JP2001195722A - Magnetic recording medium and magnetic recording and reproducing system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a coating type magnetic recording medium which produce a small noise and is suitable for a system using an MR head. SOLUTION: In the magnetic recording medium having a magnetic layer on the nonmagnetic substrate by way of a nonmagnetic layer containing a nonmagnetic powder dispersed in a resin binder and used in reproduction with an MR head, the magnetic layer is disposed by coating the top of the nonmagnetic layer formed on the nonmagnetic substrate by coating, drying and curing with a magnetic coating material, a magnetic metal powder having 0.03-0.08 μm average major axis length and 100-130 Am2/kg saturation magnetization σs is contained in the magnetic layer and the center line average roughness Ra of the surface of the magnetic layer is <=5 nm.

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 an ultra-thin coating type magnetic layer, and more particularly to an MR recording medium.
(Magnetic resistance) The present invention relates to a coating type magnetic recording medium corresponding to a head.

[0002]

2. Description of the Related Art In the course of increasing the density of magnetic recording media,
A magnetic recording system combining an MR head and a coating type magnetic recording medium has begun to be studied. For example, JP-A-10-
In No. 312525, the magnetic layer having hexagonal ferrite powder has a saturation magnetic flux density of 300 to 1000 G and a coercive force of 200.
0 Oe or more, or a magnetic layer having a ferromagnetic metal powder has a saturation magnetic flux density of 800 to 1500 G and a coercive force of 20 G
It is stated that a magnetic recording medium excellent in economy and low in noise and excellent in high-density characteristics can be obtained by setting it to 00 Oe or more. In Japanese Patent Application Laid-Open No. 10-302243, the height of the protrusion on the surface of the magnetic layer and the magnetization reversal volume are defined, and the coercive force of the magnetic layer is set to 2000 Oe or more.
It is said that it is suitable for reproduction with an MR head and can improve durability and noise.

[0003] On the other hand, looking at a recent method of applying a high-density recording medium, Japanese Patent Publication No. 05-59490 discloses a method in which a non-magnetic paint is applied to a non-magnetic support, and the non-magnetic paint is applied in a wet state.
A method for applying a magnetic layer having a thickness of not more than μm is disclosed.

[0004]

However, the above-mentioned prior art is not enough to obtain a low-noise medium suitable for an MR head. For example, as described in Japanese Patent Publication No. In the method of applying a non-magnetic paint to a magnetic layer having a thickness of 1 μm or less in a wet state, the surface property of the non-magnetic support directly affects the magnetic layer, causing noise deterioration. Further, in the related art, at present, the relationship between the magnetic powder used and the noise is not described in detail.

An object of the present invention is to provide a coating type magnetic recording medium which has low noise and is suitable for a system using an MR head.

[0006]

The above objects are achieved by the present invention described below. (1) A magnetic recording medium which has a magnetic layer on a non-magnetic support via a non-magnetic layer in which non-magnetic powder is dispersed in a binder resin. Is provided by applying a magnetic paint on the dried and cured non-magnetic layer applied to a non-magnetic support, and the magnetic layer has an average major axis length of 0.03 to
0.08 μm, saturation magnetization _s is 100 to 130 Am ² / k
g of metal magnetic powder, and a center line average roughness Ra of the magnetic layer surface is 5 nm or less. (2) The magnetic recording medium according to (1), wherein the binder resin contained in the nonmagnetic layer is an electron beam curable resin. (3) The magnetic recording medium according to (1) or (2), wherein the non-magnetic powder contains at least carbon black. (4) A magnetic recording / reproducing system in which recording is performed on a magnetic recording medium having a magnetic layer via a nonmagnetic layer in which nonmagnetic powder is dispersed in a binder resin on at least one surface of a nonmagnetic support, and reproduction is performed by an MR head. In the magnetic layer, the magnetic layer has an average major axis length of 0.03 to 0.08 μm and a saturation magnetization _s
A magnetic recording / reproducing system comprising 130 Am ² / kg of metal magnetic powder and having a center line average roughness Ra of 5 nm or less on the surface of the magnetic layer.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, a specific configuration of the present invention will be described in detail. Generally, when an MR head is used as a reproducing head, a reproduction output several times higher than that of a conventional magnetic head can be obtained. On the other hand, noise is also detected more strongly than magnetic heads, so when using an MR head, the point is how to keep the noise low.

In the present invention, a needle-like or spindle-shaped metal magnetic powder is used as the magnetic powder. In order to reduce noise, the average long-axis diameter of the metal magnetic powder should be 0.03 to 0.03.
It needs to be 8 μm. More preferably, 0.
04 to 0.07 μm. Average long axis diameter is 0.03μm
If it is smaller, dispersion becomes insufficient, and noise is increased due to poor dispersion. On the other hand, when the thickness exceeds 0.08 μm, the magnetic noise is increased due to the large size of the magnetic powder.

The saturation magnetization σ _{s of the} magnetic metal powder used is
Is 100 to 130 Am ² / kg, more preferably 110 to 125 Am ² / kg. If it is smaller than 100, the output will be insufficient, and if it is larger than 130, the output will be produced. However, the magnetic noise will increase accordingly, which is disadvantageous for reproduction by the MR head. In addition, when σ _s is increased, magnetic cohesion in the magnetic coating material is increased, and as a result, there is a problem that coatability is deteriorated and orientation becomes difficult. By setting the X-ray crystal particle diameter Dx of the metal magnetic powder to 50 to 150 °, preferably 50 to 120 °, it is effective to reduce magnetic noise. Further, the balance between magnetic noise and output is optimized by setting σ _s (Am ² / kg) / Dx (Å) to 0.9 or less, preferably 0.8 or less, more preferably 0.7 or less. It becomes easier.

As such a metal magnetic powder, α-F
e, Fe-Co, Fe-Co-Ni, Co, Co-Ni
Etc. as a main component, and the metal (F
e, Co, Ni, etc.) or 70% by weight or more of an alloy, and more preferably 75% by weight or more.

In order to reduce noise, it is important that these metal magnetic powders have no branches, have very few lattice defects and pores on the surface of the magnetic powder, and have a uniform particle size.

[0012] Such a magnetic powder can be obtained as follows.

