JPH10116417A - Disk type magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably provide a disk type magnetic recording medium having enough low noise, a large short wavelength output and a high C/N, which enables a high density recording which is not realized in conventional medium. SOLUTION: In this magnetic recording medium having one or more magnetic layers containing a ferromagnetic material dispersed in a binder on at least one surface of a nonmagnetic supporting body, the ferromagnetic material in the uppermost layer is a hexagonal ferrite, and it is made to be a random orientation disk having 0.5×10<-17> to 1.5×10<-17> magnetization inversion volume measured in the plane of the uppermost magnetic layer and >=0.60 coercive squareness ratio S*<1> , or, a perpendicular orientation disk having >=0.9 coercive force squareness ratio S*<2> measured in the perpendicular direction of the uppermost magnetic layer with demagnetizing field correction and >=0.75 squareness ratio SQp in the perpendicular direction with demagnetizing field correction.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium for high-density recording having one or more magnetic layers or non-magnetic layers, and including hexagonal ferrite particles as a ferromagnetic material on the uppermost layer. .

[0002]

2. Description of the Related Art In the field of magnetic disks, 2 MB MF-2HD floppy disks using Co-modified iron oxide have been standardly mounted on personal computers. However, in today's rapidly increasing data capacity, the capacity cannot be said to be sufficient, and it has been desired to increase the capacity of floppy disks.

Conventionally, video tapes, audio tapes,
Magnetic recording media such as computer tapes and magnetic disks include ferromagnetic iron oxide, Co-modified ferromagnetic iron oxide, Cr
A magnetic layer in which O ₂ , ferromagnetic metal powder, hexagonal ferrite or the like is dispersed in a binder is applied to a nonmagnetic support, and is widely used. A 10 MB MF-2T is used as a large-capacity disk using ferromagnetic metal fine powder having excellent high-density recording characteristics.
D, 21MB MF-2SD, 100MB ZIP, or 4MB MF-2ED, 21MB floptical, etc. as a large capacity disk using hexagonal ferrite, but the capacity and performance are not sufficient. . Under such circumstances, many attempts have been made to improve the high-density recording characteristics. An example is shown below.

In order to improve the characteristics of a disk-shaped magnetic recording medium, JP-A-64-84418 discloses the use of a vinyl chloride resin having an acidic group, an epoxy group and a hydroxyl group.
In Japanese Patent Publication No. 3-12374, a metal fine powder having a Hc of 1000 Oe or more and a specific surface area of 25 to 70 m ² / g is used.
It has been proposed to include an abrasive.

[0005] In the field of magnetic recording, there is a demand for a reduction in noise as well as an increase in short-wavelength output. In particular, in the field of digital recording, this is an essential characteristic for reducing the error rate. Many known techniques have been disclosed for reducing noise of a magnetic recording medium using hexagonal ferrite. JP-A-64-89022 discloses that the saturation magnetization is 60 emu / g or more, the specific surface area by the BET method is 25 to 70 m ² / g, the average particle diameter is 0.01 to 0.2 μm, and the coercive force is 400 to 2
000 Oe and the polar group has at least 1 × 10 ⁻⁵ e
A magnetic recording medium using a binder containing q / g is disclosed, which has improved reproduction output, high C / N, and improved running durability.

Japanese Patent Publication No. 5-40370 discloses that 10 to 40 parts by weight of a resin binder is used for 100 parts by weight of a magnetic powder having a specific surface area of 23 to 45 m ² / g and a coercive force of 400 to 2000 Oe. The present invention discloses a dispersed magnetic recording medium and provides a magnetic recording medium for high-density recording with low noise and excellent orientation. As is known in the prior art, it is most effective to reduce the noise of a magnetic recording medium by making the ferromagnetic powder finer, and the particle size of the ferromagnetic material used in the above-described prior art is also described. ing.

A known example of improving the characteristics of a magnetic recording medium by treating the surface of hexagonal ferrite particles is Japanese Patent Publication No. Sho 62
No. -50890 discloses an oxide or hydroxide of an alkaline metal selected from Ca, Mg, Ba, Sr, Al and Zn. Japanese Patent Publication No. 62-50886
JP-A-57-1986 discloses a magnetic recording medium in which hexagonal ferrite particles are coated with a vinyl monomer having a hydrophilic group on the surface and a vinyl monomer having a lipophilic group having 4 or more carbon atoms.
06 shows a magnetic recording medium using a ferromagnetic material treated with an Al.Zr compound.

The above prior arts are all effective in improving electromagnetic conversion characteristics or practical characteristics. However, high output and low noise can be obtained by using fine-particle hexagonal ferrite, for example, having an average particle diameter of 20 to 70 nm. This is an insufficient technique for stably obtaining a magnetic recording medium capable of achieving a high recording density, and it has been desired to find conditions for stably obtaining such a magnetic recording medium.

[0009]

SUMMARY OF THE INVENTION The present invention stably provides a disk-shaped magnetic recording medium having sufficiently low noise, high short-wavelength output, high C / N, and capable of high-density recording, which has not been achieved conventionally. It is intended to provide.

[0010]

As a result of studying the C / N improvement of a magnetic recording medium, hexagonal ferrite having a large coercive force as much as possible for recording with a short wavelength output is excellent. In studying noise reduction, it is essential that the hexagonal ferrite particle size is small. However, as the particle size becomes smaller, the output becomes lower at a certain particle size or less, and the C / N becomes rather lower. The present inventors have conducted studies using a fine particle magnetic substance, and reached the present invention.

That is, the present invention has the following constitution. (1) In a magnetic recording medium having at least one magnetic layer formed by dispersing a ferromagnetic material in a binder on at least one side of a nonmagnetic support, the ferromagnetic material contained in the uppermost layer is hexagonal Based ferrite having a magnetization reversal volume of 0.5 × 10 ^{−17 to} 1.5 × 10 ⁻¹⁷ m measured in the plane of the uppermost magnetic layer.
1 and the coercive force squareness ratio S ^{* 1} measured in the plane of the uppermost magnetic layer is 0.60 or more. (2) In a magnetic recording medium having at least one magnetic layer formed by dispersing a ferromagnetic material in a binder on at least one side of a nonmagnetic support, the ferromagnetic material contained in the uppermost layer is hexagonal Based ferrite having a magnetization reversal volume of 0.5 × 10 ^{−17 to} 1.5 × 10 ⁻¹⁷ m measured in the plane of the uppermost magnetic layer.
l, the coercive force squareness ratio S ^{* 2} measured in the vertical direction of the uppermost magnetic layer is 0.9 or more in demagnetizing field correction value, and the perpendicular direction squareness ratio SQp corrected in demagnetizing field is 0.75 or more. A vertically oriented disk-shaped magnetic recording medium characterized by the following. (3) A non-magnetic layer in which non-magnetic powder is dispersed is formed between the magnetic layer and the non-magnetic support, and the thickness of the magnetic layer is 0.15 to 0.35 μm. Or (2)
Disk-shaped magnetic recording medium.

[0012] The random-oriented disk-shaped magnetic recording medium or the perpendicularly-oriented disk-shaped magnetic recording medium of the present invention (hereinafter referred to simply as "magnetic recording medium" or "medium"
It is not clear why the magnetic recording medium having a specific magnetization reversal volume (common to both) and S ^{* 1} , or S ^{* 2} and SQp exhibits excellent electromagnetic conversion characteristics, but the following is considered. ing.

Although fine particle magnetic material is used to reduce noise, when fine particles are used, the output sharply drops below a certain particle size, and the C / N decreases rather with the use of fine particles. A comparison between a medium having a low C / N ratio and a medium having a high C / N ratio shows that there is a significant difference in the coercive force squareness ratio S ^* (both S ^{* 1} and S ^{* 2} ). Was. The coercive force squareness ratio S ^* is a characteristic value representing the slope of the magnetic hysteresis curve, and it is considered that the distribution of Hc is sharper when S ^* is larger. It is considered that the distribution of Hc becomes easier when the particles are made finer, and the components that do not contribute to recording increase, resulting in a lower output. In a medium having a large S ^* and a sharp Hc distribution, it is considered that most of the magnetic components contribute to the recording and the output becomes high. In addition, although the use of a fine-particle magnetic material is indispensable, as a result of the study, there has been an example in which the noise is not necessarily reduced by using the fine particles, but rather increases.

