JPH077498B2 - Magnetic recording medium - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium having a coating type magnetic recording layer, and more particularly to a magnetic recording medium characterized by the magnetic recording layer.

2. Description of the Related Art At present, magnetic recording media are widely used in the fields of audio, video, computers, magnetic disks, 8 m / m, etc. It is expected to be used in the field of high-density floppy disks, etc., and accordingly, the amount of information recorded on magnetic recording media is also increasing year by year. Therefore, there is an increasing demand for higher recording density for magnetic recording media. Is becoming more common. Conventionally, in magnetic recording media such as magnetic tapes, the magnetic characteristics have been improved by orienting the needle-shaped magnetic powder in the magnetic recording layer in the longitudinal direction, but the needle-shaped magnetic powder is oriented in the longitudinal direction. Although high output can be obtained in the low frequency band, there is a limit to high density recording.

For this reason, recently, a magnetic recording medium has been proposed in which the magnetic powder is a flat plate and barium ferrite magnetic powder having an easy axis of magnetization in the vertical direction is used for the magnetic recording layer (Japanese Patent Laid-Open No. 57-195328). ).

However, the use of these barium ferrite magnetic powders has a short wavelength recording property, but has a drawback of poor durability running property. Especially, when used for a floppy disk, durability running property is poor, which causes a problem in use. There is.

Means for Solving the Problems The inventors of the present invention have conducted extensive studies to solve the above problems, and as a result, the durability running property of a magnetic recording medium using a hexagonal plate-like ferrite magnetic powder is The present invention provides a new finding that the modulus (E ″) is improved, particularly when the Young's modulus (E ′) of a conductive undercoat and the Young's modulus (E ″) of a magnetic layer are specified. Has reached.

That is, according to the present invention, in a magnetic recording medium having a coating type magnetic recording layer provided on a non-magnetic substrate, hexagonal plate-like ferrite magnetic powder is used for the magnetic recording layer, and the Young's modulus (E ') of the conductive undercoat is And the Young's modulus (E ″) of the magnetic layer is E ′ /
The present invention relates to a magnetic recording medium having E ″ <1.

The hexagonal plate-like ferrite magnetic powder used in the present invention is barium ferrite magnetic powder, strontium ferrite magnetic powder and the like.

The hexagonal tabular barium ferrite used in the magnetic recording layer is represented by the chemical formula BaO · 6Fe ₂ O ₃ , and in addition to this, some of Ba and Fe in this chemical formula are Ti, Cr, Co, Zn, In, Mn. , Cu, Ge, Nb, Ca,
Those substituted with metals such as Sr, Pb, Ni and Sn are included.

The magnetic powder of barium ferrite, strontium ferrite, etc. has a diameter of 0.2μ or less, preferably 0.15μm or less, more preferably 0.1μm or less. The plate ratio is not limited, but a plate ratio of 6 or more, more preferably 7 or more is vertical. It is easy to orient. Since barium ferrite has a hexagonal plate shape, it has a larger effect on the surface roughness than the acicular magnetic powder, and if it is larger than the above-mentioned diameter, the surface roughness is greatly reduced, which is not preferable. When the particle size is in the above range, the surface smoothness of the magnetic layer is good, noise is sufficiently low, and high density recording can be achieved.

As a method for producing barium ferrite, there are a ceramic method, a coprecipitation-firing method, a hydrothermal synthesis method, a flux method, a glass crystallization method, an alkoxide method, a plasma jet method and the like, and any method can be used.

In the present invention, a hexagonal plate-shaped ferrite magnetic powder, for example a magnetic recording layer containing barium ferrite magnetic powder,
The ratio of the Young's modulus (E ′) of the conductive undercoat to the Young's modulus (E ″) of the magnetic layer must be E ′ / E ″ <1.

When hexagonal tabular ferrite magnetic powder, such as barium ferrite magnetic powder, is used, the Young's modulus of the magnetic layer becomes high and brittleness appears. Therefore, the durability of magnetic recording media using them cannot be sufficiently covered.

Unexpectedly, when the Young's modulus (E ′) of the undercoat is higher than that of the magnetic layer (E ″), the durability of the magnetic recording medium is reduced, and when it is lower, the backcoat It was found that the layer cushion mechanism works to obtain a magnetic recording medium having a sufficient running durability.

The Young's modulus (E ') of the undercoat layer can be adjusted by (1) selecting the type and amount of pigment, (2) selecting a binder, and the like.

Further, since barium ferrite itself has high electric resistance, it is preferable to make the undercoat layer conductive so that the electric resistance can be lowered. When the electric resistance of the magnetic recording layer is high, it is difficult to completely suppress the dropout caused by it, but the dropout can be suppressed by providing the conductive undercoat layer.

The conductive undercoat layer can be obtained by including a conductive substance in the undercoat layer. Any of the conductive materials can be used, but carbon black, graphite, graphitized carbon black, etc. are used.

Carbon black used in the undercoat layer of the present invention is a furnace, channel, acetylene, thermal,
Although it may be manufactured by any method such as a lamp,
Acetylene black, furnace black, channel black, roller and disc black and German naphthalene black are preferred. The particle size of the carbon black used in the present invention may be any, but preferred is 10 to 100 m measured by electron microscopy.
μ, and particularly preferably 10 to 80 mμ. Further, in terms of particle size, when the particle size exceeds 100 mμ, the surface roughness of the undercoat layer surface deteriorates, which causes deterioration of the characteristics after coating the magnetic layer. If it is less than 10 mμ, the dispersion will not be successful and the surface roughness of the undercoat will be poor.

A special type of carbon black is graphitized carbon black, and graphitized carbon black can also be used in the present invention.

