JP2012043508A - Magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic recording medium having a smooth magnetic layer surface, large output and good dimensional stability.
[Solution]
On one main surface of the nonmagnetic support, a resin layer, an undercoat layer containing nonmagnetic powder and a binder on the resin layer, and a magnetic powder and a binder on the undercoat layer A magnetic recording medium having at least one magnetic layer and a backcoat layer containing a nonmagnetic powder and a binder on the other main surface of the nonmagnetic support, wherein the resin contained in the resin layer is an alcohol. It is a soluble resin and is cured by crosslinking.
[Selection figure] None

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. Accordingly, products with a storage capacity of 1 TB or more per volume have been commercialized, and in order to cope with the further increase in the capacity of hard disks, it is essential to increase the capacity of backup tapes 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 problems, in addition to making the magnetic powder finer, more highly packed, and smoothing the surface of the magnetic layer, the magnetic recording medium includes a non-magnetic support for improving the volume density. It is required to reduce the total thickness.
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 is reduced. For this purpose, 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, but due to the high production cost and operability problems in the process, the protrusions are extremely small, It was difficult to obtain a small number of nonmagnetic supports.
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 non-magnetic layer is provided on the resin layer, if the resin layer dissolves, the interface between the resin layer and the non-magnetic 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, the above-described conventional technology requires a large radiation irradiation facility for curing (Patent Document 1), requires a paint preparation facility corresponding to water instead of an organic solvent, a drying facility, etc., and makes a new investment. Since the resin solution in the aqueous medium tends to generate bubbles, a smooth coating film cannot be obtained due to the bubbles, or since the cross-linking and curing is not performed, the Young's modulus is small and the rigidity of the entire magnetic recording medium is reduced. 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, an undercoat layer containing a nonmagnetic powder and a binder on the resin layer, and a magnetic powder bonded on the undercoat layer A magnetic recording medium having at least one magnetic layer containing an agent, and having a backcoat layer containing a nonmagnetic powder and a binder on the other main surface of the nonmagnetic support,
The resin contained in the resin layer is an alcohol-soluble resin and is cured by crosslinking. The term “soluble in alcohol” as used herein means that the target resin dissolves in alcohol up to a concentration of 10 wt%.

Since the resin contained in the resin layer provided between the non-magnetic support and the non-magnetic layer is an alcohol-soluble resin, conventional equipment compatible with organic solvents can be used. Since the alcohol-soluble resin of the layer is finally cured by cross-linking, the Young's modulus is increased and the rigidity of the magnetic recording medium is not reduced. 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 an alcohol-soluble resin is provided on a nonmagnetic support. The alcohol here means an alcohol having 5 or less carbon atoms. Since the solvent is skipped when the resin layer is formed and drying is performed, an alcohol having 5 or less carbon atoms is preferable from the viewpoint of productivity.

