JP3509837B2 - Hematite particle powder for a non-magnetic underlayer of a magnetic recording medium using iron-based metal magnetic particle powder, non-magnetic underlayer of a magnetic recording medium using the hematite particle powder, and the non-magnetic underlayer Magnetic recording medium and method for producing said hematite particle powder - Google Patents

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a hematite particle powder suitable for a non-magnetic underlayer of a magnetic recording medium using a metal magnetic particle powder containing iron as a main component, that is, a dispersion in a binder resin. It has excellent properties, is low in the content of soluble sodium salts and soluble sulfates, and has a powder pH.
A needle-like hematite particle powder having a value of 8 or more is provided.

[0002]

2. Description of the Related Art In recent years, as video recording and audio magnetic recording / reproducing devices have been recorded for a long time and have been reduced in size and weight, magnetic recording media such as magnetic tapes and magnetic disks have been improved in performance, that is, high density recording. There is an increasing demand for higher performance, higher output characteristics, especially improved frequency characteristics, and lower noise.

Various attempts have been made in order to improve these characteristics of the magnetic recording medium, both from the viewpoint of improving the performance of the magnetic particle powder and reducing the thickness of the magnetic layer.

First, the performance improvement of magnetic particle powder will be described.

The characteristics of the magnetic particle powder suitable for satisfying the above requirements for the magnetic recording medium are that it has a high coercive force and a large saturation magnetization.

In recent years, needle-shaped magnetic metal particles containing iron as a main component obtained by heating and reducing needle-shaped goethite particles or needle-shaped hematite particles as a magnetic particle powder suitable for high output and high density recording in a reducing gas. Powders are widely known.

The acicular metal magnetic particle powder containing iron as a main component has a high coercive force and a large saturation magnetization, but the acicular metal magnetic particle containing iron as a main component used for magnetic recording media. The particle powder is 1 μm or less, especially 0.01 to
Since they are very fine particles of about 0.3 μm, they are liable to corrode, magnetic properties are deteriorated, and in particular, saturation magnetization and coercive force are reduced.

Therefore, in order to maintain the characteristics of the magnetic recording medium using the metal magnetic particle powder containing iron as the main component as the magnetic particle powder for a long period of time, the acicular metal magnetic material containing iron as the main component is used. It is strongly required to suppress the corrosion of particles as much as possible.

Next, the thinning of the magnetic recording layer will be described.

Recently, the demand for higher image quality of video tapes has been increasing, and the frequency of carrier signals recorded is higher than that of conventional video tapes. That is, the wavelength has shifted to the short wavelength region, and as a result, the depth of magnetization from the surface of the magnetic tape has become extremely shallow.

In order to improve the high output characteristics of the magnetic recording medium, particularly the S / N ratio, for a short wavelength signal, there is a strong demand for a thin magnetic recording layer. This fact is explained, for example, in “Development of Magnetic Materials and Highly Dispersion Technology of Magnetic Powder”, published by Sogo Gijutsu Center Co., Ltd. (1982), p.
The condition for high-density recording on the coated tape is that it can maintain high output characteristics with low noise for short wavelength signals, but for that reason, both coercive force Hc and residual magnetization Br are large. And the thickness of the coating film needs to be thinner. "..." is as described.

[0012] As the magnetic recording layer becomes thinner, some problems occur. First, there is a problem of smoothing and uneven thickness of the magnetic recording layer. As is well known, in order to make the magnetic recording layer smooth and free from uneven thickness, the surface of the base film must also be smooth. . This fact is, for example, published by the Engineering Information Center, "Magnetic Tape-Factor Caused by Friction and Wear of Head Running System and Trouble Countermeasures-Comprehensive Technical Data Collection (-hereinafter referred to as General Technical Data Collection-)" (Showa 62).
Years) 180 and 181, "... The surface roughness of the magnetic layer after curing strongly depends on the surface roughness (back surface roughness) of the base, and both are in a substantially proportional relationship. As the surface of the base is made smoother, a uniform and large head output is obtained and the S / N is improved.

Secondly, the base film is also becoming thinner like the magnetic layer is becoming thinner, and as a result, the strength of the base film is becoming a problem. This fact is, for example, the big theme imposed on the present magnetic tapes by "... High density recording" on page 77 of "Development of magnetic materials and high dispersion technology of magnetic powder" mentioned above. However, it is important not only to reduce the length of the tape and downsize the cassette but also to record for a long time.To do this, it is necessary to reduce the thickness of the film base. ...
As the tape becomes thinner in this way, the stiffness of the tape decreases sharply, making it difficult for the recorder to run smoothly. With the thinning of video tapes, there is great demand for improvement in this stiffness in both longitudinal and width directions. "..." is as described.

Thirdly, there is a problem that the light transmittance is increased by making the magnetic particles finer and making the magnetic recording layer thinner. That is, the running of a magnetic recording medium such as a magnetic tape, particularly a video tape, is stopped by detecting a portion of the magnetic recording medium having a high light transmittance with a video deck. If the light transmittance of the entire magnetic recording layer increases as the magnetic recording medium becomes thinner and the magnetic particle powder dispersed in the magnetic recording layer becomes ultrafine, it becomes difficult for the video deck to detect the magnetic recording. Carbon black or the like is added to the layer to reduce the light transmittance. Therefore, it is essential to add carbon black or the like to the magnetic recording layer in the current video tape.

However, the addition of non-magnetic carbon black and the like not only hinders high density recording but also hinders thinning of the magnetic tape. In order to make the tape thinner, it is not desirable to add non-magnetic particle powder other than magnetic particle powder to the magnetic recording layer.

Therefore, by providing at least one nonmagnetic underlayer in which a nonmagnetic particle powder such as hematite particles is dispersed in a binder on a nonmagnetic support, the light transmittance is improved and the surface property is deteriorated. It has been proposed and put into practical use to solve problems such as deterioration of electromagnetic conversion characteristics and electromagnetic characteristics. (Japanese Patent Publication No. 6-93297, JP-A-62-1)
59338, JP-A-63-187418,
JP-A-4-167225, JP-A-4-32591
5, JP-A-5-73882, JP-A-5-18
2177, JP-A-5-347017, JP-A-6-60362, etc.)

[0017]

Non-magnetic particles can be dispersed in a binder resin to provide a non-magnetic underlayer of a magnetic recording medium having excellent surface smoothness and strength. When a magnetic recording layer is provided on the ground layer, it is possible to obtain a thin magnetic recording layer having a low light transmittance, a smooth and uniform thickness, and moreover, iron dispersed in the magnetic recording layer Nonmagnetic particle powders for nonmagnetic underlayers capable of suppressing corrosion of metallic magnetic particle powders as the main component are currently most demanded, but such nonmagnetic particle powders have not yet been obtained. .

That is, as described in JP-A-63-187418, etc., when hematite particle powder is used as the nonmagnetic particle powder for the nonmagnetic underlayer, the surface of the nonmagnetic underlayer is smoothed. It can improve the sex and strength,
It has been reported that, when a magnetic recording layer is provided on the non-magnetic underlayer, the light transmittance of the magnetic recording layer can be reduced to form a smooth and thin layer without uneven thickness. It has been pointed out that, after the manufacture of the magnetic recording medium, the metal magnetic particle powder containing iron as a main component dispersed in the magnetic recording layer is corroded, resulting in a significant decrease in magnetic characteristics.

Therefore, the present invention can improve the surface smoothness and strength of the non-magnetic underlayer, and when the magnetic recording layer is provided on the non-magnetic underlayer, the light transmittance of the magnetic recording layer is improved. Can be made into a small layer that is smooth and has no unevenness in thickness, and can suppress deterioration of magnetic properties due to corrosion of the metal magnetic particle powder mainly composed of iron dispersed in the magnetic recording layer. A technical task is to obtain a non-magnetic particle powder for a non-magnetic underlayer that can be obtained.

[0020]

The above technical problems can be achieved by the present invention as follows.

That is, in the present invention, the average major axis diameter is 0.3 μm.
Below, the distribution of the major axis diameter of the particles is 1.50 in terms of geometric standard deviation.
Below, the BET specific surface area value is 35 m ² / g or more,
Powder acicular hematite particle powder having a pH value of 8 or more, a soluble sodium salt content of 300 ppm or less in terms of Na and a soluble sulfate content of 150 ppm or less in terms of SO ₄ Hematite particle powder for a non-magnetic underlayer of a magnetic recording medium using a metal magnetic particle powder containing iron as a main component, where necessary, the particle surface is a hydroxide of aluminum, an oxide of aluminum, A magnetic recording medium using a metal magnetic powder containing iron as a main component, characterized in that the acicular hematite particle powder is coated with at least one of a hydroxide of silicon and an oxide of silicon. A non-magnetic underlayer of a magnetic recording medium comprising a hematite particle powder for a non-magnetic underlayer and a coating film composition containing a non-magnetic particle powder formed on a non-magnetic support and a binder resin. Hematite particles for a non-magnetic underlayer of a magnetic recording medium using a metal magnetic particle powder containing iron as a main component, characterized in that the non-magnetic particle powder comprises any of the acicular hematite particle powders described above. Powder,
A non-magnetic underlayer composed of a coating composition containing a non-magnetic support, a non-magnetic particle powder formed on the non-magnetic support and a binder resin, and iron as a main component formed on the non-magnetic underlayer. In a magnetic recording medium comprising a magnetic recording layer comprising a coating composition containing a metal magnetic particle powder and a binder resin, wherein
The magnetic recording medium is characterized in that the non-magnetic particle powder comprises any of the acicular hematite particle powders described above.

In the present invention, needle-shaped goethite particles whose surface is coated with a sintering inhibitor, or needle-shaped hematite particles obtained by heating and dehydrating the needle-shaped goethite particles are used.
The needle-like hematite particles densified by heating at a temperature of 50 ° C. or higher are obtained, and the slurry containing the densified needle-like hematite particles is wet-milled, and then the slurry has a pH value of 1
Heat treatment at a temperature of 3 ° C or higher and a temperature of 80 ° C or higher, followed by filtration,
It is washed with water, dried, or, if necessary, the needle-like hematite particles obtained by filtering and washing with water are redispersed in water to obtain a water suspension, and an aluminum compound, a silicon compound or the For a non-magnetic underlayer of a magnetic recording medium using a metal magnetic particle powder containing iron as a main component, characterized in that acicular hematite particles are obtained by adding and mixing an aqueous solution containing both compounds This is a method for producing hematite particle powder.

Next, various conditions for carrying out the present invention will be described.

The acicular hematite particle powder according to the present invention will be described.

The acicular hematite particle powder according to the present invention is
The average major axis diameter is 0.3 μm or less, the distribution of the major axis diameter of particles is 1.50 or less in geometric standard deviation, and the BET specific surface area value is 35.
m ² / g or more, powder pH value of 8 or more, soluble sodium salt content of 300 ppm or less in terms of Na, soluble sulfate content of 150 ppm in terms of SO 4
The following are densified needle-shaped particles.

Here, the acicular particles have an axial ratio (average major axis diameter: average minor axis diameter, hereinafter simply referred to as "axial ratio") of 2:
Particles of 1 or more, preferably 3: 1 or more are preferable, and in consideration of dispersibility in a vehicle, the upper limit thereof is 20:
Particles of 1 or less, preferably 10: 1 or less are preferred. The shape of the particles may be needle-like, spindle-like, rice-like or the like.

If the axial ratio is less than 2, it becomes difficult to obtain the desired coating strength.

The average major axis diameter of the acicular hematite particles is 0.3.
If it exceeds μm, the particle size is too large and
It is not preferable because it impairs the surface smoothness of the film. Average major axis diameter
Lower limit of 0.005μm, less than 0.005μm
In the case of, dispersion in the vehicle becomes difficult. Considering the dispersibility in the vehicle and the surface smoothness of the coating film, 0.02 to 0.2 μm is preferable.

The average minor axis diameter of the acicular hematite particles is 0.0
When it is less than 025 μm, it becomes difficult to disperse it in the vehicle, which is not preferable. Average minor axis diameter is 0.15μ
When it exceeds m, the particle size is too large and the surface smoothness of the coating film is impaired, which is not preferable. 0.0 considering the dispersibility in the vehicle and the surface smoothness of the coating film.
1 to 0.10 μm is preferable.

The degree of densification of the acicular hematite particles in the present invention is determined by the specific surface area S _BET measured by the BET method.
The ratio is represented by the ratio between the value and 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.

When the S _BET / S _TEM value of the needle-like hematite particles is less than 0.5, although the densification of the needle-like hematite particles has been achieved, it is possible to sinter the particles and the particles with each other. Cohesion occurs, the particle size is increased, and the surface smoothness of the coating film is not sufficient. When the value of S _BET / S _TEM exceeds 2.5, the densification is not sufficient, a large number of pores are present on the particle surface, and the dispersibility in the vehicle becomes insufficient. Considering the surface smoothness of the coating film and the dispersibility in the vehicle, the value of S _BET / S _TEM is preferably 0.7 to 2.0, more preferably 0.8 to 1.6.

The particle size distribution of the major axis diameter of the acicular hematite particles is 1.50 or less in geometric standard deviation. When it exceeds 1.50 , coarse particles present adversely affect the surface smoothness of the coating film, which is not preferable. Considering the surface smoothness of the coating film, it is preferably 1.40 or less, more preferably 1.35 or less. Taking industrial productivity into consideration, the lower limit of the particle size distribution of the major axis diameter of the needle-like hematite particles obtained is 1.01 in geometric standard deviation.

The BET specific surface area value of the acicular hematite particles is 35 m ² / g or more. If it is less than 35 m ² / g, the acicular hematite particles are coarse or particles are formed by sintering between particles, which adversely affects the surface smoothness of the coating film. It is preferably 40 m ² / g or more, more preferably 45 m ² / g or more, and its upper limit value is 150 m ² / g. Considering the dispersibility in the vehicle, it is preferably 100 m ² / g or less, more preferably 80 m ² / g or less.

The powder pH value of the acicular hematite particles is 8 or more. When the powder pH value is less than 8, the metallic magnetic particle powder mainly composed of iron contained in the magnetic recording layer formed on the non-magnetic underlayer is gradually corroded to deteriorate the magnetic characteristics. cause. Considering the corrosion prevention effect of the metal magnetic particle powder containing iron as a main component, the powder pH value is preferably 8.5 or more, more preferably the powder pH value is 9.0 or more. The upper limit is a powder pH value of 12 or less, preferably a powder pH value of 11 or less, more preferably a powder pH value of 10.
It is 5 or less.

The content of the soluble sodium salt in the acicular hematite particles is 300 ppm or less in terms of Na. 300
If it exceeds ppm, the metallic magnetic particle powder mainly composed of iron contained in the magnetic recording layer formed on the non-magnetic underlayer is gradually corroded to cause deterioration of magnetic characteristics. Further, the dispersive properties of the needle-like hematite particles in the vehicle are likely to be impaired, and the white flower phenomenon may occur in the storage state of the magnetic recording medium, particularly in an environment with high humidity. Considering the anticorrosion effect of the metallic magnetic particle powder containing iron as a main component, it is preferably 250 ppm or less,
It is more preferably 200 ppm or less, still more preferably 150 ppm or less. In consideration of industrial properties such as productivity, the lower limit value is about 0.01 ppm.

The content of the soluble sulfate in the acicular hematite particles is 150 ppm or less in terms of SO ₄ . 150 pp
When it exceeds m, the metal magnetic particle powder mainly composed of iron contained in the magnetic recording layer formed on the non-magnetic underlayer is gradually corroded to cause deterioration of magnetic characteristics.
In addition, the dispersibility of the needle-like hematite particles in the vehicle is likely to be impaired, the storage state of the magnetic recording medium,
Especially in an environment of high humidity, a white flower phenomenon may occur. Considering the anticorrosion effect of the metal magnetic particle powder containing iron as the main component, it is preferably 70 ppm or less, more preferably 50 ppm or less. In consideration of industrial properties such as productivity, the lower limit value is about 0.01 ppm.

The needle-like hematite particles according to the present invention may have the particle surface coated with at least one of aluminum hydroxide, aluminum oxide, silicon hydroxide and silicon oxide, if necessary. Good. Needle-shaped hematite particles whose surface is coated with a coating have good compatibility with the binder resin when dispersed in a vehicle,
It is easy to obtain the desired degree of dispersion.

The amount of the above coating is such that aluminum hydroxide or aluminum oxide is converted to Al for the acicular hematite particles, and silicon hydroxide or silicon oxide is Si.
It is preferably 0.01 to 50% by weight in terms of O2. 0.01
When it is less than 5% by weight, the effect of improving dispersibility by addition is scarce, and when it exceeds 50.00% by weight, the coating effect is saturated, so there is no point in adding more than necessary.
Considering dispersibility in vehicle and productivity, 0.05-
20% by weight is more preferred.

The non-magnetic underlayer of the magnetic recording medium according to the present invention is formed by applying a non-magnetic coating material containing acicular hematite particles, a binder resin and a solvent on a non-magnetic support to form a coating film. Obtained by drying.

As the non-magnetic support, polyethylene terephthalate, polyethylene, polypropylene, polycarbonate, polyethylene naphthalate, polyamide, polyamide imide, which are currently widely used for magnetic recording media,
A synthetic resin film such as polyimide, a foil or plate of metal such as aluminum or stainless steel, and various kinds of paper can be used, and the thickness thereof is different depending on the material thereof, but is usually preferably 1.0 to 300 μm, and more preferably 2.0
Is about 200 μm. In the case of a magnetic disk, polyethylene terephthalate is usually used as the non-magnetic support, and its thickness is usually 50 to 300 μm, preferably 6
It is 0 to 200 μm. In the case of magnetic tape, the thickness of polyethylene terephthalate is usually 3 to 10
0 μm, preferably 4 to 20 μm. In the case of polyethylene naphthalate, its thickness is usually 3 to 50 μm, preferably 4 to 20 μm, and in the case of polyamide, its thickness is usually 2 to 10 μm, preferably 3 to 7 μm.

The coating thickness of the underlayer after coating the coating composition on the non-magnetic support in the present invention and drying it is 0.
It is in the range of 2 to 10.0 μm. If it is less than 0.2 μm, not only the surface roughness of the non-magnetic support cannot be improved, but also the strength is insufficient. In order to obtain a thin magnetic recording medium, the upper limit is preferably about 10.0 μm,
The range is more preferably 0.5 to 5.0 μm.

As the binder resin, a vinyl chloride / vinyl acetate copolymer, a urethane resin, a vinyl chloride / vinyl acetate / maleic acid copolymer, a urethane elastomer, a butadiene acrylonitrile copolymer, which are currently widely used in the production of magnetic recording media, are used. , Polyvinyl butyral, cellulose derivatives such as nitrocellulose, polyester resins, synthetic rubber resins such as polybutadiene, epoxy resins, polyamide resins, polyisocyanates , electron beam curable acrylic urethane resins and the like, and mixtures thereof can be used. In addition, each binder resin contains -OH, -COOH, -S.
Polar groups such as O ₃ M, —OPO ₂ M ₂ and —NH ₂ (however,
M is H, Na, K. ) May be included.

The mixing ratio of the acicular hematite particles to the binder resin is 5 to 2000 parts by weight of acicular hematite particles, preferably 100 to 100 parts by weight of the binder resin.
It is 1000 parts by weight.

The non-magnetic underlayer contains a lubricant, an abrasive, an antistatic agent, etc., which are commonly used in the production of magnetic recording media.
You may add as needed.

The non-magnetic underlayer containing the acicular hematite particles according to the present invention has a gloss of 190 to 280%,
Preferably 195-280%, more preferably 200-
280%, coating film surface roughness Ra is 2.0 to 10.0 nm,
Preferably 2.0 to 9.0 nm, more preferably 2.0.
~ 8.0 nm.

In the magnetic recording medium, a coating composition containing metallic magnetic particle powder containing iron as a main component, a binder resin and a solvent is coated on a nonmagnetic underlayer formed on a nonmagnetic support. It is obtained by forming a coating film and then drying to form a magnetic recording layer.

The acicular metal magnetic particles containing iron as a main component have an average major axis diameter of 0.01 to 0.50 μm, preferably 0.0.
Particles having an axial ratio of 3 to 0.30 μm and a ratio of 3: 1 or more, preferably 5: 1 or more, and in consideration of dispersibility in a vehicle, the upper limit thereof is 15: 1 or less, preferably Is a particle of 10: 1 or less, and the shape of the particle may be not only needle-like but also spindle-like, rice grain-like, or the like.

The composition is particles containing iron in an amount of 50 to 99% by weight, preferably 60 to 95% by weight, and if necessary, Co, Al, Ni, P, Si, B, N other than iron.
It may contain d, La, Y or the like.

Regarding the magnetic characteristics of the acicular metal magnetic particle powder containing iron as a main component, the coercive force is preferably 1200 to 3200 Oe, more preferably 1500 to 3200 Oe in consideration of characteristics such as high density recording. , Saturation magnetization is 100 ~
170 emu / g is preferable, and more preferably 130-
It is 150 emu / g.

As the binder resin in the magnetic recording layer, the binder resin used for forming the non-magnetic underlayer can be used.

The coating thickness of the magnetic recording layer after coating the coating composition on the non-magnetic underlayer and drying is 0.01 to 5.
It is in the range of 0 μm. If it is less than 0.01 μm, it is not preferable because it is difficult to apply it uniformly and the phenomenon such as uneven coating is likely to occur. When it exceeds 5.0 μm, it is difficult to obtain desired electromagnetic conversion characteristics due to the influence of the demagnetizing field.
It is preferably in the range of 0.05 to 1.0 μm.

In the magnetic recording layer, the acicular metal magnetic particle powder containing iron as the main component and the binder resin are mixed in such a ratio that 100 parts by weight of the binder resin is mixed with the acicular metal magnetic particle powder containing iron as the main component. Is 200 to 2000 parts by weight, preferably 30
0 to 1500 parts by weight.

Lubricants, abrasives, antistatic agents and the like which are usually used may be added to the magnetic recording layer.

The magnetic recording medium having a non-magnetic underlayer containing acicular hematite particles according to the present invention has a coercive force of 90.
0-3500 Oe, preferably 1000-3500 Oe
e, more preferably 1500 to 3500 Oe, and the squareness ratio (residual magnetic flux density Br / saturated magnetic flux density Bm) is 0.85 to
0.95, preferably 0.86-0.95, the gloss of the coating film is 200-300%, preferably 210-300%,
The coating film surface roughness Ra is 10.0 nm or less, preferably 2.
0-9.0 nm, more preferably 2.0-8.0 nm,
The linear absorption coefficient of the coating film is 1.10 to 2.00 μm ^−1, preferably 1.20 to 2.00 μm ⁻¹ , and the corrosiveness indicated by the change rate (%) of coercive force is 10.0% or less, preferably 9 The corrosiveness is 0.5% or less, and the corrosiveness indicated by the change rate (%) of Bm is 10.0% or less, preferably 9.5% or less.

The method for producing the acicular hematite particle powder according to the present invention will be described.

The acicular hematite particle powder according to the present invention is
Add a suspension containing ferrous hydroxide colloid obtained by adding an equivalent amount or more of an aqueous alkali hydroxide solution to the ferrous salt solution.
A method of generating needle-shaped goethite particles by aerating an oxygen-containing gas at a temperature of H11 or higher and a temperature of 80 ° C. or lower to generate acicular goethite particles, and FeCO ₃ obtained by reacting a ferrous salt aqueous solution with an alkaline carbonate aqueous solution. A suspension containing aging, after aging if necessary, a method of generating goethite particles in the form of spindles by aerating an oxygen-containing gas to carry out an oxidation reaction, and an alkali hydroxide less than the equivalent amount in the ferrous salt aqueous solution. A needle-shaped goethite core particle is produced by aerating an oxygen-containing gas through an aqueous ferrous salt solution containing a ferrous hydroxide colloid obtained by adding an aqueous solution or an aqueous solution of alkali carbonate to generate acicular goethite core particles, and then In a ferrous salt aqueous solution containing acicular goethite core particles, Fe ²⁺ in the ferrous salt aqueous solution is ^added.
After adding an equivalent or more alkaline hydroxide aqueous solution to,
Method of growing acicular goethite core particles by aerating oxygen-containing gas and ferrous iron colloid obtained by adding less than equivalent amount of an aqueous solution of ferrous hydroxide or an aqueous solution of alkali carbonate A needle-shaped goethite nucleus particle is generated by aerating an oxygen-containing gas in a salt solution to carry out an oxidation reaction, and then obtained by a usual method such as a method of growing the needle-shaped goethite nucleus particle in an acidic or neutral region. The obtained acicular goethite particles are used as precursor particles, and the acicular goethite particles are heated and dehydrated.

It should be noted that during the formation reaction of goethite particles, different kinds of Ni, Zn, P, Si, Al and the like, which are usually added to improve various characteristics such as major axis diameter, minor axis diameter and axial ratio of the particles. There is no problem even if an element is added. The acicular goethite particle powder obtained usually has a soluble sodium salt content of 3 in terms of Na.
0 to 1500 ppm, soluble sulfate 1 in SO ₄ conversion
The BET specific surface area value is about 50 to 250 m ² / g.

The densified needle-like hematite particle powder according to the present invention is the above-mentioned needle-like goethite particle powder, or
It is obtained by subjecting the acicular goethite particle powder to heat dehydration to obtain low-density acicular hematite particles at a high temperature of 550 ° C. or higher. In order to obtain densified needle-like hematite particles that retain and inherit the particle morphology of needle-like goethite particles, it is preferable to use the latter needle-like hematite particles obtained by heating and dehydrating.

Prior to the high temperature heat treatment for increasing the density, it is necessary to perform a coating treatment with a sintering inhibitor in advance. Needle-shaped goethite particle powders whose surface is coated with a sintering inhibitor usually contain soluble sodium salt in N
500 to 2000 ppm in terms of a, soluble sulfate is SO
BET content of 300-3000ppm in ₄ conversion
The specific surface area value is about 50 to 250 m ² / g. The coating treatment with the sintering inhibitor is carried out by adding the sintering inhibitor to an aqueous suspension containing needle-shaped goethite particles or needle-shaped hematite particles obtained by heating and dehydrating the needle-shaped goethite particles, and after mixing and stirring. It may be filtered, washed with water, and dried.

As the sintering inhibitor, a commonly used phosphorus compound such as sodium hexametaphosphate, polyphosphoric acid, orthophosphoric acid, No. 3 water glass, sodium orthosilicate, sodium metasilicate, silicon compound such as colloidal silica, boric acid, etc. Such as boron compounds, aluminum acetate, aluminum sulfate, aluminum chloride, aluminum nitrate, and other aluminum salts, sodium aluminate and other aluminate salts, alumina sol and other aluminum compounds, and titanyl sulfate and other titanium compounds can be used. .

The low-density acicular hematite particles are obtained by combining acicular hematite particles whose surface is coated with an antisintering agent.
It may be heated at a low temperature in the temperature range of 50 to 400 ° C. The low-density acicular hematite particle powder usually contains a soluble sodium salt of 500 to 2000 ppm in terms of Na and a soluble sulfate of 300 to 4000 ppm in terms of SO ₄ ,
The BET specific surface area value is about 70 to 350 m ² / g.
When the heating temperature is lower than 250 ° C, it takes a long time for the dehydration reaction. If the heating temperature exceeds 400 ° C., a dehydration reaction rapidly occurs, the shape of the particles is likely to collapse, and sintering between particles is not preferable, which is not preferable. Acicular hematite particles obtained by heat treatment, the needle
H ₂ O is dehydrated from the granular goethite particles, which is a low-density particle having a large number of dehydration pores, and has a BET specific surface area value of about 1.2 to 2 times that of the acicular goethite particle that is the precursor particle.

Next, the low-density acicular hematite particle powder is heated at a high temperature of 550 ° C. or higher to obtain acicular hematite particles having a high density. The upper limit of the heating temperature is preferably 8
It is 50 ° C. The high-density acicular hematite particle powder is usually a soluble sodium salt of 500 to 4000 in terms of Na.
ppm, soluble sulfate of 300 to 5000 in terms of SO ₄
ppm content, BET specific surface area value is 35-150
It is about m ² / g. When the heating temperature is lower than 550 ° C., the densification is insufficient and a large number of dehydration pores are present inside and on the surface of the acicular hematite particles, resulting in poor dispersibility in the vehicle. It is sufficient, and it is difficult to obtain a coating film having a smooth surface when the nonmagnetic underlayer is formed. When the heating temperature exceeds 850 ° C., the needle-shaped hematite particles have been sufficiently densified, but since the particles and the particles are sintered, the particle size increases, and It is difficult to obtain a coating film with a smooth surface.

The densified needle-like hematite particles are coarsely pulverized by a dry method to loosen the coarse particles, then made into a slurry, and then wet pulverized to further loosen the coarse particles. The wet pulverization may be performed using a ball mill, a sand grinder, a dyno mill, a colloid mill or the like so that coarse particles of at least 44 μm or more are eliminated. Wet grinding degree is 4
10% or less of coarse particles of 4 μm or more, preferably 5% or less,
It is more preferably 0%. 10 coarse particles of 44 μm or more
If the amount of the residual component exceeds the range of%, it is difficult to obtain the treatment effect in the alkaline aqueous solution in the next step.

A slurry containing needle-like hematite particles from which coarse particles have been removed is adjusted to a pH value of 13 or more by adding an alkaline aqueous solution such as sodium hydroxide to the slurry, and then 8
Heat treatment is performed at a temperature of 0 ° C. or higher.

PH value including acicular hematite particles powder is 1
The concentration of the alkaline suspension of 3 or more is 50 to 250 g.
/ L is preferred.

[0066] When the pH value of the alkaline suspension containing the acicular hematite particles is less than 13, a solid cross-linked due to the acicular Hematai <br/> sintering inhibitor present on the particle surfaces of the bets particles Cannot be removed effectively, and the soluble sodium salts, soluble sulfates, etc. present inside and on the surface of the particles cannot be washed out. The upper limit of the pH value is about 14. Removal of solid cross-links caused by the sintering inhibitor present on the surface of acicular hematite particles and the effect of washing out soluble sodium salts, soluble sulfates, etc., and sodium adhering to the surface of acicular hematite particles during alkaline aqueous solution treatment. Considering the cleaning effect for removing the alkali such as the above, the pH value is preferably in the range of 13.1 to 13.8.

PH value including acicular hematite particles powder is 1
The heating temperature of the alkaline aqueous solution of 3 or more is preferably 80 ° C. or higher, more preferably 90 ° C. or higher. If the temperature is lower than 80 ° C., it becomes difficult to effectively remove solid crosslinks due to the sintering inhibitor present on the surface of the acicular hematite particles. The upper limit of the heating temperature is preferably 103 ° C, more preferably 100 ° C. When the temperature exceeds 103 ° C, the solid crosslinks can be effectively removed, but it becomes industrially unfavorable such as the need for an autoclave or the boiling of the liquid to be treated under normal pressure.

The needle-shaped hematite particles which have been heat-treated in an alkaline aqueous solution are separated by filtration and washed with water by a conventional method to obtain soluble sodium salts and soluble sulfates washed out from inside and on the surface of the particles and needles during the alkaline aqueous solution treatment. Jo f <br/> alkali to remove such as sodium adhered to hematite particle surface and then dried.

As the washing method with water, there are commonly used methods such as decantation, diluting with a filter thickener, and washing with water passing through a filter press. You can use it.

If the soluble sodium salt or soluble sulfate contained in the particles of the high-density needle-like hematite particles is washed out with water and washed out, the subsequent steps, for example,
Even if soluble sodium salts or soluble sulfates adhere to the particle surfaces of the acicular hematite particles in the coating treatment step described later, they can be easily removed by washing with water.

The needle-like hematite particles according to the present invention are, if necessary, heat-treated in an alkaline aqueous solution, filtered by a conventional method and washed with water, and then aluminum hydroxide, aluminum oxide, silicon water. It is coated with at least one of an oxide and an oxide of silicon.

The coating treatment is carried out by adding an aluminum compound, a silicon compound or both compounds to an aqueous suspension obtained by dispersing acicular hematite particles in an aqueous solution and mixing and stirring, or if necessary, By adjusting the pH value, on the particle surface of the acicular hematite particles,
Aluminum hydroxide, aluminum oxide, silicon hydroxide and silicon oxide may be applied and then filtered, washed with water, dried and pulverized. If necessary, deaeration / consolidation may be further performed.

As the aluminum compound in the present invention, the same one as the above-mentioned sintering inhibitor can be used.

The amount of the aluminum compound added is 0.01 to 50.00 in terms of Al based on the acicular hematite particle powder.
% By weight. When it is less than 0.01% by weight, the dispersion in the vehicle is insufficient, and when it exceeds 50.00% by weight, the coating effect is saturated, so that it is meaningless to add more than necessary.

As the silicon compound in the present invention, the same one as the above-mentioned sintering inhibitor can be used.

The amount of the silicon compound added is 0.01 to 50.00% by weight in terms of SiO ₂ with respect to the acicular hematite particle powder. If the amount is less than 0.01% by weight, the dispersion in the vehicle is insufficient and the amount is 50.00% by weight.
If it exceeds, the coating effect will be saturated and it is meaningless to add more than necessary.

When the aluminum compound and the silicon compound are used in combination, the total amount of Al and SiO ₂ is 0.01 to 0.01 with respect to the acicular hematite particle powder.
50.00% by weight is preferred.

[0078]

The most important point in the present invention is that the dispersibility in the binder resin is excellent, the soluble sodium content is 300 ppm or less in terms of Na, and the soluble sulfate content is 150 ppm in terms of SO _4. Below,
In addition, when high-density acicular hematite particles having a powder pH value of 8 or more are used as the non-magnetic particle powder for the non-magnetic underlayer, the dispersibility in the binder resin is excellent. Then, the surface smoothness and strength of the non-magnetic underlayer can be improved, and when the magnetic recording layer is provided on the non-magnetic underlayer, the light transmittance of the magnetic recording layer is reduced to be smooth. It is possible to make a thin film without uneven thickness,
The fact is that deterioration of magnetic properties due to corrosion of the metal magnetic particle powder containing iron as a main component dispersed in the magnetic recording layer can be suppressed.

With respect to the reason that the surface smoothness of the non-magnetic underlayer and the strength of the non-magnetic support could be further improved, the inventors of the present invention have strongly considered that the high density needle-like hematite particles are strongly cross-linked and aggregated. Due to the fact that the soluble sodium salts and soluble sulfates that have become, can be sufficiently removed by washing with water, the aggregates can be disentangled to form substantially independent particles. It is believed that this is because needle-like hematite particles having excellent dispersibility in the vehicle can be obtained.

This fact will be described below.

The acicular goethite particle powder used as the precursor is manufactured by various manufacturing methods as described above.

[0082] The main raw materials sulfate naturally reaction mother liquor in the case of the ferrous sulfate to produce the acicular goethite particles in any of the methods [SO ₄ ^-] is the abundant.

Particularly, when goethite particles are produced from an acidic solution, water-soluble sulfates such as Na ₂ SO ₄ are simultaneously produced, and K ⁺ , NH ₄ ⁺ , N are added to the reaction mother liquor.
Since it contains an alkali metal such as a ⁺ , a precipitate containing an alkali metal or a sulfate is liable to be formed. This precipitate is RFe ₃ (S
It is represented by O ₄ ) (OH) ₆ (R = K ⁺ , NH ₄ ⁺ , Na ⁺ ). These precipitates are sparingly soluble sulfate-containing salts and cannot be removed by washing with water by a conventional method. This sparingly soluble salt becomes soluble sodium salt or soluble sulfate in the subsequent heat treatment step, but this soluble sodium salt or soluble sulfate salt forms a needle-like hematite particle in the high temperature heat treatment step for densification. By the sintering inhibitor, which is essential to prevent deformation and sintering between particles, the needle-like hematite particles are strongly bonded to each other inside the particle while cross-linking the needle-like hematite particles with each other. The cohesion between them is further strengthened. As a result, it becomes extremely difficult to remove the soluble sulfate and the soluble sodium salt, which are trapped inside the particles and inside the aggregate, by washing with water by a conventional method.

When acicular goethite particles are produced in an alkaline aqueous solution using ferrous sulfate and sodium hydroxide, the sulfate produced simultaneously is Na ₂ SO ₄ , and the mother liquor contains NaOH. Since they are both soluble, it should be possible to essentially remove Na ₂ SO ₄ and NaOH by sufficiently washing the acicular goethite particles with water. However, in general since the small crystalline needles goethite particles, poor washing efficiency, when washed with water by a conventional method, should be noted that the soluble sulphate in the particle [SO ₄ ^-], a soluble sodium salt [Na ^+] and the like Contains water-soluble components. And, as described above, the water-soluble component is strongly bonded to the inside of the particles and the surface of the particles while cross-linking the needle-shaped hematite particles with each other by the sintering inhibitor, so that the aggregation between the needle-shaped hematite particles is further enhanced. Get stronger. As a result, it becomes extremely difficult to remove the soluble sulfate and the soluble sodium salt, which are trapped inside the particles and inside the aggregate, by washing with water by a conventional method.

As described above, the high density needle-like hematite particles in which the soluble sodium salt or the soluble sulfate salt is strongly bound to the inside of the particle, the surface of the particle and the inside of the agglomerate through the sintering inhibitor are included. After wet pulverizing to loosen coarse particles, the pH value of the slurry is adjusted to 13 or more, and heat treatment is performed at a temperature of 80 ° C. or more, the alkaline aqueous solution sufficiently penetrates into the inside of the high-density needle-like hematite particles, As a result, the binding force of the sintering inhibitor strongly bonded to the inside of the particle, the surface of the particle, and the inside of the agglomerate is gradually weakened, and is dissociated from the inside of the particle, the surface of the agglomerate, and the inside of the agglomerate. It is considered that the soluble sulfate can be easily removed by washing with water.

For the reason that deterioration of magnetic properties due to corrosion of metal magnetic particle powder containing iron as a main component dispersed in the magnetic recording layer is suppressed, the present inventor has found that soluble sodium which promotes corrosion of metal is used. iron-based powder pH value of that soluble components such as salts or soluble sulfates is less dense acicular hematite particles and acicular f <br/> hematite particles themselves due to 8 or more and high It is considered that the progress of corrosion of the metal magnetic particle powder can be suppressed.

As a matter of fact, the present inventor, as shown in the examples and comparative examples below, showed that the densified needle-like hematite particles after the wet pulverization had a temperature of 80 ° C. or higher and a pH value. When heat-treated with an alkaline aqueous solution of less than 13, the densified needle-like hematite particles after wet grinding were densified when heat-treated with an alkaline aqueous solution having a temperature of less than 80 ° C. and a pH value of 13 or more. Needle-like hematite particles were subjected to a pH value of 13 at a temperature of 80 ° C. or higher without wet pulverization and containing coarse particles.
The effect of the present invention cannot be obtained in any of the cases where heat treatment is carried out in the above alkaline aqueous solution. Therefore, due to the synergistic effect that the soluble content is small and the powder pH value is 8 or more, iron It has been confirmed that the progress of corrosion of the metal magnetic particle powder containing as a main component can be suppressed.

[0088]

BEST MODE FOR CARRYING OUT THE INVENTION A typical embodiment of the present invention is as follows.
It is as follows.

As for the remaining amount of the sieve, the slurry concentration after the wet pulverization was separately obtained, and an amount of the slurry corresponding to 100 g of the solid content was passed through a 325-mesh sieve (opening 44 μm) to remove the solid remaining in the sieve. It was determined by quantifying the amount of minutes.

The average major axis diameter and the average minor axis diameter of the particles are long for about 350 particles shown in a photograph (× 120,000) obtained by magnifying an electron micrograph (× 30000) four times in the longitudinal direction and the transverse direction. The shaft diameter and the minor axis diameter were measured, and the average value was shown. The axial ratio is the ratio of the average major axis diameter to the average minor axis diameter.

Geometric standard deviation value (σg) of major axis diameter of particles
Is shown by the value obtained by the following method. That is, the value obtained by measuring the major axis diameter of the particles shown in the enlarged photograph, the horizontal axis on the lognormal probability paper according to a statistical method from the actual major axis diameter and the number of particles calculated from the measured values. The major axis diameter of the particles is plotted on the vertical axis, and the cumulative number of particles belonging to each of the predetermined major axis diameter sections (under integrated sieve) is plotted on the vertical axis as a percentage. And from this graph, the number of particles is 50% and 8
The value of the major axis diameter corresponding to each 4.13% is read, and the geometric standard deviation value (σg) = under the integrated sieve 84.13.
The major axis diameter in% / the major axis diameter (geometric mean diameter) at 50% under the integrated sieve is shown as a value calculated. The closer the geometric standard deviation value is to 1, the better the particle size distribution of the major axis diameter of the particles.

The specific surface area is shown by the value measured by the BET method.

The degree of densification of acicular hematite particles is
As described above, it is shown by S _BET / S _TEM . Where S
_BET is the value of the specific surface area measured by the BET method. S _TEM is a value calculated according to the following formula, assuming that the particles are rectangular parallelepipeds using the average major axis diameter 1 cm and the average minor axis diameter wcm of the particles measured from the electron micrograph. S _TEM (m ² / g) = [(4lw + 2w ² ) / (lw ² · ρ _p )] × 10 ⁻⁴ (where ρ _p is the true specific gravity of hematite, 5.2 g /
cm ³ was used. )

The amount of Al and the amount of SiO ₂ present on the surface of the acicular hematite particles were measured by fluorescent X-ray analysis.

The powder pH value was obtained by weighing 5 g of the sample in a 300 ml Erlenmeyer flask, adding 100 ml of boiled pure water, heating and maintaining the boiled state for about 5 minutes, then capping and allowing to cool to room temperature. Then, water corresponding to the weight reduction was added, the stopper was plugged again, the mixture was shaken for 1 minute, left standing for 5 minutes, and then the pH of the obtained supernatant was measured according to JIS Z 8802-7.
The obtained value was defined as the powder pH value.

The content of the soluble sodium salt and the content of the soluble sulfate were the same as those of the supernatant prepared for measuring the powder pH value. After filtering with 5C filter paper, the N
a ⁺ and SO ₄ ²⁻ were measured by using an inductively coupled plasma emission spectroscopic analyzer (manufactured by Seiko Instruments Inc.).

The paint viscosity was measured by measuring the paint viscosity of the obtained paint at 25 ° C. using an E-type viscometer EMD-R (manufactured by Tokyo Keiki Co., Ltd.), and a shear rate D = 1.92 l / se.
The value in c is shown.

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

The surface roughness Ra is "Surfcom-57".
5A "(manufactured by Tokyo Seimitsu Co., Ltd.) was used to measure the center line average roughness of the coating film.

The coating film strength was determined by measuring the Young's modulus of the coating film using "Autograph" (manufactured by Shimadzu Corporation). Young's modulus is a commercial video tape "AV T-120
(Manufactured by Victor Company of Japan, Ltd.) ”. The higher the relative value, the better.

The magnetic characteristics are as follows: "Vibration sample magnetometer VSM-
3S-15 "(manufactured by Toei Industry Co., Ltd.) was used, and the external magnetic field was measured up to 10 kOe .

The change with time of the magnetic characteristics of the magnetic recording medium due to the corrosion of the metal magnetic particle powder containing iron as the main component in the magnetic recording layer was observed under the conditions of the temperature of 60 ° C. and the relative humidity of 90%. The sample was allowed to stand for a day, the coercive force value and the saturation magnetic flux density value before and after standing were measured, and the value obtained by dividing the amount of change by the value before standing was shown as a percentage change.

The light transmittance of the magnetic sheet is shown by the linear absorption coefficient measured by using "photoelectric spectrophotometer UV-2100" (manufactured by Shimadzu Corporation). The linear absorption coefficient is defined by the following equation, and the larger the value, the more difficult it is for light to pass through. Linear absorption coefficient (μm ⁻¹ ) = {ln (1 / t)} / FT t: λ = light transmittance at 900 nm (−) FT: thickness of coating film composition layer of film used for measurement (μ
m)

The thickness of each of the nonmagnetic support, the nonmagnetic underlayer and the magnetic recording layer constituting the magnetic recording medium was measured as follows. Digital electronic micrometer K35
First, the film thickness (A) of the non-magnetic support is measured using 1C (manufactured by Anritsu Electric Co., Ltd.). Next, the thickness (B) of the non-magnetic support and the non-magnetic underlayer formed on the non-magnetic support (total of the thickness of the non-magnetic support and the thickness of the non-magnetic underlayer) was measured in the same manner. To do. Furthermore, 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 similarly measured. The thickness of the non-magnetic underlayer is shown by BA, and the thickness of the magnetic recording layer is shown by CB.

<Production of Needle-like Hematite Particles> Needle-like goethite particle powder (average major axis diameter 0.220 μm, average minor axis diameter 0.0275) obtained by the above-described method for producing goethite particles.
μm, axial ratio 8.00: 1, BET specific surface area value 125 m ²
/ G, soluble sodium salt content is 452 in terms of Na
ppm, content of soluble sulfate is 283p in SO ₄ conversion
pm, pH value 7.1 and geometric standard deviation value 1.27) 75
0 g was suspended in water to make a slurry, and the solid concentration was 5
It was adjusted to g / l. 150 l of this slurry was heated to a temperature of 60 ° C., and a 0.1 N NaOH aqueous solution was added to adjust the pH value of the slurry to 9.0.

Next, 22.5 g of No. 3 water glass as a sintering inhibitor was gradually added to the above alkaline slurry, and after the addition was completed, aging was carried out for 60 minutes. Next, 0.1N acetic acid solution was added to this slurry to adjust the pH value of the slurry to 6.0. Then, filtration, washing with water, drying, and pulverization were carried out by a conventional method to obtain acicular goethite particle powder in which the surface of the particle was covered with silicon oxide. The amount of SiO ₂ contained in the acicular goethite particle powder is 0.86 wt%
Met.

700 g of the obtained acicular goethite particle powder
Was placed in a stainless steel rotary furnace and heat-treated in air at 300 ° C. for 60 minutes while being rotationally driven for dehydration to obtain low-density acicular hematite particles. The obtained low-density acicular hematite particles have an average major axis diameter of 0.150 μm, an average minor axis diameter of 0.0216 μm, an axial ratio of 6.94: 1, a BET specific surface area value (S _BET ) of 157.6 m ² / g, Degree of density S _BET
/ S _TEM is 4.13, soluble sodium salt content is N
1183ppm in terms of a, soluble sulfate content is SO
_It was 1735 ppm in terms of ₄ , a powder pH value of 6.3 and a geometric standard deviation value of 1.32.

Next, a low-density acicular hematite particle powder 65
0 g was put into a ceramic rotary furnace, and heat-treated in air at 650 ° C. for 10 minutes while being rotationally driven to seal the dehydration holes. The densified needle-like hematite particles have an average major axis diameter of 0.148 μm and an average minor axis diameter of 0.0
217 μm, axial ratio 6.82: 1, BET specific surface area value (S _BET ) 53.1 m ² / g, degree of densification S _BET
/ S _TEM is 1.40, soluble sodium salt content is N
1386ppm in terms of a, soluble sulfate content is SO
_It was 2739 ppm in terms of ₄ , the powder pH value was 5.6, and the geometric standard deviation value was 1.34. The amount of SiO2 contained in the acicular hematite particles was 0.95 wt%.

600 g of the obtained densified needle-like hematite particle powder was coarsely crushed in advance with a Nara crusher and then added to 3.5 l of pure water, using a homomixer (manufactured by Tokushu Kika Kogyo Co., Ltd.). Peptized for 60 minutes.

Next, while the obtained slurry of densified needle-like hematite particles was circulated in a horizontal SGM (Dispamat SL: manufactured by SDC Adchem Co., Ltd.), the mixture was mixed for 3 hours under a shaft rotation speed of 2000 rpm. Dispersed. 325 mesh of acicular hematite particles in the obtained slurry
The sieve residue at (opening 44 μm) was 0%.

The concentration of the obtained densified needle-like hematite particles was 100 g / l and the slurry was 5 l. The pH value of the slurry was adjusted to 13.5 by adding a 6N NaOH aqueous solution while stirring the slurry. Next, this slurry was heated with stirring to raise the temperature to 95 ° C. and kept at that temperature for 3 hours.

Next, this slurry was washed with water by a decantation method to obtain a slurry having a pH value of 10.5. For accuracy, the slurry concentration at this point was confirmed to be 96 g / l.

Next, it was filtered using a Buchner funnel, pure water was passed through to wash with water until the electric conductivity of the filtrate became 30 μs or less, and after that, it was dried by a conventional method and then pulverized,
The target acicular hematite particle powder was obtained. The obtained acicular hematite particle powder has a major axis diameter of 0.148 μm, a minor axis diameter of 0.0220 μm, an axial ratio of 6.73: 1, and a particle size (major axis diameter) geometric standard deviation value σg of 1. .33, BET specific surface area value (S _BET ) 52.5 m ² / g, degree of densification (S _BET / S _TEM ) 1.40, powder pH value 9.
2. Soluble sodium salt content is 144p in terms of Na
pm, content of soluble sulfate is 20ppm in SO ₄ conversion
Met.

<Production of Nonmagnetic Underlayer> 12 g of the acicular hematite particle powder obtained above and a binder resin solution (30% by weight of vinyl chloride-vinyl acetate copolymer resin having sodium sulfonate group and 70% by weight of cyclohexanone). ) And cyclohexanone are mixed to obtain a mixture (solid content of 72
%), And the mixture was further kneaded for 30 minutes with a plastomill. This kneaded product was taken out, and in a 140 ml glass bottle, 95 g of 1.5 mmφ glass beads, a binder resin solution (30% by weight of a polyurethane resin having a sodium sulfonate group, a solvent (methyl ethyl ketone: toluene = 1: 1)
70% by weight), cyclohexanone, methyl ethyl ketone and toluene, and added with a paint shaker to 6
The coating composition was obtained by time-wise mixing and dispersion.

The composition of the coating material containing the obtained hematite particles was as follows. Needle-like 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 9.9 parts by weight

The coating material containing the obtained acicular hematite particles was applied on a polyethylene terephthalate film having a thickness of 14 μm with an applicator to a thickness of 55 μm, and then dried to form a non-magnetic underlayer.
The thickness of the nonmagnetic underlayer was 3.5 μm.

The gloss of the obtained non-magnetic underlayer was 197%,
Surface roughness Ra is 6.8 nm, Young's modulus (relative value) is 12
It was 0.

<Production of Magnetic Recording Layer> Acicular metal magnetic particle powder containing iron as a main component (average major axis diameter 0.15 μm, average minor axis diameter 0.022 μm, axial ratio 6.8: 1, coercive force 1690).
Oe, saturation magnetization value 131 emu / g) 12 g, abrasive (trade name: AKP-30, manufactured by Sumitomo Chemical Co., Ltd.) 1.2
g, carbon black (trade name: # 3250B, manufactured by Mitsubishi Kasei Co., Ltd.) 0.36 g, binder resin solution (30% by weight of vinyl chloride-vinyl acetate copolymer resin having sodium sulfonate group and 70% by weight of cyclohexanone) And cyclohexanone were mixed to obtain a mixture (solid content 78%), and this mixture was further kneaded for 30 minutes with a plastomill. Take out this kneaded product and put it in a 140 ml glass bottle.
95 g of 5 mmφ glass beads, binder resin solution (30 wt% of polyurethane resin having sodium sulfonate group, solvent (methyl ethyl ketone: toluene = 1: 1) 7
0% by weight), cyclohexanone, methyl ethyl ketone and toluene, and mixed and dispersed for 6 hours with a paint shaker to obtain a magnetic coating material. After that, add lubricant and hardener, and add 15 with a paint shaker.
Mixed and dispersed for minutes.

The composition of the obtained magnetic coating material was as follows. Metal magnetic particle powder 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 (AKP-30) 10 parts by weight Parts carbon black (# 3250B) 3.0 parts by weight lubricant (myristic acid: butyl stearate = 1: 2) 3.0 parts by weight curing agent (polyisocyanate) 5.0 parts by weight cyclohexanone 65.8 parts by weight methyl ethyl ketone 164 0.5 parts by weight Toluene 98.7 parts by weight

A magnetic coating material was applied on the non-magnetic underlayer to a thickness of 15 μm using an applicator, oriented and dried in a magnetic field, calendered, and then cured at 60 ° C. for 24 hours. The reaction was performed and slitting was performed to a width of 0.5 inch to obtain a magnetic tape. The thickness of the magnetic recording layer was 1.2 μm.

The Hc of the obtained magnetic tape was 1862O.
e, squareness ratio 0.86, gloss 235%, surface roughness Ra
Was 5.8 nm, Young's modulus (relative value) was 133, and linear absorption coefficient was 1.23. The change with time of the magnetic characteristics of the magnetic tape was 6.8% for the coercive force and 5.8% for the saturation magnetic flux density.

[0122]

EXAMPLES Next, examples and comparative examples will be given.

<Type of acicular goethite particle powder> The following precursors 1 to 7 were prepared as precursors for producing acicular hematite particles.

[0124]

[Table 1]

<Production of Low Density Needle Hematite Particle Powder> Examples 1 to 15 and Comparative Examples 1 to 14 Type of needle-shaped goethite particle powder as a precursor, type and amount of sintering inhibitor, heating dehydration temperature and Low-density needle-like hematite particles were obtained in the same manner as in the embodiment of the present invention except that the time was changed variously.

Main manufacturing conditions and various characteristics at this time are shown in Tables 2 and 3.

[0127]

[Table 2]

[0128]

[Table 3]

<Production of High Density Needle-like Hematite Particles> Examples 16 to 30 and Comparative Examples 15 to 27 Except that the type of particle powder to be treated, the temperature and time of the densification heat treatment were variously changed. High-density needle-shaped hematite particles were obtained in the same manner as the embodiment of the present invention.

Main manufacturing conditions and various characteristics at this time are shown in Tables 4 and 5.

[0131]

[Table 4]

[0132]

[Table 5]

<Treatment of Needle Hematite Particles in Alkaline Aqueous Solution> Examples 31 to 45 and Comparative Examples 28 to 35 Types of acicular hematite particle powder, presence / absence of wet pulverization, presence / absence of heat treatment in alkaline aqueous solution, and slurry pH
Needle-shaped hematite particles were obtained in the same manner as in the embodiment of the present invention except that the value, heating temperature and heating time were changed variously.

Main manufacturing conditions and various characteristics at this time are shown in Tables 6 and 7.

[0135]

[Table 6]

[0136]

[Table 7]

<Surface coating treatment of acicular hematite particles> Example 46 The pH value of Example 31 obtained by washing with water by a decantation method after heat treatment in an alkaline aqueous solution was 1
The 0.5 slurry had a slurry concentration of 96 g / l. 5 l of this slurry was heated again to 60 ° C., and 533 ml of 1.0 N NaAlO ₂ solution was added to this slurry.
(Corresponding to 3.0 wt% in terms of Al based on the acicular hematite particles) was added and held for 30 minutes, and then the pH value was adjusted to 8.5 using acetic acid. Then, in the same manner as in the embodiment of the present invention, it was filtered, washed with water, dried and pulverized to obtain a needle-like hematite particle powder having a particle surface coated with a coating material.

Table 8 shows the main production conditions and various characteristics at this time.

Examples 47 to 60 Needle-shaped hematite particles were obtained in the same manner as in Example 46, except that the type of acicular hematite particle powder and the type and amount of the surface-treated product were variously changed.

Table 8 shows the main production conditions and various characteristics at this time.

[0141]

[Table 8]

<Production of Nonmagnetic Underlayer> Examples 61 to 90 and Comparative Examples 36 to 50 Examples 31 to 60 and Comparative Examples 1 to 15, 15 to 18 and 2
Using the acicular hematite particles obtained in Nos. 3, 28 to 35, a nonmagnetic underlayer was obtained in the same manner as in the embodiment of the present invention.

Main manufacturing conditions and various characteristics at this time are shown in Tables 9 to 11.

[0144]

[Table 9]

[0145]

[Table 10]

[0146]

[Table 11]

<Production of Magnetic Recording Medium Using Metallic Magnetic Particle Powder Containing Iron as Main Component> Examples 91 to 120 and Comparative Examples 51 to 65 Obtained in Examples 61 to 90 and Comparative Examples 36 to 50. Metal magnetic powder containing iron as a main component in the same manner as the embodiment of the present invention, except that the type of non-magnetic underlayer and the type of acicular metal magnetic particle powder containing iron as a main component were variously changed. A magnetic recording medium using is manufactured.

Table 12 shows the main manufacturing conditions and various characteristics at this time.
Through Table 14.

[0149]

[Table 12]

[0150]

[Table 13]

[0151]

[Table 14]

[0152]

EFFECTS OF THE INVENTION The acicular hematite particle powder for a non-magnetic underlayer according to the present invention has excellent strength as a base film due to its excellent dispersion in the vehicle as shown in the above-mentioned Examples. And a non-magnetic underlayer having excellent surface properties can be obtained, and when used as a magnetic recording medium, a thin magnetic recording layer having a small light transmittance, a smooth and uniform thickness can be obtained, and acicular hematite particles Corrosion of the acicular metal magnetic particle powder containing iron as a main component in the magnetic recording layer due to the fact that the content of soluble Na salt and soluble sulfate is small and the powder pH value is 8 or more. It is possible to suppress the deterioration of the magnetic characteristics associated with the above, and it is possible to maintain the characteristics of the magnetic recording medium for a long period of time.

Continuation of the front page (56) Reference JP-A-6-195684 (JP, A) JP-A-7-182654 (JP, A) JP-A-7-296360 (JP, A) (58) Fields investigated (Int .Cl. ⁷ , DB name) B22F 1/00 C01G 49/06 G11B 5/738 H01F 1/00 (54) [Title of Invention] Magnetic recording medium using metallic magnetic particle powder containing iron as a main component Hematite particle powder for non-magnetic underlayer, non-magnetic underlayer of magnetic recording medium using the hematite particle powder, magnetic recording medium using the non-magnetic underlayer, and method for producing the hematite particle powder

Claims (6)

(57) [Claims] 1. A powder pH having an average major axis diameter of 0.3 μm or less, a distribution of major axis diameters of particles of 1.50 or less as a geometric standard deviation value, and a BET specific surface area value of 35 m ² / g or more. Value is 8
Above, the iron is characterized by comprising a densified needle-like hematite particle powder having a soluble sodium salt content of 300 ppm or less in terms of Na and a soluble sulfate content of 150 ppm or less in terms of SO _4. Hematite particle powder for a non-magnetic underlayer of a magnetic recording medium, which uses metal magnetic particle powder containing as a main component. 2. The acicular hematite particle powder according to claim 1, wherein the particle surface is coated with at least one of aluminum hydroxide, aluminum oxide, silicon hydroxide and silicon oxide. A hematite particle powder for a non-magnetic underlayer of a magnetic recording medium, wherein the magnetic metal particle powder containing iron as a main component is used. 3. The nonmagnetic underlayer of a magnetic recording medium comprising a coating composition comprising a nonmagnetic particle powder and a binder resin formed on a nonmagnetic support, wherein the nonmagnetic particle powder is used. Alternatively, a non-magnetic underlayer of a magnetic recording medium using the magnetic metal particle powder containing iron as a main component, which is the acicular hematite particle powder according to claim 2. 4. A nonmagnetic underlayer comprising a coating composition containing a nonmagnetic support, nonmagnetic particle powder formed on the nonmagnetic support and a binder resin, and a nonmagnetic underlayer formed on the nonmagnetic underlayer. 3. A magnetic recording medium comprising a metal magnetic particle powder containing iron as a main component and a magnetic recording layer comprising a coating composition containing a binder resin, wherein the non-magnetic particle powder is the magnetic recording medium according to claim 1 or 2. A magnetic recording medium using a metallic magnetic particle powder containing iron as a main component, which is an acicular hematite particle powder. 5. A needle-shaped goethite particle whose surface is coated with a sintering inhibitor or a needle-shaped hematite particle obtained by heating and dehydrating the needle-shaped goethite particle is heated at a temperature of 550 ° C. or higher to increase the temperature. Obtaining densified needle-like hematite particles,
After wet pulverizing the slurry containing the densified needle-like hematite particles, the slurry is subjected to a pH value of 13 or more and a temperature of 8
A metallic magnetic particle powder containing iron as a main component, characterized in that the needle-shaped hematite particles according to claim 1 are obtained by heating at 0 ° C or higher, then filtering, washing with water and drying. Manufacturing method of hematite particle powder for non-magnetic underlayer of magnetic recording medium. 6. A needle-shaped goethite particle having a particle surface coated with a sintering inhibitor or a needle-shaped hematite particle obtained by heating and dehydrating the needle-shaped goethite particle is heated at a temperature of 550 ° C. or higher to increase the temperature. Obtaining densified needle-like hematite particles,
After wet pulverizing the slurry containing the densified needle-like hematite particles, the slurry is subjected to a pH value of 13 or more and a temperature of 8
The needle-like hematite particles obtained by heating at 0 ° C. or higher, and then filtering and washing with water are redispersed in water to obtain an aqueous suspension, and an aluminum compound, a silicon compound, or both of them is added to the aqueous suspension. A non-magnetic underlayer of a magnetic recording medium using an iron-based metal magnetic particle powder, wherein the acicular hematite particles according to claim 2 are obtained by adding and mixing an aqueous solution containing a compound. Manufacturing method of hematite particle powder.