JPH05109061A - Magnetic recording disk and its manufacture and magnetic recording/reproduction method - Google Patents

Abstract

PURPOSE:To provide a magnetic recording disk, its manufacturing method, and a magnetic recording/reproducing method which is superb in overwriting characteristics and running durability and can record digital data highly densely with a recording wavelength of 1.5mum or less. CONSTITUTION:Title items are a magnetic recording disk, where a non-magnetic layer containing a conductive particle and a thinlayer magnetic layer with a high coercive force and a random orientation in that the coercive force is 1400 oersted or more and an orientation degree ratio is equal to or more than 0.85 and is equal to or less than 0.5mu are formed on a non-magnetic support in this order so that a coating liquid of a non-magnetic layer is coated while it is in wetting state, and its manufacturing method and magnetic recording and reproducing are performed by using a magnetic head with a gap length of delta and the above magnetic recording disk with a magnetic layer thickness of 1.25 delta or less.

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, a method of manufacturing the same, and a magnetic recording / reproducing method, and is most suitable for a recording / reproducing method having a shortest recording wavelength of 1.5 μm or less. Magnetic recording disk, its manufacturing method, and magnetic recording / reproducing method.

[0002]

2. Description of the Related Art In magnetic recording technology, a medium can be repeatedly used, signals can be easily digitized, and a system can be constructed by combining it with peripheral devices.
Video, audio, because it has excellent advantages over other recording methods such as easy signal modification.
It has been widely used in various fields including computer applications. Further, in order to meet demands such as downsizing of equipment, improvement of quality of recording / reproducing signal, lengthening of recording, increase of recording capacity, further improvement of recording density is always desired for a recording medium. Came. Therefore, attempts have been made to improve the surface property of the magnetic layer, the dispersibility of magnetic particles, and the magnetic material.

As for the floppy disk, which is an external storage medium for data, the capacity of 10 Mbytes or more has been increased due to the recent popularization of personal computers, sophistication of application software, and increase in processing information. There is a strong demand. Then, the conventional 1.
A recording system using a high-density code having a wide frequency component region of 5 times or more has been proposed, and the shortest recording wavelength of a recording signal recorded on a floppy disk is 1.5 μm.
It's about to be: In order to improve the recording density, naturally, the gap length of the magnetic head is further narrowed down to 0.5 μm or less. In order to enable recording with a short recording wavelength and a large recording density,
First, it is necessary to increase the coercive force of the magnetic layer. For example, JP-A-58-122623 and JP-A-61-7.
Japanese Patent No. 4137 and the like propose a method of using a ferromagnetic metal powder in the magnetic layer of a disk-shaped medium.

In a magnetic recording system for computers such as a floppy disk, it is indispensable to overwrite recording signals having different recording wavelengths. In the past, it would have been good if two types of signals having a frequency double relationship, 1f and 2f signals, could be overwritten. However, in the RLL method described above, not only the recording wavelength was shortened but also the frequency ratio was 3: 8.
Overwriting of a plurality of signals in the area is required.
As described above, in order to successfully overwrite a short-wavelength signal on a long-wavelength signal by using a signal having a short recording wavelength and a large difference in recording frequency, the above-mentioned JP-A-58-1 has been proposed.
As disclosed in Japanese Unexamined Patent Publication No. 22623 and Japanese Unexamined Patent Publication No. 61-74137, there is a limit in merely improving the magnetic characteristics of the magnetic layer. That is, even if the short wavelength recording signal is overwritten on the long wavelength recording signal previously recorded, the lines of magnetic force do not reach the deep portion of the magnetic layer. I couldn't erase it.
In order to solve this problem, it was effective to reduce the coercive force of the magnetic layer or to thin the magnetic layer.

However, lowering the coercive force of the magnetic layer lowers the resolution of the recording signal and the reproduction output, so that high-density recording was impossible. Further, when the magnetic layer is made thin, there are the following problems. That is, in general, it is required for a magnetic recording disk to prevent the generation of dropouts such as dust and dirt adhering to the surface of the magnetic layer due to electrification. For that purpose, carbon black is added to the magnetic layer. However, when the magnetic layer is made thin, the amount of carbon black that can be retained in the magnetic layer is limited. Furthermore, it is desirable to avoid adding carbon black to the magnetic layer as much as possible in order to maintain high magnetic properties. In addition, the shorter the wavelength of the recording signal on the magnetic recording disk, the greater the influence of drop-out and the deterioration of running durability. It becomes an important issue when designing a disc.

As another method for improving the problem of charging property, a magnetic recording medium has been proposed in which a nonmagnetic layer containing carbon black or the like is provided between a magnetic layer and a nonmagnetic support. JP-A-55-55432, JP-A-50-104003, US3440091, JP-A-62-214513, JP-A-62-2
14514, JP-A-62-231417,
It is disclosed in JP-A-63-31027. However, the thickness of the magnetic layer of the magnetic recording medium disclosed in these prior arts is not sufficiently thin for the currently required large capacity magnetic recording disk.

Further, as the magnetic layer becomes thinner, it becomes easier to peel it off, and the peeled magnetic layer causes a new drop-out. Therefore, it is necessary to deal with this problem.
The problem of peeling of the magnetic layer cannot be avoided even if the nonmagnetic layer is formed between the magnetic layer and the nonmagnetic support. As described above, in order to make a medium having a large capacity as a magnetic recording disk, it is necessary to deal with the above various problems, and means for satisfying all of them has not been proposed yet.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above problems of the prior art, and to provide a magnetic recording medium having good electromagnetic conversion characteristics and excellent running durability, and a method for manufacturing the same. It is to be. In particular, it is an object of the present invention to provide a magnetic recording disk which has excellent overwrite characteristics at high recording density and has a large recording capacity, and a method for manufacturing the same. Another object of the present invention is to provide a digital data recording / reproducing method having a large recording capacity and excellent in overwriting suitability.

[0009]

The object of the present invention is to provide a magnetic recording disk in which a non-magnetic layer and a magnetic layer are formed in this order on a non-magnetic support, wherein the non-magnetic layer comprises non-magnetic particles and bonding. A layer mainly composed of a binder resin and part or all of the non-magnetic particles are conductive particles, the magnetic layer is a layer mainly composed of ferromagnetic particles and a binder resin, The magnetic recording disk is characterized by having a thickness of 0.5 μm or less, a coercive force of 1400 oersteds or more, and an orientation ratio of the ferromagnetic particles in the magnetic layer of 0.85 or more.

In the magnetic recording disk of the present invention, by setting the coercive force of the magnetic layer to 1400 oersteds or more, the output characteristics are improved, the electromagnetic conversion characteristics are excellent, and the high-density short-wavelength digital data recording with a small recording frequency is recorded. Shows excellent reliability. In addition, since the thickness of the magnetic layer is as thin as 0.5 μm or less, overwriting of short wavelength signals can be performed well. And, between the magnetic layer and the non-magnetic support,
By providing a non-magnetic layer containing conductive particles,
It is possible to obtain a magnetic recording disk having excellent running durability, which is less likely to be charged and is less likely to cause drop-out. Further, in the present invention, by setting the orientation ratio to 0.85 or more, uniform output in the circumferential direction required for the magnetic recording disk can be achieved.

