JP2566085B2 - Magnetic recording media - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high density magnetic recording medium, and more particularly to a magnetic recording medium suitable for a magnetic disk for high capacity data recording.

[0002]

2. Description of the Related Art Magnetic recording technology is capable of repeatedly using a medium, is easy to digitize a signal, enables a system to be constructed in combination with peripheral electronic devices, and easily modifies a signal. Since it has excellent features not found in other recording methods such as what it can do, it has been widely used in various fields such as video, audio, and computer applications. Further, in order to meet the demands for downsizing of devices, high quality of recording / reproducing signals, longer recording, increase of recording capacity, etc., it is always desired to further improve the recording density of the recording medium. It has been rare.

For this reason, various measures have been attempted such as improving the magnetic substance, improving the surface property of the magnetic layer, and improving the dispersibility and filling degree of the magnetic substance particles in the magnetic layer.

The thickness of the magnetic layer is 1.0 μm in order to reduce the thickness loss during recording / reproduction and self-demagnetization to increase the output.
Means for reducing the thickness to m or less are effective as means for increasing the density and capacity of the magnetic recording medium. In particular, the thin magnetic layer is used for high-definition VT for video applications.
As a video tape for R, and in recent years, due to the popularization of personal computers, the sophistication of application software, and the trend of increasing processing information, there has been a strong demand for a high capacity of 10 Mbytes or more, such as a floppy disk. Also in the magnetic recording disk for digital recording, in order to increase the capacity of the magnetic recording medium in accordance with the narrow track of the magnetic head, it is important in terms of improvement of output and improvement of overwriting characteristics. That is, normally, in a magnetic recording medium for computer use such as a floppy disk, it is necessary to overwrite recording signals having different recording wavelengths. However, conventionally, two kinds of recording signals having a double frequency relationship are used. It would have been good if signal, 1f and 2f signals could be overwritten, but for a high capacity magnetic recording disk of 10 Mbytes or more, which has been strongly demanded recently, not only the recording wavelength has become shorter, but also RLL signals, etc. Frequency ratio 3: 8
Overwriting of multiple signals in the area is required. When a signal having a short recording wavelength and a large recording frequency difference is used, in order to successfully overwrite a signal having a short recording wavelength on a signal having a long recording wavelength, JP-A-58-122623 is recommended. Japanese Patent Laid-Open No. Sho 61-
As disclosed in Japanese Laid-Open Patent Publication No. 74137 and the like, there is a limit in merely improving the magnetic characteristics of the magnetic layer.

That is, in the conventional magnetic layer having a thickness of 1.0 μm or more, even if the shorter recording signal is overwritten on the previously recorded recording signal having the longer wavelength, the magnetic lines of force are deep in the magnetic layer. Since it does not reach this point, the previously recorded signal with a longer wavelength cannot be erased.

On the other hand, as the magnetic layer becomes thinner, the magnetic layer becomes easier to peel off, and the peeled magnetic layer becomes a new drop.
This will cause out, so it is necessary to address this issue as well. The problem of peeling of the magnetic layer was unavoidable even if the nonmagnetic layer was formed between the nonmagnetic support. In particular, the problem of peeling of the magnetic layer was remarkable in the case of so-called sequential multi-layer coating in which the coating method for forming the layer was such that the lower layer was dried and then the upper layer was coated.

As a coating method, for example, Japanese Patent Laid-Open No. 63-19
When the non-magnetic layer coated on the non-magnetic support disclosed in Japanese Patent No. 1315, etc. is wet, the magnetic layer coating liquid is applied by a wet-on-wet coating method to separate the magnetic layer. The problem of is considerably reduced.

If too much abrasive is added in order to improve the durability of the magnetic recording medium, the magnetic layer is thin and the filling degree of the ferromagnetic powder is originally low, so that the electromagnetic conversion characteristics cannot be improved, resulting in high density. It was difficult to obtain a high capacity magnetic recording medium.

Many methods have been proposed for adding an abrasive to the magnetic layer. For example, a magnetic recording medium in which particles having a high Mohs hardness are added as an abrasive in a magnetic layer is disclosed in JP-A-57-179945 and JP-A-62-9212.
7 and JP-B-58-45088, and JP-B is magnetic recording medium was added to the magnetic layer of particles identified particle size and Mohs hardness as an abrasive 49-39402
JP-B-55-15771, JP-A-57-57
No. 162129.

However, all of these methods are technologies based on the fact that the magnetic layer is relatively thick, and when applied to a relatively thin magnetic layer having a thickness of 1 μm or less, the surface property of the magnetic layer deteriorates, Further, there is a problem that the effect of the abrasive is not fully utilized when the magnetic layer is applied by the above-mentioned wet-on-wet method.

As a technique for adding an abrasive to a thin magnetic layer, Japanese Patent Laid-Open No. 62-89223 discloses a Mohs hardness of 6 or more, which is 0.4 to 0.65 times the thickness of the magnetic layer. A magnetic disk with an abrasive having an average particle size is described.

However, according to this method, wet
When the magnetic layer is formed by the on-wet method, there is a problem that the polishing agent does not function effectively.

The durability problem tends to be reduced particularly when the ferromagnetic powder in the magnetic layer is a ferromagnetic metal or hexagonal ferrite having excellent magnetic properties.

Furthermore, with the recent widespread use of magnetic recording media in the consumer field, the environmental conditions under which they have been used have become extremely widespread and have become a major problem. That is, it is often used outdoors in all environmental conditions for video camera applications such as 8 mm video, and for magnetic recording disks such as floppy disks for computer applications, it is used for a long time, not to mention environmental conditions. Is becoming more frequent. Further, in a floppy disk or the like, a medium is loaded into a cartridge or a jacket for use, but since a liner made of a non-woven fabric provided inside the cartridge or the jacket comes into contact with the magnetic layer, durability against it is also required.

As described above, it is effective to reduce the thickness of the magnetic layer to 1 μm or less in order to realize high density recording and high capacity of the magnetic recording medium. No effective method has been proposed yet.

[0016]

SUMMARY OF THE INVENTION The object of the present invention was made in view of the problems of the prior art described above, and it is a high-density recording / high-capacity magnetic recording having good electromagnetic conversion characteristics and excellent running durability. It is an object of the present invention to provide a medium, and particularly to provide a magnetic recording medium which is excellent in overwriting characteristics at high recording density and suitable for a magnetic recording disk having a large recording capacity.

