JP2001338413A - Magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a smooth magnetic recording medium having very superior electromagnetic transducing characteristics and running durability, retaining high output and ensuring a low error rate. SOLUTION: The magnetic recording medium is obtained by disposing an under layer containing a nonmagnetic powder and a binder on a nonmagnetic base and one or more magnetic layers containing a ferromagnetic metal powder having 0.01-0.10 μm average major axis size and 80-180 Å crystallite size or a ferromagnetic hexagonal ferrite powder having 5-40 nm average plate diameter and a binder on the under layer, the thickness of the magnetic layers is 0.01-0.5 μm and a polyester resin having a diphenylmethane skeleton and a polar group and/or a polyurethane resin obtained from the polyester resin is contained as the binder in the magnetic layers.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a magnetic recording medium having a lower layer containing a non-magnetic powder and a binder on a non-magnetic support, and further having a magnetic layer on the lower layer. The present invention relates to a magnetic recording medium having extremely excellent electromagnetic conversion characteristics and running durability, including a polyester resin having a polar group and / or a polyurethane resin obtained from the polyester resin.

[0002]

2. Description of the Related Art The following are known as magnetic recording media containing a polyurethane resin having a polar group in a magnetic layer. The magnetic recording medium described in JP-A-54-157603 is characterized by using a polyurethane resin having a metal sulfonic acid salt of 10 to 2000 equivalent / 10 ⁶ g per resin as a binder for the magnetic layer. Japanese Patent Application Laid-Open No. 54-157603 describes that a polyester polyol is preferable as a polyhydroxy compound to be combined with a polyisocyanate, and many carboxylic acid components and glycol components constituting the polyester polyol are exemplified. The compounds are not described in any of them.

[0003] A magnetic recording medium described in JP-A-8-293115 is a polyether polyurethane comprising a short-chain diol having a cyclic structure, a long-chain diol having a defined ether group content, and an organic diisocyanate as a binder for a magnetic layer. It is characterized by using a resin. JP-A-8-293115 exemplifies specific structures of a short-chain diol having a cyclic structure and a long-chain diol having a prescribed amount of ether groups, but any compound having a diphenylmethane skeleton as a polyol component is described. It has not been.

[0004] The polyol component in the polyurethane resin described in JP-A-54-157603 and JP-A-8-293115 does not contain a diphenylmethane skeleton, and diphenylmethane diisocyanate is used as an organic diisocyanate for polyurethane synthesis. Only in this case are diphenylmethane skeletons derived from organic diisocyanates introduced. When trying to secure the diphenylmethane skeleton content necessary for improving dispersibility with diphenylmethane diisocyanate, the urethane group concentration becomes abnormally high, solvent solubility deteriorates due to urethane group cohesion, paint viscosity rises, and conversely dispersion occurs. Is reduced.

The magnetic recording medium described in JP-A-56-74824 contains a copolymerized polyester resin having a sulfonic acid metal base as a magnetic layer binder, a urethane prepolymer, and a trifunctional low molecular weight isocyanate compound. It is characterized by: JP-A-56-74824 exemplifies a carboxylic acid component and a glycol component constituting polyester, but does not describe any compound having a diphenylmethane skeleton. Attempting to achieve the dispersibility required for the ultrafine magnetic particles used in recent magnetic recording media and the non-magnetic powder in the lower layer using only the metal sulfonate base results in an abnormally high metal sulfonate concentration, Deterioration in solubility and increase in paint viscosity are observed, and conversely, dispersibility decreases.

Further, the average major axis length of the magnetic material is not described except for Japanese Patent Application Laid-Open No. 8-293115 (0.12 μm). The effect of dispersibility of the fine ferromagnetic metal powder having an average major axis length of 0.1 μm or less and the fine ferromagnetic hexagonal ferrite powder having an average plate diameter of 40 nm or less is insufficient. Or the surface properties of the medium cannot be secured.

[0007]

An object of the present invention is to provide a lower layer containing a non-magnetic powder and a binder on a non-magnetic support, and further comprising a ferromagnetic fine powder and a binder thereon. It is an object of the present invention to provide a magnetic recording medium having extremely excellent electromagnetic conversion characteristics and running durability.

Specifically, the object of the present invention is as follows:
An object of the present invention is to provide a magnetic recording medium which maintains a high output, is smooth, and has a low error rate.

Specifically, an object of the present invention is to provide a lower layer containing a non-magnetic powder on a non-magnetic support, and further provide a ferromagnetic metal fine powder having an average major axis length of 0.1 μm or less thereon. Alternatively, a magnetic layer containing a ferromagnetic hexagonal ferrite fine powder having an average plate diameter of 40 nm or less and a thickness of 0.5 μm or less is provided, and a polyester resin containing a diphenylmethane skeleton and a polar group as a binder for the magnetic layer and / or the polyester An object of the present invention is to provide the following magnetic recording medium by using a polyurethane resin obtained from a resin. A magnetic recording medium in which the ferromagnetic powder used in the magnetic layer has high dispersibility and excellent electromagnetic conversion characteristics. A magnetic recording medium with excellent magnetic layer smoothness and electromagnetic conversion characteristics. A magnetic recording medium with less running of the magnetic layer and less contamination of the head, and excellent running durability. A magnetic recording medium with excellent storage properties under high temperature and high humidity.

[0010]

According to the present invention, a lower layer containing a non-magnetic powder and a binder is provided on a non-magnetic support, on which an average major axis length of 0.01 μm to 0.10 μm and a crystallite size of 80-180 ° ferromagnetic metal powder or average plate diameter 5n
at least one magnetic layer containing a ferromagnetic hexagonal ferrite powder having a thickness of from about 40 nm to about 40 nm and a binder, wherein the thickness of the magnetic layer is from 0.01 μm to 0.5 μm, and a diphenylmethane skeleton is used as a binder of the magnetic layer. And a polyester resin having a polar group and / or a polyurethane resin obtained from the polyester resin.

In the present invention, the following aspects are preferable. 1. When the magnetic layer contains a ferromagnetic metal powder, the magnetic layer has a thickness of 0.01 to 0.1 μm. 2. When the magnetic layer contains ferromagnetic hexagonal ferrite powder, the magnetic layer has a thickness of 0.01 to 0.2 μm. 3. The ferromagnetic metal powder contains Fe as a main component, 10 to 40 at% of Co, 2 to 20 at% of Al,
Y is contained at 1 to 15 atomic%, and coercive force is 2000 to 300
0 Oersted (Oe) (160-240 kA / m)
And a saturation magnetic flux density of 150 to 300 mT. 4. The coercive force of the ferromagnetic hexagonal ferrite powder is 2000
A magnetic recording medium characterized by being hexagonal barium ferrite having a saturation magnetic flux density of 150 to 300 mT at 〜3000 Oe (160 to 240 kA / m). 5. A magnetic recording medium comprising, in the lower layer, a polyester resin having the diphenylmethane skeleton and a polar group and / or a polyurethane resin obtained from the polyester resin. 6. A magnetic recording medium, wherein the magnetic recording medium is a magnetic disk or a magnetic tape for digital signal recording applied to a recording / reproducing system equipped with an MR reproducing head.

[0012]

DETAILED DESCRIPTION OF THE INVENTION Binder [Polyester resin and polyurethane resin obtained from the polyester resin] In the magnetic recording medium of the present invention,
As the binder for forming the magnetic layer and, if necessary, the lower layer, a polyester resin having a diphenylmethane skeleton and a polar group and / or a polyurethane resin obtained from the polyester resin is used. Polyester resins are obtained by polycondensation of dihydric alcohols and dibasic acids, and polyurethane resins can be produced from the polyester resins and polyisocyanates.

In the present invention, the diphenylmethane skeleton refers to a structure represented by the following general formula, wherein the benzene ring is an alkyl group such as a methyl group, an ethyl group or a butyl group; a methoxy group;
It may be substituted with an alkoxy group such as an ethoxy group; a halogen group such as Cl or Br.

[0014]

Embedded image

In order to introduce a diphenylmethane skeleton into the polyester resin, for example, a dihydric alcohol having a diphenylmethane skeleton may be used when producing the polyester resin. Specific examples of the dihydric alcohol having a diphenylmethane skeleton include bisphenol F, tetramethylbisphenol F, 4,4′-methylenebis (2,
6-di-tert-butylphenol), 2,2′-methylenebis (4-methyl-6-tert-butylphenol), 2,2′-methylenebis (4,6-di-ter
t-butylphenol), 2,2′-methylenebis (p
-Cresol), or their ethylene oxide adducts, propylene oxide adducts, and the like.

