JPS63273211A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a recording medium which allows high-density recording by forming said medium of magnetic material particles, the crystals of which have X-ray diffraction rays substantially as spinel, the axis of easy magnetization of which has the direction perpendicular to the plate plane and which has a specific average grain size and platy ratio. CONSTITUTION:Hexagonal ferrite powder, into the crystals of which at least one kind of metal elements among Ba, Sr, Pb, and Ca are incorporated in the form of crystals and which crystals have the X-ray diffraction rays substantially as spinel and a material consisting of glycoxides, saccharides, etc., are brought into contact with each other to form the magnetic material particles. These particles are so adjusted as to consist of the platy particles having 0.01-1.0mum grain size and 2-30 platy ratio. The axis of easy magnetization is specified to the direction perpendicular to the particle plate plane in the same direction as the direction of the axis of easy magnetization of hexagonal ferrite. The magnetic layer contg. such magnetic material particles is provided on a base to form the medium. The recording medium which allows the high- density recording is thus obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a novel magnetic recording medium having improved high output and in which the temperature dependence of coercive force is arbitrarily adjusted.

(Prior Art and Problems) In recent years, magnetic recording media for use in digital recording, video recording, etc., in which hexagonal ferrite is coated on a support, have been studied. this house.

Magnetic cards using hexagonal ferrite already form part of the market. And as a high density record! In the perpendicular magnetic recording system used in I11, recording media coated with hexagonal ferrite are being actively researched and developed.

That is, the general formula MO'6FezOs (M is Ba, Sr.

At least one metal element selected from 1'b, Ca, etc.), or furthermore, a so-called hexagonal crystal in which a part of the trivalent Fe is replaced with a metal element whose average valence is 3 Ferrite can obtain a wide range of coercive force by adjusting the 1M1 anisotropy, and its axis of easy magnetization is (00
1) The shaft is single-axis.

This is because it is suitable as a magnetic powder used in the magnetic recording medium as described above. - However, the drawbacks of the hexagonal ferrite that have been pointed out so far are that its coercive force has a large temperature dependence compared to magnetic recording media using other oxide magnetic materials, and that it cannot be adjusted to an arbitrary value. That's something I didn't get. This characteristic originates from the essence of hexagonal ferrite.1For example, all of the temperature dependence of the coercive force of hexagonal ferrite disclosed so far have been reported to have values of +3 to +5 (Oe/'C). ing. Therefore, magnetic recording media using magnetic particles whose coercive force is highly temperature-dependent have poor thermal stability, and cannot achieve the desired performance as designed in advance when used in environments with large temperature changes. This could lead to various troubles as it became impossible to move around. This phenomenon becomes more pronounced as the recording density becomes higher, that is, as the recording wavelength becomes shorter. Therefore, it is even argued that it is difficult to apply this method to floppy disks with highly dense carbonization. That is, the coercive force of a magnetic recording medium greatly affects the electromagnetic conversion characteristics.

If this electromagnetic conversion characteristic changes, it immediately causes a change in the recording, reproducing, and erasing characteristics. Therefore, if a magnetic recording medium with such a large temperature change in coercive force is used in a place where the environmental temperature is significantly different, recording errors may occur. However, there has been a problem in that a reduction in reproduction output or a failure in erasing records occurs, resulting in a significant deterioration in the function as a magnetic recording medium.

On the other hand, the output is higher and more stable than the conventional magnetic recording medium using hexagonal ferrite (temperature dependence of d force (θ, 1c)
includes around 0 (Oa/”C), 0≧θ, ≧-6 (00
Spinel type ferrite is a magnetic material that can be used as a magnetic recording medium in the range of /'C).

However, although some spinel ferrites have a small coercive force dependence on temperature, their shape is acicular,
Furthermore, even if it is plate-like, its easy tn axis is not the fli axis of the (001) axis as in the case of hexagonal ferrite, but the 1
Since it exists in the (001) plane parallel to the grain plate surface, there is an essential problem that it cannot fully achieve the purpose of high-density magnetic recording like hexagonal ferrite.

Typical conventional spinel ferrites include (a);
General formula M O・Fezes (M is Fe”
″.

A ferrite represented by Mg+at least one metal element selected from Mn, Zn, and Ni.

(b), COO・F e t O3.

cc), 7-F modified with r-FetOs or Co
Examples include e2O2.

Among the above, spinel type ferrite (a) is called a soft magnetic material, and the temperature dependence of 1 coercive force (θ□) is θHc'
:O, but the coercive force (tlc) is tlc < 40
0 (Oe), and the easy axis of magnetization is on the (001) plane, not a single (001) axis like hexagonal ferrite.

