JP2002367140A - Magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic recording medium less in TA and excellent in high density characteristics by combining a coating type magnetic recording medium which is conventionally used and excellent in productivity and can be provided at low price and an MR head. SOLUTION: The magnetic recording medium is obtained by providing a substantially non-magnetic lower layer and a magnetic layer in which hexagonal ferrite powders are dispersed in a binder, in this order on a non-magnetic substrate. The magnetic layer has <10 pieces/900 cm<2> protrusions having 2-100 μm diameter and >=100 nm height on the surface thereof.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a coating type magnetic recording medium for high density recording.

[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 is mounted on a personal computer as standard. However, today, the amount of data to be handled is rapidly increasing, and the capacity has become insufficient, and it is desired to increase the capacity and density of floppy disks.

[0003] In the field of magnetic tapes, with the spread of office computers such as personal computers and workstations in recent years, research on magnetic tapes (so-called backup tapes) for recording computer data as external storage media has been conducted. It is being actively performed. For practical use of such magnetic tape,
In particular, in order to achieve large-capacity recording and miniaturization in combination with miniaturization of computers and increase in information processing capacity, there is a strong demand for higher recording capacity and higher density.

As one direction for realizing high density,
Improvements in magnetic heads are underway. A conventionally used magnetic head based on the principle of electromagnetic induction (induction type magnetic head) needs to increase the number of coil turns of the reproducing head in order to obtain a large reproducing output. However, when the inductance increases and the resistance at high frequencies increases, there is a problem in that the reproduction output is reduced, and there has been a limit to high-density recording / reproduction.

On the other hand, a reproducing head based on the operating principle of MR (magnetic resistance) has been proposed, and has begun to be used in hard disks and the like. A magnetoresistive magnetic head (MR head) has a reproduction output several times higher than that of an inductive magnetic head, and does not use an induction coil. The improvement of the recording / reproducing characteristics can be expected.

However, a problem when using an MR head is that the magnetic resistance changes due to thermal energy generated when the magnetic head collides with a protrusion existing on the magnetic recording medium, and the DC resistance increases.
There is a phenomenon (thermal asperity: TA) in which the level changes like a spike. If TA occurs frequently, there arises a problem that error correction becomes impossible, and the head itself may be destroyed. Therefore, it is necessary to minimize the occurrence of TA. In other words, if the number of protrusions on the magnetic recording medium is reduced, good recording and reproduction can be performed, and the high-density recording characteristics can be dramatically improved. However, it has not been known how to reduce the number of protrusions of any shape to obtain good recording and reproduction.

[0007]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a TA type magnetic recording medium by combining a conventionally used coating magnetic recording medium which is excellent in productivity and can be provided at a low price, and an MR head. It is an object of the present invention to provide a magnetic recording medium excellent in high-density characteristics with little noise.

[0008]

In order to obtain a magnetic recording medium having good electromagnetic conversion characteristics and in which the occurrence of TA is remarkably suppressed particularly in a high-density recording area, the present inventors have studied a sample in which TA has occurred. We worked diligently. As a result, it was found that the size of the projections serving as the nucleus of the TA had a diameter (equivalent circle diameter) of 2 to 100 μmΦ and a height of 100 nm or more. Therefore, the present inventors have found out that the above object can be achieved by suppressing the occurrence of projections that cause the occurrence of TA based on the above findings, and have completed the present invention. That is, an object of the present invention is to provide a magnetic recording medium in which a substantially nonmagnetic lower layer and a magnetic layer obtained by dispersing hexagonal ferrite powder in a binder are provided in this order on a nonmagnetic support. The magnetic layer has a surface with a diameter of 2 to 100 μm and a height of 100 nm.
This is achieved by a magnetic recording medium characterized by having less than 10 protrusions / 900 cm ² .

Preferred embodiments of the present invention are as follows. (1) The magnetic recording medium is a digital signal recording disk or tape mounted with an MR reproducing head. (2) The average plate diameter of the hexagonal ferrite powder is 0.04
μm or less, and the plate ratio is 3 or more.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the magnetic recording medium of the present invention will be described in more detail. [Magnetic layer] In the magnetic recording medium of the present invention, among the protrusions present on the surface of the magnetic layer, the diameter is in the range of 2 to 100 µm.
The number of protrusions having a height of 100 nm or more is 10/90
Less than 0 cm ² . The number of protrusions of the above dimensions is 10/9
If it is not less than 00 cm ² , the chances of the MR head colliding with the projections during reproduction by the MR head increase, and the occurrence of thermal asperity increases, which may cause an error, and in some cases, the MR head is destroyed. Sometimes. The number of protrusions of the above dimensions is 10/900 cm ²
There is no limitation as long as it is less than 0, and it may be 0 pieces / 900 cm ² .

The surface protrusions of the magnetic layer of the present invention are classified into protrusions caused by the support and protrusions related to the coating layer. The protrusions caused by the support and the surface protrusions of the magnetic layer satisfy the above conditions. Control the protrusions associated with the coating layer. Usually, fine projections are formed on the surface of the support in order to obtain desired electromagnetic conversion characteristics and durability or suitability for handling the support. In order to form fine surface projections on the surface, the support contains fine inorganic or organic fillers. In order to obtain the required electromagnetic conversion characteristics, durability, and handling properties, surface protrusions are formed by changing the particle size and particle size distribution of the filler, or by mixing fillers having different particle sizes. Even if the particle size of the fine particles to be added to the support is relatively large, the particle size distribution is broad and large particles are included, the filler is insufficiently dispersed, and aggregates are present, or the dispersion can be dispersed. So-called coarse protrusions are formed when the liquid is conveyed to the film machine or aggregated during film formation. The finer the filler, the more difficult it is to disperse, and the more likely it is for aggregation to occur. Therefore, the protrusions on the surface of the support that cause the protrusions of the magnetic layer are controlled by the type of filler added to the support, the particle size, the particle size distribution, the dispersion conditions, and the filter conditions for removing coarse particles and aggregated particles. can do.

The effect of the protrusions on the surface of the support is reduced by increasing the thickness of the coating layer. As a result, the protrusions on the surface of the magnetic layer can be reduced. The protrusions of the coating layer are formed of inorganic material such as a magnetic substance, an abrasive, carbon black contained in the upper layer (magnetic layer), a nonmagnetic powder, an abrasive, carbon black contained in the lower layer (nonmagnetic layer). Particle size, types of binders and lubricants that disperse them,
It can be controlled by kneading conditions, dispersion conditions, coating layer thickness, coating and drying conditions, calendering conditions, surface treatment conditions of the magnetic layer surface, and the like when preparing the lower layer solution. When the particle size of the inorganic powder is reduced, it becomes difficult to disperse the binder in the binder, and it becomes easy to form projections. The dispersion state also changes depending on the combination with the binder, and the number of protrusions changes. Regarding the kneading conditions, when the kneading is performed with a small amount of the solvent to be added, the kneaded material is difficult to disperse, and the number of protrusions tends to increase. Conversely, when the amount of the solvent is increased to weakly knead, the number of projections tends to decrease. As the dispersion conditions, the dispersion time is determined by the hardness of the dispersion medium used for sand mill dispersion,
It can be appropriately changed depending on the specific gravity or the like. If the dispersion time is short, the number of protrusions increases. On the other hand, even if the dispersion time is excessively long, aggregation of particles occurs due to mixing of impurities due to wear of the disperser and the dispersion medium, and the number of protrusions increases. Calendar conditions are generally strong (calender pressure,
When the temperature and the roll hardness are increased and the speed is reduced), the number of protrusions can be reduced.

As a method of surface treatment of the magnetic layer, a known treatment method called a so-called burnish treatment can be used for a floppy disk. The number of protrusions having a diameter of 2 to 100 μm and a height of 100 nm or more existing on the surface of the magnetic layer is 10/900 cm by controlling the number and pressing pressure of the polishing tape by a method in which the polishing tape is pressed against the surface of the magnetic layer and polished. Can be controlled to less than ² . In the case of a tape, see JP-A-63-25983.
No. 0, a polishing treatment method using a polishing tape (lapping tape blade method), a sapphire blade method, a diamond wheel method, and the like can be used.
Depending on the selection of these methods and the setting of the respective processing conditions, the diameter 2-100 μm and the height 1
The number of protrusions of 00 nm or more can be controlled to less than 10/900 cm ² . This surface treatment can reduce the number of protrusions on the surface of the magnetic layer even when there are many surface protrusions on the support and protrusions on the coating layer. As described above, there are various methods for controlling the protrusions on the surface of the magnetic layer, and these methods can be appropriately combined and used to obtain the surface state defined by the magnetic recording medium of the present invention.