As a first method, an aqueous solution of a ferrous salt such as iron chloride or iron sulfate is neutralized by adding an alkali such as cobalt chloride and sodium hydroxide and heated while blowing an oxidizing gas to carry out the oxidation reaction. Is performed to produce needle-like goethite (α-FeOOH), which is heat-treated in a non-reducing atmosphere to be dehydrated to generate α-Fe ₂ O ₃ , and then reduced while blowing hydrogen gas to reduce the metal magnetic powder. obtain. In this production method, by setting the amount of alkali to be twice or more, preferably 3 to 10 times the amount of the neutralization equivalent, branching of the obtained goethite is reduced. Further, it is preferable to add Al or Si during the goethite generation reaction because sintering due to heat can be prevented and the shape can be controlled. The addition of Si is also effective for improving the coercive force. In addition, when the heat treatment temperature in the dehydration step of goethite is set to 400 to 700 ° C., the number of voids of α-Fe ₂ O ₃ generated is reduced, and the surface of the magnetic powder is also significantly reduced in unevenness, resulting in a reduction in noise. Therefore, it is preferable. Further, the surface of the metal magnetic powder obtained by adding rare earth elements such as Y, Nd, and Sm can be made smooth, and as a result, the dispersibility of the magnetic paint is excellent, and even when the paint is formed, A very smooth magnetic layer surface can be obtained.

Second, an aqueous solution of a ferrous salt is neutralized with an alkali carbonate to produce FeCO ₃ , and an oxidizing gas is blown therein to obtain spindle-shaped goethite. It is also possible to obtain metal magnetic powder. Also in this case, the metal magnetic powder of the present invention can be obtained by performing the above control. In a metal magnetic powder containing Fe as a main component and at least Co, the F
The amount of Co atoms with respect to e atoms is 0 to 40 mol%, preferably 6 to 35 mol%.

In order to obtain the saturation magnetization of the present invention,
It is preferable to form an oxide film on the surface of the metal magnetic powder, or to partially carbonize or nitride the surface, or to form a carbonaceous film on the surface, and may contain a small amount of hydroxide or oxide. .

The content of the metal magnetic powder in the magnetic layer is 5
0 to 85 wt%, preferably 55 to 75 wt%.
In the magnetic layer, in addition to the above metal magnetic powder, carbon black,
α-alumina, β-alumina, γ-alumina, dichromium trioxide, α-iron oxide, γ-iron oxide, goethite, SiO
_{2, ZnO, TiO 2, ZrO} 2, SnO 2 or the like abrasive, further higher fatty acids, higher fatty acid esters, paraffins, may be included lubricants such as fatty acid amides. Furthermore, in the present invention, the center line surface roughness Ra of the magnetic layer surface needs to be 5 nm or less, and more preferably 4.5 nm or less. If Ra exceeds 5 nm, the noise component becomes large, and as a result, there is a problem that S / N deteriorates.

The particle size of the abrasive used here is 0.5 × T, where T is the thickness of the magnetic layer and D is the average particle size of the abrasive.
It is preferable that a relationship of ≦ D ≦ 1.5 × T is satisfied. 0.5
If it is less than × T, the polishing ability of the magnetic layer is insufficient, and the durability is deteriorated. On the other hand, if it exceeds 1.5 × T, the abrasive will fall off and scratch the magnetic layer, or the abrasive exposed on the magnetic layer will come into contact with the MR head, causing thermal noise. .

As the binder used in the magnetic layer of the present invention, a thermoplastic resin, a thermosetting or reactive resin, an electron beam-sensitive modified resin, or the like is used. The combination thereof depends on the characteristics of the medium and the process conditions. They are appropriately selected and used together.

The constitution of the coating film of the present invention has a nonmagnetic layer between the nonmagnetic support and the magnetic layer. By providing this non-magnetic layer, the roughness of the non-magnetic support can be reduced, and a magnetic layer with good surface properties can be obtained. Further, by adding a lubricant to the non-magnetic layer, the lubricant can be gradually supplied from the non-magnetic layer to the magnetic layer, and a magnetic recording medium with good durability can be obtained.

For this purpose, it is desirable to include carbon black in the nonmagnetic layer. By including carbon black, a large amount of lubricant can be retained. It also has the function of lowering the surface electric resistance of the magnetic layer. In addition to this carbon, other non-magnetic powders can be used in combination, and such materials are not limited to α-Fe ₂ O ₃ , α-Al ₂ O ₃ , Cr ₂ O ₃ , Si
O ₂ , ZnO, TiO ₂ , ZrO ₂ , SnO _{2 and the} like can be mentioned. Among them, the needle-like α having an average major axis diameter of 200 nm or less
-Fe ₂ O ₃ or 20 to 100 nm granular α-Fe ₂ O ₃
When used together, the thixotropy can be reduced and the coating film can be hardened as compared with a paint containing only carbon black. Further, the abrasive has an average particle diameter of 0.1 to 1.
When 0 μm α-Al ₂ O ₃ or Cr ₂ O ₃ is used in combination, the strength of the nonmagnetic layer is increased.

The proportion of carbon black in these non-magnetic powders is 5 wt% to 100 wt%, preferably 1 wt%.
0 to 100 wt%. If the amount is less than 5 wt%, the holding force of the added lubricant decreases, and the durability deteriorates.
In addition, the surface electric resistance of the magnetic layer increases, and the light transmittance increases. The carbon black used is not particularly limited, but has an average particle size of 10 nm to 80 nm.
nm of carbon black is preferred. Such carbon black can be selected from furnace carbon black, thermal carbon black, acetylene black and the like, and may be a single type or a mixed type.

The carbon black that can be used in the present invention is
For example, "Carbon Black Handbook", edited by Carbon Black Association can be referred to.

As the resin used for the lower coating, an electron beam-curable resin is desirable. If a thermosetting resin is used, a thermosetting step is required after the application of the non-magnetic layer, so that the raw material is undesirably deformed due to the thermosetting. Also, when used without heat curing, when a magnetic paint is applied thereon, the solvent permeates into the nonmagnetic layer and swells, or the nonmagnetic layer is dissolved, which deteriorates the surface properties of the magnetic layer, which is not preferable. .

