JP2000036404A - Magnetic recording medium needle black composite magnetic granular powder and magnetic recording medium using the needle black composite magnetic granular powder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain magnetic granular powder through which magnetic recording medium can be realized, where the magnetic recording medium is small in light transmittance, even if carbon black added to a magnetic recording layer is reduced to an irreducible minimum amount, low in surface electric resistance, and high in surface smoothness. SOLUTION: Needle magnetic granular powder is coated with organosilane compound, made of alcoxysilane for the formation of this magnetic granular powder, and carbon black fine granular powder 0.002 to 0.05 μm in average grain diameter is attached to organosilane compound coating for the formation of needle black composite magnetic granular powder 0.051 to 0.72 μm in average major axis, wherein 0.5 to 10 pts.wt. of carbon black fine granular powder is attached with respect to 100 pts.wt. of needle magnetic granular powder.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a magnetic material having excellent dispersibility in a vehicle due to a small amount of carbon black fine particles desorbing from the particle surface, and having a high blackness and a low volume resistivity. Along with providing the acicular black composite magnetic particle powder for a recording medium, by using the acicular black composite magnetic particle powder, light transmission is achieved even if the amount of carbon black 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 but hinders high density recording. In addition to causing a reduction in the thickness of the magnetic recording layer, the carbon black fine particle powder is a fine particle powder having an average particle diameter of about 0.002 to 0.05 μm, and has a large BET specific surface area, Due to the property of poor wetting by
Since dispersion in the vehicle is difficult, it is difficult to obtain a magnetic recording medium having a smooth surface.

Therefore, the amount of carbon black added to the magnetic recording layer is as small as possible.
Even if it is less than 6 parts by weight, it is strongly required that the light transmittance is small enough.

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. 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 value of the magnetic recording medium to about 10 ¹⁰ Ω / sq or less. It has been conventionally used to add carbon black fine particle powder.

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 a bulky powder which 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 the magnetic particle powder itself is improved by containing Fe ²⁺ by weight% or more (Japanese Unexamined Patent Publication (Kokai) No. 3-1).
02617).

[0012]

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

That is, 6.0% by weight of the above-mentioned known Fe ²⁺ is used.
The magnetic recording medium obtained using the needle-shaped cobalt-coated magnetic iron oxide particle powder containing the above as the magnetic particle powder, because the blackness of the magnetic particle powder is still insufficient, as shown in the comparative examples below. It was difficult to say that the light transmittance was sufficiently small and the surface electric resistance value was sufficiently low. Since the magnetic particles contain Fe ²⁺ , the dispersibility in the vehicle is reduced, and it is difficult to obtain a magnetic recording layer having a smooth surface.

Therefore, according to the present invention, even if the amount of carbon black added to the magnetic recording layer is made as small as possible, the light transmittance is small, the surface electric resistance is low, and the surface is smooth. It is a technical object to obtain a magnetic particle powder from which a magnetic recording medium can be obtained.

[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 an organosilane compound formed from alkoxysilane, and the organosilane compound coating is coated with carbon having an average particle diameter of 0.002 to 0.05 μm. Average major axis diameter 0.051 to which black fine particle powder adheres
0.72 μm acicular black composite magnetic particle powder, wherein the carbon black fine particle powder is the acicular magnetic particle powder 1
A needle-like black composite magnetic particle powder for a magnetic recording medium, which is attached at a ratio of 0.5 to 10 parts by weight with respect to 00 parts by weight, and aluminum as a lower layer on the particle surface of the needle-like magnetic particle powder. One or more selected from hydroxides, aluminum oxides, silicon hydroxides and silicon oxides, and coated with an organosilane compound formed from alkoxysilane as an upper layer, Average particle size 0.002 to organosilane compound coating
Acicular black composite magnetic particle powder having an average major axis diameter of 0.051 to 0.72 μm to which 0.05 μm carbon black fine particle powder is adhered, wherein the carbon black fine particle powder is 100% by weight of the acicular magnetic particle powder 0.5 per part
A needle-like black composite magnetic particle powder for a magnetic recording medium, a non-magnetic support, a magnetic particle powder and a binder resin formed on the non-magnetic support, wherein the powder is attached at a ratio of 10 to 10 parts by weight. A magnetic recording medium comprising a magnetic recording layer comprising: a magnetic recording medium, 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.
An organosilane compound formed from an alkoxysilane is coated, and an average major axis diameter of 0.051 to 0 .0 to which carbon black fine particles having an average particle diameter of 0.002 to 0.05 µm is attached to the organosilane compound coating. 72
μm needle-shaped black composite magnetic particle powder.

