239000000654 additive Substances 0.000 description 1
- 230000000996 additive effect Effects 0.000 description 1
- 238000005273 aeration Methods 0.000 description 1
- 229910001854 alkali hydroxide Inorganic materials 0.000 description 1
- 229910000288 alkali metal carbonate Inorganic materials 0.000 description 1
- 150000008041 alkali metal carbonates Chemical class 0.000 description 1
- 150000008044 alkali metal hydroxides Chemical class 0.000 description 1
- 150000004645 aluminates Chemical class 0.000 description 1
- 150000003868 ammonium compounds Chemical class 0.000 description 1
- 150000001450 anions Chemical class 0.000 description 1
- 238000000137 annealing Methods 0.000 description 1
- 159000000007 calcium salts Chemical class 0.000 description 1
- 229910052799 carbon Inorganic materials 0.000 description 1
- 239000006229 carbon black Substances 0.000 description 1
- 150000001722 carbon compounds Chemical class 0.000 description 1
- ZMIGMASIKSOYAM-UHFFFAOYSA-N cerium Chemical compound [Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce][Ce] ZMIGMASIKSOYAM-UHFFFAOYSA-N 0.000 description 1
- 230000008859 change Effects 0.000 description 1
- 239000007795 chemical reaction product Substances 0.000 description 1
- 150000001805 chlorine compounds Chemical class 0.000 description 1
- 150000001868 cobalt Chemical class 0.000 description 1
- 229910001429 cobalt ion Inorganic materials 0.000 description 1
- XLJKHNWPARRRJB-UHFFFAOYSA-N cobalt(2+) Chemical compound [Co+2] XLJKHNWPARRRJB-UHFFFAOYSA-N 0.000 description 1
- ASKVAEGIVYSGNY-UHFFFAOYSA-L cobalt(ii) hydroxide Chemical compound [OH-].[OH-].[Co+2] ASKVAEGIVYSGNY-UHFFFAOYSA-L 0.000 description 1
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- 230000006872 improvement Effects 0.000 description 1
- 238000010348 incorporation Methods 0.000 description 1
- 238000005342 ion exchange Methods 0.000 description 1
- YWXYYJSYQOXTPL-SLPGGIOYSA-N isosorbide mononitrate Chemical compound [O-][N+](=O)O[C@@H]1CO[C@@H]2[C@@H](O)CO[C@@H]21 YWXYYJSYQOXTPL-SLPGGIOYSA-N 0.000 description 1
- 229910052746 lanthanum Inorganic materials 0.000 description 1
- FZLIPJUXYLNCLC-UHFFFAOYSA-N lanthanum atom Chemical compound [La] FZLIPJUXYLNCLC-UHFFFAOYSA-N 0.000 description 1
- 229910001092 metal group alloy Inorganic materials 0.000 description 1
- 229910021645 metal ion Inorganic materials 0.000 description 1
- 239000007769 metal material Substances 0.000 description 1
- 229910044991 metal oxide Inorganic materials 0.000 description 1
- 150000004706 metal oxides Chemical class 0.000 description 1
- 238000000465 moulding Methods 0.000 description 1
- QEFYFXOXNSNQGX-UHFFFAOYSA-N neodymium atom Chemical compound [Nd] QEFYFXOXNSNQGX-UHFFFAOYSA-N 0.000 description 1
- 150000002823 nitrates Chemical class 0.000 description 1
- 239000003960 organic solvent Substances 0.000 description 1
- 229920000139 polyethylene terephthalate Polymers 0.000 description 1
- 239000005020 polyethylene terephthalate Substances 0.000 description 1
- 229920005749 polyurethane resin Polymers 0.000 description 1
- TYJJADVDDVDEDZ-UHFFFAOYSA-M potassium hydrogencarbonate Chemical compound [K+].OC([O-])=O TYJJADVDDVDEDZ-UHFFFAOYSA-M 0.000 description 1
- 229910001414 potassium ion Inorganic materials 0.000 description 1
- PUDIUYLPXJFUGB-UHFFFAOYSA-N praseodymium atom Chemical compound [Pr] PUDIUYLPXJFUGB-UHFFFAOYSA-N 0.000 description 1
- 238000012545 processing Methods 0.000 description 1
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- 238000010298 pulverizing process Methods 0.000 description 1
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- KZUNJOHGWZRPMI-UHFFFAOYSA-N samarium atom Chemical compound [Sm] KZUNJOHGWZRPMI-UHFFFAOYSA-N 0.000 description 1
- 229910052706 scandium Inorganic materials 0.000 description 1
- SIXSYDAISGFNSX-UHFFFAOYSA-N scandium atom Chemical compound [Sc] SIXSYDAISGFNSX-UHFFFAOYSA-N 0.000 description 1
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Abstract
Description
【０００１】
【発明の属する技術分野】
本発明は、微細な粒子、殊に、平均長軸径が０．０２〜０．０８μｍの微粒子でありながら、高い保磁力を示し、低飽和磁化値でありながら、磁性塗膜の保磁力分布Ｓ．Ｆ．Ｄ．に優れたＦｅ及びＣｏを主成分とする紡錘状合金磁性粒子粉末を提供するものであり、当該Ｆｅ及びＣｏを主成分とする紡錘状合金磁性粒子粉末は磁気記録媒体用磁性材料として好適なものである。
【０００２】
【従来の技術】
近年、オーディオ用、ビデオ用、コンピューター用の磁気記録再生用機器の小型軽量化、長時間記録化、記録の高密度化、若しくは記憶容量の増大化が著しく進行しており、磁気記録媒体である磁気テープ、磁気ディスクに対する高性能化、高密度記録化の要求が益々高まってきている。
【０００３】
即ち、磁気記録媒体の高画像画質、高出力特性、殊に周波数特性の向上が要求され、その為には、磁気記録媒体に起因するノイズの低下、高い保磁力Ｈｃと保磁力分布Ｓ．Ｆ．Ｄ．が優れていることが要求されている。加えて、保存特性及び耐久性の向上が要求されており、その為には耐候性△Ｂｍが優れており、塗膜中の可溶性塩の含有量が低減されている事が要求されている。
【０００４】
磁気記録媒体のこれらの諸特性は磁気記録媒体に使用される磁性粒子粉末と密接な関係を有しており、近年においては、従来の磁性酸化鉄粒子粉末に比較して高い保磁力と大きな飽和磁化値σｓを有する鉄を主成分とする金属磁性粒子粉末が注目され、デジタルオーディオテープ（ＤＡＴ）、８ｍｍビデオテープ、Ｈｉ−８テープ、さらにハイビジョン用のＷ−ＶＨＳテープ、デジタル記録方式のＤＶＣテープ等に、コンピューター用ではＤＤＳ、ＤＬＴ、ＴＲＡＶＡＮなど外部記憶システム用テープ、Ｚｉｐ、スーパーディスク、Ｈｉ−ＦＤ等のリムーバブルディスクにも使用されている。
【０００５】
そこで、鉄を主成分とする金属磁性粒子粉末についても更なる特性改善が強く望まれている。
【０００６】
即ち、前記諸特性を満たす磁気記録媒体を得るためには、鉄を主成分とする金属磁性粒子粉末が微粒子であって、より高い保磁力を有し、保磁力分布Ｓ．Ｆ．Ｄ．に優れていることが強く要求されている。加えて、酸化安定性△σｓに優れ、しかも可溶性塩の含有量が可及的に低減されていることが要求されている。
【０００７】
まず、金属磁性粒子粉末の微粒子化については、特開２０００―２５１２４３号公報の「……磁気記録媒体の高記録密度を達成するため、使用する信号の短波長化が強力に進められている。信号を記録する領域の長さに対して、使用される磁性体が比較出来る大きさになると明瞭な磁化遷移領域を作り出すことが出来ないので、実質的に記録不可能となる。このため使用する高記録密度化のために、磁性体の微粒子化が長年にわたり指向されている。」なる記載の通り、短波長領域での高出力、ノイズが低減された磁気記録媒体を得るためには、金属磁性粒子粉末の微粒子化、即ち、長軸径の低減が必要になる。
【０００８】
また、近年では、これまで用いられてきた誘導型磁気ヘッドに替わり、磁気抵抗型ヘッドがコンピューター用テープ再生ヘッドとして導入され始めている。磁気抵抗型ヘッドは、誘導型磁気ヘッドに比べて再生出力が得られやすく、しかも、誘導コイルに起因するインピーダンスノイズが発生しないため、システムノイズの大幅な低減に寄与する。このため、磁気記録媒体ノイズを低減することができれば、高いＣ／Ｎ比を達成することが可能となる。したがって、磁気記録媒体ノイズのうち、粒子性ノイズの低減の観点からも金属磁性粒子粉末の更なる微粒子化が求められている。
【０００９】
加えて、金属磁性粒子の微細化に伴い、全体粒子における酸化被膜の比率が上昇するため、酸化被膜生成による保磁力の低下や保磁力分布Ｓ．Ｆ．Ｄ．が拡大する傾向にある。よって、磁気記録媒体の短波長領域での出力向上のためには、微粒子でありながら、保磁力分布Ｓ．Ｆ．Ｄ．（Ｓｗｉｔｃｈｉｎｇ Ｆｉｅｌｄ Ｄｉｓｔｒｉｂｕｔｉｏｎ）が優れている事が要求されている。
【００１０】
更に、磁気抵抗型ヘッドは感度が高いため、磁気記録媒体の残留磁化値が過剰な場合には磁気抵抗型ヘッドの飽和を引き起こし、再生特性に歪みを生じ易い。最近の高感度磁気抵抗型ヘッドの開発に伴い、磁気記録媒体の残留磁化値の低減が進められており、そこで、金属磁性粒子粉末の飽和磁化値の低減が必要とされている。従来、金属磁性粒子粉末の粒子表面に厚い酸化被膜を形成することにより、金属磁性粒子粉末の飽和磁化値を低減する方法が提案されているが、それに伴い保磁力分布Ｓ．Ｆ．Ｄ．が拡大するため、前記磁気記録媒体に対する要求を満足出来るものではなかった。そこで、微粒子でありながら、保磁力分布Ｓ．Ｆ．Ｄ．を維持すると共に、低い飽和磁化値の金属磁性粒子粉末が強く要求されている。
【００１１】
一方、磁性粒子粉末の保磁力は、一般に、その形状磁気異方性に起因して生じるため、高い保磁力の磁性粒子粉末を得るためには、粒子の軸比（平均長軸径／平均短軸径）を大きくする必要がある。しかし、微粒子であるほど軸比が低下する傾向にあるため、高い保磁力を有する金属磁性粒子粉末を得ることが困難となる。この事実は特開平１０−８３９０６号公報の「・・・上記金属粉末の保磁力は、一般的には粒子の大きさに密接に関係しており、粒子が細かくなればなるほど保磁力を保つことが困難になる。例えば、針状粒子の短軸径が一定の場合、その保磁力は、軸比（長軸径／短軸径）が大であるほど高くなるが、・・・・・・保磁力を高く保ち且つ短波長領域における高出力を得るためには、粒子の長軸が限定されてしまう以上、短軸を短くして軸比を大きくすることにより保磁力を高めるしかない。しかしながら、粒子の短軸径があまり小さくなると、いわゆる超常磁性が発現して保磁力を示さないことが知られ、短軸径の短縮化にも限界があった。」なる記載の通りである。
【００１２】
保磁力と飽和磁化値とを限定した金属磁性粒子粉末が、特公平５−４４１６２号公報、特開２０００−３２３３１６号公報、特開２００１−９３７１１号公報、特開２００１−２８３４２１号公報等に記載されている。
【００１３】
また、金属磁性粒子の微細化に伴い短軸径が短縮化し、金属磁性粒子粉末の結晶子サイズが減少して比表面積が増大するため、高い酸化安定性を維持することが非常に困難になることが知られている。金属磁性粒子粉末の酸化安定性は、磁気記録媒体の保存特性及び耐久性に大きく寄与することから、微粒子でありながら、高い酸化安定性を有することが強く望まれている。
【００１４】
一方、金属磁性粒子粉末は、その製造法に由来して、アルカリ金属などの不純物を含有している。この事実について詳述する。
【００１５】
即ち、鉄を主成分とする金属磁性粒子粉末は、硫酸第一鉄などの第一鉄塩水溶液と水酸化ナトリウム、炭酸ナトリウムなどのアルカリ水溶液とを反応して得られる鉄含有沈殿物を含む水懸濁液を空気等の酸素含有ガスを通気して酸化反応を行い得られるゲータイト粒子粉末、該ゲータイト粒子粉末を加熱脱水して得られるヘマタイト粒子粉末又はこれら粒子粉末に鉄以外の異種元素を含有させた粒子粉末を出発原料として用い、該出発原料を還元性ガス雰囲気下で加熱還元することにより得られている。
【００１６】
前記製造法に由来して、金属磁性粒子粉末は可溶性ナトリウム及び硫酸イオンや製法上不可避的に存在する可溶性カルシウムを含有しており、可溶性ナトリウム塩、可溶性カルシウム塩及び硫酸イオンを含有している場合には、磁気記録媒体に使用したときに含有している前記可溶性塩に起因した化合物が磁性塗膜及び磁気ヘッドに析出することが問題となっている。この事実は、特開平９−３０５９５８号公報の「各層に使用される磁性体、非磁性体、カーボンブラック、フィラーが含有している水溶性イオンの総和がある量を超えると高温高湿条件で保存後走行させると摩擦係数が増加し、極端な場合は張り付き現象が発生し走行停止する現象が認められた。さらに極端な場合、析出物がスペーシングロスとなり、磁気テープの再生出力が低下する。また金属ヘッドを腐食し、記録再生特性を劣化させてしまう。」という記載からも明らかである。
【００１７】
金属磁性粒子粉末中の可溶性塩を低減させる方法としては、１）原料として水酸化ナトリウム等のアルカリ金属からなるアルカリ水溶液を用いない、２）水洗によって可溶性塩を低減する、のどちらかの方法が採られている。
【００１８】
水洗によって可溶性塩を低減する場合には、金属磁性粒子粉末に至るまでの各生成物ごとに水洗することが考えられるが、前記金属磁性粒子粉末の製造法において、出発原料であるゲータイト粒子粉末及びヘマタイト粒子粉末の段階で水洗を行っても、除去されるのは粒子表面に存在する可溶性塩だけである。そのため、還元して金属磁性粒子粉末とした場合には、粒子中に含有している不溶性不純物が粒子表面に移動し可溶性塩となって析出することが知られており、完全に除去できるものではない。一方、金属磁性粒子粉末とした後に水洗を行った場合、特に、粒子形状が紡錘状の場合には、保磁力などの磁気特性が低下し、磁性塗料中での分散性も低下する傾向がある。
【００１９】
従って、水洗によって可溶性塩を低減する技術では、可溶性塩を低減することはできるが、ゼロにすることは容易ではなく、また磁気特性の低下を招くことになるため好ましくない。そこで、原料として水酸化ナトリウム等のアルカリ金属からなるアルカリ水溶液を用いないことによって、残存する不純物を限りなく無くし、高純度の金属磁性粒子粉末を得ることが要求されている。
【００２０】
従来、アルカリ金属からなるアルカリ水溶液を用いることなくゲータイト粒子粉末を製造する技術やゲータイト粒子粉末を加熱脱水した後のヘマタイト粒子粉末及び金属磁性粒子粉末を水洗する技術が試みられている（特開昭６１−１７４１１９号公報、特開平７−２２２２４号公報、特開平７−３２６０３５号公報、特開平８−７２５６号公報、特開平８−１８５６２４号公報、特開平８−１８６０１５号公報、特開平８−２７９１３７号公報、特開平８−２７９１３８号公報、特開平８−３０６０３１号公報、特開平９−１０６５３５号公報、特開平９−３０５９５８号公報、特開平１０−６９６２９号公報、特開平１０−８３９０６号公報、特開２００１−８１５０６号公報、特開２００１−１７６０５２号公報、ＷＯ００／３８２０１号公報、特開２００１−１９２２１１号公報等）。
【００２１】
【発明が解決しようとする課題】
微粒子でありながら、高い保磁力を示し、しかも、低飽和磁化値でありながら、磁性塗膜の保磁力分布Ｓ．Ｆ．Ｄ．に優れた紡錘状合金磁性粒子粉末は、現在最も要求されているところであるが、前記諸特性を十分満足する鉄を主成分とする金属磁性粒子粉末は未だ提供されていない。
【００２２】
