JPH1064039A - Magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the change of tape traveling property caused by the long term preservation or under a severe environment of high temp. and high humidity while keeping excellent electromagnetic transducing characteristic in a coating type high density magnetic recording medium. SOLUTION: This magnetic recording medium is prevented substantially from increasing fine protrusions having >=30nm height on the surface after 7 days preservation under the environment of 60 deg.C and 90% RH by providing an under coating layer containing mainly an inorganic powder and a binder on a non-magnetic supporting body, providing one or more layers of a magnetic layer containing at least a ferromagnetic metallic powder and a binder on the under coating layer, controlling the thickness of the magnetic layer to >=0.05μm to <=0.5μm and the surface roughness of the outermost layer of the magnetic layer to <=3nm and containing a fatty acid in the under coating layer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium, and more particularly to a magnetic recording medium for recording and reproducing digital signals at high density, and more particularly to a coating type magnetic recording medium having improved storage characteristics. .

[0002]

2. Description of the Related Art Magnetic recording media are widely used as recording tapes, video tapes, computer tapes, disks, etc., and are becoming denser and shorter in recording wavelength year by year. Have been.

To meet this demand for higher density, magnetic recording media using a metal thin film for the magnetic layer have been studied. However, ferromagnetic powder is used as a binder in terms of practical reliability such as productivity and corrosivity. A so-called coating type magnetic recording medium which is dispersed and coated on a support is excellent.

[0004] The coating type magnetic recording medium is inferior in electromagnetic conversion characteristics due to the lower filling degree of the magnetic substance as compared with the metal thin film type magnetic recording medium. Type magnetic recording media have been proposed.

In order to improve the electromagnetic conversion characteristics of a coating type magnetic recording medium, it is necessary to improve the magnetic characteristics of a ferromagnetic powder,
It is effective to smooth the surface of the magnetic layer. In particular, as a method of realizing the smoothness of the magnetic layer, there is a method of applying a wet-on-wet method which enables the magnetic layer to be made extremely thin and smooth via a non-magnetic layer by improving the dispersibility of the magnetic particles. Has been put to practical use.

On the other hand, with the recent development of recording media,
Huge amounts of recorded images and information are stored permanently around the world, but among the recording media, magnetic recording media are superior to other recording media in long-term storage. Changes in long-term storage of characteristics and changes in input / output characteristics have been confirmed.

[0007]

Further, magnetic recording tapes for video recording also have a width of 2 inches to 1 inch,
The recording density has been improved as the width has become smaller, such as 1/2 inch and 8 mm, and the surface of the magnetic layer has been smoothed. However, in the case of a coating type magnetic recording tape which competes with a metal thin film type magnetic tape formed by vapor deposition or the like in recent years, the surface roughness of the magnetic layer is reduced to 3%.
nm or less, and the magnetic recording tape having such a smooth magnetic layer is subjected to a severe environment, for example, 60 ° C.-90 °.
After storage in a% environment, it was newly confirmed that the runnability, which had no problem before storage, deteriorated remarkably, resulting in poor running.

Conventionally, by removing as much alkali and alkaline earth metal components as possible from the magnetic layer, precipitation of fatty acid calcium and the like on the surface of the magnetic layer can be suppressed even after storage in a severe environment. It is known that deterioration of running performance is suppressed (for example,
No. 146519).

However, it has been found that even when this technique is applied to a magnetic recording tape having a magnetic layer having a surface roughness of 3 nm or less, deterioration in running properties after storage in a severe environment cannot be suppressed. .

SUMMARY OF THE INVENTION An object of the present invention is to provide a high-density magnetic recording medium having good electromagnetic conversion characteristics. In particular, a change in tape running characteristics under a severe environment of long-term storage or high temperature and high humidity is minimized. It is an object of the present invention to provide a good coating type high density magnetic recording medium.

[0011]

The above object of the present invention is attained by the following constitutions.

That is, the magnetic recording medium according to the present invention comprises:
A lower coating layer containing an inorganic powder, a fatty acid and a binder is provided on a flexible support, and a magnetic layer having a thickness of 0.05 μm or more and 0.5 μm or less consisting of a ferromagnetic metal powder and a binder is provided on the lower coating layer. A magnetic layer having a surface roughness of 3 nm.
The following magnetic recording medium, characterized in that after storage in a 60 ° C.-90% RH environment for 7 days, substantially no increase in fine protrusions having a height of 30 nm or more is observed on the surface of the magnetic layer. Is what you do.

The above object of the present invention is also achieved by the following constitution.

That is, the magnetic recording medium according to the present invention comprises:
On a flexible support, a lower layer containing an inorganic powder, a fatty acid and a binder is provided, and the thickness containing the ferromagnetic metal powder and the binder on the lower layer is 0.05 μm or more and 0.5 μm or less. A magnetic recording medium comprising a magnetic layer, wherein the surface roughness of the uppermost layer of the magnetic layer is 3 nm or less, and the dynamic friction coefficient on the surface of the magnetic layer varies by 7 ° C. in a 60 ° C.-90% RH environment.
It is within ± 10% before and after storage for days.

In a particularly preferred embodiment of the present invention, the inorganic powder used in the lower coating layer has an average major axis length of 0.05 to 0.25 μm, more preferably 0.1 to 0.25 μm.
In the range of 0.6 to 0.15 μm and the pH is 7 to 1.
Α-Fe ₂ O ₃ of 1 or titanium oxide having a specific surface area of 50 to 80 m ² / g and a pH of 8 to 11 is used, and most preferably α-Fe ₂ O ₃ as described above is used. used.

When the above-mentioned α-Fe ₂ O ₃ is used, the shape is preferably a needle or spindle shape, the average short axis length is in the range of 0.01 to 0.035 μm, and the long axis length / Those having an axis ratio of the short axis length in the range of 2 to 20 are preferred. Also, 1.0 to ₂ wt% of SiO ₂ ,
It is more preferable to use those containing 1.0～4Wt% of Al ₂ O ₃ and 50ppm or less of P. When titanium oxide is used, 6
It is particularly preferable to use one containing 10 wt% to 10 wt% Al ₂ O ₃ .

The pH of the inorganic powder can be adjusted in a water washing step in the process of producing the inorganic powder, for example, by removing remaining acidic components, for example, SO ₄ ²⁻ ions,
By raising the isoelectric point of the particles, the pH of the powder can be increased from 7 to 11
Can be adjusted to a desired range. The isoelectric point of the particles can be changed by adjusting the amounts of Si and Al in the surface treatment agent. The inventors found that the pH of the inorganic powder was 60 ° C. and 90% RH in the combined configuration of the upper magnetic layer and the lower non-magnetic layer.
It was discovered that it was related to the fluctuation of the dynamic friction coefficient after storage, and specifically, it was found that the increase in the dynamic friction coefficient was suppressed by setting the pH of the inorganic powder to the alkaline side. This is because precipitation of fatty acid metal salts including fatty acid iron salts on the surface of the magnetic layer, which causes an increase in the dynamic friction coefficient, is suppressed.

If the pH of the inorganic powder is too high, for example, when a polyurethane resin is used as a binder, hydrolysis is promoted, which causes inconvenience. Therefore, it is preferably 8 to 11, and most preferably. It is in the range of 9 to 10.

Incidentally, regarding the specification of the fatty acid metal salt, 60
Observation of the tape surface after storage in an environment of 90 ° C.-90% RH with an AMF (atomic force) microscope reveals that micro-projections are observed in those with an increase in μ value, and in particular, those with a projection height of 30 nm or more increase remarkably. It was confirmed that. By analyzing the microprojections, fatty acid metal salts were detected, and the causative substance that increased the dynamic friction coefficient could be identified. The present inventors have found that these microprojections are fatty acid metal salts, and that their formation is correlated with the pH of the lower nonmagnetic powder. Thus, a high-output coating type magnetic recording medium having an ultra-smooth surface with an average surface roughness of 3 nm or less has been obtained.

The present invention also defines a coating type magnetic recording medium having high storability by limiting the fluctuation of the dynamic friction coefficient on the surface of the magnetic layer, and preserving by limiting the degree of the fluctuation of the dynamic friction coefficient. It defines a coating type magnetic recording medium having high performance.

[0021]

According to the magnetic recording medium of the present invention, a lower coating layer mainly containing an inorganic powder and a binder is provided on a nonmagnetic support, and at least a ferromagnetic metal powder and a binder are coated on the lower coating layer. One or more magnetic layers, wherein the thickness of the magnetic layer is 0.05 μm or more and 0.5 μm or less, the surface roughness of the uppermost layer of the magnetic layer is 3 nm or less, and the lower coating layer contains a fatty acid. With this configuration, 6
After storage for 7 days in a 0 ° C.-90% RH environment, 3
Substantially no increase in microprojections with a height of 0 nm or more was observed, or the dynamic friction coefficient of the magnetic layer surface fluctuated within ± 10% before and after storage. A good coating-type high-density magnetic recording medium in which a change in tape running characteristics is suppressed as much as possible can be realized.

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a magnetic recording medium according to the present invention will be described in detail.

In a consumer digital VCR, the recording wavelength is 22 μm.
Is adopted as a synchronization signal, and a data signal has a recording wavelength of 0.488 μm. In order to reduce the weight, an overwrite erasure is adopted by omitting an erasing head. In order to employ overwrite erasure, it is necessary to erase the synchronizing signal with a data signal, and it is said that the overwrite erasure rate is desirably -20 dB or less. As a characteristic required for a recording medium, it is desired that the overwrite erasing rate be as low as possible. Overwrite characteristics can be improved by reducing the thickness of the magnetic layer.However, simply reducing the thickness of the magnetic layer reduces the total amount of magnetization. Output drops. In order to improve the output of a long-wavelength signal, a large amount of magnetization is required, and for that purpose, a high magnetic flux density and a certain thickness must be secured.

As described above, the overwrite characteristic and the long-wavelength signal output have a conflicting relationship. However, in order to reduce the overwrite erasure rate, not only the magnetic layer can be made thinner, but also it can be improved by recording a short wavelength signal such as a data signal deep into the magnetic layer. To this end, it is effective to supply as much recording current as possible during data signal recording. For compatibility with ME, it is desirable that the optimum recording current is as large as that of ME. However, it is desirable to supply as much recording current as possible from the viewpoint of overwrite characteristics.

In addition to the above factors, in order to improve the overwrite characteristics, it is desirable to smooth the surface roughness of the magnetic layer within the range permitted by the running property, and the squareness ratio of the magnetic layer is high. It was found that the lower the SFD and the lower the SFD, the better the overwrite characteristics.

Based on the above-described mechanism of action, the present inventors have conducted intensive experiments, and as a result, provided a lower coating layer mainly containing an inorganic powder and a binder on a non-magnetic support. In a magnetic recording medium provided with at least one magnetic layer containing at least a ferromagnetic metal powder and a binder, the thickness of the magnetic layer is 0.05 μm or more and 0.5 μm or less (preferably 0.07 μm or less).
μm or more and 0.2 μm or less), the Bm of the magnetic layer measured with an external magnetic field of 10 kOe is 3700 gauss or more and 6000 gauss or less, and the Hc of the magnetic layer is 2000 Oe or more and 3000 Oe or less.
A digital video tape that can be used in a consumer digital VCR has been obtained.

Next, the details of the lower coating layer will be described.

The inorganic powder used in the lower coating layer of the present invention may be either a magnetic powder or a non-magnetic powder. For example, in the case of non-magnetic powder, it can be selected from inorganic compounds such as metal oxides, metal carbonates, metal sulfates, metal nitrides, metal carbides, and metal sulfides. As the inorganic compound, for example, α
Α-alumina, β-alumina, γ-alumina, θ-alumina, silicon carbide, chromium oxide, cerium oxide, α-iron oxide, goethite, corundum, silicon nitride, titanium carbide, titanium oxide, Silicon dioxide, tin oxide, magnesium oxide, tungsten oxide, zirconium oxide, boron nitride, zinc oxide, calcium carbonate,
Calcium sulfate, barium sulfate, molybdenum disulfide and the like are used alone or in combination. Particularly preferred are titanium dioxide, zinc oxide, iron oxide, barium sulfate,
More preferred are titanium dioxide and α-iron oxide. The particle size of these non-magnetic powders is 0.005 to 2 μm. However, if necessary, non-magnetic powders having different particle sizes may be combined, or even a single non-magnetic powder may have a wide particle size distribution to achieve the same effect. You can also have The surface of the lower layer paint after drying becomes smoother as the fine particles of the nonmagnetic powder used become finer. Practically, fine particles having a major axis length or a particle diameter of 0.2 μm or less are preferred. On the other hand, it becomes more difficult to disperse the non-magnetic powder into the temporary particles as the particles become finer. Particularly preferred particle sizes are from 0.05 μm to 0.25 μm, most preferably from 0.06 to 0.15 μm. The tap density is 0.05 to 2 g / ml, preferably 0.2 to 1.5 g / ml. The water content of the nonmagnetic powder is 0.1 to 5% by weight, preferably 0.2 to 3% by weight,
More preferably, it is 0.3 to 1.5% by weight. The pH of the non-magnetic powder is usually in the range of 2 to 11, but is preferably in the range of 7 to 11, more preferably 8 to 11, and most preferably 9 to 10 for achieving the object. The specific surface area of the non-magnetic powder is 1 to 100 m ² / g. Preferably 30 to 80 m
² / g, and more preferably 50 to 80 m ² / g. The crystallite size of the nonmagnetic acicular crystal powder is 0.004 to 1 μm, preferably 0.075 μm.
０．２0.2 μm. Oil absorption using DBP is 5-10
0 ml / 100 g, preferably 10-80 ml / 100
g, more preferably 20 to 60 ml / 100 g.
The specific gravity is 1 to 12, preferably 3 to 6. The shape may be any of a needle shape, a spherical shape, a polyhedral shape, and a plate shape.

It is preferable that the ignition loss is 20% by weight or less, and it is considered that it is most preferable that there is no ignition loss. Mohs hardness of the inorganic powder used in the present invention is 4 or more,
Those having 12 or less are preferred. The roughness factor of the powder surface is preferably 0.8 to 1.5, and more preferably 0.9 to 1.2. SA (stearic acid) adsorption amount of inorganic powder is 1 to 20 μmol
/ M ² , more preferably ² to 15 μmol / m ² . The heat of wetting of the lower coating layer non-magnetic powder in water at 25 ° C. is preferably in the range of 200 erg / cm ^{2 to} 600 erg / cm ² . Further, a solvent having a range of the heat of wetting can be used. The amount of water molecules on the surface at 100 to 400 ° C is suitably 1 to 10 / 100A. The pH of the isoelectric point in water is preferably between 7 and 9.

On the surface of these nonmagnetic powders, Al
₂ O ₃ , SiO ₂ , TiO ₂ , ZrO ₂ , SnO ₂ , S
It is preferable to perform a surface treatment with b ₂ O ₃ , ZnO, or phosphate. Particularly preferred for dispersibility are Al ₂ O ₃ , SiO ₂ ,
TiO ₂ and ZrO ₂ , more preferably A
l ₂ O ₃ , SiO ₂ and ZrO ₂ . These may be used in combination or may be used alone.
In addition, a co-precipitated surface treatment layer may be used according to the purpose, or a method of treating the surface layer with silica and then treating the surface layer with silica, or vice versa, may be employed. The surface treatment layer may be a porous layer depending on the purpose, but it is generally preferable that the surface treatment layer be homogeneous and dense.

Specific examples of the non-magnetic powder used in the lower coating layer of the present invention include Nanotight manufactured by Showa Denko, HIT-100, ZA-G1 manufactured by Sumitomo Chemical, and DPN-250 and DPN-250B manufactured by Toda Kogyo.
X, DPN-245, DPN-270BX, DPN550BX, DPN550RX, Ishihara Sangyo Titanium Oxide TTO-51B, TTO-55A, TTO-55B, TTO-55C, TTO-5
5S, TTO-55D, SN-100, α-iron oxide E270, E271, E300, titanium industrial STT-4D, STT-30D, STT-30, STT-65C, Teika MT
-100S, MT-100T, MT-150W, MT-500B, MT-600B, MT-100F, MT-5
00HD. Sanex Chemical FINEX-25, BF-1, BF-10, BF-20, ST-M, Dowa Mining DEFC-Y, DEFIC-R, Nippon Aerosil AS2BM, TiO ₂ P2
5, 100A, 500A manufactured by Ube Industries, Y-LOP manufactured by Titanium Kogyo, and baked products thereof.

Particularly preferred inorganic powder in the present invention is α-iron oxide or titanium oxide as described above, and most preferably α-iron oxide. The method of synthesizing α-iron oxide can be referred to the description in JP-A-6-60362.

By mixing carbon black in the lower coating layer, it is possible to lower Rs, which is a known effect, to reduce light transmittance, and to obtain a desired micro-Vickers hardness. For this purpose, furnace for rubber, thermal for rubber, black for color, acetylene black and the like can be used.

The specific surface area of carbon black is 100 to 5
00 m ² / g, preferably 150 to 400 m ² / g, DB
P oil absorption is 20-400ml / 100g, preferably 3
It is 0 to 200 ml / 100 g. The particle size of the carbon black is 5 to 80 mμ, preferably 10 to 50 mμ, and more preferably 10 to 40 mμ. The carbon black preferably has a pH of 2 to 10, a water content of 0.1 to 10%, and a tap density of 0.1 to 1 g / ml. Specific examples of the carbon black used in the present invention include BLACKPEARLS 2000, 1300, manufactured by Cabot Corporation.
1000, 900, 800, 880, 700, VULC
AN XC-72, manufactured by Mitsubishi Chemical Industry Co., Ltd., # 3050B,
3150B, 3250B, # 3750B, # 3950
B, # 950, # 650B, # 970B, # 850B,
MA-600, manufactured by Konlon Via Carbon, CONDU
CTEX SC, RAVEN 8800,8000,7
000,5750,5250,3500,2100,2
000, 1800, 1500, 1255, 1250, Ketchen Perak EC manufactured by Akzo Corporation, and the like. Surface treatment of carbon black with a dispersant,
It may be used by grafting with a resin, or by partially graphitizing the surface. Further, the carbon black may be dispersed in a binder before adding it to the paint. These carbon blacks can be used in an amount not exceeding 50% by weight and not exceeding 40% of the total weight of the nonmagnetic layer based on the inorganic powder. These carbon blacks can be used alone or in combination.

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

An organic powder may be added to the lower coating layer according to the purpose. For example, acrylic styrene-based resin powder, benzoguanamine resin powder, melamine-based resin powder, phthalocyanine-based pigments, but also polyolefin-based resin powder, polyester-based resin powder, polyamide-based resin powder, polyimide-based resin powder, and polyfluoroethylene resin Can be used. As the production method, those described in JP-A-62-18564 and JP-A-60-255827 can be used.

The undercoat layer is provided on a general magnetic recording medium. The undercoat layer is provided to improve the adhesive strength between the support and the magnetic layer, and has a thickness of 0.5 μm. The following are common.

The binder, lubricant, dispersant, additive, solvent, dispersing method, etc. of the lower coating layer can be the same as those of the magnetic layer. In particular, with respect to the amount and type of the binder, the amount of the additive and the type of the dispersant, and the type of the magnetic layer, known techniques for the magnetic layer can be applied.

Although the lower coating layer used in the present invention is a substantially non-magnetic layer, the lower coating layer contains a magnetic substance within a range that does not substantially affect the electromagnetic conversion characteristics of the upper magnetic layer. You can do it.

Next, the magnetic layer will be described in detail.

The ferromagnetic powder used in the upper magnetic layer of the present invention includes γ-FeOx (x = 1.33 to 1.5), Co-modified γ-FeOx (x = 1.33 to 1.5), α Known ferromagnetic powders such as ferromagnetic alloy powder containing Fe or Ni or Co as a main component (75% or more), barium ferrite, and strontium ferrite can be used. preferable. These ferromagnetic powders include Al, Si, S, Sc, C
a, Ti, V, Cr, Cu, Y, Mo, Rh, Pd, A
g, Sn, Sb, Te, Ba, Ta, W, Re, Au,
Hg, Pb, Bi, La, Ce, Pr, Nd, P, C
It may contain atoms such as o, Mn, Zn, Ni, Sr, and B. In particular, in the case of a metal magnetic material, Al, Si,
Ca, Y, Ba, La, Nd, Co, Ni and B are α-F
It is important as an element contained other than e. These ferromagnetic powders have dispersants, lubricants, surfactants,
The treatment may be carried out before dispersion with an antistatic agent or the like. Specifically, Japanese Patent Publication No. 44-14090, Japanese Patent Publication No. 45-1
8372, JP-B 47-22062, JP-B 47-22513, JP-B
46-28466, JP-B-46-38755, JP-B-47-4286, JP-B-47-12422, JP-B-47-17284, JP-B-47-18509
No., JP-B-47-18573, JP-B-39-10307, JP-B-48-3
No. 9639, U.S. Patent Nos. 3026215, 3031341, 3100194
No. 3242005 and No. 3389014.

Among the ferromagnetic powders, the ferromagnetic alloy fine powder may contain a small amount of hydroxide or oxide. A ferromagnetic alloy fine powder obtained by a known production method can be used, and the following method can be used. A method of reducing a complex organic acid salt (mainly oxalate) with a reducing gas such as hydrogen, a method of reducing iron oxide with a reducing gas such as hydrogen to obtain Fe or Fe—Co particles, Thermal decomposition method, reduction method by adding reducing agent such as sodium borohydride, hypophosphite or hydrazine to aqueous solution of ferromagnetic metal, reduction of fine powder by evaporating metal in low pressure inert gas And how to get it. The ferromagnetic alloy powder thus obtained is subjected to a known slow oxidation treatment, that is, a method of immersing in an organic solvent and then drying, and immersing in an organic solvent and then feeding an oxygen-containing gas to form an oxide film on the surface and drying. Any of the methods of forming an oxide film on the surface by adjusting the partial pressure of oxygen gas and inert gas without using an organic solvent can be used.

Expressed [0043] The ferromagnetic powder in the magnetic layer of the present invention in specific surface area by the BET method 45~80m was ² / g, preferably 50 to 70 m ² / g. If it is less than 25 m ² / g, noise increases, and if it is more than 80 m ² / g, it is difficult to obtain surface properties, which is not preferable. The crystallite size of the ferromagnetic powder of the magnetic layer of the present invention is from 350 to 80 angstroms, preferably from 250 to 100 angstroms, more preferably from 200 to 140 angstroms.

The σS of the magnetic metal powder is 100 to 180 em
u / g is preferable, and 110-170e is more preferable.
mu / g, more preferably 125-160 emu / g
It is. The coercive force of the metal powder is 1,500 Oe or more, 3.0
00 Oe or less, more preferably 1,800
It is Oe or more and 2,700 Oe or less. The needle ratio of the ferromagnetic powder is preferably 3 or more and 10 or less, more preferably 3 or more and 8 or less. The water content of the ferromagnetic powder is 0.01 to 2%
It is preferred that It is preferable to optimize the water content of the ferromagnetic powder depending on the type of the binder.

It is preferable that the pH of the ferromagnetic powder is optimized by the combination with the binder used. The range is 4-1
2, but preferably 6 to 10. The ferromagnetic powder may be subjected to a surface treatment with Al, Si, P or an oxide thereof, if necessary. The amount thereof is 0.1 to 10% with respect to the ferromagnetic powder, and it is preferable that the surface treatment is performed so that the adsorption of a lubricant such as a fatty acid becomes 100 mg / m ² or less. Ferromagnetic powder contains soluble Na, Ca, Fe, Ni,
May contain inorganic ions such as Sr, but 200ppm
If it is below, there is no possibility of affecting the initial characteristics. However, considering the change with time when the magnetic recording medium is stored, it is preferably 10 ppm.

The ferromagnetic powder used in the present invention preferably has a small number of vacancies, and the value is preferably 20% by volume or less, more preferably 5% by volume or less. The shape may be any of acicular, granular, rice granular, and plate-like shapes as long as the above-mentioned characteristics regarding the particle size are satisfied. In the case of acicular ferromagnetic powder, the acicular ratio is preferably from 4 to 12.
In order to achieve the SFD of the ferromagnetic powder of 0.6 or less, it is necessary to reduce the distribution of Hc of the ferromagnetic powder.
For that purpose, γ-
There is a method of preventing sintering of hematite.

Particularly preferred ferromagnetic alloy fine powders usable in the present invention are described in, for example, JP-A-7-22224 and JP-A-8-165501.
Nos., Etc. are listed.

As the binder used in the present invention, conventionally known thermoplastic resins, thermosetting resins, reactive resins and mixtures thereof are used. As the thermoplastic resin, the glass transition temperature is −100 to 150 ° C., and the number average molecular weight is 1,0.
00 to 200,000, preferably 10,000 to 10
000 and a degree of polymerization of about 50 to 1,000.

Such examples include vinyl chloride, vinyl acetate, vinyl alcohol, maleic acid, acuric acid,
Acrylic acid ester, vinylidene chloride, acrylonitrile, methacrylic acid, methacrylic acid ester, styrene,
There are polymers or copolymers containing butadiene, ethylene, vinyl butyral, vinyl acetal, vinyl ether, and the like as constituent units, polyurethane resins, and various rubber resins. In addition, as a thermosetting resin or a reactive resin, a phenol resin, an epoxy resin, a polyurethane curing resin, a urea resin, a melamine resin, an alkyd resin, an acrylic reaction resin, a formaldehyde resin, a silicone resin,
Examples 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. Further, a known electron beam-curable resin can be used for the lower coating layer or the upper magnetic layer.

[0050] These examples and the production method thereof are described in detail in JP-A-62-256219. The above resins can be used alone or in combination, but preferred are vinyl chloride resin, vinyl chloride vinyl acetate resin,
Examples include a combination of at least one selected from vinyl chloride vinyl acetate vinyl alcohol resin and vinyl chloride vinyl acetate maleic anhydride copolymer with a polyurethane resin, or a combination of these with a polyisocyanate. Known polyurethane resin structures such as polyester polyurethane, polyether polyurethane, polyether polyester polyurethane, polycarbonate polyurethane, polyester polycarbonate polyurethane, polycaprolactone polyurethane, and polyolefin polyurethane can be used. For all binding agents indicated herein, if necessary in order to obtain more excellent dispersibility and durability, -COOM, -SO ₃ M, -OS
_{O 3 M, -P = O (} OM) 2, -O-P = O (OM) 2,
(Wherein M represents a hydrogen atom or an alkali metal _{salt,), - OH, -NR 2} , -N + R 3 (R is a hydrocarbon group)
It is preferable to use one in which at least one or more polar groups selected from an epoxy group, -SH, -CN, sulfobetaine, phosphobetaine, carboxybetaine and the like are introduced by a copolymerization or addition reaction. The amount of such a polar group is 10 ^-1 to 10 ^-8 mol / g, preferably 10 ^-2.
Is 10 ^-6 mol / g.

Specific examples of these binders used in the present invention include VAGH and V manufactured by Union Carbide.
YHH, VMCH, VAGF, VAGD, VROH, V
YES, VYNC, VMCC, XYHL, XYSG, P
KHH, PKHJ, PKHC, PKFE, manufactured by Nissin Chemical Industries, MPR-TA, MPR-TA5, MPR-TA
L, MPR-TSN, MPR-TMF, MPR-TS,
MPR-TM, MPR-TAO, 1000 manufactured by Denki Kagaku
W, DX80, DX81, DX82, DX83, 100
FD, ZEON MR-104, MR-105,
MR110, MR100, 400X-110A, Nipporan N2301, N2302, N
2304, Pandex T-510 manufactured by Dainippon Ink and Chemicals, Inc.
5, T-R3080, T-5201, Burnock D-4
00, D-210-80, Crisbon 6109, 720
9, Toyobo Co. Byron UR8200, UR8300,
UR-8600, UR-5500, UR-4300, R
V530, RV280, manufactured by Dainichi Seika, diferamine 4020, 5020, 9020, 9022, 7020,
MX5004, manufactured by Mitsubishi Kasei Co., Ltd., Samplen SP-150, TIM-3003, TIM-3005, manufactured by Sanyo Kasei
Asahi Kasei Corporation's Saran F310, F210 and the like. Among them, MR-104, MR110, UR-820
0, UR8300, UR-8600, UR-5500,
UR-4300 and TIM-3005 are preferred.

The radius of inertia of the urethane of the present invention varies depending on the urethane structure. In particular, the radius of inertia can be changed without significantly impairing the characteristics of the urethane by the amount of urethane groups and ether bonds in the urethane skeleton. Can be done. Regarding the preferred urethane, further,
It is preferable to increase the radius of inertia by changing the amount of urethane groups and the amount of ether bonds. The radius of gyration in the cyclohexanone solution is preferably 5 nm or more and 50 nm or less, more preferably 5 nm or more and 30 nm or less, and even more preferably 5 nm or more and 20 nm or less. The radius of gyration in polymer chemistry can be determined by light scattering using the spread of a polymer in a solution from its center of gravity as the radius of gyration. The radius of gyration of a polymer is described in “Mashiro Hasegawa” and “Toshio Nishi”, Basic Polymer Science, and the like. The method of measuring the radius of gyration is such that a polyurethane resin is dissolved in cyclohexanone, and 0.2%, 0.4%, 0.6%,
A 0.8% diluted solution was prepared, and Pho manufactured by Otsuka Electronics Co., Ltd.
The measurement was performed using tal-DLS-700.

Further, the glass transition point T of the polyurethane resin
g generally greatly affects the surface formation of the magnetic layer. If the polyurethane resin Tg is high, calendering of the magnetic layer is deteriorated. On the other hand, if the polyurethane resin Tg is low, the Tg of the magnetic layer decreases, and blocking with the back layer becomes a problem. In the present invention, the polyurethane resin Tg used for the uppermost layer is made higher, the polyurethane resin Tg used for the lower layer is made lower than the uppermost urethane, the uppermost magnetic layer Tg is made 80 ° C. or more, With this configuration, both calender moldability and prevention of blocking during high-temperature storage could be achieved.

The binder used in the magnetic layer of the present invention ranges from 5 to 25% by weight, preferably from 7 to 25% by weight, based on the ferromagnetic powder.
It is used in the range of 24% by weight. 5 to 30% by weight when using a vinyl chloride resin, 2 to 20% by weight when using a polyurethane resin, 2 to 20% by weight of polyisocyanate
It is preferable to use them in combination in the range of weight%. In particular, a configuration containing a polyurethane resin and a polyisocyanate without a vinyl chloride resin in the upper layer is desirable,
7 to 2 in total of polyurethane resin and polyisocyanate
It is in the range of 4% by weight, preferably in the range of 7 to 15% by weight.

When polyurethane is used in the present invention, the glass transition temperature is -50 to 100 ° C., and the breaking elongation is 10
0-2,000%, breaking stress 0.05-10Kg / c
m ² and the yield point are preferably 0.05 to 10 kg / cm ² .

The magnetic recording medium of the present invention comprises two or more coating layers. Therefore, the amount of binder, vinyl chloride resin in the binder, polyurethane resin, polyisocyanate,
Alternatively, the amount of the other resin, the molecular weight of each resin forming the magnetic layer, the amount of the polar group, or the physical properties of the resin described above are changed between the lower coating layer and the upper magnetic layer and other magnetic layers as necessary. It is of course possible to apply a known technique for the multilayer magnetic layer. For example, when changing the amount of binder in the upper and lower layers and the intermediate layer, it is effective to increase the amount of binder in the upper magnetic layer in order to reduce scratches on the surface of the magnetic layer, and to improve the head touch with the head. Is achieved by increasing the amount of binder in the magnetic layer other than the upper magnetic layer or in the intermediate layer so as to have flexibility.

The polyisocyanate used in the present invention includes tolylene diisocyanate, 4-4'-diphenylmethane diisocyanate, hexamethylene diisocyanate, xylylene diisocyanate, naphthylene-1,
Use of isocyanates such as 5-diisocyanate, o-toluidine diisocyanate, isophorone diisocyanate, triphenylmethane triisocyanate, products of these isocyanates and polyalcohols, and polyisocyanates formed by condensation of isocyanates can do. Commercially available trade names of these isocyanates include Nippon Polyurethane Co., Ltd., Coronate L, Coronate HL, Coronate 2030, Coronate 2031, Millionate MR.
Millionate MTL, Takeda Pharmaceutical Co., Ltd., Takenate D-1
02, Takenate D-110N, Takenate D-20
0, Takenate D-202, manufactured by Sumitomo Bayer, Desmodur L, Desmodur IL, Desmodur N Desmodur HL, etc. These are used alone or in combination of two or more using the difference in curing reactivity. It can be used for both the lower coating layer and the upper magnetic layer.

The carbon black used in the present invention may be furnace black for rubber, thermal black for rubber, black for color,
Acetylene black and the like can be used. Specific surface area is 5-500 m ² / g, DBP oil absorption is 10-400
ml / 100 g, particle size is 5-300 mμ, pH is 2-
10, water content 0.1 ~ 10%, tap density 0.1 ~
1 g / CC is preferred. Specific examples of carbon black used in the present invention include BLAC manufactured by Cabot Corporation.
KPEARLS 2000, 1300, 1000, 90
0, 800, 700, VULCAN XC-72, manufactured by Asahi Carbon Co., Ltd., # 80, # 60, # 55, # 50, # 3
5, # 2400B, # 2300, #, manufactured by Mitsubishi Chemical Corporation
900, # 1000 # 30, # 40, # 10B, CONDUCTEX SC, RA, manufactured by Konlon Via Carbon
VEN 150, 50, 40, 15 and the like.
Carbon black may be used after being surface-treated with a dispersant or the like or grafted with a resin, or may be used in which a part of the surface is graphitized. Before adding the carbon black to the magnetic paint, the carbon black may be dispersed in a binder in advance. These carbon blacks can be used alone or in combination. When carbon black is used, the amount of 0.1 to the ferromagnetic powder is used.
Preferably, it is used at up to 30%. Carbon black has functions such as antistaticity of the magnetic layer, reduction of friction coefficient, provision of light-shielding properties, and improvement of film strength, and these differ depending on the carbon black used. Therefore, these carbon blacks used in the present invention are different in type, amount and combination in the upper magnetic layer and the lower coating layer and the non-magnetic layer, and various properties such as particle size, oil absorption, electric conductivity and pH are shown above. It is, of course, possible to use differently according to the purpose based on. The carbon black that can be used in the magnetic layer of the present invention can be referred to, for example, “Carbon Black Handbook” edited by Carbon Black Association.

Examples of the abrasive used in the present invention 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 of 90% or more. Known materials having a Mohs of 6 or more, such as silicon titanium carbide, titanium oxide, silicon dioxide, and boron nitride, are used alone or in combination. Further, a composite of these abrasives (abrasive whose surface is treated with another abrasive) may be used. These abrasives may contain compounds or elements other than the main component, but the effect remains unchanged if the main component is 90% or more. The particle size of these abrasives is 0.0
The thickness is preferably from 1 to 2 μm, but if necessary, abrasives having different particle sizes may be combined, or even a single abrasive may have the same effect by broadening the particle size distribution. Tap density is 0.3-2g / cc, water content is 0.1-5%,
PH is preferably ^{2 to} 11, and specific surface area is preferably 1 to 30 m ² / g. The shape of the abrasive used in the present invention is acicular, spherical,
Any of a dice shape may be used, but a shape having a corner in a part thereof is preferable because of high abrasiveness. Specific examples of the abrasive used in the present invention include AKP- manufactured by Sumitomo Chemical Co., Ltd.
20, AKP-30, AKP-50, HIT-50, H
IT-60, HiT-60A, HIT-70A, HIT
-80, HIT-80G, HIT-100, manufactured by Nippon Chemical Industry Co., Ltd., G5, G7, S-1, manufactured by Toda Kogyo Co., Ltd., TF-1
00, TF-140 and the like. The abrasive used in the present invention can be of different types, amounts and combinations for the lower coating layer and the upper magnetic layer, and can be of course used according to the purpose. These abrasives may be added to the magnetic paint after being subjected to dispersion treatment with a binder in advance. The abrasive present on the surface of the magnetic layer and the end face of the magnetic layer of the magnetic recording medium of the present invention is preferably 5/100 μm ² or more.

As the additives used in the present invention, those having a lubricating effect, an antistatic effect, a dispersing effect, a plasticizing effect and the like are used. Molybdenum disulfide, tungsten graphite disulfide, boron nitride, graphite fluoride, silicone oil, silicone with polar groups, fatty acid-modified silicone, fluorine-containing silicone, fluorine-containing alcohol,
Fluorine-containing esters, polyolefins, polyglycols, alkyl phosphates and alkali metal salts thereof, alkyl sulfates and alkali metal salts thereof, polyphenyl ethers, fluorine-containing alkyl sulfates and alkali metal salts thereof, containing 10 to 24 carbon atoms Basic fatty acids (which may contain unsaturated bonds or may be branched), and metal salts thereof (Li,
Na, K, Cu, etc., or monovalent, divalent, trivalent, tetravalent, pentavalent, hexavalent alcohols having 12 to 22 carbon atoms (including unsaturated bonds and may be branched) ),
C12-C22 alkoxy alcohol, C10
~ 24 monobasic fatty acids (which may contain unsaturated bonds or may be branched) and monovalent fatty acids having 2 to 12 carbon atoms,
Mono- or di-fatty acid ester or tri-fatty acid ester comprising any one of dihydric, trihydric, tetrahydric, pentahydric and hexahydric alcohols (which may contain an unsaturated bond or may be branched) Esters, fatty acid esters of monoalkyl ethers of alkylene oxide polymers, fatty acid amides having 8 to 22 carbon atoms, aliphatic amines having 8 to 22 carbon atoms, and the like can be used.

Specific examples thereof include lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, butyl stearate, oleic acid, linoleic acid, linolenic acid, elaidic acid, octyl stearate, amyl stearate, and stearic acid. Isooctyl, octyl myristate, butoxyethyl stearate, anhydrosorbitan monostearate, anhydrosorbitan distearate, anhydrosorbitan tristearate, oleyl alcohol, lauryl alcohol. Also, nonionic surfactants such as alkylene oxides, glycerin, glycidol, alkylphenol ethylene oxide adducts, cyclic amines, ester amides, quaternary ammonium salts, hydantoin derivatives, heterocycles, phosphonium or sulfoniums, etc. Cationic surfactants, carboxylic acids, sulfonic acids,
Anionic surfactants containing acidic groups such as phosphoric acid, sulfate ester groups, phosphate ester groups, etc., amphoteric surfactants such as amino acids, aminosulfonic acids, sulfuric acid or phosphate esters of amino alcohols, alkylbedine type, etc. Can be used. These surfactants are described in detail in "Surfactant Handbook" (published by Sangyo Tosho Co., Ltd.). These lubricants, antistatic agents, etc. are always 100%
It is not pure and may contain impurities such as isomers, unreacted products, by-products, decomposed products, oxides, etc. in addition to the main components. These impurities are preferably 30% or less, more preferably 10% or less.

The type and amount of these lubricants and surfactants used in the present invention can be selected as needed in the intermediate layer and the magnetic layer. For example, controlling bleeding to the surface using fatty acids having different melting points in the intermediate layer and the magnetic layer, controlling bleeding to the surface using esters having different boiling points and polarities, adjusting the amount of surfactant It can be considered to improve the stability of coating and to improve the lubricating effect by increasing the amount of the lubricant added in the intermediate layer, and it is needless to say that the present invention is not limited to the examples shown here.

All or a part of the additives used in the present invention may be added at any step in the production of the magnetic paint. For example, when mixing with the ferromagnetic powder before the kneading step, the ferromagnetic powder may be added. In a kneading step using a solvent and a binder and a solvent, there is a case where it is added in a dispersion step, a case where it is added after dispersion, and a case where it is added just before coating. In some cases, the purpose may be achieved by applying a part or all of the additive simultaneously or sequentially after applying the magnetic layer according to the purpose. Depending on the purpose, a lubricant may be applied to the surface of the magnetic layer after calendering or after the slit is completed.

Commercial examples of these lubricants used in the present invention include NAA-102 and NAA-4 manufactured by NOF Corporation.
15, 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, Nimeen L-201, Nimeen L-202, Nimeen 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, Monogly MB, Nonion DS-6
0, Anone BF, Anone LG, butyl stearate, butyl laurate, erucic acid, manufactured by Kanto Kagaku, oleic acid, manufactured by Takemoto Yushi, FAL-205, FAL-123,
Engelbu LO, Enjorbu IP, manufactured by Shin Nippon Rika Co., Ltd.
M, Sansocizer-E4030, manufactured by Shin-Etsu Chemical Co., Ltd., 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, manufactured by Lion Armor Company, Armid P, Armid C, Armoslip C
P, manufactured by Lion Yushi, Duyomin TDO, manufactured by Nisshin Oil, BA-41G, manufactured by Sanyo Kasei, Profan 2012
E, Newpole PE61, Ionnet MS-400,
IONET MO-200 IONET DL-200, IONET DS-300, IONET DS-1000 IONET DO-200 and the like.

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 and tetrahydrofuran, methanol, ethanol, propanol, butanol, isobutyl alcohol and isopropyl alcohol. Alcohols such as methylcyclohexanol, esters such as methyl acetate, butyl acetate, isobutyl acetate, isopropyl acetate, ethyl lactate, and glycol acetate; glycol ethers such as glycol dimethyl ether, glycol monoethyl ether, and dioxane; benzene; Aromatic hydrocarbons such as toluene, xylene, cresol, chlorobenzene, methylene chloride, ethylene chloride, carbon tetrachloride, Chloroform, ethylene chlorohydrin, dichlorobenzene, chlorinated hydrocarbons and the like, N,
N-dimethylformamide, hexane and the like can be used. These organic solvents are not necessarily 100% pure, and may contain impurities such as isomers, unreacted products, by-products, decomposed products, oxides, and moisture in addition to the main components. These impurities are preferably 30% or less, more preferably 10% or less. The type of the organic solvent used in the present invention is preferably the same for the magnetic layer and the intermediate layer. The amount added may be changed. Use a solvent with a high surface tension (cyclohexanone, dioxane, etc.) for the intermediate layer to improve coating stability. Specifically, the arithmetic average value of the solvent composition of the upper magnetic layer should not be lower than the arithmetic average value of the solvent composition of the lower coating layer. Is essential. In order to improve the dispersibility, it is preferable that the polarity is somewhat strong.
It is preferable that a solvent having a dielectric constant of 15 or more and 20 or less be contained in an amount of 50% by weight or more. The dissolution parameters are 8 to 11
It is preferred that

The thickness structure of the magnetic recording medium of the present invention is such that the flexible support has a thickness of 1 to 100 μm, and is particularly effective when a thin flexible support of 1 to 8 μm is used.

The total thickness of the upper magnetic layer and the lower coating layer is 1/100 to 2 times the thickness of the flexible support. Further, an adhesive layer for improving adhesion is provided between the flexible support and the lower coating layer.

The thickness of the adhesive layer is 0.01 to 2 μm, preferably 0.02 to 0.5 μm. Further, a back coat layer may be provided on the side of the flexible support opposite to the magnetic layer side. This thickness is 0.1-2 μm, preferably 0.3
１．０1.0 μm. Known adhesive layers and back coat layers can be used. Particularly preferred back layers include those described in JP-B Nos. 4-81261 and 5-46018 and JP-A-2-7223.

The flexible support used in the present invention is preferably non-magnetic and has a micro Vickers hardness of 7
A known film such as polyethylene naphthalate, polyamide, polyimide, polyamide imide, aromatic polyamide, polybenzoxydazole, etc., having a weight of 5 kg / mm ² or more and biaxially stretched can be used. In particular, a flexible support using an aramid resin or polyethylene naphthalate is preferred.

These flexible supports may be previously subjected to corona discharge treatment, plasma treatment, easy adhesion treatment, heat treatment, dust removal treatment and the like. In order to achieve the object of the present invention, the center line average surface roughness of the surface of the flexible support on which the magnetic layer is coated is 10 nm or less, 0.1 nm or more, preferably 6 nm or less, 0.2 nm or more, more preferably 4 nm. It is necessary to use one having a thickness of 0.5 nm or more. Also,
These flexible supports preferably have not only a small center line average surface roughness but also no coarse projections of 1 μm or more. The surface roughness can be freely controlled by the size and amount of the filler added to the flexible support as needed. Examples of these fillers include oxides and carbonates of Al, Ca, Si, Ti and the like, whether crystalline or amorphous, and organic fine powders such as acrylic or melamine. Also, in order to achieve compatibility with running durability, it is preferable that the surface on which the back layer is applied is rougher than the surface on which the magnetic layer is applied.
The center line surface roughness of the back layer coating surface is preferably 1 nm or more, more preferably 4 nm or more. When the roughness between the magnetic layer application surface and the back layer application surface is changed, a dual-structured support may be used or may be changed by providing a coating layer.

The F-5 value of the flexible support used in the present invention in the tape running direction is preferably 10 to 50 kg / mm.
^2. The F-5 value in the tape width direction is preferably 10 to 30K.
g / mm ² , and the F-5 value in the longitudinal direction of the tape is generally higher than the F-5 value in the tape width direction. However, especially when the strength in the width direction needs to be increased, Not. The heat shrinkage of the flexible support in the tape running direction and the width direction at 100 ° C. for 30 minutes is preferably 3% or less.
More preferably 1.5% or less, the heat shrinkage at 80 ° C. for 30 minutes is preferably 1% or less, more preferably 0.5% or less.
It is as follows. The breaking strength is 5 to 100 kg / m in both directions.
m ² and the elastic modulus are preferably 100 to 2,000 Kg / mm ² . The light transmittance at 900 nm in the present invention is 30%.
Or less, more preferably 3% or less.

The step of producing the magnetic paint of the magnetic recording medium of the present invention comprises at least a kneading step, a dispersing step, and a mixing step provided before and after these steps as necessary. Each step may be divided into two or more steps. All the raw materials such as the ferromagnetic powder, binder, carbon black, abrasive, antistatic agent, lubricant, and solvent used in the present invention may be added at the beginning or during any step. Further, each raw material may be divided and added in two or more steps. For example, polyurethane may be divided and supplied in a kneading step, a dispersing step, and a mixing step for adjusting the viscosity after dispersion. In order to achieve the object of the present invention, it is a matter of course that a conventional known manufacturing technique can be used as a part of the process, but the kneading process has a strong kneading force such as a continuous kneader or a pressure kneader. By using the magnetic recording medium, it was possible to obtain a high Br of the magnetic recording medium of the present invention for the first time. When a continuous kneader or a pressure kneader is used, all or a part of the ferromagnetic powder and the binder (however, 30% or more of the total binder is preferable) and the ferromagnetic powder 1
The kneading treatment is performed in the range of 15 to 500 parts with respect to 00 parts.
For details of these kneading processes, JP-A-1-166338,
It is described in JP-A-64-79274. When preparing a non-magnetic layer liquid for the lower coating layer, it is desirable to use a dispersion medium having a high specific gravity, and zirconia beads are preferred.

The following configuration can be proposed as an example of an apparatus and method for applying a magnetic recording medium having a multilayer configuration as in the present invention.

1. First, a lower coating layer is applied by a gravure coating, roll coating, blade coating, extrusion coating device or the like which is generally used for applying a magnetic paint.
While the lower coating layer is in a wet state, the upper magnetic layer is coated by a support pressurization type extrusion coating apparatus disclosed in Japanese Patent Publication No. 46846/1994, 238179/1985 and 2-265672 / 1990. I do.

2, JP-A-63-88080, JP-A-2-17971
The upper and lower layers are applied almost simultaneously by one coating head having two built-in slits for passing the coating liquid as disclosed in JP-A-2-265672.

3. The upper and lower layers are applied almost simultaneously by an extrusion coating apparatus with a backup roll disclosed in JP-A-2-174965.

Incidentally, in order to prevent the electromagnetic conversion characteristics of the magnetic recording medium from deteriorating due to the aggregation of the magnetic particles, Japanese Patent Application Laid-Open No.
It is desirable to apply shear to the coating liquid inside the coating head by a method as disclosed in JP-A No. 74 and JP-A-1-236968. Further, regarding the viscosity of the coating liquid,
It must satisfy the numerical range disclosed in 8471.

In order to obtain the magnetic recording medium of the present invention, it is necessary to perform strong orientation. It is preferable to use a solenoid of 1,000 G or more and a cobalt magnet of 2,000 G or more in the same polarity facing each other, and to provide an appropriate drying step before orientation so that the orientation after drying is the highest. preferable. It is known that in order to perform high-density recording, it is effective to incline the axis of easy magnetization in the vertical direction regardless of the needle shape or the plate shape, and it is also effective to combine it with this.

Further, prior to simultaneous application of the non-magnetic layer and the magnetic layer, a known method of providing an adhesive layer containing a polymer as a main component, or corona discharge, UV irradiation, or EB irradiation to enhance the adhesion is combined. Is preferred.

Furthermore, a heat-resistant plastic roll such as epoxy, polyimide, polyamide, or polyimide amide is used as the calendering roll. Further, the treatment can be performed between metal rolls. The treatment temperature is preferably 70 to 120 ° C, more preferably 80 to 100 ° C.
° C or higher. Linear pressure is preferably 200-500 kg
/ Cm, more preferably 300 to 400 kg / cm or more.

The friction coefficient of the surface of the magnetic layer of the magnetic recording medium of the present invention and the opposite surface thereof to SUS420J is preferably 0.1 to 0.5, more preferably 0.2 to 0.3. The surface resistivity is preferably 10 ⁴ to 10 ¹² ohm / sq, and the elastic modulus at 0.5% elongation of the magnetic layer is preferably 100 to 2,000 kg / m in both the running direction and the width direction.
m ² , the breaking strength is preferably 1 to 30 kg / cm ² , the elastic modulus of the magnetic recording medium is preferably 100 to 1,500 kg / mm ^{2 in} both the running direction and the long direction, and the residual elongation is preferably 0.5% or less; The heat shrinkage at any temperature of 100 ° C. or less is preferably 1% or less, more preferably 0.5% or less.
Below, most preferably 0.1% or less, 0% is ideal. The glass transition temperature of the magnetic layer (the maximum point of the loss elastic modulus in dynamic viscoelasticity measurement measured at 110 HZ) is preferably 50 ° C. or more and 120 ° C. or less, and that of the lower coating layer is 0-10
0 ° C. is preferred. Loss modulus is 1 × 10 ⁸ to 8 × 10 ⁹ d
yne / cm ² , and the loss tangent is preferably 0.2 or less. If the loss tangent is too large, adhesion failure is likely to occur. The residual solvent contained in the magnetic layer is preferably 100 mg / m ² or less, more preferably 10 mg / m ² or less, and it is preferable that the residual solvent contained in the upper magnetic layer is smaller than the residual solvent contained in the lower coated layer. The porosity of the magnetic layer is preferably 30% by volume or less, more preferably 20% by volume or less, for both the non-magnetic lower layer coating layer and the magnetic layer. The porosity is preferably small in order to achieve high output, but it may be better to secure a certain value depending on the purpose. For example, in a magnetic recording medium for data recording in which repetitive use is emphasized, a higher porosity is often preferable in running durability.

The magnetic characteristics of the magnetic recording medium of the present invention are as follows.
When measured by VSM at 0 kOe, H in the tape running direction
c is 2000-3000 Oe, more preferably 210
0 to 2500 Oe. The squareness ratio is 0.75 or more, preferably 0.80 or more, and more preferably 0.85 or more. The squareness ratio in two directions perpendicular to the tape running direction is preferably 80% or less of the squareness ratio in the running direction. The SFD of the magnetic layer is preferably 0.6 or less, more preferably 0.5 or less, and ideally 0 or less.
It is.

The surface roughness of the upper magnetic layer is the center line average surface roughness Ra, which is usually 1 to 10 nm. In the electromagnetic conversion characteristics, the gap loss between the magnetic head and the tape surface is reduced, and the higher output is obtained. 5 nm or less is required in order to obtain. On the other hand, if the surface is smoothed, the kinetic friction coefficient (so-called running μ value) will be increased, and the durability will deteriorate. Therefore, in order to achieve both electromagnetic conversion characteristics and durability, adjustment of the amount of lubricant and physical properties of the magnetic layer are required. Improvement (for example, increase in Tg) is required. In order to achieve the object, the lower layer contains a fatty acid, and the average surface roughness Ra determined by an optical interference method is preferably 3 nm or less, and more specifically, 1 to 3 nm.

Although the magnetic recording medium of the present invention has a lower coating layer and an upper magnetic layer, it is easily presumed that these physical properties can be changed between the lower coating layer and the magnetic layer 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 lower coating layer is made lower than that of the magnetic layer to improve the contact of the magnetic recording medium with the head. It is also effective in the present invention to improve the head contact by changing the method of tensifying the support, and the support tensified in the direction perpendicular to the longitudinal direction of the tape has better head contact. Often.

[0085]

Hereinafter, specific examples of the present invention will be described.
The present invention is not limited to this. In the examples,
The indication “parts” indicates “parts by weight”.

Lower coating layer (non-magnetic): Comparative Examples 1 to 12, Examples 1 to 10 Non-magnetic powder αFe ₂ O ₃ hematite 80 parts Long axis length Tables 1 to 5 Specific surface area by BET method Tables 1 to 5 pH Table 1-5 tap density 0.8 surface treatment agent _{Al 2 O 3, SiO 2,} P Table 1-5 carbon black 20 parts average primary particle size 16Emumyu DBP oil absorption of 80ml / 100g pH 8.0 BET method specific surface area by 250m ² / g Volatile content 1.5% Vinyl chloride copolymer 12 parts MR-104 polyester polyurethane resin manufactured by ZEON 5 parts Neopentyl glycol / caprolactone polyol / MDI = 0.9 / 2.6 / 1-SO ₃ Na group containing 1 × 10 ^-4 eq / g α-Al ₂ O ₃ (average particle diameter 0.2 [mu] m) 1 part butyl stearate 1 part stearic acid 1 part Methyl ethyl ketone 10 Parts Cyclohexanone 50 parts Toluene 50 parts lower coating layer (nonmagnetic): Comparative Example 13-17, the specific surface area table according to Examples 11 to 15 the non-magnetic powder TiO ₂ Titanium oxide 80 parts Average primary particle diameter Table 6-8 BET method 6 to 8 pH Tables 6 to 8 Tap density 0.8 Surface treatment agent Al ₂ O ₃ , SiO ₂ carbon black 20 parts Average primary particle diameter 16 μm DBP oil absorption 80 ml / 100 g pH 8.0 Specific surface area by BET method 250 m ² / g Volatile content 1.5% Vinyl chloride copolymer 12 parts MR-104 polyester polyurethane resin manufactured by Zeon 5 parts Neopentyl glycol / caprolactone polyol / MDI = 0.9 / 2.6 / 1 -SO ₃ Na group 1 × 10 ^-4 eq / g containing α-Al ₂ O ₃ (average particle diameter 0.2 [mu] m) 1 part butyl stearate 1 part 1 part of stearic acid Tyl ethyl ketone 100 parts Cyclohexanone 50 parts Toluene 50 parts Magnetic paint (magnetic layer): Ferromagnetic metal fine powder 100 parts Long axis length 0.085μ Fe-Co alloy Sintering inhibitor Y / Al Hc 2250 Oe σs 140 emu / g Polyester polyurethane Resin 12 parts α-Al ₂ O ₃ (average particle size 0.15 μm) 5 parts Carbon black (average particle size 0.08 μm) 0.5 part Butyl stearate 1 part Stearic acid 5 parts Methyl ethyl ketone 90 parts Cyclohexanone 30 parts Toluene 60 Part For each of the above coating materials, each component was kneaded with an open kneader, and then dispersed using a sand mill. To the resulting lower layer dispersion, 5 parts of a polyisocyanate (Coronate L manufactured by Nippon Polyurethane Co., Ltd.) was added to the lower layer coating solution, and 5 parts of the magnetic coating were added, and 40 parts of a mixed solvent of methyl ethyl ketone and cyclohexanone were added to each. The solution was filtered using a filter having an average pore size of 1 μm to prepare a coating solution for forming a lower coating layer and a magnetic layer.

The obtained lower coating layer coating solution was prepared in
The coating is applied to a thickness of 1.5 μm, and immediately thereafter, the thickness of the magnetic layer is set to 5.5 μm so that the thickness of the magnetic layer becomes the thickness described in Table 2 above. A simultaneous multi-layer coating is performed on a polyethylene naphthalate support having a roughness of 0.002 μm, and while both layers are still in a wet state, they are oriented by a cobalt magnet having a magnetic force of 4000 G and a solenoid having a magnetic force of 4000 G, and then dried. The treatment is performed at a temperature of 90 ° C. at a speed of 200 m / min. Using a seven-stage calender composed of only metal rolls.
A μm back layer was applied. Slit to a width of 8mm,
An 8 mm video tape was manufactured.

In Table 1, a liquid was prepared according to the particle size of the lower α-iron oxide (hematite) powder and formed into a tape. The RF output is improved by reducing the particle size of α iron oxide of the lower nonmagnetic powder. However, when the pH of the lower layer powder is 7 or less,
The kinetic friction coefficient after storage at 0 ° C. and 90% RH for 7 days has increased. However, when the particle size is reduced as in Comparative Example-6, dispersion becomes difficult, and the smoothness of the magnetic layer surface deteriorates.

Table 2 shows the pH of the lower α iron oxide (hematite).
Separately, and the thickness of the magnetic layer was changed to prepare a tape. p
At the level where H is on the alkaline side, the coefficient of kinetic friction does not increase even after storage at 60 ° C. and 90% RH for 7 days. AF protrusion on the surface
M, it was 3 in the comparative example where the dynamic friction coefficient was increased.
Although the number of protrusions increased by about 70 times to 1000, there was no increase in the number of protrusions in the case where the coefficient of dynamic friction did not increase. In Comparative Example 10, the thickness of the magnetic layer was large, and the output was low due to self-demagnetization. When the thickness of the magnetic layer of Comparative Example 11 was 0.05 μm, the amount of magnetization decreased, and the output also decreased.

Table 3 shows that the amount of Al, a surface treatment agent for α-iron oxide (hematite), was changed, and a tape was prepared after the preparation. There is a region where the Al content balances the kinetic friction coefficient after storage with the output. When the Al amount is small as in Comparative Example 8, the kinetic friction coefficient after storage at 60 ° C. and 90% RH for 7 days increases. Also, as in Comparative Example 9, when the Al content exceeds 4%, dispersion tends to deteriorate, the surface becomes rough, and the output tends to decrease.

Table 4 shows tapes prepared according to the amount of the surface treatment agent Si for α-iron oxide (hematite). This also has an area where the dynamic friction coefficient after storage and the output balance as with the Al amount,
If the amount of Si in the surface treatment agent was small, the coefficient of kinetic friction increased after storage at 60 ° C. and 90% RH for 7 days. Conversely, if the amount was small, the dispersion deteriorated, the surface became rough, and the output decreased.

Table 5 shows that the surface treatment agent for α-iron oxide and the phosphorus content of the dispersant were changed to prepare a liquid and tape. When the amount of phosphorus is small, the output tends to improve, but there is no change in the increase in μ value after storage at 60 ° C. and 90% RH for 7 days.

In Table 6, a liquid was prepared according to the particle size of titanium oxide in place of α-iron oxide (hematite) and taped. The output was improved as the particle size was smaller. When the pH was 7 or less, the μ value increased.

In Table 7, the pH of the titanium oxide was changed, and the mixture was prepared into a tape. As a result, as in the case of α-iron oxide, when the pH was on the alkaline side, the μ value did not increase after storage. Observation of the number of protrusions by AFM of the sample revealed that the number of protrusions was remarkably increased in Comparative Examples 15 and 17 in which the μ value was increased.

In Table 8, a liquid was prepared according to the amount of Al in the lower layer titanium oxide and taped. If the Al content is 6% or less, the dispersion tends to deteriorate, the surface becomes rough, and the output tends to decrease.

[0096]

[Table 1]

[0097]

[Table 2]

[0098]

[Table 3]

[0099]

[Table 4]

[0100]

[Table 5]

[0101]

[Table 6]

[0102]

[Table 7]

[0103]

[Table 8]

Evaluation Method <Method of Measuring Thickness of Magnetic Layer> The magnetic recording medium was cut out to a thickness of about 0.1 μm with a diamond cutter along the longitudinal direction, observed with a transmission electron microscope at a magnification of 30,000, and photographed. Was done. The print size of the photo is A4 size. After that, the interface is visually judged by focusing on the shape difference between the ferromagnetic powder and the non-magnetic powder of the magnetic layer and the non-magnetic layer, and the edge is blackened,
Also, the surface of the magnetic layer was similarly blackened. Then Zei
The interval between the bordered lines was measured by an image processing device IBAS2 manufactured by ss Corporation. The length of the sample photograph was over a range of 21 cm, and measurement was performed by taking measurement points. The simple average value of the measured values at that time was defined as the thickness of the magnetic layer.

<Specific Surface Area by BET Method> Canter soap (manufactured by US Canter Chrome Co.) was used. 250 ° C, 3
After dehydration in a nitrogen atmosphere for 0 minutes, BET single point method (partial pressure 0.3
0).

<Center line average surface roughness> TOY manufactured by WYKO
Using PO3D, the medium surface is about 250 by MIRAU method.
Ra of an area of nm × 250 nm was measured. The measurement wavelength was about 650 nm, and spherical and cylindrical corrections were added. This method is a non-contact surface roughness meter that measures by light interference.

<Particle Size of Ferromagnetic Powder and Non-Magnetic Powder> A method of taking a transmission electron micrograph and directly reading the short axis diameter and the long axis diameter of the ferromagnetic powder from the photograph, and an image analyzer Carl Zeiss The average particle diameter was determined by appropriately using a method of tracing and reading a transmission microscope photograph with IBASS1 manufactured by KK.

<Ferromagnetic Powder Crystallite Size> According to X-ray diffraction, the (4,4,0) plane and (2,4)
It was determined from the spread of the half width of the diffraction line on the (2,0) plane.
In the case of a metal ferromagnetic powder, it is similarly obtained from the spread of the half value width of the diffraction lines on the (1,1,0) plane and the (2,2,0) plane.

<Electromagnetic Conversion Characteristics> The “output at recording wavelengths of 0.488 μm and 22 μm” was a reference ME tape manufactured by the Company, and the output was measured at a relative speed of 10.2 m / sec using an external drum tester. The head used was an Fe head and had a Bs of 1.5.
T. It is to be noted that the values are obtained when recording and reproduction are performed at the optimum recording current defined below.

The output at a recording wavelength of 0.488 μm is preferably as high as possible. The output of 22μ is preferably in the range of −2 dB or more and +2 dB or less.

<Optimal recording current> +4 from the recording current value at the output at which 90% of the maximum reproduction output of the input / output characteristic curve is obtained.
dB large recording current. It is preferable to be in the range of ± 1.0 dB from the reference.

<Measurement of Dynamic Friction Coefficient> The measurement was performed using SUS420J as a sliding member in an environment of 23 ° C. and 50%.

<Measurement Method of Element> The measurement of the element was performed by analyzing the composition of the ferromagnetic metal powder by the following method.

<Analytical Method of Ferromagnetic Metal Powder Composition> 0.1 g
(If the composition of the ferromagnetic metal powder in the magnetic layer is to be determined, a magnetic layer equivalent to 0.1 g of the ferromagnetic metal powder is collected.) Dilute and dilute with a 1N hydrochloric acid solution so that the concentration matches the standard solution, adjust the concentration, and use it as a test solution. This test solution was analyzed using an ICP emission spectrometer (S
PS1200A) to determine the content of each element,
The ratio to Fe is represented by atomic%. As a standard solution, a commercially available reagent for atomic absorption analysis (metal standard solution) was used.

<Microprojections> The microprojections were measured with an AFM microscope (atomic force microscope).

Evaluation apparatus: Nanoscope III manufactured by Digital Instruments Co., Ltd. Evaluation conditions: Contact AFM mode, scan speed 4
MHz sample: 200 μm square

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Hiroaki Takano 2-2-1-1, Ogimachi, Odawara-shi, Kanagawa Inside Fuji Photo Film Co., Ltd.

Claims (6)

[Claims] An undercoating layer containing an inorganic powder, a fatty acid and a binder is provided on a flexible support, and the thickness of the ferromagnetic metal powder and the binder is 0.05 μm or more on the undercoating layer. A magnetic recording medium provided with a magnetic layer having a thickness of 0.5 μm or less, wherein the surface roughness of the magnetic layer is 3 nm or less.
A magnetic recording medium, wherein substantially no increase in minute protrusions having a height of 30 nm or more is observed on the surface of the magnetic layer after storage in a 90% RH environment for 7 days. 2. A lower coating layer containing an inorganic powder, a fatty acid and a binder is provided on a flexible support, and the thickness containing the ferromagnetic metal powder and the binder is 0.05 μm or more on the lower coating layer. A magnetic recording medium comprising a magnetic layer having a thickness of 0.5 μm or less, and a surface roughness of an uppermost layer of the magnetic layer being 3 nm or less,
The fluctuation of the dynamic friction coefficient on the surface of the magnetic layer is 60 ° C.-90% R
A magnetic recording medium characterized by being within ± 10% before and after storage for 7 days in an H environment. 3. The inorganic powder has an average major axis length of 0.06.
Α in the range of ０．１0.15 μm and a pH of 7-11.
The magnetic recording medium of claim 1, wherein a is -fe ₂ O _3. 4. The method according to claim 1, wherein the particle surface of the α-Fe ₂ O ₃ inorganic powder contains 1.0 to ₂ wt% of SiO ₂ , 1.0 to 4 wt% of Al ₂ O _3, and 50 ppm or less of P. 3. The magnetic recording medium according to claim 2, wherein: 5. The magnetic recording medium according to claim 1, wherein the inorganic powder is titanium oxide having a specific surface area of 50 to 80 m ² / g and a pH of 8 to 11. 6. The particle surface of the titanium oxide inorganic powder,
The magnetic recording medium of claim 5, wherein the containing Al ₂ O ₃ of 6~10wt%.