[0017]

The above object of the present invention is to provide a non-magnetic layer mainly composed of non-magnetic powder and a binder resin and a magnetic layer mainly composed of ferromagnetic powder and a binder resin on a non-magnetic support. However, in the magnetic recording medium formed in this order, the thickness of the magnetic layer is 1.0 μm or less, and the magnetic layer is obtained by applying the non-magnetic layer coating liquid onto the non-magnetic support. While the coating layer is in a wet state, the magnetic layer coating solution is applied onto the coating layer, and the magnetic layer has a Mohs hardness of 6 or more and a magnetic layer of the magnetic layer. than the thickness can be further achieved in the magnetic recording medium body, characterized in that it contains an abrasive larger average particle size.

In the magnetic recording medium of the present invention, at least the non-magnetic layer and the magnetic layer are formed in this order on the non-magnetic support. Since the magnetic layer is as thin as 1 μm, the output is reduced due to thickness loss or the like. Is suitable for use as a high-density recording medium and a high-capacity magnetic recording disk because the overwriting characteristics, which is a problem when shortening the recording wavelength in a magnetic recording disk for computers, can be reduced. Is. Further, by forming the non-magnetic layer under the magnetic layer, the uniformity of the thickness of the magnetic layer and the like is superior to the case where the magnetic layer is formed alone on the non-magnetic support.

The inclusion of an abrasive having a Mohs hardness of 6 or more and having an average particle diameter larger than the thickness of the magnetic layer in the magnetic layer improves the decrease in durability, which is a problem when the magnetic layer becomes as thin as 1 μm. It is possible to provide a magnetic recording medium that has been recorded.

The magnetic recording medium of the present invention is manufactured by coating the coating liquid for the magnetic layer on the coating layer for the non-magnetic layer while the coating liquid for the non-magnetic layer is still wet. A magnetic layer having a uniform thickness is obtained, and when the thickness of the magnetic layer is thin, the problematic adhesion is improved.

In particular, in the method for producing a magnetic recording medium of the present invention , even if the average particle size of the abrasive contained in the magnetic layer is larger than the thickness of the magnetic layer, the coating layer for the non-magnetic layer is The coating liquid for the magnetic layer is applied to the magnetic layer while it is in a wet state, so that some of the abrasive particles in the magnetic layer also enter the non-magnetic layer, so that the abrasive particles project onto the surface of the magnetic layer. By doing so, the surface property of the magnetic layer is not deteriorated, and since the abrasive particles are present on the surface of the magnetic layer, it is possible to obtain a magnetic recording medium having excellent electromagnetic conversion characteristics and excellent durability.

The thickness of the magnetic layer of the magnetic recording medium of the present invention is
1 μm or less, preferably 0.05 to 0.8 μm
Or less, more preferably 0.1 to 0.5 μm or less
It

[0023] The thickness of the magnetic layer is increased, the output is lowered, so also lowered overwrite characteristic is not preferable. Further, when the thickness of the magnetic layer is thin, it is not preferable because a magnetic layer having a uniform thickness cannot be obtained and the output is lowered.

The magnetic layer of the magnetic recording medium of the present invention contains an abrasive having a Mohs hardness of 6 or more and an average particle diameter larger than the thickness of the magnetic layer. That is, the Mohs hardness of the abrasive is contained in the magnetic layer of the magnetic recording medium of the present invention is Der Ritaira average particle diameter above 6 have larger than the thickness of the magnetic layer.

Further, the average particle size of the abrasive containing the magnetic layer of the magnetic recording medium of the present invention, larger than the thickness of the magnetic layer
In particular, it is preferably 1.1 times or more the thickness of the magnetic layer.

It is contained in the magnetic layer of the magnetic recording medium of the present invention.
The average particle size of the abrasive used is larger than the thickness of the magnetic layer.
Is required, but 0.05 to 3 μm, preferably
It is 0.2 to 1.5 μm.

The average particle diameter of Ken Migakuzai decreases and becomes smaller than the thickness of the magnetic layer decreases the durability of the magnetic recording medium, also necessary to contain a large number of abrasive by to maintain the durability Therefore, it becomes difficult to obtain a magnetic recording medium having high electromagnetic conversion characteristics.

Included in the magnetic layer of the magnetic recording medium of the present invention.
The content of the abrasive contained is as follows.

The content of the abrasive average particle diameter is larger than the thickness of the magnetic layer in the magnetic layer of the magnetic recording medium definitive to the onset Ming is 1 to 20% by weight of the ferromagnetic powder, preferably 3 to Ru 18 weight% der.

If the content is too large, the surface property of the magnetic layer is deteriorated and the filling degree of the ferromagnetic powder is deteriorated, so that the electromagnetic conversion characteristics of the magnetic recording medium are deteriorated. If the content is too small, the durability of the magnetic recording medium is deteriorated. There has name undesirable because reduced.

As the abrasive contained in the magnetic layer of the magnetic recording medium of the present invention, various conventionally known abrasives can be used.

Examples of the abrasive average particle diameter is larger than the thickness of the onset bright Mohs hardness definitive in the magnetic layer in 6 above, for example, alpha-alumina, beta-alumina, .gamma.-alumina, silicon carbide, cerium oxide, α-iron oxide, silicon nitride, titanium carbide, titanium oxide, silicon dioxide, boron nitride,
Fused alumina, silicon carbide, chromium oxide (Cr ₂ O ₃ ),
Examples include corundum, artificial corundum, diamond, artificial diamond, garnet, emery (main components: corundum and magnetite).

Among them, alumina can reduce the fluctuation of the friction coefficient between the magnetic head and the magnetic layer, and can obtain a magnetic recording medium having stable characteristics against so-called stick-slip.

Specific examples of alumina include AKP-10, AKP-12, AKP-15 and 2 manufactured by Sumitomo Chemical Co., Ltd.
0, AKP-30, AKP-50, AKP-1520,
AKP-1500, Nippon Kagaku Kogyo KK, G5, G7, S
-1, chromium oxide K, UB40B manufactured by Uemura Kogyo Co., Ltd., WA8000 and WA10000 manufactured by Fujimi Abrasive Co., Ltd., and TF180 manufactured by Toda Kogyo Co., Ltd. are listed.

Next, when manufacturing the magnetic recording medium of the present invention,
The case will be described in detail.

The method of incorporating an abrasive into the magnetic recording medium of the present invention is not particularly limited, and it is added together with other components of the magnetic layer.
It may be, may be added to the magnetic coating After dispersion treatment an abrasive with a binder resin.

As the ferromagnetic powder used in the magnetic layer of the magnetic recording medium of the present invention, iron oxide-based ferromagnetic powder, ferromagnetic metal powder, plate-like hexagonal ferrite powder or the like can be used. In particular, when a ferromagnetic metal powder or barium ferrite having a small particle size, which is suitable for a magnetic recording medium for high-density recording, is used as the ferromagnetic powder, the durability of the magnetic layer often causes a problem. In the magnetic recording medium of, the problem is considerably improved.