The dihydric alcohol other than the dihydric alcohol having a diphenylmethane skeleton used for producing the polyester resin includes ethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butane. Diol, 1,5-pentanediol, 1,6-hexanediol, neopentyl glycol, diethylene glycol, dipropylene glycol,
2,2,4-trimethyl-1,3-pentanediol,
Examples thereof include 1,4-cyclohexanedimethanol, an ethylene oxide adduct of bisphenol A, an ethylene oxide adduct and a propylene oxide adduct of hydrogenated bisphenol A, polyethylene glycol, polypropylene glycol, and polytetramethylene glycol. Further, tri- and tetraols such as trimethylolethane, trimethylolpropane, glycerin and pentaerythritol may be used in combination.

The dibasic acids used for producing the polyester resin include aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, orthophthalic acid and 1,5-naphthalic acid, succinic acid, adipic acid, azelaic acid, and the like. Aliphatic dicarboxylic acids such as sebacic acid and dodecanedicarboxylic acid can be mentioned, and if necessary, aromatic oxycarboxylic acids such as p-oxybenzoic acid and p- (hydroxyethoxy) benzoic acid, trimellitic acid, trimesic acid, Tri and tetracarboxylic acids such as pyromellitic acid may be used in combination. As the dibasic acid, especially terephthalic acid,
Isophthalic acid is preferred.

The diphenylmethane skeleton unit is 50 ×
^{10 -5 eq / g~200 × 10 -5} eq / g are preferred.
If it is less than 50 × 10 ⁻⁵ eq / g, no effect on dispersibility can be obtained. If it exceeds 200 × 10 ⁻⁵ eq / g, the solubility of the resin in organic solvents such as ketones and esters is hindered.

The polar group in the present invention is not particularly limited as long as it has a function of improving the dispersibility of ferromagnetic fine powder and the like. As the polar _group, -SO 3 _M, -PO (O
M) ₂ , —COOM (M represents a hydrogen atom, an alkali metal or ammonium), an amino group, and a quaternary ammonium base are preferred, and among them, —SO ₃ M is particularly preferred because of its excellent dispersibility.

In order to introduce -SO ₃ M into the polyester resin, for example, when producing the polyester resin, -SO ₃ M
Carboxylic acids having ₃ M may be used together. -SO ₃ that can be used to introduce a -SO ₃ M in the polyester resin
Examples of the carboxylic acid containing M include 5-sodium sulfoisophthalic acid, 5-potassium sulfoisophthalic acid, 5-sulfoisophthalic acid, 2-sodium sulfoterephthalic acid, 2-potassium sulfoterephthalic acid, 2-sulfoterephthalic acid and the like. And the like. In addition to these representative compounds, both shall apply organic acids previously exemplified as the carboxylic acid is an organic acid having a -SO ₃ M can be used, also sulfo (iso or tele) phthalate (N
EO (ethylene oxide) adduct of may also be) in a or K salt, PO (propylene oxide) adduct, EO adducts of sulfamic acids such as aminoethane sulphonic acid, the -SO ₃ M polyhydric alcohol PO adducts It is also possible to use the introduced compound.

The polar group content is 1 × 10^-6~ 50 × 10^-Five
eq / g, more preferably 5 × 10 ^-6~ 20 × 10^-Fivee
q / g-resins are preferred. 1 × 10^-6less than eq / g
No effect, 50 × 10^-FiveIf eq / g is exceeded, paint
Viscosity increases and workability deteriorates significantly, making handling difficult.
Become.

The polyisocyanate used for forming the polyurethane resin by reacting with the above polyester resin is not particularly limited, and those generally used can be used. For example, hexamethylene diisocyanate, tolidine diisocyanate, isophorone diisocyanate, 1,3-xylylene diisocyanate, 1,4-xylylene diisocyanate, cyclohexane diisocyanate, toluidine diisocyanate,
2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, p-phenylene diisocyanate, m-phenylene diisocyanate, 1,5-naphthalene diisocyanate, 3,3-dimethylphenylene diisocyanate, etc. Can be mentioned. Among them, 4,4′-diphenylmethane diisocyanate, 2,4-tolylene diisocyanate, and 2,6-tolylene diisocyanate are preferred.

In the magnetic layer and, if necessary, the lower layer of the present invention, the polyester resin having a diphenylmethane skeleton and a polar group and / or the polyurethane resin obtained from the polyester resin may be a ferromagnetic powder or a non-magnetic powder having a mass of 100%. It is preferable that the content is contained in the range of 40 to 240 parts by mass with respect to parts. In particular, by setting the content within the range of 60 to 220 parts by mass, a phenomenon such as an increase in the glossiness of the surface of the magnetic layer or the lower layer appears, and the dispersion state of the ferromagnetic powder or the nonmagnetic powder is good. It can be seen that it is. Further, the content is 80 to 20
By setting the amount within the range of 0 parts by mass, the electromagnetic conversion characteristics are significantly improved. If the content is less than 40 parts by mass, the ferromagnetic powder or non-magnetic powder is not bonded, powder falling occurs, and even if more than 200 parts by mass is blended,
The state of dispersion of the ferromagnetic powder or the non-magnetic powder does not improve any more, and the magnetic layer may have a reduced degree of filling of the ferromagnetic powder and the electromagnetic conversion characteristics may be reduced.

[Other Resins] In the present invention, other resins may be used as a binder together with the polyester resin and / or the polyurethane resin. Other resins that can be used in combination are not particularly limited, and vinyl chloride, vinylidene chloride, (meth) acrylate ester, acrylonitrile, styrene, ethylene, vinyl butyral, vinyl acetal, which have been conventionally used as a binder,
Thermosetting resins such as thermoplastic resins such as polymers containing vinyl ether and butadiene as constituent units, phenolic resins, phenoxy resins, epoxy resins, urea resins, melamine resins, alkyd resins, formaldehyde resins, silicone resins, epoxy-polyamide resins, etc. Resins, reactive resins and mixtures thereof can be used in combination. Other resins may or may not have polar groups introduced,
Particularly preferred are polar group-containing vinyl copolymers and / or polar group-containing polyurethane resins.

The vinyl copolymerizable monomers usable in the polar group-containing vinyl copolymer include vinyl chloride, vinylidene chloride; methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, and butyl. (Meth) acrylate, isobutyl (meth) acrylate, pentyl (meth) acrylate, hexyl (meth) acrylate, octyl (meth) acrylate, 2
-Ethylhexyl (meth) acrylate, lauryl (meth) acrylate, stearyl (meth) acrylate,
Alkyl (meth) acrylates such as cyclohexyl (meth) acrylate; glycidyl (meth) acrylate; alkoxyalkyl (meth) acrylates such as methoxyethyl (meth) acrylate and butoxyethyl (meth) acrylate; benzyl (meth) acrylate;
(Meth) acrylates having a benzene ring such as phenoxyethyl (meth) acrylate, phenoxypolyethylene glycol (meth) acrylate, and nonylphenol ethylene oxide adduct (meth) acrylate;
(Meth) acrylamide, diacetone (meth) acrylamide, N-methylol (meth) acrylamide, N
-Methoxymethyl (meth) acrylamide, N-ethoxymethyl (meth) acrylamide, N-butoxymethyl (meth) acrylamide, dimethylaminopropyl (meth) acrylamide, dimethylaminomethyl (meth) acrylate, dimethylaminoethyl (meth) acrylate, Diethylaminomethyl (meth) acrylate, diethylaminoethyl (meth) acrylate, dimethylaminopropyl (meth) acrylate, (meth) acryloyl morpholine, morpholinoethyl (meth) acrylate, N-vinyloxazolidone, N-vinyl-2-pyrrolidone, N- Vinyl carbazole, 2-vinyl-4,6
-Diamino-5-triazine, 2-vinylpyridine, 4
-Radical polymerizable monomers having nitrogen, such as -vinylpyridine, maleimide, N-phenylmaleimide, and acrylonitrile; allyl glycidyl ether, methyl vinyl ether, ethyl vinyl ether, isobutyl vinyl ether, n-butyl vinyl ether, 2-ethylhexyl vinyl ether, n- Examples thereof include alkyl vinyl ethers such as octyl vinyl ether, lauryl vinyl ether, cetyl vinyl ether, and stearyl vinyl ether; vinyl esters such as vinyl acetate and vinyl propionate; and copolymerizable monomers such as maleic anhydride (anhydride). These monomers may be used alone or in combination of two or more. Here, (meth) acrylate is a general term for acrylate and methacrylate.

