JP2001143243A - Magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain magnetic particle powder capable of obtaining a magnetic recording medium having a low light transmissivity even if the volume of carbon black added to the magnetic recording layer is reduced as possible, a low surface electric resistance value and a smooth surface. SOLUTION: An acicular black composite magnetic particle powder for the magnetic recording medium, which has a coating layer consisting of an organo-silane compound formed from alkoxysilane and applied on the particle surface of an acicular magnetic particle powder, carbon black particulate powder having 0.002-0.05 μm average particle size and adhered to the coating layer consisting of the organo-silane compound and 0.051-0.72 μm average major axis diameter, is characterized in so that 0.5-10 pts.wt. carbon black particulate powder is adhered to 100 pts.wt. acicular magnetic particle powder.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a needle-like material having excellent dispersibility in a vehicle due to a small amount of carbon black detached from the particle surface, and having excellent blackness and low volume resistivity. It is an object of the present invention to provide a magnetic recording medium having a smoother surface, a smaller light transmittance and a lower surface electric resistance value by using black composite magnetic particle powder as the magnetic 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.

In particular, the demand for high-density recording of video tapes is increasing, and the frequency of a carrier signal to be recorded is higher than that of conventional video tapes. That is, it has shifted to the short wavelength region, and as a result,
The magnetization depth from the surface of the magnetic tape is extremely shallow.

In order to improve the output characteristics of a magnetic recording medium, especially the S / N ratio, for a short wavelength signal, it is necessary to reduce the size of the magnetic particle powder, reduce the thickness of the magnetic recording layer, and improve the magnetic particle powder. High dispersion and smoothness of the magnetic coating surface are required.

On the other hand, at present, the end of a magnetic recording medium such as a video tape is determined by detecting a portion of the magnetic recording medium having a high light transmittance by a video deck. As described above, with the demand for higher performance of the magnetic recording medium, when the magnetic particle powder dispersed in the magnetic recording layer becomes finer and the magnetic recording medium becomes thinner, the light transmittance of the entire magnetic recording layer becomes higher. And detection by the VCR becomes difficult. Therefore, it has been practiced to add a carbon black fine particle powder to the magnetic recording layer, usually in an amount of about 6 to 12 parts by weight based on 100 parts by weight of the magnetic particle powder, to reduce the light transmittance. For this reason, in current video tapes, it is essential to add carbon black fine particles to the magnetic recording layer.

[0006] As described above, adding a large amount of non-magnetic carbon black fine particles to the magnetic recording layer not only lowers the electromagnetic conversion characteristics of the magnetic recording medium but hinders high density recording. In addition to causing the magnetic recording layer to become thinner, the carbon black fine particle powder has a large BET specific surface area value and has poor wettability with a solvent. This makes it difficult to obtain a magnetic recording medium having a smooth surface.

Further, when the magnetic recording medium has a high surface electric resistance value, it causes an increase in the electrostatic charge amount.
There is a problem that cutting debris, dust and the like of the magnetic recording medium adhere to the surface of the magnetic recording medium, and as a result, dropout increases. In view of this, the magnetic recording medium is provided in the magnetic recording layer not only for reducing the light transmittance as described above but also for reducing the surface electric resistance of the magnetic recording medium particularly to about 10 ⁸ Ω / sq or less. It has been conventionally used to add carbon black fine particle powder.

However, as described above, increasing the amount of carbon black fine particles that do not contribute to magnetism in the magnetic recording layer decreases the electromagnetic conversion characteristics of the magnetic recording medium and reduces the thickness of the magnetic recording layer. In addition to causing a hindrance, the surface smoothness is also reduced.

Further, the carbon black fine particle powder has a low bulk density of about 0.1 g / cm ^3, and is a bulky powder which is difficult to handle and has poor workability.
Furthermore, safety and hygiene problems such as carcinogenicity have been pointed out.

[0010] The demand for higher performance of magnetic recording media is not limited, and in addition to the above-described high-density recording, there is also a strong demand for further improvement in physical characteristics such as running properties.

The running property of the magnetic recording medium is generally such that the magnetic recording layer formed on the magnetic recording medium generally contains about 0.5 to 5% by weight of myristic acid or stearic acid based on the magnetic particle powder. It is ensured by adding a fatty acid (hereinafter, referred to as "myristic acid") and adjusting the myristic acid so that it gradually oozes into the surface of the magnetic recording layer to make the surface of the magnetic recording layer slippery.

If the amount of myristic acid leaching on the surface of the magnetic recording layer is too small, the running property of the magnetic recording medium cannot be ensured. On the other hand, the amount of myristic acid leaching is increased so that the amount of myristic acid leaching increases. When a large amount is added to the magnetic recording layer, myristic acid is preferentially adsorbed on the particle surface of the magnetic particle powder dispersed in the magnetic recording layer, and the adsorption between the magnetic particle powder and the resin is hindered. Dispersion of the powder in the vehicle becomes difficult. Further, problems such as a decrease in the magnetic properties of the magnetic recording medium due to an increase in the amount of myristic acid as a non-magnetic component and a decrease in the strength of the magnetic recording medium due to the myristic acid acting as a plasticizer also occur.

Recently, the absolute amount of myristic acid which can be added decreases with the thinning of the magnetic recording layer, and the magnetic particle powder becomes finer with the increase in the recording density, thereby increasing the BET specific surface area. Since the amount of myristic acid adsorbed on the particle surface of the magnetic particle powder increases, it is increasingly difficult to adjust the leaching of myristic acid added to the magnetic recording layer and ensure the traveling properties of the magnetic recording layer It has become.

Therefore, while the thickness of the magnetic recording layer is becoming increasingly thinner, the amount of myristic acid that seeps into the surface of the magnetic recording layer is well adjusted to ensure the running property of the magnetic recording medium. Is strongly required.

Conventionally, a chemical vapor deposition (CV) method has been used to improve the electric resistance and running durability of a magnetic recording medium.
By D) method and physical vapor deposition (PVD) method, a gas phase growth method, a reduction method of an organic compound, a thermal decomposition method of a hydrocarbon or the like, and an incomplete combustion method, 0.2 to 10.0% by weight (magnetic (Corresponding to 0.2 to 11.11 parts by weight with respect to 100 parts by weight of the powder). A magnetic powder having carbon and / or graphite adhered to the particle surface is disclosed (JP-A-10-2695).
No. 58).

Conventionally, as the thickness of the magnetic recording layer and the thickness of the non-magnetic support become thinner, various attempts have been made to improve the substrate for forming the magnetic recording layer so that the surface is smooth and the stiffness is increased. An underlayer formed by dispersing iron-based non-magnetic particles such as acicular hematite particles or acicular iron oxide hydroxide particles in a binder on a non-magnetic support such as a base film. At least one layer (hereinafter referred to as a "non-magnetic underlayer") has been provided, and has already been put into practical use (Japanese Patent Publication No. 6-93297, Japanese Unexamined Patent Publication No. Sho 6-93).
2-159338, JP-A-63-187418, JP-A-4-167225, JP-A-4-32
5915, JP-A-5-73882, JP-A-5-73882
182177, JP-A-5-347017, JP-A-6-60362 and the like.

As the non-magnetic particle powder for the non-magnetic underlayer, the surface of the aluminum hydroxide is preferably used for the purpose of improving the dispersibility in a vehicle in order to smooth the surface of the substrate and increase the stiffness. Non-magnetic particle powders treated with aluminum oxide, silicon hydroxide, silicon oxide and the like are known (Japanese Patent No. 2571350).
JP, JP-A-2582051, JP-A-6-60
362, JP 9-22524, JP 9
-27117 gazette).

In order to reduce the light transmittance of the magnetic recording medium by reducing the amount of carbon black added to the magnetic recording layer, a black-brown acicular hematite particle powder or a black-brown needle is used as the non-magnetic particle powder for the non-magnetic underlayer. Hydrated iron oxide particles may be used (JP-A-7-66020, JP-A-8-2
No. 59237, JP-A-9-167333, etc.), on the particle surface of acicular hematite particles or acicular hydrous iron oxide particles, with respect to 100 parts by weight of the particles.
It is also known to use acicular non-magnetic particle powder to which 1 to 20 parts by weight of carbon black fine particle powder is attached (EP-A-0 824 690).

It is also known to use a mixed powder of non-magnetic iron oxide particles and carbon black particles as the non-magnetic particles for the non-magnetic underlayer in order to reduce the surface electric resistance of the magnetic recording medium. (Japanese Unexamined Patent Publication No. 1-213)
No. 822, JP-A-1-300419, JP-A-6-23
6542, JP-A-9-297911, etc.).

[0020]

The surface is smooth,
A magnetic recording medium having smaller light transmittance and lower surface electric resistance is the most demanded at present, but a magnetic recording medium that sufficiently satisfies such characteristics has not yet been obtained.

That is, in the magnetic powder described in the above-mentioned Japanese Patent Application Laid-Open No. 10-269558, carbon on the particle surface is easily desorbed.
The glossiness, surface roughness, linear absorption coefficient, friction coefficient, and running durability are all poor.

Therefore, according to the present invention, the surface is smooth,
To obtain needle-like magnetic particle powder used for obtaining a magnetic recording medium having a smaller light transmittance and a lower surface electric resistance value, and having a small friction coefficient and excellent running durability, if necessary. This is a technical issue.

[0023]

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

That is, the present invention provides a nonmagnetic support, a nonmagnetic particle powder formed on the nonmagnetic support, a nonmagnetic underlayer containing a binder resin, and a magnetic particle powder formed on the nonmagnetic underlayer. And a magnetic recording layer comprising a binder resin and a magnetic recording layer containing a binder resin, wherein the magnetic particle powder is a cobalt-coated needle-like magnetic iron oxide particle powder or a needle-like metal magnetic particle powder containing iron as a main component and a core particle powder. An organosilane compound or polysiloxane formed from alkoxysilane is coated on the particle surface of the core particle powder, and at least a part of the coating is 0.5 to 40 parts by weight based on 100 parts by weight of the core particle powder. A magnetic recording medium characterized by comprising acicular black composite magnetic particles having an average major axis diameter of 0.051 to 0.35 μm to which carbon black is adhered. (Invention 1)

The present invention also provides a non-magnetic support, a non-magnetic particle powder formed on the non-magnetic support, a non-magnetic underlayer containing a binder resin, and a magnetic particle powder formed on the non-magnetic under layer. And a magnetic recording medium comprising a magnetic recording layer containing a binder resin, wherein the magnetic particle powder is formed on the particle surface of a cobalt-coated needle-like magnetic iron oxide particle powder or a needle-like metal magnetic particle powder containing iron as a main component. One or more selected from aluminum hydroxide, aluminum oxide, silicon hydroxide and silicon oxide as a lower layer, and an organosilane compound or polysiloxane formed from alkoxysilane as an upper layer Is coated,
A needle-like black composite magnet having an average major axis diameter of 0.051 to 0.35 μm, wherein 0.5 to 40 parts by weight of carbon black is adhered to at least one part of the coating based on 100 parts by weight of the core particle powder. A magnetic recording medium characterized by being a particle powder. (Invention 2)

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

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

The magnetic recording medium according to the present invention is formed on a nonmagnetic support, a nonmagnetic underlayer containing nonmagnetic particles and a binder resin formed on the nonmagnetic support, and formed on the nonmagnetic underlayer. A magnetic recording layer containing magnetic particle powder and a binder resin.

The magnetic particle powder according to the present invention is formed on the surface of cobalt-coated needle-like magnetic iron oxide particle powder, which is a core particle powder, or needle-like metal magnetic particle powder containing iron as a main component, by using an organosilane produced from alkoxysilane. A needle-like black composite magnetic particle powder coated with a silane compound or polysiloxane and having carbon black adhered to at least a part of the organosilane compound coating or polysiloxane coating.

The cobalt needle-like magnetic iron oxide particles, which are the core particles in the present invention, are magnetite particles ( F
eO _x .Fe ₂ O ₃ ) (0 <x ≦ 1), maghemite particle powder (γ-Fe ₂ O ₃ ), acicular magnetic iron oxide particle powder such as a belt oxide compound which is an intermediate oxide between maghemite and magnetite Is a particle powder in which cobalt or cobalt and iron or the like are adhered to the particle surface.

The acicular metal magnetic particles containing iron as a main component, which is the core particle powder in the present invention, may be selected from the group consisting of acicular metallic iron magnetic particles and Co, Al, Ni, P, Zn, S, other than iron and iron.
i, B, acicular metal magnetic particle powder containing a dissimilar metal such as a rare earth metal, and the like.

The particle shape of the core particle powder in the present invention is as follows:
It has a needle shape. Here, the term "needle-shaped" means a needle-like shape, a spindle shape, a rice grain shape, and the like, as well as a literal needle-like shape.

The particle size of the acicular magnetic particle powder is preferably from 0.05 to 0.34 μm, more preferably from 0.05 to 0.33 μm, even more preferably from 0.0 to 0.33 μm.
5 to 0.32 μm.

When the average major axis diameter exceeds 0.34 μm, the obtained acicular black composite magnetic particle powder also becomes coarse particles, and when the magnetic recording layer is formed using this,
The surface smoothness of the coating film is easily impaired. The average major axis diameter is 0.
When the particle size is less than 05 μm, aggregation tends to occur due to an increase in intermolecular force due to finer particles. Adhesion treatment becomes difficult.

The axial ratio of the core particle powder is preferably 2.0 to 20.0, more preferably 2.5 to 18.0, and still more preferably 3.0 to 15.0.

When the axial ratio exceeds 20.0, the entanglement of the particles increases, and it is difficult to uniformly coat the surface of the core particle powder with the alkoxysilane and to uniformly adhere the carbon black fine particle powder. Become. When the axial ratio is less than 2.0, the coating strength of the obtained magnetic recording medium decreases.

The geometric standard deviation of the major axis diameter of the core particle powder is preferably 2.0 or less, more preferably 1.8 or less, and even more preferably 1.6 or less. When the geometric standard deviation value exceeds 2.0, uniform dispersion is hindered by the existing coarse particles, so that the particle surface of the acicular magnetic particle powder is uniformly coated with alkoxysilane and the carbon black fine particle powder is treated. Makes it difficult to perform uniform adhesion treatment. The lower limit of the geometric standard deviation is 1.01,
Those less than 1.01 are difficult to obtain industrially.

The BET specific surface area of the core particle powder is 20 to 1
It is preferably 50 m ² / g, more preferably 25 to 120.
m ² / g, still more preferably 28~100m ² / g. When the BET specific surface area value is less than 20 m ² / g,
When the core particle powder is coarse or particles that have undergone sintering between the particles, and the resulting acicular black composite magnetic particle powder also becomes coarse particles, and the magnetic recording layer is formed using this. , The surface smoothness of the coating film is easily impaired.
When the BET specific surface area value exceeds 150 m ² / g,
Aggregation is likely to occur due to an increase in intermolecular force due to finer particles, so that it is difficult to uniformly coat the surface of the core particle powder with the alkoxysilane and uniformly apply the carbon black fine particle powder.

As for the blackness of the core particle powder, the lower limit of the L ^* value usually exceeds 18.0, and the upper limit is 34, preferably 32. When the L ^* value is more than 34, the lightness is increased and acicular black composite magnetic particles having sufficient blackness cannot be obtained.

The volume resistivity value of the core particle powder is usually 5.
It is 0 × 10 ¹⁰ Ω · cm or less.

The myristic acid adsorption amount of the core particle powder is usually about 0.40 to 1.5 mg / m ² .

The magnetic properties of the core particle powder are as follows.
00Oe is preferred, and more preferably 550-1700.
Oe, and the saturation magnetization value is preferably from 60 to 90 emu / g, more preferably from 65 to 90 emu / g,
In the case of metal magnetic particle powder containing iron as a main component, the coercive force value is preferably from 800 to 3500 Oe, more preferably 90 to 3500 Oe.
0-3500 Oe, and the saturation magnetization value is 90-170
emu / g is preferred, and more preferably 100 to 170.
emu / g.

The organosilane compound produced from alkoxysilane in the present invention (hereinafter referred to as "organosilane compound") is an organosilane compound produced from the alkoxysilane represented by Chemical Formula 1 through a drying or heating step.

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As the alkoxysilane, specifically,
Methyltriethoxysilane, dimethyldiethoxysilane, phenyltriethoxysilane, diphenyldiethoxysilane, dimethyldimethoxysilane, methyltrimethoxysilane, phenyltrimethoxysilane, diphenyldimethoxysilane, isobutyltrimethoxysilane, decyltrimethoxysilane, etc. Can be

In consideration of the desorption rate and adhesion effect of carbon black, an organosilane compound formed from methyltriethoxysilane, methyltrimethoxysilane, dimethyldimethoxysilane, isobutyltrimethoxysilane, and phenyltriethoxysilane is preferable. Most preferred are organosilane compounds formed from ethoxysilane and methyltrimethoxysilane.

The coating amount of the organosilane compound is preferably from 0.02 to 5.0% by weight, more preferably from 0.03 to 4.0% by weight in terms of Si, based on the core particle powder coated with the organosilane compound. 0% by weight, and even more preferably 0.05 to 3.0% by weight.

If the amount is less than 0.02% by weight, it is difficult to sufficiently deposit carbon black to such an extent that the blackness and volume resistivity of the obtained acicular black magnetic particles can be improved.

If it exceeds 5.0% by weight, carbon black can be sufficiently adhered, but the effect is saturated and there is no point in adding more than necessary.

As the polysiloxane in the present invention, a polysiloxane represented by Chemical formula 2, a modified polysiloxane represented by Chemical formula 3, a terminal modified polysiloxane represented by Chemical formula 4, or a mixture thereof can be used.

[0050]

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[0051]

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[0052]

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In consideration of the desorption rate and adhesion effect of carbon black, polysiloxanes having methyl hydrogen siloxane units, polyether-modified polysiloxanes, and terminal carboxylic acid-modified polysiloxanes whose terminals have been modified with carboxylic acids are preferred.

The coating amount of polysiloxane is 0.02 to 0.02 in terms of Si with respect to the core particle powder coated with polysiloxane.
It is preferably 5.0% by weight, more preferably 0.03 to 4.0% by weight, and even more preferably 0.05 to 3.0% by weight.

When the amount is less than 0.02% by weight, it is difficult to sufficiently attach carbon black to such an extent that the blackness and volume resistivity of the obtained acicular black composite magnetic particles can be improved.

If it exceeds 5.0% by weight, carbon black can be sufficiently adhered, but the effect is saturated and there is no point in adding more than necessary.

In the present invention, the total amount of carbon black adhered is 0.5 to 40 parts by weight based on 100 parts by weight of the core particle powder.

If the amount is less than 0.5 part by weight, it is difficult to obtain acicular black composite magnetic particles having excellent blackness and a low volume resistivity since the amount of carbon black attached is small.

When the amount exceeds 40 parts by weight, the effect of improving the blackness and volume resistivity of the obtained acicular black composite magnetic particles is saturated, and it is meaningless to attach more than necessary.

A large amount of carbon black adheres.
If it is more than 0 parts by weight, a needle-like black composite magnetic particle powder having a reduced myristic acid adsorption amount is obtained. That is, the acicular black composite magnetic particle powder having a carbon black adhesion amount of 10 parts by weight or less based on 100 parts by weight of the core particle powder has a myristic acid adsorption amount of 0.34 mg / m ² or more. Acicular black composite magnetic particle powder having carbon black attached thereto in an amount of more than 10 parts by weight with respect to parts by weight (hereinafter referred to as "acicular black composite magnetic particle powder having a large amount of carbon black attached").
Has a myristic acid adsorption amount of 0.3 mg / m ² or less.

As the carbon black fine particle powder, commercially available furnace black, channel black and the like can be used, and specifically, # 3050, # 3150, # 3
250, # 3750, # 3950, MA100, MA
7, # 1000, # 2400B, # 30, MA77, M
A8, # 650, MA11, # 50, # 52, # 45,
# 2200B, MA600, etc. (trade name: Mitsubishi Chemical Co., Ltd.) Seast 9H, Seat 7H, Seast 6,
Seast 3H, Seast 300, Seast FM, etc. (trade name, Tokai Carbon Co., Ltd.), Raven 12
50, Raven 860, Raven 1000, Ra
ven 1190ULTRA (Product name: Colombian ・
Chemicals Company (manufactured)), Ketjen Black EC, Ketjen Black EC600JD (trade name: Ketjen Black International K.K.), BLACK PEARLS-L, BLACK
PEARLS 1000, BLACK PEARLS
4630, VULCAN XC72, REGAL 6
60, REGAL 400 (trade name: Cabot Specialty Chemicals, Inc.) or the like can be used.

In consideration of the effect of reducing the amount of adsorbed myristic acid, it is preferable to use carbon black fine particles having a powder pH of 9.0 or less.
# 3150, # 3250, # 3750, # 3950, M
A100, MA7, # 1000, # 2400B, # 3
0, MA77, MA8, # 650, MA11, # 50,
# 52, # 45, # 2200B, MA600, etc. (trade name: Mitsubishi Chemical Co., Ltd.) Seast 9H, Seast 7H, Seast 6, Seast 3H, Seast 300, Seast FM, etc. (trade name, Tokai Carbon Co., Ltd. Manufactured)), Raven 1250, Raven 86
0, Raven 1000, Raven 1190UL
TRA (trade name: Colombian Chemicals Company (product)), BLACKPEARLS-L, BLACK
PEARLS 1000, BLACK PEARLS
4630, REGAL 660, REGAL 400
(Product Name: Cabot Specialty Chemicals
Ink (manufactured)) is preferred.

In consideration of a more uniform adhesion treatment to the organosilane compound coating layer or the polysiloxane, it is preferable to use carbon black fine particles having a DBP oil absorption of 180 ml / 100 g or less.
050, # 3150, # 3250, MA100, MA
7, # 1000, # 2400B, # 30, MA77, M
A8, # 650, MA11, # 50, # 52, # 45,
# 2200B, MA600, etc. (trade name: Mitsubishi Chemical Co., Ltd.) Seast 9H, Seat 7H, Seast 6,
Seast 3H, Seast 300, Seast FM, etc. (trade name, Tokai Carbon Co., Ltd.), Raven 12
50, Raven 860, Raven 1000, Ra
ven 1190ULTRA (Product name: Colombian ・
Chemicals Company (product), BLACK PEA
RLS-L, BLACK PEARLS 1000, B
LACK PEARLS 4630, REGAL 66
0, REGAL 400 (trade name: Cabot Specialty Chemicals, Inc.).

The average particle diameter of the carbon black fine particles used for the adhesion treatment is preferably 0.002 to 0.05 μm, more preferably about 0.002 to 0.035 μm.

When the average particle size of the carbon black fine particle powder used for the adhesion treatment is less than 0.002 μm, the carbon black fine particle powder becomes too fine.
Handling becomes difficult.

When the thickness exceeds 0.05 μm, since the particle size of the carbon black fine particles is large, a very large mechanical shearing force or the like is required to uniformly adhere to the alkoxysilane coating or the polysiloxane coating.
Industrially disadvantageous.

If the amount of the carbon black used in the present invention is large, especially if it exceeds 10 parts by weight with respect to 100 parts by weight of the core particle powder, at least two layers having the layers bonded thereto may be used if necessary. It may be applied to an organosilane compound coating or polysiloxane coating formed from alkoxysilane.

In consideration of the desorption rate and adhesion effect of carbon black, a carbon black layer (hereinafter referred to as carbon black) formed by adhering to an organosilane compound coating or polysiloxane coating formed from alkoxysilane in the present invention. Is preferably 0.5 to 10 parts by weight, more preferably 3 to 10 parts by weight, based on 100 parts by weight of the core particle powder.
The amount of adhesion of the carbon black layer (hereinafter referred to as the carbon black second layer) formed by being adhered to the surface of the first layer in the present invention is as follows.
It is 1 to 30 parts by weight, preferably 5 to 25 parts by weight based on 0 parts by weight.

The carbon black layer in the present invention may be bonded between carbon black layers with an adhesive. In order to firmly and uniformly adhere the layers and suppress the myristic acid adsorption amount, dimethylpolysiloxane represented by Chemical Formula 5 is preferable. The amount of the adhesive can be 0.1 to 5 parts by weight based on 100 parts by weight of the core particle powder.

[0070]

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When the amount of the adhesive is less than 0.1 part by weight, it is difficult to sufficiently adhere the second layer made of carbon black, and the amount of adsorbed myristic acid of the obtained acicular black composite magnetic particles cannot be improved. .

When the amount exceeds 5 parts by weight, carbon black can be sufficiently adhered, but the effect is saturated and there is no point in adding more than necessary.

The particle shape and particle size of the acicular black composite magnetic particle powder in the present invention greatly depend on the particle shape and particle size of the core particle powder, and have a particle shape similar to the core particle powder. It has a particle size slightly larger than the core particles.

That is, the acicular black composite magnetic particles according to the present invention have an average major axis diameter of 0.051 to 0.35 μm, preferably 0.051 to 0.34 μm, more preferably 0.051 to 0.33 μm. And the axial ratio is 2.0 to 2
0.0, preferably 2.5 to 18.0, more preferably 3.0 to 15.0.

When the average major axis diameter exceeds 0.35 μm, the acicular black composite magnetic particles become large particles, and when the magnetic recording layer is formed using this, the surface smoothness of the coating film is reduced. Easily damaged. When the average major axis diameter is less than 0.051 μm, aggregation tends to occur due to an increase in intermolecular force due to finer particles, so that dispersibility in a vehicle at the time of producing a magnetic coating material is reduced.

When the axial ratio exceeds 20.0, the entanglement of the particles increases, and the dispersibility in the vehicle during the production of the magnetic paint may become poor, or the viscosity may increase. When the axial ratio is less than 2.0, the coating strength of the obtained magnetic recording medium decreases.

The geometric standard deviation of the major axis diameter of the acicular black composite magnetic particles is preferably 2.0 or less. 2.0
If the average particle size is larger than the above range, the existing coarse particles are not preferable because they adversely affect the surface smoothness of the coating film. In consideration of the surface smoothness of the coating film, it is preferably 1.8 or less, more preferably 1.6 or less. Considering industrial productivity,
The lower limit value of the geometric standard deviation of the major axis diameter of the acicular black composite magnetic particle powder is 1.01, and those having less than 1.01 are difficult to obtain industrially.

The acicular black composite magnetic particles according to the present invention having a large amount of carbon black adhered thereto have an adsorbed amount of myristic acid of 0.01 to 0.3 mg / m ² , preferably 0.01 to 0.3 mg / m ² . 29 mg / m ^2, more preferably from 0.01~0.28mg / m ^2.

When the amount of adsorbed myristic acid is in the above range, the amount of adsorbed myristic acid adsorbed on the acicular black composite magnetic particles is appropriate. It is easy and can maintain a sufficiently low friction coefficient for repeated use of the tape for a long period of time, so that excellent running properties can be secured.

The BET specific surface area of the acicular black composite magnetic particles is preferably 21 to 160 m ² / g, more preferably 26 to 130 m ² / g, and even more preferably 29 to ¹ m ² / g.
10 m ² / g. When the BET specific surface area value is less than 21 m ² / g, the acicular black composite magnetic particle powder is coarse or the particles are sintered between the particles. Is formed, the surface smoothness of the coating film tends to be impaired. BET specific surface area value is 160m
When it exceeds ² / g, aggregation tends to occur due to an increase in intermolecular force due to finer particles, so that dispersibility in a vehicle at the time of producing a magnetic coating material is reduced.

[0081] blackness of acicular black complex magnetic particles is 23 upper limit in L ^* value is preferably L ^* value 22, more preferably L ^* value 21. If the L ^* value exceeds 23,
Brightness is high and blackness is not sufficient. The lower limit value of the blackness of the acicular black composite magnetic particle powder is L ^* value of 15.

The volume resistivity of the acicular black composite magnetic particles is preferably 1.0 × 10 ⁷ Ω · cm or less, more preferably 1.0 × 10 ^{3 to} 5.0 × 10 ⁶ Ω.・
cm, still more preferably 1.0 × 10 ^{3 to} 1.0 × 1
0 is a ^{6 Ω} · cm. Volume specific resistance value is 1.0 × 10 ⁷ Ω
If it exceeds cm, it is difficult to sufficiently reduce the surface electric resistance of the obtained magnetic recording medium.

The carbon black desorption rate of the acicular black composite magnetic particles is preferably 20% or less, more preferably 10% or less. Desorption rate of carbon black is 20%
In the case where the ratio exceeds 1, the carbon black that has been released may inhibit uniform dispersion in the vehicle during the production of the magnetic recording medium.

The magnetic properties of the acicular black composite magnetic particles according to the present invention are as follows. When acicular cobalt-coated iron oxide magnetic particles are used as the core particles, the coercive force value is 500 to 17;
00Oe is preferred, and more preferably 550-1700.
Oe, and the saturation magnetization value is preferably from 60 to 90 emu / g, more preferably from 65 to 90 emu / g,
When a needle-shaped metal magnetic particle powder containing iron as a main component is used as the core particle powder, the coercive force value is preferably 800 to 3500 Oe, more preferably 900 to 3500 Oe, and the saturation magnetization value is 90 to 170 emu / g. Is preferred,
More preferably, it is 100 to 170 emu / g.

The adhesion thickness of carbon black is 0.04
μm or less, more preferably 0.02 μm or less, and still more preferably 0.01 μm or less.

The acicular black composite magnetic particles according to the present invention may be prepared by preliminarily arranging the particle surfaces of the core particles in advance.
One or more compounds selected from aluminum hydroxide, aluminum oxide, silicon hydroxide, and silicon oxide (hereinafter, referred to as “coating with aluminum hydroxide or the like”). It may be coated, and it is possible to further reduce the desorption of carbon black from the particle surface of the core particle powder as compared with the case where the coating is not coated with aluminum hydroxide or the like. Dispersibility in the inside is improved.

The coating amount of aluminum hydroxide or the like is calculated based on the core particle powder coated with aluminum hydroxide or the like in terms of Al, SiO _2, or Al.
The total amount is preferably 0.01 to 20% by weight in terms of the O ₂ conversion amount.

If the amount is less than 0.01% by weight, the effect of reducing the rate of desorption of carbon black from the particle surface of the core particle powder cannot be obtained, so that the effect of improving the dispersibility in the vehicle during the production of the magnetic paint is improved. Can not be obtained.

When the content exceeds 20% by weight, the effect of reducing the desorption rate of carbon black from the particle surface of the core particle powder is sufficiently obtained, but there is no point in coating more than necessary.

The acicular black composite magnetic particle powder according to the present invention coated with aluminum hydroxide or the like is the same as the acicular black composite magnetic particle powder according to the present invention not coated with aluminum hydroxide or the like. Particle size, geometric standard deviation value, BET specific surface area value, blackness L almost the same as in the case
^{* Has} values, volume resistivity and magnetic properties.

The desorption rate of carbon black is improved by coating with aluminum hydroxide or the like, and the desorption rate is preferably 10% or less, more preferably 5% or less.

As the non-magnetic support, polyethylene terephthalate, polyethylene, polypropylene, polycarbonate, polyethylene naphthalate, polyamide, polyamide imide, and the like which are currently widely used for magnetic recording media are used.
Synthetic resin film such as polyimide, aluminum, metal foils and plates such as stainless steel and various papers can be used, the thickness of which varies depending on the material, but usually preferably 1.0 to 300 μm, more preferably 2.0
２００200 μm.

In the case of a magnetic disk, polyethylene terephthalate is usually used as the nonmagnetic support, and its thickness is usually 50 to 300 μm, preferably 60 to 200 μm.
μm. In the case of a magnetic tape, in the case of polyethylene terephthalate, the thickness is usually 3 to 100 μm, preferably 4 to 20 μm, and in the case of polyethylene naphthalate, the thickness is usually 3 to 50 μm, preferably 4 to 2 μm.
0 μm, in the case of polyamide, the thickness is usually 2 to 10
μm, preferably 3 to 7 μm.

Examples of the binder resin include vinyl chloride-vinyl acetate copolymer resins, urethane resins, vinyl chloride-vinyl acetate-maleic acid copolymer resins, urethane elastomers, butadiene resins commonly used in the production of magnetic recording media. Acrylonitrile copolymer resin, polyvinyl butyral, cellulose derivatives such as nitrocellulose, polyester resins, synthetic rubber resins such as polybutadiene, epoxy resins, polyamide resins, polyisocyanates, electron beam curable acrylic urethane resins and the like and mixtures thereof can be used. it can.

Further, each binder resin has --OH, --COO
_{H, -SO 3 M, -OPO 2} M 2, polar groups such as -NH ₂ (where, M is H, Na, a K.) May be contained. Considering the dispersibility of the acicular black composite magnetic particles powder,
-COOH, binder resin containing -SO ₃ M are preferable as a polar group.

The coating thickness of the magnetic recording layer formed on the non-magnetic support is in the range of 0.01 to 5.0 μm. 0.
When the thickness is less than 01 μm, it is not preferable because uniform coating is difficult and uneven coating is likely to occur. If it exceeds 5.0 μm, it becomes difficult to obtain desired electromagnetic conversion characteristics due to the influence of a demagnetizing field. Preferably 0.1 to 4.0 μm
Range.

The mixing ratio of the acicular black composite magnetic particle powder and the binder resin in the magnetic recording layer is determined by the ratio of the binder resin
5 to 200 parts by weight of the acicular black composite magnetic particles
0 parts by weight, preferably 100 to 1000 parts by weight.

When the acicular black composite magnetic particle powder is less than 5 parts by weight, the amount of the acicular black composite magnetic particle powder in the magnetic paint is too small. A continuously dispersed layer cannot be obtained, and the smoothness and the strength of the coating film surface become insufficient. If it exceeds 2,000 parts by weight, the acicular black composite magnetic particle powder is not sufficiently dispersed in the magnetic paint because the acicular black composite magnetic particle powder is too large relative to the amount of the binder resin. When formed into a coating film, it is difficult to obtain a coating film having a sufficiently smooth surface. Further, since the acicular black composite magnetic particle powder is not sufficiently bound by the binder resin, the obtained coating film tends to be brittle.

In the magnetic recording medium according to the present invention, the amount of carbon black added to the magnetic recording layer can be less than 6 parts by weight, preferably 5 parts by weight, per 100 parts by weight of the acicular black composite magnetic particle powder. It can be less than parts by weight, more preferably less than 3 parts by weight.

When the acicular black composite magnetic particle powder having a large particle size is used as the magnetic particle powder, addition of the carbon black fine particle powder to the magnetic recording layer can be expected to be omitted.

The magnetic recording layer needs lubricants, abrasives, antistatic agents and the like used in the manufacture of ordinary magnetic recording media, if necessary, in an amount of about 0.1 to 50 parts by weight with respect to 100 parts by weight of the binder resin. May be included.

The non-magnetic underlayer in the present invention preferably has a coating thickness of 0.2 to 10.0 μm. 0.2 μm
If it is less than 1, it becomes difficult to improve the surface roughness of the nonmagnetic support, and the stiffness tends to be insufficient.
In consideration of the thinning of the magnetic recording medium and the stiffness of the coating film, the thickness is more preferably in the range of 0.5 to 5.0 μm.

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

The mixing ratio of the acicular black composite particle powder and the binder resin in the nonmagnetic underlayer is such that the acicular black composite particle powder is 5 to 2,000 parts by weight, preferably 100 to 100 parts by weight, based on 100 parts by weight of the binder resin. 1000 parts by weight.

When the amount of the acicular black composite particles is less than 5 parts by weight, the amount of the acicular black composite particles in the non-magnetic paint is too small. A dispersed layer cannot be obtained, and the smoothness of the coating film surface and the stiffness of the substrate become insufficient. If the amount exceeds 2,000 parts by weight, the acicular black composite magnetic particle powder is not sufficiently dispersed in the nonmagnetic paint because the acicular black composite magnetic particle powder is too large relative to the amount of the binder resin. When formed into a coating film, it is difficult to obtain a coating film having a sufficiently smooth surface. Further, since the acicular black composite particle powder is not sufficiently bound by the binder resin, the obtained coating film tends to be brittle.

The lubricant, abrasive, 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.

As the non-magnetic particle powder for the non-magnetic under layer in the present invention, a non-magnetic inorganic powder usually used for a non-magnetic under layer for a magnetic recording medium can be used. Specifically, hematite, hydrous iron oxide, titanium oxide, zinc oxide, tin oxide, tungsten oxide, silicon dioxide, α-
Alumina, β-alumina, γ-alumina, chromium oxide,
Cerium oxide, silicon carbide, titanium carbide, silicon nitride, boron nitride, calcium carbonate, barium carbonate, magnesium carbonate, strontium carbonate, calcium sulfate, barium sulfate, molybdenum disulfide, barium titanate, etc. may be used alone or in combination. Yes, especially
Hematite, hydrous iron oxide, titanium oxide and the like are preferred.

In order to improve the dispersibility in the vehicle during the production of the non-magnetic paint, if necessary, the surface of the non-magnetic particle powder is treated with aluminum hydroxide, aluminum oxide, silicon hydroxide, The surface may be treated with an oxide of silicon or the like, and if necessary, to improve various characteristics such as light transmittance, surface electric resistance, mechanical strength, surface smoothness, and durability of the obtained magnetic recording medium. , A inside the particle
You may contain l, Ti, Zr, Mn, Sn, Sb, etc.

The particle shape of the non-magnetic particle powder may be spherical, granular, hexahedral, octahedral, polyhedral, or acicular. Here, the term "needle-shaped" means a needle-like shape, a spindle shape, a rice grain shape, and the like, as well as a literal needle-like shape. In consideration of the surface smoothness of the selected nonmagnetic underlayer, the shape of the nonmagnetic particle powder is preferably acicular.

The particle size of the nonmagnetic particle powder is such that the average major axis diameter is 0.01 to 0.3 μm, preferably 0.01 to 0.3 μm.
5 to 0.25 μm, more preferably 0.02 to 0.2 μm
m.

Coated with aluminum hydroxide, etc.
Uncoated cobalt-coated magnetic iron oxide particles
Needle-like black composite magnetic particle powder according to the present invention as a powder
The magnetic recording medium used has a coercive force value of 500 to 1700.
Oe, preferably 550-1700 Oe, squareness ratio (residual
Magnetic flux density Br / saturated magnetic flux density Bm) is 0.85 to 0.9
5, preferably 0.86 to 0.95, and the glossiness of the coating film is 1
65-300%, preferably 170-300%, coating film table
Surface roughness Ra is 11.0 nm or less, preferably 2.0 to 1
0.5 nm, more preferably 2.0 to 10.0 nm,
125-160, preferably 126-160,
The linear absorption coefficient of the coating film is 1.40 to 10.0 μm^-1, Preferred
1.45 to 10.0 μm^-1, The surface electric resistance value is 1.
0x10 ⁹Ω / sq or less, preferably 7.5 × 10⁸Ω /
sq or less, more preferably 5.0 × 10⁸Ω / sq or less
Under, running durability is more than 25 minutes, preferably more than 26 minutes
is there.

As magnetic particles, a large amount of carbon
Using needle-shaped black composite magnetic particle powder
In addition to having the above properties,
Has a linear absorption coefficient of 1.80 to 10.00 μm^-1, Preferably
Is 1.85 to 10.00 μm ^-1, Surface electric resistance of coating film
Is 1.0 × 10⁸Ω / sq or less, preferably 7.5 × 1
0⁷Ω / sq or less, more preferably 5.0 × 10⁷Ω / s
q or less, the coefficient of friction is 0.25 to 0.30, preferably
0.25 to 0.29, running durability of 26 minutes or more, preferred
Or more than 27 minutes.

Coated with aluminum hydroxide, etc.
Core of iron-like metal magnetic particles not mainly composed of iron
Acicular black composite magnetic particle powder according to the present invention as particle powder
Has a coercive force value of 800 to 3500.
Oe, preferably 900-3500 Oe, squareness ratio (residual
Magnetic flux density Br / saturated magnetic flux density Bm) is 0.85 to 0.9
5, preferably 0.86 to 0.95, and the glossiness of the coating film is 1
85-300%, preferably 195-300%, coating film table
Surface roughness Ra is 11.0 nm or less, preferably 2.0 to 1
0.5 nm, more preferably 2.0 to 10.0 nm,
125-160, preferably 126-160,
The linear absorption coefficient of the coating film is 1.40 to 10.0 μm^-1, Preferred
1.45 to 10.0 μm^-1, The surface electric resistance value is 1.
0x10 ⁹Ω / sq or less, preferably 7.5 × 10⁸Ω /
sq or less, more preferably 5.0 × 10⁸Ω / sq or less
Under, running durability is more than 25 minutes, preferably more than 26 minutes
is there.

[0114] A large amount of carbon
Using needle-shaped black composite magnetic particle powder
In addition to having the above properties,
Has a linear absorption coefficient of 1.80 to 10.00 μm^-1, Preferably
Is 1.85 to 10.00 μm ^-1, Surface electric resistance of coating film
Is 1.0 × 10⁸Ω / sq or less, preferably 7.5 × 1
0⁷Ω / sq or less, more preferably 5.0 × 10⁷Ω / s
q or less, the coefficient of friction is 0.25 to 0.30, preferably
0.25 to 0.29, running durability of 26 minutes or more, preferred
Or more than 27 minutes.

The magnetic recording medium using the acicular black composite magnetic particle powder according to the present invention, in which the cobalt-coated acicular magnetic iron oxide particle powder coated with an aluminum hydroxide or the like is used as the core particle powder, is used. Magnetic force value is 500-1700O
e, preferably 550 to 1700 Oe, and a squareness ratio (residual magnetic flux density Br / saturated magnetic flux density Bm) of 0.85 to 0.9
5, preferably 0.86 to 0.95, and the glossiness of the coating film is 1
70 to 300%, preferably 175 to 300%, and the coating film surface roughness Ra is 10.0 nm or less, preferably 2.0 to
9.5 nm, more preferably 2.0 to 9.0 nm, Young's modulus is 127 to 160, preferably 128 to 160, and the linear absorption coefficient of the coating film is 1.45 to 10.0 μm ⁻¹ , preferably 1.50. 10.0 μm ⁻¹ , surface electric resistance value is 1.0
× 10 ⁹ Ω / sq or less, preferably 7.5 × 10 ⁸ Ω / s
q or less, more preferably 5.0 × 10 ⁸ Ω / sq or less,
The running durability is at least 27 minutes, preferably at least 28 minutes.

As magnetic particles, a large amount of carbon
Using needle-shaped black composite magnetic particle powder
In addition to having the above properties,
Has a linear absorption coefficient of 1.85 to 10.00 μm^-1, Preferably
Is 1.90 to 10.00 μm ^-1, Surface electric resistance of coating film
Is 5.0 × 10⁷Ω / sq or less, preferably 2.5 × 1
0⁷Ω / sq or less, more preferably 1.0 × 10⁷Ω / s
q or less, the coefficient of friction is 0.21 to 0.26, preferably
0.21-0.25, running durability 27 minutes or more, preferred
Or more than 28 minutes.

The magnetic recording medium using the acicular black composite magnetic particle powder according to the present invention, in which the acicular metal magnetic particle powder containing iron as a main component and coated with a hydroxide of aluminum or the like as the core particle powder, is used. , Coercive force value is 800-3500O
e, preferably 900 to 3500 Oe, and a squareness ratio (residual magnetic flux density Br / saturated magnetic flux density Bm) of 0.85 to 0.9
5, preferably 0.86 to 0.95, and the glossiness of the coating film is 1
90 to 300%, preferably 200 to 300%, and the coating film surface roughness Ra is 10.0 nm or less, preferably 2.0 to
9.5 nm, more preferably 2.0 to 9.0 nm, Young's modulus is 127 to 160, preferably 128 to 160, and the linear absorption coefficient of the coating film is 1.45 to 10.0 μm ⁻¹ , preferably 1.50. 10.0 μm ⁻¹ , surface electric resistance value is 1.0
× 10 ⁹ Ω / sq or less, preferably 7.5 × 10 ⁸ Ω / s
q or less, more preferably 5.0 × 10 ⁸ Ω / sq or less,
The running durability is at least 27 minutes, preferably at least 28 minutes.

As magnetic particles, a large amount of carbon
Using needle-shaped black composite magnetic particle powder
In addition to having the above properties,
Has a linear absorption coefficient of 1.85 to 10.00 μm^-1, Preferably
Is 1.90 to 10.00 μm ^-1, Surface electric resistance of coating film
Is 5.0 × 10⁷Ω / sq or less, preferably 2.5 × 1
0⁷Ω / sq or less, more preferably 1.0 × 10⁷Ω / s
q or less, the coefficient of friction is 0.21 to 0.26, preferably
0.21-0.25, running durability 27 minutes or more, preferred
Or more than 28 minutes.

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

As the core particle powder in the present invention, a known cobalt-coated needle-like magnetic iron oxide particle powder or a needle-like metal magnetic particle powder containing iron as a main component may be used.

The core particle powder is coated with the alkoxysilane or polysiloxane by mechanically mixing and stirring the core particle powder and the alkoxysilane solution or the polysiloxane.
What is necessary is just to mechanically mix and stir while spraying the alkoxysilane solution or polysiloxane onto the core particle powder. Almost all of the added alkoxysilane or polysiloxane is coated on the particle surface of the core particle powder.

In order to uniformly coat the surface of the particles with the alkoxysilane or polysiloxane, it is preferable to disintegrate the core particles in advance using a pulverizer.

Mixing and stirring of the core particle powder and the alkoxysilane solution or polysiloxane or mixing of the carbon black fine particle powder described later with the core particle powder having the particle surface coated with an organosilane compound or polysiloxane formed from alkoxysilane. As a device for stirring,
A device capable of applying a shearing force to the powder layer is preferable, and in particular, a device capable of simultaneously performing shearing, spatula and compression is more preferable, for example, a wheel-type kneader, a ball-type kneader, a blade-type kneader, A roll-type kneader can be used.

Specifically, use of a mix miller, a Simpson mill, a sand mill, a multimill, a Stotts mill, a wet pan mill, a conner mill, a Henschel mixer, a ring miller, a rotary mill, a vibration mill, a pressure kneader, an extruder and a screw mixer Can be.
Preferably, a mix muller, a Simpson mill, a sand mill, a multi-mill, a Stotts mill, a wet pan mill,
Conner mills and Henschel mixers, and in particular, mix millers, Simpson mills, sand mills, and multimills are more preferable.

The conditions for mixing and stirring are such that the linear load is 2 to 200 kg / cm, preferably 10 to 150 kg / cm, more preferably 15 to ensure that the surface of the core particle powder is coated with the alkoxysilane as uniformly as possible. -10
0 kg / cm, treatment time is 5 to 120 minutes, preferably 1
The processing conditions may be appropriately adjusted within a range of 0 to 90 minutes. The stirring speed is 2 to 2000 rpm, preferably 5 to 1 rpm.
The processing conditions may be appropriately adjusted within the range of 000 rpm, more preferably in the range of 10 to 800 rpm.

The addition amount of the alkoxysilane or polysiloxane is 0.15 to 4 parts by weight per 100 parts by weight of the core particle powder.
5 parts by weight are preferred. If less than 0.15 parts by weight,
It is difficult to attach carbon black to such an extent that the blackness can be improved and the volume resistivity value can be sufficiently reduced. If it exceeds 45 parts by weight, carbon black can be sufficiently adhered, but there is no point in adding more than necessary.

After coating the surface of the core particle powder with alkoxylan or polysiloxane, carbon black fine particle powder is added, and the mixture is stirred to deposit carbon black on the alkoxylan coating or polysiloxane coating. Heat treatment.

It is preferable that the carbon black fine particle powder is added little by little over time, especially over about 5 to 60 minutes.

The conditions for mixing and stirring are such that the linear load is 2 to 200 kg so that the carbon black is uniformly attached.
/ Cm, preferably 10 to 150 kg / cm, more preferably 15 to 100 kg / cm, and the treatment time is 5 to 120 kg / cm.
The processing conditions may be appropriately adjusted within minutes, preferably within the range of 10 to 90 minutes. In addition, the stirring speed is 2-2000 rpm,
Preferably 5-1000 rpm, more preferably 10-
The processing conditions may be appropriately adjusted within the range of 800 rpm.

The addition amount of the carbon black fine particle powder is as follows:
It is 0.5 to 40 parts by weight based on 100 parts by weight of the core particle powder. If the amount is less than 0.5 part by weight, it is difficult to obtain acicular black composite magnetic particles having excellent blackness and a low volume resistivity since the amount of carbon black attached is small. If the amount exceeds 40 parts by weight, the effect of improving the blackness and volume resistivity of the obtained acicular black composite magnetic particles is saturated, and there is no point in attaching more than necessary.

In particular, when obtaining acicular black composite magnetic particle powder having a large amount of carbon black adhered thereto, it is preferable to add the carbon black in two or more portions and repeat the addition and attachment. . In particular, when the carbon black fine particles constituting the second layer are added to the carbon black constituting the first layer, an adhesive is adhered onto the carbon black constituting the first layer prior to the addition. It is more preferable to keep it.

That is, an adhesive is added to the acicular black composite magnetic particle powder on which the first layer of carbon black is formed,
After mixing and agitating and bonding, a carbon black fine particle powder is further added, and the mixture is agitated and the second layer of carbon black may be bonded to the first layer of carbon black.

The conditions for mixing and stirring the adhesive are such that the linear load is 2 to 200 kg / min so that the adhesive is uniformly adhered to the surface of the acicular black composite magnetic particles on which the first layer of carbon black is formed. cm, preferably 10-150k
g / cm, more preferably 15 to 100 kg / cm, and processing time may be appropriately adjusted within the range of 5 to 120 minutes, preferably 10 to 90 minutes. The stirring speed is 2
The processing conditions may be appropriately adjusted within the range of 2,000 rpm, preferably 5-1,000 rpm, and more preferably 10-800 rpm.

The amount of the adhesive added is based on the amount of the core particle powder.
0.1 to 5 parts by weight. If the amount is less than 0.1 part by weight, it becomes difficult to sufficiently adhere the second layer made of carbon black. If it exceeds 5 parts by weight, the adhesive effect is saturated, so that there is no point in adding more than necessary.

The conditions for mixing and stirring the carbon black in the second layer are such that the linear load is 2 to 200 kg / cm, preferably 10 to 150 kg / cm, more preferably, so that the adhesive and the carbon black adhere uniformly. 15-10
0 kg / cm, treatment time is 5 to 120 minutes, preferably 1
The processing conditions may be appropriately adjusted within a range of 0 to 90 minutes. The stirring speed is 2 to 2000 rpm, preferably 5 to 1 rpm.
The processing conditions may be appropriately adjusted within the range of 000 rpm, more preferably in the range of 10 to 800 rpm.

The addition amount of the carbon black fine particles constituting the second layer is 1 to 100 parts by weight of the core particles.
30 parts by weight. If the amount is less than 1 part by weight, the total amount of carbon black becomes insufficient, and it becomes difficult to further improve blackness and further reduce the volume resistivity, and the amount of myristic acid adsorbed is not improved. If it exceeds 30 parts by weight, carbon black tends to be detached from the surface of the obtained acicular black composite magnetic particle powder, and as a result, dispersibility in the vehicle is reduced.

The acicular black composite magnetic particles according to the present invention are dried or heated after carbon black is attached to the core particles. The heating temperature in the drying or heating step is usually preferably from 40 to 200 ° C, more preferably 6
The heating time is preferably from 10 minutes to 12 hours, more preferably from 30 minutes to 3 hours. The alkoxysilane becomes an organosilane compound by this drying or heating step.

If necessary, the core particle powder may be prepared from an aluminum hydroxide, an aluminum oxide, a silicon hydroxide and a silicon oxide before mixing and stirring with the alkoxysilane solution or the polysiloxane. It may be coated with one or more selected compounds.

The coating of aluminum with hydroxide or the like is as follows:
To an aqueous suspension obtained by dispersing the core particle powder, an aluminum compound, a silicon compound or both compounds are added and mixed and stirred, or, if necessary, by adjusting the pH value after mixing and stirring, At least one compound selected from the group consisting of hydroxides of aluminum, oxides of aluminum, hydroxides of silicon and oxides of silicon is applied to the surface of the core particle powder, and then filtered. Wash, dry, pulverize. If necessary, a deaeration / consolidation treatment may be performed.

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

The addition amount of the aluminum compound is 0.01 to 20% by weight in terms of Al with respect to the core particle powder. 0.
If the content is less than 01% by weight, it is difficult to coat a sufficient amount of aluminum hydroxide or the like on the particle surface, and the desorption rate of carbon black cannot be effectively improved. If it exceeds 20% by weight, the coating effect is saturated, so that there is no point in adding more than necessary.

As the silicon compound, No. 3 water glass, sodium orthosilicate, sodium metasilicate and the like can be used.

The addition amount of the silicon compound is 0.01 to 20% by weight in terms of SiO ₂ with respect to the core particle powder. 0.0
If the amount is less than 1% by weight, it is difficult to coat a sufficient amount of silicon oxide or the like on the particle surface, and the desorption rate of carbon black cannot be effectively improved. 20% by weight
If it exceeds 3, the coating effect is saturated, and there is no point in adding more than necessary.

When the aluminum compound and the silicon compound are used in combination, the amount of addition is based on
The total of the reduced amount and the reduced amount of SiO ₂ is preferably 0.01 to 50% by weight.

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

In the magnetic recording medium according to the present invention, a non-magnetic paint containing non-magnetic particle powder, a binder resin and a solvent is applied on a non-magnetic support and dried by a conventional method to form a non-magnetic underlayer. A magnetic paint containing needle-like black composite magnetic particle powder, a binder resin and a solvent is applied on the non-magnetic underlayer to form a coating film, and the resultant is then oriented in a magnetic field.

For kneading and dispersing the non-magnetic paint and the magnetic paint, for example, a kneader may be a twin-screw kneader, a twin-screw extruder, a pressure kneader, a two-roll mill, a three-roll mill, or the like. , Ball mill,
Sand grinders, attritors, dispersers, homogenizers, ultrasonic dispersers and the like can be used.

In applying the non-magnetic paint and the magnetic paint, a gravure coater, a reverse roll coater, a slit coater, a die coater or the like can be used. The applied sheet can be oriented in a magnetic field by the orientation of a counter magnet, the orientation of a solenoid magnet, or the like.

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

The amount of the solvent used is 65 to 1000 parts by weight in total with respect to 100 parts by weight of the nonmagnetic particle powder or the acicular black composite magnetic particle powder. 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. 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.

[0151]

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

The average major axis diameter and average minor axis diameter of the core particle powder, the acicular black composite magnetic particle powder, and the average particle diameter of the carbon black fine particle powder were measured with an electron microscope photograph (× 3000).
The major axis diameter, the minor axis diameter or the particle diameter was measured for about 350 particles shown in the photograph obtained by enlarging 0) four times in the vertical and horizontal directions, respectively, and the average value was shown.

The axial ratio was shown 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%, the value of the major axis diameter was read, and the geometric standard deviation value = 84.13% under the integrated screen.
And the value 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 amounts of Al, Si, and Co present inside and on the surface of the core particle powder and the acicular black composite magnetic particles, and the organosilane compound formed from the alkoxysilane coated on the acicular black composite magnetic particles. , And the amount of Si contained in the polysiloxane or dimethylpolysiloxane is determined according to JIS K0119 using “X-ray fluorescence spectrometer 3063M” (manufactured by Rigaku Corporation).
The measurement was performed in accordance with “General rules for X-ray fluorescence analysis”.

The content of Fe ²⁺ in the core particle powder was shown by the value obtained by the following chemical analysis method.

That is, under an inert gas atmosphere, 25 ml of a mixed solution containing phosphoric acid and sulfuric acid at a ratio of 2: 1 to 0.5 g of the core particle powder was added to dissolve the core particle powder. After adding a few drops of diphenylamine sulfonic acid as an indicator to the diluted solution of the dissolved aqueous solution, redox titration was performed using an aqueous solution of potassium dichromate. The end point was defined as the time when the diluted solution turned purple, and the amount was determined from the amount of the aqueous potassium dichromate solution used up to the end point.

The amount of carbon adhering to the acicular black composite magnetic particle powder was measured using a Horiba Metal Carbon / Sulfur Analyzer EMIA
-200 type "(manufactured by Horiba, Ltd.) and the amount of carbon was measured.

The blackness of the core particle powder and the acicular black composite magnetic particle powder was determined by kneading 0.5 g of a sample and 1.5 ml of castor oil with a Hoover-type muller to form a paste, and adding 4.5 g of clear lacquer to the paste. In addition, kneaded and made into a coating, and a coated piece (coating thickness: about 30 μm) formed on a cast-coated paper using a 6 mil applicator was prepared.
The paint piece was subjected to a multi-source spectrophotometer MSC-IS-2.
D (manufactured by Suga Test Instruments Co., Ltd.)
Color index L ^* according to SZ 8729
Indicated by value.

Here, the L ^* value represents lightness, and the smaller the L ^* value, the better the blackness.

The volume resistivity of each of the core particles and the acicular black composite magnetic particles was 0.5 g of the particle powder.
And KBr tablet press (Shimadzu Corporation)
Was pressed under a pressure of 140 kg / cm ² to prepare a cylindrical sample to be measured.

Next, after the sample to be measured was exposed to an environment at a temperature of 25 ° C. and a relative temperature of 60% for 12 hours or more, the sample to be measured was set between stainless steel electrodes, and an electric resistance measuring device (model 4329A Yokogawa Kita) was used. The resistance value R (Ω) was measured by applying a voltage of 15 V with Tatsuden Electric Co., Ltd.).

Next, the area A (cm ² ) and thickness t ₀ (cm) of the upper surface of the sample to be measured (cylindrical) were measured, and the measured values were inserted into the following equations to obtain the volume resistivity (Ω).・ Cm)
I asked.

Volume specific resistance (Ω · cm) = R × (A / t ₀ )

The thickness of the carbon black adhering to the acicular black composite magnetic particles was determined by the transmission electron microscope JE.
Electron micrographs taken with an M-2010 (manufactured by JEOL Ltd.) at an acceleration voltage of 200 kV (×
Photo (500,000) magnified 10 times (× 5,000)
(000) was measured by measuring the average thickness of the carbon black adhering to the surface of the particles shown in FIG.

The desorption rate (%) of the carbon black adhering to the acicular black composite magnetic particles was shown by the value obtained by the following method. The closer the desorption rate of carbon black is to 0%, the smaller the desorption amount of carbon black from the particle surface of the acicular black composite magnetic particle powder is.

3 g of the acicular black composite magnetic particles and 40 ml of ethanol were placed in a 50 ml settling tube, subjected to ultrasonic dispersion for 20 minutes, allowed to stand for 120 minutes, and separated from the acicular black composite magnetic particles by a difference in specific gravity. The separated carbon black fine particle powder was separated. Next, 40 ml of ethanol was again added to the acicular black composite magnetic particle powder, ultrasonic dispersion was further performed for 20 minutes, and the mixture was allowed to stand for 120 minutes to separate the detached carbon black from the acicular black composite magnetic particle powder. The acicular black composite magnetic particle powder was dried at 100 ° C. for 1 hour, and the above-mentioned “HORIBA Metal Carbon / Sulfur Analyzer EMIA-2”
The carbon content was measured using a "200 type" (manufactured by Horiba, Ltd.), and the value determined according to the following equation was defined as the desorption rate (%) of carbon black.

Desorption rate (%) of carbon black = {(W
a-We) / Wa} × 100 Wa: Amount of carbon black attached to acicular black composite magnetic particle powder We: Amount of carbon black attached to acicular black composite magnetic particle powder after desorption test

The amount of myristic acid adsorbed on each of the core particle powder and the acicular black composite magnetic particle powder was determined by the following method. As the amount of adsorbed myristic acid is smaller, the fatty acid is more likely to seep out when formed into a magnetic tape, and the friction coefficient can be reduced.

First, 1.5 m was placed in a 140 ml glass bottle.
100 g of mφ glass beads, 9 g of the particle powder to be measured, and 45 ml of a tetrahydrofuran solution containing myristic acid just enough to coat the surface of the particle powder to be measured,
The mixture was dispersed by a paint shaker for 60 minutes.

Next, the mixed dispersion is taken out into a 50 ml sedimentation tube, and centrifuged at 10,000 rpm for 15 minutes to separate a solid portion and a solvent portion. And
The myristic acid concentration contained in the solvent portion was quantified by a gravimetric method, and the amount was subtracted from the amount of myristic acid.
The amount of myristic acid present in the solid portion was determined, and this was defined as the amount of myristic acid adsorbed on the particles (mg / m ² ).

[0174] Paint viscosity, the coating viscosity at 25 ° C. The resulting coating was measured using an E-type viscometer EMD-R (manufactured by Tokyo Keiki), shear rate D = 1.92sec ^{- 1}
The values are indicated by

The glossiness of the coating surface of 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.).

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

The 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 of the core particle powder, the acicular black composite magnetic particle powder, and the magnetic recording medium are described in “Vibration sample type magnetometer VS
M-3S-15 "(manufactured by Toei Kogyo Co., Ltd.) using an external magnetic field of up to 10 KOe.

The degree of light transmission is described in “Self-recording photoelectric spectrophotometer U
V-2100 "(manufactured by Shimadzu Corporation) was used to calculate the light transmittance of the magnetic recording medium, and this was represented by the 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 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: the coating composition layer of the magnetic recording medium used in the measurement Thickness (μm)

The surface electric resistance value of the coating film was determined by exposing the coating film to be measured in an environment of a temperature of 25 ° C. and a relative humidity of 60% for 12 hours or more, and then applying a 6 mm width metal electrode having a width of 6.5 mm.
Put the coating film slit in the so that the coating surface is in contact with the metal electrode, with a 170g weight on each end,
After the coating film was brought into close contact with the electrodes, a DC voltage of 500 V was applied between the electrodes, and the surface electric resistance was measured.

The coefficient of friction of the magnetic recording medium was measured by measuring the frictional force between the magnetic tape surface and the metal surface (aluminum mirror surface) using a tensile tester Tensilon (manufactured by Shimadzu Corporation).
It was shown by the value obtained from the ratio to the fruit tree.

The running durability of the magnetic recording medium is “Medi
a Durability Tester MDT-3
000 "(Steinberg Associates
(Manufactured by the company) and the actual movable time at a load of 200 gw and a relative speed of 16 m / s between the head and the tape was evaluated. The longer the actual operating time, the better the running durability.

The thickness of each of the nonmagnetic support and the magnetic recording layer constituting the magnetic recording medium was measured as follows.

[Digital Electronic Micrometer K351]
First, the film thickness (A) of the nonmagnetic support is measured using "C" (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 Acicular Black Composite Magnetic Particle Powder> Cobalt is 2.33% by weight based on the acicular magnetite particle powder, and Fe ²⁺ is 15.3% by weight based on the acicular magnetite particle powder.
Acicular cobalt-coated magnetite particle powder containing 4% by weight (average major axis diameter 0.270 μm, average minor axis diameter 0.032)
9 μm, axial ratio 8.2, geometric standard deviation 1.36, BET
Specific surface area value 38.9 m ² / g, blackness L ^* value 22.5, volume resistivity value 7.4 × 10 ⁷ Ω · cm, myristic acid adsorption amount 0.79 mg / m ² , coercive force value 698 Oe, saturation 20 kg of a magnetized value of 80.6 emu / g) were brought into contact with 150 liters of pure water using a stirrer in order to dissolve the coagulation, and further, "TK pipeline homomixer" (product name, manufactured by Tokushu Kika Kogyo Co., Ltd.) The slurry was passed three times to obtain a slurry containing acicular cobalt-coated magnetite particles.

Next, the slurry containing the acicular cobalt-coated magnetite particle powder was subjected to a horizontal sand grinder “Mighty Mill MHG-1.5L” (product name, manufactured by Inoue Seisakusho Co., Ltd.) at a shaft rotation speed of 2000 rpm for 5 minutes. The dispersion was passed twice to obtain a dispersion slurry containing acicular cobalt-coated magnetite particle powder.

[0189] The obtained dispersion slurry was 325 mesh
The sieve residue at (opening 44 μm) was 0%. The dispersion slurry was separated by filtration and washed with water to obtain a cake of acicular cobalt-coated magnetite particle powder. After drying the cake of the acicular cobalt-coated magnetite particle powder at 120 ° C., 11.0 kg of the dried powder is transferred to an edge runner “MPU
V-2 "(product name, manufactured by Matsumoto Cast Iron Works, Ltd.) and 30 kg / c while blowing 2 l of nitrogen per minute.
The mixture was stirred for 15 minutes at m.

Next, 165 g of methyltriethoxysilane
Was added and mixed with 200 ml of ethanol, and a methyltriethoxysilane solution obtained was added to the above-mentioned acicular cobalt-coated magnetite particle powder in which the agglomeration of the particles was loosened while operating the edge runner, and a linear load of 40 kg / cm was applied. Mixing and stirring were performed for 30 minutes. The stirring speed at this time was 22 rpm.

Next, carbon black fine particle powder B (particle shape: granular, average particle diameter 0.022 μm, geometric standard deviation value 1.78, BET specific surface area value 133.5 m ² / g,
825 g of blackness L ^* value 14.6) was added over 10 minutes while operating the edge runner, and an additional 30 kg /
The mixture was stirred with a linear load of 30 cm for 30 minutes to attach carbon black to the methyltriethoxysilane coating. The stirring speed at this time was 22 rpm.

The obtained acicular black composite magnetic particles were aged at 80 ° C. for 120 minutes using a drier to evaporate residual water, ethanol and the like. The needle-shaped black composite magnetic particles had an average major axis diameter of 0.
273 μm, the average minor axis diameter was 0.0331 μm, and the axial ratio was 8.2. The geometric standard deviation is 1.36 and B
ET specific surface area value is 40.2 m ² / g, blackness L ^* value is 1
9.7, the volume resistivity value is 9.8 × 10 ⁴ Ω · cm, the desorption rate of carbon black is 7.8%, and the attached amount of carbon black is 6.88% by weight (based on 100 parts by weight of the core particle powder). The coercive force value is 682.
Oe, the saturation magnetization was 79.3 emu / g, and the coating amount of methyltriethoxysilane was 0.22% by weight in terms of Si. As a result of electron microscopic observation, almost no carbon black fine particle powder was recognized, and it was confirmed that almost the entire amount of the carbon black fine particle powder was attached to the organosilane compound coating generated from methyltriethoxysilane.

The thickness of the carbon black adhering to the surface of the acicular black magnetic particles was 0.0
It was 018 μm.

For comparison, treated particles obtained by mixing and stirring needle-like cobalt-coated magnetite particles and carbon black particles with an edge runner in the same manner without coating with methyltriethoxysilane were treated with an electron microscope. As a result of the observation, it was confirmed that the carbon black did not adhere to the particle surface of the acicular cobalt-coated magnetite particle powder, and that both particle powders were mixed separately.

<Production of Nonmagnetic Underlayer> Nonmagnetic particle powder 1 (type: hematite particles, particle shape: spindle shape, average major axis diameter 0.187 μm, average minor axis diameter 0.02) shown in Table 9 below
40 μm, axial ratio 7.8, geometric standard deviation 1.33, BE
T specific surface area value 43.3 m ² / g, volume specific resistance value 8.6
× 10 ⁸ Ω · cm, blackness L ^* value 32.6), 12 g of a binder resin solution (30% by weight of a vinyl chloride-vinyl acetate copolymer resin having a sodium sulfonate group and 70% by weight of cyclohexanone) and cyclohexanone The mixture was mixed to obtain a mixture (solid content: 72%), and the mixture was further kneaded with a plastmill for 30 minutes to obtain a kneaded product.

This kneaded material was mixed with 1.5 mmφ glass beads 9
5 g, additional binder resin solution (30% by weight of polyurethane resin having sodium sulfonate group, 70% by weight of solvent (methyl ethyl ketone: toluene = 1: 1)), cyclohexanone, methyl ethyl ketone and toluene were added to a 140 ml glass bottle, and then added to a paint shaker. At 6
Mixing and dispersion were performed for a time to obtain a coating composition. Thereafter, a lubricant was added, and the mixture was further mixed and dispersed with a paint shaker for 15 minutes.

The composition of the obtained nonmagnetic paint was as follows.

Nonmagnetic Particle Powder 1 100 parts by weight Vinyl chloride-vinyl acetate copolymer resin having a sodium sulfonate group 10 parts by weight Polyurethane resin having a sodium sulfonate group 10 parts by weight Lubricant (myristic acid: butyl stearate = 1) 1) 2 parts by weight Cyclohexanone 56.9 parts by weight Methyl ethyl ketone 142.3 parts by weight Toluene 85.4 parts by weight

The viscosity of the obtained nonmagnetic paint was 310 c.
P.

Next, the above non-magnetic paint was applied to a thickness of 55 μm on a polyethylene terephthalate film having a thickness of 12 μm using an applicator, and then dried to form a non-magnetic underlayer.

The thickness of the obtained nonmagnetic underlayer was 3.4 μm.
m, gloss: 193%, surface roughness Ra: 8.2 nm, Young's modulus (relative value): 123, linear absorption coefficient: 1.01c
m ^-1 and the surface electric resistance were 1.1 × 10 ¹⁴ Ω · cm.

<Production of magnetic recording medium> 12 g of the acicular black composite magnetic particle powder obtained above and an abrasive (trade name: AK)
P-30, manufactured by Sumitomo Chemical Co., Ltd.) 1.2 g, carbon black fine particle powder (trade name: # 2400B, manufactured by Mitsubishi Kasei Corporation) 0.06 g, binder resin solution (vinyl chloride-acetic acid having a sodium sulfonate group) A mixture (solid content: 78%) was obtained by mixing 30% by weight of vinyl copolymer resin with 70% by weight of cyclohexanone and cyclohexanone. The mixture was further kneaded with a plast mill for 30 minutes to obtain a kneaded product.

This kneaded material was placed in a 140 ml glass bottle for 1.5 times.
95 g of mmφ glass beads, additional binder resin solution (30% by weight of polyurethane resin having sodium sulfonate group, solvent (methyl ethyl ketone: toluene = 1: 1)) 7
0% by weight), cyclohexanone, methyl ethyl ketone and toluene, and mixed and dispersed for 6 hours with a paint shaker to obtain a magnetic paint. Thereafter, a lubricant and a curing agent were added, and the mixture was further mixed and dispersed with a paint shaker for 15 minutes.

The composition of the obtained magnetic paint was as follows. Acicular black composite magnetic 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 Abrasive (AKP-30) 10 parts by weight carbon black (# 2400B) 0.5 part by weight Lubricant (myristic acid: butyl stearate = 1: 2) 3.0 parts by weight Curing agent (polyisocyanate) 5.0 parts by weight Cyclohexanone 65.8 parts by weight Methyl ethyl ketone 164.5 parts by weight Parts toluene 98.7 parts by weight

The viscosity of the obtained magnetic paint was 2,338.
cP.

After applying the obtained magnetic paint to a thickness of 15 μm on the non-magnetic underlayer using an applicator, orienting and drying in a magnetic field, and then performing a calendering treatment, Perform a curing reaction for 24 hours.
A magnetic tape was obtained by slitting to a width of 5 inches. The thickness of the obtained coating film was 3.4 μm.

The obtained magnetic tape has a coercive force value of 746.
Oe, squareness ratio (Br / Bm) 0.89, glossiness 17
4%, surface roughness Ra is 7.4 nm, Young's modulus (relative value)
Was 138, the linear absorption coefficient was 1.54 cm ^-1 , the surface electric resistance was 5.3 × 10 ⁷ Ω / sq, and the running durability was 29.5 minutes.

[0208]

The important point in the present invention is that the magnetic recording medium according to the present invention obtained by using the acicular black composite magnetic particle powder as the magnetic particle powder can reduce the amount of carbon black in the magnetic recording layer as much as possible. Even if it is reduced, the light transmittance is small, and
This is the fact that the surface electric resistance is low and the surface smoothness of the magnetic recording layer is improved.

Regarding the reason why the light transmittance of a magnetic recording medium is reduced with a small amount of carbon black, the present inventor has found that carbon black fine particles which usually behave as aggregates due to the fact that they are fine particles are used in the present invention. In the case of the acicular black composite magnetic particle powder according to the above, it is considered that the individual carbon black fine particle powder functions more effectively by being uniformly and densely attached to the particle surface of the core particle powder. .

The reason why the surface electric resistance of the magnetic recording medium is reduced with a small amount of carbon black is based on the fact that the acicular black composite magnetic particles are uniformly dispersed in the coating film. This is considered to be due to the fact that the carbon black fine particles uniformly and densely adhering to the particle surface of the acicular magnetic particle powder are in contact with each other and connected with the continuous cotton.

Regarding the reason that the magnetic recording medium according to the present invention has excellent surface smoothness, the present inventor has concluded that the acicular black composite magnetic particles according to the present invention include carbon black fine particles which are detached from the particle surface. Since the carbon black particles can be reduced as much as possible and the amount of the carbon black fine particles added to the magnetic recording layer can be reduced as much as possible, the dispersibility of the acicular black composite magnetic particles in the vehicle during the production of the magnetic paint is reduced by the carbon black. This is considered to be due to the fact that the particles are not hindered by the fine particle powder and that the acicular black composite magnetic particle powder itself has excellent dispersibility.

The magnetic recording medium according to the present invention using the acicular black composite magnetic particles having a reduced amount of adsorbed myristic acid has a low coefficient of friction and excellent running durability.

Regarding the reason why the coefficient of friction of the magnetic recording medium according to the present invention was able to be reduced, the present inventor has determined that the adsorption of myristic acid on the surface of the acicular black composite magnetic particles contained in the magnetic layer in a large amount. It is thought that as a result of the suppression within the specific range, the function as a lubricant could be effectively exerted by leaching onto the surface of the magnetic recording layer over a long period of time while adjusting the appropriate amount of myristic acid.

Regarding the reason why the running durability of the magnetic recording medium according to the present invention is excellent, the inventor of the present invention, for the same reason as above, leached the magnetic recording layer surface while adjusting the appropriate amount of myristic acid. It is thought that stable running durability was obtained.

[0215]

Next, examples and comparative examples will be described.

Core Particles 1 to 5 Various needle-like magnetic particle powders obtained by a known production method are prepared, and needle-like magnetic particle powders whose coagulation has been loosened are obtained in the same manner as in the embodiment of the present invention. Was.

Table 1 shows the characteristics of the acicular magnetic particle powder.

[0218]

[Table 1]

Core Particles 6 Cobalt-coated needle-shaped maghemite particles were prepared in the same manner as in the embodiment of the present invention, using 20 kg of acicular cobalt-coated maghemite particles whose core particles 1 were loosened and 150 l of water. A slurry containing the powder was obtained. The pH value of the redispersed slurry containing the obtained cobalt-coated acicular maghemite particles was adjusted to 10.5 using sodium hydroxide, and then water was added to the slurry to adjust the slurry concentration to 98.
g / l. Heat 150 liters of this slurry to 6
The temperature was adjusted to 0 ° C., 5444 ml of a 1.0 mol / l sodium aluminate solution (corresponding to 1.0% by weight in terms of Al with respect to the cobalt-coated acicular maghemite particles) was added to the slurry, and the mixture was maintained for 30 minutes. Thereafter, the pH was adjusted to 7.5 using acetic acid. After maintaining in this state for 30 minutes, filtration, washing with water, drying and pulverization were performed to obtain cobalt-coated needle-shaped maghemite particles having a particle surface coated with aluminum hydroxide.

The main production conditions at this time are shown in Table 2, and various characteristics of the obtained needle-coated cobalt-coated acicular maghemite particles whose surface is coated with aluminum hydroxide are shown in Table 3.

[0221]

[Table 2]

[0222]

[Table 3]

Core Particles 7 to 10 Surface-treated needle-like magnetic particle powders were obtained in the same manner as in the case of core particles 6, except that the type of core particle powder and the type and amount of additives in the surface treatment step were variously changed.

The main treatment conditions at this time are shown in Table 2, and various properties of the obtained surface-treated needle-like magnetic particle powder are shown in Table 3.

In the surface treatment step in Table 2, A is aluminum hydroxide and S is silicon oxide.

<Production of Acicular Black Composite Magnetic Particle Powder> Examples 1 to 12, Comparative Examples 1 to 5 Types of core particle powder, presence / absence, type and amount of alkoxysilane, polysiloxane or silicon compound in coating step, Except for changing the processing conditions by the edge runner, the type and amount of the carbon black fine particles in the step of attaching the carbon black fine particles, and the processing conditions by the edge runner, the needle-like black composite was prepared in the same manner as in the embodiment of the invention. Magnetic particle powder was obtained. Example 1
The needle-like black composite magnetic particle powder obtained in each of the 12 examples, as a result of electron microscopic observation, almost no carbon black is recognized, almost all of the carbon black is coated with an organosilane compound formed from alkoxysilane or It was confirmed that it adhered to the polysiloxane coating.

Table 4 shows the properties of the carbon black fine particle powders A to F used.

The main processing conditions at this time are shown in Table 5, and various properties of the obtained acicular black composite magnetic particles are shown in Table 6.

The additives used in each of Examples 8 to 10 are all polysiloxanes. "TSF
484 "(trade name: Toshiba Silicone Co., Ltd.) is a methyl hydrogen polysiloxane, and" BYK
-080 "(trade name: Big Chemie Japan K.K.) is a modified polysiloxane, and" TSF-47 "
70 "(trade name: Toshiba Silicone Co., Ltd.) is a terminal carboxyl-modified polysiloxane.

[0230]

[Table 4]

[0231]

[Table 5]

[0232]

[Table 6]

<Production of Acicular Black Composite Magnetic Particle Powder Attached with a Large Amount of Carbon Black> Example 13 Acicular Black Composite Magnetic Particle Powder 5.0 Obtained in the Embodiment
kg to the edge runner "MPUV-2" (product name,
(Matsumoto Cast Iron Works), 30kg / cm
The mixture was stirred for 30 minutes at, and the agglomeration of the particle powder was lightly loosened.

Next, 100 g of dimethylpolysiloxane
Was added to the acicular black composite magnetic particle powder while operating the edge runner, and 30 kg / cm linear load was applied.
Mixing and stirring were performed for minutes, to obtain acicular black composite magnetic particles having dimethylpolysiloxane uniformly adhered to the surface.

Next, the above carbon black fine particle powder B
500 g was added over a period of 10 minutes while the edge runner was running, and mixed and stirred for a further 30 minutes at a linear load of 45 kg / cm, and dimethylpolysiloxane was adhered to the surface of the first layer composed of carbon black using an adhesive. Then, a second layer made of carbon black was adhered to obtain acicular black composite magnetic particle powder. The stirring speed at this time was 22 rpm.

The obtained acicular black composite magnetic particles were dried at 105 ° C. for 60 minutes using a drier. As a result of observation by an electron microscope, the acicular black composite magnetic particles had an average major axis diameter of 0.278 μm and an average minor axis diameter of 0.078.
341 μm, and the axial ratio was 8.2. The geometric standard deviation value is 1.37, and the BET specific surface area value is 43.5 m ² /
g, blackness L ^* value is 18.6, volume resistivity value is 2.1
× 10 ⁴ Ω · cm, myristic acid adsorption amount 0.27mg
/ M ² , the carbon black desorption rate is 7.6%,
The coercive force value is 675 Oe, and the saturation magnetization value is 77.4 emu /
g, and the total amount of carbon black adhering and adhering thereto is 14.62% by weight in terms of C (corresponding to 17.5 parts by weight with respect to 100 parts by weight of the core particle powder). The coating amount was 0.71% by weight in terms of Si. As a result of electron microscopic observation, almost no carbon black was observed, and it was confirmed that almost all of the carbon black was adhered to the first layer of carbon black.

The thickness of the carbon black adhering to the surface of the acicular black magnetic particle powder was 0.0
020 μm.

Examples 14 to 25, Comparative Examples 6 to 12 Types of acicular black composite magnetic particles, types and amounts of adhesives in an adhesive treatment step, addition amounts and treatment conditions by an edge runner, carbon black adhesion steps Acicular black composite magnetic particle powder to which a large amount of carbon black is adhered was obtained in the same manner as in Example 13 except that the type and amount of the carbon black fine particle powder and the processing conditions by the edge runner were variously changed. Was.

The acicular black composite magnetic particle powder to which a large amount of carbon black was attached obtained in each of Examples 14 to 25 showed almost no carbon black as a result of electron microscopic observation. From this, it was confirmed that almost all of the carbon black was adhered to the first layer of the carbon black.

Table 7 shows the main processing conditions at this time, and Table 8 shows various characteristics of the obtained acicular black composite magnetic particles to which a large amount of carbon black is adhered.

[0241]

[Table 7]

[0242]

[Table 8]

<Production of Non-Magnetic Underlayer> Non-magnetic underlayers were produced in the same manner as in the embodiment of the present invention using various non-magnetic particle powders.

Table 9 shows the properties of the nonmagnetic particle powders 1 to 6 used.

[0245]

[Table 9]

Table 10 shows the main manufacturing conditions and various characteristics of the selected nonmagnetic underlayer.

[0247]

[Table 10]

<Manufacture of Magnetic Recording Medium> Examples 26 to 50 and Comparative Examples 13 to 29 A magnetic recording medium was manufactured in the same manner as in the above embodiment of the invention except that the type of the acicular magnetic particle powder was changed variously. Obtained.

Table 11 shows the main manufacturing conditions and various characteristics at this time.
And Table 13 below.

[0250]

[Table 11]

[0251]

[Table 12]

[0252]

[Table 13]

[0253]

The magnetic recording medium according to the present invention has a non-magnetic underlayer and, as described above, a needle-like black composite magnetic particle powder having excellent blackness and a low volume resistivity. Due to its use as particle powder,
It has low light transmittance, low surface electric resistance, and can minimize the amount of carbon black fine particles added to the magnetic recording layer as much as possible. It is preferable as a magnetic recording medium for high-density recording because its surface is smooth in combination with its improved dispersibility.

The magnetic recording medium according to the present invention using the acicular black composite magnetic particle powder to which a large amount of carbon black is adhered has the above-mentioned magnetic particle powder due to the reduced myristic acid adsorption amount. It is preferable for high-density recording because it has various characteristics, as well as a small friction coefficient and excellent running durability.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yasuyuki Tanaka 1-1-1 Shinoki, Onoda-shi, Yamaguchi Prefecture Inside the Onoda Plant of Toda Kogyo Co., Ltd. (72) Keisuke Iwasaki 4 Funairi Minami, Naka-ku, Hiroshima-shi, Hiroshima Chome 1-2 Toda Kogyo Co., Ltd. Creative Center

Claims (2)

[Claims] 1. A non-magnetic underlayer comprising a non-magnetic support, a non-magnetic particle powder formed on the non-magnetic support and a binder resin, and a magnetic particle powder and a binder resin formed on the non-magnetic under layer In the magnetic recording medium comprising a magnetic recording layer containing, the magnetic particle powder, the core-coated iron-based magnetic iron oxide powder powder or iron-based cobalt-coated needle-shaped magnetic iron oxide particles, An organosilane compound or polysiloxane formed from alkoxysilane is coated on the particle surface of the particle powder, and at least a part of the coating is 0.5 to 40 parts by weight of carbon black based on 100 parts by weight of the core particle powder. A magnetic recording medium characterized by acicular black composite magnetic particles having an average major axis diameter of 0.051 to 0.35 μm to which particles are adhered. 2. A non-magnetic underlayer containing a non-magnetic support, non-magnetic particle powder formed on the non-magnetic support, and a binder resin, and magnetic particle powder and a binder resin formed on the non-magnetic under layer. In the magnetic recording medium comprising a magnetic recording layer containing, the magnetic particle powder, aluminum as a lower layer on the particle surface of the cobalt-coated acicular magnetic iron oxide particles powder or acicular metal magnetic particle powder containing iron as a main component. One or more selected from hydroxides, aluminum oxides, silicon hydroxides and silicon oxides, and coated with an organosilane compound or polysiloxane formed from alkoxysilane as an upper layer. And at least one part of the coating contains 0.5 parts by weight based on 100 parts by weight of the core particle powder.
A magnetic recording medium characterized by acicular black composite magnetic particle powder having an average major axis diameter of 0.051 to 0.35 µm to which carbon black of up to 40 parts by weight is adhered.