JPH09167333A - Magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attain an excellent travelling property and to increase the output by forming a back coat layer so as to contain a acicular Mn-containing magnetic iron oxide powder in a magnetic recording medium having a magnetic layer and the back coat layer. SOLUTION: The magnetic recording medium 1 has a supporting body 2, the magnetic layer 3 provided on the surface of the supporting body 2 and the back coat layer 4 provided on the rear side of the supporting body 2. And, an intermediate layer 5 is provided at need between the supporting body 2 and the magnetic layer 3. In this constitution, the back coat layer 4 provided on the rear side of the supporting body 2 is a layer formed by applying a back coating material on the supporting body 2. The back coating material is a coating material containing a Mn-containing non-magnetic iron oxide powder having a specific form and concretely a coating material consisting essentially of the Mn-containing non-magnetic iron oxide powder, a binder and a solvent is preferably used.

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 having excellent light-shielding properties, running properties, antistatic properties and electromagnetic conversion characteristics.

[0002]

2. Description of the Related Art A magnetic recording medium is formed by providing a magnetic layer on the surface side of a support. For the purpose of increasing the light-shielding property and further imparting appropriate conductivity to suppress adhesion of dust due to charging, various types in which a back coat layer is provided on the back side of the support have been proposed. . In particular, with the recent demand for higher density, the entire magnetic recording medium or the magnetic layer has become thinner, and the above-mentioned properties of the back coat layer have become important.

[0003] However, in the conventional back coat layer, a back coat layer mainly composed of carbon black and a binder has been frequently used, but the carbon black has a high oil absorption and its content cannot be increased much. Therefore, the conventionally proposed magnetic recording medium has a problem that the rigidity (so-called “stiffness”) does not increase, and it is difficult to obtain good contact (good head touch) between the magnetic surface and the magnetic head. Therefore, it has been proposed to increase the rigidity of the medium by adding a non-magnetic powder instead of carbon black. As an example of the disclosure of adding a powder other than carbon black to the back coat layer, Japanese Patent Application Laid-Open No.
30503, JP-A-57-88529, JP-A-59-14124, JP-A-59-92436
JP, JP-A-60-50619, JP-A-62-50
Japanese Patent Application Laid-Open No. 295216 and the like can be cited, but when a nonmagnetic powder is used as described above, light-shielding properties and conductivity are reduced.

It has also been proposed to add black iron oxide powder to the back coat layer.
JP-A-60-85424, JP-A-60-1799
29, JP-A-60-179934 and JP-A-62-75929. However, even with these proposals, the effect of improving the rigidity of the medium is still poor, and the surface properties of the back coat layer also tend to decrease.

In short, the conventionally proposed back coat layer cannot satisfy all of the above-mentioned running properties, light-shielding properties, conductivity, surface properties, and rigidity. Development is currently being requested.

Accordingly, an object of the present invention is to improve the running performance of a magnetic recording medium to increase the output, and to increase the light-shielding property,
It is still another object of the present invention to provide a magnetic recording medium capable of imparting appropriate conductivity and suppressing adhesion of dust due to charging.

[0007]

Means for Solving the Problems The present inventors have conducted intensive studies to solve the above-mentioned problems, and as a result, have found that a magnetic recording having a back coat layer containing a non-magnetic iron oxide powder containing Mn having a specific shape. It has been found that the medium can achieve the above object.

The present invention has been made based on the above findings, and comprises a support, a magnetic layer provided on the front side of the support, and a back coat layer provided on the back side of the support. In the magnetic recording medium having, the back coat layer,
It is an object of the present invention to provide a magnetic recording medium containing acicular Mn-containing nonmagnetic iron oxide powder.

[0009] In the present invention, the back coat layer may include:
The present invention further provides the above magnetic recording medium containing carbon black.

Further, according to the present invention, the thickness of the magnetic layer is preferably
The present invention provides the above magnetic recording medium having a thickness of 0.05 to 1.0 μm, and the magnetic layer contains a needle-like ferromagnetic metal powder and has a coercive force of 1500 to 2400 Oe. Or the magnetic layer contains a hexagonal ferrite powder, provides the magnetic recording medium having a coercive force of 1300 to 2300 Oe, and an intermediate layer is provided between the magnetic layer and the support. The magnetic layer and the intermediate layer provide the above-described magnetic recording medium, wherein the magnetic recording medium and the intermediate layer are each formed by simultaneously applying a multi-layer of a magnetic paint and an intermediate layer forming paint.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The magnetic recording medium of the present invention will be described below in detail. First, a preferred configuration of the magnetic recording medium of the present invention will be described with reference to FIG.

A magnetic recording medium 1 of the present invention shown in FIG. 1 has a support 2 and a magnetic layer 3 provided on the surface side of the support 2.
And a back coat layer 4 provided on the back side of the support 2. An intermediate layer 5 is provided between the support 2 and the magnetic layer 3 as needed.

In the magnetic recording medium of the present invention, in addition to the support, the magnetic layer, the intermediate layer, and the backcoat layer, a magnetic recording medium is further provided between the support and the intermediate layer or the backcoat layer. Other layers such as a primer layer to be used and a signal recording layer provided for recording a servo signal or the like corresponding to a hard system using a long wavelength signal may be provided. The intermediate layer may not be provided, and in this case, the magnetic layer is directly provided on the support.

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 is 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.

Examples of the polymer resin forming the flexible film or the disk include polyesters such as polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polycyclohexylene dimethylene terephthalate, and polyethylene bisphenoxycarboxylate; , Polyolefins such as polypropylene, cellulose acetate butyrate,
Cellulose derivatives such as cellulose acetate propionate, polyvinyl chloride, vinyl resins such as polyvinylidene chloride, or polyamide, polyimide, polycarbonate, polysulfone, polyetheretherketone, polyurethane, etc. Two or more can be used in combination.

In the magnetic recording medium of the present invention, the magnetic layer provided on the surface side of the support is formed by applying a magnetic paint on the support or the intermediate layer. As the magnetic paint, a paint containing the ferromagnetic powder, a binder and a solvent as main components is preferably used.

Examples of the ferromagnetic powder include a ferromagnetic metal powder mainly composed of iron and a hexagonal ferrite powder. The coercive force of the ferromagnetic metal powder is 1600 to 25
00Oe, preferably 1700-2400 Oe
Is more preferable. The coercive force of the hexagonal ferrite powder is preferably 1300 to 2300 Oe. When the coercive force of the ferromagnetic metal powder and the hexagonal ferrite powder are each less than the above lower limit, the short-wavelength output is reduced due to easy demagnetization. Is insufficient, the writing ability is insufficient, and the overwrite characteristics are further deteriorated. The saturation magnetization of the ferromagnetic metal powder is preferably from 100 to 180 emu / g, and more preferably from 110 to 160 emu / g. The saturation magnetization of the hexagonal ferrite powder is preferably 30 to 70 emu / g, and more preferably 45 to 70 emu / g.
More preferably, it is emu / g. When the saturation magnetization of the ferromagnetic metal powder and the hexagonal ferrite powder are each less than the lower limit, the magnetic flux density decreases,
If the output decreases, and if the output exceeds the above upper limit, the interaction between the magnetic powders increases, and the magnetic powders in the magnetic paint become aggregated, and it becomes difficult to obtain a desired output. , Preferably within the above range.

Therefore, the coercive force of the magnetic layer containing the ferromagnetic metal powder is preferably 1500-2400 Oe,
The coercive force of the magnetic layer containing the hexagonal ferrite powder is more preferably 1800 to 2300 Oe. Also,
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 Is preferably 1500 to 2500 Gauss, more preferably 1600 to 2500 Gauss.

The ferromagnetic metal powder has a metal content of 5
0% by weight or more, and 60% by weight or more of the metal component is Fe.
The ferromagnetic metal powder which is 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 0.2 μm. The preferred acicular ratio is 3 to 20, and the preferred X-ray particle size is 130 to 250 °.
It is.

As the hexagonal ferrite powder, fine tabular barium ferrite and strontium ferrite, and some of their Fe atoms are Ti and C.
magnetic powders substituted with atoms such as o, Ni, Zn, V, and the like. Further, the hexagonal ferrite powder preferably has a plate diameter of 0.01 to 0.08 μm and a plate ratio of 2 to 7.

In addition, the magnetic powder may include, if necessary,
Rare earth elements and transition metal elements can be included. In the present invention, the magnetic powder may be subjected to a surface treatment in order to improve the dispersibility and the like of the magnetic powder. The above-mentioned surface treatment is described in the section "Characterization of Powder
Surfaces ": a method similar to the method described in Academic Press and the like, for example, a method of coating the surface of the magnetic powder with an inorganic oxide.
In this case, the inorganic oxide that can be used includes Al ₂ O ₃ , SiO ₂ , TiO ₂ , ZrO ₂ , and Sn.
O ₂ , Sb ₂ O ₃ , ZnO and the like can be mentioned, and when used, they can be used alone or as a mixture of two or more kinds. The surface treatment can be performed by an organic treatment such as a silane coupling treatment, a titanium coupling treatment, and an alumina coupling treatment, in addition to the above method.

The binder used in the present invention includes a thermoplastic resin, a thermosetting resin, and a reactive resin. When used, they can be used alone or as a mixture. Specific examples of the binder include:
Examples thereof include vinyl chloride-based resins, polyesters, polyurethanes, nitrocellulose, epoxy resins, and the like. In addition, JP-A-57-162128, page 2, upper right column 1
Resins and the like described in line 9 to page 2, lower right column, line 19 and the like can be mentioned. Further, the binder may contain a polar group for improving dispersibility and the like.

Examples of the solvent include ketone solvents, ester solvents, ether solvents, aromatic hydrocarbon solvents, chlorinated hydrocarbon solvents, and the like. Solvents described in JP-A-57-162128, page 3, lower right column, line 17 to page 4, lower left column, line 10 can be used. The amount of the solvent used is preferably 80 to 500 parts by weight, more preferably 100 to 350 parts by weight, based on 100 parts by weight of the ferromagnetic powder.

In addition, additives commonly used in magnetic recording media such as dispersants, lubricants, abrasives, antistatic agents, rust inhibitors, antifungal agents, and hardeners are added to the magnetic paint. It can be added as needed. As the above additives,
Specifically, it is described in page 2, upper left column, line 6 to page 2, upper right column, line 10 and page 3, upper left column, line 6 to page 3, upper right column, line 18 of JP-A-57-162128. And various additives.

In order to prepare the magnetic coating, 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 And a method of mixing the remaining solvent.

The thickness of the magnetic layer is 0.05 to 1.0.
μm, more preferably 0.05 to 0.8 μm, and most preferably 0.05 to 0.5 μm. If the thickness is less than 0.05 μm, uniform coating becomes difficult, and the durability may decrease. If the thickness exceeds 1.0 μm, the thickness loss increases, the high-frequency output decreases, and the overwrite characteristics are extremely poor. Therefore, it is preferable to be within the above range.

The magnetic layer has a thickness of 0.05 to 0.05.
When the thickness is 0.5 μm, the magnetic layer contains the acicular ferromagnetic metal powder and has a coercive force of 1500 to 240.
It is preferably 0 Oe or contains the above hexagonal ferrite powder, and has a coercive force of 1300 to 2300 Oe. The thickness of the magnetic layer is 0.05 to 0.5 μm.
When m, an intermediate layer is provided between the magnetic layer and the support, and the magnetic layer and the intermediate layer are respectively referred to as a magnetic paint and a paint for forming an intermediate layer (described later). It is preferable to form by simultaneous multi-layer coating.

In the present invention, the back coat layer provided on the back side of the support is a layer formed by applying a back coat paint on the support. The backcoat paint is a paint containing Mn-containing nonmagnetic iron oxide powder of a specific shape, and specifically, a paint mainly containing Mn-containing nonmagnetic iron oxide powder, a binder and a solvent is preferably used.

The specific shape of the Mn-containing nonmagnetic iron oxide powder is acicular. Those having no needle shape have a poor rigidity improving effect, and further, the surface smoothness of the surface of the obtained back coat layer becomes insufficient. Here, “needle-shaped” means a shape having a major axis length of preferably 0.05 to 0.2 μm and an axial ratio of preferably 5 to 15. Further, the above Mn
The specific surface area S _BET of the contained nonmagnetic iron oxide powder is preferably from 20 to 100 m ² / g. The Mn content in the Mn-containing nonmagnetic iron oxide powder is preferably 10 to 500 parts by weight with respect to 100 parts by weight of Fe. As the Mn-containing nonmagnetic iron oxide powder, “PA-
Commercially available products such as "8192M" and "PA-8301M" (both trade names, Sakai Chemical Industry Co., Ltd.) can also be used.

It is preferable that the back coat layer further contains carbon black, since the light shielding property and the conductivity can be further improved. Therefore, the back coat paint preferably contains the carbon black. The carbon black that can be used at this time can be used without any particular limitation as long as it is generally used for a magnetic recording medium, but has a primary particle diameter of 5 to 150 nm and a specific surface area S _BET of 12 to 100.
0m ² / g, oil absorption DBP value is 40 ~ 300ml / 10
The weight is preferably 0 g, and commercially available furnace black and acetylene black for color and conductivity can be used.

When the carbon black is used in combination, the mixing ratio of the carbon black and the Mn-containing nonmagnetic iron oxide powder is as follows: carbon black: Mn-containing nonmagnetic iron oxide powder (weight ratio) = 5: 95 to 95: It is preferably 5 and more preferably 5:95 to 90:10. If the compounding ratio of the carbon black is less than 5, the electric resistance of the medium increases, and if it exceeds 95, the rigidity of the medium tends to decrease.

Examples of the binder include a thermoplastic resin, a thermosetting resin, and a reactive resin. When used, they can be used alone or as a mixture.
Specific examples of the binder include vinyl chloride resins,
Polyester, polyurethane, nitrocellulose, epoxy resin, etc .;
No. 2128, page 2, upper right column, line 19 to page 2, lower right column 1
Resins and the like described in line 9 are exemplified. further,
The binder may contain a polar group for improving dispersibility and the like. The amount of the binder used is about 5 parts by weight per 100 parts by weight of the Mn-containing nonmagnetic iron oxide powder (when carbon black is used, the total amount with the carbon black).
The amount is preferably from 400 to 400 parts by weight, particularly preferably from 10 to 300 parts by weight.

Examples of the solvent include ketone solvents, ester solvents, ether solvents, aromatic hydrocarbon solvents, chlorinated hydrocarbon solvents, and the like. Solvents described in JP-A-57-162128, page 3, lower right column, line 17 to page 4, lower left column, line 10 can be used. The amount of the solvent to be used is preferably 150 to 1000 parts by weight with respect to 100 parts by weight of the Mn-containing nonmagnetic iron oxide powder (when carbon black is used, the total amount with the carbon black).
0 to 700 parts by weight is more preferred.

In addition, the back coat paint includes an inorganic powder such as an abrasive; a dispersant; a lubricant; an antistatic agent;
Additives, such as an antifungal agent and a curing agent, which are usually used in a back coat layer of a magnetic recording medium can be added as needed.

In order to prepare the above back coat paint, for example, the above Mn-containing nonmagnetic iron oxide powder and the above binder together with a part of the solvent are put into a Nauta mixer or the like and premixed to obtain a mixture. The mixture is kneaded by a continuous twin-screw extruder or the like, then diluted with a part of the solvent and subjected to a dispersion treatment using a sand mill or the like, and then additives such as a lubricant are mixed and filtered, and polyisocyanate is further added. It can be easily obtained by a method of mixing a curing agent such as the above and the remaining solvent.

The thickness of the back coat layer is 0.1 to 5
μm, more preferably 0.2 to 3 μm. When the thickness is less than 0.1 μm, uniform coating becomes difficult, and the durability may decrease. When the thickness exceeds 5 μm, cupping, curling, or the like occurs, the head contact becomes poor, and the envelope characteristics may be significantly reduced. Therefore, it is preferable to be within the above range.

In the present invention, the intermediate layer optionally provided between the support and the magnetic layer includes an intermediate non-magnetic layer and an intermediate magnetic layer.

The intermediate non-magnetic layer is a layer formed by applying a non-magnetic paint on the support, and the non-magnetic paint is a paint comprising a non-magnetic powder, a binder and a solvent, or A paint comprising an agent and the above solvent is preferably used. The non-magnetic powder is not particularly limited as long as it is non-magnetic, but titanium oxide, zinc oxide, calcium oxide,
Metal oxide powders such as magnesium oxide, cerium oxide, non-magnetic chromium oxide, and non-magnetic iron oxide; carbon black, graphite, barium sulfate, zinc sulfide, magnesium carbonate, calcium carbonate, tungsten disulfide,
Molybdenum disulfide, boron nitride, tin dioxide, silicon dioxide, alumina, silicon carbide, corundum, artificial diamond, garnet, garnet, quartzite, silicon nitride, molybdenum carbide, boron carbide, tungsten carbide, titanium carbide, diatomaceous earth, dolomite And other non-magnetic powders such as resinous powders, among others, carbon black, titanium oxide, barium sulfate, calcium carbonate, alumina,
Nonmagnetic iron oxide (α-Fe ₂ O ₃ ) or the like is preferably used, and when used, one kind or a mixture of two or more kinds may be used. The above-mentioned non-magnetic powder may be subjected to the above-mentioned surface treatment in order to improve the dispersibility of the non-magnetic powder.

When a nonmagnetic powder is contained in the intermediate nonmagnetic layer, the particle diameter of the nonmagnetic powder is preferably 0.001 to 3 μm, more preferably 0.005 to 1 μm.
m, most preferably 0.005 to 0.5 μm. The non-magnetic powder is preferably contained in the intermediate non-magnetic layer formed by applying the non-magnetic paint in an amount of 5 to 99% by weight, more preferably 30 to 95% by weight, and most preferably 50 to 95% by weight. It is desirable to mix it in the above-mentioned non-magnetic paint so that it is contained by weight%.

As the binder and the solvent, the same binders and solvents as those used in the magnetic paint can be used as appropriate. Further, the same additives as those used for the magnetic paint can be appropriately added to the non-magnetic paint as needed.

To prepare the above non-magnetic paint, for example,
The nonmagnetic powder, the binder and the fatty acid together with a part of the solvent are charged into a Nauter mixer or the like to be premixed to obtain a mixture, and the obtained mixture is kneaded by a continuous twin-screw extruder or the like, and then, After diluting it with a part of the solvent and subjecting it to dispersion treatment using a sand mill or the like, mixing additives such as a lubricant, filtering, and further mixing the remaining solvent and curing agent may be mentioned. it can.

The thickness of the intermediate non-magnetic layer is preferably 0.2 to 5 μm.

The intermediate magnetic layer provided as an intermediate layer in the present invention is a layer formed by applying an intermediate magnetic coating on the support, and the intermediate magnetic coating includes a ferromagnetic powder, a binder and a binder. A paint containing a solvent as a main component can be preferably used.

The ferromagnetic powder includes hard magnetic powder and soft magnetic powder. 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, Mn-Zn ferrite and N
i-Zn ferrite is preferred. Also, when using
Can be used alone, but
More than one species may be used in combination.

Further, as the soft magnetic powder, Fe-S
i alloy, Fe-Al alloy (Alperm, Alfenol, Alfer), permalloy (Ni-Fe-based binary alloy, and Mo,
Multi-component alloys containing Cu, Cr, etc.), sendust (Fe-Si-Al [9.6% by weight of Si, 5.4% of Al, the balance being Fe]), Fe-Co alloys, etc. Metal soft magnetic powders can also be mentioned. In use, one kind thereof can be used alone, or two or more kinds thereof can be used in combination.

The coercive force of the oxide soft magnetic powder is usually 0.1 to 150 Oe, and the saturation magnetization thereof is usually 30 to 9 Oe.
0 emu / g. The coercive force of the metal soft magnetic powder is usually 0.02 to 100 Oe, and the saturation magnetization is usually 50 to 100 Oe.
~ 500 emu / g. In particular, in the present invention, a spinel-type ferrite powder having a coercive force of less than 150 Oe can be preferably used. That is, in the present invention, the intermediate magnetic layer preferably has a spinel-type ferrite powder having a coercive force of less than 150 Oe. The soft magnetic powder preferably has a particle size of 1 nm to 1 μm, more preferably 1 nm to 500 nm.

The coercive force of the intermediate magnetic layer is 600 to 2200 when the hard magnetic powder is used as the ferromagnetic powder.
Oe is preferable, and when the above soft magnetic powder is used as the ferromagnetic powder, it is preferably less than 180 Oe. When the hard magnetic powder is used as the ferromagnetic powder, the saturation magnetic flux density of the intermediate magnetic layer is 1500 to 4%.
It is preferably 2,000 gauss, and preferably 500 to 2,200 gauss when the above soft magnetic powder is used as the ferromagnetic powder.

The binder and the solvent used in the intermediate magnetic paint can be the same as the binder and the solvent used in the magnetic paint. In addition, the same additives as those used in the magnetic paint can be appropriately used in the intermediate magnetic paint, and non-magnetic powder used in the non-magnetic paint can also be added.

Further, the compounding ratio of the binder in the intermediate magnetic paint is 5 with respect to 100 parts by weight of the total amount of the ferromagnetic powder and the non-magnetic powder optionally added.
The amount is preferably from 200 to 200 parts by weight, more preferably from 5 to 100 parts by weight. The mixing ratio of the solvent in the intermediate magnetic paint was 8 parts by weight with respect to 100 parts by weight of the ferromagnetic powder.
0 to 500 parts by weight is preferable, and 100 to 350 parts by weight is more preferable.

When the intermediate magnetic layer is provided, the thickness is preferably 0.2 to 5 μm, and 0.5 to 4 μm.
More preferably, it is most preferably 0.5 to 2.5 μm. If it is less than 0.2 μm, the rigidity of the obtained magnetic recording medium is low, and if it exceeds 5 μm,
Curling or cupping occurs, the head contact is reduced and the output is reduced, and the overwrite characteristics are reduced.

The intermediate layer is not limited to a single layer. The intermediate layer has a multilayer structure of two or more layers formed by combining the intermediate nonmagnetic layer and the intermediate magnetic layer in an arbitrary configuration. You can also.

The magnetic recording medium of the present invention is suitable as a magnetic tape such as an 8 mm video tape or a DAT tape, but can also be applied as another magnetic recording medium such as a floppy disk.

Next, an outline of a method for manufacturing the magnetic recording medium of the present invention will be described. In the following description, a case where an intermediate layer is provided will be described. When the intermediate layer is not provided, that is, when the magnetic layer is directly provided on the support, the magnetic layer can be easily manufactured according to a generally known manufacturing method. In order to manufacture the magnetic recording medium of the present invention, first, the magnetic paint and the intermediate non-magnetic paint or the intermediate magnetic paint (hereinafter referred to as “intermediate layer forming paint”) are collectively referred to as Is applied by simultaneous multilayer coating such as a wet-on-wet method. Next, after applying the magnetic field orientation treatment to the formed magnetic layer and intermediate layer coating film, a drying treatment is performed, and thereafter, a calendering treatment is performed if necessary, and then the film is wound up.
Further, a back coat layer is formed. Then, if necessary, for example, to obtain a magnetic tape, 40 to 70 ° C.
Under the aging treatment for 6 to 72 hours, slit to a desired width.

The above simultaneous multi-layer coating method is disclosed in JP-A-5-73.
No. 883, column 42, line 31 to column 43, line 31, etc., which is a method of applying the magnetic coating material for forming the magnetic layer before the intermediate layer forming coating material dries. Therefore, since the interface between the magnetic layer and the intermediate layer is smooth and the surface properties of the magnetic layer are also good,
A magnetic recording medium with little dropout, capable of coping with high-density recording, and having excellent durability of the coating film (magnetic layer and nonmagnetic layer) can be obtained.

The magnetic field orientation treatment is performed before the magnetic paint and the intermediate layer are dried. For example, when the magnetic recording medium of the present invention is a magnetic tape, the magnetic paint is applied to the coated surface of the magnetic paint. A method in which a magnetic field of about 500 Oe or more, preferably about 1000 to 10000 Oe is applied in a parallel direction, or a method in which the magnetic paint and the intermediate layer forming paint pass through a solenoid of 1000 to 10000 Oe in a wet state. And the like.

The drying treatment is carried out, for example, at 30 to 120 ° C.
The heating can be performed by supplying the gas heated to the above temperature. At this time, the drying degree of the coating film can be controlled by controlling the temperature of the gas and the supply amount thereof.

The calendering treatment can be performed by a super calendering method in which a metal roll and a cotton roll or a synthetic resin roll, a metal roll and a metal roll are passed between two rolls. Also,
The conditions of the calender treatment are as follows: the roll surface temperature is 60 to 1;
At 40 ° C., the roll linear pressure can be 100 to 500 kg / cm.

The back coat layer can be easily formed by applying the back coat paint to the back surface of the support (the surface on which the magnetic layer is not provided).

In the production of the magnetic recording medium of the present invention, a finishing step such as a polishing or cleaning step for the surface of the magnetic layer can be performed, if necessary. The magnetic coating material and the intermediate layer-forming coating material can be applied by a generally known sequential multi-layer coating method.

[0061]

Next, 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 Using a magnetic coating material A having the following composition and a non-magnetic coating material (a) having the following composition, and using a back coating material A having the following composition as a back coating material, Manufacturing method], a non-magnetic layer as an intermediate layer is formed by the non-magnetic paint (a) shown in [Table 1], and a magnetic layer as the uppermost layer is formed by the magnetic paint A. Thus, a magnetic tape as a magnetic recording medium was obtained. When the coercive force and the saturation magnetic flux density of the magnetic layer formed using the magnetic paint A were measured according to the [measurement method] described later, the coercive force was 1890 Oe and the saturation magnetic flux density was 3540 gauss. Was.

Magnetic coating A : 100 parts by weight of acicular ferromagnetic metal powder mainly composed of iron Fe: Al: Ba: Si: Ni: Co (weight ratio) = 88: 2: 1: 1: 3: 5 Magnetic force: 1840 Oe, saturation magnetization: 134 emu / g Average major axis length: 0.12 μm, specific surface area: 58 m ² / g X-ray particle size: 150Å 8 parts by weight of “AKP-50” [trade name, Sumitomo Chemical Co., Ltd. 2) parts by weight of "Raven 1060" [trade name, carbon black manufactured by Columbian Chemicals Company]-10 parts by weight of "MR-110" [trade name, manufactured by Zeon Corporation, containing sulfonic acid group] Vinyl chloride polymer] 23 parts by weight of "Vylon UR-8200" [Trade name, Toyobo Co., Ltd., sulfonic acid group-containing polyurethane resin] 2 parts by weight of 2-ethylhexyl stearate 2 palmitic acid The amount part, "Coronate L" 4 parts by weight of [trade name, Nippon Polyurethane Industry Co., Ltd., a polyisocyanate compound] Methyl ethyl ketone 132 parts by weight Toluene 88 parts by weight of cyclohexanone 44 parts by weight

Nonmagnetic paint (a) 100 parts by weight of needle-like α-Fe ₂ O ₃ Long axis length 0.12 μm, needle ratio 8 ・ 2 parts by weight of “Conductex SC” [trade name, manufactured by Columbia Chemicals Company] Carbon black]-"MR-110" 10 parts by weight [trade name, manufactured by Nippon Zeon Co., Ltd., sulfonic acid group-containing vinyl chloride polymer]-"Byron UR-8200" 23 parts by weight [trade name, Toyobo Co., Ltd.] Sulfonic acid group-containing polyurethane resin manufactured by Co., Ltd.] 2 parts by weight of 2-ethylhexyl stearate 1 part by weight of palmitic acid 4 parts by weight of "Coronate L" [trade name, manufactured by Nippon Polyurethane Industry Co., Ltd., polyisocyanate compound] 96 parts by weight of methyl ethyl ketone 64 parts by weight of toluene 32 parts by weight of cyclohexanone

(Blending of backcoat paint A) 80 parts by weight of "PA-8301M" [trade name, Mn-containing needle-shaped nonmagnetic iron oxide powder, manufactured by Sakai Chemical Industry Co., Ltd .; 12 μm, needle ratio 10] 20 parts by weight of “Raven 1255” [trade name: carbon black manufactured by Columbian Chemicals Company] 15 parts by weight of “MR-110” [trade name: sulfonic acid group manufactured by Nippon Zeon Co., Ltd.] -Containing vinyl chloride-based copolymer]-"Vylon UR-8200" 50 parts by weight [Product name; polyurethane resin containing sulfonic acid group, manufactured by Toyobo Co., Ltd.]-"Coronate HX" 5 parts by weight [Product name: Nippon Polyurethane Polyisocyanate manufactured by Kogyo Co., Ltd.] 1 part by weight of 2-ethylhexyl stearate 1 part by weight of palmitic acid 210 parts by weight of methyl ethyl ketone 140 parts by weight of toluene 70 parts by weight of cyclohexanone

[Manufacture of Magnetic Recording Medium] The dry thickness of the magnetic paint A is 0.3 μm on the surface of a polyethylene naphthalate film having a thickness of 6 μm, and the non-magnetic paint (a) is used.
The line speed is set to 100 so that the dry thickness becomes 2.2 μm.
The magnetic coating material A and the nonmagnetic coating material (a) were applied at a rate of m / min by a simultaneous multilayer coating method to form a coating film of a magnetic layer and a nonmagnetic layer as an intermediate layer. Next, the coating film was passed through a 5000 Oe solenoid in a wet state to perform a magnetic field orientation treatment, and was dried for 30 seconds in a drying furnace in which hot air at a temperature of 90 ° C. was supplied at a wind speed of 15 m / sec. Next, a calender treatment was performed under the conditions of a roll surface temperature of 90 ° C. and a roll linear pressure of 350 kg / cm to form a magnetic layer and an intermediate layer, followed by winding. Then, a back coat paint is applied on the back surface of the non-magnetic support so that the dry thickness becomes 0.5 μm, and 90 ° C.
And dried. After this, 8mm width, 12
The tape was cut to a recording length (106 m) for 0 minutes to obtain a magnetic tape, and the obtained magnetic tape was loaded into a cassette case for an 8 mm VTR to produce an 8 mm VTR cassette.
The coating and calendering were performed on the same line (in-line method).

The magnetic tape as the obtained magnetic recording medium was evaluated for light transmittance, surface electric resistance of the back coat layer, C / N characteristics, and surface roughness of the back coat layer and the magnetic layer as described below. The results are shown in [Table 1].

[Measurement method] ◎ Coercive force and saturation magnetic flux density For the magnetic layer coated on the non-magnetic support and the intermediate layer, only the magnetic layer was separated from the non-magnetic support and the intermediate layer using an adhesive tape. Is peeled off, the magnetic layer is punched into a predetermined size and shape, and an applied magnetic field of 10 k is applied using a vibrating magnetometer.
In Oe, the coercive force and the saturation magnetic flux density were measured, respectively.

◎ Light transmittance EUROPEAN COMPUTER MANUFACTURERS ASSOCIATION (ECMA)
According to Annex D of STANDARD ECMA-139 (June 1990), which is a collection of specifications, a light source of 850 nm ± 50 nm was used. ◎ Surface electrical resistance EUROPEAN COMPUTER MANUFACTURERS ASSOCIATION (ECMA)
STANDARD ECMA-170 "Electrical Resista"
nce of Coated Surfaces ". In this method, the surface electric resistance ρ
Is calculated by ρ = rw / l, where w is the width of the magnetic tape, l is the electrode spacing, and r is the measured resistance value. The measurement of the light transmittance and the surface electric resistance was 3.81 mm
It measured using the magnetic tape obtained by slitting to width. ◎ C / N characteristics (Evaluation of 8mm cassette) Using an 8mm video deck modified from a commercially available Hi8 deck, a single 9MHz wave was recorded, the reproduction output (C) was observed with a spectrum analyzer, and the noise level was 8MHz noise. C / N was expressed as the level (N).

Surface roughness Center line surface roughness Ra of the surface of the back coat layer and the magnetic layer The obtained magnetic recording medium was manufactured by Tokyo Seimitsu Co., Ltd.
Using a surface roughness shape measuring instrument "Surfcom 553A", center line surface roughness Ra under the conditions of a needle radius of 2 μm, a load of 30 mg, a magnification of 200,000, and a cutoff of 0.08 mm.
Was measured. The center line surface roughness Ra is obtained by extracting a portion of the measurement length L from the roughness curve in the direction of the center line, setting the center line of the extracted portion as the X axis and the direction of the longitudinal magnification as the Y axis. Is represented by y = f (x), the value obtained by the following equation is represented by [nm].

[0071]

[Equation 1]

Comparative Example 1 A magnetic tape was obtained in the same manner as in Example 1 except that the following back coat paint B was used instead of the back coat paint A, and the obtained magnetic tape was the same as in Example 1. evaluated. The results are shown in [Table 1]. [Blending of back coat paint B] Same as back coat paint A except that the following needle-like α-Fe ₂ O ₃ powder containing no Mn was used instead of “PA-8301M”.・ Acicular α-Fe ₂ O ₃ powder (major axis length 0.14 μm, acicular ratio 10, specific surface area 56 m ² / g)

Comparative Example 2 A magnetic tape was obtained in the same manner as in Example 1 except that the following back coat paint C was used in place of the back coat paint A, and the obtained magnetic tape was the same as in Example 1. evaluated. The results are shown in [Table 1]. [Blending of backcoat paint C]-100 parts by weight of "Raven 1255" [trade name: carbon black manufactured by Columbian Chemicals Company]-15 parts by weight of "MR-110" [trade name: sulfonic acid, manufactured by Zeon Corporation of Japan] Group-containing vinyl chloride copolymer]-"Vylon UR-8200" 50 parts by weight [trade name; Toyobo Co., Ltd., sulfonic acid group-containing polyurethane resin]-"Coronate HX" 5 parts by weight [trade name; Japan Polyisocyanate manufactured by Polyurethane Industry Co., Ltd.] 1 part by weight of 2-ethylhexyl stearate 1 part by weight of palmitic acid 360 parts by weight of methyl ethyl ketone 240 parts by weight of toluene 120 parts by weight of cyclohexanone

Comparative Example 3 A magnetic tape was obtained in the same manner as in Example 1 except that the following back coat paint D was used in place of the back coat paint A, and the obtained magnetic tape was the same as in Example 1. evaluated. The results are shown in [Table 1]. [Blending of back coat paint D]-100 parts by weight of "Raven 1255" [trade name: carbon black manufactured by Columbian Chemicals Company]-50 parts by weight of "MR-110" [trade name: sulfonic acid, manufactured by Zeon Corporation of Japan] Group-containing vinyl chloride copolymer]-"Vylon UR-8200" 167 parts by weight [trade name; Toyobo Co., Ltd., sulfonic acid group-containing polyurethane resin]-"Coronate HX" 10 parts by weight [trade name; Japan Polyisocyanate manufactured by Polyurethane Industry Co., Ltd.] 2 parts by weight of 2-ethylhexyl stearate 1 part by weight of palmitic acid 480 parts by weight of methyl ethyl ketone 320 parts by weight of toluene 160 parts by weight of cyclohexanone

Comparative Example 4 A magnetic tape was obtained in the same manner as in Example 1 except that the following back coat paint F was used in place of the back coat paint A, and the obtained magnetic tape was the same as in Example 1. evaluated. The results are shown in [Table 1]. [Blending of backcoat paint F] "Dipoxide color # 9550" (trade name, manufactured by Dainichi Seika Co., Ltd., granular black oxide containing Cu, Fe and Mn) instead of "PA-8301M" Powder coating, specific surface area 28 m ² / g, average particle size 0.1 μm], except that the above-mentioned back coat paint A was used.

[0076]

[Table 1]

[Example 2] A magnetic tape was obtained in the same manner as in Example 1 except that the following intermediate magnetic paint Q was used in place of the non-magnetic paint (a). Was evaluated in the same way as The results are shown in [Table 2]. [Intermediate magnetic paint Q] 100 parts by weight of acicular Co-containing FeOx powder (1.33 <x <1.5) Saturation magnetization; 84 emu / g Coercive force; 890 Oe Average particle size; 0.18 μm Axis ratio; 10 Specific surface area 41 m ² / g 3 parts by weight of HIT-80 [trade name: alumina powder manufactured by Sumitomo Chemical Co., Ltd.] 2 parts by weight of Conductex SC [trade name: carbon black manufactured by Columbian Chemicals Company] ・ MR- 110 "12 parts by weight [trade name; vinyl chloride copolymer containing sulfonic acid group, manufactured by Nippon Zeon Co., Ltd.] 26 parts by weight of" Byron UR-8200 "[trade name: sulfonic acid, manufactured by Toyobo Co., Ltd.] Group-containing polyurethane resin]-1 part by weight of 2-ethylhexyl palmitate-1 part by weight of butoxyethyl palmitate-4 parts by weight of polyisocyanate [Nippon Polyurethane Industry ( ) Ltd., trade name "Coronate HX"] Methyl ethyl ketone 90 parts by weight Toluene 60 parts by weight of cyclohexanone, 30 parts by weight

Example 3 A magnetic tape was obtained in the same manner as in Example 2 except that the following magnetic paint B was used in place of the magnetic paint A, and the obtained magnetic tape was evaluated in the same manner as in Example 1. did. The results are shown in [Table 2]. The coercive force of the magnetic layer is 1740 Oe, and the saturation magnetic flux density is 2020.
Gauss was. Magnetic paint B · Hexagonal ferrite powder 100 parts by weight (hexagonal plate-shaped Co—Ti-substituted barium ferrite powder) Coercive force: 1670 Oe, saturation magnetization: 56 emu / g Average plate diameter: 0.04 μm, plate ratio: 4 AKP-50 ”5 parts by weight [Alumina powder manufactured by Sumitomo Chemical Co., Ltd.] 2 parts by weight of“ Raven 1060 ”[Product name: carbon black manufactured by Columbian Chemicals Company] ・ MR-110 7 parts by weight Part [trade name, manufactured by Nippon Zeon Co., Ltd., sulfonic acid group-containing vinyl chloride polymer] 15 parts by weight of "Vylon UR-8200" [trade name, manufactured by Toyobo Co., Ltd., sulfonic acid group-containing polyurethane resin]・ 1.5 parts by weight of 2-ethylhexyl stearate ・ 1.5 parts by weight of palmitic acid ・ 4 parts by weight of “Coronate L” [trade name, manufactured by Nippon Polyurethane Industry Co., Ltd.] Polyisocyanate Compound] Methyl ethyl ketone 96 parts Toluene 64 parts Cyclohexanone 32 parts by weight

Comparative Example 5 A magnetic tape was obtained in the same manner as in Example 3 except that the following backcoat paint E was used in place of the backcoat paint A, and the obtained magnetic tape was treated in the same manner as in Example 1. evaluated. The results are shown in [Table 2]. [Blending of backcoat paint E] Same as backcoat paint A except that the following plate-like α-Fe ₂ O ₃ powder containing no Mn was used in place of “PA-8301M”.・ Plate-like α-Fe ₂ O ₃ powder (plate diameter 0.03 μm, plate ratio 4, specific surface area 40 m ² / g)

Comparative Example 6 A magnetic tape was obtained in the same manner as in Example 3 except that the backcoat paint D was used in place of the backcoat paint A, and the obtained magnetic tape was the same as in Example 1. evaluated. The results are shown in [Table 2].

Comparative Example 7 A magnetic tape was obtained in the same manner as in Example 2 except that the following back coat paint G was used in place of the back coat paint A, and the obtained magnetic tape was the same as in Example 1. evaluated. The results are shown in [Table 2]. [Blending of backcoat paint G] Instead of "PA-8301M", "Dipiroxide Color # 9510" (trade name, manufactured by Dainichi Seika Co., Ltd., granular black oxide containing Co, Fe and Cr) Powder, specific surface area 2.0 m ² / g, average particle size 2.4 μm].

[0082]

[Table 2]

[0083]

According to the magnetic recording medium of the present invention, the running performance of the magnetic recording medium is improved to increase the output, the light-shielding property is enhanced, the control in the running system is improved, and the appropriate conductivity is further improved. It is possible to suppress adhesion of dust due to charging.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view showing the structure of a magnetic recording medium of the present invention.

Claims (6)

[Claims] 1. A magnetic recording medium having a support, a magnetic layer provided on the front surface side of the support, and a backcoat layer provided on the back surface side of the support, wherein the backcoat layer comprises: A magnetic recording medium comprising a needle-shaped Mn-containing non-magnetic iron oxide powder. 2. The magnetic recording medium according to claim 1, wherein the back coat layer further contains carbon black. 3. The thickness of the magnetic layer is 0.05 to 1.0.
2. The magnetic recording medium according to claim 1, wherein the diameter of the magnetic recording medium is μm. 4. The magnetic recording medium according to claim 3, wherein the magnetic layer contains acicular ferromagnetic metal powder and has a coercive force of 1500 to 2400 Oe. 5. The magnetic recording medium according to claim 3, wherein the magnetic layer contains hexagonal ferrite powder and has a coercive force of 1300 to 2300 Oe. 6. An intermediate layer is provided between the magnetic layer and the support, and the magnetic layer and the intermediate layer are respectively formed.
4. The magnetic recording medium according to claim 3, wherein the magnetic coating material and the intermediate layer forming coating material are formed by simultaneous multi-layer coating.