Examples of the method for introducing a polar group into a polar group-containing vinyl copolymer used in the present invention include the following methods. A method of polymerizing a vinyl copolymer containing no polar group and adding the polar group to the vinyl copolymer by a reaction. For example, as a method for introducing —SO ₃ M into a vinyl copolymer, first, a vinyl monomer and a copolymerizable monomer having a glycidyl group and, if necessary, another monomer copolymerizable therewith. The copolymer may be added to the copolymer by reacting it with a compound having —SO ₃ M and reacting with a glycidyl group, simultaneously with or after the copolymer is obtained. Examples of the copolymerizable monomer having a glycidyl group include glycidyl (meth) acrylate and glycidyl vinyl ether. Also, -SO ₃ M
As a compound having and reacting with a glycidyl group,
Sulfite and sodium sulfite, sodium bisulfite,
Sulfites such as potassium sulfite and ammonium sulfite,
Sulfuric acid and sodium hydrogen sulfate, potassium hydrogen sulfate, hydrogen sulfate such as ammonium hydrogen sulfate, taurine, sodium taurine, potassium taurine, ammonium taurine, sulfamic acid, sodium sulfamate, potassium sulfamate, ammonium sulfamate,
And aminosulfonic acids such as sulfanilic acid, sodium sulfanilate, potassium sulfanilate, and ammonium sulfanilate.

A method of copolymerizing a copolymerizable polar group-containing monomer. Examples of the copolymerizable monomer having —SO ₃ M include unsaturated hydrocarbon sulfones such as 2-acrylamido-2-methylpropanesulfonic acid, vinylsulfonic acid, (meth) acrylsulfonic acid, and p-styrenesulfonic acid. Examples thereof include acids and salts thereof, sulfoalkyl esters of (meth) acrylic acid such as sulfoethyl (meth) acrylate and sulfopropyl (meth) acrylate, and salts thereof.

In producing the copolymer, for example, a method of copolymerizing a monomer mixture using a polar group-containing radical polymerization initiator such as ammonium persulfate, potassium persulfate, and sodium persulfate.

A method of producing a copolymer by copolymerizing a monomer mixture in the presence of a chain transfer agent having a polar group at one end. Examples of the chain transfer agent having a polar group at one end include 2-chloroethanesulfonic acid, sodium 2-chloroethanesulfonate, 4-chlorophenylsulfoxide, 4-chlorobenzenesulfonamide, p-chlorobenzenesulfonate, and p-chlorobenzenesulfonate Halogenated compounds such as sodium, sodium 2-bromoethanesulfonate, sodium 4- (bromomethyl) benzenesulfonate, 2-mercaptoethanesulfonic acid (salt), 3-mercapto-1,2propanediol, mercaptoacetic acid (salt) 2-mercapto-5-benzimidazolesulfonic acid (salt), 3-mercapto-2
-Butanol, 2-mercaptobutanol, 3-mercapto-2-propanol, N- (2-mercaptopropyl) glycine, ammonium thioglycolate, and β-mercaptoethylamine hydrochloride.

The vinyl copolymer having a polar group includes:
It is preferable to have a hydroxyl group together with the —SO ₃ M group and the like. Examples of a method for introducing a hydroxyl group into the vinyl copolymer include a method of copolymerizing a copolymerizable monomer having a hydroxyl group. Examples of the copolymerizable monomer having a hydroxyl group include hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, polyethylene glycol mono (meth) acrylate, polypropylene glycol mono (meth) acrylate, and polyethylene glycol polypropylene glycol mono ( Hydroxyalkyl (meth) acrylates such as meth) acrylate, glycerol mono (meth) acrylate and 3-chloro-2-hydroxypropyl (meth) acrylate; vinyl ethers such as hydroxyethyl vinyl ether, hydroxypropyl vinyl ether and hydroxybutyl vinyl ether; Ethyl mono (meth) allyl ether, hydroxypropyl mono (meth) allyl ether, hydroxybutyl mono (meth) ) (Meth) allyl ethers such as allyl ether, diethylene glycol mono (meth) allyl ether, dipropylene glycol mono (meth) allyl ether, glycerin mono (meth) allyl ether, 3-chloro-2-hydroxypropyl (meth) allyl ether Kind,
(Meth) allyl alcohol and the like. Also, a hydroxyl group can be introduced by copolymerizing vinyl acetate, vinyl propionate, or the like, and performing a saponification reaction with a caustic alkali in a solvent.

The polar group-containing polyurethane resin used in the present invention can be produced from a polyol such as a polyester polyol, a polycarbonate polyol or a polyether polyol and a polyisocyanate.

The above polyester polyol is, for example,
Examples include those obtained by polycondensation of a dihydric alcohol and a dibasic acid, and those obtained by ring-opening polymerization of lactones such as caprolactone.

Examples of the dihydric alcohol include ethylene glycol, propylene glycol, butanediol,
Glycols such as 1,6-hexanediol and cyclohexanedimethanol, bisphenol A, hydrogenated bisphenol A, bisphenol S, bisphenol P and their ethylene oxide, propylene oxide adducts, cyclohexanedimethanol, cyclohexanediol,
Hydroquinone, bis (2-hydroxyethyl) tetrabromobisphenol A, bis (2-hydroxyethyl) tetrabromobisphenol S, bis (2-hydroxyethyl) tetramethylbisphenol S, bis (2
-Hydroxyethyl) diphenylbisphenol S, bis (2-hydroxyethyl) diphenylbiphenol,
Bis (2-hydroxyethyl) thiodiphenol, biphenol, bisphenol fluorene, bisphenol fluorene hydroxyethyl ether and the like can be exemplified.

Examples of the dibasic acid include adipic acid, pimelic acid, azelaic acid, sebacic acid, phthalic acid, terephthalic acid and the like.

As the polycarbonate polyol, for example, a polycarbonate polyol synthesized by condensation or transesterification of a polyhydric alcohol with phosgene, chloroformate, dialkyl carbonate or diallyl carbonate, or condensation of the polycarbonate polyol with a divalent carboxylic acid Can be mentioned.

Examples of the polyether polyols include, for example, polyethylene oxides such as bisphenol A, hydrogenated bisphenol A, bisphenol S and bisphenol P and / or adducts of polypropylene oxide, and polypropylenes such as polypropylene glycol, polyethylene glycol and polytetramethylene glycol. Ether polyols can be used.

The polyisocyanate used for forming the polyurethane by reacting with the above-mentioned polyol is not particularly limited, and those described above can be used.

As the chain extender, substances known per se,
Polyhydric alcohols, aliphatic polyamines, alicyclic polyamines, aromatic polyamines and the like can be used.

In order to introduce a polar group into the polyurethane resin used in combination in the present invention, the polyurethane resin can be produced from a polar group-containing polyol such as a polyester polyol, a polycarbonate polyol or a polyether polyol having a polar group and a diisocyanate. The polar group-containing polyol has a polar group in the main chain or side chain of the polyol, and can be introduced by the same compound / method as used for introducing a polar group into the polyester resin.

The glass transition temperature of the resin used as a binder in the present invention is preferably -100 to 150 ° C, more preferably 0 to 120 ° C. Also, the number average molecular weight is
1000 to 200,000 is preferred. More preferably, 1
000 to 100,000. If it is less than 1,000, the physical strength of the magnetic layer is reduced, for example, the magnetic layer becomes brittle, and the durability of the magnetic tape or the like is affected. If it exceeds 200,000, the viscosity of the paint at a predetermined concentration increases, the workability deteriorates remarkably, and the handling becomes difficult.

The amount of hydroxyl group of the resin used as a binder in the present invention is preferably from 2 to 40 per molecule, more preferably from 2 to 40, more preferably from 1 to 2 in terms of curability and durability. 3 to 20 pieces.

The resin used as a binder in the present invention is:
It is preferred to use up to 90% by weight in the binder.

It is also possible to use a polyisocyanate as a crosslinking agent in the binder to improve the abrasion resistance and the like of the magnetic layer. Examples of the polyisocyanate that can be used as a crosslinking agent include tolylene diisocyanate, 4,4 ′
Diisocyanates such as diphenylmethane diisocyanate, hexamethylene diisocyanate, xylylene diisocyanate, naphthylene-1,5-diisocyanate, o-toluidine diisocyanate, isophorone diisocyanate, triphenylmethane triisocyanate, and the formation of these isocyanates and polyalcohols Products, and polyisocyanates formed by condensation of isocyanates can be used.
Commercially available trade names of these isocyanates include Nippon Polyurethane Co., Ltd., Coronate L, Coronate HL, Coronate 2030, Coronate 2031, Millionate MR, Millionate MTL, Takeda Pharmaceutical Co., Ltd.
Takenate D-102, Takenate D-110N, Takenate D-200, Takenate D-202, manufactured by Sumitomo Bayer, Desmodur L, Desmodur IL, Desmodur N, Desmodur HL, etc. These are used alone. Alternatively, each layer can be used in combination of two or more utilizing the difference in curing reactivity.