即ち、前出特公平５−４４１６２号公報には、金属磁性粒子粉末を徐酸化後、酸素含有ガス中で加熱処理することにより、厚い酸化物層を形成させ、低飽和磁化し、酸化安定性を改良した金属磁性粒子粉末を製造することが記載されているが、得られた金属磁性材料は厚い酸化物層を形成させるため、保磁力分布Ｓ．Ｆ．Ｄが広く、保磁力も１０００Ｏｅ程度であり、高保磁力化、保磁力分布Ｓ．Ｆ．Ｄ．の要求を十分満足していない。
【００２３】
また、前出特開２０００−３２３３１６号公報には、磁性領域を覆うように特定比率の非磁性領域が形成された金属系材料が、磁気抵抗ヘッドを用いた再生システムにおいて、低ノイズ化が図れる事により、高Ｓ／Ｎ化出来ることが記載されている。しかしながら、Ｃｏとの合金化が十分に検討されておらず、非磁性領域拡大による低飽和磁化は著しい保磁力分布Ｓ．Ｆ．Ｄ．の拡大を招き、保磁力分布Ｓ．Ｆ．Ｄ．の要求を満足出来ないものである。また、飽和磁化値も１００Ａｍ２／ｋｇ（１００ｅｍｕ／ｇ）以上であり、低飽和磁化の要求に対し、不十分である。
【００２４】
また、前出特開２００１−９３７１１号公報には、全Ｆｅに対してＣｏ換算で４５〜３００重量％に高めた金属磁性粒子粉末を用いることにより、磁気記録媒体での耐酸化性に優れ、出力レベルダウンを防止することが記載されているが、微粒子化、高保磁力化への対応が不十分であり、加えて、飽和磁化値が１１０Ａｍ２／ｋｇ（１１０ｅｍｕ／ｇ）以上と高く、低飽和磁化の要求を十分満たしていない。
【００２５】
また、前出特開２００１−２８３４２１号公報には、平均長軸長が０．１μｍ以下、飽和磁化値が１２０Ａｍ２／ｋｇ（１２０ｅｍｕ／ｇ）以下であり、且つ、保磁力が２１００ｋＡ／ｍ（２１００Ｏｅ）以上である針状強磁性粒子粉末を用いた磁気記録媒体が磁気抵抗ヘッドを再生に用いる高密度記録に適していることが記載されているが、飽和磁化値が１００Ａｍ２／ｋｇ（１００ｅｍｕ／ｇ）程度と低飽和磁化の要求に対し、十分とは言えず、また、Ｃｏ含有量が全Ｆｅに対してＣｏ換算で３３原子％と低く、飽和磁化値を１００Ａｍ２／ｋｇ（１００ｅｍｕ／ｇ）以下に低減した場合、保磁力分布Ｓ．Ｆ．Ｄ．劣化が著しく、保磁力分布Ｓ．Ｆ．Ｄ．の要求を満足出来ないものである。
【００２６】
また、前出特開昭６１−１７４１１９号公報には、炭酸アンモニウム水溶液に硫酸第一鉄水溶液を用いてゲータイト粒子粉末を製造することが記載されているが、得られたゲータイト粒子粉末はコバルトを含有していないため、該粒子粉末を出発物質として得られた金属磁性粒子粉末の酸化安定性は十分とは言い難いものである。
【００２７】
また、前出特開平７−２２２２４号公報にはヘマタイト粒子粉末又は金属磁性粒子粉末を水洗することが記載されているが、得られた磁性金属粒子粉末は長軸径が０．０８μｍ以上、飽和磁化値が１２０Ａｍ２／ｋｇ（１２０ｅｍｕ／ｇ）以上であって、微粒子化・低飽和磁化の要求を十分満たしていない。
【００２８】
また、前出特開平７−３２６０３５号公報及び特開平８−７２５６号公報には、第一鉄塩水溶液と炭酸アンモニウム及びアンモニア水とを用いて得られたゲータイト粒子粉末を用いて金属磁性粒子粉末を製造することが記載されているが、平均長軸径が０．０８μｍ以上、飽和磁化値が１２０Ａｍ２／ｋｇ（１２０ｅｍｕ／ｇ）以上と大きいので、微粒子化・低飽和磁化の要求を十分満たしていない。
【００２９】
また、前出特開平８−１８５６２４号公報にはヘマタイト粒子又は金属磁性粒子を水洗してナトリウムイオンとカリウムイオンとの含有割合を特定範囲に制限することが記載されているが、平均長軸径が０．１３μｍ程度、飽和磁化値が１２０Ａｍ２／ｋｇ（１２０ｅｍｕ／ｇ）以上と大きく、可溶性ナトリウム含有量が２００ｐｐｍ以下と多いので、微粒子化・高保磁力化、低飽和磁化および酸化安定性向上の要求を十分満たしていない。
【００３０】
また、前出特開平８−２７９１３７号公報及び特開平８−３０６０３１号公報には、第一鉄塩水溶液と炭酸アンモニウム及びアンモニア水とを用いて得られたゲータイト粒子粉末を用いて金属磁性粒子粉末を製造することが記載されており、得られる金属磁性粒子粉末は、平均長軸径が０．０５〜０．１３μｍであって、粒子の表層部が粒子全体に比べアルミニウム、希土類元素及び酸素の含有割合が高くなっている。しかしながら、ゲータイト粒子を生成し、水洗した後、アルミニウム化合物を添加しているため、アルミニウムを結晶中に含有させたゲータイト粒子が得られておらず、加熱還元処理時の還元速度の制御が十分行われないため、焼結が進行するので、微粒子かつ磁気特性・酸化安定性に優れた金属磁性粒子粉末が得られない。加えて、飽和磁化値が１３０Ａｍ２／ｋｇ（１３０ｅｍｕ／ｇ）以上であり、低飽和磁化への要求を十分満たしていない。
【００３１】
また、前出特開平９−１０６５３５号公報には、第一鉄塩水溶液と炭酸アンモニウム及びアンモニア水とを用いて得られたゲータイト粒子粉末を用いて金属磁性粒子粉末を製造することが記載されており、長軸径が０．０３〜０．０８μｍで保磁力１９００〜２４００Ｏｅの金属磁性粒子粉末が得られているが、酸化安定性向上の要求を十分満たしていない。加えて、飽和磁化値が１３０Ａｍ２／ｋｇ（１３０ｅｍｕ／ｇ）以上であり、低飽和磁化への要求を十分満たしていない。
【００３２】
また、前出特開平９−１７１９１４号公報には、ゲータイト粒子にＣｏ、Ａｌ、Ｓｉ及びＣａから選ばれる１種以上の化合物と希土類化合物を被着させ、水洗した後、最外層に炭素化合物を被着させ、次いで、加熱脱水、還元して金属磁性粒子粉末を得ることが記載されているが、ゲータイト粒子中にコバルト及びアルミニウムが固溶していないため、得られる金属磁性粒子粉末の磁気特性が未だ十分とは言い難いものである。また、Ｓ及びＣｌ含有量を低減することを目的として、Ｃｏ、Ａｌ、Ｓｉ及びＣａから選ばれる１種以上の化合物と希土類化合物を被着させたゲータイト粒子を水洗することが記載されているが、該粒子を還元して金属磁性粒子粉末とした場合には、粒子中に含有している不溶性不純物が粒子表面に移動し可溶性塩となって析出してくることが知られており、Ｓ及びＣｌ含有量は十分に低減されない。また、飽和磁化値が１２０Ａｍ２／ｋｇ（１２０ｅｍｕ／ｇ）以上であり、低飽和磁化への要求を十分満たしていない。
【００３３】
また、前出特開平９−３０５９５８号公報には、アルカリ金属を含まない炭酸アルカリを用いてゲータイト粒子粉末を得、更に、金属磁性粒子粉末とするまでに水洗して金属磁性粒子粉末中の水溶性イオンの含有量を低減することが記載されているが、添加物としてアルカリ金属を含有する化合物を用いているため、ゲータイト粒子中にアルカリ金属を含有しており、高純度のゲータイト粒子が得られているとは言い難いものである。加えて、飽和磁化値が１３０Ａｍ２／ｋｇ（１３０ｅｍｕ／ｇ）以上であり、低飽和磁化への要求に対応出来ていない。
【００３４】
また、前出特開平１０−６９６２９号公報には、ゲータイト粒子、ヘマタイト粒子又は金属磁性粒子のいずれかの段階で水洗することが記載されているが、完全に除去できるとは言い難いものである。一方、金属磁性粒子粉末とした後に水洗を行った場合、飽和磁化、保磁力などの磁気特性が低下し、磁性塗料中での分散性も低下するので好ましくない。加えて、飽和磁化値が１３０Ａｍ２／ｋｇ（１３０ｅｍｕ／ｇ）以上であり、低飽和磁化への要求を十分満たしていない。
【００３５】
また、前出特開平１０−８３９０６号公報には、塩化第一鉄とアンモニア水溶液からなる水酸化アルカリと炭酸アンモニウム等からなる炭酸アルカリからゲータイト粒子粉末を製造することが記載されているが、アンモニア水で水洗することは記載されておらず、また、ゲータイト粒子を生成するときの反応ｐＨが高いため、コバルトイオンがアンミン錯体として溶出するため、高い保磁力を有する金属磁性粒子粉末を得ることが困難となる。加えて、飽和磁化値が１３０Ａｍ２／ｋｇ（１３０ｅｍｕ／ｇ）以上であり、低飽和磁化への要求を十分満たしていない。
【００３６】
また、特開２００１−８１５０６号公報には、Ｃｏを含有し、Ａｌを固溶したオキシ水酸化鉄または酸化鉄の粒子表面に、希土類とＳｉを被着させ、該粒子粉末をガス還元して金属磁性粒子粉末を得ることが記載されているが、平均長軸径が０．１０μｍと大きいものであり、且つ、飽和磁化値が１４０Ａｍ２／ｋｇ（１２０ｅｍｕ／ｇ）以上であり、微粒子化・低飽和磁化の要求を十分満たしていない。
【００３７】
また、特開２００１−１７６０５２号公報及び特開２００１−１７６０５３号公報には、第一鉄塩水溶液と炭酸アンモニウム及びアンモニア水とを用いて得られたゲータイト粒子粉末を用いて金属磁性粒子粉末を製造することが記載されているが、ゲータイト粒子の生成反応後、コバルト化合物を添加しているため、ゲータイト結晶中にコバルトを含有するゲータイト粒子が得られておらず、加熱還元処理時の還元速度の制御が十分行われないため、焼結が進行するので、微粒子かつ磁気特性・酸化安定性に優れた金属磁性粒子粉末が得られない。また、飽和磁化値が１５０Ａｍ２／ｋｇ（１５０ｅｍｕ／ｇ）であり、低飽和磁化への要求を十分満たしていない。
【００３８】
また、ＷＯ００／３８２０１号公報には、第二鉄塩水溶液、コバルト塩水溶液およびアルミニウムの水可溶性塩を水酸化ナトリウム水溶液と混合・熟成することでコバルトとアルミニウムを含有させたオキシ水酸化鉄粒子を得た後、該粒子表面を更に希土類元素の化合物で被覆したオキシ水酸化鉄粒子粉末を加熱還元して、金属磁性粒子粉末を製造することが記載されている。しかしながら、アルカリ源として水酸化ナトリウムを用いているため、Ｎａ等の可溶性塩を十分に低減できるとは言い難い。また、飽和磁化値が１３０Ａｍ２／ｋｇ（１３０ｅｍｕ／ｇ）であり、低飽和磁化への要求を十分満たしていない。
【００３９】
また、特開２００１−１９２２１１号公報には、第一鉄塩水溶液と炭酸アンモニウム及びアンモニア水とを用いて得られたゲータイト粒子粉末を用いて金属磁性粒子粉末を製造することが記載されているが、前記ゲータイト粒子粉末の粒子表面にコバルト化合物及び希土類化合物を被覆する際に、同時に被覆を行っており、還元処理時の焼結防止効果が不十分であるため、平均長軸径が０．０２〜０．０８μｍの微粒子であって、高い保磁力を示し、かつ酸化安定性に優れた金属磁性粒子粉末を得ることは困難である。加えて、飽和磁化値が１４０Ａｍ２／ｋｇ（１４０ｅｍｕ／ｇ）以上と高く、低飽和磁化への要求を十分満たしていない。
【００４０】
そこで、本発明は、平均長軸径が０．０２〜０．０８μｍの微粒子でありながら、高い保磁力を示し、且つ、低飽和磁化値でありながら、磁性塗膜の保磁力分布Ｓ．Ｆ．Ｄ．に優れた紡錘状合金磁性粒子粉末、加えて、更に酸化安定性に優れ、且つ、可溶性塩が可及的に低減された前記紡錘状合金磁性粒子粉末を提供することを技術的課題とする。
【００４１】
【課題を解決するための手段】
前記技術的課題は、次の通りの本発明によって達成できる。
【００４２】
即ち、本発明は、全Ｆｅに対してＣｏ換算で５０〜１１０原子％のコバルトを含有する平均長軸径が０．０２〜０．０８μｍのＦｅ及びＣｏを主成分とする紡錘状合金磁性粒子粉末であり、該Ｆｅ及びＣｏを主成分とする紡錘状合金磁性粒子粉末の保磁力が１４３．２〜２３８．７ｋＡ／ｍ（１８００〜３０００Ｏｅ）であり、飽和磁化値σｓが６０〜１００Ａｍ２／ｋｇ（６０〜１００ｅｍｕ／ｇ）であり、且つ、該Ｆｅ及びＣｏを主成分とする紡錘状合金磁性粒子粉末を用いて作製した磁性塗膜のＳ．Ｆ．Ｄ．が０．７以下であることを特徴とする磁気記録用紡錘状合金磁性粒子粉末である（本発明１）。
【００４３】
また、本発明は、全Ｆｅに対してＣｏ換算で５０〜１１０原子％のコバルトを含有する平均長軸径が０．０２〜０．０８μｍのＦｅ及びＣｏを主成分とする紡錘状合金磁性粒子粉末であり、該Ｆｅ及びＣｏを主成分とする紡錘状合金磁性粒子粉末の保磁力が１４３．２〜２３８．７ｋＡ／ｍ（１８００〜３０００Ｏｅ）であり、飽和磁化値σｓが６０〜１００Ａｍ２／ｋｇ（６０〜１００ｅｍｕ／ｇ）であり、可溶性Ｎａ含有量が３０ｐｐｍ以下であって可溶性Ｃａ含有量が１００ｐｐｍ以下であり、且つ、該Ｆｅ及びＣｏを主成分とする紡錘状合金磁性粒子粉末を用いて作製した磁性塗膜のＳ．Ｆ．Ｄが０．７以下であることを特徴とする磁気記録用紡錘状合金磁性粒子粉末である（本発明２）。
【００４４】
また、本発明は、全Ｆｅに対してＣｏ換算で５０〜１１０原子％のコバルト、Ａｌ換算で３〜２０原子％のアルミニウム及び希土類元素換算で１０−３０原子％の希土類元素を含有する平均長軸径が０．０２〜０．０８μｍのＦｅ及びＣｏを主成分とする紡錘状合金磁性粒子粉末であり、該Ｆｅ及びＣｏを主成分とする紡錘状合金磁性粒子粉末の保磁力が１４３．２〜２３８．７ｋＡ／ｍ（１８００〜３０００Ｏｅ）であり、飽和磁化値σｓが６０〜１００Ａｍ２／ｋｇ（６０〜１００ｅｍｕ／ｇ）であり、可溶性Ｎａ含有量が３０ｐｐｍ以下であって可溶性Ｃａ含有量が１００ｐｐｍ以下であり、酸化安定性Δσｓが１０％以下であり、且つ、該Ｆｅ及びＣｏを主成分とする紡錘状合金磁性粒子粉末を用いて作製した磁性塗膜のＳ．Ｆ．Ｄが０．７以下であることを特徴とする磁気記録用紡錘状合金磁性粒子粉末である（本発明３）。
【００４５】
また、本発明は、全Ｆｅに対しＣｏ換算で１５〜５０原子％のコバルト及び全Ｆｅに対しＡｌ換算で３〜１５原子％のアルミニウムを含有するゲータイト粒子を含む水懸濁液にコバルト化合物及び炭酸アルカリ水溶液を添加して、ゲータイト粒子の粒子表面に全Ｆｅに対してＣｏ換算で１５〜６０原子％の炭酸コバルトを被覆し、次いで、全Ｆｅに対して希土類元素換算で１０〜３０原子％の希土類化合物によって前記炭酸コバルトで被覆されたゲータイト粒子の粒子表面を被覆した後、該表面被覆したゲータイト粒子粉末又は該表面被覆したゲータイト粒子粉末を非還元性雰囲気中、４００〜７５０℃で加熱処理して得られたヘマタイト粒子粉末を還元性雰囲気中、３５０〜７００℃で加熱還元してＦｅ及びＣｏを主成分とする紡錘状合金磁性粒子粉末を得ることを特徴とする本発明１乃至３のいずれかに記載の磁気記録用紡錘状合金磁性粒子粉末の製造法である（本発明４）。
【００４６】
また、本発明は、硫酸第一鉄水溶液と該硫酸第一鉄水溶液に対する当量比が１．７〜３．０である炭酸水素アンモニウム水溶液及び水酸化アンモニウム水溶液からなる混合アルカリ水溶液とを反応させて得られる第一鉄含有沈殿物を含む水懸濁液を非酸化性雰囲気下において熟成させた後に、該水懸濁液中に酸素含有ガスを通気して酸化反応によってゲータイト種晶粒子を生成させ、次いで、該種晶粒子と第一鉄含有沈澱物とを含む水懸濁液中に酸素含有ガスを通気して酸化反応によって該種晶粒子の粒子表面上にゲータイト層を成長させてゲータイト粒子を生成させるにあたり、
前記混合アルカリ水溶液として、該混合アルカリ水溶液に対して前記水酸化アンモニウム水溶液が５５〜８５ｍｏｌ％の割合で配合されているものを使用すると共に、前記種晶粒子の生成時において、酸化反応開始前の熟成中の第一鉄含有沈澱物を含む水懸濁液に全Ｆｅに対しＣｏ換算で１５〜５０原子％のＣｏ化合物を添加し、酸化反応を全Ｆｅ２＋の２０〜８０％の範囲で行い、
前記ゲータイト層の成長時においては、前記種晶粒子と第一鉄含有沈殿物とを含む水懸濁液のｐＨが９．０未満となるように全Ｆｅに対しＡｌ換算で３〜１５原子％のＡｌ化合物を添加し、
生成させた前記ゲータイト粒子を濾別した後、ｐＨ９．５〜１１．５のアンモニア水で水洗することによってゲータイト粒子粉末とし、
次いで、得られたゲータイト粒子を含む水懸濁液にコバルト化合物及び炭酸アルカリ水溶液を添加して、ゲータイト粒子の粒子表面に全Ｆｅに対してＣｏ換算で１５〜６０原子％の炭酸コバルトを被覆し、次いで、全Ｆｅに対して希土類元素換算で１０〜３０原子％の希土類化合物によって前記炭酸コバルトで被覆されたゲータイト粒子の粒子表面を被覆した後、該表面被覆したゲータイト粒子粉末又は該表面被覆したゲータイト粒子粉末を非還元性雰囲気中、４００〜７５０℃で加熱処理して得られたヘマタイト粒子粉末を還元性雰囲気中、３５０〜７００℃で加熱還元してＦｅ及びＣｏを主成分とする紡錘状合金磁性粒子粉末を得ることを特徴とする本発明１乃至３のいずれかに記載の磁気記録用紡錘状合金磁性粒子粉末の製造法である（本発明５）。
【００４７】
また、本発明は、前記磁気記録用紡錘状合金磁性粒子粉末の製造法において、前記加熱還元が、還元性雰囲気中、３００〜６００℃の温度範囲で加熱還元を行って紡錘状合金磁性粒子粉末を得る第１工程、第１工程で得た紡錘状合金磁性粒子粉末を酸素含有不活性ガス雰囲気下で６０〜２００℃の温度範囲で表面酸化を行って該紡錘状合金磁性粒子粉末の飽和磁化値を８５〜１３５Ａｍ２／ｋｇとする第２工程、第２工程を経由した紡錘状合金磁性粒子粉末を還元性ガス雰囲気中、第１工程の還元温度よりも５０℃以上高く、且つ、４００〜７００℃の温度範囲まで昇温し、次いで、還元性ガス雰囲気に切り替えた後、４００〜７００℃の温度範囲で再度加熱還元を行う第３工程及び第３工程を経由した紡錘状合金磁性粒子粉末を５〜１０ｇ／ｍ３の水蒸気と酸素とを含んだ不活性ガス雰囲気下で４０〜１６０℃の温度範囲で再度表面酸化を行うことによって紡錘状合金磁性粒子粉末を得る第４工程からなることを特徴とする本発明４又は本発明５の磁気記録用紡錘状合金磁性粒子粉末の製造法である（本発明６）。
【００４８】
本発明の構成を詳しく説明すれば、次の通りである。
【００４９】
まず、本発明に係る紡錘状合金磁性粒子粉末について述べる。
【００５０】
本発明に係る紡錘状合金磁性粒子粉末は、紡錘状であって、平均長軸径は０．０２〜０．０８μｍであり、平均長軸径が０．０２μｍ未満の場合には、酸化安定性が急激に低下し、同時に高い保磁力、良好な保磁力分布Ｓ．Ｆ．Ｄ．が得られ難くなる。０．０８μｍを越える場合には、短波長領域での高出力、ノイズが低減された磁気記録媒体を得るための磁性体粒子としては、粒子サイズが大きいため好ましくない。好ましくは０．０２５〜０．０７５μｍである。
【００５１】
本発明に係る紡錘状合金磁性粒子粉末の軸比は２以上が好ましく、軸比が２未満の場合には目的とする高い保磁力を得ることができない。より好ましくは３〜８である。
【００５２】
本発明に係る紡錘状合金磁性粒子粉末の結晶子サイズＤ１１０は９０〜１７０Åが好ましく、結晶子サイズが９０Å未満の場合には、磁気記録媒体にした場合に粒子性ノイズ低減の点では有利となるが、保磁力の低下や保磁力分布Ｓ．Ｆ．Ｄ．が拡大しやすく、また酸化安定性も低下する。１７０Å以上の場合には粒子性ノイズが増加するため好ましくない。より好ましくは９０〜１５０Åである。
【００５３】
本発明に係る紡錘状合金磁性粒子粉末のＢＥＴ比表面積値は４０〜８０ｍ２／ｇが好ましく、４０ｍ２／ｇ未満の場合には、ノイズ、分散性を満足する紡錘状合金磁性粒子粉末が得られない。８０ｍ２／ｇを超える場合には、塗料化時に分散し難くなり、また、塗料の高粘度化を招くため好ましくない。より好ましくは５０〜８０ｍ２／ｇである。
【００５４】
また、紡錘状合金磁性粒子粉末のコバルト含有量は全Ｆｅに対してＣｏ換算で５０〜１１０原子％であり、コバルト含有量が５０原子％未満の場合には、良好な保磁力分布Ｓ．Ｆ．Ｄ．を維持した状態で低い飽和磁化値を得ることができず、また、高い保磁力が得られ難い。１１０原子％を超える場合には、保磁力の低下、また必要以上の飽和磁化の低下を招く。好ましくは５５〜１００原子％である。
【００５５】
アルミニウム含有量は全Ｆｅに対してＡｌ換算で３〜２０原子％が好ましく、希土類元素含有量は全Ｆｅに対して希土類元素換算で１０〜３０原子％が好ましい。アルミニウム含有量及び希土類元素含有量が前記各下限値未満の場合には、加熱還元過程における焼結防止効果が低下するため、保磁力が低下し、保磁力分布Ｓ．Ｆ．Ｄ．が拡大する。上限値を超える場合には、水素還元に必要な温度が著しく高くなり、製造上好ましくない。
【００５６】