When the ferromagnetic powder is a ferromagnetic metal powder, its particle size preferably has a specific surface area of 30 to 60 m ^2.
/ G, and the crystallite size determined by the X-ray diffraction method is 100 to 300 A (angstrom). If the specific surface area is too small, it will not be possible to adequately support high-density recording, and if it is too large, it will not be possible to disperse sufficiently and a magnetic layer with a smooth surface cannot be formed. .

On the other hand, the plate-like hexagonal ferrite powder has a specific surface area of 25 to 50 m ² / g, a plate ratio of 2 to 6 and a particle length of 0.02 to 1.0 μm.
For the same reason as the ferromagnetic metal powder, high density recording becomes difficult if the particle size is too large or too small.

It is necessary that the ferromagnetic metal powder contains at least Fe, and specifically, Fe, Fe-C.
It is a simple metal or alloy mainly composed of o, Fe-Ni or Fe-Ni-Co. In order to increase the recording density of the magnetic recording medium of the present invention, it is necessary that the particle size is small as described above, and at the same time, the saturation magnetization is at least 110 emu / g or more, preferably 120 as a magnetic property.
It is more than emu / g. Also, the coercive force is 800 Oe
(Oersted) or higher, preferably 900 Oe or higher. And, it is desirable that the axial ratio of the particles is 5 or more. In order to further improve the properties, B, C, A in the composition
Non-metals such as l, Si and P may be added. Usually, an oxide layer is formed on the particle surface of the metal powder in order to stabilize it chemically.

The plate-shaped hexagonal ferrite is a plate-shaped ferromagnetic substance having an axis of easy magnetization in a direction perpendicular to the plate surface, and includes barium ferrite, strontium ferrite, lead ferrite, calcium ferrite, or those. And the like, and the cobalt-substituted barium ferrite and the cobalt-substituted strontium ferrite are particularly preferable. In addition, In, Zn, Ge, Nb, V may be added to improve the characteristics as necessary.
You may add elements, such as. In order to increase the recording density of the magnetic recording medium of the present invention, the particle size of the plate-shaped hexagonal ferrite powder needs to be small as described above, and at the same time, the saturation magnetization is at least 50e as a magnetic property.
It is at least mu / g, preferably at least 53 emu / g.
The coercive force is preferably 500 Oe or more and 600 Oe or more. The output of hexagonal ferrite is lower than that of other magnetic particles in the case of long-wavelength recording, but when the recording wavelength in the high frequency band is short wavelength of 1.0 μm or less, it is rather lower than that of other magnetic particles. It is characterized by high output. Further, in 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. For that purpose, it is necessary that the in-plane orientation ratio is as high as possible. . When hexagonal ferrite is used as magnetic particles, a high orientation ratio of 0.9 or more can be realized.

The magnetic properties of the ferromagnetic powder, such as the saturation magnetization and the coercive force, were set to a maximum applied magnetic field of 10 kOe using VSM-PI (manufactured by Toei Industry Co., Ltd.). In addition, the specific surface area was measured using a cantersorb (B, manufactured by Canterchrome, USA) B
This is based on the ET method. It is a value measured by the BET single point method (partial pressure 0.30) after dehydration in a nitrogen atmosphere at 250 ° C. for 30 minutes.

The water content of these ferromagnetic powders is preferably 0.01 to 2% by weight. The water content is preferably optimized depending on the type of binder resin. PH of ferromagnetic powder
It is preferable to optimize the combination with the binder resin used. The range is 4 to 12, but preferably 5 to 10.

The binder resin which can be used in the magnetic recording medium of the present invention can be used essentially without distinction whether it is a magnetic layer or a non-magnetic layer. As the binder resin, conventionally known thermoplastic resins, thermosetting resins, reactive resins and mixtures thereof are used. The thermoplastic resin has a glass transition temperature of −100 ° C. to 150 ° C., a number average molecular weight of 1,000 to 200,000, preferably 10,000 to 100,000, and a degree of polymerization of about 50 to 1,000.

Examples of such binder resin include vinyl chloride, vinyl acetate, vinyl alcohol, maleic acid, acetic acid.
Acrylic acid, acrylic acid esters, vinylidene chloride, acrylonitrile, methacrylic acid, methacrylic esters, styrene, butadiene, ethylene, Binirubuchira - le, Biniruaseta - le, Binirue - polymers or copolymers containing ether, such as constituent units, There are polyurethane resins and various rubber resins.

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, Examples thereof include epoxy-polyamide resin, a mixture of polyester resin and isocyanate prepolymer, a mixture of polyester polyol and polyisocyanate, and a mixture of polyurethane and polyisocyanate.

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 first layer or the second layer. These examples and their manufacturing method 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 vinyl alcohol.
Resin, vinyl chloride vinyl acetate maleic anhydride copolymer, nitrocellulose, a combination of at least one selected from the group and a polyurethane resin, or a combination of these with polyisocyanate. The structure of polyurethane resin is polyester polyurethane, polyester
Known materials such as terpolyurethane, polyether polyesterpolyurethane, polycarbonate-polyurethane, polyester polycarbonate-polyurethane, and polycaprolactone polyurethane can be used. For all of the binders listed here, COOM, SO ₃ M, OSO, and
₃ M, P = O (OM) ₃ , O-P = O (OM) ₂ , (wherein M is a hydrogen atom or an alkali metal base), O
H, NR ₂ , N ⁺ R ₃ (R is a hydrocarbon group) Epoxy group, S
It is preferable to use one having at least one polar group selected from H, CN, etc. 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.
g.

Specific examples of these binders used in the present invention include VAGH and V manufactured by Union Carbite Corporation.
YHH, VMCH, VAGF, VAGD, VROH, V
YES, VYNC, VMCC, XYHL, XYSG, P
KHH, PKHJ, PKHC, PKFE, manufactured by Nisshin Chemical Industry Co., Ltd., MPR-TA, MPR-TA5, MPR-TA
L, MPR-TSN, MPR-TMF, MPR-TS,
MPR-TM, 1000W manufactured by Denki Kagaku, DX80, D
X81, DX82, DX83, MR11 manufactured by Zeon Corporation
0, MR100, 400X110A, Nippon Polyurethane Co., Ltd. Nipporan N2301, N2302, N2304,
Dainippon Ink and Company Pandex T-5105, T-R3
080, T-5201, Barnock D-400, D-2
10-80, Crisbon 6109, 7209, Byron UR8200, UR8300, UR860 manufactured by Toyobo Co., Ltd.
0, RV530, RV280, manufactured by Dainichiseika, Daiferamine 4020, 5020, 5100, 5300, 90
20,9022,7020, Mitsubishi Kasei, MX500
4, Sanyo Kasei Co., Sampren SP-150, Asahi Kasei Co., Saran F310, F210 and the like.

