JPH09198650A - Magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the traveling property, output and light shieldability and to suppress the adhesion of dust by electrification by providing the rear surface side of a base provided with a magnetic layer on its front surface side with a back coating layer contg. magnetite powder having a specified plate diameter and plate shape ratio. SOLUTION: The front surface side of the base 2 is provided with an intermediate layer 5 and the magnetic layer 3 in this order and the rear surface side thereof is provided with the back coating layer 4 contg. the magnetite powder having the plate diameter of 0.05 to 2.0μm and the plate shape ratio of 3 to 40 and carbon black. The thickness of the layer 3 is specified to 0.05 to 1.0μm. Acicular ferromagnetic metallic powder having coercive force of 1500 to 2400 Oe or hexagonal ferrite powder having coercive force of 1300 to 2300 Oe is incorporated into the layer. The magnetic recording medium 1 composed of such base 2 and the layers 3 to 5 is improved in rigidity and is improved in the electrical conductivity of the layer 4 as well. As a result, the traveling property is improved, the output is enhanced and the light shieldability is enhanced, thereby, the control of the traveling system is improved and the adhesion of the dust by electrification is suppressed.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a light-shielding property, a running property,
The present invention relates to a magnetic recording medium excellent in both antistatic property and electromagnetic conversion property.

[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, JP-A-62-75929, and the like, and the addition of granular magnetite to the back coat layer is also proposed. JP-A-58-199437, JP-A-58-200429 and the like can be mentioned. 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 As a result of intensive studies to solve the above problems, the present inventors have found that by adding a magnetite powder having a specific shape to a back coat layer, the magnetic properties of the magnetite powder are It has been found that the rigidity of the magnetic recording medium itself is improved and the conductivity of the back coat layer is also improved irrespective of the direct relationship.

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,
The present invention provides a magnetic recording medium containing a plate-like magnetite powder.

According to the present invention, the magnetite has a plate diameter of 0.05 to 2.0 μm and a plate ratio of 3 to 4.
The above-mentioned magnetic recording medium of 0 is provided. The present invention also provides the above magnetic recording medium, wherein the back coat layer further contains 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. Further, the preferable acicular ratio is 3 to 40, and the preferable X-ray particle size is 130 to 250Å
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. The solvents described in JP-A-57-162128, page 3, lower right column, line 17 to page 4, upper 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 1.0 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 1.0 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 back coat paint is a paint containing a specific shape of magnetite powder, and specifically, a paint containing magnetite powder, a binder and a solvent as main components is preferably used.

The specific shape of the magnetite powder is a plate shape. If it is not in a plate shape, the rigidity of the magnetic recording medium cannot be improved to a desired level.

The magnetite powder has a plate diameter (average plate diameter) of preferably 0.05 to 2.0 μm, more preferably 0.08 to 1.5 μm. The plate ratio (plate diameter / plate thickness) of the magnetite powder is preferably 3 to.
40, more preferably 3 to 20. The plate diameter is
If it is less than 0.05 μm or the plate ratio is less than 3, the light-shielding property becomes insufficient, and if the plate diameter is 2.0 μm or the plate ratio exceeds 40, the surface property of the back coat layer deteriorates. However, the back coat layer may be transferred to the surface of the magnetic layer and the output may be reduced, so that the above range is preferable. The specific surface area of the magnetite powder is preferably 5 to 100 m ² / g, more preferably 1
It is 0 to 90 m ² / g. The saturation magnetization of the magnetite powder is preferably 20 to 90 emu / g, more preferably 30 to 85 emu / g. The squareness ratio of the magnetite powder is preferably 0.05 to 0.3, more preferably 0.08 to 0.25. The coercive force of the magnetite powder is preferably 10 to 200 O.
e, more preferably 20 to 150 Oe.

As the magnetite powder, an alkaline suspension containing ferric hydroxide or goethite is subjected to hydrothermal treatment using an autoclave to produce plate-like hematite particles from the aqueous solution, and the plate-like hematite particles are reduced. Plate-like magnetite powder obtained by the method of heating and reducing in a neutral gas, plate-like magnetite powder obtained by the method of rapidly oxidizing an alkaline suspension containing ferrous hydroxide with a strong oxidant, from an aqueous solution Examples of the plate-shaped magnetite powder obtained by the method of directly generating magnetite powder, the magnetite powder obtained by the method is a non-sintered and non-porous plate-shaped magnetite powder, so it is preferably used in the present invention. To be Here, the non-sintered and non-porous magnetite powder refers to a magnetite powder that does not use a reducing gas and thus does not have pores in which water molecules are removed during the reduction reaction.

Details of the method for producing the above-mentioned non-sintered and non-porous plate-like magnetite powder are described in JP-A-63-20.
1019, JP-A-1-176233, and JP-A-3-752.
28, etc., specific examples of the manufacturing method include the following manufacturing method and the like. Fe produced by reacting an aqueous solution of ferrous salt with an aqueous solution of alkali carbonate
A production method in which CO ₃ ²⁻ and Fe ²⁺ are brought to desired concentrations when oxygen is passed through an aqueous solution containing CO ₃ to oxidize it.

Further, it is preferable that the back coat layer further contains carbon black because 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 compounding ratio of the carbon black and the magnetite powder is preferably carbon black: magnetite powder (weight ratio) = 5: 95 to 95: 5, preferably 5: 9.
More preferably, it is 5 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.

The binder may be a thermoplastic resin, a thermosetting resin, a reactive resin or the like, which may 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 to 400 with respect to 100 parts by weight of the magnetite powder (the total amount of the carbon black when carbon black is used).
It is preferably in the range of 10 to 300 parts by weight, particularly preferably 10 to 300 parts by weight.

Examples of the above solvent include ketone solvents, ester solvents, ether solvents, aromatic hydrocarbon solvents, chlorinated hydrocarbon solvents, and the like. The solvents described in JP-A-57-162128, page 3, lower right column, line 17 to page 4, upper left column, line 10 can be used. The amount of the solvent used is preferably 150 to 1000 parts by weight, and 150 to 70 parts by weight, relative to 100 parts by weight of the magnetite powder (the total amount of the carbon black when carbon black is used).
0 weight part is more preferable.

In the above back coat paint, inorganic powders such as abrasives; dispersants; lubricants; antistatic agents; antirust agents;
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 magnetite powder and the binder are charged together with a part of the solvent into a Nauter mixer or the like and premixed to obtain a mixture. After kneading with a shaft extruder or the like, and then diluting with a part of the solvent and dispersing using a sand mill or the like, additives such as a lubricant are mixed and filtered, and a curing agent such as polyisocyanate or the like is added. It can be easily obtained by a method of mixing 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, examples of the intermediate layer provided between the support and the magnetic layer as required include an intermediate nonmagnetic layer and an intermediate magnetic layer.

The intermediate non-magnetic layer is a layer formed by coating a non-magnetic paint on the support, and the non-magnetic paint is a paint comprising non-magnetic powder, a binder and a solvent, or the above-mentioned binder. 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 the intermediate non-magnetic layer contains non-magnetic powder, the particle size of the non-magnetic 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 ones as those used in the above magnetic paint can be appropriately used. 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.

When the intermediate nonmagnetic layer is provided, the thickness 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 ferromagnetic powder, binder and A paint containing a solvent as a main component can be preferably used.

Examples of the ferromagnetic powder include hard magnetic powder and soft magnetic powder. Examples of the hard magnetic powder include the ferromagnetic metal powder and the hexagonal ferrite powder.

The soft magnetic powder is a spinel type powder.
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 coercive force of the above oxide soft magnetic powder is usually 0.1 to 150 Oe, and the saturation magnetization is usually 30 to 9.
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.

As the binder and the solvent used in the intermediate magnetic coating material, the same binder and solvent as those used in the magnetic coating material can be appropriately used. 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.

The blending ratio of the binder in the intermediate magnetic coating material is 5 with respect to 100 parts by weight of the total amount of the ferromagnetic powder and the non-magnetic powder added as needed.
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 above intermediate magnetic layer is provided, the thickness is preferably 0.2 to 5 μm, and 0.5 to 4
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, and has a multilayer structure of two or more layers formed by combining the intermediate nonmagnetic layer and the intermediate magnetic layer in any desired 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 the method for producing 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-mentioned 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 carried out before the magnetic coating material and the intermediate layer are dried. For example, when the magnetic recording medium of the present invention is a magnetic tape, the magnetic coating surface is coated with the magnetic coating material. And applying a magnetic field of about 500 Oe or more, preferably about 1000 to 10000 Oe in a parallel direction, or passing the magnetic paint and the intermediate layer forming paint through a solenoid magnet of 1000 to 10000 Oe in a wet state. It can be performed by a method or the like.

The above 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 coating composition to the back surface of the support (the surface on the side where the magnetic layer is not provided).

In the production of the magnetic recording medium of the present invention, finishing steps such as polishing and cleaning of the magnetic layer surface may be carried out, if necessary. The magnetic coating material and the intermediate layer-forming coating material can be applied by a generally known sequential multilayer coating method.

[0063]

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 A magnetic coating material A having the following composition and a non-magnetic coating material (a) having the following composition were used, and a back coating material A1 having the following composition was used as a back coating material. A magnetic tape is manufactured according to the manufacturing method] to form a non-magnetic layer as an intermediate layer by the non-magnetic coating material (a) shown in [Table 1], and a magnetic layer as the uppermost layer by the magnetic coating material A. A magnetic tape as a magnetic recording medium thus obtained was obtained. The coercive force and the saturation magnetic flux density of the magnetic layer formed using the magnetic paint A will be described later in [Measurement method].
The coercive force was 1890 Oe and the saturation magnetic flux density was 3540 gauss.

Magnetic paint A : acicular ferromagnetic metal powder mainly composed of iron 100 parts by weight 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 ・ "AKP-50" 8 parts by weight [Product name, Sumitomo Chemical Co., Ltd. ) Alumina powder]-"Raven 1060" 2 parts by weight [trade name, carbon black manufactured by Columbian Chemicals Company]-"MR-110" 10 parts by weight [trade name, manufactured by Zeon Corporation, containing sulfonic acid group] Vinyl chloride-based polymer] "Byron UR-8200" 23 parts by weight [Trade name, manufactured by Toyobo Co., Ltd., sulfonic acid group-containing polyurethane resin] 2-ethylhexyl stearate 2 parts by weight Palmitic acid 2 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

Non-magnetic paint (a) 100 parts by weight of needle-shaped α-Fe ₂ O ₃ 0.12 μm in major axis length, needle-shaped ratio 8 ・ 2 parts by weight of "Conductex SC" [trade name, manufactured by Columbian Chemicals Company Carbon black]-"MR-110" 10 parts by weight [trade name, manufactured by Nippon Zeon Co., Ltd., vinyl chloride polymer containing sulfonic acid group]-"Byron UR-8200" 23 parts by weight [trade name, Toyobo Co., Ltd., sulfonic acid group-containing polyurethane resin] 2-ethylhexyl stearate 2 parts by weight Palmitic acid 1 part by weight "Coronate L" 4 parts by weight [trade name, manufactured by Nippon Polyurethane Industry Co., Ltd., polyisocyanate compound] ] -Methyl ethyl ketone 96 parts by weight-Toluene 64 parts by weight-Cyclohexanone 32 parts by weight

(Blending of backcoat paint A1) “Plate magnetite powder” 80 parts by weight Plate diameter 0.4 μm, plate ratio 7, specific surface area 15 m ² / g, saturation magnetization 83 emu / g, coercive force 98 Oe Raven 1255 "20 parts by weight [trade name; carbon black manufactured by Columbian Chemicals Company] ・ MR-110" 15 parts by weight [trade name; manufactured by Nippon Zeon Co., Ltd., sulfonic acid group-containing vinyl chloride copolymer] "Byron UR-8200" 50 parts by weight [Product name: Toyobo Co., Ltd., sulfonic acid group-containing polyurethane resin] "Coronate HX" 5 parts by weight [Product name: Polyisocyanate manufactured by Nippon Polyurethane Industry Co., Ltd.] 2-ethylhexyl stearate 1 part by weight Palmitic acid 1 part by weight Methyl ethyl ketone 180 parts by weight Toluene 120 parts by weight Rohekisanon 60 parts by weight

[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, while the coating film was in a wet state, the coating film was passed through a 5000 Oe solenoid magnet for magnetic field orientation treatment, and 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.
After drying at 0 ° C., it was wound up. After this, 8mm width,
It was cut to a recording length (106 m) for 120 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 obtained magnetic tape as a magnetic recording medium was evaluated for light transmittance, surface electric resistance of the backcoat layer, C / N characteristics, and surface roughness of the backcoat layer and the magnetic layer as follows. The results are shown in [Table 1].

[Measurement Method] ◎ Coercive force and saturation magnetic flux density For the above-mentioned magnetic layer coated on the above-mentioned non-magnetic support and intermediate layer, an adhesive tape was used to remove only the magnetic layer from the non-magnetic support and intermediate layer. The magnetic layer, and 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 Ra 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].

[0073]

[Equation 1]

Example 2 Example 1 was repeated except that the following backcoat paint A2 was used instead of the backcoat paint A1.
A magnetic tape was obtained in the same manner as above, and the obtained magnetic tape was evaluated in the same manner as in Example 1. The results are shown in [Table 1]. [Blending of back coat paint A2] Back coat paint A1
The same as the back coat paint A1 except that the magnetite powder described below was used instead of the magnetite powder used in. -Plate shaped magnetite powder (plate diameter 0.8 μm, plate ratio 15, specific surface area 10 m ² /
g, saturation magnetization 86 emu / g, coercive force 105 Oe)

Comparative Example 1 A magnetic tape was obtained in the same manner as in Example 1 except that the following backcoat coating material B was used in place of the backcoat coating material A1. evaluated. The results are shown in [Table 1]. [Blending of backcoat paint B] Same as backcoat paint A1 except that the following needle-shaped α-Fe ₂ O ₃ powder was used instead of “magnetite powder”.・ Acicular α-Fe ₂ O ₃ powder (long 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 backcoat coating material C was used in place of the backcoat coating material A1, and the obtained magnetic tape was processed in the same manner 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 backcoat coating material D was used in place of the backcoat coating material A1. The obtained magnetic tape was obtained in the same manner 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 backcoat coating material F was used in place of the backcoat coating material A1, and the obtained magnetic tape was processed in the same manner as in Example 1. evaluated. The results are shown in [Table 1]. [Blending of back coat paint F] Instead of "magnetite powder", "Dai Pyroxide color # 9550" [trade name, manufactured by Dainichiseika Co., Ltd., granular black oxide powder containing Cu, Fe and Mn] , Specific surface area 28 m ² / g, average particle size 0.1 μm].

[0079]

[Table 1]

[Example 3] A magnetic tape was obtained in the same manner as in Example 1 except that the following intermediate magnetic coating material Q was used in place of the above non-magnetic coating material (a). It evaluated similarly to. 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 4 A magnetic tape was obtained in the same manner as in Example 3 except that the following magnetic paint B was used in place of the above 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

Example 5 Example 4 was repeated except that the following backcoat paint A3 was used in place of the backcoat paint A1.
A magnetic tape was obtained in the same manner as above, and the obtained magnetic tape was evaluated in the same manner as in Example 1. The results are shown in [Table 2]. [Blending of back coat paint A3] Back coat paint A1
Same as the back coat paint A1 except that the following magnetite powder was used in place of the magnetite powder used in.・ Plate shaped magnetite powder (plate diameter 0.2 μm, plate ratio 5, specific surface area 12 m ² / g,
Saturation magnetization 83 emu / g, coercive force 89 Oe)

[Comparative Example 5] A magnetic tape was obtained in the same manner as in Example 3 except that the following backcoat coating material E was used in place of the backcoat coating material A1, and the obtained magnetic tape was processed in the same manner as in Example 1. evaluated. The results are shown in [Table 2]. [Blending of backcoat paint E] The same as backcoat paint A1 except that the following tabular Mn-free α-Fe ₂ O ₃ powder was used in place of the “magnetite powder”.・ Plate-like α-Fe ₂ O ₃ powder (plate diameter 0.4 μm, plate ratio 7, specific surface area 28 m ² / g)

[Comparative Example 6] A magnetic tape was obtained in the same manner as in Example 3 except that the above-mentioned backcoat coating material D was used in place of the backcoat coating material A1, and the obtained magnetic tape was processed in the same manner 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 backcoat coating material G was used in place of the backcoat coating material A1, and the obtained magnetic tape was processed in the same manner as in Example 1. evaluated. The results are shown in [Table 2]. [Blending of back coat paint G] Instead of "magnetite powder", "Dai Pyroxide color # 9510" [trade name, manufactured by Dainichiseika Co., Ltd., granular black oxide powder containing Co, Fe and Cr] , Specific surface area of 2.0 m ² / g, average particle diameter of 2.4 μm].

[0086]

[Table 2]

[0087]

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 drawings]

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

Claims (7)

[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 plate-shaped magnetite powder. 2. The plate diameter of the magnetite is 0.0
The magnetic recording medium according to claim 1, wherein the magnetic recording medium has a thickness of 5 to 2.0 μm and a plate ratio of 3 to 40. 3. The magnetic recording medium according to claim 1, wherein the back coat layer further contains carbon black. 4. The magnetic layer has a thickness of 0.05 to 1.0.
2. The magnetic recording medium according to claim 1, wherein the diameter of the magnetic recording medium is μm. 5. The magnetic recording medium according to claim 4, wherein the magnetic layer contains acicular ferromagnetic metal powder and has a coercive force of 1500 to 2400 Oe. 6. The magnetic recording medium according to claim 4, wherein the magnetic layer contains hexagonal ferrite powder and has a coercive force of 1300 to 2300 Oe. 7. An intermediate layer is provided between the magnetic layer and the support, and the magnetic layer and the intermediate layer are respectively formed.
The magnetic recording medium according to claim 4, wherein the magnetic recording medium and the intermediate layer-forming coating material are formed by simultaneous multi-layer coating.