Although the cobalt ferrite (b) has a high coercive force, its temperature dependence is as large as -6 (Oe/'C), and its easy axis of magnetization is on the same < (001) plane. Furthermore, (C) y-Fe, 03 or y-Fe, Os modified with Co, is usually used as acicular particles, and in this case, the magnetization generation mechanism is based on shape anisotropy, so the magnetization This is distinct from the mechanism in which the activation mechanism is based on crystal anisotropy.

On the other hand, a plate-shaped magnetic powder made of crystals belonging to the cubic system is disclosed in JP-A-62-41717.

As specific substances, 7-F (lx 02+ Co metamorphosed 7-Fezos, Fe, and Oa are shown. However, it is described that all of them are characterized by in-plane magnetization in the (001) plane. As expected, it is difficult to provide an ff!-easy axis to a single (001) axis like hexagonal ferrite.

Furthermore, in JP-A No. 60-255629, the particle surface is composed of magnetite (Fe0- ・FetOz, where o<y≦1
), but according to this publication, the only metal element distributed on the surface of the Ba ferrite particles is Fa. The invention described in this publication is based on the idea that by stacking hexagonal ferrite and spinel ferrite, the advantages and disadvantages of both can be compensated for. In this case, two independent crystal structures, hexagonal ferrite and spinel ferrite, are stacked together. It can be thought of as existing in a state of

Therefore, although it may have the unique properties of both crystal structures, it cannot be said that it is a single crystal structure that can essentially eliminate the drawbacks of hexagonal ferrite and spinel ferrite. For this reason, it will not be possible to simultaneously solve the above-mentioned problems of spinel ferrite and the temperature dependence of coercive force of hexagonal ferrite.

(Purpose of the invention) An object of the present invention is to solve the above-mentioned problems.

It is an object of the present invention to provide a high-output magnetic recording medium whose coercive force has low temperature dependence and is capable of high-density magnetic recording.

[Structure of the Invention] The present invention provides a magnetic recording medium in which a magnetic layer containing magnetic particles is provided on a support, in which the magnetic particles have an average particle size of 0.01 to 1.0 p va. Shape ratio is 2-3
consists of 0 plate-like crystals and contains Ba, Sr, Pb or Ca
At least one metal element is included in the crystal structure as an element constituting the crystal, and the crystal has an X-ray diffraction line substantially as a spinel, and the axis of easy magnetization is in the same direction as the hexagonal ferrite ( 001) To provide a magnetic recording medium characterized in that it is made of crystals having crystals in the axle direction of the shaft (direction perpendicular to the plate surface).

As will be demonstrated later, the magnetic recording medium according to the present invention has the following features:
It has an X-ray diffraction peak as a spinel, but like hexagonal ferrite, it has a magnetic layer containing magnetic particles whose easy axis of magnetization is in the uniaxial direction of the (001) axis (direction perpendicular to the plate surface). The temperature dependence of the coercive force (θ1lc) of the magnetic particles is +2≧03, which cannot be obtained with conventional hexagonal ferrite. c≧−5(OL
! 2. Since the magnetic recording medium of the present invention uses magnetic particles having a substantially spinel structure, the saturation magnetization is high and the temperature dependence of the coercive force is within the same range as that of the magnetic particles. , that is, +2≧θ, ≧-5(Oe/”C)
within the range of

The temperature dependence of coercive force (θ□) is generally evaluated as follows.

T-T.

here T is the measurement temperature ('C).

To is room temperature ("C).

Hc is the coercive force (Oe) measured when the temperature of the magnetic material is T ('C).

Hc' is the coercive force (Oe) measured when the temperature of the magnetic material is To ("c).

θ□ of the magnetic recording medium made of magnetic particles of the present invention is +2≧
θ□≧−50e/′C, and the temperature dependence is smaller than θ□≧+3 of conventional hexagonal ferrite. This is because θ□ of the magnetic particles of the present invention has an X-ray diffraction line as a spinel type ferrite. The Tli-based particles ++c are substantially unchanged from θ□ of the magnetic recording medium.
The value is .

The magnetic particles constituting the magnetic recording medium according to the present invention are
Substantially has a spinel crystal structure, but its easy axis of magnetization is the (001) axis in the same direction as hexagonal ferrite t1'L
It is a completely new type of magnetic material in that it has an axial direction (direction perpendicular to the plate surface). Even in the spinel type, at least one metal element of Ba, Sr, Pb, or Ca is present in the crystal structure as an element constituting the crystal.

In other words, Ba, which is an element constituting hexagonal ferrite,
, Sr, Pb, or Ca, and as a result, like hexagonal ferrite, it has an axis of easy magnetization in the uniaxial direction of the (001) axis.