As the electron beam-curable resin used in the present invention, there are many such as vinyl chloride resin, polyurethane resin, polyester resin, epoxy resin, phenoxy resin, fiber resin, polyether resin and polyvinyl alcohol resin. However, among these, a vinyl chloride resin and a polyurethane resin are typical, and it is preferable to use a mixture of both.

The electron beam-curable vinyl chloride resin is synthesized by modifying the vinyl chloride resin as a raw material with an electric shock. The raw material vinyl chloride resin has a vinyl chloride content of 60
-100% by weight, particularly preferably 60-95% by weight. Such vinyl chloride resins include vinyl chloride-vinyl acetate-vinyl alcohol copolymer, vinyl chloride-hydroxyalkyl (meth) acrylate copolymer,
Vinyl chloride-vinyl acetate-maleic acid copolymer, vinyl chloride-vinyl acetate-vinyl alcohol-maleic acid copolymer, vinyl chloride-hydroxyalkyl (meth) acrylate-maleic acid copolymer, vinyl chloride-vinyl acetate-vinyl Alcohol-glycidyl (meth) acrylate copolymer, vinyl chloride-hydroxyalkyl (meth) acrylate-glycidyl (meth) acrylate copolymer, vinyl chloride-hydroxyalkyl (meth) acrylate-allyl glycidyl ether copolymer, vinyl chloride -Vinyl acetate-vinyl alcohol-allyl glycidyl ether copolymer, etc., and particularly preferred is a copolymer of vinyl chloride and a monomer containing an epoxy (glycidyl) group. The average degree of polymerization is preferably from 100 to 900, and more preferably from 100 to 600.

Further, in order to enhance dispersibility, -SO ₄ Y, -SO ₃ Y, -POY, -PO ₂ Y, -P
O ₃ Y, —COOY (Y is hydrogen or an alkali metal),
^{_{-SR, -NR 2, NR + 3}} Cl - (R is hydrogen or a hydrocarbon), phosphobetaine, sulfobetaine, phosphamine, it is also preferable that the polar group of sulphamic etc. introduced in any manner. In order to enhance thermal stability, it is also preferable to introduce an epoxy group.

As a method for modifying the vinyl chloride resin with an electron beam, a resin having a hydroxyl group or a carboxylic acid group is reacted with a compound having a (meth) acryl group and a carboxylic anhydride or a dicarboxylic acid. Modification method, TDI (tolylene diisocyanate) and 2-HEM
A method of reacting with a reaction product (adduct) with A (hexaethylene methacrylate) to modify the product, and one or more ethylenically unsaturated double bonds and one isocyanate group.
A typical method is to react a monomer having a molecule and not having a urethane bond in the molecule.
The second method is excellent in the easiness of the modification and the dispersibility and physical properties after the modification, and the third method is preferable. Examples of such a monomer include 2-isocyanatoethyl (meth) acrylate. It is preferable that the content of the acryl group or the methacryl group in the molecule is about 1 to 20, more preferably 2 to 15 on average in the molecule.

The electron beam-curable polyurethane resin is a urethane resin having at least one acrylic bond in the molecule, and is a polyurethane acrylate compound bonded to an acrylic double bond-containing compound via a urethane bond.

The term "acrylic double bond" as used herein means a residue (acryloyl group or methacryloyl group) such as acrylic acid, acrylic ester, acrylamide, methacrylic acid, methacrylic ester, and methacrylamide. Examples of the acrylic double bond-containing compound include mono (meth) acrylates of glycols such as ethylene glycol, diethylene glycol and hexamethylene glycol, mono (meth) acrylates of triol compounds such as trimethylolpropane, glycerin and trimethylolethane, and di ( Hydroxyl group-containing acryl such as mono (meth) acrylate and di (meth) acrylate, tri (meth) acrylate, glycerin monoallyl ether and glycerin diallyl ether of polyols having four or more valences such as meth) acrylate, pentaerythritol and dipentaerythritol A system compound is suitable. These acrylic double bonds must be present in the binder molecule in at least one or more, preferably 2 to 20.

The polyurethane acrylate resin is generally obtained by reacting a hydroxyl group-containing resin, a hydroxyl group-containing acrylic compound and a polyisocyanate-containing compound. Examples of the hydroxy group-containing resin include polyalkylene glycols such as polyethylene glycol, polybutylene glycol, and polypropylene glycol, alkylene oxide adducts of bisphenol A, various glycols, and polyester polyols having a hydroxyl group at a molecular chain terminal.
Among these, a polyurethane acrylate resin obtained by using a polyester polyol as one component is preferable.

Examples of the carboxylic acid component of the polyester polyol include aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, orthophthalic acid and 1,5-naphthalic acid, p-oxybenzoic acid, and p- (hydroxyethoxy).
Aromatic oxycarboxylic acids such as benzoic acid, succinic acid, adipic acid, azelaic acid, sebacic acid, aliphatic dicarboxylic acids such as dodecanedicarboxylic acid, fumaric acid, maleic acid, itaconic acid, tetrahydrophthalic acid, hexahydrophthalic acid And tri- and tetracarboxylic acids such as alicyclic dicarboxylic acid, trimellitic acid, trimesic acid and pyromellitic acid.

The glycol components of the polyester polyol include ethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol and neopentyl glycol. , Diethylene glycol, dipropylene glycol, 2,2,4-trimethyl-1,3-pentanediol, 1,4-cyclohexanedimethanol, ethylene oxide adducts such as bisphenol A and propylene oxide adducts, hydrogenated bisphenol A Examples include ethylene oxide and propylene oxide adducts, polyethylene glycol, polypropylene glycol, and polytetramethylene glycol. Further, tri- and tetraols such as trimethylolethane, trimethylolpropane, glycerin and pentaerythritol may be used in combination. Examples of the polyester polyol include a lactone-based polyester diol chain obtained by ring-opening polymerization of a lactone such as caprolactone.

The polyisocyanates used include:
2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, p-phenylene diisocyanate,
Biphenylmethane diisocyanate, m-phenylene diisocyanate, hexamethylene diisocyanate, tetramethylene diisocyanate, 3,3'-dimethoxy 4,4'-biphenylene diisocyanate, 2,4-naphthalenedi isocyanate, 3,3'-dimethyl 4,
4'-biphenylene diisocyanate, 4,4'-diphenylene diisocyanate, 4,4'-diisocyanate-diphenyl ether, 1,5-naphthalene diisocyanate, p-xylylene diisocyanate, m-xylylene diisocyanate, 1,3-diisocyanate methyl cyclohexane Diisocyanate compounds such as 1,4-diisocyanatomethylcyclohexane, 4,4'-diisocyanatedicyclohexane, 4,4'-diisocyanatocyclohexylmethane, and isophorone diisocyanate; Trimer of diisocyanate,
And triisocyanate compounds such as trimers of hexamethylene diisocyanate.