II. Magnetic Material [Ferromagnetic Metal Powder] The ferromagnetic metal powder used in the present invention is not particularly limited as long as it is mainly composed of Fe (including an alloy). Ferromagnetic alloy powders are preferred. These ferromagnetic metal powders include Al, Si, S, Sc, Ca, Ti,
V, Cr, Cu, Y, Mo, Rh, Pd, Ag, Sn,
Sb, Te, Ba, Ta, W, Re, Au, Hg, P
b, Bi, La, Ce, Pr, Nd, P, Co, Mn,
It may contain atoms such as Zn, Ni, Sr, and B.
Al, Si, Ca, Y, Ba, La, Nd, Co, N
Preferably, at least one of i and B is contained other than α-Fe, and particularly preferably, Co, Al and Y are contained. More specifically, Co is 10 to 4
0 atomic%, Al is 2 to 20 atomic%, Y is 1 to 15 atomic%
Preferably it is included.

These ferromagnetic metal powders may be preliminarily treated with a dispersant, a lubricant, a surfactant, an antistatic agent and the like before dispersion before dispersion. Further, the ferromagnetic metal powder may contain a small amount of water, hydroxide or oxide. The water content of the ferromagnetic metal powder is 0.01
It is preferably set to ２2%. It is preferable to optimize the water content of the ferromagnetic powder depending on the type of the binder.

The crystallite size of the ferromagnetic metal powder is 80 to
180 °, preferably 100-180 °,
Particularly preferably, it is 120 to 160 °. When the crystallite size is less than 80 °, the demagnetization increases, and when the crystallite size exceeds 180 °, noise increases, and both are unsuitable. The crystallite size was determined by using an X-ray diffractometer (RINT2000 series manufactured by Rigaku Denki) and using a radiation source CuKα.
1. The average value obtained by the Scherrer method from the half width of the diffraction peak under the conditions of a tube voltage of 50 kV and a tube current of 300 mA was used.

The average major axis length of the ferromagnetic metal powder is 0.01
０．１0.10 μm, preferably 0.03 to 0.09
μm, and particularly preferably 0.05 to 0.08 μm. If the average major axis length is less than 0.01 μm, stable magnetization cannot be obtained due to thermal fluctuation, and the average major axis length is 0.10 μm.
If m exceeds m, noise increases, and all are unsuitable. The average major axis length is determined by taking a transmission electron microscope photograph and directly reading the minor axis length and the major axis length of the ferromagnetic metal powder from the photograph.

Ferromagnetic metal powder used in the magnetic layer of the present invention
The specific surface area (SBET) by the BET method is 30 m^Two
/ G or more 50m^Two/ G is preferred. Moreover 38 ~
48m ^Two/ G is preferred. Thereby, good surface properties and
Low noise compatibility can be achieved.

It is preferable that the pH of the ferromagnetic metal powder is optimized depending on the combination with the binder used. The range is usually 4 to 12, but preferably 7 to 10.
The ferromagnetic metal powder may be subjected to a surface treatment with Al, Si, P, or an oxide thereof, if necessary.
The amount is 0.1 to 10% with respect to the ferromagnetic metal powder.
00 mg / m ² or less, which is preferable. The ferromagnetic metal powder may contain soluble inorganic ions such as Na, Ca, Fe, Ni, and Sr, but if it is 200 ppm or less, there is little effect on the characteristics. The ferromagnetic metal powder used in the present invention preferably has a small number of vacancies, and its value is 20% by volume or less, more preferably 5% by volume or less.

The shape may be any of acicular, granular, rice granular or plate-like as long as the characteristics of the particle size described above are satisfied. In particular, acicular ferromagnetic metal powder should be used. Is preferred. In the case of the acicular ferromagnetic metal powder, the average acicular ratio (the arithmetic average of the acicular ratio (major axis length / minor axis length)) is preferably 4 or more and 12 or less, more preferably 5 or more and 12 or less.

The coercive force Hc of the ferromagnetic metal powder is preferably 2000 to 3000 Oe (160 to 240 kA / m).
And more preferably 2100 to 2900 Oe (17
0 to 230 kA / m), the saturation magnetic flux density is preferably
150 to 300 mT, more preferably 160 to 2 mT
90 mT. σs is preferably 140 to 170A
· M ² / kg, more preferably 145 to 160 A · m ² /
kg.

[Ferromagnetic hexagonal ferrite powder] Particularly when reproducing with a magnetoresistive head to increase the track density,
The ferromagnetic hexagonal ferrite powder used in the present invention needs to have low noise, and the average plate diameter is 40 nm. However, if the average plate diameter is less than 5 nm, stable magnetization cannot be expected due to thermal fluctuation. The preferred range of the average plate diameter is 10 nm to
35 nm, and a more preferable range of the average plate diameter is 15 nm.
nm to 30 nm.

The average tabular ratio {the arithmetic average of the plate ratio (plate diameter / plate thickness)} is preferably 1 to 15. More preferably 1 to 7
It is. When the average plate ratio is small, the filling property in the magnetic layer is increased, which is preferable, but sufficient orientation cannot be obtained. If it is larger than 15, noise increases due to stacking between particles. The specific surface area of the particle size range by the BET method is as follows:
10 to ²⁰⁰ m ² / g. The specific surface area generally corresponds to an arithmetic calculation value from the particle plate diameter and the plate thickness. Generally, the narrower the distribution of particle plate diameter and plate thickness, the better. Particle plate diameter and plate thickness are
500 particles are measured from a particle TEM photograph. The distribution is often not a normal distribution, but when calculated and expressed as a standard deviation with respect to the average size, σ / average size = 0.1 to 2.0. In order to sharpen the particle size distribution, the particle generation reaction system is made as uniform as possible, and the generated particles are subjected to a distribution improving treatment. For example, a method of selectively dissolving ultrafine particles in an acid solution is also known.

The coercive force Hc measured on the magnetic material is 500
It can be made up to about 5000 Oe (40 kA / m to 400 kA / m). A higher Hc is advantageous for high-density recording, but is limited by the capability of the recording head. In the present invention, Hc
Is preferably 2000 to 3000 Oe (160 to 24
0 kA / m), but more preferably 2200-200 kA / m).
It is 2800 Oe (175 to 220 kA / m). When the saturation magnetization of the head exceeds 1.4T, 2000 Oe
(160 kA / m) or more. Hc
Is the particle size (diameter and thickness), the type and amount of contained elements,
It can be controlled by the substitution site of the element, the particle generation reaction conditions and the like. Saturation magnetization σs ^{is, 40A · m 2 / kg~80A ·} m 2
/ Kg is preferred. σs is preferably higher, but tends to be smaller as the particles become finer. It is well known to combine spinel ferrite with magnetoplumbite ferrite to improve σs, and to select the type of element contained and the amount added, etc. It is also possible to use W-type hexagonal ferrite.

When dispersing the magnetic material, the surface of the magnetic material particles is also treated with a substance suitable for the dispersion medium and the polymer. As the surface treatment material, an inorganic compound or an organic compound is used. Typical examples of the main compound include compounds such as Si, Al, and P, various silane coupling agents, and various titanium coupling agents. The amount is 0.1 to 10 based on the magnetic material.
%. The pH of the magnetic material is also important for dispersion. Usually 4 ~
The optimum value is about 12 depending on the dispersion medium and the polymer, but about 6 to 11 is selected from the chemical stability and storage stability of the medium. Water contained in the magnetic material also affects dispersion. Dispersion medium,
There is an optimum value depending on the polymer, but usually 0.01 to 2.0%
Is selected.

The ferromagnetic hexagonal ferrite powder is prepared by mixing barium oxide, iron oxide, and a metal oxide to replace iron with boron oxide or the like as a glass-forming substance so as to have a desired ferrite composition, and then melting the mixture. A glass crystallization method in which a barium ferrite crystal powder is obtained by quenching to obtain an amorphous body, followed by reheating treatment, followed by washing and pulverization to obtain barium ferrite crystal powder. A hydrothermal reaction method in which a barium ferrite composition metal salt solution is neutralized with an alkali to remove by-products, heated in a liquid phase at 100 ° C. or higher, washed, dried, and pulverized to obtain barium ferrite crystal powder. A coprecipitation method in which a barium ferrite composition metal salt solution is neutralized with an alkali to remove by-products, dried, treated at 1100 ° C. or lower, and pulverized to obtain barium ferrite crystal powder. In the present invention, ferromagnetic hexagonal barium ferrite powder is particularly preferred.

III. Nonmagnetic Powder The magnetic recording medium of the present invention is provided with a lower layer containing a binder and a nonmagnetic powder on a support.