The surface protrusions of the magnetic recording medium of the present invention can be obtained as follows. The surface of the magnetic recording medium is observed with a differential interference microscope, and the protrusions are marked. Then, a WYKO HD-2000 (50 × objective lens, 0.5 × intermediate lens, measuring range: 242 μm ×
184 μm) to measure the height and width of the protrusion. The width is 2 to 100 μm and the height is 1
By counting more than 00 nm, 900 c
The number of protrusions per m ² can be determined.

The magnetic layer of the present invention contains a hexagonal ferrite powder as a magnetic material. Hexagonal ferrite powder is suitable for high-density recording because of its excellent high-density characteristics.
As the hexagonal ferrite, there are various substitution products of barium ferrite, strontium ferrite, lead ferrite, and calcium ferrite, and Co substitution products. 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 further containing a part of spinel phase. , Other than predetermined atoms, Al, Si, S, Sc, Ti, V,
Cr, Cu, Y, Mo, Rh, Pd, Ag, Sn, S
b, Te, Ba, Ta, W, Re, Au, Hg, Pb,
Bi, La, Ce, Pr, Nd, P, Co, Mn, Z
It may contain atoms such as n, Ni, Sr, B, Ge, and Nb. Generally, Co-Ti, Co-Ti-Zr, C
o-Ti-Zn, Ni-Ti-Zn, Nb-Zn-C
A substance to which an element such as o, Sb-Zn-Co, or Nb-Zn is added can be used. Some raw materials and production methods contain specific impurities.

The average plate diameter of the hexagonal ferrite powder used in the present invention is preferably 0.04 μm or less,
More preferably, it is 0.01 to 0.035 μm, and still more preferably, it is 0.015 to 0.030 μm. When the average plate diameter is 0.04 μm or less, medium noise can be reduced, and even if aggregates are formed, high projections are not easily formed, which is preferable.

The plate ratio (plate diameter / plate thickness) of the hexagonal ferrite is preferably 3 or more, and more preferably 3 to 5. When the plate ratio is small, the filling property in the magnetic layer is increased, which is preferable, but sufficient orientation cannot be obtained. If it exceeds the above range, noise increases due to stacking between particles. BE in this particle size range
The specific surface area by the T method is 10 to ²⁰⁰ m ² / g. The specific surface area generally corresponds to an arithmetic calculation value from the particle plate diameter and the plate thickness. The crystallite size is 50-450 °, preferably 100
Å350 °. The distribution of particle plate diameter and plate thickness is generally preferably as narrow as possible. Although it is difficult to make a numerical value, it can be compared by randomly measuring 500 particles from a particle TEM photograph. The distribution is often not a normal distribution, but when calculated and expressed as a standard deviation with respect to the average size, σ / average size = 0.1 to 2.
0. In order to sharpen the particle size distribution, the particle generation reaction system is made as uniform as possible, and the generated particles are subjected to a distribution improving treatment. For example, a method of selectively dissolving ultrafine particles in an acid solution is also known. The coercive force Hc measured on the magnetic material is 40 to 400
It can be made up to about kA / m (500-5000 Oe). A higher Hc is advantageous for high-density recording, but is limited by the capability of the recording head. Usually 64kA / m (800O
e) to about 318 kA / m (4000 Oe), preferably 119 kA / m (1500 Oe) or more.
It is 279 kA / m (3500 Oe) or less. When the saturation magnetization of the head exceeds 1.4 Tesler, 159 kA
/ M (2000 Oe) or more. Hc
Can be controlled by the particle size (plate diameter / plate thickness), the type and amount of the contained element, the substitution site of the element, the particle generation reaction conditions and the like. Saturation magnetization σs is 40~80A · m ² / kg (40~
80 emu / g). The higher the value of σs, the better, but the smaller the fine particles, the lower the tendency. It is well known to combine spinel ferrite with magnetoplumbite ferrite to improve σs, and to select the type of element contained and the amount to be added. It is also possible to use W-type hexagonal ferrite.

As a method for producing hexagonal ferrite, a metal oxide for replacing barium oxide, iron oxide, and iron and boron oxide or the like as a glass-forming substance are mixed so as to have a desired ferrite composition, then melted, and quenched. Into an amorphous body,
A glass crystallization method in which barium ferrite crystal powder is obtained by washing and pulverizing after reheating treatment. Barium ferrite composition metal salt solution is neutralized with alkali, by-products are removed, and then liquid phase heating is performed at 100 ° C or higher, followed by washing, drying,
A hydrothermal reaction method in which pulverized barium ferrite crystal powder is obtained. The barium ferrite composition metal salt solution is neutralized with an alkali, and after removing by-products, dried, treated at 1100 ° C. or lower, and pulverized to obtain a barium ferrite crystal powder. We do not choose manufacturing method.

When dispersing the hexagonal ferrite, the surface of the magnetic particles may be treated with a substance suitable for the dispersion medium and the polymer. As the surface treatment material, an inorganic compound or an organic compound is used. Typical examples of the main compound include oxides or hydroxides of Si, Al, P, etc., various silane coupling agents, and various titanium coupling agents. The amount is 0.1 to 10% based on the magnetic material. The pH of the magnetic material is also important for dispersion. Usually, the optimum value is about 4 to 12 depending on the dispersion medium and the polymer.
About 10 are selected. Water contained in the magnetic material also affects dispersion. There is an optimum value depending on the dispersion medium and the polymer, but usually 0.01 to 2.0% is selected.

Carbon black can be added to the magnetic layer of the present invention. As the carbon black, for example, furnace for rubber, thermal for rubber, black for color, acetylene black and the like can be used. Specific surface area is 5 to 500 m ² / g, DBP oil absorption is 10 to 4
00 ml / 100 g, particle diameter is 5 to 300 nm, pH is 2 to 10, water content is 0.1 to 10% by weight, and tap density is preferably 0.1 to 1 g / ml. Specific examples of the carbon black used in the present invention include BLACKPEARLS 2000, 1300, 100 manufactured by Cabot Corporation.
0, 900, 800, 700, VULCAN XC-7
2. # 80, # 60, # 55, # 50 manufactured by Asahi Carbon Co., Ltd.
# 35, # 2400B, # 2300, manufactured by Mitsubishi Chemical Corporation
# 900, # 1000 # 30, # 40, # 10B, CONDUCTEX SC, RAV manufactured by Columbia Carbon Co.
EN 150, 50, 40, 15 and the like. Carbon black may be used after being surface-treated with a dispersant or the like or grafted with a resin, or may be one obtained by partially graphitizing the surface. Before adding the carbon black to the magnetic paint, the carbon black may be dispersed in a binder in advance. These carbon blacks alone,
Or they can be used in combination. When carbon black is used, it is preferably used in an amount of 0.1 to 30% by weight based on the amount of hexagonal ferrite.

Carbon black is used to prevent the magnetic layer from being charged.
It has the functions of reducing the coefficient of friction, imparting light-shielding properties, and improving the film strength, and these differ depending on the carbon black used. Therefore, these carbon blacks used in the present invention are different in type, amount, and combination in the magnetic layer and the lower layer, and are used for the purpose based on the above-mentioned properties such as particle size, oil absorption, conductivity, and pH. Of course, it is possible to use them properly. The carbon black that can be used in the magnetic layer of the present invention can be referred to, for example, “Carbon Black Handbook” (edited by Carbon Black Association).

