JP3334190B2 - Magnetic recording media - Google Patents

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 constituting 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 coating material obtained by kneading and dispersing a ferromagnetic powder, a binder, a dispersant, a lubricant, an abrasive and the like in an organic solvent is applied to a non-magnetic material such as a polyester film. A magnetic layer is formed by coating on a support.

[0003] In such a coating type magnetic recording medium, as a binder, vinyl chloride / vinyl acetate copolymer, vinyl chloride / vinyl acetate / vinyl alcohol copolymer, vinyl chloride / vinylidene chloride copolymer, polyether Polyurethane resin, polyester polyurethane resin, polycarbonate polyurethane resin, acrylonitrile-butadiene copolymer, nitrocellulose, epoxy resin, acrylic resin, etc. are used, among these resins,
A polyester polyurethane resin or a polycarbonate polyurethane resin having excellent dispersibility, toughness, and abrasion resistance;
Binders combining polyvinyl chloride or nitrocellulose, which imparts film strength to the magnetic paint formed, are generally used.

[0004]

In the case of magnetic recording media, the demand for high-density recording has made it possible to reduce the thickness and the size of magnetic powder, and as described above, nitrocellulose was used as a binder. In this case, sufficient dispersibility cannot be imparted, and when polyvinyl chloride is used, sufficient coating strength cannot be obtained. Furthermore, when polyvinyl chloride is used, toxic chlorine gas is emitted when the tape is exhausted and incinerated.

Therefore, a polyvinyl acetal resin has been proposed as a substitute for polyvinyl chloride. The polyvinyl acetal resin is a resin having extremely excellent coating film strength, dispersibility, and electromagnetic conversion characteristics, and is also a resin having an effect of improving the kneading property during kneading by adding the polyvinyl acetal resin. Further, since chlorine gas is not generated at the time of tape incineration, it is also preferable in terms of suppressing environmental pollution. In addition, since the polyvinyl acetal resin has a relatively high glass transition point and is hard and brittle under the use environment of the magnetic recording medium, it is preferable to use the polyvinyl acetal resin in combination with another resin. When combined as a substitute for polyester polyurethane resin or polycarbonate polyurethane resin and polyvinyl chloride as described above, the compatibility is not very good, and the magnetic layer cannot be provided with sufficient dispersibility and durability, and A magnetic recording medium having excellent magnetic characteristics and running durability cannot be obtained.

Accordingly, the present invention has been proposed in view of the conventional circumstances, and has improved the compatibility between a polyester polyurethane resin or a polycarbonate polyurethane resin and a polyvinyl acetal resin to provide a magnetic layer having excellent dispersibility and durability. It is an object of the present invention to provide a magnetic recording medium having excellent magnetic properties and running durability.

[0007]

In order to achieve the above object, the present invention provides a magnetic recording medium using a polyester polyurethane resin and a polyvinyl acetal resin as a binder constituting a magnetic layer formed on a nonmagnetic support. In the above, the urethane group concentration of the polyester polyurethane resin is 2.5 mmol / g to 4.0 mmol / g,
Further, the ratio of the polyester polyurethane resin in the binder is 20 to 80% by weight, and the ratio of the polyvinyl acetal resin is 80 to 20% by weight.

In order to achieve the above-mentioned object, the present invention provides a magnetic recording medium using a polycarbonate polyurethane resin and a polyvinyl acetal resin as a binder constituting a magnetic layer formed on a non-magnetic support.
The urethane group concentration of the polycarbonate polyurethane resin is 2.5 mmol / g to 4.0 mmol / g,
Further, the proportion of the polycarbonate polyurethane resin in the binder is 20 to 80% by weight, and the proportion of the polyvinyl acetal resin is 80 to 20% by weight.

As shown in FIG. 1, the magnetic recording medium according to the present invention comprises a nonmagnetic support 1, a magnetic powder formed thereon, and a magnetic layer 2 mainly composed of a binder.