Graphitized carbon black has a shell-like structure in which the carbon layer planes are parallel to each other on the surface, and voids are seen near the inner center. There is also a hollow capsule-like shape with a slight angle. Therefore, graphitized carbon black is structurally different from carbon black and can be clearly distinguished by an electron microscope. This surface shell is smooth because it is graphitized.

Graphitized carbon black is a very distinctive carbon black in which the amount of trace impurities (S, C1) contained in the carbon black is extremely small and the water adsorption is weak. When the water adsorption power is weak, the dispersibility of carbon black usually deteriorates. However, the graphitized carbon black does not have a low dispersibility even though it has a surprisingly low water content. Moreover, since the surface is graphitized and becomes a shell, it has very low friction and weak water adsorption, so that the one containing graphitized carbon is preferable when used under high temperature and high humidity. Effective.

Although carbon black has conductivity, the smaller the particles, the better the conductivity. The crystal structure of the graphitized carbon gives conductivity as the graphitization proceeds. And since volatile substances and oily substances on the surface of carbon black impede conductivity, removing them improves conductivity, which is also advantageous in terms of antistatic property. It is possible to obtain a magnetic recording medium having a small amount of noise.

Graphitized carbon black is a carbon black such as acetylene black, furnace black, channel black, roller and disk black and German naphthalene black, which is heat-treated at a temperature of 2,700 to 3,000 ° C., and an average particle diameter of 10 to 100 mμ. Preferably 10 to 80 mμ, specific surface area BET ^{20 to} 300 m ² / g, volatile content 1.0
% Or less, and examples thereof include # 4000B (Mitsubishi Kasei Kogyo Co., Ltd.).

The graphitized carbon black that may be used in the present invention preferably has a pH of 8 or more.

By providing such an undercoat layer, it is possible to prevent sticking of the medium to the head, sticking of guide rollers, calendar rollers and the like during the manufacturing process such as the coating process and the occurrence of discharge noise and the like.

The thickness of the undercoat layer is preferably about 10Å to 5 μm.

The mixing ratio of carbon black or the like is 5 to 200 parts by weight of conductive carbon black or the like per 100 parts by weight of the binder.

In the present invention, the Young's modulus (E ″) of the magnetic layer is 9 × 10 ¹⁰ dyn /
It is preferably at least cm ² . When the Young's modulus (E ″) of the magnetic layer is 9 × 10 ¹⁰ dyn / cm ² or more, further clogging and abrasion of the coating film are less likely to occur, and since it is hard, the cleaning effect is increased and the durability running property is improved. The Young's modulus of the magnetic layer can be adjusted by the plate ratio of the hexagonal plate ferrite magnetic powder used, the dispersion method, the coating method, the processing method, etc.
For example, when the plate ratio of the magnetic powder is high, the Young's modulus (E ″) of the magnetic layer also tends to be high. When the plate ratio is 6 or more, the value of E ″ may be satisfied. it can.

In the present invention, other Co-containing iron oxide powder, γFe ₂ O ₃ powder, F
e ₃ O ₄ powder, Co ferrite powder, metal powder, etc. can also be used.

For the magnetic recording layer and the undercoat layer of the present invention, a commonly used organic binder, inorganic pigment, lubricant, dispersant, antistatic agent, etc. can be used according to a conventional method.

As the organic binder used in the magnetic recording layer and the undercoat layer of the present invention, a thermoplastic, thermosetting or reactive resin or a mixture thereof which has been conventionally used for magnetic recording media is used. From the viewpoint of film strength and the like, a curable resin, particularly a radiation curable resin is preferable.

The thermoplastic resin has a softening temperature of 150 ° C. or lower, an average molecular weight of 10,000 to 200,000, and a degree of polymerization of about 200 to 2,000, for example, vinyl chloride-vinyl acetate copolymer (including those containing carboxylic acid), Vinyl chloride-vinyl acetate-vinyl alcohol copolymer (including carboxylic acid introduced), vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, acrylic ester-acrylonitrile copolymer, acrylic ester -Vinylidene chloride copolymer, acrylic acid ester-styrene copolymer, methacrylic acid ester-acrylonitrile copolymer, methacrylic acid ester-vinylidene chloride copolymer, methacrylic acid ester-styrene copolymer, urethane elastomer, nylon-silicone Resin, nitrocellulose-polyamide resin , Polyvinyl fluoride, vinylidene chloride-acrylonitrile copolymer, butadiene-acrylonitrile copolymer, polyamide resin, polyvinyl butyral, cellulose derivative (cellulose acetate, cellulose diacetate, cellulose triacetate, cellulose propionate, nitrocellulose, etc.), Styrene-butadiene copolymers, polyester resins, chlorovinyl ether-acrylic acid ester copolymers, amino resins, various synthetic rubber thermoplastic resins, and mixtures thereof are used.

The thermosetting resin or reactive resin has a molecular weight of 200,000 or less in the state of a coating liquid, and by heating after coating and drying, the molecular weight becomes infinite due to reactions such as condensation and addition. Further, among these resins, those which do not soften or melt before the resin is thermally decomposed are preferable. Specifically, for example, phenol resin, epoxy resin,
Polyurethane curable resin, urea resin, melamine resin, alkyd resin, silicone resin, acrylic reaction resin, epoxy-polyamide resin, nitrocellulose melamine resin, mixture of high molecular weight polyester resin and isocyanate prepolymer, methacrylate copolymer and Mixtures of diisocyanate prepolymers, mixtures of polyester polyols and polyisocyanates, urea formaldehyde resins, low molecular weight glycol / high molecular weight diol / triphenylmethane triisocyanate mixtures, polyamine resins, and mixtures thereof.