また、可溶性Ｎａの含有量は３０ｐｐｍ以下が好ましく、より好ましくは２０ｐｐｍ以下、更に好ましくは１０ｐｐｍ以下であり、可溶性Ｃａの含有量は１００ｐｐｍ以下が好ましく、より好ましくは８０ｐｐｍ以下、更に好ましくは７０ｐｐｍ以下である。前記各不純物含有量が上限値を超えた場合には、これに起因した化合物が磁性塗膜表面に析出する可能性があるため好ましくない。また、残存硫黄量は６０ｐｐｍ以下が好ましく、より好ましくは５０ｐｐｍ以下である。
【００５７】
本発明に係る紡錘状合金磁性粒子粉末は、保磁力Ｈｃが１４３．２〜２３８．７ｋＡ／ｍ（１８００〜３０００Ｏｅ）である。１４３．２ｋＡ／ｍ未満の場合には、短波長領域で十分な高出力が得られない。２３８．７ｋＡ／ｍを超える場合には、記録ヘッドの飽和を引き起こし、目的とする短波長領域での高出力が得られない。好ましくは１５９．２〜２２２．８ｋＡ／ｍ（２０００〜２８００Ｏｅ）である。
【００５８】
本発明に係る紡錘状合金磁性粒子粉末は、飽和磁化値σｓが６０〜１００Ａｍ２／ｋｇ（６０〜１００ｅｍｕ／ｇ）である。６０Ａｍ２／ｋｇ未満の場合には、残留磁化値が低下するため、短波長領域で十分な高出力が得られない。加えて、高い保磁力、良好な保磁力分布Ｓ．Ｆ．Ｄ．を持つ紡錘状合金磁性粒子粉末が得られない。１００Ａｍ２／ｋｇを超える場合には、過剰な残留磁化を生じ、磁気抵抗ヘッドの飽和を引き起こし、再生特性に歪みを生じ易く、短波長領域での高Ｃ／Ｎ出力が得られない。好ましくは７０〜１００Ａｍ２／ｋｇ（７０〜１００ｅｍｕ／ｇ）である。
【００５９】
本発明に係る紡錘状合金磁性粒子粉末の酸化安定性Δσｓは、１０％以下が好ましく、より好ましくは８％以下である。
【００６０】
本発明に係る紡錘状合金磁性粒子粉末は、角型比（σｒ／σｓ）が０．５１〜０．５５が好ましい。
【００６１】
本発明に係る紡錘状合金磁性粒子粉末を用いて得られた磁性塗膜の保磁力分布Ｓ．Ｆ．Ｄ．は０．７０以下である。Ｓ．Ｆ．Ｄ．が０．７０を超える場合には、磁化反転領域が拡大し、短波長領域で十分な出力が得られない。より好ましくは０．６０以下、更に好ましくは０．５０以下である。
【００６２】
また、本発明に係る紡錘状合金磁性粒子粉末を用いて得られた磁性塗膜は、保磁力Ｈｃ１４３．２〜２３８．７ｋＡ／ｍ（１８００〜３０００Ｏｅ）が好ましく、角形比（Ｂｒ／Ｂｍ）０．８２以上が好ましく、酸化安定性ΔＢｍ８％未満が好ましい。
【００６３】
次に、本発明に係る紡錘状合金磁性粒子粉末の製造法について述べる。
【００６４】
本発明においては、下記詳述する方法によって紡錘状ゲータイト粒子を形成した後、当該ゲータイト粒子を含有する水懸濁液にコバルト化合物及びアルカリ金属の炭酸塩を含有する水溶液を添加して前記紡錘状ゲータイト粒子の粒子表面を炭酸コバルトで被覆し、更に、前記炭酸コバルトの表面に希土類化合物を被覆し、得られた表面被覆ゲータイト粒子粉末又は該ゲータイト粒子粉末を４００〜７５０℃で加熱脱水して得られた紡錘状ヘマタイト粒子粉末を、３５０〜７００℃で加熱還元することによってＦｅ及びＣｏを主成分とする紡錘状合金磁性粒子粉末を得ることができる。
【００６５】
本発明における紡錘状ゲータイト粒子粉末は、硫酸第一鉄水溶液と該硫酸第一鉄水溶液に対する当量比が１．７〜３．０である炭酸水素アンモニウム水溶液及び水酸化アンモニウム水溶液からなる混合アルカリ水溶液とを反応させて得られる第一鉄含有沈殿物を含む水懸濁液を非酸化性雰囲気下において熟成させた後に、該水懸濁液中に酸素含有ガスを通気して酸化反応によって紡錘状ゲータイト種晶粒子を生成させ、次いで、該種晶粒子と第一鉄含有沈澱物とを含む水懸濁液中に酸素含有ガスを通気し酸化反応によって該種晶粒子の粒子表面上にゲータイト層を成長させて紡錘状ゲータイト粒子を生成させるにあたり、
前記混合アルカリ水溶液として、該混合アルカリ水溶液に対して前記水酸化アンモニウム水溶液が５５〜８５ｍｏｌ％の割合で配合されているものを使用すると共に、前記種晶粒子の生成時においては、酸化反応開始前の熟成中の第一鉄含有沈澱物を含む水懸濁液に全Ｆｅに対しＣｏ換算で１５〜５０原子％のＣｏ化合物を添加して酸化反応を全Ｆｅ２＋の２０〜８０％の範囲で行い、
前記ゲータイト層の成長時においては、前記種晶粒子と第一鉄含有沈殿物とを含む水懸濁液のｐＨが９．０未満となるように全Ｆｅに対しＡｌ換算で０．５〜２０原子％のＡｌ化合物を添加し、
生成させた前記紡錘状ゲータイト粒子を濾別した後、ｐＨ９．５〜１１．５のアンモニア水で水洗することによって得ることができる。
【００６６】
前記紡錘状ゲータイト種晶粒子の生成反応において、硫酸第一鉄水溶液を用いるのは、硫酸第一鉄水溶液以外では、例えば、塩化第一鉄水溶液では、塩素を含有するため好ましくない。前記硫酸第一鉄水溶液と前記混合アルカリ水溶液との混合後の第一鉄濃度は０．１〜１．０ｍｏｌ／ｌが好ましく、０．１ｍｏｌ／ｌ未満の場合には、収量が少なく工業的でない。１．０ｍｏｌ／ｌを越える場合には、粒径分布が大きくなるため好ましくない。より好ましくは０．２〜０．８ｍｏｌ／ｌである。
【００６７】
本発明においては炭酸水素アンモニウム水溶液（ＮＨ４ＨＣＯ３）及び水酸化アンモニウム水溶液（ＮＨ４ＯＨ）を用いる。アルカリ金属からなるアルカリ水溶液を用いた場合には、粒子中にアルカリ金属が残存するため本発明の目的とする可溶性塩が除去された紡錘状合金磁性粒子粉末を得ることができない。炭酸水素アンモニウム水溶液と水酸化アンモニウム水溶液との混合割合は、混合アルカリ水溶液に対して水酸化アンモニウム水溶液が５５〜８５ｍｏｌ％であり、好ましくは５７〜８０ｍｏｌ％である。炭酸水素アンモニウムが多い場合には、得られるゲータイト粒子の軸比が小さくなる。一方、水酸化アンモニウムが多くなりすぎるとマグネタイトが発生しやすくなると共にコバルトの溶出も起こりやすい。
【００６８】
前記炭酸水素アンモニウム水溶液と水酸化アンモニウム水溶液の合計使用量は、硫酸第一鉄水溶液中の全Ｆｅに対する当量比として１．７〜３．０であり、１．７未満の場合には、マグネタイトが混在しやすくなり、３．０を越えると工業的に好ましくない。好ましくは１．７５〜２．８５である。
【００６９】
本発明における第一鉄含有沈殿物を含む水懸濁液のｐＨは７．５〜９．５が好ましく、ｐＨ７．５未満の場合にはマグネタイトが混在するため好ましくない。ｐＨが９．５を超える場合には、コバルトの溶出が顕著になるため好ましくない。より好ましくは８．０〜９．０である。
【００７０】
前記紡錘状ゲータイト種晶粒子の熟成反応は、非酸化性雰囲気下で攪拌して行う。非酸化性雰囲気とは、不活性ガス（窒素ガスなど）又は還元性ガス（水素ガスなど）を液中に通気する。好ましくは窒素ガスである。
【００７１】
前記紡錘状ゲータイト種晶粒子の熟成反応における反応温度は、非酸化性雰囲気下の前記水懸濁液を、通常、４０〜８０℃の温度範囲で行うことが好適である。４０℃未満の場合には、軸比が小さく十分な熟成効果が得られ難く、８０℃を越える場合には、マグネタイトが混在してくることがある。熟成時間としては、３０〜３００分間である。３０分間未満の場合には、十分に軸比を大きくすることができない。３００分間を越える場合には、アンモニアが揮発するため十分な熟成効果を得ることが困難となる。
【００７２】
前記紡錘状ゲータイト種晶粒子の生成反応における酸化手段は、酸素含有ガス（例えば空気）を液中に通気することにより行う。
【００７３】
前記紡錘状ゲータイト種晶粒子の生成反応における温度は、通常、ゲータイト粒子が生成する８０℃以下の温度で行えばよい。８０℃を越える場合には、紡錘状ゲータイト粒子中にマグネタイトが混在することがある。好ましくは４５〜５５℃の範囲である。
【００７４】
前記紡錘状ゲータイト種晶粒子の生成反応において、酸化反応を行う前の熟成後の第一鉄含有沈澱物を含む水懸濁液に、硫酸コバルトや硝酸コバルト等のＣｏ化合物を添加する。前記Ｃｏ化合物の添加量は、得られる最終の紡錘状ゲータイト粒子中の全Ｆｅに対してＣｏ換算で１５〜５０原子％であり、１５原子％未満の場合には、紡錘状合金磁性粒子粉末とした場合に磁気的特性の向上効果がなく、５０原子％を越える場合には、微細化のため軸比の著しい低下や反応生成物中にゲータイト以外の異物の混在を招き易い。好ましくは１８〜４０原子％である。
【００７５】
前記紡錘状ゲータイト種晶粒子の生成反応は全Ｆｅ２＋の２０〜８０％の範囲で行う。２０％未満の場合には、軸比が小さくなり過ぎ、紡錘状合金磁性粒子粉末とした場合に高い保磁力が得られ難く、一方、８０％を超える場合には、ゲータイト粒子の生成が終了間近であり、添加するＡｌ化合物の効果が十分得られず保磁力が低下する。
【００７６】
前記紡錘状ゲータイト種晶粒子を含む水懸濁液中に、酸素含有ガスを通気して、前記紡錘状ゲータイト種晶粒子の粒子表面上にゲータイト層を成長させるにあたり、水懸濁液にＡｌ化合物を添加することによって、アルミニウムを含有した紡錘状ゲータイト粒子粉末を得ることができる。
【００７７】
Ａｌ化合物としては、硫酸アルミニウム、硝酸アルミニウム等の酸性塩、アルミン酸アンモニウム等のアルミン酸塩を使用することができる。Ａｌ化合物の添加時期は、成長反応において酸素含有ガスを通気する前の紡錘状ゲータイト種晶粒子と第一鉄含有沈殿物とを含む水懸濁液若しくは成長反応中の水懸濁液のいずれかに添加すればよい。殊に、ゲータイト層の成長反応を開始する前が好ましい。また、Ａｌ化合物を分割添加したり連続的及び間欠的に添加してもよい。
【００７８】
前記Ａｌ化合物の添加量は、得られる最終の紡錘状ゲータイト粒子中の全Ｆｅに対してＡｌ換算で３〜２０原子％が好ましく、３原子％未満の場合には焼結防止効果がなく、２０原子％を越える場合には軸比が低下する。より好ましくは３．５〜１５原子％である。
【００７９】
前記ゲータイト層の成長反応における反応溶液のｐＨ値は９．０未満が好ましく、ｐＨが９．０を越える場合にはコバルトの溶出が起こりやすくなり、紡錘状合金磁性粒子粉末とした場合に目的とする高い保磁力が得られない。好ましくは７．０〜８．８の範囲である。なお、ｐＨ値が７．０未満の場合には、マグネタイトが混入することがあるため好ましくない。
【００８０】
前記ゲータイト層の成長反応における酸化手段は、酸素含有ガス（例えば空気）を液中に通気することにより行う。
【００８１】
前記ゲータイト層の成長反応における温度は、通常、ゲータイト粒子が生成する８０℃以下の温度で行えばよい。８０℃を越える場合には、紡錘状ゲータイト粒子中にマグネタイトが混在することがある。好ましくは４５〜５５℃の範囲である。
【００８２】
得られた紡錘状ゲータイト粒子粉末をｐＨ９．５〜１１．５のアンモニア水で水洗する。アンモニア水で洗浄することによって硫酸イオンを除去することができる。アンモニア水のｐＨが上記範囲以外の場合には、硫酸イオンを十分に除去することができない。アンモニア水の温度範囲は２０〜５０℃が好ましい。２０℃未満の場合には洗浄効率が低下し、また５０℃を超える場合にはアンモニアが揮発するため好ましくない。
【００８３】
アンモニア水で洗浄した後、更に、水洗することが好ましい。洗浄水としてはイオン交換水が好ましい。
【００８４】
得られた紡錘状ゲータイト粒子粉末は、平均長軸径０．０４〜０．１５μｍが好ましく、より好ましくは０．０５〜０．１４μｍであり、軸比３〜１２が好ましく、より好ましくは４〜１０であり、ＢＥＴ比表面積値１００〜２５０ｍ２／ｇが好ましい。Ｃｏ含有量は紡錘状ゲータイト粒子粉末中の全Ｆｅに対してＣｏ換算で１５〜５０原子％であり、Ａｌ含有量が全Ｆｅに対してＡｌ換算で３〜２０原子％である。
【００８５】
本発明においては、前記紡錘状ゲータイト粒子の粒子表面を炭酸コバルトで被覆することが重要である。ゲータイト粒子表面を炭酸コバルトで被覆することによって、還元速度の制御を容易にすることができるので焼結防止効果が向上する。
【００８６】
紡錘状ゲータイト粒子を含有する水懸濁液に添加するコバルト化合物の水溶液としては、酢酸コバルト水溶液又は硝酸コバルト水溶液が好ましい。コバルト化合物の添加量は、紡錘状ゲータイト粒子が含有するＣｏ量との合計で全Ｆｅに対してＣｏ換算で１１０原子％を超えない範囲で添加する。
【００８７】
コバルト化合物が存在する紡錘状ゲータイト粒子の水懸濁液にアルカリ金属からなる炭酸アルカリ水溶液を添加することによって、紡錘状ゲータイト粒子の粒子表面に炭酸コバルトを被覆する。アルカリ金属の炭酸アルカリ水溶液としては、炭酸ナトリウム水溶液、炭酸カリウム水溶液が好ましい。アルカリ金属の炭酸アルカリ水溶液以外のアルカリ水溶液では、炭酸コバルトによって被覆することが困難となり、分散性及び酸化安定性に優れた紡錘状合金磁性粒子粉末を得ることができない。なお、被覆反応によって付着したアルカリ金属は水洗することによって容易に除去することができる。
【００８８】
炭酸コバルトで被覆した紡錘状ゲータイト粒子の粒子表面を被覆する希土類元素としては、イットリウム、ネオジム、ランタン、セリウム、スカンジウム、プラセオジム及びサマリウム等の１種又は２種以上が好適である。添加する希土類化合物としては、前記希土類元素の塩化物、硝酸塩を使用することが好ましい。
【００８９】
前記希土類化合物の添加量は、紡錘状ゲータイト粒子の全Ｆｅに対して希土類元素換算で１０〜３０原子％が好ましく、１０原子％未満の場合には、焼結防止効果が十分でなく、紡錘状合金磁性粒子粉末とした場合に保磁力分布Ｓ．Ｆ．Ｄ．の悪化や保磁力が低下する。３０原子％を越える場合には水素還元に必要な温度が著しく高くなり、製造上好ましくない。より好ましくは１５〜２８原子％である。
【００９０】
添加した希土類化合物は、炭酸アルカリ水溶液を添加して反応溶液のｐＨを調整することによって炭酸コバルトが被覆された紡錘状ゲータイト粒子の粒子表面に被覆することができる。希土類化合物は炭酸塩又は水酸化物の状態で被覆されている。なお、被覆反応によって付着したアルカリ金属は水洗することによって容易に除去することができる。
【００９１】
前記表面被覆されたゲータイト粒子は、コバルトとアルミニウムを含有する紡錘状ゲータイト粒子の粒子表面が炭酸コバルトで被覆され、更に当該炭酸コバルトの表面が希土類元素からなる化合物で被覆されている。
【００９２】
紡錘状ゲータイト粒子の粒子表面を炭酸コバルトによって表面被覆し、更に当該粒子表面を希土類化合物によって表面被覆することで、粒子及び粒子相互間の焼結が防止され、紡錘状ゲータイト粒子の粒子形状及び軸比を保持継承した紡錘状ヘマタイト粒子粉末を得ることができ、これによって、前記形状等を保持継承し、個々に独立した紡錘状合金磁性粒子粉末が得られやすくなる。
【００９３】
次に、表面被覆した紡錘状ゲータイト粒子粉末の加熱還元処理を行う。
【００９４】
なお、磁気特性、粉体特性及び粉体形状の制御ためには、還元処理に先立って、あらかじめ、常法により、表面被覆した紡錘状ゲータイト粒子粉末を非還元性ガス雰囲気中において加熱脱水処理を行って、紡錘状ヘマタイト粒子粉末とすることが好ましい。
【００９５】
非還元性雰囲気としては、空気、酸素ガス、窒素ガス等から選択される一種以上のガス流通下が好ましい。加熱処理温度は４００〜７５０℃の範囲で行うことができ、該加熱処理温度は、紡錘状ゲータイト粒子の被覆処理に用いた化合物の種類に応じて適宜選択することがより好ましい。４００℃未満では加熱処理に長時間を要し、７５０℃を超える場合には、粒子の変形と粒子及び粒子相互間の焼結を引き起こす。
【００９６】
本発明における紡錘状ヘマタイト粒子粉末は、平均長軸径０．０４〜０．１５μｍが好ましく、より好ましくは０．０５〜０．１４μｍであり、軸比３〜１２が好ましく、より好ましくは３〜１０であり、ＢＥＴ比表面積値３０〜１４０ｍ２／ｇが好ましい。
【００９７】
紡錘状ヘマタイト粒子粉末のコバルト含有量は全Ｆｅに対してＣｏ換算で５０〜１１０原子％が好ましく、アルミニウム含有量は全Ｆｅに対してＡｌ換算で３〜２０原子％が好ましく、希土類元素の含有量は全Ｆｅに対して希土類元素換算で１０〜３０原子％が好ましい。
【００９８】
本発明における還元装置としては、固定層を形成させた還元装置が好ましく、具体的には、静置式還元装置（バッチ式）もしくはベルト上に固定層を形成して該ベルトを移送させながら還元する移動式還元装置（連続式）が好ましい。
【００９９】
本発明における固定層の層高は、３０ｃｍ以下が好ましい。３０ｃｍを超える場合には、多量にＣｏを含有するため還元促進作用が顕著であるのと同時に、固定層の層下部の急激な還元による水蒸気分圧の増大によって、固定層上部の保磁力が低下する等の問題が起こり、全体として特性が劣化する。工業的な生産性を考慮すると、３〜３０ｃｍがより好ましい。なお、バッチ式（特開昭５４−６２９１５号公報、特開平４−２２４６０９号公報等）、連続式（特開平６−９３３１２号公報等）では生産性が異なるため、バッチ式の固定層還元装置では４ｃｍを超え、３０ｃｍ以下が好ましい。
【０１００】
本発明における加熱還元処理の温度範囲は３５０〜７００℃が好ましい。３５０℃未満である場合には、還元反応の進行が遅く、長時間を要する。また、紡錘状合金磁性粒子粉末の結晶成長が不十分であるため、飽和磁化値、保磁力などの磁気特性が著しく低下する。７００℃を超える場合には、還元反応が急激に進行して粒子の変形と、粒子及び粒子相互間の焼結を引き起こす。
【０１０１】
本発明における加熱還元後の紡錘状合金磁性粒子粉末は、周知の方法、例えば、トルエン等の有機溶剤中に浸漬する方法、還元後の紡錘状合金磁性粒子の雰囲気を一旦不活性ガスに置換した後、不活性ガス中の酸素含有量を徐々に増加させながら最終的に空気とする方法及び酸素と水蒸気を混合したガスを使用して徐酸化する方法等により空気中に取り出すことができる。
【０１０２】
本発明においては、加熱還元工程を４工程に分割して行うことによって、保磁力に優れた紡錘状合金磁性粒子粉末を得ることができる。
【０１０３】
本発明では、第１工程及び第３工程の加熱還元温度まで昇温する期間の雰囲気は不活性ガス雰囲気、あるいは還元性ガス雰囲気である。不活性ガス雰囲気としては、窒素ガス、ヘリウムガス、アルゴンガス等が好ましく、殊に、窒素ガスが好適である。還元性ガス雰囲気で昇温する場合、４０分以下、好ましくは２０分以下の時間で急速昇温することで、金属磁性粒子生成時の還元温度が一定にすることが出来る。
【０１０４】
なお、第１工程及び第３工程の昇温速度は、還元性雰囲気の場合、２０〜１００℃／ｍｉｎが好ましい。
【０１０５】
本発明の第１工程及び第３工程の加熱還元工程における雰囲気は、還元性ガスであり、還元性ガスとしては水素が好適である。
【０１０６】
本発明における第１工程の加熱還元温度は３００〜６００℃であり、好ましくは３５０〜５５０℃である。加熱還元温度は、出発原料の被覆処理に用いた化合物の種類、量に応じて上記温度範囲から適宜選択することが好ましい。加熱還元温度が３００℃未満の場合には、還元の進行が非常に遅く工業的でなく、得られた紡錘状合金磁性粒子粉末の飽和磁化値も低いものとなる。６００℃を超える場合には、還元反応が急激に進行して粒子の形状破壊や粒子及び粒子相互間の焼結を引き起こしてしまい、保磁力が低下する。
【０１０７】
本発明における第１工程の還元性ガスのガス空塔速度は、４０〜１５０ｃｍ／ｓが好ましい。ガス空塔速度が４０ｃｍ／ｓ未満の場合、出発原料の還元で発生した水蒸気が系外に運ばれる速度が非常に遅くなるため、層上部の保磁力、ＳＦＤが低下し、全体として高い保磁力が得られない。１５０ｃｍ／ｓを超える場合、目的とする紡錘状合金磁性粒子粉末は得られるが、還元温度が高温を要したり、造粒物が飛散し破壊されるなどの問題が起こり易く好ましくない。
【０１０８】