In order to further improve the dispersibility, if necessary, -SO ₄ Y, -SO ₃ Y, -POY, -PO ₂ Y, -PO ₃
Y, -COOY (Y is hydrogen or an alkali metal), -S
It is also preferable to introduce a polar group such as R, —NR ₂ , NR ⁺ ₃ Cl ⁻ (R is hydrogen or hydrocarbon), phosphobetaine, sulfobetaine, phosphamine, and sulfamine by any method. In order to enhance thermal stability, it is also preferable to introduce an epoxy group.

On the other hand, apart from the above-mentioned electron beam-curable urethane synthesis method, electron beam modification may be carried out using a thermosetting polyurethane resin as a raw material in the same manner as for a PVC resin.

If necessary, an electron beam-curable monomer or oligomer may be used, and the use thereof can increase the degree of crosslinking of the coating film. The addition amount is preferably 30 parts by weight or less, more preferably 20 parts by weight or less, based on the resin contained in the nonmagnetic layer.
If the amount is more than 30 parts by weight, the shock applied to the paint is large, and the gloss is reduced. The time of addition of the electron beam-curable monomer or oligomer may be at the time of dispersion after the preparation of the paint.

The irradiation dose of the electron beam used in the present invention is 1 to
10 Mrad is preferable, and 3 to 7 Mrad is preferable, and the irradiation energy (acceleration voltage) is preferably 100 kV or more. The irradiation with the electron beam is preferably performed before winding after coating and drying, but may be performed after winding.

The non-magnetic support of the present invention preferably has a center line average roughness Ra of 10 nm or less, more preferably 9 nm or less, on the surface on which the magnetic layer is provided. When the thickness is larger than 10 nm, the surface property of the magnetic layer is deteriorated, so that noise is increased and the electromagnetic conversion characteristics are deteriorated.

The surface roughness of the non-magnetic support is freely controlled by the size and amount of the filler added to the non-magnetic support. Examples of these fillers include Ca, Si, T
In addition to oxides and carbonates such as i and Al, fine powders of an organic resin such as an acrylic resin can be given, and a combination of Al ₂ O ₃ and fine powders of an organic resin is preferable.

Further, even if the center line average roughness Ra on the side on which the magnetic layer is provided is 10 nm or less, when a filler having an average particle diameter of more than 0.3 μm is used as the filler in the base, coarse protrusions are formed on the magnetic layer, and dropout is caused. May be deteriorated and thermal noise may be generated.

The material used for such a non-magnetic support is not particularly limited, and may be selected from various flexible materials and various rigid materials according to the purpose. And dimensions. For example, as a flexible material, polyethylene terephthalate (PE)
T), polyesters such as polyethylene naphthalate,
Various resins such as polyolefins such as polypropylene, polyamide, polyimide, and polycarbonate are exemplified.

Since the magnetic recording medium of the present invention uses very fine metal magnetic powder, it is necessary to pay attention to dispersion and reagglomeration when a magnetic coating material is used. If the needle-shaped magnetic powder is excessively dispersed, the magnetic powder may be broken and the magnetic properties may be deteriorated. In the present invention, it is preferable to use ceramic beads having a specific gravity of 4 or more, preferably zirconia beads having a specific gravity of about 6. The particle size is 1 mm or less, preferably 0.7 mm or less. By dispersing the beads having a small particle size and a relatively large specific gravity as a dispersion medium, the magnetic powder can be dispersed into uniform primary particles without breaking. In the case of applying a thin magnetic layer as in the present invention, the application becomes difficult unless the content ratio of the magnetic powder in the magnetic paint is as low as 15 wt% or less. Reagglomeration is likely to occur. Therefore, it is effective to apply the magnetic paint immediately after the magnetic paint is ultrasonically dispersed as soon as possible.

The method of applying the non-magnetic layer and the magnetic layer is wet-on-dry application in which the non-magnetic layer is applied, dried and cured, and then the magnetic layer is applied.
By performing wet-on-dry coating, the undulation at the interface between the non-magnetic layer and the magnetic layer is extremely reduced, so that a magnetic recording medium having good surface properties and less unevenness in the thickness of the magnetic layer can be obtained. As the application means, various known application means such as a gravure coat, a reverse roll coat, a die nozzle coat, and a bar coat can be used.

Hereinafter, the present invention will be described in detail with reference to examples.

[Examples / Comparative Examples] Disk sample (1) Example 1 <Nonmagnetic paint 1> 55 parts by weight of granular α-Fe ₂ O ₃ (FRO-3 manufactured by Sakai Chemical Industry Co., Ltd.) (average particle size = 30 nm, BET = 45 m ² / g) ) Carbon black (Mitsubishi Chemical Corporation: # 45B) 30 parts by weight (Average particle diameter = 24 nm, BET = 125 m ² / g, DBP oil absorption = 47 ml / 100 g) α-Al ₂ O ₃ (Sumitomo Chemical Industries, Ltd.) 15 parts by weight (average particle size = 0.20 μm, BET = 8 m ² / g) 12 parts by weight of an electron beam-curable vinyl chloride copolymer (degree of polymerization = 300, polar group: —OSO) ₃ K = 2 / molecule) Electron beam-curable polyurethane resin 4 parts by weight (Mn = 25000, polar group: phosphorus compound = 1 / molecule) Trifunctional acrylic monomer (TA505, manufactured by Sanyo Chemical Industries, Ltd.) 2 parts by weight Isocet Rustearate 10 parts by weight Butyl stearate 4 parts by weight MEK (methyl ethyl ketone) 126 parts by weight Toluene 38 parts by weight Cyclohexanone 38 parts by weight After kneading the above composition, it is dispersed by a sand grinder mill to prepare a non-magnetic paint 1. did. <Magnetic paint 1> 100 parts by weight of metal magnetic powder (Hc = 158 kA / m, σ _s = 120 Am ² / kg, BET = 48 m ² / g, PH = 10, average major axis length = 0.07 μm Fe / Co = 100/20 (weight ratio), additive elements including Al and Y as) vinyl copolymers chloride polymer (Nippon Zeon: MR 110) 14 parts by weight (polymerization degree = 300, polar group: -OSO ₃ K) -SO ₃ Na-containing polyurethane resin 6 parts by weight (Mn = 25000, polar group concentration = 1 / molecule) Abrasive α-Al ₂ O ₃ (Sumitomo Chemical Co., Ltd .: HIT82) 10 parts by weight (average particle size) Diameter = 0.12 μm, BET = 20 m ² / g) Carbon black (manufactured by Mitsubishi Chemical Corporation: CF-9) 3 parts by weight (average particle size = 40 nm, BET = 60 m ² / g, DBP oil absorption = 64 ml / 100 g) sorbita Monostearate 3 parts by weight Irisetyl stearate 3 parts by weight butyl stearate 2 parts by weight MEK 380 parts by weight Toluene 130 parts by weight Cyclohexanone 130 parts by weight After kneading the above composition, disperse it with a sand grinder mill and perform magnetic coating. 1 was created.