The magnetic layer is formed, for example, by dispersing a magnetic powder in a binder and, depending on the type of the binder, from ethers, esters, ketones, aromatic hydrocarbons, aliphatic hydrocarbons, chlorinated hydrocarbons and the like. It can be formed by applying a magnetic paint prepared by kneading with a selected organic solvent on a non-magnetic support.

The magnetic powder forming the magnetic coating of the magnetic layer is as follows:
In general, any material can be used as long as it is used as a magnetic powder of this type of magnetic recording medium. Such magnetic powder, _γ-Fe 2 _{O 3,} cobalt coating _γ-Fe 2 _{O 3}
Ferromagnetic iron oxide particles, ferromagnetic chromium dioxide particles, etc.
Examples thereof include ferromagnetic metal-based particles made of a metal such as Fe, Co, and Ni and alloys containing these, hexagonal plate-like hexagonal ferrite fine particles, and the like. In addition, a dispersant, an abrasive, an antistatic agent and the like may be added to the magnetic paint as additives in addition to the magnetic powder and the binder.

The binder forming the magnetic coating material is composed of a polyester polyurethane resin or a polycarbonate polyurethane resin and a polyvinyl acetal resin as shown in Chemical formula 1, and the ratio of the polyester polyurethane resin or the polycarbonate polyurethane resin in the binder is determined. It is preferable that the content of the polyvinyl acetal resin is 80 to 20% by weight and the content of the polyvinyl acetal resin is 20 to 80% by weight. If the compounding ratio of the polyvinyl acetal resin is less than 20% by weight, the magnetic paint is too soft, and there is a high possibility that the obtained magnetic recording medium will stick to the magnetic head during running.
If it exceeds 80% by weight, the magnetic paint becomes hard and brittle, and the durability of the obtained magnetic recording medium may be insufficient.

[0013]

Embedded image

The polyester polyurethane resin is a resin obtained by urethanizing a polyester polyol and a polyisocyanate, and the polycarbonate polyurethane resin is a resin obtained by urethanizing a polycarbonate polyol and a polyisocyanate. 0.5 mmol / g or more;
It is preferably from 5 to 7.0 mmol / g. If the urethane group concentration is less than 2.5 mmol / g, the compatibility with the polyvinyl acetal resin is not sufficient, and the
If the amount is more than ol / g, aggregation of urethane groups occurs, dispersibility of the magnetic powder or the like in the polyester polyurethane resin or the polycarbonate polyurethane resin is reduced, and its production is extremely difficult.

The polyester polyol forming the polyester polyurethane resin is, as a polyhydric alcohol, ethylene glycol, propylene glycol, 1,4-butanediol, 1,3-butanediol, 1,5-pentanediol, 1,6-hexane. Diol or neopentyl glycol can be used, as a polycarboxylic acid,
Terephthalic acid, isophthalic acid, 1,5-naphthalic acid, adipic acid, succinic acid, azelaic acid and the like can be used. The polycarbonate polyol forming the polycarbonate polyurethane resin is obtained by condensation of a conventionally known polyhydric alcohol with diallyl carbonate or dialkyl carbonate. In addition, as polyisocyanate, tolylene diisocyanate (TDI),
4-4'-diphenylmethane diisocyanate (MD
I), hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI) and the like.

In producing a polyester polyurethane resin from a polyester polyol and a polyisocyanate, or producing a polycarbonate polyurethane resin from a polycarbonate polyol and a 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 and an aromatic polyamine. Further, such a polyester polyurethane resin or a polycarbonate polyurethane resin may have a known proportion of a known polar group such as a sulfonate metal base in an appropriate ratio in order to improve the adsorption of the resin to the magnetic powder and the dispersibility of the magnetic powder. Can be introduced.