Note that 2' being substantially 1 spinel means that a small amount of hexagonal ferrite phase may coexist. Furthermore, the present invention may be more advantageously achieved if a small amount of hexagonal ferrite phase coexists. In any case, the magnetic particles according to the present invention include Ba, Sr, P
At least one metal element, B or Ca, was present throughout the crystal as an element constituting the crystal, both inside and on the surface.In addition, it is a new crystal that has never existed before in that it exhibits the crystal structure of spinel. It can be said that it is an anisotropic ferrite.

In the present invention, the average particle size of the magnetic particles is 0.01μ1.
The reason why the distance is limited to 1 to 0.1//1 m is as follows. In general, fine particles are preferable for high-density magnetic recording media, but when the magnetic particles according to the present invention are smaller than 0.01 μm, they exhibit superparamagnetism and the saturation magnetization decreases markedly; This is because when the magnetic field becomes larger, the particles tend to become multi-domain particles, which reduces the residual magnetization.

Furthermore, in the present invention, the platelet ratio of the magnetic particles is set to 2 to 30 when forming the magnetic layer in a magnetic recording medium. This is because the thickness of the particles becomes thinner, making them bulkier, which reduces the ability to fill the magnetic layer, and is also unfavorable in terms of handling.

The magnetization mechanism of magnetic particles according to the present invention is based on crystal anisotropy. The magnetic particles have a plate-like shape. It is difficult to give these plate-like particles uniaxial anisotropy due to shape anisotropy like needle-like particles. For this purpose, the crystal (
The basic feature of the present invention is that crystal anisotropy is imparted so that the easy axis of magnetization is on a single axis (001). The fact that the easy axis of magnetization of a plate crystal is a uniaxial (001) axis means that it is possible to have an easy axis of magnetization in a direction perpendicular to the two-particle plate surface. The magnetic recording medium may advantageously have its axis of easy magnetization oriented perpendicular to the surface of the support. In some cases, it is also possible to orient the axis of easy magnetization parallel to the support surface by aligning the plate-like particles in a direction perpendicular to the support surface, or in some cases, it is possible to perform random orientation. is also possible.

The magnetic recording medium of the present invention comprises a support and a magnetic layer, and the magnetic layer is formed of the above-mentioned novel magnetic particles, which can be formed using a binder resin. At this time, additives such as 2 dispersants, lubricants, antistatic agents, and abrasives are added as necessary.

Although any material used in conventional magnetic recording media can be used as the support/body, generally polyethylene terephthalate, polyethylene, vinyl chloride, nylon resin, etc. are used.

Binder resins for forming the magnetic layer include vinyl chloride-vinyl acetate copolymer, polyvinyl butyral,
Dispersants include vinyl resins such as vinylidene chloride-acrylonitrile copolymer, fiber resins such as nitrocellulose and acetylcellulose, and crosslinkable resins such as epoxy, phenoxy, and urethane.Dispersants include fatty acid-based resins,
Examples include polycarboxylic acid type, amine type, lecithin, etc. Stearic acid and silicone are used as lubricants.

There are fluorine compounds and other antistatic agents.

Carbon black, etc., and as abrasives, alumina fine powder, chromium oxide, etc. are added as necessary.

In order to manufacture a magnetic recording medium using the magnetic particles according to the present invention, binder resin and the above-mentioned additives may be used depending on the purpose. After selecting IR and determining the magnetic particles and their blending ratio, the magnetic paint is prepared by kneading with a predetermined amount of solvent.

As the solvent used here, methyl ethyl ketone, methyl isobutyl ketone, toluene, cyclohexanone, etc. can generally be used, and as the kneader, a general paint dispersion machine such as a sand mill or a Devers mill can be used. The obtained magnetic coating material is applied to a support, and in some cases, a magnetic field orientation treatment is performed.9 Then, after a drying treatment, a smoothing treatment is performed6.
At that time, the coating machine was 2 ordinary gravure rolls,
Reverse roll etc. can be used. The magnetic field orientation treatment is a treatment in which a magnetic field is applied perpendicularly or parallel to the surface of the support to align the easy axis of magnetization of the magnetic particles in these directions.

When the magnetic particles of the present invention are plate-shaped, they can be mechanically oriented using a calender roll or the like without using a magnetic field. At this time, the plate surface of the magnetic particles is parallel to the support surface, while the axis of easy magnetization is perpendicular to the support surface. In some cases, the plate surface of the magnetic particles was randomly distributed with respect to the support surface. Therefore, it is also possible to manufacture an isotropic magnetic recording medium in which the easy axis of magnetization is randomly distributed. The purpose of the smoothing treatment is to smooth the coating area, and a calendar roll is used. In this case, the plate-shaped magnetic particles are mechanically oriented as described above.