The binder used in the present invention is used in the range of 5 to 50% by weight, preferably 10 to 30% by weight, based on the magnetic substance and non-magnetic powder of each layer. It is preferable to use a combination of 5 to 100% by weight when using a vinyl chloride resin, 2 to 50% by weight when using a polyurethane resin, and 2 to 100% by weight of polyisocyanate.

In the present invention, when polyurethane is used, the glass transition temperature is −50 ° C. to 100 ° C., the elongation at break is 100 to 2000%, and the stress at break is 0.05 to 10.
Preferably, the yield point is 0.05 to 10 kg / cm ² , and the yield point is preferably 0.05 to 10 kg / cm ² .

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 Co., Ltd.
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 the first layer and the second layer.

In addition to the above, a lubricant, an antistatic agent, a dispersant, a plasticizer, an antifungal agent and the like can be added to the magnetic layer of the magnetic recording medium of the present invention.

As the lubricant used in the magnetic layer of the present invention, dialkyl polysiloxane (alkyl has 1 to 5 carbon atoms), dialkoxy polysiloxane (alkoxy has 1 to 4 carbon atoms), monoalkyl monoalkoxy poly Siloxane (alkyl has 1 to 5 carbon atoms, alkoxy has 1 to 4 carbon atoms), phenyl polysiloxane, fluoroalkyl polysiloxane (alkyl has 1 to 5 carbon atoms)
Silicone oil such as); conductive fine powder such as graphite; inorganic powder such as molybdenum disulfide and tungsten disulfide; plastic fine powder such as polyethylene, polypropylene, polyethylene vinyl chloride copolymer, polytetrafluoroethylene; α -Olefin polymer; unsaturated aliphatic hydrocarbon that is liquid at normal temperature (a compound in which an n-olefin double bond is bonded to a terminal carbon, carbon number about 20); monobasic fatty acid and carbon having 12 to 20 carbon atoms Number 3 to 12
Fatty acid esters consisting of individual monohydric alcohols, fluorocarbons and the like can be used.

Of these, fatty acid esters are most preferred.

The alcohol used as the raw material of 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 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, as fatty acids, acetic acid, propionic acid, octanoic acid, 2-ethylhexanoic acid, lauric acid,
Examples thereof include aliphatic carboxylic acids such as myristic acid, stearic acid, palmitic acid, behenic acid, arachiic acid, oleic acid, linoleic acid, linolenic acid, elaidic acid, and palmitoleic acid, and mixtures thereof.

Specific examples of the fatty acid ester include butyl stearate, sec-butyl stearate, isopropyl stearate, butyl oleate, amyl stearate, 3-methylbutyl stearate, 2-ethylhexyl stearate, 2-hexyl decyl. Stearate,
Butyl palmitate, 2-ethylhexyl myristate, a mixture of butyl stearate and butyl palmitate, butoxy ethyl stearate, 2-butoxy-1-
Propyl stearate, dipropylene glycol monobutyl ether esterified with stearic acid, diethylene glycol dipalmitate, hexamethylene diol esterified with myristic acid to give a diol, and various ester compounds such as glycerin oleate You can

Further, in order to reduce the hydrolysis of the 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 be used as the lubricant. That is, silicone oil, graphite, molybdenum disulfide, boron nitride, fluorinated graphite, fluoroalcohol, polyolefin, polyglycol, alkyl phosphate, tungsten disulfide and the like.

These lubricants can also be added to the non-magnetic layer, and the amount of addition is 0.2 to 20 parts by weight based on 100 parts by weight of the total non-magnetic powder. By adding a lubricant to the non-magnetic layer, it is possible to make up for the deficiency in the magnetic layer. In particular, this effect is particularly effective because the amount of lubricant that can be held by the magnetic layer is limited when the magnetic layer is as thin as 1 μm or less.

All or a part of the additives used in the present invention may be added in any step of the magnetic coating production, for example, when mixed with the magnetic material before the kneading step, the additives are combined with the magnetic material. When added in the kneading step with the agent and the solvent, when added in the dispersion step, when added after dispersion,
There are cases where it is added immediately before application.

Dispersants usable in the magnetic layer of the magnetic recording medium of the present invention include caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, oleic acid, elaidic acid, linoleic acid, Fatty acids having 12 to 18 carbon atoms such as linolenic acid and stearolic acid (R1 COOH, R1 is an alkyl or alkenyl group having 11 to 17 carbon atoms); Alkali metals (Li, Na, K, etc.) of the above fatty acids or Alkaline earth metal (M
g, Ca, Ba) metal soap; fluorine-containing compound of the above fatty acid ester; amide of the above fatty acid; polyalkylene oxide alkyl phosphate ester; lecithin; trialkylpolyolefinoxy quaternary ammonium salt (where alkyl is carbon Number 1 to 5, olefins such as ethylene and propylene); and the like are used. In addition to these, higher alcohols having 12 or more carbon atoms, and other than these, sulfuric acid esters and the like can also be used. These dispersants are added in the range of 0.5 to 20 parts by weight with respect to 100 parts by weight of the binder resin.

To the magnetic layer, carbon black, graphite, metal powder or the like may be added as an antistatic agent in order to prevent dusts and other deposits due to charging.

The content of the antistatic agent is usually 1 to 20% by weight of the ferromagnetic powder. If the amount of the antistatic agent is too large, the filling degree of the ferromagnetic powder is lowered, which is not preferable.

The nonmagnetic layer of the magnetic recording medium of the present invention is a layer mainly composed of nonmagnetic powder and a binder resin. The weight ratio of the non-magnetic powder to the binder resin is 100: 10 to 10.
It is preferably 0:50.

The thickness of the nonmagnetic layer is 0.5 to 10 μm,
It is preferably 0.5 to 5 μm. If the thickness of the non-magnetic layer is too thin, a magnetic layer having a uniform thickness cannot be obtained, and if it is too thick, the contact with the magnetic head deteriorates, which is not preferable.

The nonmagnetic powder contained in the nonmagnetic layer is not particularly limited, and various conventionally known nonmagnetic powders can be used. Among them, the antistatic agent which can be contained in the magnetic layer is contained in the non-magnetic layer, and the magnetic layer of the present invention weakens the charging property of the magnetic recording medium because of the thinness of the magnetic layer. It is effective in preventing kimono.

