JPH1027331A - Magnetic recording medium and method of manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic recording medium for high-density recording which has improved compatibility between an acrylic copolymer resin and a polyester polyurethane resin, and has excellent dispersibility and durability. SOLUTION: A binder provided to a magnetic recording medium is obtained by adding a monoisocyanate compound to an acrylic copolymer having a hydroxyl group and a urethane bond of 0.2 mmol / g or more and 1 mmol or more.
/ G or less and a polyurethane resin. In the production method, a binder obtained by modifying a resin in which a urethane group amount is changed from 0.2 mmol / g to 1 mmol / g to an acrylic copolymer having a hydroxyl group, a binder having a polyurethane resin, and a magnetic powder are kneaded. And forming a magnetic layer by applying the magnetic paint to a non-magnetic support. [Effect] Since the magnetic powder in the magnetic layer can be uniformly dispersed, a magnetic recording medium which can cope with high-density recording and has excellent durability can be provided.

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 and a method for manufacturing the same, and more particularly, to a magnetic recording medium in which a magnetic layer mainly composed of a magnetic powder and a binder is formed on a non-magnetic support, and a method for manufacturing the same. About the method.

[0002]

2. Description of the Related Art In recent years, in the field of magnetic recording, video equipment has been improved in image quality or conversion from analog recording to digital recording has been attempted, and magnetic recording / reproducing apparatuses have been moving toward shorter wavelength recording. Therefore, the magnetic recording medium has both the smoothness of the surface to reduce the spacing loss, the high filling property of the magnetic powder for improving the electromagnetic conversion characteristics, and the high durability that can withstand long-time and multiple use. Is required. The use of finer magnetic powder in response to the demand for smoothing the surface of the magnetic recording medium and the high filling property of the magnetic powder improves the smoothing of the surface and the high filling property of the magnetic powder. As the surface area increases, the surface energy also increases, and the dispersibility of the magnetic powder deteriorates. When the dispersibility deteriorates, the filling property also deteriorates. Therefore, many voids are formed in the magnetic layer formed on a non-magnetic support such as a polyester film, and the number of voids is determined by the voids required by the supplied lubricant. It may be more than the number. When extra voids are formed, the magnetic coating film becomes very brittle.For example, when a magnetic tape, which is an example of a magnetic recording medium, slides on a recording / reproducing head or the like, magnetic powder, additives, binders, etc. There is a possibility that the recording / reproducing characteristics such as dropout and dropout may be deteriorated.

[0003] As means for improving the above-mentioned dispersibility and improving the detachment of the magnetic powder and the like from the magnetic layer, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acetic acid are used as a binder. Vinyl-propionic acid copolymer, vinyl chloride-vinyl acetate-vinyl alcohol copolymer, vinyl chloride-vinyl acetate-maleic acid copolymer,
Is proposed an acrylic copolymer, further -SO ₃ M Binders which _{such, -OSO 3 M, -OH, -COOH} , -
_{PO 3 M 2, -OPO 3 M} 2, -N <, - CON <( where, M is a hydrogen atom or an alkali metal) By Awasemota one or more hydrophilic functional groups such as, the magnetic powder It has been proposed to have an effect on dispersibility.

[0004] However, even with the use of such a binder, it is a fact that a sufficiently satisfactory dispersibility has not been obtained with a finer magnetic powder. For this reason, a step of kneading the magnetic powder, the binder and various additives with a high shearing force, a step of diluting and dispersing the kneaded mixture for a long time, and a dispersion having a large frictional force such as a bead mill. A step of dispersing by a machine is required, and these steps require many steps involving heat generation. Further, the vinyl chloride-based copolymer generates chlorine gas upon heating, and is not only corrosive to the magnetic powder but also poses a problem from the viewpoint of environmental protection. As a binder to improve such problems,
Acrylic copolymer resins such as (meth) acrylate copolymers and (meth) acrylate-acrylonitrile copolymers have been proposed, which have dispersibility,
It is also excellent in solvent resistance and environmental protection. However, because the glass transition temperature is relatively high,
A magnetic layer formed on a non-magnetic support such as a polyester film is hard and brittle, and has a problem in durability as a magnetic recording medium.

Therefore, a combination with a polyester polyurethane resin which is excellent in both adhesiveness and dispersibility with a (meth) acrylic acid ester resin or the like is attracting attention. However, when this (meth) acrylic acid ester resin or the like is used in combination with another resin, the compatibility, dispersibility, powder dropout and adhesiveness with a polyester polyurethane resin having a polar portion such as a urethane group are obtained. It was not good, and there was a problem in durability as a magnetic recording medium. Accordingly, there is a strong need for a technique for improving the compatibility, dispersibility, powder falling, adhesiveness, and the like of a (meth) acrylate resin resin or the like and a polyester polyurethane resin having a polar portion such as a urethane group.

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to improve the compatibility and dispersibility of an acrylic copolymer resin and a polyester polyurethane resin, etc., and to provide a magnetic recording medium having excellent durability and high density recording. An object of the present invention is to provide a recording medium and a manufacturing method thereof.

[0007]

Means for Solving the Problems In order to solve the above-mentioned problems, in a magnetic recording medium in which a magnetic layer mainly composed of a magnetic powder and a binder is formed on a non-magnetic support according to the present invention, the binder is used. A monoisocyanate compound is added to a hydroxyl group-containing acrylic copolymer by adding a urethane group in an amount of 0.2 mmol / g to 1 mmol / g, preferably 0.2 mmol / g.
It is characterized by having a modified resin of at least 0.8 mmol / g and a polyurethane resin.

In the method for producing a magnetic recording medium of the present invention, a monocyanate compound is added to an acrylic copolymer having a hydroxyl group so that a urethane group content is 0.2 mmol / g or more and 1 m
a step of kneading a magnetic powder with a binder having a modified resin and a polyurethane-based resin modified with a modified resin of not more than 0.2 mol / g, preferably 0.2 mmol / g or more and 0.8 mmol / g or less; On a non-magnetic support,
Forming a magnetic layer.

In a preferred embodiment of the magnetic recording medium and the method for producing the same, an acrylic copolymer is used in an amount of 20 to 80 parts by weight based on 100 parts by weight of a binder.
It should be less than parts by weight.

The effects of the above-mentioned means are to improve the compatibility, dispersibility, powder falling and adhesion between (meth) acrylic acid ester resin and the like and polyester polyurethane resin having a polar part such as urethane group. That is.

[0011]

The polyester polyurethane resin used in the present invention is obtained by the addition reaction of a polyester polyol obtained by a dehydration reaction of a polycarboxylic acid and a polyhydric alcohol with a (poly) isocyanate compound having at least two isocyanates. Resin. Polyester polyols can be used as polyhydric alcohols, such as ethylene glycol, propylene glycol, 1,4-butanediol, 1,3-butanediol, 1,5-pentanediol, 1,6-hexanediol, neopentyl glycol, and the like, As the polycarboxylic acid, terephthalic acid, isophthalic acid, 1,5-naphthalic acid, adipic acid, succinic acid, azelaic acid and the like can be used. Polyisocyanate is tolylene diisocyanate, 4, 4 '
-Diphenylmethane diisocyanate, hexamethylene diisocyanate or isophorone diisocyanate can be used. In producing a polyester polyurethane resin from a polyester polyol and a polyisocyanate, it is preferable to use an appropriate amount of a known chain extender such as the above-mentioned polyhydric alcohols, aliphatic polyamines, alicyclic polyamines, and aromatic polyamines. As a method for producing a polyester polyurethane resin, a method in which a polyester polyol and a (poly) isocyanate compound and / or a polycarboxylic acid or a polyhydric alcohol, or a compound containing a polyvalent amino group are reacted in a solution, There is a method in which a reaction is carried out by stirring while controlling the temperature with a kneader, and then dehydration is performed to obtain a semi-solid or solid resin, but any of them can be used without any problem.
The polyester polyurethane resin thus obtained contains -SO ₃ M, -OSO for the purpose of improving the adsorbability between the magnetic powder and the resin and improving the dispersibility of the magnetic powder.
_{3 M, -OH, -COOH, -PO} 3 M 2, -OPO 3
A compound having at least one hydrophilic functional group such as M ₂ , -N <, -CON <(where M is a hydrogen atom or an alkali metal) is selected, and the above-mentioned known polar group is added at an appropriate ratio. Can be included. Generally, the average molecular weight is from 5,000 g / mol to 100,000 g / mol, preferably from 10,000 g / mol to 600 g / mol.
The amount is from 10 to 90 parts by weight, preferably from 20 to 80 parts by weight, based on 100 parts by weight of the total binder resin contained in the magnetic layer. .

The resin obtained by modifying a hydroxyl group acrylic copolymer with a monoisocyanate compound is mainly composed of an acrylic monomer and an acrylic monomer having a hydroxyl group, and / or a radical polymerizable monomer and a hydroxyl group. Is a resin in which a monoisocyanate compound is modified on an acrylic copolymer obtained by copolymerizing a radical polymerizable monomer having the following formula: Acrylic monomers include methyl (meth) acrylate, ethyl (meth) acrylate, and propyl (meth)
Acrylic (meth) acrylates such as acrylate, butyl (meth) acrylate, isobutyl (meth) acrylate, octyl (meth) acrylate, stearyl (meth) acrylate, and 2-ethyl (meth) acrylate; methoxyethyl (meth) acrylate; Alkoxyalkyl (meth) acrylates such as butoxyethyl (meth) acrylate, polyethylene glycol mono (meth) acrylate, polypropylene glycol mono (meth) acrylate, polyethylene glycol polypropylene glycol mono (meth) acrylate, polyethylene glycol polytetramethylene glycol mono ( Polyoxyalkylene glycol mono (meth) acrylates such as meth) acrylate, cyclohexyl (meth)
Acrylate, (meth) acrylamide, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, (meth) acrylic acid, glycidyl (meth) acrylate, hydroxypropyltrimethylammonium methacrylate, glycerol mono (meth) There are acrylate, 2-sulfoethyl (meth) acrylate, dimethylaminoethyl (meth) acrylate, diethylaminoethyl (meth) acrylate and the like. The acrylic monomer may be at least one kind, and is a radical monomer having a hydroxyl group. Even if it does not contain a body, no problem arises if the acrylic monomer having a hydroxyl group of the present invention is used in combination. As the radical monomer other than the acrylic monomer described above,
There are styrene, α-methylstyrene, acrylonitrile, vinyl acetate, vinyl propionate, maleic anhydride, itaconic acid, phenylmaleimide, etc., and these monomers are 50 parts by weight based on 100 parts by weight of the acrylic monomer. It can be used in the following ranges.

The kind and amount of the monomer used in the present invention are determined by the glass transition temperature of the obtained copolymer, the compatibility with other resins used for the magnetic recording medium, for example, urethane resin, and the magnetic layer. After modifying the hydroxyl-containing acrylic copolymer of the present invention with a monoisocyanate compound, the glass transition temperature and the compatibility with the urethane resin, the physical properties of the magnetic layer may be satisfied. Should be selected.

The monoisocyanate compound for modifying the acrylic copolymer having a hydroxyl group includes isobutyl isocyanate, isopropyl isocyanate, propenyl isocyanate, methyl isocyanate, ethyl isocyanate, phenyl isocyanate, α-naphthyl isocyanate and β-naphthyl isocyanate. There are isocyanates such as naphthyl isocyanate and tolyl isocyanate, and there is no problem as long as the compound has monoisocyanate. As a method of modifying a monoisocyanate to an acrylic copolymer having a hydroxyl group, a monoisocyanate compound is added to a solution in which the acrylic copolymer is dissolved in a solvent such as cyclohexanone, methyl ethyl ketone or acetone, and the mixture is stirred and heated as necessary. Monoisocyanate compounds such as a method of reacting by adjusting and controlling, a method of adding monoisocyanate to a solution in which an acrylic copolymer is dissolved and storing in a container capable of blocking moisture, or a method of storing while heating if necessary. Any method can be used as long as it is a modification method in which the acrylic copolymer and the acrylic copolymer react sufficiently. Was the acrylic copolymer modified with an isocyanate compound, in order to improve the adsorptive and dispersion of the resin to the magnetic _{powder, -SO 3 M, -OSO 3 M} , -OH, -C
_{OOH, -PO 3 M 2, -OPO} 3 M 2, -N <, - C
A compound having at least one hydrophilic functional group such as ON <(where M is a hydrogen atom or an alkali metal) is selected,
It may have the above-mentioned known polar group at an appropriate ratio. Generally, the average molecular weight is 5000 g / m
ol or more and 100000 g / mol or less, desirably 10000 g / mol or more and 60000 g / mol or less. And preferably not less than 20 parts by weight and not more than 80 parts by weight. If the mixing ratio of the acrylic copolymer to the binder resin is less than 10 parts by weight, the magnetic layer is too soft, and the magnetic head is likely to stick, and if it exceeds 80 parts by weight, the magnetic layer is hard and brittle. And the possibility of deteriorating the durability increases.

The amount of the monoisocyanate compound that modifies the acrylic copolymer having a hydroxyl group is such that the urethane bond has a content of 0.2 to 1 mmol / g, preferably 0.2 to 0.8 mmol / g. Is appropriate. If the amount of modification of the monoisocyanate compound is 0.2 mmol / g or less, the content of urethane bonds common to the skeleton with the polyurethane resin is small, and sufficient compatibility is not obtained, and unevenness in composition when a coating film is formed cannot be obtained. This is likely to occur, and the amount of powder falling during running of the magnetic recording medium or the like increases, and the durability deteriorates. When the modification amount of the monoisocyanate compound is 1 mmol / g or more, the compatibility becomes sufficient because the content of the urethane bond common to the skeleton with the polyurethane resin is large, but the polar portion of the urethane bond portion is large. Because it becomes too much, the solubility in the paint adjustment solvent becomes insufficient, the dispersibility is reduced or the composition becomes uneven when the coating film is formed, and the powder falls off during running of the magnetic recording medium. And the durability deteriorates.

The magnetic recording medium of the present invention can be applied to a coating type magnetic recording medium in which a magnetic layer is formed by first applying a magnetic paint to the surface of a non-magnetic support.
As the nonmagnetic support and the magnetic powder constituting the magnetic layer, any of conventionally known ones can be applied. Examples of magnetic powder include γ-Fe ₂ O ₃ , Fe ₃ O ₄ , γ-F
a belt-ride compound of e ₂ O ₃ and Fe ₃ O ₄ , γ-Fe ₂ O ₃ containing Co, Fe ₃ O ₄ containing Co,
Belt compound of Co-containing γ-Fe ₂ O ₃ and Fe ₃ O ₄ , CrO ₂ containing one or more metal elements such as Te, Sb, Fe, Bi, etc., oxide, Fe, Metals such as Co and Ni, Fe-Co, Fe-N
i, Fe-Al, Fe-Ni-Al, Fe-Al-P,
Fe-Ni-Si-Al, Fe-Ni-Si-Al-M
n, Fe-Mn-Zn, Fe-Ni-Zn, Co-N
i, Co-P, Fe-Co-Ni, Fe-Co-Ni-
Cr, Fe-Co-Ni-P, Fe-Co-B, Fe-
Co-Cr-B, Mn-Bi, Mn-Al, Fe-Co
Alloys such as -V, iron nitride, iron carbide and the like. Of course,
Even if an appropriate amount of a light metal element such as Al, Si, P, or B is added for the purpose of preventing sintering or maintaining the shape during reduction, the effect of the present invention is not prevented.

As another resin binder usable in the present invention, a resin obtained by modifying the acrylic copolymer having a hydroxyl group of the monoisocyanate of the present invention is used in an amount of 10 to 90 parts by weight, and a urethane resin is used. In addition to using 10 parts by weight or more and 90 parts by weight or less, an acrylonitrile-butadiene copolymer, polyvinyl butyral, a cellulose derivative (cellulose acetate butyrate, cellulose diacetate, cellulose triacetate, cellulose triacetate) may be used as long as the effects of the present invention are not impaired. (Pionate, nitrocellulose), styrene-butadiene copolymer, polyester resin, synthetic rubber, and other thermoplastic resins can be used. Further, the thermoplastic resin as a conventionally known binder includes a thermosetting resin such as a phenol resin and an epoxy resin silicone resin. These binders in the magnetic layer and the lower non-magnetic layer are used in an amount of 1 to 20 parts by weight based on 100 parts by weight of the magnetic powder and the lower non-magnetic layer.
0 parts by weight or less, preferably 1 part by weight or more and 50 parts by weight or less. If the amount of the binder is too large, the ratio of the magnetic powder in the magnetic layer relatively decreases, causing a decrease in output,
If the amount is too small, the mechanical strength of the magnetic layer and the lower non-magnetic layer decreases, and the possibility of deteriorating the durability increases.

In the present invention, an appropriate amount of a lubricant, non-magnetic reinforcing particles, conductive particles, a surfactant and the like can be contained in the magnetic layer and the lower non-magnetic layer, if necessary. As a lubricant, graphite, molybdenum disulfide, silicone oil,
There are fatty acids having 10 to 22 carbon atoms, fatty acid esters composed of fatty acids having 10 to 22 carbon atoms and alcohols having 2 to 26 carbon atoms, terpene compounds, oligomers of terpene compounds, and the like. Non-magnetic reinforcing particles include aluminum oxide, chromium oxide, silicon carbide, diamond, garnet, emery, boron nitride and the like, and 20 parts by weight, preferably 1 part by weight, per 100 parts by weight of magnetic powder.
0 parts by weight or less is good. The average particle size is 1.0 μm or less, preferably 0.5 μm or less. Examples of the conductive particles include carbon black, graphite, and other metal particles. Surfactants include nonionic, anionic, cationic and amphoteric surfactants.

Examples of the non-magnetic support include polyesters such as polyethylene terephthalate and polyethylene-2,6-naphthalate; polyolefins such as polypropylene;
Examples include celluloses such as cellulose triacetate and cellulose diacetate, polymer materials represented by vinyl resins, polyimides, and polycarbonates, metals, glass, and ceramics.

In order to form a magnetic layer on a non-magnetic support, a coating material for forming a magnetic layer is applied to a non-magnetic support and dried, and acetone or methyl ethyl ketone is used as a solvent when the magnetic layer forming material is used as a coating material. , Methyl isobutyl ketone, ketone solvents such as cyclohexanone, methanol,
Ethanol, alcohol solvents such as propanol, methyl acetate, ethyl acetate, butyl acetate, propyl acetate, ethyl lactate, ester solvents such as ethylene glycol acetate, ether solvents such as diethylene glycol dimethyl ether, 2-ethoxyethanol, tetrahydrofuran, dioxane, Examples include aromatic hydrocarbon solvents such as benzene, toluene, and xylene, and halogenated hydrocarbon solvents such as methylene chloride, ethylene chloride, carbon tetrachloride, chloroform, and chlorobenzene.

A roll mill, a ball mill, a sand mill,
Agitators, kneaders, extruders, homogenizers, ultrasonic dispersers, etc. are used, and gravure coaters, knife coaters, wire bar coaters, doctor blade coaters, reverse roll coaters, dipping coaters, etc. An air knife coater, a die coater or the like is used. Then, in a state where the lower non-magnetic layer is coated on the non-magnetic support and is in a wet state, the magnetic layer may be coated on the lower non-magnetic layer by a die coater or the like, and the magnetic layer may be coated as long as the effects of the present invention are not impaired. The method is optional.

Hereinafter, specific embodiments of the present invention will be described, but it goes without saying that the present invention is not limited to these embodiments.

Example 1 First, a polymethyl methacrylate resin containing 70 parts by weight of methyl methacrylate, 15 parts by weight of benzyl methacrylate, and 15 parts by weight of 2-hydroxyethyl methacrylate is synthesized.

Next, 5 parts by weight of phenyl isocyanate was added to a cyclohexanone solution in which 100 parts by weight of an acrylic copolymer had been dissolved, and the inside of the container was replaced with nitrogen gas, followed by stirring for 4 hours while heating to 60 ° C. Let it.

Next, the solution containing the modified acrylic copolymer is dropped into 5000 parts by weight of methanol, and 5000 parts by weight of methanol is again added to the precipitate except the supernatant, followed by filtration and washing. Then, by drying this, an acrylic copolymer is obtained. The characteristics of this acrylic copolymer are shown below. Weight average molecular weight 56000 g / mol N element amount 0.04% by weight However, weight average molecular weight of this resin (in terms of polystyrene)
Is measured by high performance liquid chromatography (manufactured by Showa Denko KK), and the amount of N element is measured by a CHN element analyzer (manufactured by Perkin Elmer). In addition, the resin obtained by drying the solution before modification of the acrylic copolymer was subjected to elemental analysis. Since the amount of N element was 0.00% by weight, modification with phenyl isocyanate containing N element was confirmed. did it.

Next, carbon and α-Al ₂ O ₃ are added as additives to the acrylic copolymer and the polyurethane resin,
The mixture was mixed, kneaded and dispersed with the following coating composition to form a coating. Magnetic powder 100 parts by weight Acrylic copolymer 10 parts by weight Polyester polyurethane resin 10 parts by weight (containing -SO ₃ Na) α-Al ₂ O ₃ 2 parts by weight (average particle size 240 nm) Methyl ethyl ketone 100 parts by weight Toluene 100 parts by weight Cyclohexanone 50 parts by weight heptyl stearate 1 part by weight Myristic acid 2 parts by weight

Next, coronate L (manufactured by Nippon Polyurethane Co., Ltd.), which is an isocyanate compound, is added as a curing agent to the obtained magnetic paint, and the resultant is coated on a 14 μm-thick polyethylene terephthalate film, oriented and dried. And
A calendering treatment was performed as a surface treatment step, and the mixture was cured in a curing oven at 60 ° C. for 24 hours to promote curing, thereby completing a magnetic tape.

Example 2 In this example, a magnetic tape was obtained in the same manner as in Example 1 except that 2.5 parts by weight of phenyl isocyanate was added, which is half of Example 1.

Example 3 In this example, a magnetic tape was obtained in the same manner as in Example 1 except that 10 parts by weight of phenyl isocyanate was added, which was double that of Example 1.

Example 4 In this example, the amount of the acrylic copolymer modified with phenyl isocyanate was changed from 10 parts by weight to 4 parts by weight in Example 1, and the amount of the polyurethane resin was changed from 10 parts by weight to 16 parts by weight. A magnetic tape was obtained in the same steps as in Example 1 except that the above-mentioned conditions were adopted.

Example 5 In this example, the amount of the acrylic copolymer modified with phenyl isocyanate was changed from 10 parts by weight of Example 1 to 16 parts by weight.
A magnetic tape was obtained in the same process as in Example 1, except that the amount of the polyurethane resin was changed from 10 parts by weight to 4 parts by weight.

Comparative Example 1 In this comparative example, the acrylic copolymer was modified with phenyl isocyanate to 10 parts by weight,
A magnetic tape was obtained in the same steps as in Example 1 except that the amount was 0 parts by weight.

Comparative Example 2 In this comparative example, a magnetic tape was obtained in the same process as in Example 1 except that 1.5 parts by weight of phenyl isocyanate was used.

Comparative Example 3 In this comparative example, a magnetic tape was obtained in the same process as in Example 1 except that phenyl isocyanate was used in an amount of 15 parts by weight.

Comparative Example 4 In this comparative example, a magnetic tape was obtained in the same process as in Example 1 except that an acrylic copolymer was prepared without adding 15 parts by weight of 2-hydroxyethyl methacrylate having a hydroxyl group. is there.

Comparative Example 5 In this comparative example, a magnetic tape was obtained in the same process as in Example 1 except that nitrocellulose 1/8 type was used in place of the acrylic copolymer modified with phenyl isocyanate. .

Comparative Example 6 In this comparative example, a vinyl chloride copolymer (trade name M) was used instead of an acrylic copolymer modified with phenyl isocyanate.
A magnetic tape was obtained in the same process as in Example 1 except that R-110AN (manufactured by Zeon Corporation) was used.

Comparative Example 7 In this comparative example, the amount of the acrylic copolymer modified with phenyl isocyanate was changed from 10 parts by weight to 1 part by weight in Example 1, and the amount of the polyurethane resin was changed from 10 parts by weight to 19 parts by weight. A magnetic tape was obtained in the same steps as in Example 1 except that the above-mentioned conditions were adopted.

Comparative Example 8 In this comparative example, the amount of the acrylic copolymer modified with phenyl isocyanate was changed from 10 parts by weight of Example 1 to 19 parts.
A magnetic tape was obtained in the same process as in Example 1 except that the amount of the polyurethane resin was changed from 10 parts by weight to 1 part by weight.

Table 1 shows the characteristics of Examples 1 to 5 and Comparative Examples 1 to 8.

[0041]

[Table 1]

As evaluations of Examples 1 to 5 and Comparative Examples 1 to 8, the dispersibility of the magnetic layer was evaluated by glossiness using a gloss meter (manufactured by Nihon Kohden Co., Ltd.). ° and according to JIS-8741. Magnetic properties were measured with a sample vibration magnetometer. The durability was evaluated using an 8 mm video tape recorder (Sony).
The MHZ signal was recorded, and the change in the reproduction output after running 200 times was measured with an oscilloscope. This is shown in Table 2.

[0043]

[Table 2]

An acrylic copolymer modified with a urethane group amount of 0.2 mmol / g or more and 1 mmol / g or less as in Examples 1, 2 and 3, and an urethane group amount as in Comparative Examples 1-4. 0.2 mmol / g or more and 1 mmol / g
Comparing the acrylic copolymer which has not been subjected to the modification treatment, it is clear that Comparative Examples 1 to 4 are inferior to Examples 1, 2 and 3 in both magnetic properties and running durability. The acrylic copolymer used in Comparative Examples 1 and 2 contains a hydroxyl group and has a strong hydrogen bond polarity, and the acrylic copolymer used in Comparative Example 4 does not contain a hydroxyl group and has a hydrogen bondable polarity. Although small, the compatibility with the polyurethane resin was poor regardless of the presence or absence of polarity. It is presumed that the magnetic properties and running durability were inferior for this reason. On the other hand, an acrylic copolymer modified with a monoisocyanate of 0.2 mmol / g or more and 1 mmol / g or less has a compatibility with the polyurethane resin because the skeleton of the urethane resin also contains an appropriate amount of a common urethane bond. Good solubility is obtained. As a result, the acrylic copolymer used in combination with the polyurethane resin has an urethane group content of 0.2 mmol / g or more and 1 mmol / g or more due to monoisocyanate.
g, if modified, dispersibility, magnetic properties,
A magnetic tape having good running durability was obtained.

Examples 1, 4 and 5 wherein the mixing ratio of the acrylic copolymer modified with isocyanate by monoisocyanate in the binder resin is 20 to 80%.
And Comparative Examples 7 and 8 in which the mixing ratio is other than 20 to 80%, it is clear that Comparative Examples 7 and 8 are inferior to Examples 1, 4 and 5 in running durability. In Comparative Example 7 where the mixing ratio was 5%, the coating film was soft and the coating film was easily broken by plastic flow and the like. In Comparative Example 8 where the mixing ratio was 95%, the coating film was too hard and the coating film was fine due to sliding. Since the powder is easily dropped due to cracks or the like, or the adhesion of the magnetic powder or the coating film is easily reduced, the running durability is inferior. From this, when the acrylic copolymer and the polyester polyurethane resin are used as the binder, it is clear that the composition ratio is important for improving the durability.

On the other hand, in Comparative Example 5 in which a mixture of nitrocellulose was used as the binder instead of the acrylic copolymer, the magnetic powder did not disperse well in the binder and a magnetic paint could not be produced. . In Comparative Example 6 in which a mixture of a vinyl chloride copolymer was used instead of the acrylic copolymer as the binder, a magnetic paint could be manufactured, but the manufactured magnetic tape had no magnetic property or running durability. Are also inferior to those of Examples 1, 2, 3, 4, and 5, and when combusted, hydrogen chloride is generated, which is a problem from the viewpoint of environmental protection.

[0047]

According to the magnetic recording medium and the method of manufacturing the same of the present invention, the compatibility between the acrylic copolymer resin and the polyester polyurethane resin is improved, and the magnetic powder in the magnetic layer can be uniformly dispersed. it can. Therefore,
A magnetic recording medium that can cope with high-density recording and has excellent durability can be provided.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification number Agency reference number FI Technical indication location C09D 175/04 PHX C09D 175/04 PHX G11B 5/842 G11B 5/842 Z

Claims (6)

[Claims] 1. A magnetic recording medium in which a magnetic layer mainly composed of a magnetic powder and a binder is formed on a non-magnetic support, wherein the binder comprises a hydroxyl group-containing acrylic copolymer and a monoisocyanate compound. Having a urethane group content of 0.2 mmol / g or more 1
A magnetic recording medium comprising: a resin modified to not more than mmol / g; and a polyurethane resin. 2. The urethane group content is 0.2 mmol / g.
2. The magnetic recording medium according to claim 1, wherein the content is 0.8 mmol / g or less. 3. The magnetic recording medium according to claim 1, wherein the amount of the acrylic copolymer is from 20 to 80 parts by weight based on 100 parts by weight of the binder. 4. An acrylic copolymer having a hydroxyl group,
The monocyanate compound has a urethane group content of 0.2 mmol.
Kneading a binder having a modified resin having a viscosity of at least 1 g / g and at most 1 mmol / g, a polyurethane resin, and a magnetic powder to form a magnetic coating; applying the magnetic coating to a non-magnetic support; Forming a layer. 5. The urethane group content is 0.2 mmol / g.
The method for producing a magnetic recording medium according to claim 4, wherein the content is not less than 0.8 mmol / g. 6. The method for producing a magnetic recording medium according to claim 4, wherein the amount of the acrylic copolymer is from 20 to 80 parts by weight based on 100 parts by weight of the binder.