JPH0724083B2 - Magnetic recording / reproducing method - Google Patents

Description

Detailed Description of the Invention

BACKGROUND OF THE INVENTION 1. Technical Field The present invention relates to a magnetic recording / reproducing method, and more particularly to a method of recording / reproducing on / from a hard disk type magnetic recording medium. Prior art and its problems In recent years, household VTRs have become popular and high-performance audio cassette tapes, video tapes, computer tapes, multi-coated tapes, magnetic disks, floppy disks, magnetic cards, etc. have been put into practical use. Various magnetic powder materials used for magnetic recording media have been developed. Among them, acicular iron oxide is a typical one. However, this alone cannot cope with the high density of magnetic recording, and further, cobalt-coated iron oxide particles and metallic magnetic particles using magnetic metal have been studied, and high-performance audio cassette tapes, video tapes, various magnetic disks, etc. Some have been put to practical use. However, among the magnetic disks, needle-shaped iron oxides are still mainly used in so-called hard disks using the rigid basic, which has the following problems. That is, the acicular iron oxide has a maximum coercive force Hc350Oe, a maximum saturation magnetization Ms3500G, Hc, Ms, a residual magnetic flux density Br,
The magnetic properties such as the squareness ratio Br / Bm are insufficient. The surface smoothness is also poor, and the D ₅₀ is insufficient at about 13 kFRPI at the maximum in terms of areal recording density during digital recording. Further, in order to increase Ms as a coating film, the content ratio of the powder has to be increased, but this causes a problem in durability. In order to improve durability and wear resistance and obtain a coating film hardness that can withstand a contact impact at high speed rotation in a hard disk, it is necessary to add alumina powder or the like as a coating film reinforcing agent. However, the addition of alumina or the like deteriorates the surface roughness and causes medium noise, or forms an unnecessary protrusion on the surface of the coating film to destabilize the flying property of the head, lowers Ms, and reduces the recording density. It has the drawback of lowering it. In order to stabilize the head flying, a polishing step for sufficiently reducing the surface roughness of the coating film, or a varnishing step for removing projections in excess of the flying amount is required,
With iron oxide, these steps are very labor intensive, complicate the production process, and are likely to be associated with quality stability and yield loss. In addition, cobalt-based or cobalt-occluding iron oxide still has a low Ms. Further, demagnetization, which is a serious problem in magnetic disks, is likely to occur, and this point is also insufficient in terms of magnetic characteristics.
Also, the surface smoothness is insufficient. For this reason,
Recording density is still insufficient. Further, in order to obtain a high coercive force and a high magnetic flux density, it is possible to apply a magnetic metal to a magnetic disk. However, magnetic metal has a high magnetic flux density and has the drawback of aggregating by itself, and in addition, it is very easily oxidized,
There is a problem that the magnetic characteristics are deteriorated. Further, the metal powder containing an iron group element as a main component is less malleable than the metal oxide because of the softness of the metal itself represented by ductility and ductility, even when compounded with a binder, Inferior in durability. Also, the coefficient of friction is large. Therefore, it is desired to develop magnetic particles that improve the above points. II Object of the invention The object of the present invention is high durability and coating hardness, good surface smoothness, good head flying property is secured, good moisture resistance, high recording density is achieved, metal oxide Saturation magnetization is higher than when magnetic powder is used, various magnetic characteristics are good, surface smoothness is good, areal recording density is high, and
It is an object of the present invention to provide a magnetic recording / reproducing method using a hard disk type magnetic recording medium which has improved durability and corrosion resistance as compared with the case of using metal magnetic powder and has extremely excellent characteristics as a whole. III DISCLOSURE OF THE INVENTION Such an object is achieved by the present invention described below. That is, the present invention provides a method for recording / reproducing by flying a magnetic head on a surface of a magnetic recording medium having a recording layer containing magnetic particles and a binder on a rigid substrate.
