JP2003346324A - Magnetic recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetic recording medium, having a magnetic layer of superior smoothness which is superior in electromagnetic conversion characteristics and traveling resistance. <P>SOLUTION: The magnetic recording medium has an undercoat layer and at least a single-layer magnetic layer, containing a ferromagnetic powder and a binder on its nonmagnetic base material, in this order. The undercoat layer contains a polyamide resin or polyamide ester resin, which contains a polymerized fatty acid as a monomer unit. <P>COPYRIGHT: (C)2004,JPO

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium having excellent coating film smoothness, electromagnetic conversion characteristics and running durability.

[0002]

2. Description of the Related Art As tape-like magnetic recording media for audio, video, and computers, and disk-like magnetic recording media such as flexible disks, γ-iron oxide,
Magnetic recording media in which a magnetic layer in which ferromagnetic fine powder such as Co-containing iron oxide, chromium oxide, and ferromagnetic metal fine powder is dispersed in a binder are provided on a nonmagnetic support are used. In general, polyethylene terephthalate, polyethylene naphthalate, or the like is used as the nonmagnetic support used in the magnetic recording medium. Since these supports are stretched and highly crystallized, they have high mechanical strength and excellent solvent resistance.

A magnetic layer obtained by applying a coating liquid in which a ferromagnetic fine powder is dispersed in a binder to a nonmagnetic support has a high filling degree of the ferromagnetic fine powder, a small elongation at break, and is brittle. Therefore, when it is formed without providing an undercoat layer, the magnetic layer is easily broken by applying a mechanical force, and may be peeled off from the nonmagnetic support. Therefore, an undercoat layer is provided on the nonmagnetic support, and the magnetic layer is strongly bonded onto the nonmagnetic support. For example, JP-A-7-2914
No. 8 proposes to provide an undercoat layer made of polyamide on a polyamide support to improve adhesion to the support.

However, conventionally used resin components for forming an undercoat layer have high solvent solubility. for that reason,
When a magnetic layer is applied on the undercoat layer, the undercoat layer swells,
There was a problem that the surface smoothness of the magnetic layer was lowered. Furthermore, since the resin component that forms the undercoat layer dissolves in the solvent used in the magnetic layer coating solution, the undercoat resin component may precipitate on the surface of the magnetic layer and form fine crystals after long-term storage. there were. Since this fine precipitate causes a dropout failure, it has a great influence on a magnetic recording medium for high-density recording, particularly with a short recording wavelength, and has become a serious problem.

[0005]

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a magnetic recording medium having excellent magnetic layer smoothness, excellent electromagnetic conversion characteristics, and excellent running durability. .

[0006]

The above object of the present invention is to provide a magnetic recording medium comprising, in this order, an undercoat layer and at least one magnetic layer containing ferromagnetic powder and a binder on a nonmagnetic support. The undercoat layer is achieved by a magnetic recording medium comprising a polyamide resin or a polyamide ester resin containing a polymerized fatty acid as a monomer unit. In the magnetic recording medium, the number of protrusions on the surface of the magnetic layer having a height of 10 to 20 nm as measured with an atomic force microscope (AFM) is preferably 5 to 1000/100 (μm) ² .

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The magnetic recording medium of the present invention will be described in detail below. [Undercoat layer] The magnetic recording medium of the present invention is characterized in that the undercoat layer contains a polyamide resin or a polyamide ester resin containing a polymerized fatty acid as a monomer unit.
When a polymerized fatty acid is used as a dibasic acid component of a polyamide resin or a polyesteramide resin, the obtained polyamide resin and polyamide ester resin are soluble in a hydrophilic solvent such as alcohol or water. As a result, it is possible to obtain an effect that it is difficult to dissolve and swell in MEK, cyclohexanone, THF or the like generally used as a solvent in the magnetic layer coating solution. Thereby, by applying the undercoat layer on the nonmagnetic support, and further applying the magnetic layer thereon, the undercoat layer swells with the solvent contained in the magnetic layer coating solution.
A decrease in surface smoothness of the magnetic layer can be suppressed. Furthermore, when polymerized fatty acids are used in place of known aliphatic dibasic acids and aromatic dibasic acids such as adipic acid, sebacic acid and phthalic acid, the resulting coating solution containing polyamide or polyamide ester has a low solution viscosity. Therefore, the leveling property of the coating layer is high, and a smooth undercoat layer can be formed. This
The surface smoothness of the magnetic layer applied on the undercoat layer can also be improved. This is presumably because the polymerized fatty acid has branched side chains, so that the association of amide groups and ester groups in the coating solution can be prevented sterically. In addition, by providing the undercoat layer, fine projections on the surface of the nonmagnetic support can be shielded, and an extremely smooth coating film can be formed, so that excellent electromagnetic conversion characteristics can be obtained. In addition, the undercoat layer used in the present invention has high adhesion to polyester films such as polyethylene terephthalate and polyethylene naphthalate generally used as a support for magnetic recording media, so that excellent running durability can be obtained. it can.

In the present invention, the polyamide resin and polyamide ester resin that can be used for the undercoat layer contain a polymerized fatty acid as an essential polymerization component. The polyamide resin is, for example, a resin obtained by condensing a dibasic acid and a diamine compound.
It can be obtained by a known polymerization method as described in “Polyamide resin” (published by Nikkan Kogyo Shimbun) or “Synthetic polymer V” (published by Asakura Shoten). The polyamide ester resin is prepared by reacting a diamine compound with a dicarboxylic acid component having an ester group obtained by transesterification of dibasic acid and glycol in an excess of dibasic acid, by the same polymerization method as that for the polyamide resin. Can be obtained. The ester compound can be obtained by a dehydration condensation reaction described in Plastic Material Course 10 “Polyester Resin” (published by Nikkan Kogyo Shimbun).

The polymerized fatty acid is a fatty acid usually obtained by polymerizing an unsaturated fatty acid having 8 to 30 carbon atoms or a fatty acid ester derivative thereof. Unsaturated fatty acids include corn oil, cottonseed oil, soybean oil, olive oil, rapeseed oil,
Vegetable oil such as safflower oil, castor oil, tall oil, beef tallow,
Animal fats and oils such as pork fat and chicken oil, fish oil such as cod oil, squid oil, sardine oil, mackerel oil and tuna oil, and purified unsaturated fatty acids such as linoleic acid and oleic acid can be used. Polymerized fatty acids obtained by polymerizing these raw materials by a known method are generally those containing dimer acid as a main component and monomer acid or polymer acid higher than trimer acid as a by-product, These general polymerized fatty acids can be used in the present invention. In addition, a polymer obtained by purifying a polymer by distillation or chromatographic methods and having a polymer acid higher than dimer acid or trimer acid can be used in the present invention. Further, hydrogenated polymerized fatty acids obtained by hydrogenating unsaturated double bonds remaining in the polymerized fatty acids can also be used in the present invention.

Of these, dimer acid and hydrogenated dimer acid represented by the following formula are preferred. The purity of the dimer acid is preferably 90% or more, more preferably 9
It is 5% or more, and hydrogenated one is preferable. Examples of commercial products of the dimer acids include Prepol manufactured by Unikema Corporation.

[0011]

[Chemical 1]

In the present invention, in the polymerization of polyamide ester resin or polyamide ester resin, it is preferable to use 10 to 100 mol% of the above polymerized fatty acid with respect to the total dibasic acid component. By using a polyamide resin or a polyamide ester resin in which the polymerized fatty acid is used in an amount within the above range, the effects of the present invention can be reliably obtained.

Polyamide resin In the present invention, the dibasic acid that can be used in combination with the above-mentioned polymerized fatty acid as the dibasic acid component of the polyamide resin includes terephthalic acid, isophthalic acid, orthophthalic acid, 1,5 naphthalene dicarboxylic acid, and 2,6 naphthalene. Dicarboxylic acid,
Aromatic dicarboxylic acids such as 4,4′diphenyldicarboxylic acid, 2,2′diphenyldicarboxylic acid, 4,4′diphenyletherdicarboxylic acid; aliphatic dicarboxylic acids such as succinic acid, adipic acid, azelaic acid, sebacic acid, and dodecanedicarboxylic acid Examples include acids; alicyclic dicarboxylic acids such as 1,4 cyclohexane dicarboxylic acid, 1,3 cyclohexyl dicarboxylic acid, 1,2, cyclohexane dicarboxylic acid, and 4 methyl 1,2 cyclohexane dicarboxylic acid. Among these, preferred are adipic acid, sebacic acid, orthophthalic acid, and 2,6 naphthalenedicarboxylic acid.

In the present invention, the diamine compound that can be used as a raw material for the polyamide resin includes propylene diamine, ethylene diamine, diaminobutane,
Hexamethylenediamine, trimethylhexamethylenediamine, nonamethylenediamine, undecamethylenediamine, dodecamethylenediamine, bis (4,4'aminocyclohexyl) methane, 4,4'diphenylmethanediamine, biphenyldiamine, metaxylylenediamine, diaminoethyl Examples include piperazine and diaminopropylpiperazine. Of these, ethylenediamine and metaxylylenediamine are preferable.

Polyamide ester resin In the present invention, a dicarboxylic acid compound having an ester group can be used in combination with the polymerized fatty acid as a dibasic acid component of the polyamide ester resin. The dicarboxylic acid compound having an ester group can be obtained, for example, by subjecting a dibasic acid and a glycol to an ester exchange reaction in an excess of the dibasic acid. In the transesterification reaction, known dibasic acids can be used, such as terephthalic acid, isophthalic acid, orthophthalic acid, 1,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid,
Aromatic dicarboxylic acids such as 4′diphenyldicarboxylic acid, 2,2′diphenyldicarboxylic acid, and 4,4′diphenyletherdicarboxylic acid; aliphatic dicarboxylic acids such as succinic acid, adipic acid, azelaic acid, sebacic acid, and dodecanedicarboxylic acid; 1,4 cyclohexanedicarboxylic acid,
Mention may be made of alicyclic dicarboxylic acids such as 1,3 cyclohexyl dicarboxylic acid, 1,2 cyclohexane dicarboxylic acid, 4 methyl 1,2 cyclohexane dicarboxylic acid. Among these, preferred are adipic acid, sebacic acid,
Orthophthalic acid, 2,6-naphthalenedicarboxylic acid.

Examples of glycol components that can be used for the dicarboxylic acid component having an ester group include ethylene glycol, diethylene glycol, propylene glycol, 1,3 propanediol, 1,4 butanediol, 1,5 pentanediol, 1,6 Hexanediol, 1,9 nonanediol, neopentyl glycol,
Triethylene glycol, tetraethylene glycol,
Dipropylene glycol, 2,2,4 trimethyl 1,3
Pentanediol, 2-ethyl-2-butyl-1,3-propanediol, cyclohexanediol, cyclohexanedimethanol, dimethyloltricyclodecane, bisphenol A, hydrogenated bisphenol A, ethylene oxide of bisphenol A, or propylene oxide adduct, hydrogenated bisphenol Examples thereof include ethylene oxide or propylene oxide adduct of A, aminobenzyl alcohol, lauric acid diethanolamide, and dimer diol. Of these, preferred are ethylene glycol, triethylene glycol and diethylene glycol.

Examples of the diamine compound used as a raw material for the polyamide ester resin include propylene diamine,
Ethylenediamine, diaminobutane, hexamethylenediamine, trimethylhexamethylenediamine, nonamethylenediamine, undecamethylenediamine, dodecamethylenediamine, bis (4,4'aminocyclohexyl)
Examples include methane, 4,4′diphenylmethanediamine, biphenyldiamine, metaxylylenediamine, diaminoethylpiperazine, and diaminopropylpiperazine. Among them, preferred is ethylenediamine,
Metaxylylenediamine.

The ratio of the amide group to the ester group in the polyamide ester resin is preferably amide group / ester group = 2/8 mol to 8/2 mol ratio. Within this range, excellent solvent solubility can be obtained.

In the present invention, the polyamide resin and the polyamide ester resin can also contain polar groups such as amino group, hydroxyl group, carboxylic acid, sulfonic acid and metal salts thereof. These polar groups can be introduced as a residue contained in the dibasic acid or glycol component, and are preferably contained in the resin in an amount of 10 eq / ton to 500 eq / ton, and an amount of 50 to 300 eq / ton More preferably, it is contained. Within this range, excellent solvent solubility can be obtained.

The glass transition temperature of the polyamide resin and the polyamide ester resin is preferably 40 to 150 ° C., more preferably 60 to 100 ° C. If the glass transition temperature is 40 ° C. or higher, the sticking failure to the roll is less likely to occur in the coating process, and if it is 150 ° C. or lower, the coating film strength is high and the adhesion is improved.

The molecular weight of the polyamide resin and the polyamide ester resin is preferably 20,000 to 200,000, more preferably 40,000 to 100,000 in terms of weight average molecular weight. 2
If it is 10,000 or more, the coating film strength is high and the adhesion to the support is improved, and if it is 200,000 or less, the solvent solubility is high and coating is easy.

In the magnetic recording medium of the present invention, the thickness of the undercoat layer containing the polyamide resin or polyamide ester resin is preferably 0.1 to 1.5 μm,
More preferably, it is 0.5-1.0 micrometer. When the thickness of the undercoat layer is 0.1 μm or more, sufficient coating film smoothness can be obtained, and when the thickness is 1.5 μm or less, the coating film is easily dried and adhesion failure is unlikely to occur. When the undercoat layer is applied, alcohols such as methanol, ethanol, propanol, isopropanol, butanol and isobutanol; and acetates such as ethyl acetate, butyl acetate and propyl acetate can be used as a solvent. Of these, isopropanol and butanol are preferred.

[Nonmagnetic Support] Nonmagnetic supports that can be used in the magnetic recording medium of the present invention include biaxially stretched polyethylene terephthalate, polyethylene naphthalate, polyamide, polyamideimide, aromatic polyamide, and the like. A publicly known thing can be mentioned. Among these, polyethylene terephthalate, polyethylene naphthalate and polyamide are preferable. These nonmagnetic supports may be subjected beforehand to corona discharge, plasma treatment, easy adhesion treatment, heat treatment and the like. The center line average surface roughness of the nonmagnetic support is preferably 3 to 10 nm at a cutoff value of 0.25 mm. These non-magnetic supports preferably have not only a small center line average surface roughness but also no coarse protrusions of 1 μm or more.

In the magnetic recording medium of the present invention, an undercoat layer containing a polyamide resin or a polyamide ester resin containing a polymerized fatty acid as a monomer unit is formed on the nonmagnetic support, and then a nonmagnetic underlayer is formed on the undercoat layer. Alternatively, it can be produced by forming the magnetic layer after forming the magnetic underlayer, or by forming the magnetic layer directly on the undercoat layer. The nonmagnetic layer, magnetic underlayer, or magnetic layer can be formed by applying a nonmagnetic powder or a composition in which magnetic powder is dispersed in a binder.

[Binder] The binder used in the non-magnetic layer, the magnetic lower layer, or the magnetic layer includes polyurethane resin, polyester resin, polyamide resin, vinyl chloride resin, styrene, acrylonitrile, methyl methacrylate, and the like. Polymerized acrylic resins, cellulose resins such as nitrocellulose, epoxy resins, phenoxy resins, polyvinyl acetals, polyvinyl alkylals such as polyvinyl butyral, and the like can be used singly or in combination. Among these, a polyurethane resin, a vinyl chloride resin, and an acrylic resin are preferable. The binder preferably has a functional group (polar group) that is adsorbed on the surface of the powder in order to improve the dispersibility of the magnetic substance and the nonmagnetic powder. Preferred functional groups include —SO ₃ M, —SO ₄ M, —PO (OM) ₂ , —O.
_{PO (OM) 2, -COOM,} > NSO 3 M,> NRS
O ₃ M, —NR ¹ R ² , —N ⁺ R ¹ R ² R ³ X ^{— and the} like can be mentioned. Here, M is hydrogen or an alkali metal such as Na or K,
R is an alkylene group, R ¹ , R ² and R ³ are an alkyl group, a hydroxyalkyl group or hydrogen, and X is a halogen such as Cl or Br. The amount of functional groups in the binder is from 10 μeq / g
It is preferably 200 μeq / g, more preferably 30 μ
It is preferable that it is eq / g-120 microeq / g. Within this range, the dispersibility is good.

In addition to the adsorptive functional group, the binder may be provided with a functional group having an active hydrogen such as an —OH group in order to react with an isocyanate curing agent to form a crosslinked structure and improve the strength of the coating film. preferable. The amount is 0.1 meq / g
It is preferably ˜2 meq / g. The molecular weight of the binder is preferably 10,000 to 200,000 in terms of weight average molecular weight, more preferably 20,000 to 10,000.
0. Within this range, the coating film strength and durability are high, and the dispersibility is good.

The polyurethane resin which is a preferable binder is described in detail in, for example, “Polyurethane Resin Handbook” (edited by Keiji Iwata, Nikkan Kogyo Shimbun, 1986). Usually, a long chain diol and a short chain diol (chain extender) are used. And may be obtained by addition polymerization of a diisocyanate compound. As the long-chain diol, polyester diol, polyether diol, polyether ester diol, polycarbonate diol, polyolefin diol and the like having a molecular weight of 500 to 5000 can be used. Depending on the type of this long-chain polyol, it is called polyester urethane, polyether urethane, polyether ester urethane, polycarbonate urethane or the like.

The polyester diol is obtained by condensation polymerization of an aliphatic dibasic acid such as adipic acid, sebacic acid or azelaic acid, or an aromatic dibasic acid such as isophthalic acid, orthophthalic acid, terephthalic acid or naphthalenedicarboxylic acid and glycol. be able to. As glycol component,
Ethylene glycol, 1,2-propylene glycol,
1,3-propanediol, 1,4-butanediol,
1,5-pentanediol, 3-methyl-1,5-pentanediol, 1,6-hexanediol, 2,2-dimethyl-1,3-propanediol, 1,8-octanediol, 1,9-nonane Diol, cyclohexanediol, cyclohexanedimethanol, hydrogenated bisphenol A, and the like can be used. In addition, polycaprolactone diol and polyvalerolactone diol obtained by ring-opening polymerization of lactone such as ε-caprolactone and γ-valerolactone can also be used as the polyester diol. From the viewpoint of hydrolysis resistance, the polyester diol is preferably one having a branched side chain, or one obtained from an aromatic or alicyclic raw material.

Polyether diols include polyethylene glycol, polypropylene glycol, polytetramethylene glycol, bisphenol A, bisphenol S, bisphenol P, and hydrogenated bisphenol A.
A product obtained by addition polymerization of an alkylene oxide such as ethylene oxide or propylene oxide to an aromatic glycol or alicyclic diol such as the above can be used.

These long-chain diols can be used in combination of a plurality of types. The short chain diol can be selected from the same group of compounds as exemplified in the glycol component of the polyester diol. In addition, when a small amount of trifunctional or higher polyhydric alcohols such as trimethylolethane, trimethylolpropane, pentaerythritol, etc. are used in combination, a branched polyurethane resin can be obtained to reduce the solution viscosity or increase the OH group at the end of the polyurethane. With this, the curability with the isocyanate curing agent can be increased.

As the diisocyanate compound, MDI
(Diphenylmethane diisocyanate), 2,4-TD
I (tolylene diisocyanate), 2,6-TDI,
1,5-NDI (Naphthalene diisocyanate), TO
Aromatic diisocyanates such as DI (tolidine diisocyanate), p-phenylene diisocyanate, XDI (xylylene diisocyanate), transcyclohexane-1,4-diisocyanate, HDI (hexamethylene diisocyanate), IPDI (isophorone diisocyanate), H ₆ XDI (hydrogen) Aliphatic and alicyclic diisocyanates such as added xylylene diisocyanate) and H _{1 2} MDI (hydrogenated diphenylmethane diisocyanate) can be used.

The composition of the long chain diol / short chain diol / diisocyanate in the polyurethane resin is preferably (80 to 15% by weight) / (5 to 40% by weight) / (15 to 50% by weight). The urethane group concentration of the polyurethane resin is preferably 1 meq / g to 5 meq / g, and more preferably 1.5 meq / g to 4.5 meq / g. Within this range, high mechanical strength can be obtained. Furthermore, if it exists in this range, since the coating-film viscosity is low, the outstanding dispersibility can be obtained. The glass transition temperature of the polyurethane resin is preferably 0 to 200 ° C, and more preferably 40 to 160 ° C. Within this range, durability is high and good calendar moldability is obtained, so that high electromagnetic conversion characteristics can be obtained. As a method for introducing the above-mentioned adsorptive functional group (polar group) into the polyurethane resin, a method using a functional group as a part of a monomer of a long-chain diol, a method using a part of a short-chain diol, or after polymerizing polyurethane, For example, a method of introducing a polar group by a polymer reaction can be used.

Examples of the vinyl chloride resin used as the binder include those obtained by copolymerizing a vinyl chloride monomer and various monomers. As copolymerization monomers, fatty acid vinyl esters such as vinyl acetate and vinyl propionate; methyl (meth) acrylate, ethyl (meth) acrylate, isopropyl (meth) acrylate, butyl (meth) acrylate, benzyl (meth) acrylate, etc. Acrylates and methacrylates; alkyl allyl ethers such as allyl methyl ether, allyl ethyl ether, allyl propyl ether, allyl butyl ether; other styrene, α-methyl styrene, vinylidene chloride, acrylonitrile, ethylene, butadiene, acrylamide, co-functional groups As polymerization monomers, vinyl alcohol, 2-hydroxyethyl (meth) acrylate, polyethylene glycol (meth) acrylate, 2-hydroxypropyl (meth) acrylate Relate, 3-hydroxypropyl (meth) acrylate, polypropylene glycol (meth) acrylate, 2-hydroxyethyl allyl ether, 2-hydroxypropyl allyl ether, 3-hydroxypropyl allyl ether, p-vinylphenol, maleic acid, maleic anhydride Acrylic acid, methacrylic acid, glycidyl (meth) acrylate, allyl glycidyl ether, phosphoethyl (meth) acrylate, sulfoethyl (meth) acrylate, p-styrene sulfonic acid, and Na salts and K salts thereof can be used. In addition, (meth) acrylate means what contains at least any one of an acrylate and a methacrylate.

The composition of the vinyl chloride monomer in the vinyl chloride resin is preferably 60 to 95% by weight. Within this range, high mechanical strength can be obtained.
Furthermore, if it exists in this range, since solvent solubility is high and solution viscosity is low, dispersibility is favorable. The preferable amount of the functional group for enhancing the curability with the adsorption functional group (polar group) and the polyisocyanate curing agent is as described above. In order to introduce these functional groups, the above-mentioned functional group-containing monomers may be copolymerized, or functional groups may be introduced by polymer reaction after copolymerization of vinyl chloride resin. The degree of polymerization is preferably 200 to 600, more preferably 24.
0-450. Within this range, high mechanical strength can be obtained, and the solution viscosity is low and the dispersibility is good.

In the present invention, a curing agent can be used to crosslink and cure the binder to increase the mechanical strength and heat resistance of the coating film. Preferable curing agents include polyisocyanate compounds. Among these, it is preferable to use a tri- or higher functional polyisocyanate. Specifically, a compound obtained by adding 3 mol of TDI (tolylene diisocyanate) to trimethylolpropane (TMP), HMP to TMP
Adduct type polyisocyanate compound such as a compound obtained by adding 3 moles of DI (hexamethylene diisocyanate), a compound obtained by adding 3 moles of IPDI (isophorone diisocyanate) to TMP, a compound obtained by adding 3 moles of XDI (xylylene diisocyanate) to TMP; Condensed isocyanurate type trimer, condensed isocyanurate pentamer of TDI, condensed isocyanurate heptamer of TDI, and mixtures thereof; isocyanurate type condensate of HDI, isocyanurate type condensate of IPDI, and crude MDI Etc. can be used. Among these, preferred are a compound obtained by adding 3 mol of TDI to TMP, an isocyanurate type trimer of TDI, and the like.

In addition to the isocyanate curing agent, a radiation curing type curing agent such as electron beam or ultraviolet ray may be used. In this case, a curing agent having two or more, preferably three or more acryloyl groups or methacryloyl groups in the molecule as a radiation curing functional group can be used. For example, TMP
(Trimethylolpropane) triacrylate, pentaerythritol tetraacrylate, urethane acrylate oligomer, and the like. In this case, it is preferable to introduce a (meth) acryloyl group into the binder in addition to the curing agent. In the case of ultraviolet curing, a photosensitizer is used in combination. It is preferable to add 0 to 80 parts by weight of the curing agent with respect to 100 parts by weight of the binder. Within this range, the dispersibility is good.

[Ferromagnetic powder] As the ferromagnetic powder contained in the magnetic layer, ferromagnetic iron oxide, cobalt-containing ferromagnetic iron oxide or ferromagnetic alloy powder can be used. That S _BET
The specific surface area is preferably 40 to 80 m ² / g,
More preferably, it is 50-70 m < ² > / g. The crystallite size is 12 to 25 nm, preferably 13 to 22 nm, and particularly preferably 14 to 20 nm. The major axis length is preferably 0.05 to 0.25 μm, more preferably 0.07 to 0.2 μm, and particularly preferably 0.08 to 0.15 μm. Ferromagnetic metal powders include Fe, Ni, Fe-Co, Fe-Ni, Co-N
i, Co—Ni—Fe and the like, and within a range of 20% by weight or less of the metal component, aluminum, silicon, sulfur, scandium, titanium, vanadium, chromium, manganese,
List alloys including copper, zinc, yttrium, molybdenum, rhodium, palladium, gold, tin, antimony, boron, barium, tantalum, tungsten, rhenium, silver, lead, phosphorus, lanthanum, cerium, praseodymium, neodymium, tellurium, bismuth be able to. Further, the ferromagnetic metal powder may contain a small amount of water, hydroxide or oxide. The manufacturing method of these ferromagnetic powders is already well-known, and the ferromagnetic powder used by this invention can also be manufactured according to a well-known method. There are no particular restrictions on the shape of the ferromagnetic powder, but needle-like, granular, dice-like, rice-like and plate-like ones are usually used. In particular, it is preferable to use acicular ferromagnetic powder.

The above resin component, curing agent and ferromagnetic powder are kneaded and dispersed together with a solvent such as methyl ethyl ketone, dioxane, cyclohexanone or ethyl acetate which is usually used in the preparation of a magnetic layer coating solution. Can be prepared. The kneading and dispersing can be performed according to a usual method. The magnetic recording medium of the present invention may be one in which an undercoat layer is provided on a nonmagnetic support and a magnetic layer is provided directly thereon, or an undercoat layer is provided on a nonmagnetic support and the upper layer is provided thereon. Further, it may have a binder containing a polyurethane resin used for the magnetic layer and a nonmagnetic lower layer coating layer or a magnetic lower layer coating layer containing a nonmagnetic powder or a ferromagnetic powder.

When the lower coating layer is a nonmagnetic layer, inorganic compounds such as metal oxides, metal carbonates, metal sulfates, metal nitrides, metal carbides and metal sulfides can be used as the nonmagnetic powder. . As an inorganic compound, for example, an alpha conversion rate of 9
0-100% α-alumina, β-alumina, γ-alumina, silicon carbide, chromium oxide, cerium oxide, α-iron oxide, corundum, silicon nitride, titanium carbide, titanium oxide, silicon dioxide, tin oxide, oxidation magnesium,
Tungsten oxide, zirconium oxide, boron nitride, zinc oxide, calcium oxide, calcium sulfate, barium sulfate, molybdenum disulfide and the like can be used alone or in combination. Particularly preferred are titanium dioxide, zinc oxide, iron oxide and barium sulfate, and more preferred is titanium dioxide. The average particle size of these nonmagnetic powders is preferably 0.005 to 2 μm,
It is more preferable that the average particle diameter is ˜0.2 μm, and if necessary, nonmagnetic powders having different average particle diameters can be combined, or even a single nonmagnetic powder can have the same effect by widening the particle diameter distribution. The pH of the nonmagnetic powder is particularly preferably between 6 and 9. Nonmagnetic powder has a specific surface area of 1-100
is preferably m ² / g, further preferably from 5 to 50 m ² / g, particularly preferably 7~40m ² / g. The crystallite size of non-magnetic powder is 0.01μm
It is preferably ~ 2 μm. The amount of oil absorption using DBP is preferably 5 to 100 ml / 100 g,
More preferably, it is 10-80ml / 100g,
It is particularly preferably 20 to 60 ml / 100 g.
The specific gravity is preferably 1 to 12, more preferably 3 to 6. The shape may be any of a needle shape, a spherical shape, a polyhedron shape, and a plate shape.

The surface of these nonmagnetic powders is Al ₂ O ₃ ,
_{SiO 2, TiO 2, ZrO 2} , SnO 2, Sb 2 O 3, Zn
A surface treatment with O is preferred. Particularly preferred for dispersibility are Al ₂ O ₃ , SiO ₂ , TiO ₂ and ZrO ₂ , and more preferred are Al ₂ O ₃ , SiO ₂ and ZrO ₂ . These may be used in combination or may be used alone. Further, a surface-treated layer co-precipitated according to the purpose may be used, or a method of first treating with alumina and then treating the surface layer with silica, or vice versa. The surface treatment layer may be a porous layer depending on the purpose, but it is generally preferable that the surface treatment layer is homogeneous and dense.

When the lower coating layer is a magnetic layer, the ferromagnetic powder includes γ-Fe ₂ O ₃ , Co-modified γ-Fe ₂ O ₃ , α-F.
An alloy containing e as a main component, CrO ₂ or the like can be used. In particular, it is preferable to use Co-modified γ-Fe ₂ O ₃ . When the magnetic recording medium of the present invention has two magnetic layers, the ferromagnetic powder used for the lower magnetic layer preferably has the same composition and performance as the ferromagnetic powder used for the upper magnetic layer. However, it is known that the performance is changed in the upper and lower layers according to the purpose. For example, in order to improve long wavelength recording characteristics, it is desirable to set Hc of the lower magnetic layer lower than that of the upper magnetic layer,
It is effective to make Br of the lower magnetic layer higher than that of the upper magnetic layer. In addition, the advantage by taking a well-known multilayer structure can be given.

Other additives used in the magnetic layer or lower coating layer of the present invention include a lubricating effect, an antistatic effect,
What has a dispersion | distribution effect, a plasticizing effect, etc. can be used. Additives include molybdenum disulfide, tungsten disulfide, graphite, boron nitride, graphite fluoride, silicone oil, silicone with polar groups, fatty acid-modified silicone, fluorine-containing silicone, fluorine-containing alcohol, fluorine-containing ester, polyolefin, Polyglycol, alkyl phosphate ester and alkali metal salt thereof, alkyl sulfate ester and alkali metal salt thereof, polyphenyl ether, fluorine-containing alkyl sulfate ester and alkali metal salt thereof, including an unsaturated bond having 10 to 24 carbon atoms, Moreover, the monobasic fatty acid which may be branched, and these metal salts (Li, Na, K, C
u, etc.), or a monovalent, divalent, trivalent, tetravalent, pentavalent, hexavalent alcohol, 12 to 22 carbon atoms, which may contain an unsaturated bond having 12 to 22 carbon atoms or may be branched. Or an alkoxy alcohol which may be branched, or an unsaturated bond having 10 to 24 carbon atoms,
Moreover, the monobasic fatty acid which may be branched, and C2-C1
A mono-, di-, or di-fatty acid ester or tri-acid comprising any one of monovalent, divalent, trivalent, tetravalent, pentavalent, and hexavalent alcohols that may contain two unsaturated bonds or may be branched. Fatty acid esters, fatty acid esters of monoalkyl ethers of alkylene oxide polymers, fatty acid amides having 2 to 22 carbon atoms, aliphatic amines having 8 to 22 carbon atoms, and the like can be used. Specific examples of these include lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, butyl stearate, oleic acid, linoleic acid, linolenic acid, elaidic acid, octyl stearate, amyl stearate, isooctyl stearate,
Octyl myristate, butoxyethyl stearate,
Examples include anhydrosorbitan monostearate, anhydrosorbitan distearate, anhydrosorbitan tristearate, oleyl alcohol, and lauryl alcohol.

As the lubricant used in the present invention, specifically, manufactured by Nippon Oil & Fats: NAA-102, castor oil hardened fatty acid, NAA-42, cationic SA, Naimine L-20
1, Nonion E-208, Anon BF, Anone LG, Butyl stearate, Butyl laurate, Erucic acid, Kanto Chemical: Oleic acid, Takemoto Yushi: FAL-205, F
AL-123, Shin Nippon Chemical Co., Ltd .: NJ Lube OL, Shin-Etsu Chemical Co., Ltd .: TA-3, Lion Armor Co., Ltd .: Armido P, Lion Co., Ltd .: Duomin TDO, Nisshin Oil Industries: B
A-41G, Sanyo Kasei: Profan 2012E, New Pole PE61, Ionette MS-400, etc. are mentioned.

Nonionic surfactants such as alkylene oxide, glycerin, glycidol, and alkylphenol ethylene oxide adducts; cyclic amines,
Cationic surfactants such as ester amides, quaternary ammonium salts, hydantoin derivatives, heterocycles, phosphonium or sulfoniums; acidic groups such as carboxylic acid, sulfonic acid, phosphoric acid, sulfate ester group, phosphate ester group Anionic surfactants including: amino acids, aminosulfonic acids, sulfuric or phosphate esters of amino alcohols, and amphoteric surfactants such as alkylbedine 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, in addition to the main components, isomers, unreacted materials, side reaction products,
Impurities such as decomposition products, oxides, etc. may be included.
These impurities are preferably 30% by weight or less, more preferably 10% by weight or less.

These lubricants and surfactants used in the present invention can be used in a nonmagnetic layer and a magnetic layer, depending on their types and amounts as required. For example, use of fatty acids with different melting points in the nonmagnetic layer and magnetic layer to control bleed to the surface, use esters with different boiling points and polarities to control bleed to the surface, and adjust the amount of surfactant. However, it is conceivable to improve the stability of coating and to increase the lubricating effect by increasing the amount of lubricant added to the nonmagnetic layer, and of course not limited to the examples shown here. Moreover, you may add all or one part of the additive used by this invention at any process at the time of manufacture of the coating liquid for a magnetic layer or a lower layer. For example, when mixing with a ferromagnetic powder before the kneading step, when adding at a kneading step with a ferromagnetic powder, a binder and a solvent, when adding at a dispersing step, when adding after dispersing, when adding just before coating, etc. There is.

A coating solution prepared from the above materials is applied to an undercoat layer formed on a nonmagnetic support with a thickness of preferably 0.1 to 1.5 μm, more preferably 0.5 to 1.0 μm. To form a lower coating layer or a magnetic layer. In the method for producing a magnetic recording medium of the present invention, for example, an undercoat layer is applied to the surface of a nonmagnetic support under running, and a magnetic layer coating solution is preferably applied thereon with a thickness of the magnetic layer after drying. 0.0
Within a range of 5 to 5 μm, more preferably 0.07 to 1 μm
Apply as follows. Here, a plurality of magnetic layer coating solutions may be applied sequentially or simultaneously, and a lower layer coating solution and a magnetic layer coating solution may be applied sequentially or simultaneously. As a coating machine for applying the above magnetic coating solution or lower layer coating solution, air doctor coating, blade coating, rod coating,
Extrusion coating, air knife coating, squeeze coating, impregnation coating, reverse roll coating, transfer roll coating, gravure coating, kiss coating, cast coating, spray coating, spin coating and the like can be used.
For example, “Latest Coating Technology” (May 31, 1983) issued by the General Technology Center Co., Ltd.
Can be referred to.

The following can be proposed as an example of an apparatus and method for applying the magnetic recording medium of the present invention. (1) First, a lower layer is applied by a coating apparatus such as a gravure, a roll, a blade, and an extrusion that are generally applied in the application of a magnetic layer coating solution, and the lower layer is in an undried state. No. 60-238
The upper layer is applied by a support pressure type extrusion coating apparatus as disclosed in Japanese Patent Application Laid-Open No. 179, Japanese Patent Application Laid-Open No. 2-265672. (2) JP-A-63-88080, JP-A-2-17
The upper and lower layers are applied almost simultaneously by a single coating head having two coating liquid passage slits as disclosed in JP-A No. 971 and JP-A-2-265672. (3) The upper and lower layers are applied almost simultaneously by an extrusion coating apparatus with a backup roll as disclosed in JP-A-2-174965.

A back coat layer (backing layer) may be provided on the surface of the nonmagnetic support used in the present invention on which the magnetic coating solution is not applied. The backcoat layer is coated with a coating solution for forming a backcoat layer in which particulate components such as abrasives and antistatic agents and a binder are dispersed in an organic solvent on the surface of the nonmagnetic support that is not coated with a magnetic coating solution. It is a layer provided as follows. 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 in combination as binders. . By using the polyurethane resin described above as the polyurethane resin used for the back coat layer, the durability can be further improved. In addition, the adhesive layer may be provided in the coating surface of the magnetic coating liquid of a nonmagnetic support body, and the coating liquid for backcoat layer formation.

The coating layer of the magnetic layer coating solution is dried after subjecting the ferromagnetic powder contained in the coating layer of the magnetic layer coating solution to a magnetic field orientation treatment. After being dried in this manner, the coating layer is subjected to a surface smoothing treatment. For the surface smoothing treatment, for example, a super calendar roll or the like can be used.
By performing the surface smoothing treatment, voids generated by removing the solvent during drying disappear and the filling rate of the ferromagnetic powder in the magnetic layer is improved, so that a magnetic recording medium having high electromagnetic conversion characteristics can be obtained. it can. As the calendering roll, a heat resistant plastic roll such as epoxy, polyimide, polyamide, polyamideimide or the like can be used.
Moreover, it can also process with a metal roll.

The magnetic recording medium of the present invention has a surface centerline average roughness of 0.1 to 0.1 at a cutoff value of 0.25 mm.
A surface having extremely excellent smoothness in the range of 5 nm, preferably 1 to 4 nm is preferable as a magnetic recording medium for high-density recording. The centerline average roughness in the above range can be obtained by subjecting the magnetic layer formed by selecting a specific ferromagnetic powder and a binder to the above calendar treatment. For this purpose, the temperature of the calendar roll is set to 60 to 1.
A range of 00 ° C, preferably a range of 70 to 100 ° C, particularly preferably a range of 80 to 100 ° C, and a pressure of 100 to 100 ° C.
In the range of 500 kg / cm, preferably 200-450k
g / cm, particularly preferably 300-400 kg /
It is preferable to perform a calendar process in the cm range. The obtained magnetic recording medium can be cut into a desired size using a cutting machine or the like.

[0051]

The present invention will be described with reference to the following examples.
The present invention is not limited to these. In the examples, “part” means “part by mass”. [Synthesis Example of Polyamide Resin, Polyamide Ester Resin] A reaction vessel equipped with a thermometer, a stirrer, a nitrogen introduction tube, and a dehydration distillation tube was charged with a dibasic acid or an ester compound and a diamine in the proportions shown in Table 1. 200 in a nitrogen gas atmosphere
The amidation reaction was carried out at ˜210 ° C. for 4 hours. Further, 100 ppm of N, N′-hexamethylene-bis (3,5-di-tert-butyl-4-hydroxycinnamic acid amide) as a stabilizer was added to the total amount, and when it became uniform, it was taken out and pelletized. . The obtained resin was dissolved in isopropyl alcohol so as to have a solid content of 5% by weight to obtain a resin solution. Polyamide resins A to E and polyamide ester resins A to E were dissolved in isopropyl alcohol so as to have a solid content of 5% by weight, and used as an undercoat layer coating solution. Since the polyamide resins F to I and the polyamide ester resins F to I are insoluble in isopropyl alcohol, they were dissolved in cyclohexanone to obtain an undercoat layer coating solution.

[Synthesis Example of Polyester Resins A to C] In a reaction vessel equipped with a thermometer, a stirrer, a nitrogen introduction tube, and a dewatering distillation tube, a glycol component with respect to 1 mol of the dibasic acid shown in Table 1. 2.5 mol of tetrabutyl titanate 1
Charged with 100 ppm of zinc acetate and 100 ppm of zinc acetate,
The transesterification was carried out at 210 ° C. for 5 hours. Next, the pressure of the reaction system was reduced to 5 mmHg over 20 minutes, and the temperature was raised to 280 ° C. during this time. 280 ° C, 0.1mmHg
The polycondensation reaction was carried out for 60 minutes. The molten polyester resin was taken out and pelletized. Since the obtained polyester resin is insoluble in isopropyl alcohol, it was dissolved in cyclohexanone so as to have a solid content of 5% by weight, and used as an undercoat layer coating solution. Table 1 shows the composition, glass transition temperature, and weight average molecular weight of the obtained polyamide resin, polyamide ester resin, and polyester resin. The analysis was performed by the following method. Polyester composition: NMR analysis Glass transition temperature: Using a dynamic viscoelasticity measuring device, 2 ° C /
Weight average molecular weight measured at a partial temperature increase and 110 Hz: GPC was used to obtain the eluent DMF and standard polystyrene conversion.

Examples having a single magnetic layer and comparative examples [Example 1] Preparation of magnetic coating solution Ferromagnetic alloy powder (composition: Fe 89 atm%, Co 5
atm%, Y 6 atm%, Hc: 159 kA / m (2
000 Oe), crystallite size: 15 nm, BET specific surface area: 59 m ² / g, major axis diameter: 0.12 μm, acicular ratio:
7, σs: 150 A · m ² / kg (150 emu /
g)) 100 parts are ground with an open kneader for 10 minutes,
Next, SO ₃ Na-containing polyurethane solution (solid content 30
%, SO ₃ Na content 70 μeq / g, weight average molecular weight 4
10 parts (solid content) and cyclohexanone 3
0 parts was added and kneaded for 60 minutes. Next, abrasive (Al ₂ O ₃ , particle size: 0.3 μm) 2 parts carbon black (particle size: 40 μm) 2 parts methyl ethyl ketone / toluene = 1/1 200 parts were added and dispersed in a sand mill for 120 minutes. 5 parts of polyisocyanate (Nihon Polyurethane Coronate 3041) (solid content) 2 parts of butyl stearate 1 part of stearic acid 1 part methyl ethyl ketone 50 parts are stirred and mixed for another 20 minutes, and then a filter having an average pore size of 1 μm is used. Filtration was performed to prepare a magnetic coating solution.

Next, the undercoat layer coating solution containing the undercoat layer resin shown in Table 2 was applied to the surface of a polyethylene naphthalate support having a thickness of 7 μm using a coil bar so that the thickness after drying was 0.5 μm. And then dried on the undercoat layer so that the thickness after drying is 1.5 μm.
The magnetic layer coating solution was applied using a reverse roll. 0.5T (5000 gauss) C with the magnetic layer undried
After magnetic field orientation with o magnet and 0.4T (4000 Gauss) solenoid magnet, calendering by combination of metal roll-metal roll-metal roll-metal roll-metal roll-metal roll-metal roll is performed at a speed of 100 m.
/ Min, linear pressure 300 kg / cm, temperature 90 ° C., and then slit to a width of 3.8 mm. The same method except that the resin for the undercoat layer was changed to the one shown in Table 2,
Examples 2 to 10 and Comparative Examples 1 to 12 were produced. In Comparative Example 12, as the resin for the undercoat layer, JP-A-7-291
AQ nylon A70 manufactured by Toray as described in Japanese Patent No. 48 was used. AQ nylon A-70 is a polyamide resin containing no polymerized fatty acid, and details thereof are disclosed in JP-A-60-2474.
No. 40 publication.

[0055]Implementation with lower non-magnetic layer and upper magnetic layer
Example, comparative example [Example 11] The upper layer magnetic coating solution is the same as in Example 1.
Was used.Preparation of nonmagnetic coating liquid for lower layer α-Fe₂O_Three(Average particle size: 0.15 μm, S_BET: 52
m²/ G, surface treatment: Al₂O_Three, SiO₂, PH: 6.5
~ 8.0) 100 parts crushed with an open kneader for 10 minutes
And then vinyl chloride / vinyl acetate / glycidyl methacrylate = 8
6/9/5 copolymer with hydroxyethyl sulfonate
Compound with added sodium salt (SO _ThreeNa = 6 × 1
0-5 eq / g, epoxy = 10-3 eq / g, Mw
30,000), 7.5 parts, and SO_ThreeNa-containing polyw
Letane solution (solid content 30%, SO_ThreeNa content 70μeq
/ G, weight average molecular weight 40,000) 10 parts (solid content),
Add 30 parts of cyclohexanone and knead for 60 minutes.
It was. Then       Methyl ethyl ketone / cyclohexanone = 6/4 200 parts Was added and dispersed in a sand mill for 120 minutes. to this       5 parts of polyisocyanate (Japan Polyurethane Coronate 3041) Solids)       Butyl stearate 2 parts       1 part of stearic acid       50 parts of methyl ethyl ketone After stirring for another 20 minutes, the average of 1 μm
Filtration using a filter having a pore size, coating solution for lower layer
Was prepared. Next, the resin for the undercoat layer shown in Table 3 is included.
The thickness of the undercoat layer coating solution after drying will be 0.5μm
Polyethylene naphth with a thickness of 7μm using a coil bar
After applying to the surface of the tartrate support, dry it and then
Lower the coating layer so that the thickness after drying is 1.5μm.
The coating thickness of the non-magnetic layer coating liquid is further reduced immediately after drying.
Reverse the upper layer magnetic coating solution to 0.05 μm
Simultaneous multilayer coating was performed using a roll. Apply magnetic coating solution
In a non-dried state of the magnetic coating solution on the non-magnetic support, 0.5
Comagnet of T (5000 Gauss) and 0.4T (4000
After magnetic field orientation with Gaussian solenoid magnet, metal
Roll-Metal roll-Metal roll-Metal roll-Metal roll
Karen by a combination of a metal roll, a metal roll and a metal roll
Dar processing, speed 100m / min, linear pressure 300kg /
cm, temperature 90 ° C, and then 3.8mm width
I did.

[Examples 12 to 20, Comparative Examples 12 to 23] Fabricated in the same manner as in Example 11 except that the resin for the undercoat layer shown in Table 3 was used. In Comparative Example 23, Toray AQ nylon A used in Comparative Example 12 was used as the resin for the undercoat layer.
-70 was used.

Measurement Method Smoothness of Coating Film Using Nanoscope III (AFM: Atomic Force Microscope) manufactured by Digital Instrument, and using a pyramid SiN probe with a ridge angle of 70 #, the number of protrusions in 10 μm square (100 μm ² ) was measured. The measurement was made every 5 nm until the height of the fine protrusion was 20 nm. A single frequency signal of 4.7 MHz was recorded with an optimum recording current using an electromagnetic conversion characteristic DDS4 drive, and the reproduction output was measured. The reproduction output of Comparative Example 1 is shown as a relative value with 0 dB. The tension (g) when the tape was pulled in the direction of 180 degrees after the magnetic layer surface of the tape having an adhesion force of 3.8 mm was applied to the 3M splicing tape, or when the tape was cut was evaluated. Driving durability is 50 ° C, 20% RH environment, the magnetic layer surface is brought into contact with the guide pole used in the DDS4 drive and the load is 10
Multiply g (T1) and repeat at a speed of 8 mm / sec.
Up to 000 passes, the tape edge after running was observed with a differential interference optical microscope and evaluated according to the following rank. Excellent: No cracks are observed. Good: Cracks are observed, but the coating film does not fall off. Bad: The coating film comes off.

[0058]

[Table 1]

[0059]

[Table 2]

[0060]

[Table 3]

Evaluation results An undercoat layer containing a polyamide resin or polyamide ester resin containing a polymerized fatty acid as a monomer unit,
In addition, Examples 1 to 10 having a single-layer magnetic layer thereon were superior to Comparative Examples 1 to 12 having a single-layer magnetic layer in terms of smoothness, electromagnetic conversion characteristics, adhesion, and durability. . Comparative Examples 1 to 3 are examples having an undercoat layer containing a polyester resin and having a single-layer magnetic layer thereon. Comparative Examples 4 to 7 and Comparative Example 12 are examples having an undercoat layer containing polyamide that does not contain a polymerized fatty acid and a single-layer magnetic layer thereon. Comparative Examples 8 to 11 are examples having an undercoat layer containing a polyamide ester not containing a polymerized fatty acid and having a single-layer magnetic layer thereon. All of the above comparative examples were inferior to Examples 1 to 10 having the same layer configuration in all of smoothness, electromagnetic conversion characteristics, adhesion, and durability. Examples 11 to 20 having an undercoat layer containing a polyamide resin or polyamide ester resin containing a polymerized fatty acid as a monomer unit, and having a lower nonmagnetic layer and an upper magnetic layer thereon, have smoothness, electromagnetic conversion characteristics, adhesion Power,
In any of the durability, it was superior to Comparative Examples 12 to 23 having the lower nonmagnetic layer and the upper magnetic layer. Moreover, although the same resin for undercoat layers was used, compared with Examples 1-10 which do not have a lower nonmagnetic layer, it was excellent in smoothness. Comparative Examples 12 to 14 are examples having an undercoat layer containing a polyester resin and having a lower nonmagnetic layer and an upper magnetic layer thereon. Comparative Examples 15 to 18 and Comparative Example 23 are examples having an undercoat layer containing polyamide that does not contain a polymerized fatty acid, and further having a lower nonmagnetic layer and an upper magnetic layer thereon. Comparative Examples 8 to 11 are examples having an undercoat layer containing a polyamide ester containing no polymerized fatty acid, and having a lower nonmagnetic layer and an upper magnetic layer thereon. All of the above comparative examples were inferior to Examples 11 to 20 having the same layer configuration in all of smoothness, electromagnetic conversion characteristics, adhesion, and durability.

[0062]

According to the present invention, a magnetic recording medium having improved electromagnetic characteristics can be provided by smoothing the coating film. Furthermore, the magnetic recording medium of the present invention has high adhesion of the coating film and is excellent in repeated running durability.

Claims (1)

[Claims] 1. A magnetic recording medium having an undercoat layer and at least one magnetic layer containing a ferromagnetic powder and a binder in this order on a nonmagnetic support, wherein the undercoat layer contains a polymerized fatty acid as a monomer unit. A magnetic recording medium comprising a polyamide resin or a polyamide ester resin.