Since the magnetic material is hexagonal plate-like particles that are hexagonal ferrite, it is likely that a magnetically strong aggregation state called stacking occurs, and noise may increase even when fine particles are used. Further, it is considered that the noise is not improved unless the individual magnetic units as measured by the magnetization reversal volume are small. However, it has been found that noise can be reduced, output can be improved, and C / N can be improved by adjusting the magnetization reversal volume, S ^* , and SQp within the range of the present invention even in the case of a fine particle magnetic material.

Next, preferred embodiments of the present invention will be described. The magnetic recording medium of the present invention comprises at least one magnetic layer, provided that a magnetic layer containing hexagonal ferrite is provided on the nonmagnetic support as the uppermost layer, and only one of the uppermost layers is provided. However, it is preferable to provide a non-magnetic layer containing a binder and a non-magnetic powder between the support and the support because the surface properties are improved and the upper layer can be easily thinned.

The particle size of the hexagonal ferrite magnetic material used for the random orientation medium and the perpendicular orientation medium of the present invention is preferably such that the plate diameter is 20 to 60 nm, and 25 to 55 nm.
Is more preferred. The plate ratio (plate diameter / plate thickness) is preferably 3 to 5. When the plate diameter exceeds 60 nm, the effect of the present invention is not obtained.
The noise will eventually increase. Even if it is less than 20 nm, there is no effect of the present invention, and it is considered that a method more devised than the present method is required for such ultrafine particles. The most effective particle size in the present invention is a plate diameter of 25 to 40 nm.

The magnetization reversal volume of the magnetic layer of the randomly oriented medium and the perpendicularly oriented medium of the present invention is 0.5 × 10 ⁻¹⁷ to 1.0.
5 × 10 ^-17 ml is required. 0.5 × 10 ^-17 ml
Less than was not obtained in the study of the present invention. 1.5 × 10
^{If it is} larger than ^-17 ml, the noise level intended by the present invention is not reached. The magnetization reversal volume V can be obtained from the following equation.

Hc = 2K / Ms ｛1-[(kT / KV)
ln (At / 0.693)] ^1/2 ｝ Hc: coercive force measured in the magnetic layer plane K: anisotropic constant Ms: saturation magnetization k: Boltzmann constant T: absolute temperature V: magnetization reversal volume A: spin age Difference frequency t: magnetic field reversal time In a randomly oriented medium, the squareness ratio (hereinafter also referred to as “SQ”) measured in the plane of the magnetic layer is about 0.45 to 0.55. In the case of hexagonal ferrite, it is likely to be three-dimensional random, and in the case of three-dimensional random orientation, the theoretical SQ is 0.1.
50. Although it is considered to be affected by the particle shape, the medium manufacturing process, and the like, the SQ changes even without any particular orientation treatment. SQ
Is less than 0.45, the vertical component increases and the output increases, but the reproduced waveform after recording becomes a dipulse shape, which is not preferable depending on the application. When the in-plane SQ exceeds 0.55, the modulation deteriorates.

In the specification of the present application, "measurement in the magnetic layer plane" means "measurement in a direction parallel to the magnetic layer film plane". The coercive force squareness ratio S ^{* 1} of the randomly oriented medium is 0.60 or more. If it is less than 0.6, the output will be low.
Preferably it is 0.7 or more. S ^{* 2} of the perpendicularly oriented medium is 0.9 or more as a demagnetizing field correction value. If it is less than 0.9, the output will be low. Preferably it is 0.95 or more.

The squareness ratio SQp in the perpendicular direction of the perpendicularly-oriented medium, which has been demagnetized, is measured from the direction perpendicular to the film surface of the magnetic layer, and is 0.75 or more. If it is less than 0.75, the output is low as a vertical alignment medium, and there is no merit of vertical alignment. Preferably it is 0.85 or more. [Description of Hexagonal Ferrite Fine Powder] As the hexagonal ferrite contained in the uppermost layer of the present invention, there are barium ferrite, strontium ferrite, lead ferrite, calcium ferrite substitution products, Co substitution products and the like.
Specific examples include magnetoplumbite-type barium ferrite and strontium ferrite, magnetoplumbite-type ferrite whose particle surface is coated with spinel, and magneto-plumbite-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, Sb, Te, Ba, Ta, W, Re, Au, H
g, Pb, Bi, La, Ce, Pr, Nd, P, Co,
It may contain atoms such as Mn, Zn, Ni, Sr, B, Ge, and Nb. Generally, Co-Ti, Co-Ti
-Zr, Co-Ti-Zn, Ni-Ti-Zn, Nb-
A substance to which an element such as Zn—Co, Sb—Zn—Co, or Nb—Zn is added can be used. Some raw materials and production methods contain specific impurities.

The specific surface area of the hexagonal ferrite particles measured by the BET method is 30 to 90 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 100-350 °. 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 plate diameter, σ / average plate diameter = 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 can be made up to about 500 Oe to 5000 Oe. A higher Hc is advantageous for high density recording,
Limited by the capabilities of the recording head. Usually from 800 Oe to 40
It is about 00 Oe, preferably 1500 Oe or more and 35
It is not more than 00 Oe. When the saturation magnetization σ _{S of the} head exceeds 1.4 Tesla, it is preferable to set it to 2000 Oe or more. Hc can be controlled by particle size (plate diameter / plate thickness), kind and amount of contained element, substitution site of element, particle generation reaction condition and the like. The saturation magnetization _s is from 40 emu / g to 80 emu / g. σ _S is preferably higher, but tends to be smaller as the particles become finer. It is well known to combine spinel ferrite with magnetoplumbite ferrite in order to improve σ _S , and to select the type of element contained and the amount to be added. It is also possible to use W-type hexagonal ferrite. When dispersing the magnetic substance, the surface of the magnetic substance particles is treated with a substance suitable for the dispersion medium and the binder. 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 binder, but about 6 to 10 is selected from the chemical stability and storage stability of the medium. Water contained in the magnetic material also affects dispersion. There is an optimum value depending on the dispersion medium and the binder, but usually 0.01 to 2.0% is selected.