A magnetic recording / reproducing method is characterized in that particles having at least a surface of iron carbide are used as the magnetic particles. IV Specific Structure of the Invention Hereinafter, the specific structure of the present invention will be described in detail. The recording layer of the magnetic recording medium used in the present invention contains magnetic particles containing at least the surface of iron carbide as a main component. Such magnetic particles are obtained by mixing an iron cyanide compound with a sulfate, a sulfite, or a sulfide, putting the mixture in an iron reactor, introducing CO, and heating, reducing and cooling the mixture. In addition, α-FeOOH (Goethite), β-FeOOH- (Akaganit
e), iron oxyhydroxide such as γ-FeOOH (Lepidocrocite), α-Fe ₂ O ₃ , γ-Fe ₂ O ₃ , Fe ₃ O ₄ , γ-Fe ₂ O ₃ -Fe ₃ O ₄ (solid solution), etc. Iron oxide and a slurry-like mixture of aqueous colloidal carbon black particle suspensions are prepared by heating at 600 ° C for about 10 hours by hydrogen reduction, carbon monoxide reduction, or mixed gas reduction of hydrogen and carbon monoxide. Good. Other than this, hexacyano iron salts such as turn blue blue and Berlin white, ferro or ferricyanide compounds such as yellow blood potassium, yellow blood soda, red blood potassium, and red blood soda are used as the iron cyanide compound, and sulfuric acid is used as an additive. Potassium, sodium sulfate, ammonium sulfate, iron sulfate, sodium hydrogen sulfate, potassium hydrogen sulfate, and other sulfates, potassium sulfite, sodium sulfite, ammonium sulfite, potassium hydrogen sulfite, and other sulfites, sodium thiosulfate, potassium thiosulfate, sodium sulfide Sulfides such as potassium sulfide, iron sulfide, sodium rhodanate, potassium rhodanide, sodium isothiocyanate, and potassium isothiocyanate can be used. The gas used for these heating and reducing atmospheres is not limited to CO, but C
A carbon-containing reducing gas such as H ₄ , water gas or propane may be used. Further, after forming pure iron particles, the above various heat reduction treatments may be performed. When reducing, the heating temperature is 300-700 ° C and the heating time is
It should be about 30 minutes to 10 hours. As the iron carbide particles produced, in FenC, n ≧
2, especially 2-3. In this case, n is an integer and does not need to have a stoichiometric composition, but Fe ₂ C, Fe ₅ C ₂ and Fe ₃ C are mainly produced. The particles may have a concentration gradient, and C does not necessarily exist in the whole area, but iron carbide preferably accounts for 10 to 100% by weight of the whole magnetic particles. The magnetic particles having at least the surface of iron carbide described above have a needle-like shape or a granular shape, and are selected depending on the use as a magnetic recording medium. When used for magnetic disks, needle-shaped ones are preferable,
It is preferably 0.2 to 2 μm and the acicular ratio is 3 to 20. In addition, such magnetic particles are 10 to 10% of the total magnetic particles.
It is preferably 0% by weight. If the amount is less than 10% by weight, the effect of the present invention cannot be realized. The magnetic particles may include, in addition to the above-mentioned magnetic particles having at least the surface made of iron carbide, metal magnetic particles or cobalt-adhered iron oxide particles, further γ-Fe ₂ O ₃ particles, and barium ferrite particles. . The metal magnetic particles used in the present invention are: 1) α-FeOOH (Goethite), β-FeOOH (Akaganite), γ-FeOOH (Lepidocrocite)
Iron oxyhydroxides such as; and iron oxides such as α-Fe ₂ O ₃ , γ-Fe ₂ O ₃ , Fe ₃ O ₄ , γ-Fe ₂ O ₃ -Fe ₃ O ₄ (solid solutions); Co, Mn Or Ni, Ti, Bi, Bo, Ag, etc. are doped with one or more metals, and the surface of which is adsorbed and adhered with an aluminum compound or silicon compound is heated and reduced in a reducing gas stream. , A method of producing iron or a magnetic powder containing iron as a main component, 2) a method of producing by liquid phase reduction from an aqueous solution of a metal salt with NaBH ₄ , 3) or evaporating a metal in an inert gas atmosphere of low pressure And the like. As the composition of the metal magnetic particles, Fe, Co, Ni units, and
For these alloys, or for these simple substances and alloys, Cr, M
A metal added with n, Co, Ni, Zn, Cu, Zr, Al, Ti, Bi, Ag, Pt and the like can be used. Further, even if a small amount of a non-metal element such as B, C, Si, P or N is added to these metals, the effect of the present invention is not lost. Alternatively, the magnetic particles may be partially-nitrided metal particles such as Fe ₄ N. Further, the metal magnetic particles may have an oxide film on the particle surface. The magnetic recording medium using the metal magnetic particles having such an oxide film is advantageous for the deterioration of the magnetic flux density due to the external environment such as temperature and humidity and the deterioration of the characteristics due to the rust of the magnetic layer. Rises, and problems due to charging during use tend to occur. The metallic magnetic particles have a needle shape or a granular shape, and are selected according to the use as a magnetic recording medium. When used for a magnetic disk, a needle-shaped one is preferable. Further, as γ-Fe ₂ O ₃ particles, α-FeOOH (goethite)
Is dehydrated at 400 ° C or higher to α-Fe ₂ O ₃ and heated in H ₂ gas at 350
What was produced by reducing Fe ₃ O ₄ at a temperature of ℃ or higher and further oxidizing at a temperature of 250 ℃ or lower may be used. As the cobalt-adhered iron oxide particles, those in which Co ²⁺ is diffused into a very thin layer within a few tens of Å from the surface of γ-Fe ₂ O ₃ may be used. As a method for producing barium ferrite, a ceramic method, a coprecipitation-firing method, a hydrothermal synthesis method, a flux method,
There are a glass crystallization method, an alkoxide method, a plasma jet method, and the like, and any method may be used in the present invention. For details of these methods, refer to “Ceramics 18 (1983) No. 10” by Yoshiyasu Koike and Osamu Kubo. The barium ferrite, hexagonal barium ferrite such as BaFe ₁₂ O ₁₉ or Ba, part of barium ferrite Ca, Sr, Pb, Co, Ni, Ti, Cr, Zn, In, Mn, Cu, Ge,
Examples thereof include those substituted with Nb, Zr and other metals. A thermosetting binder or an electron beam curable binder can be used as the binder used when the magnetic powder is used as the magnetic paint. In this case, as the thermosetting resin or reactive resin used for the binder, by coating, drying and then heating,
The molecular weight becomes infinite due to reactions such as condensation and addition, and among these resins, those that do not soften or melt before the resin thermally decomposes are preferable. Specifically, for example, phenol resin, epoxy resin, polyurethane curable resin, urea resin, butyral resin, formal resin, melamine resin, alkyd resin, silicone resin, acrylic reaction resin, polyamide resin, epoxy-polyamide resin, saturated polyester resin. , Polycondensation resins such as urea-formaldehyde resin or mixtures of high molecular weight polyester resins and isocyanate prepolymers, mixtures of methacrylate copolymers and diisocyanate prepolymers, mixtures of polyester polyols and polyisocyanates, low molecular weight glycol / high molecular weight Mixtures of the above-mentioned polycondensation resin and a crosslinking agent such as an isocyanate compound, such as a mixture of diol / triphenylmethane triisocyanate, vinyl chloride-vinyl acetate, vinyl chloride-vinyl alcohol. -Vinyl acetate, vinyl chloride-vinylidene chloride, vinyl chloride-acrylonitrile, vinyl butyral, a mixture of a vinyl copolymer resin such as vinyl formal and a cross-linking agent, nitrocellulose, a cellulose resin such as cellulose acetobutyrate A mixture with a cross-linking agent,
A mixture of a synthetic rubber system such as butadiene-acrylonitrile and a cross-linking agent, and further a mixture thereof is preferable. And, in particular, a mixture of an epoxy resin, a butyral resin, and a phenol resin, a mixture of an epoxy resin described in US Pat. No. 3,058,844, a polyvinyl methyl ether, and a methylol phenol ether, and JP-A-49-131101.
A mixture of the bisphenol A type epoxy resin described in the above item and an acrylic acid ester or methacrylic acid ester polymer is preferable. Specific examples of the radiation curable compound include an acrylic double bond having an unsaturated double bond exhibiting radical polymerizability, an acrylic double bond such as acrylic acid or methacrylic acid, or an ester compound thereof, or an allyl diacrylate such as diallyl phthalate. It is a resin containing or introducing into a molecule of a thermoplastic resin a group such as a heavy bond, an unsaturated bond such as maleic acid or a maleic acid derivative, which is crosslinked or polymerized by irradiation with radiation. In addition, any compound having an unsaturated double bond that undergoes cross-linking polymerization upon irradiation with radiation can be used. The following unsaturated polyester resin is a resin containing a group that is crosslinked or polymerized and dried by irradiation with radiation in the molecule of the thermoplastic resin. A polyester compound containing a radiation-curable unsaturated double bond in its molecular chain, for example, a saturated polyester resin composed of the ester bond of polybasic acid and polyhydric alcohol of (2) below, and part of the polybasic acid as maleic acid. An unsaturated polyester resin containing a radiation-curable unsaturated double bond may be mentioned. The radiation-curable unsaturated polyester resin is prepared by adding maleic acid, fumaric acid, etc. to at least one polybasic acid component and at least one polyhydric alcohol component, in the usual manner, that is, in the presence of a catalyst, at 180 to 200 ° C under a nitrogen atmosphere After dehydration or dealcoholization reaction, heat up to 240-280 ℃, 0.5-1mmHg
It can be obtained by condensation reaction under reduced pressure. The content of maleic acid, fumaric acid or the like is 1 to 40 mol%, preferably 10 to 30 mol% in the acid component due to crosslinking during production, radiation curability and the like. Examples of the thermoplastic resin that can be modified into a radiation curable resin include the following. (1) Vinyl chloride copolymer Vinyl chloride-vinyl acetate-vinyl alcohol copolymer, vinyl chloride-vinyl alcohol copolymer, vinyl chloride-vinyl alcohol-vinyl propionate copolymer, vinyl chloride-vinyl acetate-malein Acid copolymer, vinyl chloride-vinyl acetate-vinyl alcohol-maleic acid copolymer, vinyl chloride-vinyl acetate-terminal OH side chain alkyl group copolymer, for example VRO manufactured by UCC
H, VYNC, VYEGX, VERR, VYES, VMCA, VAGH and the like are mentioned, and an acrylic double bond, a maleic acid double bond and an allyl double bond are introduced into these to carry out radiation-sensitive modification. These may contain a carboxylic acid. (2) Saturated polyester resin Saturated polybasic acid such as phthalic acid, isophthalic acid, terephthalic acid, succinic acid, adipic acid, sebacic acid and ethylene glycol, diethylene glycol, glycerin, trimethylolpropane, 1,2 propylene glycol, 1 , 3
Obtained by ester linkage with polyhydric alcohols such as butanediol, dipropylene glycol, 1,4 butanediol, 1,6 hexanediol, pentaerythritol, sorbitol, glycerin, neopentyl glycol, 1,4 cyclohexanedimethanol Examples include saturated polyester resins or resins obtained by modifying these polyester resins with SO ₃ Na or the like (for example, Vylon 53S), and these also undergo radiation sensitive modification. (3) Polyvinyl alcohol resin Polyvinyl alcohol, butyral resin, acetal resin, formal resin and copolymers of these components,
Radiation-sensitive modification is performed on the hydroxyl groups contained in these resins. (4) Epoxy resin, phonoxy resin Epoxy resin obtained by reaction of bisphenol A with epichlorohydrin, methyl epichlorohydrin, for example, Shell Chemical (Epicoat 152, 154, 828, 1001, 1004, 100
7), made by Dow Chemical (DEN431, DER732, DER511, DER33
1), made by Dainippon Ink (Epiclon 400, 800), and phenoxy resin (PKHA, PKHC, PKHH) made by UCC, which is a high-polymerization resin of the above epoxy, a copolymer of brominated bisphenol A and epichlorohydrin, large Products manufactured by Nippon Ink Chemical Co., Ltd. (Epiclon 145, 152, 153, 1120) are available, and those containing a carboxylic acid group are also included. Radiation-sensitive modification is carried out using the epoxy groups contained in these resins. (5) Fibrin derivatives Various types are used, but particularly effective ones are nitrification cotton, cellulose acetobutyrate, ethyl cellulose,
Radiation-sensitive modification is carried out by utilizing the hydroxyl group in the resin, which is preferably butyl cellulose, acetyl cellulose, or the like. Other resins that can be used for radiation-sensitive modification include polyfunctional polyester resins, polyetherester resins, polyvinylpyrrolidone resins and derivatives (PVP olefin copolymers), polyamide resins, polyimide resins, phenolic resins, spiroacetal resins, An acrylic resin containing at least one of a hydroxyl group-containing acrylic ester and a methacrylic ester as a polymerization component is also effective. Examples of the elastomer or prepolymer will be given below. (1) Polyurethane Elastomer or Prepolymer Use of Polyurethane Abrasion Resistance and Base Film,
For example, it is particularly effective in that the adhesion of PET film is good. As an example of the urethane compound, as the isocyanate, 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, 1,3-xylene diisocyanate, 1,4
-Xylene diisocyanate, 1,5-naphthalene diisocyanate, m-phenylene diisocyanate, p-phenylene diisocyanate, 3,3'-dimethyl-4,4'-
Diphenylmethane diisocyanate, 4,4'-diphenylmethane diisocyanate, 3,3'-dimethylbiphenylene diisocyanate, 4,4'-biphenylene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, dicyclohexylmethane diisocyanate, Desmodur L, Desmodur N, etc. Polyvalent isocyanate and linear saturated polyester (ethylene glycol, diethylene glycol, glycerin, trimethylolpropane, 1,4-butanediol,
Polyhydric alcohols such as 1,6-hexanediol, pentaerythritol, sorbitol, neopentyl glycol, 1,4-cyclohexanedimethanol and phthalic acid, isophthalic acid, terephthalic acid, succinic acid, adipic acid, sebacic acid Such as polycondensation with saturated polybasic acid),
Polyurethane elastomers and prepolymers composed of polycondensation products of various polyesters such as linear saturated polyether (polyethylene glycol, polypropylene glycol, polytetramethylene glycol), caprolactam, hydroxyl-containing acrylic acid ester, hydroxyl-containing methacrylic acid ester, etc. are effective. is there. By reacting a terminal isocyanate group or hydroxyl group of these urethane elastomers with a monomer having an acrylic double bond or an allyl double bond,
Radiation-sensitive modification is very effective. It also includes those containing OH, COOH or the like as a polar group at the terminal. Further, a monomer having an unsaturated double bond having an active hydrogen that reacts with an isocyanate group and having a radiation-curable unsaturated double bond, such as a mono- or diglyceride of a long-chain fatty acid having an unsaturated double bond, is also included. (2) Acrylonitrile-Butadiene Copolymer Elastomer Acrylonitrile butadiene copolymer prepolymer with a terminal hydroxyl group commercially available as Sinclair Petrochemical PolyBD Retied Resin or an elastomer such as Hiker 1432J manufactured by Nippon Zeon Co., Ltd. The heavy bond is suitable as an elastomer component which causes radicals to be cross-linked and polymerized by radiation. (3) Polybutadiene Elastomer A prepolymer having a low molecular weight terminal hydroxyl group such as Poly BD Retied Range R-15 manufactured by Sinclair Petrochemical Co. is particularly preferable in terms of compatibility with a thermoplastic resin. R-15
Since the molecular end of the prepolymer is a hydroxyl group, it is possible to increase the radiation sensitivity by adding an acrylic unsaturated double bond to the end of the molecule, which is more advantageous as a binder. Also cyclized polybutadiene, CBR-M90 made by Japan Synthetic Rubber
1 also has excellent properties when combined with a thermoplastic resin. Other suitable thermoplastic elastomers and prepolymers thereof include styrene-butadiene rubber, chlorinated rubber, acrylic rubber, isoprene rubber and cyclized products thereof (CIR701 manufactured by Japan Synthetic Rubber), epoxy-modified rubber, internal Elastomers such as plasticized saturated linear polyester (Toyobo Byron # 300) can also be effectively used by subjecting them to radiation-sensitive modification treatment. As the compound having a radiation-curable unsaturated double bond used in the present invention as an oligomer or a monomer, styrene, ethyl acrylate, ethylene glycol diacrylate, ethylene glycol dimethacrylate, diethylene glycol diacrylate, diethylene glycol dimethacrylate, 1,6- Hexane glycol diacrylate, 1,6-hexane glycol dimethacrylate,
N-vinylpyrrolidone, pentaerythritol tetraacrylate (methacrylate), pentaerythritol triacrylate (methacrylate), trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, polyfunctional oligoester acrylate (Aronix M-7100, M-5400, 5500, 5700, Toa Gosei), urethane elastomer (Nippon Run 4040)
Acrylic modified products of these, or those into which functional groups such as COOH have been introduced, trimethylolpropane diacrylate (methacrylate) acrylate (methacrylate) of phenol ethylene oxide adduct, pentaerythritol condensed ring represented by the following general formula A compound having an acryl group (methacryl group) or ε-caprolactone-acryl group, In the formula, a compound of m = 1, a = 2, b = 4 (hereinafter referred to as a special pentaerythritol condensate A), a compound of m = 1, a = 3, b = 3 (hereinafter referred to as a special pentaerythritol condensate B) , M = 1, a = 6, b = 0 compound (hereinafter referred to as special pentaerythritol condensate C), m = 2, a = 6, b = 0 compound (hereinafter referred to as special pentaerythritol compound D) ), And special acrylates represented by the following general formula, and the like. _{1) (CH 2 = CHCOOH 2} ) 3 -CCH 2 OH ( special acrylate _{A) 2) (CH 2 =} CHCOOH 2) 3 -CCH 2 OH 3 ( special acrylate B) 3) [CH ₂ = CHOC (OC ₃ H ₆ ) n-OCH ₂ ] _3- CCH ₂ CH ₃ (special acrylate C) _{8) CH 2 = CHCOO- (CH} 2 CH 2 O) 4 -COCH = CH 2 ( special acrylate H) Next, a radiation-sensitive binder synthesis example will be described. a) Synthesis of acrylic modified vinyl chloride vinyl acetate copolymer resin (radiation sensitive modified resin) 750 parts of partially saponified vinyl chloride-vinyl acetate copolymer having OH groups (average degree of polymerization n = 500) and toluene 1250 Part, cyclohexanone
Charge 500 parts into 51 four-necked flask, heat and dissolve,
After heating to ℃, add 61.4 parts of 2-hydroxyethylmethacrylate adduct of tolylene diisocyanate, 0.012 parts of tin octylate and 0.012 parts of hydroquinone,
React in N ₂ stream at 80 ℃ until the NCO reaction rate reaches 90%. After completion of the reaction, the mixture is cooled and 1250 minutes of methyl ethyl ketone is added for dilution.

[* Manufacturing method of 2-hydroxyethylmethacrylate (2HEMA) adduct of tolylene diisocyanate (TDI) After heating 348 parts of TDI to 80 ° C in a four-necked flask of 11 in N ₂ stream, 260 parts of 2-ethylenemethacrylate, octylic acid 0.07 parts of tin and 0.05 parts of hydroquinone are used in the reactor at a temperature of 80
The reaction is completed by stirring at 80 ° C for 3 hours after completion of the dropwise addition while controlling the cooling so that the temperature becomes ~ 85 ° C. After the reaction was completed, it was taken out, cooled, and then white paste TDI
I got 2 HEMA. B) Synthesized to acrylic modified Bratil resin (radiation sensitive modified resin) Butyral resin Sekisui Chemical's BM-S 100 parts toluene 191.2
, 5 parts of cyclohexanone and 71.4 minutes of cyclohexanone were charged into a four-necked flask of 51, heated and dissolved, and after heating at 80 ° C, 7.4 parts of 2HEMA adduct * of TDI was added, and 0.015 parts of tin octylate and 0.015 parts of hydroquinone were added, and at 80 ° C. NCO reaction rate in N ₂ gas flow is 90
React until it becomes over%. After the reaction is complete, it is cooled and diluted with methyl ethyl ketone. c) Saturated polyester resin Synthesis of acrylic modified product (Radiation sensitive modified resin) Saturated polyester resin (Toyobo Byron RV-200), 100
Parts were dissolved in 116 parts of toluene and 116 parts of methyl ethyl ketone by heating and heated to 80 ° C, 3.55 parts of 2HEMA adduct * of TDI was added, and 0.007 parts of tin octylate and 0.0 of hydroquinone were added.
Add 07 parts and react at 80 ° C in N ₂ stream until the NCO reaction rate becomes 90% or more. d) ◎ Synthesis of modified acrylic resin of epoxy resin (radiation sensitive modified resin) 400 parts of epoxy resin (Epicoat 1007 manufactured by Shell Chemical Co., Ltd.) was dissolved in 50 parts of toluene and 50 parts of methyl ethyl ketone by heating,
N, N-dimethylbenzylamine 0.006 parts, hydroquinone
Add 0.003 parts to 80 ° C and add 69 parts acrylic acid dropwise.
The reaction is carried out at 0 ° C until the acid value becomes 5 or less. ◎ Synthesis of modified phenoxy resin acrylics (radiation sensitive modified resin) Phenoxy resin with OH group (PKHH: UCC molecular weight 30
000) 600 parts, methyl ethyl ketone 1800 parts were charged into a 31 four-necked flask, heated and dissolved, and heated to 80 ° C, 6.0 parts of tolylene diisocyanate 2-hydroxyethyl methacrylate adduct was further added, and tin octylate 0.012 parts and hydroquinone were added. Add 0.012 parts and react at 80 ° C in N ₂ stream until the NCO reaction rate becomes 90%. The phenoxy modified product has a molecular weight of 35,000 and one double bond per molecule. e) Synthesis of urethane elastomer acrylic modified product (radiation-curable elastomer) Diphenylmethane diisocyanate (MDI) -based urethane prepolymer with terminal isocyanate (Nipporan 3119 made by Nippon Polyurethane) 250 parts, 2HEMA 32.5 parts, hydroquinone 0.07 parts, tin octylate 0.009 80 parts
After melting by heating at ℃, 43.5 parts of TDI is heated to 80 ~ 90
Add dropwise while cooling to reach 80 ° C
React until the reaction rate reaches 95% or more. f) Synthesis of polyether-based urethane-terminated elastomer-modified acrylic (radiation-curable elastomer) Polyether PTG-500 manufactured by Nippon Polyurethane Company, 250 parts, 2
HEMA32.5 parts, hydroquinone 0.07 parts, tin octylate 0.
After putting 009 parts in a reaction vessel and heating to 80 ° C. to dissolve, 43.5 parts of TDI was added dropwise while cooling so that the temperature in the reaction vessel was 80 to 90 ° C., and after completion of the dropping, a reaction rate of 95 at 80 ° C. React until it becomes less than%. g) Synthesis of acrylic modified polybutadiene elastomer (radiation-curable elastomer) Low molecular weight terminal hydroxyl group polybutadiene poly BD manufactured by Sinclair Petrochemical Co., Ltd. BD Rquitite Rendine R-15 250 parts, 2HE
MA32.5 parts, hydroquinone 0.07 parts, tin octylate 0.00
After 9 parts were placed in a reaction vessel and heated to 80 ° C to dissolve, 43.5 parts of TDI was added dropwise while cooling so that the temperature in the reaction vessel was 80 to 90 ° C. React until it becomes over%. It is known that a polymer is one which is disintegrated by irradiation with radiation and one which causes intermolecular crosslinking. Those that cause cross-linking between molecules include pyriethylene, polypropylene, polystyrene, polyacrylic acid ester,
Polyacrylamide, polyvinyl chloride, polyester,
There are polyvinylpyrrolidone rubber, polyvinyl alcohol, and polyacrolene. With such a cross-linking polymer, a cross-linking reaction occurs even if the above-mentioned modification is not particularly performed. Therefore, in addition to the modified product, these resins can be used as they are as a back coating resin for radiation cross-linking. is there. The mixing ratio of the magnetic powder and these binders is about 3/1 to 1/1 by weight. In any of the binders, alumina having a coating film reinforcing agent average particle size of 1.0 μm or less may be further added, and the addition amount is about 0 to 5% by weight with respect to the binder. It is possible to eliminate the need to add a coating film reinforcing agent, or since the amount is very small compared to the conventional one, it is possible to eliminate the adverse effect of the addition. In addition, it is effective to use various antistatic agents, lubricants, dispersants and the like according to the application, if necessary. The thickness of the recording layer containing the magnetic particles and the binder is
It is about 0.3 to 1.0 μm. As the rigid substrate, an Al alloy or the like in which a trace additive is added to a Mg alloy mainly composed of Al to control the crystallization of crystallized substances is preferable, and glass, polymethyl methacrylate (PMMA), polycarbonate, Examples of the plastic include epoxy. The thickness of the base is 1.2 to 4 mm. Further, an underlayer may be provided between the recording layer and the substrate, if necessary. That is, chromate pretreatment, alumite pretreatment, Ni-P plating pretreatment, etc. are performed to improve the dispersion of intermetallic compounds in the material, improve the surface finish, prevent oxidation of Al alloy, improve the hardness of Al substrate surface. The durability may be improved by In order to form the recording layer on the substrate, thin film coating is performed by a spin coating method, and then the magnetic film is polished to
The thin film has a thickness of μm or less. The magnetic disk of the present invention is generally a magnetic coating prepared by dispersing magnetic particles on a substrate in a binder using a high-boiling solvent (eg, xylene, isophorone, butyrolacetone, etc.) and kneading with a) using a ball mill or the like. After b) is applied by spin coating, the steps of c) orientation, d) curing or curing, e) polishing, f) lubricant application, and g) burnishing are performed. V Specific Actions and Effects of the Invention The magnetic recording medium used in the present invention has high durability, abrasion resistance, and coating film hardness because it contains magnetic particles having at least the surface of iron carbide. Also, the wear coefficient is small. The magnetic characteristics are also good. The surface smoothness is also good. For this reason, it is unnecessary to add a coating film reinforcing agent (alumina or the like), or a small amount is added, so that a high recording density can be achieved, and a magnetic recording medium which easily polishes or burnishes can be obtained. In addition, there is little demagnetization and the moisture resistance is extremely good. For this reason, as a whole, a hard disk type medium with extremely high performance is realized. More specifically, compared with the case of using acicular iron oxide,
Magnetic properties are remarkably improved, surface smoothness is improved, and extremely high recording density can be obtained. Further, even when compared with the case of using Co-based iron oxide, the magnetic characteristics are similarly improved, the surface smoothness is improved, and a high recording density can be obtained. And, compared with the case of using the metal magnetic powder, the moisture resistance,
Corrosion resistance is remarkably improved, coating film strength is remarkably improved, frictional strength is also improved, and durability is remarkably improved. VI Specific Examples of the Invention The effects of the present invention will be described in more detail below by showing specific examples and comparative examples of the present invention. Example First, a magnetic coating material was prepared. The composition is as follows. Magnetic powder (Table 1) 100 parts by weight Solvent (xylene / isophorone / vinylolacetone: weight ratio 20/50/30) 500 parts by weight Binder (epoxy resin / butyral resin / phenolic resin: 50/30/20) 50 parts by weight Coating film reinforcing agent (α-Al ₂ O ₃ ) 3 parts by weight Dispersant (soybean oil lecithin) 2 parts by weight However, as shown in Table 1 below, the above magnetic powder is a powder whose surface is at least FenC (hereinafter referred to as “FenC”). FenC powder)
Is a main component, and is mixed with needle-like Fe powder or Co-deposited iron oxide powder (hereinafter referred to as Co-γFe ₂ O ₃ powder) in different mixing ratios (parts by weight). In this case, the total amount of magnetic powder is shown as 100 parts by weight. Here, the acicular FenC powder is acicular α-FeOOH 90 parts by weight,
An aqueous suspension of carbon black having an average particle diameter of 30 mμ (10 parts by weight of carbon solid content) is kneaded into a slurry,
After dehydration and drying, it was pulverized and heated in an electric furnace in a mixed gas atmosphere of CO and H ₂ (mixing ratio 1: 1) at 600 ° C. for 5 hours. It was confirmed by X-ray diffraction that the obtained product was a mixed crystal of Fe ₃ C and Fe. This one has coercive force Hc = 900-910Oe,
The powder has a saturation magnetization σs of 82 emu / g. The acicular Fe powder is obtained by reducing acicular α-FeOOH with hydrogen, has an average particle length of 0.2 μm, an axial ratio of 8, and a coercive force Hc = 9.
It is a powder having 00 Oe and a saturation magnetization σs = 155 emu / g. Co-γFe ₂ O ₃ powder is obtained by diffusing Co ²⁺ into a very thin layer within a few tens of Å from the surface of γ-Fe ₂ O ₃ particles. This is a powder with a coercive force Hc = 750 Oe. Disperse the above magnetic powder in a binder using a solvent,
It was kneaded for 36 hours in a ball mill. The magnetic coating material thus prepared was diluted on an Al substrate to a thickness of 0.7 to 1.5 μm by spin coating and oriented in the circumferential direction with a permanent magnet. After that, curing was performed at 180 ° C., the surface was polished, a lubricant was applied, and burnished. Then, the thickness of the magnetic layer was finished to 0.6 μm. The following characteristics of the magnetic disk manufactured in this manner were measured. 1) Magnetic characteristics Coercive force Hc, residual magnetic flux density Br and squareness ratio Br / Bm were measured with a vibrating sample magnetometer. 2) Recording density D ₅₀ Ferrite head Head gap 0.3μm, linear velocity 9.99m
The recording density at which the output was 50% was measured at / sec. 3) Surface roughness R _{20 It} was measured by Talystep (manufactured by TAYLOR-HOBSON). 20 points were selected from the maximum and the minimum in the distribution of roughness in the circumferential direction, and the average value was calculated. 4) Durability (CSS test) Set the contact start / stop cycle of the magnetic head.
15 seconds, the rise and fall of disk rotation is 5 seconds each,
The number of contact start / stops at which scratches were generated on the coating film was examined. 5) Coating hardness The value at 300 g was measured with a Vickers hardness meter. 6) Friction coefficient A friction angle measuring device (manufactured by Tokyo Seiki) was used to incline a load of 1 g, and the friction coefficient was calculated from the angle tan θ when the load slipped off. 7) Moisture resistance A magnetic disk is held for 7 days at a humidity of 90% and a temperature of 60 ° C, and then magnetic measurement is performed. Saturation magnetic flux density θ from the initial state
The reduction rate Δφm (%) of m was determined. The results are shown in Table 3. Comparative Example The same measurement as that of the example was performed on the magnetic disk manufactured by the same method as the example except that the magnetic powder in the magnetic paint in the example was changed as shown in Table 2. The results are shown in Table 3 together with the examples. From the above, the effects of the present invention described above are clear. Even when iron carbide was present on the surface and the amount of iron carbide was 10 wt%, the same characteristics as above were obtained.

Claims (3)

[Claims] 1. A method for recording / reproducing by flying a magnetic head on a surface of a magnetic recording medium having a recording layer containing magnetic particles and a binder on a rigid substrate, wherein at least the surface of the magnetic particles is iron carbide. And a magnetic recording / reproducing method characterized by using the particles. 2. The magnetic recording / reproducing method according to claim 1, wherein the iron carbide particles of which at least the surface is iron carbide have a composition of FenC (n is 2 or more). 3. The magnetic recording / reproducing method according to claim 1, wherein the particles having iron carbide on at least the surface account for 10% by weight or more of the magnetic particles.