On the other hand, as the polyvinyl acetal resin represented by the above chemical formula 1, the degree of polymerization of the polyvinyl acetal resin represented by the chemical formula 1 is 200 to 600, and the constituent ratio (mol%) of each monomer component k, l, m and p are k + l +
m + p = 100, 65 ≦ k ≦ 85, 1 ≦ l ≦ 20, 5 ≦
It is preferable that m ≦ 30 and 0.1 ≦ p ≦ 2. That is, when the composition ratio k of the first monomer component is less than 65, the hardness is insufficient, and sufficient durability cannot be imparted to the magnetic layer. And is not actually available. The composition ratio 1 of the second monomer component affects compatibility with other resins, durability, and softening property, and the above range is preferable in order to improve these characteristics. Further, the composition ratio m of the third monomer component is preferably in the above range from the viewpoint of compatibility with other resins, water resistance, and reactivity with isocyanate.
Note that the composition ratio p of the fourth monomer component is preferably in the above range from the viewpoint of dispersibility of the magnetic powder and the like.

Further, R constituting the first monomer component in Chemical formula ₁ is Cn H _{2n + 1} (n = 0, 1, 2, 3, 3)
4,5,6), and the fourth compound in Chemical formula 1
X constituting the monomer component of -SO ₃ Na,
_{-SO 3 K, -SO 3 H,} -OSO 3 Na, -OSO 3
K, -COOH, -OPO (OH) ₂ , -OPO (OL
i) ₂ , -OPO (ONa) ₂ , -OPO (OK) ₂ ,
-PO (OH) ₂ , -PO (OLi) ₂ , -PO (ON
a) ₂ , —PO (OK) _{2 and the} like.

The polyvinyl acetal resin can be synthesized by saponifying polyvinyl acetate into polyvinyl alcohol, and reacting the polyvinyl alcohol with an aldehyde.

As the non-magnetic support of the magnetic recording medium, any one which is usually used as a non-magnetic support of this type of magnetic recording medium can be used. For example, polyesters, polyolefins, cellulose derivatives,
Examples include a polymer support represented by a vinyl resin, polyimides, polyamides, and polycarbonate, a metal plate glass substrate made of an aluminum alloy, a titanium alloy, and the like. The form is not limited at all, and may be any form such as a tape form, a sheet form, and a drum form. Further, the nonmagnetic support may be subjected to a surface treatment for forming fine irregularities in order to control the surface property.

As the magnetic recording medium according to the present invention, in addition to the magnetic recording medium having a magnetic layer formed on the above-described non-magnetic support, one surface of a non-magnetic support 11 as shown in FIG. A magnetic layer 12 is formed on the other side, and a non-magnetic powder made of, for example, carbon black and a back coat layer 13 mainly composed of a binder are formed on the other surface, or a non-magnetic support 21 as shown in FIG. Examples include magnetic layers 22 and 33 formed on both surfaces. Further, the magnetic recording medium of the present invention may be provided with a top coat layer (not shown) made of a rust preventive or the like.

[0022]

According to the present invention, in a magnetic recording medium using a polyester polyurethane resin or a polycarbonate polyurethane resin as a binder constituting a magnetic layer and a polyvinyl acetal resin, the urethane group concentration of the polyester polyurethane resin or the polycarbonate polyurethane resin is 2.5 mmol. / G to 4.0 mmol / g, the compatibility between the polyester polyurethane resin or the polycarbonate polyurethane resin and the polyvinyl acetal resin is good, and a magnetic layer having good dispersibility and durability is formed.

In the magnetic recording medium of the present invention,
20-80% by weight of the polyester polyurethane resin or the polycarbonate polyurethane resin in the binder,
It is desirable that the ratio of the polyvinyl acetal resin is 80 to 20% by weight, and a magnetic layer having an appropriate hardness is formed.

[0024]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, specific embodiments to which the present invention is applied will be described.

Example 1 In this example, the magnetic properties of a magnetic recording medium using a polyester polyurethane resin and a polyvinyl acetal resin as binders were investigated.

First, a magnetic paint was prepared at the following compounding ratio. To prepare the magnetic paint, magnetic powder, carbon, alumina, and a polyester polyurethane resin and a polyvinyl acetal resin are kneaded in a kneader, and then the other materials are added and mixed with a disperser and a mixture is formed using a sand mill. I went.