The alcohol-soluble resin used in the present invention is not particularly limited as long as it has a crosslinkable reactive group in the molecule. For example, as a semi-synthetic polymer, a modified starch compound, an alginic acid compound, Examples include modified cellulose compounds.
Synthetic polymers can also be used as alcohol-soluble resins, such as partially saponified polyvinyl alcohol, acetoacetylated polyvinyl alcohol, carboxy-modified polyvinyl alcohol, sulfonic acid-modified polyvinyl alcohol, olefin-modified polyvinyl alcohol, and nitrile-modified. Modified polyvinyl alcohol, amide modified polyvinyl alcohol, modified polyvinyl alcohol compounds such as polyvinyl pyrrolidone, pyrrolidone modified polyvinyl alcohol, polyethylene oxide glycidyl adduct, polyacrylic acid, polymethacrylic acid, polyacrylic acid compound, polymethacrylic acid compound, Polyvinyl pyrrolidone, polyvinyl pyridine, polyvinyl sulfoxide, polymaleic acid copolymer, vinyl acetate resin, polyvinyl butyler Or the like can be used. Among the above resins, partially saponified polyvinyl alcohol, polyvinyl pyrrolidone, vinyl acetate resin and the like are preferable because of their excellent physical properties such as glass transition temperature and solubility.
When using partially saponified polyvinyl alcohol, the saponification degree is preferably 30 to 60 mol%, more preferably 45 to 50 mol%, from the viewpoint of solubility. As alcohol-soluble resin, what is in the range of 500-5000 degree of polymerization is preferable. If the degree of polymerization is 500 or more, blocking (sticking) at the end face does not occur, and if it is 5000 or less, the viscosity at the time of dissolution is good, and a resin layer can be sufficiently applied.
The glass transition temperature of the alcohol-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 may occur. 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 alcohol-soluble resin and a crosslinking agent suitable for each of them to form a resin layer. The crosslinking agent is not particularly limited, and a conventionally known crosslinking agent is used. For example, for water-soluble resins having a hydroxyl group such as partially saponified polyvinyl alcohols, glyoxal, glutaraldehyde, and alcohol-soluble epoxy compounds can be used, and organic titanium compounds or zirconium compounds are particularly preferable. Among these, 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 excellent in crosslinkability. preferable.
For an alcohol-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 an alcohol mixed with the alcohol-soluble resin and the crosslinking agent, or mixed with additives such as an antifoaming agent, a dispersant, an antifungal agent, an antiseptic agent, and a rust inhibitor as necessary. It is formed by applying a resin layer coating solution prepared as an alcohol solution obtained by dissolving in a non-magnetic 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 from the provided resin layer. If the thickness exceeds 2.0 μm, the magnetic recording medium having the thickness of the resin layer This is because the influence on the thickness is increased, which may adversely affect the rigidity of the magnetic recording medium and the head contact. Further, since the rigidity is lowered, it is disadvantageous for dimensional stability.
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. You can also do the method.
As a method for forming the resin layer on the surface of the nonmagnetic support, it is preferable to form the resin layer on the surface of the nonmagnetic support by a conventionally known coating method. Coating methods include air doctor coater, blade coater, rod coater, extrusion coater, air knife coater, squeeze coater, impregnation coater, reverse roll coater, transfer roll coater, gravure coater, kiss coater, cast coater, curtain coater, spray coater, die coater. And spin coater.
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 a thermoplastic resin such as a polymer or copolymer, phenol resin, epoxy resin, urea resin, melamine resin, alkyd resin, acrylic reaction resin, formaldehyde resin, silicone resin, polyamide resin, polyamideimide Thermosetting resins such as fats, epoxy-polyamide resins, polyurethane resins, urethane-urea resins, polyester resins, mixtures of polyester resins and isocyanate prepolymers, mixtures of polyester polyols and polyisocyanates, and mixtures of polyurethanes and polyisocyanates A reactive resin or a mixture thereof can be used. Of these, polyester resins are preferred because they are excellent in physical properties such as adhesion, glass transition temperature and solubility.
Magnetic tapes for computers with a recording capacity of 1 TB or more are used to increase the surface recording density by reducing the track width of the recording tracks to increase the recording density in the width direction of the magnetic tape and reducing the recording wavelength. The recording density in the longitudinal direction is increased. For this reason, in a magnetic tape for computers with a recording capacity of 1 TB or more, the recording wavelength is as extremely small as 0.5 μm or less, and the thickness of the magnetic layer is recorded in order to reduce the thickness loss during recording / reproduction due to the self-demagnetization action. The 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 is practically difficult to form a uniform magnetic layer, or sufficient output may not be obtained. This is because the thickness loss during reproduction 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.

Hereinafter, the components of the present invention will be described in detail.
<Magnetic powder>
A conventionally well-known magnetic powder can be used for the magnetic powder used for manufacture of a magnetic coating material in this invention. For example, ferromagnetic iron metal magnetic powder, iron nitride magnetic powder, plate-shaped hexagonal ferrite magnetic powder and the like are preferably used. The average particle size of the magnetic powder is preferably 10 nm or more and 50 nm or less. 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 diameter is obtained by measuring the particle size of a photograph taken with a transmission electron microscope (TEM) and calculating the number average value of at least 300.
<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 etc. which are contained in a binder, and bridge | crosslinks.
Examples of such crosslinking agents include tolylene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, reaction products of these isocyanates with 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 at a ratio of 5 to 50 parts by weight with respect to 100 parts by weight of the binder.
Further, instead of the thermosetting crosslinking agent as described above, a radiation curable resin may be used if possible in terms of equipment. As the radiation curable resin, an acrylic monomer or an acrylic oligomer is used.
<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, conventionally known 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.
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. If necessary, two or more carbon blacks having different average particle diameters may be used. The content of the abrasive is preferably 1 to 15 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. As the fatty acid, it is preferable to use a fatty acid having 10 or more carbon atoms. 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>
Conventionally known dispersants can be used to satisfactorily disperse additives such as magnetic powder, abrasive and carbon black. In any layer, the dispersant is usually added in the range of 0.5 to 10 parts by weight with respect to 100 parts by weight of the binder resin.
In the present invention, an organic solvent, an additive component, and the like are used together with the magnetic powder and binder described above to produce a magnetic paint by dispersion, and then this magnetic paint is used in accordance with a conventional method. A magnetic recording medium is manufactured by applying on a magnetic support and drying to form a magnetic layer and passing through the required processing steps.

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. When the magnetic layer is formed on one side of the nonmagnetic support, it is preferable to form a backcoat layer on the back side.
<Non-magnetic support>
The thickness of the nonmagnetic support is usually 1.5 to 11 μm. 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. 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. At present, the mechanism is unknown, but from the entrance side of the track of the magnetic head. This is because the output variation between the output sides becomes large (flatness is inferior). 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, especially in the linear recording type, 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 non-magnetic support and the effect of improving the durability are reduced, and if it exceeds 1.0 μm, 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 30 to 100 nm and the minor axis length is 5 to 30 nm. Is preferred. In the case of a granular shape, a particle size of 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.
As the calendering roll used in the smoothing process of the coating type recording medium, heat-resistant plastic rolls such as epoxy, polyester, nylon, polyimide, polyamide, polyimide amide (kneaded with carbon, metal and other inorganic compounds) It may be present) and a combination of metal rolls (a combination of 3 to 7 stages) or metal rolls.
<Magnetic layer>
The thickness of the magnetic layer is preferably in the range of 10 to 150 nm, and in order to further improve the short wavelength recording characteristics, the range of 20 to 100 nm is more preferable, and the range of 30 to 70 nm is more preferable. 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, and more preferably 0.0036 to 0.05 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 with 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 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.
Example 1
<Resin liquid component>
・ Polyacrylic acid 100 parts ・ Crosslinking agent Epoxy (TETRAD-C manufactured by Mitsubishi Gas Chemical Company) 10 parts ・ Isopropanol 1320 parts << Undercoat paint component >>
(1) Component, acicular iron oxide (average major axis length 100 nm) 68 parts, carbon black (average particle diameter 25 nm) 20 parts, granular alumina powder (average particle diameter 100 nm) 12 parts, methyl acid phosphate 1 part, chloride 9 parts of vinyl-hydroxypropyl acrylate copolymer (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 (THF) 13 parts ・ Cyclohexanone 63 parts ・ Methyl ethyl ketone (MEK) 137 parts (2) component ・ Butyl stearate 2 parts ・ Cyclohexanone 50 parts ・ Toluene 50 parts (3) ingredient ・ Polyisocyanate 2.5 parts ・ Cyclohexanone 9 Part / 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 diameter: 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) Compounding process component / polyisocyanate 1.5 parts / methyl ethyl ketone / cyclohexanone (MEK / A) 29 parts In the above primer coating component, after kneading component (1) with a batch kneader, add component (2) After stirring, dispersion treatment was performed using a sand mill with a residence time of 60 minutes, and after adding (3), stirring and filtering, a primer coating was obtained.

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 blending process component (3) to this, 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 consisting of a metal roll under conditions of a coating 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 0.8 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 30 parts) ・ cyclohexanone 260 parts ・ toluene 260 parts ・ methyl ethyl ketone (MEK) 525 parts The above coating composition for a back coat layer was dispersed in a sand mill for a residence time of 45 minutes, and then 15 parts of a polyisocyanate was added to the paint for the back coat layer. After filtering and filtering, it was applied to the opposite surface of the magnetic layer of the magnetic sheet prepared above 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 an organic titanium compound, ORGATICS TA-10 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.
(Comparative Example 3)
A magnetic tape for evaluation was obtained in the same manner as in Example 1 except that the resin of the resin liquid component was changed to polyvinyl alcohol and the solvent was changed to water.
The measurement method and evaluation method performed in the present invention are described below.
<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.
<Evaluation of error>
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% 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. If the number of errors is less than 100, there is no practical problem.

<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 / 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. Practically, it may be within 1200 ppm.

表１から分るように、本発明に係る、実施例１〜６の評価用磁気テープは、非磁性支持体の突起高さが抑えられるため、エラーが少なく、膨張率も小さい。これに対して、樹脂層を設けない、比較例１は、エラーが多く、膨張率が大きい。また、樹脂層を設けても、架橋させていない比較例２は、エラーは少ないものの、膨張率が大きい。水溶性樹脂を用いた比較例３は、樹脂液において泡が多く発生するために、支持体の突起は被覆するものの塗布中の消泡による塗膜表面にあらたな突起が発生するので、エラー個数が多い。

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. In Comparative Example 3 using a water-soluble resin, since many bubbles are generated in the resin liquid, the protrusions of the support are coated, but new protrusions are generated on the surface of the coating film due to defoaming during application. There are many.

Claims (2)

On one main surface of the nonmagnetic support, a resin layer, an undercoat layer containing nonmagnetic powder and a binder on the resin layer, and a magnetic powder and a binder on the undercoat layer A magnetic recording medium having at least one magnetic layer, and having a backcoat layer containing a nonmagnetic powder and a binder on the other main surface of the nonmagnetic support.
A magnetic recording medium, wherein the resin contained in the resin layer is an alcohol-soluble resin and cured by crosslinking. The magnetic recording medium according to claim 1, wherein the resin layer has a thickness of 0.1 to 2.0 μm.