The method for producing hexagonal ferrite is, for example, as follows, but the present invention is not limited to the method. Barium oxide / iron oxide / metal oxide replacing iron and boron oxide etc. as a glass-forming substance were mixed to a desired ferrite composition, melted, quenched to form an amorphous body, and then re-heated. Thereafter, the glass crystallization method of obtaining barium ferrite crystal powder by washing and pulverizing. A hydrothermal reaction method in which a barium ferrite composition metal salt solution is neutralized with an alkali to remove by-products, heated in a liquid phase at 100 ° C. or higher, washed, dried, and pulverized to obtain barium ferrite crystal powder. A coprecipitation method in which a barium ferrite composition metal salt solution is neutralized with an alkali to remove by-products, dried, treated at 1100 ° C. or lower, and pulverized to obtain barium ferrite crystal powder. [Description of Non-Magnetic Layer] In the present invention, when a non-magnetic layer is provided between the non-magnetic support and the magnetic layer, the non-magnetic layer (hereinafter, also referred to as “lower layer”) basically comprises a binder and a non-magnetic layer. Consists of powder. Hereinafter, the details of the nonmagnetic layer will be described. The main component of the non-magnetic powder used in the non-magnetic layer of the present invention is a non-magnetic inorganic powder. As non-magnetic powder,
Although carbon black is also included, it is included in a different category from nonmagnetic inorganic powder. The nonmagnetic inorganic powder can be selected from, for example, inorganic compounds such as metal oxides, metal carbonates, metal sulfates, metal nitrides, metal carbides, and metal sulfides. Examples of the inorganic compound include α-alumina, β-alumina, γ-alumina, and θ-alumina having an α conversion of 90% or more.
Alumina, silicon carbide, chromium oxide, cerium oxide, α
-Iron oxide, goethite, corundum, silicon nitride, titanium carbide, titanium oxide, silicon dioxide, tin oxide, magnesium oxide, tungsten oxide, zirconium oxide,
Boron nitride, zinc oxide, calcium carbonate, calcium sulfate, barium sulfate, molybdenum disulfide and the like are used alone or in combination. Particularly preferred are titanium dioxide, zinc oxide, iron oxide and barium sulfate because of their small particle size distribution and many means for imparting functions, and more preferred are titanium dioxide and α-iron oxide. The particle size of these non-magnetic inorganic powders is preferably from 0.005 to 2 μm, but if necessary, non-magnetic inorganic powders having different particle sizes may be combined, or even a single non-magnetic inorganic powder may have a similar particle size distribution. It can also be effective. Particularly preferably, the particle size of the nonmagnetic inorganic powder is 0.01 μm.
m to 0.2 μm. In particular, when the nonmagnetic inorganic powder is a granular metal oxide, the average particle size is preferably 0.08 μm or less, and when the nonmagnetic inorganic powder is an acicular metal oxide, the major axis length is 0.1 μm.
It is preferably 3 μm or less. Tap density is 0.05-2g / m
l, preferably 0.2-1.5 g / ml. The water content of the nonmagnetic inorganic powder is 0.1 to 5% by weight, preferably 0.2 to 5% by weight.
It is 3% by weight, more preferably 0.3 to 1.5% by weight. The pH of the nonmagnetic inorganic powder is from 2 to 11, and the pH is particularly preferably from 5.5 to 10. The specific surface area of the nonmagnetic inorganic powder is 1 to 100 m ² / g, preferably 5 to 80 m ² / g, more preferably 10 to 70 m ² / g. The crystallite size of the nonmagnetic inorganic powder is preferably 0.004 μm to 1 μm,
0.04 μm to 0.1 μm is more preferable. Oil absorption using DBP (dibutyl phthalate) is 5-100ml / 100
g, preferably 10-80 ml / 100 g, more preferably 2
It is 0 to 60 ml / 100 g. The specific gravity is 1 to 12, preferably 3 to 6. The shape may be any of a needle shape, a spherical shape, a polyhedral shape, and a plate shape.

It is preferable that the ignition loss is 20% by weight or less, and it is considered that it is most preferable that there is no ignition loss. The Mohs hardness of the non-magnetic inorganic powder used in the present invention is 4
The number is preferably 10 or less. The roughness factor of the surface of these powders is preferably 0.8 to 1.5, and more preferably 0.9 to 1.2.
The adsorption amount of SA (stearic acid) of the nonmagnetic inorganic powder is 1-2.
It is 0 μmol / m ² , preferably ² to 15 μmol / m ² , more preferably 3 to 8 μmol / m ² . 25 of non-magnetic inorganic powder
The heat of wetting water at ℃ the 200erg / cm ² ~600erg / cm ²
Is preferably in the range of Further, a solvent having a range of the heat of wetting can be used. Preferably, the pH is between 3 and 6. Water-soluble Na of non-magnetic inorganic powder
Is 0 to 150 ppm, and water-soluble Ca is 0 to 50 ppm.

On the surface of these nonmagnetic inorganic powders, Al_Two
O_Three, SiO_Two, TiO_Two, ZrO _Two, SnO_Two, Sb
_TwoO_Three, ZnO, Y_TwoO_ThreeSurface treatment is preferred
No. Particularly preferred for dispersibility is Al_TwoO_Three, SiO_Two,
TiO_Two, ZrO_TwoHowever, more preferred is Al_Two
O_Three, SiO_Two, ZrO_TwoIt is. These are combinations
Or may be used alone. Ma
Further, a surface treatment layer coprecipitated according to the purpose may be used.
First, after treating with alumina, the surface layer is treated with silica.
And vice versa.
The surface treatment layer may be a porous layer according to the purpose.
Nonetheless, it is generally preferred that it be homogeneous and dense.

Specific examples of the non-magnetic inorganic 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, and α manufactured by Toda Kogyo.
Hematite DPN-250, DPN-250BX, DP
N-245, DPN-270BX, DBN-SA1, D
BN-SA3, Titanium oxide TTO-51B manufactured by Ishihara Sangyo,
TTO-55A, TTO-55B, TTO-55C, T
TO-55S, TTO-55D, SN-100, α hematite E270, E271, E300, E303, titanium oxide STT-4D, STT-30D, S manufactured by Titanium Industry
TT-30, STT-65C, α-hematite α-40,
MT-100S, MT-100T, MT-15 manufactured by Teika
0W, MT-500B, MT-600B, MT-100
F, MT-500HD, Sakai Chemical FINEX-25, B
F-1, BF-10, BF-20, ST-M, Dowa Mining DEFIC-Y, DEFIC-R, Nippon Aerosil AS2BM, TiO2P25, Ube Industries 100A, 5
00A, and those obtained by firing the same.

Particularly preferred non-magnetic inorganic powders are titanium dioxide and α-iron oxide. α-Iron oxide (hematite) is carried out under the following conditions. That is, the α-Fe ₂ O ₃ particle powder in the present invention is prepared by adding a suspension containing a ferrous hydroxide colloid obtained by adding an equivalent amount or more of an alkali hydroxide aqueous solution to a normal ferrous aqueous solution at a pH of 11 or more. 80
A method of generating needle-like goethite particles by performing an oxidation reaction by passing an oxygen-containing gas at a temperature of not more than ℃, a suspension containing FeCO ₃ obtained by reacting an aqueous ferrous salt solution and an aqueous alkali carbonate solution A method of producing spindle-shaped goethite particles by carrying out an oxidation reaction by passing an oxygen-containing gas through, obtained by adding an aqueous solution of an alkali hydroxide or an alkali carbonate in an equal amount or less to an aqueous ferrous salt solution. An oxygen-containing gas is passed through an aqueous ferrous salt solution containing ferrous hydroxide colloid to cause an oxidation reaction to generate acicular goethite core particles, and then the ferrous salt containing the acicular goethite core particles in aqueous solution, after the addition of more aqueous alkali hydroxide solution equivalent amount with respect to Fe ²⁺ in said ferrous salt aqueous solution, a method by passing an oxygen-containing gas to grow the acicular goethite nucleus particles, By passing an oxygen-containing gas through a ferrous salt aqueous solution containing a ferrous hydroxide colloid obtained by adding an aqueous solution of an alkali hydroxide or an alkali carbonate less than the same amount as the aqueous solution of ferrous iron and an oxidation reaction, Acicular goethite nucleus particles are generated, and then acicular goethite particles obtained by a method of growing the acicular goethite nucleus particles in an acidic to neutral region are used as precursor particles.

It is to be noted that Ni, Zn, and Ni, which are usually added to improve the properties of the particle powder during the reaction for forming goethite particles, are used.
There is no problem even if different elements such as P and Si are added.
Needle-like goethite particles, which are precursor particles, are prepared at 200-500.
Dehydrate in the temperature range of ℃, or if necessary, add
Annealing is performed by heat treatment in a temperature range of -800 ° C to obtain acicular α-Fe ₂ O ₃ particles. Note that P, Si, B, Z are added to the surface of the acicular goethite particles to be dehydrated or annealed.
There is no problem even if sintering inhibitors such as r and Sb are attached.
Annealing by heat treatment in a temperature range of 350 to 800 ° C. is performed by annealing pores formed on the particle surface of the acicular α-Fe ₂ O ₃ particles obtained by dehydration, so that the extreme surface of the particles is formed. This is because it is preferable that the pores are closed by melting to form a smooth surface.

The α-Fe ₂ O ₃ used in the present invention
The particle powder is obtained by dispersing needle-like α-Fe ₂ O ₃ particles obtained by dehydration or annealing in an aqueous solution to form a suspension,
An α-Fe ₂ O ₃ was added by adding an Al compound and adjusting the pH.
After coating the additive compound on the particle surface of the particles, filtration,
It can be obtained by washing with water, drying, pulverizing, and further performing deaeration / consolidation as required. As the Al compound to be used, aluminum salts such as aluminum acetate, aluminum sulfate, aluminum chloride and aluminum nitrate and alkali aluminates such as sodium aluminate can be used. In this case, the addition amount of the Al compound is 0.01 to 50% by weight in terms of Al with respect to the α-Fe ₂ O ₃ particle powder. 0.0
When the amount is less than 1% by weight, the dispersion in the binder resin is insufficient, and when the amount exceeds 50% by weight, Al compounds floating on the particle surface interact with each other, which is not preferable. In the lower non-magnetic inorganic powder of the present invention, including a Si compound together with an Al compound,
The coating may be performed using one or more compounds selected from P, Ti, Mn, Ni, Zn, Zr, Sn, and Sb. The amount of each of these compounds used together with the Al compound is in the range of 0.01 to 50% by weight based on the α-Fe ₂ O ₃ particle powder. If it is less than 0.01% by weight, there is almost no effect of improving dispersibility by addition, and if it is more than 50% by weight, compounds floating on the surfaces other than the particle surface interact with each other, which is not preferable.

The method for producing titanium dioxide is as follows. The methods for producing these titanium oxides are mainly a sulfuric acid method and a chlorine method. In the sulfuric acid method, a source ore of illuminite is digested with sulfuric acid, and Ti, Fe, and the like are extracted as sulfates. Iron sulfate is removed by crystallization separation, and the remaining titanyl sulfate solution is filtered and purified, and then thermally hydrolyzed to precipitate hydrous titanium oxide. After filtration and washing, impurities are washed and removed, a particle size regulator and the like are added, and the mixture is calcined at 80 to 1000 ° C. to obtain crude titanium oxide. Rutile type and anatase type are classified according to the type of nucleating agent added at the time of hydrolysis. The crude titanium oxide is prepared by pulverizing, sizing and surface treatment. Natural or synthetic rutile is used as the raw ore in the chlorine method. Ore is chlorinated in high-temperature reduction state, Ti
Fe becomes FeCl _{2 in} iCl ₄ , and iron oxide which has become solid by cooling is separated from liquid TiCl ₄ . The obtained crude TiCl ₄ is purified by rectification, then a nucleating agent is added, and reacted with oxygen instantaneously at a temperature of 1000 ° C. or more,
Obtain crude titanium oxide. The finishing method for imparting pigmentary properties to the crude titanium oxide produced in this oxidative decomposition step is the same as the sulfuric acid method.

In the surface treatment, after the above-mentioned titanium oxide material is dry-pulverized, water and a dispersant are added thereto, and wet-pulverization and centrifugal separation are performed to classify coarse particles. Thereafter, the fine slurry is transferred to a surface treatment tank, where the metal hydroxide is coated on the surface. First, a predetermined amount of Al, Si, Ti, Zr, Sb, S
an aqueous solution of a salt such as n or Zn, and an acid for neutralizing the solution;
Alternatively, the surface of the titanium oxide particles is coated with a hydrated oxide by adding an alkali. Water-soluble salts produced as by-products are removed by decantation, filtration and washing, and finally the slurry is adjusted in pH and filtered, and washed with pure water. The washed cake is dried with a spray drier or a band drier. Finally, the dried product is pulverized by a jet mill into a product.

In addition, it is also possible to apply Al and Si surface treatment by passing steam of AlCl ₃ and SiCl ₄ into the titanium oxide powder and then flowing steam into the titanium oxide powder. For other pigment preparation methods, see GDParfitt and KSW S
ing ”Characterization of Powder Surfaces” Academi
c Press, 1976. By mixing carbon black in the non-magnetic layer, it is possible to lower the surface electric resistance Rs, which is a known effect, to reduce the light transmittance, and to obtain a desired micro Vickers hardness. In addition, it is possible to bring about the effect of storing the lubricant by including carbon black in the lower layer.
Examples of carbon black include furnace black for rubber, thermal black for rubber, black for color, acetylene black, and the like. The following characteristics of the carbon black in the lower layer should be optimized depending on the desired effect, and the combined effect may provide more effects.

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 20-400ml / 100g, preferably 30
~ 200ml / 100g. The particle size of carbon black is 5 nm to 80 nm, preferably 10 to 50 nm, and more preferably 10 to 40 nm. Carbon black p
H is preferably 2 to 10, the water content is preferably 0.1 to 10%, and the tap density is preferably 0.1 to 1 g / ml. Car used in the present invention
A specific example of Bon Black is Cabot 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 manufactured by Columbian Carbon Co., Ltd.
Raven 8800,8000,7000,575
0,5250,3500,2100,2000,180
0, 1500, 1255, 1250, and Ketjen Black EC manufactured by Akzo Corporation. Carbon black may be used after being surface-treated with a dispersant or the like or grafted with a resin, or may be used after a part of the surface is graphitized. The carbon black may be dispersed with a binder before adding the carbon black to the paint. These carbon blacks are contained in an amount not exceeding 50% by weight with respect to the above-mentioned nonmagnetic inorganic powder, ie, 4% of the total weight of the nonmagnetic layer.
It can be used within a range not exceeding 0%. 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).

An organic powder may 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.

A binder resin, a lubricant, a dispersant,
Additives, solvents, dispersion methods and the like can be applied to those of the magnetic layer described below. In particular, with respect to the amount and type of the binder resin, the amount of the additive and the type of the dispersant, and the type thereof, a known technique for the magnetic layer can be applied. [Description of 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 Mn of 1000 to 2
00000, preferably 10,000 to 100,000, and a degree of polymerization of about 50 to 1,000. In the case of the hexagonal ferrite fine particles of the present invention, particularly when the particle diameter is 35 nm or less, the lower polymerization degree (250 or less) is preferable from the viewpoint of enhancing the dispersibility of the magnetic substance. The degree of polymerization is particularly preferably from 100 to 200. Such examples include vinyl chloride, vinyl acetate, vinyl alcohol, maleic acid, acrylic acid,
Acrylic acid ester, vinylidene chloride, acrylonitrile, methacrylic acid, methacrylic acid ester, styrene,
There are polymers or copolymers containing butadiene, ethylene, vinyl butyral, vinyl acetal, vinyl ether, and the like as constituent units, polyurethane resins, and various rubber resins. Examples of the thermosetting resin or the reactive resin include phenol resin, epoxy resin, polyurethane curable resin, urea resin, melamine resin, alkyd resin, acrylic reaction resin, formaldehyde resin, silicone resin, and 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. In addition, a known electron beam-curable resin can be used for each layer. These examples and the production method thereof are described in JP-A-62-256219.
In more detail. 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, vinyl chloride vinyl acetate maleic anhydride copolymer, And a combination of a polyurethane resin and at least one selected from the group consisting of polyisocyanates.

As the structure of the polyurethane resin, known ones such as polyester polyurethane, polyether polyurethane, polyether polyester polyurethane, polycarbonate polyurethane, polyester polycarbonate polyurethane, and polycaprolactone polyurethane can be used. For all of the binders shown here, COO is required to obtain better dispersibility and durability.
M, SO ₃ M, OSO ₃ M, P = O (OM) ₂ , OP
ＯO (OM) ₂ , where M is a hydrogen atom or an alkali metal base, OH, NR ₂ , N ⁺ R ₃ (R is a hydrocarbon group), epoxy group, SH, CN, etc. It is preferable to use one obtained by introducing one or more polar groups 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 Nissin Chemical 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, 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, 5 manufactured by Dainichi Seika
100, 5300, 9020, 9022, 7020, Mitsubishi Kasei Co., Ltd., MX5004, Sanyo Chemical Co., Ltd. Samprene S
P-150 and Saran F310, F210 manufactured by Asahi Kasei Corporation. Among them, MR555, MR110, UR8
200, UR8700 and the like are preferable.

The binder used in the non-magnetic layer and the magnetic layer of the present invention is 5 to 50% by weight based on the non-magnetic powder or the magnetic substance.
, Preferably in the range of 10 to 30% by weight. 5 to 30% by weight when using a vinyl chloride resin,
When a polyurethane resin is used, it is preferable to use a combination of these in a range of 2 to 20% by weight and for a polyisocyanate in a range of 2 to 20% by weight. Alternatively, 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%, the breaking stress is 0.05 to 10 kg / cm ² , and the yield point is 0.05-1
0 kg / cm ² is preferred.