In this way, the novel magnetic recording medium of the present invention is obtained, and the magnetic particles forming the basis of the present invention, that is, the average particle size is 0.01 to 1.071 m and the plate interposition is 2 to 3
consists of 0 plate-like crystals and contains Ba, Sr, Pb or Ca
At least one metal element is included in the crystal structure as an element constituting the crystal, and the crystal has an X-ray diffraction line substantially as a spinel.

And the easy axis of magnetization is in the same direction as the hexagonal ferrite (00
1) Magnetic particles consisting of crystals having their axes in a uniaxial direction (perpendicular to the plate surface) can be produced by the method described below.

That is, at least one of Ba, Sr, Pb or Ca
Hexagonal ferrite powder in which the seed metal element is included in the crystal structure as an element constituting the crystal and has an average particle size of 5 μm or less, and glycoside m, tl! w, at least one substance selected from the group consisting of polyhydric alcohols, oxycarboxylic acids, or salts thereof are brought into contact with each other in the presence of an alkali in a medium at a temperature exceeding 100'C.

The composition of the hexagonal ferrite that can be used in this method can be represented by the composition formula (1) shown below,
The manufacturing method may be a coprecipitation method, a glass method, a hydrothermal synthesis method, or a conventional dry method.

Composition formula (1): M'O・n (Fez-, M'', Oz)
...(+) However, in equation (1).

M' is at least one metal element selected from Ba, Sr, Ca, and Pb.

n is 4≦n≦6°X is 0≦X≦0.71 M2 is at least one metal element selected from Sb, V+Ti+Sn+Ta+Zr, St, 1Mg, Mn,
Ni.

A combination with at least one metal element selected from F e”+ C11, CG12 rl, and this M
Although t does not necessarily have to exist (in the case of x=0).

If it exists, the coercive force can be adjusted more effectively and higher saturation magnetization can be obtained more advantageously. It is also useful as an element for adjusting the temperature dependence of coercive force to a desired value.

In the following, as an example, the case where hexagonal ferrite having the composition of the above composition formula (1) is manufactured by hydrothermal synthesis method,
The details of the manufacturing method will be explained.

First, a hexagonal ferrite having the composition represented by the above composition formula (1) is produced by hydrothermal synthesis as follows.

In a 11□O medium containing a predetermined ratio of metal components represented by the above compositional formula (1) and at a temperature exceeding 100°C and in the presence of an alkali in an amount whose alkali equivalent ratio to acid radical exceeds 1.0, or one reaction Hexagonal ferrite particles are formed by hydrothermal treatment in the presence of an alkali such that the pH of the system becomes 11 or higher.

The compositional formula (+) substantially corresponds to the required ratio of metal components present during hydrothermal synthesis.The reason why the molar ratio n in the formula 0 is set to 4 to 6 is because molar ratios outside of this range result in a predetermined hexagonal crystal structure. This is because ferrite cannot be obtained. In addition, M2, which is a substituted component, is a component useful for controlling coercive force,
The reason for setting the substituent X in the range of 0 to 0.7 is that if it exceeds 0.7, the saturation magnetization of the crystal anisotropic oxide of the present invention will be 40e.
This is because it becomes less than mu/g. F in ferrite lattice
The substitution component M2 with e atom is +Sb+V,'
At least one element selected from the group consisting of ri, srt, T'alZr, and Si, or at least one element selected from the group consisting of this element and N iI CO + Ctl + Mg, Mn, Fe'' and Zn. The coercive force can be adjusted most effectively by combining the components.

Next, in a 11.0 medium with a temperature of 100'C and in the presence of an alkali in an amount in which the alkali equivalent ratio to the acid radical exceeds 1.0 or in the presence of an alkali such that the PTT of the reaction system is 11 or more, hexagonal crystals are formed. Ferrite is produced by mixing a raw material mixture adjusted to have the composition of formula (1) using water as a medium in the presence of a specified alkali.
This means that the ferrite production reaction is carried out at a temperature exceeding 100°C, using an autoclave (temperatures exceeding 100°C are virtually impossible to obtain without an autoclave). Furthermore, the hydrothermal synthesis method refers to a ferrite synthesis reaction in an autoclave using water as a medium. To carry out this hydrothermal synthesis, it is first necessary to mix and adjust the raw materials and adjust the alkali.

The raw material is prepared by preparing a mixture in which metal components are uniformly mixed in a predetermined ratio based on the ferrite composition of formula (1). The raw materials that provide these metal components are halides,
It may be a nitrate or other water-soluble metal salt or hydroxide. At this time, when all the raw materials are water-soluble metal salts, the raw material mixture is an aqueous solution containing metal ions in a predetermined ratio, whereas when hydroxide is selected as the raw material, the raw material mixture is a slurry-like mixture. becomes. Moreover, when a water-soluble metal salt and a hydroxide are allowed to coexist, a slurry containing metal ions and metal hydroxide is obtained.

Note that iron oxyhydroxide can also be used as a raw material that provides the Fe component.

Next, this raw material mixture adjusted to a predetermined ratio is brought into contact with an alkali (an alkaline solution containing an alkaline substance), whereby a precipitate is usually formed to obtain an alkaline slurry-like substance. The amount of alkali used is such that the equivalent ratio of alkali to acid radical exceeds 1.0. If no acid radical is present, the pH of the alkaline slurry obtained by contacting the above raw $4 mixture with an alkaline solution
The amount of alkali is such that is 11.0 or more. In any case, the alkaline slurry-like substance is a slurry containing a metal hydroxide, a slurry containing a metal hydroxide and iron oxyhydroxide, or a slurry-like substance containing metal ions therein. The reason why the amount of alkali is specified within this range is that if it is outside this range, the amount of hexagonal ferrite phase produced will be significantly reduced. The alkaline solution used is NaOH.

It is selected from solutions of KOH, LiOH, NH=OH, mixed solutions thereof, and solutions containing other strongly alkaline substances.

Regarding the reaction temperature of the ferritization reaction in the autoclave, the temperature exceeds 100"C, preferably 120"C.
~400°C is suitable. The temperature inside the autoclave is 4
If the temperature exceeds 00'C, the pressure becomes extremely high, which is economically disadvantageous. On the other hand, below 120° C., the amount of hexagonal ferrite produced is small, making it unsuitable as the raw material hexagonal ferrite used in the present invention. The holding time at this temperature and pressure is 1
It is sufficient if the time is within 0 hours, and in some cases, the purpose may be achieved even with about 1 hour.

The magnetic particles used in the magnetic recording medium of the present invention are made of hexagonal ferrite of the composition formula (1) prepared as described above, glycosides, Flu, polyhydric alcohol 1, oxycarboxylic acid or its salt. At least one selected substance (hereinafter referred to as intermediate agent) is
It can be produced by contacting in a zO medium and in the presence of an alkali.

At that time, there are three cases regarding the timing of adding medium.

(1) When producing hexagonal ferrite of compositional formula (1), a medium is added in the process of conditioning the raw material alkaline slurry material to be subjected to the autoclave (before the hydrothermal synthesis reaction of hexagonal ferrite in the autoclave). Added.

(2) A medium is added during the hydrothermal synthesis of the hexagonal ferrite of Weiwu (1).In this case, a solution containing a predetermined amount of medium is fed at high pressure into an autoclave that has reached a predetermined temperature and pressure. to liquefy

(3) Separately synthesized hexagonal ferrite of compositional formula (1) is used as a starting material. In this case, a predetermined amount of hexagonal ferrite and a medium are mixed and adjusted in an alkaline solution containing an alkaline substance in the atmosphere, and then hydrothermal treatment is performed.

Note 1. Of course, in the case of (3), it is not necessary to use hexagonal ferrite produced by a hydrothermal synthesis method as a starting material.

In both cases, although the timing of addition of the medium is different, the medium comes into contact with fine hexagonal ferrite with an average particle size of 5μ or less in the presence of an alkali in a medium over 100°C. Therefore, the novel magnetic particles of the present invention can be produced.

Specific examples of intermediate preparations that can be used in the powder method include glycosides such as β-methyl glucoside and arbutin; monoses, dioses, maltose, sucrose, cellulose, dextran, glycogen, and dextrin.

mM of starch, alginic acid, etc.: Tetritol.

#Nl alcohols such as bentitol and hexitol;
Ethylene glycol, diethylene glycol.

Polyethylene glycol, propylene glycol.

Polyhydric alcohols such as glycerin, cholesterol, and stigmasterol; mononitrate esters.

At least one substance selected from esters such as benzoic a ester; oxycarboxylic acids such as ascorbic acid, tartaric acid, sodium citrate, or their salts; It is 0.1 weight percent or more based on the amount of ferrite.

Note that a method for hydrothermally synthesizing magnetoblanbite type ferrite in the presence of the above-described organic substance has already been disclosed in Japanese Patent Laid-Open No. 61-40823 by the present inventors. Here, the organic substances corresponding to glycosides m, ti, polyhydric alcohols, oxycarboxylic acids, or salts thereof are those described as agents O in the above publication. however.

The effects of this agent B described in the above publication are as follows. When hydrothermally synthesizing magnetobrambite-type ferrite, ferrite powder obtained by conventional hydrothermal synthesis has a low saturation magnetization.

For the purpose of improving the saturation magnetization, the intermediate agents described in the publication are present as main reaction aids, and in some cases, the effect of these intermediate agents is further promoted by using them in combination with the agent O, which significantly improves the saturation magnetization. It is said that it was made a government office. As described above, the action of the agent O in this publication is aimed at providing an auxiliary effect to improve the saturation magnetization of ferrite powder during the hydrothermal synthesis of magnetobrambite ferrite, which is one of the objects of the present invention. The effect is substantially different from the formation of spinel type ferrite. Furthermore, in order to obtain a ferrite powder having +2≧θ and ≧−50e/”C like the product of the present invention, it cannot be obtained by the combination of the intermediate agent and the O agent by the method described in the above-mentioned publication; It is necessary to use only organic matter and to adopt the specific conditions.

The amount of alkali used in the alkali adjustment (alkali adjustment when bringing the hexagonal ferrite into contact with the medium) is 1! This is the amount of free alkali that can exist in the alkaline slurry material after conditioning. Alkaline solutions include NaOH, KOH, L
A solution of iOH, NH, OH, a mixed solution thereof, or a solution containing other strongly alkaline substances can be used.

Regarding the hydrothermal treatment temperature in an autoclave (the temperature at which the hexagonal ferrite and medium are brought into contact).

Temperatures above 100"C, more preferably 120-300
°C is appropriate. The temperature inside the autoclave is 300°C
If the temperature exceeds 120°C, coarse particles will be produced and the particle size distribution will be poor (on the other hand, if it is below 120°C, the amount of the desired magnetic material produced will decrease.The holding time at this temperature and pressure is usually 1 to 3 hours. It is enough.

Since the slurry-like material containing the crystalline anisotropic oxide magnetic material obtained in this manner exhibits high causticity, it is repeatedly filtered and washed with water to sufficiently remove impurities. After this washing, known acidic substances such as HC1, Hc10=, HNO
s, HCOOH, HsPO4, etc., in which case, after the treatment.

Furthermore, wash with water to remove acidic substances.

In this way, the particle shape is plate-like and the plate-like ratio is 2~
30, preferably with an average particle size of 0.30. Magnetic particles according to the present invention having a diameter of ~1.0 μm are obtained. As shown in Examples below, this powder was identified by X-ray diffraction and was found to have a substantially spinel structure, with a small amount of hexagonal ferrite phase also being observed in some cases.

Furthermore, when measuring the metal components present on the surface of one particle, for example, using Auger electrons, the M1 element of the composition formula (1) (i.e., Ba, Sr, Pb) is found up to the surface layer of the second particle.
It is recognized that at least one metal element such as Ca or Ca) is distributed.

According to the results obtained by the present inventors, the magnetic particles obtained in this way have a temperature dependence (θ,) of coercive force measured in a l(+(to Oe) magnetic field) of +2≧θ□≧−5( Os/°C), and the saturation magnetization (σ, ) were both higher values than the starting material hexagonal ferrite.

The highest threshold value was 63 emu/g. and.

It has been found that these properties are substantially maintained even when a magnetic recording medium is produced using these magnetic particles.

Furthermore, the magnetic particles are X as spinel as described above.
Despite having a linear diffraction line, it was confirmed that the easy axis of magnetization was perpendicular to the particle plate surface ((001>axis). This was confirmed by a simple method to prepare a tape. Let me explain with an example.

Using the ferrite powder having a plate-like ratio of 1O according to the present invention obtained as described above, a magnetic paint having the following composition was prepared with a dispersion time of 4 hours, and the resulting paint was applied onto a polyethylene terephthalate film using an applicator. After drying, a tape was prepared by calendering, and a comparison was made using hexagonal ferrite powder with a plate ratio of 10 using the same method as above. The result was different.

[Composition of magnetic paint]

Ferrite powder ioo parts by weight vinyl chloride, vinyl acetate.

Vinyl alcohol copolymer 5 parts by weight lecithin
1 part by weight polyurethane resin
5 parts by weight methyl ethyl ketone
70 parts by weight cyclohex, Sanon 70
Parts by weight: 70 parts by weight The squareness ratio and orientation ratio were as follows.

Here, SO(, L) represents the squareness ratio in the direction perpendicular to the surface of the base film, and 5Q(=) represents the squareness ratio in the direction parallel to the base film surface.

In this way, the tape using the magnetic particles of the present invention has its S
O(±) is as large as 0.818, which is comparable to that using hexagonal ferrite powder, so the axis of easy magnetization is perpendicular to the particle plate surface ((001) axis).
It was confirmed that it exists.

〔Effect of the invention〕

(1)0 The temperature dependence of coercive force (θHc) of the magnetic recording medium of the present invention is arbitrarily adjusted within the range of +2≧θ□≧-5 (Oe/'C). Unlike magnetic recording media, it has the great advantage of being widely applicable depending on changes in the recording system or the environment temperature in which it is used.

(2) 8 The magnetic recording medium of the present invention has higher B- than the conventional magnetic recording medium using hexagonal ferrite.

Since it is a magnetic recording medium with improved output, it can provide a more advantageous magnetic recording medium than conventional magnetic recording media using hexagonal ferrite.

(3) In particular, the magnetic recording medium according to the present invention, in which the easy axis of magnetization is aligned perpendicular to the support, can be used in a perpendicular magnetic recording system, and cannot be obtained with conventional hexagonal ferrite. It is possible to provide the market with a product with excellent properties.

Typical examples of the present invention are listed below.

(Example 1) As a composition, Ba0 ・5.9 (Fe+, aZro
, 3Zn*, +sFe''., +5Os), the platelet ratio is 12, the average particle size is 0.11//11, and 10
The coercive force measured by VSM in the magnetic field of (koe) is 65
．． 0 (Oe), and the temperature dependence of its coercive force is +3. Q(O
e/ “C)” and the saturation magnetization is 51.5 emu/
7 g of Ba-ferrite powder H was suspended in 480 ml of an aqueous solution containing 0.547 mol of sodium hydroxide, and then 5.85 mol of diethylene glycol was added to this suspension.
After adding 520 tal of an aqueous solution containing g and stirring and mixing thoroughly, an alkaline slurry was prepared.

The alkaline slurry was heated at 280°C in an autoclave.
Hydrothermal treatment was carried out for 60 minutes. After thoroughly washing the reaction product obtained in this way and removing impurities,
Dry pulverization was performed to obtain magnetic particles.

As a result of 5X-ray diffraction, the obtained magnetic particles were found to have one strong spinel structure diffraction line in addition to an extremely weak magnetobrambite structure diffraction line, as shown in FIG.

As shown in the photograph of FIG. 2, the magnetic particles have a plate ratio of 14.
The average particle size was 0.16 μm.

' Furthermore, when measured with VSM in a magnetic field of 10 (koe), the coercive force was 640 (Oe), the temperature dependence of the coercive force was 10,15 (Oe/''C), and the saturation magnetization was 61 emu/g. Met.

In addition, as measured by Auger electron, the metal component 1 present on the particle surface of the 6I substance particles + B a + Z
The presence of r + Zn and Fe was confirmed.

Using the magnetic particles obtained in this way.

A magnetic coating material with the following composition was prepared by kneading and disintegrating it in a sand mill for 120 minutes.

[Composition of magnetic paint] Magnetic powder 100 parts by weight Vinyl chloride, vinyl acetate 1 part by weight Copolymer polyurethane resin 5 parts by weight Acetylacetone 1 part by weight Butyl stearate 1 part by weight Carbon blank
2 parts by weight Alumina 6 parts by weight Methyl ethyl ketone 80 parts by weight Toluene 40 parts by weight Cyclohexanone 40 parts by weight The magnetic paint thus prepared was applied onto a polyethylene terephthalate film using an applicator, and then applied in a direction perpendicular to the film surface. After passing through a 1500G magnetic field,
It was immediately dried and then calendered to produce a magnetic recording medium.

When the manufactured magnetic recording medium was evaluated using VSM in a magnetic field of 10 (kOe), the coercive force was 690 (Oe).
).

Temperature dependence of coercive force is +〇, IQ (Oe/'C),
Squareness ratio in the direction perpendicular to the film surface (SQ(1)
: value after demagnetizing field correction) is 0.86. The squareness ratio SQ(·) in the direction parallel to the film surface is 0.28. Then, the orientation ratio, that is, SQ(±)/5Q(=) is 3.07
Met. Also.

[3m was 1710 (G).

This SQ (upper) and SQ (upper) / 5Q (=) (straight) are comparable to (approximately) the comparative example (1) described later, so the magnetic material used here is It was confirmed that the magnetization axis of the particle is perpendicular to the particle surface.The temperature dependence of the coercive force of this magnetic recording medium is +0.10.
(Oe/''C) and is stable against changes in the operating environment temperature, making it suitable as a magnetic recording medium used in the 5 perpendicular magnetic recording force type.

[Example 2] The composition is Ba0 ・5.5 (Fe1.*Zro
, osCOe, os03), the platelet ratio is 2, the average particle size is 0.06 μI, and the coercive force measured by VSM in a magnetic field of 10 (koe) is 890 (Oe),
The temperature dependence of the coercive force is +4.4 (Oa/'C), and the saturation magnetization is 55. 'Ba- which is 5 emu/g
117g of ferrite powder 0.54ml of sodium hydroxide
Suspend in 480 #l of an aqueous solution containing 1 mol of ascorbic acid 9, then add to this suspension an aqueous solution 5 containing 5.85 g of ascorbic acid.
After adding 20 ml and sufficiently stirring and mixing to prepare an alkaline slurry, the alkaline slurry was hydrothermally treated in an autoclave at 280°C for 60 minutes.

The thus obtained reaction product was thoroughly washed to remove impurities, and then dried and pulverized to obtain magnetic particles.

As a result of X-ray diffraction, the obtained magnetic particles were found to be Example (1)
Similarly, in addition to the very weak diffraction line of the magnetobrambite type structure, one strong diffraction line of the spinel structure was observed.

The magnetic particles had a plate ratio of 3 and an average particle size of 0.07 μm. Furthermore, 10 (KOe) '611, VS
When measured at ,,M, the coercive force was 850 (Oe)
, the temperature dependence of its coercive force is -4,l (Oe/'C
), and the saturation magnetization was 63 emu/g. Also, when the metal component present on the particle surface of the magnetic particles was measured by Auger electron, it was found that B at Z r
The presence of +Co and Fe was confirmed.

The thus obtained magnetic particles were kneaded and dispersed in a sand mill for 120 minutes to prepare a magnetic paint having the following composition.

[Composition of magnetic paint]

Magnetic powder 100 parts by weight Vinyl chloride, vinyl acetate 15 parts by weight Copolymer polyurethane resin 5 ffi parts Acetylacetone 1 part Butyl stearate 1 part by weight Carbon black
2 parts by weight Alumina 6 parts by weight Methyl ethyl ketone 80 parts by weight Toluene 40 parts by weight Cyclohexanone 40 parts by weight
After applying the produced magnetic paint onto a polyethylene terephthalate film using an applicator, it is passed through a tsooc magnetic field applied in a direction parallel to the film surface, immediately dried, and then calendered to form a magnetic recording medium. was created.

When the manufactured magnetic recording medium was evaluated using VSM in a magnetic field of 10 (kOe), the coercive force was 950 (Oe).
), the temperature dependence of coercive force is -4.2 (Oe) °C), and the squareness ratio in the direction perpendicular to the film surface (on SQC) after two demagnetizing fields hli is 0.37. The squareness ratio SQ(·) in the direction parallel to the film surface is 0.82. The orientation ratio, ie, 5Q(=)/SQ(upper), was 2.22.

Also, theory B was 1780 (G).

In this way, the magnetic recording medium is well oriented in the in-plane direction,
Also, the temperature dependence of coercive force is −4.2 (Oe/“C),
Met.

[Comparative example]

A coating material and a magnetic recording medium were prepared in the same manner as in Example (1) using the Ba ferrite powder used in Example (1). Regarding the obtained magnetic recording medium, 1
When evaluated using VSM in a magnetic field of 0 (koe), the force maintained was 750 (Oe), and the temperature dependence of coercive force was +
3.1 (Oa) °C), SQ (top) is 0.88. 5
Q (=) is 0.26°, and the orientation ratio SQ (Sat)/5
Q(=) was 3.38. Also, Bm is 1320 (
G).

Although this magnetic recording medium has good perpendicular alignment, the temperature dependence of the coercive force is as large as +3.1 (Oe/'C), making it a thermally unstable recording medium. Compared to 1), BIll is smaller and the output is inferior.

[Brief explanation of the drawing]

FIG. 1 is an X-ray diffraction diagram of the magnetic particles of Example 1. FIG. 2 is an electron micrograph (30,000 times magnification) showing the crystalline state of the magnetic particles of Example 1.

Claims (1)

[Claims] In a magnetic recording medium in which a magnetic layer containing magnetic particles is provided on a support, the magnetic particles have an average particle size of 0.
．． 01 to 1.0 μm and a platelet ratio of 2 to 30, and at least one metal element of Ba, Sr, Pb, or Ca is included in the crystal structure as an element constituting the crystal. is composed of a crystal that has X-ray diffraction lines substantially like that of spinel, and whose easy axis of magnetization is in the uniaxial direction (perpendicular to the plate surface) of the (001) axis, which is in the same direction as the hexagonal ferrite. A magnetic recording medium characterized by: