JPH06111279A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To eliminate harmful gas and to improve magnetic characteristics, feeding durability by using mixture of polymethacrylate ester resin and polyurethane resin as binder of a magnetic coating layer having magnetic powder and the binder. CONSTITUTION:A magnetic recording medium is formed by coating a nonmagnetic base 1 with a magnetic coating film 2 containing magnetic powder and binder as main ingredients. The film 2 contains magnetic paint kneaded together with organic solvent selected in response to a type of the binder by dispersing the magnetic powder in the binder and coating the base 1 with the magnetic paint. The binder uses mixture of polymethacrylate ester resin and polyurethane resin. The polyurethane resin has excellent dispersibility, toughness and wear resistance, and the polymethacrylate ester resin adds coating film strength to the binder and generates no harmful gas. Thus, the medium having excellent magnetic characteristics, feeding durability and no generation of harmful gas can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium,
In particular, the present invention relates to improvement of a binder forming a magnetic layer in a coating type magnetic recording medium.

[0002]

2. Description of the Related Art In a so-called coating type magnetic recording medium, a magnetic paint prepared by kneading and dispersing a ferromagnetic powder, a binder, a dispersant, a lubricant, an abrasive and the like in an organic solvent is a non-magnetic substrate such as a polyester film. A magnetic coating film is formed by applying it on the surface.

As a binder in such a coating type magnetic recording medium, a vinyl chloride / vinyl acetate copolymer, a vinyl chloride / vinyl acetate / vinyl alcohol copolymer, a vinyl chloride / vinylidene chloride copolymer, a polyether polyurethane are used. Resin, polyester polyurethane resin, acrylonitrile-butadiene copolymer, nitrocellulose, epoxy resin, acrylic resin, etc. are used. Among these resins, polyurethane excellent in dispersibility to magnetic powder, toughness, and abrasion resistance Binders that combine a resin and polyvinyl chloride or nitrocellulose that impart coating strength to the magnetic coating formed are commonly used.

However, in recent years, magnetic recording media have been made thinner and magnetic powders have been made finer in response to the demand for high-density recording. As described above, when nitrocellulose is used as a binder, sufficient dispersion is achieved. Can not be imparted,
Further, when polyvinyl chloride is used, not only sufficient coating strength cannot be added, but also toxic chlorine gas is emitted at the time of kneading and the like, which is not preferable from the viewpoint of protecting the global environment.

Therefore, the present invention has been proposed in view of the above-mentioned conventional circumstances, and there is no possibility of generating harmful gas such as chlorine gas during manufacturing or burning, and from the viewpoint of global environment protection. Good with dispersibility, toughness,
An object of the present invention is to provide a magnetic recording medium having a magnetic coating film having excellent abrasion resistance and coating film strength, and having excellent magnetic properties and running durability.

[0006]

[Means for Solving the Problems] In order to achieve the above-mentioned object, as a result of intensive investigations by the present inventors, as a result of using a combination of a polyurethane resin and a polymethacrylic acid ester resin, a binder is required. Therefore, we have come to the knowledge that we can obtain what has all the requirements, namely, dispersibility, toughness, wear resistance, and coating strength.

The present invention has been completed on the basis of such findings, and provides a magnetic recording medium comprising a non-magnetic substrate and a magnetic coating film composed mainly of magnetic powder and a binder. The above binder is characterized by containing a polymethacrylic acid ester resin and a polyurethane resin. Further, the polyurethane group has a urethane group concentration of 2.5 mmol / g or more.

Further, the polyurethane resin is polyester polyurethane.
Further, the polyurethane resin is polycarbonate polyurethane.

As shown in FIG. 1, the magnetic recording medium of the present invention comprises a non-magnetic substrate 1, a magnetic powder formed on the non-magnetic substrate 1, and a magnetic coating film 2 mainly composed of a binder.

In the magnetic coating film, for example, magnetic powder is dispersed in a binder, and ethers, esters, ketones, aromatic hydrocarbons, aliphatic hydrocarbons,
It is formed by applying a magnetic paint prepared by kneading with an organic solvent selected from chlorinated hydrocarbons and the like onto a non-magnetic substrate.

In the present invention, a mixture of polymethacrylic acid ester resin and polyurethane resin is used as the binder constituting the above magnetic coating film. The polyurethane resin is
It is a resin having excellent dispersibility, toughness, and abrasion resistance, and the above-mentioned polymethacrylic acid ester resin is for adding coating strength to the binder. Conventionally, nitrocellulose or polyvinyl chloride has been used as a resin for adding coating strength, but these resins have insufficient dispersibility, insufficient coating strength, harmful gas It has drawbacks such as occurrence. The polymethacrylic acid ester resin used in the present invention has excellent coating film strength, good dispersibility and electromagnetic conversion characteristics, and does not generate harmful gas. Therefore, by using such a polymethacrylic acid ester resin in combination with a polyurethane resin, the requirements required for the binder can be sufficiently satisfied.

Here, when the polymethacrylic acid ester resin and the polyurethane resin are mixed, the mixing ratio of the polymethacrylic acid ester is 20 to 80% by weight of the total binder resin.
It is preferable that Polymethacrylic acid ester is
It is a resin having a relatively high glass transition point, and is a hard and brittle resin in an environment where a magnetic recording medium is used. Therefore, when the mixing ratio of the polymethacrylic acid ester resin exceeds 80% by weight, the magnetic coating film becomes hard and brittle, leading to lack of durability, and when it is less than 20% by weight, the magnetic coating film is soft. There is a high possibility that the magnetic recording medium will stick to the head during running because it has passed.

The above-mentioned polyurethane resin has a urethane group concentration of 2.5 mmol / g or more, further 2.5 to
It is preferable to use one of 7.0 mmol / g.
When the urethane group concentration is less than 2.5 mmol / g, the compatibility with another resin constituting the binder, the polymethacrylate resin, is insufficient, and the binder does not have good dispersibility, There is a possibility that a problem may occur in running durability. When the urethane group concentration exceeds 7.0 mmol / g, the urethane groups are agglomerated with each other, so that the synthesis is difficult and the dispersibility is not good.

As the polyurethane resin, a polyurethane resin used as a binder in this type of magnetic recording medium, such as a polyester polyurethane resin or a polycarbonate polyurethane resin, is usually used.

Among the above polyurethane resins, the polyester polyurethane resin is synthesized by the urethanization reaction of polyester polyol and polyisocyanate.

Polyester polyols include polyhydric alcohols such as ethylene glycol, propylene glycol, 1,4-butanediol, 1,3-butanediol, 1,5-pentanediol, 1,6-hexanediol or neopentyl glycol. And polyvalent carboxylic acids such as terephthalic acid, isophthalic acid, 1,5-naphthalic acid, adipic acid, succinic acid, and azelaic acid.

Examples of polyisocyanates include tolylene diisocyanate (TDI), 4,4'-diphenylmethane diisocyanate (MDI), hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI) and the like.

When synthesizing polyester polyurethane from polyester polyol and polyisocyanate, the above-mentioned polyhydric alcohol, aliphatic polyamine,
It is preferable to use an appropriate amount of a known chain extender such as an alicyclic polyamine or an aromatic polyamine. Further, in order to improve the adsorption of the resin to the magnetic powder and the dispersibility of the magnetic powder, a component containing a known polar group such as a metal sulfonate group in an appropriate ratio may be introduced.

Among the polyurethane resins, the above-mentioned polycarbonate polyurethane resin is synthesized by urethanization reaction of polycarbonate polyol and polyisocyanate.

As the polycarbonate polyol, one obtained by a condensation reaction of a conventionally known polyhydric alcohol and diallyl carbonate or dialkyl carbonate is used.

Examples of the polyisocyanate include tolylene diisocyanate (TDI), 4,4'-diphenylmethane diisocyanate (MDI), hexamethylene diisocyanate (HDI) and isophorone diisocyanate (IPDI).

When synthesizing a polycarbonate polyurethane resin from a polycarbonate polyol and a polyisocyanate, a known chain such as the above-mentioned polyhydric alcohol, aliphatic polyamine, alicyclic polyamine, aromatic polyamine, etc. is used as in the case of the polyester polyurethane resin. It is preferable to use an appropriate amount of the extender. In addition,
In order to improve the adsorbability of the resin to the magnetic powder and the dispersibility of the magnetic powder, a component containing a known polar group such as a metal sulfonate group at an appropriate ratio may be introduced.

On the other hand, the polymethacrylic acid ester resin used in combination with the polyurethane resin is a methacrylic acid ester, an unsaturated monomer having a --R--OH group (where R is an organic residue), --SO ₃ X. group or -OSO ₃ X
It can be synthesized by copolymerizing a monomer having a group with a radical generator, and further copolymerizing these monomers with an unsaturated monomer copolymerizable with these monomers. In this case, the average degree of polymerization of the polymethacrylic acid ester resin is 200 to
700 is suitable.

The methacrylic acid ester is represented by the general formula (1).

[0025]

[Chemical 1]

In the unsaturated monomer having a —R—OH group, the organic residue R is C _n H _2n , OC.
_n H _2n , COOC _n H _2n , CONHC _n H _2n (n is 1 to
5) and the like. Examples of such an unsaturated monomer having a —R—OH group include α-unsaturated acids such as (meth) acrylic acid-2-hydroxyethyl ester and (meth) acrylic acid-2-hydroxypropyl ester, Alkanol esters of unsaturated dicarboxylic acids such as C2-C4 alkanol esters of β-unsaturated acids, maleic acid mono-2-hydroxypropyl ester and maleic acid di-2-hydroxypropyl ester, 3-
Examples include olefin 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, and acrylamide such as N-methylol acrylamide.

The amount of hydroxyl groups introduced into the polymethacrylic acid ester resin by these unsaturated monomers is 0.1 to 3.
It is desirable to adjust the content to be 0% by weight. In the above polymethacrylic acid ester resin, the amount of hydroxyl groups is 0.
If it is less than 1% by weight, the reactivity with isocyanate becomes low, and if the amount of hydroxyl groups exceeds 3.0% by weight, the viscosity of the coating increases due to the hydrogen bond between the hydroxyl groups, resulting in insufficient dispersibility.

Further, examples of the monomer having -SO ₃ X group or -OSO ₃ X group include radically polymerizable unsaturated monomer having sulfonic acid, sulfuric acid and alkali metal salt or ammonium salt thereof. . Specifically, methyl vinyl sulfonate, methyl vinyl sulfonic acid, (meth)
Acrylic sulfonic acid, ethyl (meth) acrylic-2-sulfonate, 2-acrylamido-2-methylpropanesulfonic acid, (meth) acrylic acid-2-ethyl sulfate, 3-
Allyloxy-2-hydroxypropane sulfuric acid and the like.

The amount of the strong acid or acid salt containing sulfur introduced by the monomer having these --SO ₃ X groups or --OSO ₃ X groups should be adjusted to 0.1 to 2.0% by weight. Is desirable. In the above polymethacrylic acid ester resin, the amount of strong acid or strong acid salt containing sulfur is 0.1
If the amount is less than 10% by weight, the dispersibility becomes insufficient, and 2.0
If it exceeds 5% by weight, the solubility in a solvent becomes poor.

Further, the polymethacrylic acid ester resin can be synthesized by copolymerizing these monomers with an unsaturated monomer copolymerizable with these monomers, if necessary. Copolymerization with other unsaturated monomers is performed for the purpose of improving the compatibility with other resins that constitute the binder, adjusting the softening point, the characteristics of the coating film and the coating process. The unsaturated monomer for copolymerization is appropriately selected according to these purposes. Examples of such unsaturated monomers include vinyl acetate such as vinyl acetate, vinyl ether such as methyl vinyl ether, vinylidene such as vinylidene chloride, diethyl maleate, di-2-hydroxyethyl maleate and methyl acrylate. And the like, olefins such as ethylene and propylene, unsaturated nitriles such as (meth) acrylonitrile, and aromatic vinyl such as styrene and α-methylstyrene.

In the magnetic recording medium, any element other than the binder constituting the magnetic coating film, such as magnetic powder, may be any one as long as it is generally used in this type of magnetic recording medium. Is. Examples of such magnetic powder include γ-Fe ₂ O ₃ and cobalt-coated γ-Fe ₂ O ₃
Ferromagnetic iron oxide particles, ferromagnetic chromium dioxide particles, etc.
Examples thereof include ferromagnetic metal-based particles made of metals such as Fe, Co, and Ni, alloys containing these, and hexagonal plate-shaped hexagonal ferrite fine particles.

The magnetic coating film contains the magnetic powder,
In addition to the binder, a dispersant, an abrasive, an antistatic agent or the like may be added as an additive.

Further, as the non-magnetic support for forming the above-mentioned magnetic coating film, any conventionally known one can be used.
It is not limited in any way. For example, a polymer support typified by polyesters, polyolefins, cellulose derivatives, vinyl resins, polyimides, polyamides, polycarbonates, etc., and a metal plate glass base made of aluminum alloy, titanium alloy, etc. .
The shape is not particularly limited, and may be any shape such as a tape shape, a sheet shape, and a drum shape. Further, this non-magnetic support may be subjected to a surface treatment for forming fine irregularities in order to control the surface property.