<Magnetic paint compounding ratio> Fe metal powder (Fe-Co alloy specific surface area: 50 m ² / g) 100 parts by weight Polyester polyurethane resin 10 parts by weight (molecular weight: 20,000 Urethane group concentration: 1.5 to 4. 0 mmol / g Tg = 30 ° C. SO ₃ Na 0.05 mol% as a functional group) Polyvinyl acetal resin 10 parts by weight (polymerization degree 300, acetalization degree 72 mol%, hydroxyl group 20 mol%, functional group SO ₃ Na 0.1 Mol%) 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

At this time, the magnetic paint having a urethane group concentration of the polyester polyurethane resin of 2.5 mmol / g was used as the sample 1, and the magnetic paint having 3.0 mmol / g was used as the sample 2, and the magnetic paint having a urethane group concentration of 3.5 mmol / g was used as the sample 2. The coating material was Sample 3, the magnetic coating having 4.0 mmol / g was designated as Sample 4, and the magnetic coating having a urethane group concentration of the polyester polyurethane resin of 1.5 mmol / g was compared with Sample 1, 2.0 mmol for comparison. / G of the magnetic paint was used as Comparative Sample 2. The urethane group concentration was calculated from the amount charged during the production of the polyester polyurethane resin.

After adding 20 parts by weight of a curing agent Coronate L (manufactured by Nippon Polyurethane Co., Ltd.) to the magnetic paint prepared as described above, the magnetic layer after drying was dried to a thickness of 4 μm on a 14 μm-thick polyethylene terephthalate film. Coating was performed so as to obtain a magnetic field orientation, followed by drying and winding. This was subjected to a calendering process, cut into 1/2 inch widths, and the sample tapes 1 to 4 and the comparative sample tapes 1 and 2 were cut.
I got

Next, the proportion of the polyester polyurethane resin in the binder in the magnetic paint was 80% by weight, the proportion of the polyvinyl acetal resin was 20% by weight, the proportion of the polyester polyurethane resin was 20% by weight, and the proportion of the polyvinyl acetal resin was The magnetic paint was prepared by changing the concentration to 80% by weight and setting the urethane group concentration to 2.5 mmol / g in the same manner as above, and using this to prepare the sample tape as described above, using the former magnetic paint. Was used as an execution sample tape 5, and the one using the latter magnetic paint was used as an execution sample tape 6.

For comparison, the ratio of the polyester polyurethane resin in the binder in the magnetic paint was 95% by weight,
The ratio of the polyvinyl acetal resin was changed to 5% by weight, the ratio of the polyester polyurethane resin was changed to 5% by weight, and the ratio of the polyvinyl acetal resin was changed to 95% by weight. The sample tape was manufactured as described above, and a sample tape using the former magnetic paint was used as a comparative sample tape 3, and a sample tape using the latter magnetic paint was used as a comparative sample tape 4.

Further, instead of the polyvinyl acetal resin used as a binder in the magnetic paint, a magnetic paint obtained by changing to nitrocellulose 1/8 type or a polyvinyl chloride copolymer (trade name: MR110, manufactured by Zeon Corporation) is used. A sample tape was prepared as described above using this, and a comparative sample tape 6 using the latter magnetic paint was prepared. The former magnetic paint had a very high viscosity and could not be applied on a non-magnetic support.

The magnetic tape and running durability of the thus prepared working sample tapes 1 to 6 and comparative sample tapes 1 to 6 were evaluated. The magnetic properties were evaluated by measuring the residual magnetic flux density and the squareness ratio with a VSM, and the running durability was 30% with a 1/2 inch VTR (manufactured by Sony Corporation).
The reduction in the reproduction output after running 00 times was measured and evaluated.
Table 1 shows the results.

[0034]

[Table 1]

From the results shown in Table 1, the urethane group concentration was 2.
Example sample tape 1 using a polyester polyurethane resin in the range of 5 mmol / g to 4.0 mmol / g, wherein the ratio of the polyester polyurethane resin in the binder used is 10% by weight and the ratio of the polyvinyl acetal resin is 10% by weight. 4, a sample tape 5 in which the proportion of the polyester polyurethane resin in the binder is 80% by weight and the proportion of the polyvinyl acetal resin is 20% by weight;
The ratio of the polyester polyurethane resin in the binder is 20
80% by weight of polyvinyl acetal resin
In the sample tape 6, the magnetic properties and the running durability were both good. This is probably because the compatibility between the polyester polyurethane resin and the polyvinyl acetal resin is good, the magnetic powder is well dispersed in the magnetic layer, and the magnetic layer has an appropriate hardness.

On the other hand, when the urethane group concentration is 2.5 mmol /
Using a polyester polyurethane resin smaller than g
The proportion of the polyester polyurethane resin in the binder used is 10% by weight, and the proportion of the polyvinyl acetal resin is 10% by weight.
In Comparative Sample Tapes 1 and 2 which are weight%, both the magnetic properties and running durability are insufficient. The urethane group concentration in the polyester polyurethane resin is low, and the compatibility between the polyester polyurethane resin and the polyvinyl acetal resin is good. This is probably because the dispersibility of the magnetic powder is not good.

From this, the urethane group concentration was 2.5 m
The magnetic paint using a polyester polyurethane resin and a polyvinyl acetal resin in the range of mol / g to 4.0 mmol / g as a binder has a good compatibility between the polyester polyurethane resin and the polyvinyl acetal resin, so that the magnetic powder binder It was confirmed that the magnetic recording medium in which the magnetic layer was formed with the magnetic paint had good magnetic properties and running durability, as well as good dispersibility in the magnetic paint.

When the urethane group concentration is 2.5 mmol
/ G to 4.0 mmol / g, a comparative sample tape 3 in which the proportion of the polyester polyurethane resin in the binder used is 95% by weight and the proportion of the polyvinyl acetal resin is 5% by weight, In Comparative Sample Tape 4 in which the ratio of the polyester polyurethane resin in the binder was 5% by weight and the ratio of the polyvinyl acetal resin was 95% by weight, both the magnetic properties and running durability were insufficient, and the polyester polyurethane resin and the polyvinyl acetal were insufficient. In the case of using a resin as a binder, it was confirmed that the composition ratio affected the characteristics. Therefore, when the ratio of the polyester polyurethane resin is 20 to 80% by weight and the ratio of the polyvinyl acetal resin is 80 to 20% by weight, a magnetic layer having an appropriate hardness can be formed, and the running durability is good. It is possible to form a simple magnetic recording medium.

On the other hand, the comparative sample tape 5 using a magnetic paint in which the polyvinyl acetal resin in the binder is changed to nitrocellulose has a high viscosity as described above, making it difficult to prepare a magnetic paint. It was not possible to apply it on the body. Further, in the comparative sample tape 6 using the magnetic paint in which the polyvinyl acetal resin in the binder was changed to a polyvinyl chloride copolymer, the magnetic properties and running durability were insufficient, and the kneading of the magnetic paint was difficult. It is not preferable from the viewpoint of environmental conservation because chlorine gas is generated.

Example 2 In this example, the magnetic properties of a magnetic recording medium using a polycarbonate polyurethane resin and a polyvinyl acetal resin as binders were investigated. First, in the same manner as in Example 1, a magnetic paint was prepared using a kneader and a sand mill at the following compounding ratio.

<Magnetic paint compounding ratio> Fe metal powder (Fe-Co alloy specific surface area: 50 m ² / g) 100 parts by weight Polycarbonate polyurethane resin 10 parts by weight (molecular weight: 20,000 Urethane group concentration: 1.5 to 4. 0 mmol / g Tg = 30 ° C. SO ₃ Na 0.05 mol% as a functional group) Polyvinyl acetal resin 10 parts by weight (polymerization degree 300, acetalization degree 72 mol%, hydroxyl group 20 mol%, functional group SO ₃ Na 0.1 Mol%) 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

At this time, the magnetic paint having a urethane group concentration of the polycarbonate polyurethane resin of 2.5 mmol / g was applied to the sample 7, and the magnetic paint of 3.0 mmol / g was applied to the sample 8, and the magnetic paint having a urethane group concentration of 3.5 mmol / g was used. The coating composition was Sample 9, a magnetic coating composition having 4.0 mmol / g was designated as Sample 10, and the urethane group concentration of the polycarbonate polyurethane resin was 1.5 mm for comparison.
ol / g of the magnetic paint was compared with Comparative Sample 7, 2.0 mm
ol / g of the magnetic paint was used as Comparative Sample 8. The urethane group concentration was calculated from the amount charged during the production of the polycarbonate polyurethane resin.

Using the magnetic paint working samples 7 to 10 and comparative samples 7 and 8 produced as described above, Example 1 was used.
Sample tapes were prepared in the same manner as described above to obtain working sample tapes 7 to 10 and comparative sample tapes 7 and 8.

Next, the proportion of the polycarbonate polyurethane resin in the binder in the magnetic paint was 80% by weight, the proportion of the polyvinyl acetal resin was 20% by weight, the proportion of the polycarbonate polyurethane resin was 20% by weight, and the proportion of the polyvinyl acetal resin was A magnetic paint was prepared in the same manner as in Example 1 except that the weight was changed to 80% by weight, and a sample tape was prepared using the magnetic paint as in Example 1. The sample tape using the former magnetic paint was used as the sample tape 11 and the latter. The sample tape 12 using the magnetic paint of Example 1 was used.

For comparison, the ratio of the polycarbonate polyurethane resin in the binder in the magnetic paint was 95% by weight, the ratio of the polyvinyl acetal resin was 5% by weight, the ratio of the polycarbonate polyurethane resin was 5% by weight, and the ratio of the polyvinyl acetal resin was 5%. Was changed to 95% by weight, and a magnetic paint was produced in the same manner as in Example 1. Using this, a sample tape was produced as in Example 1, and a tape using the former magnetic paint was used as a comparative sample tape. 9. A comparative sample tape 10 using the latter magnetic paint.

Further, instead of the polyvinyl acetal resin used as a binder in the magnetic paint, a magnetic paint obtained by changing to nitrocellulose 1/8 type or a polyvinyl chloride copolymer (trade name: MR110, manufactured by Zeon Corporation) is used. The sample tape was manufactured and used as in Example 1, and the comparative sample tape 12 using the latter magnetic paint was prepared. The former magnetic paint has a very high viscosity and cannot be applied on a non-magnetic support.
For convenience, the comparative sample tape 11 is used.

The magnetic tapes and running durability of the thus prepared working sample tapes 7 to 12 and comparative sample tapes 7 to 12 were evaluated in the same manner as in Example 1.
Table 2 shows the results.

[0048]

[Table 2]

From the results shown in Table 2, the urethane group concentration was 2.5 m
mol / g to 4.0 mmol / g, a sample polyurethane tape having a polycarbonate polyurethane resin content of 90% by weight and a polyvinyl acetal resin content of 10% by weight in a binder used. 10, a sample tape 11 in which the ratio of the polycarbonate polyurethane resin in the binder is 80% by weight and the ratio of the polyvinyl acetal resin is 20% by weight, the ratio of the polycarbonate polyurethane resin in the binder is 20% by weight, and the polyvinyl acetal resin Was 80% by weight, the magnetic properties and running durability were both good. This is presumably because the compatibility between the polycarbonate polyurethane resin and the polyvinyl acetal resin is good, the magnetic powder is well dispersed in the magnetic layer, and the magnetic layer has an appropriate hardness.

On the other hand, when the urethane group concentration is 2.5 mmol /
g of comparative sample tapes 7 and 8 in which the proportion of the polycarbonate polyurethane resin in the binder used is 90% by weight and the proportion of the polyvinyl acetal resin is 10% by weight. It is considered that this is because the urethane group concentration in the polycarbonate polyurethane resin is low, the compatibility between the polycarbonate polyurethane resin and the polyvinyl acetal resin is not good, and the dispersibility of the magnetic powder is not good.