The acicular magnetic particle powder as 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 belt oxide compound which is an intermediate oxide between maghemite and magnetite,
Co, Al, other than Fe,
Ni, P, Zn, Si, magnetic iron oxide particles containing different elements such as B, magnetic iron oxide particles or the above-mentioned magnetic iron oxide particles containing different elements containing cobalt or cobalt Particle powder coated with iron or the like (hereinafter, referred to as “needle-shaped cobalt-coated magnetic iron oxide particle powder”), needle-shaped metal magnetic particles containing iron as a main component, and Co, Al, Ni other than iron, Needle-like iron alloy magnetic particles containing P, Zn, Si, B, rare earth metals 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 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 0.7 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 coarse particles, and when this is used to form a magnetic recording layer,
The surface smoothness of the coating film is easily impaired. The average major axis diameter is 0.
When the particle diameter is less than 05 μm, aggregation tends to occur due to an increase in intermolecular force due to finer particles. Therefore, uniform coating treatment of the needle-like magnetic particle powder on the particle surface with alkoxysilane and uniform adhesion of the carbon black fine particle powder. Processing 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 the uniform coating treatment with the alkoxysilane and the uniform adhesion treatment with the carbon black fine particle powder on the surface of the acicular magnetic particle powder are required. It will be difficult.
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 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 value is 1.01, and a value less than 1.01 is difficult to obtain industrially.

The BET specific surface area of the acicular magnetic particle powder is 1
5 to 150 m ² / g is preferable, and more preferably 20 to 150 m ² / g.
120 m ² / g, even more preferably 25-100 m 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 among 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 a uniform coating treatment of the particle surface of the acicular magnetic particle powder with alkoxysilane is performed. It becomes difficult to perform a uniform adhesion treatment using carbon black fine particle powder.

The blackness of the needle-shaped magnetic particles usually has a lower limit of L ^* value of more than 18.0 and an upper limit of 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 of the acicular magnetic particles 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 acicular iron oxide magnetic particle powder, the coercive force value is 250 to 500 Oe.
Is preferably 300 to 500 Oe, and the saturation magnetization value is preferably 60 to 90 emu / g, more preferably 65 to 90 emu / g. In the case of acicular cobalt-coated iron oxide magnetic particles, Magnetic force value is 500 ~
1700 Oe is preferred, and more preferably 550-17.
00 Oe, and the saturation magnetization is 60 to 90 emu / g.
And more preferably 65 to 90 emu / g. In the case of acicular metal magnetic particles and acicular iron alloy magnetic particles containing iron as a main component, the coercive force value is 800 to 3500 Oe.
Is preferably 900 to 3500 Oe, and the saturation magnetization value is preferably 90 to 170 emu / g, and more preferably 100 to 170 emu / 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 which is the core particle powder, and are similar to the core particle powder. It has a morphology and 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 21~130m ² / g, even more preferably from 26 to 1
10 m ² / g. BET specific surface area value of 16 m ² / g
If less than, the acicular black composite magnetic particles powder is coarse or particles that have been sintered between particles,
When a magnetic recording layer is formed by using this, the surface smoothness of the coating film tends to be impaired. BET specific surface area value of 160
If it exceeds m ² / g, aggregation tends to occur due to an increase in intermolecular force due to finer particles, so that the dispersibility in a vehicle at the time of producing a magnetic paint is reduced.

The 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, the lightness increases and the blackness is not sufficient. The lower limit of the blackness of the acicular black composite magnetic particle powder 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 ×
10 ⁶ Ω · cm. Volume specific resistance value is 1.0 × 10
If it exceeds ⁷ Ω · cm, it is difficult to sufficiently reduce the surface electric resistance of the obtained magnetic recording medium.

