JPH10162348A - Magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a magnetic recording medium not contaminating a head and excellent in running durability and electromagnetic transducing characteristics. SOLUTION: A magnetic layer contg. at least ferromagnetic powder and a binder is formed on a nonmagnetic substrate to obtain the objective magnetic recording medium. The binder is produced by allowing polyol to react with an isocyanato compd. and a compd. having one or more epoxy groups and one or more hydroxyl groups in one molecule and allowing the resultant polyurethane resin to react with a compd. having at least one of polar groups represented by the formulae -SO3 M and -OSO3 M (where M is H, an alkali metal, an alkaline earth metal or an ammonium salt).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION In a magnetic recording medium having a magnetic layer on which a ferromagnetic fine powder and a binder are dispersed on a nonmagnetic support, extremely excellent electromagnetic conversion characteristics, running durability and high temperature and humidity TECHNICAL FIELD The present invention relates to a magnetic recording medium having a storage property under a magnetic field, and more particularly to a magnetic recording medium which does not cause head contamination.

[0002]

2. Description of the Related Art Magnetic recording media are widely used as recording tapes, video tapes, floppy disks and the like. In a magnetic recording medium, a magnetic layer in which ferromagnetic powder is dispersed in a binder is laminated on a nonmagnetic support. The magnetic recording medium is required to be at a high level in various characteristics such as electromagnetic conversion characteristics, running durability and running performance. That is, audio tapes for recording and reproducing music are required to have higher original sound reproduction capabilities. Also, video tapes are required to have excellent electromagnetic conversion characteristics such as excellent original image reproduction capability. The magnetic recording medium is required to have good running durability while having such excellent electromagnetic conversion characteristics. In order to obtain good running durability, an abrasive and a lubricant are generally added to the magnetic layer.

In a device using a magnetic recording medium, since the medium and the magnetic head are in sliding contact with each other, low-molecular components in the binder of the magnetic recording medium float near the surface of the magnetic layer and adhere to the magnetic head. There was a problem that occurs. The dirt on the magnetic head causes deterioration of the electromagnetic conversion characteristics. In particular, in a device for high-density recording, the rotation speed of a magnetic head is increasing. In a digital video tape recorder, the rotation speed of a magnetic head is 9600 rotations / minute, which is 1800 rotations / minute for a consumer analog video tape recorder.
The rotation speed is much higher than that of 5000 rpm for business use, and the sliding speed between the magnetic recording medium and the magnetic head is high. Also, a small magnetic head such as a thin film head is used. It is used, and there is a demand for improvement of contamination of a magnetic head by a component generated from a magnetic recording medium.

As a method for solving such a problem, Japanese Patent Application Laid-Open No. Sho 58-168669 describes a magnetic paint using a polyurethane resin in which an epoxy group is opened and an OH group is introduced. The epoxy group introduced into the polyurethane resin is opened for the purpose of improving
Since the H group was introduced, sufficient dispersibility could not be obtained with the OH group generated by ring opening.

Japanese Patent Application Laid-Open No. 60-238306 discloses a resin to which a salt of an epoxy group-containing polyvinyl chloride, a strong acid containing sulfur and phosphorus is added, and a vinyl chloride resin synthesized by this method. Has good dispersibility,
There is a bias in the binding of the polar group to the binder resin, and there are many binder molecules that do not contain the polar group, so there are many molecules bleeding through the coating film and the running durability is insufficient. Met.

Japanese Patent Publication No. 63-55549 discloses an epoxy or SO ₃ M-containing polyurethane resin containing at least one of amines, carboxylic acids and phenols.
JP-A-8-104731 describes a binder made of a polyurethane resin having an OH group introduced by reacting a seed.
Japanese Patent Application Laid-Open Publication No. H10-157, discloses a curable polyurethane resin composition comprising a polyurethane having a terminal epoxy group having a specific molecular weight, a vinyl chloride polymer having a specific degree of polymerization, an alicyclic acid anhydride and a tertiary amine. JP-A-8-153320 discloses a binder comprising a polyurethane resin having a terminal epoxy group and a sulfonic acid group, a carboxylic acid group, or a quaternary ammonium group and having a number average molecular weight in a specific range. Have been described. These are both introduces an epoxy group and a polar group in the binder molecule, since an epoxy group and a polar group is introduced SO ₃ M groups using diols having separate SO ₃ M , SO ₃
Since the compound for introducing M 2 has a reaction rate greatly different from that of other diols, the introduction of polar groups into the binder resin is biased, and a large number of binder molecules containing no polar groups are present, resulting in poor dispersibility. there were.

Further, Japanese Patent Application Laid-Open No. 54-157603 describes that fine magnetic powder particles are uniformly dispersed and contained in a polyurethane resin having a specific amount of a metal sulfonate group. In addition, the present applicant has filed Japanese Patent Application No. 7-370.
No. 09 proposes increasing the dispersibility by using a polyurethane comprising a short-chain polyol, a long-chain polyol, and an isocyanate. In these, since a polyurethane resin is synthesized using a polar group-containing compound to introduce a polar group, the introduction of the polar group is biased, and a large number of binder molecules containing no polar group exist, resulting in poor dispersibility.

In addition, in the conventional binder, the distribution of the polar group is not uniform, and the binder molecule having no polar group has a considerable amount within the range in which the average amount of introduction of the entire binder is described. Exists. Such a binder molecule containing no polar group is hardly adsorbed on the ferromagnetic powder or the non-magnetic powder, so that not only the dispersibility is inferior, but also the binder molecules move in the coating film and ooze to the surface to be printed on the head. Sliding with the head causes dirt on the head, causing clogging and a decrease in output, thereby lowering reliability. As a result,
The running durability is poor due to the dispersibility and migration of the non-adsorbed resin to the surface of the magnetic layer.

[0009]

DISCLOSURE OF THE INVENTION The present invention provides a coating layer having a high dispersibility, a magnetic layer having excellent surface smoothness, excellent electromagnetic conversion characteristics, excellent running durability in which head dirt, clogging, etc. are prevented, and high temperature. It is an object of the present invention to provide a magnetic recording medium which has excellent storage stability under high humidity and has a small change in the amount of surface binder before and after running.

[0010]

According to the present invention, there is provided a magnetic recording medium having a magnetic layer containing at least a ferromagnetic powder and a binder on a non-magnetic support, wherein the binder is a polyol, an isocyanate compound, One or more epoxy groups and one
-SO ₃ M, -OSO ₃ M (here, M
Is a magnetic recording medium containing a polyurethane resin obtained by reacting a compound containing at least one polar group selected from hydrogen, an alkali metal, an alkaline earth metal, and an ammonium salt). Further, on a non-magnetic support, a lower coating layer containing at least one of a non-magnetic powder and a magnetic powder and a binder, and an upper magnetic layer containing at least a ferromagnetic powder and a binder were provided thereon. In a magnetic recording medium having a plurality of layers, a polyol, an isocyanate compound, and at least one epoxy group and at least one hydroxyl group in a molecule are contained as a binder of at least one of the lower nonmagnetic layer and the upper magnetic layer. -SO ₃ M compounds in the polyurethane resin obtained by reaction of (here M hydrogen, alkali metal, alkaline earth metal, ammonium salts) -OSO ₃ M contains at least one polar group selected from A magnetic recording medium containing a polyurethane resin obtained by reacting a compound and a vinyl chloride resin. The polyurethane resin has a diol having a cyclic structure and a diol having an alkylene oxide added thereto, and a polyol having a molecular weight of 500 to 5000 is contained in the polyurethane resin in an amount of from 0 to 50% by weight, and the diol having a cyclic structure or the diol having a cyclic structure is added to an alkylene oxide. Containing 15 to 50% by weight of a short-chain diol having a molecular weight of 200 to 500 and an ether group derived from the diol and the polyol of 1 to 6 mmol / g with respect to the entire polyurethane resin. The magnetic recording medium described above, wherein the polyurethane resin comprises a polyurethane resin having at least one kind of polar group.
The average polar group content in the polyurethane resin is 3 × 1
The above magnetic recording medium, wherein the magnetic recording medium has a range of 0 ⁻⁵ to 30 × 10 ⁻⁵ eq / g.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS That is, the present invention includes, as a binder, a polyurethane resin having a polar group introduced by reacting a polar group-containing compound with an epoxy group after synthesizing an epoxy group-containing polyurethane. Introducing a polar group into all molecules is advantageous for dispersibility and preventing migration of low molecular components, but in order to introduce the polar group more evenly, the polar group is It has been found that it is possible to uniformly introduce a polar group into a molecule by introducing a polar group after preparation.

When a polar group is introduced into the monomer in advance, the hydrophobicity becomes strong, and the polymer reaction hardly proceeds.
We found that a polar group can be uniformly introduced into a molecule by making a polymer with an epoxy group introduced into the molecule and reacting a sultone such as propane sultone, which can introduce a polar group into the epoxy group. It is a thing.

Hitherto, polyurethane resins and vinyl chloride resins having good mechanical strength and high solubility in selected solvents have been used together with polyisocyanates as binders for magnetic recording media. Further, in the case of a magnetic recording medium having a ferromagnetic powder used for a magnetic layer and a lower coating layer, as a means for further increasing the dispersibility of the lower powder in order to increase the recording density, the above-mentioned polyurethane resin and vinyl chloride resin are used. -SO ₃ M in the binder molecule of
_{-OSO 3 M, -PO (OM)} 2, -COOM ( wherein M represents a hydrogen atom, an alkali metal or ammonium salt), quaternary ammonium salt, it is proposed to introduce a polar group such as an amino group.

[0014] Regarding the storage stability, all the binder molecules used in the magnetic layer and the non-magnetic layer are strongly adsorbed on the magnetic powder and the non-magnetic powder, or react with the polyisocyanate used in combination to form a crosslink.・ It is not fixed, and part remains uncrosslinked in the magnetic coating film.
In particular, storage at high temperature and high humidity causes bleeding on the surface of the magnetic layer and sliding causes head and running system stains during running. Such bleeding depends on the thickness of the magnetic layer,
Not only in the case of a single magnetic layer, but also in a magnetic recording medium in which two or more coating layers are formed using a lower coating layer containing at least one of a nonmagnetic powder and a magnetic powder, It is seen even when the layer is very thin.

These are binders obtained by a conventionally known method which contain a polar group of an average of 10 × 10 ^-5 eq / g-binder, or a binder which does not contain a polar group. Derived from the fact that the agent molecules are contained in a high proportion, the binder molecules that do not contain this polar group are not adsorbed on the magnetic powder and non-magnetic powder, reduce the dispersibility and at the same time preserve, especially Exuded on the magnetic layer surface by storage under high temperature and high humidity,
It was found that this could cause head contamination.

The present inventors have focused on a method of introducing a polar group of a binder resin used for forming a magnetic layer and a coating layer of a nonmagnetic layer on a nonmagnetic support, and have studied dispersibility, runnability, and durability. We have made intensive studies on manufacturing magnetic recording media with excellent electromagnetic conversion characteristics such as storability and storage stability, and practical characteristics.

As a result, a magnetic recording medium in which a magnetic layer containing a ferromagnetic powder and a binder is provided on a nonmagnetic support, or at least one of a nonmagnetic powder and a magnetic powder, and a binder. In a magnetic recording medium having at least two or more layers provided with a lower coating layer containing at least an upper magnetic layer containing at least a ferromagnetic powder and a binder, a magnetic layer, or a lower coating layer or an upper layer As a binder for at least one of the magnetic layers, a polyol, an isocyanate compound, and a polyurethane resin obtained by reacting a compound containing one or more epoxy groups and one or more hydroxyl groups in a molecule with -SO ₃ M,- OSO ₃ M adding a (where M is hydrogen, alkali metal, alkaline earth metal, ammonium salt) compound containing at least one polar group selected from By using a polyurethane resin that is made to react, there are few binder molecules that do not contain polar groups and excellent dispersibility, and because there are few binder molecules that do not contain polar groups, they move in the coating film and bleed to the surface Have been found to provide a highly reliable magnetic recording medium with less clogging and lower output.

The polyurethane resin of the present invention contains a polyol having a molecular weight of 500 to 5,000, which is obtained by adding an alkylene oxide to a diol having a cyclic structure as the skeleton of the polyurethane resin, and contains 0 to 50% by weight of the polyurethane resin. At least one of a diol and a diol obtained by adding an alkylene oxide to a diol having a cyclic structure and having a molecular weight of 200 to 5;
Polyurethane resin containing 15 to 50% by weight of a short-chain diol of No. 00 and containing ether groups derived from the diol and the polyol in an amount of 1 to 6 mmol / g with respect to the entire polyurethane resin is preferable because of its excellent durability. It may be produced from a polyurethane prepolymer such as a polyol, a chain extender and a diisocyanate.

When the polyurethane resin of the binder of the present invention comprises a short-chain diol having a cyclic structure and a long-chain diol having an ether group, the content of the short-chain diol having a cyclic structure in the polyurethane is as follows: It is preferably from 20 to 35% by weight, and if it is less than 20% by weight, the mechanical strength is reduced and the durability is reduced. If the content is 35% by weight or more, the solubility in a solvent decreases, and the dispersibility decreases. Further, the coating film tends to be brittle, and the durability is also reduced.

Specific examples include the following short-chain diols. Bisphenol A, hydrogenated bisphenol A, bisphenol S, bisphenol P and their ethylene oxide, propylene oxide adduct, cyclohexane dimethanol, cyclohexanediol, hydroquinone, bis (2-hydroxyethyl) tetrabromobisphenol A, bis (2-hydroxyethyl ) Tetrabromobisphenol S, bis (2-hydroxyethyl) tetramethylbisphenol S, bis (2-hydroxyethyl) diphenylbisphenol S, bis (2
-Hydroxyethyl) diphenylbiphenol, bis (2-hydroxyethyl) thiodiphenol, bis (2
-Hydroxyethyl) bisphenol F, biphenol, bisphenol fluorene, and bisphenol fluorene hydroxyethyl ether are preferred.

