JP3046057B2 - Manufacturing method of magnetic recording medium - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for manufacturing a magnetic recording medium, and more particularly, to a method for manufacturing a magnetic recording medium suitably used as a magnetic recording medium for a floppy disk.

[Prior Art and Problems to be Solved by the Invention] A magnetic recording medium is generally formed by dispersing a ferromagnetic powder in a polymer material (resin material) called a binder on a non-magnetic support. An abrasive, an antistatic agent such as carbon black, a lubricant, a hardener and other additives uniformly dispersed in a magnetic paint obtained by appropriately adding a solvent as necessary, It is manufactured by coating on a support and drying.

In recent years, there has been a strong demand for magnetic recording media to increase their storage capacity and recording / reproducing output.

To increase the storage capacity, while increasing the information recording density per unit area of the magnetic recording medium, the write magnetic flux generated from the magnetic head must be concentrated on a small area to increase the information recording density. The head must be miniaturized and the amount of generated magnetic flux must be reduced. Therefore, in order to reverse the direction of magnetization with a minute amount of magnetic flux, it is necessary to reduce the thickness of the magnetic layer.

Also, in order to increase the recording / reproducing output, it is necessary to increase the residual magnetic flux of the magnetic layer, and it is necessary to increase the thickness of the magnetic layer.

However, when the magnetic layer is thickened, the high frequency characteristics deteriorate. Therefore, in order to increase the residual magnetic flux and improve the high-frequency characteristics, it is necessary to make the magnetic layer thin and increase the coercive force of the magnetic material.

In order not to lower the low-frequency characteristics further, a magnetic recording medium having a relatively low coercive force and a thin magnetic layer made of a high coercive magnetic material provided on a thick magnetic layer made of a magnetic material having a large residual magnetic flux. Has been requested.

In JP-A-62-212933, when a thin magnetic layer comprising at least two or more magnetic layers on a non-magnetic support and the uppermost dry film having a thickness of 2 μm or less is provided, at least two magnetic layers are simultaneously coated. It is described that a magnetic recording medium with high characteristics can be obtained by providing at least two magnetic layers at the same time and applying a magnetic field during the drying.

However, it has been known that a binder plays an important role in dispersing ferromagnetic powder, and a vinyl chloride resin or nitrocellulose is used in combination with a relatively soft binder, polyurethane.

However, the combination of these binders has a problem that the surface roughness of the magnetic layer, TS / N and CS / N are somewhat insufficient.

Therefore, the conventional binder composition having a multilayer structure is used in such a manner that all the binders contained in both the upper layer (the second magnetic layer) and the lower layer (the first magnetic layer) are used in the same ratio with respect to the ferromagnetic powder (for example, Japanese Patent Application Laid-Open No. Sho 62-62).
No. 212993, JP-A-54-145104, etc.), and the total amount of the binder used in the upper layer is considerably larger than the amount of the total binder used in the lower layer (JP-A-58129).
-56231).

However, when the binder is used in the same ratio in both the upper layer and the lower layer, the surface roughness of the magnetic layer is good, but the T.S / N
And that the C / S / N is not sufficient.

Also, if the difference in the amount of the total binder used for the upper layer and the lower layer in the magnetic layer is large, the surface roughness also deteriorates,
There is also a problem that C / S / N is significantly deteriorated.

On the other hand, as described above, when two magnetic layers are formed by applying the magnetic layer paint by the simultaneous multilayer coating method, the density difference caused by the inorganic filler contained in the magnetic paint and the carbon black The difference between the EBT of the magnetic powder and the amount of the binder resulting from the difference in the amount of lubrication may cause a large difference in the applicability, and the disturbance of the superimposed interface may be reflected on the surface of the magnetic layer, and the Deteriorating surface properties,
There is a problem that electromagnetic conversion characteristics are deteriorated.

 The present invention has been made based on the above circumstances.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for manufacturing a magnetic recording medium having improved storage capacity, recording / reproducing output, and durability.

[Means for Solving the Problems] The invention according to claim 1 for achieving the above object,
A lower layer formed by applying a coating for a non-magnetic layer containing carbon black as a main component on a non-magnetic support, and the lower layer in a wet state. Containing magnetic particles whose easy axis of magnetization is almost perpendicular to the plane of the plate, and the weight ratio A / A of the total amount of binder in the non-magnetic layer (A) to the total amount of binder in the magnetic layer (B). A method for producing a magnetic recording medium, comprising subjecting an upper layer formed by applying a coating material for a magnetic layer in which B is adjusted to 2 or more and 7 or less to a calender treatment after drying.

According to a second aspect of the present invention, in the method for manufacturing a magnetic recording medium according to the first aspect, the binder forming the nonmagnetic layer has a functional group or a functional group forming an internal salt. It is a resin obtained by denaturation.

 Hereinafter, the present invention will be described in detail.

According to the present invention, a magnetic recording medium is provided on a non-magnetic support,
A paint for the non-magnetic layer, which is a conductive layer containing carbon black, and a paint for the magnetic layer containing ferromagnetic barium ferrite particles are applied in this order by a wet-on-wet multilayer coating method. Formed.

-Non-magnetic support-Examples of the non-magnetic support include polyesters such as polyethylene terephthalate and polyethylene-2,6-naphthalate, polyolefins such as polypropylene, cellulose triacetate, cellulose diacetate and the like. Plastics such as cellulose derivatives, polyamides, and polycarbonates may be used.

In addition, metals such as Cu, Al, and Zn, glass, boron nitride, and ceramics such as Si carbide can also be used.

The thickness of these non-magnetic supports is about 3 to 100 μm, preferably 5 to 50 μm in the case of a film or a sheet, and about 30 μm to 10 mm in the case of a disk or a card. Is used in a cylindrical shape, and its shape is determined according to the recorder used.

Incidentally, an intermediate layer or an undercoat layer may be provided on the surface of the non-magnetic support in order to improve the adhesiveness.

-Non-magnetic layer- The non-magnetic layer is formed by applying a conductive layer having carbon black and a binder on a non-magnetic support.

The non-magnetic layer is a conductive layer containing carbon black as a main component.

Examples of carbon black used in such a conductive layer include Conductex 975 (specific surface area 250 m ² / g, particle diameter 24 mμ) of Columbia Carbon Japan,
Conductex 900 (specific surface area 125m ² / g, particle size 27m
μ), Conductex 40-220 (particle diameter 20mμ), Conductex SC (particle diameter 20mμ), Cabot Vulcan XC-72 (specific surface area 254m ² / g, particle diameter 30m, manufactured by Cabot Corporation)
μ), Vulcan P (particle size 20mμ) (Raben 1040, 420,
There are conductive carbon blacks such as Black Pearls L2000 (particle size: 16 μm) and # 44 from Mitsubishi Kasei Kogyo. When the carbon black has an oil absorption of 90 ml (DBP) / 100 g or more, it is desirable because it easily has a structure structure and exhibits higher conductivity.

The average particle size of carbon black contained in the nonmagnetic layer is 5 to 30 mμ, preferably 10 to 25 mμ.

Further, among carbon blacks having the above average particle size, it is preferable that the pH is less than 5.

Examples of such a carbon black having a specific pH include MONARCH 1400 (average particle size; 13.0 nm, pH; 2.5) and MONARCH 1300 (average particle size; 13.0, manufactured by Cabot Corporation, USA).
nm, pH; 2.5), MONARCH 1000 (average particle size; 16.0 nm, pH; 2.
5), MOGUL L (BLACH PEARLS L, average particle size; 24.0 nm, pH;
3.0), REGAL 400R (REGAL 400, average particle size; 25.0 nm, pH;
3.0) etc., and ROYAL SPE manufactured by Columbian Carbon Co., Ltd.
CTRA (average particle size; 10.0 nm, pH; 4.0), NEO SPEDTRA MARK
I (average particle size; 11.0nm, pH; 4.0), NEO SPECTRA MARK II
(Average particle size; 13.0 nm, pH; 3.0), NEO SPECTRA AG (average particle size; 13.0 nm, pH; 3.0), SUPERBA (average particle size: 15.0 nm, p
H; 3.2), NEO SPECTRA MARK IV (average particle size; 16.0 nm, pH;
4.5), RAVEN 5000 (average particle size; 12.0 nm, pH; 2.8), RAVE
N 7000 (average particle size; 15.0 nm, pH; 2.1), RAVEN 5750 (average particle size: 15.0 nm, pH; 2.1), RAVEN 5250 (average particle size: 20.0)
nm, pH; 2.2), RAVEN 3500 (average particle size; 16.0 nm, pH; 2.
5), RAVEN 1255 (average particle size; 23.0 nm, pH; 2.5), RAVEN
1040 (average particle size; 28.0 nm, pH; 2.8), RAVEN 1035 (average particle size: 27.0 nm, pH; 3.5), RAVEN 14 powder (average particle size: 5)
9.0 nm, pH; 3.0).

The amount of carbon black to be added is generally 10 to 400 parts by weight, preferably 100 to 35 parts by weight, per 100 parts by weight of a binder described later.
0 parts by weight.

As a binder (also referred to as a binder), which is one component of the nonmagnetic layer, a conventionally used binder can be used, and a functional group or a functional group that forms an internal salt is used. Is preferred.

As the functional group in the resins, for example, -SO
₃ M, -OSO ₃ M, -COOM, and -PO (OM ¹ ) [wherein, M is any one of a hydrogen atom, an alkali atom, and an ammonia group, and M ¹ is a hydrogen atom, an alkali metal, Is one of Two OMs bonded to the phosphorus atom
M ¹ in ¹ may be the same or different. ) And the like.

Examples of resins into which these functional groups are introduced include resins such as vinyl chloride resins, polyester resins, and polyurethane resins.

Among various resins modified by introducing a functional group,
Preferred is a polyurethane resin having the above functional group. Further, among polyurethane resins having a functional group, a polyurethane resin having a repeating unit having —SO ₃ Na is preferable.

Such a polyurethane resin can be produced, for example, as follows.

Generally, a polyurethane resin can be produced by reacting a polyisocyanate compound with a polyol component. As the polyol component, a polyester polyol obtained by reacting a polyol with a polybasic acid is used.

Polyurethane resin, according to a conventional method, using a polybasic acid having a specific polar group as a part of the polybasic acid to prepare a polyester polyol having a specific polar group, the obtained polyester polyol and a polyisocyanate compound Can be obtained by reacting

Examples of polybasic acids having a polar group include 5-sulfoisophthalic acid, 2-sulfoisophthalic acid, 4-sulfoisophthalic acid, 3-sulfoisophthalic acid, and their sodium and potassium salts.

Examples of polyol components include trimethylolpropane, hexanetriol, glycerin, trimethylolpropane, neopentyl glycol, pentaerythritol, ethylene glycol, propylene glycol, butylene glycol, and diethylene glycol.

Examples of the dicarboxylic acids of the polybasic acids include phthalic acid, isophthalic acid, terephthalic acid, adipic acid, dimerized linoleic acid, sebacic acid, and maleic acid.

The number average molecular weight of the thus obtained polyester polyol having a polar group is usually in the range of 500 to 8,000.

Examples of the polyisocyanate compound include a reaction product of 3 moles of a diisocyanate such as diphenylmethane-4,4'-diisocyanate, tolylene diisocyanate, and xylylene diisocyanate with 1 mole of trimethylolpropane, and a burette adduct of 3 moles of hexamethylene diisocyanate. Compound, tolylene diisocyanate 5
Moles of isocyanurate adduct compound, 3 moles of isocyanurate adduct compound, and polymers of diphenylmethane diisocyanate.

The reaction between the polyester polyol and the polyisocyanate compound is such that the number average molecular weight of the oily polyurethane resin is usually 10,000 to 200,000, preferably 15,000 to 60,00.
The reaction is performed under conditions adjusted to fall within the range of 0.

In addition to the above-described production method, for example, a polyurethane resin into which -OH is introduced is produced, and the polyurethane resin is reacted with a compound containing a polar group and chlorine described below (dehydrochlorination reaction) to form a polyurethane resin. A method of introducing a polar group into the resin may be employed.

(However, M and M ¹ have the same meanings as described above.) The content of the functional group-containing polyurethane resin in the repeating resin having the functional group is usually 0.01 to 5 mol%, preferably 0.1 to 5 mol%. It is preferably in the range of 2.0 mol%.

As described above, the introduction of the functional group into the polyurethane resin is described in JP-B-51-157603 and JP-B-58-41565.
And JP-A-57-92422 and JP-A-57-92423, and in the present invention, a functional group-containing polyurethane resin obtained by the method described therein is preferably used. can do.

Preferred specific examples of the functional group-containing binder include-
COOH-containing polyurethane (“TIM-300” manufactured by Sanyo Chemical Industries, Ltd.)
5 "), - SO ₃ Na-containing polyurethane (Toyobo Co., Ltd." UR-8300 "," UR-8600 "), - COOH-containing vinyl chloride-vinyl acetate copolymer (Nippon Zeon Co., Ltd." 400 × 110
A "), - SO ₃ Na-containing vinyl chloride-vinyl acetate copolymer (Nippon Zeon Co., Ltd." MR-1101 "), and the like. The content of the functional group is preferably in the range of 1 to 10,000 equivalents / 10 ⁶ gr. Further, the molecular weight is preferably from 300 to 200,000.

Examples of the resin modified by introducing a functional group that forms an internal salt include a polyurethane resin that is modified by introducing a functional group that forms an internal salt and a functional group that forms a functional group that forms an internal salt. And the like.

A polyurethane resin modified by introducing a functional group that forms an intramolecular salt can be produced as follows.

Similar to the ordinary polyurethane synthesis method, it is produced by reacting a high molecular weight polyol (molecular weight: 500 to 3,000) such as polycarbonate polyol, polyester polyol, polylactone polyol, polyether polyol, and a polyfunctional aromatic or aliphatic isocyanate. . As a result, a polyester polyurethane, a polyether polyurethane, and a polycarbonate polyurethane carbonated with phosgene or diphenyl carbonate are obtained.

These polyurethanes are mainly produced by the reaction of a polyisocyanate with a polyol and optionally other copolymers, and are also in the form of urethane resins or urethane prepolymers containing free isocyanate groups and / or hydroxyl groups, or Those which do not contain these reactive terminal groups (for example, in the form of a urethane elastomer) may be used.

As the isocyanate component, various diisocyanate compounds such as hexamethylene diisocyanate (HM
DI), diphenylmethane diisocyanate (MDI), hydrogenated MDI (H ₁₂ MDI), toluene diisocyanate (TD
I), 1,5-naphthalenediisocyanate (NDI), tolidine diisocyanate (TODI), lysine diisocyanate methyl ester (LDI), isophorone diisocyanate (IPDI) and the like can be used.

If necessary, a low molecular weight polyfunctional alcohol such as 1,4-butanediol, 1,6-hexanediol, 1,3-butanediol is used to adjust the molecular weight, adjust the resin properties, and the like.

The functional group forming the intramolecular salt may be introduced into the isocyanate component, but may be introduced into the polyol component, and may be introduced into the above low-molecular-weight polyfunctional alcohol.

Polyester polyols in which the functional groups form internal salts include various dicarboxylic acid components and polyhydric alcohol components, and dicarboxylic acid components in which the functional groups form internal salts and / or the functional groups form internal salts. Can be synthesized by polycondensation of the polyhydric alcohol component forming

Examples of the dicarboxylic acid component include terephthalic acid, isophthalic acid, sebacic acid, adipic acid, dimerized linoleic acid, and maleic acid.

As the polyhydric alcohol component, ethylene glycol,
Propylene glycol, butylene glycol, diethylene glycol, glycols such as trimethylolpropane, hexanetriol, glycerin, trimethylolpropane, trimethylolethane, any two or more selected from polyhydric alcohols such as pentaerythritol Examples can be given.

The polycarbonate polyol in which the functional group forms an inner salt can be generally synthesized by a transesterification method between a polyhydric alcohol and a dialkyl carbonate or diallyl carbonate, or obtained by condensation of a polyhydric alcohol with phosgene. You can also.

In producing the above polyester polyol and polycarbonate polyol (including polycarbonate polyester polyol), the following aromatic polyhydric alcohols can be used. In reacting the above-mentioned polyester polyol or polycarbonate polyol with polyisocyanate, the following aromatic polyhydric alcohols can be used.

Aromatic polyhydric alcohol: [However, n is 1 or 2. ] [Where R is-(CH ₂ ) _2- , -CH (CH ₃ ) -CH ₂ CH _2-
Is shown. X is _{-SO 2 -, - CO -,} - C (CH 3) 2 -, - C
_{(CH 3) 2 -C 6 H} 4 -C (CH 3) 2 - shows a. ] [However, R ¹ represents a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, and R ² represents a hydrogen atom or an alkyl group or an aryl group having 1 to 7 carbon atoms. ] [However, m represents an integer of 1 to 10. ] [However, k represents 1 or 2. ] [However, k represents 1 or 2. ] [However, k represents 1 or 2. ] [However, k represents 1 or 2. ] [However, k represents 1 or 2. In the polyurethane having the aromatic polyhydric alcohol component in the main chain, the content of these components is desirably 5 mol% or more of the entire polyhydric alcohol component.

To produce a lactone-based polyester polyol having a functional group forming an inner salt, s-caprolactam,
The above functional group may be introduced into lactams such as α-methyl-1-caprolactam, s-methyl-s-caprolactam and γ-butyrolactam.

In order to produce a polyether polyol having a functional group forming an inner salt, the above functional group may be introduced into ethylene oxide, propylene oxide, butylene oxide, or the like.

A betaine group can be mentioned as a functional group forming an intramolecular salt.

The polyester polyol having a functional group forming an inner salt is further described.

As a general polyester synthesis method, an aliphatic, an aromatic polyfunctional acid or an acid component having a derivative thereof,
There is a method utilizing a condensation reaction with an aliphatic or aromatic alcohol component.

The introduction of an intramolecular amphoteric base such as a betaine group can be performed by using the acid component containing a betaine group, or an alcohol component containing a betaine group,
Alternatively, a method of introducing a betaine group or the like into the polyester by utilizing a polymer reaction may be used. However, in consideration of the adverse effect due to the remaining unreacted components and the introduction rate, it is preferable to use a monomer to which an intramolecular amphoteric base such as a betaine group is introduced in advance.

Examples of the betaine group include a sulfobetaine group, a phosphobetaine group, and a carboxybetaine group. The general formula of these betaine-type functional groups can be represented as follows.

[However, the nitrogen atom in the above formula is incorporated in the urethane chain, and A represents a hydrogen atom and an alkyl group having 1 to 60 carbon atoms. B ^{- _{is, -SO 3 -, -O-SO}} 3 -, -COO -, -O-PO
Represents ₃ H ⁻ , —OPO ₃ ⁻ , or —OPO ₂ H ₂ ^— . K represents an integer of 1 to 10. ] [However, the nitrogen atom in the above formula is incorporated in the urethane chain, and R ³ represents an alkyl group, an alkenyl group or an aryl group having 1 to 12 carbon atoms. D is -COO- or -C
Represents ONH-, and B ^- and K have the same meanings as described above. Examples of the betaine group-containing monomer that can be used include the compounds exemplified below. Needless to say, the polyurethane resin having a functional group that forms an intramolecular salt is not limited to those obtained by using these monomers.

The monomer in which the functional group forms an inner salt can be obtained as a commercially available drug, but can also be easily synthesized by the following method.

(A) Synthesis method using monochloroacetic acid [However, R ⁴ represents a lower alkyl group such as a methyl group or an ethyl group. (B) Synthetic method using monochlorosuccinic acid [However, R ⁴ has the same meaning as described above.] (C) Synthetic method using propane sultone [However, R ⁴ has the same meaning as described above.] A reaction for introducing a betaine group or the like into a polymer as a polymer reaction will be described.

This is a method in which a compound having a betaine group or the like is reacted with an OH group present at a terminal or a side chain of the polyurethane which has been chain-extended to a predetermined molecular weight in advance by a polymerization reaction. In this case, first, a compound having a hydroxyl group and a betaine group is synthesized, and this is reacted with a polyfunctional isocyanate such as diisocyanate in an equimolar manner to obtain a reaction product of one NCO group of diisocyanate and a hydroxyl group in the compound. Then, by reacting the OH group of the polyurethane with the unreacted NCO group, it is possible to obtain a polyurethane into which a betaine group or the like has been introduced.

Examples of the above-mentioned compound having a hydroxyl group and a betaine group include the following compounds.
However, it is not limited to these.

The amount of betaine groups introduced into the polyurethane resin is 0.01 to
It is preferably 1.0 mmol% / g, more preferably 0.1 to 0.5 mmol% / g. If the amount of the betaine group or the like introduced is less than 0.01 mmol% / g, it is difficult to obtain a sufficient effect on the dispersibility of the ferromagnetic powder. If the amount of the functional group introduced exceeds 1.0 mmol% / g, intermolecular or intramolecular aggregation is likely to occur, not only adversely affecting the dispersibility, but also causing selectivity to the solvent, making it difficult to use a general-purpose solvent. There is also a possibility that it cannot be used.

The number average molecular weight of the polyurethane resin used in the present invention is
It is more preferably from 5,000 to 100,000 and more preferably from 10,000 to 50,000.
When the number average molecular weight is less than 5,000, the resin film-forming ability becomes insufficient, and when the number average molecular weight exceeds 100,000, problems occur in the steps of preparing, mixing, transferring, applying, etc. in the preparation of magnetic paint. There is.

Next, a vinyl chloride resin having a functional group forming an inner salt will be described.

The vinyl chloride resin having a functional group forming an intramolecular salt includes a vinyl chloride monomer, a “copolymerizable monomer having a functional group forming an internal salt” described below, and other copolymers, if necessary. It can be obtained by copolymerizing a polymerizable monomer. Alternatively, a vinyl chloride-based copolymer may be once produced, and a functional group forming an internal salt by a polymer reaction may be introduced into the vinyl chloride-based copolymer.

Examples of the "functional group forming an inner salt" include a betaine group, and specific examples of such a betaine group include a sulfobetaine group, a phosphobetaine group, and a carboxybetaine group. Examples of the “copolymerizable monomer having a functional group forming an inner salt” include the following compounds.

In addition, as a method for introducing a betaine group or the like by a polymer reaction, first, a double bond existing at a terminal or a side chain of a vinyl chloride-based copolymer which has been chain-extended to a predetermined molecular weight in advance by a polymerization reaction is used. Then, there is a method of reacting a compound having a betaine group or the like.

Examples of the compound used in this method include the above-mentioned copolymerizable monomers having a functional group forming an inner salt.