It is preferable to use a binder obtained by curing a radiation curable compound.

Specific examples of the radiation curable compound include acrylic double bonds having an unsaturated double bond showing radical polymerizability such as acrylic double bonds such as acrylic acid, methacrylic acid, or ester compounds thereof, and allyl close bonds such as diallyl phthalate. It is a resin in which a group of a double bond, an unsaturated bond such as a maleic acid or a maleic acid derivative, which is crosslinked by irradiation with radiation or polymerized and dried is contained or introduced in the molecule of the thermoplastic resin.
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 having 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 is changed to 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, VYBGX, VERR, VYES, VMCA, VAGH, VCARMAG52
0, VCARMAG528, and the like, and an acrylic double bond, a maleic acid double bond, and an allyl double bond are introduced into this by a method described below to perform radiation-sensitive modification.

(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, Byron 53S),
These are also subjected to radiation-sensitive modification.

(3) Polyvinyl alcohol-based resin Polyvinyl alcohol, butyral resin, acetal resin, formal resin, and copolymers of these components are used, and the hydroxyl groups contained in these resins are subjected to radiation-sensitive modification by the method described below.

(4) Epoxy resin, phenoxy 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) Various fibrin derivatives are used, but particularly effective ones are nitrification cotton, cellulose acetobutyrate, ethyl cellulose,
Butyl cellulose, acetyl cellulose and the like are preferable, and the hydroxyl group in the resin is utilized to carry out radiation-sensitive modification by the method described below.

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,
Phenol resins, spiro acetal resins, acrylic resins containing at least one hydroxyl group-containing acrylic ester and methacrylic ester as a polymerization component are also effective.

Examples of the elastomer or prepolymer will be given below.

(1) Polyurethane Elastomer or Prepolymer The use of polyurethane is particularly effective in terms of good abrasion resistance and good adhesion to a base film, such as a PET film. 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 consisting of polycondensation products of various polyesters such as linear saturated polyethers (polyethylene glycol, polypropylene glycol, polytetramethylene glycol), caprolactam, hydroxyl-containing acrylic acid ester, hydroxyl-containing methacrylic acid ester, etc. are effective. is there.

It is very effective to modify these urethane elastomers by reacting the isocyanate group or hydroxyl group at the terminal with a monomer having an acrylic double bond or an allyl double bond, etc. to make it radiation sensitive. is there. In addition, those containing OH, COOH, etc. as polar groups at the ends are also included.

Further, a monomer having an unsaturated double bond having an active hydrogen capable of reacting an isocyanate group and having an 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 having a terminal hydroxyl group, which is commercially available as Sinclair Petrochemical PolyBD Retied Resin, or 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 crosslinked and polymerized by radiation.

(3) Polybutadiene Elastomer A prepolymer having a low molecular weight terminal hydroxyl group such as poly BD retired resin R-15 manufactured by Sinclair Petrochemical Co., Ltd. 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-M901 made by Japan Synthetic Rubber
Also has excellent properties when combined with a thermoplastic resin.

Other suitable thermoplastic elastomers and prepolymers thereof are styrene-butadiene rubber,
There are chlorinated rubbers, acrylic rubbers, isoprene rubbers and cyclized products thereof (CIR701 manufactured by Japan Synthetic Rubber), and elastomers such as epoxy modified rubber and internally plasticized saturated linear polyester (Toyobo Byron # 300) are also treated by the radiation sensitive modification treatment described below. Can be effectively used by applying.

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,
Trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, polyfunctional oligoester acrylate (Aronix M-7100, M-5400, 55
00, 5700 etc., Toagosei), acrylic modified urethane elastomer (Nipporan 4040), or those into which functional groups such as COOH are introduced, trimethylolpropane diacrylate (methacrylate), phenol ethylene oxide adduct Acrylate (methacrylate), a compound having an acryl group (methacryl group) or ε-caprolactone acryl group on the pentaerythritol condensed ring represented by the following general formula, In the formula, a compound of m-1, a = 2, b = 4 (hereinafter referred to as a special pentaerythritol condensate A), m = 1, a =
3, b = 3 compound (hereinafter referred to as special pentaerythritol condensate B), m = 1, a = 6, b = 0 compound (hereinafter referred to as special pentaerythritol condensate C), m = 2, a = 6, a compound of b = 0 (hereinafter referred to as special pentaerythritol condensate D), and special acrylates represented by the following general formula.

_{(1) (CH 2 = CHCOOCH} 2) 3 -CCH 2 OH ( special acrylate _{A) (2) (CH 2} = CHCOOCH 2) 3 -CCH 2 CH 3 ( special acrylate B) (3) [CH ₂ = CHCOOC ₃ H ₆₎ n-OCH _{2] 3 -CCH 2 CH 3 (n ≒} 3) ( special acrylate C) _{(8) CH 2 CHCOO- (CH} 2 CH 2 O) 4 -COCH = CH 2 ( special acrylate H) A: Acrylic acid, X: Polyhydric alcohol Y: Polybasic acid (special acrylate K) 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 acetate vinyl chloride copolymer having OH groups (average degree of polymerization n = 500) and toluene 1250 Parts and cyclohexanone 500 parts in a four-necked flask of 51 and heated to dissolve,
After heating to ℃, add 61.4 parts of 2-hydroxyethylmethacrylate adduct * of tolylene diisocyanate, add 0.012 parts of tin octylate and 0.012 parts of hydroquinone, and add 80 ℃.
To react in N ₂ stream until NCO reaction rate reaches 90%. After completion of the reaction, the mixture is cooled and 1250 parts of methyl ethyl ketone is added for dilution.