The magnetic recording medium of the present invention can be composed of two or more layers. Accordingly, 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 amount described above. It is of course possible to change the physical properties of the resin between the non-magnetic layer and each magnetic layer, if necessary. Rather, it should be optimized for each layer, and a known technique for a multilayer magnetic layer 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. Can be made flexible by increasing the amount of binder.

Examples of the polyisocyanate used in the present invention include tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, hexamethylene diisocyanate, xylylene diisocyanate, and naphthylene.
Isocyanates such as 1,5-diisocyanate, o-toluidine diisocyanate, isophorone diisocyanate and triphenylmethane triisocyanate;
Products of these isocyanates and polyalcohols, and polyisocyanates formed by condensation of isocyanates can be used. Commercially available trade names of these isocyanates include Nippon Polyurethane Co., Ltd., Coronate L, Coronate HL,
CORONATE 2030, CORONATE 2031, Millionet
MR, Millionet MTL, Takeda Pharmaceutical, Takene
D-102, Takenet D-110N, Takenet D
-200, Takenet D-202, manufactured by Sumitomo Bayer,
Desmodule L, Desmodule IL, Desmodule
N, Desmodur HL, etc., which can be used alone or in combination of two or more by utilizing the difference in curing reactivity. [Description of Carbon Black and Abrasive] As carbon black used in the magnetic layer of the present invention, furnace black for rubber, thermal black for rubber, black for color, acetylene black and the like can be used. Specific surface area is 5-50
0 m ² / g, DBP oil absorption 10-400 ml / 100
g, particle size is 5 nm to 300 nm, pH is 2 to 10, water content is 0.1 to 10%, tap density is 0.1 to 1 g / c.
c is preferred. Specific examples of carbon black used in the present invention include BLACKPE manufactured by Cabot Corporation.
ARLS 2000, 1300, 1000, 900, 9
05, 800, 700, VULCAN XC-72, manufactured by Asahi Carbon Co., Ltd., # 80, # 60, # 55, # 50, # 3
5. # 2400B, # 2300, #, manufactured by Mitsubishi Kasei Kogyo Co., Ltd.
900, # 1000, # 30, # 40, # 10B, manufactured by Columbian Carbon, CONDUCTEX SC, R
AVEN 150, 50, 40, 15, RAVE-M
TP, manufactured by EC Japan, Ketjen Black EC, 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 after a part of the surface is graphitized.
Before adding the carbon black to the magnetic paint, the carbon black may be dispersed in a binder in advance. These carbon blacks can be used alone or in combination. When carbon black is used, it is preferred to use 0.1 to 30% by weight of the magnetic substance. Carbon black has functions such as preventing the magnetic layer from being charged, reducing the coefficient of friction, imparting light-shielding properties, and improving the film strength. These functions differ depending on the carbon black used. Therefore, these carbon blacks used in the present invention are different in type, amount and combination between the magnetic layer and the non-magnetic layer, and have the above-mentioned various properties such as particle size, oil absorption, conductivity and pH. Of course, it is possible to use them properly according to the purpose, and rather, it should be optimized in each layer. The carbon black that can be used in the magnetic layer of the present invention can be referred to, for example, "Carbon Black Handbook" edited by Carbon Black Association.

Examples of the abrasive used in the present invention include α-alumina, β-alumina, silicon carbide, chromium oxide, cerium oxide, α-iron oxide, corundum, artificial diamond, silicon nitride, and silicon carbide having an α conversion of 90% or more. Silicon titanium car
Known materials mainly having a Mohs hardness of 6 or more, such as a bite, titanium oxide, silicon dioxide, and boron nitride, are used alone or in combination. Further, a composite of these abrasives (abrasive whose surface is treated with another abrasive) may be used. These abrasives may contain compounds or elements other than the main component, but the effect remains unchanged if the main component is 90% or more. The particle size of these abrasives is preferably 0.01 to 2 μm, and in particular, in order to enhance the 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 particle sizes as needed, or to achieve the same effect by widening the particle size distribution even with a single abrasive. The tap density is preferably 0.3 to ² g / cc, the water content is 0.1 to 5%, the pH is 2 to 11, and the specific surface area is preferably 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. Specifically, AK manufactured by Sumitomo Chemical Co., Ltd.
P-12, AKP-15, AKP-20, AKP-3
0, AKP-50, HIT20, HIT-30, HIT
-55, HIT60, HIT70, HIT80, HIT
100, manufactured by Reynolds, ERC-DBM, HP-DB
M, HPS-DBM, manufactured by Fujimi Abrasives, WA1000
0, Uemura Industry Co., Ltd., UB20, Nippon Chemical Industry Co., Ltd., G-
5, Chromex U2, Chromex U1, Toda Kogyo Co., Ltd., TF100, TF140, Ibiden Co., Ltd., Beta Random Ultra Fine, Showa Mining Co., Ltd., B-3, and the like. These abrasives can be added to the nonmagnetic layer as needed. By adding to the non-magnetic layer, the surface shape can be controlled, and the projected state of the abrasive can be controlled. The particle size and amount of the abrasive added to the magnetic layer and the non-magnetic layer should of course be set to optimal values. [Description of Additives] As the additives used in the magnetic layer and the nonmagnetic layer of the present invention, those having a lubricating effect, an antistatic effect, a dispersing effect, a plasticizing effect and the like are used. Molybdenum disulfide, tungsten disulfide, graphite, boron nitride, graphite fluoride, silicone oil, silicone with polar group, 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, phenylphosphonic acid, aminoquinones, various silane coupling agents, titanium coupling agent, fluorine-containing alkyl sulfate Esters and alkali metal salts thereof, having 10 to 2 carbon atoms
4 monobasic fatty acids (which may contain an unsaturated bond or may be branched), and metal salts thereof (L
i, Na, K, Cu, etc. or monovalent, divalent, trivalent, tetravalent, pentavalent, hexavalent alcohols having 12 to 22 carbon atoms (although containing unsaturated bonds, they are also branched) C12 to C22 alkoxy alcohols, C10 to C24 monobasic fatty acids (which may contain unsaturated bonds or may be branched) and C2 to C12
A monofatty acid ester comprising a monovalent, divalent, trivalent, tetravalent, pentavalent, or hexavalent alcohol (which may contain an unsaturated bond or may be branched) or Di- or tri-fatty acid esters, mono-alkyl ether fatty acid esters 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 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. No. Esters include butyl stearate, octyl stearate, amyl stearate, isooctyl stearate, butyl myristate, octyl myristate, butoxyethyl stearate, butoxydiethyl stearate, 2-ethylhexyl stearate, and 2-octyldodecyl palmitate. , 2-hexyldecyl palmitate, isohexadecyl stearate, oleyl oleate, dodecyl stearate, tridecyl stearate, and alcohols such as oleyl alcohol, stearyl alcohol, and lauryl alcohol. Also, nonionic surfactants such as alkylene oxides, glycerin, glycidols, alkylphenol ethylene oxide adducts, cyclic amines, ester amides, quaternary ammonium salts, hydantoin derivatives, heterocycles, phosphoniums Or a cationic surfactant such as a sulfonium, a carboxylic acid, a sulfonic acid, a phosphoric acid, a sulfate group, a phosphate group,
Anionic surfactants containing acidic groups such as amino acids,
Aminosulfonic acids, sulfuric acid or phosphoric acid esters of amino alcohol, alkylbedine-type amphoteric surfactants, and the like can also be used. For these surfactants,
It is described in detail in "Surfactant Handbook" (published by Sangyo Tosho Co., Ltd.). These lubricants, antistatic agents, and the like are not necessarily 100% pure, and may contain impurities such as isomers, unreacted materials, by-products, decomposed products, oxides, and the like in addition to the main components. These impurities are preferably 30% by weight or less, more preferably 10% by weight or less.

