JPH11353637A - Acicular hematite particle powder for nonmagnetic base layer and magnetic recording medium having nonmagnetic base layer using the acicular hematite particle powder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain acicular hematite particle powder suitable for nonmagnetic particle powder of a nonmagnetic base layer of a magnetic recording medium which has small transmittance for light, smooth surface, large strength and excellent durability and which suppresses deterioration in the magnetic characteristics. SOLUTION: This hematite particle powder is obtd. by dissolving an aq. suspension of an acicular hematite particle powder with an acid under conditions of >=1.0 N acid concn., <=3.0 pH, and 20 to 100 deg.C temp. range, then controlling the pH to >=13, and heat treating at 80 to 103 deg.C. The obtd. powder has 0.004 to 0.295 μm average major axial length, 35.9 to 212 m<2> /g BET specific surface area, >=8 pH of the powder, <=300 ppm soluble sodium salts amt. expressed in terms of Na, <=150 ppm soluble sulfates amt. expressed in terms of SO4 , and 0.05 to 50 wt.% aluminum expressed in terms of Al in the particle.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a low light transmittance, smooth surface, high strength, excellent durability, and
A needle suitable as a non-magnetic particle powder for a non-magnetic underlayer of a magnetic recording medium in which deterioration of magnetic characteristics due to corrosion of iron-based needle-like metal magnetic particles dispersed in a magnetic recording layer is suppressed. And a magnetic recording medium having a non-magnetic underlayer containing the acicular hematite particle powder.

[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.

Various attempts have been made by those skilled in the art to improve the properties of the magnetic recording medium, both in terms of improving the performance of the magnetic particle powder and reducing the thickness of the magnetic layer.

[0004] First, improvement of the performance of the magnetic particle powder will be described.

[0005] The characteristics of the magnetic particle powder suitable for satisfying the above requirements for the magnetic recording medium are to have a high coercive force value and a large saturation magnetization value.

In recent years, as a magnetic particle powder suitable for high-output and high-density recording, an acicular metal mainly composed of iron obtained by heating and reducing acicular goethite particle powder or acicular hematite particle powder in a reducing gas. Magnetic particle powders are widely used.

[0007] Needle-like metal magnetic particles containing iron as a main component have a high coercive force value and a large saturation magnetization value. The magnetic particle powder is 1 μm or less, especially 0.01 to
Since they are very fine particles of about 0.3 μm, they are susceptible to corrosion and magnetic properties are degraded. In particular, they have the drawback of decreasing coercive force and saturation magnetization.

Accordingly, in order to maintain the characteristics of the magnetic recording medium using the acicular metal magnetic particles containing iron as a main component as the magnetic particles for a long period of time, the acicular metal magnet containing iron as the main component must be used. It is strongly required to minimize the corrosion of the particle powder.

Next, the thickness reduction of the magnetic recording layer will be described.

In recent years, the demand for higher image quality and higher image quality of video tapes has been increasing, and the frequency of carrier signals to be recorded has been increasing more and more than conventional video tapes. That is, the wavelength shifts to the short wavelength region, and as a result, the magnetization depth from the surface of the magnetic tape becomes extremely shallow.

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. ‥‥ ”.

As the thickness of the magnetic recording layer has been reduced, several problems have arisen. First, there is a problem of smoothing and uneven thickness of the magnetic recording layer. To make the magnetic recording layer smooth and free of uneven thickness, the surface of the base film must also be smooth. 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) 18
"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 in a proportional relationship. 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.

Second, the thickness of the base film has also been reduced as in the case of the magnetic layer, and as a result, the strength of the base film has become a problem. This fact is described, for example, in the above-mentioned “Development of Magnetic Materials and Technology for Highly Dispersing Magnetic Particles” on page 77, “‥‥ High Density Recording is a major theme that has been imposed on current magnetic tapes. This is important in reducing the length of the tape to reduce the size of the cassette and for long-time recording, which requires reducing the thickness of the film base. The stiffness of the tape suddenly decreases as the thickness decreases, making it difficult for the recorder to run smoothly.
It is greatly desired to improve the stiffness in both width directions. ‥‥ ”.

Further, the demand for higher performance of the magnetic recording medium in recent years has never stopped, and with the thinner magnetic recording layer and the thinner non-magnetic support, the surface of the magnetic recording layer and the Since the durability of the recording medium itself decreases, there is a strong demand for improving the durability of the magnetic recording layer surface and the durability of the magnetic recording medium itself.

This fact is described in Japanese Unexamined Patent Publication No. Hei 5-298679, entitled "... In recent years, with the development of magnetic recording, the demand for high image quality and high sound quality has been increasing more and more. Of fine particles and high density
Further, it is required to reduce noise and increase C / N by smoothing the surface of the magnetic tape. ... However, as the friction coefficient of the contact between the magnetic layer and the device system increases while the magnetic tape is running, the magnetic layer of the magnetic recording medium is likely to be damaged or the magnetic layer will be peeled off in a short time use. There is. Particularly, in the case of a video tape, since the video head and the magnetic recording medium run while contacting each other at a high speed, the ferromagnetic powder tends to fall off the magnetic layer, which causes clogging of the magnetic head. Therefore, it is desired to improve the running durability of the magnetic layer of the magnetic recording medium. .. ".

By the way, at present, determination of the end of a magnetic tape of a magnetic recording medium such as a video tape is performed by detecting a portion of the magnetic recording medium having a large light transmittance by a video deck. If the light transmittance of the entire magnetic recording layer increases with the thinning of the magnetic recording medium and the ultrafine particle size of the magnetic particles dispersed in the magnetic recording layer, it becomes difficult to detect the magnetic recording layer with a VCR. The light transmittance is reduced by adding carbon black or the like to the layer, and in current video tapes, the addition of carbon black or the like to the magnetic recording layer is essential.

However, adding a large amount of non-magnetic carbon black or the like not only hinders high-density recording, but also hinders thinning. In order to make the magnetization depth from the surface of the magnetic tape shallower and to further reduce the thickness of the magnetic tape, it is strongly required to reduce the amount of non-magnetic particles such as carbon black added to the magnetic recording layer as much as possible. I have.

Therefore, there is a strong demand for a magnetic recording medium having a small light transmittance even if the amount of carbon black added to the magnetic recording layer is reduced.

As the magnetic recording layer is made thinner and the nonmagnetic support is made thinner, nonmagnetic particles such as hematite particles are formed on a nonmagnetic support such as a base film to form a magnetic recording layer. Is provided in at least one nonmagnetic underlayer in which is dispersed in a binder, and has already been put into practical use (Japanese Patent Publication No. 6-93297, Japanese Patent Application Laid-Open No. Sho 62-62).
-159338, JP-A-63-187418, JP-A-4-167225, JP-A-4-325
915, JP-A-5-73882, JP-A-5-73882
No. 182177, JP-A-5-347017,
JP-A-6-60362).

However, a magnetic recording medium in which a non-magnetic underlayer in which a non-magnetic powder is dispersed in a binder resin is formed on a non-magnetic support, and a magnetic recording layer is provided thereon, Although smoothness and strength are improved, there is a problem that durability is poor.

This fact is described in Japanese Unexamined Patent Publication No. Hei 5-182177: "... a non-magnetic thick undercoat layer is provided on the support surface, and then the magnetic layer is provided as the upper layer. Although the influence of roughness can be eliminated, there is a problem that head wear and durability are not improved, because conventionally, since a thermosetting resin is used as a binder as a non-magnetic lower layer, the lower layer hardens. The reason is that friction between the magnetic layer and the head and contact with other members are performed in an unbuffered state, and that the magnetic recording medium having such a lower layer is somewhat less flexible. It can be considered .... ".

Accordingly, as the thickness of the magnetic recording layer and the thickness of the non-magnetic support are reduced, the light transmittance is small, the surface is smooth, the strength is high, the durability is excellent, and the magnetic recording layer has a small thickness. Magnetic recording media in which deterioration of magnetic properties due to corrosion of acicular metal magnetic particles containing iron as a main component dispersed in iron are suppressed most at present, but such various properties are required. A sufficiently satisfactory magnetic recording medium has not yet been obtained.

[0023]

SUMMARY OF THE INVENTION Accordingly, the present invention is based on the object that iron having a small light transmittance, a smooth surface, a high strength, excellent durability, and iron dispersed in a magnetic recording layer is a main component. It is a technical object to obtain acicular hematite particle powder suitable as a nonmagnetic particle powder for a nonmagnetic underlayer of a magnetic recording medium in which deterioration of magnetic properties due to corrosion of acicular metal magnetic particle powder is suppressed.

[0024]

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

That is, the present invention relates to a needle-like hematite particle powder for a non-magnetic underlayer of a magnetic recording medium using a needle-like metal magnetic particle powder containing iron as a main component as a magnetic particle powder,
An aqueous suspension of acicular hematite particle powder having an average major axis diameter of 0.005 to 0.30 μm and a BET specific surface area of 35 to 150 m ² / g has an acid concentration of 1.0 N or more, a pH value of 3.0 or less, and a temperature. The dissolution treatment with an acid is performed under the condition of the range of 20 to 100 ° C. to dissolve 5 to 50% by weight of the total amount of the acicular hematite particles present in the aqueous suspension, and then the remaining acicular hematite particles are left. The aqueous suspension of acicular hematite particle powder obtained by washing with water is adjusted to a pH value of 13 or more by adding an aqueous alkali solution, and then heat-treated in a temperature range of 80 to 103 ° C., and then separated by filtration. The average major axis diameter obtained by washing and drying is 0.004 to 0.295 μm, the BET specific surface area value is 35.9 to 212 m ² / g, the powder pH value is 8 or more, and the content of the soluble sodium salt is 3 in Na conversion
00ppm or less, the content of soluble sulfate salt is at 150ppm or less in terms ^of SO ^4, and 0.05 to 50 wt% of the needle aluminum nonmagnetic underlayer contains a shaped hematite particles calculated as Al within the particles It is a powder.

Further, according to the present invention, the surface of the acicular hematite particles for the non-magnetic underlayer of the magnetic recording medium using the acicular metal magnetic particle powder containing iron as the main component as the magnetic particle powder is made of aluminum water. Oxides, oxides of aluminum,
The needle-like hematite particle powder for a non-magnetic underlayer described above, which is coated with at least one of silicon hydroxide and silicon oxide.

The present invention also 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 iron formed on the non-magnetic under layer. In a magnetic recording medium comprising a magnetic recording layer composed of acicular metal magnetic particle powder and a binder resin having as a main component,
A magnetic recording medium, wherein the nonmagnetic particle powder is the acicular hematite particle powder for each nonmagnetic underlayer.

Further, the present invention is characterized in that needle-like metal magnetic particles containing iron as a main component and containing 0.05 to 10% by weight of aluminum in terms of Al are used as the magnetic particles. A magnetic recording medium as described above.

The structure of the present invention will be described in more detail as follows.

First, the acicular hematite particle powder for a nonmagnetic underlayer according to the present invention will be described.

The particle shape of the acicular hematite particles for a non-magnetic underlayer according to the present invention is substantially the same as the particle shape of the particles to be treated. Here, the needle shape means not only a literal needle shape but also a spindle shape or a rice grain shape.

The average major axis diameter of the acicular hematite particle powder for a nonmagnetic underlayer according to the present invention is 0.004 to 0.295 μm.
m. If the average major axis diameter exceeds 0.295 μm, the particle size is too large, which impairs the surface smoothness of the coating film, which is not preferred. If it is less than 0.004 μm, aggregation tends to occur due to an increase in intermolecular force due to finer particles, so that dispersibility in the vehicle is reduced. Considering the dispersibility in the vehicle and the surface smoothness of the coating film, the average major axis diameter of the acicular hematite particle powder is 0.00
It is preferably from 8 to 0.275 μm, more preferably from 0.0 to 0.275 μm.
16 to 0.245 μm.

The average minor axis diameter of the acicular hematite particles for a nonmagnetic underlayer according to the present invention is 0.002 to 0.1.
It is preferably 47 μm. Average short axis diameter is 0.14
If it exceeds 7 μm, the particle size is too large, and the surface smoothness of the coating film tends to be impaired. 0.0
If the particle size is less than 02 μm, aggregation tends to occur due to an increase in intermolecular force due to finer particles, so that dispersion in the vehicle tends to be difficult. In consideration of dispersibility in a vehicle and surface smoothness of a coating film, the average minor axis diameter is more preferably 0.004 to 0.123 μm, and still more preferably 0.0079 to 0.098.
μm one should be chosen.

The axial ratio (average major axis diameter / average minor axis diameter, hereinafter simply referred to as “axial ratio”) of the acicular hematite particle powder for a nonmagnetic underlayer according to the present invention is 2 or more, preferably 3 or more. And the upper limit is 20, preferably 10.

When the axial ratio is less than 2, it is difficult to obtain a coating having sufficient strength. When the axial ratio exceeds 20, the entanglement of particles in the vehicle increases,
Dispersibility may worsen or viscosity may increase.

The BET specific surface area of the acicular hematite particle powder for a non-magnetic underlayer according to the present invention is 35.9 to 212 m ^2.
/ G. If it is less than 35.9 m ² / g, the acicular hematite particles are coarse, or the particles are sintered between the particles, and adversely affect the surface smoothness of the coating film. If it exceeds 212 m ² / g, aggregation tends to occur due to an increase in intermolecular force due to finer particles, so that dispersibility in the vehicle decreases. Considering the dispersibility in the vehicle and the surface smoothness of the coating film, B
ET specific surface area is preferably 38.0~141.4m ² / g, more preferably 41.0~113.1m ² / g.

The acicular hematite particle powder for a nonmagnetic underlayer according to the present invention preferably has a geometric standard deviation value of a major axis diameter of 1.50 or less, more preferably 1.48 or less. If it exceeds 1.50, the existing coarse particles tend to have an adverse effect on the surface smoothness of the coating film. In consideration of the surface smoothness of the coating film, one having a value of 1.45 or less should be selected. In consideration of industrial productivity, the lower limit of the geometric standard deviation of the major axis diameter of the obtained acicular hematite particle powder is 1.01.

The needle-like hematite particles for a non-magnetic underlayer according to the present invention have a high degree of density. The ratio S between the specific surface area value S _BET measured for the degree of densification by the BET method 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 expressed as _BET / S _TEM value, it has a value of 0.5 to 2.5.

When the S _BET / S _TEM value exceeds 2.5, the density is not sufficiently increased, and a large number of dehydrated pores are present inside the particles and on the surface of the particles, so that the dispersibility in the vehicle is insufficient. Becomes Considering the dispersibility in the vehicle and the surface smoothness of the coating film, the S _BET / S _TEM value is preferably from 0.7 to 2.0, more preferably from 0.8 to 2.0.
1.6.

The acicular hematite particle powder for a non-magnetic underlayer according to the present invention is 0.05% in terms of Al with respect to the total weight of the particles.
５０50% by weight of aluminum is almost uniformly contained inside the particles.

When the content is less than 0.05% by weight, the resulting magnetic recording medium having a nonmagnetic underlayer does not have sufficient durability. When the content exceeds 50% by weight, the obtained magnetic recording medium having a nonmagnetic underlayer has sufficient durability, but the effect is saturated and there is no point in containing more than necessary. Considering the durability of the obtained magnetic recording medium, it is preferably 0.5 to 50% by weight, more preferably 1.0 to 50% by weight.
50% by weight.

The pH of the acicular hematite particles for a non-magnetic underlayer according to the present invention is 8 or more. When the powder pH value is less than 8, the needle-like metal magnetic particles containing iron as a main component dispersed in the magnetic recording layer formed on the nonmagnetic underlayer are gradually corroded, This causes deterioration of magnetic characteristics. In consideration of the anticorrosion effect of the needle-shaped metal magnetic particles containing iron as a main component, the powder pH is preferably 8.5 to 11, more preferably 9.0 to 10.
5

The content of the soluble sodium salt in the needle-like hematite particles for a nonmagnetic underlayer according to the present invention is 300 ppm or less in terms of Na. If it exceeds 300 ppm, the iron-based acicular metal magnetic particles contained in the magnetic recording layer formed on the non-magnetic underlayer gradually corrode, causing deterioration of magnetic properties. . Also,
The dispersion characteristics of the acicular hematite particle powder in the vehicle may be easily impaired, or a whitening phenomenon may occur in the storage state of the magnetic recording medium, particularly in an environment with high humidity. Taking into account the anticorrosion effect of the acicular metal magnetic particles containing iron as a main component, it is preferably 250 ppm or less, more preferably 200 ppm or less, and even more preferably 1 ppm or less.
It is 50 ppm or less. In consideration of industrial properties such as productivity, the lower limit is about 0.01 ppm.

The soluble sulfate content of the acicular hematite particles for a nonmagnetic underlayer according to the present invention is 15 in terms of SO _4.
It is 0 ppm or less. If it exceeds 150 ppm,
The needle-like metal magnetic particle powder containing iron as a main component dispersed in the magnetic recording layer formed on the non-magnetic underlayer gradually corrodes, causing deterioration of magnetic characteristics. In addition, the dispersion characteristics of the acicular hematite particle powder in the vehicle may be easily damaged, and the whitening phenomenon may occur in the storage state of the magnetic recording medium, particularly in an environment with high humidity. In consideration of the anticorrosion effect of the acicular metal magnetic particles containing iron as a main component, the content is preferably 70 ppm or less, more preferably 50 ppm or less. In consideration of industrial properties such as productivity, the lower limit is about 0.01 ppm.

The acicular hematite particles for a non-magnetic underlayer according to the present invention have a resin adsorption strength of 65% or more, preferably 68% or more, more preferably 70% or more. The upper limit is about 95%.

The acicular hematite particle powder for a non-magnetic underlayer according to the present invention may optionally contain aluminum hydroxide,
The particle surface may be coated with at least one of aluminum oxide, silicon hydroxide and silicon oxide (hereinafter referred to as “coating with aluminum hydroxide or the like”). The acicular hematite particle powder whose particle surface is coated with an aluminum hydroxide or the like, when dispersed in a vehicle, has good compatibility with the binder resin, and easily obtains a desired degree of dispersion.

The coating amount of the aluminum hydroxide or the like is calculated in terms of Al in the case of aluminum hydroxide or aluminum oxide, in terms of SiO _{2 in} the case of silicon hydroxide or silicon oxide, or in terms of Al. 0.01 to 50 wt% relative to the total weight of the particles by the sum of the equivalent amount and the SiO ₂ equivalent amount is preferred.

When the amount is less than 0.01% by weight, there is almost no effect of improving the dispersibility by the coating, and when it exceeds 50% by weight, the effect of the coating is saturated, so that it is meaningless to add more than necessary. In consideration of the effect of improving dispersibility in the vehicle and the productivity, 0.05 to 20% by weight is more preferable.

The acicular hematite particle powder for a non-magnetic underlayer according to the present invention, which is coated with an aluminum hydroxide or the like, is used for the non-magnetic underlayer according to the present invention which is not coated with an aluminum hydroxide or the like. It has particle size, geometric standard deviation, BET specific surface area, S _BET / S _TEM value, powder pH value, soluble sodium salt content and soluble sulfate content which are almost the same as those of the acicular hematite particles. ing.

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 papers can be used, and the thickness thereof varies depending on the material, but 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 a nonmagnetic support, and its thickness is usually 50 to 300 μm, preferably 6 to 300 μm.
0 to 200 μm. In the case of a magnetic tape, in the case of polyethylene terephthalate, the thickness is usually 3 to 10.
0 μm, preferably 4 to 20 μm, in the case of polyethylene naphthalate, the thickness is usually 3 to 50 μm, 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 in the present invention comprises the acicular hematite particle powder according to the present invention or the acicular hematite particle powder coated with the aluminum hydroxide or the like according to the present invention and a binder resin. Become.

As the binder resin, vinyl chloride-vinyl acetate copolymers, urethane resins, vinyl chloride-vinyl acetate-maleic acid copolymers, urethane elastomers, butadiene which are currently widely used in the production of magnetic recording media -Use of acrylonitrile copolymer, polyvinyl butyral, cellulose derivative such as nitrocellulose, polyester resin, synthetic rubber-based resin such as polybutadiene, epoxy resin, polyamide resin, polyisocyanate, electron beam-curable acrylic urethane resin and the like, and mixtures thereof. be able to.

Further, 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 particle powder, the polar group
COOH, binder resins that contain -SO ₃ M are preferable.

The mixing ratio of the acicular hematite particle powder and the binder resin is 5 to 2000 parts by weight, preferably 10 to 2000 parts by weight, based on 100 parts by weight of the binder resin.
0 to 1000 parts by weight.

When the acicular hematite particle powder is less than 5 parts by weight, the amount of the acicular hematite particle powder in the non-magnetic paint is too small. As a result, the surface smoothness and strength of the coating film become insufficient. If the amount exceeds 2,000 parts by weight, the acicular hematite particle powder is not sufficiently dispersed in the non-magnetic paint because the acicular hematite particle powder is too large relative to the amount of the binder resin. It is difficult to obtain a coating film having a sufficiently smooth surface. Further, since the acicular hematite particle powder is not sufficiently bound by the binder resin, the obtained coating film tends to be brittle.

The nonmagnetic underlayer in the present invention preferably has a coating thickness in the range of 0.2 to 10.0 μm. 0.2 μm
If it is less than 3, it becomes difficult to improve the surface roughness of the nonmagnetic support, and the strength of the coating film tends to be insufficient. Considering the thickness of the magnetic recording medium and the strength of the coating film, the thickness is more preferably in the range of 0.5 to 5.0 μm.

A lubricant, an abrasive, an antistatic agent, and the like used in the manufacture of a normal magnetic recording medium are required for the non-magnetic underlayer. If necessary, about 0.1 to 50 parts by weight with respect to 100 parts by weight of the binder resin. May be included.

The nonmagnetic underlayer containing the acicular hematite particle powder whose particle surface is not covered with aluminum hydroxide or the like has a glossiness of the coating film of 187 to 300%,
Preferably 193 to 300%, more preferably 195 to 300%
300%, coating film surface roughness Ra is 0.5 to 8.5 nm, preferably 0.5 to 8.0 nm, more preferably 0.5 to 8.5 nm.
7.5 nm, Young's modulus (relative value) of coating film is 119 to 16
0, preferably 120-160.

The nonmagnetic underlayer containing acicular hematite particle powder whose particle surface is coated with aluminum hydroxide or the like has a glossiness of the coating film of 190 to 300%, preferably 195 to 300%. Preferably 197-3
00%, the coating film surface roughness Ra is 0.5 to 8.3 nm, preferably 0.5 to 7.8 nm, more preferably 0.5 to 7.8 nm.
7.3 nm, Young's modulus (relative value) of the coating film is 120 to 16
0, preferably 123 to 160.

The magnetic recording layer according to the present invention comprises acicular metallic magnetic particles containing iron as a main component and a binder resin.

The needle-like magnetic metal particles containing iron as a main component in the present invention contain 50 to 99% by weight of iron, preferably 6 to 99% by weight.
0 to 95% by weight of magnetic particle powder, and if necessary, Al, Co, Ni, P, Si, B, N
d, La, Y, etc. may be contained in an amount of about 0.05 to 10% by weight.

In the present invention, the needle-like metal magnetic particle powder containing iron as a main component preferably contains 0.05 to 10% by weight of aluminum in terms of Al with respect to the total weight of the magnetic particle powder.

When the magnetic recording medium according to the present invention is manufactured using needle-like metal magnetic particle powder containing iron as a main component in which 0.05% by weight or more of aluminum exists with respect to the total weight of the magnetic particle powder. Since the resin adsorption strength of the acicular metal magnetic particle powder containing iron as a main component in which aluminum exists is improved, the durability is further improved. If it exceeds 10% by weight, the magnetic recording medium has sufficient durability, and there is no point in having it present more than necessary. In addition, the magnetic property of the acicular metal magnetic particle powder containing iron as a main component is impaired due to the increase of aluminum which is a non-magnetic component.

The location of aluminum is substantially uniform from the center to the surface when it is contained only in the central portion of the needle-shaped metal magnetic particles containing iron as a main component, when it is contained only in the surface layer portion. May be used, or a coating layer may be formed on the surface of the particle, or a combination of these various existing positions may be used. Considering the durability of the magnetic recording medium, acicular metallic magnetic particles containing aluminum almost uniformly from the center to the surface and having a coating layer formed on the particle surface are mainly composed of iron. Powders are preferred.

As is well known, acicular metal magnetic particle powder containing iron as a main component and containing aluminum therein,
In the production reaction step of the acicular goethite particles, by changing the addition time of the aluminum compound in various ways, to obtain acicular goethite particle powder containing aluminum at a desired position inside the particles, the acicular goethite particle powder or The acicular goethite particles can be obtained by heating and reducing a needle-like hematite particle powder containing aluminum at a desired position inside the particles obtained by heating and dehydrating the acicular goethite particles in a temperature range of 300 to 500 ° C.

The acicular metal magnetic particle powder mainly composed of iron whose surface is coated with aluminum is a needle-like goethite whose surface is coated with an aluminum compound such as aluminum oxide or hydroxide. A particle-like powder or a needle-like hematite particle powder whose surface is coated with an aluminum compound such as aluminum oxide or hydroxide is obtained by heating and dehydrating the needle-like goethite particle powder.
It is obtained by heat reduction in a temperature range of 0 to 500 ° C.

When a magnetic recording medium is manufactured using acicular metal magnetic particle powder containing iron as a main component in which Al and a rare earth metal such as Nd, La, and Y are present, more durable. A magnetic recording medium having excellent properties can be obtained. In particular, needle-like metal magnetic particles containing iron as a main component and containing Al and Nd are more preferable.

In the present invention, the shape of the acicular metallic magnetic particles containing iron as a main component is acicular. Here, the needle shape means not only a literal needle shape but also a spindle shape or a rice grain shape.

The average major axis diameter of the acicular metal magnetic particles containing iron as a main component is 0.01 to 0.5 μm, preferably 0.0 to 0.5 μm.
3 to 0.3 μm, and the average short axis diameter is 0.0007 to
It is 0.17 μm, preferably 0.003 to 0.1 μm.

The axial ratio of the acicular metal magnetic particles containing iron as a main component is 3 or more, preferably 5 or more. In consideration of dispersibility in a vehicle, the upper limit of the axial ratio is 15, and preferably the upper limit is 15. It is 10.

In particular, the resin adsorption strength of the iron-like metal magnetic particles containing iron as a main component and containing aluminum is 65% or more, preferably 68% or more, and more preferably 70% or more.

The magnetic properties of the acicular metal magnetic particles containing iron as a main component in the present invention have a coercive force value of 900 to 3500 Oe, preferably 1500 to 3500 Oe, taking into account characteristics such as high density recording. Magnetization value of 100 to 17
0 emu / g, preferably 120-170 emu / g.

The coating thickness of the magnetic recording layer provided on the nonmagnetic underlayer is in the range of 0.01 to 5.0 μm.
When the thickness is less than 0.01 μm, uniform coating is difficult, and phenomena such as uneven coating are likely to occur. 5.0
If it exceeds μm, it is difficult to obtain desired electromagnetic conversion characteristics due to the influence of the demagnetizing field. Preferably 0.05 to
The range is 1.0 μm.

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

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

In the magnetic recording medium according to the present invention, when the acicular hematite particle powder according to the present invention, which is not coated with aluminum hydroxide or the like, is used as the nonmagnetic particle powder for the nonmagnetic underlayer, the magnetic recording medium is protected. Magnetic force value is 900-3500
Oe, preferably 1000-3500 Oe, and a squareness ratio (residual magnetic flux density Br / saturated magnetic flux density Bm) of 0.86-0.
95, preferably 0.87 to 0.95, the glossiness of the coating film is 195 to 300%, preferably 200 to 300%, and the coating film surface roughness Ra is 8.5 nm or less, preferably 0.5 to
8.3 nm, more preferably 0.5 to 8.0 nm, and the Young's modulus (relative value) of the coating film is 122 to 160, preferably 1
24-160, the linear absorption coefficient of the coating film is 1.10-2.00
[mu] m ^-1, preferably 1.20～2.00Myuemu ^-1, running durability of the durable 22 minutes or more, preferably 23 minutes or more, more preferably 24 minutes or more, abrasion characteristics B or A , Preferably A, and the corrosiveness represented by the rate of change (%) of the coercive force value is 10.0% or less, and preferably 9.
5% or less, and the corrosiveness represented by the change rate (%) of the saturation magnetic flux density is 10.0% or less, preferably 9.5% or less.

When the acicular hematite particle powder according to the present invention coated with a hydroxide of aluminum or the like is used as the nonmagnetic particle powder for the nonmagnetic underlayer, the coercive force value is 900 to 3500 Oe, preferably 1000-35
00Oe, squareness ratio (residual magnetic flux density Br / saturated magnetic flux density B
m) is from 0.86 to 0.95, preferably from 0.87 to 0.
95, the glossiness of the coating film is 200 to 300%, preferably 2
05-300%, the coating film surface roughness Ra is 8.3 nm or less,
Preferably from 0.5 to 8.0 nm, more preferably from 0.5 to 8.0 nm.
7.8 nm, Young's modulus (relative value) of the coating film is 124 to 1
60, preferably 126 to 160, and a linear absorption coefficient of the coating film of 1.10 to 2.00 μm ⁻¹ , preferably 1.20 to 20,000 μm ⁻¹ .
2.00 μm ⁻¹ , and the running durability is 2
3 minutes or more, preferably 24 minutes or more, more preferably 25 minutes or more.
Min or more, the abrasion property is B or A, preferably A,
The corrosiveness represented by the change rate (%) of the coercive force value is 10.0% or less, preferably 9.5% or less, and the corrosiveness represented by the change rate (%) of the saturation magnetic flux density is 10.0% or less, preferably 9.
5% or less.

As the non-magnetic particle powder for the non-magnetic underlayer, the acicular hematite particle powder according to the present invention, which is not coated with aluminum hydroxide or the like, is used. When the acicular metal magnetic particle powder is used, the coercive force value is 900
~ 3500 Oe, preferably 1000-3500 Oe,
The squareness ratio (residual magnetic flux density Br / saturated magnetic flux density Bm) is 0.
86 to 0.95, preferably 0.87 to 0.95, and the glossiness of the coating film is 200 to 300%, preferably 205 to 30.
0%, the coating film surface roughness Ra is 8.3 nm or less, preferably 0.5 to 8.0 nm, more preferably 0.5 to 7.8 n.
m, the Young's modulus (relative value) of the coating film is 124 to 160, preferably 126 to 160, and the linear absorption coefficient of the coating film is 1.10 to 1.10.
2.00 μm ⁻¹ , preferably 1.20 to 2.00 μm
^-1 , the running durability is 23 minutes or more, preferably 24 minutes or more, more preferably 25 minutes or more, and the scratch characteristic is B or A, preferably A. The corrosiveness represented by (%) is 10.0% or less, preferably 9.5% or less, and the corrosiveness represented by the change rate (%) of the saturation magnetic flux density is 10.0% or less, preferably 9.5% or less. is there.

The acicular hematite particle powder according to the present invention, which is coated with a hydroxide of aluminum or the like, is used as the nonmagnetic particle powder for the nonmagnetic underlayer, and iron as a magnetic particle powder is mainly composed of iron. When the acicular metal magnetic particle powder is used, the coercive force value is 900 to
3500 Oe, preferably 1000 to 3500 Oe, squareness ratio (residual magnetic flux density Br / saturated magnetic flux density Bm) of 0.8
6 to 0.95, preferably 0.87 to 0.95, and the glossiness of the coating film is 205 to 300%, preferably 210 to 300%.
%, The coating film surface roughness Ra is 8.0 nm or less, preferably 0.5 to 7.8 nm, more preferably 0.5 to 7.5 n.
m, the Young's modulus (relative value) of the coating film is 126 to 160, preferably 128 to 160, and the linear absorption coefficient of the coating film is 1.10 to 1.10.
2.00 μm ⁻¹ , preferably 1.20 to 2.00 μm
^-1 , the running durability is 24 minutes or more, preferably 25 minutes or more, more preferably 26 minutes or more, and the scratch characteristic is B or A, preferably A, and the rate of change of the coercive force value. The corrosiveness represented by (%) is 10.0% or less, preferably 9.5% or less, and the corrosiveness represented by the change rate (%) of the saturation magnetic flux density is 10.0% or less, preferably 9.5% or less. is there.

Next, a method for producing the acicular hematite particle powder for a non-magnetic underlayer according to the present invention will be described.

The acicular hematite particle powder for a non-magnetic underlayer according to the present invention is obtained by treating an aqueous suspension of acicular hematite particle powder as a particle powder to be treated with an acid concentration of 1.0 N or more and a pH value of 3.0 or less. Dissolving treatment under the condition of a temperature range of 20 to 100 ° C. to dissolve 5 to 50% by weight of the total amount of the acicular hematite particles present in the aqueous suspension; Can be obtained by adding an aqueous alkali solution to an aqueous suspension of acicular hematite particle powder obtained by washing with water, adjusting the pH value to 13 or more, and then performing a heat treatment in a temperature range of 80 to 103 ° C.

The acicular hematite particles as the particles to be treated can be obtained by various methods. For example, there are a method of directly producing acicular hematite particle powder by a wet method, a method of producing akagenite (β-FeOOH) particle powder, and then heating and dehydrating to obtain acicular hematite particle powder. As a production method, a method of producing acicular goethite particle powder, which is a precursor of acicular hematite particle powder, by a wet method, and heating and dehydrating the obtained acicular goethite particle powder to obtain acicular hematite particle powder. It is industrially preferable.

First, a general method for producing acicular goethite particle powder, which is a starting material of acicular hematite particle powder as the particles to be treated, will be described.

As described in detail below, the acicular goethite particle powder is obtained by reacting ferrous salt with any one of alkali hydroxide, alkali carbonate or a mixed alkali of alkali hydroxide and alkali carbonate. An oxygen-containing gas such as air is passed through a suspension containing a ferrite-containing precipitate such as hydroxide or iron carbonate to form acicular goethite particles.

A typical basic reaction of acicular goethite particles is, as is well known, a suspension containing a ferrous hydroxide colloid obtained by adding an equivalent amount or more of an aqueous alkali hydroxide solution to an aqueous ferrous salt solution. A method for producing needle-like goethite particles by passing an oxygen-containing gas at a temperature of 80 ° C. or lower at a pH value of 11 or higher to generate needle-like goethite particles, which is obtained by reacting an aqueous ferrous salt solution with an aqueous alkali carbonate solution. FeCO ₃
The suspension containing aging is, if necessary, ripened and then subjected to an oxygen-containing gas to carry out an oxidation reaction to produce spindle-shaped goethite particles, a ferrous salt aqueous solution and an alkali carbonate aqueous solution, and a hydroxide. A method of producing spindle-shaped goethite particles by performing an oxidation reaction by passing an oxygen-containing gas after aging a suspension containing an iron-containing precipitate obtained by reacting with an alkali, if necessary,
An oxygen-containing gas is passed through an aqueous ferrous salt solution containing a ferrous hydroxide colloid obtained by adding a less than equivalent amount of an aqueous alkali hydroxide solution or an aqueous alkali carbonate solution to an aqueous ferrous salt solution to perform an oxidation reaction. After generating acicular goethite core particles, and then adding an aqueous solution of an alkali hydroxide at least equivalent to Fe ²⁺ in the aqueous ferrous salt solution to the aqueous ferrous salt solution containing the acicular goethite core particles, A method of growing the needle-like goethite core particles by passing an oxygen-containing gas, comprising a ferrous hydroxide colloid obtained by adding a less than equivalent aqueous solution of an alkali hydroxide or an alkali carbonate to an aqueous ferrous salt solution. An oxygen-containing gas is passed through the aqueous solution of ferrous salt to perform an oxidation reaction to generate acicular goethite core particles, and then the ferrous salt aqueous solution containing the acicular goethite core particles contains A method of growing an acicular goethite nucleus particle by passing an oxygen-containing gas in an amount equal to or more than the equivalent of Fe ²⁺ in an aqueous ferrous salt solution and then passing an oxygen-containing gas, and a method of preparing an aqueous solution of an aqueous solution less than an equivalent amount of an aqueous ferrous salt solution An oxygen-containing gas is passed through an aqueous ferrous salt solution containing a ferrous hydroxide colloid obtained by adding an alkali or alkali carbonate aqueous solution to generate an acicular goethite nucleus particle by performing an oxidation reaction. And a method of growing the acicular goethite core particles in a neutral region.

During the formation reaction of the acicular goethite particles, different kinds of Ni, Zn, P, Si, etc., 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. There is no problem even if the element is added.

The acicular hematite particles as the particles to be treated contain 0.05 to 50% by weight of aluminum in terms of Al relative to the total weight of the particles inside the particles. Is desirably added in advance as an aluminum compound in the reaction for forming acicular goethite particles and contained in the acicular goethite particles.

In the reaction for producing the acicular goethite particle powder, an aqueous solution of ferrous salt, an alkali hydroxide, an alkali carbonate, a mixed alkali of alkali hydroxide and alkali carbonate, or a hydroxide of iron or ferrous iron such as iron carbonate The aluminum compound may be added to any solution of the suspension containing the precipitate, and is preferably an aqueous ferrous salt solution.

As the aluminum compound, aluminum salts such as aluminum acetate, aluminum sulfate, aluminum chloride and aluminum nitrate, alkali aluminates such as sodium aluminate, alumina sol, aluminum hydroxide and the like can be used.

The addition amount of the aluminum compound is 0.05 to 50% by weight in terms of Al based on the produced goethite particle powder.
It is.

The acicular goethite particle powder as a starting material in the present invention usually has an average major axis diameter of 0.005 to 0.005.
0.4 μm, the average minor axis diameter is 0.0025 to 0.2 μm, the axial ratio is 2 to 20, the geometric standard deviation of the major axis diameter is 1.70 or less, and the BET specific surface area value is 50 to 250 m ^2. /
g, powder pH value is 3 to 9, aluminum is 0.05 to 50% by weight in terms of Al, and soluble sodium salt is Na
300-1500 ppm in conversion, soluble sulfate was converted to SO ₄
It contains 100-3000 ppm in conversion.

Next, a method for producing acicular hematite particles as the particles to be treated will be described.

The acicular hematite particles as the particles to be treated can be obtained by heating and dehydrating the acicular goethite particles as the starting material in a temperature range of 550 to 850.

When the temperature of the heat dehydration treatment is lower than 550 ° C., since the densification is insufficient, a large number of dehydration holes are present inside the particles of the acicular hematite particles and on the surface of the particles. During the treatment, the particle shape is not maintained due to the progress of dissolution from the dehydration holes, the dispersibility of the obtained acicular hematite particle powder in the vehicle becomes insufficient, and the surface becomes smooth when the nonmagnetic underlayer is formed. It is difficult to obtain a proper coating film. When the temperature exceeds 850 ° C., the densification of the acicular hematite particle powder is sufficient, but sintering occurs between the particles and the particles, so that the particle diameter increases, and similarly, the coating film has a smooth surface. Is difficult to obtain. The upper limit of the heating dehydration temperature is preferably 800 ° C.

The acicular hematite particles as the particles to be treated in the present invention are obtained by subjecting the acicular goethite particles to a low-temperature heating dehydration treatment at a temperature in the range of 250 to 500 ° C. to obtain low-density acicular hematite particles. Then, it is preferable that the low-density acicular hematite particle powder is a densified acicular hematite particle powder obtained by subjecting the low-density acicular hematite particle powder to high-temperature heat treatment in a temperature range of 550 to 850 ° C.

[0098] If the low-temperature heat dehydration temperature is lower than 250 ° C, it is not preferable because the dehydration reaction requires a long time. When the low-temperature heating dehydration temperature exceeds 500 ° C., a dehydration reaction occurs rapidly, and the shape of the particles may be easily collapsed or sintering between the particles may be caused. Low-density acicular hematite particle powder obtained by low-temperature heat dehydration treatment,
H ₂ O is dehydrated from the acicular goethite particle powder, and is composed of low-density particles having a large number of dehydration pores, and the BET specific surface area is about 1.2 to 2 times that of the acicular goethite particle powder as a starting material.

The obtained low-density acicular hematite particles usually have an average major axis diameter of 0.005 to 0.30 μm, an average minor axis diameter of 0.0025 to 0.15 μm and an axial ratio of 2 to 2. ~ 20, geometric standard deviation of major axis diameter is 1.70 or less,
BET specific surface area value is 70 to 350 m ² / g, S _BET /
S _TEM value is 2.6 or more, powder pH value is 3-9,
It contains aluminum in an amount of 0.05 to 50% by weight in terms of Al.
000 ppm, soluble sulfate 300 to _{4 in} terms of SO ₄
000 ppm.

Next, the low-density hematite particle powder was added to 55
A high-temperature heat treatment at 0 to 850 ° C. is performed to obtain a densified acicular hematite particle powder. High temperature heat treatment temperature is 550 ℃
If the concentration is less than 1, the densification is insufficient, so that a large number of dehydration holes are present inside the particles and on the particle surface of the acicular hematite particles, and the dissolution proceeds from the dehydration holes during the dissolution treatment with an acid. Due to the above, the particle shape is not maintained, the dispersibility of the obtained acicular hematite particle powder in the vehicle becomes insufficient, and when a non-magnetic underlayer is formed, it is difficult to obtain a coating having a smooth surface. When the temperature exceeds 850 ° C., the densification of the acicular hematite particle powder is sufficient, but sintering between the particles and the particles occurs. It is difficult to obtain. The upper limit of the heating dehydration temperature is preferably 800 ° C.

The resulting high-density acicular hematite particles usually have an average major axis diameter of 0.005 to 0.30 μm, an average minor axis diameter of 0.0025 to 0.15 μm, and an axial ratio of 2 to 2. ~ 20, geometric standard deviation of major axis diameter is 1.70 or less,
BET specific surface area value is 35 to 150 m ² / g, S _BET /
S _TEM value 0.5-2.5, powder pH value 2.5-9
Containing 0.05 to 50% by weight of aluminum in terms of Al, and converting soluble sodium salt into 5% in terms of Na.
00 to 4000 ppm, soluble sulfate in SO ₄ equivalent of 3
It contains from 0.00 to 5000 ppm.

[0102] The acicular hematite particle powder in the present invention may be preliminarily coated with a sintering inhibitor before the heat dehydration treatment or the high-temperature heat treatment in the temperature range of 550 to 850 ° C. preferable. The coating treatment with the sintering inhibitor is performed in an aqueous suspension containing acicular goethite particle powder, which is a starting material particle powder, or low-density acicular hematite particle powder, which is obtained by performing a low-temperature heating dehydration treatment at a temperature of 250 to 500 ° C. After adding a sintering inhibitor to the mixture and mixing and stirring, the mixture may be filtered, washed with water, and dried.

Examples of the sintering inhibitor include commonly used phosphorus compounds such as sodium hexametaphosphate, polyphosphoric acid, and orthophosphoric acid, No. 3 water glass, silicon compounds such as sodium orthosilicate, sodium metasilicate, and colloidal silica; Boron compounds such as acids, aluminum salts such as aluminum acetate, aluminum sulfate, aluminum chloride and aluminum nitrate; alkali aluminates such as sodium aluminate; aluminum compounds such as alumina sol and aluminum hydroxide; titanium compounds such as titanium oxysulfate Can be used.

The amount of the sintering inhibitor present on the particle surface of the acicular goethite particle powder varies depending on various conditions such as the type and amount of the sintering inhibitor, the pH value in an alkaline aqueous solution, and the heat treatment temperature. 0.05-1 based on the total weight of the powder
0% by weight.

Next, the acicular hematite particles as the particles to be treated in the present invention will be described.

The acicular hematite particles as the particles to be treated in the present invention may be acicular hematite particles obtained by heating and dehydrating the acicular goethite particles in a temperature range of 550 to 850, and acicular goethite. The particle powder is subjected to a low-temperature heat dehydration treatment in a temperature range of 250 to 500 ° C to obtain a low-density acicular hematite particle powder, and then the low-density acicular hematite particle powder is subjected to a high-temperature heat treatment in a temperature range of 550 to 850 ° C. Any of the densified acicular hematite particle powders obtained by performing the method can be used.

The particle shape of the acicular hematite particles as the particles to be treated is acicular. Here, the needle shape means not only a literal needle shape but also a spindle shape or a rice grain shape.

The acicular hematite particles as the particles to be treated have an average major axis diameter of 0.005 to 0.3 μm and a BET specific surface area of 35 to 150 m ² / g.

When the average major axis diameter of the acicular hematite particles as the particles to be treated exceeds 0.3 μm, the particle size of the acicular hematite particles in the present invention obtained after the above treatment is too large. It is not preferable because it impairs the surface smoothness of the coating film. If it is less than 0.005 μm, dispersion in the vehicle becomes difficult due to an increase in intermolecular force due to the reduction of the size of the acicular hematite particles obtained in the present invention after the above treatment. Considering the dispersibility in the vehicle and the surface smoothness of the coating,
The average major axis diameter is preferably from 0.02 to 0.25 μm.

The reason for setting the lower limit and the upper limit of the BET specific surface area of the acicular hematite particles as the particles to be treated is the same as the reason for setting the upper and lower limits of the average major axis diameter. . Considering the surface smoothness of the dispersibility and coating in the vehicle, BET specific surface area value is preferably 37~135m ² / g.

The acicular hematite particles as the particles to be treated have an average minor axis diameter of 0.0025 to 0.15 μm,
The geometric standard deviation of the major axis diameter is 1.70 or less, S _BET / S
_{TE M} value is 0.5 to 2.5, the powder pH value of a 2.5 to 9, soluble sodium salt calculated as Na 500-40
00 ppm, soluble sulfate is 300 to 50 in terms of SO ₄
It is preferably at most 00 ppm.

The acicular hematite particles, which are the particles to be treated, are 0.1% in terms of Al with respect to the acicular hematite particles.
It contains from 0.5 to 50% by weight of aluminum.

Next, the dissolution treatment of the acicular hematite particles as the particles to be treated in the present invention with an acid will be described.

The acicular hematite particle powder as the particle to be treated is subjected to a dry-type coarse pulverization to loosen the coarse particles before the dissolution treatment with an acid, and then to a slurry, and then to a wet pulverization. It is preferable to loosen coarse particles. The wet pulverization may be performed using a ball mill, a sand grinder, a colloid mill or the like so that at least coarse particles of 44 μm or more of secondary aggregated particles are eliminated. The degree of wet grinding is 10% of coarse particles of 44 μm or more.
Or less, preferably 5% or less, more preferably 0%. If coarse particles of 44 μm or more remain in excess of 10%, it is difficult to obtain the effect of the dissolution treatment with an acid in the next step.

The concentration of the acicular hematite particles in the aqueous suspension used for the dissolution treatment with an acid is preferably from 1 to 500 g / l, more preferably from 10 to 250 g / l. 1g /
If it is less than 1, the processing amount per processing unit is too small, which is not industrially preferable. When it exceeds 500 g / l, it is difficult to perform a uniform dissolution treatment.

As the acid used for the dissolution treatment with an acid, any of sulfuric acid, hydrochloric acid, nitric acid, sulfurous acid, chloric acid, perchloric acid and oxalic acid can be used. Sulfuric acid is preferable in consideration of the case where the treatment is performed at a high temperature or the corrosion, deterioration, economy, etc. of the container for performing the dissolution treatment.

The acid concentration in the dissolution treatment with an acid is as follows.
0N or more, preferably 1.2N or more, more preferably 1.5N or more. If it is less than 1.0 N, it takes an extremely long time to dissolve the acicular hematite particle powder, which is industrially disadvantageous.

The initial pH value in the dissolution treatment with an acid is as follows:
The pH value is 3.0 or less, preferably 2.0 or less, more preferably 1.0 or less. Considering the dissolution time and the like, a pH value of 1.0 or less is suitable. When the pH value exceeds 3.0, it takes an extremely long time to dissolve the acicular hematite particle powder, which is industrially disadvantageous.

The temperature range of the aqueous suspension in the dissolution treatment with an acid is 20 to 100 ° C., preferably 50 to 100 ° C.
More preferably, it is 70 to 100 ° C. If the temperature is lower than 20 ° C., it takes an extremely long time to dissolve the acicular hematite particles, which is industrially disadvantageous. 100 ℃
When it exceeds, the dissolution of the particles proceeds rapidly, making it difficult to control the dissolution, and requires an apparatus such as an autoclave, which is not industrially preferable.

In the case where the average major axis diameter of the acicular hematite particles as the particles to be treated is 0.05 to 0.30 μm, which is a region where the average major axis diameter is relatively large, the conditions for the dissolution treatment with acid are hard conditions. For example, an acid concentration of 1.5 N or more,
It is preferably carried out at a pH value of 1.0 or less and a temperature range of 70 to 100 ° C. In the case where the average major axis diameter is in a relatively small range of 0.005 to 0.05 μm, the conditions for dissolution treatment with an acid are soft. Conditions, for example, an acid concentration of 1.0-1.
It is preferable to carry out the reaction at 5 N, a pH value of 1.0 to 3.0 and a temperature range of 20 to 70 ° C.

The dissolution treatment with an acid is carried out in an amount of 5 to 50% by weight, preferably 10 to 45% by weight, more preferably 15 to 40% by weight of the total amount of the acicular hematite particles, which are the particles to be treated.
Perform until the weight% is dissolved. If the content is less than 5% by weight, the fine particle component is not sufficiently removed by dissolution, and
If the content is more than 10% by weight, the whole particle powder becomes fine and the loss due to dissolution is large.

The aqueous solution of the iron salt dissolved by the dissolution treatment with an acid is separated from the slurry by filtration, and is used as a ferrous salt raw material for producing acicular goethite particle powder from the viewpoint of resource reuse. Can be used.

Next, the heat treatment of the acicular hematite particles as the particles to be treated in an alkaline suspension will be described.

In the heat treatment of the acicular hematite particle powder in the alkaline suspension, the aqueous suspension of the residual acicular hematite particle powder after the dissolution treatment with an acid is separated by filtration, and the cake obtained by washing with water is washed again. An aqueous suspension of acicular hematite particle powder dispersed in water or an aqueous suspension of remaining acicular hematite particle powder washed with water by decantation Is preferred.

The concentration of the acicular hematite particles in the alkaline suspension used for the heat treatment of the alkaline suspension is 5%.
0 to 250 g / l is preferred.

As the aqueous alkali solution, an aqueous solution of an alkali hydroxide such as sodium hydroxide, potassium hydroxide, calcium hydroxide or the like can be used.

The pH value of the alkaline suspension containing the acicular hematite particles is 13 or more. When the pH is less than 13, solid crosslinking caused by the sintering inhibitor present on the particle surface of the acicular hematite particle powder cannot be effectively removed, and the soluble sodium salt present inside the particle and on the particle surface cannot be removed. Sulfate etc. cannot be washed out. The upper limit is a pH value of 14. The effect of removing solid cross-links due to the sintering inhibitor present on the particle surface of the acicular hematite particles and the washing out of soluble sodium salts, soluble sulfates, etc. The pH value is preferably in the range of 13.1 to 13.8 in consideration of the washing effect for removing alkali such as sodium attached to the surface of the hematite particle powder.

The heating temperature of the alkaline suspension containing the acicular hematite particles and having a pH value of 13 or more is preferably 80 ° C. or more, more preferably 90 ° C. or more. 80
When the temperature is lower than ℃, it is difficult to effectively remove solid crosslinking caused by the sintering inhibitor present on the particle surface of the acicular hematite particle powder. The upper limit of the heating temperature is 103
C is preferable, and more preferably 100C. 103
When the temperature exceeds ℃, solid crosslinking can be effectively removed, but it is industrially disadvantageous, for example, an autoclave or the like is required, and the liquid to be treated is boiled under normal pressure.

The acicular hematite particle powder heat-treated in the alkaline suspension is separated by filtration and washed with water by a conventional method, so that the soluble sodium salt or soluble sulfate washed out from the inside of the acicular hematite particle and from the particle surface is removed. During the heat treatment of the alkaline suspension, alkali such as sodium adhered to the particle surface of the acicular hematite particle powder is removed, and then dried.

Examples of the water washing method include a method generally used in industry such as a method of washing by decantation, a method of washing by a dilution method using a filter thickener, and a method of washing by passing water through a filter press. Just use it.

If the soluble sodium salt or soluble sulfate contained in the particles of the acicular hematite particles is washed out with water, the subsequent steps, for example,
Even if soluble sodium salt or soluble sulfate adheres to the particle surface of the acicular hematite particle powder in the coating process described later, it can be easily removed by washing with water.

Next, the surface coating treatment of the acicular hematite particle powder coated with an aluminum hydroxide or the like 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 suspension, by adding and mixing and stirring an aluminum compound, a silicon compound or both compounds, or, if necessary, by adjusting the pH value after mixing and stirring, on the particle surface of the acicular hematite particle powder, An aluminum hydroxide, an aluminum oxide, a silicon hydroxide and a silicon oxide may be coated, and then filtered, washed with water, dried and pulverized. 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.

The addition amount of the aluminum compound is 0.01 to 50% by weight in terms of Al with respect to the acicular hematite particle powder.
It is. When the amount is less than 0.01% by weight, the effect of improving the dispersibility by the coating is scarcely present, and when the amount exceeds 50% by weight, the effect of the coating is saturated.

The addition amount of the silicon compound is 0.01 to 50% by weight in terms of SiO ₂ with respect to the acicular hematite particle powder. When the amount is less than 0.01% by weight, the effect of improving the dispersibility by the coating is almost nil. When the amount is more than 50% by weight, the effect of the coating is saturated.

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.

Next, a method for manufacturing the nonmagnetic underlayer according to the present invention will be described.

The nonmagnetic underlayer according to the present invention is applied by applying a nonmagnetic paint containing the needle-like hematite particles for a nonmagnetic underlayer according to the present invention, a binder resin and a solvent onto a nonmagnetic support. It is obtained by drying after forming a film.

As the solvent, there can be used methyl ethyl ketone, toluene, cyclohexanone, methyl isobutyl ketone, tetrahydrofuran, a mixture thereof and the like, which are currently widely used for magnetic recording media.

The amount of the solvent used is 50 to 1000 parts by weight in total with respect to 100 parts by weight of the acicular hematite particle powder. If the amount is less than 50 parts by weight, the viscosity becomes too high when a non-magnetic paint is used, and application becomes difficult. If the amount exceeds 1000 parts by weight, the amount of the solvent volatilized when forming a coating film is too large, which is industrially disadvantageous.

Next, a method for manufacturing a magnetic recording medium according to the present invention will be described.

The magnetic recording medium according to the present invention comprises, on a non-magnetic underlayer formed on a non-magnetic support, acicular metal magnetic particles containing iron as a main component, a binder resin, and a solvent. It is obtained by applying a magnetic paint to form a coating film and then drying to form a magnetic recording layer.

Solvents used for producing magnetic paints include:
The solvent used to form the non-magnetic underlayer can be used.

The amount of the solvent used is 65 to 1 in total with respect to 100 parts by weight of the acicular metal magnetic particles containing iron as a main component.
000 parts by weight. If the amount is less than 65 parts by weight, the viscosity becomes too high when a magnetic coating material is used, and application becomes difficult. 100
If the amount exceeds 0 parts by weight, the amount of the solvent volatilized at the time of forming the coating film becomes too large, which is industrially disadvantageous.

[0145]

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

For the remaining sieve, the slurry concentration after wet pulverization was separately determined, and a slurry corresponding to 100 g of solids was passed through a 325 mesh (opening 44 μm) sieve, and the amount of solids remaining in the sieve was determined. It was determined by quantifying the amount.

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 (× 30000), which was magnified 4 times in the vertical and horizontal directions, respectively, for about 350 particles. The shaft diameters were measured and indicated by the average value.

The axial ratio was represented by the ratio between the average major axis diameter and the average minor axis diameter.

The geometric standard deviation of the major axis diameter of the particles was 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 is calculated from the measured major axis diameter and the actual number of the major axis diameter of the particles, and the horizontal axis is plotted on a lognormal probability paper according to a statistical method. The major axis diameter of the particle
On the vertical axis, the cumulative number of particles belonging to each of the predetermined major axis diameter sections (under the integrated screen) is plotted as a percentage. The graph shows that the number of particles is 50% and 84.13.
%, Read the value of the major axis diameter corresponding to each%, and calculated the geometric standard deviation = the major axis diameter at 84.13% under the integrated screen /
The value was calculated according to the major axis diameter (geometric mean diameter) at 50% below the integrated screen. 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 was indicated by a value measured by the BET method.

The degree of densification of the acicular hematite particles is as follows:
As described above, S _BET / S _TEM values were used. Here, the S _BET value is a value of the specific surface area measured by the BET method. S _TEM value is an average major axis diameter lcm of particles measured from the electron micrograph, the average particle using short axis diameter wcm assuming cuboid is a value calculated according to the following equation.

S_TEMValue (m²/ G) = [(4lw + 2
w²) / (Lw²・ Ρ_p)] × 10 ^-4  (However, ρ_pIs the true specific gravity of hematite, and 5.2 g
/ Cm³Was used. )

The contents of Al, Si, P and Nd present inside the particles or on the particle surface of the acicular hematite particle powder or the acicular metal magnetic particle powder containing iron as a main component are determined by using a fluorescent X-ray analyzer. The measurement was performed according to JIS K0119 "General rules for X-ray fluorescence analysis" using "Type 3063M" (manufactured by Rigaku Corporation).

The powder pH value was determined by weighing 5 g of a 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 stoppering and allowing to cool to room temperature. Then, water equivalent to the weight loss was added, stoppered again, shaken for 1 minute, allowed to stand for 5 minutes, and 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 of the acicular hematite particle powder are determined by the above-mentioned powder p.
The supernatant prepared for the measurement of the H value was No. Filtration was performed using a 5C filter paper, and Na ⁺ and SO ₄ ^2- in the filtrate were measured using an inductively coupled plasma emission spectrometer (manufactured by Seiko Instruments Inc.).

The resin adsorption strength indicates the degree to which the resin is adsorbed on acicular hematite particles or acicular metallic magnetic particles containing iron as a main component. % Indicates that the resin is strongly adsorbed on the particle surface of the acicular hematite particles or the acicular metallic magnetic particles containing iron as a main component.

First, the resin adsorption amount Wa is determined.

A mixed solvent in which 20 g of the particles to be measured and 2 g of a vinyl chloride resin having a sodium sulfonate group were dissolved (27.0 g of methyl ethyl ketone, 16.2 of toluene)
g, cyclohexanone 10.8 g) 56 g and 3 mmφ
Put into a 100 ml poly bottle together with 120 g of steel beads and mix and disperse on a paint shaker for 60 minutes.

Next, 50 g of this coating composition was taken out and the
The mixture is placed in a 0 ml settling tube and centrifuged at 10,000 rpm for 15 minutes to separate a solid portion and a solvent portion.
Then, the resin solid content concentration contained in the solvent portion is quantified by a gravimetric method, and the amount of the resin present in the solid portion is obtained by subtracting from the charged resin amount, and this is used as the resin adsorption amount Wa (mg / g) for the particles. And

Next, only the solid portion separated previously
The whole amount was taken out into a 2 ml tall beaker, and mixed solvent (25.0 g of methyl ethyl ketone, 15.0 ml of toluene)
g, cyclohexanone 10.0 g) and 50 g.
After ultrasonic dispersion for a minute, the suspension is put into a 50 ml sedimentation tube and centrifuged at 10,000 rpm for 15 minutes to separate a solid portion and a solvent portion. Then, by measuring the resin solid content concentration in the solvent portion, the amount of resin extracted into the solvent phase among the resin adsorbed on the particle surface is quantified.

Further, the operation from the removal of the entire amount of only the solid portion into a 100 ml tall beaker to the determination of the amount of the resin dissolved in the solvent phase was repeated twice, and the total amount of the resin extracted in the solvent phase was totaled three times. We (mg / g) was determined, and the value determined according to the following equation was defined as the resin adsorption strength (%).

Resin adsorption strength (%) = [(Wa-We) /
Wa] × 100

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 coating surface of the nonmagnetic 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
5A "(manufactured by Tokyo Seimitsu Co., Ltd.), the center line average roughness Ra of the coating film was measured.

Regarding the durability of the magnetic recording medium, the following running durability and scratch characteristics were evaluated.

The running durability was measured in “Media Durab”.
ility Tester MDT-3000 ”(St
einberg Associates), a load of 200 gw and a relative speed of 16 between the head and the tape.
Evaluation was made based on the actual operating time at m / s. The longer the actual operating time, the better the running durability.

The scratch characteristics were evaluated by observing the surface of the tape after running with a microscope and visually checking for scratches.
A rating was given on a scale. A: There is no scratch B: There is some scratch C: There is scratch D: There is severe scratch

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

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.

The change over time in the magnetic properties of the magnetic recording medium due to the corrosion of the acicular metal magnetic particles containing iron as a main component dispersed in the magnetic recording layer was measured at a temperature of 60 ° C.
The sample was allowed to stand for 14 days in an environment with a relative humidity of 90%, and the coercive force value and the saturation magnetic flux density before and after the measurement were measured. The value obtained by dividing the change by the value before the test was expressed as a percentage as a change rate.

The degree of light transmission was determined according to “Self-Recording Spectrophotometer UV-
The value of the light transmittance measured for the magnetic recording medium using "2100" (manufactured by Shimadzu Corporation) was shown as a linear absorption coefficient calculated by inserting the value into the following equation. The larger the linear absorption coefficient is, the harder it is to transmit light. In measuring the value of the light transmittance, the same non-magnetic support as the non-magnetic support used for the magnetic recording medium was used as a blank.

Linear absorption coefficient (μm ⁻¹ ) = [ln (1 / t)] / FT t: Light transmittance at λ = 900 nm (−) FT: Coating layer of film used for measurement (non-magnetic underlayer (Sum of the thickness of the magnetic recording layer and the thickness of the magnetic recording layer) (μm)

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 method.

That is, the digital electronic micrometer K3
First, the film thickness (A) of the nonmagnetic support is measured using 51C (manufactured by Anritsu Electric Co., Ltd.). Next, the thickness (B) (sum of the thickness of the nonmagnetic support and the thickness of the nonmagnetic underlayer) of the nonmagnetic support and the nonmagnetic underlayer formed on the nonmagnetic support is measured in the same manner. I do. 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).

<Production of Spindle-Shaped Hematite Particle Powder> Using an aqueous solution of ferrous sulfate and an aqueous solution of sodium carbonate, 1.12% by weight of aluminum in terms of Al obtained by the above-mentioned method of producing goethite particle powder was added to the inside of the particles. Spindle-shaped goethite particles powder (average major axis diameter 0.
167 μm, average short axis diameter 0.0196 μm, axial ratio 8.
5, geometrical standard deviation 1.32 of major axis diameter, BET specific surface area 165.3m ² / g, the powder pH value 6.8, the content of soluble sodium salt (Na terms) 1821Ppm, containing a soluble sulfate The amount (SO ₄ terms) 2162ppm) 120
0 g is suspended in water to form a slurry, and the solid content concentration is 8
g / l. 150 liters of this slurry was heated to a temperature of 60 ° C., and a pH value of the slurry was adjusted to 10.0 by adding a 0.1N aqueous sodium hydroxide solution.

Next, 24 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. After that, filtration, washing with water,
Drying and pulverization were performed to obtain spindle-shaped goethite particle powder in which silicon oxide was coated on the particle surface. S contained
The amount of iO ₂ was 0.52% by weight.

The obtained spindle-shaped goethite particle powder 100
0 g into a stainless steel rotary furnace and do not rotate.
Heat treatment at 350 ° C for 40 minutes in air
Water treatment to obtain low-density spindle-shaped hematite particle powder
Was. The obtained low-density spindle-shaped hematite particle powder has an average
The major axis diameter is 0.143 μm and the average minor axis diameter is 0.0191 μm
m, the axial ratio is 7.5, and the geometric standard deviation of the major axis diameter is 1.3.
2. BET specific surface area (S _BETValue) is 188.9m²
/ G, degree of densification (S_BET/ S_TEMValue) is 4.4
0, contains 1.23% by weight of aluminum in terms of Al
The content of soluble sodium salt is calculated as Na
1682 ppm, soluble sulfate is SO₄976 in conversion
ppm, SiO₂The amount is 0.57% by weight, the powder pH value is
6.1.

Next, 850 g of the above-mentioned low-density spindle-shaped hematite particle powder was placed in a ceramic rotary furnace, and heat-treated at 650 ° C. for 30 minutes in the air while being rotated to seal the dewatered holes. The densified spindle-shaped hematite particles have an average major axis diameter of 0.141 μm, an average minor axis diameter of 0.0192 μm, an axial ratio of 7.3, and a geometric standard deviation of the major axis diameter of 1.33; BET specific surface area (S
_BET value) is 56.1 m ² / g and the degree of densification (S
_(BET / S _TEM value) is 1.31, 1.23 in terms of Al
% Of aluminum, the content of soluble sodium salt is 2538 ppm in terms of Na, the content of soluble sulfate is 2859 ppm in terms of SO ₄ , the amount of SiO ₂ is 0.57 wt%, and the pH value of the powder is 5. It was 6.

After 800 g of the obtained spindle-shaped hematite particles having a high density was coarsely pulverized in advance with a Nara-type pulverizer, the mixture was poured into 4.7 L of pure water, and a homomixer (manufactured by Tokushu Kika Kogyo Co., Ltd.) was used. Peptized for 60 minutes.

Next, while the obtained slurry of the densified spindle-shaped hematite particles was circulated by a horizontal SGM (Dispamat SL: manufactured by SC Adichem Co., Ltd.), the slurry was cooled at a shaft rotation number of 2000 rpm. Mix and disperse for time. The sieve residue of the needle-like hematite particle powder in the obtained slurry at 325 mesh (mesh size: 44 μm) was 0%.

<Solution Treatment of Spindle-Shaped Hematite Particle Powder with Acid> Water was added to the obtained slurry of the densified spindle-shaped hematite particle powder to reduce the concentration of the slurry to 10%.
After adjusting to 0 g / l, 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 adjusted to 0.58. Next, this slurry was heated with stirring to raise the temperature to 80 ° C., and the solution was kept at that temperature for 5 hours to perform a dissolving treatment, and the total amount of spindle-shaped hematite particles present in the liquid was 29.5. % By weight was dissolved.

Next, this slurry was filtered to separate a filtrate (aqueous aqueous solution of iron sulfate) and then washed with water by a decantation method to obtain a washed slurry having a pH value of 5.0.
When the slurry concentration at this time was confirmed, 68 g / l
Met.

Here, a part of the obtained water-washing slurry was fractionated, separated by filtration using a Buchner funnel, passed through pure water, and washed with water until the conductivity of the filtrate became 30 μs or less. After drying by a conventional method, the resultant was pulverized to obtain spindle-shaped hematite particles. The obtained spindle-shaped hematite particle powder has an average major axis diameter of 0.133 μm, an average minor axis diameter of 0.0182 μm, an axial ratio of 7.3, a geometric standard deviation of the major axis diameter of 1.33, and a BET ratio. the degree surface area _{(S BET} value) of 60.3m ² / g, the density _(S BET _/ S _{T EM}
Value of 1.34, containing 1.23% by weight of aluminum in terms of Al, having a soluble sodium salt content of 131 ppm in terms of Na, a soluble sulfate content of 424 ppm in terms of SO ₄ , The body pH was 4.9.

<Heat Treatment of Spindle-Shaped Hematite Particles in Alkaline Suspension> Water was added to the water-washed slurry of spindle-shaped hematite particles after the above-mentioned dissolution treatment with acid to a concentration of 50 g / l, and 5 l of the slurry. Collected. While stirring the slurry, a 6N aqueous NaOH solution was added to adjust the pH value of the slurry to 13.6. Next, this slurry was heated with stirring 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 the sake of accuracy, the slurry concentration at this time was confirmed to be 98 g / l.

Next, 1 liter of the obtained water-washed slurry was separated by filtration using a Buchner funnel, and pure water was passed through to wash the filtrate until the conductivity of the filtrate became 30 μs or less, and then dried by a conventional method. Thereafter, the resultant was pulverized to obtain a desired spindle-shaped hematite particle powder. The obtained spindle-shaped hematite particle powder has an average major axis diameter of 0.133 μm and an average minor axis diameter of 0.0
182 μm, axial ratio 7.3, major axis diameter geometric standard deviation 1.33, BET specific surface area value (S _BET value) 60.1
m ² / g, the density (S _BET / S _TEM value) is 1.33, the aluminum content is 1.23% by weight in terms of Al, the powder pH value is 9.4, and the soluble sodium The salt content was 97 ppm in terms of Na, the soluble sulfate content was 20 ppm in terms of SO ₄ , and the resin adsorption strength was 72.5%.

<Manufacture of Magnetic Recording Medium-Formation of Nonmagnetic Underlayer on Nonmagnetic Support> 12 g of the spindle-shaped hematite particles obtained above and a binder resin solution (vinyl chloride having a sodium sulfonate group) Vinyl acetate copolymer resin 30
(By weight, cyclohexanone 70% by weight) and cyclohexanone were mixed to obtain a mixture (solid content: 72%), and this mixture was further kneaded with a plastmill for 30 minutes to obtain a kneaded product.

The kneaded material was placed in a 140 ml glass bottle for 1.5 times.
glass beads 95 g, binder resin solution (polyurethane resin having sodium sulfonate group 30% by weight,
A solvent (methyl ethyl ketone: toluene = 1: 1) 70% by weight), cyclohexanone, methyl ethyl ketone and toluene were added, and the mixture was mixed and dispersed for 6 hours with a paint shaker to obtain a coating composition.

The composition of the coating material containing the obtained spindle-shaped hematite particles was 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 viscosity of the obtained nonmagnetic paint was 362 c.
P.

A coating containing the obtained spindle-shaped hematite particles was applied to a polyethylene terephthalate film having a thickness of 12 μm to a thickness of 55 μm using an applicator, and then dried to form a non-magnetic underlayer. The thickness of the nonmagnetic underlayer was 3.5 μm.

The obtained non-magnetic underlayer had a gloss of 212.
%, The surface roughness Ra was 6.1 nm, and the Young's modulus (relative value) of the coating film was 127.

<Manufacture of Magnetic Recording Medium-Formation of Magnetic Recording Layer> 1.24% by weight in terms of Al in the center of the particle, and A in the surface layer
Needle-shaped magnetic metal mainly composed of iron in which 0.83% by weight in terms of l and 0.94% by weight in terms of Al in the surface coating portion of aluminum and 0.53% by weight of Nd are present. Particle powder (average major axis diameter 0.112 μm, average minor axis diameter 0.0147 μm, axial ratio 7.6, coercive force value 190
8Oe, saturation magnetization value: 136.3 emu / g, geometric standard deviation value: 1.36, resin adsorption strength: 82.0%) 12 g, abrasive (trade name: AKP-30, manufactured by Sumitomo Chemical Co., Ltd.)
2 g, carbon black (trade name: # 3250B, manufactured by Mitsubishi Kasei Corporation) 0.12 g, binder resin solution (vinyl chloride-vinyl acetate copolymer resin having sodium sulfonate group 30% by weight and cyclohexanone 70% by weight) and Cyclohexanone and a mixture (solid content 78
%), And this mixture was further kneaded with a plastmill for 30 minutes to obtain a kneaded material.

This kneaded material was placed in a 140 ml glass bottle for 1.5 times.
glass beads 95 g, binder resin solution (polyurethane resin having sodium sulfonate group 30% by weight,
Solvent (methyl ethyl ketone: toluene = 1: 1) 70% by weight), cyclohexanone, methyl ethyl ketone and toluene were added, mixed and dispersed in a paint shaker for 6 hours, and then a lubricant and a curing agent were added.
The mixture was dispersed and mixed with a paint shaker for 15 minutes to obtain a magnetic paint.

The composition of the obtained magnetic paint was as follows. Needle-shaped metal 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 (AKP-30) 10 parts by weight Carbon black (# 3250B) 3.0 parts by weight Lubricant (myristic acid: butyl stearate = 1: 2) 3.0 parts by weight Hardener (polyisocyanate) 5.0 parts by weight Cyclohexanone 65.8 parts by weight Methyl ethyl ketone 164.5 parts by weight Toluene 98.7 parts by weight

After applying the 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, the coating was applied at 60 ° C. for 24 hours. A curing reaction was performed and slits were formed to a width of 0.5 inch to obtain a magnetic tape. The thickness of the magnetic recording layer was 1.1 μm.

The obtained magnetic tape had a Hc of 1983O.
e, squareness ratio (Br / Bm) 0.87, glossiness 234
%, The surface roughness Ra was 6.1 nm, the Young's modulus (relative value) of the coating film was 131, the linear absorption coefficient was 1.24 μm ⁻¹ , the running durability was 29.2 minutes, and the scratch characteristics were A. .

The rate of change of the coercive force indicating the corrosion resistance of the magnetic tape was 4.5%, and the rate of change of the saturation magnetic flux density was 2.6.
%Met.

[0200]

The most important points in the present invention are that the average major axis diameter is 0.005 to 0.30 μm and the BET specific surface area value is 35 to 1
An aqueous suspension of acicular hematite particle powder of 50 m ² / g is subjected to dissolution treatment with an acid under the conditions of an acid concentration of 1.0 N or more, a pH value of 3.0 or less and a temperature range of 20 to 100 ° C. After dissolving 5 to 50% by weight of the total amount of the acicular hematite particles present in the suspension, the remaining acicular hematite particles are washed with water. Add an aqueous solution to adjust the pH to 13
After the above preparation, heat treatment was performed at a temperature in the range of 80 to 103 ° C., followed by filtration, washing with water, and drying. The average major axis diameter was 0.004 to 0.295 μm, and the BET specific surface area was 3.
5.9-212 m ² / g, powder pH value is 8 or more, soluble sodium salt content is 300 ppm or less in Na conversion,
The content of the soluble sulfate is 150 ppm or less in terms of SO ₄ , and 0.05 to 50% by weight in terms of Al inside the particles.
When the acicular hematite particle powder containing aluminum is used as the non-magnetic particle powder for the non-magnetic underlayer, the non-magnetic property is high due to the excellent dispersibility in the binder resin. The surface smoothness and strength of the underlayer can be improved, and when the magnetic recording layer using the acicular metal magnetic particle powder containing iron as a main component is provided on the nonmagnetic underlayer, the magnetic recording layer And a magnetic recording medium having a low light transmittance, a high strength, a smoother surface, and more excellent durability,
This is a fact that deterioration of magnetic characteristics due to corrosion of acicular metal magnetic particle powder containing iron as a main component dispersed in the magnetic recording layer can be suppressed.

Regarding the reason why the acicular hematite particle powder for a non-magnetic underlayer according to the present invention is excellent in dispersibility, the present inventor has proposed an aqueous suspension containing acicular hematite particle powder, which is a particle powder to be treated. , Acid concentration 1.0N or more, pH value 3.0
Hereinafter, by performing a dissolution treatment with an acid in a temperature range of 20 to 100 ° C., the geometric standard deviation of the major axis diameter is 1.5.
A needle-like hematite particle powder having few coarse or fine particles having a particle diameter of 0 or less can be obtained, the BET specific surface area value is 35.9 to 212 m ² / g, and dehydration pores are formed inside the particles and on the particle surface. Due to the small number of particles and the ability to sufficiently wash and remove the soluble sodium salts and soluble sulfates that cause the high-density acicular hematite particles to be strongly crosslinked and aggregated, Is thought to be due to a synergistic effect such as that the particles can be unraveled and become substantially independent particles.

The reason why the surface smoothness of the magnetic recording medium according to the present invention is improved is based on the fact that the needle-like hematite particles for a nonmagnetic underlayer according to the present invention have excellent dispersibility. It is believed that the surface smoothness of the non-magnetic underlayer was improved.

The reason why the deterioration of the magnetic characteristics due to the corrosion of the acicular metal magnetic particles containing iron as a main component dispersed in the magnetic recording layer of the magnetic recording medium according to the present invention is suppressed is as follows. It is said that the soluble components such as soluble sodium salts and soluble sulfates that promote metal corrosion are less in the acicular hematite particle powder according to the present invention and the acicular hematite particle powder itself has a powder pH value of 8 or more. It is considered that the progress of corrosion of the acicular metal magnetic particle powder containing iron as a main component was suppressed due to the high value.

The reason why the strength of the non-magnetic underlayer provided on the non-magnetic support has been improved and the durability of the magnetic recording medium has been improved is not yet clear. Due to the fact that aluminum is contained inside the particles of the matite particle powder, the resin adsorption strength of the aluminum-containing acicular hematite particle powder contained in the non-magnetic underlayer with the binder resin is improved, As a result, it is considered that the degree of adhesion between the nonmagnetic underlayer and the nonmagnetic support and the magnetic recording layer was increased.

[0205]

Next, examples and comparative examples will be described.

<Types of Acicular Goethite Particle Powder> Starting Materials 1 to 7 Table 1 shows various properties of acicular goethite particle powder which is a starting material of acicular hematite particle powder.

[0207]

[Table 1]

<Production of low-density acicular hematite particle powder> Examples 1 to 7, Comparative Examples 1 to 6 The type of acicular goethite particle powder as a starting material, the type and amount of a sintering inhibitor, the thermal dehydration temperature and A low-density acicular hematite particle powder was obtained in the same manner as in the embodiment of the invention except that the time was variously changed. The particle powder obtained in Comparative Example 4 is acicular goethite particle powder.

The main production conditions at this time are shown in Table 2, and various characteristics of the obtained low-density acicular hematite particle powder are shown in Table 3.

[0210]

[Table 2]

[0211]

[Table 3]

<Production of High Density Acicular Hematite Particle Powder> Examples 8 to 14, Comparative Examples 7 to 11 Except that the type of low density acicular hematite particle powder and the temperature and time of the heat treatment for densification were changed variously In the same manner as in the embodiment of the present invention, a high-density acicular hematite particle powder was obtained.

The main production conditions at this time are shown in Table 4, and various characteristics of the obtained high-density acicular hematite particle powder are shown in Table 5.

[0214]

[Table 4]

[0215]

[Table 5]

<Dissolution Treatment of Acicular Hematite Particle Powder with Acid> Examples 15 to 21, Comparative Examples 12 to 13 Kinds of high-density acicular hematite particle powder, presence or absence of wet pulverization, acid concentration, pH value of slurry, heating A needle-like hematite particle powder was obtained in the same manner as in the embodiment of the invention except that the temperature and the heating time were variously changed.

The main production conditions at this time are shown in Table 6, and various properties of the obtained acicular hematite particle powder are shown in Table 7.

[0218]

[Table 6]

[0219]

[Table 7]

<Heat Treatment of Alkaline Suspension of Acicular Hematite Particle Powder> Examples 22 to 28, Reference Examples 1-2 Types of acicular hematite particle powder, presence / absence of heat treatment of alkaline suspension, pH of slurry Needle-like hematite particles were obtained in the same manner as in the embodiment of the invention except that the values, heating temperature and heating time were variously changed.

The main production conditions at this time are shown in Table 8, and various characteristics of the obtained acicular hematite particle powder are shown in Table 9.

[0222]

[Table 8]

[0223]

[Table 9]

<Surface Coating Treatment of Acicular Hematite Particle Powder> Example 29 The pH value of Example 22 obtained by heating in an alkaline suspension and washing with water by a decantation method was 1
The 0.5 washed slurry had a slurry concentration of 50 g / l. 4 l of the water-washed slurry was heated again to 60 ° C., and 74.1 ml of a 1.0 N aqueous sodium aluminate solution (Al-based powder of acicular hematite particles)
It corresponds to 1.0% by weight in conversion. ) Was added and the mixture was kept for 30 minutes, and then the pH value was adjusted to 8.0 using an aqueous acetic acid solution. Next, in the same manner as in the embodiment of the invention, filtration, washing with water, drying and pulverization were performed to obtain acicular hematite particle powder whose particle surface was covered with aluminum hydroxide.

The main production conditions at this time are shown in Table 10, and various characteristics of the obtained acicular hematite particle powder are shown in Table 11.

In the surface treatment, A of the type of the coating is aluminum hydroxide, and S is an oxide of silicon.

Examples 30 to 35 The procedure of Example 29 was repeated, except that the type of the acicular hematite particle powder and the type and amount of the surface-treated product were variously changed.
A needle-like hematite particle powder whose particle surface was coated with aluminum hydroxide or the like was obtained by a conventional method.

The main production conditions at this time are shown in Table 10, and various characteristics of the obtained acicular hematite particle powder are shown in Table 11.

[0229]

[Table 10]

[0230]

[Table 11]

<Manufacture of Magnetic Recording Medium-Formation of Nonmagnetic Underlayer on Nonmagnetic Support> Examples 36 to 49, Comparative Examples 14 to 22, Reference Examples 3 to 11 Examples 15 to 35, Comparative Example 1 A non-magnetic underlayer was formed in the same manner as in the embodiment of the present invention using the acicular hematite particles obtained in Examples 3, 3, 13 and Reference Examples 1 and 2.

Table 12 shows the main manufacturing conditions and various characteristics at this time.
This is shown in Table 13.

[0233]

[Table 12]

[0234]

[Table 13]

<Manufacture of Magnetic Recording Medium-Formation of Magnetic Recording Layer> Table 14 shows needle-like metal magnetic particles containing iron as a main component used for forming the magnetic recording layer and their properties.

[0236]

[Table 14]

Examples 50 to 63, Comparative Examples 23 to 31, Reference Examples 12 to 20 Examples 36 to 49, Comparative Examples 14 to 22, and Reference Examples 3-1
A magnetic recording medium was manufactured in the same manner as in the embodiment of the invention except that the type of the nonmagnetic underlayer obtained in Step 1 and the type of the acicular metal magnetic particles containing iron as a main component were variously changed. did.

Table 15 shows the main manufacturing conditions and various characteristics at this time.
And Table 16 below.

[0239]

[Table 15]

[0240]

[Table 16]

[0241]

The acicular hematite particle powder according to the present invention, when used as a non-magnetic particle powder for a non-magnetic underlayer,
Since the dispersibility in the vehicle is excellent, a non-magnetic underlayer having excellent surface smoothness can be obtained. When the non-magnetic underlayer is used as a magnetic recording medium, the light transmittance is low and the surface smoothness is low. , High strength, and a magnetic recording medium with excellent durability. Further, the powder pH of the acicular hematite particles as the non-magnetic particles is 8 or more, It is possible to obtain a magnetic recording medium in which the deterioration of the magnetic properties due to the corrosion of the acicular metal magnetic particle powder containing iron as a main component dispersed in the magnetic recording layer due to the small content is suppressed. Therefore, it is suitable as a nonmagnetic particle powder for a nonmagnetic underlayer of a high density magnetic recording medium.

As described above, the magnetic recording medium according to the present invention has a low light transmittance, a smooth surface, a high strength, an excellent durability, and an iron dispersed in the magnetic recording layer. It is suitable as a high-density magnetic recording medium because deterioration of magnetic properties due to corrosion of acicular metal magnetic particle powder as a main component is suppressed.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hiroko Morii 4-1-2, Funariminami, Naka-ku, Hiroshima-shi, Hiroshima Toda Kogyo Co., Ltd.

Claims (4)

[Claims] 1. A needle mainly composed of iron as a magnetic particle powder.
Of magnetic recording media using powdered metallic magnetic particles
Needle-like hematite particles for a conductive underlayer, having an average major axis
Diameter 0.005 to 0.30 μm, BET specific surface area value 35 to
150m²/ G of acicular hematite particle powder
The turbid solution was prepared with an acid concentration of 1.0 N or more, a pH value of 3.0 or less, and a temperature range of
A solution treatment with an acid is carried out at a temperature of 20 to 100 ° C.
Total amount of needle-like hematite particles present in aqueous suspension
After dissolving 5 to 50% by weight of
Needle-like hematite particles obtained by washing
An aqueous alkaline solution is added to the aqueous suspension to obtain a pH value of 1
After adjusting to 3 or more, heat in the temperature range of 80 to 103 ° C
The average length obtained by treating, then filtering, washing and drying
Shaft diameter 0.004 to 0.295 μm, BET specific surface area 3
5.9-212m ²/ G, powder pH value is 8 or more, and
Soluble sodium salt content is 300ppm in Na conversion
Hereinafter, when the content of soluble sulfate is SO₄150pp in conversion
m or less, and 0.05 to
Characterized in that it contains 50% by weight of aluminum
Acicular hematite particles for a non-magnetic underlayer. 2. A magnetic recording medium using needle-like metal magnetic particle powder mainly composed of iron as the magnetic particle powder, wherein the particle surface of the needle-like hematite particle powder for the non-magnetic underlayer is aluminum hydroxide. 2. The acicular hematite particle powder for a nonmagnetic underlayer according to claim 1, which is coated with at least one of aluminum oxide, silicon hydroxide and silicon oxide. 3. A non-magnetic support, a non-magnetic underlayer composed of non-magnetic particle powder formed on the non-magnetic support and a binder resin, and iron formed on the non-magnetic under layer as a main component. 3. A magnetic recording medium comprising a magnetic recording layer comprising a needle-like metal magnetic particle powder and a binder resin, wherein the non-magnetic particle powder is the needle-like hematite particle powder for a non-magnetic underlayer according to claim 1 or 2. A magnetic recording medium characterized by the above-mentioned. 4. A magnetic particle powder having an Al equivalent of 0.05.
4. The magnetic recording medium according to claim 3, wherein acicular metal magnetic particles containing iron as a main component and 10 to 10% by weight of aluminum are used.