本発明における第２工程は、酸素を含んだ不活性ガス雰囲気で表面酸化処理を行う。不活性ガス雰囲気としては、窒素ガス、ヘリウムガス、アルゴンガス等が好ましく、殊に窒素ガスが好適である。酸素の含有量は０．１〜５ｖｏｌ％が好ましく、所定量まで徐々に酸素量を増加させることが好ましい。
【０１０９】
本発明における第２工程の反応温度は、６０〜２００℃であり、好ましくは６０〜１８０℃である。６０℃未満の場合には、十分な厚さを有する表面酸化層を形成することが困難である。２００℃を超える場合には、粒子の形骸変化、特に酸化物が多量に生成されるため短軸が極端に膨張し、場合によっては、形骸破壊が起こりやすいため好ましくない。
【０１１０】
第２工程を終了した紡錘状合金磁性粒子粉末は、飽和磁化値が８５〜１３５Ａｍ２／ｋｇ（８５〜１３５ｅｍｕ／ｇ）であり、好ましくは９０〜１３０Ａｍ２／ｋｇ（９０〜１３０ｅｍｕ／ｇ）である。飽和磁化値が８５Ａｍ２／ｋｇ未満の場合には、表面酸化層が厚くなりすぎるため、第３工程の加熱還元処理を行っても保磁力の大きな紡錘状合金磁性粒子粉末を得ることができない。１３０Ａｍ２／ｋｇを超える場合には、表面酸化層の形成が不十分であるため、緻密な表面酸化層を形成することができない。
【０１１１】
なお、第２工程において粒子全体を酸化した場合には、粒子の形骸変化、特に短軸成長が起こり、酸化物が多量に生成されるため短軸が極端に膨張し、場合によっては、形骸破壊が起こるため、再度還元しても既に形状が崩れているので、保磁力は向上しない。
【０１１２】
本発明における第３工程の加熱還元温度は、第１工程の加熱還元温度よりも５０℃以上高い温度で、且つ、４００〜７００℃の温度範囲である。第１工程の加熱還元温度よりも５０℃以上高くない場合及び４００℃未満の場合には、還元の進行が非常に遅く工業的でなく、第２工程で形成した表面酸化層の還元及び粒子全体の緻密化が困難となる。７００℃を超える場合には、粒子の形状破壊や粒子及び粒子相互間の焼結を引き起こしてしまい、保磁力が低下する。第３工程の加熱還元温度は、好ましくは４５０〜６５０℃である。
【０１１３】
本発明における第３工程の加熱還元工程での還元性ガスのガス空塔速度は、前記第１工程と同様に４０〜１５０ｃｍ／ｓが好ましい。
【０１１４】
なお、第３工程においては、還元工程の後、アニール処理を行ってもよく、処理温度は５００〜７００℃が好ましく、雰囲気は水素ガス、不活性ガスが好ましく、殊に、窒素ガスが好ましい。
【０１１５】
本発明における第４工程は、５〜１０ｇ／ｍ３の水蒸気と酸素を含んだ不活性ガス雰囲気で表面酸化処理を行う。水蒸気の含有量が５ｇ／ｍ３未満の場合には、緻密で薄い表面酸化層を形成することが難しく、保磁力の向上も十分とは言い難いものである。水蒸気の含有量が１０ｇ／ｍ３を超える場合には、目的とする効果が得られるため、必要以上に含有させる意味がない。水蒸気の含有量は好ましくは、２〜８ｇ／ｍ３である。また、酸素の含有量は０．１〜５ｖｏｌ％が好ましく、所定量まで徐々に増加させることが好ましい。不活性ガスとしては、窒素ガス、ヘリウムガス及びアルゴンガス等が好ましく、殊に、窒素ガスが好適である。
【０１１６】
本発明における第４工程の反応温度は４０〜１６０℃であり、好ましくは４０〜１４０である。なお、第４工程の反応温度は、第２工程の表面酸化処理温度よりも低いことが好ましい。４０℃未満の場合には、表面酸化層の形成が不十分なため好ましくない。１６０℃を超える場合には、表面酸化層が厚くなり、磁性塗膜のＳ．Ｆ．Ｄが劣化するため好ましくない。
【０１１７】
【発明の実施の形態】
本発明の代表的な実施の形態は次の通りである。
【０１１８】
本発明における紡錘状ゲータイト粒子粉末、紡錘状へマタイト粒子粉末及び紡錘状合金磁性粒子粉末の平均長軸径、平均短軸径及び軸比は、いずれも電子顕微鏡写真から測定した数値の平均値で示した。
【０１１９】
本発明における紡錘状ゲータイト粒子粉末、紡錘状へマタイト粒子粉末及び紡錘状合金磁性粒子粉末のＣｏ量、Ａｌ量、希土類元素量、Ｎａ量、Ｃａ量及びその他の金属元素の含有量は、「誘導結合プラズマ発光分光分析装置ＳＰＳ４０００」（セイコー電子工業（株）製）を使用して測定した。
【０１２０】
紡錘状合金磁性粒子粉末の残存硫黄分量は、「炭素・硫黄測定装置」（Ｈｏｒｉｂａ製）を使用して測定した。
【０１２１】
本発明における紡錘状ゲータイト粒子粉末、紡錘状へマタイト粒子粉末及び紡錘状合金磁性粒子粉末のＢＥＴ比表面積値は、「モノソーブＭＳ−１１」（カンタクロム（株）製）を使用して、ＢＥＴ法により測定した値で示した。
【０１２２】
結晶子サイズＤ１１０（紡錘状合金磁性粒子粉末のＸ線結晶粒径）は、「Ｘ線回折装置」（Ｒｉｇａｋｕ製）（測定条件：ターゲットＣｕ、管電圧４０ｋＶ、管電流４０ｍＡ）を使用して、Ｘ線回折法で測定される結晶粒子の大きさを、紡錘状合金磁性粒子粉末の（１１０）結晶面のそれぞれに垂直な方向における結晶粒子の厚さを表したものであり、各結晶面についての回折ピーク曲線から、下記のシェラーの式を用いて計算した値で示したものである。
【０１２３】
Ｄ１１０＝Ｋλ／βｃｏｓθ
但し、β＝装置に起因する機械幅を補正した真の回折ピークの半値幅（ラジアン単位）。
Ｋ＝シェラー定数（＝０．９）、
λ＝Ｘ線の波長（Ｃｕ Ｋα線 ０．１５４２ｎｍ）、
θ＝回折角（（１１０）面の回折ピークに対応）。
【０１２４】
紡錘状合金磁性粒子粉末及び磁性塗膜片の磁気特性は、「振動試料磁力計ＶＳＭ−３Ｓ−１５」（東英工業（株）製）を使用して、外部磁場７９５．８ｋＡ／ｍ（１０ｋＯｅ）で測定した。
【０１２５】
磁性塗膜片の磁気特性は、下記の成分を１００ｍｌのポリビンに下記の割合で入れた後、ペイントシェーカー（レッドデビル社製）で８時間混合分散を行うことにより調製した磁性塗料を厚さ２５μｍのポリエチレンテレフタートフィルム上にアプリケータを用いて５０μｍの厚さに塗布し、次いで、５００ｍＴ（５ｋＧａｕｓｓ）の磁場中で乾燥させることにより得た磁性塗膜片の磁気特性を測定した。
【０１２６】
紡錘状合金磁性粒子粉末： １００重量部、
スルホン酸ナトリウム基を有するポリウレタン樹脂： ３０重量部、
シクロヘキサノン： ８３．３重量部、
メチルエチルケトン： ８３．３重量部、
トルエン： ８３．３重量部、
３ｍｍφスチールボール： ８００重量部。
【０１２７】
紡錘状合金磁性粒子粉末の飽和磁化値の酸化安定性を示すΔσｓ及び磁性塗膜の飽和磁束密度Ｂｍの耐候性を示すΔＢｍは、温度６０℃、相対湿度９０％の恒温槽に粒子粉末又は磁性塗膜片を一週間静置する促進経時試験の後に、粒子粉末の飽和磁化値σｓ’及び磁性塗膜の飽和磁束密度Ｂｍ’をそれぞれ測定し、試験開始前に測定したσｓ及びＢｍと促進経時試験一週間後のσｓ’及びＢｍ’との差（絶対値）を試験開始前のσｓ及びＢｍでそれぞれ除した値をΔσｓ、ΔＢｍとして算出した。Δσｓ、ΔＢｍが０％に近いほど酸化安定性が優れていることを示す。
【０１２８】
＜紡錘状ゲータイト粒子粉末の製造＞
炭酸水素アンモニウム２０ｍｏｌと、アンモニア水を６０ｍｏｌ（混合アルカリに対し水酸化アンモニア水溶液は規定換算で７５ｍｏｌ％に該当する。）を含む混合アルカリ水溶液２８ｌを、気泡分散翼を備えた撹拌機付き反応塔の中に投入し、毎分４００回転の速度で撹拌機を回転させながら、毎分６０ｌの流量で窒素ガスを通気しながら５０℃に調整する。次いでＦｅ２＋として２０ｍｏｌを含む硫酸第一鉄水溶液１６ｌ（硫酸第一鉄に対し混合アルカリ水溶液は規定換算で１．８７５当量に該当する。）を気泡塔中に投入して３０分間熟成した後、Ｃｏ２＋として６．０ｍｏｌを含む硫酸コバルト水溶液４ｌ（全Ｆｅに対しＣｏ換算で３０原子％に該当する。）を添加し、さらに３時間熟成した後、毎分１ｌの流量で空気を通気しながら全Ｆｅ２＋の３０％が酸化するまで反応を行った。
【０１２９】
次いで、Ａｌ３＋１．６ｍｏｌを含む硫酸アルミニウム水溶液１ｌ（全Ｆｅに対しＡｌ換算で８原子％に該当する。）を添加し、さらに反応終了まで酸化反応を行った。反応終了時のｐＨは、８．３であった。
【０１３０】
得られたゲータイト粒子含有スラリーをプレスフィルターを用いて濾別し、アンモニアを使用してｐＨ＝１０．５に調整したアンモニア水を用いて洗浄し、その後、イオン交換水にてさらに洗浄してプレスケーキとした。濾別後の濾液からは３０ｐｐｍのＣｏが検出された。
【０１３１】
前記ケーキの一部を常法により乾燥、粉砕を行って得られた紡錘状ゲータイト粒子粉末は、平均長軸径が０．０８６μｍ、平均短軸径が０．０１２μｍ、軸比が７．２、ＢＥＴ比表面積値が１８１．１ｍ２／ｇ、粒子全体としてコバルト含有量が全Ｆｅに対して２９．９原子％、アルミニウム含有量が全Ｆｅに対して８原子％であった。コバルトの吸着率（コバルトの残存量／コバルトの添加量）は、９９．７％であった。
【０１３２】
＜紡錘状へマタイト粒子粉末の製造＞
ここに得た紡錘状ゲータイト粒子粉末のプレスケーキを水中に十分分散させた後、酢酸コバルト水溶液（全Ｆｅに対して４０原子％）を添加し十分攪拌した。次いで攪拌しながら、炭酸ナトリウム水溶液を添加して水溶液のｐＨを８．８に調整し、次いで、硝酸イットリウム水溶液（全Ｆｅに対して２５原子％）を添加して攪拌混合し、炭酸ナトリウム水溶液を添加して水溶液のｐＨを９．３に調整する。その後、フィルタープレスで濾過、水洗し、プレスケーキを得た。得られたプレスケーキを、押出し成型機を用いて孔径３ｍｍの成型板で押出し成型して造粒し、次いで１２０℃で乾燥し、全Ｆｅに対してＣｏ換算で４０原子％の炭酸コバルトと全Ｆｅに対してＹ換算で２５原子％のＹ化合物とが被覆された紡錘状ゲータイト粒子粉末の造粒物を得た。得られた紡錘状ゲータイト粒子粉末中のＣｏの含有量は全Ｆｅに対して７０原子％、Ａｌの含有量は全Ｆｅに対して８原子％、Ｙの含有量は全Ｆｅに対して２５原子％であった
【０１３３】
前記炭酸コバルトとＹ化合物が被覆された紡錘状ゲータイト粒子粉末の造粒物を空気中３５０℃で脱水し、その後、同雰囲気中５００℃で加熱脱水して紡錘状ヘマタイト粒子粉末の造粒物を得た。
【０１３４】
＜鉄を主成分とする金属磁性粒子粉末の製造＞
ここに得た紡錘状ヘマタイト粒子粉末の顆粒状造粒物１００ｇ（平均径：２．６ｍｍ）を内径７２ｍｍのバッチ式固定層還元装置に入れ、層高を７ｃｍとした後、水素ガス空塔速度５０ｃｍ／ｓで通気しながら、３５０℃で排気ガス露点が−３０℃に達するまで加熱還元して紡錘状合金磁性粒子粉末を得た（第１工程）。
【０１３５】
その後、再び窒素ガスに切り替えて７０℃まで冷却し、品温を７０℃で保持し、次いで空気を混合して酸素濃度を０．３５ｖｏｌ％まで徐々に増加させて品温が［保持温度＋１］℃になるまで（最大品温１４０℃、処理時間２時間）表面酸化処理を行い、粒子表面に表面酸化層を形成した（第２工程）。
【０１３６】
第２工程終了後の紡錘状合金磁性粒子粉末の飽和磁化値は８８．１Ａｍ２／ｋｇ（８８．１ｅｍｕ／ｇ）であった。次に、水素ガス雰囲気下で５００℃まで１０分で昇温し、水素ガス空塔速度６０ｃｍ／ｓにて排気ガス露点が−３０℃に達するまで再度加熱還元した（第３工程）。
【０１３７】
その後、再び窒素ガスに切り替えて７０℃まで冷却し、品温を７０℃で保持し、次いで水蒸気６ｇ／ｍ３と空気を混合して酸素濃度を０．３５ｖｏｌ％まで徐々に増加させて、品温が［保持温度＋１］℃となるまで（最大品温１１０℃、処理時間３時間）表面酸化処理を行い、粒子表面に安定な表面酸化層を形成して紡錘状合金磁性粒子の成型物を得た（第４工程）。
【０１３８】
ここに得た紡錘状合金磁性粒子粉末は、平均長軸径が０．０４６μｍ、軸比が４．６、ＢＥＴ比表面積値が６９．０ｍ２／ｇ、結晶子サイズＤ１１０が１００Åの粒子からなり、紡錘状かつ粒度が均整で樹枝状粒子がないものであった。また、該粒子中のＣｏ含有量は全Ｆｅに対して７０原子％、Ａｌ含有量は全Ｆｅに対して８原子％、Ｙ含有量は２５原子％であった。
【０１３９】
また、可溶性Ｎａ含有量が９ｐｐｍ、可溶性Ｃａ含有量が５８ｐｐｍ、残存硫黄分が５３ｐｐｍであり、紡錘状合金磁性粒子粉末から可溶性Ｆｅは検出されなかった。
【０１４０】
また、該紡錘状合金磁性粒子粉末の磁気特性は、保磁力Ｈｃが１７７．５ｋＡ／ｍ（２２３０Ｏｅ）、飽和磁化値σｓが９０．１Ａｍ２／ｋｇ（９０．１ｅｍｕ／ｇ）、角型比（σｒ／σｓ）が０．５２８、飽和磁化値の酸化安定性Δσｓが絶対値として６．１％（実測値−６．１％）であった。
【０１４１】
また、磁性塗膜の特性は、保磁力Ｈｃが１９３．３ｋＡ／ｍ（２４３０Ｏｅ）、角形比（Ｂｒ／Ｂｍ）が０．８４０、ＳＦＤが０．４８８、酸化安定性ΔＢｍが絶対値として３．３％（実測値−３．３％）であった。
【０１４２】
【作用】
本発明において最も重要な点は、紡錘状合金磁性粒子粉末のコバルト含有量を全Ｆｅに対してＣｏ換算で５０〜１１０原子％まで高めたことによって、平均長軸径が０．０２〜０．０８μｍの微粒子でありながら、高い保磁力を示し、且つ、低飽和磁化値でありながら、保磁力分布Ｓ．Ｆ．Ｄ．に優れ、しかも酸化安定性に優れ、可溶性塩が可及的に低減された磁気記録媒体用紡錘状合金磁性粒子粉末が得られるという事実である。
【０１４３】
従来、高い飽和磁化値及び酸化安定性の向上を目的にしてＦｅ−Ｃｏ合金化が図られてきた。一方で、バルクの場合、特定のＦｅ−Ｃｏ合金比率において飽和磁化値が最大値を示し、等量を大幅に上回るＣｏ合金化により飽和磁化値が徐々に低下することは公知であった。反面、コバルト含有量の増大は保磁力の低下や保磁力分布Ｓ．Ｆ．Ｄ．の拡大を伴い、短波長記録の要求を満たす低い飽和磁化値を有する磁気記録媒体用磁性粒子粉末を得ることは困難であった。
【０１４４】
本発明においては、アルカリ金属を残存させないために炭酸水素アンモニウム水溶液と水酸化アンモニウム水溶液を用いる。従来、アルカリ水溶液としてアンモニウム化合物を用いた場合には、アンミン錯体（［Ｍ（ＮＨ３）ａ］ｎ＋、但し、Ｍはｎ価の金属イオン）形成によるコバルトの溶出のため、Ｆｅ含有沈殿物を含む水懸濁液のｐＨを高くすることができず、また、ｐＨを低くするとマグネタイトが混在したり、ゲータイト粒子の軸比が小さくなる弊害があった。本発明では、水懸濁液のｐＨをマグネタイトが混在せず、しかも軸比が小さくならない領域を特定し、ゲータイト粒子の生成反応を行うことによって多量のＣｏを含有させることができた。
【０１４５】
一方、第一鉄含有沈殿物を含む水懸濁液のｐＨを７．５〜９．５の範囲に特定したことにより、アルカリ金属が存在しないため、ゲータイト粒子がアニオンを吸着しやすく、硫酸イオンを多量に含有するゲータイト粒子となり、通常の水を用いた洗浄では十分に除去できなかった。本発明ではｐＨが９．５〜１１．５のアンモニア水を用いて前記ゲータイト粒子を洗浄することによって、硫酸イオンも除去することが可能となり、紡錘状合金磁性粒子粉末の不純物量を低減することができた。
【０１４６】
また、前述した通り、コバルトはアンモニア化合物の存在下では十分に吸着させることができないが、ゲータイト粒子の粒子表面をコバルトで被覆する際に、炭酸アルカリ水溶液を使うことによって、大量に添加したコバルト化合物のほぼ全量を炭酸コバルトとしてゲータイト粒子粉末の粒子表面に被覆することができた。本発明においては、ゲータイト粒子の粒子表面を炭酸コバルトで被覆することによって、還元速度の制御を容易にすることができるので焼結防止効果が向上する。この理由は未だ明らかではないが、炭酸コバルト微粒子が前記ゲータイト粒子の粒子表面を均一に被覆するため、水酸化コバルト等の他の化合物で被覆した場合と比較して、焼結防止効果が向上したものと推定している。
【０１４７】
更に、本発明においては、当該炭酸コバルトの表面に希土類化合物が被覆されている。難還元性の希土類化合物がゲータイト粒子の最外層を被覆していることにより、各粒子間距離を近接することなく維持できるので還元処理時に焼結を抑制することができ、紡錘状の粒子形状が保持される。
【０１４８】
なお、本発明において、コバルト含有量を全Ｆｅに対してＣｏ換算で５０〜１１０原子％まで高めたことによって、低飽和磁化にも係わらず、保磁力分布Ｓ．Ｆ．Ｄ．に優れ、しかも酸化安定性に優れた紡錘状合金磁性粉末が得られた理由は未だ明かではないが、Ｃｏ合金化による飽和磁化値の低減、Ｃｏ合金化による酸化被膜の均一化の相乗効果によるものと推定している。
【０１４９】
結果、微粒子であるにも係わらず、全Ｆｅに対してＣｏ換算で５０〜１１０原子％と大量のＣｏ含有量においても、保磁力低下や保磁力分布Ｓ．Ｆ．Ｄ．を損なう事なく、効率的に最小限のＣｏ導入量で低飽和磁化し、酸化安定性に優れた紡錘状合金磁性粒子粉末が得られたものと本発明者は推定している。
【０１５０】
なお、被覆反応によって付着したアルカリ金属は水洗することによって容易に除去することができる。
【０１５１】
【実施例】
次に、実施例及び比較例を挙げる。
【０１５２】
実施例１、２、比較例１〜３：
前記発明の実施の形態の製造条件を種々変化させて紡錘状ゲータイト粒子粉末を得た。得られた紡錘状ゲータイト粒子粉末の諸特性を表１に、Ｃｏ、Ｙで被覆された紡錘状ゲータイト粒子粉末の組成を表２に示す。
【０１５３】
なお、表２の種類中のゲータイト９では被覆されたゲータイト粒子にＣｏ化合物粒子が単独析出し、混入していた。
【０１５４】
【表１】
【表２】
表２に示した諸特性を有するＣｏ、Ｙで被覆された紡錘状ゲータイト粒子粉末を用いて前記発明の実施の形態と同様にして紡錘状ヘマタイト粒子粉末を得た。このときの製造条件及び得られた紡錘状ヘマタイト粒子粉末の諸特性を表３に示す。
【０１５７】
【表３】
表３に示した諸特性を有する紡錘状ヘマタイト粒子粉末を用いて前記発明の実施の形態と同様にして紡錘状合金磁性粒子粉末を得た。このときの製造条件及び得られた紡錘状合金磁性粒子粉末の諸特性を表４及び表５に示す。更に、得られた紡錘状合金磁性粒子粉末を用いて作製した磁性塗膜の諸特性を表６に示す。なお、実施例２では、表２に示した焼結防止処理を行った後のゲータイト粒子６をヘマタイト化することなく加熱還元処理を行った。
【０１５９】
【表４】
【表５】
【表６】
【発明の効果】
本発明に係る紡錘状合金磁性粒子粉末は、平均長軸径が０．０２〜０．０８μｍの微粒子でありながら、高い保磁力を示し、且つ、低飽和磁化値でありながら、磁性塗膜の保磁力分布Ｓ．Ｆ．Ｄ．に優れ、しかも、酸化安定性に優れ、可溶性塩が可及的に低減されているので、磁気抵抗ヘッドを再生に用いた短波長領域で高出力、高Ｃ／Ｎ、しかも、信頼性が高く耐候性が向上した磁気記録媒体用磁性粒子粉末として好適である。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention provides fine particles, particularly fine particles having an average major axis diameter of 0.02 to 0.08 μm, exhibits a high coercive force, and has a low saturation magnetization value, and yet has a coercive force distribution of a magnetic coating film. S. F. D. The present invention provides a spindle-shaped alloy magnetic particle powder containing Fe and Co as a main component, and the spindle-shaped alloy magnetic particle powder containing Fe and Co as a main component is suitable as a magnetic material for a magnetic recording medium. It is.
[0002]
[Prior art]
In recent years, magnetic recording / reproducing equipment for audio, video, and computers has been significantly reduced in size and weight, long-time recording, high-density recording, or increased storage capacity, and is a magnetic recording medium. Demands for higher performance and higher density recording of magnetic tapes and magnetic disks are increasing.
[0003]
That is, the magnetic recording medium is required to have high image quality, high output characteristics, and particularly to improve the frequency characteristics. To this end, noise caused by the magnetic recording medium is reduced, the coercive force Hc and the coercive force distribution S.I. F. D. Is required to be excellent. In addition, there is a demand for improved storage characteristics and durability. For this purpose, it is required that the weather resistance ΔBm is excellent and the content of the soluble salt in the coating film is reduced.
[0004]
These characteristics of the magnetic recording medium are closely related to the magnetic particle powder used in the magnetic recording medium, and in recent years, the coercive force and the saturation have been higher than those of the conventional magnetic iron oxide particle powder. Attention has been paid to metal magnetic particle powder mainly composed of iron having a magnetization value σs, and digital audio tape (DAT), 8 mm video tape, Hi-8 tape, W-VHS tape for high-definition television, and DVC tape of digital recording system For computers, it is also used for tapes for external storage systems such as DDS, DLT and TRAVAN, and removable disks such as Zip, Superdisk, Hi-FD and the like.
[0005]
Therefore, there is a strong demand for further improvement in the properties of magnetic metal particles containing iron as a main component.
[0006]
That is, in order to obtain a magnetic recording medium that satisfies the above-mentioned characteristics, the metal magnetic particle powder containing iron as a main component is a fine particle, has a higher coercive force, and has a coercive force distribution S.P. F. D. It is strongly required to be excellent. In addition, it is required that the oxidation stability 安定 σs be excellent and the content of the soluble salt be reduced as much as possible.
[0007]
First, regarding the reduction of the size of the metal magnetic particle powder, Japanese Patent Application Laid-Open No. 2000-251243 discloses a technique for reducing the wavelength of a signal used in order to achieve a high recording density of a magnetic recording medium. If the magnetic material used has a comparable size with respect to the length of the signal recording area, a clear magnetization transition area cannot be created, so that recording becomes substantially impossible. For a long time, fine particles of a magnetic material have been used for higher recording density. ”As described in the description, to obtain a magnetic recording medium with high output in a short wavelength region and reduced noise, metal is required. It is necessary to make the magnetic particle powder finer, that is, to reduce the major axis diameter.
[0008]
In recent years, a magnetoresistive head has begun to be introduced as a tape reproducing head for a computer in place of the inductive magnetic head used so far. The magnetoresistive head can easily obtain a reproduction output compared to the inductive magnetic head, and does not generate impedance noise due to the induction coil, thus contributing to a significant reduction in system noise. For this reason, if the magnetic recording medium noise can be reduced, a high C / N ratio can be achieved. Therefore, further reduction in the size of the metal magnetic particle powder is required from the viewpoint of reducing particulate noise among magnetic recording medium noise.
[0009]
In addition, as the metal magnetic particles become finer, the ratio of the oxide film in the whole particles increases, so that the coercive force decreases and the coercive force distribution S.P. F. D. Tend to expand. Therefore, in order to improve the output of the magnetic recording medium in the short wavelength region, the coercive force distribution S.P. F. D. (Switching Field Distribution) is required to be excellent.
[0010]
Further, since the magnetoresistive head has high sensitivity, when the residual magnetization value of the magnetic recording medium is excessive, saturation of the magnetoresistive head is caused, and the reproduction characteristics are easily distorted. With the recent development of a high-sensitivity magnetoresistive head, reduction of the residual magnetization value of a magnetic recording medium has been promoted. Therefore, reduction of the saturation magnetization value of the metal magnetic particle powder is required. Conventionally, a method of reducing the saturation magnetization value of the metal magnetic particle powder by forming a thick oxide film on the particle surface of the metal magnetic particle powder has been proposed. F. D. However, the demand for the magnetic recording medium cannot be satisfied. Thus, despite being fine particles, the coercive force distribution S.P. F. D. In addition, there is a strong demand for metal magnetic particles having a low saturation magnetization.
[0011]
On the other hand, since the coercive force of the magnetic particle powder is generally generated due to its shape magnetic anisotropy, in order to obtain a magnetic particle powder having a high coercive force, the axial ratio (average major axis diameter / average short axis) of the particles is required. (Shaft diameter) needs to be increased. However, the finer the particles, the lower the axial ratio tends to be, which makes it difficult to obtain metal magnetic particles having a high coercive force. This fact indicates that the coercive force of the above metal powder is generally closely related to the size of the particles, and the finer the particles, the more the coercive force is maintained. For example, when the minor axis diameter of the acicular particles is constant, the coercive force increases as the axial ratio (major axis diameter / minor axis diameter) increases, but ... In order to maintain a high coercive force and obtain a high output in a short wavelength region, since the long axis of the particle is limited, the only option is to increase the coercive force by shortening the short axis and increasing the axial ratio. It is known that when the minor axis diameter of the particles is too small, so-called superparamagnetism is exhibited and no coercive force is exhibited, and there is a limit in shortening the minor axis diameter. "
[0012]
Metal magnetic particle powders with limited coercive force and saturation magnetization are described in Japanese Patent Publication No. 5-44162, JP-A-2000-323316, JP-A-2001-93711, JP-A-2001-283421, and the like. Have been.
[0013]
In addition, with the miniaturization of the metal magnetic particles, the minor axis diameter is shortened, and the crystallite size of the metal magnetic particles is reduced and the specific surface area is increased, so that it is very difficult to maintain high oxidation stability. It is known. Since the oxidation stability of the metal magnetic particle powder greatly contributes to the storage characteristics and durability of the magnetic recording medium, it is strongly desired that the metal magnetic particles have high oxidation stability even though they are fine particles.
[0014]
On the other hand, the metal magnetic particle powder contains impurities such as alkali metals due to the production method. This fact will be described in detail.
[0015]
That is, metal magnetic particle powder containing iron as a main component is an aqueous solution containing an iron-containing precipitate obtained by reacting an aqueous solution of a ferrous salt such as ferrous sulfate with an aqueous solution of an alkali such as sodium hydroxide and sodium carbonate. A goethite particle powder obtained by performing an oxidation reaction by passing an oxygen-containing gas such as air through the suspension, a hematite particle powder obtained by heating and dehydrating the goethite particle powder, or a heterogeneous element other than iron in these particle powders The starting material is obtained by heating and reducing the starting material under a reducing gas atmosphere.
[0016]
Derived from the above production method, the metal magnetic particle powder contains soluble sodium and sulfate ions and soluble calcium inevitably present in the production method, and contains soluble sodium salts, soluble calcium salts and sulfate ions. There is a problem in that a compound derived from the soluble salt contained when used in a magnetic recording medium precipitates on a magnetic coating film and a magnetic head. This fact is described in Japanese Unexamined Patent Publication No. 9-305958, which states that, when the total amount of the water-soluble ions contained in the magnetic material, the non-magnetic material, the carbon black and the filler used in each layer exceeds a certain amount, under high temperature and humidity When running after storage, the coefficient of friction increased, and in extreme cases, the phenomenon of sticking occurred and the running was stopped, and in extreme cases, the precipitates resulted in spacing loss and the reproduction output of the magnetic tape decreased. Further, the metal head is corroded and the recording / reproducing characteristics are deteriorated. "
[0017]
As a method of reducing the soluble salt in the metal magnetic particle powder, either of 1) a method of not using an aqueous alkali solution composed of an alkali metal such as sodium hydroxide as a raw material, and 2) a method of reducing the soluble salt by washing with water. Has been adopted.
[0018]
When the soluble salts are reduced by washing with water, it is conceivable to wash each product up to the metal magnetic particle powder, but in the method for producing the metal magnetic particle powder, goethite particle powder as a starting material and Even if washing is performed at the stage of the hematite particle powder, only the soluble salt present on the particle surface is removed. Therefore, when reduced to metal magnetic particle powder, it is known that insoluble impurities contained in the particles move to the particle surface and precipitate as soluble salts, and those that can be completely removed are not used. Absent. On the other hand, when the metal magnetic particles are washed with water after being made into powder, particularly when the particle shape is a spindle shape, magnetic properties such as coercive force are reduced, and dispersibility in the magnetic paint tends to be reduced. .
[0019]
Therefore, in the technique of reducing the soluble salt by washing with water, the soluble salt can be reduced, but it is not easy to reduce the soluble salt to zero and the magnetic properties are deteriorated, which is not preferable. Therefore, there is a demand for obtaining high-purity metal magnetic particle powder by eliminating the remaining impurities as much as possible by not using an alkaline aqueous solution composed of an alkali metal such as sodium hydroxide as a raw material.
[0020]
Conventionally, technologies for producing goethite particle powder without using an aqueous alkali solution composed of an alkali metal and technologies for washing hematite particle powder and metal magnetic particle powder after heating and dehydrating goethite particle powder have been attempted (Japanese Patent Application Laid-Open No. 61-174119, JP-A-7-22224, JP-A-7-326035, JP-A-8-7256, JP-A-8-185624, JP-A-8-186015, and JP-A-8-186 279137, JP-A-8-279138, JP-A-8-306031, JP-A-9-106535, JP-A-9-305958, JP-A-10-69629, JP-A-10-83906 Gazette, JP-A-2001-81506, JP-A-2001-176052, WO00 / 3820 , JP No. 2001-192211 Publication).
[0021]
[Problems to be solved by the invention]
Even though it is a fine particle, it shows a high coercive force, and yet has a low saturation magnetization value, yet has a coercive force distribution S.P. F. D. A spindle-shaped alloy magnetic particle powder excellent in the above has been most demanded at present, but a metal magnetic particle powder containing iron as a main component which sufficiently satisfies the above-mentioned characteristics has not been provided yet.
[0022]
That is, Japanese Patent Publication No. Hei 5-44162 discloses that a metal oxide particle is gradually oxidized and then heat-treated in an oxygen-containing gas so that a thick oxide layer is formed, low saturation magnetization is obtained, and oxidation stability is improved. It is described to produce a metal magnetic particle powder having an improved coercive force distribution. F. D is wide, the coercive force is about 1000 Oe, the coercive force is increased, and the coercive force distribution F. D. Does not fully satisfy the requirements.
[0023]
Japanese Patent Application Laid-Open No. 2000-323316 discloses that a metal-based material in which a non-magnetic region having a specific ratio is formed so as to cover a magnetic region can reduce noise in a reproducing system using a magnetoresistive head. It describes that the S / N ratio can be increased. However, alloying with Co has not been sufficiently studied, and low saturation magnetization due to expansion of the nonmagnetic region has a remarkable coercive force distribution. F. D. Of the coercive force distribution S. F. D. Can not satisfy the requirements of Also, the saturation magnetization value is 100 Am 2 / Kg (100 emu / g) or more, which is insufficient for the demand for low saturation magnetization.
[0024]
In addition, Japanese Patent Application Laid-Open No. 2001-93711 discloses that, by using metal magnetic particle powder which is increased to 45 to 300% by weight in terms of Co with respect to all Fe, the magnetic recording medium is excellent in oxidation resistance, Although it is described that the output level is prevented from being reduced, it is insufficient to cope with fine particles and a high coercive force. In addition, the saturation magnetization value is 110 Am 2 / Kg (110 emu / g) or more, and does not sufficiently satisfy the requirement of low saturation magnetization.
[0025]
Also, in the above-mentioned Japanese Patent Application Laid-Open No. 2001-283421, the average major axis length is 0.1 μm or less and the saturation magnetization value is 120 Am 2 / Kg (120 emu / g) or less and a magnetic recording medium using acicular ferromagnetic particles having a coercive force of 2100 kA / m (2100 Oe) or more are suitable for high-density recording using a magnetoresistive head for reproduction. It is described that the saturation magnetization value is 100 Am 2 / Kg (100 emu / g), which is not enough for the requirement of low saturation magnetization, and the Co content is as low as 33 atomic% in terms of Co with respect to all Fe, and the saturation magnetization value is 100 Am 2 / Kg (100 emu / g) or less, the coercive force distribution F. D. The deterioration is remarkable, and the coercive force distribution S.P. F. D. Can not satisfy the requirements of
[0026]
Japanese Patent Application Laid-Open No. Sho 61-174119 discloses that goethite particle powder is produced by using an aqueous solution of ferrous sulfate in an aqueous solution of ammonium carbonate, but the obtained goethite particle powder contains cobalt. Since it is not contained, the oxidation stability of the metal magnetic particle powder obtained using the particle powder as a starting material is hardly sufficient.
[0027]
Also, Japanese Patent Application Laid-Open No. Hei 7-22224 discloses that hematite particle powder or metal magnetic particle powder is washed with water, but the obtained magnetic metal particle powder has a major axis diameter of 0.08 μm or more and is saturated. Magnetization value is 120 Am 2 / Kg (120 emu / g) or more, and does not sufficiently satisfy the requirements for fine particle size and low saturation magnetization.
[0028]
Japanese Patent Application Laid-Open Nos. Hei 7-326035 and Hei 8-7256 disclose a metal magnetic particle powder using a goethite particle powder obtained using an aqueous ferrous salt solution, ammonium carbonate and aqueous ammonia. Which has an average major axis diameter of 0.08 μm or more and a saturation magnetization of 120 Am 2 / Kg (120 emu / g) or more, which does not sufficiently satisfy the requirements for fine particle size and low saturation magnetization.
[0029]
Japanese Patent Application Laid-Open No. 8-185624 discloses that hematite particles or metal magnetic particles are washed with water to limit the content ratio of sodium ions and potassium ions to a specific range. Is about 0.13 μm and the saturation magnetization is 120 Am 2 / Kg (120 emu / g) or more, and the soluble sodium content is as high as 200 ppm or less, and thus does not sufficiently satisfy the requirements of finer particles, higher coercive force, lower saturation magnetization, and improved oxidation stability.
[0030]
Japanese Patent Application Laid-Open Nos. Hei 8-279137 and Hei 8-306031 disclose a metal magnetic particle powder using a goethite particle powder obtained using an aqueous ferrous salt solution, ammonium carbonate and aqueous ammonia. Is produced, and the obtained metal magnetic particle powder has an average major axis diameter of 0.05 to 0.13 μm, and the surface layer portion of the particle has aluminum, a rare earth element and oxygen more than the entire particle. The content ratio is high. However, since goethite particles were formed and washed with water, and the aluminum compound was added, goethite particles containing aluminum in the crystal were not obtained, and the reduction rate during the heat reduction treatment was sufficiently controlled. Therefore, sintering proceeds, so that it is not possible to obtain metal magnetic particle powder having fine particles and excellent magnetic properties and oxidation stability. In addition, the saturation magnetization value is 130 Am 2 / Kg (130 emu / g) or more, which does not sufficiently satisfy the requirement for low saturation magnetization.
[0031]
Also, Japanese Patent Application Laid-Open No. 9-106535 describes that a metal magnetic particle powder is produced using a goethite particle powder obtained using an aqueous ferrous salt solution, ammonium carbonate and aqueous ammonia. Thus, metal magnetic particle powder having a major axis diameter of 0.03 to 0.08 μm and a coercive force of 1900 to 2400 Oe is obtained, but does not sufficiently satisfy the demand for improving oxidation stability. In addition, the saturation magnetization value is 130 Am 2 / Kg (130 emu / g) or more, which does not sufficiently satisfy the requirement for low saturation magnetization.
[0032]
Japanese Patent Application Laid-Open No. Hei 9-171914 discloses that goethite particles are coated with one or more compounds selected from Co, Al, Si and Ca and a rare earth compound, washed with water, and then coated with a carbon compound in the outermost layer. It is described that a metal magnetic particle powder is obtained by applying, followed by heat dehydration and reduction, but since cobalt and aluminum are not dissolved in goethite particles, the magnetic properties of the obtained metal magnetic particle powder are described. Is still not enough. Further, for the purpose of reducing the content of S and Cl, goethite particles coated with one or more compounds selected from Co, Al, Si and Ca and a rare earth compound are washed with water. It is known that when the particles are reduced to metal magnetic particle powder, insoluble impurities contained in the particles move to the particle surface and precipitate as soluble salts, and S and The Cl content is not reduced sufficiently. Further, the saturation magnetization value is 120 Am 2 / Kg (120 emu / g) or more, which does not sufficiently satisfy the demand for low saturation magnetization.
[0033]
Japanese Patent Application Laid-Open No. Hei 9-305958 discloses that goethite particle powder is obtained by using an alkali carbonate containing no alkali metal, and further washed with water until the metal magnetic particle powder is obtained. Although it is described to reduce the content of ionic ions, since a compound containing an alkali metal is used as an additive, the alkali metal is contained in the goethite particles, and high-purity goethite particles are obtained. It is hard to say that it has been done. In addition, the saturation magnetization value is 130 Am 2 / Kg (130 emu / g) or more, and cannot meet the demand for low saturation magnetization.
[0034]
In the above-mentioned Japanese Patent Application Laid-Open No. 10-69629, washing with water at any stage of goethite particles, hematite particles or metal magnetic particles is described, but it is hard to say that it can be completely removed. . On the other hand, washing with water after forming the metal magnetic particles is not preferable because magnetic properties such as saturation magnetization and coercive force are reduced and dispersibility in a magnetic paint is also reduced. In addition, the saturation magnetization value is 130 Am 2 / Kg (130 emu / g) or more, which does not sufficiently satisfy the requirement for low saturation magnetization.
[0035]
Also, Japanese Patent Application Laid-Open No. 10-83906 mentioned above describes that goethite particles are produced from an alkali hydroxide composed of ferrous chloride and an aqueous ammonia solution and an alkali carbonate composed of ammonium carbonate or the like. It is not described to wash with water, and because the reaction pH when producing goethite particles is high, cobalt ions are eluted as an ammine complex, so that it is possible to obtain metal magnetic particle powder having high coercive force. It will be difficult. In addition, the saturation magnetization value is 130 Am 2 / Kg (130 emu / g) or more, which does not sufficiently satisfy the requirement for low saturation magnetization.
[0036]
Japanese Patent Application Laid-Open No. 2001-81506 discloses that a rare earth element and Si are coated on the surface of iron oxyhydroxide or iron oxide containing Co and containing Al as a solid solution, and the particle powder is subjected to gas reduction. It is described that a metal magnetic particle powder is obtained, but the average major axis diameter is as large as 0.10 μm, and the saturation magnetization value is 140 Am 2 / Kg (120 emu / g) or more, which does not sufficiently satisfy the requirements for fine particle size and low saturation magnetization.
[0037]
Further, JP-A-2001-176052 and JP-A-2001-176053 disclose production of metal magnetic particle powder using goethite particle powder obtained using an aqueous ferrous salt solution and ammonium carbonate and aqueous ammonia. However, since the cobalt compound is added after the formation reaction of the goethite particles, goethite particles containing cobalt are not obtained in the goethite crystals, and the reduction rate during the heat reduction treatment is reduced. Since sintering proceeds because control is not sufficiently performed, fine metal particles having excellent magnetic properties and oxidation stability cannot be obtained. Further, the saturation magnetization value is 150 Am 2 / Kg (150 emu / g), which does not sufficiently satisfy the requirement for low saturation magnetization.
[0038]
WO 00/38201 discloses iron oxyhydroxide particles containing cobalt and aluminum by mixing and aging a ferric salt aqueous solution, a cobalt salt aqueous solution, and a water-soluble salt of aluminum with an aqueous sodium hydroxide solution. It is described that, after obtaining, a metal magnetic particle powder is produced by heating and reducing an iron oxyhydroxide particle powder whose surface is further coated with a compound of a rare earth element. However, since sodium hydroxide is used as an alkali source, it cannot be said that soluble salts such as Na can be sufficiently reduced. Further, the saturation magnetization value is 130 Am 2 / Kg (130 emu / g), which does not sufficiently satisfy the requirement for low saturation magnetization.
[0039]
Japanese Patent Application Laid-Open No. 2001-192221 describes that metal magnetic particle powder is produced using goethite particle powder obtained using an aqueous solution of ferrous salt, ammonium carbonate and aqueous ammonia. When coating the surface of the particles of the goethite particles with the cobalt compound and the rare earth compound, the coating is performed at the same time, and the effect of preventing sintering during the reduction treatment is insufficient. It is difficult to obtain metal magnetic particles having a fine particle size of about 0.08 μm, exhibiting a high coercive force, and having excellent oxidation stability. In addition, the saturation magnetization value is 140 Am 2 / Kg (140 emu / g) or more, and does not sufficiently satisfy the demand for low saturation magnetization.
[0040]
Therefore, the present invention provides fine particles having an average major axis diameter of 0.02 to 0.08 μm, shows a high coercive force, and has a low coercive force distribution S.E. F. D. Another object of the present invention is to provide a spindle-shaped alloy magnetic particle powder having excellent oxidative stability and a reduced soluble salt as much as possible in addition to the excellent spindle-shaped alloy magnetic particle powder.
[0041]
[Means for Solving the Problems]
The technical problem can be achieved by the present invention as described below.
[0042]
That is, the present invention provides a spindle-shaped alloy magnetic particle containing 50 to 110 atomic% of cobalt in terms of Co with respect to all Fe and having an average major axis diameter of 0.02 to 0.08 μm and containing Fe and Co as main components. And the coercive force of the spindle-shaped alloy magnetic particles mainly composed of Fe and Co is 143.2 to 238.7 kA / m (1800 to 3000 Oe), and the saturation magnetization value s is 60 to 100 Am 2 / Kg (60 to 100 emu / g), and S.P. of a magnetic coating film produced using the spindle-shaped alloy magnetic particles containing Fe and Co as main components. F. D. Is 0.7 or less (Mix 1).
[0043]
Also, the present invention provides a spindle-shaped alloy magnetic particle containing Fe and Co as main components and having an average major axis diameter of 0.02 to 0.08 μm containing 50 to 110 atomic% of cobalt in terms of Co with respect to all Fe. And the coercive force of the spindle-shaped alloy magnetic particles mainly composed of Fe and Co is 143.2 to 238.7 kA / m (1800 to 3000 Oe), and the saturation magnetization value s is 60 to 100 Am 2 / Kg (60-100 emu / g), the soluble Na content is 30 ppm or less, the soluble Ca content is 100 ppm or less, and the spindle-shaped alloy magnetic particle powder containing Fe and Co as main components is used. S. of the magnetic coating film produced using F. A spindle-shaped alloy magnetic particle powder for magnetic recording, wherein D is 0.7 or less (Invention 2).
[0044]
Further, the present invention provides an average length containing 50 to 110 atomic% of cobalt in terms of Co, 3 to 20 atomic% of aluminum in terms of Al, and 10 to 30 atomic% of a rare earth element in terms of a rare earth element with respect to all Fe. Spindle-shaped alloy magnetic particle powder mainly composed of Fe and Co having a shaft diameter of 0.02 to 0.08 µm, and the coercive force of the spindle-shaped alloy magnetic particle powder mainly composed of Fe and Co is 143.2. ２238.7 kA / m (1800 to 3000 Oe), and the saturation magnetization σs is 60 to 100 Am 2 / Kg (60-100 emu / g), the soluble Na content is 30 ppm or less, the soluble Ca content is 100 ppm or less, the oxidation stability Δσs is 10% or less, and the Fe and Co S. of a magnetic coating film produced using a spindle-shaped alloy magnetic particle powder as a main component. F. A spindle-shaped alloy magnetic particle powder for magnetic recording, wherein D is 0.7 or less (Invention 3).
[0045]
The present invention also provides a water suspension containing goethite particles containing 15 to 50 atomic% of cobalt in terms of Co with respect to all Fe and 3 to 15 atomic% of aluminum in terms of Al with respect to total Fe, which contains a cobalt compound and An aqueous alkali carbonate solution is added to coat the particle surface of the goethite particles with 15 to 60 atomic% of cobalt carbonate in terms of Co with respect to the total Fe, and then 10 to 30 atomic% in terms of rare earth elements with respect to the total Fe. After coating the surface of the goethite particles coated with cobalt carbonate with the rare earth compound, heat treating the surface-coated goethite particle powder or the surface-coated goethite particle powder at 400 to 750 ° C. in a non-reducing atmosphere. Spindle-shaped alloy containing Fe and Co as main components by heating and reducing the hematite particle powder obtained by heating at 350 to 700 ° C. in a reducing atmosphere. A present invention 1 to the preparation of the magnetic recording spindle-shaped alloy magnetic particles as described in any one of the 3, characterized in that to obtain a sexual particles (Invention 4).
[0046]
In the present invention, the aqueous ferrous sulfate solution is reacted with a mixed alkali aqueous solution comprising an aqueous ammonium hydrogen carbonate solution and an aqueous ammonium hydroxide solution having an equivalent ratio to the aqueous ferrous sulfate solution of 1.7 to 3.0. After aging the obtained aqueous suspension containing ferrous precipitate in a non-oxidizing atmosphere, an oxygen-containing gas is passed through the aqueous suspension to produce goethite seed particles by an oxidation reaction. Then, an oxygen-containing gas is passed through an aqueous suspension containing the seed crystal particles and the ferrous-containing precipitate to form a goethite layer on the particle surface of the seed crystal particles by an oxidation reaction, thereby forming a goethite particle. In generating
As the mixed alkaline aqueous solution, an aqueous solution in which the ammonium hydroxide aqueous solution is blended at a ratio of 55 to 85 mol% with respect to the mixed alkaline aqueous solution is used, and at the time of generation of the seed crystal particles, To the aqueous suspension containing the ferrous-containing precipitate during the aging, a Co compound of 15 to 50 atomic% in terms of Co with respect to the total Fe is added, and the oxidation reaction is performed with the total Fe. 2+ In the range of 20-80% of
During the growth of the goethite layer, 3 to 15 atomic% in terms of Al with respect to the total Fe so that the pH of the aqueous suspension containing the seed crystal particles and the ferrous-containing precipitate is less than 9.0. Of an Al compound,
After the generated goethite particles are separated by filtration, they are washed with aqueous ammonia having a pH of 9.5 to 11.5 to obtain goethite particles,
Next, a cobalt compound and an aqueous alkali carbonate solution are added to the obtained aqueous suspension containing the goethite particles to coat the surface of the particles of the goethite particles with 15 to 60 atomic% of cobalt carbonate in terms of Co with respect to all Fe. Then, the surface of the goethite particles coated with cobalt carbonate was coated with a rare earth compound in an amount of 10 to 30 atomic% in terms of a rare earth element with respect to all Fe, and then the surface-coated goethite particles or the surface-coated goethite particles were coated. Hematite particle powder obtained by heat-treating goethite particle powder in a non-reducing atmosphere at 400 to 750 ° C. is heat-reduced at 350 to 700 ° C. in a reducing atmosphere to obtain a spindle-shape mainly composed of Fe and Co. 4. A method for producing a spindle-shaped alloy magnetic particle powder for magnetic recording according to any one of the first to third aspects, wherein the alloy magnetic particle powder is obtained. The present invention 5).
[0047]
The present invention also provides the method of manufacturing spindle-shaped alloy magnetic particle powder for magnetic recording, wherein the heat reduction is performed by heating and reducing in a reducing atmosphere at a temperature in the range of 300 to 600 ° C. A first step of obtaining the magnetic flux of the spindle-shaped alloy, and subjecting the spindle-shaped alloy magnetic particles obtained in the first step to surface oxidation in an oxygen-containing inert gas atmosphere at a temperature in the range of 60 to 200 ° C. to obtain a saturation magnetization of the spindle-shaped alloy magnetic particles. 85-135 Am 2 / Kg in the second step, the spindle-shaped alloy magnetic particles passing through the second step, in a reducing gas atmosphere, at least 50 ° C. higher than the reduction temperature of the first step and up to a temperature range of 400 to 700 ° C. After raising the temperature and then switching to a reducing gas atmosphere, the spindle-shaped alloy magnetic particles powder passing through the third step and the third step of performing heat reduction again in a temperature range of 400 to 700 ° C. is 5 to 10 g / m 2. 3 A fourth step of obtaining the spindle-shaped alloy magnetic particles by performing surface oxidation again in a temperature range of 40 to 160 ° C. in an inert gas atmosphere containing water vapor and oxygen. Alternatively, the present invention provides a method for producing a spindle-shaped alloy magnetic particle powder for magnetic recording of the present invention 5 (present invention 6).
[0048]
The configuration of the present invention will be described in detail as follows.
[0049]
First, the spindle-shaped alloy magnetic particles according to the present invention will be described.
[0050]
The spindle-shaped alloy magnetic particles according to the present invention are spindle-shaped, have an average major axis diameter of 0.02 to 0.08 μm, and have an oxidation stability when the average major axis diameter is less than 0.02 μm. Sharply decreases, and at the same time, high coercive force and good coercive force distribution S.I. F. D. Is difficult to obtain. If the thickness exceeds 0.08 μm, the magnetic particles for obtaining a magnetic recording medium with high output in a short wavelength region and reduced noise are not preferable because of their large particle size. Preferably it is 0.025 to 0.075 μm.
[0051]
The axis ratio of the spindle-shaped alloy magnetic particles according to the present invention is preferably 2 or more, and if the axis ratio is less than 2, the desired high coercive force cannot be obtained. More preferably, it is 3-8.
[0052]
Crystallite size D of spindle-shaped alloy magnetic particles according to the present invention 110 Is preferably 90 to 170 °, and when the crystallite size is less than 90 °, the magnetic recording medium is advantageous in terms of particle noise reduction, but the coercive force decreases and the coercive force distribution S.P. F. D. Easily expand, and the oxidative stability also decreases. When the angle is 170 ° or more, the particle noise is undesirably increased. More preferably, it is 90 to 150 °.
[0053]
The BET specific surface area of the spindle-shaped alloy magnetic particles according to the present invention is 40 to 80 m. 2 / G, preferably 40 m 2 If it is less than / g, spindle-shaped alloy magnetic particles satisfying noise and dispersibility cannot be obtained. 80m 2 If it exceeds / g, it is difficult to disperse when forming the paint, and the viscosity of the paint is increased. More preferably 50-80m 2 / G.
[0054]
The cobalt content of the spindle-shaped alloy magnetic particles is 50 to 110 at% in terms of Co with respect to the total Fe, and when the cobalt content is less than 50 at%, a good coercive force distribution S.P. F. D. , A low saturation magnetization cannot be obtained, and a high coercive force is hardly obtained. If it exceeds 110 atomic%, the coercive force will decrease and the saturation magnetization will decrease more than necessary. Preferably it is 55 to 100 atomic%.
[0055]
The aluminum content is preferably 3 to 20 atomic% in terms of Al with respect to all Fe, and the rare earth element content is preferably 10 to 30 atomic% with respect to all Fe in terms of rare earth element. If the aluminum content and the rare earth element content are less than the above lower limits, the sintering prevention effect in the heat reduction process is reduced, so that the coercive force is reduced and the coercive force distribution S.P. F. D. Expands. If it exceeds the upper limit, the temperature required for hydrogen reduction becomes extremely high, which is not preferable in production.
[0056]
Further, the content of soluble Na is preferably 30 ppm or less, more preferably 20 ppm or less, further preferably 10 ppm or less, and the content of soluble Ca is preferably 100 ppm or less, more preferably 80 ppm or less, and still more preferably 70 ppm or less. is there. If the content of each of the impurities exceeds the upper limit, it is not preferable because a compound resulting therefrom may precipitate on the surface of the magnetic coating film. Further, the residual sulfur content is preferably at most 60 ppm, more preferably at most 50 ppm.
[0057]
The spindle-shaped alloy magnetic particles according to the present invention have a coercive force Hc of 143.2 to 238.7 kA / m (1800 to 3000 Oe). If it is less than 143.2 kA / m, a sufficiently high output cannot be obtained in a short wavelength region. When it exceeds 238.7 kA / m, the recording head is saturated, and a high output in a target short wavelength region cannot be obtained. It is preferably 159.2 to 222.8 kA / m (2000 to 2800 Oe).
[0058]
The spindle-shaped alloy magnetic particles according to the present invention have a saturation magnetization value? S of 60 to 100 Am. 2 / Kg (60-100 emu / g). 60 Am 2 If it is less than / kg, a sufficiently high output cannot be obtained in a short wavelength region because the residual magnetization value decreases. In addition, high coercivity, good coercivity distribution F. D. Cannot be obtained. 100 Am 2 If it exceeds / kg, excessive remanent magnetization is generated, which causes saturation of the magnetoresistive head, which tends to cause distortion in reproduction characteristics, and does not provide high C / N output in a short wavelength region. Preferably 70-100 Am 2 / Kg (70-100 emu / g).
[0059]
The oxidation stability Δσs of the spindle-shaped alloy magnetic particles according to the present invention is preferably 10% or less, more preferably 8% or less.
[0060]
The spindle-shaped alloy magnetic particles according to the present invention preferably have a squareness ratio (σr / σs) of 0.51 to 0.55.
[0061]
The coercive force distribution of a magnetic coating film obtained by using the spindle-shaped alloy magnetic particles according to the present invention. F. D. Is 0.70 or less. S. F. D. Exceeds 0.70, the magnetization reversal region expands, and a sufficient output cannot be obtained in the short wavelength region. It is more preferably 0.60 or less, further preferably 0.50 or less.
[0062]
The magnetic coating film obtained by using the spindle-shaped alloy magnetic particles according to the present invention preferably has a coercive force Hc of 143.2 to 238.7 kA / m (1800 to 3000 Oe) and a squareness ratio (Br / Bm) of 0. 0.82 or more is preferable, and the oxidation stability ΔBm is preferably less than 8%.
[0063]
Next, a method for producing the spindle-shaped alloy magnetic particles according to the present invention will be described.
[0064]
In the present invention, after forming spindle-shaped goethite particles by the method described in detail below, an aqueous solution containing a cobalt compound and an alkali metal carbonate is added to an aqueous suspension containing the goethite particles, and the spindle-shaped goethite particles are added. The surface of the goethite particles is coated with cobalt carbonate, the surface of the cobalt carbonate is coated with a rare earth compound, and the obtained surface-coated goethite particle powder or the goethite particle powder is heated and dehydrated at 400 to 750 ° C. By heating and reducing the obtained spindle-shaped hematite particles at 350 to 700 ° C., spindle-shaped alloy magnetic particles containing Fe and Co as main components can be obtained.
[0065]
The spindle-shaped goethite particle powder in the present invention is a mixed alkali aqueous solution comprising an aqueous solution of ferrous sulfate and an aqueous solution of ammonium hydrogen carbonate and an aqueous solution of ammonium hydroxide having an equivalent ratio to the aqueous solution of ferrous sulfate of 1.7 to 3.0. After aging the aqueous suspension containing the ferrous-containing precipitate obtained by reacting under a non-oxidizing atmosphere, an oxygen-containing gas is passed through the aqueous suspension, and spindle-like goethite is oxidized by an oxidation reaction. A seed crystal particle is generated, and then a goethite layer is formed on the particle surface of the seed crystal particle through an oxidation reaction by passing an oxygen-containing gas through an aqueous suspension containing the seed crystal particle and the ferrous precipitate. In growing and producing spindle-shaped goethite particles,
As the mixed alkaline aqueous solution, a mixture of the aqueous ammonium hydroxide solution and the mixed alkaline aqueous solution in a ratio of 55 to 85 mol% is used. To the aqueous suspension containing the ferrous-containing precipitate during the ripening, a Co compound of 15 to 50 atomic% in terms of Co with respect to the total Fe was added to carry out the oxidation reaction. 2+ In the range of 20-80% of
During the growth of the goethite layer, 0.5 to 20 in terms of Al with respect to all Fe so that the pH of the aqueous suspension containing the seed crystal particles and the ferrous-containing precipitate is less than 9.0. Atomic% Al compound is added,
The produced spindle-shaped goethite particles can be obtained by filtering, followed by washing with aqueous ammonia having a pH of 9.5 to 11.5.