Therefore, from this fact, the magnetic paint using a polycarbonate polyurethane resin and a polyvinyl acetal resin having a urethane group concentration in the range of 2.5 mmol / g to 4.0 mmol / g as a binder is a polycarbonate polyurethane resin and a polyvinyl acetal resin. Has good compatibility with magnetic powder and good dispersibility of the magnetic powder in the binder. It has been confirmed that the magnetic recording medium having the magnetic layer formed with the magnetic paint has good magnetic properties and running durability. Was done.

When the urethane group concentration is 2.5 mmol /
g of a polycarbonate polyurethane resin having a ratio of at least 95% by weight in the binder used and a comparative sample tape 9 in which the ratio of the polyvinyl acetal resin is 5% by weight. 5% by weight,
In the comparative sample tape 10 in which the ratio of the polyvinyl acetal resin was 95% by weight, both the magnetic properties and the running durability were insufficient, and when the polycarbonate polyurethane resin and the polyvinyl acetal resin were used as the binder, their composition ratios Was found to affect the characteristics. Therefore, when the proportion of the polycarbonate polyurethane resin is 20 to 80% by weight and the proportion of the polyvinyl acetal resin is 80 to 20% by weight, a magnetic layer having an appropriate hardness can be formed, and the running durability is good. It is possible to form a simple magnetic recording medium.

[0053]

As described above, according to the present invention, in a magnetic recording medium using a polyester polyurethane resin or a polycarbonate polyurethane resin as a binder and a polyvinyl acetal resin, the urethane group concentration of the polyester polyurethane resin or the polycarbonate polyurethane resin is set to 2. The range is from 5 mmol / g to 4.0 mmol / g, and the ratio of the polyester polyurethane resin or the polycarbonate polyurethane resin in the binder is 20 to
80% by weight, the proportion of polyvinyl acetal resin is 80 to
Since the content is 20% by weight, the compatibility between the polyester polyurethane resin or the polycarbonate polyurethane resin and the polyvinyl acetal resin is good, and the magnetic layer having good dispersibility and durability and having appropriate hardness is formed. Thus, a magnetic recording medium having good magnetic properties and running durability can be obtained.

[0054]

[Brief description of the drawings]

FIG. 1 is a sectional view showing an example of a magnetic recording medium according to the present invention.

FIG. 2 is a sectional view showing another example of the magnetic recording medium according to the present invention.

FIG. 3 is a sectional view showing still another example of the magnetic recording medium according to the present invention.

[Explanation of symbols]

1,11,21 non-magnetic support, 2,12,22,3
3 Magnetic layer

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-54-126511 (JP, A) JP-A-57-138040 (JP, A) JP-A-2-310822 (JP, A) JP-A-62 62422 (JP, A) JP-A-4-139618 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G11B 5/70-5/718

Claims (2)

(57) [Claims] 1. A magnetic recording medium using a polyester polyurethane resin and a polyvinyl acetal resin as a binder constituting a magnetic layer formed on a nonmagnetic support, wherein the polyester polyurethane resin has a urethane group concentration of 2.5 mmol / g. ~ 4.0 mmol / g , and of the polyester polyurethane resin in the binder.
20-80% by weight, polyvinyl acetal
A magnetic recording medium , wherein the proportion of the resin is 80 to 20% by weight . 2. A magnetic layer formed on a nonmagnetic support.
Polycarbonate polyurethane resin as binder to form
And magnetic recording media using polyvinyl acetal resin
Stomach, of the polycarbonate polyurethane resin urethane Motoko
Degree is 2.5 mmol / g to 4.0 mmol / g, and the polycarbonate polyurethane resin in the binder is
Fat is 20-80% by weight, polyvinyl aceta
Characterized in that the ratio of the resin is 80 to 20% by weight.
Magnetic recording medium.