[Non-Magnetic Layer] Next, the details of the non-magnetic layer (substantially non-magnetic lower layer) will be described.
The non-magnetic layer of the present invention may contain a non-magnetic powder and a binder, and the non-magnetic powder may be, for example, a metal oxide, a metal carbonate, a metal sulfate, a metal nitride, a metal carbide, a metal sulfide. , And the like. Examples of the inorganic compound include α-alumina, β-alumina, γ-alumina, θ-alumina, silicon carbide, chromium oxide, cerium oxide, α-iron oxide, hematite, goethite, corundum, and nitride having an α conversion of 90% or more. Silicon, titanium carbide, titanium oxide, silicon dioxide, tin oxide, magnesium oxide, tungsten oxide, zirconium oxide, boron nitride, zinc oxide, calcium carbonate, calcium sulfate, barium sulfate, molybdenum disulfide, etc. are used alone or in combination. You. Particularly preferred are:
Due to the small particle size distribution and many means for imparting functions,
Titanium dioxide, zinc oxide, iron oxide and barium sulfate are more preferable, and titanium dioxide and α-iron oxide are more preferable. The particle size of these nonmagnetic powders is 0.005 to 0.5.
The thickness is preferably 5 μm, but if necessary, nonmagnetic powders having different particle sizes may be combined, or even a single nonmagnetic powder may have the same effect by broadening the particle size distribution.
Particularly preferably, the particle size of the nonmagnetic powder is 0.0
It is 1 μm to 0.2 μm. In particular, when the nonmagnetic powder is a granular metal oxide, the average particle size is preferably 0.08 μm or less, and when the nonmagnetic powder is a needle-shaped metal oxide, the major axis length is 0.1 μm.
Suitably, it is 2 μm or less, preferably 0.15 μm or less, more preferably 0.1 μm or less. The needle ratio of the non-magnetic powder is suitably 2 to 20, preferably 3 to 10. The tap density is suitably from 0.05 to 2 g / ml, preferably from 0.2 to 1.5 g / ml. The water content of the nonmagnetic powder is suitably 0.1 to 5% by weight, preferably 0.2 to 3% by weight, and more preferably 0.3 to 1.5% by weight. The pH of the nonmagnetic powder is 2
It is 11, but the pH is particularly preferably between 5.5 and 10. Since these have high adsorptivity to functional groups, they have good dispersion and high mechanical strength of the coating film.

The specific surface area of the nonmagnetic powder is 1 to 100 m ² /
g, preferably 5 to 80 m ² / g, more preferably 10 m ² / g.
Suitably, it is ７０70 m ² / g. The crystallite size of the nonmagnetic powder is preferably 0.004 μm to 1 μm,
0.04 μm to 0.1 μm is more preferable. The oil absorption using DBP (dibutyl phthalate) is 5 to 100 ml /
It is suitable that the amount is 100 g, preferably 10 to 80 ml / 100 g, and more preferably 20 to 60 ml / 100 g. The specific gravity is suitably from 1 to 12, preferably from 3 to 6. The shape may be any of a needle shape, a spherical shape, a polyhedral shape, and a plate shape. The Mohs' hardness is preferably 4 or more and 10 or less. The SA (stearic acid) adsorption amount of the nonmagnetic powder is 1 to 20 μmol / m ² , preferably ² to 15 μmol.
/ M ² , more preferably 3 to 8 μmol / m ² . Preferably, the pH is between 3 and 6. The surface of these non-magnetic powders is surface-treated and
₂ O ₃ , SiO ₂ , TiO ₂ , ZrO ₂ , SnO ₂ , Sb
It is preferable that ₂ O ₃ , ZnO, and Y ₂ O ₃ be present. Particularly preferred for dispersibility are Al ₂ O ₃ , SiO ₂ , Ti
O ₂ and ZrO ₂ , more preferably Al ₂ O ₃ ,
SiO ₂ and ZrO ₂ . These may be used in combination or may be used alone. In addition, a co-precipitated surface treatment layer may be used according to the purpose, or a method of treating the surface layer with silica and then treating the surface layer with silica, or vice versa, may be employed. Also, the surface treatment layer may be a porous layer depending on the purpose,
Homogeneous and dense are generally preferred.

Specific examples of the non-magnetic powder used in the non-magnetic layer of the present invention include Nanotite manufactured by Showa Denko, HIT-100, ZA-G1 manufactured by Sumitomo Chemical, α-hematite DPN-250 manufactured by Toda Kogyo, and DPN. -250BX, DPN-
245, DPN-270BX, DPN-500BX, D
BN-SA1, DBN-SA3, Titanium oxide TTO-51B, TTO-55A, TTO-55B, T manufactured by Ishihara Sangyo
TO-55C, TTO-55S, TTO-55D, SN
-100, α hematite E270, E271, E30
0, E303, titanium oxide STT-4D manufactured by Titanium Industry,
STT-30D, STT-30, STT-65C, α-hematite α-40, MT-100S manufactured by Teica, MT-1
00T, MT-150W, MT-500B, MT-60
0B, MT-100F, MT-500HD, Sakai Chemical F
INEX-25, BF-1, BF-10, BF-20,
ST-M, Dowa Mining DEFIC-Y, DEFIC-
R, AS2BM, TiO2P25, manufactured by Nippon Aerosil, 100A, 500A, manufactured by Ube Industries, Ltd., and fired products thereof. Particularly preferred non-magnetic powders are titanium dioxide and α-iron oxide.

By mixing carbon black in the non-magnetic layer, it is possible to reduce the surface electric resistance Rs, which is a known effect, to reduce the light transmittance, and to obtain a desired micro-Vickers hardness. As the type of carbon black, furnace for rubber, thermal for rubber, black for color, acetylene black and the like can be used. The specific surface area of the carbon black used in the non-magnetic layer is 100 to 500 m ² / g, preferably 150 to 400 m ²
/ G and DBP oil absorption are suitably from 20 to 400 ml / 100 g, preferably from 30 to 400 ml / 100 g. The particle size of the carbon black is 5 to 80 nm, preferably 10 to 50 nm, more preferably 10 to 40 n.
Suitably, m. The carbon black has a pH of 2 to 10, a water content of 0.1 to 10%, and a tap density of 0.1.
1-1 g / ml is preferred. Specific examples of the carbon black used in the present invention include Cabot's B
LACKPEARLS 2000, 1300, 100
0, 900, 800, 880, 700, VULCAN
XC-72, manufactured by Mitsubishi Kasei Kogyo Co., Ltd. # 3050B, # 31
50B, # 3250B, # 3750B, # 3950B,
# 950, # 650B, # 970B, # 850B, MA
-600, MA-230, # 4000, # 4010, CONDUCTEX SC, R manufactured by Columbia Carbon Co.
AVEN 8800, 8000, 7000, 5750,
5250, 3500, 2100, 2000, 1800,
1500, 1255, 1250, Ketjen Black EC manufactured by Akzo Corporation, and the like. Carbon black may be used after being surface-treated with a dispersant or the like or grafted with a resin, or may be used with a part of the surface being graphitized. Further, the carbon black may be dispersed in a binder before adding it to the paint. These carbon blacks are used in an amount of 50 to the inorganic powder.
It can be used within a range not exceeding 40% by weight and a range not exceeding 40% of the total weight of the nonmagnetic 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).

Further, an organic powder can be added to the non-magnetic layer according to the purpose. For example, acrylic styrene-based resin powder, benzoguanamine resin powder, melamine-based resin powder, phthalocyanine-based pigments, but also polyolefin-based resin powder, polyester-based resin powder, polyamide-based resin powder, polyimide-based resin powder, and polyfluoroethylene resin Can be used. As the production method, those described in JP-A-62-18564 and JP-A-60-255827 can be used. The binder resin, lubricant, dispersant, additive, solvent, dispersing method, etc. of the nonmagnetic layer described below can be applied to the magnetic layer.
In particular, binder resin amount, type, additive, dispersant addition amount,
As for the type, a known technique for the magnetic layer can be applied.

[Binder] A binder, a lubricant, and a binder for the magnetic layer and the non-magnetic layer of the present invention and, when used, the back coat layer.
Known techniques for the magnetic layer, non-magnetic layer, and back coat layer can be applied to the dispersant, additive, solvent, dispersion method, and the like. In particular, with respect to the amount and type of the binder, the amount of the additive and the type of the dispersant, and the type of the magnetic layer, known techniques can be applied. Examples of the binder used in the present invention include conventionally known thermoplastic resins, thermosetting resins, reactive resins, and mixtures thereof. As a thermoplastic resin, the glass transition temperature is −100 to 150 ° C., and the number average molecular weight is 1,000 to
200,000, preferably 10,000-100,00
0, the degree of polymerization is suitably about 50 to 1,000.

Examples of such binders include vinyl chloride, vinyl acetate, vinyl alcohol, maleic acid, acrylic acid, acrylic acid ester, vinylidene chloride, acrylonitrile, methacrylic acid, methacrylic acid ester, styrene, butadiene, ethylene, Examples thereof include polymers or copolymers containing vinyl butyral, vinyl acetal, vinyl ether, and the like as constituent units, polyurethane resins, and various rubber resins. Further, as the thermosetting resin or the reactive resin, phenol resin, epoxy resin, polyurethane curable resin, urea resin, melamine resin, alkyd resin, acrylic-based reactive resin, formaldehyde resin, silicone resin, epoxy-polyamide resin, polyester resin And mixtures of isocyanate prepolymers, mixtures of polyester polyols and polyisocyanates, and mixtures of polyurethanes and polyisocyanates. These resins are described in detail in "Plastic Handbook" published by Asakura Shoten. In addition, a known electron beam-curable resin can be used for each layer. These examples and the production method thereof are described in
It is described in detail in Japanese Patent Publication No. 256219. The above resins can be used alone or in combination, but preferred are vinyl chloride resin, vinyl chloride vinyl acetate copolymer, vinyl chloride vinyl acetate vinyl alcohol copolymer,
Examples include a combination of at least one selected from vinyl chloride vinyl acetate / maleic anhydride copolymer and a polyurethane resin, or a combination of these with a polyisocyanate.

The structure of the polyurethane resin is polyester polyurethane, polyether polyurethane, polyether polyester polyurethane, polycarbonate polyurethane, polyester polycarbonate polyurethane,
Known materials such as polycaprolactone polyurethane can be used. For all binders shown here, -CO is required to obtain better dispersibility and durability.
_{OM, -SO 3 M, -OSO 3} M, -P = O (OM) 2,
—OP = O (OM) ₂ (wherein M is a hydrogen atom,
Or alkali metal base), —OH, —NR ₂ , —N ⁺ R
Preferably, at least one polar group selected from ₃ (R is a hydrocarbon group), an epoxy group, —SH, and —CN is introduced by copolymerization or addition. The amount of such a polar group is 10 ^-1 to 10 ^-8 mol / g,
Preferably, it is suitably from 10 ^-2 to 10 ^-6 mol / g.

Specific examples of these binders used in the present invention include VAGH, V
YHH, VMCH, VAGF, VAGD, VROH, V
YES, VYNC, VMCC, XYHL, XYSG, P
KHH, PKHJ, PKHC, PKFE, Nissin Chemical Industries' 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, ZEON Corporation MR-104, MR-105, MR
110, MR100, MR555, 400X-110
A, Nipporan N2301, N2 manufactured by Nippon Polyurethanes
302, N2304, Pandex T manufactured by Dainippon Ink and Chemicals, Inc.
-5105, T-R3080, T-5201, Burnock D-400, D-210-80, Crisbon 610
9, 7209, Toyobo Byron UR8200, UR
8300, UR-8700, RV530, RV280,
Daiferamine 4020, 5020, 51 manufactured by Dainichi Seika
00, 5300, 9020, 9022, 7020, MX5004 manufactured by Mitsubishi Kasei, Samprene SP- manufactured by Sanyo Kasei
150, Saran F310 and F210 manufactured by Asahi Kasei Corporation.

The binder used in the nonmagnetic layer and the magnetic layer of the present invention is 5 to 50% of the nonmagnetic powder or the magnetic powder.
, Preferably in the range of 10 to 30%. 5-30% when using vinyl chloride resin,
When a polyurethane resin is used, it is preferable to use a combination of 2 to 20% and a polyisocyanate in a range of 2 to 20%. For example, when head corrosion occurs due to a slight amount of dechlorination, only polyurethane is used, or It is also possible to use only polyurethanes and isocyanates. In the present invention, when polyurethane is used, the glass transition temperature is −50 to 150 ° C., preferably 0 ° C. to 100 ° C., the breaking elongation is 100 to 2000%, and the breaking stress is 0.05 to 10 kg / mm ² (0. 49-98M
Pa), and the yield point is 0.05 to 10 kg / mm ² (0.4
9 to 98 MPa) is preferred.

The magnetic recording medium of the present invention comprises at least two layers including an upper magnetic layer and a lower nonmagnetic layer.
Therefore, the amount of the binder, the amount of the vinyl chloride resin, the polyurethane resin, the polyisocyanate or the other resin in the binder, the molecular weight of each resin forming the magnetic layer, the amount of the polar group, or the resin described above. It is of course possible to change the physical characteristics and the like of the non-magnetic layer and each magnetic layer as necessary. Rather, it should be optimized for each layer, and a known technique for a multilayer magnetic layer can be applied. For example, when the amount of the binder is changed in each layer, it is effective to increase the amount of the binder in the magnetic layer in order to reduce the abrasion on the surface of the magnetic layer. The flexibility can be increased by increasing the amount of the binder in the magnetic layer.

The polyisocyanate used in the present invention includes tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, hexamethylene diisocyanate, xylylene diisocyanate, naphthylene-1,
Use of isocyanates such as 5-diisocyanate, o-toluidine diisocyanate, isophorone diisocyanate, triphenylmethane triisocyanate, products of these isocyanates and polyalcohols, and polyisocyanates formed by condensation of isocyanates can do. Commercially available trade names of these isocyanates include Coronate L, Coronate HL, Coronate 2030, Coronate 2031, Millionate MR, manufactured by Nippon Polyurethane Co., Ltd.
Millionate MTL, Takeda Pharmaceutical Takenate D-10
2, Takenate D-110N, Takenate D-200,
Takenate D-202, Desmodur L, Desmodur IL, Desmodur N, Desmodur HL, etc., manufactured by Sumitomo Bayer Co. Can be used.

An abrasive can be used for the magnetic layer and the non-magnetic layer of the present invention. Examples of the abrasive include α-alumina, β-alumina, silicon carbide, chromium oxide, and oxide having an α conversion of 90% or more. Cerium, α-iron oxide, corundum, artificial diamond, silicon nitride, silicon carbide, titanium carbide,
Known materials mainly having a Mohs hardness of 6 or more, such as titanium oxide, silicon dioxide, and boron nitride, can be used alone or in combination. In addition, a composite of these abrasives (abrasive whose surface has been treated with another abrasive) may be used. These abrasives may contain compounds or elements other than the main component, but the effect remains unchanged if the main component is 90% by weight or more. Tap density is 0.3-2
g / ml, water content 0.1-5% by weight, pH 2-1
1. The specific surface area is preferably from 1 to 30 m ² / g. The shape of the abrasive used in the present invention may be any of a needle shape, a spherical shape, and a dice shape, but a shape having a part of a corner is preferable because of high abrasiveness. Specific examples of the abrasive used in the present invention include AKP-20 and AKP-3 manufactured by Sumitomo Chemical Co., Ltd.
0, AKP-50, HIT-50, HIT-55, HI
T-60A, HIT-70, HIT-100, Nihon Kagaku Kogyo Co., Ltd. G5, G7, S-1, Toda Kogyo Co., Ltd. TF-10
0, TF-140 and the like. The abrasive used in the present invention can be of different types, amounts, and combinations for the magnetic layer (upper and lower layers) and the non-magnetic layer, and can be used properly according to the purpose. These abrasives may be added to the magnetic paint after being subjected to dispersion treatment with a binder in advance.

In the present invention, additives having a lubricating effect, an antistatic effect, a dispersing effect, a plasticizing effect and the like can be used. Molybdenum disulfide, tungsten graphite disulfide, boron nitride, graphite fluoride, silicone oil, polar group silicone, fatty acid modified silicone,
Fluorine-containing silicone, fluorine-containing alcohol, fluorine-containing ester, polyolefin, polyglycol, alkyl phosphate and its alkali metal salt, alkyl sulfate and its alkali metal salt, polyphenyl ether, fluorine-containing alkyl sulfate and its alkali metal salt, A monobasic fatty acid having 10 to 24 carbon atoms (which may contain an unsaturated bond or may be branched), and a metal salt thereof (such as Li, Na, K, or Cu), or
C12 to C22 monovalent, divalent, trivalent, tetravalent, pentavalent and hexavalent alcohols (which may contain an unsaturated bond or may be branched), and C12 to C22 alkoxy alcohols A monobasic fatty acid having 10 to 24 carbon atoms (which may contain an unsaturated bond or may be branched) and a monovalent, divalent, trivalent, tetravalent, pentavalent, and C2 to 12 carbon atom; A mono-fatty acid ester or a di-fatty acid ester or a tri-fatty acid ester consisting of any one of hexahydric alcohols (which may contain an unsaturated bond or may be branched);
Fatty acid esters of monoalkyl ethers of alkylene oxide polymers, fatty acid amides having 8 to 22 carbon atoms, aliphatic amines having 8 to 22 carbon atoms, and the like can be used.

Specific examples thereof include lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid,
Butyl stearate, oleic acid, linoleic acid, linolenic acid, elaidic acid, octyl stearate, amyl stearate, isooctyl stearate, octyl myristate, butoxyethyl stearate, anhydrosorbitan monostearate, anhydrosorbitan distearate , Anhydrosorbitan tristearate, oleyl alcohol, lauryl alcohol. In addition, alkylene oxide, glycerin,
Nonionic surfactants such as glycidol, alkylphenol ethylene oxide adducts, etc., cyclic amines, ester amides, quaternary ammonium salts, hydantoin derivatives, heterocycles, cationic surfactants such as phosphonium or sulfoniums, carboxylic acids, Sulfonic acid,
Also used are anionic surfactants containing acidic groups such as phosphoric acid, sulfate ester groups, phosphate ester groups, etc., amino acids, aminosulfonic acids, sulfuric acid or phosphate esters of amino alcohols, and amphoteric surfactants such as alkylbedine-type surfactants. it can.

These surfactants are described in detail in "Surfactant Handbook" (published by Sangyo Tosho Co., Ltd.). These lubricants, antistatic agents, etc.
It is not 0% pure and may contain impurities such as isomers, unreacted products, by-products, decomposed products, oxides, etc. in addition to the main components. These impurities are preferably 30% or less, more preferably 10% or less.

The type and amount of these lubricants and surfactants used in the present invention can be properly used in the lower layer and the magnetic upper layer as needed. For example, controlling the oozing to the surface using fatty acids having different melting points in the lower layer and the magnetic upper layer,
Controls bleeding to the surface using esters with different boiling points and polarities, improves coating stability by adjusting the amount of surfactant, and increases the amount of lubricant added to the non-magnetic layer for lubricating effect However, it is needless to say that the present invention is not limited to the example shown here. Further, all or a part of the additives used in the present invention may be added at any step of the production of the magnetic paint, for example, when mixed with the ferromagnetic powder before the kneading step, the ferromagnetic powder and the binder , A kneading step with a solvent, a dispersing step, a dispersing step, a dispersing step, and a dissolving step immediately before coating. In some cases, the purpose may be achieved by applying a part or all of the additive simultaneously or sequentially after applying the magnetic layer according to the purpose. Depending on the purpose, after calendaring or after slitting,
A lubricant can be applied to the surface of the magnetic layer.

Examples of commercial products of these lubricants used in the present invention include NAA-102 and NAA-41 manufactured by NOF Corporation.
5, NAA-312, NAA-160, NAA-18
0, NAA-174, NAA-175, NAA-22
2, NAA-34, NAA-35, NAA-171, N
AA-122, NAA-142, NAA-160, NA
A-173K, castor hardened fatty acid, NAA-42, NA
A-44, Cation SA, Cation MA, Cation A
B, Cation BB, Nimeen L-201, Nimeen L-202, Nimeen S-202, Nonion E-20
8, Nonion P-208, Nonion S-207, Nonion K-204, Nonion NS-202, Nonion NS-
210, nonion HS-206, nonion L-2, nonion S-2, nonion S-4, nonion O-2, nonion LP-20R, nonion PP-40R, nonion SP
-60R, Nonion OP-80R, Nonion OP-85
R, Nonion LT-221, Nonion ST-221, Nonion OT-221, Monogly MB, Nonion DS-6
0, Anone BF, Anone LG, butyl stearate, butyl laurate, erucic acid, oleic acid manufactured by Kanto Chemical Co.,
Takemoto Yushi FAL-205, FAL-123, Nippon Rika Co., Ltd. Engelbu LO, Engelbu IPM, Sansocizer E4030, Shin-Etsu Chemical TA-3, KF-
96, KF-96L, KF96H, KF410, KF4
20, KF965, KF54, KF50, KF56, K
F907, KF851, X-22-819, X-22
822, KF905, KF700, KF393, KF-
857, KF-860, KF-865, X-22-98
0, KF-101, KF-102, KF-103, X-
22-3710, X-22-3715, KF-910,
KF-3935, Armamide P manufactured by Lion Armor,
Armide C, Armoslip CP, Duomin TDO manufactured by Lion Yushi, BA-41G manufactured by Nisshin Oil, Profan 2012E manufactured by Sanyo Chemical, New Pole PE61,
Ionnet MS-400, Ionnet MO-200, Ionnet DL-200, Ionnet DS-300, and Ionnet DS-1000 Ionnet DO-200.

[Layer Structure] In the thickness structure of the magnetic recording medium of the present invention, the thickness of the nonmagnetic support is suitably 2 to 100 μm, preferably 2 to 80 μm. The thickness of the nonmagnetic support of the floppy disk is suitably from 20 to 800 μm, preferably from 25 to 70 μm. The thickness of the non-magnetic support of the computer tape is 3.0 to 10 μm.
m, preferably in the range of 3.0 to 8.0 μm, more preferably in the range of 3.0 to 5.5 μm. The thickness of the magnetic layer is preferably from 0.01 to 0.5 μm. If the upper layer is too thin, a uniform recording layer will not be formed, and if it is too thick, the surface will be rough and the electromagnetic conversion characteristics will be reduced. The object of the present invention can be achieved by using a single magnetic layer or a plurality of magnetic layers. The thickness of the nonmagnetic layer is preferably from 0.5 to 3 μm. If the thickness is too small, the durability decreases. If the thickness is too large, the surface becomes rough and the electromagnetic conversion characteristics deteriorate. The total thickness of the upper layer and the lower layer is suitably in the range of 1/100 to 2 times the thickness of the nonmagnetic support.

An undercoat layer may be provided between the non-magnetic support and the non-magnetic layer to improve adhesion. The thickness of the undercoat layer is 0.01 to 2 μm, preferably 0.02 to 2 μm.
Suitably, it is 0.5 μm. Known undercoat layers can be used.

[Backcoat layer] A backcoat layer may be provided on the surface of the non-magnetic support used in the present invention, which is opposite to the surface on which the magnetic layer is provided. Normally, the backcoat layer is coated with a backcoat layer-forming paint in which particulate components such as abrasives and antistatic agents and a binder are dispersed in an organic solvent on the surface of the nonmagnetic support opposite to the surface on which the magnetic layer is provided. This is a layer provided as follows. Note that an adhesive layer may be provided on the surface of the non-magnetic support on which the magnetic paint and the back coat layer forming paint are applied. When the backcoat layer is provided on the nonmagnetic support on the side opposite to the magnetic layer side, the thickness of the backcoat layer is 0.1 to 2
μm, preferably 0.3 to 1.0 μm.

In general, magnetic tapes for recording computer data are required to have a higher repetitive running property than video tapes and audio tapes. In order to maintain such high running durability, the back coat layer includes
It preferably contains carbon black and inorganic powder. It is preferable to use two types of carbon black having different average particle sizes in combination.
In this case, fine carbon black having an average particle size of 10 to 20 nm and an average particle size of 230 to 300 n
It is preferable to use a combination of m coarse carbon black particles. In general, the surface electric resistance of the back coat layer can be set low and the light transmittance can be set low by the addition of the fine carbon black as described above.
Some magnetic recording devices use the light transmittance of the tape,
In many cases, the addition of fine carbon black is effective in such cases because many of them are used for operation signals. In addition, fine particle carbon black generally has excellent holding power for a liquid lubricant, and contributes to a reduction in friction coefficient when used in combination with a lubricant. On the other hand, the particle size is 230 to 300 n
The coarse-grained carbon black having a function of m has a function as a solid lubricant, and also forms minute projections on the surface of the back layer to reduce the contact area and contribute to the reduction of the friction coefficient. However, the coarse-grained carbon black has a drawback that in a severe running system, the tape slides easily to drop off from the back coat layer, leading to an increase in the error ratio.

Specific products of the particulate carbon black include the following. RAVE
N2000B (18 nm), RAVEN 1500B (1
7 nm) (all manufactured by Columbia Carbon Co., Ltd.), BP80
0 (17 nm) (Cabot), PRINTENTEX
90 (14 nm), PRINTEX 95 (15 nm),
PRINTEX85 (16 nm), PRINTEX75
(17 nm) (all manufactured by Degussa), # 3950 (16
nm) (manufactured by Mitsubishi Chemical Corporation). Specific examples of commercial products of coarse particle carbon black include thermal black (270 nm) (manufactured by Khancarb) and RAVEN.
MTP (275 nm) (manufactured by Columbia Carbon Co., Ltd.) can be mentioned.

In the case of using two types having different average particle sizes in the back coat layer, 10 to 20 nm
The content ratio (weight ratio) of the fine particle carbon black to the coarse particle carbon black having a particle size of 230 to 300 nm is preferably in the range of former: latter = 98: 2 to 75:25, more preferably 95: 5. Suitably, it is in the range of 85:15. The content of carbon black (or the total amount when two types are used) in the back coat layer is usually 3 parts by weight with respect to 100 parts by weight of the binder.
0 to 80 parts by weight, preferably 45 to 65 parts by weight.
Suitably, it is in the range of parts by weight.

It is preferable to use two kinds of inorganic powders having different hardnesses in combination. Specifically, Mohs hardness 3 ~
It is preferable to use a 4.5 soft inorganic powder and a 5 to 9 Mohs hardness hard inorganic powder. Mohs hardness is 3-4.
By adding the soft inorganic powder of No. 5, the friction coefficient can be stabilized by repeated running. Further, with the hardness in this range, the sliding guide pole is not cut off. The average particle size of this inorganic powder is 30 to 50.
It is preferably in the range of nm. Mohs hardness is 3 ~
As the soft inorganic powder of 4.5, for example, calcium sulfate, calcium carbonate, calcium silicate, barium sulfate,
Mention may be made of magnesium carbonate, zinc carbonate, and zinc oxide. These can be used alone or in combination of two or more. Among these, calcium carbonate is particularly preferred.

The content of the soft inorganic powder in the back coat layer is 10 to 14 with respect to 100 parts by weight of carbon black.
It is preferably in the range of 0 parts by weight, more preferably 35 to 100 parts by weight. By adding a hard inorganic powder having a Mohs hardness of 5 to 9,
The strength of the back coat layer is enhanced, and the running durability is improved. When these inorganic powders are used together with carbon black or the above-mentioned soft inorganic powders, they are less deteriorated even in repeated sliding and form a strong backcoat layer. In addition, the addition of the inorganic powder provides an appropriate polishing force, and reduces the adhesion of shavings to the tape guide pole and the like. In particular, when used in combination with a soft inorganic powder (among others, calcium carbonate), the sliding characteristics with respect to a guide pole having a rough surface are improved, and the friction coefficient of the back coat layer can be stabilized. Hard inorganic powder has an average particle size of 80 to 250 nm.
(More preferably, 100 to 210 nm).

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 preferred. The content of the hard inorganic powder is usually 3 to 30 parts by weight, preferably 3 to 20 parts by weight, based on 100 parts by weight of carbon black. When the soft inorganic powder and the hard inorganic powder are used in combination in the back coat 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, particularly 3 or more). It is preferable to select and use a soft inorganic powder and a hard inorganic powder as follows. The back coat layer preferably contains two types of inorganic powders having different specific Mohs hardnesses each having the specific average particle size, and two types of carbon blacks each having the different average particle size. In particular, in this combination, it is preferable that calcium carbonate is contained as the soft inorganic powder. The back coat layer can contain a lubricant. The lubricant can be appropriately selected from the above-mentioned lubricants that can be used for the nonmagnetic layer or the magnetic layer. In the back coat layer, the lubricant is
It can be added usually in the range of 1 to 5 parts by weight based on 100 parts by weight of the binder.

[Non-magnetic flexible support] The non-magnetic flexible support used in the present invention includes polyesters such as polyethylene terephthalate and polyethylene naphthalate, polyolefins, cellulose triacetate, polycarbonate, polyamide, polyimide and polyamide. Known films such as imide, polysulfone, aramid, and aromatic polyamide 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.

In order to achieve the object of the present invention, the shape of the surface roughness of the non-magnetic support is freely controlled by the size and amount of the filler added to the support as required. Examples of these fillers include Ca,
In addition to oxides and carbonates such as Si and Ti, acryl-based organic powders and the like can be mentioned. Maximum support height SRmax
Is 1 μm or less, ten-point average roughness SRz is 0.5 μm or less,
The center plane peak height SRp is 0.5 μm or less, the center plane valley depth SRv is 0.5 μm or less, and the center plane area ratio SSr is 10%.
Not less than 90% and the average wavelength Sλa is not less than 5 μm and not more than 30%.
It is preferably 0 μm or less. In order to obtain desired electromagnetic conversion characteristics and durability, it is necessary to form fine projections on the surface of the support, and usually, a filler having an average particle diameter of 0.01 to 0.2 μm is used in a range of 0 to 20,000 particles / mm ² . Can be controlled by adding and dispersing to a resin forming a support. In this case, since coarse particles or agglomerated particles in the particle size distribution are usually present, there are coarse projections formed thereby. In the present invention, the number of protrusions of the support having a height of 0.273 μm or more is 100 / 100c.
m ² or less, more preferably 80 pieces / 100 cm ² or less, and even more preferably 50 pieces / 100 cm ² or less.

F-5 of non-magnetic support used in the present invention
The value is preferably 0.049 to 0.49 GPa (5 to 5 GPa).
0 kg / mm ² ), and the heat shrinkage of the support at 100 ° C. for 30 minutes is preferably 3% or less, more preferably 1.
The heat shrinkage at 5% or less, 80 ° C. and 30 minutes is preferably 1
%, More preferably 0.5% or less. The breaking strength is 0.049-0.98 GPa (5-100 kg / mm
² ), the elastic modulus is 0.98 to 19.6 GPa (100 to 2
000 kg / mm ² ) is preferred. Thermal expansion coefficient is 10
^-4 to 10 ^-8 / ° C, preferably 10 ^-5 to 10 ^-6 / ° C
It is appropriate that Humidity expansion coefficient is 10 ^-4 / RH
%, Preferably 10 ⁻⁵ / RH% or less. It is preferable that these thermal characteristics, dimensional characteristics, and mechanical strength characteristics are substantially equal to each other in the in-plane direction of the support with a difference of 10% or less.

[Method of Manufacturing Magnetic Recording Medium] The magnetic recording medium of the present invention can be manufactured by applying and drying a coating material for forming each layer. The step of producing the paint comprises at least a kneading step, a dispersing step, and a mixing step provided before and after these steps as necessary. Each step may be divided into two or more steps. All the raw materials such as the ferromagnetic powder, binder, carbon black, abrasive, antistatic agent, lubricant, and solvent used in the present invention may be added at the beginning or during any step. Further, individual raw materials may be added in two or more steps in a divided manner. For example, polyurethane may be divided and supplied in a kneading step, a dispersing step, and a mixing step for adjusting viscosity after dispersion.

The organic solvent used in the method for producing a magnetic recording medium of the present invention may be any ratio of ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, diisobutyl ketone, cyclohexanone, isophorone and tetrahydrofuran, methanol, ethanol and propanol. Alcohols such as butanol, isobutyl alcohol, isopropyl alcohol and methylcyclohexanol, esters such as methyl acetate, butyl acetate, isobutyl acetate, isopropyl acetate, ethyl lactate and glycol acetate, glycol dimethyl ether, glycol monoethyl ether and dioxane. Glycol ether type,
Aromatic hydrocarbons such as benzene, toluene, xylene, cresol, chlorobenzene, chlorinated hydrocarbons such as methylene chloride, ethylene chloride, carbon tetrachloride, chloroform, ethylene chlorohydrin, dichlorobenzene, N, N- Dimethylformamide, hexane and the like can be used. These organic solvents are not necessarily 100% pure, and may contain impurities such as isomers, unreacted products, by-products, decomposed products, oxides, and moisture in addition to the main components.
These impurities are preferably 30% or less, more preferably 10% or less. The type of the organic solvent used in the present invention is preferably the same for the magnetic layer and the non-magnetic layer.
The amount added may be changed. It is preferable to use a solvent having a high surface tension (such as cyclohexanone or dioxane) for the non-magnetic layer to increase the coating stability. Specifically, it is preferable that the arithmetic average value of the upper solvent composition does not fall below the arithmetic average value of the lower solvent composition. In order to improve the dispersibility, it is preferable that the polarity is somewhat strong, and it is preferable that the solvent composition contains 50% or more of a solvent having a dielectric constant of 15 or more. Further, the dissolution parameter is preferably from 8 to 11.

In order to manufacture the magnetic recording medium of the present invention, it is needless to say that a conventional known manufacturing technique can be used as a part of the process. However, in the kneading step, a strong kneading such as a continuous kneader or a pressure kneader is used. By using a material having a force, a magnetic recording medium having a high residual magnetic flux density (Br) can be obtained. 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)
The kneading treatment can be performed in a range of 15 to 500 parts by weight based on 100 parts by weight of the ferromagnetic powder. Details of these kneading processes are described in JP-A-1-106338 and JP-A-64-79274. When preparing the lower non-magnetic layer liquid, it is desirable to use a dispersion medium having a high specific gravity, and zirconia beads are preferable.

A coating solution for forming a nonmagnetic layer containing a nonmagnetic powder and a binder and a coating solution for forming a magnetic layer containing a ferromagnetic powder and a binder are coated on a nonmagnetic flexible support. A method in which a magnetic layer is formed on a non-magnetic flexible support simultaneously or sequentially so that a magnetic layer is formed thereon, and a smoothing process and a magnetic field orientation can be performed while the coated layer is in a wet state. .

The apparatus and method for applying the magnetic recording medium having the above-mentioned multilayer structure include, for example, the following method and apparatus. (1) First, a lower layer is applied by a gravure coating, roll coating, blade coating, extrusion coating device or the like which is generally used for applying a magnetic paint, and the lower layer is wet while the lower layer is in a wet state. JP-A-60-
The upper layer is coated by a support pressure type extrusion coating apparatus disclosed in Japanese Patent Application Laid-Open No. 238179/1990 and Japanese Patent Application Laid-Open No. 2-265672. (2) JP-A-63-88080, JP-A-2-17
No. 971 and Japanese Unexamined Patent Publication No. Hei 2-265672, the upper and lower layers are applied almost simultaneously by one coating head having two built-in coating liquid passage slits. (3) The upper and lower layers are coated almost simultaneously by an extrusion coating device with a backup roll disclosed in Japanese Patent Application Laid-Open No. 2-174965.

Incidentally, in order to prevent the electromagnetic conversion characteristics and the like of the magnetic recording medium from deteriorating due to the aggregation of the magnetic particles, Japanese Patent Application Laid-Open No.
It is desirable to apply a shear to the coating liquid inside the coating head by a method disclosed in Japanese Patent Application Laid-Open No. 95174 or Japanese Patent Application Laid-Open No. 1-236968. Further, it is appropriate that the viscosity of the coating liquid satisfies the numerical range disclosed in JP-A-3-8471. Further, the smoothing treatment can be performed, for example, by applying a stainless steel plate to the surface of the coating layer on the web. In addition, a method using a solid smoother as described in Japanese Patent Publication No. Sho 60-57387, a method in which a coating liquid is scraped off by a rod that is stationary or that rotates in a direction opposite to the web running direction and measured. Alternatively, a method may be employed in which a flexible sheet is brought into surface contact with the surface of the coating liquid film for smoothing. Also, 100 mT (1000
It is preferable to use a solenoid of G) or more and a cobalt magnet of 200 mT (2000 G) or more in the same polarity. When the present invention is applied to a disk medium, an orientation method for randomizing the orientation is required.

Further, a heat-resistant plastic roll such as epoxy, polyimide, polyamide, or polyimide amide can be used as the calendering roll. Further, the treatment can be performed between metal rolls. The processing temperature is preferably 70 ° C. or higher, more preferably 8 ° C.
Suitably, it is 0 ° C. or higher. The linear pressure is preferably 200 kg / cm, more preferably 300 kg / cm
It is appropriate that the above is true. The coefficient of friction of SUS420J between the magnetic layer surface and the opposite surface of the magnetic recording medium of the present invention is preferably 0.5 or less, more preferably 0.3 or less.
Hereinafter, the surface resistivity is preferably 10 ⁴ to 10 ¹² ohm / sq, the elastic modulus of the magnetic layer at 0.5% elongation is the running direction,
0.98 to 19.6 GPa (10 in the width direction)
0-2000 kg / mm ² ), and the breaking strength is preferably 0.
98 to 29.4 GPa (1 to 30 kg / cm ² ), and the elastic modulus of the magnetic recording medium is preferably 0.98 to 14.7 GPa (100 to 1500 kg / m) in both the running direction and the longitudinal direction.
m ² ), the residual elongation is preferably 0.5% or less, the heat shrinkage at any temperature of 100 ° C. or less is preferably 1% or less,
More preferably, it is suitably 0.5% or less, most preferably 0.1% or less. The glass transition temperature (the maximum point of the loss elastic modulus in dynamic viscoelasticity measurement measured at 110 Hz) of the magnetic layer is preferably from 50 ° C to 120 ° C, and that of the lower layer is preferably from 0 ° C to 100 ° C. The loss modulus is 1 × 10 ⁷ to 8 × 10 ⁸ N / cm ² (1 × 10 ⁸
８8 × 10 ⁹ dyn / cm ² ), and the loss tangent is preferably 0.2 or less. If the loss tangent is too large, adhesion failure is likely to occur.

The residual solvent contained in the magnetic layer is preferably 100 mg / m ² or less, more preferably 10 mg / m ^2.
Suitably, it is less than m ² . The porosity of the magnetic layer is preferably 30% by volume or less, more preferably 20% by volume or less, for both the lower layer and the magnetic layer. The porosity is preferably small to achieve high output,
Depending on the purpose, it may be better to secure a certain value.
For example, in a magnetic recording medium for data recording in which repetitive use is emphasized, a higher porosity is often preferable in running durability. The magnetic characteristics of the magnetic recording medium of the present invention are as follows.
When measured in Oe, the squareness ratio in the tape running direction is 0.7
It is suitably 0 or more, preferably 0.80 or more, and more preferably 0.90 or more. The squareness ratio in two directions perpendicular to the tape running direction is 8 which is the squareness ratio in the running direction.
It is preferably 0% or less. SFD of magnetic layer
(Ching Field Distribution) is preferably 0.6 or less.

Although the magnetic recording medium of the present invention has a non-magnetic layer and a magnetic layer, it is easily presumed that the physical properties of the non-magnetic layer and the magnetic layer can be changed according to the purpose. . For example, the elastic modulus of the magnetic layer is increased to improve running durability, and at the same time, the elastic modulus of the nonmagnetic layer is made lower than that of the magnetic layer to improve the contact of the magnetic recording medium with the head. What kind of physical properties are to be provided to each of the two or more magnetic layers can be referred to a known technique regarding the magnetic layer. For example, there are many inventions such as JP-B-37-2218 and JP-A-58-56228, in which the Hc of the magnetic layer is made higher than the Hc of the non-magnetic layer. Makes it possible to record even with a higher Hc magnetic layer.

[0061]

EXAMPLES Examples of the present invention will be shown below, and the present invention will be described in more detail. "Parts" described below are "parts by weight".
Is shown. [Preparation of magnetic paint] Magnetic paint 1 (for disk) barium ferrite magnetic powder 100 parts Plate diameter: 0.03 μm Plate ratio: 3 Hc: 195.8 kA / m (2460 Oe) Vinyl chloride copolymer 5 parts MR555 (Nihon Zeon) 3 parts UR8200 (manufactured by Toyobo) α-alumina 10 parts HIT55 (manufactured by Sumitomo Chemical) carbon black 1 part $ 55 (manufactured by Asahi Carbon Co.) Phenylphosphonic acid 2 parts butyl stearate 10 parts butoxyethyl steaer Rate 5 parts Isohexadecyl stearate 3 parts Stearic acid 2 parts Methyl ethyl ketone 125 parts Cyclohexanone 125 parts

Magnetic paint 2 (for tape) Barium ferrite magnetic powder 100 parts Plate diameter: 0.03 μm Plate ratio: 3 Hc: 195.8 kA / m (2460 Oe) Vinyl chloride copolymer 6 parts MR555 (manufactured by Zeon Corporation) Polyurethane resin 3 parts UR8200 (manufactured by Toyobo) α-alumina 2 parts HIT55 (manufactured by Sumitomo Chemical Co., Ltd.) Carbon black 5 parts $ 55 (manufactured by Asahi Carbon Co., Ltd.) Butyl stearate 1 part Stearic acid 2 parts Methyl ethyl ketone 125 parts Cyclohexanone 125 parts

[Preparation of Non-Magnetic Paint] Non-magnetic paint 1 (for disk) Non-magnetic powder TiO ₂ , crystalline rutile 80 parts Average primary particle diameter: 0.035 μm Specific surface area by BET method: 40 m ² / g pH: 7 TiO ₂ content: 90% or more DBP oil absorption: 27~38g / 100g surface treatment agent: Al ₂ O ₃ (manufactured by Columbia carbon Co.) (8 wt%) carbon black 20 parts CONDUCTEX Tex SC-U-vinyl copolymerization chloride 12 parts MR110 (manufactured by Zeon Corporation) polyurethane resin 5 parts UR8200 (manufactured by Toyobo Co., Ltd.) 4 parts phenylphosphonic acid 10 parts butyl stearate 10 parts butoxyethyl stearate 5 parts isohexadecyl stearate 2 parts stearic acid 3 parts methyl ethyl ketone / cyclohexanone (8/2 mixed solvent) 250 parts

Non-magnetic paint (for tape) Non-magnetic support TiO ₂ , crystalline rutile 80 parts Average primary particle diameter: 0.035 μm Specific surface area by BET method: 40 m ² / g pH: 7 TiO ₂ content: 90% Above DBP oil absorption: 27 to 38 g / 100 g Surface treatment agent: Al ₂ O ₃ (8% by weight) Carbon black 20 parts Conductex SC-U (manufactured by Columbia Carbon Co.) Vinyl chloride copolymer 12 parts MR110 (Zeon Corporation) Polyurethane resin 5 parts UR8200 (manufactured by Toyobo Co., Ltd.) Phenylphosphonic acid 4 parts Butyl stearate 1 part Stearic acid 3 parts Methyl ethyl ketone / cyclohexanone (8/2 mixed solvent) 250 parts

Manufacturing Method 1: Preparation of Discs Each of the above-mentioned magnetic paint 1 and non-magnetic paint 1 was kneaded with a kneader, and then dispersed using a sand mill. Next, 10 parts of polyisocyanate was added to the obtained dispersion for nonmagnetic layer and dispersion for magnetic layer, and 40 parts of cyclohexanone was further added to each.
Filtration using a filter having an average pore size of 1 μm,
A coating solution for forming a non-magnetic layer and a coating solution for forming a magnetic layer were each prepared. The obtained coating liquid for forming a non-magnetic layer has a thickness of 2.2 μm after drying, and further immediately thereafter, the coating liquid for forming a magnetic layer has a thickness of 0.2 μm after drying. Fifteen
Simultaneous multi-layer coating was performed on a polyethylene terephthalate support having a thickness of 62 μm and a center plane average surface roughness of 11 nm so that the thickness became 62 μm. Thereafter, while both layers are still wet, they are passed through an AC magnetic field generator having a frequency of 50 Hz and a magnetic field strength of 25 mT (250 gauss) or a frequency of 50 Hz and a magnetic field strength of 12 mT (120 gauss). After the treatment and drying, the treatment was carried out at a temperature of 90 ° C. and a linear pressure of 300 kg / cm using a seven-stage calender, and punched into 3.5 inches to obtain a disk medium.

Production Method 2: Preparation of Disc A disk medium was obtained in the same manner as in Production Method 1, except that the coating solution for forming a nonmagnetic layer was applied so that the thickness after drying became 1.7 μm.

Production Method 3: Preparation of a Disc A base (polyethylene terephthalate having a thickness of 62 μm and a center line surface roughness of 11 nm) which suppresses agglomeration of a filler forming the surface roughness of the support as compared with the support used in Production Method 1 The coating liquid for forming the non-magnetic layer has a thickness of 1% using a support (the aggregation of the filler is suppressed and the coarse protrusions are reduced, but the center line surface roughness is not affected). 0.7μ
m, except that it was applied to obtain m.
I got a disk medium.

Production Method 4: Preparation of Disc A coating solution for forming a non-magnetic layer was applied to a thickness of 1.7 μm after drying, punched out to 3.5 inches, and then subjected to burnishing. Was performed in the same manner as in Production Method 1 to obtain a disk medium.

Production method 5: Preparation of disk A disk medium was obtained in the same manner as in Production method 1, except that the dispersion time of the sand mill was reduced to half.

Production Method 6: Preparation of Computer Tape Each of the above-mentioned magnetic paint 2 and non-magnetic paint 2 was kneaded with a kneader, and then dispersed using a sand mill. Next, 2.5 parts of polyisocyanate was added to the obtained dispersion for nonmagnetic layer and 3 parts to the dispersion for magnetic layer,
Furthermore, 40 parts of cyclohexanone was added to each, and 1 μm
The mixture was filtered using a filter having an average pore size of 1 to prepare a coating solution for forming a nonmagnetic layer and a coating solution for forming a magnetic layer. The obtained coating liquid for forming a non-magnetic layer was further coated thereon immediately after drying so that the thickness after drying became 1.7 μm.
Simultaneous multilayer coating was performed on a PET support having a thickness of 6 μm and an average surface roughness of 8 nm so that the thickness of the coating liquid for forming a magnetic layer after drying was 0.15 μm. Then, while both layers are still wet, 0.6 T (6000 G)
Cobalt magnet with magnetic force of 0.6T (6000G)
Oriented by a solenoid having a magnetic force of After drying, treatment is performed at a temperature of 85 ° C. at 200 m / min with a seven-stage calender composed of only metal rolls, and then a 0.5 μm-thick back coat layer (carbon black (average particle size: 17 nm) 100 Parts, 80 parts of calcium carbonate (average particle size: 40 nm) and 5 parts of α-alumina (average particle size: 200 nm) were dispersed in 110 parts of nitrocellulose resin, 16 parts of polyurethane resin, and 54 parts of polyisocyanate. Was applied.
Slit to a width of 3.8 mm, send out slit products,
A non-woven fabric and a razor blade were attached to a device having a winding device so as to press against the magnetic surface, and the magnetic layer was cleaned by a tape cleaning device to obtain a tape sample.

Production method 7: Preparation of computer tape A tape sample was obtained in the same manner as in Production method 6, except that the dispersion time of the sand mill was reduced to 1/2.

Production method 8: Preparation of computer tape A tape sample was obtained in the same manner as in Production method 6, except that the support was changed to a PEN support having a thickness of 6 μm and a center plane average surface roughness of 9 nm.

Preparation Method 9: Preparation of Computer Tape A tape sample was obtained in the same manner as in Preparation Method 6, except that tape cleaning was not performed.

Measurement method (1) Magnetic characteristics (Hc, Bm, SQ) Using a vibration sample type magnetometer (manufactured by Toei Kogyo Co., Ltd.), Hm 79
It was measured at 6 kA / m (10 kOe). (2) TA (thermal asperity) count disk Using a spin stand SS60 manufactured by Kyodo Denshi and RWA-1601 manufactured by GUZI, a SAL-MR head (W
RITE WIDTH: 2.4 μm, GAP: 0.4 μm
m, READ WIDTH: 1.9 μm, GAP: 0.
24 μm, ABS Negative pressur
e) using a linear recording density of 100 KFCI and a linear velocity of 6.
The measurement was performed under the condition of 3 m / sec. When ten discs were prepared and the reproduction output was Ep and the TA peak output was H for both sides, the number of TA peaks satisfying H / Ep> 2 was determined. Tape A fixed MR head (8 tracks) was attached to the tape running system, and the tape was run at a relative feed speed of 1 m / s. 60m tape
Five lengths were evaluated, and when the reproduction output when recording and reproducing at λ = 1 μm was Ep and the TA peak output was H, H / E
The number of samples satisfying p> 2 was determined, and those less than 5 were evaluated as good. (3) Counting the number of protrusions on the medium surface Using a differential interference microscope, the medium surface is 30 cm × 30 cm.
Observe and find protrusions and mark them. Then, W
YKO Optical Profiler HD-2000
Using an objective lens: 50 times, an intermediate lens: 0.5
The height and width of the projections were measured under the conditions of × 2, measurement range: 242 μm × 184 μm, and the number of projections having a diameter of 2 to 100 μm and a height of 100 nm or more was counted.

[0075]

[Table 1]

[0076]

[Table 2]

The diameter existing on the surface of the magnetic layer is 2 to 100 μm.
m, the number of protrusions with a height of 100 nm or more is 10/900 cm
^In Examples 1 to 4, which is ² , the number of TAs is small,
The occurrence of TA was suppressed. On the other hand, in the magnetic recording media of Comparative Examples 1 to 5 having the number of protrusions exceeding the range of the present invention, the number of TAs was large as compared with the examples, and TA was remarkably generated.

[0078]

According to the present invention, in combination with an MR head, it is possible to obtain a magnetic recording medium having a low TA and excellent high density characteristics.

Claims (1)

[Claims] 1. A magnetic recording medium comprising a nonmagnetic support and a substantially nonmagnetic lower layer and a magnetic layer formed by dispersing hexagonal ferrite powder in a binder in this order. Has a diameter of 2 to 100 μm and a height of 1
A magnetic recording medium comprising 10 projections of not less than 00 nm / less than 900 cm ² .