JP2000011358A - Magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a coating type magnetic recording medium having excellent smoothness of the surface of a magnetic recording layer and excellent travelling durability. SOLUTION: A smectite powder is added to the magnetic recording layer 2. The amt. of the smectite powder added is controlled to between >=0.3 pts.wt. and <=10 pts.wt. to 100 pts.wt. of the magnetic powder. Thus, the obtd. magnetic recording medium has both of high electromagnetic conversion characteristics and high durability.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium, and more particularly to a coating type magnetic recording medium having excellent running durability.

[0002]

2. Description of the Related Art As a magnetic recording medium such as a magnetic recording tape or a magnetic disk used in a magnetic recording / reproducing device as a peripheral device such as an audio device, a video device or a computer device, a coating type and a thin film type are mainly used. Have been. Among these, the coating type magnetic recording medium applies a magnetic paint prepared by dispersing and kneading magnetic powder such as Fe metal or iron oxide, a binder and various additives in an organic solvent, onto a non-magnetic support. , A magnetic recording layer formed by drying, smoothing and curing.

In these various magnetic recording devices, in recent years, miniaturization and lightening, high image quality, long time, digital recording, and the like have progressed, and there has been a strong demand for high-density recording of magnetic recording media. It has become so. To meet this demand, recent magnetic recording media prevent output loss due to recording demagnetization in a short wavelength region by reducing the thickness of a magnetic recording layer. Also, the surface of the magnetic recording layer is smoothed to a state close to a mirror surface, and the magnetic head /
There is also a trend to narrow the gap between the magnetic recording layers and reduce the spacing loss as much as possible.

On the other hand, the magnetic recording medium has excellent running properties and durability, good storage stability, low output attenuation after repeated running, and small damage to the magnetic head during recording / reproducing. There is also a strong demand for reliability.

[0005] Even in a coating type magnetic recording medium, in order to improve electromagnetic conversion characteristics such as RF output and C / N in a short wavelength recording region, in addition to a method of improving magnetic characteristics of a magnetic recording layer, a magnetic head is used. It is effective to reduce the spacing loss between the magnetic recording layer and the magnetic recording layer as much as possible. To reduce the spacing loss, it is required to smooth the surface of the magnetic recording layer, that is, to reduce the surface roughness.

[0006]

However, smoothing the surface of the magnetic recording layer may reduce the running durability of the magnetic recording medium. For example, as a smoothing process, there is a process of applying a calendar process after coating and drying the magnetic recording layer. If this calendering is performed at high temperature and high pressure, the surface of the magnetic recording layer is highly smoothed. On the other hand, there is a phenomenon that pores opened on the surface of the magnetic recording layer are closed, so that the lubricant inside the magnetic recording layer is hardly leached to the surface. In such a case, supply of new lubricant is interrupted, and there is a problem that the running property and durability of the magnetic recording medium are reduced.

The present invention has been proposed in view of the prior art. In a coated magnetic recording medium for high-density recording, even when the surface of the magnetic recording layer is highly smoothed, the running property and the durability thereof are improved. It is an object of the present invention to provide a magnetic recording medium which is excellent and has good electromagnetic conversion characteristics.

[0008]

SUMMARY OF THE INVENTION A magnetic recording medium of the present invention is proposed to solve the above-mentioned problems, and comprises a magnetic recording medium containing a magnetic powder, a binder and a lubricant on a non-magnetic support. A magnetic recording medium having a layer, wherein the magnetic recording layer further comprises a smectite powder.

[0009] The content of the smectite powder in the magnetic recording layer is 0.3 parts by weight or more to 100 parts by weight of the magnetic powder.
It is desirable that the content be 0 parts by weight or less. If the amount is less than 0.3 parts by weight, the effect of improving running properties and durability cannot be sufficiently obtained. Further, when it is added in excess of 10 parts by weight, the residual magnetic flux density and gloss before calendering slightly decrease, and with this, the electromagnetic conversion characteristics, especially the YC / N, are seen to decrease.

