JPH10241145A - Magnetic recording medium and method of manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable high density recording and provide a magnetic recording medium having high electro-magnetic conversion characteristic and excellent durability by forming a magnetic layer with magnetic paint including magnetic powder and binder and then including polyurethane-based resin A and B of the particular mean molecules to the binder. SOLUTION: A magnetic paint to form a magnetic layer is formed by ferro- magnetic powder, binder and solvent. The ferro-magnetic powder should be iron-based ferro-magnetic metal powder, hexagonal system ferrite powder or magnetic iron oxide, etc., to satisfy the high density recording. Coercive force of ferro-magnetic metal powder should be 1500 to 2600Oe, saturated magnetization should be 100 to 180emu/g, coercive force of hexagonal system ferrite powder should be 1300 to 2700Oe and saturated magnetization should be 30 to 70emu/g. As the binder, the polyulethane based resin A having optimum coating film hardness, running durability holding, number mean molecule for giving high filling property of magnetic powder of 10000 to 20000 and the polyulethane based resin B having running durability effect holding, number mean molecules of 21000 to 50000 to improve dispersion property of magnetic powder are used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a magnetic recording medium capable of high-density recording and having excellent durability.

[0002]

2. Description of the Related Art Magnetic recording media are widely used as recording tapes, video tapes, floppy disks and the like. In general, as such a magnetic recording medium, a medium having a support and a magnetic layer as an uppermost layer is widely used. In recent years, magnetic recording media have been required to be capable of high-density recording. For this reason, a magnetic recording medium having a multilayer structure in which an intermediate layer is provided between the support and the magnetic layer. Has been proposed. The advantage of such a multilayer structure is that the magnetostatic properties can be improved by reducing the thickness of the magnetic layer, but on the other hand, the durability is reduced because the thickness of the magnetic layer is thin. There was a problem.

Therefore, in order to improve the durability, a conventional magnetic recording medium is added with an abrasive or a lubricant. However, in order to improve the durability by adding the abrasive, it is necessary to increase the amount of the abrasive, and if the amount of the abrasive is increased, the content of the magnetic powder necessarily decreases, and The characteristics are degraded. It has also been proposed to use an abrasive having a relatively large particle size to improve the durability. However, if such an abrasive having a large particle size is used, the abrasive will protrude from the surface of the magnetic layer, and the abrasive will be removed. Pacing loss results, and the electromagnetic conversion characteristics deteriorate. Also, when the durability is improved by adding a lubricant, it is necessary to increase the amount of addition, and as a result, there is a problem that plasticization of the magnetic layer is caused.

[0004] Therefore, as a fundamental measure for improving the durability, a binder for improving the durability has been studied. As one example, there has been proposed a method of increasing the magnetic layer hardness by using a hard binder such as a vinyl chloride-based binder (by increasing the addition ratio). However, in this proposal, although the hardness of the magnetic layer is increased, the brittleness becomes remarkable, and the magnetic layer and the magnetic head come into contact with each other, so that dropout easily occurs or a magnetic tape as a magnetic recording medium is manufactured. In this case, there is a problem that a crack is easily generated in the edge at the time of slitting.

[0005] In short, with the conventional magnetic recording medium, a magnetic recording medium capable of high density recording as required in recent years and having high durability has not yet been obtained.

Accordingly, it is an object of the present invention to provide a magnetic recording medium capable of high-density recording, having high electromagnetic conversion characteristics, and having excellent durability.

[0007]

Means for Solving the Problems The inventors of the present invention have made intensive studies to solve the above problems, and as a result, a magnetic recording medium using a binder containing two kinds of polyurethane resins having different molecular weights has been described. It was found that the purpose could be achieved.

The present invention has been made based on the above findings. In a magnetic recording medium having a support and a magnetic layer as an uppermost layer, the magnetic layer is formed by using a magnetic paint containing a magnetic powder and a binder. Is formed, the binder is a polyurethane resin A having a number average molecular weight of 10,000 to 20,000, and a number average molecular weight of 21,000 to
The present invention provides a magnetic recording medium characterized by containing 50,000 polyurethane resins B.

Further, the present invention further provides a magnetic recording medium having an intermediate layer located between the support and the magnetic layer, and the intermediate layer contains at least a binder and an inorganic powder. An object of the present invention is to provide a magnetic recording medium which is formed using a forming paint and contains a polyurethane resin having a number average molecular weight of 10,000 to 50,000 as the binder. Further, in the present invention, the polyurethane-based resin A and the polyurethane-based resin B are each -COOM,
_{-SO 3 M, -P = O (} OM) 2, -NH 2 and -O-
P = O (OM) ₂ wherein M represents hydrogen or an alkali metal, and contains, on average, 0.5 to 5 polar groups in one molecule selected from one or more polar groups selected from the group consisting of: A magnetic recording medium is provided.

Further, the present invention provides a magnetic recording medium wherein the amount of the polyurethane resin A and the amount of the polyurethane resin B used is 2 to 30 parts by weight based on 100 parts by weight of the magnetic powder. Is provided. Also,
The present invention, the binder may further magnetic recording medium containing a vinyl chloride copolymer, and the salt of vinyl-based _{copolymer, -COOM, -SO 3 M, -P} = O (O
M) ₂ , -NH ₂ and -OP = O (OM) ₂ [provided that
In the formula, M represents hydrogen or an alkali metal]. The present invention provides a magnetic recording medium containing one or more polar groups selected from the group consisting of:

The present invention also provides, as a preferred method for producing the above magnetic recording medium, at least a magnetic powder and a polyurethane resin A having a number average molecular weight of 10,000 to 20,000.
A step of applying a magnetic paint obtained by dispersing a binder system containing a polyurethane resin B having a number average molecular weight of 21,000 to 50,000 in a solvent on a support to form a coating film of a magnetic layer; The present invention provides a method for manufacturing a magnetic recording medium, comprising: a step of performing an orientation treatment by a magnetic field before drying, and a step of further performing a calendaring process, and performing each step in this order.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, a magnetic recording medium of the present invention will be described in detail. The magnetic recording medium of the present invention is characterized in that the magnetic layer is formed by applying a magnetic paint containing a ferromagnetic powder and a specific binder on a support.
In the present invention, the magnetic layer may be a single layer or a multilayer. Also, even if the magnetic layer is formed directly on the support,
Alternatively, it may be formed via an intermediate layer or the like. That is, the “on the support” means above the support.

First, the magnetic paint for forming the magnetic layer will be described. As the magnetic paint, a paint containing the ferromagnetic powder and the binder and further containing a solvent is used.

As the above ferromagnetic powder, a ferromagnetic metal powder mainly composed of iron, a hexagonal ferrite powder, a magnetic iron oxide and the like can be mentioned in order to meet the demand for high density recording.
The coercive force of the above ferromagnetic metal powder is 1500-2600O
e is preferable, 1600 to 2500 Oe is more preferable, and 1700 to 2400 Oe is most preferable. The coercive force of the hexagonal ferrite powder is
It is preferably from 1300 to 2700 Oe. The saturation magnetization of the ferromagnetic metal powder is 100 to 180 emu / g.
Is more preferable, and more preferably 110 to 160 emu / g. The saturation magnetization of the hexagonal ferrite powder is preferably 30 to 70 emu / g.
More preferably, it is 70 emu / g.

Therefore, the coercive force of the magnetic layer containing the ferromagnetic metal powder is preferably 1500 to 2500O.
e, more preferably 1700-2400 Oe, most preferably 1800-2300 Oe, and the coercive force of the magnetic layer containing the hexagonal ferrite powder is:
Preferably it is 1300-2600 Oe. Further, the saturation magnetic flux density of the magnetic layer containing the ferromagnetic metal powder is preferably 3000 to 4500 gauss, more preferably 3200 to 4000 gauss, and the saturation magnetic flux density of the magnetic layer containing the hexagonal ferrite powder is high. The magnetic flux density is
Preferably it is 1500-2600 gauss, more preferably 1600-2500 gauss.

The ferromagnetic metal powder has a metal content of 5%.
0% by weight or more, and 50% by weight or more of the metal component is Fe.
Ferromagnetic metal powder. Specific examples of the ferromagnetic metal powder include, for example, Fe-Co, Fe-Ni,
Fe-Co-Ni, Fe-Ni-Zn, Fe-Al, F
e-Al-Si, Fe-Ni-Al, Fe-Ni-Al
—Zn and the like. The shape of the ferromagnetic metal powder is preferably acicular, and its major axis is preferably 0.05 to 0.25 μm. The preferred acicular ratio is 3 to 20, the preferred X-ray particle size is 13 to 25 nm, and more preferably 13.5 to 19.5 nm.

Further, as the hexagonal ferrite powder, barium ferrite and strontium ferrite in the form of a small flat plate, and a part of their Fe atoms are Ti, C
magnetic powders substituted with atoms such as o, Ni, Zn, V, and the like. Further, the shape of the hexagonal ferrite powder has a plate diameter of 0.01 to 0.08 μm and a plate ratio of 2 to 10 μm.
Is preferably

The above-mentioned ferromagnetic powder may optionally contain
It can contain rare earth elements and transition metal elements.
Wear. In the present invention, the dispersion of the ferromagnetic powder is
The ferromagnetic powder is subjected to a surface treatment to improve its properties.
May be. The above surface treatment is referred to as “Characterization of
Powder Surfaces "; described in Academic Press
It can be performed by the same method as the method, for example,
Method of coating the surface of ferromagnetic powder with inorganic oxide
Can be At this time, the inorganic oxide that can be used
As Al_TwoO_Three, SiO_Two, TiO_Two, Zr
O _Two, SnO_Two, Sb_TwoO_Three, ZnO, etc.
When using, use alone or as a mixture of two or more.
Can be. The above-mentioned surface treatment may be performed in addition to the above-described method.
Coupling agent treatment, titanium coupling agent treatment and
This can be done by organic treatment such as alumina coupling agent treatment.
Can also be.

The binder used in the magnetic coating composition according to the present invention has a number average molecular weight of 10,000 to 2
0000 polyurethane resin A and a number average molecular weight of 2
1000 to 50,000 polyurethane resin B. Further, the number average molecular weight of the polyurethane resin A is preferably 10,000 to 15,000,
The number average molecular weight of the polyurethane resin B is 25,000
Preferably it is ~ 35,000. When the number average molecular weight of the polyurethane resin A is less than 10,000, the coating film becomes soft, the running durability is reduced, and 200
If it exceeds 00, the filling property of the magnetic powder decreases. Also,
The number average molecular weight of the polyurethane resin B is 2100
If it is less than 0, the effect of contributing to running durability is reduced, and if it is more than 50,000, the dispersibility of the magnetic powder is reduced.

The molecular weight distribution of the polyurethane resin A is expressed by the following formula: weight average molecular weight (Mw) / number average molecular weight (M
n) is preferably 1 to 6, and more preferably 1 to 4. The molecular weight distribution of the polyurethane resin B is preferably Mw / Mn of 1 to 8, more preferably 1 to 8.
4 is more preferred. The above polyurethane resin A
If the Mw / Mn of the compound exceeds 6, plasticization of the coating film due to the low molecular weight component occurs, which is not preferable. When the Mw / Mn of the polyurethane resin B exceeds 8, dispersion deterioration occurs due to a high molecular weight component, which is not preferable. The number average molecular weight and the weight average molecular weight were determined by gel permeation chromatography (GPC) in the same manner as in a conventional method.
It is determined by polystyrene conversion.

The structure of the polyurethane resin A and the polyurethane resin B is not particularly limited as long as it is a polyurethane resin having a number average molecular weight within the above range. Is preferably used. Molecular structure; having a polyurethane backbone in the main _{chain, -COOM, -SO 3 M, -P} = O (O
M) ₂ , -NH ₂ and -OP = O (OM) ₂ [provided that
In the formula, M represents hydrogen or an alkali metal such as Na or K]
The average of one or more polar groups selected from the group consisting of preferably 0.5 to 5 and more preferably 1 to 5
Structure containing ~ 3. If the content of the polar group is less than 0.5, the dispersibility may not be sufficient,
If the number exceeds the above range, the viscosity of the paint may increase.

That is, in the present invention, the polyurethane resin A and the polyurethane resin B may have the same molecular structure as long as each has a number average molecular weight within the above range.

The molecular structure will be described in more detail. As the polar group, specifically, -COOH, -COO
_{Na, -COOK, -SO 3 H,} -SO 3 Na, -P =
_{O (OH) 2, -P =} O (ONa) 2, -NH 2 and -
OP = O (OH) ₂ , -OP = O (ONa) _{2 and the} like.

Examples of the polyurethane resin A include polyurethanes “UR-8530” and “U
R-5537 "," UR-H "," UR-G "(above,
Commercially available products such as “UR-8300”, “UR-8700”, and “UR” manufactured by Toyobo can be used as the polyurethane resin B.
Commercially available products such as "-D" (all trade names) and polyurethane "N2301" (trade name) made by Nippon Polyurethane can be used.

The total amount of the polyurethane resin A and the polyurethane resin B is preferably 2 to 30 parts by weight, preferably 3 to 15 parts by weight, based on 100 parts by weight of the magnetic powder. More preferably, If the amount of the polyurethane resin A and the amount of the polyurethane resin B are less than 2 parts by weight, a sufficient effect for improving the durability cannot be obtained. If the amount exceeds 30 parts by weight, the filling ratio of the magnetic powder decreases. , The output is low, so that it is preferable to be within the above range.

The mixing ratio of the polyurethane resin A and the polyurethane resin B is preferably 50 to 200 parts by weight of the polyurethane resin B with respect to 100 parts by weight of the polyurethane resin A. 1
More preferably, it is 50 parts by weight. If the compounding ratio of the polyurethane resin B is less than 50 parts by weight, the effect of improving the filling property of the magnetic powder by the low molecular weight urethane is not exhibited, and if it exceeds 200 parts by weight, the improvement of the durability by the high molecular weight urethane is not achieved. Since the effect is not exhibited, it is preferable to be within the above range.

In the present invention, as the binder, a binder consisting of only the polyurethane resin A and the polyurethane resin B described above may be used, and further, a binder containing a vinyl chloride-based copolymer may be used. Can also be used. As the vinyl chloride copolymer (structure and average molecular weight), those usually used in magnetic recording media can be used without any particular limitation, but those having the following molecular structures are preferably used. Molecular structure; having a vinyl chloride skeleton in the main chain, -COOM,
_{-SO 3 M, -P = O (} OM) 2, -NH 2 and -O-
P = O (OM) ₂ [where M is hydrogen, Na, K
At least one polar group selected from the group consisting of
A structure containing up to 5, more preferably 0.8 to 3. When the content of the polar group is less than 0.5, the dispersibility of the magnetic powder is not sufficient, and when the content exceeds 5, the viscosity of the paint may increase. preferable.

The molecular structure will be described in more detail. As the polar group, specifically, -COOH, -COO
_{Na, -COOK, -SO 3 H,} -SO 3 Na, -P =
_{O (OH) 2, -P =} O (ONa) 2, -NH 2 and -
OP = O (OH) ₂ , -OP = O (ONa) _{2 and the} like. As the molecular structure, specifically, the following structures are exemplified.

[0029]

Embedded image

In the above formula, l, m, n and p are arbitrary numbers satisfying the above-mentioned molecular structure and depending on a desired average molecular weight.

As the vinyl chloride copolymer, commercially available products such as "MR110" and "MR104" (all trade names) manufactured by Zeon Corporation and "VAGH" (trade name) manufactured by Union Carbide may be used. it can.

The mixing ratio of the vinyl chloride copolymer is as follows:
50 parts by weight of 100 parts by weight of the polyurethane resin A
It is preferable to set it to 500 parts by weight. When the vinyl chloride copolymer is used, the compounding ratio of the binder is preferably 3 to 35 parts by weight, and more preferably 5 to 20 parts by weight based on 100 parts by weight of the magnetic powder. More preferred.

Further, as the binder, a resin to which a resin generally used as a binder in a magnetic recording medium is added in such an amount as not to impair the desired effect of the present invention can be used.

Examples of the solvent used in the magnetic paint include ketone solvents, ester solvents, ether solvents, aromatic hydrocarbon solvents, and chlorinated hydrocarbon solvents. Specifically, JP-A-57-162
No. 128, page 3, lower right column, line 17 to page 4, upper left column, 10
The solvents described in the lines and the like can be used. The amount of the solvent used is preferably 80 to 600 parts by weight, and more preferably 100 to 35 parts by weight based on 100 parts by weight of the magnetic powder.
0 parts by weight is more preferred.

Further, a dispersant,
Additives commonly used in magnetic recording media, such as lubricants, abrasives, antistatic agents, rust inhibitors, and fungicides, can be added as needed.

In order to prepare the magnetic paint, for example, the ferromagnetic powder and the binder are put into a Nauta mixer or the like together with a part of the solvent and premixed to obtain a mixture. After kneading with a twin-screw extruder or the like, then diluting with a part of the solvent, dispersing using a sand mill or the like, mixing additives such as lubricant, filtering, and further curing agent such as polyisocyanate It can be easily obtained in accordance with a normal method for producing a magnetic paint such as a method of mixing the remaining solvent.

Next, the structure of the magnetic recording medium of the present invention will be specifically described with reference to the drawings. Here, FIG.
FIG. 1 is a schematic sectional view showing one embodiment of a magnetic recording medium of the present invention.

The magnetic recording medium 1 of the present invention shown in FIG. 1 includes a support 2 and a magnetic layer 3 provided as an uppermost layer on the surface side of the support 2.
And a back coat layer 5 provided on the back side of the support 2 as necessary.

The magnetic recording medium of the present invention may be composed of the support 2 and a magnetic layer provided on the support, that is, the medium without the intermediate layer. 2. In addition to the magnetic layer 3, the intermediate layer 4, and the back coat layer 5, a primer layer provided between the support 2 and the intermediate layer 4 or the back coat layer 5 or a long wavelength signal is used. Another layer such as a signal recording layer provided for recording a servo signal or the like corresponding to the hardware system to be used may be provided.

Hereinafter, the magnetic recording medium of the present invention will be described according to the above structure.

As the above-mentioned support used in the magnetic recording medium of the present invention, generally known ones can be used without any particular limitation. Specifically, a flexible film or disk made of a polymer resin can be used. A film, a disc, a card, or the like made of a nonmagnetic metal such as Cu, Al, or Zn, or a ceramic such as glass, porcelain, or ceramics can be used.

The magnetic layer provided as the uppermost layer in the magnetic recording medium of the present invention is formed by applying the above-mentioned magnetic paint on the above-mentioned intermediate layer. When the configuration is such that the intermediate layer is not provided, the magnetic layer includes:
It is formed by applying the magnetic paint on the support.

The thickness of the magnetic layer is 0.05 to 3.0 μm.
m, and more preferably 0.08 to 2.5 μm. If the thickness is less than 0.05 μm, the durability of the coating film of the magnetic layer may be deteriorated, or a problem may occur in the coating process. It may be disadvantageous, so that it is preferable to be within the above range.

In the present invention, the back coat layer optionally provided on the back side of the support (surface opposite to the surface on which the magnetic layer is provided) may be formed by coating a known back coat paint. It is a layer formed by coating on the body.

Further, the thickness of the back coat layer is set to 0.1.
1 to 1.5 μm, preferably 0.3 to 1.0 μm
m is more preferable.

The intermediate layer provided between the support and the magnetic layer, if necessary, is a layer formed by applying a coating material for forming an intermediate layer. A layer having no magnetism (hereinafter, referred to as an “intermediate nonmagnetic layer”);
Layer having normal magnetism (hereinafter, referred to as "intermediate magnetic layer")
And the like.

The intermediate non-magnetic layer is a layer formed by applying a non-magnetic coating as a coating for forming an intermediate layer on the support, and the non-magnetic coating comprises a non-magnetic powder, a binder and the solvent. (Same as the solvent described in the description of the magnetic layer).

The non-magnetic powder is not particularly limited as long as it is non-magnetic. Carbon black, graphite, titanium oxide, barium sulfate, zinc sulfide, magnesium carbonate, calcium carbonate, zinc oxide, calcium oxide,
Magnesium oxide, tungsten disulfide, molybdenum disulfide, boron nitride, tin dioxide, silicon dioxide, nonmagnetic chromium oxide, alumina, silicon carbide, cerium oxide, corundum, artificial diamond, nonmagnetic iron oxide, garnet,
Garnet, silica, silicon nitride, molybdenum carbide, boron carbide, tungsten carbide, titanium carbide, diatomaceous earth,
Dolomite, resinous powder, and the like can be mentioned, and among them, carbon black, titanium oxide, barium sulfate, calcium carbonate, alumina, and nonmagnetic iron oxide are preferably used. The non-magnetic powder may be subjected to the same surface treatment as that of the magnetic powder, in order to improve the dispersibility of the non-magnetic powder.

[0049] Examples of the binder include the following. Polyurethane resins such as polyester polyurethane and polyurethane, polyvinyl chloride copolymer, polyester and the like. Among these, the number average molecular weight is 10
000 to 50,000 polyurethane resins are preferably used. As the polyurethane-based resin, those having the same structure as the above-described polyurethane-based resins A and B (including the commercially available products specifically exemplified) can be used. When a binder having such a molecular weight is blended into the coating material for forming an intermediate layer, the adhesion between the obtained intermediate layer and the magnetic layer and the electromagnetic conversion characteristics are improved, and this effect is particularly exhibited when the production is performed by a wet-on-wet method. Will be noticeable.

The mixing ratio of the binder and the solvent in the non-magnetic paint is preferably 5 to 30 parts by weight with respect to 100 parts by weight of the non-magnetic powder, and the solvent is preferably 80 to 30 parts by weight. Preferably it is 500 parts by weight.

The intermediate magnetic layer is a layer formed by applying an intermediate magnetic paint as a paint for forming an intermediate layer on the support, and the intermediate magnetic paint comprises a ferromagnetic powder, the binder Further, a coating material containing the above solvent (the same solvent as described in the description of the magnetic layer) as a main component and further containing the above nonmagnetic powder as necessary can be preferably used.

The ferromagnetic powder is not particularly limited as long as it is generally used for the intermediate magnetic layer.
For example, a hard magnetic powder and a soft magnetic powder can be used. Examples of the hard magnetic powder include the ferromagnetic metal powder and the hexagonal ferrite powder.

As the soft magnetic powder, a spinel type ferrite
Oxide soft magnetic powder such as light powder is preferably used,
As the spinel type ferrite powder, magnetite,
MnFe_TwoO_Four, CoFe_TwoO_Four, NiFe_TwoO_Four, M
gFe_TwoO_Four, Li_0.5Fe _2.5O_FourAnd Mn-Zn system
Ferrite, Ni-Zn ferrite, Ni-Cu ferrite
Ferrite, Cu-Zn ferrite, Mg-Zn ferrite
Light, Li-Zn ferrite, etc.
Among these, magnetite, Mn-Zn-based ferrite
Light and Ni—Zn ferrite are preferred. Ma
Also, when using, it may be used alone
However, two or more of them can be used in combination.

The soft magnetic powder may be Fe-S
i alloy, Fe-Al alloy (Alperm, Alfenol, Alfer),
Permalloy (Ni-Fe based binary alloy and M
o, Cu, Cr, etc.), Sendust (Fe-Si-Al [9.6% by weight of Si, 5.4% by weight of Al, composition with the balance being Fe]), Fe-Co Metal soft magnetic powders such as alloys can also be mentioned. In use, one kind thereof can be used alone, or two or more kinds thereof can be used in combination.

As the binder used in the above-mentioned intermediate magnetic paint, the same binder as the above-mentioned binder used in the above-mentioned non-magnetic paint can be used. Therefore, the intermediate layer (intermediate magnetic layer and intermediate nonmagnetic layer) is formed using an intermediate layer forming paint containing at least a binder and an inorganic powder (the ferromagnetic powder or the nonmagnetic powder), The binder preferably contains a polyurethane resin having a number average molecular weight of 10,000 to 50,000.

The mixing ratio of the binder and the solvent in the intermediate magnetic paint is preferably 5 to 80 parts by weight with respect to 100 parts by weight of the ferromagnetic powder. Preferably it is 500 parts by weight.

In addition, the above-mentioned coating material for forming an intermediate layer contains additives commonly used in magnetic recording media such as dispersants, lubricants, abrasives, antistatic agents, rust preventives, and antifungal agents. It can be added according to. In addition, the coating material for forming an intermediate layer can be produced according to a conventional method.

The thickness of the intermediate layer (both the intermediate magnetic layer and the intermediate nonmagnetic layer) is preferably from 0.5 to 3.0 μm, more preferably from 0.7 to 2.5 μm. preferable.

The magnetic recording medium of the present invention is suitable as a magnetic tape such as an 8 mm video tape, Data8, DAT tape, or DDS tape, but is also applicable to other magnetic recording media such as a disk-shaped magnetic recording medium such as a floppy disk. can do.

Next, an example of a method for manufacturing a magnetic recording medium according to the present invention will be outlined. In the magnetic recording medium of the present invention, the magnetic paint is applied on the support by an ordinary method to form a coating film of a magnetic layer. Next, the coating film can be easily obtained by performing a magnetic field orientation treatment, followed by a drying treatment and winding. That is, the magnetic recording medium of the present invention is obtained by applying the above-mentioned magnetic paint obtained by dispersing at least a magnetic powder and a binder system containing the above-mentioned polyurethane resin A and the above-mentioned polyurethane resin B on a solvent. Then, a step of forming a coating film of the magnetic layer, a step of performing an orientation treatment by a magnetic field before the coating film is dried, and a step of further performing a calendaring process are performed in this order. When an intermediate layer is also formed,
In addition to the above steps, before the step of forming the magnetic layer coating film, a step of applying an intermediate layer forming coating material on the support to form an intermediate layer coating film is performed. It can be manufactured by the following. Specifically, the coating material for forming the intermediate layer and the magnetic layer is formed on the support by performing the known simultaneous multi-layer coating of the coating material for forming the intermediate layer and the magnetic coating material by a wet-on-wet method. Next, the coating film can be easily obtained by performing a magnetic field orientation treatment, followed by a drying treatment and winding. The coating for forming the intermediate layer is particularly preferably a coating obtained by dispersing a binder system containing a polyurethane resin having a number average molecular weight of 10,000 to 50,000 in a solvent.

[0061]

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples, but the present invention is not limited to these examples.

[Example 1] A magnetic tape and a paint for forming an intermediate layer having the following composition were used, and a backcoat paint having the following composition was used as the backcoat paint. Was manufactured to obtain a magnetic tape as a magnetic recording medium in which an intermediate layer and a magnetic layer were formed on a support. When the coercive force and the saturation magnetic flux density of the magnetic layer formed using the magnetic paint were measured according to the [measurement method] described later, the coercive force of the magnetic layer was 1
650 Oe, and the saturation magnetic flux density was 2500 Gauss.

(Magnetic paint) Blending Blending amount • Iron-based acicular ferromagnetic metal powder 100 parts by weight Coercivity: 1670 Oe Saturation magnetization: 125 emu / g Average major axis length; 0.15 μm Needle ratio: 8 BET Specific surface area: 55 m ² / g X-ray particle size: 170Å ・ “MR-110” 12 parts by weight [trade name, manufactured by Zeon Corporation, hydroxyl- and sulfonate-containing vinyl chloride] ・ Polyurethane resin A 5 parts by weight "UR-H" (trade name, manufactured by Toyobo, urethane containing hydroxyl group and sulfonic acid group)-5 parts by weight of polyurethane resin B "UR-8300" [trade name, manufactured by Toyobo, urethane containing hydroxyl group and sulfonic acid group] Alumina (abrasive, average particle size 0.2 μm) 10 parts by weight ・ Butyl stearate (lubricant) 2 parts by weight ・ Myristic acid (lubricant) 2 parts by weight ・ "Coronate L" (Curing agent) 4 parts by weight [trade name, polyisocyanate compound manufactured by Nippon Polyurethane Industry Co., Ltd.] 300 parts by weight of methyl ethyl ketone / toluene / cyclohexanone (weight ratio: 1: 1: 1 mixed solvent)

(Backcoat paint) blending ・ 97 parts by weight of carbon black (average primary particle size 20 μm) ・ 3 parts by weight of carbon black (average primary particle size 300 μm) ・ “Nipporan 2301” [trade name, Nippon Polyurethane Industry ( Polyurethane manufactured by K.K.) 40 parts by weight-Nitrocellulose 60 parts by weight (having a viscosity of 1/2 second manufactured by Hercules Powder Co.)-Polyisocyanate 20 parts by weight [Takeda Pharmaceutical Co., Ltd., trade name " D-250N "] 1100 parts by weight of methyl ethyl ketone / toluene / cyclohexanone (weight ratio: 1: 1: 1 mixed solvent)

(Coating for forming intermediate layer) Blending Blending amount 100 parts by weight of nonmagnetic inorganic powder α-Fe ₂ O ₃ (Bengara) (major axis length: 0.15 μm) 5 parts by weight of alumina 2 μm ・ Carbon black 2 parts by weight Central particle diameter: 0.02 μm ・ “MR-110” 12 parts by weight [trade name, manufactured by Zeon Corporation, hydroxyl- and sulfonate-containing vinyl chloride copolymer] Hydroxyl content 3 × 10 ⁻⁴ equivalents / g Sulfonate group content; 1 × 10 ⁻⁴ equivalents / g Average degree of polymerization; 300 Number average molecular weight; 12000 Weight average molecular weight; 28000 ・ “UR-8300” 8 parts by weight [trade name , Toyobo Co., Ltd., hydroxyl group and sulfonate group-containing urethane resin] hydroxyl content; 7 × 10 ^-5 eq / g acid base content; 3 × 10 ^-5 eq / g number-average molecular weight; 28000 & Listinic acid (lubricant) 2 parts by weight-Butyl stearate 1 part by weight-"Coronate L" 4 parts by weight [Product name, Nippon Polyurethane Industry Co., Ltd., polyisocyanate compound]-Methyl ethyl ketone / toluene / cyclohexanone 250 parts by weight ( (Weight ratio: 1: 1: 1 mixed solvent) ・ Tri (methylamino) hexane 1 part by weight

[Manufacture of magnetic recording medium] The above-mentioned magnetic paint and the above-mentioned paint for forming an intermediate layer were coated on the surface of a polyretylene terephthalate (support) having a thickness of 6 μm, and the dry thickness was 0.2 μm and 2.5 μm, respectively. Coating was carried out so that the magnetic layer and the intermediate layer were formed. Next, the coating film is passed through a 5000 Oe solenoid magnet in a wet state to perform a magnetic field orientation treatment, and a drying treatment is performed at 60 to 100 ° C., and then the roll surface temperature is 85 ° C. and the roll linear pressure is 300.
After calendering under the condition of kg / cm to form a magnetic layer and an intermediate layer, the film was wound up. Next, a back coat paint was applied on the back surface of the support so as to have a dry thickness of 0.6 μm, dried at 90 ° C., and wound up. Thereafter, aging treatment was performed at 50 ° C. for 16 hours, and slit into 8 mm width to obtain a magnetic tape having 8 mm width. The surface roughness of the obtained magnetic tape was evaluated as follows. The results are shown in [Table 1]. Also,
The obtained tape was loaded into an 8 mm video cassette, and
mm video cassette tape, and output using the obtained 8 mm video cassette tape as follows (C / N characteristics)
And the number of endurance passes were evaluated. The results are also shown in [Table 1].

[Measurement Method] ◎ Coercive Force and Saturation Magnetic Flux Density The magnetic layer coated on the support was punched out of a magnetic tape into a predetermined size and shape, and a magnetic field of 10 kOe was applied using a vibrating magnetometer. The coercive force and the saturation magnetic flux density were measured respectively.

Surface roughness (center line surface roughness) The obtained magnetic tape was cut into an appropriate size to prepare a sample for measurement, and the sample was placed on a microscope slide glass so as to prevent wrinkles from occurring. It was fixed with adhesive tape. Then
This fixed sample piece was purchased from Zygo under the trade name "La
ser Interferometric Microscope Maxim3D Mode
l 5700 ”by the Maxim AdvancedTexture Applic
Cutoff Freq
uency = 4.236 1 / mm, Cutoff Wavelength = 0.236mm,
The center line surface roughness Ra of each of the magnetic layer and the backcoat layer of the magnetic tape was calculated from the following equation, with Removed as cylinder and Trimmed as 0 (before storage). In the following formula, yi is the absolute value of the deviation from the i-th center line when the sampling length is divided into N.

[0069]

(Equation 1)

C / N characteristics (Evaluation of 8 mm) Using an 8 mm video deck obtained by modifying a commercially available Hi 8 deck, a single 9 MHz wave was recorded, the reproduction output (C) was observed with a spectrum analyzer, and the noise level was measured. 8MH
C / N was expressed as the z noise level (N).

◎ Number of endurance passes Using a DDS drive, writing / reading was repeated for a tape length of 50 cm, and a hard error occurred and running was slow.
The number of times of writing / reading up to the TOP was determined as the number of endurance passes.

Examples 2 and 3 and Comparative Examples 1 and 2
A magnetic tape was obtained in the same manner as in Example 1 except that the polyurethane resin A and the polyurethane resin B used in the magnetic paint were as shown in Table 1, respectively. It was evaluated similarly. The results are shown in [Table 1].

[0073]

[Table 1]

[0074]

The magnetic recording medium of the present invention is capable of high-density recording, has high electromagnetic conversion characteristics, and has excellent durability. It is not clear why the above-mentioned effects are achieved in the present invention, but by using two types of polyurethane resins having different number average molecular weights, it is possible to improve the electromagnetic conversion characteristics while improving the durability. It is thought that it is because.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing one embodiment of a magnetic recording medium of the present invention.

Claims (10)

[Claims] 1. A magnetic recording medium comprising a support and a magnetic layer as an uppermost layer, wherein the magnetic layer is formed using a magnetic paint containing a magnetic powder and a binder. Molecular weight 10,000-200
And a number average molecular weight of 210
A magnetic recording medium comprising 0.005 to 50000 polyurethane resin B. 2. The magnetic recording medium according to claim 1, further comprising an intermediate layer located between said support and said magnetic layer. 3. The intermediate layer is formed using a coating for forming an intermediate layer containing at least a binder and an inorganic powder, and has a number average molecular weight of 10,000 to 5,000 as the binder.
3. The magnetic recording medium according to claim 2, wherein the magnetic recording medium contains a polyurethane resin. 4. The polyurethane resin A and the polyurethane resin B are respectively -COOM and -SO ₃
M, -P = O (OM) 2, -NH 2 and -O-P = O
One or more polar groups selected from the group consisting of (OM) ₂ wherein M represents hydrogen or an alkali metal;
2. The magnetic recording medium according to claim 1, wherein 0.5 to 5 molecules are contained in one molecule on average. 5. The use amount of the polyurethane resin A and the polyurethane resin B is 2 to 30 parts by weight based on 100 parts by weight of the magnetic powder in total. 2. The magnetic recording medium according to 1. 6. The magnetic recording medium according to claim 1, wherein the binder further contains a vinyl chloride copolymer. 7. The vinyl chloride copolymer is —COO
_{M, -SO 3 M, -P =} O (OM) 2, -NH 2 and -
7. The magnetic material according to claim 6, wherein the magnetic material contains at least one polar group selected from the group consisting of OP = O (OM) ₂ , wherein M represents hydrogen or an alkali metal. recoding media. 8. At least a magnetic powder and a number average molecular weight of 1
A magnetic coating formed by dispersing a polyurethane resin A having a number average molecular weight of 21,000 to 50,000 and a binder resin containing a polyurethane resin B having a number average molecular weight of 21,000 to 50,000 in a solvent is coated on a support to form a magnetic layer coating film. And a step of performing an orientation treatment by a magnetic field before the coating film is dried, and a step of further performing a calendar treatment,
A method for manufacturing a magnetic recording medium, wherein each step is performed in this order. 9. The method according to claim 1, further comprising, before the step of forming the coating film of the magnetic layer, a step of applying a coating material for forming an intermediate layer on the support to form a coating film of the intermediate layer. The method for manufacturing a magnetic recording medium according to claim 8, wherein 10. The magnetic recording according to claim 9, wherein the intermediate layer forming coating material is a coating material obtained by dispersing a binder system containing a polyurethane resin having a number average molecular weight of 10,000 to 50,000 in a solvent. The method of manufacturing the medium.