The nonmagnetic powder which can be used for the lower layer may be an inorganic substance or an organic substance. Further, carbon black or the like can be used. Examples of the inorganic substance include metals, metal oxides, metal carbonates, metal sulfates, metal nitrides, metal carbides, metal sulfides, and the like. Specifically, titanium oxide such as titanium dioxide, cerium oxide, tin oxide, tungsten oxide, ZnO, ZrO ₂ , SiO ₂ , Cr ₂ O ₃ , α
Α-alumina, β-alumina, γ with a conversion of 90 to 100%
-Alumina, α-iron oxide, goethite, corundum, silicon nitride, titanium carbide, magnesium oxide, boron nitride, molybdenum disulfide, copper oxide, MgCO ₃ , CaC
O ₃ , BaCO ₃ , SrCO ₃ , BaSO ₄ , silicon carbide, titanium carbide and the like are used alone or in combination of two or more. Preferred are α-iron oxide and titanium oxide.

The shape of the nonmagnetic powder may be any of acicular, spherical, polyhedral, and plate shapes. The crystallite size of the non-magnetic powder is preferably 0.004 μm to 1 μm, and 0.04 μm
To 0.1 μm is more preferable. If it is smaller than 0.004 μm, dispersion tends to be difficult. If it is larger than 1 μm, the surface roughness tends to increase.

The average particle size of these nonmagnetic powders is 0.00
The thickness is preferably from 5 to 2 μm, but if necessary, non-magnetic powders having different average particle diameters may be combined, or even a single non-magnetic powder may have the same effect by broadening the particle diameter distribution. Particularly preferred is 0.01 to 0.2 μm. 0.
If it is smaller than 005 μm, dispersion tends to be difficult, and if it is larger than 2 μm, the surface roughness tends to increase.

The specific surface area of the nonmagnetic powder is 1 to 100 m ^2.
/ G, preferably 5 to 70 m ² / g. And more preferably it is 10-65 m < ² > / g. 1m ² / g
If it is smaller, the surface roughness tends to be large, and if it is larger than 100 m ² / g, it tends to be difficult to disperse, for example, it is impossible to disperse with a desired amount of binder.

The oil absorption using dibutyl phthalate (DBP) is 5 to 100 ml / 100 g, preferably 10 to 100 ml / 100 g.
80 ml / 100 g, more preferably 20-60 ml /
100 g. Specific gravity is 1 to 12, preferably 3 to 6
It is.

The tap density is 0.05 to 2 g / ml, preferably 0.2 to 1.5 g / ml. 0.05g /
If it is smaller than ml, there is a tendency that the amount of scattered particles is large and the operation becomes difficult. If it is larger than 2 g / ml, it tends to stick to the device and the operation tends to be difficult.

The pH of the nonmagnetic powder is preferably from 2 to 11, but the pH is particularly preferably from 6 to 9. pH
Is smaller than 2, the coefficient of friction under high temperature and high humidity tends to increase. If the pH is higher than 11, the amount of released fatty acids tends to decrease, and the friction coefficient tends to increase.

The water content of the nonmagnetic powder is 0.1 to 5% by mass, preferably 0.2 to 3% by mass, more preferably 0.1 to 3% by mass.
3 to 1.5% by mass. If it is less than 0.1% by mass, dispersion tends to be difficult. If it is more than 5% by mass, the viscosity of the paint after dispersion tends to be unstable.

The loss on ignition is preferably 20% by mass or less, and the loss on ignition is preferably small.

When the nonmagnetic powder is an inorganic powder, the Mohs' hardness is preferably 4 or more and 10 or less. If the Mohs hardness is smaller than 4, durability tends to be insufficient.

The amount of stearic acid adsorbed on the non-magnetic powder ranges from 1 to
20 μmol / m ² , more preferably ^{2 to} 15 μmol
/ M ² .

The heat of wetting of the nonmagnetic powder in water at 25 ° C. is
200 erg / cm ^{2 to} 600 erg / cm ² (200 to
It is preferably in the range of 600 mJ / m ² ). Further, a solvent having a range of the heat of wetting can be used. The amount of water molecules on the surface at 100 to 400 ° C is 1 to 1
0 pieces / 100 ° is appropriate. PH of isoelectric point in water
Is preferably between 3 and 9.

The surface of these nonmagnetic powders is subjected to a surface treatment so that Al ₂ O ₃ , SiO ₂ , TiO ₂ , ZrO ₂ , S
Preferably, nO ₂ , Sb ₂ O ₃ and ZnO are present. Particularly preferred for dispersibility are Al ₂ O ₃ , SiO ₂ , T
iO ₂ and ZrO ₂ , more preferably Al ₂ O ₃ ,
SiO ₂ and ZrO ₂ . These may be used in combination or may be used alone. Further, a surface treatment layer coprecipitated may be used according to the purpose, or a method in which alumina is first present and silica is present in the surface layer, or the reverse method may be employed. Also, the surface treatment layer may be a porous layer depending on the purpose,
Homogeneous and dense are generally preferred.

Specific examples of the non-magnetic powder used for the lower layer of the present invention include Nanotight manufactured by Showa Denko, HIT-100 and ZA-G1 manufactured by Sumitomo Chemical, and DPN-2 manufactured by Toda Kogyo.
50, DPN-250BX, DPN-245, DPN-
270BX, DPB-550BX, DPN-550R
X, Titanium oxide manufactured by Ishihara Sangyo TTO-51B, TTO-5
5A, TTO-55B, TTO-55C, TTO-55
S, TTO-55D, SN-100, MJ-7, α-iron oxide E270, E271, E300, ST manufactured by Titanium Industry
T-4D, STT-30D, STT-30, STT-6
5C, Teika MT-100S, MT-100T, MT
-150W, MT-500B, MT-600B, MT-
100F, MT-500HD, FINEX-2 manufactured by Sakai Chemical
5, BF-1, BF-10, BF-20, ST-M, Dowa Mining DEFIC-Y, DEFIC-R, Nippon Aerosil AS2BM, TiO2P25, Ube Industries 100
A, 500A, Y-LOP manufactured by Titanium Kogyo Co., Ltd. and fired products thereof. Particularly preferred non-magnetic powders are titanium dioxide and α-iron oxide.

In the lower layer, carbon black is mixed with nonmagnetic powder to reduce the surface electric resistance (Rs), reduce the light transmittance, and obtain a desired micro-Vickers hardness. it can.

The micro Vickers hardness of the lower layer is usually
25 to 60 kg / mm ² (245 to 588 MPa), preferably 30 to 50 k
g / mm ² (294 to 490 MPa), and a ridge angle of 80 using a thin film hardness tester (NEC HMA-400).
It can be measured using a diamond triangular pyramid needle with a tip radius of 0.1 μm at the tip of the indenter. The light transmittance is standardized so that the absorption of infrared rays having a wavelength of about 900 nm is generally 3% or less, for example, 0.8% or less for a VHS magnetic tape. For this purpose, a furnace for rubber,
Thermal rubber, black for color, acetylene black and the like can be used.

[0074] The specific surface area of the carbon black used in the lower layer of the present invention is generally, 100 to 500 m ² / g, preferably from 150 to 400 m ² / g, DBP oil absorption, typically, 20 to 400 ml / 100 g, preferably 30-2
It is 00 ml / 100 g. The average particle size of the carbon black is 5 to 80 nm, preferably 10 to 50 nm, and more preferably 10 to 40 nm. The carbon black preferably has a pH of 2 to 10, a water content of 0.1 to 10%, and a tap density of 0.1 to 1 g / ml.

Specific examples of carbon black used in the present invention include BLACKPEAR manufactured by Cabot Corporation.
LS 2000, 1300, 1000, 900, 80
0, 880, 700, VULCAN XC-72, # 3050B, 3150B, 3250B, manufactured by Mitsubishi Kasei Kogyo Co., Ltd.
# 3750B, # 3950B, # 950, # 650B,
# 970B, # 850B, MA-600, CONDUCTEX SC, RAVEN 8 manufactured by Columbia Carbon Co.
800, 8000, 7000, 5750, 5250, 3
500, 2100, 2000, 1800, 1500, 1
255, 1250, Akzo Ketjen Black E
C and the like. Carbon black may be used after being surface-treated with a dispersant or the like or grafted with a resin, or may be used after a part of the surface is graphitized. Further, the carbon black may be dispersed in a binder before adding it to the paint. These carbon blacks can be used in a range not exceeding 50% by mass and not exceeding 40% of the total mass of the lower layer based on the inorganic powder. These carbon blacks can be used alone or in combination. The carbon black that can be used in the lower layer of the present invention can be referred to, for example, "Carbon Black Handbook" edited by Carbon Black Association.

An organic powder may be added to the lower layer according to the purpose. For example, acrylic / styrene-based resin powder, benzoguanamine resin powder, melamine-based resin powder, phthalocyanine-based pigment may be mentioned, but polyolefin-based resin powder, polyester-based resin powder, polyamide-based resin powder, polyimide-based resin powder, and polyfluoroethylene resin Can also be used.

