JP2010218653A - Magnetic recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetic recording medium wherein a magnetic layer surface is smooth and the power output is large, and the dimensional stability is excellent. <P>SOLUTION: The magnetic recording medium includes: a resin layer including a water-soluble resin; a primer coat layer including non-magnetic powder and a binder; a magnetic layer including magnetic powder and a binder on the primer coat layer, on one principal surface of a non-magnetic substrate; and a back coat layer including non-magnetic powder and a binder on the other principal surface, wherein the water-soluble resin included in the resin layer is cured with crosslinking. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  A nonmagnetic support comprising at least one subbing layer containing nonmagnetic powder and a binder on one main surface of the nonmagnetic support, and a magnetic layer containing magnetic powder and binder on the subbing layer, The present invention relates to a magnetic recording medium having a back coat layer on the other main surface of a support, and more particularly to a coating type magnetic recording medium optimal for ultra-high density recording such as digital video tape and computer backup tape. It is.

  Magnetic tape, one of the magnetic recording media, has various uses such as audio tape, video tape, and computer tape. Especially in the field of computer tape for data backup, the capacity of the hard disk to be backed up is increased. Along with this, products with a storage capacity of several hundred GB or more per roll have been commercialized, and it is indispensable to increase the capacity of the backup tape in order to cope with further increase in the capacity of the hard disk in the future.

  In order to achieve the above high capacity, it is necessary to shorten the wavelength of the recording signal and narrow the recording track width. In order to cope with these, in addition to making the magnetic powder fine particles, increasing the packing density, smoothing the surface of the magnetic layer, etc., to reduce the total thickness of the magnetic recording medium in order to improve the volume density. Is required.

Generally, the total thickness of a high-capacity coating type magnetic recording medium in which a nonmagnetic layer is provided on one main surface of a nonmagnetic support, a magnetic layer is further provided on the main surface, and a back layer is provided on the other main surface. In order to reduce the thickness, conventionally, the nonmagnetic support is thinned or the nonmagnetic layer is thinned.
However, if the non-magnetic support is made thinner, the rigidity of the magnetic recording medium decreases, the contact state (head contact) of the magnetic layer with the magnetic head changes, the reproduction output decreases, and the dimensions of the magnetic recording medium If the problem of decreasing stability occurs or the non-magnetic layer is thinned, the amount of lubricant contained in the non-magnetic layer is insufficient, resulting in decreased durability or surface protrusions on the non-magnetic support. Thus, there is a problem that an error occurs during reproduction due to the influence of the protrusion of the nonmagnetic support on the surface of the magnetic layer.

  For smoothing the surface of the magnetic layer, it is effective to use a non-magnetic support with a smooth surface. However, in terms of manufacturing cost and handling, it is extremely small to obtain a non-magnetic support with few projections. It was difficult.

  As a method of covering the surface protrusions of the nonmagnetic support, a method of providing a relatively thin resin layer between the nonmagnetic support and the nonmagnetic layer has been proposed. In this case, when the nonmagnetic layer is provided on the resin layer, if the resin layer is dissolved, the interface between the resin layer and the nonmagnetic layer is disturbed, and the smoothness of the magnetic layer surface is lowered. The use of a curable resin (Patent Document 1) or the use of a water-soluble resin (Patent Document 2) has been proposed.

JP 2003-132522 A JP 2003-263728 A

  However, in the above conventional technique, a large radiation irradiation facility for curing is necessary (Patent Document 1), or since the crosslinking is not cured, the Young's modulus is small and the rigidity of the entire magnetic recording medium is lowered. For this reason, there is a problem that the head contact is changed and the output is lowered or the dimensional stability is lowered (Patent Document 2).

  An object of the present invention is to solve the above-mentioned problems of the prior art, and to provide a magnetic recording medium having a smooth magnetic layer surface, large output, and good dimensional stability.

  As a result of intensive studies on the resin layer provided on the non-magnetic support, the present inventors have found that the above-described purpose can be achieved by configuring the resin layer as follows, and the present invention has been achieved. .

That is, on one main surface of the nonmagnetic support, a resin layer containing a water-soluble resin, an undercoat layer containing nonmagnetic powder and a binder, and a magnetic powder and a binder on the undercoat layer A magnetic recording medium having a backcoat layer containing a nonmagnetic powder and a binder on the other main surface,
The water-soluble resin contained in the resin layer is crosslinked and cured.

The cross-linking curing is performed with an organic titanium compound or a zirconium compound.

Since the resin layer provided between the non-magnetic support and the non-magnetic layer is water-soluble, the resin layer does not dissolve when the magnetic layer is applied, so the interface between the resin layer and the non-magnetic layer is There is no disturbance, and the water-soluble resin of the resin layer is finally crosslinked and cured, so that the Young's modulus is increased and the rigidity of the magnetic recording medium is not lowered. As a result, a magnetic layer having a smooth surface can be obtained, and a magnetic recording medium having excellent dimensional stability can be provided.