[0066]
In the production reaction of the spindle-shaped goethite seed particles, it is not preferable to use an aqueous ferrous sulfate solution other than the aqueous ferrous sulfate solution, for example, an aqueous ferrous chloride solution contains chlorine. The concentration of ferrous iron after the mixing of the aqueous ferrous sulfate solution with the mixed alkaline aqueous solution is preferably 0.1 to 1.0 mol / l, and when less than 0.1 mol / l, the yield is low and the method is not industrial. . If it exceeds 1.0 mol / l, the particle size distribution is undesirably large. More preferably, it is 0.2 to 0.8 mol / l.
[0067]
In the present invention, an aqueous solution of ammonium bicarbonate (NH 4 HCO 3 ) And aqueous ammonium hydroxide (NH 4 OH). When an alkaline aqueous solution composed of an alkali metal is used, the spindle metal alloy particle powder from which the soluble salt has been removed cannot be obtained because the alkali metal remains in the particles. The mixing ratio of the aqueous ammonium bicarbonate solution and the aqueous ammonium hydroxide solution is such that the aqueous ammonium hydroxide solution is 55 to 85 mol%, preferably 57 to 80 mol%, based on the mixed alkaline aqueous solution. When the amount of ammonium bicarbonate is large, the axial ratio of the obtained goethite particles becomes small. On the other hand, if the amount of ammonium hydroxide is too large, magnetite is likely to be generated, and cobalt is easily eluted.
[0068]
The total amount of the aqueous ammonium bicarbonate solution and the aqueous ammonium hydroxide solution used is 1.7 to 3.0 as an equivalent ratio with respect to all Fe in the aqueous ferrous sulfate solution. Mixing tends to occur, and if it exceeds 3.0, it is industrially undesirable. Preferably it is 1.75 to 2.85.
[0069]
The pH of the aqueous suspension containing the ferrous-containing precipitate in the present invention is preferably 7.5 to 9.5. If the pH is lower than 7.5, magnetite is mixed, which is not preferable. If the pH exceeds 9.5, the elution of cobalt becomes remarkable, which is not preferable. More preferably, it is 8.0 to 9.0.
[0070]
The ripening reaction of the spindle-shaped goethite seed crystal particles is carried out with stirring under a non-oxidizing atmosphere. In the non-oxidizing atmosphere, an inert gas (such as nitrogen gas) or a reducing gas (such as hydrogen gas) is passed through the liquid. Preferably, it is nitrogen gas.
[0071]
As for the reaction temperature in the ripening reaction of the spindle-shaped goethite seed particles, it is preferable that the aqueous suspension in a non-oxidizing atmosphere is usually carried out in a temperature range of 40 to 80 ° C. If the temperature is lower than 40 ° C., the axial ratio is small, and it is difficult to obtain a sufficient aging effect. If the temperature exceeds 80 ° C., magnetite may be mixed. The aging time is 30 to 300 minutes. If the time is less than 30 minutes, the axial ratio cannot be sufficiently increased. When the time exceeds 300 minutes, it is difficult to obtain a sufficient aging effect because ammonia is volatilized.
[0072]
The oxidizing means in the production reaction of the spindle-shaped goethite seed crystal particles is performed by passing an oxygen-containing gas (for example, air) through the liquid.
[0073]
The temperature in the reaction for producing the spindle-shaped goethite seed crystal particles may be usually at a temperature of 80 ° C. or less at which goethite particles are produced. When the temperature exceeds 80 ° C., magnetite may be mixed in the spindle-shaped goethite particles. Preferably it is in the range of 45 to 55 ° C.
[0074]
In the formation reaction of the spindle-shaped goethite seed crystal particles, a Co compound such as cobalt sulfate or cobalt nitrate is added to an aqueous suspension containing a ferrous-containing precipitate after aging before performing an oxidation reaction. The amount of the Co compound added is 15 to 50 atomic% in terms of Co with respect to the total Fe in the final spindle-shaped goethite particles to be obtained. In this case, there is no effect of improving the magnetic properties, and if it exceeds 50 atomic%, a remarkable reduction in the axial ratio due to miniaturization and the incorporation of foreign substances other than goethite in the reaction product are likely to occur. Preferably it is 18 to 40 atomic%.
[0075]
The formation reaction of the spindle-shaped goethite seed crystal particles was carried out by all Fe 2+ Is performed in the range of 20 to 80% of the above. If it is less than 20%, the axial ratio is too small, and it is difficult to obtain a high coercive force when the spindle-shaped alloy magnetic particles are used. On the other hand, if it exceeds 80%, the generation of goethite particles is almost completed. In this case, the effect of the added Al compound cannot be sufficiently obtained, and the coercive force decreases.
[0076]
An oxygen-containing gas is passed through the aqueous suspension containing the spindle-shaped goethite seed particles to grow a goethite layer on the particle surface of the spindle-shaped goethite seed particles. By adding, spindle-shaped goethite particles containing aluminum can be obtained.
[0077]
As the Al compound, acid salts such as aluminum sulfate and aluminum nitrate and aluminates such as ammonium aluminate can be used. The addition time of the Al compound may be either an aqueous suspension containing spindle-shaped goethite seed crystal particles and a ferrous-containing precipitate before aeration with an oxygen-containing gas in the growth reaction, or an aqueous suspension during the growth reaction. May be added. It is particularly preferable before starting the growth reaction of the goethite layer. Further, the Al compound may be dividedly added, or added continuously and intermittently.
[0078]
The addition amount of the Al compound is preferably 3 to 20 atomic% in terms of Al with respect to the total Fe in the final spindle-shaped goethite particles to be obtained. If it exceeds atomic%, the axial ratio decreases. More preferably, it is 3.5 to 15 atomic%.
[0079]
The pH value of the reaction solution in the growth reaction of the goethite layer is preferably less than 9.0, and when the pH exceeds 9.0, cobalt is easily eluted. High coercive force cannot be obtained. It is preferably in the range of 7.0 to 8.8. If the pH value is less than 7.0, magnetite may be mixed, which is not preferable.
[0080]
The oxidizing means in the growth reaction of the goethite layer is performed by passing an oxygen-containing gas (for example, air) through the liquid.
[0081]
Usually, the temperature in the growth reaction of the goethite layer may be a temperature of 80 ° C. or less at which goethite particles are generated. When the temperature exceeds 80 ° C., magnetite may be mixed in the spindle-shaped goethite particles. Preferably it is in the range of 45 to 55 ° C.
[0082]
The obtained spindle-shaped goethite particles are washed with aqueous ammonia having a pH of 9.5 to 11.5. Sulfate ions can be removed by washing with ammonia water. If the pH of the aqueous ammonia is outside the above range, the sulfate ions cannot be sufficiently removed. The temperature range of the aqueous ammonia is preferably from 20 to 50C. If the temperature is lower than 20 ° C., the washing efficiency is reduced. If the temperature is higher than 50 ° C., ammonia is volatilized, which is not preferable.
[0083]
After washing with ammonia water, it is preferable to further wash with water. As the washing water, ion exchange water is preferable.
[0084]
The obtained spindle-shaped goethite particle powder has an average major axis diameter of preferably 0.04 to 0.15 μm, more preferably 0.05 to 0.14 μm, and an axial ratio of 3 to 12, more preferably 4 to 10. 10 and a BET specific surface area value of 100 to 250 m. 2 / G is preferred. The Co content is 15 to 50 atomic% in terms of Co with respect to all Fe in the spindle-shaped goethite particles, and the Al content is 3 to 20 atomic% in terms of Al with respect to all Fe.
[0085]
In the present invention, it is important to coat the surface of the spindle-shaped goethite particles with cobalt carbonate. By coating the surface of the goethite particles with cobalt carbonate, the control of the reduction rate can be facilitated, so that the effect of preventing sintering is improved.
[0086]
As the aqueous solution of the cobalt compound to be added to the aqueous suspension containing the spindle-shaped goethite particles, an aqueous solution of cobalt acetate or an aqueous solution of cobalt nitrate is preferable. The addition amount of the cobalt compound is not more than 110 atomic% in terms of Co with respect to all Fe in total with the amount of Co contained in the spindle-shaped goethite particles.
[0087]
By adding an aqueous alkali carbonate solution composed of an alkali metal to an aqueous suspension of spindle-shaped goethite particles in which a cobalt compound is present, the surface of the spindle-shaped goethite particles is coated with cobalt carbonate. As the aqueous alkali carbonate solution of the alkali metal, an aqueous sodium carbonate solution and an aqueous potassium carbonate solution are preferable. With an aqueous alkali solution other than an aqueous alkali carbonate solution of an alkali metal, it is difficult to coat with cobalt carbonate, and spindle-shaped alloy magnetic particles having excellent dispersibility and oxidation stability cannot be obtained. The alkali metal attached by the coating reaction can be easily removed by washing with water.
[0088]
As the rare earth element for coating the particle surface of the spindle-shaped goethite particles coated with cobalt carbonate, one or more of yttrium, neodymium, lanthanum, cerium, scandium, praseodymium, and samarium are suitable. As the rare earth compound to be added, it is preferable to use chlorides and nitrates of the rare earth elements.
[0089]
The amount of the rare earth compound to be added is preferably 10 to 30 atomic% in terms of the rare earth element relative to the total Fe of the spindle-shaped goethite particles, and when less than 10 atomic%, the effect of preventing sintering is not sufficient, and Coercive force distribution S. F. D. And the coercive force decrease. If it exceeds 30 atomic%, the temperature required for hydrogen reduction becomes extremely high, which is not preferable in production. More preferably, it is 15 to 28 atomic%.
[0090]
The added rare earth compound can be coated on the surface of the spindle-shaped goethite particles coated with cobalt carbonate by adjusting the pH of the reaction solution by adding an aqueous alkali carbonate solution. The rare earth compound is coated in a state of carbonate or hydroxide. The alkali metal attached by the coating reaction can be easily removed by washing with water.
[0091]
In the surface-coated goethite particles, the surface of spindle-shaped goethite particles containing cobalt and aluminum is coated with cobalt carbonate, and the surface of the cobalt carbonate is coated with a compound composed of a rare earth element.
[0092]
By coating the surface of the spindle-shaped goethite particles with cobalt carbonate and further coating the surface of the particles with a rare earth compound, sintering between the particles and the particles is prevented, and the particle shape and axis of the spindle-shaped goethite particles Spindle-shaped hematite particles having the same ratio can be obtained, whereby it is easy to obtain spindle-shaped alloy magnetic particles that have the above-mentioned shape and the like and are independent from each other.
[0093]
Next, the surface-coated spindle-shaped goethite particles are subjected to a heat reduction treatment.
[0094]
In order to control the magnetic characteristics, powder characteristics and powder shape, prior to the reduction treatment, the surface-coated spindle-shaped goethite particles were subjected to a heat dehydration treatment in a non-reducing gas atmosphere by a conventional method. It is preferable to perform spindle-shaped hematite particle powder.
[0095]
The non-reducing atmosphere is preferably under a gas flow of one or more gases selected from air, oxygen gas, nitrogen gas and the like. The heat treatment temperature can be in the range of 400 to 750 ° C., and it is more preferable that the heat treatment temperature is appropriately selected depending on the type of the compound used for the coating treatment of the spindle-shaped goethite particles. If the temperature is lower than 400 ° C., a long time is required for the heat treatment, and if the temperature exceeds 750 ° C., deformation of the particles and sintering between the particles and the particles are caused.
[0096]
The spindle-shaped hematite particles in the present invention preferably have an average major axis diameter of 0.04 to 0.15 μm, more preferably 0.05 to 0.14 μm, and an axial ratio of 3 to 12, more preferably 3 to 12. 10 and a BET specific surface area value of 30 to 140 m 2 / G is preferred.
[0097]
The cobalt content of the spindle-shaped hematite particles is preferably 50 to 110 atomic% in terms of Co with respect to all Fe, the aluminum content is preferably 3 to 20 atomic% in terms of Al with respect to all Fe, and rare earth element content. The amount is preferably from 10 to 30 atomic% in terms of rare earth elements with respect to all Fe.
[0098]
As the reduction device in the present invention, a reduction device having a fixed layer formed thereon is preferable. Specifically, a stationary reduction device (batch type) or a fixed layer is formed on a belt and reduction is performed while transferring the belt. Mobile reduction devices (continuous) are preferred.
[0099]
The layer height of the fixed layer in the present invention is preferably 30 cm or less. If it exceeds 30 cm, a large amount of Co is contained, so that the effect of promoting reduction is remarkable, and at the same time, the coercive force of the upper part of the fixed layer decreases due to an increase in the partial pressure of water vapor due to the rapid reduction of the lower part of the fixed layer. Problems occur, and the characteristics deteriorate as a whole. In consideration of industrial productivity, 3 to 30 cm is more preferable. Since the productivity differs between the batch type (JP-A-54-62915, JP-A-4-224609, etc.) and the continuous type (JP-A-6-93312, etc.), a batch-type fixed-bed reducing device is used. Is preferably more than 4 cm and 30 cm or less.
[0100]
The temperature range of the heat reduction treatment in the present invention is preferably 350 to 700 ° C. When the temperature is lower than 350 ° C., the progress of the reduction reaction is slow, and a long time is required. Further, since the crystal growth of the spindle-shaped alloy magnetic particles is insufficient, magnetic properties such as a saturation magnetization value and a coercive force are significantly reduced. If the temperature exceeds 700 ° C., the reduction reaction proceeds rapidly, causing deformation of the particles and sintering between the particles and the particles.
[0101]
The spindle-shaped alloy magnetic particles powder after heat reduction in the present invention is a known method, for example, a method of immersing in an organic solvent such as toluene, and the atmosphere of the spindle-shaped alloy magnetic particles after reduction was once replaced with an inert gas. Thereafter, it can be taken out into the air by a method of finally forming air while gradually increasing the oxygen content in the inert gas, or a method of gradually oxidizing using a mixed gas of oxygen and water vapor.
[0102]
In the present invention, a spindle-shaped alloy magnetic particle powder having excellent coercive force can be obtained by dividing the heating and reducing step into four steps.
[0103]
In the present invention, the atmosphere during the period in which the temperature is raised to the heat reduction temperature in the first step and the third step is an inert gas atmosphere or a reducing gas atmosphere. As the inert gas atmosphere, nitrogen gas, helium gas, argon gas and the like are preferable, and nitrogen gas is particularly preferable. When the temperature is increased in a reducing gas atmosphere, the temperature is rapidly increased in a period of 40 minutes or less, preferably 20 minutes or less, so that the reduction temperature at the time of forming the metal magnetic particles can be kept constant.
[0104]
In addition, the temperature rising rate in the first step and the third step is preferably 20 to 100 ° C./min in a reducing atmosphere.
[0105]
The atmosphere in the first and third heating and reducing steps of the present invention is a reducing gas, and hydrogen is preferably used as the reducing gas.
[0106]
The heat reduction temperature in the first step in the present invention is 300 to 600 ° C, preferably 350 to 550 ° C. It is preferable that the heat reduction temperature is appropriately selected from the above temperature range according to the type and amount of the compound used for the coating treatment of the starting material. When the heat-reduction temperature is lower than 300 ° C., the progress of the reduction is extremely slow and is not industrial, and the saturation magnetization value of the obtained spindle-shaped alloy magnetic particles is low. If the temperature exceeds 600 ° C., the reduction reaction proceeds rapidly, causing shape destruction of the particles and sintering between the particles, and the coercive force decreases.
[0107]
The gas superficial velocity of the reducing gas in the first step in the present invention is preferably 40 to 150 cm / s. If the gas superficial velocity is less than 40 cm / s, the speed at which the steam generated by the reduction of the starting material is carried out of the system becomes extremely slow, so that the coercive force and SFD at the upper part of the layer are reduced, and the overall coercive force is high. Can not be obtained. If it exceeds 150 cm / s, the desired spindle-shaped alloy magnetic particle powder can be obtained, but it is not preferable because problems such as a high reduction temperature being required, and granulated matter being scattered and broken are likely to occur.
[0108]
In the second step of the present invention, a surface oxidation treatment is performed in an inert gas atmosphere containing oxygen. As the inert gas atmosphere, nitrogen gas, helium gas, argon gas and the like are preferable, and nitrogen gas is particularly preferable. The oxygen content is preferably 0.1 to 5 vol%, and it is preferable to gradually increase the oxygen content to a predetermined amount.
[0109]
The reaction temperature of the second step in the present invention is from 60 to 200 ° C, preferably from 60 to 180 ° C. If the temperature is lower than 60 ° C., it is difficult to form a surface oxide layer having a sufficient thickness. If the temperature is higher than 200 ° C., the shape of the particles is changed, particularly, a large amount of oxide is generated, so that the short axis is extremely expanded. In some cases, the shape is easily broken, which is not preferable.
[0110]
The spindle-shaped alloy magnetic particles having undergone the second step have a saturation magnetization of 85 to 135 Am. 2 / Kg (85-135 emu / g), preferably 90-130 Am 2 / Kg (90-130 emu / g). Saturation magnetization value is 85 Am 2 If it is less than / kg, the surface oxide layer becomes too thick, so that spindle-shaped alloy magnetic particles having a large coercive force cannot be obtained even if the heat reduction treatment in the third step is performed. 130 Am 2 If it exceeds / kg, a dense surface oxide layer cannot be formed because the surface oxide layer is insufficiently formed.
[0111]
If the whole particles are oxidized in the second step, the particles change shape, especially the short-axis growth, and a large amount of oxide is generated, so that the short axis expands extremely, and in some cases, the shape breaks. Therefore, the coercive force does not improve because the shape is already collapsed even if reduced again.
[0112]
The heat reduction temperature in the third step in the present invention is a temperature higher by 50 ° C. or more than the heat reduction temperature in the first step, and is in a temperature range of 400 to 700 ° C. When the temperature is not higher than the heating reduction temperature of the first step by 50 ° C. or more and is lower than 400 ° C., the progress of the reduction is very slow and not industrial, and the reduction of the surface oxide layer formed in the second step and the whole particles Becomes difficult to densify. If the temperature exceeds 700 ° C., the shape of the particles is broken and sintering between the particles is caused, and the coercive force is reduced. The heat reduction temperature in the third step is preferably 450 to 650 ° C.
[0113]
The gas superficial velocity of the reducing gas in the third step of the heating and reducing step in the present invention is preferably 40 to 150 cm / s as in the first step.
[0114]
In the third step, an annealing treatment may be performed after the reduction step, the treatment temperature is preferably 500 to 700 ° C., and the atmosphere is preferably a hydrogen gas or an inert gas, and particularly preferably a nitrogen gas.
[0115]
The fourth step in the present invention is 5 to 10 g / m 3 The surface oxidation treatment is performed in an inert gas atmosphere containing water vapor and oxygen. Water vapor content of 5 g / m 3 If it is less than 1, it is difficult to form a dense and thin surface oxide layer, and it is hard to say that the coercive force is sufficiently improved. The water vapor content is 10 g / m 3 In the case where the content exceeds, the intended effect can be obtained, so that there is no point in containing more than necessary. The content of water vapor is preferably 2 to 8 g / m 3 It is. Further, the content of oxygen is preferably 0.1 to 5 vol%, and is preferably gradually increased to a predetermined amount. As the inert gas, nitrogen gas, helium gas, argon gas and the like are preferable, and nitrogen gas is particularly preferable.
[0116]
The reaction temperature of the fourth step in the present invention is from 40 to 160 ° C, preferably from 40 to 140. Note that the reaction temperature in the fourth step is preferably lower than the surface oxidation treatment temperature in the second step. If the temperature is lower than 40 ° C., the formation of a surface oxide layer is insufficient, which is not preferable. When the temperature exceeds 160 ° C., the surface oxide layer becomes thick, and the S.V. F. This is not preferable because D deteriorates.
[0117]
BEST MODE FOR CARRYING OUT THE INVENTION
A typical embodiment of the present invention is as follows.
[0118]
The spindle-shaped goethite particles in the present invention, the average major axis diameter, the average minor axis diameter, and the axial ratio of the spindle-shaped hematite particles powder and the spindle-shaped alloy magnetic particles are all the average values measured from electron micrographs. Indicated.
[0119]
The amount of Co, Al, rare earth element, Na, Ca, and other metal elements in the spindle-shaped goethite particles, spindle-shaped hematite particles, and spindle-shaped alloy magnetic particles in the present invention are defined as “induction”. The measurement was performed using a coupled plasma emission spectrometer SPS4000 (manufactured by Seiko Instruments Inc.).
