JP2003151102A - Magnetic recording reproducing system and magnetic recording medium used for the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a recording and reproducing system having preferable electromagnetic conversion characteristics, in particular, significantly improved S/N ratio in a high density recording region and having the combination of an inductive head and an MR head and to provide a coating type magnetic recording medium having excellent productivity and high density characteristics with low noise in the recording and reproducing system in combination with an MR head. SOLUTION: The gap length gl of the inductive head satisfies gl<=0.3 μm, gl/10<=Dmax<=gl/2, gl/100<=Dmin<=gl/5 and gl/10<=t<=gl/2, wherein Dmax is the maximum particle diameter of the ferromagnetic powder, Dmin is the minimum particle diameter of the ferromagnetic powder and t is the thickness of the magnetic layer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-density recording / reproducing system and a magnetic recording medium. In particular, a magnetoresistive head (M
Higher S in a system that reproduces using R head)
/ N relating to the magnetic recording medium.

[0002]

2. Description of the Related Art In the field of magnetic disks, a 2 MB MF-2HD floppy (registered trademark) disk using Co-modified iron oxide has come to be standardly installed in a personal computer. However, in the present day when the data capacity to be handled is rapidly increasing, the capacity cannot be said to be sufficient, and it has been desired to increase the capacity of the floppy disk. Also in the field of magnetic tapes, magnetic tapes (so-called backup tapes) for recording computer data as an external storage medium have been actively researched with the spread of office computers such as minicomputers, personal computers, and workstations in recent years. Has been done. In practical use of magnetic tapes for such applications, improvement in recording capacity is strongly demanded in order to achieve recording capacity increase and size reduction, especially in combination with computer size reduction and information processing capacity increase. .

Conventionally, a magnetic recording medium has a magnetic layer in which iron oxide, Co-modified iron oxide, CrO ₂ , ferromagnetic metal powder, and hexagonal ferrite powder are dispersed in a binder and coated on a non-magnetic support. Is widely used. In recent years, magnetoresistive heads (MR heads) used in hard disks have also begun to be used in systems using flexible recording media. Since the MR head has a high sensitivity, a sufficient reproduction output can be obtained. Therefore, when a magnetic material having a relatively low saturation magnetization σs and a fine particle is used, a high C / N ratio can be obtained due to low noise.
For example, Japanese Patent Application Laid-Open No. 10-302243 discloses an example in which barium ferrite (BaFe) fine powder is used for reproduction by an MR head. High recording density (especially linear recording density)
In a high recording system, it is necessary to optimize the relationship between the recording conditions and the medium in addition to using the MR head during reproduction. Generally, at high linear recording density, the gap of the recording head is made small in order to reduce the effects of recording demagnetization, bit shift, etc. that occur during recording. However, due to this, the recording magnetic field is narrowed, and overwriting and thickness loss are traded off. Furthermore, since the magnetization reversal width becomes narrower, the influence of the magnetization disorder in the magnetization transition region cannot be ignored. As a result, S / N loss and deterioration of overwrite suitability occur.

[0004]

SUMMARY OF THE INVENTION The present invention provides a recording / reproducing system combining an inductive head and an MR head, which has a good electromagnetic conversion characteristic and has a significantly improved S / N ratio particularly in a high density recording area. Another object of the present invention is to provide a coating type magnetic recording medium which is a magnetic recording medium having excellent productivity and which is excellent in high density characteristics with low noise in a recording / reproducing system combined with an MR head.

[0005]

SUMMARY OF THE INVENTION The present invention is a magnetic recording / reproducing system for recording a signal on a magnetic recording medium by an inductive head and reproducing the signal by a magnetoresistive head, wherein the magnetic recording medium is on a support. A magnetic layer containing a ferromagnetic powder and a binder, the gap length of the inductive head is 0.3 μm or less, and the maximum particle diameter of the ferromagnetic powder is 1 / g of the gap length of the inductive head. 10 to 1/2, the minimum particle diameter of the ferromagnetic powder is 1/100 to 1/5 of the gap length of the inductive head, and the thickness of the magnetic layer is the gap length of the inductive head. The magnetic recording / reproducing system is characterized by being 1/10 to 1/2 of the above. Further, in the present invention, the gap length is 0.
A magnetic recording medium for use in a magnetic recording / reproducing system in which a signal is recorded by an inductive head of 3 μm or less and the signal is reproduced by a magnetoresistive head, the magnetic recording medium comprising a ferromagnetic powder and a binder on a support. And a maximum particle diameter of the ferromagnetic powder is 1/10 to 1/2 of a gap length of the inductive head, and a minimum particle diameter of the ferromagnetic powder is equal to that of the inductive head. The magnetic recording medium is characterized in that it has a gap length of 1/100 to 1/5 and a thickness of the magnetic layer is 1/10 to 1/2 of the gap length of the inductive head. Preferred embodiments of the present invention are as follows. (1) The ferromagnetic powder has an average major axis length of 20 to 100 nm,
It is a ferromagnetic alloy powder mainly composed of Fe having an average acicular ratio of 3 to 10. (2) The ferromagnetic powder is a hexagonal ferrite powder having an average plate diameter of 10 to 40 nm and an average plate shape ratio of 3 to 10.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, the maximum particle diameter (Dmax) of a ferromagnetic powder means that the powder shape is needle-like, spindle-like, or columnar (however, the height is larger than the maximum major axis of the bottom surface).
In the case of etc., the length of the major axis that constitutes the powder (that is, the major axis length)
It is represented by the arithmetic mean of, ie, the average major axis length, and when the powder shape is plate-like or column-like (however, the thickness or height is smaller than the maximum major axis of the plate surface or the bottom surface), It is represented by the arithmetic average of the maximum major axis (that is, the plate diameter), that is, the average plate diameter.
In addition, the minimum particle diameter (Dmin) of the ferromagnetic powder constitutes a powder when the powder has a needle shape, a spindle shape, a columnar shape (however, the height is larger than the maximum major axis of the bottom surface). It is represented by the arithmetic mean of the lengths of the short axis (the largest axis perpendicular to the long axis) (that is, the short axis length), that is, the average short axis length, and the powder shape is plate-like or columnar (however, the thickness Or the height is smaller than the maximum major axis of the plate surface or the bottom surface), it is represented by the arithmetic mean of the maximum values of the thickness or height (that is, the plate thickness), that is, the average plate thickness. The average of each of the above is measured for 500 particles, and the measurement uses a high resolution transmission electron micrograph and an image analyzer. In the system and the magnetic recording medium of the present invention, when the gap length of the inductive head is gl, gl ≦ 0.3 μm, gl / 10 ≦ Dmax ≦ gl / 2.
(Ie, 2Dmax ≦ gl ≦ 10Dmax), gl / 100 ≦
Dmax ≦ gl / 5 (that is, 5Dmin ≦ gl ≦ 100Dmi
n), and gl / 10 ≦ t ≦ gl / 2 (that is, 2t ≦ g
It is necessary to satisfy l ≦ 10t). Where t
Indicates the thickness of the magnetic layer. Hereinafter, the present invention will be described for each component.

[Magnetic Layer] In the magnetic recording medium of the present invention, a magnetic layer may be provided directly on the support or a magnetic layer may be provided via a non-magnetic lower layer. Since the magnetic layer is thinned to 1/10 to 1/2 of the gap length of the recording head, that is, substantially 30 to 150 nm, a multilayer structure using a non-magnetic lower layer is preferable. The coercive force Hc of the magnetic layer is 158 to 350 kA / m (2000 to
4430 Oe) is preferable, and 170 to 280 kA / m is more preferable. 80kA in magnetization distribution
It is more preferable that the component whose magnetization is inverted by an applied magnetic field of / m or less is less than 1% at the maximum, more preferably 0.7% or less, and particularly 0.5% or less. The magnetic layer thickness is 1/10 to 1/2 of the gap length of the recording head,
It is preferably 1/8 to 1/3. 1/1 of the gap length
If it is less than 0, the reproduction output is insufficient and the gap length is 1/2.
If the thickness is thicker, a phase difference occurs between the magnetization component of the deep layer portion and the magnetization component of the surface layer portion, and the asymmetry of the waveform increases. In addition, the overwrite erasing rate decreases. The squareness ratio SQ of the magnetic layer measured by the in-plane method is usually 0.5 to 0.95, preferably 0.6 to 0.85. The squareness ratio SQ⊥ measured in the direction perpendicular to the magnetic layer surface is usually 0.5 or less, preferably 0.
It is 4 or less, more preferably 0.35 or less. Squareness S
The lower limit of Q⊥ is 0, but in reality it is 0.1 or more.