In the present invention, a resin layer containing a water-soluble resin is provided on a nonmagnetic support. The water-soluble resin used in the present invention is not particularly limited as long as it has a crosslinkable reactive group such as a hydroxyl group, a carboxyl group, or a glycidyl group in the molecule. Semi-synthetic polymers include starch, oxidized starch, etherified starch, dialdehyde starch, modified starch compounds such as esterified starch, alginic acid compounds such as sodium alginate and propylene glycol alginate, casein, gelatin, pullulan, dextran, chitin And modified cellulose compounds such as chitosan, rubber latex, gum arabic, funori, natural gum, dextrin, methylcellulose, ethylcellulose, hydroxycellulose, carboxymethylcellulose, and the like.

  Synthetic polymers can also be used as water-soluble resins, such as fully saponified or partially saponified polyvinyl alcohol, acetoacetylated polyvinyl alcohol, esterified product of polyvinyl alcohol and polyvalent carboxylic acid, carboxy-modified polyvinyl alcohol. , Modified polyvinyl alcohol compounds such as sulfonic acid modified polyvinyl alcohol, olefin modified polyvinyl alcohol, nitrile modified polyvinyl alcohol, amide modified polyvinyl alcohol, pyrrolidone modified polyvinyl alcohol, polyethylene oxide glycidyl adduct, polyacrylic acid compound, Polyvinyl pyrrolidone, polymaleic acid copolymer, water-soluble alkyd resin and the like can be used. Among the above resins, completely saponified or partially saponified polyvinyl alcohol, acetoacetylated polyvinyl alcohol, esterified product of polyvinyl alcohol and polyvalent carboxylic acid, carboxy modified polyvinyl alcohol, sulfonic acid modified polyvinyl alcohol, olefin modified Modified polyvinyl alcohols such as polyvinyl alcohol, nitrile modified polyvinyl alcohol, amide modified polyvinyl alcohol, pyrrolidone modified polyvinyl alcohol are preferred because of their excellent physical properties such as glass transition temperature and solubility. Alternatively, partially saponified polyvinyl alcohol and polyethylene oxide glycidyl adduct are preferred.

When using completely saponified or partially saponified polyvinyl alcohol, the saponification degree is preferably 80 to 100 mol%, more preferably 85 to 100 mol%, particularly 90 to 100 mol% from the viewpoint of solubility. preferable. As the completely saponified or partially saponified polyvinyl alcohol, those having a polymerization degree in the range of 500 to 5000 are preferable. If the degree of polymerization is 500 or more, blocking at the end face does not occur, and if it is 5000 or less, the viscosity at the time of dissolution is good, and it is possible to apply a resin layer sufficiently.
As the polyethylene oxide glycidyl adduct, those having a molecular weight in the range of 10,000 to 10,000,000 can be used, those having a molecular weight of 50,000 to 500,000 are preferable, and those having a molecular weight of 80,000 to 300,000 are particularly preferable. . If the molecular weight is 10,000 or more, no blocking or the like occurs at the end face, and if it is 10000000 or less, the viscosity at the time of dissolution in water is good, and the resin layer can be sufficiently applied.

  The glass transition temperature of the water-soluble resin is preferably 30 to 120 ° C., more preferably 40 to 80 ° C. If the glass transition temperature is 30 ° C. or higher, blocking at the end face or the like is caused. If it is 120 degrees C or less, the internal stress in a resin layer can be relieved and it is excellent also in adhesive force.

It is preferable to form a resin layer by combining the water-soluble resin and a cross-linking agent suitable for each of them, and the cross-linking agent is not particularly limited, and a conventionally known cross-linking agent is used. For example, for water-soluble resins having a hydroxyl group such as polyvinyl alcohols, glyoxal, glutaraldehyde or dialdehyde starch, water-soluble epoxy compounds, and methylol compounds can be used, particularly organic titanium compounds or zirconium compounds. Among them, organic titanium compounds such as titanium lactate, titanium lactate, and titanium alkoxide, and zirconium compounds such as basic zirconyl chloride, zirconium oxychloride, zirconyl ammonium carbonate, zirconyl sulfate, and zirconyl nitrate are more crosslinkable. It is excellent and preferable.
For a water-soluble resin having a carboxyl group such as polyacrylic acids, for example, various metal oxides are used as a crosslinking agent.

  For a water-soluble resin having a glycidyl group such as a polyethylene oxide glycidyl adduct, for example, various diamines are used as a crosslinking agent.

  In the present invention, the resin layer is mixed with the water-soluble resin and the crosslinking agent or mixed with additives such as an antifoaming agent, a dispersant, an antifungal agent, an antiseptic, and a rust inhibitor as necessary. It is formed by applying a resin layer coating solution prepared as an aqueous solution obtained by dissolving on a nonmagnetic support surface by a conventional method.

The resin layer has a thickness of 0.1 to 2.0 μm, preferably 0.2 to 1.5 μm, and more preferably 0.3 to 1.0 μm. If the thickness of the resin layer is less than 0.1 μm, the protrusions present on the surface of the nonmagnetic support cannot be blocked by providing the resin layer. If the thickness exceeds 2.0 μm, the magnetic recording of the thickness of the resin layer is not possible. The influence on the medium thickness is increased, which may affect the rigidity of the magnetic recording medium and thus the head contact.
In the present invention, the maximum height of the protrusions existing on the surface of the resin layer is 150 nm or less, preferably 10 to 100 nm, and more preferably 20 to 80 nm. If the height of the protrusions present on the surface of the resin layer exceeds 150 nm, the surface properties of the magnetic layer are greatly affected, causing errors and increasing dropout.