In the vinyl chloride resin having a functional group forming an internal salt, the content of the copolymerizable monomer having a functional group forming an internal salt is preferably 0.01 to 30 mol%. If the content of the copolymerizable monomer having a functional group forming an intramolecular salt is too large, the solubility in a solvent is deteriorated or gelation is easily caused, and the copolymerizable monomer of this kind is also used. If the content is too small, desired characteristics may not be obtained.

Since various types of copolymerizable monomers having a functional group capable of forming an internal salt exist as described above, in order to optimally adjust the properties of a vinyl chloride resin having a functional group capable of forming an internal salt. It is better to select and use them appropriately.

The vinyl chloride resin having a functional group capable of forming an inner salt may be obtained by copolymerizing an epoxy group-containing monomer and / or a hydroxyl group-containing monomer as another copolymerizable monomer. The hydroxyl group present in the vinyl chloride resin having a functional group that forms an inner salt may be derived from the hydroxyl group-containing monomer, but may be derived from another copolymerizable monomer such as a fatty acid such as vinyl acetate. It may be introduced by partial hydrolysis of a vinyl chloride resin obtained using vinyl.

As the above-mentioned epoxy group-containing monomer, allyl glycidyl ether, glycidyl ethers of unsaturated alcohols such as methacryl glycidyl ether, glycidyl acrylate, glycidyl methacrylate, glycidyl-p-vinyl benzoate, methyl glycidyl vinyl itaconate, glycidyl ethyl malate, Glycidyl vinylsulfonate, glycidyl esters of unsaturated acids such as glycidyl (meth) allyl sulfonate, butadiene monooxide, vinylcyclohexene monooxide, epoxide olefins in 2-methyl-5,6-epoxyhexene building, and the like. Can be.

The hydroxyl group-containing monomer, -R ⁵ -OH [however, R ⁵
Represents C _p H _2p , COOC _p H _2p , or CONHC _p H _2p (where p is an integer of 1 to 4). And a monomer having an organic residue represented by the formula:

Such a monomer having —R ⁵ —OH includes carbon atoms of α, β-unsaturated acids such as (meth) acrylic acid-2-hydroxyethyl ester and (meth) acrylic acid-2-hydroxypropyl ester. Alkanol esters of the formulas 2 to 4, mono-2-hydroxypropyl maleate, di-2-hydroxypropyl maleate,
And alkanol esters of unsaturated dicarboxylic acids such as itaconic acid mono-2-hydroxybutyl ester;
Olefinic alcohols such as buten-1-ol and 5-hexen-1-ol; alkanol vinyl ethers such as 2-hydroxyethyl vinyl ether and 2-hydroxypropyl vinyl ether; acrylamides such as N-methylolacrylamide and N-methylolmethacrylamide; Can be mentioned. Further, -R ⁵ bonded to a vinyl chloride resin containing a functional group forming an inner salt.
The content of hydroxyl group based on -OH is preferably 0.1 to 2.0% by weight. If the amount is less than 0.1% by weight, the crosslinking effect of the coating film by the isocyanate compound will not be exhibited. If the amount is more than 2.0% by weight, the pot life of the magnetic paint will be too short to be used. Although the amount of the hydroxyl group is much smaller than that of the vinyl chloride-vinyl alcohol-vinyl acetate copolymer conventionally known for magnetic coatings, the crosslinking reaction with the isocyanate compound is not much. Achieved well. The reason is not clear, but it is thought to be due to the fact that the hydroxyl groups involved in the reaction are farther away from the main chain of the copolymer, increasing the degree of freedom, and that the distribution of hydroxyl groups in the polymer is uniform. .

As other copolymerizable monomers that can be copolymerized as needed, there can be mentioned known polymerizable monomers, some of which are exemplified below.

The vinyl chloride copolymer preferably includes a copolymer containing vinyl chloride-vinyl acetate (hereinafter, referred to as "vinyl chloride-vinyl acetate copolymer"). Examples of vinyl chloride-vinyl acetate copolymers include vinyl chloride-vinyl acetate-vinyl alcohol, vinyl chloride-vinyl acetate-maleic anhydride, vinyl chloride-vinyl acetate-vinyl alcohol-maleic anhydride, and vinyl chloride-acetic acid. Examples include vinyl-vinyl alcohol-maleic anhydride-maleic acid copolymers, and among vinyl chloride-vinyl acetate copolymers, partial hydrolysis is also preferred.

The above copolymer that can be used in the present invention can be obtained by a polymerization method such as emulsion polymerization, solution polymerization, suspension polymerization, or bulk polymerization. In any of the methods, a known technique such as the use of a molecular weight regulator and a polymerization initiator, or the divisional or continuous addition of monomers can be used as required.

By the way, a conventional vinyl chloride-based copolymer resin (for example, VAGH manufactured by UCC) is composed of the following copolymer components.

However, here, it is considered that the —O—COCH ₃ group hardly contributes to a crosslinking reaction with a curing agent or the like.
Therefore, instead of -O-COCH _3, It is preferable to contain an epoxy group such as

The polymerization degree of the vinyl chloride copolymer used in the present invention is preferably from 100 to 500, and more preferably from 150 to 400.

As a method for measuring the degree of polymerization, the vinyl chloride resin was dissolved in cyclohexanone by heating, and JI was performed at 30 ° C.
The specific viscosity of the solution is measured in accordance with SK6721, and this is converted to the JIS specific viscosity using nitrobenzene to determine the degree of polymerization.

In the above general formula [I], it is preferred that the betaine group and the epoxy group are both present in the copolymer, in which case the betaine group is 0.5 to 4% by weight and the epoxy group is 0.5% by weight.
〜3% by weight, and the vinyl chloride monomer unit is preferably contained in a proportion of 95-80% by weight.

In the copolymer represented by the above general formula [I], when the copolymer is used as a binder for a magnetic recording medium and exhibits the required effects, the vinyl chloride repeating unit is If the vinyl chloride component is too small, the mechanical strength required for the magnetic recording medium cannot be obtained.If the vinyl chloride component is too large, the solubility in the solvent will be poor, and the resin glass The transition temperature (Tg) also tends to increase.

In addition, the repeating unit containing an epoxy group improves the thermal stability of vinyl chloride and also reacts with a cross-linking curing agent such as isocyanate to crosslink the binder to make it a higher molecular weight, and to obtain another polymer such as polyurethane. It participates in binding with a binder resin and enhances durability such as thermal stability and abrasion resistance. Also, there is an effect of adjusting the glass transition temperature (Tg) and the plasticizing effect of the binder resin by the content. For this reason, a reactive hydroxyl group such as vinyl alcohol is not required, but it does not cause any problem.

The repeating unit having a betaine group contributes to the dispersibility.If the content is too small, the effect becomes small, and if it is too large, it does not contribute to further improvement in the dispersibility, and On the contrary, the moisture resistance deteriorates, which is not preferable.

The vinyl chloride copolymer represented by the general formula [I] includes:
In addition to the above-mentioned repeating unit, a carboxyl group or a salt residue thereof, for example, -COOM (where M represents a hydrogen atom, an alkali metal atom or an ammonium group) for the purpose of further improving dispersibility such as-(Z) _d- ) Or a repeating unit having a hydrophilic functional group such as a hydroxyl group may be introduced.
The carboxyl group has a higher effect of improving the binding property and dispersibility of the binder to the magnetic powder (iron oxide, metal powder) than the hydroxyl group.

Further, a repeating unit having an effect of improving the strength or solvent solubility of the resin or the compatibility of other resins, improving the lubricity or improving the flexibility may be introduced.

Next, specific examples of the copolymer having a block represented by the above general formula will be described, but the copolymer is not limited to the following examples.

Next, the synthesis of a vinyl chloride copolymer containing a functional group capable of forming an inner salt will be further described.

When a functional group that forms an internal salt such as a betaine group is introduced by a polymer reaction after synthesizing a vinyl chloride copolymer containing no betaine group, since this is a polymer reaction, an unreacted compound There are problems that it is difficult to remove the presence and by-products, and it is difficult to adjust the reaction rate. Further, there is a problem that the introduced epoxy group reacts with hydrochloric acid during the reaction, or a ring-opening reaction of the epoxy ring occurs during the synthesis. Therefore, in order to avoid these problems at all, a method of copolymerizing a copolymerizable monomer having a functional group such as betaine is advantageous.

That is, for example, a predetermined amount of a reactive monomer having an unsaturated bond from which the repeating unit represented by the general formula [I] is derived is poured into a reaction vessel such as an autoclave, and a general polymerization initiator such as benzoyl By using a polymerization initiator such as a peroxide, a radical polymerization initiator such as azobisisobutyronitrile or a redox polymerization initiator, an anionic polymerization initiator, or a cationic polymerization initiator, thereby polymerizing the reactive monomer. A copolymer can be synthesized.

Specific examples of the reactive monomer for introducing the epoxy group include glycidyl acrylate, glycidyl methacrylate and the like, and various compounds described above. As the reactive monomer for introducing a betaine group, any of those described above can be used.

If a carboxylic acid or a salt thereof is introduced, acrylic acid, methacrylic acid and the like may be used.

The following azo compounds or organic peroxides can be used as the oil-soluble radical polymerization initiator.

For example, 2,2'-azobisisobutyronitrile, 2,2
2'-azobis (2-methyl-valeronitrile), 2,2 '
-Azobis (2,4-dimethylbutyronitrile), 2,2'-
Azobis (2-methylcapronitrile), 2,2'-azobis (2,3,3-trimethylbutyronitrile), 2,2'-azobis (2,4,4-trimethylvaleronitrile), 2,2 '-
Azobis (2,4-dimethylvaleronitrile), 2,2'-azobis (2,4-dimethyl-4-ethoxyvaleronitrile), 2,2'-azobis (2,4-dimethyl-4-n-butoxyvalero) Nitrile) and the like can be used. Examples of organic peroxides include, for example, acetyl peroxide, propionyl peroxide, isobutyryl peroxide, octanoyl peroxide, decanoyl peroxide, lauroyl peroxide, 3,5,5-
Diacyl peroxides such as trimethylhexanoyl peroxide, benzoylhexanoyl purge isopropyl peroxydicarbonate, di-2-ethylhexylperoxydicarbonate, t-butylperoxyisobutyrate, t-butylperoxyvivalate, t
Peroxyesters such as -butylperoxylaurate and the like can be used. Of course, two or more of the above oil-soluble radical polymerization initiators can be used in appropriate combination. Among them, azo compounds are preferred from the viewpoint of handling safety and performance, and 2,2'-azobisisobutyronitrile or 2,2'-azobis (2,4-dimethylvaleronitrile) is particularly preferred. It should be noted that although it is difficult to uniquely define the amount of such an initiator,
It is used in a range of about 0.2 to 2.0% by weight based on the monomer.

Further, regarding the pH of the polymerization system, if the acidity is too strong, ring-opening of the epoxy group is caused during the polymerization, and if the alkalinity is too strong, hydrolysis of the resulting polymer is caused.
It is recommended to set within the range of 2 to 9, preferably 2 to 7.

The polymerization temperature depends on the type of the initiator, but as the temperature increases, a ring-opening reaction of the epoxy group or a part of the monomer is emulsified to cause emulsion polymerization to form a latex-like fine polymer. About 80 ° C.
Hereinafter, a temperature range of preferably 40 to 70 ° C. is recommended.

As the polymerization solvent, it is desirable to use water, but it is also acceptable to allow a water-miscible organic solvent to coexist or an electrolyte salt to coexist.

By using a resin modified by introducing the above functional group or a functional group that forms an inner salt into the non-magnetic layer, the dispersibility of carbon black can be improved, and a highly smooth magnetic recording medium can be obtained. Can be.

In the present invention, in addition to the binder, an unmodified vinyl chloride resin conventionally used as necessary,
Polyurethane resin or polyester resin can be mixed, and cellulose resin, phenoxy resin or thermoplastic resin with specific usage method, thermosetting resin, reactive resin, electron beam curing resin, etc. May be.

The above-mentioned resins are complementary in length and length, and can be used by selecting the kind and the optimum point of the amount thereof as a binder constituting the nonmagnetic layer.

As will be described in detail later, the amount of the binder in the non-magnetic layer is as follows:
The amount of (A) is determined by the amount (B) of the total binder in the magnetic layer described below.
It is important that a specific weight ratio be obtained between the two.

The non-magnetic layer serving as the conductive layer is obtained by fixing the carbon black with the binder resin serving as the binder, and may further include, for example, a lubricant as an optional component.

Fatty acids and / or fatty acid esters can be contained as a lubricant added to the nonmagnetic layer. In this case, the amount of the fatty acid and / or fatty acid ester added is preferably 0 to 30 parts by weight based on the carbon black. When the magnetic layer is formed as a thin film, the total amount of the lubricant is reduced and durability is deteriorated. If the amount of the lubricant in the magnetic layer is increased beyond the range, the lubricant is likely to exude or the output is liable to decrease. Therefore, it is effective to add a lubricant to the non-magnetic layer so as to be a lubricant supply source for the magnetic layer from the viewpoint of improving the durability of the magnetic layer.

The fatty acid may be a monobasic acid or a dibasic acid, and preferably has 6 to 30 carbon atoms, and more preferably 12 to 22 carbon atoms. Examples of fatty acids are caproic, caprylic, capric, lauric, myristic, palmitic, stearic, isostearic, linolenic, linoleic, oleic, elaidic, behenic, malonic,
Examples include succinic acid, maleic acid, glutaric acid, adipic acid, bimeric acid, azelaic acid, sebacic acid, 1,12-dodecanedicarboxylic acid, and octanedicarboxylic acid.

Oleyl oleate as an example of the fatty acid ester,
Isocetyl stearate, dioleyl malate, butyl myristate, octyl myristate, octyl palmitate, pentyl stearate, pentyl palmitate, isobutyl oleate, stearyl stearate,
Lauryl oleate, octyl oleate, isobutyl oleate, ethyl oleate, isotridecyl oleate, 2-ethylhexyl stearate, ethyl stearate, 2-ethylhexyl palmitate, isopropyl palmitate, isopropyl myristate, butyl laurate, Cetyl-2-ethylhexarate, dioleyl adipate, diethyl adipate, diisobutyl adipate, diisodecyl adipate, oleyl stearate, 2-ethylhexyl myristate, isopentyl palmitate, isopentyl stearate, diethylene glycol-monobutyl ether palmitate, diethylene glycol- Mono-butyl ether palmitate and the like can be mentioned.

In addition to the above fatty acids and fatty acid esters, other lubricants such as silicone oil and fatty acid amide may be added to the magnetic layer.

The lubricants may be used alone or in combination of two or more, and may be the same or different from the lubricant of the magnetic layer.

An inorganic filler may be added as another optional component added to the nonmagnetic layer. As a specific example, γ-Fe
Magnetic powders such as ₂ O ₃ , Co-γ-Fe ₂ O ₃ , metal, Ba-ferrite, abrasives such as SiC, α-Al ₂ O ₃ , α-Fe ₂ O ₃ , Cr ₂ O ₃ , low
BET type carbon black and the like can be mentioned.

In the magnetic recording medium according to the present invention, the dry film thickness of the nonmagnetic layer is usually 0.1 to 4.0 μm, preferably 0.1 to 4.0 μm.
3 to 2.0 μm.

-Magnetic layer- According to the present invention, a magnetic recording medium is provided on a non-magnetic support,
The above-mentioned paint for the non-magnetic layer, which is the conductive layer, and the paint for the magnetic layer containing specific magnetic particles are applied in this order by a wet-on-wet multilayer coating method.

In the magnetic layer of the magnetic recording medium of the present invention, ferromagnetic barium ferrite (hereinafter abbreviated as Ba-ferrite) is used as the magnetic particles.

The preferred Ba-ferrite magnetic powder that can be used in the present invention is a Ba-ferrite powder in which at least a part of Fe is present.
Average particle size substituted with Co and Zn (diagonal height of hexagonal ferrite plate surface) 400 to 900 mm, plate ratio (diagonal length of hexagonal ferrite plate surface divided by plate thickness) Value) 2.
Ba-ferrite having a coercive force of 450 to 15000 and a coercive force of 450 to 15,000.

The Ba-ferrite powder has a coercive force controlled to an appropriate value by partially substituting Fe with Co, and further substituting Zn with a part to provide high saturation magnetization that cannot be obtained only by Co substitution. As a result, it is possible to obtain a magnetic recording medium having high reproduction output and excellent electromagnetic conversion characteristics. Further, by substituting a part of Fe with Hb, it is possible to obtain a magnetic recording medium having higher reproduction output and excellent electromagnetic conversion characteristics. Further, the Ba-ferrite of the present invention further comprises
Part of Fe may be replaced by a transition metal such as Ti, In, Mn, Cu, Ge, or Sn.

When Ba-ferrite used in the present invention is represented by the following general formula (M is a substituted metal), BaO · n ((Fe _{1 -m} M _m ) ₂ O ₃ [where m> 0.36 (however, Co + Zn = 0.08 to 0.3, Co / Zn =
0.5 to 10)] n is 5.4 to 6.0, and M is preferably a magnetic particle which is a combination of two or more elements having an average number of 3.

In the present invention, the reason why the average particle size, plate ratio, and coercive force of Ba-ferrite are preferably in the above preferred ranges is as follows. That is, when the average particle diameter is less than 400 mm, the reproduction output when the magnetic recording medium is used is insufficient, and when it exceeds 900 mm, the surface smoothness when the magnetic recording medium is remarkably deteriorated, and the noise level is reduced. If the plate ratio is less than 2.0, the perpendicular orientation ratio suitable for high-density recording cannot be obtained when the plate ratio is less than 2.0. When the medium is used, the surface smoothness deteriorates significantly, the noise level becomes too high, and when the coercive force is less than 350 Oe, it becomes difficult to hold the recording signal. Is caused by a decrease in saturation, which makes recording difficult.

As a method for producing the magnetic powder used in the present invention,
For example, the oxides and carbonates of each element necessary to form the desired Ba-ferrite are melted together with a glass-forming substance such as boric acid, and the obtained melt is quenched to form glass. Then, the glass is heat-treated at a predetermined temperature to precipitate the desired Ba-ferrite crystal powder, and finally, a glass crystallization method of removing the glass component by heat treatment, as well as a co-precipitation-firing method, A hydrothermal synthesis method, a flux method, an alkoxide method, a plasma jet method, or the like can be applied.

In the present invention, not to impair the effects of the present invention,
A known arbitrary magnetic substance can be contained in the magnetic layer together with the “magnetic particles having a tabular shape and an axis of easy magnetization being substantially perpendicular to the plane of the plate” as the magnetic particles.

For example, Co-γ-Fe ₂ O ₃ , Fe ₃ O ₄ , Co-containing Fe ₃ O ₄ such as γ-Fe ₂ O ₃ , Co-containing γ-Fe ₂ O ₃ or Co-coated γ-Fe ₂ O ₃
Or _{Co-γ-Fe 3 O 4} , CrO 2 oxide magnetic material such as Co-coated Fe ₃ O _4, and other, for example Fe, Ni, Fe-Ni alloy, Fe
-Co alloy, Fe-Ni-P alloy, Fe-Ni-Co alloy, Fe-Mn-
Zn alloy, Fe-Ni-Zn alloy, Fe-Co-Ni-Cr alloy, Fe-Co
-Fe, Ni, Co such as Ni-P alloy, Co-P alloy, Co-Cr alloy
And the like.
In addition, Si, Cu, Zn,
Elements such as Al, P, Mn, and Cr or compounds thereof may be included.

As the binder used in the magnetic layer, the same binder as the binder used in the non-magnetic layer is used.

Amount of binder to ferromagnetic powder in magnetic layer (B)
Is 5 to 30% by weight.

In the present invention, the amount (B) of the binder in the magnetic layer is determined by:
It is important that the amount (A) of the total binder in the nonmagnetic layer is adjusted to a specific weight ratio.

That is, the ratio of the total amount of binder (A) in the non-magnetic layer (A) to the total amount of binder in the magnetic layer (B), that is, A / B (weight ratio) is 2 or more and 7 or less. More preferably, A / B is 2
~ 5.

When the ratio A / B of the binder exceeds 7, the difference in the shrinkage ratio due to the drying of the coating film resulting from the difference in the amount of the binder occurs, and during the simultaneous multilayer coating, the interface between the magnetic coating layer and the magnetic layer is disturbed, The surface properties of the obtained magnetic layer deteriorate.

When A / B is less than 2, the total binder in the non-magnetic layer decreases, the dispersibility of the coating material deteriorates, and the surface property of the magnetic layer deteriorates. Further, the adhesiveness of the non-magnetic layer deteriorates, and the durability deteriorates.

Incidentally, in order to improve the durability of the magnetic layer of the magnetic recording medium of the present invention, various hardeners may be contained in the magnetic paint, and the magnetic layer may be formed by a method described later.

Examples of such curing agents include isocyanates such as aromatic isocyanates and aliphatic isocyanates.

The aromatic isocyanate includes, for example, tolylene diisocyanate (TDI) and adducts with these isocyanate active hydrogen compounds, and those having an average molecular weight in the range of 100 to 3,000 are suitable.

Examples of the aliphatic isocyanate include hexamethylene diisocyanate (HMDI) and the like, and adducts of these isocyanates and active hydrogen compounds. Among these aliphatic isocyanates and adducts of these isocyanates and active hydrogen compounds, those having a molecular weight in the range of 100 to 3,000 are preferred. Among the aliphatic isocyanates, non-alicyclic isocyanates and adducts of these compounds with active hydrogen compounds are preferred.

The magnetic layer may contain a dispersant contained in the magnetic paint used to form the magnetic layer, and if necessary, additives such as a lubricant, an abrasive, and an antistatic agent. May be contained.

Examples of the dispersant used in the present invention include phosphate esters,
Amine compounds, alkyl sulfates, fatty acid amides,
There are higher alcohols, polyethylene oxide, sulfosuccinic acid, sulfosuccinate, known surfactants and salts thereof, and negative organic groups (eg, -COOH).
Can be used.

Examples of the dispersant include caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, fatty acids having 12 to 22 carbon atoms such as oleic acid, and salts of these alkali metals or salts of alkaline earth metals. Examples thereof include amides thereof; polyalkylene oxide alkyl phosphates; lecithin; trialkyl polyolefin oxyquaternary ammonium acids; and azo compounds having a carboxyl group and a sulfonic acid group. These dispersants are added in the range of 0.5 to 5% by weight based on the ferromagnetic powder.

These dispersants may be used alone or in combination of two or more.

For the magnetic layer, silicone oil, graphite, carbon black graft polymer, molybdenum disulfide, tungsten disulfide, fatty acid and fatty acid ester can be used as a lubricant.

The fatty acid may be a monobasic acid or a dibasic acid. Examples of fatty acids are caproic acid, caprylic acid,
Capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, isostearic acid, linolenic acid, linoleic acid, oleic acid, elaidic acid, behenic acid, malonic acid, succinic acid, maleic acid, glutaric acid, adipic acid, vimelic acid , Azelaic acid, sebacic acid, 1,12-dodecanedicarboxylic acid, octanedicaric acid and the like.

Oleyl oleate as an example of the fatty acid ester,
Isocetyl stearate, dioleyl malate, butyl myristate, octyl myristate, octyl palmitate, pentyl stearate, pentyl palmitate, isobutyl oleate, stearyl stearate,
Lauryl oleate, octyl oleate, isobutyl oleate, ethyl oleate, isotridecyl oleate, 2-ethylhexyl stearate, ethyl stearate, 2-ethylhexyl palmitate, isopropyl palmitate, isopropyl myristate, butyl laurate, Cetyl-2-ethylhexarate, dioleyl adipate, diethyl adipate, diisobutyl adipate, diisodecyl adipate, oleyl stearate, 2-ethylhexyl myristate, isopentyl palmitate, isopentyl stearate, diethylene glycol-mono-butyl ether palmitate, diethylene glycol -Mono-butyl ether palmitate and the like.

These lubricants are used in an amount of 0.2 to 100 parts by weight of the binder.
It is added in the range of 20 parts by weight.

 Also, non-magnetic abrasive particles may be added.

The abrasive may be a commonly used material such as alumina (α-Al ₂ O ₃ , β-Al ₂ O ₃ , γ-Al ₂ O ₃ , δ
−Al ₂ O ₃ , ζ−Al ₂ O ₃ , η−Al ₂ O ₃ , θ−Al ₂ O ₃ , κ−Al ₂ O
₃ , χ-Al ₂ O ₃ , ρ-Al ₂ O ₃ etc.), alumina hydrate, alumina silicate, other silicates, silicon carbide, boron carbide,
Other non-magnetic oxides such as chromium oxide and iron oxide, nitrides such as boron nitride, and the like are used. These abrasives have an average particle size of 0.05 to 5 μm, and particularly preferably 0.1 to 2 μm. These abrasives are added in the range of 1 to 20 parts by weight based on 100 parts by weight of the binder.

It is not necessary to add a usual antistatic agent to the magnetic layer. That is, according to the present invention, since the conductive layer containing carbon black is provided between the magnetic layer and the nonmagnetic support, the conductive layer sufficiently lowers the surface electric resistance of the magnetic layer. Because you can. And the magnetic layer,
The packing density and dispersibility of Ba-ferrite magnetic powder are improved.

However, in the present invention, the durability of the magnetic recording medium can be improved by further adding carbon black to the magnetic layer.

In this case, the particle size of the carbon black added to the magnetic layer is desirably in the range of 20 to 500 nm, preferably 4 to 500 nm.
Those having a size of 0 to 100 nm are desired.

Specific examples of carbon black added for the purpose of improving durability include BLACK PEARLS 2 manufactured by Cabot Corporation of the United States.
80 (average particle size; 41 nm), BLACK PEARLS 170 (average particle size; 50
nm), BLACK PEARLS 160 (average particle size; 50 nm), BLACK PEA
RLS 130 (average particle size; 75 nm), BLACK PEARLS 120 (average particle size: 75 nm), etc., and RAVEN manufactured by Columbian Carbon Co., Ltd.
500 (average particle size; 52.9 nm), RAVEN 450 (average particle size; 75.4 n)
m), RAVEN 430 (average particle size; 82.1 nm), RAVEN 420 (average particle size; 85.7 nm), RAVEN 410 (average particle size; 100.6 nm), RAVE
NT230 (average particle size; 56.2 nm), RAVEN H20 Powder (average particle size; 59.9 nm), RAVEN 22 Powder (average particle size; 82.6 n)
m), RAVEN 16 powder (average particle size; 67.8 nm), RAVEN 14
powder (average particle size; 54.6 nm), RAVEN MT-P (average particle size:
Such as # 22B (average particle size; 40.0) nm, CF-9 (average particle size; 40.0 nm), # 3500 (average particle size; 40.0 nm) manufactured by Mitsubishi Kasei Kogyo Co., Ltd. HS-100 (average particle size; 53.
0-nm) HS-500 (Average particle size; 7
6.0 nm).

An important point in the present invention is that the dry thickness of the magnetic layer is 0.1
To 4.0 μm, preferably 0.1 to 2.0 μm.

When the thickness of the magnetic layer exceeds 4.0 μm, the surface resistivity of the magnetic layer increases, and the dropout of the magnetic recording medium increases. On the other hand, when the thickness of the magnetic layer is smaller than 0.1 μm, the influence of the nonmagnetic layer appears strongly, the surface of the magnetic layer becomes rough, and the Lumi S / N and chroma S / N of the magnetic recording medium decrease.

-Manufacturing method of magnetic recording medium-When forming a non-magnetic layer and a magnetic layer on a support,
A method in which coating and drying steps are stacked one by one (so-called wet-on-dry coating method) and a method in which the next layer is applied simultaneously or successively on a layer in a wet state that has not been dried (so-called wet-on-wet method). Coating method = wet multi-layer coating method), but in the method of manufacturing a magnetic recording medium of the present invention, a wet coating
Simultaneous multilayer coating is performed by an on-wet multilayer coating method.

According to the present invention, a magnetic recording medium comprises, as shown in FIG. 1, for example, a conductive layer 2 containing carbon black, which is the above-mentioned nonmagnetic layer, on both surfaces of a nonmagnetic support 1.
A magnetic layer 4 containing Ba-ferrite magnetic powder and, if necessary, an overcoat layer (not shown) are laminated in this order.

The magnetic recording medium shown in FIG. 1 may be provided with an undercoat layer (not shown) between the conductive layer 2 and the support 1, or may not be provided with an undercoat layer. (The same applies hereinafter). The support may be subjected to corona discharge treatment.

 Next, a preferred example of the present invention will be described with reference to FIG.

In this manufacturing apparatus, in manufacturing the medium shown in FIG. 1, as shown in FIG. 2, first, the film-like support 1 pulled out from the supply roll 32 is extruded by the extrusion-type extrusion coaters 10 and 11 as described above. Each paint for the conductive layer 2 and the magnetic layer 4, which are the non-magnetic layers, was wet-on-coated.
After the multi-layer coating is performed by a wet method, it passes through a magnet for non-orientation or a magnet for vertical orientation 33 and is introduced into a drier 34, where it is dried by blowing hot air from nozzles arranged above and below.
Next, the dried support 1 with each coating layer is guided to a super calender device 37 composed of a combination of calender rolls 38, where it is calendered, and then wound up on a take-up roll 39. Thereafter, the conductive layer 2 and the magnetic layer 4 are applied to the other surface of the support 1 in the same manner as described above, dried, and calendered. The magnetic film thus obtained is punched into a desired shape, for example, a disk shape, and housed in a cassette to produce a 3.5-inch floppy disk.

In the above method, each paint may be supplied to the extrusion coaters 10 and 11 through an inline mixer (not shown). Note that, in the figure, the arrow D indicates the transport direction of the non-magnetic base film. Extruder coaters 10 and 11 respectively
Liquid reservoirs 13 and 14 are provided, and the paint from each coater is overlaid in a wet-on-wet manner. That is, immediately after the application of the coating material for the conductive layer (when it is in an undried state), the coating material for the magnetic layer is applied in multiple layers.

In the wet-on-wet multilayer coating method, in addition to the two extrusion coaters [FIG. 3 (a)], an extrusion coater of the type shown in FIGS. 3 (b) and (c) is used.
Can also be used.

In addition, a combination of a reverse roll and an extrusion coater, a combination of a gravure roll and an extrusion coater, and the like can also be used. Further, an air doctor coater, blade coater, air knife coater, squeeze coater, impregnation coater, transfer roll coater, kiss coater, cast coater, spray coater, and the like can be combined.

In the multi-layer coating by the wet-on-wet method, the upper magnetic layer is applied while the lower conductive layer is kept wet, so that the surface of the lower layer (that is, the boundary surface with the upper layer) becomes smooth. The surface properties of the upper layer are improved, and the adhesion between the upper and lower layers is also improved. As a result, in particular, the performance required for high-density recording, such as a magnetic disk, which requires high output and low noise is satisfied, and high durability performance is required unlike a magnetic tape or the like. In this case, film peeling is eliminated, film strength is improved, and durability is sufficient. In addition, the wet-on-wet multilayer coating method can reduce dropout and improve reliability.

Between the upper and lower layers formed by the above wet-on-wet multi-layer coating method, a boundary region in which components of both layers are mixed with a certain thickness, except when a clear boundary substantially exists. Although there are cases where the magnetic layer and the conductive layer are formed on the upper or lower layer excluding such a boundary region, they are included in the scope of the present invention.

Acetone, methyl ethyl ketone,
Ketones such as methyl isobutyl ketone and cyclohexanone; alcohols such as methanol, ethanol, propanol and butanol; esters such as methyl acetate, ethyl acetate, butyl acetate, ethyl lactate and ethylene glycol cenoacetate; glycol dimethyl ether and glycol monoethyl ether Ethers such as benzene, dioxane, and tetrahydrofuran; aromatic hydrocarbons such as benzene, toluene, and xylene; and halogenated hydrocarbons such as methylene chloride, ethylene chloride, carbon tetrachloride, chloroform, and dichlorobenzene.

These various solvents can be used alone, or two or more of them can be used in combination.

The magnetic field in the non-oriented magnet or the vertically oriented magnet is about 20 to 5000 gauss in AC or DC,
The drying temperature of the dryer is about 30 to 120 ° C, and the drying time is about 0.1 to 10 minutes.

[Example] Hereinafter, an example of the present invention will be described.

The components, ratios, operation orders, and the like shown below can be variously changed without departing from the scope of the present invention. In the following examples, "parts" are all parts by weight.

(Examples 1 to 12) The following components were sufficiently kneaded and dispersed by a kneader and a ball mill, and then immediately before coating, a polyisocyanate compound (Coronate L: Nippon Polyurethane Co., Ltd.)
Of the magnetic layer (I) and the carbon black paint (I) for the non-magnetic layer and the conductive layer.
I) was prepared.

Magnetic paint (I) and carbon black paint (II)
Used a polyurethane resin and a vinyl chloride-vinyl acetate-vinyl alcohol copolymer as a binder.

The blending amounts of binders and A / B in Examples 1 to 12 are as shown in Table 1.

Next, the carbon black paint (II-) was coated on a polyethylene terephthalate base film having a thickness of 75 μm.
A) and the magnetic paint (I) were sequentially applied by a wet-on-wet method using an extrusion-type extrusion coater as shown in FIG. 3 (a), and calendered after drying. Thereafter, each of the paints (II) and (I) was similarly applied to the opposite side of the polyethylene terephthalate base film in the same manner, dried, and then calendered.

The magnetic film thus obtained was punched into a disk having a diameter of 86 mm and housed in a cassette to manufacture a magnetic disk.

Each of the obtained magnetic disks was measured according to the following items.

Measurement method (1) Dispersibility Evaluation was made by measuring the glossiness with a VG-ID type gloss meter / digital variable gloss meter manufactured by Nippon Denshoku Industries.

(2) Smoothness The surface roughness was indicated by Ra.

Stylus type surface roughness meter [SE3FK type, manufactured by Kosaka Laboratory Co., Ltd.]
Was evaluated by.

The upper row shows the surface roughness at the time of multilayering, and the parentheses show the surface roughness of the nonmagnetic layer single layer.

(3) Reproduction output Recording was performed using a 500 KHz sine wave signal, and the reproduction RF output was measured.

Drive: PD-211 manufactured by TOSHIBA CORPORATION The measured reproduction RF output is shown as a relative value when the floppy disk manufactured in Example (6) is taken as 100%.

 The higher the RF output, the better one magnetic disk.

(4) Conductivity (Surface Electric Resistivity) An electrode having a width of 10 mm was separated by 10 mm, a sample was placed between the electrodes, and the surface electric resistance was measured at a voltage of 100 V.

 The higher the value, the higher the surface electrical resistivity.

(5) Coating property The coating film surface during and after coating was visually observed and evaluated.

：: Very good △: Poor ○: Good ×: Very poor (6) Calender stain (calender heat roll stain) The degree of stain on the calender roll used for the calender treatment in the magnetic medium manufacturing process was visually observed.

◎: No dirt △: Dirt ○: Almost no dirt ×: Lots of dirt (7) Durability Loaded in a recording / reproducing device, and a magnetic head manufactured by Toshiba Corporation
Using a 4MB drive PD-211, slide and contact at a pressure of 20 g / cm ₂ and rotate the disk at a rotational speed of 300 rpm. We changed and evaluated.

(Comparative Examples 1 to 4) In Examples, measurement was performed in the same manner as in the other examples except that the A / B ratio of the binder was 7 or more.

 Table 1 shows the evaluation results.

(Examples 13 to 20) The same operation as in Example 1 was carried out except that the binders of the types shown in Table 2 of the above Examples were mixed in the mixing ratios shown in Table 2.

The amounts of the binder and A / B are as shown in Table 2.

 Table 2 shows the evaluation results.

[Effects of the Invention] According to the present invention, storage capacity and recording / reproduction output are increased,
A magnetic recording medium with improved durability can be manufactured.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a cross section of a magnetic recording medium obtainable by the present invention, and FIG. 2 is a schematic view showing a manufacturing apparatus as an example that can be employed in the method of manufacturing a magnetic recording medium of the present invention. FIG. 3 (a), (b)
And (c) are each wet-coated with an extrusion coater.
It is a schematic explanatory drawing which shows an on-wet multilayer coating system. 1 ... non-magnetic support, 2 ... non-magnetic layer, 3 ... magnetic layer.

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Hiromichi Enomoto 1 Konica Corporation, Sakura-cho, Hino-shi, Tokyo (56) References JP-A-62-214524 (JP, A) JP-A-62-92132 (JP, A) JP-A-1-122024 (JP, A) JP-A-62-38523 (JP, A) JP-A-62-219331 (JP, A) (58) Fields investigated (Int. Cl. ⁷⁾ G11B 5/702 G11B 5/842

Claims (2)

(57) [Claims] 1. A lower layer formed by applying a coating for a non-magnetic layer containing carbon black as a main component on a non-magnetic support, and a lower layer formed on the lower layer while the lower layer remains wet. The weight of the total amount of the binder in the non-magnetic layer (A) and the amount of the total binder in the magnetic layer (B) containing magnetic particles having a shape and an easy axis of magnetization almost perpendicular to the plane of the plate. A method for producing a magnetic recording medium, comprising subjecting an upper layer formed by applying a coating material for a magnetic layer having a ratio A / B of at least 2 to at most 7 to a calender treatment after drying. 2. The production of a magnetic recording medium according to claim 1, wherein the binder constituting the non-magnetic layer is a resin obtained by introducing and modifying a functional group or a functional group forming an internal salt. Method.