The desorption rate of the carbon black fine particles from the acicular black composite magnetic particles is preferably 20% or less, more preferably 10% or less. When the desorption rate of the carbon black fine particles exceeds 20%, uniform dispersion in the vehicle may be hindered by the detached carbon black fine particles 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 is preferably from 250 to 500 Oe.
More preferably, it is 300 to 500 Oe, and the saturation magnetization value is preferably 60 to 90 emu / g, more preferably 65 to 90 emu / g, and needle-like cobalt-coated iron oxide magnetic particle powder is used as the core particle powder. In this case, the coercive force value is preferably 500 to 1700 Oe, more preferably 5 to 1700 Oe.
50 to 1700 Oe, and the saturation magnetization value is 60 to 90
emu / g is preferable, and more preferably 65 to 90 em
In the case of using acicular metal magnetic particle powder and acicular iron alloy magnetic particle powder mainly composed of iron as the core particle powder, the coercive force value is preferably 800 to 3500 Oe, more preferably 900. -3500 Oe, and the saturation magnetization is preferably 90-170 emu / g, more preferably 100-170 emu / g.

The organosilane compound in the acicular black magnetic particle powder is produced from the alkoxysilane represented by the chemical formula 1 through a drying or heating step.

## STR1 ## R_aSix_4-a  R: -C₆H₅,-(CH₃)₂CHCH₂, -NC
_mH_{2m + 1}  X: -OCH₃, -OC₂H₅  m: an integer of 1 to 18 a: an integer of 0 to 3

As the alkoxysilane, specifically,
Methyltriethoxysilane, dimethyldiethoxysilane, tetraethoxysilane, phenyltriethoxysilane, diphenyldiethoxysilane, dimethyldimethoxysilane, methyltrimethoxysilane, tetramethoxysilane, phenyltrimethoxysilane, diphenyldimethoxysilane, isobutyltrimethoxysilane And decyltrimethoxysilane.

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

The coating amount of the organosilane compound generated from the alkoxysilane is preferably 0.02 to 5.0% by weight in terms of Si based on the powder of the organosilane compound-coated acicular magnetic particles. More preferably, 0.03 to
2.0% by weight, more preferably 0.05 to 1.5% by weight
It is.

When the amount is less than 0.02% by weight, the carbon black fine particles are sufficiently adhered to the surface of the needle-like magnetic particles so that the blackness of the obtained needle-like black composite magnetic particles can be improved. Have difficulty.

When the content exceeds 5.0% by weight, the carbon black fine particles can be sufficiently adhered to the surface of the acicular magnetic particles, but the blackness of the obtained acicular black composite magnetic particles is saturated. It does not make sense to coat more than necessary.

As the carbon black fine particles in the acicular black composite magnetic particles according to the present invention, commercially available furnace black, channel black and the like can be used. Specifically, # 3050, # 3150, # 325
0, # 3750, # 3950, MA100, MA7, #
1000, # 2400B, # 30, MA77, MA8,
# 650, MA11, # 50, # 52, # 45, # 22
00B, MA600, etc. (trade name: Mitsubishi Chemical Co., Ltd.) Seat 9H, Seat 7H, Seast 6, Seast 3H, Seast 300, Seast FM, etc. (trade name, Tokai Carbon Co., Ltd.) can be used. . Considering the affinity with the organosilane compound generated from the alkoxysilane, # 3150, # 3250, MA1
00, MA7, # 1000, # 2400B, and # 30 are preferable, and in consideration of conductivity, # 3150 and # 3
250 is more preferred.

The average particle size of the carbon black fine particles is 0.002 to 0.05 μm, more preferably 0.002 to 0.05 μm.
2 to 0.035 μm.

When the particle size is less than 0.002 μm, the carbon black fine particles become too fine, so that handling becomes difficult.

When the particle size exceeds 0.05 μm, the particle size of the carbon black fine particle powder becomes too large with respect to the particle size of the acicular magnetic particle powder, so that the adhesion strength to the organosilane compound coating formed from the alkoxysilane decreases. In some cases, the rate of desorption of the carbon black fine particles increases, and as a result, the dispersibility in the vehicle during the production of the magnetic paint may decrease.

The ratio between the average major axis diameter of the acicular magnetic particle powder and the average particle diameter of the carbon black fine particle powder is preferably 2 or more. If the particle size is smaller than 2, the particle size of the carbon black fine particle powder becomes too large with respect to the particle size of the acicular magnetic particle powder, so that the adhesion strength to the organosilane compound coating formed from the alkoxysilane becomes insufficient, and The desorption rate of the fine particle powder increases, and as a result, the dispersibility in the vehicle during the production of the magnetic paint may decrease.

The adhesion amount of the carbon black fine particles is
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, it is difficult to obtain acicular black composite magnetic particles having a sufficient degree of blackness because the amount of the carbon black fine particles attached is small.

When the amount exceeds 10 parts by weight, the obtained acicular black composite magnetic particle powder has a sufficient degree of blackness, but the amount of the carbon black fine particle powder attached is large.
The carbon black fine particle powder is likely to be 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 acicular black composite magnetic particle powder according to the present invention may be used, if necessary, in advance by treating the surface of the acicular magnetic particle powder with aluminum hydroxide, aluminum oxide, silicon hydroxide and silicon oxide. 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, SiO _2, or the sum of the Al conversion and SiO ₂ conversion. Is preferably 0.01 to 20% by weight.

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

If it exceeds 20% by weight, the effect of improving dispersibility in the vehicle during the production of the magnetic paint can be sufficiently obtained, but there is no point in covering more than necessary.

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 fine particle powder.

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, and a magnetic recording layer containing acicular black composite magnetic particles formed on the non-magnetic support and a binder resin.

Examples of the non-magnetic support include polyethylene terephthalate, polyethylene, polypropylene, polycarbonate, polyethylene naphthalate, polyamide, polyamide imide, which are widely used in magnetic recording media at present.
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.

Each of the binder resins has --OH, --COO
A polar group such as H, —SO ₃ M, —OPO ₂ M ₂ , and —NH ₂ (where M is H, Na, or K) may be included. Considering dispersibility of the acicular black complex magnetic particles, -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.

The particle size of the acicular black composite magnetic particles is large and the amount of the carbon black fine particles attached is large. In particular, 7 to 10 parts by weight of the carbon black fine particles are added to 100 parts by weight of the acicular magnetic particles. When the acicular black composite magnetic particle powder attached in parts by weight 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.

In the magnetic recording layer, lubricants, abrasives, antistatic agents and the like used in the production of ordinary magnetic recording media are required. If necessary, about 0.1 to 50 parts by weight with respect to 100 parts by weight of the binder resin. May be included.

The magnetic recording medium according to the present invention uses the acicular black magnetic particles according to the present invention, wherein acicular iron oxide magnetic particles not coated with aluminum hydroxide or the like are used as the magnetic particles. When the particle powder is used, the coercive force value is 250 to 500 Oe, preferably 300
５００500 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, glossiness of the coating film is 150 to 300%, preferably 160 to 300%, and coating film surface roughness Ra is 12.0 nm
Hereinafter, preferably 2.0 to 11.0 nm, more preferably 2.0 to 10.0 nm, Young's modulus is 124 to 160,
It is preferably 125 to 160, and the coating has a linear absorption coefficient of 1.3.
0 to 10.0 μm ⁻¹ , preferably 1.35 to 10.0
μm ⁻¹ , surface electric resistance value is 1.0 × 10 ¹⁰ Ω / sq
Or less, preferably 7.5 × 10 ⁹ Ω / sq or less, more preferably 5.0 × 10 ⁹ Ω / sq or less.

When the acicular black magnetic particle powder according to the present invention using the acicular cobalt-coated iron oxide magnetic particle powder not coated with aluminum hydroxide or the like as the core particle powder is used as the magnetic particle powder. Has a coercive force value of 5
00 to 1700 Oe, preferably 550 to 1700 O
e, the squareness ratio (residual magnetic flux density Br / saturated magnetic flux density Bm) is 0.85 to 0.95, preferably 0.86 to 0.95;
The glossiness of the coating film is 160 to 300%, preferably 165 to
300%, the coating film surface roughness Ra is 12.0 nm or less, preferably 2.0 to 11.0 nm, more preferably 2.0 to 11.0 nm.
10.0 nm, Young's modulus is 124-160, preferably 125-160, and the linear absorption coefficient of the coating film is 1.30-10.
0μm ^-1, preferably 1.35~10.0μm ^-1,
The surface electric resistance is 1.0 × 10 ¹⁰ Ω / sq or less, preferably 7.5 × 10 ⁹ Ω / sq or less, more preferably 5.0 × 10 ⁹ Ω / sq or less.