[* Manufacturing method of 2-hydroxyethyl methacrylate (2HEMA) adduct of tolylene diisocyanate (TDI) After heating 348 parts of TDI to 80 ° C in a four-neck flask of 11 in N ₂ stream, 260 parts of 2-ethylene methacrylate, octyl 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 completion of the reaction, the product was taken out and cooled, and then white paste-like 2HEMA of TDI was obtained. B) Synthesis of acrylic modified butyral resin (radiation sensitive modified resin) Butyral resin Sekisui Chemical's BM-S 100 parts toluene 191.2
Part, and cyclohexanone 71.4 parts were charged into a 51-necked 4-necked flask, dissolved by heating, and heated to 80 ° C, and then the TDI 2HEMA adduct * was added.
In addition to 7.4 parts, 0.015 part of tin octylate and 0.015 part of hydroquinone are added and reacted at 80 ° C. in an N ₂ gas stream until the NCO reaction rate becomes 90% or more. After the reaction is complete, it is cooled and diluted with methyl ethyl ketone.

c) Synthesis of saturated polyester resin modified acrylics (radiation sensitive modified resin) Saturated polyester resin (Vylon RV-200 manufactured by Toyobo), 10
Dissolve 0 part in 116 parts toluene and 116 parts methyl ethyl ketone by heating and raise the temperature to 80 ° C, then add 3.55 parts of 2HEMA adduct * of TDI,
Add 0.007 parts of tin octylate and 0.007 parts of hydroquinone and react at 80 ° C in N ₂ stream until NCO reaction rate is 90% or more.

d) ◎ Synthesis of epoxy resin modified acrylic resin (radiation sensitive modified resin) Epoxy resin (Epicoat 1007 manufactured by Shell Chemical Co., Ltd.), 400 parts by heating and dissolving in 50 parts of toluene and 50 parts of methyl ethyl ketone, and then 0.006 parts of N, N-dimethylbenzylamine Then, 0.003 parts of hydroquinone was added to 80 ° C., 69 parts of acrylic acid was added dropwise, and the mixture was reacted at 80 ° C. until the acid value became 5 or less.

◎ Phenoxy resin Synthesis of acrylic modified product (Radiation sensitive modified resin) Phenoxy resin having OH group (PKHH: UCC molecular weight 3
600 parts, 1800 parts of methyl ethyl ketone and 1800 parts of methyl ethyl ketone are charged into a 31-necked 4-neck flask, heated and dissolved, and heated to 80 ° C, 6.0 parts of 2-hydroxyethyl methacrylate adduct of tolylene diisocyanate is added, and 0.012 parts of tin octylate and hydroquinone 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 modified urethane elastomer acrylic (radiation curable elastomer) 250 parts of diphenylmethane diisocyanate (MDI) -based urethane prepolymer with terminal isocyanate (Nipporan 3119 made by Nippon Polyurethane), 2HEMA32.5 parts, hydroquinone 0.07 parts, tin octylate 0.009 80 parts
After melting by heating at ℃, 43.5 parts of TDI was heated to 80-90 ℃ in the reactor.
Add dropwise while cooling so that after the completion of the dropwise addition, react at 80 ° C until the reaction rate reaches 95% or more.

f) Synthesis of Polyether-based Urethane Modified Elastomer Acrylic Modified (Radiation-curable Elastomer) Polyether PTG-500 manufactured by Nippon Polyurethane Company, 250 parts, 2H
EMA32.5 parts, hydroquinone 0.007 parts, tin octylate 0.
After putting 009 parts in a reaction can and heating and melting at 80 ° C, 43.5 parts of TDI was added dropwise while cooling so that the temperature in the reaction can was 80 to 90 ° C, and after completion of the dropping, a reaction rate of 95% or more at 80 ° C. Let it react until it becomes.

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 Resin R-15, 250 parts, 2HE
MA32.5 parts, hydroquinone 0.007 parts, tin octylate 0.0
Put 09 parts in a reaction can, heat and dissolve it at 80 ° C, add 43.5 parts TDI while cooling so that the temperature in the reaction can is 80-90 ° C, and after completion of the dropping, at 80 ° C a reaction rate of 95% or more Let it react until it becomes.

It is known that a polymer is one that is disintegrated by irradiation with radiation and one that causes intermolecular crosslinking. Those that cause intermolecular crosslinking include polyethylene, polypropylene, polystyrene, polyacrylic acid ester, polyacrylamide, polyvinyl chloride, polyester, polyvinylpyrrolidone rubber, polyvinyl alcohol, and polyacrolein. 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 for radiation cross-linking.

Furthermore, according to this method, even a solventless resin that does not use a solvent can be cured in a short time,
Such a resin can be used.

By using such a radiation-curable resin, a so-called jumbo roll having a large diameter is free from winding tightness, and there is no difference in electromagnetic conversion characteristics inside and outside the jumbo roll, and the characteristics are improved. Also, because it can be done online, productivity is improved.

Magnetic powder / binder is 1 / 1-9 / 1 by weight ratio, especially 2 / 1-8
It is preferably / 1.

When the ratio is less than 1/1, the saturation magnetic flux density becomes low, and when it exceeds 9/1, the surface roughness becomes poor due to poor dispersion and the coating film becomes brittle, which is not preferable.

In the present invention, a non-reactive solvent is used if necessary. The solvent is not particularly limited, but is appropriately selected in consideration of the solubility and compatibility of the binder.