As the conductive particles contained in the non-magnetic layer, carbon black is preferable, and the furnace for rubber, the thermal for rubber, the black for color, the acetylene black and the like can be used. Specific surface area is 5 to 5
00m2 / g, DBP oil absorption is 10 to 1500ml /
100 g (DBP oil absorption of carbon black, dibutyl phthalate is added little by little to carbon black powder,
Observe the state of carbon black while kneading, find a point that forms one lump from the dispersed state, and add the amount of dibutyl phthalate (ml) at that time to DBP
The amount of oil absorption was used. ), The particle size is 5 to 300 mμ, P
It is preferable that H is 2 to 10, the water content is 0.1 to 10% by weight, and the tap density is 0.1 to 1 g / CC. Specific examples of the carbon black used in the present invention include BLACKPEARLS2000, 130 manufactured by Cabot Corporation.
0, 1000, 900, 800, 700, VULCAN
XC-72, Asahi Carbon Co., Ltd., # 80, # 60, # 5
5, # 50, # 35, Mitsubishi Kasei Co., Ltd., # 3950
B, # 2400B, # 2300, # 900, # 1000
# 30, # 40, # 10B, Columbia Carbon Co.,
CONDUCTEX SC, RAVEN 150, 5
0, 40, 15, Ketjen Black EC, Ketjen Black ECDJ-500, Ketjen Black ECDJ-600 and the like manufactured by Lion Aguzo. Surface treatment of carbon black with a dispersant,
It may be used by grafting with a resin or by using a part of the surface graphitized. Also, the car
It is possible to disperse the bond black in advance with the binder before adding it to the coating dispersion.

When carbon black is used in the magnetic layer, the amount based on the ferromagnetic powder is preferably 0.1 to 30% by weight. Further, the nonmagnetic layer preferably contains 3 to 20% by weight based on the total amount of the nonmagnetic powder. Carbon black has the functions of preventing static charge of the magnetic layer and non-magnetic layer, reducing the friction coefficient, imparting light-shielding properties, improving the film strength, etc. These differ depending on the carbon black used. Therefore, these carbon blacks used in the present invention have different types, amounts, and combinations, and have different particle sizes, oil absorptions, electric conductivities,
Of course, it is possible to use differently according to the purpose based on the above-mentioned various properties such as pH. The carbon black that can be used can be referred to, for example, in "Carbon Black Handbook" edited by Carbon Black Association .

As the non-magnetic powder contained in the non-magnetic layer, the above-mentioned abrasives contained in the magnetic layer can be used.

The particle size of these non-magnetic powders is 0.01.
However, it is also possible to combine non-magnetic powders having different particle sizes, or to use a single non-magnetic powder to widen the particle size distribution to obtain the same effect. The tap density is 0.3 to 2 g / cc, and the water content is 0.
It is preferably 1 to 5% by weight, pH is 2 to 11, and specific surface area is 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:
Sumitomo Chemical Co., Ltd., AKP-20, AKP-30, AKP-
50, HIT-50, manufactured by Nippon Kagaku Kogyo Co., Ltd., G5, G7,
S-1, Toda Kogyo Co., Ltd., TF-100, TF-120,
TF-140, TT055 series made by Ishihara Sangyo Co., ET
Examples include 300 W and STT30 manufactured by Titanium Industry Co., Ltd.

The binder resin used in the non-magnetic layer is essentially the same as that used in the magnetic layer, and the same binder resin can be used.

[0075] The above were mixed together with an organic solvent of the composition binder resin, and dispersed with a mixed kneading disperser to form a homogeneous coating solution.

Each material added to the magnetic layer or the non-magnetic layer is not necessarily 100% pure, and in addition to the main component, impurities such as isomers, unreacted products, by-products, decomposed products and oxides are contained. It does not matter if it is included. These impurities are 3
It is preferably 0% by weight or less, more preferably 10% by weight.
It is the following.

All or a part of each material used in the present invention may be added in any step of producing a coating liquid, for example, when mixed with a magnetic material before the kneading step, It may be added in the kneading step with the binder and the solvent, in the dispersing step, after the dispersing, or just before the 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, methanol, ethanol, propanol, Butanol, isobutyl alcohol, isopropyl alcohol, methyl cyclohexanol, and other alcohols, methyl acetate, butyl acetate, isobutyl acetate, isopropyl acetate, ethyl lactate, glycol acetate, and other esters, glycol Glycol ethers such as dimethyl ether, glycol monoethyl ether, dioxane, etc., aromatic hydrocarbons such as benzene, toluene, xylene, cresol, chlorobenzene, methylene chloride, ethylene chloride, carbon tetrachloride Chloroform, ethylene chlorohydrin, dichlorobenzene, chlorinated hydrocarbons and the like, 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. These impurities are preferably 30% by weight or less, more preferably 10% by weight 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 non-magnetic layer.

A solvent having a high volatility is used in the coating liquid for the upper magnetic layer to improve the surface property, and a solvent having a high surface tension (cyclohexanone, dioxane, etc.) is used in the coating liquid for the lower non-magnetic layer to improve the stability of coating. 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.

In the production of the magnetic recording medium of the present invention, the step of producing the coating liquid comprises at least a kneading step, a dispersing step, and a mixing step provided before and after these steps, if necessary. Each process may be divided into two or more steps. All raw materials such as magnetic particles, binder resin, abrasive, non-magnetic particles, antistatic agent, lubricant and solvent used in the present invention may be added at any stage of any step. Further, individual raw materials may be added in two or more steps in a divided manner. 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 goes without saying that a conventionally known manufacturing technique can be used as a part of the steps, but in the kneading step, a continuous kneader or a pressure kneader is used. The residual magnetic flux density (Br) of the magnetic recording disk of the present invention can be increased by using a material having a strong kneading force.
Can be higher. 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. Against 1
Kneading is performed in the range of 5 to 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 more efficiently produce by using the simultaneous multi-layer coating method as disclosed in JP-A-62-212933.

[0082] The method of coating the non-magnetic layer and the magnetic layer in the manufacture of magnetic recording medium of the present invention, while the non-magnetic layer coating layer coated on a nonmagnetic support is still wet, It is preferable to employ a so-called wet-on-wet type coating method in which the magnetic layer coating liquid is coated thereon.
By adopting this coating method, the adhesion of the magnetic layer to the non-magnetic layer can be improved, and even if the magnetic layer is as thin as 1.0 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 is unlikely to occur. Further, it is possible to obtain a magnetic layer having a high uniformity of thickness even if it is thin. In the method in which the non-magnetic layer coating liquid is applied and dried to form the non-magnetic layer and then the magnetic layer is applied thereon, the adhesion between the non-magnetic layer and the magnetic layer may be due to the extremely thin magnetic layer. This 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 wet-on-wet coating method, (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, and While the layer is still in a wet state, for example, Japanese Patent Publication No. 46186/1989 and Japanese Patent Laid-Open No. 6-186186.
No. 0-238179 and Japanese Unexamined Patent Publication No. 2-265672, a method of coating an upper layer by a non-magnetic support pressure type extrusion coating apparatus, (2) Japanese Unexamined Patent Publication No. 63-88080, Japanese Unexamined Patent Publication No. -17
A method of applying a lower layer coating solution and an upper layer coating solution almost at the same time by a coating head having two slits for passing the coating solution as disclosed in Japanese Patent Application No. 971 and Japanese Patent Application Laid-Open No. 2-265672. ) A method of coating the upper layer and the lower layer almost at the same time by using the extrusion coating apparatus with a backup roll disclosed in JP-A-2-174965.

In order to prevent the particles dispersed in the coating liquid from aggregating, 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 viscoelasticity between the upper layer and the lower layer coating liquid, when the coating is performed, the liquids are mixed at the interface between the upper layer coating layer and the lower layer coating layer. When the thickness is very thin, problems such as deterioration of the surface property of the magnetic layer are likely to occur.

In order to make the viscoelastic characteristics of the coating liquid as close as possible, it is effective to first make the dispersed particles of the upper layer and the lower layer the same, but in the case of the present invention, this is not possible. In order to match with the structural viscosity brought about by the structure structure in which the magnetic particles are formed by magnetism in the coating liquid, particles that easily form a structural viscosity such as carbon black are used as the non-magnetic particles in the lower non-magnetic layer coating liquid. Is desirable. Therefore, in the present invention, it is effective to use carbon black having a large oil absorption and a small particle size, but at the same time, 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 are likely to be a coating liquid having a structural viscosity of particles due to proper aggregation.

The non-magnetic support used in the magnetic recording medium of the present invention includes polyesters such as polyethylene terephthalate and polyethylene naphthalate, polyolefins,
Known films such as cellulose triacetate, polycarbonate, polyamide, polyimide, polyamideimide, and polysulfone can be used. These supports may be subjected to corona discharge treatment, plasma treatment, easy adhesion treatment, heat treatment, dust removal treatment, or the like in advance.

The thickness of the magnetic recording medium of the present invention is 1 to 1.
The thickness is 00 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 provided on the non-magnetic support to improve adhesion. Their thickness is usually 0.01 to 2 μm, preferably 0.0
It is 5 to 0.5 μm.

The nonmagnetic layer and magnetic layer of the magnetic recording medium of the present invention are provided on one side or both sides of the nonmagnetic 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 (R
It is desirable to use a) having a (cutoff value of 0.25 mm) of 0.03 μm or less, preferably 0.02 μm or less, and more preferably 0.01 μm μ 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. These fillers
Examples thereof include oxides and carbonates of Ca, Si, Ti and the like, as well as organic resin fine powders of acrylic and the like. 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-5 value in the web width direction is preferably 3 to 30 kg / mm.
^In general, the F-5 value in the long direction of the web is higher than the F-5 value in the web width direction.

The heat shrinkage ratio of the non-magnetic 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, 80 ° C. 3
The heat shrinkage percentage at 0 minutes is preferably 1% or less, more preferably 0.5% or less. Breaking strength is 5 to 100 kg / mm ^{2 in} both directions, elastic modulus is 100 to 2000 kg
/ Mm ² is desirable.

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 preferably 10 ^{5 to} 5 × 10 ⁹ ohm / sq.
The elastic modulus of the magnetic layer at 0.5% elongation is preferably 100 to 2000 kg / mm ² in both the web coating direction and the width direction,
The breaking strength is preferably 1 to 30 kg / cm ² , the elastic modulus of the magnetic recording medium is preferably 100 to 1500 kg / mm ^{2 in} the web application direction and the width direction, and the residual spread is preferably 0.5% or less and 100 ° C. or less. The heat shrinkage at any temperature is preferably 1% or less, more preferably 0.5.
% Or less, and most preferably 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 in both the magnetic layer and the nonmagnetic layer.
Volume% or less. The porosity of the non-magnetic layer is preferably larger than that of the magnetic layer, but it may be small if the porosity of the non-magnetic layer is 5% or more.

The magnetic recording medium of the present invention has a non-magnetic layer and a magnetic layer, but 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 it does not decrease and the running durability does not decrease even with high density recording such that the shortest recording wavelength is 1.5 μm or less.

The advantage is due to the above characteristics brought about by the constitution of the magnetic disk of the present invention and the manufacturing method thereof, and in particular, the constitution of the layer formed on the non-magnetic support and the coating method of the layer. Due to.

Further, by using 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 separation property is reduced. 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, 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 with reference to the following examples and comparative examples. All "parts" mean "parts by weight".

[0102]

[Example 1]

(Composition for non-magnetic layer) Non-magnetic powder TiO ² (TY50 manufactured by Ishihara Sangyo) 90 parts (average particle diameter 0.34 μm, specific surface area by BET method 5.9 m ² / g, pH 5.9) carbon black (Lion Aguzo company) Ketjen Black EC) 10 parts (average particle size 30 mμ, DBP oil absorption 350 ml / 100 g, specific surface area by BET method 950 m ² / g) Vinyl chloride-vinyl acetate-vinyl alcohol copolymer 14 parts (-N (CH ₃ ) ₃ ⁺ Cl ^- polar groups of 5 × 10 ^-6 eq / g containing composition ratio 86: 13: 1 degree of polymerization 400) 5 parts polyester polyurethane resin (neopentyl glycol / caprolactone polyol / MDI = 0.9 / 2. 6/1 -SO ₃ Na group containing 1 × 10 ^-4 eq / g) sec over butyl stearate 5 parts 2-butoxy -1 chromatography propyl stearate 5 parts 1 part of oleic acid Methyl ethyl ketone 200 parts

(Composition for Magnetic Layer) Ferromagnetic Metal Powder (Composition Fe: Ni = 96: 4) 100 Parts (Coercive Force Hc 1600 Oe, Specific Surface Area 58 m ² / g Crystallite Size 195 A, Saturation Magnetization σ _s 130 emu / g Particles Size (major axis diameter) 0.20μ, acicular ratio 10) Vinyl chloride copolymer 14 parts (-SO ₃ Na content: 1 x 10 ^-4 eq / g) Polyester polyurethane resin 3 parts (neopentyl glycol / Caprolactone polyol / MDI = 0.9 / 2.6 / 1-SO ₃ Na group 1 × 10 ^-4 eq / g included) α-alumina (AKP-15 manufactured by Sumitomo Chemical Co., Ltd.) 10 parts (average particle size 0.7 μm) a specific surface area of 3.1m ² / g, a Mohs hardness of 9.0) Ca - carbon black (particle size 0.10 .mu.m) 0.5 parts isohexadecyl stearate 6 parts 2 parts of methyl ethyl oleate Ton 200 parts

The above magnetic layer composition and nonmagnetic compatible composition were each kneaded with a continuous kneader and then dispersed using a sand mill. Polyisocyanate was added to the obtained dispersion liquid in an amount of 10 parts for the coating liquid for the non-magnetic layer, 12 parts for the coating liquid for the magnetic layer, and 40 parts by weight of butyl acetate for each, and a filter having an average pore size of 1 μm. It filtered using-and prepared the coating liquid for non-magnetic layer formation and the magnetic layer formation, respectively. The obtained non-magnetic layer coating solution is dried so that the non-magnetic layer has a thickness of 2 μm, and the magnetic layer coating solution is applied thereon, and the magnetic layer has a dried thickness of 0.45 μm. So that the thickness is 62 μm and the centerline surface roughness is 0.01 μm.
Simultaneous multi-layer coating was performed on the polyethylene terephthalate support, and while both layers were still in a wet state, a frequency of 5 was applied.
0 Hz, magnetic field strength 200 gauss or frequency 50 Hz, 1
After passing through two 20-gauss magnetic field strength AC magnetic field generators, random orientation treatment was performed, and after drying, it was treated with a 7-stage calender at a temperature of 90 ° C and a linear pressure of 300 kg / cm, and punched into 3.5 inches. After the surface polishing treatment, the liner was put into a 3.5-inch cartridge with the inside installed, and predetermined mechanical parts were added to prepare a 3.5-inch floppy disk sample.

Example 2 The same conditions as in Example 1 except that the α-alumina used in the magnetic layer in Example 1 was changed to the following, and 3.5
A sample of the inch floppy disk was prepared. α-alumina (Sumitomo Chemical Co., Ltd. AKP-10) 10 parts Average particle size 1.0 μm, specific surface area 2.1 m ² / g

Example 3 In Example 1, the thickness of the non-magnetic layer coating solution after drying was 2
A 3.5-inch floppy disk sample was prepared under the same conditions as in Example 1 except that the dry coating was performed so that the dry thickness of the upper magnetic layer was 0.2 μm. .

Example 4 A 3.5-inch floppy disk sample was prepared under the same conditions as in Example 1, except that the addition amount of α-alumina used in the magnetic layer was changed as follows. Created. α-alumina (AKP-15 manufactured by Sumitomo Chemical Co., Ltd.) 3 parts Average particle size 0.7 μm, specific surface area 3.1 m ² / g

Example 5 A 3.5-inch floppy disk sample was prepared in the same manner as in Example 1 except that the addition amount of α-alumina used in the magnetic layer was changed as follows. α-alumina (Sumitomo Chemical Co. AKP-15) 18 parts Average particle size 0.7 μm, specific surface area 3.1 m ² / g

Comparative Example 1 A 3.5-inch floppy disk sample was prepared under the same conditions as in Example 1 except that the α-alumina used in the magnetic layer was changed as follows. α-alumina (Sumitomo Chemical Co., Ltd. HIT-50) 10 parts Average particle size 0.25 μm, specific surface area 8.5 m ² / g

Comparative Example 2 A 3.5-inch floppy disk sample was prepared under the same conditions as in Example 1, except that the α-alumina used in the magnetic layer in Example 3 was changed to the following. α-alumina (Sumitomo Chemical Co., Ltd. HIT-100) 10 parts Average particle size 0.06 μm, specific surface area 26 m ² / g

Comparative Example 3 A 3.5-inch floppy disk sample was prepared under the same conditions as in Example 1 except that α-alumina was removed from the composition of the magnetic layer.

Comparative Example 4 In Example 1, only the non-magnetic coating solution was applied onto the support so that the thickness after drying was 2 μm, and then dried and calendered under the conditions of Example 1. . After that, a magnetic layer was coated on the non-magnetic layer so that the thickness after drying was 0.45 μm, and random alignment was performed under the same conditions as in Example 1 while the coated layer of the magnetic layer was in a wet state. A sample of 3.5-inch floppy disk was prepared by drying, calendaring.

Comparative Example 5 In Example 1, the thickness of the magnetic layer after drying was 1.2 μm.
2. Under the same conditions as in Example 1, except that
A 5 inch floppy disk sample was prepared.

Comparative Example 6 3.5 inches under the same conditions as in Example 1 except that the nonmagnetic layer was not formed and only the magnetic layer was applied under the same conditions as in Example 1. A floppy disk sample was prepared.

The 3.5-inch floppy disk samples prepared as described above were evaluated under the following measurement conditions.

(Orientation degree ratio) Using a vibration sample type magnetometer (manufactured by Toei Industry Co., Ltd.), Hm 10k
Oe magnetic field is applied and measured, the magnetic field is rotated every 10 degrees from 0 to 360 degrees to obtain the squareness ratio, and the value obtained by dividing the minimum value of the squareness ratio by the maximum value is calculated as the orientation degree. did.

(Measurement of reproduction output) Disk tester SK606B manufactured by Tokyo Engineering Co., Ltd.
A metal-in-gap head with a gap length of 0.45 μm and a recording frequency of 625 kHz and a radius of 2
After recording at a position of 4.6 mm, the reproduction output of the head amplifier was measured with a Tektronix oscilloscope model 7633. The output of Example 1 was set as 100 and shown as a relative value.

(Modulation) Using the same conditions and apparatus as those for the reproduction output measurement, the maximum value Vmax and the minimum value Vmin in one round of the reproduction waveform are calculated by ((Vma
x-Vmin) / (Vmax + Vmin)) x 100 (wt%).

(Overwriting property) The overwriting property was measured by using the above-mentioned test apparatus and the radius was 39.5 mm.
At the position of AC degaussing, 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 Corporation. Immediately after overwriting with 1 MHz, 31
Overwrite from the output O2 (dB) of the 2.5 kHz component O
2-O1 (dB) was calculated.