[0120]
The residual sulfur content of the spindle-shaped alloy magnetic particles was measured using a “carbon / sulfur measurement device” (manufactured by Horiba).
[0121]
The BET specific surface area value of the spindle-shaped goethite particle powder, the spindle-shaped hematite particle powder, and the spindle-shaped alloy magnetic particle powder in the present invention is determined by the BET method using “Monosorb MS-11” (manufactured by Kantachrome Co., Ltd.). The values are shown as measured values.
[0122]
Crystallite size D 110 (X-ray crystal particle diameter of the spindle-shaped alloy magnetic particles) was measured by an X-ray diffraction method using an “X-ray diffractometer” (manufactured by Rigaku) (measurement conditions: target Cu, tube voltage 40 kV, tube current 40 mA). Is the thickness of the crystal grains in the direction perpendicular to each of the (110) crystal faces of the spindle-shaped alloy magnetic particles, and the diffraction peak curve for each crystal face. Therefore, the values are calculated using the following Scherrer's formula.
[0123]
D 110 = Kλ / βcosθ
Here, β = half-width (in radians) of a true diffraction peak corrected for the mechanical width caused by the apparatus.
K = Scherrer constant (= 0.9),
λ = X-ray wavelength (Cu Kα ray 0.1542 nm),
θ = diffraction angle (corresponding to the diffraction peak on the (110) plane).
[0124]
The magnetic properties of the spindle-shaped alloy magnetic particles and the magnetic coating film pieces were measured using an external magnetic field of 795.8 kA / m (10 kOe) using a “vibrating sample magnetometer VSM-3S-15” (manufactured by Toei Industry Co., Ltd.). ).
[0125]
The magnetic properties of the magnetic coating film pieces were determined by adding the following components to a 100 ml polybin at the following ratio, and then mixing and dispersing for 8 hours using a paint shaker (manufactured by Red Devil Co.) to obtain a magnetic coating having a thickness of 25 μm. Was applied to a thickness of 50 μm on a polyethylene terephthalate film using an applicator, and then dried in a magnetic field of 500 mT (5 kGauss).
[0126]
Spindle-shaped alloy magnetic particle powder: 100 parts by weight,
Polyurethane resin having sodium sulfonate group: 30 parts by weight,
Cyclohexanone: 83.3 parts by weight,
Methyl ethyl ketone: 83.3 parts by weight,
Toluene: 83.3 parts by weight,
3 mmφ steel ball: 800 parts by weight.
[0127]
Δσs indicating the oxidation stability of the saturation magnetization value of the spindle-shaped alloy magnetic particle powder and ΔBm indicating the weather resistance of the saturation magnetic flux density Bm of the magnetic coating film were obtained by placing the particle powder or the magnetic powder in a thermostat at a temperature of 60 ° C. and a relative humidity of 90%. After the accelerated aging test in which the coating film pieces were allowed to stand for one week, the saturation magnetization value σs ′ of the particle powder and the saturation magnetic flux density Bm ′ of the magnetic coating film were measured, respectively. Values obtained by dividing the difference (absolute value) between σs ′ and Bm ′ one week after the test by σs and Bm before the start of the test, respectively, were calculated as Δσs and ΔBm. The closer the Δσs and ΔBm are to 0%, the better the oxidation stability.
[0128]
<Production of spindle-shaped goethite particle powder>
28 l of a mixed alkali aqueous solution containing 20 mol of ammonium hydrogen carbonate and 60 mol of aqueous ammonia (aqueous ammonia hydroxide solution corresponds to 75 mol% with respect to the mixed alkali with respect to the mixed alkali) was added to a reaction tower equipped with a stirrer equipped with bubble dispersion blades. Then, while stirring the stirrer at a speed of 400 rpm, the temperature is adjusted to 50 ° C. while passing nitrogen gas at a flow rate of 60 l / min. Then Fe 2+ 16 l of an aqueous solution of ferrous sulfate containing 20 mol (a mixed alkali aqueous solution with respect to ferrous sulfate corresponds to 1.875 equivalents in terms of a specified conversion) in a bubble column, aged for 30 minutes, and then cooled with Co. 2+ 4 l of an aqueous solution of cobalt sulfate containing 6.0 mol (corresponding to 30 atomic% in terms of Co with respect to the total Fe), and aged for 3 hours. 2+ The reaction was carried out until 30% of the oxidized.
[0129]
Then, Al 3+ One liter of an aqueous solution of aluminum sulfate containing 1.6 mol (corresponding to 8 atomic% in terms of Al with respect to all Fe) was added, and an oxidation reaction was further performed until the reaction was completed. The pH at the end of the reaction was 8.3.
[0130]
The obtained goethite particle-containing slurry is separated by filtration using a press filter, washed with ammonia water adjusted to pH = 10.5 using ammonia, and then further washed with ion-exchanged water and pressed. I made a cake. From the filtrate after filtration, 30 ppm of Co was detected.
[0131]
A spindle-shaped goethite particle powder obtained by drying and pulverizing a part of the cake by a conventional method has an average major axis diameter of 0.086 μm, an average minor axis diameter of 0.012 μm, an axial ratio of 7.2, BET specific surface area value is 181.1m 2 / G, the total cobalt content of the particles was 29.9 atomic% based on the total Fe, and the aluminum content was 8 atomic% based on the total Fe. The cobalt adsorption ratio (remaining amount of cobalt / added amount of cobalt) was 99.7%.
[0132]
<Production of spindle-shaped hematite particle powder>
After the obtained press cake of spindle-shaped goethite particles was sufficiently dispersed in water, an aqueous solution of cobalt acetate (40 atomic% based on the total Fe) was added thereto, and the mixture was sufficiently stirred. Then, while stirring, an aqueous solution of sodium carbonate was added to adjust the pH of the aqueous solution to 8.8, and then an aqueous solution of yttrium nitrate (25 atomic% based on the total Fe) was added and mixed by stirring. The pH of the aqueous solution is adjusted to 9.3 by addition. Thereafter, the mixture was filtered and washed with a filter press to obtain a press cake. The obtained press cake was extruded with a molding plate having a hole diameter of 3 mm using an extruder and granulated, then dried at 120 ° C., and 40 atomic% of cobalt carbonate in terms of Co with respect to total Fe and total A granulated product of spindle-shaped goethite particles coated with 25 atomic% of a Y compound in terms of Y with respect to Fe was obtained. The content of Co in the obtained spindle-shaped goethite particles was 70 atom% with respect to all Fe, the content of Al was 8 atom% with respect to all Fe, and the content of Y was 25 atom with respect to all Fe. %Met
[0133]
The granulated product of the spindle-shaped goethite particles coated with the cobalt carbonate and the Y compound is dehydrated at 350 ° C. in the air, and then heated and dehydrated at 500 ° C. in the same atmosphere to obtain a granulated product of the spindle-shaped hematite particles. Obtained.
[0134]
<Production of metal magnetic particle powder mainly composed of iron>
100 g (average diameter: 2.6 mm) of the obtained granulated spindle-shaped hematite particles was put into a batch-type fixed-bed reduction device having an inner diameter of 72 mm, and the bed height was set to 7 cm. The resultant was heated and reduced at 350 ° C. until the dew point of the exhaust gas reached −30 ° C. while ventilating at 50 cm / s to obtain spindle-shaped alloy magnetic particles (first step).
[0135]
After that, switching to nitrogen gas again, cooling to 70 ° C., maintaining the product temperature at 70 ° C., and then mixing air to gradually increase the oxygen concentration to 0.35 vol%, thereby increasing the product temperature to [retaining temperature + 1] The surface oxidation treatment was performed until the temperature reached 140 ° C (maximum product temperature 140 ° C, treatment time 2 hours) to form a surface oxide layer on the particle surface (second step).
[0136]
After completion of the second step, the saturation magnetization value of the spindle-shaped alloy magnetic particles is 88.1 Am 2 / Kg (88.1 emu / g). Next, the temperature was raised to 500 ° C. in a hydrogen gas atmosphere in 10 minutes, and reduced by heating again at a hydrogen gas superficial velocity of 60 cm / s until the exhaust gas dew point reached −30 ° C. (third step).
[0137]
After that, switching to nitrogen gas again, cooling to 70 ° C., keeping the product temperature at 70 ° C., and then steam 6 g / m 2 3 And the air are mixed to gradually increase the oxygen concentration to 0.35 vol%, and the surface oxidation treatment is performed until the product temperature becomes [holding temperature +1] ° C (maximum product temperature 110 ° C, processing time 3 hours), A stable surface oxide layer was formed on the particle surface to obtain a molded product of spindle-shaped alloy magnetic particles (fourth step).
[0138]
The spindle-shaped alloy magnetic particles obtained here have an average major axis diameter of 0.046 μm, an axial ratio of 4.6, and a BET specific surface area of 69.0 m. 2 / G, crystallite size D 110 Was composed of particles of 100 ° and had a spindle-like shape, a uniform particle size and no dendritic particles. The Co content in the particles was 70 atomic% based on the total Fe, the Al content was 8 atomic% based on the total Fe, and the Y content was 25 atomic%.
[0139]
The soluble Na content was 9 ppm, the soluble Ca content was 58 ppm, the residual sulfur content was 53 ppm, and no soluble Fe was detected from the spindle-shaped alloy magnetic particles.
[0140]
The magnetic properties of the spindle-shaped alloy magnetic particles are as follows: the coercive force Hc is 177.5 kA / m (2230 Oe), and the saturation magnetization σs is 90.1 Am 2 / Kg (90.1 emu / g), the squareness ratio (σr / σs) is 0.528, and the oxidation stability Δσs of the saturation magnetization is 6.1% (actual measurement value-6.1%) as an absolute value. Was.
[0141]
The properties of the magnetic coating film are as follows: the coercive force Hc is 193.3 kA / m (2430 Oe), the squareness ratio (Br / Bm) is 0.840, the SFD is 0.488, and the oxidation stability ΔBm is 3. It was 3% (actual value -3.3%).
[0142]
[Action]
The most important point in the present invention is that the cobalt content of the spindle-shaped alloy magnetic particles is increased to 50 to 110 atomic% in terms of Co with respect to all Fe, so that the average major axis diameter is 0.02 to 0. 08 μm fine particles, exhibit high coercive force, and have low coercive force distribution and low coercive force distribution S.P. F. D. This is a fact that a spindle-shaped alloy magnetic particle powder for a magnetic recording medium, which is excellent in oxidization stability and excellent in oxidative stability and in which soluble salts are reduced as much as possible, can be obtained.
[0143]
Conventionally, Fe-Co alloying has been attempted for the purpose of improving the saturation magnetization and the oxidation stability. On the other hand, in the case of bulk, it has been known that the saturation magnetization value shows the maximum value at a specific Fe-Co alloy ratio, and the saturation magnetization value gradually decreases due to the Co alloying which greatly exceeds the equivalent amount. On the other hand, an increase in the cobalt content decreases the coercive force and increases the coercive force distribution. F. D. Accordingly, it has been difficult to obtain magnetic particle powder for a magnetic recording medium having a low saturation magnetization value that satisfies the demand for short-wavelength recording.
[0144]
In the present invention, an aqueous solution of ammonium hydrogen carbonate and an aqueous solution of ammonium hydroxide are used in order not to leave alkali metals. Conventionally, when an ammonium compound is used as an alkaline aqueous solution, an ammine complex ([M (NH 3 ) a ] n + However, since M is n-valent metal ion), the pH of the aqueous suspension containing the Fe-containing precipitate cannot be increased due to the elution of cobalt due to the formation of magnetite. However, there was a problem that the axial ratio of the goethite particles was reduced. In the present invention, a large amount of Co was able to be contained by specifying a region where the magnetite is not mixed with the pH of the aqueous suspension and in which the axial ratio is not reduced, and performing a reaction for generating goethite particles.
[0145]
On the other hand, when the pH of the aqueous suspension containing the ferrous-containing precipitate is specified in the range of 7.5 to 9.5, since the alkali metal does not exist, the goethite particles easily adsorb anions, and the sulfate ion In a large amount, and could not be sufficiently removed by washing with ordinary water. In the present invention, by washing the goethite particles with aqueous ammonia having a pH of 9.5 to 11.5, sulfate ions can be removed, and the amount of impurities in the spindle-shaped alloy magnetic particles can be reduced. Was completed.
[0146]
As described above, cobalt cannot be sufficiently adsorbed in the presence of an ammonia compound.However, when coating the surface of the goethite particles with cobalt, a large amount of a cobalt compound added by using an alkali carbonate aqueous solution is used. Could be coated on the particle surface of the goethite particle powder as cobalt carbonate. In the present invention, by coating the surface of the goethite particles with cobalt carbonate, the control of the reduction rate can be facilitated, and the sintering prevention effect is improved. Although the reason for this is not yet clear, the effect of preventing sintering is improved as compared with the case where the cobalt carbonate fine particles uniformly coat the surface of the goethite particles with another compound such as cobalt hydroxide. It is estimated that.
[0147]
Further, in the present invention, the surface of the cobalt carbonate is coated with a rare earth compound. Since the hardly-reducible rare earth compound covers the outermost layer of the goethite particles, the distance between the particles can be maintained without approaching each other, so that sintering can be suppressed during the reduction process, and the spindle-shaped particle shape is reduced. Will be retained.
[0148]
In the present invention, by increasing the cobalt content to 50 to 110 atomic% in terms of Co with respect to the total Fe, the coercive force distribution S.P. F. D. The reason why a spindle-shaped alloy magnetic powder with excellent oxidation stability and excellent oxidation stability was obtained is not yet clear, but it is due to the synergistic effect of reducing the saturation magnetization value by Co alloying and making the oxide film uniform by Co alloying. It is estimated that.
[0149]
As a result, even if the Co content is as large as 50 to 110 atomic% in terms of Co with respect to the total Fe, despite the fine particles, the coercive force decreases and the coercive force distribution S.P. F. D. The present inventors presume that a spindle-shaped alloy magnetic particle powder that is efficiently magnetized with a minimum amount of Co and has a low saturation and that has excellent oxidation stability without impairing the particle diameter is obtained.
[0150]
The alkali metal attached by the coating reaction can be easily removed by washing with water.
[0151]
【Example】
Next, examples and comparative examples will be described.
[0152]
Examples 1 and 2, Comparative Examples 1 to 3:
Spindle-shaped goethite particles were obtained by variously changing the production conditions of the embodiment of the invention. Table 1 shows the properties of the obtained spindle-shaped goethite particle powder, and Table 2 shows the composition of the spindle-shaped goethite particle powder coated with Co and Y.
[0153]
In Goethite 9 of the types shown in Table 2, Co compound particles were separately precipitated and mixed in the coated goethite particles.
[0154]
[Table 1]
[Table 2]
Spindle-shaped hematite particle powder was obtained in the same manner as in the embodiment of the present invention using spindle-shaped goethite particle powder coated with Co and Y having the properties shown in Table 2. Table 3 shows the production conditions at this time and various properties of the obtained spindle-shaped hematite particle powder.
[0157]
[Table 3]
Spindle-shaped alloy magnetic particle powders were obtained in the same manner as in the embodiment of the present invention using spindle-shaped hematite particles having various properties shown in Table 3. Tables 4 and 5 show the production conditions and various properties of the obtained spindle-shaped alloy magnetic particles at this time. Further, Table 6 shows various properties of the magnetic coating film produced using the obtained spindle-shaped alloy magnetic particle powder. In Example 2, the goethite particles 6 after the sintering prevention treatment shown in Table 2 were subjected to the heat reduction treatment without hematite formation.
[0159]
[Table 4]
[Table 5]
[Table 6]
【The invention's effect】
The spindle-shaped alloy magnetic particle powder according to the present invention has a high coercive force while being a fine particle having an average major axis diameter of 0.02 to 0.08 μm, and has a low saturation magnetization value. Coercive force distribution F. D. , Excellent oxidation stability, and reduced soluble salts as much as possible. Therefore, high output, high C / N, and high reliability in a short wavelength region used for reproducing a magnetoresistive head. It is suitable as a magnetic particle powder for a magnetic recording medium having improved weather resistance.
Claims (6)
前記混合アルカリ水溶液として、該混合アルカリ水溶液に対して前記水酸化アンモニウム水溶液が５５〜８５ｍｏｌ％の割合で配合されているものを使用すると共に、前記種晶粒子の生成時において、酸化反応開始前の熟成中の第一鉄含有沈澱物を含む水懸濁液に全Ｆｅに対しＣｏ換算で１５〜５０原子％のＣｏ化合物を添加し、酸化反応を全Ｆｅ２＋の２０〜８０％の範囲で行い、
前記ゲータイト層の成長時においては、前記種晶粒子と第一鉄含有沈殿物とを含む水懸濁液のｐＨが９．０未満となるように全Ｆｅに対しＡｌ換算で３〜１５原子％のＡｌ化合物を添加し、
生成させた前記ゲータイト粒子を濾別した後、ｐＨ９．５〜１１．５のアンモニア水で水洗することによってゲータイト粒子粉末とし、
次いで、得られたゲータイト粒子を含む水懸濁液にコバルト化合物及び炭酸アルカリ水溶液を添加して、ゲータイト粒子の粒子表面に全Ｆｅに対してＣｏ換算で１５〜６０原子％の炭酸コバルトを被覆し、次いで、全Ｆｅに対して希土類元素換算で１０〜３０原子％の希土類化合物によって前記炭酸コバルトで被覆されたゲータイト粒子の粒子表面を被覆した後、該表面被覆したゲータイト粒子粉末又は該表面被覆したゲータイト粒子粉末を非還元性雰囲気中、４００〜７５０℃で加熱処理して得られたヘマタイト粒子粉末を還元性雰囲気中、３５０〜７００℃で加熱還元してＦｅ及びＣｏを主成分とする紡錘状合金磁性粒子粉末を得ることを特徴とする請求項１乃至請求項３のいずれかに記載の磁気記録用紡錘状合金磁性粒子粉末の製造法。A ferrous sulfate-containing solution obtained by reacting an aqueous ferrous sulfate solution with a mixed alkali aqueous solution comprising an aqueous solution of ammonium hydrogen carbonate and an aqueous solution of ammonium hydroxide having an equivalent ratio to the aqueous solution of ferrous sulfate of 1.7 to 3.0. After aging the aqueous suspension containing the precipitate in a non-oxidizing atmosphere, an oxygen-containing gas is passed through the aqueous suspension to generate goethite seed crystal particles by an oxidation reaction. In forming a goethite layer by growing a goethite layer on the particle surface of the seed crystal particles by oxidizing by passing an oxygen-containing gas through an aqueous suspension containing the particles and the ferrous-containing precipitate,
As the mixed alkaline aqueous solution, a mixture of the aqueous ammonium hydroxide solution and the mixed alkaline aqueous solution at a rate of 55 to 85 mol% is used, and at the time of generation of the seed crystal particles, To the aqueous suspension containing the ferrous-containing precipitate during aging, a Co compound of 15 to 50 atomic% in terms of Co with respect to the total Fe is added, and the oxidation reaction is performed in the range of 20 to 80% of the total Fe 2+. ,
During the growth of the goethite layer, 3 to 15 atomic% in terms of Al with respect to the total Fe so that the pH of the aqueous suspension containing the seed crystal particles and the ferrous-containing precipitate is less than 9.0. Of an Al compound,
After the generated goethite particles are separated by filtration, they are washed with aqueous ammonia having a pH of 9.5 to 11.5 to obtain goethite particles,
Next, a cobalt compound and an aqueous alkali carbonate solution are added to the obtained aqueous suspension containing the goethite particles, and the particle surfaces of the goethite particles are coated with 15 to 60 atomic% of cobalt carbonate in terms of Co with respect to the total Fe. Next, after coating the surface of the goethite particles coated with cobalt carbonate with a rare earth compound in an amount of 10 to 30 atomic% in terms of a rare earth element with respect to the total Fe, the goethite particle powder coated with the surface or the surface coated was coated. Hematite particle powder obtained by heat-treating goethite particle powder in a non-reducing atmosphere at 400 to 750 ° C is heat-reduced in a reducing atmosphere at 350 to 700 ° C to form a spindle having Fe and Co as main components. 4. A method for producing a spindle-shaped alloy magnetic particle powder for magnetic recording according to claim 1, wherein an alloy magnetic particle powder is obtained.
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