IV. Other Additives In the magnetic recording medium of the present invention, additives for imparting a dispersing effect, a lubricating effect, an antistatic effect, a plasticizing effect, and the like may be used in the magnetic layer or the lower layer. These additives include molybdenum disulfide, tungsten disulfide, graphite, boron nitride, graphite fluoride, silicone oil, polar group-containing silicone, fatty acid-modified silicone,
Fluorine-containing silicone, fluorine-containing alcohol, fluorine-containing ester, polyolefin, polyglycol, polyphenylether, phenylphosphonic acid, benzylphosphonic acid, phenethylphosphonic acid, α-methylbenzylphosphonic acid, 1-methyl-1-phenethylphosphonic acid, Diphenylmethylphosphonic acid, biphenylphosphonic acid, benzylphenylphosphonic acid, α-cumylphosphonic acid, toluylphosphonic acid, xylylphosphonic acid, ethylphenylphosphonic acid, cumenylphosphonic acid, propylphenylphosphonic acid, butylphenylphosphonic acid, heptylphenylphosphonic acid, Benzene ring-containing organic phosphonic acids such as octylphenylphosphonic acid and nonylphenylphosphonic acid and alkali metal salts thereof, octylphosphonic acid, 2-
Ethylhexylphosphonic acid, isooctylphosphonic acid,
(Iso) nonylphosphonic acid, (iso) decylphosphonic acid, (iso) undecylphosphonic acid, (iso) dodecylphosphonic acid, (iso) hexadecylphosphonic acid, (iso) octadecylphosphonic acid, (iso) eicosylphosphon Alkylphosphonic acids such as acids and alkali metal salts thereof, phenyl phosphate, benzyl phosphate, phenethyl phosphate, α-methylbenzyl phosphate, 1-methyl-1-phenethyl phosphate, diphenylmethyl phosphate, biphenyl phosphate, benzylphenyl phosphate, α-phosphate Aromatic phosphates such as cumyl, toluyl phosphate, xylyl phosphate, ethylphenyl phosphate, cumenyl phosphate, propylphenyl phosphate, butylphenyl phosphate, heptylphenyl phosphate, octylphenyl phosphate, nonylphenyl phosphate and the like, and alkali metal salts thereof, octyl phosphate, phosphoric acid 2-ethyl Hexyl, isooctyl phosphate,
(Iso) nonyl phosphate, (iso) decyl phosphate, (iso) undecyl phosphate, (iso) dodecyl phosphate, phosphoric acid (iso)
Alkyl phosphates such as hexadecyl, (iso) octadecyl phosphate and (iso) eicosyl phosphate and their alkali metal salts, alkyl sulfonates and their alkali metal salts, fluorine-containing alkyl sulfates and their alkali metal salts, lauric acid, myristic acid Monobasic which may contain or have an unsaturated bond having 10 to 24 carbon atoms, such as palmitic acid, stearic acid, behenic acid, butyl stearate, oleic acid, linoleic acid, linolenic acid, elaidic acid and erucic acid Fatty acids and their metal salts, or butyl stearate, octyl stearate, amyl stearate, isooctyl stearate, octyl myristate, butyl laurate, butoxyethyl stearate, anhydrosorbitan monostearate, ammonium hydroxide Nitroso ruby Tanji stearate, carbon atoms, such as anhydrosorbitan tristearate 10
A monobasic fatty acid which may contain 24 unsaturated bonds or may be branched, and a mono- or hexahydric alcohol which may contain or branched an unsaturated bond having 2 to 22 carbon atoms, or 12 to 2 carbon atoms.
Mono-fatty acid ester, di-fatty acid ester or poly-fatty acid ester composed of any one of alkoxy alcohols or alkylene oxide polymer monoalkyl ethers which may or may contain two unsaturated bonds, having 2 to 22 carbon atoms Fatty acid amides and aliphatic amines having 8 to 22 carbon atoms can be used. In addition to the above hydrocarbon groups, nitro groups and F, Cl, Br, CF ₃ , CC
It may have an alkyl group, an aryl group, or an aralkyl group substituted by a group other than a hydrocarbon group such as a halogen-containing hydrocarbon such as l ₃ or CBr ₃ .

Nonionic surfactants such as alkylene oxides, glycerins, glycidols, and alkylphenol ethylene oxide adducts; cyclic amines;
Ester amides, quaternary ammonium salts, hydantoin derivatives, heterocycles, cationic surfactants such as phosphonium or sulfoniums, anionic surfactants containing acidic groups such as carboxylic acid, sulfonic acid, sulfate groups, amino acids , Aminosulfonic acids, sulfuric acid or phosphoric acid esters of aminoalcohols, and amphoteric surfactants such as alkyl betaine type can also be used. These surfactants are described in detail in "Surfactant Handbook" (published by Sangyo Tosho Co., Ltd.). These lubricants, antistatic agents, etc. are not necessarily pure,
Impurities such as unreacted products, by-products, decomposed products, and oxides may be contained. These impurities are preferably at most 30% by mass, more preferably at most 10% by mass.

Examples of these are Nippon Yushi Co., Ltd .: N
AA-102, castor oil hydrogenated fatty acid, NAA-42, cation SA, Nymeen L-201, Nonion E-20
8, Anon BF, Anon LG, manufactured by Takemoto Yushi: FAL-
205, FAL-123, manufactured by Nippon Rika Co., Ltd .: Nujielbu OL, manufactured by Shin-Etsu Chemical Co., Ltd .: TA-3, manufactured by Lion Armor Co .: Armide P, manufactured by Lion Co., Ltd., Duomin TDO,
Nisshin Oil Co., Ltd .: BA-41G, Sanyo Chemical Co., Ltd .: Profan 2012E, New Pole PE61, Ionnet MS
-400 and the like.

The type and amount of these dispersants, lubricants and surfactants used in the present invention can be selected as needed in the lower layer and the magnetic layer. For example, the dispersant is, of course, not limited to the examples shown here, but has the property of adsorbing or binding with a polar group, and is mainly on the surface of the ferromagnetic powder in the magnetic layer and in the lower layer. Adsorbed or bonded mainly to the surface of the non-magnetic powder with the polar group,
It is presumed that the dispersant once adsorbed is difficult to desorb from the surface of the metal or metal compound. Accordingly, since the surface of the ferromagnetic powder or non-magnetic powder of the present invention is in a state of being coated with an alkyl group, an aromatic group or the like, the affinity of the ferromagnetic powder or non-magnetic powder for the binder resin component is reduced. The dispersion stability of the ferromagnetic powder or the non-magnetic powder is also improved. In addition, since it exists in a free state as a lubricant, the bleeding to the surface is controlled by using fatty acids having different melting points in the lower layer and the magnetic layer, and the bleeding to the surface is controlled by using esters having different boiling points and polarities. , Improve the stability of coating by adjusting the amount of surfactant,
It is conceivable to increase the amount of lubricant added in the lower layer to improve the lubricating effect. Further, all or a part of the additives used in the present invention may be added in any step of producing a coating solution for the magnetic layer or the lower layer. For example, when mixing with a ferromagnetic powder before a kneading step, when adding in a kneading step with a ferromagnetic powder, a binder and a solvent, when adding in a dispersing step, when adding after dispersing, when adding just before coating, and the like. There is.

V. Support The coating solution prepared from the above materials is coated on a support to form a lower layer or a magnetic layer. As the support that can be used in the present invention, a known support such as biaxially stretched polyethylene terephthalate, polyethylene naphthalate, polyamide, polyimide, polyamideimide, aromatic polyamide, and polybenzoxdazole can be used. Preferred are polyethylene terephthalate, polyethylene naphthalate and aromatic polyamide. These supports may be subjected to corona discharge, plasma treatment, easy adhesion treatment, heat treatment, or the like in advance. Further, the support which can be used in the present invention has a center plane average surface roughness by the Mirau method of 0.2 mm at a cutoff value of 0.25 mm.
The surface preferably has excellent smoothness in the range of 1 to 20 nm, preferably 1 to 10 nm. Also,
These supports preferably have not only a small center line average surface roughness but also no coarse projections of 1 μ or more.

The arithmetic mean roughness of the obtained support is (R
a) [JIS B0660-1998, ISO 4
287-1997] is preferably 0.1 μm or less, since noise of the obtained magnetic recording medium is reduced.

The preferable thickness of the support in the magnetic recording medium of the present invention is preferably 3 to 80 μm.

