JPH04370521A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To intensify mechanical strength by regulating the sizes of the respective Co-contg. iron oxides of upper and lower layers and regulating SQ1, the Young's modulus of the lower layer and SQ2. CONSTITUTION:The upper magnetic layer contains the Co-contg. iron oxide having >=60m<2>/g BET specific surface area as ferromagnetic powder and is formed to have >=0.4 squareness ratio (SQ1) in the direction vertical to the plane of a nonmagnetic base and >=200kg/mm<2> Young's modulus. The lower magnetic layer contains the Co-contg. iron oxide having BET specific surface area ranging from 20 to 50m<2>/g as the ferromagnetic powder and is formed to have >=0.7 squareness ratio (SQL2) in the horizontal direction and >=300kg/mm<2> Young's modulus in the horizontal direction. The mechanical strength of the recording medium is then intensified and the traveling durability is improved. Powder dislodging, etc., are suppressed and the surface characteristic of the upper layer are improved, by which the output in a high-frequency region and S/N are improved and the electromagnetic conversion characteristics in the low-frequency region to be contributed by the lower layer are well assured.

Description

[Detailed description of the invention]

0001

FIELD OF THE INVENTION The present invention relates to a magnetic recording medium having a multilayer structure and having excellent electromagnetic conversion characteristics and running durability.

0002

2. Description of the Related Art It is a well-known technique to form a multilayer structure in order to improve the electromagnetic conversion characteristics and running durability of a magnetic recording medium. By having a multilayer structure, it is possible to change the coercive force and residual magnetic flux density of the magnetic layer, or the particle size of the ferromagnetic powder (represented by crystallite size and specific surface area) between the upper and lower layers, making it possible to It is possible to achieve both improved electromagnetic conversion characteristics by increasing output and running durability (expressed by broken edges and powder falling).

[0003] Examples of this type are disclosed in Japanese Unexamined Patent Publication Nos. 52-51908, 54-21304, and 54-48504.
No. 58-56228, No. 58-5622
Publication No. 9, Publication No. 53-54002, JP-A-2-10
This method is disclosed in Japanese Patent Publication No. 8232 and Japanese Patent Application Laid-Open No. 2-260123.

In order to achieve high output at short wavelengths, plate-shaped ferromagnetic powder such as barium ferrite is used in the upper layer, or short needle-shaped ferromagnetic powder or triaxially anisotropic ferromagnetic powder containing Co as a solid solution is vertically oriented. By doing so, high output at short wavelengths can be achieved without deteriorating the electromagnetic conversion characteristics of the conventional multilayer structure.

[0005] Such an example is disclosed in Japanese Patent Application Laid-Open No. 57-195329.
No., JP-A-57-200936, JP-A-58-139
No. 336. However, when barium ferrite is used to improve the vertical alignment component of the upper layer, its dispersibility is significantly inferior to that of iron oxide ferromagnetic powder, so although it is possible to improve the output on the short wavelength side by increasing the vertical alignment component, the surface properties deteriorate. Inferior S/N deteriorates. Furthermore, since the affinity with the binder is significantly poor, durability is inevitably deteriorated. Further, since the short needle-shaped ferromagnetic powder has small shape anisotropy, it is difficult to deposit Co on it, and high coercive force cannot be obtained. Also Co
Ferromagnetic powder with solid solution of Co can easily obtain high coercive force, but ferromagnetic powder with Co in solid solution changes the position of Co in the ferromagnetic powder depending on the temperature, so the coercive force decreases with temperature change. It changes and stable electromagnetic conversion characteristics cannot be obtained. It has also been found that a vertically oriented magnetic recording medium using acicular ferromagnetic powder in the upper layer has a lower Young's modulus in the horizontal direction than a horizontally oriented magnetic recording medium, is more likely to cause actual damage such as powder falling, and is inferior in running durability.

Specifically, JP-A No. 58-139335 discloses that iron oxide-based ferromagnetic powder is oriented on a non-magnetic support so that it has a rectangular shape of 0.7 or more in the horizontal direction of the magnetic layer. A first magnetic layer is formed on the first magnetic layer, and triaxially anisotropic ferromagnetic powder in which cobalt is dissolved inside the particles of iron oxide ferromagnetic powder is formed in a rectangular shape in the perpendicular direction of the magnetic layer. A magnetic recording medium is disclosed in which a second magnetic layer having a magnetic flux of .4 or higher is formed in a multilayered manner. However, although triaxially anisotropic cobalt solid solution type ferromagnetic powder can be easily oriented in the vertical direction, the coercive force (Hc) tends to deteriorate, and good results have not been obtained. Triaxial anisotropy is something that has a dice-like shape.

Therefore, the present inventors have developed a magnetic material that does not suffer from Hc deterioration, has excellent strength, and is capable of perpendicular recording by using ordinary Co-containing iron oxide powder and orienting it perpendicularly to the surface of a non-magnetic support. The present invention has been achieved by discovering that a recording medium can be obtained.

[0008]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a magnetic recording medium that has high output at short wavelengths and excellent running durability.

[0009]

[Means for Solving the Problems] As a result of intensive research into the coexistence of electromagnetic conversion characteristics and running durability of a multilayered magnetic recording medium, the present inventors have found that the present inventors have achieved excellent electromagnetic conversion characteristics and running durability that cannot be obtained with conventional techniques. The present invention was achieved by discovering a durable magnetic recording medium. That is, the present invention provides a magnetic recording medium having a plurality of magnetic layers including a lower magnetic layer containing ferromagnetic powder and a binder on the surface of a non-magnetic support and an upper magnetic layer provided thereon. Contains Co-containing iron oxide with a BET specific surface area of 60 m2/g or more as a ferromagnetic powder, has a squareness ratio perpendicular to the non-magnetic support surface of 0.4 or more, and has a Young's modulus of 200 kg/mm2.
The above is described above, and the lower magnetic layer is made of BET as the ferromagnetic powder.
A magnetic recording comprising Co-containing iron oxide having a specific surface area of 20 to 50 m2/g, a horizontal squareness ratio of 0.7 or more, and a horizontal Young's modulus of 300 kg/mm2 or more. It is a medium.

[0010] The present invention provides a magnetic recording medium with a multilayer structure, in which the type of ferromagnetic powder in the upper magnetic layer (hereinafter also simply referred to as upper layer) and the lower layer magnetic layer (hereinafter simply referred to as lower layer) and B
The ET specific surface area, that is, the size, is defined, and the horizontal squareness ratio (hereinafter referred to as SQ1) and horizontal Young's modulus of the lower magnetic layer are controlled to a predetermined value or more, and the vertical direction of the upper magnetic layer is controlled. By setting the squareness ratio (hereinafter referred to as SQ2) to a predetermined value and ensuring the Young's modulus in the horizontal direction, the mechanical strength of the magnetic recording medium is strengthened and running durability is improved. It is possible to suppress drop-off and the like, improve the surface properties of the upper layer, improve the output and S/N in the high frequency region, and ensure good electromagnetic conversion characteristics in the low frequency region, which is the responsibility of the lower layer.

In the present invention, the squareness ratio is defined as the residual magnetic flux density (
Br)/maximum magnetic flux density (Bm), and the squareness ratio when the sample is set horizontally against the external magnetic field of the VSM measuring machine is taken as the horizontal squareness ratio, and the sample is set vertically. Let the squareness ratio in the vertical direction be the squareness ratio in the vertical direction. Also, the samples are set in this way and the squareness ratio of each is measured.

In addition, in the present invention, Young's modulus in the horizontal direction is determined by measuring the strength of the tape by pulling it in the longitudinal direction.
．． This is the strength when elongated by 5%. In the present invention, the ferromagnetic powder of the upper magnetic layer is Co-containing iron oxide, and BET
Specific surface area is 60 m2 /g or more, preferably 60 to 10
It is in the range of 0m2/g. The shape of the ferromagnetic powder is preferably acicular, the crystallite size is 25 nm or less, preferably 25 to 18 nm, the major axis length is 140 nm or less, preferably 140 to 100 nm, and the acicular ratio is 3 or more. ,
Preferably it is 5-10. SQ2 is 0.4 or more, preferably in the range of 0.4 to 0.65.

The ferromagnetic powder of the upper magnetic layer is Co-containing iron oxide, and if the BET specific surface area is less than 60 m 2 /g, the noise level at short wavelengths is high. Further, if the BET specific surface area is larger than 100 m2/g, the dispersibility decreases and the S/N decreases due to surface property deterioration. Furthermore, SQ2 is 0
．． If it is smaller than 4, sufficient output at short wavelengths cannot be obtained, and if it is smaller than 0.
When it is larger than 65, Young's modulus in the horizontal direction decreases significantly and dropouts due to falling powder increase.

The ferromagnetic powder of the lower magnetic layer is Co-containing iron oxide and has a BET specific surface area of 20 to 50 m2/g. The shape of the ferromagnetic powder is preferably acicular, and the crystallite size is 40 nm or less, preferably 25 to 40 nm,
The long axis length is 250 nm or less, preferably 150 to 250 nm.
nm, and the acicular ratio is 3 or more, preferably 5 to 10. The squareness ratio in the horizontal direction, that is, SQ1, is 0.7 or more, and the Young's modulus in the horizontal direction is 300 kg/mm2 or more.

[0015] If the BET specific surface area of the magnetic powder contained in the lower layer is smaller than 20 m2/g, the noise level at long wavelengths will be high, and if it is larger than 50 m2/g, sufficient dispersion cannot be obtained and SQ1 sufficient for the purpose cannot be obtained. The low frequency output cannot be obtained sufficiently. Also, the specific surface area is 20~50m2/g
Even within this range, if SQ1 is smaller than 0.7, the residual magnetic flux density at long wavelengths decreases, making it impossible to obtain low-frequency output. Also,
If the Young's modulus in the horizontal direction is less than 300 kg/mm2, the lower Young's modulus cannot compensate for the lower Young's modulus of the entire layer due to the lower Young's modulus due to the vertical orientation of the upper layer, and as a result, dropouts such as powder dropout increase. Durability deteriorates.

In the present invention, the means for adjusting SQ1 and SQ2 is not particularly limited, but it usually depends on the rheological properties such as the viscosity of each coating liquid of the upper magnetic layer and the lower magnetic layer and the time of magnetic field orientation to each magnetic layer. It is adjusted by the direction of the magnetic field, the timing of drying each magnetic layer after coating, and the magnetic field orientation (for example, by providing an appropriate drying step in advance before orientation). For example, the magnetic recording medium of the present invention can be manufactured using a sequential multilayer method in which a lower layer is coated, horizontally aligned, dried, an upper layer is placed thereon, vertically aligned, and then dried; Examples include a method in which after simultaneous multilayer coating, horizontal alignment is performed, and further vertical alignment is applied, so that only the upper layer is vertically aligned.

For this orientation, it is preferable to use a solenoid of 1000 G (Gauss) or more and a cobalt magnet of 2000 G or more in combination. After drying, the surface is smoothed and cut into a desired shape to produce a magnetic recording medium. This surface smoothing process is performed by calendering process.

As the calendering roll, a heat-resistant plastic roll made of epoxy, polyimide, polyamide, polyimide amide, etc. is used. Further, the treatment can also be carried out using metal rolls. The treatment temperature is preferably 7
The temperature is 0°C or higher, more preferably 80°C or higher. The linear pressure is preferably 200 kg/cm, more preferably 30 kg/cm.
It is 0 kg/cm or more.

In the present invention, a vibrating sample magnetometer (manufactured by Toei Kogyo) can be used to measure SQ1 or SQ2. The process of producing the magnetic paint for the upper layer and the lower layer consists of at least a kneading process, a dispersion process, and a mixing process provided before and after these processes as necessary. Each individual process may be divided into two or more stages.

All raw materials used in the present invention, such as ferromagnetic powder, binder, carbon black, abrasive, antistatic agent, lubricant, and solvent, may be added at the beginning or during any step. In addition, individual raw materials may be added in portions in two or more steps. For example, polyurethane may be added in portions during a kneading process, a dispersion process, and a mixing process for adjusting the viscosity after dispersion.

[0021] In the present invention, it is possible to use conventional known manufacturing techniques for some of the processes, but in the kneading process, by using a device with a strong kneading force such as a continuous kneader or a pressure kneader, High B of magnetic recording media
We can obtain r.

When using a continuous kneader or a pressure kneader, 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 carried out in a range of 15 to 500 parts per 00 parts. For details of these kneading processes, see Japanese Patent Application Laid-Open No. 1-1063.
No. 38 and JP-A-1-79274.

The coefficient of friction of the magnetic layer surface and the opposite surface of the magnetic recording medium of the present invention against SUS420J is preferably 0.5 or less, more preferably 0.3 or less, and the surface resistivity is preferably 10-5 to 10-12 ohms/ sq, the breaking strength is preferably 1 to 30 kg/cm2, the residual elongation is preferably 0.5% or less, and the heat shrinkage rate at any temperature below 100°C is preferably 1% or less, more preferably 0.
It is 5% or less, most preferably 0.1% or less.

The residual solvent contained in the magnetic layer is preferably 100 mg/m2 or less, more preferably 10 mg/m2.
2 or less, and it is preferable that the residual solvent contained in the upper layer is smaller than the residual solvent contained in the lower layer.

The porosity of the magnetic layer is preferably 30% by volume or less, more preferably 10% by volume in both the lower layer and the upper layer.
It is as follows. It is preferable that the porosity of the lower layer is larger than that of the upper layer, but it may be smaller as long as the porosity of the lower layer is 5% or more. The SFD of the magnetic layer is preferably 0.6 or less.

In the present invention, each of the upper magnetic layer and the lower magnetic layer is usually composed of a single layer, but each may have a single layer structure or a multilayer structure as long as they satisfy the above composition and specified conditions. The content of ferromagnetic powder in the upper layer is preferably 70% or more. When the ferromagnetic powder content is less than 70%, the degree of filling decreases and the electromagnetic conversion characteristics deteriorate. The ferromagnetic powder content here refers to the weight percent of (ferromagnetic powder)/(ferromagnetic powder + binder + additives, etc. contained in the magnetic layer).

The ferromagnetic powder used in the present invention has a σS of 50 emu/g or more, preferably 70 emu/g or more. Moreover, it is preferable that the water content is 0.01 to 2%. It is preferable to optimize the moisture content of the ferromagnetic powder depending on the type of binder.

When cobalt-modified iron oxide is used as the ferromagnetic powder of the present invention, the ratio of divalent iron to trivalent iron is preferably 0 to 33.3%, more preferably 5%.
~10%. The amount of cobalt atoms relative to iron atoms is 0 to 15%, preferably 3 to 8%.

The pH of the ferromagnetic powder is preferably optimized depending on the combination with the binder used. The range is 4 to 1
It is 2. The ferromagnetic powder may be surface-treated with Al, Si, P, or oxides thereof. Its amount is 0.1-10% based on the ferromagnetic powder.

Both the lower and upper ferromagnetic powders contain soluble Na.
Although it may contain inorganic ions such as , Ca, Fe, Ni, and Sr, it has no particular effect if the amount is 500 ppm or less. The Co-containing iron oxide used in the present invention is Co-modified γ-
Known ferromagnetic powders such as FeOx (x=1.33 to 1.5) can be used. In addition to the specified atoms, these ferromagnetic powders contain Al, Si, S, Sc, Ti, V, Cr, Cu, and Y.
, Mo, Rh, Pd, Ag, Sn, Sb, Te, Ba,
Ta, W, Re, Au, Hg, Pb, Bi, La, Ce
, Pr, Nd, P, Co, Mn, Zn, Ni, Sr, B
It does not matter if it contains atoms such as. These ferromagnetic powders may be treated with a dispersant, lubricant, surfactant, antistatic agent, etc., which will be described later, before being dispersed. Further, it is preferable that the ferromagnetic powder used in the present invention has fewer pores, and the value thereof is preferably 20% by volume or less, and more preferably 5% by volume or less. The ferromagnetic powder used in the present invention can be manufactured according to a known method.

As the binder used in the present invention, conventionally known thermoplastic resins, thermosetting resins, reactive resins, and mixtures thereof can be used. The thermoplastic resin has a glass transition temperature of -100 to 150°C and a number average molecular weight of 100.
0-200000, preferably 10000-10000
0, the degree of polymerization is about 50 to 1000. Such examples include vinyl chloride, vinyl acetate, vinyl alcohol, maleic acid, acrylic acid, acrylic esters, vinylidene chloride, acrylonitrile, methacrylic acid, methacrylic esters, styrene, butadiene, ethylene, vinyl butyral, vinyl acetal, There are polymers or copolymers containing vinyl ether and the like as constituent units, polyurethane resins, and various rubber-based resins. In addition, as thermosetting resins or reactive resins, phenolic resins,
Epoxy resin, polyurethane curable resin, urea resin, melamine resin, alkyd resin, acrylic reaction resin, formaldehyde resin, silicone resin, epoxy-polyamide resin, mixture of polyester resin and isocyanate prepolymer, mixture of polyester polyol and polyisocyanate, Examples include mixtures of polyurethane and polyisocyanate. These resins are described in detail in the "Plastic Handbook" published by Asakura Shoten. Further, it is also possible to use a known electron beam curable resin. These examples and their manufacturing methods are described in detail in Japanese Patent Laid-Open No. 62-256219. The above resins can be used alone or in combination, but preferred ones include vinyl chloride resin, vinyl chloride vinyl acetate resin, vinyl chloride vinyl acetate vinyl alcohol resin, vinyl chloride vinyl acetate maleic anhydride copolymer, and at least one resin selected from among them. Examples include combinations of seeds and polyurethane resins, or combinations of these with polyisocyanates. The structure of polyurethane resin is polyester polyurethane, polyether polyurethane, polyether polyester polyurethane, polycarbonate polyurethane,
Known materials such as polyester polycarbonate polyurethane and polycaprolactone polyurethane can be used. For all binders listed here, COOM, SO
3 M, OSO3 M, P=O(OM)2, O-P=
O(OM)2, (M is a hydrogen atom or an alkali metal base), OH, NR2, N+ R3, R
It is preferable to use one into which at least one polar group selected from a hydrocarbon group), an epoxy group, SH, CN, etc. is introduced by copolymerization or addition reaction. The amount of such polar groups is 10-1 to 10-8 mol/g, preferably 10-2 to 10-6 mol/g. Specific examples of these binders used in the present invention include those manufactured by Union Carbide: VAGH, VYHH, VMCH, V
AGF, VAGD, VROH, VYES, VYNC, V
MCC, XYHL, XYSG, PKHH, PKHJ, P
KHC, PKFE, Nissin Chemical Industry Co., Ltd.: MPR-TA,
MPR-TA5, MPR-TAL, MPR-TSN, M
PR-TMF, MPR-TS, MPR-TM, Denki Kagaku: 1000W, DX80, DX81, DX82, D
X83, manufactured by Zeon Corporation: MR110, MR100, 4
00X110A, manufactured by Nippon Polyurethane Co., Ltd.: Nipporan N
2301, N2302, N2304, manufactured by Dainippon Ink Co., Ltd.: Pandex T-5105, T-R3080, T-5
201, Burnock D-400, D-210-80, Chrisbon 6109, 7209, Toyobo Co., Ltd.: Byron U
R8200, UR8300, RV530, RV280,
Manufactured by Dainichiseika: Daiferamine 4020, 5020, 5
100, 5300, 9020, 9022, 7020, Mitsubishi Kasei: MX5004, Sanyo Kasei: Samplen SP-150, Asahi Kasei: Saran F310, F210
etc. The binder used in the present invention is an upper layer,
Both the lower layer and the ferromagnetic powder are used in an amount of 5 to 50% by weight, preferably 10 to 30% by weight, based on the ferromagnetic powder of each layer. It is preferable to use a combination of 5 to 30% by weight when using a vinyl chloride resin, 2 to 20% by weight when using a polyurethane resin, and 2 to 20% by weight when using a polyisocyanate. In the present invention, when polyurethane is used, the glass transition temperature is -50 to 100°C, the elongation at break is 100 to 2000%, and the stress at break is 0.05 to 10.
Kg/cm2, yield point is 0.05-10Kg/cm2
is preferred. Examples of the polyisocyanate used in the present invention include tolylene diisocyanate, 4-4'-diphenylmethane diisocyanate, hexamethylene diisocyanate, xylylene diisocyanate, naphthylene-1,
5-diisocyanate, o-toluidiisocyanate,
Isocyanates such as isophorone diisocyanate and triphenylmethane triisocyanate, products of these isocyanates and polyalcohols,
Polyisocyanates etc. produced by condensation of isocyanates can be used. Commercially available product names of these isocyanates include: Coronate L, Coronate HL, Coronate 2030, Coronate 2031, Millionate MR, Millionate MTL, manufactured by Nippon Polyurethane Co., Ltd.; Takenate D-10, manufactured by Takeda Pharmaceutical Co., Ltd.
2. Takenate D-110N, Takenate D-200,
Takenate D-202, manufactured by Sumitomo Bayer: Desmodur L, Desmodur IL, Desmodur N, Desmodur HL, etc. These can be used alone or in combination of two or more by taking advantage of the difference in curing reactivity. Both the lower layer and the upper layer can be used.

As the carbon black used in the magnetic layer of the present invention, furnace black for rubber, thermal black for rubber, black for color, acetylene black, etc. can be used. Specific surface area is 5-500m2/g, DBP oil absorption is 1
0~400ml/100g, particle size is 5mμ~300m
μ, pH is preferably 2 to 10, water content is preferably 0.1 to 10%, and tap density is preferably 0.1 to 1 g/cc. Specific examples of carbon black used in the present invention include BLACKPEARLS 2000 and 1300 manufactured by Cabot.
, 1000, 900, 800, 700, VULCAN
XC-72, manufactured by Asahi Carbon: #80, #60, #5
5, #50, #35, manufactured by Mitsubishi Chemical Corporation: #2400B
, #2300, #900, #1000, #30, #40
, #10B, manufactured by Conlonbia Carbon Co., Ltd.: CONDUC
TEX SC, RAVEN 150, 50, 40,
15 etc. Even if carbon black is surface treated with a dispersant or grafted with a resin,
It is also possible to use a material whose surface is partially graphite. Further, carbon black may be dispersed in advance with a binder before being added to the magnetic paint. These carbon blacks can be used alone or in combination. When carbon black is used, it is preferably used in an amount of 0.1 to 30% of the amount of the magnetic material. Carbon black has functions such as preventing static electricity on the magnetic layer, reducing the coefficient of friction, imparting light-shielding properties, and improving film strength, and these functions vary depending on the carbon black used. Therefore, these carbon blacks used in the present invention have different types and types in the lower layer and upper layer.
Change the amount and combination, particle size, oil absorption, electrical conductivity, pH
It is of course possible to use them differently depending on the purpose based on the characteristics shown above. For carbon black that can be used in the magnetic layer of the present invention, reference may be made to, for example, "Carbon Black Handbook" (edited by Carbon Black Association).

[0033] The abrasives 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 carbide with an α-ization rate of 90% or more. Known materials having Mohs 6 or higher, such as silicon titanium carbide, titanium oxide, silicon dioxide, and boron nitride, are used singly or in combination. Further, a composite of these abrasives (an abrasive whose surface is treated with another abrasive) may also be used. These abrasives may contain compounds or elements other than the main component, but as long as the main component is 90% or more, the effect remains the same. The particle size of these abrasives is 0.01
~2μ is preferred, but if necessary, abrasives with different particle sizes may be combined, or a single abrasive may be used with a wide particle size distribution to provide the same effect. Tap density is 0.3-2g/cc, moisture content is 0.1-5%, pH is 2
-11, and the specific surface area is preferably 1-30 m2/g. The shape of the abrasive used in the present invention may be needle-like, spherical, or dice-like, but it is preferable to have a part of the shape with a corner because of its high abrasiveness. Specific examples of the abrasive used in the present invention include AKP-20 manufactured by Sumitomo Chemical Co., Ltd.
AKP-30, AKP-50, HIT-50, manufactured by Nihon Kagaku Kogyo Co., Ltd.: G5, G7, S-1, manufactured by Toda Kogyo Co., Ltd.: 100
Examples include ED, 140ED, etc. These abrasives may be dispersed in advance with a binder and then added to the magnetic paint.

The additives used in the present invention include those having a lubricating effect, an antistatic effect, a dispersing effect, a plasticizing effect, etc. 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 their alkali metal salts, alkyl sulfates and their alkali metal salts, polyphenyl ethers, fluorine-containing alkyl sulfates and their alkali metal salts, monobases with 10 to 24 carbon atoms fatty acids (which may contain unsaturated bonds or be branched), and their metal salts (Li, Na, K,
Cu, etc.) or monovalent, divalent, trivalent, tetravalent, pentavalent, hexavalent alcohol with 12 to 22 carbon atoms (it doesn't matter if it contains an unsaturated bond or is branched), 12 carbon atoms ~2
2 alkoxy alcohol, monobasic fatty acid with 10 to 24 carbon atoms (which may contain unsaturated bonds or be branched), and monovalent, divalent, trivalent, or tetravalent with 2 to 12 carbon atoms , mono-, di-, or tri-fatty acid esters consisting of any one of pentahydric and hexahydric alcohols (which may contain unsaturated bonds or be branched), and alkylene oxide polymer monomers. Fatty acid esters of alkyl ethers, 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 of these 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, isooctyl stearate, and myristic acid. Examples include octyl acid, butoxyethyl stearate, anhydrosorbitan monostearate, anhydrosorbitan distearate, anhydrosorbitan tristearate, oleyl alcohol, and lauryl alcohol. In addition, nonionic surfactants such as alkylene oxide type, glycerin type, glycidol type, alkylphenol ethylene oxide adducts, cyclic amines, ester amides, quaternary ammonium salts, hydantoin derivatives,
Cationic surfactants such as heterocycles, phosphoniums or sulfoniums, anionic surfactants containing acidic groups such as carboxylic acids, sulfonic acids, phosphoric acids, sulfuric ester groups, phosphoric ester groups, amino acids, amino sulfonic acids, etc. Amphoteric surfactants such as sulfuric acid or phosphoric acid esters of amino alcohols, alkylbedine type surfactants, etc. can also be used. For information on these surfactants, please refer to the "Surfactant Handbook"
(published by Sangyo Tosho Co., Ltd.) is described in detail. These lubricants, antistatic agents, etc. are not necessarily 100% pure, and may contain impurities such as isomers, unreacted products, side reactants, decomposed products, oxides, etc. in addition to the main components. The content of these impurities is preferably 30% or less, more preferably 10% or less. These lubricants and surfactants used in the present invention can be used in different types and amounts in each layer as required. In addition, all or part of the additives used in the present invention may be added at any step in the production of magnetic paint. In some cases, it is added in the kneading step, in the dispersion step, after dispersion, or just before coating.

The organic solvent used in the present invention includes 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 in any ratio. , alcohols such as methylcyclohexanol, esters such as methyl acetate, butyl acetate, isobutyl acetate, isopropyl acetate, ethyl lactate, glycol acetate, glycol ethers such as glycol dimethyl ether, glycol monoethyl ether, dioxane, benzene, toluene,
Aromatic hydrocarbons such as xylene, cresol, chlorobenzene, chlorinated hydrocarbons such as methylene chloride, ethylene chloride, carbon tetrachloride, chloroform, ethylene chlorohydrin, dichlorobenzene, N,N-
Dimethylformamide, hexane, etc. can be used.

The thickness of the magnetic recording medium of the present invention is such that the non-magnetic support has a thickness of 1 to 100 μm, preferably 6 to 20 μm, and the lower magnetic layer has a thickness of 0.5 to 10 μm, preferably 1.5 to 1.5 μm.
5 μm, and 0.05 μm to 2 μm of the upper magnetic layer, preferably 0.2 to 1.0 μm. The thickness of the magnetic layer used is in the range of 1/100 to 2 times the thickness of the nonmagnetic support. Further, an intermediate layer such as an undercoat layer for improving adhesion or a layer containing carbon black for preventing static electricity may be provided between the nonmagnetic support and the lower layer. The thickness of these is 0
．． 01-2μ, preferably 0.05-0.5μ. Further, a back coat layer may be provided on the side opposite to the magnetic layer side of the non-magnetic support. This thickness is 0.1~2μ,
Preferably it is 0.3 to 1.0μ. These middle class
A known back coat layer can be used.

The non-magnetic support used in the present invention includes known polyesters such as polyethylene terephthalate and polyethylene naphthalate, polyolefins, cellulose triacetate, polycarbonate, polyamide, polyimide, polyamideimide, polysulfone, aramid, aromatic polyamide and the like. Films can be used. These supports may be subjected to corona discharge treatment, plasma treatment, adhesion treatment, heat treatment, dust removal treatment, etc. in advance. In order to achieve the object of the present invention, it is necessary to use a nonmagnetic support having a center line average surface roughness of preferably 0.02 or less, more preferably 0.01 μ or less. Furthermore, it is preferable that these nonmagnetic supports not only have a small center line average surface roughness, but also have no coarse protrusions of 1 μm or more. Further, the surface roughness and shape can be freely controlled by the size and amount of filler added to the support as necessary. Examples of these fillers include oxides and carbonates of Ca, Si, and Ti, as well as organic fine powders such as acrylic fillers.

[0038]

[Example] Example 1 Lower magnetic layer cobalt modified iron oxide
100 copies
Hc 600Oe, specific surface area 35m2 /
g Crystallite size 400 angstroms
Particle size (major axis diameter) 0.25μ, acicular ratio 10 Vinyl chloride-vinyl acetate-maleic anhydride copolymer 10 parts Composition ratio
86:13:1 Polymerization degree 400 Polyester polyurethane resin
5 parts Carbon black (particle size 0.05 μm) 3 parts
butyl stearate
1 part stearic acid
2nd part
butyl acetate
200 parts Upper magnetic layer Cobalt modified iron oxide
100 copies
Hc 1000Oe, specific surface area 60m2
/g Crystallite size 350 angstroms Particle size (major axis diameter) 0.20μ, needle ratio 12 Vinyl chloride-vinyl acetate-maleic anhydride copolymer 12 parts Composition ratio
86:13:1 Polymerization degree 400 Polyester polyurethane resin
6 parts (contains carboxyl group 10-4 mol/g) α-alumina (particle size 0.3 μm)
3 parts carbon black (particle size 0.10μm)
Part 3 Butyl stearate
1 part stearic acid

2 parts Butyl acetate

200 parts For each of the above two paints, after kneading each component with a continuous kneader,
It was dispersed using a sand mill. To the obtained dispersion, 5 parts of polyisocyanate was added to the lower layer coating liquid, 6 parts to the upper layer coating liquid, and 40 parts of butyl acetate was added to each, and the mixture was filtered using a filter having an average pore size of 1 μm. Coating liquids for forming the lower magnetic layer and for forming the upper magnetic layer were prepared respectively. The obtained lower magnetic layer coating liquid was applied to a dry thickness of 3.0 μm, oriented in the horizontal direction, and immediately thereafter, an upper magnetic layer was applied on top of it to a thickness of 0.5 μm. Apply it vertically, then dry. Next, the temperature was 120℃ using a 7-stage calender consisting only of metal rolls.
The tape was then processed and slit to a width of 1/2 inch to produce a videotape.

Example 2 The specific surface area of the upper layer of ferromagnetic powder in Example 1 was 82 m2/
A videotape was obtained by the method described in Example 1, except that the upper magnetic layer was formed in the same manner as in Example 1, and the lower magnetic layer was formed using the same magnetic paint as in Example 1.

Example 3 The specific surface area of the upper layer of ferromagnetic powder in Example 1 was 98 m2/
A videotape was obtained by the method described in Example 1, except that the upper magnetic layer was formed in the same manner as in Example 1, and the lower magnetic layer was formed using the same magnetic paint as in Example 1.

Comparative Example 1 The specific surface area of the upper layer of ferromagnetic powder in Example 1 was set to 45 m2/
A videotape was obtained by the method described in Example 1, except that the upper magnetic layer was formed in the same manner as in Example 1, and the lower magnetic layer was formed using the same magnetic paint as in Example 1.

Comparative Example 2 The specific surface area of the upper layer of ferromagnetic powder in Example 1 was 110 m2.
A videotape was obtained by the method described in Example 1, except that the upper magnetic layer was formed in the same manner as in Example 1, and the lower magnetic layer was made of the same magnetic paint as in Example 1.

Example 4 The upper magnetic layer was formed in the same manner as in Example 1 except that SQ2 in Example 1 was changed to 0.55, and the lower magnetic layer was formed using the same magnetic paint as in Example 1. A videotape was obtained by the method described in 1.

Example 5 The upper magnetic layer was formed in the same manner as in Example 1 except that SQ2 in Example 1 was changed to 0.65, and the lower magnetic layer was formed using the same magnetic paint as in Example 1. A videotape was obtained by the method described in 1.

Comparative example. 3 The upper magnetic layer was formed in the same manner as in Example 1 except that SQ2 in Example 1 was changed to 0.23, and the lower magnetic layer was formed by the method described in Example 1 using the same magnetic liquid as in Example 1. I got a videotape.

Comparative example. 4 The upper magnetic layer was formed in the same manner as in Example 1 except that SQ2 in Example 1 was changed to 0.71, and the lower magnetic layer was formed by the method described in Example 1 using the same magnetic liquid as in Example 1. I got a videotape.

Example. 6 The specific surface area of the lower layer ferromagnetic powder in Example 1 was 21 m2/
A videotape was obtained by the method described in Example 1, except that the lower magnetic layer was formed in the same manner as in Example 1, and the upper layer was made of the same magnetic liquid as in Example 1.

Example. 7 The specific surface area of the lower layer ferromagnetic powder in Example 1 was 48 m2/
A videotape was obtained by the method described in Example 1, except that the lower magnetic layer was formed in the same manner as in Example 1, and the upper layer was made of the same magnetic liquid as in Example 1.

Comparative example. 5 The specific surface area of the ferromagnetic powder of the lower magnetic layer in Example 1 was 14 m
A videotape was obtained by the method described in Example 1, except that the lower magnetic layer was formed in the same manner as in Example 1, and the upper layer was made of the same magnetic liquid as in Example 1.

Comparative example. 6 The specific surface area of the lower layer ferromagnetic powder in Example 1 was 55 m2/
A videotape was obtained by the method described in Example 1, except that the lower magnetic layer was formed in the same manner as in Example 1, and the upper layer was made of the same magnetic liquid as in Example 1.

Comparative example. 7 The lower magnetic layer was formed in the same manner as in Example 1 except that SQ1 in Example 1 was changed to 0.60, and the upper layer was formed using the same magnetic liquid as in Example 1, and a video film was formed by the method described in Example 1. Got the tape.

Evaluation method RF output (Y-S) Image signal A video signal of 50 IRE was recorded at a standard recording current. The average value of the envelope of this reproduced RF output was measured using an oscilloscope, and calculated using the following formula. RF output (dB) = 20 log10 (V/V0)
V Average value V0 Standard value chroma output (C-S) After superimposing the chroma signal on the video signal of the image signal 50IRE and recording it at the standard recording current, the average value of the envelope of the reproduced chroma output was measured with an oscilloscope and calculated in the same way. . Y-S/N, C-S/N Using a noise meter (925R) manufactured by Shibasoku, the difference in S/N ratio was determined using the tape obtained in Comparative Example 1 as a reference tape. The VTR used was Matsushita NV-8300. Using a powder removal VTR (Matsushita Electric AG-6200), the test tape was run for 2 hours and 300 passes, and the degree of dirt adhering to the audio control head and poles inside the deck and half was observed, and a score of 5 points was given. It was displayed in

1: Very poor 2: Inferior 3: Normal 4: Good 5: Very good

[0054]

[Table 1]

From Comparative Examples 1 and 2 and Examples 1 to 3, if the specific surface area of the upper layer ferromagnetic powder is small, the noise level is high, and if it is too large, the noise level is undesirably high due to poor surface properties due to deterioration of dispersibility. Recognize. Compared to Comparative Examples 3 and 4 and Examples 1, 4, and 5, if the squareness ratio in the vertical direction of the upper layer is small, sufficient output cannot be obtained, and if it is too large, output can be obtained, but powder falling off due to a decrease in Young's modulus worsens. I don't like it. From Comparative Examples 5 and 6 and Examples 6 and 7, if the specific surface area of the ferromagnetic powder in the lower layer is small, the noise level will be high, and if it is too large, the horizontal squareness ratio due to deterioration of dispersibility will not be obtained sufficiently, and the Young's modulus will be This is not preferable because powder falling due to the drop worsens. Even if a magnetic layer having the same specific surface area as that of Comparative Example 7 and Example 1 is used as a lower layer, if the horizontal squareness ratio of the lower layer is not sufficient, powder falling due to a decrease in Young's modulus will worsen, which is not preferable.

From the above results, it is clear that the magnetic tape according to the present invention exhibits excellent characteristics, particularly in improved output at short wavelengths and excellent running durability.

[0057]

Effects of the Invention The present invention maintains good electromagnetic conversion characteristics in the long wavelength range by specifying the size of each of the Co-containing iron oxides in the lower layer and the upper layer, as well as specifying SQ1, the Young's modulus of the lower layer, and SQ2. At the same time, it is possible to provide a magnetic recording medium with improved electromagnetic conversion characteristics in a short wavelength region and excellent running durability.

Claims (3)

[Claims] 1. A magnetic recording medium having a plurality of magnetic layers on the surface of a non-magnetic support, including a lower magnetic layer containing ferromagnetic powder and a binder, and an upper magnetic layer provided thereon, the upper magnetic layer comprising: As a ferromagnetic powder, the BET specific surface area is 60m
2 /g or more of Co-containing iron oxide, the squareness ratio in the direction perpendicular to the surface of the nonmagnetic support is 0.4 or more, the Young's modulus in the horizontal direction is 200 kg/mm2 or more, and the lower magnetic layer is As a ferromagnetic powder, the BET specific surface area is 20 to 50.
Contains Co-containing iron oxide in the range of m2/g, has a horizontal squareness ratio of 0.7 or more, and has a horizontal Young's modulus of 300k.
A magnetic recording medium characterized in that it has a magnetic recording capacity of at least g/mm2. 2. B of the ferromagnetic powder containing the upper magnetic layer.
The magnetic recording medium according to claim 1, characterized in that the ET specific surface area is in the range of 60 to 100 m2/g. 3. The magnetic recording medium according to claim 1, wherein the vertical squareness ratio of the upper magnetic layer is in the range of 0.4 to 0.65.