JP2000143250A - Nonmagnetic particulate powder for nonmagnetic underlayer of magnetic recording medium, its production and magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain nonmagnetic particulate powder for a nonmagnetic underlayer of a magnetic recording medium excellent in surface smoothness and uniform in minor axis size by specifying the geometric standard deviations of major and minor axis sizes of acicular hematite particles and the BET specific surface area and average major axis size of the particles. SOLUTION: Nonmagnetic particulate powder comprises acicular hematite. The geometric standard deviations of major and minor axis sizes of the powder are <=1.5 and <=1.3, respectively, the BET specific surface area of the powder is 40-150 m2/g and the average major axis size is 0.01-0.2 μm. The acicular hematite particulate powder is preferably coated with a surface coating comprising at least one selected from hydroxides and oxides of aluminum and silicon. The average minor axis size of the powder is preferably 0.005-0.1 μm and the axial ratio of the powder (ratio between average major and minor axis sizes) is preferably 2-20.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention provides a needle-like hematite particle powder suitable as a non-magnetic particle powder for a non-magnetic underlayer of a magnetic recording medium having better surface smoothness.

[0002]

2. Description of the Related Art In recent years, as long-term recording and miniaturization of video and audio magnetic recording / reproducing devices have progressed, the performance of magnetic recording media such as magnetic tapes and magnetic disks has been improved. There is an increasing demand for higher performance, higher output characteristics, especially improved frequency characteristics, and lower noise.

In particular, in recent years, the demand for higher image quality and higher image quality of video tapes has been increasing more and more, and the frequency of a carrier signal to be recorded has shifted to a short wavelength region as compared with conventional video tapes. As a result, the magnetization depth from the surface of the magnetic tape is extremely shallow.

[0004] In order to improve the high output characteristics of a magnetic recording medium, especially the S / N ratio, for a short wavelength signal, it is strongly required to make the magnetic recording layer thinner. This fact is described in, for example, “‥ Development of Magnetic Materials and Technology for Highly Dispersing Magnetic Powder” published by Sogo Gijutsu Center (1982), p.
The condition for high-density recording in a coating type tape is to be able to maintain high output characteristics with low noise for a short wavelength signal. For this purpose, both the coercive force Hc and the residual magnetization Br are large. And the thickness of the coating film must be thinner. ‥‥ ”.

[0005] As the thickness of the magnetic recording layer is reduced, the problems of smoothness and uneven thickness of the magnetic recording layer have arisen. As is well known, the surface of the base film must also be smooth in order to make the magnetic recording layer smooth and without thickness unevenness. This fact can be found, for example, in the Engineering Information Center Publishing Division, "Magnetic Tape-Factors Arising from Friction and Wear in Head Running System and Troubleshooting-Comprehensive Technical Data Collection (hereinafter referred to as" Comprehensive Technical Data Collection ")," (1987) “The surface roughness of the magnetic layer after curing strongly depends on the surface roughness (back surface roughness) of the base, and both are almost proportional to each other. The smoother the surface of the base is, the more uniform and large the head output is obtained, and the higher the S / N ratio is.

Therefore, at least an underlayer (hereinafter referred to as a nonmagnetic underlayer) formed by dispersing nonmagnetic particles such as acicular hematite particles in a binder resin on a nonmagnetic support such as a base film. It has been proposed and has been put to practical use to solve problems such as deterioration of surface properties of the magnetic recording layer and deterioration of electromagnetic conversion characteristics by providing one layer. (JP-B-6-93297, JP-A-62-159338, JP-A-63-187418, JP-A-4-16
7225, JP-A-4-325915, JP-A-5-73882, JP-A-5-182177, JP-A-9-170003, etc.

Improvement of the surface smoothness of the underlayer has been strongly demanded. Attempts have been made to improve the dispersibility of acicular hematite particles, which are nonmagnetic particles, by focusing on the particle diameter of the major axis. I have been. (JP-A-9-170003, JP-A-10-198948, JP-A-10-1989)
No. 273325).

[0008] Further, in order to make the surface of the underlayer more smooth, it is desired to improve the dispersibility of acicular hematite particle powder. An application for an invention relating to hematite particles from which fine particles have been removed has been filed (Japanese Patent Application No. 9-342163).

[0009]

The particles having a uniform particle size, particularly those having a short axis diameter, which are suitable as a nonmagnetic particle powder for a nonmagnetic underlayer of a magnetic recording medium having more excellent surface smoothness. Certain acicular hematite particle powders are currently the most demanded, but have not yet been obtained.

That is, Japanese Patent Application Laid-Open No. 9-170003 discloses that acicular goethite particles or acicular hematite particles obtained by heating and dehydrating the acicular goethite particles are heated at a temperature of 550 ° C. or more. Although a method for obtaining densified needle-like hematite particles has been described, as shown in Comparative Examples below, the geometric standard deviation of the minor axis is high, and the particle diameter of the minor axis is sufficiently uniform and uniform. Not at all.

[0011] Also, Japanese Patent Application No. 9-342163 mentioned above,
By dissolving the acicular hematite particle powder in acid, the acicular hematite fine particle component present in the acicular hematite particle powder is dissolved to improve the particle size distribution of the particle diameter. As shown, since the minor axis diameter has a high geometric standard deviation value, it is difficult to say that the minor axis diameter is sufficiently uniform.

Therefore, the present invention provides a needle having a uniform particle size, particularly a short axis diameter, which is suitable as a nonmagnetic particle powder for a nonmagnetic underlayer of a magnetic recording medium having excellent surface smoothness. It is a technical object to obtain powdery hematite particles.

[0013]

The above technical object can be achieved by the present invention as described below.

That is, according to the present invention, the geometric standard deviation of the major axis is 1.5 or less and the geometric standard deviation of the minor axis is 1.3.
Or less, and the BET specific surface area value is 40 to 150 m
Non-magnetic particle powder for a non-magnetic underlayer of a magnetic recording medium, characterized by comprising acicular hematite particle powder having an average major axis diameter of 0.01 to 0.2 μm of ² / g (the present invention 1). .

Further, according to the present invention, the particle surface of the acicular hematite particles according to the present invention is characterized in that the particle surface is made of at least one selected from aluminum hydroxide, aluminum oxide, silicon hydroxide and silicon oxide. A non-magnetic particle powder for a non-magnetic underlayer of a magnetic recording medium, which is characterized by being coated with a surface coating (the present invention 2).

In addition, the present invention relates to a method of heating and dehydrating acicular goethite particles in a temperature range of 550 to 850 ° C. to obtain acicular hematite particles. 10 particles powder
The non-magnetic underlayer for a magnetic recording medium according to the above, wherein the goethite ultrafine particles contained in the goethite particle powder are absorbed by the goethite particles by performing a heat treatment in a temperature range of 0 to 200 ° C. This is a method for producing magnetic particle powder.

Further, the present invention provides a non-magnetic support, a non-magnetic underlayer comprising a non-magnetic particle powder formed on the non-magnetic support and a binder resin, and a magnetic layer formed on the non-magnetic under layer. In a magnetic recording medium comprising a magnetic recording layer composed of particle powder and a binder resin, the non-magnetic particle powder is the non-magnetic particle powder for a non-magnetic underlayer according to the first and second aspects of the present invention. Magnetic recording medium.

Next, the structure of the present invention will be described in more detail.

First, the acicular hematite particles according to the present invention will be described.

The acicular hematite particle powder according to the present invention comprises:
Average major axis having a geometric standard deviation value of the major axis diameter of 1.5 or less, a geometric standard deviation value of the minor axis diameter of 1.3 or less, and a BET specific surface area value of 40 to 150 m ² / g. The diameter is 0.
It consists of needle-like hematite particles having a size of from 01 to 0.2 μm.

The particle shape of the acicular hematite particles according to the present invention is acicular. Here, the term "needle-shaped" means a needle-like shape, a spindle shape, a rice grain shape, and the like, as well as a literal needle-like shape.

When the geometric standard deviation of the major axis exceeds 1.5 and the geometric standard deviation of the minor axis exceeds 1.3, the existing coarse particles adversely affect the surface smoothness of the coating film. Is not preferred to give. In consideration of the surface smoothness of the coating film, the geometric standard deviation of the major axis diameter is preferably 1.40.
Or less, more preferably 1.35 or less. Further, the geometric standard deviation value of the minor axis diameter is preferably 1.28 or less, more preferably 1.25. In consideration of industrial productivity, the lower limit of the geometric standard deviation of the major axis diameter and the minor axis diameter of the obtained acicular hematite particles is 1.01.

When the average major axis diameter of the acicular hematite particle powder according to the present invention is less than 0.01 μm, dispersion in a vehicle becomes difficult due to an increase in intermolecular force due to finer particles. If the average major axis diameter exceeds 0.2 μm, the particle size is too large, which impairs the surface smoothness of the coating film, which is not preferred. Considering the dispersibility in the vehicle and the surface smoothness of the coating film, the average major axis diameter is 0.0
2 to 0.1 μm is preferred.

The average minor axis diameter of the acicular hematite particles according to the present invention is preferably 0.005 to 0.1 μm.

The reason for setting the lower limit and the upper limit of the average minor axis diameter of the acicular hematite particles according to the present invention is the same as in the case of the average major axis diameter. Considering the dispersibility in the vehicle and the surface smoothness of the coating film, the average minor axis diameter is 0.0
1 to 0.05 μm is preferred.

The acicular hematite particle powder according to the present invention comprises:
BET specific surface area value is 40-150m ²/ G. BE
The reason for setting the lower limit and upper limit of the T specific surface area value is described above.
It is the same as the upper limit value and the lower limit value of the average major axis diameter. Vehicle
Considering the dispersibility in and the surface smoothness of the coating,
BET specific surface area value is 45-100m²/ G is preferred,
More preferably 50-80m²/ G.

The acicular hematite particle powder according to the present invention comprises:
The axial ratio (ratio of average major axis diameter to average minor axis diameter) is preferably 2 to 20. When the axial ratio is less than 2, it is difficult to obtain a coating film having a sufficient stiffness. When the axial ratio exceeds 20, the entanglement of the particles in the vehicle increases, and the dispersibility may deteriorate or the viscosity may increase.

The degree of densification of the acicular hematite particles according to the present invention is preferably 0.5 to 2.5. The degree of densification is determined by the ratio of the specific surface area S _BET value measured by the BET method to the surface area S _TEM value calculated from the major axis diameter and the minor axis diameter measured from the particles shown in the electron micrograph (S
_(BET / S _TEM value).

When the S _BET / S _TEM value is less than 0.5, although the densification of the acicular hematite particle powder has been achieved, the particle diameter is reduced due to sintering between the particles and the particles. It is so large that a coating film having sufficient surface smoothness cannot be obtained. If the S _BET / S _TEM value exceeds 2.5, the density is not sufficiently increased, and a large number of dehydration pores are present inside the particles and on the surface of the particles, so that the dispersibility in the vehicle becomes insufficient. Taking into account the dispersibility in the vehicle and the surface smoothness of the coating film, the S _BET / S _TEM value is 0.1.
7 to 2.0 is preferable, and 0.8 to 1.6 is more preferable.
It is.

The acicular hematite particle powder according to the present invention comprises:
If necessary, the particle surface may be coated with a surface coating made of at least one selected from aluminum hydroxide, aluminum oxide, silicon hydroxide and silicon oxide. The acicular hematite particle powder whose particle surface is coated with a surface coating has good compatibility with a binder resin when dispersed in a vehicle, and a desired degree of dispersion is easily obtained.

The amount of the coating is such that aluminum hydroxide and aluminum oxide are converted to Al and silicon hydroxide and silicon oxide are converted to SiO ₂ with respect to the acicular hematite particle powder. 0.01 to 50% by weight is preferred. When the amount is less than 0.01% by weight, the effect of improving the dispersibility by the coating is almost nil. Considering the effect of improving dispersibility in the vehicle and industrial productivity, 0.05 to 20% by weight is more preferable.

When the aluminum compound and the silicon compound are used in combination, the total amount of the converted amount of Al and the converted amount of SiO ₂ is 0.01 to
50% by weight is preferred.

The acicular hematite particle powder coated with the surface coating according to the present invention has substantially the same particle size and geometry as the acicular hematite particle powder according to the present invention not coated with the surface coating. It has a standard deviation value, an axial ratio, a BET specific surface area value, and an S _BET / S _TEM value.

Next, a method for producing acicular hematite particles according to the present invention will be described.

The acicular hematite particle powder according to the present invention comprises:
An oxygen-containing gas such as air is added to a suspension containing an iron-containing precipitate obtained by reacting with a ferrous salt and an aqueous solution of an alkali hydroxide aqueous solution, an alkali carbonate aqueous solution or an alkali hydroxide / alkali carbonate aqueous solution. To generate goethite particle powder,
After the heat treatment in the temperature range of ℃, further 550-850 ℃
In the above temperature range.

The goethite particle powder as the starting material particle powder in the present invention has a geometric standard deviation of the major axis diameter of 1.
7 or less, the geometric standard deviation of the minor axis diameter is 1.5 or less, the average major axis diameter is 0.01 to 0.25 μm, and the average minor axis diameter is 0.00.
5 to 0.17 μm, BET specific surface area 50 to 250 m
² / g is used.

During the formation reaction of the goethite particles, different elements such as Ni, Zn, P, and Si, which are usually added to improve various properties such as the major axis diameter, the minor axis diameter, and the axial ratio of the particles, are used. There is no problem even if added.

When the heat treatment temperature is lower than 100 ° C., it is difficult to sufficiently absorb goethite ultrafine particles into goethite particles, and particles having a uniform particle size cannot be obtained. When the temperature exceeds 200 ° C., dehydration of the goethite particles starts in the presence of the ultra-fine goethite particles, so that sintering occurs between the particles and particles having a uniform particle size cannot be obtained. The heat treatment temperature is preferably 120 to 200 ° C. in consideration of industrial productivity and the like.

The heating time is preferably 5 to 60 minutes.

The goethite particle powder heat-treated in a temperature range of 100 to 200 ° C. has an average major axis diameter of 0.01 to 0.1.
2 μm, average minor axis diameter 0.007 to 0.18 μm, major axis diameter geometric standard deviation 1.5 or less, minor axis diameter geometric standard deviation 1.3 or less, BET specific surface area 50 to 50 250m
² / g.

When the temperature of the heat dehydration treatment is lower than 550 ° C., since the densification is insufficient, a large number of dehydrated pores are present inside and on the surface of the hematite particles. Dispersibility becomes insufficient, and when a nonmagnetic underlayer is formed, it is difficult to obtain a coating film having a smooth surface. When the temperature is higher than 850 ° C., the densification of the acicular hematite particles is sufficient, but sintering between the particles and the particles occurs. It is difficult to obtain. The upper limit of the heating temperature is preferably 8
00 ° C.

The needle-like hematite particles according to the present invention may be obtained by heating and dehydrating goethite particles at a temperature of 100 to 200 ° C. at a temperature of 250 to 500 ° C. Hematite particle powder, and then the low-density acicular hematite particle powder
It is preferably a high-density acicular hematite particle powder obtained by baking in a temperature range of 850 ° C.

When the heat dehydration temperature for lowering the density is lower than 250 ° C., a long time is required for the dehydration reaction. When the heating dehydration temperature exceeds 500 ° C., a dehydration reaction occurs rapidly,
There is a possibility that the shape of the particles is easily collapsed and sintering between the particles is caused. The acicular hematite particles obtained by the heat dehydration treatment are low-density particles having a large number of dehydrated pores in which H ₂ O is dehydrated from goethite particles, and have a BET specific surface area of 1.2 to 2 times that of the acicular goethite particles. About.

When the baking temperature is lower than 550 ° C., the densification is insufficient, so that a large number of dehydrated pores exist inside and on the surface of the hematite particles. When the nonmagnetic underlayer is formed, it is difficult to obtain a coating film having a smooth surface.
When the temperature is higher than 850 ° C., the densification of the acicular hematite particles is sufficient, but sintering between the particles and the particles occurs. It is difficult to obtain. The upper limit of the heating temperature is preferably 800
° C.

The acicular hematite particle powder according to the present invention comprises:
Prior to the heat dehydration treatment at 550 to 850 ° C. or the baking treatment for densification, it is preferable to coat the particle surface with a sintering inhibitor in advance. The coating treatment with the sintering inhibitor is performed by heating and dehydrating the acicular goethite particle powder as the starting material particle powder or the acicular goethite particle powder after the heat treatment at 100 to 200 ° C. in the temperature range of 250 to 500 ° C. The sintering inhibitor may be added to the resulting aqueous suspension containing the low-density acicular hematite particles, mixed, stirred, filtered, washed with water, and dried.

Examples of the sintering inhibitor include phosphorus compounds such as sodium hexametaphosphate, polyphosphoric acid and orthophosphoric acid which are usually used, No. 3 water glass, silicon compounds such as sodium orthosilicate, sodium metasilicate and colloidal silica, and boric acid. Aluminum compounds such as aluminum acetate, aluminum sulfate, aluminum chloride, and aluminum nitrate; alkali aluminates such as sodium aluminate; aluminum compounds such as alumina sol; and titanium compounds such as titanyl sulfate. .

Next, the surface coating treatment of the acicular hematite particles coated with the surface coating according to the present invention is performed by dispersing the acicular hematite particle powder according to the present invention in an aqueous solution. To the particle surface of the acicular hematite particles by adding an aluminum compound, a silicon compound, or both compounds, and mixing and stirring, or, if necessary, adjusting the pH value after mixing and stirring. Oxide, aluminum oxide, silicon hydroxide and silicon oxide may be coated,
Filter, wash, dry and pulverize. If necessary, a deaeration / consolidation treatment or the like may be further performed.

As the aluminum compound and silicon compound used for the surface coating treatment, the same aluminum compound and silicon compound used as the above-mentioned sintering inhibitor can be used.

Next, the magnetic recording medium according to the present invention will be described.

The magnetic recording medium according to the present invention comprises a non-magnetic support, a non-magnetic underlayer formed on the non-magnetic support, and a magnetic recording layer formed on the non-magnetic under layer.

As the non-magnetic support, polyethylene terephthalate, which is currently widely used for magnetic recording media,
Polyethylene, polypropylene, polycarbonate, polyethylene naphthalate, polyamide, polyamide imide, synthetic resin film such as polyimide, aluminum,
Metal foils and plates such as stainless steel and various types of paper can be used. Although the thickness varies depending on the material, it is usually preferably 1.0 to 300 μm, more preferably 2.0 to 200 μm. In the case of a magnetic disk, polyethylene terephthalate is usually used as the nonmagnetic support, and its thickness is usually 50 to 300 μm, preferably 60 to 200 μm. In the case of magnetic tape, the thickness of polyethylene terephthalate is usually 3
１００100 μm, preferably 4-20 μm, in the case of polyethylene naphthalate, the thickness is usually 3-50 μm,
The thickness is preferably 4 to 20 μm, and in the case of polyamide, the thickness is usually 2 to 10 μm, preferably 3 to 7 μm.

The nonmagnetic underlayer according to the present invention comprises the acicular hematite particle powder according to the present invention or the acicular hematite particle powder coated with the surface coating according to the present invention and a binder resin.

As the binder resin, vinyl chloride-vinyl acetate copolymers, urethane resins, vinyl chloride-vinyl acetate-
Maleic acid copolymer, urethane elastomer, butadiene-acrylonitrile copolymer, polyvinyl butyral, cellulose derivatives such as nitrocellulose, polyester resin, synthetic rubber resin such as polybutadiene, epoxy resin, polyamide resin, polyisocyanate, electron beam curable acrylic Urethane resins and the like and mixtures thereof can be used. Also, each binder resin has -OH, -COO
A polar group such as H, —SO ₃ M, —OPO ₂ M ₂ , and —NH ₂ (where M is H, Na, or K) may be included. Considering the dispersibility of the needle-like hematite particles according to the present invention in a vehicle, -COOH as a polar group,
Binder resins that contain -SO ₃ M are preferable.

The mixing ratio of the acicular hematite particle powder according to the present invention or the acicular hematite particle powder coated with the surface coating according to the present invention and the binder resin is as follows.
The acicular hematite particle powder is 5 to 20 parts by weight with respect to 00 parts by weight.
00 parts by weight, preferably 100 to 1000 parts by weight.

The coating thickness of the nonmagnetic underlayer formed on the nonmagnetic support is 0.2 to 10 μm. If it is less than 0.2 μm, it becomes difficult to improve the surface roughness of the nonmagnetic support, and the stiffness tends to be insufficient. In consideration of the thinning of the magnetic recording medium and the stiffness of the coating film, the thickness of the coating film is more preferably 0.5 to 5 μm.

Incidentally, a lubricant, an abrasive, an antistatic agent and the like used in the manufacture of a normal magnetic recording medium may be added to the non-magnetic underlayer, if necessary.

The nonmagnetic underlayer using the acicular hematite particle powder according to the present invention in which the particle surface is not covered with the surface coating has a glossiness of the coating film of 188 to 300%,
Preferably 193 to 300%, more preferably 198 to
300%, and the coating film surface roughness Ra is 0.5 to 8.8.
nm, preferably 0.5 to 8.2 nm, more preferably 0.5 to 7.8 nm, the stiffness of the coating film is
Young's modulus (relative value) is 119 to 160, preferably 12
0 to 160.

The non-magnetic underlayer using the acicular hematite particle powder according to the present invention in which the particle surface is coated with the surface coating has a glossiness of the coating film of 193 to 300%, preferably 196 to 300%. %, More preferably 200-3
00%, and the coating film surface roughness Ra is 0.5 to 8.0 n.
m, preferably 0.5 to 7.5 nm, more preferably 0.5 to 7.0 nm, and the stiffness of the coating film is
Young's modulus (relative value) is 120 to 160, preferably 12
3 to 160.

The magnetic recording layer according to the present invention comprises magnetic particle powder and a binder resin.

The magnetic particles include maghemite particles (γ-Fe ₂ O ₃ ) and magnetite particles ( Fe
Co-coated magnetic iron oxide particles obtained by coating Co or Co and Fe on magnetic iron oxide particles such as O _x .Fe ₂ O ₃ , 0 <x ≦ 1); Co-coated magnetic iron oxide particles containing different elements such as Co, Al, Ni, P, Zn, Si, B, and rare earth metals other than Fe, and metal magnetic particles containing iron as a main component , Iron alloy magnetic particles containing Co, Al, Ni, P, Zn, Si, B, etc. other than iron, plate-like ferrite particles containing Ba, Sr, Ba-Sr, etc. Ferrite particle powder and Co, Ni,
Any one of plate-like magnetoplumbite-type ferrite particles containing one or more coercive force reducing agents selected from divalent and tetravalent metals of Zn, Mn, Mg, and Ti is used. Can be.

In consideration of recent short-wavelength recording and high-density recording, metal magnetic particle powder containing iron as a main component, Co, Al, Ni, P, Zn, Si, B, rare earth metal, etc. other than iron Is preferred.

The magnetic particle powder has an average major axis diameter (average particle diameter in the case of plate-like particles) of 0.01 to 0.5 μm, preferably 0.03 to 0.3 μm. The shape of the particles of the magnetic particle powder is preferably needle-like or plate-like. Here "needle"
The meaning of the term includes not only a needle-like shape in a literal sense but also a spindle shape, a rice grain shape and the like.

When the particle shape of the magnetic particle powder is acicular, the axial ratio is 3 or more, preferably 5 or more. In consideration of dispersibility in a vehicle, the upper limit is 15, and preferably the upper limit is 15. It is 10.

When the particle shape of the magnetic particle powder is plate-like, the plate-like ratio (the ratio of the average particle diameter of the particles to the average thickness of the particles) (hereinafter referred to as “plate-like ratio”) is 2 or more, preferably 3. As described above, when the dispersibility in the vehicle is taken into consideration, the upper limit is 20 and preferably 15.

The magnetic properties of the magnetic particles are as follows.
00-3200 Oe, preferably 550-3200 Oe
And the saturation magnetization is 50 to 170 emu / g, preferably 60 to 170 emu / g. Considering high-density recording and the like, the coercive force value is more preferably 900 to 3
200 Oe, the saturation magnetization value is more preferably 70 to 17
0 emu / g.

As the binder resin, the binder resin used for forming the nonmagnetic underlayer can be used.

The coating thickness of the magnetic recording layer provided on the non-magnetic underlayer is in the range of 0.01 to 5 μm. 0.01
When the thickness is less than μm, uniform application is difficult and phenomena such as uneven coating are likely to occur, which is not preferable. If it exceeds 5 μm, it becomes difficult to obtain desired electromagnetic conversion characteristics due to the influence of a demagnetizing field. Preferably 0.05 to 1 μm
Range.

The mixing ratio of the magnetic particle powder to the binder resin is such that the magnetic particle powder is 2 parts per 100 parts by weight of the binder resin.
It is 00 to 2000 parts by weight, preferably 300 to 1500 parts by weight.

The magnetic recording layer may contain commonly used lubricants, abrasives, antistatic agents and the like.

The magnetic recording medium according to the present invention, when using Co-coated magnetic iron oxide particles as the magnetic particle powder,
Coercive force value of 500 to 1500 Oe, preferably 550 to
1500 Oe, squareness ratio (residual magnetic flux density Br / saturated magnetic flux density Bm) of 0.85 to 0.95, preferably 0.86 to 0.96
0.95, the glossiness of the coating film is 130 to 200%, preferably 140 to 200%, and the coating film surface roughness Ra is 12.0 nm.
Hereinafter, preferably 2.0 to 11.0 nm, more preferably 2.0 to 10.0 nm, Young's modulus is 125 to 160,
Preferably it is 130-160.

When acicular metal magnetic particles containing iron as a main component or iron alloy magnetic particles are used as the magnetic particles, the coercive force value is 800 to 3200 Oe, preferably 9 to 3200 Oe.
00-3200 Oe, and the squareness ratio (residual magnetic flux density Br / saturated magnetic flux density Bm) is 0.87-0.95, preferably 0.1-0.
88 to 0.95, glossiness of the coating film is 193 to 300%, preferably 198 to 300%, and coating film surface roughness Ra is 8.8.
nm or less, preferably 2.0 to 8.3 nm, more preferably 2.0 to 7.8 nm, and a Young's modulus of 126 to 160,
Preferably it is 131-160.

When plate-like magnetoplumbite type ferrite particles are used as the magnetic particles, the coercive force value is 800 to 3200 Oe, preferably 900 to 3200 Oe.
Oe, squareness ratio (residual magnetic flux density Br / saturated magnetic flux density Bm)
Is 0.85 to 0.95, preferably 0.86 to 0.9
5. The glossiness of the coating film is 160 to 300%, preferably 17
0 to 300%, the coating film surface roughness Ra is 12.0 nm or less,
Preferably from 2.0 to 11.0 nm, more preferably from 2.
It is from 0 to 10.0 nm and its Young's modulus is from 124 to 160, preferably from 128 to 160.

As a solvent used for forming the nonmagnetic underlayer and the magnetic recording layer, methyl ethyl ketone, toluene, cyclohexanone, methyl isobutyl ketone, tetrahydrofuran, a mixture thereof and the like commonly used for magnetic recording media can be used. Can be.

The amount of the solvent used is 65 to 1000 parts by weight in total with respect to 100 parts by weight of the particle powder. If the amount is less than 65 parts by weight, the viscosity becomes too high in the case of a paint, and application becomes difficult. If the amount exceeds 1000 parts by weight, the amount of the solvent volatilized when forming a coating film becomes too large, which is industrially disadvantageous.

[0075]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A typical embodiment of the present invention is as follows.
It is as follows.

The average major axis diameter and average minor axis diameter of the particles were determined for the approximately 350 particles shown in the electron micrograph (× 30,000) enlarged four times in the vertical and horizontal directions, respectively. And the minor axis diameter were measured, and the average value was shown.

The axial ratio is the ratio between the average major axis diameter and the average minor axis diameter, and the plate ratio is the ratio between the average particle diameter and the average thickness.

The particle size distribution of the major axis diameter and the minor axis diameter (hereinafter, referred to as “particle diameter”) of the particles was shown by the value obtained by the following method.

That is, the value obtained by measuring the particle size of the particles shown in the above enlarged photograph is plotted on a log-normal probability paper in accordance with a statistical method from the actual particle size and the number of particles calculated from the measured values. The axis is plotted with the particle diameter, and the vertical axis is plotted as a percentage of the cumulative number of particles belonging to each of the predetermined particle diameter sections (under the integrated screen). Then, from this graph, the values of the particle diameters corresponding to 50% and 84.13% of the number of particles are read, and the geometric standard deviation value = 8
The value was calculated according to the particle diameter at 4.13% / the particle diameter (geometric mean diameter) at 50% under the integrated screen.
The smaller the geometric standard deviation value, the better the particle size distribution of the particles.

The specific surface area was indicated by a value measured by the BET method.

The amount of Al, the amount of Si, and the amount of P existing inside and on the surface of the acicular hematite particles were measured using a “X-ray fluorescence spectrometer 3063M” (manufactured by Rigaku Corporation) according to JIS K0119. The measurement was performed according to “General rules for X-ray fluorescence analysis”.

The degree of densification of the acicular hematite particles was indicated by the S _BET / S _TEM value as described above. here,
The S _BET value is a value of the specific surface area measured by the above BET method. S _TEM value is the electron micrograph from an average major axis diameter lcm of the measured particles is a value calculated according to Equation 1 by assuming the particles a rectangular parallelepiped with an average short axis diameter wcm.

[0083]

[Equation 1] S_TEMValue (m²/ G) = [(4lw + 2
w²) / (Lw²・ Ρ_p)] × 10^-4  (However, ρ_pIs the true specific gravity of hematite particles, and 5.2
g / cm³Was used. )

The paint viscosity was measured at 25 ° C. using an E-type viscometer EMD-R (manufactured by Tokyo Keiki Co., Ltd.), and the shear rate D was 1.92 sec.
^It was shown by the value at ^-1 .

The glossiness of the surface of the coating film of the non-magnetic underlayer and the magnetic recording layer was determined by measuring the 45 ° glossiness of the coating film using “Gloss Meter UGV-5D” (manufactured by Suga Test Instruments Co., Ltd.). Was.

The surface roughness Ra is calculated as follows: Surfcom-57
The center line average roughness of the coating film was measured using “5A” (manufactured by Tokyo Seimitsu Co., Ltd.).

The stiffness of the coating film was measured using an “autograph”
It was determined by measuring the Young's modulus of the coating film using (manufactured by Shimadzu Corporation). Young's modulus was measured on a commercial videotape "AV T
-120 (manufactured by Victor Company of Japan, Ltd.) ". The higher the relative value, the better the stiffness of the coating film.

The thickness of each of the nonmagnetic support, the nonmagnetic underlayer, and the magnetic recording layer constituting the magnetic recording medium was measured by the following measuring method.

Digital electronic micrometer K351C
First, the film thickness (A) of the nonmagnetic support is measured using (manufactured by Anritsu Electric Co., Ltd.). Next, the thickness (B) of the nonmagnetic support and the nonmagnetic underlayer formed on the nonmagnetic support
(Sum of the thickness of the nonmagnetic support and the thickness of the nonmagnetic underlayer)
Is measured in the same manner. Further, the thickness (C) of the magnetic recording medium obtained by forming the magnetic recording layer on the nonmagnetic underlayer (the sum of the thickness of the nonmagnetic support, the thickness of the nonmagnetic underlayer, and the thickness of the magnetic recording layer) ) Is measured in the same manner. The thickness of the nonmagnetic underlayer is shown by (B)-(A), and the thickness of the magnetic recording layer is shown by (C)-(B).

The magnetic characteristics are described in “Vibrating sample magnetometer VSM-
3S-15 "(manufactured by Toei Industry Co., Ltd.) using an external magnetic field of up to 10 KOe.

<Production of Spindle-Shaped Hematite Particle Powder> Spindle-shaped goethite particle powder (average major axis diameter 0.0812) obtained using an aqueous ferrous sulfate solution and an aqueous sodium carbonate solution.
μm, geometric standard deviation of major axis diameter 1.53, average minor axis diameter 0.0110 μm, geometric standard deviation of minor axis diameter 1.33,
(Axial ratio 7.4 and BET specific surface area value 168.9 m ² / g)
1200 g was suspended in water to form a slurry, and the solid content concentration was adjusted to 8 g / l. 150 liters of this slurry was heated to a temperature of 60 ° C., and the pH value of the slurry was adjusted to 10.0 by adding a 0.1N aqueous NaOH solution.

Next, 36.0 g of No. 3 water glass as a sintering inhibitor was gradually added to the alkaline slurry, and after the addition was completed, aging was performed for 60 minutes. Next, a 0.1 N acetic acid solution was added to the slurry to adjust the pH value of the slurry to 6.0. Thereafter, filtration, washing with water, drying, and pulverization were performed by a conventional method to obtain spindle-shaped goethite particles having a silicon oxide coating on the particle surfaces. The silicon content was 0.78% by weight in terms of SiO ₂ .

The obtained spindle-shaped goethite particles were placed in a heat treatment furnace made of metal and heated at 150 ° C. for 30 minutes to allow the spindle-shaped goethite particles to absorb the ultra-fine goethite particles contained in the spindle-shaped goethite particles. Was.

Next, the obtained spindle-shaped goethite particles were again placed in a metal heat treatment furnace and subjected to a heat dehydration treatment at 320 ° C. for 30 minutes to dehydrate the spindle-shaped goethite particles to obtain low-density spindle-shaped hematite particles. A powder was obtained. The obtained low-density spindle-shaped hematite particle powder has an average major axis diameter of 0.7.
856 μm, geometric standard deviation of major axis diameter 1.38, average minor axis diameter 0.0118 μm, geometric standard deviation of minor axis diameter 1.1
6, axial ratio 6.1, BET specific surface area value 190.3 m ² /
g, S _BET / S _TEM value was 2.70. The silicon content was 0.78% by weight in terms of SiO ₂ .

Next, 850 g of the above-mentioned low-density spindle-shaped hematite particle powder was placed in a ceramic rotary furnace, and heat-treated in air at 650 ° C. for 30 minutes while being rotated to seal the dewatered holes. The densified spindle-shaped hematite particles have an average major axis diameter of 0.0727 μm, a geometric standard deviation of the major axis diameter of 1.38, and an average minor axis diameter of 0.01.
20 μm, geometric standard deviation of minor axis diameter is 1.17, axial ratio is 6.1, BET specific surface area is 86,8 m ² / g, S
_{The BET} / S _TEM value was 1.25. The silicon content was 0.87% by weight in terms of SiO ₂ .

<Formation of Non-Magnetic Underlayer> The obtained high-density spindle-shaped hematite particles were mixed with a binder resin and a solvent and kneaded at a solid content of 75% by weight using a plast mill for 30 minutes. Thereafter, a predetermined amount of the kneaded material was taken out, added to a glass bottle together with the glass beads and a solvent, and mixed and dispersed for 6 hours with a paint conditioner.

The composition of the obtained non-magnetic paint is as follows. Spindle-shaped hematite particle powder 100 parts by weight Vinyl chloride-vinyl acetate copolymer resin having sodium sulfonate group 10 parts by weight Polyurethane resin having sodium sulfonate group 10 parts by weight Cyclohexanone 44.6 parts by weight Methyl ethyl ketone 111.4 parts by weight Toluene 66 .9 parts by weight

The obtained nonmagnetic paint was applied on a polyethylene terephthalate film having a thickness of 14 μm to a thickness of 55 μm using an applicator, and then dried to form a nonmagnetic underlayer.

The resulting nonmagnetic underlayer has a gloss of 213%,
The surface roughness Ra was 6.0 nm and the Young's modulus was 131.

<Formation of Magnetic Recording Layer> Needle-like metal magnetic particles containing iron as a main component (average major axis diameter 0.103 μm, average minor axis diameter 0.0152 μm, axial ratio 6.8, coercive force value 191)
(0 Oe, saturation magnetization value: 136 emu / g), a binder resin and a solvent, and kneaded at a solid content of 78% by weight using a plastmill for 30 minutes to obtain a kneaded product. This kneaded material was added to a glass bottle together with a glass bead and a solvent, and mixed and dispersed for 6 hours with a paint conditioner.

Thereafter, an abrasive, a lubricant and a hardener were added, and the mixture was further mixed and dispersed for 15 minutes. The composition of the obtained magnetic paint was as follows. Acicular metallic magnetic particles containing iron as a main component 100 parts by weight Vinyl chloride-vinyl acetate copolymer resin having sodium sulfonate group 10 parts by weight Polyurethane resin having sodium sulfonate group 10 parts by weight Abrasive 10 parts by weight carbon black # 3250B 1.0 parts by weight Lubricant 3.0 parts by weight Curing agent 5 parts by weight Cyclohexanone 64.9 parts by weight Methyl ethyl ketone 162.2 parts by weight Toluene 97.3 parts by weight

After applying the obtained magnetic paint to a thickness of 15 μm on the nonmagnetic underlayer using an applicator, orienting and drying in a magnetic field, and then performing a calendering treatment, Perform a curing reaction for 24 hours.
A magnetic tape was obtained by slitting to a width of 5 inches.

The Hc of the obtained magnetic tape was 2011O.
e, squareness ratio (Br / Bm) is 0.88, glossiness is 235
%, Surface roughness Ra was 6.0 nm, and Young's modulus was 133.

[0104]

The important point in the present invention is that, prior to the heat dehydration treatment, the acicular goethite particles are heated in a temperature range of 100 to 200 ° C. so that the geometric standard deviation of the major axis diameter becomes 1.5. Due to the fact that it is possible to obtain a needle-like hematite particle powder having a uniform particle size with a geometrical standard deviation of the minor axis diameter of 1.3 or less, particularly with a uniform minor axis diameter. is there.

Regarding the reason why the acicular hematite particle powder having a uniform particle size according to the present invention can be obtained, the present inventor has proposed that the acicular goethite particle powder is subjected to heat treatment in a temperature range of 100 to 200 ° C. Since the fine particles are absorbed by the acicular goethite particles, the ultrafine particle component is small,
Needle-like goethite particles having a uniform major axis diameter and a uniform minor axis diameter are obtained, and the goethite ultrafine particle component is reduced. It is considered that the sintering between the particles is less likely to occur, so that it is possible to obtain acicular hematite particle powder that maintains the uniform particle size of the acicular goethite particles.

The magnetic recording medium according to the present invention has excellent surface smoothness when the acicular hematite particle powder according to the present invention is used as the nonmagnetic particle powder for the nonmagnetic underlayer.

Regarding the reason why the surface smoothness of the magnetic recording medium according to the present invention is improved, the present inventor has determined that the geometric standard deviation of the major axis diameter of the acicular hematite particles according to the present invention is 1.5.
Hereinafter, the geometric standard deviation value of the minor axis diameter is 1.3 or less, the presence of coarse particles and fine particles is less uniform particles, and the BET specific surface area value is 40 to 150 m ² / g, It is thought that the synergistic effect of the particles having few dewatered pores inside the particles and on the surface of the particles further improved the dispersibility in the vehicle, and as a result, the surface smoothness of the obtained nonmagnetic underlayer was further improved. ing.

[0108]

Next, examples and comparative examples will be described.

Goethite Particles 1-2 Needle-like goethite particle powders 1 and 2 having the properties shown in Table 1 were prepared as starting material particles.

[0110]

[Table 1]

Goethite particles 3 to 5 The sintering prevention treatment was carried out in the same manner as in the embodiment of the present invention, except that the type of the starting material particles and the type and amount of the sintering inhibitor were variously changed. Acicular goethite particle powder was obtained.

Table 2 shows the properties of the obtained acicular goethite particles.

[0113]

[Table 2]

<Heat treatment> Goethite particles 6 to 9 Acicular goethite particles 6 to 9 were obtained in the same manner as in the embodiment of the invention except that the type of starting material particles, and the temperature and time in the heat treatment were variously changed. Was.

The main production conditions at this time are shown in Table 3, and various properties of the obtained acicular goethite particle powder are shown in Table 4.

[0116]

[Table 3]

[0117]

[Table 4]

<Production of low-density acicular hematite particle powder>
Low-density acicular hematite particles 1 to 4 were obtained in the same manner as in the embodiment of the invention except that the type of goethite particles and the temperature and time in the heat dehydration treatment were variously changed.

Table 5 shows the main production conditions at this time, and Table 6 shows the properties of the obtained low-density acicular hematite particle powder.

[0120]

[Table 5]

[0121]

[Table 6]

Examples 1 to 4 and Comparative Examples 1 to 5 Acicular hematite particles were obtained in the same manner as in the embodiment of the invention except that the type of particles to be treated and the temperature and time in the high-temperature heat treatment were variously changed. Was.

Table 7 shows the main production conditions at this time, and Table 8 shows various properties of the obtained acicular hematite particle powder.

[0124]

[Table 7]

[0125]

[Table 8]

Comparative Example 6 (Example of Additional Tests in Japanese Patent Application No. 9-342163) <Production of High-Density Acicular Hematite Particle Powder> 1000 g of goethite particle powder 5 (starting material particle powder) was put into a stainless steel rotary furnace. And rotate and drive in air.
Heat treatment was performed at 0 ° C. for 30 minutes, followed by heat dehydration to obtain low-density acicular hematite particles. The obtained low-density acicular hematite particle powder has an average major axis diameter of 0.0839 μm, a geometric standard deviation of the major axis diameter of 1.52, and an average minor axis diameter of 0.01.
34 μm, geometric standard deviation of minor axis diameter is 1.38, axial ratio is 6.3, BET specific surface area value is 213.6 m ² / g, S
_BET / S _TEM value is 3.45, silicon content is Si
O ₂ was 1.21 wt% in terms of.

Next, 850 g of the low-density acicular hematite particle powder was put into a ceramic rotary furnace, and heat-treated at 630 ° C. for 20 minutes in the air while being rotated to seal the dewatering holes. The densified acicular hematite particle powder has an average major axis diameter of 0.0830 μm, a geometric standard deviation of the major axis diameter of 1.52, and an average minor axis diameter of 0.0138.
μm, the geometric standard deviation of the minor axis diameter is 1.38, and the axial ratio is 6.
0, BET specific surface area value is 69.4 m ² / g, S _BET /
The S _TEM value was 1.15 and the silicon content was 1.22% by weight in terms of SiO ₂ .

Obtained high-density acicular hematite particle powder 8
After coarsely pulverizing 00 g with a Nara-type pulverizer, the mixture was poured into 4.7 l of pure water, and pulverized for 60 minutes using a homomixer (manufactured by Tokushu Kika Kogyo Co., Ltd.). The mixture was dispersed for 3 hours at a shaft rotation speed of 2,000 rpm while circulating with S.C. The sieve residue of the high-density acicular hematite particle powder in the obtained slurry at 325 mesh (mesh size of 44 μm) was 0%.

<Dissolution Treatment of High-Density Acicular Hematite Particle Powder with Acid> Water was added to the obtained slurry of the high-density acicular hematite particle powder to reduce the concentration of the slurry to 100 g / g.
After reducing to 1, 7 l of the slurry was collected. While stirring the collected slurry, a 70% by weight aqueous sulfuric acid solution was added to adjust the sulfuric acid concentration to 1.3 N, and the pH value of the slurry was set to 0.5.
Adjusted to 9. Next, the slurry is heated with stirring to raise the temperature to 80 ° C., and the solution is kept at that temperature for 3 hours to perform a dissolving treatment, so that the total amount of the high-density acicular hematite particles present in the liquid is reduced. 20.2% by weight were dissolved.

Next, this slurry was filtered to separate a filtrate (an aqueous solution of iron sulfate), followed by washing with water by a decantation method to obtain a washing slurry having a pH value of 5.0. When the slurry concentration at this time was confirmed, it was 79 g / l.

Next, 2 l of the obtained water-washing slurry was
-Filtered using a funnel and passed through pure water to conduct the filtrate.
Is washed with water until it is 30 μs or less.
After drying, pulverize to obtain high-density acicular hematite particles.
A powder was obtained. Obtained high-density acicular hematite particle powder
Is 0.0785 μm average major axis diameter, geometric standard of major axis diameter
Deviation value is 1.46, average minor axis diameter is 0.0128 μm, short
The geometric standard deviation of the shaft diameter is 1.33, the axial ratio is 6.1, BE
T specific surface area value is 74.8m²/ G, S_BET/ S _TEM
Value of 1.15 and silicon content of SiO₂1.3 in conversion
It was 3% by weight.

<Surface Coating Treatment> Examples 5 to 8 The embodiment of the present invention is the same as the above embodiment except that the kind of particles to be treated, the pH value before addition in the coating step, the kind of additive, the amount added and the final pH are variously changed. Similarly, acicular hematite particles coated with the surface coating were obtained.

Table 9 shows the main production conditions at this time, and Table 10 shows various properties of the acicular hematite particle powder coated with the obtained surface coating.

[0134]

[Table 9]

[0135]

[Table 10]

Examples 9 to 16 and Comparative Examples 7 to 16 Examples 1 to 8, Hematite Particles 1 to 4 and Comparative Examples 1 to 6
A nonmagnetic underlayer was formed in the same manner as in the embodiment of the present invention using the respective particle powders obtained in the above.

Table 11 shows the main manufacturing conditions and various characteristics of the obtained non-magnetic underlayer.

[0138]

[Table 11]

Magnetic Particles a to e Magnetic particles a to e were prepared as magnetic particles for a magnetic recording medium.

Table 12 shows properties of the magnetic particles a to e.

[0141]

[Table 12]

Examples 17 to 24 and Comparative Examples 17 to 26 Magnetic recording media were obtained in the same manner as in the embodiment of the invention except that the type of the nonmagnetic underlayer and the type of the magnetic particles were variously changed.

Table 13 shows the main manufacturing conditions and various characteristics of the obtained magnetic recording medium.

[0144]

[Table 13]

[0145]

The acicular hematite particle powder according to the present invention, when used as a non-magnetic particle powder for a non-magnetic underlayer,
A non-magnetic underlayer having excellent surface smoothness can be obtained. When a magnetic recording medium is formed using the non-magnetic underlayer, a magnetic recording medium having excellent surface smoothness can be obtained. It is suitable as a non-magnetic particle powder for a non-magnetic underlayer of a medium.

As described above, the magnetic recording medium according to the present invention has excellent surface smoothness and is therefore suitable as a high-density magnetic recording medium.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4G002 AA06 AA12 AB00 AB03 AD01 AE03 5D006 CA04 FA00

Claims (4)

[Claims] 1. A geometric standard deviation value of a major axis diameter of 1.5 or less, a geometric standard deviation value of a minor axis diameter of 1.3 or less, and a BET specific surface area value of 40 to 150 m ² / g. 3. A non-magnetic particle powder for a non-magnetic underlayer of a magnetic recording medium, comprising acicular hematite particle powder having an average major axis diameter of 0.01 to 0.2 μm. 2. The surface coating of the acicular hematite particle powder according to claim 1, wherein the particle surface is made of at least one selected from hydroxide of aluminum, oxide of aluminum, hydroxide of silicon and oxide of silicon. Non-magnetic particle powder for a non-magnetic underlayer of a magnetic recording medium, which is coated with a material. 3. A method of preparing acicular goethite particles from 550 to 85.
Prior to the heating and dehydrating treatment, the goethite particle powder is heated and dehydrated in a temperature range of 100 to 200 ° C. prior to the heating and dehydrating treatment to form the goethite particles. 2. The method for producing a non-magnetic particle powder for a non-magnetic underlayer of a magnetic recording medium according to claim 1, wherein goethite ultra-fine particles contained in the particle powder are absorbed by the goethite particles. 4. A non-magnetic support, a non-magnetic underlayer composed of a non-magnetic particle powder formed on the non-magnetic support and a binder resin, and bonding to a magnetic particle powder formed on the non-magnetic under layer 3. A magnetic recording medium comprising a magnetic recording layer comprising a resin material, wherein the non-magnetic particle powder is the non-magnetic particle powder for a non-magnetic underlayer according to claim 1 or 2.