VI. Backcoat layer and undercoat layer A backcoat layer (backing layer) may be provided on the surface of the support used in the present invention where the magnetic layer is not provided. The back coat layer was provided by applying a back coat layer forming paint in which a particulate component such as an abrasive and an antistatic agent and a binder were dispersed in an organic solvent on the surface of the support on which the magnetic layer was not provided. Layer. Various inorganic pigments and carbon black can be used as the particulate component, and resins such as nitrocellulose, phenoxy resin, vinyl chloride resin, and polyurethane can be used alone or as a mixture of these as a binder. . An adhesive layer may be provided on the surface of the support of the present invention on which the magnetic paint and the backcoat layer forming paint are applied.

In the magnetic recording medium of the present invention,
An undercoat layer may be provided. By providing the undercoat layer, the adhesive strength between the support and the magnetic layer or the lower layer can be improved. As the undercoat layer, a polyester resin soluble in a solvent is used. The undercoat layer has a thickness of 0.5
Those having a size of μm or less are used.

VII. Manufacturing Method The magnetic recording medium of the present invention is manufactured, for example, by applying a lower layer coating solution and a magnetic layer coating solution to the surface of a running support so as to have a predetermined thickness. Here, a plurality of magnetic layer coating solutions may be sequentially or simultaneously multi-layer coated,
The lower layer coating solution and the magnetic layer coating solution may be sequentially or simultaneously multi-layer coated. As a coating machine for applying the magnetic layer coating solution or the lower layer coating solution, air doctor coat, blade coat, rod coat, extrusion coat, air knife coat, squeeze coat, impregnation coat, reverse roll coat, transfer roll coat, gravure coat, Kiss coat, cast coat, spray coat, spin coat and the like can be used. For these, for example, "Latest Coating Technology" (May 31, 1983) published by Sogo Gijutsu Center can be referred to.

When applied to the magnetic recording medium of the present invention, the following can be proposed as an example of a coating apparatus and method. (1) First, a lower layer is applied by a coating apparatus such as gravure, roll, blade, or extrusion which is generally applied in the application of a magnetic layer coating liquid, and the lower layer is dried while the lower layer is in an undried state. No., JP-A-60-23
The upper layer is applied by a support pressure type extrusion coating apparatus as disclosed in JP-A-8179, JP-A-2-265672 and the like. (2) JP-A-63-88080, JP-A-2-1
No. 7971 and Japanese Unexamined Patent Publication No. 2-265672 disclose the upper and lower layers almost simultaneously by one coating head having two coating liquid passage slits. (3) The upper and lower layers are coated almost simultaneously by an extrusion coating device with a backup roll as disclosed in JP-A-2-174965.

The thickness of the magnetic layer of the magnetic recording medium according to the present invention depends on the saturation magnetization of the head used, the head gap length,
Optimized according to the recording signal bandwidth, 0.01-0.5μ
m, when the magnetic layer contains a ferromagnetic metal powder, the thickness of the magnetic layer is preferably 0.01 to 0.1 μm, and when the magnetic layer contains a ferromagnetic hexagonal ferrite powder, Is preferably 0.01 to 0.2 μm. The magnetic layer may be separated into two or more layers having different magnetic characteristics, and a known configuration relating to a multilayer magnetic layer can be applied. When a plurality of magnetic layers are provided, the thickness of the magnetic layer
It is the thickness of each magnetic layer.

To stably apply this ultrathin magnetic layer, a lower layer containing an inorganic powder is interposed on a support,
It is desirable to apply a magnetic layer thereon on a wet-on-wet basis.

In the case of a magnetic tape, the ferromagnetic powder contained in the coating layer of the magnetic layer coating solution is subjected to a magnetic field orientation treatment in the longitudinal direction using a cobalt magnet or solenoid. In the case of a disk, a sufficient isotropic orientation may be obtained even without orientation using an orientation device, but known random orientation such as alternately arranging cobalt magnets diagonally or applying an AC magnetic field with a solenoid. Preferably, an apparatus is used. In the case of ferromagnetic metal fine powder, isotropic orientation is generally preferably in-plane two-dimensional random,
Three-dimensional randomness can be obtained by adding a vertical component. In the case of ferromagnetic hexagonal ferrite powder, three-dimensional randomness in the in-plane and vertical directions generally tends to occur, but in-plane two-dimensional randomness is also possible. In addition, by using a known method such as a different-magnet opposed magnet and performing vertical alignment, it is also possible to impart isotropic magnetic characteristics in the circumferential direction.
In particular, when performing high-density recording, vertical alignment is preferable. In addition, circumferential orientation may be performed using spin coating.

It is preferable that the drying position of the coating film can be controlled by controlling the temperature, air volume, and coating speed of the drying air. The coating speed is 20 m / min to 1000 m / min, and the temperature of the drying air is 60 ° C. The above is preferred. Also, an appropriate preliminary drying can be performed before entering the magnet zone.

After being dried, the coating layer is subjected to a surface smoothing treatment. For the surface smoothing treatment, for example, a super calender roll or the like is used. By performing the surface smoothing treatment, pores generated by removing the solvent during drying disappear, and the filling ratio of the ferromagnetic powder in the magnetic layer is improved, so that a magnetic recording medium with high electromagnetic conversion characteristics can be obtained. Can be. For calendering rolls, epoxy, polyimide,
Heat-resistant plastic rolls such as polyamide and polyamide-imide can be used. Moreover, it can also process with a metal roll. The magnetic recording medium of the present invention has a surface M
The center plane average surface roughness by the irau method is 0.1 to 4 nm at a cutoff value of 0.25 mm, preferably 1 to 4 nm.
It is preferable that the surface has an extremely excellent smoothness in the range of 3 nm. As a method for this, for example, a magnetic layer formed by selecting a specific ferromagnetic powder and a binder as described above is subjected to the above calendering treatment. The calendering conditions are as follows: the temperature of the calender roll is in the range of 60 to 100 ° C., preferably 70 to 100 ° C., particularly preferably 80 to 100 ° C., and the pressure is 100 to 500 kg / cm (98 to 490 kN). / M)
, Preferably 200 to 450 kg / cm
(196 to 441 kN / m), particularly preferably 300 to 400 kg / cm (294 to 392 kN / m).
m). The obtained magnetic recording medium can be used after being cut into a desired size using a cutting machine or the like.

[0093]

EXAMPLES The present invention will be described below in detail with reference to examples, but the present invention is not limited to these examples. In the examples, “parts” indicates “parts by mass” unless otherwise specified.

Synthesis Example 1 Synthesis of Polyester Resin A In a polymerization vessel equipped with a stirrer, a condenser, a thermometer and a nitrogen gas inlet, 194 parts of dimethyl terephthalate, 176 parts of dimethyl isophthalate, and dimethyl 5-sodium sulfoisophthalate 28 Part, ethylene glycol 21
Part, 36 parts of neopentyl glycol, bisphenol F
427 parts of ethylene oxide 2 adduct, zinc acetate 0.
6 parts and sodium acetate 0.06 parts were charged, and after the replacement with nitrogen, transesterification and esterification were performed at 140 to 230 ° C. for 5 hours. Subsequently, the pressure inside the system was gradually reduced, and the excess glycol component was distilled off.
mmHg. And 0.2 mmHg at 250 ° C
After performing the polycondensation reaction for 0 minutes, the pressure was returned to normal pressure with nitrogen gas to obtain a polyester resin A. The diphenylmethane skeleton content was 170 × 10 ⁻⁵ eq / g, and the sodium sulfonate group content was 11 × 10 ⁻⁵ eq / g.

[Synthesis Examples 2 and 3] Synthesis of Polyester Resins B and c Polyester resins B and c were obtained in the same manner as in Synthesis Example 1 with the kinds and ratios of the compounds shown in Table 1.

[Synthesis Example 4] Synthesis of Polyester Polyurethane D Resin The polycondensation time after removing excess glycol by using the same apparatus and composition as in Example 1 was reduced to 40 minutes, and a polyester polyol having a weight average molecular weight of 1,000 was used. Obtained. Next, after replacing the reactor equipped with a stirrer, condenser, thermometer and nitrogen gas inlet with nitrogen, 560 parts of toluene, 560 parts of methyl ethyl ketone, 560 parts of cyclohexanone, 500 parts of the polyester polyol obtained above, and diphenylmethane 59 parts of diisocyanate and 0.5 part of dibutyltin dilaurate were charged, and a urethanization reaction was performed at 80 ° C. for 8 hours to obtain a polyester polyurethane resin D. The diphenylmethane skeleton content is 195 × 10 ⁻⁵ eq /
g, sodium sulfonate group content is 10 × 10 ⁻⁵ eq.
/ G.

[Synthesis Examples 5 and 6] Synthesis of Polyester Polyurethane Resins E and f Polyester polyurethane resins E and f were obtained in the same manner as in Synthesis Example 4 with the kinds and ratios of the compounds shown in Table 1.

[0098]

[Table 1]

Example 1 Preparation of Coating Solution for Magnetic Layer 100 parts of ferromagnetic needle-shaped metal powder Composition: Fe / Co / Al / Y = 68/20/7/5, Surface treatment layer: Al ₂ O ₃ , Y ₂ O ₃ , Hc: 2500 Oe (200 kA / m), crystallite size: 14 nm, average major axis length: 0.08 μm, average needle ratio: 6, BET specific surface area: 46 m ² / g, σs: 150 A · m ² / Kg Polyester resin A 18 parts Phenylphosphonic acid 3 parts α-Al ₂ O ₃ (average particle diameter: 0.15 μm) 2 parts Carbon black (average particle diameter: 20 nm) 2 parts Cyclohexanone 110 parts Methyl ethyl ketone 100 parts Toluene 100 parts Butyl Stearate 2 parts Stearic acid 1 part

Preparation of lower layer coating liquid Non-magnetic inorganic powder 85 parts α-iron oxide Surface treatment layer: Al ₂ O ₃ , SiO ₂ , average major axis length: 0.15 μm, tap density: 0.8, average needle ratio : 7, BET specific surface area: 52 m ² / g, pH 8, DBP oil absorption: 33 ml / 100 g Carbon black 20 parts DBP oil absorption: 120 ml / 100 g, pH: 8, BET specific surface area: 250 m ² / g, volatile matter: 1 0.5% Polyester resin A 18 parts Phenylphosphonic acid 3 parts α-Al ₂ O ₃ (average particle diameter: 0.2 μm) 1 part Cyclohexanone 140 parts Methyl ethyl ketone 170 parts Butyl stearate 2 parts Stearic acid 1 part

Each of the magnetic layer coating solution and the lower layer coating solution was kneaded with an open kneader for 60 minutes, and then dispersed in a sand mill for 120 minutes. To the obtained dispersion, 6 parts of a trifunctional low-molecular-weight polyisocyanate compound (Coronate 3041 manufactured by Nippon Polyurethane) is added, and the mixture is further stirred and mixed for 20 minutes. A liquid and a lower layer coating liquid were prepared.

The lower layer coating solution was applied on a polyethylene terephthalate support having a thickness of 6 μm and a center surface roughness of 5 nm so that the thickness after drying was 1.8 μm, and immediately thereafter, the magnetic layer coating solution was applied. The thickness after drying is 0.08 μm
At the same time. In a state where both layers are not dried, a magnetic field orientation is performed with a magnet of 300 mT, and further dried,
A 7-stage calender consisting of metal rolls only, with a speed of 100 m / min and a linear pressure of 300 kg / cm (294 kN
/ M) after performing a surface smoothing treatment at a temperature of 90 ° C.
A heat curing treatment was performed at 0 ° C. for 24 hours, and a slit was made into a 3.8 mm width to prepare a magnetic tape.

[Examples 2 to 4] Polyester resins are shown in Table 2.
And the magnetic tapes of Examples 2 to 4 were prepared in the same manner as in Example 1.

[Comparative Examples 1 to 4] Magnetic tapes of Comparative Examples 1 to 4 were prepared in the same manner as in Example 1 except that the polyester resin and the magnetic material were changed as shown in Table 2.

Example 5 The floppy (registered trademark) disk of Example 5 was prepared by changing the magnetic material as described below. Preparation of Magnetic Layer Coating Solution Ferromagnetic plate-like hexagonal ferrite powder 100 parts Composition (molar ratio): Ba / Fe / Co / Zn = 1 / 9.1 / 0.2 / 0.8, Hc: 2450 Oe (195 kA / m), average plate diameter: 26 nm, average plate ratio: 4, BET specific surface area: 50 m ² / g, σs: 60 Am ² / kg 18 parts of polyester resin A 3 parts of phenylphosphonic acid α-Al ₂ O ₃ ( 2 parts carbon black (average particle diameter: 20 nm) 2 parts cyclohexanone 110 parts methyl ethyl ketone 100 parts toluene 100 parts butyl stearate 2 parts stearic acid 1 part

A magnetic layer coating solution was prepared in the same manner as in Example 1 using each component of the magnetic layer coating solution.

Further, on a polyethylene terephthalate support having a thickness of 62 μm and a center plane average surface roughness of 5 nm,
The thickness after drying of the same lower layer coating solution as in Example 1 is 1.5 μm.
m, and immediately thereafter, the above-mentioned magnetic layer coating solution is simultaneously coated with a multilayer so that the thickness after drying becomes 0.12 μm. While both layers are still in a wet state, the frequency is 50 Hz, Magnetic field strength 25 mT and frequency 50 Hz,
Two magnetic field strengths of 12 mT are passed through an AC magnetic field generator to perform a random orientation process. After drying, the film is dried at a temperature of 90 ° C. and a linear pressure of 300 kg / cm (294 k
N / m), punched out to 3.7 inches, polished the surface, placed in a 3.7-inch Zip-disk cartridge with a liner installed inside, and added predetermined mechanical parts Then, a 3.7 inch floppy disk was obtained.

[Examples 6 to 8] Polyester resins are shown in Table 3.
The floppy disks of Examples 6 to 8 were prepared in the same manner as in Example 5, except that the above-mentioned conditions were changed.

Comparative Example 5 A floppy disk of Comparative Example 5 was prepared in the same manner as in Example 15 except that the polyester resin and the magnetic material were changed as shown in Table 3.

[Measurement method] Magnetic properties (Hc): Vibration sample type magnetometer (manufactured by Toei Kogyo Co., Ltd.)
And measured at Hm10 kOe (800 kA / m).

Magnetic layer thickness: A magnetic recording medium was cut out to a thickness of about 0.1 μm with a diamond cutter along the longitudinal direction, and a transmission electron microscope was used to magnify 10,000 to 1,000 times.
The photograph was observed at a magnification of 00, preferably 20,000 to 50,000, and photographed. Photo print size is A
4-A5. Thereafter, the interface was visually judged by focusing on the shape difference between the surface of the magnetic layer, the magnetic layer, and the lower layer of the ferromagnetic powder and the non-magnetic powder. Thereafter, the length of the cut line was measured by an image processing apparatus IBAS2 manufactured by Zeiss. If the length of the sample photograph is 21 cm, measure
It was performed 00 times. The average of the measured values at that time was defined as the magnetic layer thickness.

Error rate (initial, after storage): 2
At 3 ° C. and 50% RH, 8-10 for tape-shaped media
The data was recorded on a tape by the converted PR1 equalization method and measured by using a DDS drive. For a disk-shaped medium, the data was recorded on a disk by a (2,7) RLL modulation method and measured. 50 ° C, 80
After storing at% RH for one week, the error rate was measured in the same manner.

[0113]

[Table 2]

[0114]

[Table 3] As is clear from Tables 2 and 3, the magnetic recording medium according to the present invention has a stable low error rate.

[0115]

According to the present invention, a lower layer containing a nonmagnetic powder is provided on a nonmagnetic support, and a ferromagnetic metal fine powder having an average major axis length of 0.1 μm or less or an average plate diameter of 4 μm or less is further provided thereon.
A magnetic layer containing a ferromagnetic hexagonal ferrite fine powder of 0 nm or less and a thickness of 0.5 μm or less is provided, and a polyester resin having a diphenylmethane skeleton and a polar group as a binder for the magnetic layer and / or obtained from the polyester resin By using a polyurethane resin, the smoothness of the coating film and the electromagnetic conversion characteristics are improved, the surface of the magnetic layer is hardly abraded, the head dirt is reduced, the storage stability is greatly improved, the error rate is not increased, and running is reduced. Due to the excellent durability and the excellent surface smoothness of the magnetic layer, a magnetic recording medium having a low error rate can be stably obtained.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4J038 DD051 DD101 DD131 DD171 DG111 DG271 DG281 DG291 GA12 HA066 HA216 KA08 KA12 MA14 NA22 PB11 5D006 BA04 BA05 BA06 BA08 BA11 BA15 BA19

Claims (1)

[Claims] 1. A lower layer containing a nonmagnetic powder and a binder is provided on a nonmagnetic support, on which an average major axis length of 0.01 μm to
Providing at least one or more magnetic layers containing a ferromagnetic metal powder having a crystallite size of 80 to 180 ° or a ferromagnetic hexagonal ferrite powder having an average plate diameter of 5 to 40 nm and a binder, and Thickness 0.01μm ~
A magnetic recording medium having a thickness of 0.5 μm and containing a polyester resin having a diphenylmethane skeleton and a polar group as a binder of a magnetic layer and / or a polyurethane resin obtained from the polyester resin.