The smectite (Smectit) used in the present invention
e) is a kind of clay mineral, bentonite (Bentni), a clay-like substance that is naturally formed by the modification of volcanic ash.
te). Industrially, a product synthesized by a hydrothermal synthesis method has also been commercialized. Smectite is a silicate layer in which two tetrahedral sheets connected by sharing the vertices of SiO ₄ tetrahedrons are bonded by ions taking the octahedral coordination with the remaining vertices facing inward, It is an intercalation compound having a structure in which a layer composed of an alkali or alkaline earth ion and a water molecule coordinated with it is overlapped with each other.

Smectite has various properties such as high swelling property, adsorptivity, cation exchange property, and viscosity increase in water or an organic solvent. In the present invention, among these properties, attention is paid to the high swelling property of smectite in an organic solvent, and this property is utilized. That is, the smectite powder swollen by absorbing the organic solvent in the magnetic paint releases the organic solvent in the step of applying and drying the magnetic paint on the non-magnetic support, and contracts its volume. At this time, voids are generated around the smectite powder inside the coating film of the magnetic recording layer. The gap is not completely closed even by the calendar process, and serves as a route for leaching the lubricant from the inside of the coating film of the magnetic recording layer, and plays a role in assisting the supply of the lubricant. Therefore, even for a coating type magnetic recording medium having a highly smooth surface, it is possible to improve the running property and the durability thereof.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a magnetic recording medium according to the present invention will be described in detail with reference to the drawings. First, FIG. 1 shows a schematic cross-sectional view of a configuration example in which the magnetic recording medium of the present invention is applied to a video tape for an 8 mm video tape recorder. That is, the magnetic recording layer 2 is formed on one main surface side of the non-magnetic support 1, and the back coat layer 3 is formed on the other main surface side.
The configuration shown in FIG. 1 is a basic configuration of a magnetic recording tape,
An undercoat layer may be formed between the nonmagnetic support 1 and the magnetic recording layer 2, and a protective layer or a topcoat layer may be formed on the surface of the magnetic recording layer 2. The magnetic recording layer 2 itself may be formed in multiple layers.

FIG. 2 is a schematic sectional view showing an example of a configuration in which the magnetic recording medium of the present invention is applied to a floppy disk. That is, the magnetic recording layer 2 is provided on both sides of the non-magnetic support 1.
Are formed. A protective layer or a top coat layer may be formed on the surface of the magnetic recording layer 2. The magnetic recording layer 2 itself may be formed in multiple layers. The outline of each component will be described.

As the nonmagnetic support 1, any of those used in ordinary magnetic recording media can be used, and polyesters such as polyethylene terephthalate and polyethylene-2,6-naphthalate, polyolefins such as polyethylene and polypropylene, Cellulose derivatives such as cellulose triacetate and cellulose diacetate,
Examples thereof include vinyl resins such as polyvinyl chloride, vinylidene resins such as polyvinylidene chloride, and organic polymers such as polycarbonate, polyamideimide, and polyimide. The thickness of the nonmagnetic support 1 is 1 to several hundred μm, preferably several to several tens μm.
m is selected. Furthermore, when the present invention is applied to a magnetic recording medium such as a hard disk, a non-magnetic support may be made of Al.
Rigid substrates such as base metals, ceramics, plastics, and glass can be used. An oxide film or an Ni-P film may be formed on the surface of the rigid substrate by alumite treatment or the like to further increase the surface hardness.

The structure of the back coat layer 3 is not particularly limited, and may be of a coating type or a thin film type or a combination thereof. The coating back coat layer is formed by dispersing non-magnetic particles in an organic binder to control the surface roughness and conductivity. Examples of the material of the non-magnetic particles include hematite, boehmite, fused alumina, α, β Alumina, mica, kaolin, talc, clay, silica, magnesium oxide, titanium oxide (rutile and anatase), zinc oxide, zinc sulfide, calcium carbonate, magnesium carbonate, barium carbonate, barium sulfate, lead sulfate , Inorganic compounds such as tungsten sulfide, polyethylene, polyvinyl chloride, polyimide,
Examples thereof include polymer resins such as polytetrafluoroethylene, starch, nonmagnetic metals, carbon, and the like. The non-magnetic particles have a mean particle size of 0.05 to 1 μm, preferably 0.1 to 0.7 μm, and are usually added in an amount of 1 to 20 parts by weight based on 100 parts by weight of the organic binder. Is done. Further, from the viewpoint of paint suitability and durability, it is preferable that the particles have an isotropic shape such as a substantially spherical shape and a substantially regular polyhedron.

The organic binder material used for the coating backcoat layer is not particularly limited, but any of conventionally used thermoplastic resins, thermosetting resins, and reactive resins can be used. It is desirable that the thermoplastic resin be used in combination with a thermosetting resin, a reactive resin, or the like.

Materials used for the thin film back coat layer include, for example, carbon, graphite, diamond-like carbon, SiO ₂ , Si ₃ N ₄ , SiON, SiC,
Al ₂ O ₃ , AlN, TiO ₂ , Cr ₂ O ₃ , TiN,
TiC, ZrO ₂ , MgO, BN, CoO, a nonmagnetic metal, or the like is used alone or as a composite film. Further, an organic polymer to which a vacuum thin film forming technique can be applied, such as polyparaxylylene (trade name: parylene) or fluororesin, can also be used. These materials may be used in a single layer or a laminate.

The method for forming the thin film back coat layer includes various sputtering methods such as a vacuum thin film forming method, that is, DC sputtering method, RF sputtering method, ion beam sputtering method, magnetron sputtering method, reactive sputtering method, vapor deposition method, and reactive sputtering method. An evaporation method, an ion plating method, or the like is employed. Plasma CVD or E
A CR plasma CVD method, a reduced pressure CVD method, or the like may be employed. In the case of an organic polymer thin film, it can be formed by an evaporation method or plasma polymerization of a raw material gas. In either method, it is desirable to form the non-magnetic support and the like while cooling the non-magnetic support and the like so as not to thermally deform the non-magnetic support and the coating backcoat layer provided thereon. A top coat layer containing a lubricant or the like may be formed on the back coat layer thus formed.

The structure of the magnetic recording layer 2 is a characteristic part of the present invention, and a magnetic paint prepared by dispersing a magnetic powder, a binder, a lubricant, an abrasive and various additives in an organic solvent is used as a non-magnetic support. It is formed on the body 1 through the steps of coating, drying, calendering, and curing. This magnetic recording layer 2 contains smectite powder.

The material of the magnetic powder is not particularly limited, and any metal magnetic powder, oxide magnetic powder or other compound magnetic powder can be used. As metal magnetic powder system, F
e, Co, Ni, and other metals and their alloys, or Al, Si, Ti, Cr, V, Mn, C
Any one or more of elements such as u, Zn, Mg, Bi, rare earth, P, B, N, and C are added. Among them, Fe or Fe—Co alloy is preferably used in terms of saturation magnetization. Further, the surface layer of these metal magnetic powders may contain a sintering preventing element or a shape maintaining element such as Al, Si, P or B.
Γ-Fe ₂ O ₃ , Fe
₃ O ₄ , a beltlide compound which is an intermediate between γ-Fe ₂ O ₃ and Fe ₃ O ₄ , Co-containing γ-Fe ₂ O ₃ , Co-containing Fe ₃ O ₄ , and Co-containing γ-Fe ₂ O ₃ Co-containing Fe
Various spinel-type iron oxides, such as belt oxide compounds, which are intermediates with ₃ O ₄ , various barium ferrites such as M-type, W-type, Y-type, and Z-type, calcium ferrite, lead ferrite, and various magnetoplumbite-type oxidations A magnetoplumbite-type iron oxide to which Co, Ti, Zn, Nb, Cu, Ni or the like is added for the purpose of improving coercive force to iron is exemplified. Examples of the iron compound include iron oxide, iron nitride, iron carbide, and iron boride. As the oxide-based material, CrO ₂ or a material obtained by adding a small amount of Te, Sb, Fe, B, or the like thereto may be used. These magnetic powders can be used alone or in combination of two or more.