[Ferromagnetic Powder] The ferromagnetic powder used in the magnetic layer of the present invention is not particularly limited, but needle-like ferromagnetic alloy powder mainly containing Fe or hexagonal ferrite powder is preferable. The ferromagnetic alloy powder is mainly composed of Fe, Co, N
i, Mn, Zn, Nd, etc. are included as alloy components. In particular, the Fe-Co alloy is known as a substance that can obtain a high coercive force Hc. The grain size is defined as follows in relation to the gap length (gl) of the recording head. That is, the average major axis length is 1/10 to 1/2 of gl, preferably 1/8 to 1/3. Average minor axis length is 1/10 of gl
It is 0 to 1/5, preferably 1/50 to 1/8. If it is too small, the magnetization is unstable due to thermal fluctuation, and if it is too large, S
/ N decreases. Σs of the ferromagnetic alloy powder is usually 80
~ 140 A · m ² / kg, preferably 90 to 130 A ·
m ² / kg, and Hc is usually 120 to 360 kA /
m, preferably 158 to 350 kA / m. Examples of the hexagonal ferrite powder include barium ferrite, strontium ferrite, lead ferrite, calcium ferrite substitutes, and Co substitutes. Specific examples include magnetoplumbite-type barium ferrite and strontium ferrite, magnetoplumbite-type ferrite whose particle surface is coated with spinel, and magnetoplumbite-type barium ferrite and strontium ferrite that partially contain a spinel phase. , Other than predetermined atoms, Al, Si, S, Sc, Ti, V, C
r, Cu, Y, Mo, Rh, Pd, Ag, Sn, Sb,
Te, Ba, Ta, W, Re, Au, Hg, Pb, B
i, La, Ce, Pr, Nd, P, Co, Mn, Zn,
It may contain atoms such as Ni, Sr, B, Ge and Nb. Generally, Co-Zn, Co-Ti, Co-Ti
-Zr, Co-Ti-Zn, Ni-Ti-Zn, Nb-
A material to which an element such as Zn-Co, Sb-Zn-Co, or Nb-Zn is added can be used. Depending on the raw material and manufacturing method, some contain unique impurities.

The hexagonal ferrite powder has an average plate diameter of g.
It is 1/10 to 1/2 of l, preferably 1/8 to 1/3. The average plate thickness is 1/100 to 1/5 of gl, preferably 1/50 to 1/8. If the above range is too small, the magnetization becomes unstable due to thermal fluctuation, and if it is too large, the S / N decreases. In particular, since reproduction is performed with an MR head in order to increase the track density, it is necessary to reduce the noise, and the average plate diameter is preferably 35 nm or less, but if it is less than 10 nm, stable magnetization cannot be expected due to thermal fluctuation. If it exceeds substantially 40 nm, noise is high and it is not suitable for the high density magnetic recording of the present invention. The average plate thickness is smaller than the element thickness of the MR head used for reproduction, and preferably 80% of the element thickness of the MR head.
Or less, more preferably 60% or less. The thinner, the better, but in reality, it is 3 nm or more. The average plate ratio (arithmetic mean of plate diameter / plate thickness) is preferably 1 to 15. It is preferably 1 to 7. When the average plate ratio is small, the filling property in the magnetic layer is high, which is preferable, but sufficient orientation cannot be obtained.
If it is larger than 15, noise increases due to stacking between particles. The specific surface area (S _BET ) by the BET method in this powder size range is 10 to 100 m ² / g. The specific surface area is generally coded as an arithmetically calculated value from the particle plate diameter and plate thickness. Generally, the narrower the distribution of particle plate diameter and plate thickness, the better. The distribution is often not a normal distribution, but the coefficient of variation calculated and expressed as the standard deviation σ with respect to the average size is σ / average size =
It is 0.1 to 2.0. To make the powder size distribution sharp, make the particle generation reaction system as uniform as possible,
Distribution improvement treatment is also performed on the generated particles. For example, a method of selectively dissolving ultrafine particles in an acid solution is also known. The hexagonal average particle volume of the ferrite powder is usually, 1000~10000nm ^3, preferably 1500~8000nm ^3, more preferably 2
000 to 8000 nm ³ . The coercive force Hc measured with a magnetic substance can usually be made up to about 40 to 400 kA / m. Higher Hc is more advantageous for high density recording, but is limited by the capability of the recording head. In the present invention, the Hc of the magnetic material is about 120 to 360 kA / m, preferably 15
8 to 350 kA / m. Head saturation magnetization is 1.4
When it exceeds Tesla, it is preferably 175 kA / m or more. Hc is powder size, kind and amount of contained element,
It can be controlled by the substitution site of the element, the reaction conditions for particle generation and the like.

The saturation magnetization σs is usually 40 to 80 A · m.
² / kg. σs tends to become smaller as the particles become finer. It is well known to combine magnetoplumbite ferrite with spinel ferrite in order to improve σs, and to select the type of contained element and the addition amount. It is also possible to use W-type hexagonal ferrite powder. At the time of dispersing the magnetic material, the surface of the magnetic material particles is also treated with a substance suitable for the dispersion medium and the polymer. An inorganic compound or an organic compound is used as the surface treatment material. Typical examples of the main compounds are oxides or hydroxides of Si, Al, P, etc., various silane coupling agents, and various titanium coupling agents. The amount is 0.1 to 10% with respect to the magnetic substance. The pH of the magnetic material is also important for dispersion. Usually, about 4 to 12 has an optimum value depending on the dispersion medium and polymer, but about 6 to 11 is selected from the chemical stability and storability of the medium. Water contained in the magnetic material also affects the dispersion. There is an optimum value depending on the dispersion medium and polymer, but 0.01 to 2.0% is usually selected. The hexagonal ferrite powder is manufactured by mixing barium oxide, iron oxide, a metal oxide substituting for iron, and boron oxide as a glass-forming substance so that the desired ferrite composition is obtained, followed by melting and quenching. A glass crystallization method in which a barium ferrite crystal powder is obtained by subjecting to a crystalline substance and then reheat treatment, followed by washing and crushing, and a barium ferrite composition metal salt solution is neutralized with an alkali to remove by-products and then 100 Hydrothermal reaction method to obtain barium ferrite crystal powder after liquid phase heating at ℃ or more, washing, drying and crushing, barium ferrite composition metal salt solution is neutralized with alkali to remove by-products and then dried 1100 There is a coprecipitation method in which barium ferrite crystal powder is obtained by treating at a temperature of not higher than 0 ° C. and crushing, but the present invention is not limited to a manufacturing method.