In producing the magnetic recording disk of the present invention, a non-magnetic coating layer containing a non-magnetic particle and a binder resin as a main component is applied onto a non-magnetic support to form a non-magnetic coating layer, By forming a coating solution for a magnetic layer in which ferromagnetic particles are dispersed in a binder resin solution while the non-magnetic coating layer is in a wet state, the magnetic layer with respect to the non-magnetic layer is formed. Adhesion of the layers becomes excellent, and even if the thickness of the magnetic layer is as thin as 0.5 μm or less, peeling of the magnetic layer hardly occurs, excellent running durability and a highly reliable magnetic recording disk can be obtained.

Further, by using ferromagnetic metal particles as the ferromagnetic particles of the magnetic layer, a magnetic recording disk having excellent magnetic characteristics of the magnetic layer can be obtained.

The inventors of the present invention have studied the magnetic data recording / reproducing method which is one of the objects of the present invention and which has a large capacity for high density recording with a short recording wavelength and is excellent in overwriting suitability. As a result of an examination focusing on the relationship between the gap length and the thickness of the magnetic layer, the following method was found and the method of the present invention was achieved. That is, a magnetic head having a gap length δ of 0.50 μm or less, a nonmagnetic layer containing nonmagnetic particles on a nonmagnetic support and a thickness of 1.25δ or less, a coercive force of 1400 oersteds or less, and an orientation ratio of 0.85. The above object can be achieved by a magnetic recording / reproducing method of recording / reproducing a signal having a shortest recording wavelength of 1.5 μm or less by using a magnetic recording disk in which the following magnetic layers are formed in this order. .. Conventionally, the preferable thickness of the magnetic layer has been discussed in relation to the recording wavelength from the viewpoint of the output loss, but in consideration of the overwriting suitability which is important in the field of digital data recording for computer purposes which is the object of the present invention. In that case, it has been found that the preferred magnetic layer thickness is strongly correlated with the gap length of the magnetic head. When a magnetic head having a short gap length for short wavelength recording is used and the thickness of the magnetic layer is 1.25 times or less the gap length, even if the shortest recording wavelength is as short as 1.5 μm or less, superposition A recording / reproducing method with excellent writing suitability can be provided. Then, the recording condition becomes high density, and the recording track width is 50 μm or less,
Even if the track density was 14 tracks / mm or more, good recording and reproducing could be performed by adopting the recording and reproducing method of the present invention. Of course, by using the above magnetic recording medium of the present invention in the recording / reproducing method of the present invention,
Good results can be obtained.

The magnetic layer of the magnetic recording disk of the present invention has a thickness of 0.5 μm or less, preferably 0.45.
It is less than or equal to μm. Although there is no particular lower limit to the thickness of the magnetic layer, it should be noted that if the thickness is too thin, the reproduction output will decrease. The total thickness of the non-magnetic layer and the magnetic layer formed on the non-magnetic support may be in the range of 1 to 3.0 μm.

The ferromagnetic particles used in the magnetic layer of the magnetic recording disk of the present invention are not particularly limited, and conventionally known iron oxide particles, chromium oxide particles, and cobalt-adhering iron oxide particles. Various types of ferromagnetic particles such as metal particles and hexagonal ferrite particles can be used. Of these, ferromagnetic metal particles or hexagonal ferrite particles are preferable in terms of magnetic properties. In particular Fe or Ni or C
Ferromagnetic metal particles containing o as a main component (75% by weight or more) are preferable for effectively achieving the object of the present invention.

When the particle size of the magnetic particles usable in the present invention is expressed by the specific surface area by the BET method, it is 25 to 80 m ² /
g, preferably 35 to 60 m ² / g. 25
If it is less than m ² / g, noise becomes high, and if it is more than 80 m ² / g, dispersion becomes difficult and the surface properties of the magnetic layer cannot be improved, which is not preferable. The crystallite size measured by X-ray diffraction analysis is 450 to 100 angstroms, preferably 350 to 150 angstroms.

The water content of the magnetic particles is preferably 0.01 to 2% by weight. It is necessary to optimize the water content of the magnetic material depending on the type of binder resin. The pH of the magnetic particles is preferably optimized by combining with the binder resin used. The range is 4 to 12, but preferably 6 to 10. In particular, when the binder resin has a polar group in the molecule, it is desirable to pay attention to pH. The magnetic particles may be surface-treated with Al, Si, P, or an oxide thereof, if necessary. The amount thereof is 0.1 to 10% with respect to the magnetic particles, and when the surface treatment is performed, adsorption of a lubricant such as fatty acid is 100 mg / m 2 or less, which is preferable. Soluble Na, Ca,
Inorganic ions such as Fe, Ni, and Sr may be contained, but if it is 500 ppm or less, the characteristics are not particularly affected.
These ferromagnetic particles include Al, Si,
S, Sc, Ti, V, Cr, Cu, Y, Mo, Rh, P
d, Ag, Sn, Sb, Te, Ba, Ta, W, Re,
Au, Hg, Pb, Bi, La, Ce, Pr, Nd,
It may contain atoms such as P, Co, Mn, Zn, Ni, Sr, and B.

These ferromagnetic fine particles may be previously treated with a dispersant, a lubricant, a surfactant, an antistatic agent, etc., which will be described later, before dispersion. When the ferromagnetic particles are ferromagnetic metal particles, they may contain a small amount of hydroxide or oxide. Ferromagnetic metal particles, which are obtained by a known manufacturing method, can be used, and the following methods can be mentioned. A method of reducing a complex organic acid salt (mainly oxalate) and a reducing gas such as hydrogen, or reducing Fe oxide with a reducing gas such as hydrogen to Fe or Fe.
-A method for obtaining Co particles, a method for thermally decomposing a metal carbonyl compound, a method for reducing by adding a reducing agent such as sodium borohydride, hypophosphite or hydrazine to an aqueous solution of a ferromagnetic metal, and a low pressure for a metal And a method of obtaining a fine powder by evaporating in an inert gas.

The ferromagnetic metal particles thus obtained are subjected to a known gradual oxidation treatment, that is, a method of immersing in an organic solvent and then drying, or a method of immersing in an organic solvent and then feeding an oxygen-containing gas to form an oxide film on the surface. Either a method of forming and then drying or 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 voids, and the value is 2
It is 0% by volume or less, more preferably 5% by volume or less.
The acicular ratio of the ferromagnetic particles is preferably 12 or less, and more preferably 10 or less. In order to enable high recording density, the magnetic recording disk of the present invention preferably has a coercive force of 1400 Oersteds or more. More preferably, it is 1500 oersteds or more. If the coercive force is too low, the self-demagnetization action causes a decrease in signal output, which is not preferable. On the other hand, if it is too high, it becomes difficult to reverse the magnetization by the magnetic recording head.

The hexagonal ferrite that can be used as the ferromagnetic particles in the magnetic layer of the magnetic recording disk of the present invention is typically a tabular ferromagnetic powder having an axis of easy magnetization perpendicular to the plane of the tabular surface. Examples of the composition of hexagonal ferrite include barium ferrite, strontium ferrite, lead ferrite, each substitution product of calcium ferrite, Co substitution product, and the like, specifically, magnetoplumbite-type barium ferrite and strontium ferrite, and further, Examples thereof include magnetoplumbite-type barium ferrite and strontium ferrite containing a part of spinel phase, and particularly preferable are barium ferrite and strontium ferrite Co.
It is a substitution product. Moreover, Co-T is added to the above hexagonal ferrite.
i, Co-Ti-Zr, Co-Ti-Zn, Ni-Ti
A material to which an element such as —Zn or Ir—Zn is added can also be used. Hexagonal ferrite usually has a hexagonal shape, and its particle diameter means the width of a hexagonal plate, and is measured using an electron microscope. In the present invention, the particle size is 0.01 to 0.2 μm, particularly preferably 0.03 to 0.
It is specified in the range of 1 μm. The average thickness (plate thickness) of the fine particles is about 0.001 to 0.2 μm, but 0.003 to 0.05 μm is particularly preferable. Furthermore, the plate ratio (particle diameter / plate thickness) is 1 to 10, preferably 3 to 7. 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 hexagonal ferrite fine powder is preferably 50 emu / g or more,
If it is less than mu / g, a sufficient reproduction output cannot be obtained, which is not suitable for high density recording.