These lubricants, surfactants and the like used in the present invention have different physical actions, and their types, amounts, and the combined ratio of the lubricants producing synergistic effects are different depending on the purpose. It should be determined optimally. To control bleeding to the surface by using fatty acids with different melting points in the non-magnetic layer and magnetic layer, to control bleeding to the surface by using esters with different boiling points, melting points and polarities, and to adjust the amount of surfactant To improve the application stability,
It is considered that the amount of the lubricant to be added is increased in the intermediate layer to improve the lubricating effect, and it is needless to say that the present invention is not limited to the examples shown here. Generally, the total amount of the lubricant is selected in the range of 0.1% by weight to 50% by weight, preferably 2% by weight to 25% by weight based on the magnetic substance or the non-magnetic powder.

All or a part of the additives used in the present invention may be added at any step in the production of magnetic and non-magnetic paints. There are a case where it is added in a kneading step using a body, a binder and a solvent, a case where it is added in a dispersion step, a case where it is added after dispersion, and a case where it is added just before coating. In some cases, the purpose may be achieved by applying a part or all of the additive simultaneously or sequentially after applying the magnetic layer according to the purpose. Depending on the purpose, a lubricant may be applied to the surface of the magnetic layer after calendering or after slitting. [Description of Solvent] The organic solvent used in the present invention may be acetone, methyl ethyl ketone, methyl isobutyl ketone, diisobutyl ketone, cyclohexanone, isophorone, tetrahydrofuran, etc.
Methanol, ethanol, propanol, butanol,
Alcohols such as isobutyl alcohol, isopropyl alcohol, methylcyclohexanol, methyl acetate, butyl acetate, isobutyl acetate, isopropyl acetate,
Esters such as ethyl lactate and glycol acetate, and glyco-
Dimethyl ether, glycol monoethyl ether,
Glycol ethers such as dioxane, benzene,
Aromatic hydrocarbons such as toluene, xylene, cresol, chlorobenzene, etc .; chlorinated hydrocarbons such as methylene chloride, ethylene chloride, carbon tetrachloride, chloroform, ethylene chlorohydrin, dichlorobenzene, etc., N, N- Those such as dimethylformamide and hexane can be used. These organic solvents are not necessarily 100% pure, and areomers, unreacted materials, by-products,
Impurities such as decomposition products, oxides, and moisture may be included. These impurities are preferably 30% by weight or less, more preferably 10% by weight or less. The type of the organic solvent used in the present invention may be the same in the magnetic layer and the non-magnetic layer, but it is preferable to use a solvent having a high surface tension (cyclohexanone, dioxane, etc.) in the non-magnetic layer to improve coating stability. Specifically, it is important that the arithmetic average value of the surface tension 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 a solvent having a dielectric constant of 15 or more be contained in the solvent composition in an amount of 50% by weight or more. Further, the dissolution parameters are preferably from 8 to 11. [Description of Layer Structure] The thickness structure of the magnetic recording medium of the present invention is such that the nonmagnetic support has a thickness of 2 to 100 μm, preferably 10 to 100 μm.
80 μm. An undercoat layer for improving adhesion may be provided between the nonmagnetic support and the nonmagnetic layer or the magnetic layer. The thickness of the undercoat layer is 0.01 to 2 μm, preferably 0.02 to 0.5 μm. In the present application, a double-sided magnetic layer disk-shaped medium in which a nonmagnetic layer and a magnetic layer are provided on both sides of the support is usually preferred, but may be provided on only one side. In this case, a back coat layer may be provided on the side opposite to the non-magnetic layer and the magnetic layer in order to obtain effects such as antistatic and curl correction. This thickness is 0.1 to 4 μm, preferably 0.3 to 2.0 μm. Known undercoat layers and backcoat layers can be used.

The thickness of the magnetic layer of the medium of the present invention depends on the layer structure,
It is optimized depending on the saturation magnetization of the head to be used, the head gap length, and the band of the recording signal, but when no nonmagnetic layer is provided, it is generally 0.1 to 5.0 μm, preferably 0.5 to 3 μm. When a non-magnetic layer is provided, the thickness is generally 0.01 to 1.0 μm, preferably 0.05 to 0.5 μm, and more preferably 0.15 to 0.5 μm.
0.35 μm. The magnetic layer may be separated into two or more layers having different magnetic properties, and a known configuration relating to a multilayer magnetic layer can be applied. In this case, the thickness of the magnetic layer indicates the sum of the respective magnetic layers.

The thickness of the nonmagnetic layer of the medium according to the present invention is generally 0.2 to 5.0 μm, preferably 0.5 to 3.0 μm.
m, more preferably 1.0 to 2.5 μm. The non-magnetic layer of the medium of the present application exerts its effect if it is substantially non-magnetic.For example, even if a small amount of a magnetic substance is included as an impurity or intentionally, the effect of the present invention is exhibited. It goes without saying that the configuration can be regarded as substantially the same as that of the present application. Substantially non-magnetic means that the residual magnetic flux density is 100 G or less or the coercive force is 100 Oe or less, and preferably, it has no residual magnetic flux density and no coercive force. [Description of Support] Non-magnetic supports used in the present invention include polyesters such as polyethylene terephthalate and polyethylene naphthalate, polyolefins, cellulose triacetate, polycarbonate, polyamide, polyimide, and the like. Polyamide-imide, polysulfone,
Known films such as polyaramid, aromatic polyamide and polybenzoxazole can be used. It is preferable to use a high-strength support such as polyethylene naphthalate or polyamide. If necessary, a laminated type support as disclosed in JP-A-3-224127 can be used to change the surface roughness of the magnetic surface and the base surface. These supports may be subjected to corona discharge treatment, plasma treatment, easy adhesion treatment, heat treatment, dust removal treatment, or the like in advance. In addition, an aluminum or glass substrate can be used as the support of the present invention.

In order to attain the object of the present invention, the center surface average surface roughness measured by the Mirau method of TOPO-3D manufactured by WYKO as a nonmagnetic support is SRa of 20 nm or less, preferably 10 nm or less, more preferably It is necessary to use one of 5 nm or less. It is preferable that these non-magnetic supports not only have a small center plane average surface roughness but also have no coarse protrusions of 0.5 μm or more. The surface roughness can be freely controlled by the size and amount of the filler added to the support as required. Examples of these fillers include oxides and carbonates such as Ca, Si, and Ti, and organic fine powders such as acryl. The maximum height SRmax of the support is 1 μm or less, the ten-point average roughness SRz is 0.5 μm or less, the height of the center plane peak is SRp of 0.5 μm or less, the center plane valley depth SRv is 0.5 μm or less, the center plane area. The rate SSr is 10% or more, 9
The average wavelength Sλa is preferably 5 μm or more and 300 μm or less. In order to obtain desired electromagnetic conversion characteristics and durability, the surface projection distribution of these supports can be arbitrarily controlled by a filler.
Each one of μm in size from 0 per 0.1 mm ² 2
It can be controlled in the range of 000 pieces.

F-5 of the non-magnetic support used in the present invention
The value is preferably 5 to 50 kg / mm ² , and 100
The heat shrinkage at 30 ° C. for 30 minutes is preferably 3% or less, more preferably 1.5% or less, and the heat shrinkage at 80 ° C. for 30 minutes is preferably 1% or less, more preferably 0.5% or less. is there. Breaking strength is 5-100 kg / mm ² , elastic modulus is 100-
2000 kg / mm ² is preferred. Temperature expansion coefficient is 10 ^-4 or more
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 properties, dimensional properties,
It is preferable that the mechanical strength characteristics be substantially equal to each other in the in-plane direction of the support with a difference within 10%. [Description of Production Method] The step of producing the magnetic paint or the non-magnetic paint of the magnetic recording medium of the present invention comprises at least a kneading step, a dispersing step, and a mixing step provided before and after these steps as necessary. Each step may be divided into two or more steps. All the raw materials such as the magnetic substance, nonmagnetic 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, kneading polyurethane,
In the dispersion step and the mixing step for adjusting the viscosity after dispersion, the mixture may be added separately. In order to achieve the object of the present invention,
Conventionally known manufacturing techniques can be used as some of the steps. In the kneading step, it is preferable to use one having a strong kneading force, such as an open kneader, a continuous kneader, a pressure kneader, or an extruder. When a kneader is used, the magnetic material or the non-magnetic powder and all or a part of the binder (however, preferably 30% by weight or more of the total binder) and 15 to 500 parts with respect to 100 parts of the magnetic material. It is kneaded. For details of these kneading processes, refer to Japanese Patent Application No. 62-2 / 1987.
64722, and Japanese Patent Application No. 62-236872. Glass beads can be used to disperse the magnetic layer solution and the non-magnetic layer solution, but zirconia beads, titania beads, and steel beads, which are high-density dispersion media, are preferable. The particle size and the filling rate of these dispersion media are optimized and used. A well-known disperser can be used.

When the magnetic layer liquid is dispersed using zirconia beads, titania beads, steel beads, or the like, the average particle diameter of the beads is preferably 0.1 to 5.0 mm.
0.5 to 3.0 mm is more preferable. Further, the dispersion time using the beads is preferably 0.5 to 20 hours,
1.0 to 5.0 hours is more preferable. When applying a magnetic recording medium having a multilayer structure in the present invention, it is preferable to use the following method. First, gravure coating, roll coating, blade coating, which are generally used in the application of magnetic paint,
First, the lower layer is applied by an extrusion coating device or the like, and the lower layer is kept wet while the lower layer is in a wet state.
And JP-A-60-238179 and JP-A-2-265672.
A method of applying an upper layer by a support pressure type extrusion coating apparatus disclosed in (1). Second, JP-A-63-8
8080, JP-A-2-17971, JP-A-2-2656
72. A method in which upper and lower layers are applied almost simultaneously by one coating head having two built-in coating liquid passage slits as disclosed in 72. A third method is to apply the upper and lower layers almost simultaneously using an extrusion coating apparatus 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 agglomeration of the magnetic particles, the coating liquid inside the coating head is applied to the coating liquid by a method disclosed in JP-A-62-95174 or JP-A-1-236968. It is desirable to apply shear. Further, regarding the viscosity of the coating solution, Japanese Patent Application No.
It is necessary to satisfy the numerical range disclosed in 312659. In order to realize the structure of the present invention, it is of course possible to use a sequential coating method in which a lower layer is applied and dried, and then a magnetic layer is provided thereon, and the effect of the present invention is not lost. However, in order to reduce coating defects and improve quality such as dropout, it is preferable to use the above-described simultaneous multilayer coating.

In order to produce a randomly oriented medium, a sufficient isotropic orientation can be obtained even without orientation without using an orientation apparatus. However, alternating current is provided by a solenoid in which cobalt magnets are arranged diagonally and alternately. It is preferable to use a known random alignment device such as applying a magnetic field. In general, hexagonal ferrite is likely to be three-dimensionally random in the plane and in the vertical direction, but may be two-dimensionally random in the plane. In any case, it is important to adjust SQ to be preferably in the above range. The orientation magnetic field is usually 0.1 to 2.0 kOe, preferably 0.5 to 1.5 kOe.
kOe.

In order to manufacture a perpendicularly oriented medium, a known method such as a different polarity opposed magnet can be used to impart isotropic magnetic characteristics in the circumferential direction. In particular, when performing high-density recording, vertical alignment is preferable. The orientation magnetic field is usually 2.0 to
It is in the range of 10 kOe, preferably 3.0 to 8.0 kOe. These orientation treatments are preferably performed so that the drying position of the coating film can be controlled by controlling the temperature of the drying air, the amount of air, and the application speed, and the application speed is 20 m / min to 1000 m /
The temperature of the drying air is preferably 60 ° C. or more, and a suitable preliminary drying can be performed before entering the magnet zone.

After the orientation treatment, the magnetic layer is usually subjected to a surface treatment such as a calendering treatment. Heat-resistant plastic rolls such as epoxy, polyimide, polyamide, and polyimideamide or metal rolls as the calendering roll.
In the case of forming a double-sided magnetic layer, it is preferable to treat with a metal roll. The processing temperature is preferably at least 50 ° C, more preferably at least 100 ° C.
The linear pressure is preferably 200 kg / cm or more, more preferably 300 kg / cm or more. [Description of Physical Properties] The maximum magnetic flux density of the magnetic layer of the magnetic recording medium according to the present invention is generally 800 to 3000 G (Gauss), preferably 1000 to 2000 G. The coercive force Hc measured in the plane of the magnetic layer is 1000 to 5000O.
e, but preferably from 1500 to 3000 Oe. The orientation ratio is preferably 0.8 or more.

In the case of a randomly oriented medium, each of the squareness ratios in the vertical direction, Br, Hc and Hr, is 0.1 to 0.1 in the in-plane direction.
It is preferable to set it within 0.5 times. The coefficient of friction of the magnetic recording medium of the present invention with respect to the head is from -10 ° C to 40
° C., 0.5 or less in the range of 0% humidity 95%, preferably 0.3 or less, the surface resistivity preferably magnetic surface 10 ⁴ to 10 ¹² O - arm / sq, charge potential from -500 V +
It is preferably within 500V. The elastic modulus of the magnetic layer at 0.5% elongation is preferably 100 to 2000 kg / m in each direction in the plane.
m ² , the breaking strength is preferably 1 to 30 kg / cm ² , and the elastic modulus of the magnetic recording medium is preferably 100 to 1500 in each in-plane direction.
Kg / mm ² , preferably 0.5% or less at 100 ° C.
The heat shrinkage at any of the following temperatures is preferably 1% or less, more preferably 0.5% or less, and most preferably 0.1% or less. Glass transition temperature of magnetic layer (11
(Maximum point of loss elastic modulus in dynamic viscoelasticity measurement measured at 0 Hz)
Is preferably from 50 ° C to 120 ° C, and that of the lower nonmagnetic layer is preferably from 0 ° C to 100 ° C. Loss modulus is 1 × 1
0 ⁸ to 8 × preferably in the 10 ⁹ dyne / cm ² range, the loss tangent is preferably 0.2 or less. If the loss tangent is too large, adhesion failure is likely to occur. It is preferable that these thermal characteristics and mechanical characteristics are substantially equal within 10% in each direction in the plane of the medium. The residual solvent contained in the magnetic layer is preferably 100 mg / m ² or less, more preferably 10 mg / m ² or less.
mg / m ² or less. The porosity of the coating layer is preferably 30% by volume or less, more preferably 20% by volume or less, for both the nonmagnetic lower 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 in which repeated use is emphasized, a larger porosity is often preferable in running durability.

The center layer surface roughness Ra of the magnetic layer measured by the Mirau method of TOPO-3D is 10 nm or less, preferably 5 nm or less, more preferably 3 nm or less.
RMS surface roughness RRMS obtained by evaluation according to
It is preferably in the range of nm. Maximum height SR of magnetic layer
max is 0.5 μm or less and ten-point average roughness SRz is 0.3 μm
m, the center plane height SRp is 0.3 μm or less, the center plane valley depth SRv is 0.3 μm or less, the center plane area ratio SSr is 20% or more and 80% or less, and the average wavelength Sλa is 5 μm or more and 300 μm or less. preferable. The number of surface protrusions of the magnetic layer is from 0.01 μm to 1 μm, and is 0 to 20 μm.
It is preferable to arbitrarily set the friction coefficient in the range of 00 to optimize the friction coefficient. These can be easily controlled by controlling the surface properties by the filler of the support, the particle size and amount of the powder to be added to the magnetic layer, and the roll surface shape of the calendar treatment. The curl is preferably within ± 3 mm.

When the magnetic recording medium of the present invention has a nonmagnetic layer and a magnetic layer, it is easily presumed that the physical properties of the nonmagnetic 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 non-magnetic layer is made lower than that of the magnetic layer to improve the contact of the magnetic recording medium with the head.

[0056]

Hereinafter, specific examples of the present invention will be described.
The present invention is not limited to this. <Characteristics of Hexagonal Ferrite Used> Magnetic coating materials were prepared using hexagonal ferrites shown in Table 1 below.

[0057]

[Table 1]

<Preparation of paint> Magnetic paint X Barium ferrite magnetic powder (shown in Table 1) 100 parts Vinyl chloride copolymer (containing polar group: -SO ₃ K) 12 parts MR555 (manufactured by Zeon Corporation) Polyurethane (Containing -SO ₃ Na): UR8200 (manufactured by Toyobo) 3 parts α-alumina (average particle size: 0.2 μm): HIT55 (manufactured by Sumitomo Chemical) 10 parts # 50 (manufactured by Asahi Carbon Co.) 5 parts butyl stearate 10 parts Butoxyethyl stearate 5 parts Isohexadecyl stearate 3 parts Stearic acid 2 parts Methyl ethyl ketone 125 parts Cyclohexanone 125 parts Nonmagnetic paint Y Nonmagnetic inorganic powder TiO ₂ crystalline rutile 80 parts Average primary particle diameter: 0.035 μm, BET Specific surface area by the method: 40 m ² / g pH: 7, TiO ₂ content: 90% or more, DBP oil absorption: 2 7 to 38 g / 100 g, Surface treatment agent: Al ₂ O ₃ 8% by weight Carbon black Conductex SC-U (manufactured by Columbian Carbon Co., Ltd.) 20 parts Vinyl chloride copolymer (polar group: containing -SO ₃ K) 12 parts MR110 (manufactured by Zeon Corporation) UR8200 5 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 [Preparation of magnetic recording medium Sample No.] A to L (Preparation of Random Oriented Medium) For each of the above two paints, each component was kneaded with a kneader and then dispersed using a sand mill. To the resulting dispersion, 10 parts of polyisocyanate was added to the coating solution for the non-magnetic layer, 10 parts to the coating solution for the magnetic layer, and 40 parts of butyl acetate was added to each. A filter having an average pore diameter of 1 μm was added. Then, a coating solution for forming a nonmagnetic layer and a coating solution for forming a magnetic layer were prepared.

The obtained coating solution for the non-magnetic layer was applied to a thickness of 62 μm so that the thickness after drying was 1.5 μm, and immediately thereafter, the thickness of the magnetic layer was 0.2 μm thereon. At the same time, a multi-layer coating is performed on a polyethylene terephthalate support having a center line surface roughness of 0.01 μm, and a 7-stage calendar is processed at a temperature of 90 ° C. and a linear pressure of 300 kg / cm.
After a 3.7-inch punched surface and polished surface, a 3.7-inch cartridge (US Iom) with a liner installed inside
For example, the sample was placed in a zip-disk cartridge manufactured by Ega Corporation, and a predetermined mechanical component was added thereto. A to 3.7 inch floppy disks were obtained.

Examples FJKL and Examples A and B were prepared by dispersing in a sand mill for 2 hours using glass beads having an average particle diameter of 1 mmφ to prepare magnetic coating solutions. An example in which zirconia beads having an average particle diameter of 0.8 mm are dispersed for 4 hours is CDDEHI. Average particle size 1
Comparative Example dispersed for 4 hours using mm glass beads was G
It is.

Sample No. M to S (Preparation of Vertically Oriented Medium) After the simultaneous multi-layer coating was performed in the same manner as in the above-mentioned random oriented medium, the coated film was allowed to pass through a vertical magnetic field composed of a pair of opposite-pole opposed magnets of 7 KOe in a wet state. While drying, each sample was prepared. Examples RS and S were prepared by dispersing glass beads having an average particle diameter of 1 mmφ in a sand mill for 2 hours to prepare a coating solution. Examples in which the dispersion was performed for 4 hours using zirconia beads having an average particle diameter of 0.8 mm are M · N, and Comparative Examples are Q. 4 using glass beads with an average particle size of 1 mm
The comparative example in which the time is dispersed is OP. In Comparative Example Q, it is considered that the amount of drying air was reduced during the vertical magnetic field orientation treatment, and drying was not performed in the magnetic field.

The samples A to L and M to S obtained above were evaluated, and the results are shown in Tables 2 and 3, respectively.

[0063]

[Table 2]

[0064]

[Table 3]

[Comparison between Example and Comparative Example] The randomly oriented disk-shaped medium and the vertically oriented disk-shaped medium of the present invention have much higher and higher C / D characteristics than conventional disk-shaped media in high-density recording. N. [Description of Measurement Method] Each sample of the floppy disk was measured by the following evaluation method. <Output> The output was measured using a disk tester manufactured by Kokusai Denshi Kogyo Co., Ltd. (former Tokyo Engineering Co., Ltd.) and a SK606B type evaluation device, using a metal-in-gap head with a gap length of 0.3 μm, and a recording wavelength at a radius of 24.6 mm. After recording at 90 KFCI, the reproduced output of the head amplifier was measured with an oscilloscope type 7633 manufactured by Tektronix. The output is shown as a relative value with the output / noise of Example-D set to 0 dB. <Measurement of C / N and noise> After AC erasing the disk for which the reproduction output was measured, TR4171 manufactured by Advantest Corporation was used.
The reproduction output (noise) was measured with a type spectro analyzer. C / N = −20 log (noise / reproduction output)
The C / N of Example-D was shown as a relative value with 0 dB. <Magnetic characteristics> Magnetic characteristics (Hc, Bm, SQ, SQp, S
^{* 1} , S ^{* 2} ): Measured with a vibration sample type magnetometer (manufactured by Toei Industry Co., Ltd.) at Hm10KOe. Note that Hc in Table 3 was measured in the vertical direction. <Magnetization reversal volume> Magnetization reversal volume: The magnetic field sweep speed of the Hc measuring unit was measured at 5 minutes and 30 minutes using the above VSM, and the magnetization reversal volume V was obtained from the following relational expression between Hc and magnetization reversal volume due to thermal fluctuation.
(Ml) was calculated.

Hc = 2K / Ms ｛1-[(kT / KV)
ln (At / 0.693)] ^1/2 ｝ Hc: coercive force measured in the magnetic layer plane K: anisotropic constant Ms: saturation magnetization k: Boltzmann constant T: absolute temperature V: magnetization reversal volume A: spin age Difference frequency t: Magnetic field reversal time <Thickness of magnetic layer> A section sample of the layer cross section was prepared, and was obtained from a cross-sectional photograph of an image taken with a scanning electron microscope (S-700, manufactured by Hitachi, Ltd.).

[0067]

According to the present invention, even in the case of a hexagonal ferrite fine particle magnetic material, noise is sufficiently reduced, short wavelength output is large, and high is achieved by adjusting the magnetization reversal volume, S ^* , and SQp to specific ranges. It is possible to stably provide a random-oriented and perpendicularly-oriented disk-shaped magnetic recording medium having C / N and capable of high-density recording that has not been achieved conventionally.

Claims (3)

[Claims] 1. The method according to claim 1, wherein at least one side of the non-magnetic support comprises:
In a magnetic recording medium provided with at least one magnetic layer in which a ferromagnetic material is dispersed in a binder, the ferromagnetic material contained in the uppermost layer is hexagonal ferrite, and measurement is performed in the plane of the uppermost magnetic layer. Magnetization switching volume is 0.5 × 10 ^{−17 to} 1.5 × 1
0 ^-17 ml, and and randomly oriented disc-like magnetic recording medium, wherein the coercivity squareness ratio were measured in the uppermost magnetic layer plane S ^{* 1} is 0.60 or more. 2. The method according to claim 1, wherein at least one side of the nonmagnetic support comprises:
In a magnetic recording medium provided with at least one magnetic layer in which a ferromagnetic material is dispersed in a binder, the ferromagnetic material contained in the uppermost layer is hexagonal ferrite, and measurement is performed in the plane of the uppermost magnetic layer. Magnetization switching volume is 0.5 × 10 ^{−17 to} 1.5 × 1
^0-17 ml, the coercive force squareness ratio S ^{* 2} measured in the vertical direction of the uppermost magnetic layer is 0.9 or more in the demagnetizing field correction value, and the squareness ratio SQp in the vertical direction after demagnetizing field correction is 0 .75
A vertically aligned disk-shaped magnetic recording medium characterized by the above. 3. A non-magnetic layer in which a non-magnetic powder is dispersed is formed between the magnetic layer and the non-magnetic support, and the thickness of the magnetic layer is 0.15 to 0.35 μm. 1 or 2 disk-shaped magnetic recording media.