[Non-Magnetic Layer] Next, a lower layer is provided between the support and the magnetic layer.
Detailed content of lower layer when non-magnetic layer is provided
Will be described. The underlayer of the present invention is substantially non-magnetic.
Then the structure should not be limited, but usually
At least a resin, preferably a powder, for example,
Inorganic powder or organic powder dispersed in resin
Can be mentioned. The inorganic powder is usually preferably a non-magnetic powder.
Although it is the end, magnetic powder in the range where the lower layer is substantially non-magnetic
The end can also be used. As the non-magnetic powder,
For example, metal oxide, metal carbonate, metal sulfate, metal nitride.
Selected from inorganic compounds such as metal oxides, metal carbides, and metal sulfides
can do. As the inorganic compound, for example, the alpha conversion rate is 9
0% or more of α-alumina, β-alumina, γ-aluminum
Na, θ-alumina, silicon carbide, chromium oxide, cerium oxide
Um, α-iron oxide, hematite, goethite, coranda
Aluminum, silicon nitride, titanium carbide, titanium oxide, dioxide
Silicon, tin oxide, magnesium oxide, tungsten oxide
Oxide, zirconium oxide, boron nitride, zinc oxide, carbon dioxide
Lucium, calcium sulfate, barium sulfate, molybdenum disulfide
Buden and the like are used alone or in combination. Especially preferred
What is important is that the particle size distribution is small and there are many ways to add functions.
And so on, titanium dioxide, zinc oxide, iron oxide, burr sulfate
Um, and more preferable are titanium dioxide and α-iron oxide.
Is. The powder size of these non-magnetic powders is 0.005
2μm is preferable, but the powder size is different if necessary
Combine non-magnetic powder or use a single non-magnetic powder
The same effect can be obtained by widening the diameter distribution.
Particularly preferred is a non-magnetic powder having a powder size of 0.0
It is 1 μm to 0.2 μm. In particular, non-magnetic powder is granular gold
In the case of a metal oxide, the average particle size is 0.08 μm or less.
In the case of the acicular metal oxide, the major axis length is preferably 0.
3 μm or less is preferable, 0.2 μm or less is more preferable.
Yes. Tap density is 0.05 to 2 g / ml, preferably
It is 0.2-1.5 g / ml. The water content of non-magnetic powder is
0.1 to 5% by mass, preferably 0.2 to 3% by mass, and
It is preferably 0.3 to 1.5% by mass. Of non-magnetic powder
The pH is 2-11, but the pH is between 5.5-10.
Is preferred. Specific surface area of non-magnetic powder is 1-100m²/
g, preferably 5-80 m²/ G, more preferably 10
~ 70m²/ G. The crystallite size of non-magnetic powder is
0.004 μm to 1 μm is preferable, and 0.04 μm to
0.1 μm is more preferable. DBP (dibutylphthale
Oil absorption using 5) is 5 to 100 ml / 100 g, preferably
10 to 80 ml / 100 g, more preferably 20
~ 60ml / 100g. Specific gravity is 1-12, preferred
It is 3-6. Shapes are needle, sphere, polyhedron, plate
Any of Mohs hardness of 4 or more and 10 or less
Is preferred. SA (stearic acid) adsorption of non-magnetic powder
The amount is 1 to 20 μmol / m², Preferably 2 to 15 μm
ol / m², And more preferably 3 to 8 μmol / m²And
It The pH is preferably between 3 and 6. these
The surface of the non-magnetic powder is treated with Al ₂
O₃, SiO₂, TiO₂, ZrO₂, SnO₂, Sb
₂O₃, ZnO, Y₂O₃Is preferably present. Special
Al is preferable for the dispersibility.₂O₃, SiO₂, TiO₂,
ZrO₂However, Al is more preferable.₂O₃, Si
O₂, ZrO₂Is. Even if these are used in combination
Good or can be used alone. Also, depending on the purpose
You may use a co-precipitated surface treatment layer.
A method of treating the surface layer with silica after the presence of
Alternatively, the reverse method can be adopted. Also, the surface treatment
The physical layer may be a porous layer depending on the purpose, but it is homogeneous
It is generally preferable that the density is high.

Specific examples of the non-magnetic powder used in the lower layer of the present invention include Nanotite manufactured by Showa Denko, HIT-100, ZA-G1 manufactured by Sumitomo Chemical, and α hematite DPN-250, DPN-250BX manufactured by Toda Kogyo. , DPN-24
5, DPN-270BX, DPN-500BX, DBN
-SA1, DBN-SA3, titanium oxide TT manufactured by Ishihara Sangyo
O-51B, TTO-55A, TTO-55B, TTO
-55C, TTO-55S, TTO-55D, SN-1
00, α-hematite E270, E271, E300, E
303, titanium oxide TTT-4D, STT manufactured by Titanium Industry
-30D, STT-30, STT-65C, α hematite α-40, Teika MT-100S, MT-100
T, MT-150W, MT-500B, MT-600
B, MT-100F, MT-500HD, Sakai Chemical Industry FI
NEX-25, BF-1, BF-10, BF-20, S
T-M, Dowa Mining DEFIC-Y, DEFIC-R,
Examples include AS2BM and TiO2P25 manufactured by Nippon Aerosil, 100A and 500A manufactured by Ube Industries, and fired products thereof. Particularly preferred non-magnetic powders are titanium dioxide and α
-Iron oxide.

By mixing carbon black in the lower layer, the surface electric resistance Rs, which is a known effect, can be lowered, the light transmittance can be reduced, and a desired micro Vickers hardness can be obtained. It is also possible to bring about the effect of lubricant storage by including carbon black in the lower layer. Furnace for rubber, thermal for rubber, black for color, acetylene black, etc. can be used as the kind of carbon black. The carbon black of the lower layer should have the following characteristics optimized depending on the desired effect, and the effect may be obtained more by using together.

The specific surface area of the lower carbon black is 10
0 to 500 m ² / g, preferably 150 to 400 m ² /
g, DBP oil absorption is 20 to 400 ml / 100 g, preferably 30 to 400 ml / 100 g. The particle size of carbon black is 5 nm to 80 nm, preferably 10 to 5
It is 0 nm, more preferably 10 to 40 nm. The carbon black has a pH of 2 to 10 and a water content of 0.1 to 10.
%, And the tap density is preferably 0.1 to 1 g / ml. Specific examples of carbon black used in the present invention include BLACKPEARLS 2000, 1 manufactured by Cabot Corporation.
300, 1000, 900, 800, 880, 700,
VULCAN XC-72, Mitsubishi Kasei Co., Ltd. # 305
0B, # 3150B, # 3250B, # 3750B, #
3950B, # 950, # 650B, # 970B, # 8
50B, MA-600, MA-230, # 4000, #
4010, CONDUCTE made by Colombian Carbon
XSC, RAVEN 8800, 8000, 7000,
5750, 5250, 3500, 2100, 2000,
1800, 1500, 1255, 1250, Ketjen Black EC manufactured by Akzo and the like. The carbon black may be surface-treated with a dispersant or the like, may be grafted with a resin, or may be partially graphitized. Further, the carbon black may be dispersed with a binder in advance before being added to the coating material. These carbon blacks can be used within a range not exceeding 50% by mass relative to the above-mentioned inorganic powder, and a range not exceeding 40% of the total mass of the non-magnetic layer. These carbon blacks can be used alone or in combination. The carbon black that can be used in the present invention can be referred to, for example, "Carbon Black Handbook" (edited by Carbon Black Association).

In the lower layer, organic powder may be used depending on the purpose.
It can also be added. For example, acrylic styrene-based resin powder, benzoguanamine resin powder, melamine-based resin powder, phthalocyanine-based pigment, but also polyolefin-based resin powder, polyester-based resin powder, polyamide-based resin powder, polyimide-based resin powder, polyfluorinated ethylene resin also Can be used. The manufacturing method is JP-A-62.
-18564 and those described in JP-A-60-255827 can be used.

As the binder resin, lubricant, dispersant, additive, solvent, dispersion method and the like for the lower layer, those of the magnetic layer described below can be applied. In particular, binder resin amount, type, additives,
As for the amount and type of the dispersant added, known techniques for the magnetic layer can be applied. [Binder] As the binder used in the present invention, conventionally known thermoplastic resins, thermosetting resins, reactive resins and mixtures thereof are used. The thermoplastic resin has a glass transition temperature of −100 to 150 ° C. and a number average molecular weight of 1.00.
0 to 200,000, preferably 10,000 to 10
The degree of polymerization is about 50,000 and the degree of polymerization is about 50 to 1,000.

Examples of such materials include vinyl chloride, vinyl acetate, vinyl alcohol, maleic acid, acrylic acid,
Acrylic ester, vinylidene chloride, acrylonitrile, methacrylic acid, methacrylic acid ester, styrene,
There are polymers or copolymers containing butadiene, ethylene, vinyl butyral, vinyl acetal, vinyl ether, etc. as constituent units, polyurethane resins, and various rubber resins. Further, as the thermosetting resin or reactive resin, phenol resin, epoxy resin, polyurethane curable resin, urea resin, melamine resin, alkyd resin, acrylic reaction resin, formaldehyde resin, silicone resin,
Examples thereof include epoxy-polyamide resin, a mixture of polyester resin and isocyanate prepolymer, a mixture of polyester polyol and polyisocyanate, a mixture of polyurethane and polyisocyanate, and the like. These resins are described in detail in "Plastic Handbook" published by Asakura Shoten. It is also possible to use a known electron beam curable resin for each layer. These examples and the method for producing them are described in detail in JP-A-62-256219. The above resins can be used alone or in combination, but as a preferable one, vinyl chloride resin,
Combination of at least one selected from vinyl chloride vinyl acetate copolymer, vinyl chloride vinyl acetate vinyl alcohol copolymer, vinyl chloride vinyl acetate maleic anhydride copolymer and polyurethane resin, or a combination of these with polyisocyanate Can be given.

As the structure of the polyurethane resin, known structures such as polyester polyurethane, polyether polyurethane, polyether polyester polyurethane, polycarbonate polyurethane, polyester polycarbonate polyurethane and polycaprolactone polyurethane can be used. In order to obtain better dispersibility and durability, it is necessary to add -COO for all the binders shown here.
_{M, -SO 3 M, -OSO 3} M, -P = O (OM) 2, -
From O—P═O (OM) ₂ , (wherein M is a hydrogen atom or an alkali metal base), OH, NR ₂ , N ⁺ R ₃ (R is a hydrocarbon group), an epoxy group, SH, CN, etc. It is preferable to use at least one selected polar group introduced by copolymerization or addition reaction. The amount of such a polar group is 10 ^-1 to 10 ^-8 mol / g, preferably 10 ^-2 to 10 ^-6 mol / g.

Specific examples of these binders used in the present invention include VAGH and VY manufactured by Union Carbide.
HH, VMCH, VAGF, VAGD, VROH, VY
ES, VYNC, VMCC, XYHL, XYSG, PK
HH, PKHJ, PKHC, PKFE, manufactured by Nisshin Chemical Industry Co., Ltd., MPR-TA, MPR-TA5, MPR-TAL,
MPR-TSN, MPR-TMF, MPR-TS, MP
R-TM, MPR-TAO, 1000W manufactured by Denki Kagaku,
DX80, DX81, DX82, DX83, 100F
D, MR-104, MR-105, MR manufactured by Zeon Corporation
110, MR100, MR555, 400X-110
A, Nippon Polyurethane Nipporan N2301, N2
302, N2304, Pandex T manufactured by Dainippon Ink and Chemicals
-5105, T-R3080, T-5201, Burnock D-400, D-210-80, Chris Bonn 610
9,7209, Toyobo Co., Ltd. Byron UR8200, UR
8300, UR-8700, RV530, RV280,
Dainichiseika Co., Ltd., Daiferamine 4020, 5020, 5
100, 5300, 9020, 9022, 7020, Mitsubishi Kasei Co., MX5004, Sanyo Kasei Samprene S
Examples include P-150 and Saran F310, F210 manufactured by Asahi Kasei.

The binder used in the nonmagnetic layer or magnetic layer of the present invention is used in the range of 5 to 50% by mass, preferably 10 to 30% by mass, based on the nonmagnetic powder or the ferromagnetic powder. 5 to 30% by mass when using a vinyl chloride resin, 2 to 20% by mass when using a polyurethane resin,
Polyisocyanates are preferably used in combination in the range of 2 to 20% by mass. However, when head corrosion occurs due to a slight amount of dechlorination, it is possible to use polyurethane alone or polyurethane and isocyanate alone. . In the present invention, when polyurethane is used, the glass transition temperature is −50 to 150 ° C., preferably 0 ° C. to 100 ° C., and the elongation at break is 100 to 2000.
%, The breaking stress is 0.05 to 10 kg / mm ² (0.49
~ 98 MPa), the yield point is 0.05-10 Kg / mm ²
(0.49 to 98 MPa) is preferable.

The magnetic recording medium of the present invention may be composed of two or more layers. Therefore, the amount of binder, vinyl chloride resin in the binder, polyurethane resin, polyisocyanate,
Alternatively, it is of course possible to change the amount of other resin, the molecular weight of each resin forming the magnetic layer, the amount of polar group, or the physical properties of the resin described above, between the non-magnetic layer and the magnetic layer, if necessary. Yes, it should rather be optimized for each layer, and known techniques for multilayer magnetic layers can be applied. For example, when changing the amount of binder in each layer, it is effective to increase the amount of binder in the magnetic layer in order to reduce scratches on the surface of the magnetic layer. Flexibility can be provided by increasing the amount of the binder in the magnetic layer.

As the polyisocyanate used in the present invention, tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, hexamethylene diisocyanate, xylylene diisocyanate, naphthylene-1,
Isocyanates such as 5-diisocyanate, o-toluidine diisocyanate, isophorone diisocyanate and triphenylmethane triisocyanate, products of these isocyanates and polyalcohols, and polyisocyanates produced by condensation of isocyanates are used. can do. Commercially available trade names of these isocyanates are Coronate L, Coronate HL, Coronate 2030, Coronate 2031 and Millionate M, manufactured by Nippon Polyurethane Company.
R, Millionate MTL, Takeda Pharmaceutical Co., Takenate D
-102, Takenate D-110N, Takenate D-2
00, Takenate D-202, Sumitomo Bayer Co., Ltd., Desmodur L, Desmodur IL, Desmodul N, Desmodul HL, and the like. These are used alone or by utilizing the difference in curing reactivity. Each layer can be used in combination.

[Carbon Black, Abrasive] The carbon black used in the magnetic layer of the present invention may be a furnace for rubber, thermal for rubber, black for color, acetylene black, or the like. Specific surface area is 5 to 50
0 m ² / g, DBP oil absorption is 10-400 ml / 100
g, particle size 5 nm to 300 nm, preferably 10 to 2
The thickness is 50 nm, more preferably 20 to 200 nm. p
H is preferably 2 to 10, the water content is 0.1 to 10%, and the tap density is preferably 0.1 to 1 g / cc. Specific examples of carbon black used in the present invention include BLACKPEARLS 2000, 1300, 1 manufactured by Cabot Corporation.
000, 900, 905, 800, 700, VULCA
NXC-72, Asahi Carbon Co., Ltd., # 80, # 60, #
55, # 50, # 35, Mitsubishi Kasei Co., Ltd., # 2400
B, # 2300, # 900, # 1000 # 30, # 4
0, # 10B, Colombian Carbon, CONDU
CTEX SC, RAVEN 150, 50, 40, 1
5, RAVEN-MT-P, manufactured by Japan EC Co., Ketjen Black EC, and the like. The carbon black may be surface-treated with a dispersant or the like, may be grafted with a resin, or may be partially graphitized. Further, the carbon black may be dispersed with a binder in advance 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% based on the amount of the magnetic material. Carbon black has the functions of preventing electrification of the magnetic layer, reducing the coefficient of friction, imparting light-shielding properties, improving film strength, etc. These differ depending on the carbon black used. Therefore, these carbon blacks used in the present invention are changed in kind, amount and combination in the upper magnetic layer and the lower non-magnetic layer, and have various characteristics such as powder size, oil absorption, electric conductivity and pH shown above. Of course, it is possible to use them properly according to the purpose, and rather it should be optimized in each layer.
Examples of carbon black that can be used in the magnetic layer of the present invention include "Carbon Black Handbook" (edited by Carbon Black Association).
Can be used as a reference.

As the abrasive used in the present invention, α-alumina, β-alumina, silicon carbide, chromium oxide, cerium oxide, α-iron oxide, corundum, artificial diamond, silicon nitride, carbonized having an α-conversion rate of 90% or more. Known materials having a Mohs hardness of 6 or more, such as silicon, titanium carbide, titanium oxide, silicon dioxide, and boron nitride, are used alone or in combination. A composite of these abrasives (abrasive surface-treated with another abrasive) may be used. These abrasives may contain compounds or elements other than the main component, but if the main component is 90% or more, the effect remains the same. The powder size of these abrasives is preferably 0.01 to 2 μm, more preferably 0.05.
To 1.0 μm, particularly preferably 0.05 to 0.5 μm. In particular, in order to improve electromagnetic conversion characteristics, it is preferable that the particle size distribution is narrow. Further, in order to improve the durability, it is possible to combine abrasives having different powder sizes as needed, or to use a single abrasive to widen the particle size distribution and to obtain the same effect. Tap density is 0.3-
2 g / cc, water content 0.1-5%, pH 2-11,
The specific surface area is preferably 1 to 30 m ² / g. The shape of the abrasive used in the present invention may be needle-like, spherical, or dice-like, but those having a corner in part of the shape are preferable because of high abradability. Specifically, Sumitomo Chemical's AKP-1
2, AKP-15, AKP-20, AKP-30, AK
P-50, HIT20, HIT-30, HIT-55,
HIT60, HIT70, HIT80, HIT100,
Reynolds, ERC-DBM, HP-DBM, HP
S-DBM, Fujimi Abrasive Co., Ltd., WA10000, Uemura Kogyo Co., Ltd., UB20, Nippon Kagaku Kogyo Co., Ltd., G-5, Klomex U2, Klomex U1, Toda Kogyo TF.
100, TF140, manufactured by Ibiden, beta random ultra fine, manufactured by Showa Mining Co., Ltd., B-3 and the like. These abrasives can be added to the non-magnetic layer as needed. By adding it to the non-magnetic layer, the surface shape can be controlled and the protruding state of the abrasive can be controlled. The particle size of the abrasive added to these magnetic layer and non-magnetic layer,
Of course, the amount should be set to the optimum value.

[Additive] As the additive used in the magnetic layer and the non-magnetic layer of the present invention, an additive having a lubricating effect, an antistatic effect, a dispersing effect, a plasticizing effect and the like is 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 ester, polyolefin, polyglycol, alkyl phosphate ester and Alkali metal salts, alkyl sulfates and alkali metal salts thereof, polyphenyl ether, phenylphosphonic acid, α-naphthylphosphoric acid, phenylphosphoric acid, diphenylphosphoric acid, p-ethylbenzenephosphonic acid, phenylphosphinic acid, aminoquinones, various silane coupling agents , Titanium coupling agents, fluorine-containing alkyl sulfates and alkali metal salts thereof, monobasic fatty acids having 10 to 24 carbon atoms (whether or not unsaturated bonds are contained or branched) There), and, these metal salts (Li,
(Na, K, Cu, etc.) or monovalent, divalent, trivalent, tetravalent, pentavalent, hexavalent alcohol having 12 to 22 carbon atoms (may contain an unsaturated bond or may be branched. ),
Alkoxy alcohol having 12 to 22 carbon atoms, 10 carbon atoms
-24 monobasic fatty acids (which may contain unsaturated bonds or may be branched) and monovalent C2-12,
Mono-fatty acid ester or di-fatty acid ester or tri-fatty acid consisting of any one of dihydric, trihydric, tetrahydric, pentahydric, and hexahydric alcohol (whether or not unsaturated bond is contained or branched) Ester, fatty acid ester of monoalkyl ether of alkylene oxide polymer, fatty acid amide having 8 to 22 carbon atoms, aliphatic amine having 8 to 22 carbon atoms, and the like can be used.

Specific examples of these fatty acids include capric acid, caprylic acid, lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, oleic acid, elaidic acid, linoleic acid, linolenic acid and isostearic acid. Can be mentioned. Among the esters, butyl stearate, octyl stearate, amyl stearate, isooctyl stearate, butyl myristate, octyl myristate, butoxyethyl stearate, butoxydiethyl stearate, 2-ethylhexyl stearate, 2-octyldodecyl palmitate. , 2-hexyldecyl palmitate, isohexadecyl stearate, oleyl oleate, dodecyl stearate, tridecyl stearate, oleyl erucate, neopentyl glycol didecanoate, ethylene glycol dioleyl, in alcohols oleyl alcohol, stearyl Examples include alcohol and lauryl alcohol. In addition, alkylene oxide-based, glycerin-based, glycidol-based, nonionic surfactants such as 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, sulfuric acid ester groups, phosphoric acid ester groups, etc., amphoteric surface active agents such as amino acids, aminosulfonic acids, sulfuric acid or phosphoric acid 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 and antistatic agents are not always 100%
Impurities such as isomers, unreacted products, by-products, decomposed products, and oxides may be contained in addition to the main component, not being pure. The content of these impurities is preferably 30% or less, more preferably 10% or less.

These lubricants and surfactants used in the present invention have different physical actions,
The type, the amount, and the combination ratio of the lubricant that produces the synergistic effect should be optimally determined according to the purpose.
To control bleeding to the surface using fatty acids with different melting points in the non-magnetic layer and magnetic layer, to control bleeding to the surface using esters with different boiling points, melting points and polarities, and to adjust the amount of surfactant It is conceivable that the coating stability will be improved and that the amount of the lubricant added will be increased in the intermediate layer to improve the lubrication effect. Of course, the present invention is not limited to the examples shown here. Generally, the total amount of lubricant is 0.1% to 50%, preferably 2% to 2 with respect to the magnetic substance or non-magnetic powder.
It is selected in the range of 5%.

Further, all or a part of the additives used in the present invention may be added at any step in the production of the magnetic and non-magnetic coating materials. For example, when the additives are mixed with the magnetic material before the kneading step, the magnetic material may be added. It may be added in the kneading step of the body, the binder and the solvent, in the dispersing step, after the dispersing, or just before the coating. In some cases, the purpose may be achieved by applying a part or all of the additives 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 calendaring or after slitting. As the organic solvent used in the present invention, known ones can be used, for example, JP-A-6-68.
The solvent described in 453 can be used.

[Layer Constitution] The thickness constitution of the magnetic recording medium of the present invention is 2-100 μm, preferably 2-80 μm for the support.
Is. Computer tape support is 3.0-
Those having a thickness in the range of 6.5 μm (preferably 3.0 to 6.0 μm, more preferably 4.0 to 5.5 μm) are used.

An undercoat layer for improving adhesion may be provided between the support and the non-magnetic layer or the magnetic layer. The thickness of the undercoat layer is 0.01 to 0.5 μm, preferably 0.02 to
It is 0.5 μm.

The thickness of the nonmagnetic layer, which is the lower layer of the medium according to the present invention, is 0.2 μm or more and 5.0 μm or less, preferably 0.
3 μm or more and 3.0 μm or less, more preferably 1.0 μm
It is not less than m and not more than 2.5 μm. The lower layer of the medium of the present invention exhibits its effect as long as it is a substantially non-magnetic layer. For example, the effect of the present invention is exhibited even if a small amount of magnetic material is intentionally included or intentionally. Needless to say, the structure can be regarded as substantially the same as that of the present invention. Substantially non-magnetic means that the residual magnetic flux density of the lower layer is 0.01 T or less or the coercive force is 7.96 kA / m (1
00 Oe or less), and preferably has no residual magnetic flux density and coercive force.

[Back Layer] In general, a magnetic tape for recording computer data is strongly required to have repetitive running property as compared with a video tape and an audio tape. In order to maintain such high running durability, the back layer preferably contains carbon black and inorganic powder.