  In the present invention, high smoothness with a maximum protrusion height of 150 nm or less on the surface of the resin layer can be realized because the surface protrusion on the surface of the support is blocked by applying a resin layer. This is because the influence of the protrusion on the surface of the resin layer can be suppressed. In the present invention, in order to achieve the smoothness, a filler having a particle diameter of 100 nm or less is dispersed in the resin layer to block the protrusions on the surface of the support and to newly form protrusions having a maximum height of 100 nm or less. The method can also be carried out further.

  As a method for forming the resin layer on the surface of the nonmagnetic support, it is preferable to form the resin layer by applying a resin liquid to the surface of the nonmagnetic support using a conventionally known coating machine. Coating machines include air doctor coaters, blade coaters, rod coaters, extrusion coaters, air knife coaters, squeeze coaters, impregnation coaters, reverse roll coaters, transfer roll coaters, gravure coaters, kiss coaters, cast coaters, curtain coaters, spray coaters, spin coaters. Etc.

  The viscosity of the resin liquid is preferably 0.02 to 0.85 Pa · s. This range is preferable because the coating suitability is improved.

  If necessary, an easy adhesion layer may be provided between the nonmagnetic support and the resin layer. By providing the easy-adhesion layer, the smoothness of the resin layer can be improved and the adhesive force between the support and the resin layer can be improved. In order to increase the surface smoothness of the resin layer, the thickness of the easy adhesion layer is preferably 0.5 μm or less, and more preferably 0.001 to 0.3 μm. As the easily adhesive layer resin used in the easily adhesive layer, a conventionally known resin can be used. For example, vinyl chloride, chlorinated vinyl chloride, vinyl acetate, vinyl acetate-maleic acid ester copolymer, maleic acid , Acrylic acid, acrylic ester, vinylidene chloride, vinylidene chloride-acrylonitrile copolymer, acrylonitrile, methacrylic acid, methacrylic ester, styrene, styrene-acrylic ester copolymer, butadiene, ethylene, vinyl butyral, vinyl acetal, vinyl ether Etc. as a structural unit such as thermoplastic resins such as polymers or copolymers, phenol resins, epoxy resins, urea resins, melamine resins, alkyd resins, acrylic reaction resins, formaldehyde resins, silicone resins, polyamide resins, polyamideimides Thermosetting resins such as fat, epoxy-polyamide resin, polyurethane resin, urethane-urea resin, polyester resin, a mixture of polyester resin and isocyanate prepolymer, a mixture of polyester polyol and polyisocyanate, a mixture of polyurethane and polyisocyanate, etc. A reactive resin or a mixture thereof can be used. Among them, the polyester resin is preferable because of its excellent physical properties such as adhesion, glass transition temperature, and solubility, and particularly, a polyester resin having a polar group such as a carboxylic acid and a salt thereof, a sulfonic acid and a salt thereof is preferable. .

  Magnetic tapes for computers with a recording capacity of several hundred GB or more have a smaller recording track width in order to increase the surface recording density, a larger recording density in the width direction of the magnetic tape, and a smaller recording wavelength. The recording density in the longitudinal direction of the tape is increased. Therefore, in a magnetic tape for computers having a recording capacity of several hundred GB or more, the recording wavelength is extremely small, 0.5 μm or less, and the thickness of the magnetic layer is set to reduce the thickness loss during recording / reproduction due to the self-demagnetization action. The recording wavelength is preferably 1/3 or less, more preferably 1/4 or less. Therefore, the magnetic layer thickness of the magnetic recording medium of the present invention is preferably in the range of 10 to 150 nm, more preferably in the range of 20 to 100 nm, and most preferably in the range of 30 to 70 nm. This range is preferable if the thickness is less than 10 nm, it may be difficult to form a uniform magnetic layer, or a sufficient output may not be obtained. This is because the thickness loss increases.

  In order to form such a magnetic layer, a resin layer is formed on a nonmagnetic support, and an undercoat layer containing nonmagnetic powder and a binder is provided thereon to form an undercoat layer having a smooth surface. In addition, it is preferable to provide a magnetic layer thereon. As long as each layer is formed in the above order, another layer may be provided between the layers.

Hereinafter, the components of the present invention will be described in detail.
<Magnetic powder>
Conventionally known magnetic powder can be used as the magnetic powder used in the production of the magnetic coating in the present invention. For example, ferromagnetic iron-based metal magnetic powder, iron nitride magnetic powder, and plate-shaped hexagonal ferrite magnetic powder. Etc. are preferably used. The average particle diameter of the magnetic powder is preferably 50 nm or less, and the average particle diameter is preferably 10 nm or more. The average particle diameter is more preferably in the range of 15 to 40 nm. This range is preferable because when the average particle diameter exceeds 50 nm, the particle noise based on the particle size increases, and when the average particle diameter is less than 10 nm, the coercive force decreases and the surface energy of the particles increases. This is because dispersion in the paint becomes difficult.

  The particle diameter as used in the present application refers to the average major axis diameter when the particles are needle-shaped, and refers to the length of the larger sheet diameter when the particles are plate-shaped, and the ratio of the major axis length to the minor axis length is 1 to 1. In the case of a spherical or elliptical shape of 3.5, it indicates the maximum passing diameter. The average particle size is obtained by measuring the particle size of a photograph taken with a transmission electron microscope (TEM) and calculating the average number of 300 particles.

<Binder>
Examples of binders used in the magnetic layer, the undercoat layer and the backcoat layer include vinyl chloride resin, vinyl chloride-vinyl acetate copolymer resin, vinyl chloride-vinyl alcohol copolymer resin, vinyl chloride-vinyl acetate-vinyl alcohol. A polyurethane resin, at least one selected from a copolymer resin, a vinyl chloride-vinyl acetate-maleic anhydride copolymer resin, a vinyl chloride-hydroxyl group-containing alkyl acrylate copolymer resin, and a cellulose resin such as nitrocellulose; And a combination of these.

Among these resins, it is preferable to use a vinyl chloride-hydroxyl group-containing alkyl acrylate copolymer resin and a polyurethane resin in combination.
Examples of the polyurethane resin include polyester polyurethane resin, polyether polyurethane resin, polyether polyester polyurethane resin, polycarbonate polyurethane resin, polyester polycarbonate polyurethane resin, and the like.

Such binding agents, as a functional _{group, -COOH, -SO 3 M, -OSO} 3 M, -P = O (OM) 3, -O-P = O (OM) 2 [In these formulas, M Represents a hydrogen atom, an alkali metal base or an amine salt], —OH, —NR ₁ R ₂ , —N ⁺ R ₃ R ₄ R ₅ [in these formulas, R ₁ , R ₂ , R ₃ , R ₄ , R ₅ represents hydrogen or a hydrocarbon group], and those having an epoxy group are preferably used.

This is because the use of such a binder improves the dispersibility of the magnetic powder and the like. When two or more kinds of resins are used in combination, the polarities of the functional groups are preferably matched, and among them, a combination of —SO ₃ M groups is preferable.

  These binders are usually used in an amount of 7 to 50 parts by weight, preferably 10 to 35 parts by weight with respect to 100 parts by weight of the magnetic powder or nonmagnetic powder. In particular, when a vinyl chloride resin and a polyurethane resin are used in combination, it is preferable to use 5 to 30 parts by weight of a vinyl chloride resin and 2 to 20 parts by weight of a polyurethane resin.

Moreover, it is preferable to use together with these binders, the thermosetting crosslinking agent couple | bonded with the functional group contained in a binder, etc., and bridge | crosslinks.
Examples of such crosslinking agents include tolylene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, reaction products of these isocyanates with those having a plurality of hydroxyl groups such as trimethylolpropane, and condensation products of the above isocyanates. Various polyisocyanates such as are preferably used.

  These crosslinking agents are usually used in a proportion of 1 to 50 parts by weight with respect to 100 parts by weight of the binder. More preferably, it is 15 to 35 parts by weight.

  Further, a radiation curable resin may be used instead of the thermosetting crosslinking agent as described above. As the radiation curable resin, an acrylic monomer or an acrylic oligomer is used. The radiation curable resin preferably has two or more double bonds in the molecule and has a weight average molecular weight of 50 to 300 per double bond. When a radiation curable resin is used for the undercoat layer, the ratio of the radiation curable resin contained in the undercoat layer is preferably 5 to 30 wt% with respect to the total amount of the binder and the radiation curable resin.

  Radiation curable resins having a weight average molecular weight of 50 to 300 per double bond include 1,3-butanediol diacrylate, 1,4-butanediol diacrylate, 1,6-hexanediol diacrylate, ethylene Glycol diacrylate, diethylene glycol diacrylate, triethylene glycol diacrylate, tetraethylene glycol diacrylate, polyethylene glycol diacrylate, propylene glycol diacrylate, dipropylene glycol diacrylate, tripropylene glycol diacrylate, ethoxylated bisphenol A diacrylate, novolak Bifunctional acrylates such as diacrylate, propoxylated neopentyl glycol diacrylate, and the same bifunctionality as the above acrylate Tacrylate, tris (2-hydroxyethyl) isocyanurate triacrylate, trimethylolpropane triacrylate, ethoxylated trimethylolpropane triacrylate, pentaerythritol triacrylate, propoxylated trimethylolpropane triacrylate, propoxylated glyceryl triacrylate, caprolactone modified tri Trifunctional acrylates such as methylolpropane triacrylate and trifunctional methacrylates similar to the above acrylate, pentaerythritol tetraacrylate, ditrimethylolpropane tetraacrylate, ethoxylated pentaerythritol tetraacrylate, dipentaerythritol hydroxypentaacrylate, dipentaerythritol hexaacrylate, etc. Four Uses acrylates with higher abilities and monomer acrylates (methacrylates) such as tetra- or higher functional methacrylates similar to the above acrylates, and oligomers obtained by extending the molecular chain with skeletons such as polyether, polyester, polycarbonate, polyurethane, etc. it can.