As for the shape of the magnetic powder, the major axis length is, for example, about 0.05 μm to 2.0 μm, preferably 0.1 μm to 2.0 μm.
About 0.5 μm and an axial ratio (aspect ratio) of 3 to 3
It is about 0, preferably about 5 to 15, and preferably has a needle-like, column-like, spindle-like or rod-like outer shape. If the major axis length is less than 0.05 μm, it is difficult to disperse the magnetic paint, and if the major axis length exceeds 2.0 μm, the noise characteristics may deteriorate, which is not preferable. If the axial ratio is less than 3, the magnetic field orientation of the individual magnetic particles deteriorates, the squareness ratio and the residual magnetic flux decrease, and as a result, the output decreases. The axial ratio is 3
If it exceeds 0, the dispersibility may decrease, which is not preferable. In the case of magnetoplumbite-type iron oxide, a fine hexagonal plate is used. This has a plate diameter of 0.01 to
Those having a thickness of about 0.5 μm and a thickness of about 0.001 to 0.2 μm are preferred. The major axis length, the axial ratio, the plate diameter, the plate thickness, and the like can be determined from the average value of particles of 100 or more samples randomly extracted from a transmission electron micrograph. The specific surface area of these magnetic powders is from 30 m ² / g to 80 m ² / g, especially 4 m ² / g.
Those having a range of 0 m ² / g to 70 m ² / g are preferred.
By selecting the specific surface area within this range, it is possible to obtain a high-density recording accompanying finer magnetic powder and a magnetic recording medium excellent in noise characteristics.

The binder used in the magnetic recording layer is not particularly limited, and a conventionally known thermoplastic resin, thermosetting resin, radiation-crosslinkable curable resin such as ultraviolet ray or electron beam, or a mixture thereof. Is used. Examples of the thermoplastic resin include a softening point temperature of about 150 ° C. or less, an average molecular weight of about 10,000 to 200,000, and a degree of polymerization of about 150.
About 2,000, specifically, vinyl chloride resin, vinyl acetate resin, vinyl fluoride resin, vinyl chloride
Vinyl acetate copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-vinyl acetate-vinyl alcohol copolymer, vinyl chloride-acrylonitrile copolymer, vinylidene chloride-acrylonitrile copolymer, acrylate-acrylonitrile copolymer Polymer, acrylate-vinyl chloride-vinylidene chloride copolymer, methacrylate-vinyl chloride copolymer, methacrylate-vinylidene chloride copolymer, methacrylate-ethylene copolymer, acrylonitrile-butadiene copolymer Coalesce, styrene-butadiene copolymer, polyurethane resin, polyester polyurethane resin, polyester resin, polycarbonate polyurethane resin, polycarbonate resin, polyamide resin, polyvinyl butyral resin, cellulose derivative ( Cellulose acetate butyrate, cellulose diacetate, cellulose triacetate, cellulose propionate, nitrocellulose), styrene-butadiene copolymer, polyester resin, amino resin, various synthetic rubber and the like. Examples of thermosetting resins and reactive resins include phenolic resins, epoxy resins, polyurethane curable resins, urea formaldehyde resins, melamine resins, alkyd resins, silicone resins, polyamine resins, high molecular weight polyester resins and isocyanate prepolymers. Examples thereof include a mixture, a mixture of a polyester polyol and a polyisocyanate, a mixture of a low molecular weight glycol, a high molecular weight diol, and an isocyanate, and a mixture of these resins.
Among these resins, it is preferable to use a polyurethane resin, a polycarbonate resin, a polyester resin, an acrylonitrile-butadiene copolymer, which is considered to impart flexibility. These resins, -SO ₃ M in order to improve the dispersibility of the acicular iron oxide particles, -OSO ₃ M, -C
OOM, or may contain a polar functional group such as —PO (OM ′) ₂ (where M is H or Li, K
a, alkali metal such as Na, M ′ is H or Li, K
a, an alkali metal such as Na, or an alkyl group). Other polar functional groups include -NR ₁ R ₂ , -N
^{_{R 1 R 2 R 3 + X}} - as the side chain type having an end group,>
A main chain type of NR ₁ R ₂ ⁺ X ⁻ (where R ₁ , R ₂ and R ₃ are a hydrogen atom or a hydrocarbon group;
X ^- represents fluorine, chlorine, bromine, halogen ion or an inorganic iodine, the organic ions). In addition, -O
It may be a polar functional group such as H, -SH, -CN, or an epoxy group. The content of these polar functional groups is 10 ^-1 to 10 ^-8
mol / g, preferably 10 ⁻² to 10 ⁻⁶ mol / g.
g. These organic binders can be used alone or in combination of two or more.
The amount of these binders in the magnetic recording layer depends on the amount of magnetic powder 1
1 to 200 parts by weight, preferably 10 to 100 parts by weight
５０50 parts by weight.

Among the above-mentioned binders, for example, a polyisocyanate or the like can be added as a curing agent for crosslinking and curing the curable resin. As the polyisocyanate, an adduct of trimethylolpropane and 2,4-tolylene diisocyanate (TDI) (for example, trade name Coronate L-50) is generally used, but 4,4-diphenylmethane diisocyanate (MDI) and hexane diisocyanate An adduct of an alkylene diisocyanate such as (HDI) may be used. In addition, polyglycidylamine compounds such as tetraglycidyl metaxylenediamine, tetraglycidyl-1,3-bisaminomethylcyclohexane, tetraglycidylaminodiphenylmethane, triglycidyl-p-aminophenol, and 2-dibutylamino-4,6-dimercapto Polythiol compounds such as substituted triazines, epoxy compounds such as triglycidyl isocyanurate, mixtures of epoxy compounds and isocyanate compounds, mixtures of epoxy compounds and oxazoline compounds, mixtures of imidazole compounds and isocyanate compounds, methyl nadic anhydride, etc. Any of them can be used. The mixing ratio of these curing agents to the curable resin is 5 to 80 parts by weight, preferably 10 to 50 parts by weight, per 100 parts by weight of the curable resin.

The lubricant added to the magnetic recording layer is not particularly limited, and any conventional lubricant can be used. That is, silicone oil, carbon number 10 to 2
Up to about 2 fatty acids, these fatty acids and 2 to 26 carbon atoms
Ester compounds with alcohols, terpene compounds, and oligomers thereof can be used. Specific examples include lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, oleic acid, linoleic acid, linolenic acid, elaidic acid, butyl stearate, pentyl stearate, heptyl stearate, octyl stearate, and stearic acid. Examples include isooctyl, octyl myristate, and the like. Further, perfluoropolyether and its compounds can also be suitably used.

There is no particular limitation on the dispersant that can disperse the magnetic powder and the like well. Conventionally known nonionic, anionic,
Various cationic and amphoteric dispersants can be used.

Additives for use in the magnetic recording layer, that is, abrasives, matting agents, etc., and solvents for converting them into a magnetic paint are not particularly limited, and all are employed in conventional coated magnetic recording tapes. Can be anything.

The thickness of the magnetic recording layer 2 depends on the purpose of use, but is usually about 1 to several μm. The magnetic recording layer 2 is used as a single layer or a multilayer. In the case of lamination,
A non-magnetic intermediate layer may be interposed.

Although not shown, a protective layer may be provided on the surface of the magnetic recording layer 2. As the material of the protective layer, carbon, diamond-like carbon, SiO ₂ , Si ₃ N
_{4, SiON, SiC, Al 2} O 3, AlN, Ti
O ₂ , Cr ₂ O ₃ , TiN, TiC, ZrO ₂ , Mg
O, BN, CoO, a nonmagnetic metal or the like is used alone or as a composite film. These materials may be used in a single layer or a laminate. The method for forming these protective layers is not particularly limited, but includes sputtering, vacuum deposition, and CVD.
A technique for forming a thin film from a gas phase such as (Chemical Vapor Deposition) is preferable in terms of uniformity and film quality.

A top coat layer for improving lubricity may be formed on the surface of the magnetic recording layer 2 or the surface of the protective layer. This top coat layer generally contains a solute such as a lubricant as a main component,
A top coat solution dissolved in a solvent such as alcohol or toluene is applied and dried to form. Lubricants include fluorocarbons, alkylamines, alkylesters,
Conventionally used lubricants such as silicones can be used.

Solvents used in the coating material for forming the magnetic recording layer 2 include ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone and cyclohexanone, alcohols such as methanol, ethanol, propanol and butanol, methyl acetate, ethyl acetate, and the like. Propyl acetate,
Esters such as butyl acetate, ethyl lactate, ethylene glycol monoacetate, ethers such as diethylene glycol dimethyl ether, glycol monoethyl ether, dioxane, tetrahydrofuran, aromatic hydrocarbons such as benzene, toluene, xylene, methylene chloride, ethylene chloride, tetrachloride Halogenated hydrocarbons such as carbon chloride, chloroform and dichlorobenzene are used.

The preparation of the coating material for the magnetic recording layer is carried out through various steps such as mixing, dispersing, kneading, etc., with a magnetic powder, a binder, a lubricant, and if necessary, other additives, an organic solvent and the like. For dispersion and kneading, a kneader, an agitator, a ball mill, a sand mill, a roll mill, an extruder, a homogenizer, an ultrasonic disperser, and the like are used. The coating method for forming the nonmagnetic lower layer on the nonmagnetic support is not particularly limited, and may be air doctor coat, blade coat, air knife coat, squeeze coat, impregnation coat, reverse roll coat, transfer roll coat, gravure coat, kiss coat, Any of the conventional methods such as cast coating, extrusion coating, die coating, and spin coating can be employed. In the case of simultaneous multi-layer coating of an undercoat layer and the like, it is desirable to use a two-lip, three-lip or four-lip type die coater or the like. Alternatively, the undercoat layer may be coated on the non-magnetic support, dried with heated air or the like to remove the organic solvent, cured if necessary, and then the magnetic recording layer may be coated and formed.

[0032]

EXAMPLES Hereinafter, preferred examples of the present invention will be described in more detail with reference to comparative examples as appropriate, but the present invention is not limited to these examples. In the following Examples and Comparative Examples, a coating type 8 m
An explanation will be given using m video tapes.

Example 1 Preparation of Paint for Magnetic Recording Layer As the magnetic powder, an iron-based acicular metal ferromagnetic powder having the following magnetic properties and shapes was employed. Saturation magnetization 138.2 Am ² / kg Coercivity 129.5 kA / m Specific surface area 57.5 m ² / g Average major axis length 0.13 μm Aspect ratio 6.5 Saturation magnetization σs and coercivity Hc are samples The measurement was performed using a vibration type magnetometer (VSM manufactured by Toei Kogyo) under the conditions of an applied magnetic field of 15 kOe and a sweep speed of 10 min / 15 kOe. The specific surface area is measured by Rapid Surface Area Analyzer (Micromerit
ics). The average major axis length and the aspect ratio were measured from an electron micrograph.

The iron-based acicular metal ferromagnetic powder and the smectite powder are mixed with a polyvinyl chloride resin or the like as a binder and additives by a planetary stirrer and then kneaded by a biaxial kneader. The composition of this kneading composition is shown below. Iron-based acicular metal ferromagnetic powder 100 parts by weight Synthetic smectite powder 0.5 parts by weight (SWN manufactured by Corp Chemical) Polyvinyl chloride resin 10 parts by weight (MR-110 manufactured by Zeon Corporation) Polyester polyurethane resin 10 parts by weight (Toyobo) UR-8200) 5 parts by weight of alumina powder (average particle size 0.3 μm) 20 parts by weight of methyl ethyl ketone 5 parts by weight of toluene 15 parts by weight of cyclohexanone

The following additives and solvents were further added to the obtained kneaded paste, which was preliminarily dispersed by a disper and then dispersed by a sand mill for 20 hours to obtain a coating composition for a magnetic recording layer. Butyl stearate 2 parts by weight Methyl ethyl ketone 145 parts by weight Toluene 145 parts by weight Cyclohexanone 73 parts by weight

Formation of Magnetic Recording Layer The coating composition for a magnetic recording layer was added with 2 parts by weight of polyisocyanate immediately before application, further mixed, and applied on a long film of polyethylene terephthalate having a thickness of 8 μm using a die coater. . The coating film was passed through a solenoid coil while it was not dried, and was oriented in a magnetic field, followed by hot-air drying. Thereafter, a temperature of 110 ° C. and a pressure of 40 kg /
The magnetic recording layer surface was smoothed by passing between the steel roll and the elastic rubber roll six times under the conditions of cm and a passage speed of 100 m / min. The thickness of the magnetic recording layer after the calendar processing was 2.0 μm. The curing process is performed in a 60 ° C constant temperature bath.
Applied for 4 hours.

Formation of Backcoat Layer The following composition was dispersed in a sand mill for 3 hours to prepare a backcoat layer paint. Carbon black (Asahi # 50) 100 parts by weight Polyester polyurethane resin 100 parts by weight (Nipporan N-2304) Methyl ethyl ketone 500 parts by weight Toluene 500 parts by weight

On the back surface of the non-magnetic support having the magnetic recording layer formed thereon, a paint for a back coat layer was applied by a die coater and dried. The thickness of the back coat layer after drying is 0.8 μm
Met.

Thereafter, the sample tape was slit into 8 mm and housed in a tape cassette to obtain a sample tape of Example 1.

Example 2 The sample tape of Example 2 was prepared in the same manner as in Example 1 except that the addition amount of the smectite powder in the kneading composition of Example 1 was changed to 1 part by weight. Obtained.

Example 3 The sample tape of Example 3 was prepared in the same manner as in Example 1 except that the amount of smectite powder added to the kneading composition of Example 1 was changed to 3 parts by weight. Obtained.

Example 4 The sample tape of Example 4 was prepared in the same manner as in Example 1 except that the addition amount of the smectite powder in the kneading composition of Example 1 was changed to 0.5 part by weight to 5 parts by weight. Obtained.

Example 5 The sample tape of Example 5 was prepared in the same manner as in Example 1 except that the addition amount of the smectite powder in the kneading composition of Example 1 was changed to 10 parts by weight. Obtained.

[Comparative Example 1] The smectite powder in the kneaded composition of the preceding Example 1 was omitted, that is, no smectite powder was added, and the other compositions and steps were the same as in Example 1, and the samples of Comparative Example 1 were used. I got the tape.

Comparative Example 2 A sample of Comparative Example 2 was prepared in the same manner as in Example 1 except that the addition amount of the smectite powder in the kneading composition of the previous Example 1 was changed to 0.5 part by weight to 0.2 part by weight. I got the tape.

