JP2982086B2 - Magnetic recording disk and method of manufacturing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording disk for high-density recording, and more particularly to a magnetic recording disk most suitable for digital signal recording of a signal having a shortest recording wavelength of 1.5 .mu.m or less.

[0002]

2. Description of the Related Art Magnetic recording technology requires that a medium can be used repeatedly, that signals can be easily digitized, and that a system can be constructed in combination with peripheral devices.
Video, audio, video, audio, etc.
It has been widely used in various fields including computer applications. In order to respond to the trend of miniaturization of equipment, the demand for improving the quality of recording / reproducing signals, the demand for longer recording time, and the demand for increasing the recording capacity, the recording density of the recording medium is further increased. Improvement has always been desired. Therefore, the surface properties of the magnetic layer, the dispersibility of the magnetic particles in the magnetic layer, and the magnetic properties of the magnetic layer have been improved.

[0003] In recent years, the spread of personal computers, the sophistication of application software, and the increase in processing information have increased even for floppy disks having a magnetic layer on a flexible non-magnetic support, which is an external storage medium for microcomputers and personal computers. 10 from the trend
There has been a strong demand for higher capacity of M bytes or more. A recording system of a high-density code having a frequency component area 1.5 times or more wider than that of a conventional RLL signal has been proposed, and the shortest recording wavelength of a recording signal recorded on a floppy disk is 3.0 μm or less. , And about 1.5 μm or less.

In order to improve the recording density, the gap length of the magnetic head is naturally further reduced.
It is about 5 μm or less. In order to enable recording with a short recording wavelength and a high recording density, it is first necessary to increase the coercive force of the magnetic layer. For that purpose, Japanese Patent Application Laid-Open
JP-A-8-122623, JP-A-61-74137, and the like have proposed methods of converting ferromagnetic particles in a magnetic layer of a medium on a disk into ferromagnetic metal powder.

The use of hexagonal ferrite typified by barium ferrite or the like as ferromagnetic particles has been disclosed in, for example, Japanese Patent Publication No. Sho 62-49656 and Japanese Patent Publication No. Sho 60-5.
No. 0323, US Pat. No. 4,629,653, US Pat.
No. 770, US Pat. No. 4,543,198 and the like.

In a magnetic recording medium for a computer such as a floppy disk, overwriting of recording signals having different recording wavelengths is indispensable. In conventional media, there are two types of signals that are twice as related in frequency:
It would have been good if the 1f and 2f signals could be overwritten. However, in the above-mentioned RLL signal, not only the recording wavelength was shortened, but also overwriting of a plurality of signals in a frequency ratio area of 3: 8 is required. As described above, when a signal having a short recording wavelength and a large difference in recording frequency is used, in order to successfully overwrite (overwrite) a signal with a short recording wavelength on a signal with a long recording wavelength, the above-described method is required. JP-A-58-122623, JP-A-61-74
As disclosed in Japanese Patent No. 137 and the like, there is a limit to simply improving the magnetic properties of the magnetic layer. That is,
Even if a shorter recording signal is overwritten on a recording signal of a longer wavelength previously recorded, the magnetic field lines do not reach deep in the magnetic layer. is there. In order to solve this problem, it is most effective to make the magnetic layer thin.

Another problem required for magnetic recording disks is the problem of medium charging. That is, it is to prevent the occurrence of drop-out due to the charging of the medium and the attachment of dust and dirt to the surface of the magnetic layer. Since the magnetic recording disk digitally records computer information, the lack of a recorded or reproduced signal due to dropout is described in B.A. E. FIG. R. (Bit error rate) increases, which is a fatal problem. Also, the shorter the recording wavelength of the recording signal on the magnetic recording disk, the greater the effect of the dropout on the magnetic layer,
This problem of chargeability is an important issue when designing a large-capacity magnetic recording disk with a high recording density. The usual method for preventing electrification is to add carbon black into the magnetic layer.However, as described above, when the magnetic layer is thinned in consideration of the problem of overwriting in recording in a region where the recording wavelength is short, There is a limit to the amount of carbon black that can be retained in the magnetic layer, and it is desirable to avoid adding carbon black to the magnetic layer as much as possible in order to maintain high magnetic properties.

As another method for improving the problem of charging property, a magnetic recording medium in which a non-magnetic layer containing carbon black or the like is provided between a magnetic layer and a non-magnetic support has been proposed. JP-A-55-55432, JP-A-50-104003, US Pat. No. 3,400,091, JP-A-62-214513, JP-A-62-2
No. 14514, JP-A-62-231417,
It is disclosed in JP-A-63-31027. A magnetic recording medium having this layer configuration has also been proposed for the purpose of improving the surface properties of the magnetic layer or running durability. However, the thickness of the magnetic layer of the magnetic recording medium disclosed in these prior arts is not sufficiently thin with respect to a recording wavelength to be recorded in a currently required large-capacity magnetic recording disk. Absent.

When the thickness of the magnetic layer is reduced in order to improve the overwriting characteristics of the magnetic recording disk, the amount of the lubricant that can be held by the magnetic layer decreases, and the running durability becomes a problem. That is, while the magnetic layer and the magnetic head repeat sliding, the lubricant becomes insufficient and the friction coefficient increases, so that the magnetic layer is scraped by the magnetic head. If too much lubricant is contained in the magnetic layer, the physical properties of the magnetic layer deteriorate, so that the content of the lubricant in the magnetic layer is naturally limited. When the ferromagnetic particles of the magnetic layer are made of ferromagnetic metal powder or hexagonal ferrite as described above in order to increase the capacity of the magnetic recording disk, the running durability of the magnetic layer tends to decrease.

[0010] Furthermore, the magnetic layer becomes easier to peel off as it becomes thinner, and the peeled magnetic layer causes a new drop-out, so it is necessary to deal with this problem. The problem of peeling of the magnetic layer could not be avoided even if a nonmagnetic layer was formed between the magnetic layer and the nonmagnetic support. As described above, in order to use a large-capacity medium as a magnetic recording disk such as a floppy disk, the above-described various problems must be dealt with, and means for satisfying all of them has not yet been proposed.

[0011]

SUMMARY OF THE INVENTION An object of the present invention has been made in view of the above-mentioned problems of the prior art, and has a magnetic recording disk which is excellent in electromagnetic conversion characteristics and excellent in running durability and is optimal for digital data recording. And a method for producing the same. In particular, it is an object of the present invention to provide a magnetic recording disk having excellent overwriting characteristics at a high recording density and a large recording capacity, and a method for manufacturing the same.

The object of the present invention is to form a non-magnetic layer mainly composed of non-magnetic particles and a binder resin and a magnetic layer mainly composed of ferromagnetic particles and a binder resin on a non-magnetic support in this order. in the magnetic recording disks, the nonmagnetic particles are inorganic powders and carbon black, wherein the nonmagnetic layer is carbon black contained 3 to 20 wt% of the non-magnetic particles, and the fatty acid ester is 3 to the non-magnetic particles 20% by weight, and the thickness of the magnetic layer is 0.5
μm or less, and the orientation ratio of the ferromagnetic particles in the magnetic layer is 0.85 or more, and the ferromagnetic particles in the magnetic layer are ferromagnetic metal powder or hexagonal ferrite. In the production of a recording disk and the magnetic recording disk, a non-magnetic coating layer is formed by applying a coating solution for a non-magnetic layer mainly composed of non-magnetic particles and a binder resin onto a non-magnetic support, and the non-magnetic coating layer is formed. A magnetic layer coating liquid in which ferromagnetic particles are dispersed in a binder resin solution is formed on the nonmagnetic coating layer while the ferrite particles are in a wet state, and then dried to form a nonmagnetic coating on the nonmagnetic support. This is achieved by a method for manufacturing a magnetic recording disk in which a layer and a magnetic layer are formed in this order.

In the magnetic recording disk of the present invention, the thickness of the magnetic layer is extremely thin, 0.5 μm or less.
Even if the shortest recording wavelength is 1.5 μm or less, and even 1.0 μm or less, there is no loss and good overwriting characteristics indispensable for digital data recording can be obtained. Further, since ferromagnetic powder or hexagonal ferrite is used as the ferromagnetic particles of the magnetic layer, the electromagnetic conversion characteristics are excellent and a high output can be obtained even if the magnetic layer is thin. The output in the circumferential direction of the magnetic recording disk can be made uniform by increasing the orientation ratio to 0.85 or more. Furthermore, by providing a non-magnetic layer containing conductive particles between the magnetic layer and the non-magnetic support, a magnetic recording disk with excellent running durability that is less likely to be charged and less likely to cause dropout. It can be.

When the magnetic recording disk of the present invention is manufactured, a coating solution for a nonmagnetic layer mainly composed of nonmagnetic particles and a binder resin is coated on a nonmagnetic support to form a nonmagnetic coating layer. While the ferromagnetic particles are dispersed in a binder resin solution while the non-magnetic coating layer is in a wet state, a coating liquid for a magnetic layer is formed on the non-magnetic coating layer, whereby the non-magnetic coating layer is formed. The adhesion of the magnetic layer is excellent, and even if the thickness of the magnetic layer is as thin as 0.5 μm or less, the magnetic layer is hardly peeled off, and a highly reliable magnetic recording disk with excellent running durability can be obtained.

When a ferromagnetic metal powder is used for the magnetic layer of the magnetic recording disk of the present invention, the needle ratio of the ferromagnetic metal powder is 3 to 12, and the coercive force of the magnetic layer is 1400.
It is desirable to set it to Elsted II or more. In the case of hexagonal ferrite, the average particle size is 0.01 to 0.5.
Preferably, the plate ratio is 2 to 2 μm, and the perpendicular diamagnetic field correction squareness ratio of the ferromagnetic particles in the magnetic layer is 0.6 or more. By using the ferromagnetic particles in the magnetic layer in this manner, high-density recording with excellent electromagnetic conversion characteristics is possible, and a magnetic layer with a large orientation ratio can be obtained.

The non-magnetic particles used in the non-magnetic layer are inorganic powders.
Powder and carbon black, and 3 of the non-magnetic particles.
To 20% by weight is carbon black, and among carbon blacks, the average particle diameter is 40 mμ or less, and DBP
If the particle size of the oil absorption is 300 ml / 100 g or more and the particle size is small and the oil absorption is large, the surface properties of the magnetic layer formed on the upper layer can be made smooth, and the spacing with the recording / reproduction head can be improved. Since the loss is reduced, a high reproduction output can be obtained. Then, carbon black easily forms a structure in the nonmagnetic layer, and as a result, a low surface electric resistance can be obtained, and the occurrence of dropout in running durability can be reduced.

Further, by adding 3 to 20% by weight of a fatty acid ester as a lubricant in the non-magnetic layer, it is possible to compensate for the problem that the content of the lubricant in the magnetic layer cannot be increased due to the thin magnetic layer. it can. That is, the lubricant is gradually consumed and insufficient due to the sliding with the recording / reproducing head, so that the magnetic layer may be scraped or the friction may increase, eventually causing a stop. This is because the lubricant that is always consumed in the magnetic layer can be supplemented by moving into the magnetic layer.

The thickness of the magnetic layer of the magnetic recording disk of the present invention is 0.5 μm or less, preferably 0.45 μm.
μm or less. As the thickness of the magnetic layer increases, the overwriting characteristics required for digital data recording deteriorate, and this tendency is particularly remarkable when the recording wavelength is 1.5 μm or less. There is no particular lower limit on the thickness of the magnetic layer, but care must be taken because if the thickness is too small, the reproduction output decreases. The total thickness of the nonmagnetic layer and the magnetic layer formed on the nonmagnetic support may be in the range of 1 to 3.0 μm.

The orientation ratio of the magnetic particles in the magnetic layer of the magnetic recording disk of the present invention is preferably 0.85 or more, more preferably 0.90 or more, and most preferably 0.95 or more. The orientation degree ratio is a value obtained by dividing the minimum squareness ratio in the circumferential direction of the disk-shaped medium by the maximum squareness ratio. Becomes To make the orientation ratio 0.85 or more, where the upper magnetic layer is in an undried state, for example, a random orientation method using a permanent magnet as disclosed in Japanese Patent Publication No. 3-41895, JP-A-63-148417, JP-A-1-304247
And a method for applying an alternating magnetic field disclosed in Japanese Patent Application Laid-Open No. Hei.

In this case, the needle ratio of the ferromagnetic metal particles is 12
Or less, desirably 10 or less.
It is necessary to make it 85 or more. The needle ratio of the ferromagnetic metal powder used in the present invention is 3 to 12, preferably 4 to 11, and more preferably 6 to 10. If the needle ratio is too large, the orientation ratio cannot be increased, and if it is too small, pressure demagnetization or the like is apt to occur.

When a ferromagnetic metal powder is used as the ferromagnetic particles to enable a high recording density, the coercive force of the magnetic layer is preferably set to 1400 Elsted or more. More preferably, it is 1500 ersted or more. If the coercive force is too low, the signal output is reduced due to the self-demagnetizing action, which is not preferable. On the other hand, if it is too high, magnetization reversal by the magnetic recording head becomes difficult. The residual magnetic flux density is 1100 gauss or more, and more desirably 1400 gauss or more.

Ferromagnetic metal powder particles usable in the present invention
25 to 80m if the size is expressed by the specific surface area by BET method
^Two/ G, preferably 35-60 m^Two/ G. 2
5m ^Two/ G or less, the noise is high and 80 m^Two/ G or less
Above, dispersion becomes difficult, and the surface properties of the magnetic layer are improved.
It is not preferable because it cannot be performed. Also, X-ray diffraction
In terms of crystallite size measured by analysis, 450 to 100
Angstroms, preferably 350-150
It is a storm.

The ferromagnetic metal powder used in the present invention comprises:
It may contain small amounts of hydroxides or oxides. As the ferromagnetic metal particles, those obtained by a known production method can be used, and the following methods can be used. A method of reducing a complex organic acid salt (mainly oxalate) with a reducing gas such as hydrogen, a method of reducing iron oxide with a reducing gas such as hydrogen to obtain Fe or Fe—Co particles, Thermal decomposition method, reduction method by adding a reducing agent such as sodium borohydride, hypophosphite or hydrazine to an aqueous solution of ferromagnetic metal, reduction of fine powder by evaporating metal in low-pressure inert gas And how to get it.

The ferromagnetic metal particles thus obtained are subjected to a known slow oxidation treatment, that is, a method of immersing in an organic solvent and then drying. Any of a method of forming and drying and a method of forming an oxide film on the surface by adjusting the partial pressure of oxygen gas and an inert gas without using an organic solvent can be used. The ferromagnetic particles used in the present invention preferably have few vacancies, and the value is preferably 2
0 vol% or less, more preferably 5 vol% or less.

The hexagonal ferrite which can be used as the ferromagnetic particles in the magnetic layer of the magnetic recording disk of the present invention is typically a ferromagnetic powder having a flat plate shape and having an easy axis of magnetization in a direction perpendicular to the flat plate surface. Examples of the composition of the hexagonal ferrite include barium ferrite, strontium ferrite, lead ferrite, calcium ferrite, and substituted cobalt ferrite, specifically, magnetoplumbite-type barium ferrite and strontium ferrite. Examples include magnetoplumbite-type barium ferrite and strontium ferrite containing a part of spinel phase, and particularly preferred are barium ferrite and strontium ferrite Co.
Is a substitution. In addition, Co-T is used for the hexagonal ferrite.
i, Co-Ti-Zr, Co-Ti-Zn, Ni-Ti
Those to which elements such as -Zn and Ir-Zn are added can also be used. Hexagonal ferrite is usually in the shape of a hexagonal plate, and its particle size means the width of the hexagonal plate,
Measure using an electron microscope. In the present invention, the particle size is 0.01 to 0.2 μm, particularly preferably 0.03 to 0.2 μm.
It is specified in the range of 0.1 μm. If the particle size is too large, noise increases, and the output in the high frequency range is unpreferably decreased. If the particle diameter is too small, the amount of saturation magnetization decreases and the output decreases, which is not preferable, and also causes problems such as difficulty in dispersion when adjusting the magnetic coating solution. The tabular ratio (plate width / plate thickness) of the hexagonal ferrite is from 3 to 20, preferably from 3 to 10. The average thickness (plate thickness) of the fine particles is 0.001 to
About 0.2 μm, especially 0.003 to 0.05 μm
m is preferred. Further, the specific surface area (S _BET ) of these hexagonal ferrite fine powders by the BET method is 25 to 70.
m ² / g is preferred. Further, the saturation magnetization of the fine hexagonal ferrite powder is preferably 50 emu / g or more.
If it is smaller than mu / g, a sufficient reproduction output cannot be obtained, and it is not suitable for high-density recording. Hexagonal ferrite has a lower output in the case of long wavelength recording than in the case of other magnetic particles, but when the recording wavelength in the high frequency band is a short wavelength recording of 1.0 μm or less, rather than other magnetic particles. There is a feature that high output can be expected. Furthermore, in the case of a disk-shaped magnetic recording medium such as a magnetic recording disk, it is desired that the output in the circumferential direction is uniform and does not fluctuate. . When hexagonal ferrite is used as the magnetic particles, an orientation ratio as high as 0.9 or more can be realized. Furthermore, when hexagonal ferrite is used, the perpendicular magnetization (remanent magnetization /
The saturation magnetization), that is, the squareness ratio after demagnetization correction is 0.6 or more, preferably 0.65 or more, and the orientation degree ratio is 0.9 or more as described above. An output magnetic recording disk can be obtained, and the capacity of the magnetic recording disk can be increased.

The ferromagnetic particles of the magnetic recording disk of the present invention may be used by partially mixing other oxide-based magnetic materials such as chromium oxide, cobalt-coated iron oxide, and γ-iron oxide. . The water content of the magnetic particles that can be used in the present invention is 0.0
It is preferable that the content be 1 to 2% by weight. It is necessary to optimize the water content of the magnetic material depending on the type of the binder resin.
It is preferable that the pH of the magnetic particles be optimized by a combination with the binder resin used. Its range is from 4 to 12, preferably from 6 to 10. In particular, when the binder resin has a polar group in the molecule, it is desirable to pay attention to the pH. The magnetic particles may be subjected to a surface treatment with Al, Si, P or an oxide thereof, if necessary. The amount is 0.1 to 10% with respect to the magnetic material particles.
/ M ² or less, and the amount of the lubricant that behaves freely in the magnetic layer increases, which is preferable. Soluble N for ferromagnetic particles
In some cases, inorganic ions such as a, Ca, Fe, Ni, and Sr may be contained, but if the content is 500 ppm or less, characteristics are not particularly affected. These ferromagnetic particles include A
1, Si, S, Sc, Ti, V, Cr, Cu, Y, M
o, Rh, Pd, Ag, Sn, Sb, Te, Ba, T
a, W, Re, Au, Hg, Pb, Bi, La, Ce,
It may contain atoms such as Pr, Nd, P, Co, Mn, Zn, Ni, Sr, and B.

The saturation magnetization and the coercive force were set to a maximum applied magnetic field of 10 KOe using VSM-PI (manufactured by Toei Kogyo). The specific surface area was measured using Cantersorb (manufactured by Cantarchrome, USA). This is a value measured by the BET one-point method (partial pressure 0.30) after dehydration in a nitrogen atmosphere at 250 ° C. for 30 minutes.

The non-magnetic layer in the magnetic recording disk of the present invention, the non-magnetic particles a binder resin a layer mainly, carbon black of partially conductive particles of the non-magnetic particles
Need to be locked . The ratio of carbon black as conductive particles in the non-magnetic particles of the non-magnetic layer,
From the viewpoint of preventing electrification of the magnetic recording disk of the present invention,
It is 3 to 20% by weight . As carbon black ,
A furnace for rubber, a thermal for rubber, black for color, acetylene black, lamp black and the like can be used. Among them, in particular, average particle size below 40mμ flat, it is preferable DBP oil absorption amount is 300 ml / 100 grams or more of carbon black. The DBP oil absorption of carbon black is determined by adding dibutyl phthalate to the carbon black powder little by little, observing the state of the carbon black while kneading it, finding a point where it forms one lump from the dispersed state, and then adding the amount of dibutyl phthalate at that time. (Ml) was taken as the DBP oil absorption. More preferably, it is from 8% by weight to 19% by weight. If it is less than 3% by weight, the surface resistivity cannot be sufficiently reduced, and if it is more than 20% by weight, the surface resistivity of the magnetic layer can be sufficiently reduced but the surface properties of the magnetic layer cannot be sufficiently smooth. The specific surface area is preferably from 5 to 1500 m2 / g, and more preferably from 700 to 1400 m2 / g.

The thickness of the non-magnetic layer is 0.5 to 10 μm, preferably 0.5 to 5 μm. If the thickness of the non-magnetic layer is too small, charging of the magnetic recording disk cannot be prevented,
If the thickness is too large, the contact with the magnetic head deteriorates, which is not preferable.

Specific examples of carbon black preferable as the carbon black used in the non-magnetic layer include # 3950B manufactured by Mitsubishi Carbon Corporation, Ketjen Black EC and Ketjen Black ECDJ-50 manufactured by Lion Azo.
0, Ketjen Black ECDJ-600 and the like.

Carbon black may be surface-treated with a dispersant or the like, grafted with a resin, or used, or a part of the surface may be graphitized. Before adding the carbon black to the magnetic paint, the carbon black may be dispersed in a binder in advance. The carbon black that can be used in the non-magnetic layer of the magnetic recording disk of the present invention can be referred to, for example, “Carbon Black Handbook” edited by Carbon Black Association. These conductive particles such as carbon black and the above-mentioned non-magnetic powder may be dispersed in a binder in advance and then added to the dispersion. As the lubricant that can be added to the nonmagnetic layer of the magnetic recording disk of the present invention, various types of conventionally known liquid lubricants can be used, and among them, fatty acid esters are most preferable. The fatty acid ester used for this nonmagnetic layer is a monobasic fatty acid having 12 to 20 carbon atoms and a fatty acid ester having 3 carbon atoms.
Fatty acid esters consisting of up to 12 monohydric alcohols are preferred.

The alcohols used as the raw materials for the fatty acid esters include ethanol, butanol, phenol, benzyl alcohol, 2-methylbutyl alcohol, 2-hexyldecyl alcohol, propylene glycol monobutyl ether, ethylene glycol monobutyl ether,
Examples include system monoalcohols such as dipropylene glycol monobutyl ether, diethylene glycol monobutyl ether, and s-butyl alcohol, and polyhydric alcohols such as ethylene glycol, diethylene glycol, neopentyl glycol, glycerin, and sorbitan derivatives. Similarly, fatty acids include acetic acid, propionic acid, octanoic acid, 2-ethylhexanoic acid, lauric acid, myristic acid, stearic acid, palmitic acid, behenic acid, arachiic acid, oleic acid, linoleic acid, linolenic acid, elaidic acid, and palmitoleic acid And the like or a mixture thereof. Preferred examples of the fatty acid ester include butyl stearate, s-butyl stearate, isopropyl stearate, butyl oleate, amyl stearate, 3-methylbutyl stearate,
-Ethylhexyl stearate, 2-hexyldecyl stearate, butyl palmitate, 2-ethylhexyl myristate, a mixture of butyl stearate and butyl palmitate, butoxyethyl stearate, 2-butoxy-1-propyl stearate, dipropylene glycol Various ester compounds such as monobutyl ether acylated with stearic acid, diethylene glycol dipalmitate, hexamethylene diol acylated with myristic acid to form a diol, and glycerin oleate can be mentioned.

Further, in order to reduce the hydrolysis of fatty acid esters which often occur when the magnetic recording medium is used under high humidity, the fatty acid and alcohol used as the raw material are branched / straight chain, isomer structure such as cis / trans, etc. A choice is made. More preferred fatty acid esters are one selected from butyl stearate and s-butyl stearate, butoxyethyl stearate, or 2-butoxy-1-propyl stearate. These lubricants have an advantage that they have a moderate molecular weight, easily move in the layer, have a high replenishment effect, and are difficult to evaporate.

These fatty acid esters are added in an amount of 3 to 20 parts by weight, preferably 5 to 15 parts by weight, based on 100 parts by weight of the whole nonmagnetic powder contained in the nonmagnetic layer. If the amount is less than 3 parts by weight, a sufficient replenishing effect cannot be obtained. If the amount is more than 20 parts by weight, the effect of replenishing the magnetic layer is too large, the amount of the lubricant present on the surface of the magnetic layer becomes excessive, the head tends to stick in running durability, and the adhesion between the magnetic layer and the non-magnetic layer also increases. Will drop.

In the non -magnetic particles used in the non -magnetic layer of the magnetic recording disk of the present invention, the inorganic powder other than the carbon black may be, for example, α-alumina or β-alumina having an α conversion of 90% or more. , Γ-alumina, silicon carbide, chromium oxide, cerium oxide, α-iron oxide, corundum, silicon nitride, titanium carbide, titanium oxide, silicon dioxide, boron nitride, zinc oxide, calcium carbonate, calcium sulfate, barium sulfate, etc. Used alone or in combination. The particle size of these inorganic powders is 0.01 to 2μ.
However, if necessary, inorganic powders having different particle sizes may be combined, or even a single inorganic powder may have the same effect by broadening the particle size distribution. The tap density is preferably 0.3 to ² g / cc, the water content is 0.1 to 5%, the pH is 2 to 11, and the specific surface area is preferably 1 to 30 m ² / g.
The shape of the inorganic powder used in the present invention may be any of a needle shape, a spherical shape, and a die shape. Specific examples of the non-magnetic powder used in the present invention include AKP-2 manufactured by Sumitomo Chemical Co., Ltd.
0AKP-30, AKP-50, HIT-50, manufactured by Nippon Kagaku Kogyo, G5, G7, S-1, manufactured by Toda Kogyo, TF
-100, TF-120, TF-140, and the like. By adding carbon black or the like to the magnetic layer, the specific resistance of the surface of the magnetic layer can be reduced, and the magnetic recording disk of the present invention can be further prevented from being charged. Can also be improved.

However, when the magnetic layer contains conductive particles such as carbon black, the amount of addition cannot be as large as that in the non-magnetic layer from the viewpoint of maintaining the magnetic properties. The desirable addition amount should be 10 parts by weight or less per 100 parts by weight of the magnetic particles. The function of carbon black in the magnetic layer is to prevent the magnetic layer from being charged, reduce the coefficient of friction, impart light-shielding properties, and improve the film strength. Therefore, these carbon blacks used in the present invention have different types, amounts, and combinations in the lower layer and the upper layer. It is of course possible to use differently according to. For example, charging is prevented by using carbon black having high conductivity in the lower layer, and the coefficient of friction is reduced by using carbon black having a large particle diameter in the upper layer.

As the binder resin in the magnetic layer and the nonmagnetic layer of the magnetic recording disk of the present invention, conventionally known thermoplastic resins, thermosetting resins, reactive resins and mixtures thereof are used. As the thermoplastic resin, the glass transition temperature is −100 to 150 ° C., and the number average molecular weight is 1000 to 200.
000, preferably 10,000 to 100,000, and a degree of polymerization of about 50 to 1,000. Such examples include vinyl chloride, vinyl acetate, vinyl alcohol,
Polymer or copolymer containing maleic acid, acuric acid, acrylic acid ester, vinylidene chloride, acrylonitrile, methacrylic acid, methacrylic acid ester, styrene, butadiene, ethylene, vinyl butyral, vinyl acetal, vinyl ether, etc. as constituent units There are polymers, polyurethane resins and various rubber resins. Examples of the thermosetting resin or the reactive resin include a phenol resin, an epoxy resin, a polyurethane curable resin, a urea resin, a melamine resin, an alkyd resin, an acrylic reaction resin, a formaldehyde resin, a silicone resin, and an epoxy-polyamide. Resin, a mixture of polyester resin and isocyanate prepolymer, a mixture of polyester polyol and polyisocyanate, a mixture of polyurethane and polyisocyanate, and the like.

[0038] These resins are described in detail in "Plastic Handbook" published by Asakura Shoten. Also, a known electron beam-curable resin can be used for the upper layer or the lower layer. These examples and the production method thereof are described in detail in JP-A-62-256219. The above resins can be used alone or in combination, but preferred are vinyl chloride resin, vinyl chloride vinyl acetate resin, vinyl chloride vinyl acetate vinyl alcohol resin, vinyl chloride vinyl acetate maleic anhydride copolymer,
Examples include a combination of at least one selected from the above with a polyurethane resin, or a combination of these with a polyisocyanate.

As the structure of the polyurethane resin, known materials such as polyester polyurethane, polyether polyurethane, polyether polyester polyurethane, polycarbonate polyurethane, polyester polycarbonate polyurethane, and polycaprolactone polyurethane can be used. For all of the binders shown here, COO is required to obtain better dispersibility and durability.
M, SO ₃ M, OSO ₃ M, P = O (OM) ₂ , OP
ＯO (OM) ₂ , where M is a hydrogen atom or an alkali metal base, OH, NR 2, N + R 3 (R is a hydrocarbon group) epoxy group, SH, CN, etc. It is preferable to use one obtained by introducing a polar group by copolymerization or addition reaction. The amount of such a polar group is 10 ^-1 to 10 ^-8 mol / g, preferably 10 ^-2 to 10 ^-6 mol / g.

Specific examples of these binders used in the magnetic recording disk of the present invention include VAGH, VYHH, VMCH, VAGF and VA manufactured by Union Carbide.
GD, VROH, VYES, VYNC, VMCC, XY
HL, XYSG, PKHH, PKHJ, PKHC, PK
FE, manufactured by Nissin Chemical Industries, MPR-TA, MPR-TA
5, MPR-TAL, MPR-TSN, MPR-TM
F, MPR-TS, MPR-TM, 100 manufactured by Denki Kagaku
0 W, DX80, DX81, DX82, DX83, MR110, MR100, 400X110 manufactured by Zeon Corporation
A, Nipporan N2301, N2 manufactured by Nippon Polyurethanes
302, N2304, Pandex T manufactured by Dainippon Ink and Chemicals, Inc.
-5105, T-R3080, T-5201, Burnock D-400, D-210-80, Crisbon 610
9,7209, Toyobo U Byron R8200, UR
8300, RV530, RV280, manufactured by Dainichi Seika, diferamine 4020, 5020, 5100, 530
0, 9020, 9022, 7020, manufactured by Mitsubishi Kasei Corporation, M
X5004, manufactured by Sanyo Kasei Co., Ltd., Samprene SP-150,
Saran F310, F210, etc., manufactured by Asahi Kasei Corporation.

The binder resin in the magnetic layer of the magnetic recording disk of the present invention is used in an amount of 5 to 50% by weight, preferably 10 to 30% by weight, based on the ferromagnetic particles. 5 to 30% by weight when using a vinyl chloride resin,
When using a polyurethane resin, it is preferable to use 2 to 20% by weight of the polyisocyanate and 2 to 20% by weight of the polyisocyanate in combination. In the present invention, when polyurethane is used, the glass transition temperature is -50 to 10
0 ° C., elongation at break is 100 to 2000%, and stress at break is 0.1%.
05-10 kg / cm ² , yield point 0.05-10 kg
/ Cm ² is preferred.

The magnetic recording disk of the present invention comprises two layers, the magnetic layer and the non-magnetic layer. Therefore, the amount of binder, vinyl chloride resin in the binder, polyurethane resin,
Of course, it is possible to change the amount of polyisocyanate or other resin, the molecular weight of each resin forming the magnetic layer, the amount of polar group, or the physical properties of the resin described above between the upper layer and the lower layer as necessary. is there.

Examples of the polyisocyanate used in the present invention include tolylene diisocyanate, 4-4'-diphenylmethane diisocyanate, hexamethylene diisocyanate, xylylene diisocyanate, and naphthylene.
Isocyanates such as 1,5-diisocyanate, o-toluidine diisocyanate, isophorone diisocyanate and triphenylmethane triisocyanate;
Products of these isocyanates and polyalcohols, and polyisocyanates formed by condensation of isocyanates can be used. Commercially available trade names of these isocyanates include Nippon Polyurethane Co., Ltd., Coronate L, Coronate HL,
CORONATE 2030, CORONATE 2031, Millionet
MR Millionate MTL, Takeda Pharmaceutical Co., Ltd., Takenet D-102, Takenet D-110N, Takenet D-
200, Takenate D-202, manufactured by Sumitomo Bayer Co., Ltd., Desmodur L, Desmodur IL, Desmodur N Desmodur HL, etc. These are used alone or by utilizing the difference in curing reactivity. One or more combinations can be used for both the magnetic layer and the non-magnetic layer.

In the production of the magnetic recording disk of the present invention, the magnetic layer is formed on the non-magnetic layer while the coating layer for the non-magnetic layer applied on the non-magnetic support is still wet. It is preferable to adopt a so-called wet-on-wet coating method in which a layer coating solution is coated thereon. By adopting this coating method, the adhesion of the magnetic layer to the non-magnetic layer can be enhanced, and the magnetic layer does not peel off even when the thickness of the magnetic layer is as thin as 0.5 μm as in the present invention. Thus, it is possible to obtain a magnetic recording disk with excellent running durability in which drop-out hardly occurs. In the method of applying a non-magnetic coating solution and drying to form a non-magnetic layer and then applying a magnetic layer thereon as in the conventional method, the magnetic recording disk of the present invention may be because the magnetic layer is extremely thin. In addition, the adhesion between the non-magnetic layer and the magnetic layer is not sufficient, and it is difficult for the two layers to have an integral structure as a layer formed on the non-magnetic support.

As a specific method of the above wet-on-wet method, (1) a lower layer is first applied by a gravure coating, a roll coating, a blade coating, or an extrusion coating device which is generally used for a magnetic coating material. While the layer is still wet, for example,
No. 86, JP-A-60-238179 and JP-A-2-265672, in which the upper layer is coated by a non-magnetic support pressurization type extrusion coating apparatus. No. 88080, JP-A-2-17971 and JP-A-2-265672 disclose a lower coating liquid and an upper coating liquid by a coating head having two built-in coating liquid passage slits. (3) JP-A-2-174
No. 965, a method of applying an upper layer and a lower layer almost simultaneously by an extrusion coating apparatus with a backup roll.

In order to prevent agglomeration of the particles dispersed in the coating solution, coating is performed by a method disclosed in, for example, JP-A-62-95174 and JP-A-1-236968. It is desirable to apply a shearing force to the coating liquid inside the head. Also, what should be noted in the wet-on-wet coating method is the viscoelastic properties (thixotropic properties) of the coating liquid. That is, when the difference between the viscoelastic properties of the upper layer and the lower layer coating solution is large, when the liquid is mixed at the interface between the upper layer and the lower layer, the mixture of the upper layer and the lower layer as in the present invention. If the thickness is very small, problems such as a decrease in the surface properties of the magnetic layer are likely to occur. To make the viscoelasticity of the coating liquid as close as possible,
First, it is effective to make the dispersed particles of the upper layer and the lower layer the same, but in the case of the present invention, it is not possible, so that a structure structure in which the magnetic particles are formed by magnetism in the coating solution of the magnetic layer results. In order to match the structural viscosity, it is desirable to use particles that easily form structural viscosity, such as carbon black, as the nonmagnetic particles of the coating solution for the lower nonmagnetic layer. Therefore, in the present invention, it is effective to use carbon black having a large oil absorption and a small particle size, but it is also effective to use non-magnetic particles having a small particle size other than carbon black. For example, particles of titanium oxide, aluminum oxide or the like having a particle size of 1 μm or less tend to form a coating liquid having the structural viscosity of the particles due to appropriate aggregation.

In the magnetic layer of the magnetic recording disk of the present invention, materials having various functions such as a lubricant and an abrasive can be added. In addition, antistatic agents, dispersants,
Plasticizers, fungicides and the like can be added.

As the lubricant used for the magnetic layer, a fatty acid ester is most desirable as in the case of the nonmagnetic layer. Specific examples thereof include those that can be used for the nonmagnetic layer.Moreover, in order to reduce the hydrolysis of fatty acid esters that often occur when the magnetic recording medium is used under high humidity,
It is possible to select the branched / straight chain, cis / trans and other isomer structures and branch positions of the fatty acids and alcohols of the raw materials. These lubricants are added in the range of 0.2 to 20 parts by weight based on 100 parts by weight of the ferromagnetic particles . As the lubricant, the following lubricants can be further used. That is,
Silicon oil, graphite, molybdenum disulfide, boron nitride, fluorinated graphite, fluorinated alcohol, polyolefin, polyglycol, alkyl phosphate, tungsten disulfide and the like. Examples of commercial products of these lubricants used in the magnetic recording disk of the present invention, manufactured by NOF Corporation,
NAA-102, NAA-415, NAA-312, N
AA-160, NAA-180, NAA-174, NA
A-175, NAA-222, NAA-34, NAA-
35, NAA-171, NAA-122, NAA-14
2, NAA-160, NAA-173K, castor hardened fatty acid, NAA-42, NAA-44, cation SA, cation MA, cation AB, cation BB, Nymin L-201, Nymin L-202, Nymin S-2
02, Nonion E-208, Nonion P-208, Nonion S-207, Nonion K-204, Nonion NS-
202, Nonion NS-210, Nonion HS-20
6, Nonion L-2, Nonion S-2, Nonion S-
4, Nonion O-2, Nonion LP-20R, Nonion PP-40R, Nonion SP-60R, Nonion OP-
80R, Nonion OP-85R, Nonion LT-22
1, Nonion ST-221, Nonion OT-221, Monogly MB, Nonion DS-60, Anone BF, Anone LG, Butyl stearate, Butyl laurate, Erucic acid, Kanto Kagaku, Oleic acid, Takemoto Yushi, FAL
-205, FAL-123, manufactured by Shin Nippon Rika Co., Ltd., Njerub LO, Njjolub IPM, Sansocizer-E40
30, manufactured by Shin-Etsu Chemical Co., Ltd., TA-3, KF-96, KF-
96L, KF96H, KF410, KF420, KF9
65, KF54, KF50, KF56, KF907, K
F851, X-22-819, X-22-822, KF
905, KF700, KF393, KF-857, KF
-860, KF-865, X-22-980, KF-1
01, KF-102, KF-103, X-22-371
0, X-22-3715, KF-910, KF-393
5, manufactured by Lion Armor, Armide P, Armide C, Armoslip CP, manufactured by Lion Yushi Co., Ltd., Deyumin TDO, manufactured by Nisshin Oil Co., Ltd., BA-41G, manufactured by Sanyo Chemical Co., Ltd., Profan 2012E , Newport PE61, Ionet MS-400, Ionet MO-200, Ionet DL-200, Ionet DS-300, Ionet DS-1000, and Ionnet DO-200.

Specific examples of the abrasive include α-alumina, β-alumina, silicon carbide, chromium oxide, cerium oxide, α-iron oxide, corundum, artificial diamond, silicon nitride, silicon carbide having an α conversion of 90% or more. Titanium carbide, titanium oxide, silicon dioxide, boron nitride, etc.
Six or more known materials are used alone or in combination. Further, a composite of these abrasives (abrasive whose surface is treated with another abrasive) may be used. These abrasives may contain compounds or elements other than the main component, but the effect remains unchanged if the main component is 90% or more. The particle size of these abrasives is 0.01-2 μm.
However, if necessary, abrasives having different particle sizes can be combined, or even a single abrasive can have a similar particle size distribution to achieve the same effect. Tap density 0.3-2g / cc, water content 0.1-5%, PH 2
To 11, and a specific surface area is preferably 1 to 30 m ² / g. The shape of the abrasive used in the present invention may be any of a needle shape, a spherical shape, and a dice shape, but a shape having a part of a corner is preferable because of high abrasiveness. In particular, as a specific example of a desirable abrasive, AKP-20AKP- manufactured by Sumitomo Chemical Co., Ltd.
30, AKP-50, HIT-50, Nippon Kagaku Kogyo Co., Ltd., G5, G7, S-1, Toda Kogyo Co., Ltd., 100ED,
140ED, and the like. These abrasives may be added to the magnetic paint after being subjected to dispersion treatment with a binder in advance. The abrasive present on the surface of the magnetic layer and the end face of the magnetic layer of the magnetic recording medium of the present invention is preferably 5/100 μm ² or more. The amount of the abrasive added to the magnetic layer is usually 3 to 20 parts by weight per 100 parts by weight of the ferromagnetic particles. If the amount of the abrasive is small, the running durability of the magnetic recording disk is not sufficient, and if the amount is too large, the output is lowered, which is not desirable.

The additives added to the magnetic layer are not necessarily 100% pure, but include impurities such as isomers, unreacted materials, by-products, decomposition products, oxides, etc. in addition to the main components. It doesn't matter. These impurities are preferably 30% or less, more preferably 10% or less. Further, all or a part of the additives used in the present invention may be added at any step of producing a magnetic coating solution.For example, when mixing with a magnetic substance before the kneading step, the magnetic substance and the binder may be added. , A kneading step with a solvent, a dispersing step, a dispersing step, a dispersing step, and a dissolving step immediately before coating.

The organic solvent used in the present invention may be any desired ratio of ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, diisobutyl ketone, cyclohexanone, isophorone, tetrahydrofuran, etc .;
Alcohols such as alcohol, ethanol, propanol, butanol, isobutyl alcohol, isopropyl alcohol, methylcyclohexanol, methyl acetate, butyl acetate, isobutyl acetate, isopropyl acetate, ethyl lactate, and glycol acetate Esters such as glycerol, glycol dimethyl ether, glycol monoethyl ether, glycol ethers such as dioxane, aromatic hydrocarbons such as benzene, toluene, xylene, cresol, chlorobenzene, methylene chloride, ethylene chloride, Chlorinated hydrocarbons such as carbon tetrachloride, chloroform, ethylene chlorohydrin, dichlorobenzene, etc .;
N-dimethylformamide, hexane and the like can be used. These organic solvents are not necessarily 100% pure, and may contain impurities such as isomers, unreacted products, by-products, decomposed products, oxides, and moisture in addition to the main components. These impurities are preferably 30% or less, more preferably 10% or less. The kind and amount of the organic solvent used in the present invention may be changed between the magnetic layer and the non-magnetic layer if necessary.

A highly volatile solvent is used for the upper magnetic layer coating solution to improve the surface properties. A lower surface tension solvent (cyclohexanone, dioxane, etc.) is used for the lower nonmagnetic layer coating solution to improve coating stability. For example, the coating liquid for the lower non-magnetic layer may be increased by using a solvent having a high solubility parameter to increase the filling degree. However, it is a matter of course that the present invention is not limited to these examples.

Non-magnetic supports used in the present invention include polyesters such as polyethylene terephthalate and polyethylene naphthalate, polyolefins, cellulose acetoacetate, polycarbonate, polyamide, polyimide, polyamideimide, and the like. A known film such as polysulfone can be used. These supports have a corona discharge treatment, a plasma treatment, an easy adhesion treatment, a heat treatment,
For example, dust removal processing may be performed. The thickness of the non-magnetic support of the magnetic recording disk of the present invention is 1 to 100 μm, preferably 20 to 85 μm. Further, an undercoat layer made of a polyester resin or the like for improving adhesion may be provided between the nonmagnetic support and the nonmagnetic layer thereon.
These thicknesses are usually 0.01 to 2 μ, desirably,
It is 0.05 to 0.5 μm. The non-magnetic layer and the magnetic layer of the magnetic recording medium of the present invention are provided on one or both sides of a non-magnetic support.

In order to effectively achieve the object of the present invention, the surface roughness of the non-magnetic support is determined by determining the center line average surface roughness (Ra).
(Cut-off value 0.25 mm) at 0.03 μm or less, preferably 0.02 μm or less, more preferably 0.01 μm or less.
It is desirable to use one having a size of μmμ or less. Further, it is preferable that these non-magnetic supports not only have a small center line average surface roughness but also have no coarse protrusions of 1 μm or more. The surface roughness can be freely controlled by the size and amount of the filler added to the non-magnetic support as needed. Examples of these fillers include oxides and carbonates such as Ca, Si, and Ti,
An organic resin fine powder such as an acrylic resin may be used. The F-5 value in the web running direction of the nonmagnetic support used in the present invention is preferably 5 to 50 kg / mm ² , and the F-5 value in the web width direction is
The -5 value is preferably 3 to 30 kg / mm ² , and the F-5 value in the long hand direction of the web is generally higher than the F-5 value in the web width direction. This is not the case when it is necessary to do so. The heat shrinkage of the support in the web running direction and the width direction at 100 ° C. for 30 minutes is preferably 3% or less, more preferably 1.5% or less, and the heat shrinkage at 80 ° C. for 30 minutes is preferably 1%. %Less than,
More preferably, it is 0.5% or less. The breaking strength is 5-100 kg / mm ^{2 in} both directions, and the elastic modulus is 100-20.
00 kg / mm ² is desirable.

The step of producing the magnetic coating material of the magnetic layer for a magnetic recording disk of the present invention comprises at least a kneading step, a dispersing step, and a mixing step provided before and after these steps as necessary. Each step may be divided into two or more steps. All raw materials such as magnetic particles, binder resin, non-magnetic particles, carbon black, abrasives, antistatic agents, lubricants, and solvents used in the present invention may be added at any stage of any process. . Further, individual raw materials may be added in two or more steps in a divided manner. For example, polyurethane may be divided and supplied in a kneading step, a dispersing step, and a mixing step for adjusting the viscosity after dispersion. In order to achieve the object of the present invention, it is a matter of course that a conventional known manufacturing technique can be used as a part of the process. By using something with kneading power,
The residual magnetic flux density (Br) of the magnetic recording disk of the present invention can be increased. When a continuous kneader or a pressure kneader is used, all or a part of the magnetic particles and the binder resin (however, preferably 30% by weight or more of the total binder resin) and 100 parts by weight of the magnetic particles 15 ~
The kneading process is performed in a range of 500 parts by weight. Details of these kneading processes are described in JP-A-1-106388 and JP-A-1-79274. In the present invention, more efficient production can be achieved by using a simultaneous multilayer coating method as disclosed in JP-A-62-212933.

Further, a heat-resistant plastic roll such as epoxy, polyimide, polyamide, or polyimide amide is used as a calendar roll used in the pressure molding treatment for smoothing the surface of the magnetic layer. Further, pressure molding can be performed between metal rolls. The processing temperature of the pressure molding is preferably 70 ° C. or more, more preferably 80 ° C.
That is all. The linear pressure is desirably 200 kg / cm, more preferably 300 kg / cm or more.

The specific resistance of the surface of the magnetic layer of the magnetic recording medium of the present invention is desirably 10 ^{5 to} 5 × 10 ⁹ ohm / sq. The direction is preferably 100 to 2000 kg / mm ² , the breaking strength is preferably 1 to 30 kg / cm ² , and the elastic modulus of the magnetic recording medium is preferably 10 in the web application direction and the width direction.
0 to 1500 kg / mm ² , and the residual growth is preferably 0.1 kg / mm ² .
The heat shrinkage at any temperature of 5% or less and 100 ° C or less is preferably 1% or less, more preferably 0.5% or less,
Most preferably, it is 0.1% or less.

The residual solvent contained in the magnetic layer is preferably 100 mg / m ² or less, more preferably 10 mg / m ^2.
It is preferable that the residual solvent contained in the magnetic layer be smaller than the residual solvent contained in the nonmagnetic layer. The porosity of the magnetic layer is preferably 30% by volume or less, more preferably 10% by volume or less for both the magnetic layer and the non-magnetic layer. It is preferable that the porosity of the non-magnetic layer is larger than the porosity of the magnetic layer.

Although the magnetic recording medium of the present invention has a non-magnetic layer and a magnetic layer, it is easily presumed that the physical properties of the non-magnetic layer and the magnetic layer can be changed according to the purpose. For example, the elastic modulus of the magnetic layer is increased to improve running durability, and at the same time, the elastic modulus of the non-magnetic layer is made lower than that of the magnetic layer to improve the contact of the magnetic recording medium with the head.

By using the magnetic recording disk of the present invention, high-density magnetic recording is possible. In particular, the overwriting characteristic essential for a digital data recording medium used for storing and reading computer information is, for example, In addition, there is an advantage that even if high-density recording is performed such that the shortest recording wavelength is 1.5 μm or less, there is no decrease and running durability does not decrease. The advantage is attributable to the above-mentioned features provided by the configuration of the magnetic disk of the present invention and the method of manufacturing the same, particularly due to the configuration of the layer formed on the non-magnetic support and the coating method of the layer. ing.

The use of the magnetic recording disk of the present invention not only when the recording wavelength is shortened but also when the track density is increased, the signal crosstalk is reduced and the peak shift separability is improved. Excellent recording is possible. Therefore, under the condition that the recording track width is 50 μm or less and the track density is 14 tracks / mm or more, recording / reproducing with excellent overwriting suitability and good running durability even when recording with a minimum recording wavelength of 1.5 μm or less. It is possible. The novel features of the present invention will be specifically described with reference to the following Examples and Comparative Examples.

[0062]

Examples (Example 1) <Coating solution for non-magnetic layer> Non-magnetic particles Titanium oxide TiO ₂ 90 parts by weight (TY50 manufactured by Ishihara Sangyo, average particle diameter: 0.34 μm,
Specific surface area by BET method: 5.9 m ² / g, pH5.
9) Carbon black: 10 parts by weight (average primary particle diameter: 16 mμ, DBP oil absorption: 80 ml)
/ 100 g, pH: 8.0, specific surface area by BET method: 250 m ² / g, volatile matter: 1.5% by weight) Binder resin Vinyl chloride-vinyl acetate-vinyl alcohol copolymer ... 14 parts by weight (-N ( 5 × 10 ⁻⁶ eq / g containing a polar group of CH ₃ ) ₃ ⁺ Cl ⁻ , monomer composition ratio: 86: 13: 1, degree of polymerization: 400) Polyester polyurethane resin: 5 parts by weight (neopentyl glycol / caprolactone polyol / MDI) = 0.9 / 2.6 / 1, -SO ₃ Na group 1 × 10 ^-4 e
q / g) sec-butyl stearate 4 parts by weight 2-butoxy-1-ethyl stearate 2 parts by weight 2-butoxy-1-ethyl palmitate 2 parts by weight oleic acid 1 part by weight methyl ethyl ketone 200 parts by weight Department

<Coating solution for magnetic layer> Ferromagnetic particles: 100 parts by weight (composition: Fe / Ni = 96/4 (atomic ratio), coercive force: 1620 Oerstedt) Specific surface area by BET method: 50 m ² / g, crystallite Size: 195 angstroms, Particle size (average major axis diameter): 0.20 μm, needle ratio: 10, Saturation magnetization σs: 130 emu / g Binder resin Vinyl chloride copolymer: 14 parts by weight (-SO3Na content 1 × 10 ⁻⁴ eq / g, degree of polymerization: 300) Polyester polyurethane resin… 5 parts by weight (neopentyl liqueur / caprolactone polyol / MDI = 0.9 / 2.6 / 1, -SO 3 Na group is 1 × 10 ^{−) 4} eq / g containing) alpha-alumina ... 2 parts by weight (average particle size 0.3 [mu] m) mosquitoes - carbon black ... 0.5 parts by weight (particle size 0.10 .mu.m) isohexadecyl stearate ... 6 weight Oleic acid: 1 part by weight Methyl ethyl ketone: 200 parts by weight The particle size and crystallite size of the ferromagnetic particles were measured as follows: Particle size of magnetic material: The average particle size of the major axis was determined by a transmission electron microscope. Crystallite size: (4,4) of ferromagnetic particles was determined by X-ray diffraction.
It was determined from the spread of the half width of the diffraction lines on the (4,0) plane and the (2,2,0) plane.

The above-mentioned coating solution for the non-magnetic layer and the coating solution for the magnetic layer were first kneaded by a continuous kneader, and then mixed and dispersed using a sand mill. To the obtained dispersion, 10 parts by weight of polyisocyanate (Coronate L, manufactured by Nippon Polyurethane Co., Ltd.) was added in a dispersion for a nonmagnetic layer, and 12 parts by weight in a dispersion for a magnetic layer. Then, 40 parts by weight of butyl acetate was added to each and mixed and stirred.
The solution was filtered through a filter having an average pore size of μm to prepare a coating solution for a nonmagnetic layer and a coating solution for a magnetic layer.

The coating solution for the non-magnetic layer and the coating solution for the magnetic layer were prepared to have a thickness of 62 μm and a surface roughness of the center line average surface roughness Ra.
(Cutoff value 0.25 mm) and 0.01 μm,
The coating solution for the non-magnetic layer and the coating solution for the magnetic layer are wetted on a polyethylene terephthalate support having a 0.1 μm-thick undercoat layer made of a polyester-based polymer for improving adhesion on the surface. By the wet simultaneous multi-layer coating, which is an on-wet method, at a coating speed of 150 m / min, the thickness of the non-magnetic layer after drying is 2 μm, and the thickness of the magnetic layer after drying is 0.5 μm. It applied so that it might become.

While both layers were still in a wet state, they were passed through two AC magnetic field generators to perform a random orientation treatment of the magnetic particles. The frequency and magnetic field strength of the two alternating magnetic fields at that time were 50 Hz from the upstream side, 200 ersted, 120 H
z, 130 ersted. After further drying, treatment was performed with a 7-stage calender (linear pressure 300 kg / cm, temperature 90 ° C.), punched into 3.5-inch size, burnished on the surface with polishing tape, and then 3.5-inch floppy disk A 3.5-inch floppy disk sample was prepared by using the predetermined mechanical parts. The magnetic layer was formed on the other surface of the nonmagnetic material under the same conditions, and a magnetic recording disk having a magnetic layer on both surfaces of a nonmagnetic support was prepared.

Example 2 A 3.5-inch floppy was prepared under the same conditions as in Example 1 except that the composition of the coating solution for the magnetic layer and the orientation conditions of the ferromagnetic particles were changed as follows. Disk samples were made.

<Coating solution for magnetic layer> Ferromagnetic particles: 100 parts by weight (ferromagnetic hexagonal barium ferrite powder (plate-like particles) Coercive force: 1400 ersted) Specific surface area by BET method: 45 m ² / g, particle size (plate Diameter): 0.06 μm, plate ratio: 5.2 Saturated magnetization σs: 65 emu / g Binder resin Vinyl chloride copolymer: 8 parts by weight (-SO3Na content: 1 × 10 ⁻⁴ eq / g, Polymerization degree: 300) Polyester polyurethane resin: 4.5 parts by weight (neopentyl glycol / caprolactone polyol / MDI = 0.9 / 2.6 / 1, containing 1 × 10 ⁻⁴ eq / g of -SO3Na group) α- Alumina 2 parts by weight (average particle size 0.3 μm) Carbon black 0.5 parts by weight (particle size 0.10 μm) Isohexadecyl stearate 6 parts by weight Oleic acid 1 part by weight methyl ethyl T ... 200 parts by weight

<Orientation Conditions> While both layers are still in a wet state, 2500 G
In order to obtain (Gaussian), the permanent magnet was vertically arranged by passing the coated surface between the permanent magnets placed vertically above and below the nonmagnetic support.

[0070]

[0071]

[0072]

(Example 3 ) In Example 1 , the thickness of the dried magnetic layer was 0.2 μm.
A 3.5-inch floppy disk sample was prepared under the same conditions as in Example 1 except that the coating was performed so that

(Example 4 ) In Example 2 , the thickness of the magnetic layer after drying was 0.2 μm.
A 3.5-inch floppy disk sample was prepared under the same conditions as in Example 1 except that the coating was performed so that

[0075] (Example 5) In Example 1, except that the following composition was changed nonmagnetic particles of the composition of the non-magnetic layer coating solution, 3.5-inch floppy under the same conditions as in Example 1 Disk samples were made.

<Non-magnetic layer coating solution> Non-magnetic particles α-Fe 2 O 3 90 parts by weight (TF100 manufactured by Toda Kogyo Co., Ltd., average particle diameter: 0.1 μm, specific surface area by BET method: 11 m ^{2 /} g, pH 5.6) Carbon black ... 10 parts by weight (Ketjen Black EC (manufactured by Lion Akzo) Average primary particle size: 20 to 30 mμ, DBP oil absorption: 340 ml / 100 g Specific surface area by BET method: 950 m ² / g, Volatile content: 1.5 wt%) binder resin chloride-vinyl vinyl acetate - vinyl alcohol copolymer ... 14 parts by weight _{(-N (CH 3) 3 +} Cl- in the polar group 5 × 10 ^-6 eq / g containing, monomer composition ratio: 86 : 13: 1 polymerization degree 400) Polyester polyurethane resin… 5 parts by weight (neopentyl glycol / caprolactone polyol / MDI = 0.9 / 2.6 / 1, -SO ₃ Na group 1 × 1) ^0-4 eq / g) sec-butyl stearate 4 parts by weight 2-butoxy-1-ethyl stearate 2 parts by weight 2-butoxy-1-ethyl palmitate 2 parts by weight Oleic acid 1 part by weight methyl ethyl ketone … 200 parts by weight

[0077] In Example 6 Example 2, except that the nonmagnetic layer coating solution was changed to that of the same composition as Example 5, 3.5 inch floppy disk under the same conditions as in Example 2 A sample was prepared.

[0078] (Example 7) Example 1, except that the following composition was changed nonmagnetic particles of the composition of the non-magnetic layer coating solution, 3.5-inch floppy under the same conditions as in Example 1 Disk samples were made.

<Non-magnetic layer coating solution> Non-magnetic particles α-Al 2 O 3 90 parts by weight (HPSX-DBM manufactured by Reinosper Co., average particle diameter: 0.1 μm, specific surface area by BET method: 10.3 m ² / g, pH 9.1) Carbon black: 10 parts by weight (Ketjen Black EC (manufactured by Lion Akzo)) Average primary particle diameter: 20 to 30 mμ, DBP oil absorption: 340 ml / 100 g Specific surface area by BET method: 950 m ² / g, volatile matter : 1.5 wt%) binder resin chloride-vinyl vinyl acetate - vinyl alcohol copolymer ... 14 parts by weight _{(-N (CH 3) 3 +} Cl- in 5 × 10 ^-6 eq / g containing a polar group, the monomer Composition ratio: 86: 13: 1, degree of polymerization: 400) Polyester polyurethane resin: 5 parts by weight (neopentyl glycol / caprolactone polyol / MDI = 0.9 / 2.6 / 1, -SO ₃ Na group) 1 × 10 ^-4 eq / g) sec-butyl stearate 4 parts by weight 2-butoxy-1-ethyl stearate 2 parts by weight 2-butoxy-1-ethyl palmitate 2 parts by weight Oleic acid 1 part by weight Parts methyl ethyl ketone… 200 parts by weight

[0080] (Example 8) Example 2, except that the nonmagnetic layer coating solution was changed to that of the same composition as Example 7, 3.5 inch floppy disk under the same conditions as in Example 2 A sample was prepared.

(Example 9 ) In Example 2 , except that only the ferromagnetic particles were changed to obtain the composition of the coating solution for the magnetic layer as described below and that the orientation conditions of the ferromagnetic particles were changed as follows. A 3.5-inch floppy disk sample was produced under the same conditions as in Example 2 .

<Coating solution for magnetic layer> Ferromagnetic particles: 100 parts by weight (ferromagnetic hexagonal barium ferrite powder (plate-like particles) Coercive force: 1380 ersted) Specific surface area by BET method: 50 m ² / g, particle size (plate Diameter): 0.045 μm, plate ratio: 9.8 Saturation magnetization σs: 65 emu / g Binder resin Vinyl chloride copolymer: 8 parts by weight (-SO3Na content: 1 × 10 ⁻⁴ eq / g, Polymerization degree: 300) Polyester polyurethane resin: 4.5 parts by weight (neopentyl glycol / caprolactone polyol / MDI = 0.9 / 2.6 / 1, containing 1 × 10 ⁻⁴ eq / g of -SO3Na group) α- Alumina: 2 parts by weight (average particle size: 0.3 μm) Carbon black: 0.5 parts by weight (particle size: 0.10 μm) Isohexadecyl stearate: 6 parts by weight Oleic acid: 1 part by weight Methyl ethyl Ketone ... 200 parts by weight

<Orientation of Ferromagnetic Particles> After applying the coating solution for the non-magnetic layer and the coating solution for the magnetic layer on the non-magnetic support, no vertical alignment was performed.

[0084] (Comparative Example 1) Example 1, after coating the non-magnetic layer coating solution and magnetic layer coating liquid on a nonmagnetic support, except that was not the orientation of magnetic particles, Example 1 A sample of a 3.5-inch floppy disk was prepared under the same conditions as described above.

Comparative Example 2 In Example 1 , the thickness of the dried magnetic layer was 0.9 μm.
Except for the following, the same conditions as in Example 1 were used.
A sample of a 5-inch floppy disk was prepared.

Comparative Example 3 In Example 2 , the thickness of the dried magnetic layer was 1.2 μm.
Except that it was set to be 3, under the same conditions as in Example 2 .
A sample of a 5-inch floppy disk was prepared.

[0087] (Example 1 0) Example 1, except that the ferromagnetic particles in the magnetic layer to those below, were prepared samples of 3.5-inch floppy disk under the same conditions as in Example 1. Ferromagnetic particles (composition: Fe / Ni = 98/2 (atomic ratio), coercive force: 1
200 oersted BET specific surface area: 30 m 2 / g, crystallite size: 290 Å, particle size (average major axis diameter): 0.29 μm, needle ratio: 1
0, saturation magnetization σs: 121 emu / g

[0088] (Example 1 1) Example 2, except that the ferromagnetic particles in the magnetic layer to those below, were prepared samples of 3.5-inch floppy disk under the same conditions as in Example 2. Ferromagnetic particles (ferromagnetic hexagonal barium ferrite powder (plate-like particles) Coercive force: 1290 Oersted Specific surface area by BET method: 30 m ² / g, Particle size (plate diameter): 0.2 μm, plate-like ratio: 3.0 Saturation magnetization amount s: 50 emu / g

Comparative Example 4 The procedure of Example 2 was repeated under the same conditions as in Example 1 except that the ferromagnetic particles used in the magnetic layer were changed as follows.
A sample of an inch floppy disk was prepared. Ferromagnetic particles Co-modified iron oxide Coercive force: 850 Oersted Specific surface area by BET method: 35 m ² / g, Average particle size (major axis diameter): 0.25 μm, Acicular ratio: 9.0 Saturated magnetization σs: 75 emu / g

(Comparative Example 5) In Example 1 , a coating solution for a nonmagnetic layer was applied and dried.
After forming the non-magnetic layer on the non-magnetic support and winding the non-magnetic support on one end of the take-up roll, use the same coating machine again to apply the magnetic layer on the non-magnetic layer. A 3.5-inch floppy disk sample was prepared under the same conditions as in Example 1 except that the liquid was applied and dried to form a magnetic layer.

(Comparative Example 6) In Example 2 , a coating solution for a nonmagnetic layer was applied and dried.
After forming the non-magnetic layer on the non-magnetic support and winding the non-magnetic support on one end of the take-up roll, use the same coating machine again to apply the magnetic layer on the non-magnetic layer. A 3.5-inch floppy disk sample was prepared under the same conditions as in Example 1 except that the liquid was applied and dried to form a magnetic layer.

[0092] (Example 1 2) Example 2, after applying the non-magnetic layer coating solution and magnetic layer coating liquid on a nonmagnetic support, except for not performing the orientation of the magnetic particles, examples A sample of a 3.5-inch floppy disk was prepared under the same conditions as in Example 2 .

[0093] In (Example 1-3) Example 2, except for changing the ferromagnetic particles in the following, to prepare a sample of the 3.5-inch floppy disk under the same conditions as in Example 2. Ferromagnetic particles (ferromagnetic hexagonal barium ferrite powder (plate-like particles) Coercive force: 1420 Oersted Specific surface area by BET method: 38 m ² / g, Particle size (plate diameter): 0.05 μm, plate ratio: 2.3 Saturation magnetization amount s: 59 emu / g

[0094] (Comparative Example 7) Example 1, except that the nonmagnetic layer coating liquid having the following composition is no conductive particles, a sample of the 3.5-inch floppy disk under the same conditions as in Example 1 Produced.

<Non-magnetic layer coating solution> Non-magnetic particles Titanium oxide TiO ₂ 90 parts by weight (TY50 manufactured by Ishihara Sangyo, average particle diameter: 0.34 μm, specific surface area by BET method: 5.9 m ² / g) , PH 5.9) Binder resin Vinyl chloride-vinyl acetate-vinyl alcohol copolymer ... 14 parts by weight (Contains 5 × 10 ^-6 eq / g of polar group of -N (CH ₃ ) ₃ + Cl-, monomer composition ratio : 86: 13: 1 degree of polymerization 400) Polyester polyurethane resin ... 5 parts by weight (neopentyl glycol / caprolactone polyol / MDI = 0.9 / 2.6 / 1, -SO ₃ Na group 1 × 10 ^-4 eq / g) Content) sec-butyl stearate 4 parts by weight 2-butoxy-1-ethyl stearate 2 parts by weight 2-butoxy-1-ethyl palmitate 2 parts by weight oleic acid 1 part by weight Methyl ethyl ketone 200 parts by weight

[0096] (Comparative Example 8) Example 2, except that the nonmagnetic layer coating liquid was the same composition as Comparative Example 7 is not electrically conductive particles, 3.5-inch floppy under the same conditions as in Example 2 Disk samples were made.

(Evaluation of Characteristics) Each sample of the floppy disk obtained as described above was measured by the following evaluation method to evaluate its characteristics.

<Coercive force and orientation ratio of magnetic layer> Maximum applied magnetic field of 10 kOe using a vibrating sample magnetometer (manufactured by Toei Kogyo)
Was measured. The orientation ratio is determined by rotating the magnetic field from 0 ° to 360 ° every 10 degrees along the measurement sample to obtain the squareness ratio, calculating the value obtained by dividing the minimum value of the squareness ratio by the maximum value, and calculating the orientation degree. did.

<Thickness of Magnetic Layer> A section sample of a layer cross section was prepared, and a scanning electron microscope (S-700, manufactured by Hitachi, Ltd.) was used.
(Type) was obtained from a cross-sectional photograph taken.

<Surface Specific Electric Resistance of Magnetic Layer (Ω / sq)
> Measured by the method described in JISX6101.9.4 using TR-8611A (digital super insulation resistance meter) manufactured by Takeda Riken.

<Reproduced Output> Gap length 0.45 using Tokyo Engineering disk tester SK606B
Using a metal in-gap head of μm, recording was performed at a recording frequency of 625 kHz and a radius of 24.6 mm, and the reproduction output of the head amplifier was measured with an oscilloscope type 7633 manufactured by Tektronix. The reproduction output was a relative value with respect to the output of Example-1 as 100 for the sample using ferromagnetic metal powder for the ferromagnetic particles of the magnetic layer, and the sample using hexagonal ferrite and the sample of Comparative Example 4 Is a relative value with the output of Example 2 taken as 100.

<Overwriting> Using a disk tester SK606B manufactured by Tokyo Engineering Co., Ltd., at a position having a radius of 39.5 mm, 312.5 kHz was recorded on an AC demagnetized sample, and the output O1 of a 312.5 kHz component was output by a TR4171 type spectrum analyzer manufactured by Advantest. Immediately after measuring (dB), 1 MHz was overwritten and 312.
Overwriting from output O2 (dB) of 5 kHz component O2-
O1 (dB) was determined.

<Modulation> Using the same conditions and apparatus as in the measurement of the reproduction output, the maximum value Vmax and the minimum value Vmin in one round of the reproduction waveform are used.
{ (Vmax-Vmin) / (Vmax + Vmin) }
× 100 × (%) was determined.

<Driving Durability> Using a floppy disk drive FD1331 type manufactured by NEC Corporation, a recording frequency of 6
After recording on a total of 240 tracks at 25 kHz, a 24-hour thermocycle test was performed at the position where the radius was 37.25 mm from the center, with the following flow as one cycle. Under these thermo conditions, running durability was evaluated based on the running state when the vehicle was run up to 12 million times in the number of passes.

[Thermocycle Flow] (1 hour at 25 ° C., 50% RH) → 2 hours heating → (6
0 ° C, 20% RH for 7 hours) → Temperature drop for 2 hours →
(25 ° C, 50% RH for 1 hour) → Temperature drop for 2 hours → (5 ° C, 50% RH for 7 hours) → Temperature rise for 2 hours →
(1 hour at 25 ° C. and 50% RH) Further, the output of all tracks was measured every 500,000 passes, and the case where the output became 45% or less of the initial value was defined as drop-out. The samples of the 3.5-inch floppy disk obtained as described above and the evaluation results are shown in Tables 1 and 2 below.
Shown in

[0106]

[Table 1]

[0107]

[Table 2]

[0108] (Example 1 4) Example 1, 3.5 inch floppy disk under the same conditions as in Example 1 except for using the composition as follows to the non-magnetic layer coating solution was changed lubricant A sample was prepared. <Non-magnetic layer coating solution> Non-magnetic particles Titanium oxide TiO ₂ 90 parts by weight (TY50 manufactured by Ishihara Sangyo, average particle diameter: 0.34 μm,
Specific surface area by BET method: 5.9 m ² / g, pH5.
9) Carbon black: 10 parts by weight (average primary particle diameter: 16 mμ, DBP oil absorption: 80 ml)
/ 100 g pH: 8.0, specific surface area by BET method: 250 m ² /
g, volatile matter: 1.5% by weight) Binder resin Vinyl chloride-vinyl acetate-vinyl alcohol copolymer: 14 parts by weight (-N (CH ₃ ) ₃ ⁺ Cl ⁻ polar group is 5 × 10 ⁻⁶ eq / g content, monomer composition ratio: 86: 13: 1 degree of polymerization 400) Polyester polyurethane resin 5 parts by weight (neopentyl glycol / caprolactone polyol / MDI = 0.9 / 2.6 / 1, -SO ₃ Na group 1 ×) 10 ^-4 e
q / g) sec-butyl stearate 2 parts by weight 2-butoxy-1-propyl stearate 2 parts by weight Methyl ethyl ketone 200 parts by weight

[0109] In (Example 1-5) Example 1, except for changing the non-magnetic layer coating liquid lubricant below were prepared a sample of 3.5-inch floppy disk under the same conditions as in Example 1. 9 parts by weight of sec-butyl stearate 9 parts by weight of 2-butoxy-1-propyl stearate

[0110] (Example 1 6) Example 1, except for changing the non-magnetic layer coating liquid lubricant below were prepared a sample of 3.5-inch floppy disk under the same conditions as in Example 1. Butyl stearate 5 parts by weight Butoxyethyl stearate 5 parts by weight

[0111]

[0112] The evaluation results of characteristics of the sample of Example 1 4 - Example 16 shown in Table 3.

[0113]

[Table 3]

By including a lubricant in the non-magnetic layer in an amount of 3 to 20% by weight, the running durability can be further improved. It was confirmed that an excellent magnetic recording disk was obtained.

[0115] (Example 17) except that the composition of the non-magnetic particles in the nonmagnetic layer coating liquid in Example 1 was prepared as described below, the sample of the 3.5-inch floppy disk under the same conditions as in Example 1 Produced. Ti0 ₂ 95 parts by weight Carbon black 5 parts by weight

[0116] except that the carbon black of the non-magnetic layer coating solution in Example 18 Example 1 was as follows, to produce a sample of the 3.5-inch floppy disk under the same conditions as in Example 1. Carbon black (Lion Agzo Ketjen Black EC600JD) Average primary particle size 25mμ DBP oil absorption 480ml / 100g pH 9.5 Specific surface area by BET method 1300m2 / g Volatile content 0.7%

[0117]

[0118] except that the carbon black of the non-magnetic layer coating solution in Example 19 Example 1 was as follows, to produce a sample of the 3.5-inch floppy disk under the same conditions as in Example 1. Carbon black (Mitsubishi Carbon Corporation # 3250B) Average primary particle size 30mμ DBP oil absorption 150ml / 100g pH 6.6 Specific surface area by BET method 250m ² / g Volatile content 1.2%

[0119] except that the carbon black (Example 2 0) non-magnetic layer coating liquid in Example 1 was as follows, to produce a sample of the 3.5-inch floppy disk under the same conditions as in Example 1 . Carbon black (Mitsubishi Carbon Co., Ltd. # 50) having an average primary particle size 80Emumyu DBP oil absorption of 63 ml / 100 g pH 5.5 specific surface area by the BET method: 23m ² / g Volatiles 1.0% Examples 17 to Example 2 0 samples Table 4 shows the evaluation results of the characteristics of
Shown in

[0120]

[Table 4]

The conductive particles of the non-magnetic layer have an average particle size of 40 μm or less and a DBP oil absorption of 300 ml / 10
0 g or more of carbon black to all non-magnetic particles
Moreover run line or it is possible to lower the surface electric resistance of the magnetic layer by containing to 20% by weight
Excellent durability, it was confirmed to be able to magnetic recording disk having an excellent high-density recording and running stability. The surface resistivity of the magnetic layer is dependent on the amount and particle size and DBP oil absorption of the carbon black to be added to the nonmagnetic layer, in Example ^{17 1 × 10 8 Ω / sq} , Example 18
In 2 × 10 ⁶ Ω / sq, real施例in 19 1 × ¹⁰ 10 Ω
/ Sq, and in Example 20 , the result was 3 × 10 ¹¹ Ω / sq.

[0122]

A magnetic recording disk in which a non-magnetic layer mainly composed of non-magnetic particles and a binder resin and a magnetic layer mainly composed of ferromagnetic particles and a binder resin are formed in this order on a non-magnetic support. in, the non-magnetic particles are inorganic powders and carbon black, wherein the nonmagnetic layer is carbon black contained 3 to 20 wt% of the non-magnetic particles, and the fatty acid ester is contained 3 to 20 wt% of the non-magnetic particles The thickness of the magnetic layer is 0.5 μm or less, and the orientation ratio of the ferromagnetic particles in the magnetic layer is 0.85
As described above, the ferromagnetic particles in the magnetic layer are made of ferromagnetic metal powder or hexagonal ferrite, so that even in short wavelength recording, the output is high, the overwriting characteristics are good, and the magnetic recording disk has excellent running durability. Can be obtained.

 ────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masaya Kojima 2-12-1, Ogimachi, Odawara-shi, Kanagawa Fuji Photo Film Co., Ltd. (56) References JP-A-62-145501 (JP, A) JP-A-61-278024 (JP, A) JP-A-55-55431 (JP, A) JP-A-3-157809 (JP, A) JP-A-2-254621 (JP, A)

Claims (5)

(57) [Claims] 1. A magnetic recording disk in which a nonmagnetic layer mainly composed of nonmagnetic particles and a binder resin and a magnetic layer mainly composed of ferromagnetic particles and a binder resin are formed on a nonmagnetic support in this order. in, the non-magnetic particles are inorganic powders and carbon black, wherein the nonmagnetic layer is carbon black contained 3 to 20 wt% of the non-magnetic particles, and the fatty acid ester is contained 3 to 20 wt% of the non-magnetic particles The thickness of the magnetic layer is 0.5 μm or less, and the orientation ratio of the ferromagnetic particles in the magnetic layer is 0.85
As described above, the ferromagnetic particles in the magnetic layer are ferromagnetic metal powder or hexagonal ferrite. 2. The magnetic recording medium according to claim 1, wherein the coercive force of the magnetic layer is 1400 Oe or more, and the ferromagnetic particles are ferromagnetic metal powder having a needle ratio of 3 to 12. 3. The ferromagnetic particles in the magnetic layer are hexagonal ferrites having an average particle diameter of 0.01 to 0.2 μm and a tabular ratio of 3 to 20, and 2. The magnetic recording medium according to claim 1, wherein the perpendicular diamagnetic field correction squareness ratio is 0.6 or more. 4. The magnetic recording medium according to claim 1, wherein the carbon black has an average particle diameter of 40 mμ or less and a DBP oil absorption of 300 ml / 100 g or more. 5. A non-magnetic coating layer is formed by applying a coating solution for a non-magnetic layer mainly composed of non-magnetic particles and a binder resin on a non-magnetic support to form a non-magnetic coating layer. A magnetic layer coating solution in which ferromagnetic particles are dispersed in a binder resin solution is formed on the nonmagnetic coating layer, and then dried to form a nonmagnetic layer and a magnetic layer on a nonmagnetic support. 5. The method according to claim 1, wherein the magnetic recording disk is formed in order.