According to the present invention, as the magnetic particle powder, acicular metal magnetic particle powder or acicular iron alloy magnetic particle powder mainly composed of iron not coated with aluminum hydroxide or the like is used as the core particle powder. When the acicular black magnetic particle powder is used, the coercive force value is 800 to 3500 Oe, preferably 900 to 3500 Oe, and the squareness ratio (residual magnetic flux density Br / saturation magnetic flux density Bm) is 0.85 to 0.95, preferably. Is 0.86 to 0.95, and the glossiness of the coating film is 180 to 3
00%, preferably 190 to 300%, and the surface roughness R of the coating film
a is 12.0 nm or less, preferably 2.0 to 11.0 n
m, 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 , and the surface electric resistance value is 1.0
× 10 ¹⁰ Ω / sq or less, preferably 7.5 × 10 ⁹ Ω
/ Sq or less, more preferably 5.0 × 10 ⁹ Ω / sq or less.

When the acicular black magnetic particle powder according to the present invention using the acicular iron oxide magnetic particle powder coated with aluminum hydroxide or the like as the core particle powder as the magnetic particle powder, Coercive force value 250-500O
e, preferably 300 to 500 Oe, squareness ratio (residual magnetic flux density Br / saturated magnetic flux density Bm) of 0.85 to 0.95,
Preferably 0.86 to 0.95, the glossiness of the coating film is 155
-300%, preferably 165-300%, and the coating film surface roughness Ra is 11.0 nm or less, preferably 2.0-10.
0 nm, more preferably 2.0～9.0Nm, Young's modulus is 126 to 160, preferably 127 to 160, the linear absorption coefficient of the coating film 1.30~10.0μm ^{- 1,} preferably from 1.35 to 10 0.0 μm ⁻¹ , and the surface electric resistance value is 1.0
× ^{10 1 0} Ω / sq or less, preferably 7.5 × 10 ⁹ Ω
/ Sq or less, more preferably 5.0 × 10 ⁹ Ω / sq or less.

When the acicular black magnetic particle powder according to the present invention is used as the magnetic particle powder, wherein the acicular cobalt-coated iron oxide magnetic particle powder coated with aluminum hydroxide or the like is used as the core particle powder. Has a coercivity value of 50
0 to 1700 Oe, preferably 550 to 1700 Oe,
The 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 165 to 300%, preferably 170 to 30
0%, and the coating film surface roughness Ra is 11.0 nm or less, preferably 2.0 to 10.0 nm, more preferably 2.0 to 9.
0 nm, Young's modulus is 126 to 160, preferably 127
~ 160, linear absorption coefficient of coating film is 1.30 ~ 10.0μm
⁻¹ , preferably 1.35 to 10.0 μm ⁻¹ , and a surface electric resistance of 1.0 × 10 ¹⁰ Ω / sq or less, preferably 7.5 × 10 ⁹ Ω / sq or less, more preferably 5.0 or less. ×
It is 10 ⁹ Ω / sq or less.

According to the present invention, as the magnetic particle powder, an acicular metal magnetic particle powder or an acicular iron alloy magnetic particle powder containing iron as a main component and coated with an aluminum hydroxide or the like is used as the core particle powder. When the acicular black magnetic particle powder is used, the coercive force value is 800 to 3500 Oe, preferably 900 to 3500 Oe, and the squareness ratio (residual magnetic flux density B
r / 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 185 to 30.
0%, preferably 195 to 300%, coating film surface roughness Ra
Is 11.0 nm or less, preferably 2.0 to 10.0 n
m, more preferably 2.0 to 9.0 nm, and a Young's modulus of 1
26 to 160, preferably 127 to 160, and the coating film has a linear absorption coefficient of 1.40 to 10.0 μm ⁻¹ , preferably 1.
45 to 10.0 μm ⁻¹ , surface electric resistance value is 1.0 × 1
0 ¹⁰ Ω / sq or less, preferably 7.5 × 10 ⁹ Ω / s
q or less, more preferably 5.0 × 10 ⁹ Ω / sq or less.

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

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

The acicular maghemite particles can be obtained by heating and oxidizing the acicular magnetite particles in an oxidizing gas at a temperature 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.

The coating of the acicular magnetic particle powder with the alkoxysilane is carried out by mechanically mixing and stirring the acicular magnetic particle powder and the alkoxysilane solution or spraying the acicular magnetic particle powder with the alkoxysilane solution. What is necessary is just to mix and stir mechanically while doing. Almost all of the added alkoxysilane is coated on the particle surface of the acicular magnetic particle powder.

In order to uniformly coat the surface of the acicular magnetic particle powder with the alkoxysilane, it is preferable to disintegrate the agglomerated acicular magnetic particle powder in advance using a pulverizer. As a device for mixing and stirring, an edge runner and a Henschel mixer can be used.

The conditions during mixing and stirring may be appropriately adjusted such as the amount ratio, the linear load, the stirring speed, and the mixing and stirring time so that the alkoxysilane is coated on the surface of the acicular magnetic particle powder as uniformly as possible. The processing time is preferably 20 minutes or more.

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 purging and processing inert gas such as N ₂ in.

The addition amount of the alkoxysilane is preferably from 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 sufficiently attach the carbon black fine particles to such an extent that the blackness and the volume resistivity can be improved. If it exceeds 45 parts by weight, the carbon black fine particles can be sufficiently adhered, but there is no point in adding more than necessary.

After coating the surface of the acicular magnetic particle powder with the alkoxysilane, the carbon black fine particle powder is added, followed by mixing and stirring to adhere the carbon black fine particle powder to the alkoxysilane coating, followed by drying or heat treatment. I do.

The carbon black fine particle powder is preferably added little by little over time, especially over about 5 to 60 minutes.

The conditions during mixing and stirring may be appropriately adjusted such as the amount ratio, the linear load, the stirring speed, and the mixing and stirring time so that the carbon black fine particles adhere uniformly. The processing time is 20 minutes or more. preferable.

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 the carbon black fine particles attached is insufficient, and thus 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 the amount of carbon black fine particles attached is large, so that carbon black fine particles may be removed from the particle surface. The powder is easily detached, and as a result, the dispersibility in the vehicle during the production of the magnetic paint decreases.

The heating temperature in the drying or heating step is usually preferably from 40 to 200 ° C., more preferably from 60 to 1 ° C.
The temperature is 50 ° C., and the treatment time is preferably 10 minutes to 12 hours, more preferably 30 minutes to 3 hours. The alkoxysilane becomes an organosilane compound by this drying or heating step.

If necessary, prior to mixing and stirring with the alkoxysilane solution, the acicular magnetic particle powder is first treated with an aluminum hydroxide, an aluminum oxide, and a silicon water. It may be coated with one or more compounds selected from oxides and oxides of silicon.

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, alkali aluminates such as sodium aluminate, alumina sol and the like 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 nonmagnetic support, forming a coating film, and then 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.

[0104]

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 this 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 shown by a value measured by the BET method.

The amount of Al, the amount of Si and the amount of Co existing 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 organosilane compound generated from the alkoxysilane coated on the acicular black composite magnetic particle powder are described in “Fluorescent X-ray Analyzer 3
063M type ”(manufactured by Rigaku Denki Kogyo Co., Ltd.)
It was measured in accordance with IS K0119 “General rules for X-ray fluorescence analysis”.

The Fe ²⁺ content in the acicular magnetic particle powder is as follows:
The values were determined by the following chemical analysis methods.

That is, under an inert gas atmosphere, phosphoric acid and sulfuric acid are mixed in a ratio of 2: 1 with respect 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 adhering to the acicular black composite magnetic particles was determined by 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 acicular magnetic particles and the acicular black composite magnetic particles was 0.5 g for the sample and 1.5 cc 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 coated on a cast-coated paper using a 6-mil applicator (coating thickness: about 30 μm). And a multi-light source spectrophotometer MSC-I
The measurement was performed using S-2D (manufactured by Suga Test Instruments Co., Ltd.), and indicated by the color index L ^* according to JIS Z 8729.

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

The volume specific resistance value 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). Pressure molding was performed at a pressure of 140 kg / cm ² to produce 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).・ C
m) was determined.