It is preferable to use two kinds of carbon black having different average particle diameters in combination.
In this case, it is preferable to use fine particle carbon black having an average particle diameter of 10 to 20 nm and coarse particle carbon black having an average particle diameter of 230 to 300 nm in combination. Generally, the surface electrical resistance of the back layer can be set to be low and the light transmittance can be set to be low by adding the above-mentioned particulate carbon black. Since many magnetic recording devices use the light transmittance of the tape for the operation signal, in such a case, the addition of finely particulate carbon black is particularly effective. In addition, finely divided carbon black is generally excellent in holding power of a liquid lubricant, and contributes to reduction of friction coefficient when used in combination with a lubricant. On the other hand, the coarse-grained carbon black having an average particle diameter of 230 to 300 nm has a function as a solid lubricant, and also forms fine protrusions on the surface of the back layer to reduce the contact area and reduce the friction coefficient. Contribute to the reduction of However, if the coarse-grained carbon black is used alone, the tape tends to slip off from the back layer due to the tape sliding in a harsh traveling system, which has a drawback of increasing the error ratio.

Specific products of the particulate carbon black include the following. The average particle size is shown in parentheses. RAVEN2000B (18n
m), RAVEN1500B (17 nm) (above, Columbia Carbon Co., Ltd.), BP800 (17 nm) (Cabot Co.), PRINTEX90 (14 nm), P
RINTEX95 (15 nm), PRINTEX85
(16 nm), PRINTEX75 (17 nm) (above, manufactured by Degussa), # 3950 (16 nm) (manufactured by Mitsubishi Kasei Co., Ltd.).

Specific examples of coarse carbon black products include thermal black (270 nm) (manufactured by Khan Kalb Co.) and RAVEN MTP (275 nm).
(Manufactured by Columbia Carbon Co., Ltd.).

When two kinds of back particles having different average particle diameters are used, the content ratio (mass ratio) of fine particle carbon black of 10 to 20 nm and coarse particle carbon black of 230 to 300 nm is the former: Latter = 9
It is preferably in the range of 8: 2 to 75:25, and more preferably in the range of 95: 5 to 85:15.

The content of carbon black (the total amount of two kinds when used in two kinds) in the back layer is usually in the range of 30 to 80 parts by mass, preferably 100 parts by mass of the binder. Is in the range of 45 to 65 parts by mass.

As the inorganic powder, it is preferable to use two kinds of inorganic powders having different hardness together. Specifically, Mohs hardness 3 to
It is preferable to use a soft inorganic powder having a hardness of 4.5 and a hard inorganic powder having a Mohs hardness of 5 to 9. Mohs hardness is 3-4.
By adding the soft inorganic powder of No. 5, it is possible to stabilize the friction coefficient by repeated running. Moreover, with the hardness in this range, the sliding guide pole is not scraped. The average particle size of this inorganic powder is 30 to 50 nm.
It is preferably in the range of.

Examples of the soft inorganic powder having a Mohs hardness of 3 to 4.5 include calcium sulfate, calcium carbonate, calcium silicate, barium sulfate, magnesium carbonate, zinc carbonate, and zinc oxide. They are,
They can be used alone or in combination of two or more.

The content of the soft inorganic powder in the back layer is preferably in the range of 10 to 140 parts by mass with respect to 100 parts by mass of carbon black, and more preferably 35.
~ 100 parts by mass.

By adding a hard inorganic powder having a Mohs hardness of 5 to 9, the strength of the back layer is enhanced and the running durability is improved. When these inorganic powders are used together with carbon black and the above-mentioned soft inorganic powders, a strong back layer is obtained with little deterioration even after repeated sliding. In addition, the addition of this inorganic powder imparts an appropriate polishing force, and reduces the adhesion of shavings to the tape guide pole or the like. Particularly when used in combination with a soft inorganic powder, the sliding characteristics with respect to a guide pole having a rough surface are improved, and the friction coefficient of the back layer can be stabilized.

The hard inorganic powder has an average particle size of 8
0 to 250 nm (more preferably 100 to 210 n)
It is preferably in the range of m).

Examples of the hard inorganic powder having a Mohs hardness of 5 to 9 include α-iron oxide, α-alumina, and chromium oxide (Cr ₂ O ₃ ). These powders may be used alone or in combination. Of these, α-iron oxide or α-alumina is preferable. The content of the hard inorganic powder is usually 3 to 30 parts by mass, preferably 3 to 20 parts by mass with respect to 100 parts by mass of carbon black.

When the soft inorganic powder and the hard inorganic powder are used together in the back layer, the difference in hardness between the soft inorganic powder and the hard inorganic powder is 2 or more (more preferably 2.5 or more, especially 3). As described above, it is preferable to select and use the soft inorganic powder and the hard inorganic powder.

The back layer preferably contains two kinds of inorganic powders each having a specific average particle size and different Mohs hardness, and two kinds of carbon black different in the average particle size.

The back layer may contain a lubricant. The lubricant can be appropriately selected and used from the above-mentioned lubricants that can be used for the non-magnetic layer or the magnetic layer. In the back layer, the lubricant is usually added in the range of 1 to 5 parts by mass with respect to 100 parts by mass of the binder.

[Support] The support used in the present invention is
Although not particularly limited, a substantially non-magnetic and flexible material is preferable. Examples of the flexible support used in the present invention include polyesters such as polyethylene terephthalate and polyethylene naphthalate, polyolefins, cellulose triacetate, polycarbonate, polyamide (aromatic such as aliphatic polyamide and aramid). Known films such as group polyamides), polyimides, polyamideimides, polysulfones, and polybenzoxazoles can be used. It is preferable to use a high strength support such as polyethylene naphthalate or polyamide. Further, if necessary, in order to change the surface roughness of the magnetic surface and the base surface, a laminated type support as shown in JP-A-3-224127 can be used. These supports may be previously subjected to corona discharge treatment, plasma treatment, easy adhesion treatment, heat treatment, dust removal treatment, and the like. It is also possible to apply an aluminum or glass substrate as the support of the present invention.

To achieve the object of the present invention, the center surface average surface roughness (Ra) measured by a surface roughness meter TOPO-3D manufactured by WYKO Co. as a support is 8.0 nm or less, preferably 4.0 nm. Hereafter, it is preferable to use one having a thickness of 2.0 nm or less. It is preferable that the support not only has a small central surface average surface roughness but also that it has no coarse protrusions of 0.5 μm or more. Further, the surface roughness shape can be freely controlled depending on the size and amount of the filler added to the support, if necessary. Examples of these fillers include oxides and carbonates of Ca, Si, Ti and the like, as well as organic fine powders of acrylic type and the like. The maximum height Rmax of the support is 1 μm or less, the ten-point average roughness Rz is 0.5 μm or less, and the center plane mountain height is Rp.
Is 0.5 μm or less, the center plane valley depth Rv is 0.5 μm or less, the center plane area ratio Sr is 10% or more and 90% or less, and the average wavelength λa is preferably 5 μm or more and 300 μm or less. In order to obtain desired electromagnetic conversion characteristics and durability, the surface protrusion distribution of these supports can be arbitrarily controlled by a filler, and those having a size of 0.01 μm to 1 μm can be selected from 0 pieces per 0.1 mm ^2. It is possible to control in the range of 2000 pieces. The F-5 value of the support used in the present invention is preferably 5 to 50 Kg / mm ² (4
9 to 490 MPa). Also, the temperature of the support is 100 ° C
The heat shrinkage percentage at 0 minutes is preferably 3% or less, more preferably 1.5% or less, and the heat shrinkage percentage at 80 ° C. for 30 minutes is preferably 1% or less, more preferably 0.5% or less.
Breaking strength is 5 to 100 kg / mm ² (≈49 to 980 M
Pa) and the elastic modulus is 100 to 2000 Kg / mm ² (≈
0.98 to 19.6 GPa) is preferable. The coefficient of thermal expansion is 10 ⁻⁴ to 10 ⁻⁸ / ° C., preferably 10 ⁻⁵ to 10
^-6 / ° C. The coefficient of humidity expansion is 10 ^-4 / RH% or less, preferably 10 ^-5 / RH% or less. These thermal characteristics, dimensional characteristics, and mechanical strength characteristics are preferably substantially equal to each other within 10% in each in-plane direction of the support.

[Manufacturing Method] The step of producing the magnetic coating material and the non-magnetic coating material 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, if necessary. Each process may be divided into two or more stages. All raw materials such as magnetic materials, non-magnetic powders, binders, carbon blacks, abrasives, antistatic agents, lubricants and solvents used in the present invention may be added at the beginning or in the middle of any step. . Also,
The individual raw materials may be divided and added in two or more steps. For example, kneading step of polyurethane, dispersing step,
It may be divided and added in the mixing step for adjusting the viscosity after dispersion. In order to achieve the object of the present invention, conventionally known manufacturing techniques can be used as a part of the steps. In the kneading process, open kneader, continuous kneader, pressure kneader,
It is preferable to use one having a strong kneading force such as an extruder. When a kneader is used, the magnetic material or non-magnetic powder and all or part of the binder (however, 30% or more of the total binder) and 100 parts of the magnetic material are mixed in a range of 15 to 500 parts. It is processed. Details of these kneading treatments are described in JP-A-1-106338 and JP-A-1-79274. Further, glass beads can be used to disperse the magnetic layer liquid and the non-magnetic layer liquid, but zirconia beads, titania beads, and steel beads, which are dispersion media having high specific gravity, are suitable. The particle size and packing rate of these dispersion media are optimized for use. A known disperser can be used.

When coating a magnetic recording medium having a multi-layer structure in the present invention, the following method is preferably used. First, a lower layer is first coated by a gravure coating, a roll coating, a blade coating, an extrusion coating device or the like which is generally used for coating a magnetic paint, and when the lower layer is in a wet state, Japanese Patent Publication No. 1-46186 or 60-238
179, a method of coating an upper layer by a support pressure type extrusion coating apparatus disclosed in JP-A-2-265672. Secondly, JP-A-63-88080 and JP-A-2-
17971, a method of coating the upper and lower layers almost simultaneously by one coating head having two slits for passing the coating liquid therein, as disclosed in JP-A-2-265672. A third method is a method of coating the upper and lower layers substantially at the same time by using an extrusion coating apparatus with a backup roll disclosed in JP-A-2-174965. In order to prevent the deterioration of the electromagnetic conversion characteristics of the magnetic recording medium due to the aggregation of magnetic particles, JP-A-62-95174 and JP-A-1-236968 are used.
It is desirable to apply shear to the coating liquid inside the coating head by the method disclosed in US Pat. Further, the viscosity of the coating liquid needs to satisfy the numerical range disclosed in JP-A-3-8471. In order to realize the constitution of the present invention, after applying the lower layer and drying, it is of course possible to use successive multilayer coating in which a magnetic layer is provided thereon.
The effects of the present invention are not lost. However, in order to reduce coating defects and improve quality such as dropout, it is preferable to use the above-mentioned simultaneous multilayer coating.

In the case of a disk, a sufficiently isotropic orientation may be obtained without using an orientation device, but the cobalt magnets are alternately arranged diagonally, and an alternating magnetic field is applied by a solenoid. It is preferable to use a known random orientation device. In the case of ferromagnetic metal fine powder, isotropic orientation is generally preferable to be in-plane two-dimensional random,
It is also possible to add a vertical component to make it three-dimensionally random. In the case of hexagonal ferrite, generally, in-plane and vertical three-dimensional random tend to occur, but in-plane two-dimensional random is also possible. In addition, it is also possible to impart isotropic magnetic characteristics in the circumferential direction by using a known method such as a magnet with opposite poles and by using a vertical orientation. Vertical alignment is particularly preferable for high-density recording. Alternatively, spin coating may be used for circumferential orientation.

In the case of a magnetic tape, it is oriented in the longitudinal direction using a cobalt magnet or a solenoid. It is preferable to control the drying position of the coating film by controlling the temperature of the drying air, the air volume, and the coating speed. The coating speed is 20 m / min.
1000 m / min, the temperature of the drying air is preferably 60 [deg.] C. or higher, and an appropriate preliminary drying can be carried out before entering the magnet zone.

After the above coating and drying, the magnetic recording medium is usually calendered. As a calendering roll, a heat-resistant plastic roll such as epoxy, polyimide, polyamide, or polyimideamide or a metal roll is used, and particularly when a double-sided magnetic layer is used, the metal rolls are used together. It is preferable. The treatment temperature is preferably 50 ° C. or higher, more preferably 100 ° C. or higher. Linear pressure is preferably 200 kg / cm (196 kN / m)
Above, more preferably 300 kg / cm (294 kN
/ M) or more.

[Physical Properties] The saturation magnetic flux density of the magnetic layer of the magnetic recording medium according to the present invention is 0.2 to 0.5 T when the ferromagnetic metal fine powder is used, and 0 when the hexagonal ferrite powder is used. 0.1 to 0.3T. Coercive force Hc and Hr
Is 1500 to 5000 Oe (120 to 400 kA / m)
However, preferably 1700 to 3000 Oe (136
~ 240 kA / m). The coercive force distribution is preferably narrow, and SFD and SFDr are preferably 0.6 or less. In the case of a magnetic tape, the squareness ratio is 0.7 or more, preferably 0.8 or more.

The coefficient of friction of the magnetic recording medium of the present invention with respect to the head has a temperature of −10 ° C. to 40 ° C. and a humidity of 0% to 95%.
Is 0.5 or less, preferably 0.3 or less, and the surface resistivity is preferably 10 ⁴ to 10 ¹² ohm / magnetic surface.
It is preferable that the sq and the charged position are within -500V and + 500V. The elastic modulus of the magnetic layer at 0.5% elongation is preferably 100 to 2000 kg / mm ² (0.98 to 1) in each in-plane direction.
9.6 GPa), breaking strength is preferably 10-70 Kg
/ Mm ² (98 to 686 MPa), the elastic modulus of the magnetic recording medium is preferably 100 to 1500 Kg / m in each in-plane direction.
m ² (0.98 to 14.7 GPa), the residual spread is preferably 0.5% or less, and the thermal shrinkage at any temperature of 100 ° C. or less is preferably 1% or less, more preferably 0.5.
% Or less, and most preferably 0.1% or less. The glass transition temperature of the magnetic layer (maximum point of loss elastic modulus in dynamic viscoelasticity measurement measured at 110 Hz) is preferably 50 ° C. or higher and 120 ° C. or lower, and that of the lower non-magnetic layer is preferably 0 ° C. to 100 ° C. Loss elastic modulus is 1 × 10 ⁹ to 8 × 10 ¹⁰ μN / c
It is preferably in the range of m ² and the loss tangent is preferably 0.2 or less. If the loss tangent is too large, sticking failure is likely to occur. It is preferable that these thermal characteristics and mechanical characteristics are substantially equal within 10% in each in-plane direction of the medium. The residual solvent contained in the magnetic layer is preferably 100 m
g / m ² or less, more preferably 10 mg / m ² or less. The porosity of the coating layer is preferably 30% by volume or less, and more preferably 20% by volume or less for both the non-magnetic 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 disk medium for which repeated use is important, a larger porosity often results in better running durability.

The center surface average surface roughness Ra of the magnetic layer is WYC.
About 250μm x 250μ using TOPO-3D manufactured by O
It is usually 4.0 nm or less, preferably 3.8 nm or less, and more preferably 3.5 nm or less when measured in the area of m. The maximum height Rmax of the magnetic layer is 0.5 μm or less, the ten-point average roughness Rz is 0.3 μm or less, the center face peak height Rp is 0.3 μm or less, and the center face valley depth Rv is 0.3 μm or less,
The center surface area ratio Sr is preferably 20% or more and 80% or less, and the average wavelength λa is preferably 5 μm or more and 300 μm or less. It is preferable to optimize the electromagnetic conversion characteristics and the friction coefficient by setting the surface protrusions of the magnetic layer as described above. These can be easily controlled by the surface control by the filler of the support, the particle size and amount of the powder added to the magnetic layer as described above, the roll surface shape of the calendar treatment, and the like. it can. The curl is preferably within ± 3 mm.

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

[0058]

EXAMPLES Hereinafter, specific examples of the present invention will be described.
The present invention should not be limited to this. The following "parts" are "parts by mass". Example 1 <Preparation of paint> Magnetic paint Barium ferrite magnetic powder 100 parts Average plate diameter 30 nm, average plate thickness 10 nm, average particle volume 5800 nm ³ Particle existence ratio of average plate diameter 10 nm or less 6% Hc: 183 kA / m, σs: 50 A · m ² / kg S _BET : 65 m ² / g vinyl chloride copolymer MR110 (manufactured by Zeon Corporation) 10 parts Polyurethane resin containing SO ₃ Na groups, Tg: 82 ° C. 5 parts α-alumina HIT55 (manufactured by Sumitomo Chemical Co., Ltd.) 5 parts Average particle size: 0.2 μm Carbon black # 55 (manufactured by Asahi Carbon Co., Ltd.) 1 part Average particle size: 0.075 μm Specific surface area: 35 m ² / g DBP oil absorption: 81 ml / 100 g pH: 7.7 Volatilization Min: 1.0% Butyl stearate 10 parts Butoxyethyl stearate 5 parts Isohexadecyl stearate 3 parts Stearic acid 2 parts Chillethylketone 125 parts Cyclohexanone 125 parts

<Non-Magnetic Paint> Non-Magnetic Powder Needle Hematite 80 parts Average major axis length: 0.15 μm, specific surface area by BET method: 50 m ² / g pH: 8.5, surface treatment layer: Al ₂ O ₃ cover - carbon black average particle diameter: 20 nm 20 parts (manufactured by Nippon Zeon Co., Ltd.) vinyl chloride copolymer MR 110 7 parts polyurethane resin SO ₃ Na group-containing, Tg: 55 ℃ 10 parts butyl stearate 1 part stearic acid 3 parts Methyl ethyl ketone / cyclohexanone (8/2 mixed solvent) 250 parts

The components of the above coating composition were kneaded with a kneader and then dispersed using a sand mill for 4 hours.
2.5 parts of polyisocyanate was added to the obtained dispersion liquid for the coating liquid for the non-magnetic layer, 3 parts for the coating liquid for the magnetic layer, and 40 parts of cyclohexanone was further added to each to have an average pore diameter of 1 μm. Filtering was performed using a filter to prepare coating solutions for forming a non-magnetic layer and for forming a magnetic layer. 3. The resulting non-magnetic layer coating liquid is dried so that the thickness of the lower layer after drying becomes 1.7 μm, and immediately thereafter, the thickness of the magnetic layer becomes 0.1 μm. Simultaneous multilayer coating is performed on an aramid support having a center surface average surface roughness of 2 nm at 4 μm. While both layers are still in a wet state, a cobalt magnet having a magnetic force of 0.6T and a solenoid having a magnetic force of 0.6T. Was oriented by. After drying, the temperature was 85 ° C. and the speed was 200 m / min. And then a back layer having a thickness of 0.5 μm (carbon black average particle size: 17 nm 100 parts, calcium carbonate average particle size: 40 nm 80 parts, α-alumina average particle size: 20).
5 parts of 0 nm was applied to a nitrocellulose resin, a polyurethane resin, and a polyisocyanate). Slit to 1/2 inch width, feed the slit product, and attach it to a device with a winding device so that the non-woven fabric and razor blade press against the magnetic surface, and use a tape cleaning device to clean the surface of the magnetic layer. Cleaning was performed to obtain a tape sample.

The tape performance and the like were evaluated by the following measuring methods. Measurement method (1) Maximum particle size and minimum particle size of ferromagnetic powder A photograph of particles was taken with a transmission electron microscope (TEM) at a magnification of 500,000, and the size of 500 particles was measured by an image analyzer. (2) Magnetic Properties Hc and σs of Ferromagnetic Powder: Measured at Hm796 kA / m (10 kOe) using a vibrating sample type magnetometer (manufactured by Toei Industry Co., Ltd.). (3) Magnetic Layer Thickness A slice of the medium was prepared and the average thickness of the magnetic layer was measured by TEM. (4) Electromagnetic conversion characteristics The magnetic head was pressed against the magnetic tape wound around the rotary drum for measurement. The diameter of the rotating drum was 60 mm, and the head / tape relative speed was 10 m / sec. For recording, an MIG head (gl: 0.2 μm, track width 18 μm) having a saturation magnetization of 1.4 T was used, and the recording current was set to the optimum recording current for each tape. An anisotropic MR head (A-MR) having an element thickness of 25 nm was used as the reproducing head. S / N ratio:
A signal with a recording wavelength of 0.2 μm is recorded, the reproduced signal is frequency-analyzed with a spectrum analyzer made by Shibasoku, and the ratio of the carrier signal (wavelength 0.2 μm) output to the integrated noise of the entire spectrum band is S / N. did. Overwrite erasure rate: The residual rate of a signal having a recording wavelength of 0.8 μm when a signal having a recording wavelength of 0.8 μm was overwritten after recording a signal having a recording wavelength of 0.8 μm was expressed in dB by the following formula. Residual rate = 20 log (output before overwriting / output after overwriting) Half-value inversion density D ₅₀ : When recording is performed by sequentially shortening the recording wavelength from 10 μm, the reproduction output is 10 μm.
It is the linear recording density when it is halved.

Examples 2 to 7 and Comparative Examples 1 to 3 Similar to Example 1 except that the changing elements shown in Table 1, that is, gl, ferromagnetic powder and magnetic layer thickness were changed as shown in the same table. Then, a tape sample was obtained. In the description of the types of ferromagnetic powder, BaFe is barium ferrite, and Fe-Co is acicular ferromagnetic alloy powder.

[0063]

[Table 1]

From the above table, the inductive head has gl ≦
0.3 μm, 2Dmax ≦ gl ≦ 10Dmax, 5Dmin ≦ g
The examples using the system satisfying 1 ≦ 100 Dmin and 2t ≦ gl ≦ 10t or the magnetic recording medium satisfying the above relationship are superior to the comparative examples in S / N, overwrite erasing rate and D _50. I know that

According to the present invention, if the gap length of the inductive head for recording the signal of the recording / reproducing apparatus is known,
Since the maximum particle diameter, the minimum particle diameter, and the magnetic layer thickness, which are optimum for reproducing the ferromagnetic powder used in the coating type magnetic recording medium by the MR head, can be known as a function of the gap length, the optimum magnetic recording / reproducing should always be performed. You can

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Claims (2)

[Claims] 1. A magnetic recording and reproducing system in which a signal is recorded on a magnetic recording medium by an inductive head and a signal is reproduced by a magnetoresistive head, wherein the magnetic recording medium contains a ferromagnetic powder and a binder on a support. A magnetic layer is provided, and the gap length of the inductive head is
0.3 μm or less, and the maximum particle diameter of the ferromagnetic powder is 1/1 of the gap length of the inductive head.
0 to 1/2 and the minimum particle diameter of the ferromagnetic powder is 1/10 of the gap length of the inductive head.
A magnetic recording / reproducing system, wherein the magnetic layer has a thickness of 0 to 1/5 and a thickness of the magnetic layer is 1/10 to 1/2 of a gap length of the inductive head. 2. A magnetic recording medium for use in a magnetic recording / reproducing system in which a signal is recorded by an inductive head having a gap length of 0.3 μm or less and the signal is reproduced by a magnetoresistive head, which magnetic recording medium is supported. A ferromagnetic layer and a magnetic layer containing a binder on the body, and the maximum particle size of the ferromagnetic powder is 1/10 to 1/2 of the gap length of the inductive head; Has a minimum particle diameter of 1/100 to 1/5 of the gap length of the inductive head, and the thickness of the magnetic layer is 1/10 of the gap length of the inductive head.
A magnetic recording medium characterized by being ˜1 / 2.