Comparative Example 3 The sample tape of Comparative Example 3 was prepared in the same manner as in Example 1 except that the amount of the smectite powder in the kneading composition of the previous Example 1 was changed to 15 parts by weight. Obtained.

The following measurements and evaluations were performed on the sample tapes of the five examples and the three comparative examples obtained above. Hereinafter, details of the measurement and evaluation methods will be described.

[Magnetic Characteristics] The residual magnetic flux density Br and the coercive force Hc were measured by a sample vibration type magnetometer (VSM manufactured by Toei Kogyo) at an applied magnetic field of 10 kOe and a sweep speed of 3 min / 10 kO.
It measured on condition of e.

[Glossiness] The glossiness of the magnetic recording layer is determined according to JIS-8741 for the sample before calendering.
It measured according to loss45 degree. That is, the incident angle of the light beam was set to 4 by a gloss meter
The gloss measured at 5 ° was expressed as a relative value, with the gloss of a reference plate having a reference surface measured in the same manner as 100%.

[Electromagnetic Conversion Characteristics (Y-C / N)] A measuring instrument obtained by modifying a commercially available Hi-8 VTR deck (manufactured by Sony Corporation) so as to extract a Y signal, a high-frequency oscillator, an oscilloscope, a spectrum analyzer, and the like. It was measured by an electromagnetic conversion characteristic measuring device. Measurement frequency is 7M
Hz and the recording wavelength are 0.49 μm. In determining Y-C / N, the noise used was a carrier signal of -1 MHz, that is, a value of 6 MHz. As a reference, the sample tape of Comparative Example 1 (without addition of smectite powder) was evaluated by a relative value when normalized to 0 dB.

[Still Characteristics] A sample tape on which a signal has been recorded in advance is reproduced by a measuring instrument obtained by modifying a commercially available Hi-8 VTR deck (manufactured by Sony Corporation) so that RF output can be obtained, and RF output is performed in a pause mode. Was evaluated based on the time required until 3 dB decreased. The measurement environment was a low temperature condition of -5 ° C.

According to each of the above-described measurement and evaluation methods, Example 1 was used.
8 and 5 kinds of sample tapes of Comparative Examples 1 to 3 were measured, and the results are shown in [Table 1] in the order of smectite powder addition.

[0053]

[Table 1]

As is evident from the results in Table 1, the addition of smectite powder dramatically improves the still characteristics. Further, by setting the addition range of 0.3 to 10 parts by weight based on 100 parts by weight of the magnetic powder, which is a preferable addition range of the smectite powder, the electromagnetic conversion characteristics are not deteriorated, and the electromagnetic conversion characteristics are good. A magnetic recording tape having both excellent electromagnetic conversion characteristics and durability can be obtained.

Although the magnetic recording medium of the present invention has been described using an 8 mm video tape as an example, the present invention can be applied to magnetic recording media such as a hard disk and a floppy disk in addition to the magnetic recording tape to obtain good results. be able to.

[0056]

As is apparent from the above description, according to the magnetic recording medium of the present invention, even when the surface of the magnetic recording layer is highly smoothed, excellent running properties and excellent durability are obtained. It is possible to provide a magnetic recording medium having good electromagnetic conversion characteristics.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view showing one configuration example when a magnetic recording medium of the present invention is applied to a magnetic recording tape.

FIG. 2 is a schematic cross-sectional view showing one configuration example when the magnetic recording medium of the present invention is applied to a floppy disk.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Non-magnetic support, 2 ... Magnetic recording layer, 3 ... Back coat layer

Claims (2)

[Claims] 1. A magnetic recording medium having a magnetic recording layer containing a magnetic powder, a binder and a lubricant on a nonmagnetic support, wherein the magnetic recording layer further contains a smectite powder. Magnetic recording medium. 2. The content of the smectite powder is 0.3 parts by weight or more to 100 parts by weight of the magnetic powder.
2. The magnetic recording medium according to claim 1, wherein the amount is 0 part by weight or less.