First, a non-magnetic coating material 1 is used as a filler to extrude a PET film having a surface roughness (Ra) of 8 nm and a thickness of 62 μm containing 500 ppm of SiO ₂ having an average particle size of 0.1 μm and a dry thickness of 2.0 μm by a die nozzle method. And dried at a drying temperature of 100 ° C., and then a linear pressure of 2940 N /
After performing a calendering treatment at a temperature of 90 ° C. and an electron beam (5 Mrad). Next, the other surface was also formed in the same procedure to form a roll of a double-sided nonmagnetic layer.

Next, 4 parts by weight of Coronate L (manufactured by Nippon Polyurethane Industry Co., Ltd.) was added to the magnetic paint 1, and the paint was extruded onto a roll coated with the nonmagnetic layer while being redispersed by an ultrasonic dispersing machine. Dry thickness of 0.1 with die nozzle method
It was applied to a thickness of 5 μm, and further non-oriented by a non-oriented magnet.
A calendar treatment was performed at N / cm and a temperature of 90 ° C. to finish a coating film on one side. Next, the other side was also formed in the same procedure to prepare a raw roll of a double-sided magnetic layer.

Finally, the raw roll was punched out into a disk shape, and then heat cured at 70 ° C. for 24 hours to prepare a disk sample. (2) Example 2 In Example 1, the major axis diameter of the metal magnetic powder of the magnetic paint 1 was set to 0.05.
A disk sample was prepared in the same manner as in Example 1 except that the thickness was changed to μm. (3) Example 3 In Example 1, σ _s of the metal magnetic powder of the magnetic paint 1 was set to 100 Am ^2.
A disk sample was prepared in the same manner as in Example 1 except that the sample was changed to / kg. (4) Example 4 In Example 1, the σ _s of the metal magnetic powder of the magnetic paint 1 was 130 Am ^2.
A disk sample was prepared in the same manner as in Example 1 except that the sample was changed to / kg. (5) Example 5 <Non-magnetic paint 2> 55 parts by weight of granular α-Fe ₂ O ₃ (manufactured by Sakai Chemical Industry Co., Ltd .: FRO-3) (average particle size = 30 nm, BET = 45 m ² / g) Carbon Black (Mitsubishi Chemical Corporation: # 45B) 30 parts by weight (Average particle size = 24 nm, BET = 125 m ² / g, DBP oil absorption = 47 ml / 100 g) α-Al ₂ O ₃ (Sumitomo Chemical Industries, Ltd. ): AKP50) 15 parts by weight (average particle size = 0.20 μm, BET = 8 m ² / g) Vinyl chloride-based copolymer 12 parts by weight (polymerization degree = 300, polar group: —OSO ₃ K = 2 / 1 molecule) Polyurethane resin 4 parts by weight (Mn = 25000, polar group: phosphorus compound = 1 piece / molecule) Isocetyl stearate 10 parts by weight Butyl stearate 4 parts by weight MEK 126 parts by weight Toluene 38 parts by weight cyclohexanone 38 parts by weight The above composition was kneaded, and then dispersed by a sand grinder mill to prepare a non-magnetic coating material 2.

First, a non-magnetic paint 2 containing 4 parts by weight of Coronate L (manufactured by Nippon Polyurethane Industry Co., Ltd.) was used as a filler, and 500 μl of SiO ₂ having an average particle size of 0.1 μm was used as a filler.
PET with a surface roughness (Ra) of 8 nm including pm and a thickness of 62 μm
Extruded die nozzle method on film, dry thickness 2.0
μm, and dried at a drying temperature of 100 ° C.
The calender treatment was performed at a linear pressure of 2940 N / cm and a temperature of 90 ° C. Next, the other surface was also formed in the same procedure to form a roll of a double-sided nonmagnetic layer. Thereafter, heat curing was performed at 60 ° C. for 24 hours.

Next, 4 parts by weight of Coronate L (manufactured by Nippon Polyurethane Industry Co., Ltd.) was added to the magnetic paint 1, and the paint was extruded onto a roll coated with the non-magnetic layer while being redispersed by an ultrasonic dispersing machine. Dry thickness of 0.1 with die nozzle method
It was applied to a thickness of 5 μm, was further non-oriented by a non-oriented magnet, and was dried at a drying temperature of 100 ° C.
A calendar treatment was performed at N / cm and a temperature of 90 ° C. to finish a coating film on one side. Next, the other side was also formed in the same procedure to prepare a raw roll of a double-sided magnetic layer.

Finally, the raw roll was punched out into a disk shape, and then heat cured at 70 ° C. for 24 hours to prepare a disk sample. (6) Comparative Example 1 The σ _s of the metal magnetic powder of the magnetic paint 1 in Example 1 was set to 150 Am ^2.
A disk sample was prepared in the same manner as in Example 1 except that the sample was changed to / kg. (7) Comparative Example 2 In Example 1, σ _s of the metal magnetic powder of the magnetic paint 1 was set to 85 Am ² /
A disk sample was prepared in the same manner as in Example 1 except that the weight was changed to kg. (8) Comparative Example 3 In Comparative Example 1, the major axis diameter of the metal magnetic powder of the magnetic paint was 0.05 μm.
A disk sample was prepared in the same manner as in Comparative Example 1, except that m was changed to m. (9) Comparative Example 4 In Example 1, the major axis diameter of the metal magnetic powder of the magnetic paint 1 was 0.12.
A disk sample was prepared in the same manner as in Example 1 except that the thickness was changed to μm. (10) Comparative Example 5 In Example 1, the major axis diameter of the metal magnetic powder of the magnetic paint 1 was set to 0.02.
A disk sample was prepared in the same manner as in Example 1 except that the thickness was changed to μm. (11) Comparative Example 6 To the non-magnetic paint 2 and the magnetic paint 1, 4 parts by weight of Coronate L (manufactured by Nippon Polyurethane Industry Co., Ltd.) was added, and the non-magnetic paint 2 was used as a filler to form a SiO.sub.2 having an average particle size of 0.1 .mu.m. _Two
Surface roughness (Ra) containing 500 ppm of 8 nm, 62 μm
Thickness is applied to a thick PET film by an extrusion die nozzle method so that the dry thickness becomes 2.0 μm, and while it is still wet, the magnetic paint 1 is redispersed by an ultrasonic dispersing machine and the extrusion die nozzle Dry thickness of 0.1
It was applied so as to have a thickness of 5 μm. After that, non-orientation is performed with a non-oriented magnet, and after drying at a drying temperature of 100 ° C, a linear pressure of 294
A calender treatment was performed at 0 N / cm and a temperature of 90 ° C. to finish a coating film on one side. Next, the other side was also formed in the same procedure to prepare a raw roll of a double-sided magnetic layer.

Finally, the raw roll was punched out into a disk shape, and then thermoset at 70 ° C. for 24 hours to prepare a disk sample. (12) Comparative Example 7 S having an average particle size of 0.1 μm using the non-magnetic paint 1 as a filler
Surface roughness (Ra) containing 500 ppm of iO ₂ 8 nm, 6
A 2 μm thick PET film is applied by an extrusion die nozzle method so as to have a dry thickness of 2.0 μm, and 4 parts by weight of Coronate L (manufactured by Nippon Polyurethane Industry Co., Ltd.) is applied to the magnetic paint 1 while it is still wet. The mixture was added, and the mixture was redispersed by an ultrasonic dispersing machine, and was applied thereon by an extrusion die nozzle method so as to have a dry thickness of 0.15 μm. Thereafter, non-orientation was carried out by a non-orientation magnet, dried at a drying temperature of 100 ° C., calendered at a linear pressure of 2940 N / cm and a temperature of 90 ° C., and then irradiated with an electron beam (5 Mrad). Next, the other surface was formed in the same procedure, and a roll of a double-sided magnetic layer was formed.

Finally, the raw roll was punched out into a disk shape, and then heat cured at 70 ° C. for 24 hours to prepare a disk sample. (13) Comparative Example 8 A disk sample was prepared in the same manner as in Example 5 except that the non-magnetic raw material was not thermally cured. 2. Tape sample (14) Example 6 <Nonmagnetic paint 3> 75 parts by weight of α-Fe ₂ O ₃ (manufactured by Toda Kogyo Co., Ltd .: DPN-250BW) (average major axis diameter = 150 nm, BET = 55 m ² / g) Carbon black (Mitsubishi Chemical Corp .: # 950B) 20 parts by weight (Average particle size = 16 nm, BET = 250 m ² / g, DBP oil absorption = 80 ml / 100 g) α-Al ₂ O ₃ (Sumitomo Chemical Industries, Ltd. 5 parts by weight (average particle size = 0.18 μm, BET = 12 m ² / g) 12 parts by weight of electron beam-curable vinyl chloride copolymer (degree of polymerization = 300, polar group: —OSO ₃₎ K) Electron beam-curable polyurethane resin 6 parts by weight (Mn = 25000, polar group: phosphorus compound = 1 / molecule) Butyl stearate 1 part by weight Stearic acid 1 part by weight MEK 150 parts by weight Toluene 5 After kneading the parts by weight Cyclohexanone 50 parts by weight The above composition to prepare a nonmagnetic coating 3 was dispersed in a sand grinder mill. <Magnetic paint 2> 100 parts by weight of metal magnetic powder (Hc = 158 kA / m, σ _s = 120 Am ² / kg, BET = 48 m ² / g, PH = 10, average major axis length = 0.07 μm Fe / Co = 100/20 (weight ratio), Al and including Y) vinyl copolymers chloride polymer 10 parts by weight as an additive element (polymerization degree = 300, polar group: -OSO ₃ K) -SO ₃ Na-containing polyurethane resin 7 parts by weight (Mn = 25000, polar group concentration = 1 / molecule) α-Al ₂ O ₃ (HIT82 manufactured by Sumitomo Chemical Co., Ltd.) 12 parts by weight (average particle size = 0.12 μm, BET = 20 m ² / g) 2) Myristic acid 2 parts by weight MEK 250 parts by weight Toluene 80 parts by weight Cyclohexanone 80 parts by weight After the above composition was kneaded, it was dispersed by a sand grinder mill to prepare a magnetic paint 2. <Backcoat layer paint> 80 parts by weight of carbon black (Columbian Carbon: Conductex SC average particle size = 20 nm, BET = 220 m ² / g) 1 part by weight of carbon black (Colombian Carbon: Sevacarb MT average particle size) = 350 nm, BET = 8 m ² / g) α-Fe ₂ O ₃ (manufactured by Toda Kogyo Co., Ltd .: TF100 average particle size = 0.1 μm) 1 part by weight 65 parts by weight of a vinyl chloride-vinyl acetate-vinyl alcohol copolymer (monomer (Weight ratio = 92: 3: 5, average degree of polymerization = 420) Polyester polyurethane resin 35 parts by weight MEK 260 parts by weight Toluene 260 parts by weight Cyclohexanone 260 parts by weight After the above composition was kneaded, it was dispersed by a sand grinder mill. Was. Next, the following additives and solvents were added to adjust the viscosity. 1 part by weight of stearic acid 1 part by weight of myristic acid 1 part by weight of butyl stearate 2 parts by weight of MEK 210 parts by weight of toluene 210 parts by weight of cyclohexanone 210 parts by weight Next, SiO ₂ having an average particle diameter of 0.1 μm is used as a filler.
First, a non-magnetic layer coating material 3 is extruded onto a 6.5 μm thick PEN film having a surface roughness (Ra) of 6 nm containing 00 ppm by a die nozzle method so as to have a dry thickness of 2.0 μm, and dried at a drying temperature of 100 ° C. And linear pressure 2940N / c
After performing a calendering process at m and a temperature of 90 ° C., electron beam irradiation (5 Mrad) was performed to prepare a roll having a non-magnetic layer applied. Next, 4 parts by weight of Coronate L (manufactured by Nippon Polyurethane Industry Co., Ltd.) was added to the magnetic paint 2, 1 part by weight was added to 100 parts by weight of the back coat layer paint, and the magnetic paint 2 was placed on the roll coated with the non-magnetic layer. Is applied by an extrusion die nozzle method so as to have a dry thickness of 0.15 μm, orientation is performed, the coating film is dried at a drying temperature of 100 ° C., and a linear pressure of 294 is applied.
A calendar treatment was performed at 0 N / cm and a temperature of 100 ° C. Next, a backcoat layer paint was applied to the base surface opposite to the magnetic layer by extrusion die coating so as to have a dry thickness of 0.5 μm to prepare a raw roll.

After leaving this raw roll at room temperature for 24 hours, it was cured in a heating oven at 60 ° C. for 24 hours.
The tape sample was cut into a 6.35 mm width. (15) Example 7 In Example 6, the major axis diameter of the metal magnetic powder of the magnetic paint 2 was set to 0.05.
A tape sample was prepared in the same manner as in Example 6 except that the thickness was changed to μm. (16) Example 8 In Example 6, σ _s of the metal magnetic powder of the magnetic paint 2 was set to 100 Am ^2.
A tape sample was prepared in the same manner as in Example 6 except that the tape sample was changed to / kg. (17) Example 9 In Example 6, the σ _s of the metal magnetic powder of the magnetic paint 2 was 130 Am ^2.
A tape sample was prepared in the same manner as in Example 6 except that the tape sample was changed to / kg. (18) Example 10 <Nonmagnetic Paint 4> 75 parts by weight of α-Fe ₂ O ₃ (manufactured by Toda Kogyo Co., Ltd .: DPN-250BW) (average major axis diameter = 150 nm, BET = 55 m ² / g) Carbon black (Mitsubishi Chemical Corp .: # 950B) 20 parts by weight (Average particle diameter = 16 nm, BET = 250 m ² / g, DBP oil absorption = 80 ml / 100 g) α-Al ₂ O ₃ (Sumitomo Chemical Industries, Ltd.) 5 parts by weight (average particle size = 0.18 μm, BET = 12 m ² / g) 12 parts by weight of vinyl chloride copolymer (degree of polymerization = 300, polar group: —OSO ₃ K) 6 parts by weight of polyurethane resin Parts (Mn = 25000, polar group: phosphorus compound = 1 / molecule) Butyl stearate 1 part by weight Stearic acid 1 part by weight MEK 150 parts by weight Toluene 50 parts by weight Cyclohexanone 50 parts by weight After the serial composition was kneaded to prepare a nonmagnetic coating 4 was dispersed in a sand grinder mill.

[0054] First 500p of SiO ₂ having an average particle size of 0.1 [mu] m 4 parts by weight added to paint to the nonmagnetic coating 4 Coronate L (manufactured by Nippon Polyurethane Industry Co.) as a filler
6.5 μm thick PE with surface roughness (Ra) of 6 nm including pm
Extruded die nozzle method on N film with dry thickness of 2.
It was applied to a thickness of 0 μm, dried at a drying temperature of 100 ° C., and calendered at a linear pressure of 2940 N / cm and a temperature of 90 ° C. Thereafter, thermosetting was performed at 60 ° C. for 24 hours to prepare a roll on which the nonmagnetic layer was applied.

Next, 4 parts by weight of Coronate L (manufactured by Nippon Polyurethane Industry Co., Ltd.) was added to the magnetic coating material 2, 1 part by weight was added to 100 parts by weight of the coating material for the back coat layer, and the mixture was placed on the roll coated with the nonmagnetic layer. The magnetic paint 2 is applied by an extrusion die nozzle method so as to have a dry thickness of 0.15 μm, oriented, dried at a drying temperature of 100 ° C., and dried at a linear pressure of 29 ° C.
The calender treatment was performed at 40 N / cm and a temperature of 100 ° C. Next, a backcoat layer paint was applied to the base surface opposite to the magnetic layer by extrusion die coating so as to have a dry thickness of 0.5 μm to prepare a raw roll.

After leaving the raw roll at room temperature for 24 hours, it was cured in a heating oven at 60 ° C. for 24 hours.
The tape sample was cut into a 6.35 mm width. (19) Comparative Example 9 In Example 6, the σ _s of the metal magnetic powder of the magnetic paint 2 was set to 150 Am ^2.
A tape sample was prepared in the same manner as in Example 6 except that the tape sample was changed to / kg. (20) Comparative Example 10 In Example 6, the σ _s of the metal magnetic powder of the magnetic paint 2 was set to 85 Am ² /
A tape sample was prepared in the same manner as in Example 6, except that the weight was changed to kg. (21) Comparative Example 11 In Comparative Example 8, the major axis diameter of the metal magnetic powder of the magnetic paint was 0.05 μm.
A tape sample was prepared in the same manner as in Comparative Example 8 except that m was changed to m. (22) Comparative Example 12 In Example 6, the long axis diameter of the metal magnetic powder of the magnetic paint was 0.12 μm.
A tape sample was prepared in the same manner as in Example 6, except that m was changed to m. (23) Comparative Example 13 In Example 6, the major axis diameter of the metal magnetic powder of the magnetic paint was set to 0.02 μm.
A tape sample was prepared in the same manner as in Example 6, except that m was changed to m. (24) Comparative Example 14 4 parts by weight of Coronate L (manufactured by Nippon Polyurethane Industry Co., Ltd.) was added to the non-magnetic paint 4 and the magnetic paint 2, and 1 part by weight was added to 100 parts by weight of the back coat layer paint. 4
Of SiO ₂ having an average particle size of 0.1 μm as a filler
A PEN film having a surface roughness (Ra) of 6 nm and a thickness of 6 nm including a thickness of 0 ppm was applied to a PEN film having a thickness of 6.5 μm by an extrusion die nozzle method so as to have a dry thickness of 2.0 μm. While redispersing with a dispersing machine, the dry thickness is 0.15μ by extrusion die nozzle method.
m. Thereafter, orientation was performed, and the coating film was dried at a drying temperature of 100 ° C., and calendered at a linear pressure of 2940 N / cm and a temperature of 100 ° C. Next, a backcoat layer paint was applied to the base surface opposite to the magnetic layer by extrusion die coating so as to have a dry thickness of 0.5 μm to prepare a raw roll.

After leaving the raw roll at room temperature for 24 hours, it was cured in a heating oven at 60 ° C. for 24 hours.
The tape sample was cut into a 6.35 mm width. (25) Comparative Example 15 4 parts by weight of Coronate L (manufactured by Nippon Polyurethane Industry Co., Ltd.) and 1 part by weight of 100 parts by weight of the backcoat layer paint were added to the magnetic paint 2, and the nonmagnetic paint 3 was averaged as a filler. A PEN film having a surface roughness (Ra) of 6 nm and a thickness of 6.5 μm containing 500 ppm of SiO ₂ having a particle size of 0.1 μm was applied by an extrusion die nozzle method so as to have a dry thickness of 2.0 μm. Meanwhile, the magnetic paint 2 was applied thereon while being redispersed by an ultrasonic dispersing machine so as to have a dry thickness of 0.15 μm by an extrusion die nozzle method. Thereafter, orientation is performed, the coating film is dried at a drying temperature of 100 ° C., a calendar process is performed at a linear pressure of 2940 N / cm and a temperature of 100 ° C., and then electron beam irradiation (5 Mrad) is performed.
Was done. Next, the backcoat layer paint was extruded onto the base surface opposite to the magnetic layer, and the dry thickness was 0.5
It was applied so as to have a thickness of μm to prepare a raw roll.

After leaving this raw roll at room temperature for 24 hours, it was cured in a heating oven at 60 ° C. for 24 hours.
The tape sample was cut into a 6.35 mm width. (26) Comparative Example 16 A tape sample was prepared in the same manner as in Example 10, except that the non-magnetic raw material was not thermally cured. The above samples were evaluated for surface properties and electromagnetic conversion characteristics. The results are shown in Tables 1 to 6. <Evaluation method> (1) Centerline surface roughness Ra Using a Talystep system manufactured by Taylor Hobson, a filter 0.18 to 9 Hz, a stylus 0.1 × 2.5 μm special stylus, stylus pressure 2 mg, measurement speed 0 .03m
The measurement was performed under the conditions of m / sec and a measurement length of 500 μm. (2) Electromagnetic conversion characteristics (S / N ratio) Disk sample A TDK experimental MR head (write side: MIG head, gap 0.15 μm, reproduction side: N)
An i-Fe element (MR head) was attached and measured. Tape sample A commercially available data drive was modified to use a tester that enabled signal input / output of the head, using a TDK experimental MR head (recording head: MIG head, gap 1.0 μm,
The measurement was performed with a reproducing head: Ni-Fe element MR head) mounted. It was measured by the above method, and 20 dB or more was regarded as acceptable.

[0059]

[Table 1] Note: EB of the non-magnetic layer resin type indicates an electron beam-curable resin, and NK indicates a thermosetting resin. -Coating method W / W (wet-on-wet coating): A method of applying a magnetic paint while the non-magnetic layer is in a wet state. W / D (wet-on-dry coating): A method in which a non-magnetic layer is coated and dried, and then a magnetic layer is coated.

[0060]

[Table 2]

[0061]

[Table 3]

[0062]

[Table 4]

[0063]

[Table 5]

[0064]

[Table 6]

[0065]

According to the present invention, the average major axis length on the non-magnetic layer is 0.03~0.08μm, σ _s is 100 to
By applying a magnetic layer having a center line average roughness Ra of 5 nm or less using a metal powder magnetic powder of 30 Am ² / kg by a wet-on-dry method, it has excellent electromagnetic conversion characteristics and is suitable for reproduction with an MR head. A magnetic recording medium can be obtained.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G11B 5/706 G11B 5/706 5/738 5/738 H01F 1/06 H01F 1/06 HF term (reference 4J038 BA021 CD021 CE021 DB001 DF001 DF061 DG001 EA011 HA026 HA066 KA07 KA20 NA22 PA12 PA17 PB11 PC08 5D006 BA04 BA05 BA08 BA19 CA01 CA04 FA09 5E040 AA11 AA14 AA19 BB05 CA06 NN06 NN15

Claims (4)

[Claims] A magnetic layer provided on a non-magnetic support via a non-magnetic layer in which non-magnetic powder is dispersed in a binder resin;
In a magnetic recording medium used for reproduction with an MR head, the magnetic layer is coated on a non-magnetic support, and dried and dried.
Are those provided by applying a magnetic coating on top of the cured non-magnetic layer, wherein the average major axis length in the magnetic layer is 0.03～0.08Myuemu, saturation magnetization sigma _s is from 100 to 13
A magnetic recording medium comprising 0 Am ² / kg of metal magnetic powder and having a center line average roughness Ra of 5 nm or less on the surface of the magnetic layer. 2. The magnetic recording medium according to claim 1, wherein the binder resin contained in the nonmagnetic layer is an electron beam curable resin. 3. The magnetic recording medium according to claim 1, wherein the non-magnetic powder contains at least carbon black. 4. A magnetic recording method in which recording is performed on a magnetic recording medium having a magnetic layer via a nonmagnetic layer in which a nonmagnetic powder is dispersed in a binder resin on at least one surface of a nonmagnetic support, and reproduction is performed by an MR head. In the reproducing system, the magnetic layer contains metal magnetic powder having an average major axis length of 0.03 to 0.08 μm and a saturation magnetization _s of 100 to 130 Am ² / kg, and a center line average roughness of the surface of the magnetic layer. A magnetic recording / reproducing system, wherein Ra is 5 nm or less.