The saturation magnetization and the coercive force are measured by VSM-P.
I (manufactured by Toei Industry Co., Ltd.) was used and the maximum applied magnetic field was set to 10 KOe. For the measurement of the specific surface area, a cantersorb (US, manufactured by Canterchrome Co.) was used. After dehydration in a nitrogen atmosphere at 250 ° C. for 30 minutes, the BET single point method (partial pressure 0.30) was used for measurement. The residual magnetic flux density of the magnetic recording disk of the present invention is preferably 1500 G (Gauss) or more.

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 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, and the larger the value, the smaller the fluctuation of the output in the circumferential direction, which is preferable as a magnetic recording disk. Becomes The orientation ratio is 0.
In order to obtain a value of 85 or more, a random orientation method using a permanent magnet, for example, as disclosed in Japanese Patent Publication No. 3-41895, is disclosed in JP-A-63-148417. Japanese Patent Laid-Open No. 1-30
The method of applying an alternating magnetic field disclosed in Japanese Patent No. 0427 and Japanese Patent Laid-Open No. 1-340028 can be used. In this case, it is necessary that the acicular ratio of the ferromagnetic metal particles be 12 or less, preferably 10 or less in order to achieve the orientation degree ratio of 0.85 or more.

The non-magnetic layer in the magnetic recording disk of the present invention is a layer mainly composed of non-magnetic particles and a binder resin, and some of the non-magnetic particles are conductive particles such as carbon black and graphite. It is necessary. The ratio of the conductive particles in the nonmagnetic particles of the nonmagnetic layer is 3% by weight or more, and preferably 10% by weight or more, from the viewpoint of preventing charging of the magnetic recording disk of the present invention.

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 thin, it will not be possible to prevent charging of the magnetic recording disk,
On the other hand, if it is too thick, the contact with the magnetic head deteriorates, which is not preferable.

As the conductive particles contained in the non-magnetic layer, there may be used a furnace for rubber, a thermal for rubber, black for color, acetylene black, lamp black and the like. The specific surface area of the carbon black is 5
~ 500m ² / g, DBP oil absorption is 10 ~ 400ml /
100 g, particle size 5 mμ to 300 mμ, PH 2-1
0, water content is 0.1-10%, tap density is 0.1-1
g / CC is preferred. A specific example of the carbon black used in the present invention is BLACK manufactured by Cabot Corporation.
PEARLS 2000, 1300, 1000, 90
0, 800, 700, VULCAN XC-72, Asahi Carbon Co., Ltd., # 80, # 60, # 55, # 50, # 3.
5, manufactured by Mitsubishi Kasei Co., Ltd., # 2400B, # 2300, #
900, # 1000 # 30, # 40, # 10B, manufactured by Conlon Via Carbon, CONDUCTEX SC, RA
VEN 150, 50, 40, 15 and the like.

The carbon black may be surface-treated with a dispersant or the like, may be grafted with a resin, or may be partially graphitized. Further, the carbon black may be dispersed with a binder before being added to the magnetic paint. 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. The 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.

There are no particular restrictions on the non-magnetic particles other than the conductive particles used in the non-magnetic layer of the magnetic recording disk of the present invention. Specifically, α-alumina and β having an α conversion rate of 90% or more
-Alumina, 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 and the like are used alone or in combination. The particle size of these non-magnetic powders is preferably 0.01 to 2μ, but if necessary, non-magnetic powders having different particle sizes may be combined, or a single non-magnetic powder may be used to broaden the particle size distribution and achieve the same effect. You can also The tap density is 0.
3-2 g / cc, moisture content 0.1-5%, pH 2-1
1, the specific surface area is preferably 1 to 30 m ² / g. The non-magnetic powder used in the present invention may be needle-shaped, spherical, or dice-shaped. Specific examples of the non-magnetic powder used in the present invention include AKP-20A manufactured by Sumitomo Chemical Co., Ltd.
KP-30, AKP-50, HIT-50, Nippon Kagaku Kogyo KK, G5, G7, S-1, Toda Kogyo TF-1,
00, TF-120, TF-140, and the like.

By using carbon black or the like for the magnetic layer, the magnetic recording disk of the present invention can be further prevented from being charged and the running durability can be improved. However, when conductive particles such as carbon black are contained in the magnetic layer, the added amount cannot be used as much as in the case of the nonmagnetic 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 the carbon black in the magnetic layer has the functions of preventing static charge of the magnetic layer, reducing the friction coefficient, imparting the light-shielding property, and improving the film strength, and these functions differ depending on the carbon black used. Therefore, these cards used in the present invention
It is of course possible to change the type, amount, and combination of the bonblack in the lower layer and the upper layer, and to use it properly according to the purpose based on the above-mentioned various properties such as particle size, oil absorption, electric conductivity, and PH. For example, it is possible to prevent charging by using a carbon black having a high conductivity in the lower layer and to reduce the friction coefficient by using a carbon black having a large particle size in the upper layer.

As the binder resin in the magnetic layer and non-magnetic layer of the magnetic recording disk of the present invention, conventionally known thermoplastic resins, thermosetting resins, reactive resins and mixtures thereof are used. The thermoplastic resin has a glass transition temperature of −100 to 150 ° C. and a number average molecular weight of 1000 to 200.
000, preferably 10,000 to 100,000, and the degree of polymerization is about 50 to 1,000. Such examples include vinyl chloride, vinyl acetate, vinyl alcohol,
A polymer or copolymer containing maleic acid, acrylic acid, acrylic acid ester, vinylidene chloride, acrylonitrile, methacrylic acid, methacrylic acid ester, styrene, butadiene, ethylene, vinyl butyral, vinyl acetal, vinyl ether, etc. as a constituent unit. There are polymers, polyurethane resins, and various rubber resins. Further, as the thermosetting resin or the reactive resin, 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, 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.

These resins are described in detail in "Plastic Handbook" published by Asakura Shoten. It is also possible to use a known electron beam curable resin for the upper layer or the lower layer. Examples of these and methods for producing the same 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 thereof include a combination of at least one selected from the above and a polyurethane resin, or a combination of these with polyisocyanate.

As the structure of the polyurethane resin, known ones such as polyester polyurethane, polyether polyurethane, polyether polyester polyurethane, polycarbonate carbonate polyurethane, polyester polycarbonate carbonate polyurethane, and polycaprolactone polyurethane can be used. In order to obtain better dispersibility and durability of all the binders shown here, COO is necessary.
_{M, SO 3 M, OSO 3} M, P = O (OM) 2, O-P
═O (OM) ₂ , (wherein M is a hydrogen atom or an alkali metal base), OH, NR2, N + R3 (R is a hydrocarbon group) epoxy group, SH, CN, and the like. It is preferable to use a polar group introduced 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. In particular, when ferromagnetic metal particles or hexagonal ferrite particles are used for the ferromagnetic particles of the magnetic layer, it is more difficult to disperse them than other ferromagnetic particles, so the binder resin containing the polar group described above is used. The use of is effective because the dispersibility of the ferromagnetic particles can be increased.