<Organic solvent>
Examples of the organic solvent used in the production of the magnetic coating in the present invention include ketone solvents such as methyl ethyl ketone, cyclohexanone and methyl isobutyl ketone, ether solvents such as tetrahydrofuran and dioxane, and acetates such as ethyl acetate and butyl acetate. And glycol solvents such as ethylene glycol, propylene glycol, ethylene glycol monoethyl ether, and propylene glycol monomethyl ether. These organic solvents are used alone or in combination, and are used in a mixture with toluene or the like.

  In the present invention, abrasives, lubricants, and dispersants can be used as additives used in the production of magnetic paints.

<Abrasive etc.>
As abrasives to be included in the magnetic layer, α-alumina, β-alumina, silicon carbide, chromium oxide, cerium oxide, α-iron oxide, corundum, artificial diamond, silicon nitride, silicon carbide, titanium carbide, titanium oxide, Those having a Mohs hardness of 6 or more, such as silicon dioxide and boron nitride, can be used alone or in combination. The particle size of these abrasives is usually preferably 10 to 200 nm as an average particle size.

  In addition, conventionally known carbon black may be added to the magnetic coating material for the purpose of improving conductivity and surface lubricity, if necessary. As carbon black, acetylene black, furnace black, thermal black, and the like can be used. Those having an average particle diameter of 10 to 100 nm are preferred. This range is preferable because when the average particle size is less than 10 nm, it is difficult to disperse carbon black. When the average particle size exceeds 100 nm, it is necessary to add a large amount of carbon black. Because it becomes. If necessary, two or more carbon blacks having different average particle diameters may be used. The content of the abrasive is preferably 5 to 20 parts by weight and more preferably 8 to 18 parts by weight with respect to 100 parts by weight of the magnetic powder.

<Lubricant>
For magnetic paints, 0.5-5% by weight fatty acid, 0.2-3% by weight ester of fatty acid, 0.5-5.0% by weight fatty acid based on the total powder contained in the paint. It is preferable to contain an amide. The addition of the fatty acid in the above range is preferable because if the amount is less than 0.5% by weight, the effect of reducing the friction coefficient is small, and if it exceeds 5% by weight, the toughness may be lost.

  It is preferable to add an ester of fatty acid within the above range. If the amount is less than 0.2% by weight, the effect of reducing the friction coefficient is small, and if it exceeds 3% by weight, the amount transferred to the magnetic layer is too large. This is because side effects such as sticking may occur. The addition of the fatty acid amide within the above range is preferable when the amount is less than 0.5% by weight, and direct contact at the head / magnetic layer interface occurs and the effect of preventing seizure is small. This is because defects such as the above may occur. As the fatty acid, it is preferable to use a fatty acid having 10 or more carbon atoms. The fatty acid having 10 or more carbon atoms may be any of isomers such as linear, branched and cis / trans, but is preferably a linear type having excellent lubricating performance. These fatty acids include lauric acid, myristic acid, stearic acid, palmitic acid, behenic acid, oleic acid, linoleic acid and the like. Among these, myristic acid, stearic acid, palmitic acid and the like are preferable.

  As the fatty acid ester, the fatty acid ester is preferably used. As the fatty acid amide, a fatty acid amide having 10 or more carbon atoms such as palmitic acid and stearic acid can be used.

<Dispersant>
A dispersing agent can be used in order to satisfactorily disperse additives such as magnetic powder, abrasive and carbon black. Examples of such a dispersant include caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, oleic acid, elaidic acid, linoleic acid, linolenic acid, stearic acid, and the like. 18 fatty acids [RCOOH (R is an alkyl group or alkenyl group having 11 to 17 carbon atoms)], a metal soap composed of an alkali metal or an alkaline earth metal of the fatty acid, a compound containing fluorine of the fatty acid ester, Fatty acid amide, polyalkylene oxide alkyl phosphate ester, lecithin, trialkyl polyolefinoxy quaternary ammonium salt (alkyl is 1 to 5 carbon atoms, olefin is ethylene, propylene, etc.), sulfate, sulfonate, phosphoric acid Various conventionally known dispersants such as salts and copper phthalocyanine And either can be used. These may be used alone or in combination. In any layer, the dispersant is usually added in the range of 0.5 to 20 parts by weight with respect to 100 parts by weight of the binder resin.

  In the present invention, together with the magnetic powder and binder described above, an organic solvent and the additive component described above are used to produce a magnetic paint by dispersion treatment according to the above method. According to a conventional method, a magnetic recording medium is produced by coating on a nonmagnetic support, drying, forming a magnetic layer, and passing through a required processing step.

  In the present invention, the magnetic layer is preferably formed via an undercoat layer. Further, a topcoat layer (the uppermost nonmagnetic layer) may be provided on the magnetic layer as necessary for the purpose of protecting the magnetic layer. Further, the above magnetic layer may be formed on both sides of the nonmagnetic support in order to increase the capacity of the magnetic recording medium. On the other hand, when the magnetic layer is formed only on one side of the nonmagnetic support, it is usually preferable to form the backcoat layer on the back side.

<Non-magnetic support>
Although the thickness of a nonmagnetic support body changes with uses, a 1.5-11 micrometers thing is normally used. The thickness of the nonmagnetic support is more preferably 2 to 7 μm. The nonmagnetic support having a thickness in this range is used because if it is less than 1.5 μm, it becomes difficult to form a film and the tape strength is reduced. If it exceeds 11 μm, the total thickness of the tape is increased. This is because the recording capacity per tape roll is reduced.

The longitudinal Young's modulus of the nonmagnetic support, preferably 5.8GPa (590kg / mm ²⁾ or more, 7.1GPa (720kg / mm ²⁾ or more is more preferable. The reason why the Young's modulus in the longitudinal direction of the nonmagnetic support is preferably 5.8 GPa or more is that the tape running becomes unstable when the Young's modulus in the longitudinal direction is less than 5.8 GPa.

  In the helical scan type, the Young's modulus (MD) in the longitudinal direction / Young's modulus (TD) in the width direction is preferably in the range of 0.6 to 0.8, and more preferably in the range of 0.65 to 0.75. The Young's modulus in the longitudinal direction / Young's modulus in the width direction is good when the range is less than 0.6 or more than 0.8. The mechanism is currently unknown, but from the entrance side of the magnetic head track. This is because the output variation (flatness) between the output sides increases. This variation is minimized when the Young's modulus in the longitudinal direction / Young's modulus in the width direction is around 0.7.

  In the linear recording type, the Young's modulus in the longitudinal direction / Young's modulus in the width direction is preferably 0.7 to 1.3, although the reason is not clear.

The temperature expansion coefficient in the width direction of the nonmagnetic support is preferably −10 to 10 × 10 ⁻⁶ , and the humidity expansion coefficient is preferably 0 to 10 × 10 ⁻⁶ . The reason why this range is preferred is that if it is outside this range, off-track occurs due to changes in temperature and humidity, and the error rate increases.

  Examples of the nonmagnetic support satisfying the above-described characteristics include biaxially stretched polyethylene terephthalate film, polyethylene naphthalate film, aromatic polyamide film, and aromatic polyimide film.

<Undercoat layer>
The thickness of the undercoat layer is preferably 0.2 μm or more and less than 1.0 μm, and more preferably 0.9 μm or less. This range is preferred if the thickness is less than 0.2 μm, the effect of concealing the surface protrusions of the nonmagnetic support and the effect of improving the durability are reduced. If the thickness is 1.0 μm or more, the total thickness of the magnetic tape is increased. This is because the recording capacity per tape roll becomes small.

  Nonmagnetic powders used for the undercoat layer include titanium oxide, iron oxide, and aluminum oxide. Iron oxide alone or a mixed system of iron oxide and aluminum oxide is preferably used. The particle shape of the non-magnetic powder may be spherical, plate-like, needle-like, or spindle-like, but in the case of needle-like or spindle-like, the major axis length is usually 50 to 200 nm and the minor axis length is 5 to 100 nm. Is preferred. In the case of a granular shape, a particle size of 5 to 200 nm, more preferably 5 to 100 nm is used.

  Furthermore, it is preferable to add carbon black having a particle size of 0.01 to 0.1 μm for the purpose of improving conductivity. In order to apply the undercoat layer smoothly and with little thickness unevenness, it is particularly preferable to use nonmagnetic powder and carbon black having a sharp particle size distribution. Instead of carbon black, plate-like ITO (indium and tin composite oxide) powder having an average particle diameter of 10 to 100 nm may be used.

  As a calendering roll, a combination of a heat-resistant plastic roll such as epoxy, polyester, nylon, polyimide, polyamide, and polyimideamide (may be kneaded with carbon, metal or other inorganic compound) and a metal roll ( It can also be treated with a combination of 3 to 7 stages) or metal rolls. The treatment temperature is preferably 70 ° C. or higher, more preferably 80 ° C. or higher, and the linear pressure is preferably 200 kg / cm (196 kN / m) or higher, more preferably 300 kg / cm (294 kN / m) or higher, The speed is in the range of 20 to 700 m / min. By performing the calendering treatment, the porosity of the undercoat layer can be controlled, and the penetration of the solvent contained in the magnetic paint in forming the magnetic layer into the undercoat layer can be controlled. The magnetic layer can be controlled.

<Magnetic layer>
The thickness of the magnetic layer is preferably in the range of 10 to 150 nm, more preferably in the range of 20 to 100 nm, and most preferably in the range of 30 to 70 nm in order to further improve the short wavelength recording characteristics. This range is preferable if it is less than 10 nm, it is difficult to form a uniform magnetic layer, and sufficient output cannot be obtained. If it exceeds 150 nm, the thickness loss during recording and reproduction due to self-demagnetization increases. Because.

  The product of the residual magnetic flux density in the tape longitudinal direction of the magnetic layer and the thickness of the magnetic layer is preferably 0.0018 to 0.05 μTm, more preferably 0.0036 to 0.05 μTm, and 0.004 to 0.00. More preferably, it is 05 μTm. This is because if the product of the residual magnetic flux density and the thickness of the magnetic layer is too small, the reproduction output by the MR head becomes small, and if it is too large, the reproduction output by the MR head tends to be distorted. A magnetic recording medium having a magnetic layer having the above product in this range can perform short wavelength recording. In addition, the reproduction output when reproduced by the MR head is large, the distortion of the reproduction output is small, and the output-to-noise ratio can be increased, which is preferable.

Examples of carbon black include acetylene black, furnace black, and thermal black.
The average particle size of carbon black is preferably 10 nm to 100 nm. If the average particle size is too small, it is difficult to disperse the carbon black, and if the average particle size is too large, a large amount of carbon black is required. Therefore, if the average particle size is too small or too large, the surface of the magnetic layer 13 becomes rough, which may reduce the output, which is not preferable. The content of carbon black is preferably 0.2 to 5 parts by weight and more preferably 0.5 to 4 parts by weight with respect to 100 parts by weight of the magnetic powder.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples. In addition, the part in an Example and a comparative example is a weight part. Moreover, the average particle diameter in an Example and a comparative example is a number average particle diameter.

<Resin liquid component>
・ Poval (degree of polymerization 500, degree of saponification 88 mol%) 100 parts ・ Crosslinking agent (organic titanium compound) (Origatix TC-310 manufactured by Matsumoto Kosho Co., Ltd.)
17 parts, 1320 parts of water << prime coating ingredient >>
(1) Component-acicular iron oxide 68 parts Carbon black 20 parts granular alumina powder 12 parts of methyl acid phosphate 1 part vinyl chloride - hydroxypropyl acrylate copolymer 9 parts (containing _-SO 3 Na group: 0 .7 × 10 ⁻⁴ equivalent / g)
Polyester polyurethane resin 5 parts (Glass transition temperature: 40 ° C., contained -SO ₃ Na group: 1 × 10 ⁻⁴ equivalent / g)
・ Tetrahydrofuran 13 parts ・ cyclohexanone 63 parts ・ methyl ethyl ketone 137 parts (2) component ・ butyl stearate 2 parts ・ cyclohexanone 50 parts ・ toluene 50 parts (3) component ・ polyisocyanate 2.5 parts ・ cyclohexanone 9 parts ・ toluene 9 parts << Magnetic paint component >>
(1) Kneading process component / magnetic powder (metal magnetic powder) 100 parts Co / Fe: 24 at%,
Al / (Fe + Co): 4.7 at%
Y / (Fe + Co): 7.9 at%
σs: 116 A · m 2 / kg (116 emu / g),
Hc: 165 kA / m (2070 Oe),
Average particle diameter: 45 nm, axial ratio: 4
・ 13 parts of vinyl chloride copolymer (MR-110 manufactured by Zeon Corporation)
Polyester polyurethane resin (PU) 4.5 parts (containing -SO3 Na group: 1.0 x 10-4 equivalent / g)
・ Particulate alumina powder (average particle size: 80 nm) 10 parts ・ Methyl acid phosphate (MAP) 2 parts ・ Tetrahydrofuran (THF) 20 parts ・ Methyl ethyl ketone / cyclohexanone (MEK / A) 9 parts (2) Diluting step components ・ Palmitic acid amide (PA) 1.5 parts, n-butyl stearate (SB) 1 part, methyl ethyl ketone / cyclohexanone (MEK / A) 350 parts (3) blending process components, polyisocyanate 1.5 parts, methyl ethyl ketone / cyclohexanone (MEK / A) 29 parts

  After kneading the component (1) with a batch kneader in the above-mentioned undercoat paint component, the component (2) is added and stirred, followed by a dispersion treatment using a sand mill with a residence time of 60 minutes. -After filtering, it was used as a primer.

  Apart from this, in the above-mentioned magnetic paint component, the mixed process component (1) is previously mixed at high speed, the mixed powder is kneaded with a continuous biaxial kneader, and further the dilution process component (2) In a continuous twin-screw kneader, dilute in at least two stages and disperse in a sand mill with a residence time of 45 minutes. Add the ingredients in (3) and stir and filter. did.

  On the base film consisting of a polyethylene naphthalate support (thickness 6.1 μm), the resin liquid is applied and dried so that the thickness after drying is 0.1 μm, and then the above-mentioned undercoat is applied thereon. A seven-stage calender made of a metal roll under conditions of a drying temperature, a processing temperature of 70 ° C., and a linear pressure of 200 kg / cm (196 kN / m) after coating with an extrusion coater so that the thickness after calendering becomes 1.2 μm. The smoothing process was performed with the apparatus. On this undercoat layer, a magnetic paint is applied, dried, applied with an extrusion type coater (sequential application) so that the thickness of the magnetic layer after the calendering process is 0.09 μm, and applied with a solenoid magnet. The magnetic material was oriented in the direction. At this time, the magnetic field strength in the field where the magnetic coating material was applied onto the support was adjusted to 400 KA / m. Thereafter, smoothing treatment was carried out with a seven-stage calendar composed of dried and metal rolls under the conditions of a treatment temperature of 100 ° C. and a linear pressure of 200 kg / cm (196 kN / m), and a magnetic sheet was obtained.

《Paint component for back coat layer》
Carbon black (average particle diameter: 25 nm) 87 parts Carbon black (average particle diameter: 350 nm) 10 parts Granular alumina powder (average particle diameter: 80 nm) 3 parts Nitrocellulose 45 parts Polyurethane resin (-SO3 Na group Contained) 30 parts ・ Cyclohexanone 260 parts ・ Toluene 260 parts ・ Methyl ethyl ketone 525 parts

  After the coating component for the backcoat layer is dispersed with a sand mill for a residence time of 45 minutes, the backcoat layer coating material is adjusted by adding 15 parts of polyisocyanate, filtered, and the opposite side of the magnetic layer of the magnetic sheet prepared above Then, it was applied so that the thickness after drying and calendering was 0.5 μm and dried.

  The magnetic sheet thus obtained is smoothed under a condition of a processing temperature of 100 ° C. and a linear pressure of 200 kg / cm (196 kN / m) with a seven-stage calendar made of a metal roll, and the magnetic sheet is wound around a core. Was aged at 70 ° C. for 72 hours to obtain a magnetic sheet for evaluation with a back layer.

This evaluation-use magnetic sheet with a back layer was cut into ½ inch widths, and servo signals were written with a servo writer to obtain an evaluation magnetic tape.
(Examples 2 to 5)
A magnetic tape for evaluation was obtained in the same manner as in Example 1 except that the resin layer thickness after drying was changed as shown in Table 1.
(Example 6)
A magnetic tape for evaluation was obtained in the same manner as in Example 1 except that the cross-linking agent of the resin liquid component was changed to a Zirconium-based compound, ORGATIXX ZBC-126, manufactured by Matsumoto Kosho Co., Ltd.
(Comparative Example 1)
A magnetic tape for evaluation was obtained in the same manner as in Example 1 except that the resin layer was not provided.
(Comparative Example 2)
A magnetic tape for evaluation was obtained in the same manner as in Example 1 except that the crosslinking agent in the resin liquid component was not used.

<Head protrusion height>
The resin layer was not provided and the surface of the support provided with the resin layer was observed with an optical microscope (magnification 100 times), the protrusions were marked at five locations, and the marked locations were general-purpose three-dimensional surfaces manufactured by ZYGO. The scan length was measured at 5 μm by a scanning white light interferometry using a structural analysis apparatus “NewView 5000” and expressed as an average value at five locations. The measurement visual field was 350 μm × 280 μm.

<Number of errors>
Using a head for LTO2, a rectangular wave with a wavelength of 0.39 um was recorded and reproduced while running the evaluation magnetic tape at a speed of 1.83 m / s, and the base-to-peak value of the reproduction signal amplitude was written immediately before. When the average was smaller than 35% of the average and the time continued continuously for 1 μsec or more, it was counted as one. It was expressed as the number per 100 m of magnetic tape.

<Dimensional stability>
Using an LTO2 drive manufactured by Hewlett-Packard Co., (1) after reciprocating the evaluation magnetic tape for 10 hr at 10 ° C. and 10% RH, recording a signal, (2) 30 ° C., After reciprocating for 10 hr under the temperature and humidity of 80% RH, the signal is reproduced, and the width of the magnetic tape is measured by measuring the track deviation width of the magnetic tape due to the temperature and humidity change from (1) to (2). The expansion coefficient in the direction was determined by the following equation.
Expansion rate (ppm) = (track deviation in temperature and humidity change from 10 ° C., 10% RH to 30 ° C., 80% RH) / (dimension from reference position to measurement track at 10 ° C., 10% RH) ) × 10 ⁶

  Table 1 shows the evaluation results.

  As can be seen from Table 1, the evaluation magnetic tapes of Examples 1 to 6 according to the present invention have a low error and a low expansion rate because the protrusion height of the nonmagnetic support is suppressed. On the other hand, Comparative Example 1 in which no resin layer is provided has many errors and a large expansion coefficient. Moreover, even if the resin layer is provided, Comparative Example 2, which is not crosslinked, has a large expansion coefficient although there are few errors.

Claims (3)

On one main surface of the nonmagnetic support, a resin layer containing a water-soluble resin, an undercoat layer containing a nonmagnetic powder and a binder, and a magnetic powder and a binder on the undercoat layer A magnetic recording medium comprising a magnetic layer and a backcoat layer comprising a nonmagnetic powder and a binder on the other main surface,
A magnetic recording medium, wherein a water-soluble resin contained in the resin layer is crosslinked and cured. The magnetic recording medium according to claim 1, wherein the cross-linking curing is performed with an organic titanium-based compound or a zirconium-based compound. The magnetic recording medium according to claim 1, wherein the resin layer has a thickness of 0.1 to 2.0 μm.