Among them, preferred are bisphenol A, hydrogenated bisphenol A, bisphenol S, bisphenol P and diols having an aromatic or alicyclic group such as ethylene oxide, propylene oxide adduct thereof, cyclohexane dimethanol and cyclohexane diol. is there. More preferably, hydrogenated bisphenol A
And its ethylene oxide and propylene oxide adducts. The molecular weight of the short-chain diol is preferably in the range of 50 to 500 in weight average molecular weight Mw. Also,
If it is 500 or more, the glass transition temperature (Tg) of the coating film decreases, and the coating film becomes soft, so that the durability decreases. If it is 500 or more, the Tg of the coating film decreases, and the coating film becomes soft, so that the durability decreases.

The content of the long-chain diol containing an ether group is preferably from 25% by weight to 45% by weight. And 3
The range of 0% by weight to 40% by weight is preferable, and if it is less than 25% by weight, the solubility in a solvent is reduced, so that the dispersibility is reduced. If it exceeds 45% by weight, the strength of the coating film is reduced, so that the durability is reduced.

Specifically, there may be mentioned the following long-chain diols. Bisphenol A, hydrogenated bisphenol A, bisphenol S, bisphenol P These polyethylene oxide and polypropylene oxide adducts,
Polypropylene glycol, polyethylene glycol,
Polytetramethylene glycol, more preferably, ethylene oxide and propylene oxide adducts such as bisphenol A and hydrogenated bisphenol A can be mentioned. The long-chain diol has a weight average molecular weight Mw of 5
It is preferably in the range of from 00 to 5000, and if it exceeds 5,000, the Tg of the coating film is lowered, and the coating film becomes soft, so that the durability is lowered.

When the polyurethane resin in the binder of the present invention is a polyurethane resin comprising a polyurethane prepolymer such as polyester polyol or polycarbonate polyol and a chain extender, the polyester polyol is, for example, a dihydric alcohol. And a dibasic acid, and ring-opening polymerization of lactones, for example, caprolactone. Typical dihydric alcohols include glycols such as ethylene glycol, propylene glycol, butanediol, 1,6-hexanediol, and cyclohexanedimethanol. Typical dibasic acids include adipic acid, pimelic acid, azelaic acid, sebacic acid,
Examples thereof include phthalic acid and terephthalic acid. Further, the polycarbonate polyol is, for example, a polyhydric alcohol having the following general formula, and HO-R-OH

[0025]

Embedded image

Condensation with phosgene, chloroformate, dialkyl carbonate or diallyl carbonate;
Or a molecular weight of 300 to 2 synthesized by transesterification
0000, a polycarbonate polyol having a hydroxyl value of 200 to 300 or a divalent carboxylic acid HOOC-R-COOH having the following general formula, wherein R is an alkylene group having 3 to 6 carbon atoms,
Represents a 1,4-, 1,3- or 1,2-phenylene group, or a 1,4-, 1,3- or 1,2-cyclohexylene group. Molecular weight 400 obtained by condensation with
Polycarbonate polyester polyol having a hydroxyl value of 5-300 and a hydroxyl value of 5-300. Other polyols such as polyether polyols, polyester ether polyols and polyesters may be blended with the above polyols up to 90% by weight of the polyols and used in combination.

The polyisocyanate used to form the polyurethane by reacting with the above-mentioned polyol is not particularly limited, and those generally used can be used. For example, hexamethylene diisocyanate, tolidine diisocyanate, isophorone diisocyanate, 1,3-xylylene diisocyanate, 1,4
-Xylylene diisocyanate cyclohexane diisocyanate, toluidine diisocyanate, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate,
p-phenylene diisocyanate, m-phenylene diisocyanate, 1,5-naphthalene diisocyanate,
4,4-diphenylmethane diisocyanate, 3,3-
Dimethyl phenylene diisocyanate and the like can be mentioned.

As the chain extender, the above-mentioned polyhydric alcohols, aliphatic polyamines, alicyclic polyamines, aromatic polyamines and the like can be used. Compounds having at least one OH group and at least one epoxy group used in the present invention include 2,3-epoxy-1-propanol, 3,4-epoxy-1-butanol, and 5,6-epoxy- Compounds having one hydroxyl group and one epoxy group at the terminal such as 1-hexanol and 7,8-epoxy-1-octanol, diglycidyl ether of glycerin, diglycidyl ether of trimethylolpropane, diglycerol polyglycidyl ether, sorbitol poly Glycidyl ether and the like are mentioned as compounds having one hydroxyl group and two or more epoxy groups. Examples of the epoxy resin having one or more OH groups and one or more epoxy groups in a molecule include a bisphenol-type epoxy resin and a novolak-type epoxy resin. Specific examples of the former bisphenol type include Epicoat 828, 834, 1001, 1
002, 1003, 1004, 1007, 1009 (all manufactured by Shell Chemical Co., Ltd.) and the like. Specific examples of the latter novolak type are phenol novolak epoxy resins such as Epicoat 152, 154, Sumitomo Chemical Industries Sumiepoxy ELPN-180, ESPN-180. , Sumi Epoxy ESCN
220L, 220F220HH, ESMN-220L
EOCN-102, 103, 104 manufactured by Nippon Kayaku Co., Ltd.
And cresol novolak epoxy resins.

Examples of the polyol having two or more hydroxyl groups and one epoxy group used in the present invention include epoxidized polydiolefin diols such as epoxidized polybutadiene diol and epoxidized polypentadiene diol, and polyglycidyl ether of polyol. Can be illustrated. Specific examples of the epoxidized polydiolefin diol include, for example, Adeka BF-1000, LPH X-31, and X-
530, X-2030, X-2100, LPH-2
060 (all manufactured by Adeka Gas Chemical Co., Ltd.), poly
bdR-45EPI (manufactured by Idemitsu Petrochemical) and the like. Specific examples of the polyglycidyl ether of the polyol include sorbitol polyglycidyl ether (trade name: Denacol EX-611, manufactured by Nagase Kasei). . The compound having an epoxy group and other polyols and isocyanates described above may be added all at once at the start of the reaction, or may be divided or added during the reaction. The resin for a binder of the present invention can be obtained by adding a compound containing a polar group to the epoxy group-containing polyurethane resin obtained as described above. The addition reaction of a polar group in the present invention can be performed in both non-aqueous and aqueous systems, but an optimum production method may be selected according to the characteristics of the polar group-containing compound used in the addition reaction.

Examples of the alkali metal or ammonium salt of a strong acid containing sulfur to be added to the epoxy group-containing polyurethane resin in the present invention include sulfites such as sodium sulfite, sodium bisulfite, ammonium sulfite, potassium sulfite, sodium hydrogen sulfate, and the like. Hydrogen sulfates such as ammonium hydrogen sulfate and potassium hydrogen sulfate, and their polar group-containing compounds can be used alone or in combination of one or more.

In the present invention, an epoxy resin curing catalyst can be used. Third used as catalyst
Examples of secondary amines include monoamines such as N, N'-dimethylcyclohexylamine and benzyldimethylamine;
N, N, N ', N'-tetramethylethylenediamine,
N, N, N ', N'-tetramethylhexane-1,6-
Diamines such as diamines, N, N, N ′, N ′, N ″,
N "-pentamethyldiethylenetriamine, N, N,
Triamines such as N ′, N ′, N ″, N ″ -pentamethylpropylenetriamine, triethylenediamine (1,
4-diazabicyclo- (2,2,2) -octane, N,
N'-dimethylpiperazine, N-methyl, N '-(2-
Cyclic amines such as dimethylamino) ethylpiperazine and 1,8-diazabicyclo (5,4,0) undec-7-ene; ethanolamines such as dimethylaminoethanol, triethanolamine and dimethylaminoethoxyethanol; And etheramines such as dimethylaminoethyl) ether. In addition, quaternary ammonium salts such as an imidazole catalyst, tetrabutylammonium bisulfate, tetrabutylammonium bromide, trimethyllaurylammonium chloride, and benzyltriethylammonium chloride, and tetrafluoroboronic acids are also included.

The above addition reaction of the present invention is usually carried out at about 30 to 10
The reaction is carried out at 0 ° C., preferably at 40 to 90 ° C. for 2 to 24 hours, but if the temperature is too high, the resin deteriorates.

The addition reaction can be carried out simultaneously with the polymerization by preparing a salt or a catalyst required for the addition reaction in the polymerization system when preparing the epoxy group-containing polyurethane resin.

In the ring-opening reaction of the present invention, it is preferable to open all the epoxy groups. However, it is needless to say that some epoxy groups may be left, and the addition reaction may be carried out so as to leave the epoxy groups. When a magnetic recording medium is used, the magnetic coating film can exhibit excellent heat stability due to the remaining epoxy group, making it possible to manufacture a highly reliable magnetic recording medium that is resistant to head corrosion. Become. Further, the coating film can be crosslinked with a polyamine compound or a polycarboxylic acid compound by utilizing the reactivity of the epoxy group.
Usually, amines or carboxylic acids are used in an amount of about 1 equivalent or less, preferably about 0.2 to 1 equivalent relative to the epoxy group.

The content of the ether group in the polyurethane resin is preferably from 1 mmol / g to 6 mmol / g. 1m
If the amount is less than mol / g, the adsorptivity to the magnetic substance decreases, and the dispersibility decreases. If it is 6 mmol / g or more, the solubility in a solvent decreases, and the dispersibility decreases.

[0036] Preferably the average polar group content in the polyurethane resin is in the range of ^{3 × 10 -5 ~30 × 10 -5} eq / g, 3.5 × 10 -5 ~20 × 10 - ⁵ e
More preferably, it is q / g. 3 × 10 ^-5 eq / g
If it is less than 30, dispersibility is insufficient, which is not preferable.
^If it exceeds ^-5 eq / g, agglomeration occurs, resulting in insufficient dispersion, which is not preferable.

The OH content in the polyurethane preferably has a branched OH group as the OH group from the viewpoint of curability and durability, preferably 2 to 40 per molecule, more preferably 3 to 40 per molecule. Pieces to 20 pieces. 2 /
When the molecular weight is smaller than the value, the reactivity with the isocyanate curing agent decreases, so that the strength of the coating film decreases and the durability decreases. 40 /
When the molecular weight is larger than the molecular weight, the solubility in the solvent is reduced, and the dispersibility is reduced.

The molecular weight of the polyurethane is from 5,000 to 10
0000 is preferred. More preferably, it is 10,000 to 50,000. If it is less than 5,000, the resulting magnetic coating film becomes brittle, and the resulting magnetic coating film becomes brittle, resulting in reduced physical strength, which also affects the durability of a magnetic tape or the like. 1000
If it exceeds 00, the solubility in a solvent is reduced, and the dispersibility is reduced. Further, the viscosity of the paint at a predetermined concentration becomes high, so that workability is remarkably deteriorated and handling becomes difficult.

Glass transition temperature (Tg) of polyurethane
Is preferably 50 ° C to 200 ° C. More preferably 80
C. to 150 C., more preferably 100 C. to 130 C.
° C. If the temperature is lower than 50 ° C., the strength of the coating film at a high temperature is reduced, so that the durability and the storage stability are reduced. If the temperature exceeds 200 ° C., calender moldability decreases, and electromagnetic conversion characteristics decrease.

Further, a vinyl chloride resin can be used in combination with the binder of the present invention. Specifically, in addition to vinyl chloride as a main monomer, vinyl acetate, vinyl alcohol, maleic acid, acrylic acid, acrylic acid ester, vinylidene chloride, acrylonitrile, methacrylic acid, methacrylic acid ester, styrene, butadiene, ethylene,
Copolymers such as vinyl butyral, vinyl acetal, vinyl ether, vinyl sulfonic acid, acrylamide, hydroxyethyl acrylate, and glycidyl acrylate can be used.

The content of the vinyl chloride unit is preferably in the range of 57 to 98% by weight. If the amount is less than 57% by weight, the strength of the obtained resin coating film is reduced, and if it exceeds 98% by weight, the solubility of the resin in organic solvents such as ketones and esters is hindered.

The vinyl alcohol unit is 2 to 16% by weight.
Is preferable. If the amount is less than 2% by weight, the solubility of a ketone or an ester in an organic solvent when preparing a coating material, the dispersibility of a nonmagnetic powder or a magnetic powder, the reactivity with an isocyanate compound used in combination with the present resin, etc. No effect on the compatibility with the resin can be obtained. If it exceeds 16% by weight, the viscosity of the coating material becomes too high, and the pot life when the isocyanate compound is added becomes short, which is disadvantageous in practical use. Other vinyl units are preferably in the range of 0 to 26% by weight. If it exceeds this range, the mechanical properties and dispersibility of the entire resin will be reduced.
Further, the obtained vinyl chloride copolymer can be saponified to convert vinyl acetate, vinyl propionate, and the like into a vinyl alcohol component.

The average degree of polymerization is preferably from 200 to 800. More preferably, it is 250 to 700. If it is less than 200, the resulting magnetic coating film becomes brittle, and the resulting magnetic coating film becomes brittle, so that the physical strength is reduced and the durability of a magnetic tape or the like is affected. On the other hand, when it exceeds 800, the viscosity of the coating material at a predetermined concentration becomes high, and the workability is remarkably deteriorated, and the handling becomes difficult.

As the binder in the present invention, together with the polar group-containing vinyl chloride resin and the polar group-containing polyurethane resin, a binder having another polar group is used in an amount equal to or less than the total amount of these resins. You may. Other resins that can be used in combination are not particularly limited, and known thermoplastic resins, thermosetting resins, reactive resins, and mixtures thereof, which are conventionally used as binders for magnetic recording media, can be used. Specifically, the thermoplastic resin has a glass transition temperature of −100 to 150 ° C. and a number average molecular weight of 1,000 to 200,000, preferably 10
000 to 100,000 and a degree of polymerization of about 50 to 1,000.

Such materials include acrylic acid, acrylic acid ester, vinylidene chloride, acrylonitrile, methacrylic acid, methacrylic acid ester, styrene,
There are polymers, copolymers, polyurethane resins, and various rubber resins containing butadiene, ethylene, vinyl butyral, vinyl acetal, vinyl ether and the like as constituent units. In addition, as thermosetting resin or reactive resin,
Examples include phenolic resins, phenoxy resins, epoxy resins, urea resins, melamine resins, alkyd resins, acrylic reaction resins, formaldehyde resins, silicone resins, epoxy-polyamide resins, and mixtures of polyester resins and isocyanate prepolymers.

The nonmagnetic powder used for the nonmagnetic lower layer of the magnetic recording medium of the present invention may be an inorganic substance or an organic substance. Further, carbon black or the like can be used. Non-magnetic powder
Examples include metals, metal oxides, metal carbonates, metal sulfates, metal nitrides, metal carbides, metal sulfides, and the like. Specifically, TiO ₂ , TiO _X , cerium oxide, tin oxide,
Tungsten oxide, ZnO, ZrO ₂ , SiO ₂ , Cr ₂
O ₃ , α-alumina, β-alumina, γ-alumina, α-iron oxide, goethite, corundum, silicon nitride, titanium carbide, magnesium oxide having an α conversion of 90% or more;
Boron nitride, molybdenum disulfide, copper oxide, MgCO ₃ ,
CaCO ₃ , BaCO ₃ , SrCO ₃ , BaSO ₄ , silicon carbide, titanium carbide and the like are used alone or in combination of two or more.

Preferred are α-iron oxide and titanium oxide, and particularly preferred is α-iron oxide.

Further, these non-magnetic powders are made into an alkaline suspension, and are heated at, for example, 60 to 200 ° C.
Surface treatment with an inorganic substance, or both in combination
H can be adjusted. The pH of the non-magnetic powder is from 8 to
A range of 11 is preferred. If the pH is less than 8, the μ value at high temperature and high humidity increases, the running property deteriorates, and the amount of decrease in the amount of surface binder increases. If the pH exceeds 11, the amount of released fatty acids decreases, so that the friction coefficient increases, the running property deteriorates, and the amount of decrease in the amount of surface binder increases.
These pH values were measured by the JIS-A method.

The particle size of these fine powders is 0.01
２2 μm is preferred. The tap density is 0.05 to
2 g / cm ³ , preferably 0.2 to 1.5 g / cm ³ ,
The water content is 0.1 to 5%, preferably 0.2 to 3%. The specific surface area is from 1 to 100 m ² / g, preferably from 5 to
Was 50 m ² / g, more preferably, 7~40m ²
/ G. DBP oil absorption 5-100ml / 100
g, preferably 10 to 80 ml / 100 g, and more preferably 20 to 60 ml / 100 g. The specific gravity is 1 to 12, preferably 2 to 8. The shape may be any of a needle shape, a spherical shape, a die shape, and a plate shape. Also,
The fine powder may be one treated with an oxide of a metal such as aluminum, silicon, titanium, zirconium, tin, antimony, and zinc, such as a titanium oxide powder whose surface has been treated with alumina. When treating the surface, the effect can be obtained if the purity is 70% by weight or more,
It is preferable that the ignition loss is 20% by weight or less. The Mohs hardness of these inorganic fine powders is preferably 4 or more.

As carbon black used in the present invention, furnace black for rubber, thermal black for rubber, black for color, acetylene black and the like can be used. The specific surface area of carbon black is 100
５００500 m ² / g, preferably 150-400 m ² / g
And the DBP oil absorption is 20 to 400 ml / 100
g, preferably 30 to 200 ml / 100 g, and more preferably 10 to 40 ml / 100 g. pH 2
-10, water content 0.1-10%, tap density 0.1
〜1 g / cm ³ is preferred.

The carbon black may be surface-treated with a dispersant or the like, or may be grafted with a resin. Also,
The carbon black may be dispersed with a binder before adding the nonmagnetic paint. These carbon blacks can be used in a range not exceeding 50% by weight based on the inorganic fine powder. These carbon blacks can be used alone or in combination.
Non-magnetic organic fine powder that can be used in the present invention, acrylic styrene resin powder, benzoguanamine resin powder, melamine resin powder, phthalocyanine pigment powder, polyolefin resin powder, polyester resin powder, And polyamide resin powder and fluororesin powder.
It can be produced by a method described in JP-A No. 255582.

The ferromagnetic powder used in the magnetic recording medium of the present invention is a ferromagnetic iron oxide, a cobalt-containing ferromagnetic iron oxide or a ferromagnetic alloy powder having an S _BET specific surface area of 40 to 80 m ² /.
g, preferably 50 to 70 m ² / g. The crystallite size is between 12 and 25 nm, preferably between 13 and 22 nm, particularly preferably between 14 and 20 nm. The major axis length is 0.05 to 0.25 μm, preferably 0.07 to
0.2 μm, particularly preferably 0.08 to 0.15
μm. Fe, Ni, Fe
-Co, Fe-Ni, Co-Ni, Co-Ni-Fe and the like, and aluminum, silicon, sulfur, scandium, titanium, vanadium, chromium, manganese, copper within a range of not more than 20% by weight of the metal component. , Zinc, yttrium, molybdenum, rhodium, palladium, gold, tin, antimony, boron, barium, tantalum, tungsten,
Examples include rhenium, silver, lead, phosphorus, lanthanum, cerium, praseodymium, neodymium, tellurium, and alloys containing bismuth. Further, the ferromagnetic metal powder may contain a small amount of water, hydroxide or oxide. The method for producing these ferromagnetic powders is already known, and the ferromagnetic powder used in the present invention can also be produced according to a known method. There is no particular limitation on the shape of the ferromagnetic powder,
Usually, needles, granules, dice, rice granules, and plate shapes are used. It is particularly 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 and ethyl acetate which are usually used in the preparation of a magnetic paint to obtain a magnetic paint. The kneading and dispersion can be performed according to a usual method. In the magnetic paint, in addition to the above components, α-Al ₂ O ₃ , Cr ₂ O _3
It may contain commonly used additives or fillers such as abrasives such as No. ₃ , antistatic agents such as carbon black, lubricants such as fatty acids, fatty acid esters and silicone oil, and dispersants. Known techniques for the magnetic layer can be applied to the lubricant, dispersant, additive, solvent, dispersion method, and the like of the upper magnetic layer or the lower nonmagnetic layer.

The magnetic coating for the upper magnetic layer and the non-magnetic coating for the lower non-magnetic layer prepared from the above materials are applied on a non-magnetic support to form a magnetic layer. As the non-magnetic support that can be used in the present invention, known materials such as biaxially stretched polyethylene naphthalate, polyethylene terephthalate, polyamide, polyimide, polyamide imide, aromatic polyamide, and polybenzoxdazole can be used. Preferred are polyethylene naphthalate and aromatic polyamide. These non-magnetic supports may be previously subjected to corona discharge, plasma treatment, easy adhesion treatment, heat treatment, and the like. The non-magnetic support which can be used in the present invention has a center line average surface roughness of a cutoff value of 0.25 m.
0.1 to 20 nm in m, preferably 1 to 10 nm
It is preferable that the surface has excellent smoothness in the range of. It is preferable that these non-magnetic supports have not only a small center line average surface roughness but also no coarse protrusions of 1 μ or more.

The method for producing a magnetic recording medium according to the present invention comprises, for example, coating a magnetic layer paint on the surface of a running nonmagnetic support, preferably having a thickness of the magnetic layer after drying of 0.05 to 5 μm. More preferably, a magnetic paint and a non-magnetic paint are sequentially or simultaneously layer-coated so as to have a thickness of 0.07 to 1 μm. Specifically, (1) First, the lower layer is applied by a coating apparatus such as gravure, roll, blade, or extrusion which is generally applied in the application of the magnetic layer, and the lower layer is placed in an undried state. The upper layer is applied by a support pressure type extrusion coating apparatus as disclosed in JP-A-1-46186, JP-A-60-238179, JP-A-2-265672, and the like. (2) JP-A-63-88080, JP-A-2-179
No. 71 and Japanese Patent Application Laid-Open No. 2-265672 disclose the upper and lower layers almost simultaneously by one coating head having two coating liquid passage slits. (3) The upper and lower layers are coated almost simultaneously by an extrusion coating device with a backup roll as disclosed in JP-A-2-174965.

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

The applied layer of the applied magnetic paint is dried after subjecting the ferromagnetic powder contained in the applied layer of the magnetic layer coating solution to a magnetic field orientation treatment. After drying in this way,
The coating layer is subjected to a surface smoothing treatment. For the surface smoothing treatment,
For example, a super calendar roll is used.
By performing the surface smoothing treatment, voids generated by the removal of 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, or polyamideimide is used. Moreover, it can also process with a metal roll.

The magnetic recording medium of the present invention has a center line average roughness of 0.1 to 0.1 at a cutoff value of 0.25 mm.
It is preferable that the surface has an extremely excellent smoothness of 4 nm, preferably 1 to 3 nm. As a method for this, for example, a magnetic layer formed by selecting a specific ferromagnetic powder and a binder as described above is subjected to the above calendering treatment. As the calendering conditions, the temperature of the calender roll is in the range of 60 to 100 ° C, preferably in the range of 70 to 100 ° C, particularly preferably 80 to 10 ° C.
The temperature is in the range of 0 ° C. and the pressure is in the range of 100 to 500 kg / cm, preferably in the range of 200 to 450 kg / cm, particularly preferably in the range of 300 to 400 kg / cm. Is preferred. The obtained magnetic recording medium can be used after being cut into a desired size using a cutting machine or the like.

[0059]

The present invention will be described in more detail with reference to the following examples. The indication of “parts” in the examples indicates “parts by weight”. The molecular weight of the binder resin indicates the molecular weight converted into the molecular weight of standard polystyrene by gel permeation chromatography (GPC), and the OH content of the polyurethane resin is determined by the OH determined by the test method of JIS K0070.
It was shown by the number of OH groups per molecule from the valency and the molecular weight determined using GPC.

Production Example A (short-chain diol + long-chain diol +
Example of synthesizing epoxy group-containing compound + diisocyanate-based polyurethane resin) In a reaction vessel equipped with a reflux condenser and a stirrer and previously purged with nitrogen, 170 parts of hydrogenated bisphenol A (Rikabinol HB manufactured by Nippon Rika), polypropylene oxide of bisphenol A 220 parts of adduct (average molecular weight: 1000), epoxidized polybutadiene diol (LPH-2 manufactured by Asahi Denka)
060), and dissolved at 60 ° C. in a nitrogen stream with 80 parts of dimethylacetamide. Next, as a catalyst, di-n-dibutyltin dilaurate was added at 60 ppm based on the total amount of the raw materials, and dissolved for 15 minutes. Further, 250 parts of phenylmethane diisocyanate and 3 parts of trimethylolpropane were added and reacted by heating at 60 ° C. for 8 hours, and 6 parts of sodium persulfate was added and reacted by heating at 90 ° C. for 3 hours to obtain a polyurethane resin A. The obtained polyurethane resin A
Represents a weight average molecular weight of 25,000, a polar group (—SO ₃ M) content of 6.1 × 10 ⁻⁵ eq / g, and an average OH group content of 3/1.
Was a molecule.

Polyurethane resins C to D shown in Table 1 were obtained by the same production method except that the amount of the epoxidized polybutadienediol was changed.

Production Example B (Synthesis Example of Epoxy Group-Containing Polyester Polyol + Diisocyanate-Based Polyurethane) (1) Synthesis of Polyester Polyol A dimethyl terephthalate was placed in a reaction vessel equipped with a thermometer, a reflux condenser and a stirrer, and previously purged with nitrogen. 776 parts, epoxidized polybutadiene diol (LPHX-
2030) 850 parts, ethylene glycol 434 parts, neopentyl glycol 728 parts, zinc acetate 0.66 parts,
Add 0.08 part of sodium acetate and add 3 to 140-220 ° C.
Transesterification was performed for hours. Then sebacic acid 12
After adding 12 parts and reacting at 210 to 230 ° C. for 2 hours,
The pressure of the reaction system was reduced to 20 mmHg over 30 minutes, and a polycondensation reaction was further performed at 230C at 5 to 20 mmHg for 30 minutes to obtain a polyester polyol b.

(2) Synthesis of Polyurethane Resin B In a reaction vessel equipped with a thermometer, a reflux condenser and a stirrer and previously purged with nitrogen, 3570 parts of dimethylacetamide, 1000 parts of the above polyester polyol b, 75 parts of diphenylmethane diisocyanate , 1.2 parts of dibutyltin dilaurate, reacted at 70-90 ° C. for 8 hours, further added 6 parts of sodium persulfate, and added
The mixture was heated for a period of time to obtain a polyurethane resin B. The obtained polyurethane resin B had a weight average molecular weight of 300000, a polar group (-SO ₃ M) content of 6.0 × 10 ⁻⁵ eq / g, and an average O of
The H group content was 3.6 / molecule.

Comparative Production Example E (Synthesis Example of Short-Chain + Long-Chain + Diisocyanate-Based Polyurethane) Hydrogenated bisphenol A (Rikabinol HB manufactured by Nippon Rika) was placed in a reaction vessel equipped with a reflux condenser and a stirrer and purged with nitrogen in advance. 138 parts, 228 parts of a bisphenol A polypropylene oxide adduct (average molecular weight: 1000), 14 parts of sulfosophthalic acid ethylene oxide adduct, and 2010 parts of dimethylacetamide were dissolved at 60 ° C. under a nitrogen stream. Next, as a catalyst, di-n-dibutyltin dilaurate was added in an amount of 60 ppm based on the total amount of the raw materials, and the mixture was further dissolved for 15 minutes. Further, 220 parts of phenylmethane diisocyanate and 4 parts of trimethylolpropane were added to obtain 9
The mixture was heated and reacted at 0 ° C. for 4 hours to obtain a polyurethane resin E. The obtained polyurethane resin E had a weight average molecular weight of 2.
50,000, polar group (—SO ₃ M) content 6.1 × 10 ⁻⁵ eq
/ G, average OH group content was 3 / molecule.

Comparative Production Example F (Synthesis Example of Polyester Polyurethane) (1) Synthesis of Polyester Polyol 743 parts of dimethyl terephthalate was placed in a reaction vessel equipped with a thermometer, a reflux condenser, and a stirrer and purged with nitrogen beforehand.
50 parts of dimethyl sodium sulfoisophthalate, 434 parts of ethylene glycol, 72 parts of neopentyl glycol
8 parts, 0.66 parts of zinc acetate and 0.08 parts of sodium acetate were added, and a transesterification reaction was performed at 140 to 220 ° C. for 3 hours. Then, 1212 parts of sebacic acid was added and
After reacting at 0 ° C. for 2 hours, the reaction system was
The pressure was reduced to 0 mmHg, and further 5 to 20 mmHg, 23
Polycondensation reaction was performed at 0 ° C. for 30 minutes to obtain polyester polyol g.

(2) Synthesis of Polyurethane Resin F In a reaction vessel equipped with a thermometer, a reflux condenser, and a stirrer, 3580 parts of dimethylacetamide, 1000 parts of the polyester polyol g, 75 parts of diphenylmethane diisocyanate, 75 parts of dibutyl 1.2 parts of tindilaurate were added and reacted at 70 to 90 ° C. for 8 hours to obtain a polyurethane resin F. Obtained polyurethane resin F
The weight average molecular weight 30,000, the polar group (-SO ₃ M) content of 6.3 × 10 ^-5 eq / g, an average OH group content 3.6
Pcs / molecule.

[0067]

[Table 1]

The amount of adsorption and the amount of non-adsorbed resin polar groups in Table 1 were measured by the following methods. The obtained polyurethane resin is dissolved in cyclohexanone so as to have a solid concentration of 5%, 50 parts of α-iron oxide is added to 200 parts of the solution, and the mixture is dispersed in a sand mill for 120 minutes. 5,000 rpm for 60 minutes to separate α-iron oxide. Then, about 2 g of the supernatant
The sample was precisely weighed and dried in vacuum at 140 ° C. for 4 hours, the solid content in the supernatant was determined, and the difference from the initial concentration was taken as the amount of resin adsorbed, and the amount of adsorption per 1 g of α-iron oxide used was determined. In addition, the amount of sulfur in the resin in the supernatant was measured by X-ray fluorescence, and the amount was taken as the amount of non-adsorbed resin polar groups.

Example 1 (Preparation of Magnetic Coating Liquid) Ferromagnetic alloy powder 100 parts (composition: Fe / Zn / Ni = 92/4/4, Hc: 2000 Oe, crystallite size: 15 nm, BET specific surface area: 59 m) ² / g, major axis diameter: 0.12 μm, needle ratio: 7, s: 140 emu / g Polyurethane resin A 10 parts Vinyl chloride resin (MR110: manufactured by Zeon Corporation) 8 parts α-Al ₂ O ₃ (particle size 0.3 μm) 2 parts Carbon black (particle size 40 nm) 2 parts Cyclohexanone 110 parts Methyl ethyl ketone 100 parts Toluene 100 parts Butyl stearate 2 parts Stearic acid 1 part The above magnetic coating composition was kneaded with an open kneader for 60 minutes. Thereafter, the mixture was dispersed in a sand mill for 120 minutes, and the resulting dispersion was converted into a trifunctional low molecular weight polyisocyanate. Thing (Nippon Polyurethane Coronate 304
After adding 6 parts of 1) and stirring and mixing for another 20 minutes, 1
The solution was filtered using a filter having an average pore diameter of μm to prepare a magnetic coating liquid.

The nonmagnetic paint obtained on a 10 μm-thick polyethylene naphthalate support was dried to a thickness of 3.0.
μm, and 30% with the magnetic layer not dried.
After performing a magnetic field orientation with a 00 Gaussian magnet and drying further,
After performing a surface smoothing treatment at a speed of 100 m / min, a linear pressure of 300 kg / cm, and a temperature of 90 ° C. using a seven-stage calender composed of only metal rolls, a heat curing treatment is performed at 70 ° C. for 24 hours to obtain 6.35 mm. The sheet was cut into a width to produce a magnetic tape.

Examples 2 to 4 Preparation of polyurethane resin for use in magnetic coating composition Example B
The magnetic tapes of Examples 2 to 4 were produced in the same manner as in Example 1 except that the polyurethane tapes of Examples 1 to 4 were changed to polyurethane resins.

Example 5 (Preparation of Upper Layer Magnetic Coating Solution) 100 parts of ferromagnetic alloy powder (composition: Fe / Zn / Ni = 92/4/4, Hc: 2000 Oe, crystallite size: 15 nm, BET specific surface area: 59m^Two/ G, major axis diameter: 0.12 μm, needle ratio: 7, s: 140 emu / g) Polyurethane resin A 10 parts Vinyl chloride resin (MR110: manufactured by Zeon Corporation) 8 parts α-Al_TwoO_Three(Particle size 0.3 μm) 2 parts Carbon black (particle size 40 nm) 2 parts Cyclohexanone 110 parts Methyl ethyl ketone 100 parts Toluene 100 parts Butyl stearate 2 parts Stearic acid 1 part (Preparation of non-magnetic coating liquid for lower layer) Non-magnetic inorganic powder 85 parts (α-iron oxide, major axis diameter: 0.12 μm, needle ratio: 7, BET surface area 55 m ^Two / G, pH 6.5) Polyurethane resin A 10 parts Vinyl chloride resin (MR110: manufactured by Nippon Zeon) 8 parts Cyclohexanone 140 parts Methyl ethyl ketone 170 parts Butyl stearate 2 parts Stearic acid 1 part Magnetic coating composition for upper layer and lower layer Non-magnetic paint composition
For each of the products, use an open kneader to
After kneading for 0 minutes, the mixture was dispersed in a sand mill for 120 minutes.
Trifunctional low molecular weight polyisocyanate is added to the resulting dispersion.
Compound (Coronate 3041 manufactured by Nippon Polyurethane)
Add 6 parts, stir and mix for another 20 minutes, then add 1 μm
Filter with a filter having a uniform pore size,
And a non-magnetic paint.

The non-magnetic paint obtained on a 10 μm-thick polyethylene naphthalate support was dried to a thickness of 2.5 μm.
μm. Immediately thereafter, a magnetic paint is applied simultaneously with a multilayer so that the thickness after drying becomes 0.5 μm, and the magnetic field orientation is performed with a 3000 Gauss magnet in a state where both layers are undried. After further drying, a 7-stage calender consisting only of metal rolls was used at a speed of 100 m / min and a linear pressure of 30.
After performing a surface smoothing treatment at 0 kg / cm and a temperature of 90 ° C., a heat hardening treatment is performed at 70 ° C. for 24 hours to obtain 6.35 m.
The resulting tape was cut into a width of m to prepare a magnetic tape.

Examples 6 to 8 The same procedure as in Example 5 was repeated except that the polyurethane resin used in the lower non-magnetic coating composition and the upper magnetic coating composition was changed to polyurethane resins B to D. A magnetic tape was produced.

Comparative Examples 1-2 The magnetic tapes of Comparative Examples 1-2 were prepared in the same manner as in Example 1, except that the polyurethane resin used in the magnetic coating composition was changed to polyurethane resins EF.

Comparative Examples 3 and 4 The magnetic tapes of Comparative Examples 3 and 4 were prepared in the same manner as in Example 5 except that the polyurethane resin used in the upper magnetic coating composition and the lower nonmagnetic layer was changed to polyurethane resins EF. Was prepared.

The magnetic tapes obtained in the above Examples and Comparative Examples were measured by the following measuring methods, and the results are shown in Table 4. Table 2 shows the magnetic tapes produced in Examples and Comparative Examples.

[0078]

[Table 2]

Note) The alphabet in the table corresponds to the symbol of the polyurethane resin in the production example. The magnetic tapes obtained in the above Examples and Comparative Examples were measured by the following measurement methods, and the results are shown in Table 3. (Measurement method) Surface roughness Ra: Digital optical profiler
The center line average roughness was defined as Ra under the condition of a cutoff of 0.25 mm by an optical interference method using (manufactured by WYKO). Electromagnetic conversion characteristics: Recording and reproduction were performed on a sample tape using a drum tester at a recording wavelength of 0.5 μm and a head speed of 10 m / sec. The relative reproduction output with respect to the tape of Example 1 was evaluated.

Repetitive running performance (output reduction, head contamination, change in surface binder amount) A tape of 60 minutes length was used at 40 ° C. 80 using a DVC-VTR (NV-BJ1) manufactured by Matsushita Electric.
The vehicle was run 100 times repeatedly in a% RH environment, the stain on the video head was observed, and the video output was continuously reproduced, and the output was reduced at the first output of 0 dB.
The video head dirt was evaluated by the following evaluation scores. 5. What is not dirty. 4. There is a little dirt on the shoulder part of the tape outlet side of the head. 3. Soil is observed on the shoulder portion on the tape outlet side of the head. 2. In addition, dirt can be seen on the head. 1. A dirt is seen on the entire surface of the head, making recording and reproduction impossible. In order to remove the lubricant existing in the surface layer of the magnetic layer, the tape before and after running was extracted with n-hexane at room temperature for 30 minutes to change the amount of surface binder before and after running.
400W (15 kV), M
g Measured at the anode for 10 minutes and for N, 2P3 of Fe
The peak intensity ratio of 1S of N to the peak of / 2 is expressed as Cl
For the peak of 2P3 / 2 of Fe
The 1S peak intensity ratio of 1 was determined.

The storage stability of the magnetic tape was stored at 60 ° C. and 90% RH for one week, and the change in friction coefficient before and after the storage was evaluated by the following evaluation scores. 5. No change in μ value. 4. Those whose μ value increase is less than 0.05. 3. Those whose μ value increase is 0.05 to 0.1. 2. Those whose μ value increase is larger than 0.1. 1. What sticks.

[0082]

[Table 3]

[0083]

According to the present invention, not only the dispersibility of the magnetic powder is excellent, but also the dispersibility of the non-magnetic powder in the lower non-magnetic layer is excellent. A magnetic recording medium with excellent conversion characteristics is obtained, and at the same time, the binder component has a high adsorptivity to magnetic powder and non-magnetic powder, preventing the unadsorbed binder component from oozing on the surface of the magnetic layer. As a result, it is possible to obtain a magnetic recording medium having excellent running durability without causing head, dirt, clogging and the like. In particular, it is possible to obtain a magnetic recording medium which is excellent in storability under high temperature and high humidity and has little change in the amount of surface binder before and after running.

Claims (5)

[Claims] 1. A magnetic recording medium having a magnetic layer containing at least a ferromagnetic powder and a binder on a non-magnetic support, wherein the binder is a polyol, an isocyanate compound, and one or more epoxy groups in the molecule. Polyurethane resin obtained by reacting a compound containing at least one hydroxyl group has -S
O ₃ M, —OSO ₃ M (where M is hydrogen, an alkali metal,
A magnetic recording medium comprising a polyurethane resin obtained by reacting a compound containing at least one polar group selected from alkaline earth metals and ammonium salts). 2. The magnetic recording medium according to claim 1, wherein the average polar group content in the polyurethane resin is in the range of 3 × 10 ⁻⁵ to 30 × 10 ⁻⁵ eq / g. 3. The polyurethane resin according to claim 1, wherein the polyurethane resin skeleton comprises a diol having a cyclic structure and an alkylene oxide added thereto, and a polyol having a molecular weight of 500 to 5,000 being contained in the polyurethane resin in an amount of 0 to 50% by weight, and having a diol having a cyclic structure or a cyclic structure. A short-chain diol having a molecular weight of 200 to 500 and at least one of a diol obtained by adding an alkylene oxide to the diol and
0% by weight, and the ether group derived from the diol and the polyol is 1 to 6 with respect to the entire polyurethane resin.
2. The magnetic recording medium according to claim 1, wherein the magnetic recording medium is a polyurethane resin containing 1 mmol / g and having at least one kind of polar group in the polyurethane resin. 4. A lower coating layer containing at least one of a nonmagnetic powder and a magnetic powder and a binder on a nonmagnetic support, and an upper magnetic layer containing at least a ferromagnetic powder and a binder thereon. In the magnetic recording medium having a plurality of layers provided with a polyol, an isocyanate compound, at least one epoxy group and at least one epoxy group in a molecule as a binder of at least one of the lower nonmagnetic layer and the upper magnetic layer. -SO ₃ M, -OSO ₃ M (where M is hydrogen polyurethane resin obtained by reacting a compound containing a hydroxyl group,
A magnetic recording medium comprising a polyurethane resin obtained by reacting a compound containing at least one polar group selected from alkali metals, alkaline earth metals and ammonium salts) and a vinyl chloride resin. 5. The magnetic recording medium according to claim 4, wherein the average polar group content in the polyurethane resin is in the range of 3 × 10 ⁻⁵ to 30 × 10 ⁻⁵ eq / g.