For example, ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; alcohols such as methanol, ethanol, propanol, butanol; ethyl formate, methyl acetate, ethyl acetate, butyl acetate, ethyl lactate, glycol acetate monoethyl ether, etc. Esters; ethers such as isopropyl ether, ethyl ether, glycol dimethyl ether, glycol monoethyl ether, dioxane; aromatic hydrocarbons such as benzene, toluene, xylene, ethylbenzene; furans such as tetrahydrofuran and furfural;
Chlorinated hydrocarbons such as methylene chloride, ethylene chloride, carbon tetrachloride, chloroform, ethylene chlorohydrin and dichlorobenzene, and other dimethylformamides are used as a single solvent or a mixed solvent thereof.

These solvents are 10 to 1000 wt% relative to the binder, especially
Used at a rate of 100-5000 wt%.

An inorganic pigment may be contained in the magnetic layer and the undercoat layer.

As the inorganic pigment, 1) conductive carbon black, graphite, graphitized carbon black,
2) SiO ₂ , TiO ₂ , Al ₂ O ₃ , Cr ₂ O ₃ as an inorganic filler,
There are SiC, CaO, CaCO ₃ , zinc oxide, goethite, γFe ₂ O ₃ , talc, kaolin, CaSO ₄ , boron nitride, graphite fluoride, molybdenum disulfide, ZnS and the like. In addition to these, the following fine particle pigments (aerosil type, colloidal type):
SiO ₂ , Al ₂ O ₃ , TiO ₂ , ZrO ₂ , Cr ₂ O ₃ , Y ₂ O ₃ , CeO ₂ , Fe
₃ O ₄ , Fe ₂ O ₃ , ZrSiO ₄ , Sb ₂ O ₅ , SnO and the like are also used. These fine particle pigments are, for example, in the case of SiO ₂ , ultrafine particle colloidal solution of silicic acid anhydride (Snowtex, water system, methanol silica sol, etc., Nissan Chemical, ultrafine particle anhydrous silica produced by burning purified silicon tetrachloride (standard product 100
Å) (Aerosil, Nippon Aerosil Co., Ltd.) and the like. Further, the ultrafine particle colloidal solution and the ultrafine aluminum oxide produced by the vapor phase method similar to the above, titanium oxide and the above-mentioned fine particle pigment may be used. It is appropriate to use 1 to 30 parts by weight with respect to 100 parts by weight of the magnetic powder for 1) and 1 to 30 parts by weight for 2) such an inorganic pigment. However, it has the disadvantage that it becomes brittle and, on the contrary, there are many dropouts.

In the undercoat layer, carbon black is 5 to 200 parts by weight per 100 parts by weight of the binder, and 2).
Is 1 to 300 parts by weight.

The diameter of the inorganic pigment is 0.1 μm for 1).
In the following, 0.05 μm or less is preferable, and with respect to 2), 0.7 μm or less, further 0.5 μm or less is preferable.

The magnetic layer may contain a dispersant.

As the dispersant, an organic titanium coupling agent, a silane coupling agent, or a surfactant is used, and as an antistatic agent, a natural surfactant such as saponin; a nonionic surfactant such as an alkylene oxide-based, glycerin-based, or glycidol-based surfactant;
Cationic surfactants such as higher alkyl amines, quaternary ammonium salts, pyridine and other heterocycles, phosphonium or sulfonium; and acidic groups such as carboxylic acid, sulfonic acid, phosphoric acid, sulfuric acid ester group, phosphoric acid ester group Anionic surface active agents; amphoteric surface active agents such as amino acids, aminosulfonic acids, sulfuric acid or phosphoric acid esters of amino alcohols, etc. are used.

The magnetic layer may contain a lubricant.

As the lubricant, silicone oil, fluorine oil, fatty acid, fatty acid ester, paraffin, liquid paraffin, surfactant and the like can be used as the lubricant conventionally used in this kind of magnetic recording medium, but fatty acid and / or fatty acid ester is used. Is preferably used.

As fatty acids, caprylic acid, capric acid, lauric acid,
Fatty acids with 12 or more carbon atoms (RCOO, such as myristic acid, palmitic acid, stearic acid, behenic acid, oleic acid, elaidic acid, linoleic acid, linolenic acid, stearolic acid)
H and R are alkyl groups having 11 or more carbon atoms), and fatty acid esters include fatty acid esters consisting of monobasic fatty acids having 12 to 16 carbon atoms and monohydric alcohols having 3 to 12 carbon atoms, carbon A fatty acid ester comprising a monobasic fatty acid having a number of 17 or more and a monohydric alcohol having a carbon number of 21 to 23 in total with the carbon number of the fatty acid is used, and an alkali metal or alkali of the fatty acid is used. Metal soaps made of earth metals, lecithin, etc. are used.

As the silicone, those which are modified with fatty acid and those which are partially modified with fluorine are used. As the alcohol, a higher alcohol is used, and as the fluorine, one obtained by electrolytic substitution, telomerization, oligomerization or the like is used.

Among the lubricants, radiation-curable lubricants are also convenient to use.

As the radiation-curable lubricant, a compound having a molecular chain exhibiting lubricity and an acrylic double bond in the molecule, for example, acrylic acid ester, methacrylic acid ester, vinyl acetate ester, acrylic acid amide compound, vinyl alcohol ester , Methyl vinyl alcohol ester, allyl alcohol ester, glyceride, etc., and when these lubricants are represented by the structural formula, CH ₂ ═CHCOOR, CH ₂ = CH-CH ₂ COOR, CH ₂ = CHCONHCH ₂ OCOR, RCOOCH ₂ —CH═CH _{2 and the} like, where R is a linear or branched saturated or unsaturated hydrocarbon group having a carbon number of 7 or more, preferably 12 or more and 23 or less. Can also be As the fluorine substitution product, CnF _{2n + 1} −, CnF _{2n + 1} (CH ₂ ) m − (where m = 1 to
5), CnF _{2n + 1} CH ₂ CH ₂ NHCH ₂ CH ₂ −, Etc.

Preferred specific examples of these radiation-curable lubricants include
Examples thereof include stearic acid methacrylate (acrylate), stearyl alcohol methacrylate (acrylate), glycerin methacrylate (acrylate), glycol methacrylate (acrylate), and silicone methacrylate (acrylate).

The magnetic recording layer containing no lubricant has a high coefficient of friction, which causes image fluctuations and jitters.Moreover, the high coefficient of friction particularly at high temperature causes the magnetic recording layer to be easily scraped, resulting in a rolling up. Is likely to occur. Further, in the disk medium, the running durability is inferior and the coating film is damaged.

The dispersant and lubricant are preferably contained in 0.1 to 20% by weight with respect to the binder.

If the amount of the binder is too large, blocking will occur, and if the amount of the binder is too small, adhesion will occur in the calendering step, which is not preferable.

The thickness of the magnetic recording layer of the present invention after coating and drying is 0.1 to 10
The range of μm is common.

When the lubricant of the magnetic layer and the organic binder are radiation-curable, the active energy ray used for the crosslinking is an electron beam using a radiation accelerator as the radiation source, and γ-using Co60 as the radiation source.
Rays, β-rays having Sr90 as a radiation source, X-rays having an X-ray generator as a radiation source, ultraviolet rays, and the like are used.

Particularly, as a radiation source, a method of using radiation by a radiation heater is advantageous from the standpoints of controlling absorbed dose, introducing it into a manufacturing process line, and shielding ionizing radiation.

Examples of the non-magnetic base material used in the present invention include polyesters such as polyethylene terephthalate, polyolefins such as polypropylene, cellulose derivatives such as cellulose triacetate, polyimide, polycarbonate, polysulfone, polyethylene naphthalate, aromatic aramid, aromatic polyester. Metal plates such as aluminum and aluminum, glass plates, etc. are used, but not limited to these. Among these, it is particularly preferable to use polyester, polyamide, polyimide or the like.

In the magnetic recording medium of the present invention, magnetic layers may be provided on both sides of the support. In particular, in the case of a floppy disk, it is preferable to provide a magnetic layer on both sides.

The magnetic recording medium of the present invention may be provided with a back coat and a top coat, if necessary.

Of these, the back coat preferably has a composition including a binder, a pigment, and a lubricant.

As the binder, the radiation-curable resin used for the magnetic layer described above can be used. For example, (A) it has two or more unsaturated double bonds that are curable by radiation.
Plastic compound with a molecular weight of 5,000-100,000, (B)
Having one or more unsaturated double bonds that are curable by radiation, or not having radiation curability, molecular weight 3,000
To 100,000 rubbery compound, and (C) one or more unsaturated double bonds curable by radiation, molecular weight
200-3,000 compounds (A) 20-70% by weight, (B) 20
A combination used in a proportion of -80 wt% and (C) 10-40 wt% is preferred.

Further, a thermoplastic resin and a thermosetting resin can be used, and those having an average molecular weight of 200,000 or less are preferable.

Particularly preferred is a thermosetting resin (using a curing agent) composed of a combination of a fibrous resin (nitrified cotton etc.), a vinyl chloride-vinyl acetate-vinyl alcohol copolymer and urethane.

As the pigment, the inorganic pigment used for the magnetic layer described above can be used. Regarding 1), binder 10
20 to 300 parts by weight for 0 parts by weight, 10 to 30 for 2)
It is preferable to include 0 part by weight.

The lubricant used for the magnetic layer can be used as the lubricant. Among them, it is preferable to use fatty acid and / or fatty acid ester.

The magnetic recording medium of the present invention may be produced by a conventional method. For example, an undercoat layer is formed on a non-magnetic substrate such as polyester, and magnetic powder is mixed and dispersed with a binder, an organic solvent or the like to form a magnetic coating material. Prepare this magnetic coating on the undercoat layer using a method such as gravure coating, reverse roll coating, air knife coating, air doctor coating, blade coating, kiss coating, spray coating, etc. May be oriented so as to be perpendicular to the magnetic layer, dried, and then heat-cured or radiation-cured according to a conventional method.
Then, a back coat and a top coat may be provided if necessary.

The orientation treatment follows a conventional method.

Permanent magnets, direct current magnets, alternating current magnets are typically used as the orientation method, and various combinations of these are used.
For example, various combinations such as a combination of vertical and horizontal, a combination of a permanent magnet or a DC magnetic field and an AC magnetic field, a mechanical orientation or a combination of the mechanical orientation and the above are used.

Then, magnetic particles are oriented outside the magnetic field due to the demagnetizing field, and the particles are disturbed and dried in the magnetic field so that the orientation is not deteriorated. It needs to be dried so that the magnetic powder does not move.

The magnetic field strength is preferably 1000 to 6000G. in this case,
In the present invention, about 1000 to 4000 G is sufficient for the purpose.

Examples The present invention will be described in more detail with reference to Examples, but it goes without saying that the present invention is not limited thereto.

The characteristics were evaluated as follows.

(1) Young's modulus Measured at 20 ° C. with a viscoelasticity spectrometer (Iwaki Seisakusho, Toyo Boardwin, Toyo Seiko Co., Ltd.).

(2) Durability running performance An experiment of durability running performance was performed at room temperature using a floppy disk drive.

Example 1 An undercoat layer as shown below was formed on both the front surface and the back surface of a polyester (PET) film having a thickness of 75 μm.

Undercoat layer 1 part by weight carbon black 20 mμm 30 (A) Acrylic modified vinyl chloride-vinyl acetate-vinyl alcohol copolymer Molecular weight 45,000 40 (B) Acrylic modified polyurethane elastomer Molecular weight
20,000 40 (C) Polyfunctional acrylate Molecular weight 1,000 20 Stearic acid 2 Butyl stearate 2 Mixed solvent (MIBK / toluene = 1/1) 300 Disperse the above composition in a ball mill for 5 hours to obtain the above 75μ.
m polyester (PET) film to a dry thickness of 0.7 μm, surface smoothing is performed, and an accelerating voltage of 150 Ke using an electron curtain type electron beam accelerator.
The undercoat layer was irradiated with an electron beam in N ₂ gas with V, electrode current 10 mA, absorbed dose 5 Mrad.

On both sides of such an undercoat layer, a magnetic layer made of a magnetic paint as shown below was further formed.

Undercoat layer 2 parts by weight Graphitized carbon black # 400B 30 mμ 30 (A) Acrylic modified vinyl chloride-vinyl acetate-vinyl alcohol copolymer Molecular weight 45,000 50 (B) Acrylic modified polyurethane elastomer Molecular weight
20,000 50 Stearic acid 2 Butyl stearate 2 Mixed solvent (MIBK / toluene = 1/1) 300 Disperse the above composition in a ball mill for 5 hours and apply it to a polyester film to a dry thickness of 1μ. Accelerating voltage of 150K using accelerator
The undercoat layer was irradiated with an electron beam in N ₂ gas at eV, electrode current 10 mA, absorbed dose 5 Mrad.

Undercoat layer 3 parts by weight Al ₂ O ₃ 0.3 mμ 26 carbon black 30 mμ 50 acrylic modified vinyl chloride-vinyl acetate-vinyl alcohol copolymer
Molecular weight 30,000 30 Acrylic modified polyurethane elastomer Molecular weight 50,000 30 Acrylic modified phenoxy resin Molecular weight 35,000 20 Polyfunctional acrylate Molecular weight 500 20 Stearic acid 4 Solvent (MEK / toluene = 1/1) 300 These were treated and manufactured in the same manner as above.

Undercoat layer 4 (thermosetting type) parts by weight carbon black 40 mμ 50 curing agent coronate L 20 stearic acid 2 vinyl chloride-vinyl acetate alcohol copolymer (VCC, V
AGH) 50 Polyurethane elastomer 50 (BF Goodrich Esten 5703) Mix well with a mixed solvent (MEK / toluene) 300.

Apply this paint on a polyester film as above,
After drying the solvent in the same manner as above, after the surface smoothing treatment,
The roll was kept in an oven kept at 80 ° C. for 48 hours to accelerate the crosslinking reaction by the isocyanate.

Magnetic layer 1 part by weight Barium ferrite 120 (Hc 7000e, variable particle size) Carbon black 30mμ 6 α-Al ₂ O ₃ powder (0.5μ granular) 2 Solvent (MEK / toluene 50/50) 100 The above composition in a ball mill For 3 hours to thoroughly wet the hexagonal plate-shaped barium ferrite.

Next, vinyl chloride-vinyl acetate-vinyl alcohol copolymer (containing maleic acid) molecular weight 40,000 6 parts (converted to solid content) Acrylic double bond-introduced vinyl chloride / vinyl acetate copolymer (containing maleic acid) molecular weight 20,000 12 parts (solid type) Minute conversion) Acrylic double bond introduction polyether urethane elastomer Molecular weight 40,0
00 9 parts (in terms of solid content) Pentaerythritol triacrylate 3 parts Solvent (MEK / toluene 50/50) 200 parts Stearic acid 4 parts Butyl stearate 2 parts A mixture of binders is thoroughly mixed and dissolved.

This is put into a ball mill that has been previously treated with magnetic powder, and dispersed again for 42 hours.

The magnetic coating material thus obtained was applied onto the undercoat layer and vertically aligned while being dried on a permanent magnet (3000 gauss), and then the solvent was continuously dried with an infrared lamp or hot air ( These may be used together at the same time), and after surface smoothing treatment, using an ESI electron curtain type electron beam accelerator, accelerating voltage 150K
The coating film was cured by irradiating it with an electron beam under an N ₂ atmosphere under the conditions of eV, electrode current 20 mA, and total irradiation amount 5 Mrad. The film thickness after curing was 1.5 μm for the magnetic layer. The film thickness was measured with an electronic micrometer. These coating films were formed on both sides of the film to give a double-sided coat.

Table 1 shows the durability running properties of the thus-prepared sample at each Young's modulus (E ′) of the undercoat layer and at each Young's modulus (E ″) of the magnetic layer.

Example 2 Magnetic layer 2 (thermosetting magnetic layer) parts by weight Barium ferrite magnetic powder 120 (Table 1, Hc6500e) Graphitized carbon black 5 (# 4000B) α-Al ₂ O ₃ powder (0.5 μ powder) 2 Dispersant (sorbitan tristearate) 3 Solvent (MEK / toluene 50/50) 100 The above composition is mixed in a ball mill for 3 hours to wet the hexagonal plate-shaped barium ferrite well with the dispersant. Next, vinyl chloride vinyl acetate copolymer 15 (VAGH manufactured by Union Carbide) thermoplastic urethane resin 15 (Nipporan 3022 manufactured by Nippon Polyurethane Co.) Solvent (MEK / toluene 50/50) 200 Lubricant (higher fatty acid-modified silicone oil) The mixture of 3 is mixed well and dissolved.

This is put into a ball mill that has been previously treated with magnetic powder, and dispersed again for 42 hours. After the dispersion, 5 parts (in terms of solid content) of an isocyanate compound (Desmodur L manufactured by Bayer Co.) capable of reacting with a functional group mainly composed of a hydroxyl group of a binder in the magnetic paint and cross-linking the solid compound, were added to the ball mill-prepared paint in 20 minutes. Mixing was performed.

2.0μ of magnetic coating is applied onto a 75μm polyester film coated with undercoat layer 3 and vertically oriented while being dried on an alternating magnetic field (2000 gauss), and the solvent is dried with an infrared lamp or hot air, and then the surface After the smoothing treatment, the roll was kept in an oven kept at 80 ° C. for 48 hours to accelerate the crosslinking reaction by isocyanate. A double-sided floppy was produced.

Backcoat layer Weight part Carbon black 20 mμ 50 Acrylic modified vinyl chloride-vinyl acetate-vinyl alcohol copolymer (molecular weight 30,000) 40 Acrylic modified polyurethane elastomer (molecular weight 20,000)
40 Polyfunctional acrylate Molecular weight 1,000 20 Stearic acid 4 Butyl stearate 2 Mixed solvent (MIBK / toluene) 250 Next, it was applied on 11μ base (including the above back coat layer) and evaluated on 8m / m deck. The results are shown in Table 2. In Table 2, Examples 1-2, 1-4, and 1-7 are as shown in Table 1, and Examples 2-1, 2-2, and 2-3 are as follows. is there.

Example 2-1: In Example 2, the magnetic powder particle size is 0.05 μm, and the plate ratio is 3 /
The same as Example 2 except that it was set to 1.

Example 2-2: In Example 2, the particle size of the magnetic powder was 0.07 μm, and the plate ratio was 6 /.
I used one. The same as Example 2 except that the orientation is not oriented.

Example 2-3: The magnetic powder particle size in Example 2 was 0.11 μm, and the plate ratio was 35.
Same as Example 2 except that / 1 was set.

The undercoat layer 3 was used as the undercoat layer in Examples 2-1, 2-2, and 2-3.

Example 3 In Example 2, the barium ferrite magnetic powder particle size was adjusted to 0.05 (Hc70
(0) /0.11 (Hc650) = 1/1, except that the undercoat layer was changed to a mixed system and the undercoat layer was the undercoat layer 4.

Example 4 To Example 1 was added 2 parts of a dispersant (soybean oil refined lecithin),
It is the same except that the undercoat layer is the undercoat layer 2.

Comparative Examples 1, 2 and 3 As magnetic layers, Examples 1-1, 1-3 and 1-4 were used, and an undercoat layer 4 and an undercoat layer 5 (undercoat layer 3 were used.
Al ₂ O _{3 (} 26 parts by weight) is the same as 140 parts by weight and carbon black (50 parts by weight is the same as 60 parts by weight).

Comparative Example 4 The magnetic layer used in Examples 1-4 was without an undercoat.

In Table 1, the undercoat layer having a variable film thickness was subjected to coating surface processing so that the film thickness of the undercoat layer 1 was as shown in Table 1.

As shown in Table 1, Comparative Examples 1 to 3 have E ′ / E ″>
Therefore, the durability is worse than that of Comparative Example 1 without the undercoat layer. On the other hand, in the embodiment, E ′ / E ″ <1
It can be seen that it has excellent durability. It can be seen that the durability is improved by satisfying the condition of E '/ E "<1. In addition, the floppy disk having the Young's modulus of the magnetic layer of 9 × 10 ¹⁰ dyn / cm ² or more is 9 × 10 ¹⁰ dyn. It can be seen that it is better than that of / cm ² or less.The durability of the undercoat of 5μ or more is not different from that of 5μ. It is not preferable because there is no difference in effect.

As shown in Table ² , it can be seen that those having a surface hardness of 9 × 10 ¹⁰ dyn / cm ² or more have no magnetic surface scraping, and therefore have little dropout and are good.

As shown in Tables 1 and 2, Young's modulus (E ') of the magnetic layer
Is 9 × 10 ¹⁰ dyn / cm ² or more, it is possible to obtain a magnetic recording medium excellent in durability running property. The Young's modulus in the above range can be obtained by selecting the plate ratio of the magnetic powder, the dispersion method, the processing method and the like.

The undercoat layer contains carbon black as a measure against electric resistance, and the electric resistance of the entire magnetic layer is 5 × 10 ⁹
Ω / cm ² (floppy electric resistance standard) or less, and a good error rate for floppy disks, 8 m / m
So dropout is good.

EFFECT OF THE INVENTION Using hexagonal plate-like ferrite magnetic powder in the magnetic recording layer, the ratio of the Young's modulus (E ′) of the conductive undercoat to the Young's modulus (E ″) of the conductive layer is E ′ / E ″ < By setting the value to 1, the durability running property can be remarkably improved, and a practically excellent magnetic recording medium without sticking of the head can be obtained.

Claims (4)

[Claims] 1. A magnetic recording medium having a coating type magnetic recording layer provided on a non-magnetic substrate, wherein hexagonal tabular ferrite magnetic powder is used for the magnetic recording layer, and Young's modulus (E ') of the conductive undercoat is used. And the Young's modulus (E ″) of the magnetic layer is E ′ / E ″
A magnetic recording medium having <1. 2. The Young's modulus (E ″) of the magnetic layer is 9 × 10 ¹⁰ dyn /
The magnetic recording medium according to claim 1, wherein the magnetic recording medium is at least cm ² . 3. The hexagonal plate-shaped ferrite magnetic powder is barium ferrite magnetic powder, as claimed in claim 1 or 2.
A magnetic recording medium according to the item. 4. The magnetic recording medium according to claim 1, 2, or 3, wherein the magnetic recording medium is a floppy disk.