(Durability) Floppy disk drive FD13 manufactured by NEC Corporation
After recording on all 240 tracks at a recording frequency of 625 kHz using a 31-inch type, a thermocycle test was performed with the following flow as one cycle at a position where the radius was 37.25 mm from the center. Under this thermal condition, the running durability was evaluated by the running state after running up to 25 million passes. [Thermocycle flow] (Hold at 25 ° C and 50% RH for 1 hour) → (Temperature rise for 2 hours) → (Hold at 60 ° C and 20% RH for 7 hours)
→ (2 hours temperature decrease) → (25 ° C 50% RH condition for 1 hour) → (2 hours temperature decrease) → (5 ° C 50% RH condition for 7 hours) → (temperature increase 2 hours) → (25 ℃ 50% R
Hold under H condition for 1 hour) → Repeatedly thereafter (center line average surface roughness (Ra)) A cut-off value of 0.25 mm was measured using a three-dimensional surface roughness meter (manufactured by Kosaka Laboratory). The evaluation results of the respective characteristic values of the examples and comparative examples obtained by the above evaluation method are shown in Table 1 below.

[0121]

[Table 1]

Examples 1 to 5 of the present invention are reproduction outputs,
Modulation, show superior properties in the electromagnetic conversion characteristics of the overwriting, that shows the result of stable even in the cycle durability.

Further, in Comparative Examples 1 to 3 in which the abrasive having an average particle size smaller than the thickness of the magnetic layer was used, the durability was stopped due to sticking of the head, or the magnetic layer was scraped. The surface roughness of Comparative Example 4 which is not simultaneous multilayer coating
Is slightly larger and the playback output is somewhat lower, but the durability is good.
It was good. . The magnetic recording medium of Comparative Example 6 in which the non-magnetic layer was not provided had deteriorated surface properties, the reproduction output was significantly reduced, and the cycle durability was insufficient.

[0124] Sufficient over light characteristics were not obtained for the magnetic layer having a large dry thickness after coating. Usually, an overwrite characteristic of -30 dB or less is required in a digital recording medium. Furthermore, the running durability was inferior to that of the example (Comparative example 5 ).

Example 6 A 3.5-inch floppy disk sample was prepared under the same conditions as in Example 1 except that the following diamond powder was used instead of α-alumina in the composition of the magnetic layer. did. Diamond powder 1 part (average particle size 0.3 μm, Mohs hardness 10)

Example 7 In Example 1, the nonmagnetic particles of the nonmagnetic layer such as TiO 2 are used.
₂ is α-Fe ₂ O ₃ (TF-100 manufactured by Toda Kogyo Co., Ltd.): average particle size 0.34 μm, non-surface area of BET method 11 m ² / g
A 3.5 inch floppy disk sample was prepared under the same conditions as in Example 1 except that the pH was changed to 5.6.

[0127] Example 8 performed in Example 6, except that the average particle size as the diamond powder in the magnetic layer were from 0.6μm Example 1
A 3.5-inch floppy disk sample was prepared under the same conditions as above.

Example 9 In Example 6 , 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 6 except that the coating was carried out as described above.

Comparative Example 7 In Example 6 , the thickness of the magnetic layer after drying was 1.2 μm.
2. Under the same conditions as in Example 6 , except that
A 5-inch floppy disk sample was prepared.

[0130] In Comparative Example 8 Example 6, except that only the magnetic layer was coated under the same conditions as in Example 6 without forming the non-magnetic layer, 3.5 under the same conditions as in Example 6 inches A floppy disk sample was prepared. The evaluation results of Examples 6 to 9 and Comparative Examples 7 and 8 are shown in Table 2 below.

[0131]

[Table 2]

[0132]

EFFECTS OF THE INVENTION A non-magnetic layer having a coating layer for a magnetic layer formed thereon and a magnetic layer of 1 μm or less are formed in this order on a non-magnetic support while the coating layer of the non-magnetic layer is in a wet state. In the magnetic recording medium described above, the magnetic layer contains an abrasive having a Mohs hardness of 6 or more and an average particle size larger than the thickness of the magnetic layer, or an abrasive having a Mohs hardness of 9 or more. In addition, it is possible to obtain a magnetic recording medium which is excellent in both electromagnetic conversion characteristics and overwrite characteristics and is excellent in running durability, and which is particularly suitable for a high capacity magnetic recording disk.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masaya Kojima 2-12-1, Ogimachi, Odawara City, Kanagawa Prefecture Fuji Photo Film Co., Ltd. (72) Inventor Toshio Kawamata 2-12-1, Ogimachi, Odawara City, Kanagawa Prefecture Fuji Photo Film Co., Ltd. (56) Reference JP-A-4-325915 (JP, A) JP-A-4-325917 (JP, A) JP-A-5-12650 (JP, A) JP-A-5-182173 (JP, A) JP 5-182177 (JP, A) JP 5-182178 (JP, A) JP 5-217149 (JP, A) JP 5-298653 (JP, A) Kaihei 7-311932 (JP, A) JP 7-326037 (JP, A) JP 7-326038 (JP, A) JP 8-50718 (JP, A) JP 4-238111 ( JP, A) JP-A-4-283416 (JP, A) JP 4-321924 (JP, A)

Claims (6)

(57) [Claims] 1. A magnetic recording medium in which a non-magnetic layer mainly composed of non-magnetic powder and a binder resin and a magnetic layer mainly composed of ferromagnetic powder and a binder resin are formed in this order on a non-magnetic support. The magnetic recording is characterized in that the magnetic layer has a thickness of 1.0 μm or less, and the magnetic layer contains an abrasive having a Mohs hardness of 6 or more and an average particle diameter larger than the thickness of the magnetic layer. Medium. 2. The ferromagnetic powder is a ferromagnetic metal powder or a ferromagnetic hexagonal ferrite powder .
The magnetic recording medium of claim 1 that. 3. The magnetic recording medium according to claim 1, wherein an orientation ratio of particles of the ferromagnetic powder in the magnetic layer is 0.85 or more and the shape is a disk. . 4. An average of abrasives contained in the magnetic layer
Contracts characterized by a particle size of 0.05 to 3 μm
The magnetic recording medium according to any one of claims 1 to 3. 5. The magnetic recording medium is magnetic for data recording.
One of claims 1 to 4, characterized in that it is for a disc.
The magnetic recording medium according to item 1. 6. A lower layer in which a non-magnetic powder is dispersed in a binder.
Coating liquid for non-magnetic layer, ferromagnetic powder and Mohs hardness of 6 or more
And the average particle size is larger than the thickness of the magnetic layer after drying.
A magnetic layer coating solution in which a polishing agent is dispersed in a binder is used.
Prepared and applied the non-magnetic layer coating solution on the non-magnetic support
The lower non-magnetic layer obtained by
The dry thickness of the magnetic layer may be simultaneously or sequentially applied with the coating of the magnetic layer.
The magnetic layer coating solution is applied to a thickness of 1 μm or less.
A method of manufacturing a magnetic recording medium, comprising: