JP2001002425A - Acicular black composite magnetic particle powder for magnetic recording medium and magnetic recording medium using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an acicular black composite magnetic particle powder which enables the production of a magnetic recording medium having low light- transmissivity even when the amount of a carbon black fine particle powder added to a magnetic recording layer is adjusted small as possible, a low surface electric resistance value and also a flat and smooth surface. SOLUTION: In this acicular magnetic particle powder, the surface of each of the particles is coated with a fluorine-containing organosilane compound formed from a fluoroalkylsilane and fine-powdery carbon black is stuck to at least a part of the resulting fluorine-containing organosilane compound coating in an amount sufficient to provide a 0.5 to 10 pts.wt. ratio of the carbon black to 100 pts.wt. of the acicular magnetic particle powder and also, the acicular particles have a 0.051-0.72 μm average major axis size.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a magnetic recording medium having excellent dispersibility in a vehicle due to a small amount of carbon black detached from the particle surface, and having a high blackness and a low volume resistivity. The present invention provides an acicular black composite magnetic particle powder for use, and the use of the acicular black composite magnetic particle powder allows light transmission even when the amount of the carbon black fine particle powder added to the magnetic recording medium layer is as small as possible. It is an object of the present invention to provide a magnetic recording medium having a low ratio, a low surface electric resistance value, and a smooth surface.

[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 and hinders high density recording, but also impairs the magnetic recording layer. In addition to causing the thinning of the recording layer, the carbon black fine particles are fine particles having an average particle diameter of about 0.002 to 0.05 μm, have a large BET specific surface area, and are wetted by a solvent. It is difficult to obtain a magnetic recording medium having a smooth surface because it is difficult to disperse it in a vehicle due to the characteristic that the magnetic recording medium is poor.

Therefore, it is necessary that the amount of carbon black fine particles added to the magnetic recording layer is as small as possible. Highly required.

Further, when the magnetic recording medium has a high surface electric resistance value, it causes an increase in the electrostatic charge amount, so that the magnetic recording medium can be produced or used at the time of manufacturing or using the magnetic recording medium.
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. Therefore, the magnetic recording medium is used 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 ¹⁰ Ω / cm ² or less. It has been conventionally used to add fine particles of carbon black to carbon black.

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

[0010] Further, the carbon black fine particle powder has a low bulk density of about 0.1 g / cm ³ and is bulky powder, so that it is difficult to handle and has poor workability.
Furthermore, safety and hygiene problems such as carcinogenicity have been pointed out.

Conventionally, as a method for reducing the light transmittance of a magnetic recording medium and reducing the surface electric resistance value by minimizing the amount of carbon black fine particle powder added to a magnetic recording layer, needle-like cobalt is used. To the adhered magnetic iron oxide particles powder,
6.0 with respect to the acicular cobalt-coated magnetic iron oxide particles.
It is known that the blackness of magnetic particle powder itself is improved by containing Fe ²⁺ by weight or more (Japanese Patent Laid-Open No. 3-10 / 1990).
No. 2617).

[0012]

The light transmittance is small, the surface electric resistance is low, and the surface is smooth even if the amount of the carbon black fine particles added to the magnetic recording layer is as small as possible. The magnetic recording medium is most demanded at present, but a magnetic recording medium that sufficiently satisfies such characteristics has not yet been obtained.

That is, a magnetic recording medium obtained by using the above-mentioned acicular cobalt-coated magnetic iron oxide particle powder containing 6.0% by weight or more of Fe ²⁺ as the magnetic particle powder, Since the blackness was still insufficient, the light transmittance was sufficiently small and the surface electric resistance value was hardly sufficiently low as shown in the comparative examples described later. And
Since the magnetic particle powder contains Fe ²⁺ , the dispersibility in the vehicle is reduced, and it has been difficult to obtain a magnetic recording layer having a smooth surface.

Therefore, according to the present invention, the light transmittance is small, the surface electric resistance is low, and the surface is smooth even if the amount of the carbon black fine particles added to the magnetic recording layer is as small as possible. It is an object of the present invention to obtain a magnetic particle powder capable of obtaining a magnetic recording medium.

[0015]

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

That is, according to the present invention, the particle surface of the acicular magnetic particle powder is coated with a fluorine-containing organosilane compound generated from fluoroalkylsilane, and carbon black is coated on at least a part of the fluorine-containing organosilane compound coating. Average long axis diameter 0.051-0.7 attached
2 μm acicular black composite magnetic particle powder, wherein the carbon black is deposited in an amount of 0.5 to 10 parts by weight based on 100 parts by weight of the acicular magnetic particle powder. One or more selected from the group consisting of aluminum hydroxide, aluminum oxide, silicon hydroxide and silicon oxide as a lower layer on the surface of the acicular black composite magnetic particle powder or the acicular magnetic particle powder. Is coated,
The upper layer is coated with a fluorine-containing organosilane compound generated from a fluoroalkylsilane, and the carbon black is attached to at least a part of the fluorine-containing organosilane compound coating.
0.72 μm acicular black composite magnetic particle powder, wherein the carbon black adhered amount is the acicular magnetic particle powder 1
A needle-like black composite magnetic particle powder for a magnetic recording medium, a nonmagnetic support, and a magnetic particle powder formed on the nonmagnetic support, wherein the powder is 0.5 to 10 parts by weight with respect to 00 parts by weight. A magnetic recording medium comprising a magnetic recording layer containing a binder resin, wherein the magnetic particle powder is any one of the acicular black composite magnetic particle powders.

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

First, the acicular black composite magnetic particle powder for a magnetic recording medium according to the present invention will be described.

The acicular black composite magnetic particle powder according to the present invention is formed on the particle surface of the acicular magnetic particle powder as the core particle powder.
A fluorine-containing organosilane compound formed from a fluoroalkylsilane is coated, and carbon black is attached to at least a part of the fluorine-containing organosilane compound coating.
Of black composite magnetic particles.

The acicular magnetic particle powder, which is the core particle powder in the present invention, is a magnetite particle powder ( FeO x .Fe ₂
O ₃ ) (0 <x ≦ 1), maghemite particle powder (γ-F
e ₂ O ₃ ), magnetic iron oxide particles such as a beltlide compound which is an intermediate oxide between maghemite and magnetite, and Co, Al, N other than Fe
i, P, Zn, Si, magnetic iron oxide particles containing a different element such as B, magnetic iron oxide particles containing the above-mentioned magnetic iron oxide particles or a magnetic iron oxide particle powder containing a different element, cobalt or cobalt on the particle surface Particle powder coated with iron etc.
It is referred to as "acicular cobalt-coated magnetic iron oxide particle powder." ),
Needle-like metal magnetic particles containing iron as a main component and C other than iron
o, Al, Ni, P, Zn, Si, B, acicular iron alloy magnetic particles containing rare earth metal and the like.

In consideration of the recent high density recording of magnetic recording media, the acicular magnetic particle powder includes acicular cobalt-coated magnetic iron oxide particles, acicular metallic magnetic particles containing iron as a main component, and Co, Al, Ni, P, Zn, S other than iron
Needle-like iron alloy magnetic particles containing i, B, rare earth metal, etc. are preferable, and needle-like cobalt-coated magnetic iron oxide particles are more preferable in consideration of oxidation stability and dispersibility.

The particle shape of the core particles in the present invention 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 0.7 μm, more preferably from 0.05 to 0.5 μm, even more preferably from 0.05 to 0.7 μm.
0.3 μm.

When the average major axis diameter exceeds 0.7 μm, the obtained acicular black composite magnetic particle powder also becomes large particles having an average major axis diameter exceeding 0.7 μm. When formed, the surface smoothness of the coating film tends to be impaired. When the average major axis diameter is less than 0.05 μm, aggregation tends to occur due to an increase in intermolecular force due to miniaturization of the particles, so that the particle surface of the acicular magnetic particle powder is uniformly coated with fluoroalkylsilane and treated. Uniform adhesion treatment with carbon black becomes difficult.

The axial ratio of the acicular magnetic particles is from 2.0 to 20.
0, more preferably 2.5 to 18.0, and even 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 acicular magnetic particle powder with the fluoroalkylsilane and uniformly attach the carbon black to the carbon black. Becomes 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 magnetic 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 fluoroalkylsilane and treated with carbon black. Uniform adhesion treatment becomes difficult. 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 acicular magnetic particle powder is 1
5 to 150 m ² / g is preferred, more preferably 20 to 150 m ² / g.
120 m ² / g, even more preferably 25~100m ² /
g. When the BET specific surface area value is less than 15 m ² / g, the core particle powder is coarse or the particles are sintered between the particles, and the obtained acicular black composite magnetic particle powder is also When the magnetic recording layer is formed by using coarse particles, the surface smoothness of the coating film tends to be impaired. When the BET specific surface area exceeds 150 m ² / g, aggregation tends to occur due to an increase in intermolecular force due to finer particles, so that uniform coating treatment of the surface of the acicular magnetic particle powder with fluoroalkylsilane is performed. In addition, it becomes difficult to perform a uniform adhesion treatment with carbon black.

As for the blackness of the acicular magnetic particles, the lower limit of the L ^* value usually exceeds 18, and the upper limit is 34, preferably 32.
It is. When the L ^* value is more than 34, the lightness becomes high, and it is not possible to obtain acicular black composite magnetic particle powder having a sufficient blackness.

The volume resistivity of the acicular magnetic particle powder is usually 5.0 × 10 ¹⁰ Ω · cm or less.

The magnetic properties of the acicular magnetic particle powder are as follows. In the case of the acicular iron oxide magnetic particle powder, the coercive force value is 19.9 to 39.8.
kA / m (250 to 500 Oe) is preferable, and more preferably 23.9 to 39.8 kA / m (300 to 500 Oe).
e), wherein the saturation magnetization is 60 to 90 Am ² / kg
(60~90emu / g), more preferably from ^{65~90Am 2 / kg (65~90emu / g} ), when the needle-shaped cobalt-coated iron oxide magnetic particles, the coercive force value 39.8～ 135.3 kA / m (500 to 170
0 Oe) is preferred, and more preferably 43.8-13.
5.3 kA / m (550-1700 Oe), and the saturation magnetization value is 60-90 Am ² / kg (60-90 emu).
/ G) is preferred, and more preferably 65 to 90 Am ² /
kg (65-90 emu / g), and the coercive force value is 63.7-278.5 kA / m (800 in the case of acicular metal magnetic particles and acicular iron alloy magnetic particles mainly composed of iron.
~ 3500 Oe), more preferably 71.6.
２278.5 kA / m (900-3500 Oe), and the saturation magnetization value is 90-170 Am ² / kg (90-1
70 emu / g), and more preferably 100 to 100 emu / g.
170Am is ^{2 / kg (100~170emu / g)} .

The particle shape and particle size of the acicular black composite magnetic particle powder according to the present invention greatly depend on the particle shape and particle size of the acicular magnetic particle powder as the core particle, and have a particle morphology similar to the core particle. And 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 0.72 μm, preferably 0.051 to 0.51 μm, more preferably 0.1 to 0.51 μm.
051-0.31 μm, and the axial ratio is 2.0-20.
0, preferably 2.5-18.0, more preferably 3.
0 to 15.0.

When the average major axis diameter exceeds 0.72 μm, the acicular black composite magnetic particles become large particles, and when the magnetic recording layer is formed using the particles, 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.

[0037] BET specific surface area of the acicular black complex magnetic particles is preferably 16~160m ² / g, more preferably 22~130m ² / g, even more preferably from 27 to 1
10 m ² / g. When the BET specific surface area value is less than 16 m ² / g, the acicular black composite magnetic particle powder is coarse or sintered between particles, and the magnetic recording layer 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.

The blackness of acicular black complex magnetic particles is 22 upper limit in L ^* value is preferably L ^* value 21.5, more preferably L ^* value 21. If the L ^* value exceeds 22, the lightness increases and the blackness is not sufficient. The lower limit of blackness of the acicular black composite magnetic particles is L ^* value of 1
5

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 ^{4 to} 5.0 × 10 ⁶ Ω.・
cm, still more preferably 1.0 × 10 ^{4 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 desorption rate of carbon black in 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 magnetic particles according to the present invention are as follows. When acicular iron oxide magnetic particles are used as the core particles, the coercive force value is 19.9 to 39.8 kA / m (250).
To 500 Oe), more preferably 23.9 to
39.8 kA / m (300 to 500 Oe), and the saturation magnetization value is 60 to 90 Am ² / kg (60 to 90 emu).
/ G) is preferred, and more preferably 65 to 90 Am ² /
kg (65-90 emu / g), and when the acicular cobalt-coated iron oxide magnetic particle powder is used as the core particle, the coercive force value is 39.8-135.3 kA / m (500-170
0 Oe) is preferred, and more preferably 43.8-13.
5.3 kA / m (550-1700 Oe), and the saturation magnetization value is 60-90 Am ² / kg (60-90 emu).
/ G) is preferred, and more preferably 65 to 90 Am ² /
kg (65-90 emu / g), and the coercive force value is 63.7-27 in the case of using acicular metal magnetic powder particles and acicular iron alloy magnetic particle powder mainly composed of iron as core particles.
8.5 kA / m (800-3500 Oe) is preferable,
More preferably, 71.6 to 278.5 kA / m (900
-3500 Oe), and the saturation magnetization value is 90-170
Am ² / kg (90-170 emu / g) is preferred,
More preferably, 100 to 170 Am ² / kg (100 to
170 emu / g).

The coating of the acicular black magnetic particles according to the present invention comprises a fluorine-containing organosilane compound produced from a fluoroalkylsilane represented by the following chemical formula 1.

Embedded image R ² _3-n CF ₃ (CF ₂ ) _m CH ₂ CH ₂ Si— (OR ¹ ) _n R ¹ : —CH ₃ , —C ₂ H ₅ R ² : —CH ₃ , —C ₂ H _{5, -OCH 3, -OC 2 H} 5 m: 0~15 n: 1~3 integer

Specific examples of the fluoroalkylsilane include trifluoropropyltrimethoxysilane, tridecafluorooctyltrimethoxysilane, heptadecafluorodecyltrimethoxysilane, heptadecafluorodecylmethyldimethoxysilane, trifluoropropylethoxysilane , Tridecafluorooctyltriethoxysilane, heptadecafluorodecyltriethoxysilane and the like.

In consideration of the adhesion effect and desorption rate of carbon black, a fluorinated organosilane compound produced from trifluoropropyltrimethoxysilane, tridecafluorooctyltrimethoxysilane, and heptadecafluorodecyltrimethoxysilane is preferred. Fluorine-containing organosilane compounds generated from fluoropropyltrimethoxysilane and tridecafluorooctyltrimethoxysilane are more preferred.

The coating amount of the fluorine-containing organosilane compound generated from the fluoroalkylsilane is preferably 0.02 to 5.0% by weight in terms of Si based on the coated needle-like magnetic particle powder. More preferably, 0.03-4.
0% by weight, still more preferably 0.05 to 3.0% by weight
It is.

If the amount is less than 0.02% by weight, it is difficult to obtain acicular black composite magnetic particles having excellent blackness and low volume resistivity.

When the content exceeds 5.0% by weight, carbon black sufficient to impart excellent blackness and a low volume resistivity can be attached to the surface of the acicular magnetic particle powder. There is no point in coating.

The amount of carbon black attached is 0.5 to 10 parts by weight based on 100 parts by weight of the acicular magnetic particle powder.

When 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 10 parts by weight, the obtained acicular black composite magnetic particles have excellent blackness and a low volume resistivity. May be easily detached from the particle surface of the acicular magnetic particle powder, and as a result, the dispersibility in the vehicle during the production of the magnetic paint may decrease.

The adhesion thickness of carbon black is 0.04
μm or less, more preferably 0.03 μm or less, and still more preferably 0.02 μm or less.

The acicular black composite magnetic particle powder according to the present invention may be used, if necessary, to prepare an aluminum hydroxide, an aluminum oxide, a silicon hydroxide and a silicon oxide beforehand. May be coated with one or more compounds selected from products (hereinafter referred to as “coating with aluminum hydroxide or the like”), compared with a case where the coating is not made with aluminum hydroxide or the like. In addition, the dispersibility in the vehicle during the production of the magnetic paint is improved.

The coating amount of aluminum hydroxide or the like is calculated by converting the acicular magnetic particle powder coated with aluminum hydroxide or the like into Al conversion, SiO ₂ conversion or the sum of the Al conversion amount and the SiO ₂ conversion amount. Is preferably 0.01 to 20% by weight.

If the amount is less than 0.01% by weight, the effect of improving the dispersibility of the acicular black composite magnetic particles in the vehicle during the production of the magnetic paint cannot be obtained.

When the amount exceeds 20% by weight, the effect of improving the dispersibility of the acicular black composite magnetic particles in the vehicle during the production of the magnetic paint can be sufficiently obtained, but there is no point in covering more than necessary. In addition, the magnetic properties of the acicular magnetic particle powder are impaired due to an increase in the amount of non-magnetic components such as aluminum hydroxide.

The acicular black composite magnetic particle powder according to the present invention coated with an aluminum hydroxide or the like is the same as the acicular black composite magnetic particle powder according to the present invention not coated with an 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
^* Value, volume resistivity, magnetic properties and desorption rate of carbon black, as well as improved dispersibility.

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

The magnetic recording medium according to the present invention comprises a non-magnetic support, a magnetic recording layer formed on the non-magnetic support and containing acicular black composite magnetic particles and a binder resin.

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

In the case of a magnetic disk, polyethylene terephthalate is usually used as the nonmagnetic support, and its thickness is usually 50 to 300 μm, preferably 60 to 200 μm.
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.

As binder resins, vinyl chloride-vinyl acetate copolymer resins, urethane resins, vinyl chloride-vinyl acetate-maleic acid copolymer resins, butadiene-acrylonitrile copolymers, which are commonly used in the production of magnetic recording media at present. Resins, cellulose derivatives such as polyvinyl butyral and 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.

Further, each of the binder resins includes —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 100
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 fine particle powder added to the magnetic recording layer can be less than 6 parts by weight based on 100 parts by weight of the acicular black composite magnetic particle powder. , Less than 5 parts by weight, more preferably less than 3 parts by weight.

The acicular black composite magnetic particle powder has a large particle size and a large amount of carbon black adhered thereto. In particular, 7 to 10 parts by weight of carbon black is adhered to 100 parts by weight of acicular magnetic particle powder. When the acicular black composite magnetic particle powder is used as the magnetic particle powder, the addition of the carbon black fine particle powder to the magnetic recording layer can be expected to be omitted.

It is to be noted that a lubricant, an abrasive, an antistatic agent, and the like used in the manufacture of a normal magnetic recording medium are required for the magnetic recording layer, and if necessary, about 0.1 to 50 parts by weight per 100 parts by weight of the binder resin. May be included.

The magnetic recording medium according to the present invention is characterized in that acicular iron oxide magnetic particles which are not coated with aluminum hydroxide or the like are used as core particles. Is used, the coercive force value is 19.9 to 39.8 kA / m (250 to 500 O
e), preferably 23.9-39.8 kA / m (300
Ｏ500 Oe), and the squareness ratio (residual magnetic flux density Br / saturated magnetic flux density Bm) is 0.85 to 0.95, preferably 0.86.
0.95, the gloss of the coating film is 150 to 300%, preferably 160 to 300%, and the coating film surface roughness Ra is 12.0 n.
m, preferably 2.0 to 11.0 nm, more preferably 2.0 to 10.0 nm, and the Young's modulus is 124 to 16.
0, preferably 125 to 160, and a linear absorption coefficient of the coating film of 1.30 to 10.0 μm ^-1 , preferably 1.35-1.
0.0 μm ⁻¹ , surface electric resistance value is 1.0 × 10 ¹⁰ Ω / c
m ² or less, preferably 7.5 × 10 ⁹ Ω / cm ² or less, more preferably 5.0 × 10 ⁹ Ω / cm ² or less.

When the acicular black magnetic particle powder according to the present invention using acicular cobalt-coated iron oxide magnetic particles not coated with aluminum hydroxide or the like as the core particles is used as the magnetic particle powder, The coercive force value is 39.8-
135.3 kA / m (500 to 1700 Oe), preferably 43.8 to 135.3 kA / m (550 to 1700
Oe), squareness ratio (residual magnetic flux density Br / saturated magnetic flux density B)
m) is from 0.85 to 0.95, preferably from 0.86 to 0.
95, the glossiness of the coating film is 160 to 300%, preferably 1
65-300%, coating film surface roughness Ra is 12.0 nm or less, preferably 2.0-11.0 nm, more preferably 2.0-10.0 nm, Young's modulus is 124-160, preferably 125-160. , The linear absorption coefficient of the coating film is 1.30
１10.0 μm ⁻¹ , preferably 1.35 to 10.0 μm
^-1 , the surface electric resistance value is 1.0 × 10 ¹⁰ Ω / cm ² or less,
It is preferably at most 7.5 × 10 ⁹ Ω / cm ² , more preferably at most 5.0 × 10 ⁹ Ω / cm ² .

Needle-like black particles according to the present invention using, as core particles, needle-like metal magnetic particles or needle-like iron alloy magnetic particles mainly composed of iron not coated with aluminum hydroxide or the like as the magnetic particle powder. When the magnetic particle powder is used, the coercive force value is 63.7 to 278.5 kA / m (800
３3500 Oe), preferably 71.6 to 278.5 k
A / m (900 to 3500 Oe), squareness ratio (residual magnetic flux density Br / saturated magnetic flux density Bm) is 0.85 to 0.95, preferably 0.86 to 0.95, and the glossiness of the coating film is 180 to
300%, preferably 190 to 300%, and the coating film surface roughness Ra is 12.0 nm or less, preferably 2.0 to 11.0
nm, more preferably 2.0 to 10.0 nm, the Young's modulus is 124 to 160, preferably 125 to 160, and the linear absorption coefficient of the coating film is 1.40 to 10.0 µm ^-1 , preferably 1.45 to 10. 0.0 μm ⁻¹ , surface electric resistance value is 1.0 ×
10 ¹⁰ Ω / cm ² or less, preferably 7.5 × 10 ⁹ Ω / c
m ² or less, more preferably 5.0 × 10 ⁹ Ω / cm ² or less.

The magnetic recording medium according to the present invention is characterized in that acicular iron oxide magnetic particles coated with aluminum hydroxide or the like are used as the magnetic particle powder. Is used, the coercive force value is 19.9 to 39.8 kA / m (250 to 500 O
e), preferably 23.9-39.8 kA / m (300
Ｏ500 Oe), and the squareness ratio (residual magnetic flux density Br / saturated magnetic flux density Bm) is 0.85 to 0.95, preferably 0.86.
0.95, the glossiness of the coating film is 155 to 300%, preferably 165 to 300%, and the coating film surface roughness Ra is 11.0 n
m, preferably 2.0 to 10.0 nm, more preferably 2.0 to 9.0 nm, the Young's modulus is 126 to 160,
It is preferably 127 to 160, and the linear absorption coefficient of the coating film is 1.3.
0 to 10.0 μm ⁻¹ , preferably 1.35 to 10.0 μm
m ^-1 , the surface electric resistance value is 1.0 × 10 ¹⁰ Ω / cm ² or less, preferably 7.5 × 10 ⁹ Ω / cm ² or less, more preferably 5.0 × 10 ⁹ Ω / cm ² or less. is there.

When the acicular black magnetic particle powder according to the present invention using acicular cobalt-coated iron oxide magnetic particles coated with aluminum hydroxide or the like as the core particles is used as the magnetic particle powder, The coercive force value is 39.8 to 1
35.3 kA / m (500 to 1700 Oe), preferably 43.8 to 135.3 kA / m (550 to 1700 Oe)
e), squareness ratio (residual magnetic flux density Br / saturated magnetic flux density Bm)
Is 0.85 to 0.95, preferably 0.86 to 0.9
5. The glossiness of the coating film is 165 to 300%, preferably 17
0 to 300%, the coating film surface roughness Ra is 11.0 nm or less,
Preferably from 2.0 to 10.0 nm, more preferably from 2.
0-9.0 nm, Young's modulus is 126-160, preferably 127-160, and the linear absorption coefficient of the coating film is 1.30-1.
0.0 μm ⁻¹ , preferably 1.35-10.0 μm ⁻¹ ,
The surface electric resistance is 1.0 × 10 ¹⁰ Ω / cm ² or less, preferably 7.5 × 10 ⁹ Ω / cm ² or less, and more preferably 5.0 × 10 ⁹ Ω / cm ² or less.

As the magnetic particle powder, acicular black magnetic particles according to the present invention using, as core particles, acicular metallic magnetic particles or acicular iron alloy magnetic particles mainly composed of iron coated with aluminum hydroxide or the like. When the magnetic particle powder is used, the coercive force value is 63.7 to 278.5 kA / m (800
３3500 Oe), preferably 71.6 to 278.5 k
A / m (900-3500 Oe), squareness ratio (residual magnetic flux density Br / saturated magnetic flux density Bm) is 0.85-0.95, preferably 0.86-0.95, and the glossiness of the coating film is 185-85.
300%, preferably 195 to 300%, and the coating film surface roughness Ra is 11.0 nm or less, preferably 2.0 to 10.0
nm, more preferably 2.0-9.0 nm, the Young's modulus is 126-160, preferably 127-160, and the linear absorption coefficient of the coating film is 1.40-10.0 μm ⁻¹ , preferably 1.
45 to 10.0 μm ⁻¹ , surface electric resistance value is 1.0 × 10
¹⁰ Ω / cm ² or less, preferably 7.5 × 10 ⁹ Ω / cm ²
Or less, more preferably 5.0 × 10 ⁹ Ω / cm ² or less.

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

In the acicular magnetic particle powder of the present invention,
The acicular magnetite particle powder is a ferrous hydroxide colloid obtained by reacting an aqueous ferrous salt solution with an aqueous alkali hydroxide solution, an aqueous alkali carbonate solution or an aqueous alkali hydroxide solution / alkali carbonate solution, and a precipitate containing iron carbonate and iron. While controlling the pH value and temperature of the suspension containing any of the above substances, an oxygen-containing gas is passed through the suspension to oxidize the suspension to produce needle-like, spindle-like or rice-like goethite particles. After filtering the goethite particle powder, washing with water, and drying, the powder can be obtained by heating and reducing at 300 to 800 ° C. in a reducing gas.

The acicular maghemite particles can be obtained by heating and oxidizing the acicular magnetite particles in an oxidizing gas at a temperature in the range of 300 to 600 ° C.

The acicular metal magnetic particles containing iron as a main component may be obtained by heating the acicular goethite particles or the acicular hematite particles obtained by heating and dehydrating the acicular goethite particles at a temperature of 300 to 500 ° C. It can be obtained by heat reduction in the range.

For coating the surface of the acicular magnetic particle powder with fluoroalkylsilane, the acicular magnetic particle powder and the fluoroalkylsilane are mechanically mixed and stirred, or the acicular magnetic particle powder is sprayed with the fluoroalkylsilane. What is necessary is just to mix and stir mechanically while doing. Almost all of the added fluoroalkyl silane is coated on the particle surface of the acicular magnetic particle powder, and a part thereof is coated as a fluorine-containing organosilane compound generated from the fluoroalkyl silane generated through the coating step. Is also good. Even in this case, it does not affect the subsequent adhesion of carbon black.

In order to uniformly coat the surface of the acicular magnetic particle powder with the fluoroalkylsilane, it is preferable that the agglomeration of the acicular magnetic particle powder is previously disentangled using a pulverizer.

Examples of equipment for mixing and stirring the acicular magnetic particle powder and the fluoroalkylsilane and mixing and stirring the carbon black fine particle powder and the acicular magnetic particle powder having the fluoroalkylsilane coated on the particle surface include: A device capable of applying a shearing force to the powder layer is preferred. In particular, a device capable of simultaneously performing shearing, spatula and compression, such as a wheel-type kneader, a ball-type kneader, a blade-type kneader, and a roll-type kneader Machine can be used. In practicing the present invention, a wheel-type kneader can be used more effectively.

Specific examples of the wheel-type kneader include edge runners (synonyms for “mix miller”, “Simpson mill”, and “sand mill”), multi-mul, Stots mill, wet pan mill, conner mill, and ring miller. And the like, preferably an edge runner, a multiple, a Stotts mill, a wet pan mill, and a ring muller, and more preferably an edge runner. Examples of the ball-type kneader include a vibration mill and the like. Specific examples of the blade type kneader include a Henschel mixer, a planetary mixer, and a Nauta mixer. Specific examples of the roll-type kneader include an extruder.

The conditions during mixing and stirring are such that the linear load is 19.6 to 1960 so that the fluoroalkylsilane is coated as uniformly as possible on the particle surface of the acicular magnetic particle powder.
N / cm (2-200 Kg / cm), preferably 98-
1470 N / cm (10 to 150 kg / cm), more preferably 147 to 980 N / cm (15 to 100 kg / cm)
cm), the treatment time is 5 to 120 minutes, preferably 10 to 9 minutes.
The processing conditions may be appropriately adjusted within a range of 0 minutes. The stirring speed is 2 to 2000 rpm, preferably 5 to 1000 rpm.
The processing conditions may be appropriately adjusted within the range of rpm, more preferably in the range of 10 to 800 rpm.

Magnetic particles that are easily oxidized such as magnetite particles, needle-like metal magnetic particles containing iron as a main component, and needle-like iron alloy magnetic particles are mixed with mixing equipment in order to prevent deterioration of magnetic properties due to oxidation. It is preferable to perform the treatment by first purging an inert gas such as N ₂ .

The addition amount of the fluoroalkylsilane is preferably 0.15 to 45 parts by weight based on 100 parts by weight of the acicular magnetic particle powder. If the amount is less than 0.15 parts by weight, it is difficult to attach carbon black sufficiently to improve blackness and volume resistivity. If it exceeds 45 parts by weight, carbon black can be sufficiently adhered, but there is no point in adding more than necessary.

The carbon black fine particles are added to the acicular magnetic particles having the fluoroalkylsilane coated on the particle surface, and mixed and stirred to deposit carbon black on the fluoroalkylsilane coating. If necessary, drying or heat treatment may be further performed.

The fluoroalkylsilane used for coating the obtained acicular black composite magnetic particle powder finally undergoes a fluorine-containing organosilane compound produced from the fluoroalkylsilane through these steps. Coated.

As the carbon black fine particle powder used for the adhesion treatment, commercially available furnace black, channel black and the like can be used.
# 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 (manufactured)), Ketjen Black EC, Ketjen Black EC600JD (trade name: Ketjen Black International Co., Ltd.), BLACK PE
ARLS-L, BLACK PEARLS 1000,
BLACK PEARLS 4630, VULCAN
XC72, REGAL 660, REGAL 400
(Product Name: Cabot Specialty Chemicals
Ink (manufactured)) can be used.

Considering the affinity with the fluorine-containing organosilane compound, # 3150, # 3250, MA-10
0, MA7, # 1000, # 2400B, # 30, BL
ACK PEARLS-L and BLACK PEARL
S 4630 is preferable, and further considering conductivity,
# 3150 and # 3250 are more preferable.

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

If the thickness is less than 0.002 μm, the carbon black fine particles become too fine, so that handling becomes difficult.

When the thickness exceeds 0.05 μm, an extremely large mechanical shearing force is required to uniformly adhere to the fluoroalkylsilane or fluorine-containing organosilane compound coating because the particle size of the carbon black fine particles is large. , Industrially disadvantageous.

The carbon black fine particles are preferably added little by little over time, especially over about 5 to 60 minutes.

The conditions during mixing and stirring are such that the linear load is 19.6 to 19 so that the carbon black adheres uniformly.
60 N / cm (2-200 kg / cm), preferably 9
8 to 1470 N / cm (10 to 150 Kg / cm), more preferably 147 to 980 N / cm (15 to 100 Kg)
g / cm), and the treatment time is 5 to 120 minutes, preferably 10 minutes.
The processing conditions may be appropriately adjusted within a range of up to 90 minutes. The stirring speed is 2 to 2000 rpm, preferably 5 to 1
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 was
It is 0.5 to 10 parts by weight based on 100 parts by weight of the acicular magnetic particle powder. If the amount is less than 0.5 part by weight, the amount of carbon black adhered is insufficient, and acicular black composite magnetic particles having sufficient blackness and low volume resistivity cannot be obtained. If it exceeds 10 parts by weight, acicular black composite magnetic particle powder having sufficient blackness and low volume resistivity is obtained, but carbon black is detached from the particle surface because the amount of carbon black attached becomes large. As a result, the dispersibility in the vehicle during the production of the magnetic paint decreases.

The heating temperature in the drying or heating treatment is usually preferably from 40 to 200 ° C., more preferably 6 to 200 ° C.
The treatment time is preferably from 10 minutes to 12 hours, more preferably from 30 minutes to 3 hours.

If necessary, prior to mixing and stirring with the fluoroalkylsilane, the surface of the acicular magnetic particle powder is treated with an aluminum hydroxide, an aluminum oxide, and a silicon hydroxide. And one or more compounds selected from oxides and silicon oxides.

The coating of aluminum with hydroxide or the like is as follows.
To an aqueous suspension obtained by dispersing the acicular magnetic particle powder, adding an aluminum compound, a silicon compound or both compounds and mixing and stirring, or, if necessary, adjusting the pH value after mixing and stirring. By coating the particle surface of the acicular magnetic particle powder with one or more compounds selected from aluminum hydroxide, aluminum oxide, silicon hydroxide and silicon oxide, , Filtered, washed with water, dried and pulverized. If necessary,
Degassing / consolidation processing 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 acicular magnetic particle powder. If the amount is less than 0.01% by weight, a sufficient amount of aluminum hydroxide or the like to obtain an effect of improving dispersibility in a vehicle at the time of manufacturing the magnetic paint is added to the particle surface of the acicular magnetic particle powder. Is difficult to coat. 20
If the content is more than 10% by weight, the coating effect is saturated, and there is no point in adding more than necessary. In addition, the magnetic property of the acicular magnetic particle powder is impaired due to the increase of aluminum which is a non-magnetic component.

As the silicon compound, No. 3 water glass, sodium orthosilicate, sodium metasilicate, colloidal silica 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 acicular magnetic particle powder. If the amount is less than 0.01% by weight, a sufficient amount of silicon oxide or the like to obtain an effect of improving dispersibility in a vehicle during the production of the magnetic paint is applied to the surface of the acicular magnetic particle powder. Difficult to coat. If it exceeds 20% by weight, the coating effect is saturated, so that there is no point in adding more than necessary. In addition, the magnetic properties of the acicular magnetic particle powder are impaired due to an increase in silicon as a nonmagnetic component.

When the aluminum compound and the silicon compound are used together, the amount of addition is 0.01 to 0.01 in terms of the total of the converted amount of Al and the converted amount of SiO ₂ with respect to the acicular magnetic particle powder.
20% by weight is preferred.

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

The magnetic recording medium according to the present invention is obtained by applying a coating composition containing acicular black composite magnetic particle powder, a binder resin and a solvent on a non-magnetic support to form a coating film, followed by drying. To form a magnetic recording layer.

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 acicular black composite magnetic particles. 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.

[0108]

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 acicular magnetic particle powder and 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 (×
30,000) was enlarged four times in the vertical and horizontal directions, respectively, and about 350 particles shown in the photograph were measured for the major axis diameter, the minor axis diameter or the particle diameter, 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.

From the graph, it is found 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 Al content, Si content and Co content present inside and on the surface of the acicular magnetic particle powder and acicular black composite magnetic particle powder
The amount of Si and the amount of Si contained in the fluorine-containing organosilane compound generated from the fluoroalkylsilane coated on the acicular black composite magnetic particle powder are each described in “Fluorescence X-ray Analyzer 3063M” (Rigaku Corporation) Was measured according to JIS K0119 “General rules for X-ray fluorescence analysis”.

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

That is, under an inert gas atmosphere, 2: 1 phosphoric acid and sulfuric acid were added to 0.5 g of the acicular magnetic particle powder.
Was added to dissolve the needle-like magnetic 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 black adhering to the acicular black composite magnetic particles was determined by measuring the amount of carbon using a “HORIBA Metal Carbon / Sulfur Analyzer EMIA-2200” (manufactured by HORIBA, Ltd.). I asked.

The thickness of the carbon black adhering to the acicular black composite magnetic particle powder was determined according to “Transmission electron microscope J
The surface of particles in an electron micrograph (× 5,000,000) of an electron micrograph taken under the condition of an acceleration voltage of 200 kV using “EM-2010” (manufactured by JEOL Ltd.). It was determined by measuring the average thickness of carbon black adhering to.

The blackness of the acicular magnetic particle powder and acicular black composite magnetic particle powder was 0.5 g for the sample and 1.5 ml for castor oil.
Was kneaded with a Hoover-type muller to form a paste, and 4.5 g of clear lacquer was added to the paste, kneaded, made into a coating, and applied to a cast-coated paper using a 150 μm (6 mil) applicator (coating thickness: About 30 μm). The paint piece was measured using a multi-source spectrophotometer MSC-IS-2D (manufactured by Suga Test Instruments Co., Ltd.), and the colorimetric index L ^* was determined according to JIS Z 8729 ^. Indicated by value.

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

The volume specific resistance of each of the acicular magnetic particle powder and the acicular black magnetic particle powder was determined by first measuring 0.5 g of the particle powder and using a KBr tablet press (Shimadzu Corporation). , 1.37 × 10 ⁷ kPa (140K
g / cm ² ) to obtain 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 the 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 desorption rate (%) of carbon black adhering to the acicular black composite magnetic particles was shown by a 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 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 needle-shaped black composite magnetic particles were dried at 100 ° C. for 1 hour, and the above-mentioned “HORIBA Metal Carbon / Sulfur Analyzer EMIA-2200” was used.
The carbon content was measured using (manufactured by Horiba, Ltd.), and the value obtained 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 coating viscosity was measured by measuring the coating viscosity of the obtained magnetic coating at 25 ° C. using an E-type viscometer EMD-R (manufactured by Tokyo Keiki Co., Ltd.), and the shear rate D = 1.92 sec.
It was shown by the value at c- ¹ .

The glossiness of the coating film 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 properties of the acicular magnetic particle powder, acicular black composite magnetic particle powder and the magnetic recording medium were measured using a “vibrating sample magnetometer VSM-3S-15” (manufactured by Toei Kogyo Co., Ltd.). The measurement was performed up to a magnetic field of 795.8 kA / m (10 kOe).

The degree of light transmission is described in “Recording of a 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: film thickness of magnetic recording layer (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 thicknesses of the nonmagnetic support and the magnetic recording layer constituting the magnetic recording medium were measured as described below.

Digital electronic micrometer K351C
First, the film thickness (A) of the nonmagnetic support is measured using (manufactured by Anritsu Electric Co., Ltd.). Next, the thickness (B) (sum of the thickness of the nonmagnetic support and the thickness of the magnetic recording layer) of the nonmagnetic support and the magnetic recording layer formed on the nonmagnetic support is measured in the same manner. The thickness of the magnetic recording layer is (B) −
(A).

<Production of Acicular Black Composite Magnetic Particle Powder> FIG.
The acicular cobalt-coated magnetite particles containing 2.21% by weight of cobalt with respect to the magnetic particles and 15.8% by weight of Fe ²⁺ with respect to the magnetic particles as shown in the electron micrograph (× 30000) Average major axis diameter 0.278 μm, average minor axis diameter 0.0330 μm, axial ratio 8.4, geometric standard deviation value 1.38, BET specific surface area value 38.7 m ² / g, blackness L ^* value 22.6, Volume resistivity 7.3 × 10 ⁷ Ω · c
m, coercive force value 54.6 kA / m (686 Oe), saturation magnetization value 79.1 Am ² / kg (79.1 emu / g) ²
In order to dissolve the agglomeration, 0 kg of water is contacted with 150 l of pure water using a stirrer, and further passed through a “TK pipeline homomixer” (product name, manufactured by Tokushu Kika Kogyo Co., Ltd.) three times to obtain a needle-shaped cobalt coating. A slurry containing magnetized particles was obtained.

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.

325 mesh of the obtained dispersion slurry
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 Casting Ironworks Co., Ltd.) and 294 N / c while blowing 2 l of nitrogen per minute.
m (30 kg / cm) for 15 minutes to carry out mixing and agitation to loosen the aggregation of particles.

Next, 220 g of tridecafluorooctyltrimethoxysilane (trade name: TSL8257: manufactured by Toshiba Silicone Co., Ltd.) was used to remove the agglomeration of the particles while operating the edge runner, and the above-mentioned acicular cobalt-coated magnetite particle powder was used. 294 N / cm (30 kg
/ Cm) with a linear load of 20 minutes to form a coating on the surface of the acicular cobalt-coated magnetite particles. The stirring speed at this time was 22 rpm.

Next, the electron micrograph (× 300) of FIG.
00) (particle shape:
Granular, particle size 0.022 μm, geometric standard deviation 1.6
8, BET specific surface area value 134 m ² / g, blackness L ^* value 1
6.6) 550 g was added over 10 minutes while operating the edge runner, and further 294 N / cm (30 kg).
/ Cm) with a linear load of 30 minutes, and the carbon black is adhered to the above-mentioned coating.
Heat treatment was performed at 0 ° C. for 120 minutes to obtain acicular black composite magnetic particles. The stirring speed at this time was 22 rpm.

The obtained acicular black composite magnetic particle powder was
As shown in the electron micrograph (× 30000) of FIG. 3, the average major axis diameter was 0.279 μm, and the average minor axis diameter was 0.0335.
μm and the axial ratio were 8.3. Geometric standard deviation is 1.3
8, the BET specific surface area value is 38.2 m ² / g, the blackness L ^* value is 19.6, and the volume resistivity value is 6.8 × 10 ⁴ Ω.
Cm, the desorption rate of carbon black is 6.5%, the coercive force value is 54.1 kA / m (680 Oe), and the saturation magnetization value is 7
A 7.1Am ² /kg(77.1emu/g), coverage of tridecafluorooctyltrimethoxysilane was 0.12 wt% in terms of Si. The amount of attached carbon black is 4.69% by weight in terms of C (equivalent to 5 parts by weight with respect to 100 parts by weight of acicular cobalt-coated magnetite particle powder), and the thickness of carbon black attached on the particle surface is It was 0.0022 μm. As a result of observation of the electron micrograph shown in FIG. 3, almost no carbon black was observed, indicating that almost all of the carbon black had adhered to the fluorine-containing organosilane compound coating generated from tridecafluorooctyltrimethoxysilane. Admitted.

For comparison, the treated particle powder obtained by mixing and stirring the acicular cobalt-coated magnetite particle powder and the carbon black particle powder in the same manner with an edge runner without coating with tridecafluorooctyltrimethoxysilane was used. 4 shows an electron micrograph (× 30000) of FIG. As shown in the electron micrograph of FIG. 4, it was confirmed that carbon black did not adhere to the particle surface of the acicular cobalt-coated magnetite particle powder, and that both particle powders were mixed.

<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.

The 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 Fine particle powder (# 2400B) 0.5 parts by weight Lubricant (myristic acid: butyl stearate = 1: 2) 3.0 parts by weight Curing agent (polyisocyanate) 5.0 parts by weight Cyclohexanone 65.8 parts by weight Methyl ethyl ketone 164. 5 parts by weight Toluene 98.7 parts by weight

The viscosity of the obtained magnetic paint was 2560c.
P.

The obtained magnetic paint was applied on a polyethylene terephthalate film having a thickness of 12 μm to a thickness of 45 μm using an applicator, and then oriented and dried in a magnetic field.
For 24 hours, and slit to a width of 1.27 cm (0.5 inch) to obtain a magnetic tape. The thickness of the magnetic recording layer was 3.5 μm.

The resulting magnetic tape had a coercive force value of 58.
5 kA / m (735 Oe), squareness ratio (Br / Bm) 0.89, gloss 176%, surface roughness Ra 7.2 n
m, Young's modulus (relative value) is 138, linear absorption coefficient is 1.5
0 cm ⁻¹ and the surface electric resistance value was 1.5 × 10 ⁸ Ω / cm ² .

[0151]

The most important point in the present invention is that acicular magnetic particle powder, and if necessary, aluminum hydroxide, aluminum oxide, silicon hydroxide and silicon hydroxide One or two selected from oxides
The fluorine-containing organosilane compound generated from fluoroalkylsilane is coated on the particle surface of any one of the acicular magnetic particle powders coated with at least one kind of compound, and at least the fluorine-containing organosilane compound coating is coated. An acicular black composite magnetic particle powder having an average particle diameter of 0.051 to 0.72 μm in which carbon black is adhered to 1 part, and the amount of the carbon black attached is 100 parts by weight of the acicular magnetic particle powder. 0.5 to 10 parts by weight of the acicular black composite magnetic particle powder has excellent dispersibility in a vehicle due to a small amount of carbon black detached from the particle surface, and has high blackness and low volume. It is the fact that it has a specific resistance value.

Regarding the reason why the blackness of the acicular black composite magnetic particles according to the present invention is excellent, the present inventor has proposed that the carbon black uniformly and densely adhered to the particle surface of the acicular magnetic particles has a core. It is believed that the color of the particles was canceled and the original color of carbon black was exhibited.

Regarding the reason why the acicular black composite magnetic particle powder according to the present invention has a low volume resistivity value, the present inventor has proposed that carbon black having excellent conductivity is provided on the surface of the acicular black composite magnetic particle powder. This is considered to be due to uniform and dense attachment.

Regarding the reason why the amount of carbon black detached from the particle surface of the acicular black composite magnetic particle powder according to the present invention is small, the present inventor has argued that Si contained in the acicular magnetic particle powder inside or on the surface of the particle. , Al, Fe or the like and a metalloxane bond (≡Si—OM (where M is Si, Al, Fe) Is formed, the fluorine-containing organosilane compound to which the carbon black is adhered is firmly bonded to the particle surface of the acicular magnetic particles. I believe in doing so.

Regarding the reason why the acicular black composite magnetic particle powder according to the present invention is excellent in dispersibility in a vehicle at the time of producing a magnetic coating material, the present inventor considered from the particle surface of the acicular black composite magnetic particle powder. Due to the small amount of carbon black to be eliminated, the dispersion in the system is not hindered by the carbon black, and irregularities occur on the particle surface due to the carbon black adhering to the particle surface of the acicular magnetic particle powder, It is thought that contact between particles is suppressed.

In the magnetic recording medium according to the present invention obtained by using the above acicular black composite magnetic particle powder as the magnetic particle powder, the amount of the carbon black fine particle powder added to the magnetic recording layer is reduced as much as possible. Even if it does, the fact is that the light transmittance is small, the surface electric resistance value is low, and the surface smoothness of the magnetic recording layer is improved.

The reason why a magnetic recording medium having a small light transmittance can be obtained even if the amount of the carbon black fine particles added to the magnetic recording layer is reduced as much as possible is based on the fact that the fine particles are fine particles. Due to the fact that the carbon black fine particle powder that normally behaves as an aggregate, in the case of the acicular black composite magnetic particle powder in the present invention, is uniformly and densely attached to the particle surface of the acicular magnetic particle powder. We believe that each of the carbon blacks is functioning more effectively.

The inventor of the present invention contemplates that a magnetic recording medium having a low surface electric resistance can be obtained even if the amount of carbon black fine particles added to the magnetic recording layer is reduced as much as possible. Due to the fact that the magnetic particle powder is uniformly dispersed in the coating film, the carbon black uniformly and densely adhered to the particle surface of the acicular magnetic particle powder is connected to the continuous cotton while contacting each other. I believe it is due to

Regarding the reason that the magnetic recording medium according to the present invention has excellent surface smoothness, the present inventors have concluded that the acicular black composite magnetic particle powder according to the present invention has a small amount of carbon black detached from the particle surface. Since the amount of carbon black fine particles added to the magnetic recording layer can be reduced as much as possible, the dispersion of the acicular black composite magnetic particles in the vehicle during the production of the magnetic paint is inhibited by the carbon black. This is considered to be due to the excellent dispersibility of the acicular black composite magnetic particle powder itself.

[0160]

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 the agglomerated needle-like magnetic particle powders are obtained in the same manner as in the embodiment of the present invention. Was.

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

[0163]

[Table 1]

Core Particles 6 Needle-shaped cobalt-coated 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 and 150 l of water in which the aggregation of core particles 1 was loosened. A slurry containing the powder was obtained. The pH value of the redispersed slurry containing the obtained acicular cobalt-coated maghemite particles was adjusted to 10.5 with an aqueous sodium hydroxide solution.
, And water was added to the slurry to adjust the slurry concentration to 98 g / l. 150 l of this slurry was heated to 60 ° C., and 5444 ml of a 1.0 mol / l NaAlO ₂ solution (corresponding to 1.0% by weight in terms of Al with respect to the acicular cobalt-coated maghemite particles powder) was added to the slurry. In addition, after holding for 30 minutes, p
The H value was adjusted to 7.5. After maintaining in this state for 30 minutes, filtration, washing with water, drying, and pulverization were performed to obtain acicular cobalt-coated maghemite particles having a particle surface coated with Al hydroxide.

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

The type A of the coating in the surface treatment step represents aluminum hydroxide, and S represents silicon oxide.

[0167]

[Table 2]

[0168]

[Table 3]

Core Particles 7 to 10 Surface-treated needle-like magnetic particles were obtained in the same manner as in the case of the core particles 6, except that the types of the core particles and the types and amounts 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.

Examples 1 to 10 and Comparative Examples 1 to 5 The types of core particles, the presence / absence of fluoroalkyl silane and silicon compound in the coating step with fluoroalkyl silane, the type and amount of addition, the processing conditions with an edge runner,
Acicular black composite magnetic particles were obtained in the same manner as in the embodiment of the present invention, except that the type and amount of carbon black added in the carbon black attaching step and the processing conditions using the edge runner were variously changed. The needle-shaped black composite magnetic particles obtained in each of Examples 1 to 10 show that almost all of the carbon black is produced from the fluoroalkylsilane, since almost no carbon black is observed as a result of electron microscopic observation. It was confirmed that it adhered to the fluorine-containing organosilane compound coating.

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

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

[0174]

[Table 4]

[0175]

[Table 5]

[0176]

[Table 6]

<Manufacture of Magnetic Recording Medium> Examples 11 to 23 and Comparative Examples 6 to 20 Except that the kind of the acicular magnetic particles and the amount of the carbon black fine particles added (as compared to the magnetic particles) were variously changed,
A magnetic recording medium was obtained in the same manner as in the embodiment of the invention.

Tables 7 and 8 show the main production conditions and various characteristics at this time.

[0179]

[Table 7]

[0180]

[Table 8]

[0181]

The acicular black composite magnetic particles according to the present invention have high blackness, low volume resistivity and excellent dispersibility, so that carbon black fine particles to be added to the magnetic recording layer. Even if the amount of powder is reduced as much as possible, it is possible to obtain a magnetic recording medium having a small light transmittance, a low surface electric resistance value and excellent surface smoothness. It is preferable as a magnetic particle powder.

As described above, the magnetic recording medium according to the present invention has a low light transmittance due to the fact that the acicular black composite magnetic particle powder has excellent blackness and low volume resistivity, and Low surface electrical resistance, and
Suitable for high-density recording because the surface is smooth because the amount of carbon black fine particles added to the magnetic recording layer can be reduced as much as possible and the dispersibility of the acicular black magnetic particles itself is improved. It is preferable as a magnetic recording medium.

Further, the magnetic recording medium according to the present invention uses a small amount of fine carbon black particles, so that
It is preferable from the viewpoint of hygiene.

[0184]

[Brief description of the drawings]

[0181]

FIG. 1 is an electron micrograph (× 30000) showing the particle structure of acicular cobalt-coated magnetite particles used in an embodiment of the present invention.

[0182]

FIG. 2 is an electron micrograph (× 30) showing the particle structure of carbon black fine particle powder used in the embodiment of the invention.
000).

[0183]

FIG. 3 is an electron micrograph (× 300) showing the particle structure of the acicular black composite magnetic particle powder obtained in the embodiment of the present invention.
00).

[0184]

FIG. 4 is an electron micrograph (× 30000) showing the particle structure of a mixed powder of acicular cobalt-coated magnetite particles and carbon black particles shown for comparison.
It is.

 ──────────────────────────────────────────────────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 1-4, Meiji Shinkai, Otake-shi, Hiroshima Prefecture Toda Kogyo Co., Ltd.

Claims (3)

[Claims] 1. A particle surface of an acicular magnetic particle powder is coated with a fluorine-containing organosilane compound generated from fluoroalkylsilane, and carbon black is attached to at least a part of the fluorine-containing organosilane compound coating. Acicular black composite magnetic particles having an average major axis diameter of 0.051 to 0.72 μm, wherein the carbon black adhered amount is 0.5 to 10 parts by weight based on 100 parts by weight of the acicular magnetic particles. Needle-like black composite magnetic particles for a magnetic recording medium. 2. A particle surface of the acicular magnetic particle powder is coated with one or more selected from aluminum hydroxide, aluminum oxide, silicon hydroxide and silicon oxide as a lower layer. A fluorine-containing organosilane compound generated from a fluoroalkylsilane is coated as an upper layer, and carbon black is attached to at least a part of the fluorine-containing organosilane compound coating. Acicular black composite magnetic particles powder, wherein the amount of carbon black attached is 0.5 to 10 parts by weight based on 100 parts by weight of the acicular magnetic particles powder.
A needle-like black composite magnetic particle powder for a magnetic recording medium, which is in parts by weight. 3. A magnetic recording medium comprising a non-magnetic support and a magnetic recording layer containing a magnetic resin powder and a binder resin formed on the non-magnetic support, wherein the magnetic particle powder is used. Item 7. A magnetic recording medium comprising the acicular black composite magnetic particle powder according to Item 2.