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 Carbite.
GD, VROH, VYES, VYNC, VMCC, XY
HL, XYSG, PKHH, PKHJ, PKHC, PK
FE, manufactured by Nissin Chemical Industry Co., Ltd., MPR-TA, MPR-TA
5, MPR-TAL, MPR-TSN, MPR-TM
F, MPR-TS, MPR-TM, 100 manufactured by Denki Kagaku
0W, DX80, DX81, DX82, DX83, Nippon Zeon's MR110, MR100, 400X110
A, Nippon Polyurethane Co. Nipporan N2301, N2
302, N2304, Pandex T made by Dainippon Ink and Chemicals
-5105, T-R3080, T-5201, Barnock D-400, D-210-80, Chris Bonn 610
9,7209, Toyobo U Byron R8200, UR
8300, RV530, RV280, manufactured by Dainichiseika, Daiferamine 4020, 5020, 5100, 530
0,9020,9022,7020, Mitsubishi Kasei Co., M
X5004, Sanyo Chemical Co., Ltd., Sampren SP-150,
Asahi Kasei Co., Ltd., Saran F310, F210 and the like can be mentioned.

The binder resin in the magnetic layer of the magnetic recording disk of the present invention is used in the range 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 a polyurethane resin is used, it is preferable to use them in combination in the range of 2 to 20% by weight and the polyisocyanate in the range of 2 to 20% by weight. In the present invention, the glass transition temperature is -50 to 10 when polyurethane is used.
0 ° C, elongation at break 100-2000%, stress at break 0.
05-10Kg / cm ² , yield point is 0.05-10Kg
/ Cm ² is preferable.

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, 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 in the upper layer and the lower layer as necessary. is there.

The polyisocyanate used in the present invention includes 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, and also
Products of these isocyanates and polyalcohols, polyisocyanates produced by condensation of isocyanates, and the like can be used. Commercially available trade names of these isocyanates are Coronate L, Coronet HL, manufactured by Nippon Polyurethane Company.
Coronate 2030, Coronet 2031, Millionaire
To MR Millionate MTL, Takeda Pharmaceutical Co., Ltd., Takenet D-102, Takenet D-110N, Takenet D-
200, Takenet D-202, Sumitomo Bayer Co., Ltd., Desmodul L, Desmodule IL, Desmodule N Desmodule HL, etc., and 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, while the coating layer for the non-magnetic layer coated on the non-magnetic support for forming the magnetic layer on the non-magnetic layer is still wet, the magnetic It is preferable to employ a so-called wet-on-wet coating method in which the layer coating liquid is applied. By adopting this coating method, the adhesion of the magnetic layer to the non-magnetic layer can be enhanced, and even if the magnetic layer is as thin as 0.5 μm as in the present invention, the magnetic layer does not peel off. Thus, it is possible to obtain a magnetic recording disk having excellent running durability in which drop-out hardly occurs. In the magnetic recording disk of the present invention, because the magnetic layer is extremely thin in the method in which a non-magnetic coating liquid is applied and dried to form a non-magnetic layer as in the conventional method, the magnetic layer is extremely thin. However, 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 integrated structure as a layer formed on the non-magnetic support.

As a specific method of the above wet-on-wet system, (1) a lower layer is first coated by a gravure coating, a roll coating, a blade coating, and an extrusion coating device which are generally used in magnetic coating, While the layer is still wet, for example,
No. 86, JP-A-60-238179 and JP-A-2-265672, a method of coating an upper layer by a non-magnetic support pressure type extrusion coating apparatus, (2) JP-A-63- The coating liquid of the lower layer and the coating liquid of the upper layer can be formed by a coating head having two slits for passing the coating liquid as disclosed in JP-A-88080, JP-A-2-17971 and JP-A-2-265672. A method of coating at substantially the same time, (3) JP-A-2-174
Examples include a method of coating the upper layer and the lower layer almost at the same time by using the extrusion coating device with a backup roll disclosed in Japanese Patent No. 965.

In order to prevent the particles dispersed in the coating liquid from agglomerating, coating is carried out 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. Further, what should be noted in the wet-on-wet coating method is the viscoelastic property (thixotropic property) of the coating liquid. That is, when there is a large difference in the viscoelastic properties of the coating liquid of the upper layer and the lower layer, when coating, mixing of the liquid occurs at the interface between the coating layer of the upper layer and the coating layer of the lower layer, the magnetic layer of the upper layer as in the present invention. When the thickness is very thin, problems such as deterioration of the surface property 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, this cannot be done, so that the structure structure in which the magnetic particles are magnetically formed in the coating liquid of the magnetic layer brings about. In order to match the structural viscosity, it is desirable to use particles such as carbon black that easily form a structural viscosity as the non-magnetic particles of the lower non-magnetic layer coating solution. It is also effective to use non-magnetic particles having a small particle size. For example, particles of titanium oxide, aluminum oxide or the like having a particle size of 1 μm or less are likely to be a coating liquid having a structural viscosity of particles due to proper aggregation.

Materials having various functions such as a lubricant and an abrasive can be added to the magnetic layer of the magnetic recording disk of the present invention. In addition, antistatic agents, dispersants,
A plasticizer, a fungicide, etc. can be added. As the lubricant, various conventionally known liquid lubricants and solid lubricants can be used. For example, dialkyl polysiloxane (alkyl has 1 to 5 carbon atoms), dialkoxy polysiloxane (alkoxy has 1 to 4 carbon atoms), monoalkyl monoalkoxy polysiloxane (alkyl has 1 carbon atoms).
~ 5 pieces, alkoxy has 1 to 4 carbon atoms), silicon oil such as phenyl polysiloxane, fluoroalkyl polysiloxane (alkyl has 1 to 5 carbon atoms), conductive fine powder such as graphite, molybdenum disulfide, two Inorganic powder such as tungsten sulfide, polyethylene, polypropylene, polyethylene vinyl chloride copolymer, plastic fine powder such as polytetrafluoroethylene; α-olefin polymer, unsaturated aliphatic hydrocarbon liquid (n-olefin double) at normal temperature A compound in which a bond is bonded to a terminal carbon, a carbon number of about 20), a fatty acid ester composed of a monobasic fatty acid having 12 to 20 carbon atoms and a monohydric alcohol having 3 to 12 carbon atoms, fluorocarbons and the like are used. it can. Of these, fatty acid esters are more preferable.

The alcohol used as the raw material for the fatty acid ester is ethanol, butanol, phenol, benzyl alcohol, 2-methylbutyl alcohol, 2-hexyldecyl alcohol, propylene glycol monobutyl ether, ethylene glycol monobutyl ether,
Examples thereof 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, arachidic acid, oleic acid, linoleic acid, linolenic acid, elaidic acid, palmitoleic acid. And aliphatic carboxylic acids or mixtures thereof. Specific examples of the fatty acid ester include butyl stearate, s-butyl stearate,
Isopropyl stearate, butyl oleate, amyl stearate, 3-methyl butyl stearate, 2-ethylhexyl stearate, 2-hexyl decyl stearate, butyl palmitate, 2-ethyl hexyl myristate, butyl stearate and butyl palmitate Mixture, butoxyethyl stearate, 2-butoxy-
1-propyl stearate, dipropylene glycol monobutyl ether acylated with stearic acid,
Various ester compounds such as diethylene glycol dipalmitate, hexamethylene diol acylated with myristic acid to give a diol, glycerin oleate and the like can be mentioned.

Further, in order to reduce the hydrolysis of fatty acid ester that often occurs when the magnetic recording medium is used under high humidity, branched / straight chain, cis / trans and other isomeric structures and branched positions of the starting fatty acid and alcohol. Is made. These lubricants are added in the range of 0.2 to 20 parts by weight with respect to 100 parts by weight of the binder. The following compounds may also be used as the lubricant. That is, silicone oil, graphite, molybdenum disulfide, boron nitride, fluorinated graphite, fluoroalcohol, polyolefin, polyglycol, alkyl phosphate ester, tungsten disulfide and the like. Examples of commercial products of these lubricants used in the present invention include NAA manufactured by NOF CORPORATION
-102, NAA-415, NAA-312, NAA-
160, NAA-180, NAA-174, NAA-1
75, NAA-222, NAA-34, NAA-35,
NAA-171, NAA-122, NAA-142, N
AA-160, NAA-173K, castor hardened fatty acid,
NAA-42, NAA-44, cation SA, cation MA, cation AB, cation BB, nymine L-2
01, Nymine L-202, Nymine S-202,
Nonion E-208, Nonion P-208, Nonion S
-207, nonion K-204, nonion NS-20
2, nonion NS-210, nonion HS-206, nonion L-2, nonion S-2, nonion S-4, nonion O-2, nonion LP-20R, nonion PP-4
0R, nonion SP-60R, nonion OP-80R,
Nonion OP-85R, Nonion LT-221, Nonion ST-221, Nonion OT-221, Monoguri M
B, nonion DS-60, anone BF, anone LG, butyl stearate, butyl laurate, erucic acid, Kanto Chemical Co., Inc., oleic acid, Takemoto Yushi Co., FAL-20.
5, FAL-123, New Japan Rika Co., Ltd., Engerb L
O, Njorb IPM, Sansosizer-E403
0, manufactured by Shin-Etsu Chemical Co., Ltd., TA-3, KF-96, KF-9
6L, KF96H, KF410, KF420, KF96
5, KF54, KF50, KF56, KF907, KF
851, X-22-819, X-22-822, KF9
05, KF700, KF393, KF-857, KF-
860, KF-865, X-22-980, KF-10
1, KF-102, KF-103, X-22-371
0, X-22-3715, KF-910, KF-393
5, Lion Armor Co., Amid P, Armide C, Amoslip CP, Lion Oil & Fat Co., Deuomin TDO, Nisshin Oil Co., BA-41G, Sanyo Kasei Co., Profan 2012E , Newport PE61, Ionet MS-400, Ionet MO-200, Ionet DL-200, Ionet DS-300, Ionet DS-1000 Ionet DO-200.

Specific examples of the polishing agent include α-alumina, β-alumina, silicon carbide, chromium oxide, cerium oxide, α-iron oxide, corundum, artificial diamond, silicon nitride and silicon carbide having an α conversion rate of 90% or more. Mainly used for titanium carbide, titanium oxide, silicon dioxide, boron nitride, etc.
6 or more known materials are used alone or in combination. Further, a composite of these abrasives (abrasive surface-treated with another abrasive) may be used. These abrasives may contain compounds or elements other than the main component, but if the main component is 90% or more, the effect remains the same. The particle size of these abrasives is 0.01 to 2 μm.
However, if desired, abrasives having different particle sizes may be combined, or a single abrasive may be used to broaden the particle size distribution to obtain the same effect. Tap density is 0.3-2 g / cc, water content is 0.1-5%, PH is 2
-11, and the specific surface area is preferably 1-30 m ² / g. The shape of the abrasive used in the present invention may be needle-like, spherical, or dice-like, but those having a corner in part of the shape are preferable because of high abradability. Particularly, specific examples of desirable abrasives include AKP-20AKP- manufactured by Sumitomo Chemical Co., Ltd.
30, AKP-50, HIT-50, Nippon Kagaku Kogyo KK, G5, G7, S-1, Toda Kogyo KK, 100ED,
140ED, etc. These abrasives may be dispersed in a binder in advance and then added to the magnetic paint. The number of abrasives present on the magnetic layer surface and the end face of the magnetic layer of the magnetic recording medium of the present invention is preferably 5 pieces / 100 μm ² or more. The amount of 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 added is small, the running durability of the magnetic recording disk is not sufficient, and if it is too large, the output is lowered, which is not desirable.

The above additives added to the magnetic layer are not necessarily 100% pure, and include impurities such as isomers, unreacted products, by-products, decomposed products and oxides in addition to the main components. It doesn't matter. The content of these impurities is preferably 30% or less, more preferably 10% or less. Various additives similar to those of the magnetic layer may be added to the lower non-magnetic layer. In particular, in the present invention, there is also a circumstance that the lubricant cannot be sufficiently retained because the upper magnetic layer is extremely thin. Therefore, by including a lubricant in the lower non-magnetic layer,
The magnetic recording layer of the present invention can be further improved by allowing the magnetic layer to be appropriately replenished. All or part of the additives used in the present invention,
It may be added in any step of producing the magnetic coating liquid, for example, when mixing with a magnetic material before the kneading step, when adding in a kneading step with a magnetic material, a binder and a solvent, or when adding in a dispersion step. In some cases, it may be added after dispersion, or just before coating.

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

A solvent with high volatility is used in the coating liquid for the upper magnetic layer to improve the surface property, and a solvent with high surface tension (cyclohexanone, dioxane, etc.) is used in the coating liquid for the lower non-magnetic layer to improve coating stability. For example, a solvent having a high solubility parameter may be used as the coating liquid for the lower non-magnetic layer to increase the filling degree, but it is needless to say that the present invention is not limited to these examples.

The non-magnetic support used in the present invention includes polyesters such as polyethylene terephthalate and polyethylene naphthalate, polyolefins, cellulose triacetate, polycarbonate, polyamide, polyimide, polyamide imide, Known films such as polysulfone can be used. Corona discharge treatment, plasma treatment, easy adhesion treatment, heat treatment,
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 may be provided between the non-magnetic support and the non-magnetic layer thereabove to improve adhesion.
These thicknesses are usually 0.01 to 2 μ, and 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 side or both sides of the non-magnetic support.

In order to effectively achieve the object of the present invention, the surface roughness of the non-magnetic support is the center line average surface roughness (Ra).
(Cutoff value 0.25 mm) 0.03 μm or less, preferably 0.02 μm or less, more preferably 0.01
It is desirable to use those 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 that they have no coarse protrusions of 1 μm or more. Further, the surface roughness shape can be freely controlled depending on the size and amount of the filler added to the non-magnetic support, if necessary. Examples of these fillers include oxides and carbonates of Ca, Si, Ti, etc.,
A fine powder of organic resin such as acrylic resin can be used. The F-5 value in the web running direction of the non-magnetic support used in the present invention is preferably 5 to 50 kg / mm ² , and the F in the web width direction is F-5.
The -5 value is preferably 3 to 30 Kg / mm ² , and the F-5 value in the long direction of the web is generally higher than the F-5 value in the web width direction, but the strength in the width direction is particularly high. This is not the case when it is necessary to do so. The heat shrinkage ratio 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 ratio at 80 ° C. for 30 minutes is preferably 1%. %Less than,
More preferably, it is 0.5% or less. The breaking strength is 5 to 100 kg / mm ^{2 in} both directions, and the elastic modulus is 100 to 20.
00 kg / mm ² is desirable.

The step of producing the magnetic coating material for 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, if necessary. Each individual process may be divided into two or more stages. 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 step. .. In addition, the individual raw materials may be divided and added in two or more steps. For example, polyurethane may be divided and added in the kneading step, the dispersing step, and the mixing step for adjusting the viscosity after dispersion. In order to achieve the object of the present invention, it is needless to say that the conventionally known manufacturing technique can be used as a part of the steps, but in the kneading step, a strong force such as a continuous kneader or a pressure kneader is used. By using one 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, 30% by weight or more of the total binder resin) and 100 parts by weight of the magnetic particles are used. For 15 ~
Kneading is performed in the range of 500 parts by weight. Details of these kneading treatments are described in JP-A-1-106388 and JP-A-1-79274. In the present invention, it is possible to produce more efficiently by using the simultaneous multi-layer 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. Alternatively, the metal rolls may be pressure-molded together. The processing temperature for pressure molding is preferably 70 ° C. or higher, more preferably 80 ° C.
That is all. The linear pressure is preferably 200 Kg / cm, more preferably 300 Kg / cm or more.

The surface resistivity of the magnetic layer surface of the magnetic recording medium of the present invention is desirably 10 ^{5 to} 5 × 10 ⁹ ohm / sq, and the elastic modulus of the magnetic layer at 0.5% elongation is the web coating direction and width. direction with preferably 100 to 2,000 kg / mm ^2, the breaking strength is preferably 1 to 30 kg / cm ^2, modulus of elasticity of the magnetic recording medium web coating direction, both the width direction preferably 10
0 to 1500 Kg / mm ² , and the residual spread is preferably 0.
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 is less than the residual solvent contained in the non-magnetic 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 nonmagnetic layer. The porosity of the nonmagnetic layer is preferably larger than that of the magnetic layer, but may be small as long as the porosity of the nonmagnetic layer is 5% or more.

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 nonmagnetic 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, and in particular, the overwriting characteristic essential for a digital data recording medium used for storing and reading computer information is, for example, However, there is an advantage that the high-density recording with the shortest recording wavelength of 1.5 μm or less does not decrease and the running durability does not decrease. The advantage is due to the above-mentioned characteristics brought about by the constitution of the magnetic disk of the present invention and the manufacturing method thereof, and particularly due to the constitution of the layer formed on the non-magnetic support and the coating method of the layer. ing. Also,
The relationship between the gap length δ of the magnetic head used for recording / reproducing digital data and the thickness of the magnetic layer is as follows.
Effectively recording / reproducing digital data having a large recording density also by using a magnetic recording disk having a non-magnetic layer containing conductive particles below the magnetic layer and adjacent to the magnetic layer. You can The magnetic recording disk preferably has a coercive force of 1400 Oersteds or more and an orientation ratio of 0.85 or more. That is, by making the thickness of the magnetic layer thinner than 1.25 times the gap length of the magnetic head, there is no problem in overwriting suitability even when the shortest recording wavelength is 1.5 μm or less. Also, good characteristics can be expected for the recording method of the RLL method, and by adopting the layer structure of the magnetic disk of the present invention, digital data recording that does not deteriorate the running durability due to the shortened recording wavelength can be performed. It can be carried out. It goes without saying that if the magnetic recording disk of the present invention is used in combination with a magnetic head having a gap length of 1 / 1.25 or more of the thickness of the magnetic layer, good recording / reproducing can be performed.

The magnetic head used in the magnetic recording / reproducing method of the present invention is not particularly limited, but a magnetic head having a metal-in-gap structure is preferable as a preferable magnetic head for short wavelength recording, and a sendust alloy is used as the material of the metal gap. Amorphous high-permeability alloys are preferred. The saturation magnetization of the gap material is 8,000 Gauss or more, preferably 10,000 Gauss or more. The gap length of the magnetic head is 0.5 μm or less, preferably 0.45 μm or less. The magnetic recording / reproducing method of the present invention is particularly effective in the case of the shortest recording wavelength, that is, the constant velocity, when the shortest recording wavelength measured on the inner peripheral surface of the magnetic recording disk is 1.5 μm or less. When it becomes 1.0 μm or less, the effect becomes more remarkable.

Further, the magnetic recording / reproducing method of the present invention is effective not only in the recording wavelength but also in the track density, the signal crosstalk is small, and recording excellent in peak shift separation can be performed. Therefore, under the condition that the recording track width is 50 μm or less and the track density is 14 tracks / mm or more, even if recording is performed with the shortest recording wavelength of 1.5 μm or less, the overwriting suitability is excellent and the recording / reproduction with good running durability can be performed. It is possible. The novel features of the present invention will be specifically described by the following examples and comparative examples.

[0056]

【Example】

(Preparation of coating liquid for non-magnetic layer and coating liquid for magnetic layer). <Nonmagnetic layer coating solution A> ... conductive particles containing non-magnetic particles of titanium oxide TiO ₂ ... 80 parts by weight (manufactured by Ishihara Sangyo TY50, average particle size: 0.34 .mu.m,
Specific surface area by BET method: 5.9 m ² / g, pH 5.
9) Carbon black 20 parts by weight (average primary particle size: 16 mμ, DBP oil absorption: 80 m
1/100 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 Containing 5 × 10 ^-6 eq / g of 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, containing —SO ₃ Na group 1 × 10 ⁻⁴ eq / g) sec-butyl stearate… 4 parts by weight butoxyethyl stearate… 2 parts by weight butoxyethyl palmitate… 2 parts of oleic acid ... 1 part by weight Methylethyl ketone 200 parts by weight <nonmagnetic layer coating solution B> ... conductive particles contains no non-magnetic particles of titanium oxide TiO ₂ ... 80 parts by weight (manufactured by Ishihara Sangyo Kaisha TY50, average particle size: 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 (containing 5 × 10 ⁻⁶ eq / g of polar group of —N (CH ₃ ) ₃ + Cl −, monomer composition ratio: 86: 13: 1 Polymerization degree 400) Polyester polyurethane resin: 5 parts by weight (neopentylglycol / caprolactonepolyol / MDI = 0.9 / 2.6 / 1, containing -SO ₃ Na group 1 × 10 ^-4 eq / g) sec -Butyl stearate: 4 parts by weight Butoxyethyl stearate: 2 parts by weight Butoxyethyl palmitate: 2 parts by weight Oleic acid: 1 part by weight Methyl ethyl ketone: 200 parts by weight

<Magnetic Layer Coating Liquid A> Ferromagnetic particles: 100 parts by weight (composition: Fe / Ni = 96/4 (atomic ratio), coercive force: 1620 Oersted, specific surface area by BET method: 50 m ² / g, Crystallite size: 195 angstroms, particle size (average major axis diameter): 0.20 μm, acicular ratio: 10, saturation magnetization σs: 130 emu / g) Binder resin Vinyl chloride copolymer: 14 parts by weight (-SO3Na content: 1 x ^10-4 eq / g, degree of polymerization: 300) Polyester polyurethane resin: 5 parts by weight (neopentylglycol / caprolactonepolyol / MDI = 0.9 / 2.6 / 1, -SO3Na group the containing 1 × 10 ^-4 eq / g) 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 ... Parts by weight Oleic acid: 1 part by weight Methyl ethyl ketone: 200 parts by weight <Coating liquid B for magnetic layer> Ferromagnetic particles: 100 parts by weight (composition: Fe / Ni = 96/4 (atomic ratio), coercive force: 1470 oersted, BET Specific surface area by method: 50 m ² / g, crystallite size: 195 Å, particle size (average major axis diameter): 0.20 μm, acicular ratio: 10, saturation magnetization σs: 130 emu / g) Binder resin Vinyl chloride copolymer: 14 parts by weight (-SO3Na content: 1 x 10 ^-4 eq / g, degree of polymerization: 300) Polyester polyurethane resin: 5 parts by weight (neopentylglycol / caprolactonepolyol / MDI = 0.9) /2.6/1, containing 1 × 10 ⁻⁴ eq / g of —SO 3 Na group) α-alumina 2 parts by weight (average particle size 0.3 μm) carbon black 0.5 parts by weight (particle size) Isohexadecyl stearate: 6 parts by weight Oleic acid: 1 part by weight Methyl ethyl ketone: 200 parts by weight <Coating liquid C for magnetic layer> Ferromagnetic particles: 100 parts by weight (composition: Fe / Ni = 96/4) (Atomic ratio), coercive force: 1320 oersteds, specific surface area by BET method: 50 m ² / g, crystallite size: 195 Å, particle size (average major axis diameter): 0.20 μm, acicular 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 ( Neohe ° Nchiruku Bu recall / capric Rorakutonho ° triol ^{/MDI=0.9/2.6/1, 1 × 10 -4 eq /} g containing -SO3Na group) alpha-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 Incidentally, the particle size and crystal of the ferromagnetic particles. The child size was measured as follows. Particle size of magnetic substance: The average particle size on the major axis was determined by a transmission electron microscope. Crystallite size: X-ray diffraction analysis of ferromagnetic particles (4,
It was obtained from the spread of the full width at half maximum of the diffraction lines of the (4,0) plane and the (2,2,0) plane.

The compositions of the coating solutions A and B for the non-magnetic layer and the coating solutions A, B and C for the magnetic layer are first kneaded with a continuous kneader, and then continuously dispersed by using a sand mill. Processed. To the obtained dispersion, 10 parts by weight of polyisocyanate (Coronate L, manufactured by Nippon Polyurethane Industry Co., Ltd.) was added to the dispersion for the non-magnetic layer, and 12 parts by weight to the dispersion for the magnetic layer. Butyl acetate 4
After adding 0 parts by weight and continuously stirring the mixture, the mixture was filtered through a filter having an average pore size of 1 μm to obtain a non-magnetic layer coating solution A.
And coating solutions A, B and C for the magnetic layer were prepared.

(Preparation of Magnetic Recording Disk) <Multilayer Coating by Wet-on-Wet Method> The above-mentioned respective non-magnetic layer coating solutions and magnetic layer coating solutions were combined as shown in Table 1, and magnetic recording disks were prepared under the following conditions. Sample-1 to sample-12 were produced. With a thickness of 62 μm, the surface roughness is 0,0 at the center line average surface roughness Ra (cutoff value 0.25 mm).
On the polyethylene terephthalate support having a thickness of 01 μm, the non-magnetic layer coating solution and the magnetic layer coating solution were wet-simultaneously multilayer coated so that the thickness of the non-magnetic layer after drying was 2 μm. The thickness of the magnetic layer after drying is 2.7,
It was applied so as to have a thickness of 0.7, 0.5 and 0.3 μm.
While both layers were still in a wet state, they were passed through two alternating magnetic field generators for random orientation of magnetic particles.
The frequencies and magnetic field strengths of the two alternating magnetic fields at that time were 50 Hz 200 Oe and 120 Hz 1300 e from the upstream side.
After further drying, a 7-stage calender device (linear pressure 300 kg / c
m, temperature 90 ° C.), punched out to 3.5 inch size, burnished the surface with polishing tape, and then used 3.5 inch floppy disk with specified mechanical parts. A disc was made.

[0060]

[Table 1] <Multilayer Coating by Sequential Coating Method> The coating solution A for nonmagnetic layer is coated so that the thickness after drying is 2 μm to form a nonmagnetic coating layer, which is dried and once wound. , The magnetic layer coating liquid A on the formed non-magnetic layer
Was applied so that the thickness of the magnetic layer after drying was 0.3 μm, and the magnetic layer was passed through two AC magnetic field generators while the magnetic layer was still in a wet state. The frequency of the two alternating magnetic fields,
Magnetic field strength is 50Hz 200Oe, 120Hz from the upstream side
1300e. After further drying, it was processed in a 7-stage calender (linear pressure 300 kg / cm, temperature 90 ° C.), punched out into 3.5 inch size, burnished the surface with polishing tape, and then 3.5 inch floppy disk. Sample 13 of 3.5-inch floppy disk medium was prepared by using the predetermined mechanical parts of. The surface roughness (Ra) of the non-magnetic support was measured at a cutoff of 0.25 mm using a three-dimensional surface roughness meter (manufactured by Kosaka Laboratory).

(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> Measurement was performed using a vibrating sample magnetometer (manufactured by Toei Industry Co., Ltd.) with a maximum applied magnetic field of 5 kOe. <Thickness of magnetic layer> A slice sample of a layer cross section was prepared, and an image was taken with a scanning electron microscope (S-700, manufactured by Hitachi Ltd.) to obtain the cross section photograph. <Playback output> Gap length 0.45 μm and 0.8 using a disk tester SK606B manufactured by Tokyo Engineering Co., Ltd.
Recording was performed at a recording frequency of 625 kHz and a radius of 24.6 mm using two types of metal in-gap heads each having a diameter of 24.6 mm, and then the reproduction output of the head amplifier was measured with a Tektronix oscilloscope model 7633. The reproduction output is shown as a relative value with the output of medium A when a head having a gap length of 0.45 μm is used as 100. <Overwriting characteristics> Radius 39.5 mm using the test equipment
At the position of AC demagnetization, 312.5 kHz was recorded, and the output O1 (dB) of the 312.5 kHz component was measured with a TR4171 type spectrum analyzer manufactured by Advantest. Immediately after overwriting with 1 MHz, 31
Overwrite from output O2 (dB) of 2.5 KHz component O
2-O1 (dB) was calculated. <Driving durability> Using a floppy disk drive FD1331 manufactured by NEC Corporation, the radius was 37.2 from the center after recording on all 240 tracks at a recording frequency of 625 kHz.
A thermocycle test was performed at the position of 5 mm with the following flow as one cycle. Under these thermo-conditions, running durability was evaluated based on the running state after running up to 12 million passes.

[Thermal cycle flow] (25 ° C., 50% RH 1 hour) → temperature rise 2 hours → (6
0 ° C 20% RH 7 hours) → temperature drop 2 hours →
(25 ° C 50% RH 1 hour) → Temperature drop 2 hours →
(5 ° C 50% RH 7 hours) → temperature rise 2 hours → (25
℃ 50% RH 1 hour) Moreover, every 500,000 passes, output of all tracks, measurement of dropout and visual inspection of medium surface appearance are performed, and the output is 60% of the initial value or 1 bit or more of 45% or less of the output. This test was discontinued if dropout occurred.

Regarding the above evaluation results, Table 2 shows the magnetic characteristics of the magnetic layer, Table 3 shows the magnetic recording characteristics, and Table 4 shows the running durability. Table 5 shows a comparison between the coating methods of the non-magnetic layer and the magnetic layer.

[0064]

[Table 2]

[0065]

[Table 3]

[0066]

[Table 4]

[0067]

[Table 5]

As in the magnetic recording disk according to claim 1 of the present invention, a sample having a magnetic layer thickness of 0.5 μm or less and a coercive force of 1400 oersteds or more has both output and overwrite characteristics. Was excellent. Further, it was found that when the cuff length of the magnetic head was 0.80 μm, the output could not be so high as compared with the case of 0.40. In the magnetic recording disk having the magnetic layer whose thickness is 1.25 times or less the buffer length of magnetic characteristics, the overwriting characteristics were better than those of the magnetic recording disk 1.25 times or more thick. It was found that Sample-10, Sample-12 and Sample-14 of the floppy disk in which the non-magnetic layer did not contain conductive particles had poor running durability. Further, it was found that the magnetic recording disk in which the non-magnetic layer and the magnetic layer were applied simultaneously by wet-on-wet was excellent in running durability.

[0069]

EFFECTS OF THE INVENTION The magnetic layer has an extremely thin thickness of 0.5 μm or less, a coercive force of 1400 oersteds or more, and an orientation degree ratio of 0.85 or more. However, by forming a multi-layer structure in which a non-magnetic layer layer containing conductive particles is formed between the non-magnetic support and the magnetic layer, the overwriting characteristics are good and short wavelength recording of 1.5 μm or less is possible. It is possible to obtain a digital data recording device having excellent running durability. In this magnetic recording disk, the running durability is further improved by applying the non-magnetic layer and the magnetic layer in a wet state in multiple layers. Further, by performing recording / reproducing using a magnetic head having a club length δ of 0.5 μm or less and the above magnetic recording disk having a magnetic layer of 1.25δ or less, excellent overwrite characteristics can be obtained. It is possible to record various short wavelength digital data.

─────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] May 27, 1992

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0041

[Correction method] Change

[Correction content]

Further, in order to reduce the hydrolysis of fatty acid ester that often occurs when the magnetic recording medium is used under high humidity, branched / straight chain, cis / trans and other isomeric structures and branched positions of the starting fatty acid and alcohol. Is made. These lubricants are in the magnetic layer
Is based on 100 parts by weight of the ferromagnetic particles , and the non-magnetic layer
0.2 to 100 parts by weight of non-magnetic particles.
It is added in the range of 20 parts by weight. That is, the magnetic recording of the present invention
In recording discs, the lubricant should be non-magnetic as well as the magnetic layer.
It can also be added to the functional layer. The following compounds may also be used as the lubricant. That is, silicon oil, graphite, molybdenum disulfide, boron nitride,
Fluorinated graphite, fluoroalcohol, polyolefin, polyglycol, alkyl phosphate, tungsten disulfide and the like. Examples of commercial products of these lubricants used in the present invention include NAA-102 and NAA-41 manufactured by NOF CORPORATION.
5, NAA-312, NAA-160, NAA-18
0, NAA-174, NAA-175, NAA-22
2, NAA-34, NAA-35, NAA-171, N
AA-122, NAA-142, NAA-160, NA
A-173K, castor hardened fatty acid, NAA-42, NA
A-44, cation SA, cation MA, cation A
B, cation BB, nymine L-201, nymine L-202, nymine S-202, nonion E-20
8, nonion P-208, nonion S-207, nonion K-204, nonion NS-202, nonion NS-
210, nonion HS-206, 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-85
R, Nonion LT-221, Nonion ST-221, Nonion OT-221, Monoguri MB, Nonion DS-6
0, anon BF, anon LG, butyl stearate, butyl laurate, erucic acid, Kanto Chemical Co., oleic acid, Takemoto Yushi Co., FAL-205, FAL-123,
Made by Shin Nippon Rika Co., Ngerb LO, Njorbu IP
M, Sansosizer-E4030, manufactured by Shin-Etsu Chemical Co., TA
-3, KF-96, KF-96L, KF96H, KF4
10, KF420, KF965, KF54, KF50,
KF56, KF907, KF851, X-22-81
9, X-22-822, KF905, KF700, KF
393, KF-857, KF-860, KF-865
X-22-980, KF-101, KF-102, KF
-103, X-22-3710, X-22-3715,
KF-910, KF-3935, Lion Armor Co., Amid P, Amid C, Amoslip C
P, manufactured by Lion Oil & Fat Co., Deuomin TDO, manufactured by Nisshin Oil Co., BA-41G, manufactured by Sanyo Chemical Co., Ltd., Profan 2012
E, Newpole PE61, Ionette MS-400,
Ionet MO-200 Ionet DL-200, Ionet DS-300, Ionet DS-1000 Ionet DO-200 and the like.

[Procedure amendment]

[Submission date] July 1, 1992

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0065

[Correction method] Change

[Correction content]

[0065]

[Table 3]

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0068

[Correction method] Change

[Correction content]

As in the magnetic recording disk according to claim 1 of the present invention, a sample having a magnetic layer thickness of 0.5 μm or less and a coercive force of 1400 oersted or more is output,
Both overwriting characteristics were excellent. Further, it was found that when the gap length of the magnetic head was 0.80 μm, the output could not be so high as compared with the case of 0.45 μm. Further, the magnetic recording disk having the magnetic layer having a thickness not more than 1.25 times the gap length of the magnetic characteristics had better overwrite characteristics than the magnetic recording disk having the thickness not less than 1.25 times.
It was found that Sample-10, Sample-12, and Sample-14 of the floppy disk in which the non-magnetic layer did not contain conductive particles had poor running durability. Further, it was found that the magnetic recording disk in which the non-magnetic layer and the magnetic layer were applied simultaneously by wet-on-wet was excellent in running durability.

Claims (4)

[Claims] 1. A magnetic recording disk in which a non-magnetic layer and a magnetic layer are formed in this order on a non-magnetic support, wherein the non-magnetic layer is a layer mainly containing non-magnetic particles and a binder resin, and Some or all of the non-magnetic particles are conductive particles, and the magnetic layer is a layer mainly composed of ferromagnetic particles and a binder resin, and the thickness of the magnetic layer is 0.5 μm.
Hereinafter, the magnetic recording disk is characterized in that its coercive force is 1400 oersteds or more, and the orientation ratio of the ferromagnetic particles in the magnetic layer is 0.85 or more. 2. A non-magnetic coating layer comprising a non-magnetic support and a binder resin as a main component is applied onto a non-magnetic support to form a non-magnetic coating layer, and the non-magnetic coating layer is in a wet state. 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. The method of manufacturing a magnetic recording disk according to claim 1. 3. The magnetic recording disk according to claim 1, wherein the ferromagnetic particles of the magnetic layer are ferromagnetic metal particles. 4. A magnetic head having a gap length δ of 0.50 μm or less and a non-magnetic support, and a non-magnetic layer containing non-magnetic particles, some or all of which are conductive particles, and a thickness of 1. 25δ or less, coercive force of 1400 oersteds or more,
A magnetic recording / reproducing method for recording / reproducing a signal having a shortest recording wavelength of 1.5 μm or less using a magnetic recording disk in which a magnetic layer having an orientation ratio of 0.85 or more is formed in this order.