Further, the magnetic recording medium may be provided with a top coat layer or a back coat layer made of a rust preventive or the like, if necessary.

[0035]

[Function] In the coating type magnetic recording medium using a mixture of polymethacrylic acid ester resin and polyurethane resin as a binder, the magnetic powder is uniformly dispersed in the magnetic coating film, and further the magnetic coating film has dispersibility and toughness. It has excellent properties, abrasion resistance, and coating strength, and exhibits good magnetic properties and running durability.

Further, since none of the resins constituting these binders have elements that cause harmful gases such as chlorine, they are suitable from the viewpoint of global environment protection. Here, the polyurethane group has a urethane group concentration of 2.5 mm.
When the amount of ol / g or more is used, the polyurethane resin has excellent compatibility especially with the polymethacrylic acid ester resin, so that the dispersibility of the magnetic coating film and the coating film durability are further improved.

[0037]

EXAMPLES Preferred examples of the present invention will be described based on experimental results.

Experimental Example 1 In this experimental example, the optimum mixing ratio of the binder composed of the polymethacrylic acid ester resin and the polyester polyurethane resin was examined.

First, a magnetic paint composition having the following composition was mixed to prepare a magnetic paint. Magnetic coating composition Fe metal powder 100 parts by weight Binder 20 parts by weight Alumina (average particle size 0.3 μm) 5 parts by weight Carbon (average particle size 0.15 μm) 5 parts by weight Stearic acid 1 part by weight Butyl stearate 1 part by weight Methyl ethyl ketone 100 parts by weight Toluene 100 parts by weight Cyclohexanone 100 parts by weight

In the above composition, the binder is a polymethacrylic acid ester resin [polymerization degree 400, methyl methacrylate 85% by weight, hydroxyl group 2.0% by weight, SO ₃ Na
0.16% by weight (functional group)] and polyester polyurethane resin [molecular weight 20000, urethane group concentration 2.5 mm
ol / g, Tg = 30 ° C., SO ₃ Na 0.05 mol%
(Functional group)], and the mixing ratio of these resins was changed as shown in Table 1.

[0041]

[Table 1]

The magnetic coating composition is mixed by kneading magnetic powder, carbon, alumina and polymethacrylic acid ester resin, polyester polyurethane resin with a kneader, and then adding other materials to the kneaded product. It was carried out by mixing with an attached stirrer and further forming a paint using a sand mill.

After adding 20 parts by weight of a hardener Coronate L (manufactured by Nippon Polyurethane Co.) to the prepared magnetic paint,
It was coated on a 14 μm polyethylene terephthalate film so that the thickness after drying was 4 μm. Next, the applied magnetic paint was subjected to magnetic field orientation, dried to form a magnetic coating film, and wound. Further, calendering was performed, and the tape was cut into 1/2 inch widths to prepare magnetic tapes (Sample Tape 1 to Sample Tape 5).

The residual magnetic flux density, the squareness ratio and the running durability of the magnetic tape manufactured in this manner were examined. Note that the residual magnetic flux density and squareness ratio are measured by the sample vibration type magnetometer (VS
M), running durability is 1/2 inch VTR (S
It was evaluated by measuring the output reduction after running 3000 times using an ONY company). The results are shown in Table 2.

[0045]

[Table 2]

As can be seen from Table 2, in the above magnetic tape, if the mixing ratio of the polymethacrylic acid ester in the binder is too large or too small, the running property becomes poor, and the optimum mixing ratio for the polymethacrylic acid ester is found. I know that there is. That is, it was found that the mixing ratio of the polymethacrylic acid ester is suitable to be 20 to 80% by weight in order to obtain good running durability.

Experimental Example 2 This experimental example is an example in which the urethane group concentration of the polyester polyurethane resin was examined in a binder composed of a polymethacrylic acid ester resin and a polyester polyurethane resin.

The mixing ratio of the polymethacrylic acid ester resin and the polyester polyurethane resin is 50% by weight, respectively.
Magnetic tapes (Sample Tape 6 to Sample Tape 11) were prepared in the same manner as in Experimental Example 1 except that the polyester polyurethane resin having the urethane group concentration shown in Table 3 was used.

[0049]

[Table 3]

Experimental Example 1 for Various Magnetic Tapes Produced
The residual magnetic flux density, squareness ratio and running durability were measured in the same manner as in. The results are shown in Table 4.

[0051]

[Table 4]

First, the urethane group concentration is 2.5 mmol /
In the magnetic tape (sample tape 8 to sample tape 11) using polyester polyurethane resin of g or more,
Magnetic powder is dispersed in magnetic paint with good dispersibility,
As can be seen from Table 4, both magnetic properties and running durability are excellent.

On the other hand, the urethane group concentration is 2.5 mm
In the magnetic tapes (sample tape 6 and sample tape 7) using a polyester polyurethane resin of less than ol / g, the polyester polyurethane has a urethane group concentration of 2.5 mmol / g or more, as compared with the case of using the polyester polyurethane resin. The compatibility between the resin and the polymethacrylic acid ester is poor, which results in insufficient magnetic properties and running durability.

From this, it was found that it is preferable to use a polyester polyurethane resin having a urethane group concentration of 2.5 mmol / g or more in the binder composed of the polymethacrylic acid ester resin and the polyester polyurethane resin.

Experimental Example 3 In this experimental example, the properties of a mixture of nitrocellulose and polyester polyurethane resin and a mixture of vinyl chloride copolymer and polyester polyurethane resin as a binder were determined from the above polymethacrylate ester resin and polyester polyurethane resin. It is the example compared with the mixture.

As a binder, a mixture of nitrocellulose 1/8 type and polyester polyurethane resin mixed at a ratio of 50:50 (wt%) or a polyvinyl chloride copolymer (manufactured by Nippon Zeon Co., Ltd., trade name MR11).
0) and a polyester polyurethane resin were mixed at a ratio of 50:50 (% by weight) to prepare a magnetic tape (Comparative Tape 1, Comparative Tape 2) in the same manner as in Experimental Example 1, Residual magnetic flux density, squareness ratio,
The running durability was examined.

Table 5 shows the binder used for each magnetic tape, the magnetic properties, and the measurement results of running durability.

[0058]

[Table 5]

First, when a mixture containing nitrocellulose is used as a binder, the magnetic powder does not disperse well in the binder, and the magnetic paint cannot be prepared. When a mixture containing a polyvinyl chloride copolymer is used as a binder, the magnetic tape prepared (although the magnetic paint can be adjusted) (comparative tape 2) contains a polymethacrylate ester resin as a binder. The magnetic properties and running durability are inferior to those of the magnetic tape using the mixture. Moreover, when burned, hydrogen chloride is produced from the polyvinyl chloride copolymer, which is inconvenient for environmental protection.

Therefore, from this, a mixture of nitrocellulose and polyester polyurethane resin,
A mixture consisting of a polyvinyl chloride copolymer and a polyester polyurethane resin does not meet the requirements required for a binder and is not suitable for use as a binder for magnetic tape for high density recording, for example. all right.

Experimental Example 4 In this experimental example, the optimum mixing ratio of the binder made of polymethacrylic acid ester resin and polycarbonate polyurethane resin was examined.

As a binder, a polymethacrylic acid ester resin [polymerization degree 400, methyl methacrylate 85% by weight,
Hydroxyl group 2.0 wt%, SO ₃ Na 0.16 wt% (functional group)] and polycarbonate polyurethane resin [molecular weight 2
0000, urethane group concentration 2.5 mmol / g, Tg =
30 ° C., SO ₃ Na 0.05 mol% (functional group)]
A magnetic tape (Sample Tape 12
-Sample tape 16) was produced.

[0063]

[Table 6]

The residual magnetic flux density, the squareness ratio and the running durability of the various magnetic tapes produced were measured in the same manner as in Experimental Example 1. The results are shown in Table 7.

[0065]

[Table 7]

As shown in Table 7, in the above magnetic tape, if the mixing ratio of the polymethacrylic acid ester in the binder is too large or too small, the running property becomes poor. I know that there is. That is, it was found that the mixing ratio of the polymethacrylic acid ester is suitable to be 20 to 80% by weight in order to obtain good running durability.

Experimental Example 5 This experimental example is an example in which the urethane group concentration of the polycarbonate polyurethane resin was examined in a binder composed of a polymethacrylic acid ester resin and a polycarbonate polyurethane resin.

Magnetic properties were the same as in Experimental Example 4 except that the mixing ratio of the polymethacrylic acid ester resin and the polycarbonate polyurethane resin was fixed at 50% by weight, and the polyurethane resin having the urethane group concentration shown in Table 8 was used. Tapes (Sample Tape 17 to Sample Tape 22) were produced.

[0069]

[Table 8]

The residual magnetic flux density, the squareness ratio and the running durability of the various magnetic tapes produced were measured in the same manner as in Experimental Example 1. The results are shown in Table 9.

[0071]

[Table 9]

First, the urethane group concentration is 2.5 mmol /
In the magnetic tapes (sample tape 19 to sample tape 22) using polyurethane resin of g or more, the magnetic powder is dispersed in the magnetic paint with good dispersibility, and as shown in Table 9, the magnetic properties and running durability are both It is also excellent in.

On the other hand, the urethane group concentration is 2.5 mm
In the magnetic tapes (sample tape 17 and sample tape 18) using a polyurethane resin of less than ol / g, compared with the case of using a polyurethane resin having a urethane group concentration of 2.5 mmol / g or more, the polyurethane resin and the poly The compatibility with methacrylic acid ester is poor, and this results in insufficient magnetic properties and running durability.

From this, it was found that it is preferable to use a polycarbonate polyurethane resin having a urethane group concentration of 2.5 mmol / g or more in the binder composed of the polymethacrylic acid ester resin and the polycarbonate polyurethane resin.

Experimental Example 6 In this experimental example, the properties of the mixture of nitrocellulose and polycarbonate polyurethane resin and the mixture of polyvinyl chloride copolymer and polycarbonate polyurethane resin as binders were evaluated as follows. It is the example compared with the mixture consisting of.

As the binder, nitrocellulose 1/8 type and polycarbonate polyurethane resin are 50:50.
(Wt%) or a mixture or polyvinyl chloride copolymer (manufactured by Zeon Corporation, trade name MR1)
10) and polycarbonate polyurethane resin 50: 5
Magnetic tapes (Comparative Tape 3 and Comparative Tape 4) were prepared in the same manner as in Experimental Example 4 except that the mixture prepared by mixing them in an amount of 0 (wt%) was used, and the residual magnetic flux density, squareness ratio and running durability were obtained. The sex was measured.

Table 10 shows the binder used for each magnetic tape, the magnetic properties, and the measurement results of running durability.

[0078]

[Table 10]

First, when a mixture containing nitrocellulose is used as the binder, the magnetic powder does not disperse well in the binder, and the magnetic paint cannot be prepared. When a mixture containing a polyvinyl chloride copolymer is used as a binder, the magnetic tape prepared (although the magnetic tape can be adjusted) (Comparative Tape 4) contains a polymethacrylic acid ester resin as a binder. The magnetic properties and running durability are inferior to those of the magnetic tape using the mixture. Moreover, when burned, hydrogen chloride is produced from the polyvinyl chloride copolymer, which is inconvenient for environmental protection.

Therefore, from this fact, the mixture of nitrocellulose and polycarbonate polyurethane resin and the mixture of polyvinyl chloride copolymer and polycarbonate polyurethane resin do not meet the requirements required for the binder, for example, high density. It has been found to be unsuitable for use as a binder in recording magnetic tape.

[0081]

As is clear from the above description, since the magnetic recording medium of the present invention uses the polymethacrylic acid ester resin and the polyurethane resin as the binder constituting the magnetic layer, the magnetic coating film has a dispersibility. Excellent in toughness, abrasion resistance and coating strength, and good magnetic properties and running durability can be obtained. Further, since none of the resins constituting these binders has an element that causes harmful gas such as chlorine, it is suitable from the viewpoint of global environment protection.

Therefore, according to the present invention, it is possible to obtain a magnetic recording medium which enables high density recording and is extremely highly practical.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view of essential parts showing a configuration example of a magnetic recording medium of the present invention.

[Explanation of symbols] 1 ... Non-magnetic substrate 2 ... Magnetic coating film

Claims (4)

[Claims] 1. A magnetic recording medium comprising a non-magnetic substrate and a magnetic coating film mainly composed of magnetic powder and a binder, wherein the binder contains a polymethacrylic acid ester resin and a polyurethane resin. A magnetic recording medium characterized by the above. 2. The magnetic recording medium according to claim 1, wherein the urethane group concentration of the polyurethane resin is 2.5 mmol / g or more. 3. The magnetic recording medium according to claim 1, wherein the polyurethane resin is a polyester polyurethane resin. 4. The magnetic recording medium according to claim 1, wherein the polyurethane resin is a polycarbonate polyurethane resin.