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

The desorption rate (%) of the carbon black fine particles 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 amount of carbon black fine particle powder detached 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 acicular black composite magnetic particle powder and the detached carbon black fine particle powder. did. The needle-shaped black composite magnetic particle powder was dried at 100 ° C. for 1 hour, and the “Horiba Metal Carbon / Sulfur Analyzer EM” described above was used.
The carbon amount was measured using "IA-2200 type" (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 fine particles attached to acicular black composite magnetic particles We: Amount of carbon black fine particles attached to acicular black composite magnetic particles 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 surface of the coating film 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 over a magnetic field of 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: film thickness of magnetic recording layer (μm)

The surface electric resistance 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 wide metal electrode to a 6.5 mm wide metal electrode.
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.

Each thickness of the non-magnetic support and the magnetic recording layer constituting the magnetic recording medium was measured as follows.

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.
Of an acicular cobalt-coated magnetite particle containing 2.21% by weight of cobalt with respect to the magnetic particle powder and 15.8% by weight of Fe ²⁺ with respect to the magnetic particle powder as shown in an electron micrograph (× 30000) (average) Major axis diameter 0.278μm,
Average short 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
Cm, coercivity 686 Oe, saturation magnetization 79.1 em
u / g) 20 kg of pure water 1
The slurry was passed through 50 liters using a stirrer and passed through a “TK pipeline homomixer” (product name, manufactured by Tokushu Kika Kogyo Co., Ltd.) three times to obtain a slurry containing acicular cobalt-coated magnetite particles.

Next, the slurry containing the acicular cobalt-coated magnetite particle powder was applied 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.

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, 220 g of methyltriethoxysilane
Is mixed with 200 ml of ethanol, and a methyltriethoxysilane solution obtained is added to the needle-like cobalt-coated magnetite particle powder in which the agglomeration of the particles has been loosened while operating the edge runner, and a linear load of 30 kg / cm is applied. Mixing and stirring were performed for 20 minutes.

Next, the electron micrograph of FIG. 2 (× 3000)
0) (particle shape: granular, average 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 the mixture was further mixed and stirred at a linear load of 30 kg / cm for 30 minutes to attach the carbon black fine particle powder to the methyltriethoxysilane coating.

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. This acicular black composite magnetic particle powder had an average major axis diameter of 0.279 μm, an average minor axis diameter of 0.0335 μm, and an axial ratio of 8.3, as shown in the electron micrograph (× 30000) of FIG. Was. The geometric standard deviation value is 1.38, and the BET specific surface area value is 33.2 m.
² / g, blackness L ^* value is 19.5, volume resistivity value is 5.2 × 10 ⁴ Ω · cm, desorption rate of carbon black fine particles is 6.8%, coercive force value is 672 Oe, saturation magnetization The value was 77.3 emu / g, and the coating amount of methyltriethoxysilane was 0.31% by weight in terms of Si. From the electron micrograph shown in FIG. 3, almost no carbon black fine particle powder was observed, indicating that almost all of the carbon black fine particle powder was attached to the organosilane compound coating generated from methyltriethoxysilane. Was.

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

<Manufacture of Magnetic Recording Medium> 12 g of the acicular black composite magnetic particles obtained above and an abrasive (trade name: AK)
P-30, manufactured by Sumitomo Chemical Co., Ltd.) 1.2 g, carbon black (trade name: # 2400B, manufactured by Mitsubishi Kasei Corporation)
0.06 g, binder resin solution (vinyl chloride-vinyl acetate copolymer resin having sodium sulfonate group 30% by weight
And cyclohexanone) and cyclohexanone were mixed to obtain a mixture (solid content: 78%), and the mixture was further kneaded with a plastmill for 30 minutes to obtain a kneaded product.

The kneaded material was placed in a 140 ml glass bottle for 1.5 times.
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 resulting magnetic paint had a paint viscosity of 2,304.
cP.

The obtained magnetic coating material 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 0.5 inch width to obtain a magnetic tape. The thickness of the magnetic recording layer was 3.5 μm.

The obtained magnetic tape had a coercive force value of 733.
Oe, squareness ratio (Br / Bm) 0.89, glossiness 17
2%, surface roughness Ra of 7.8 nm, Young's modulus (relative value)
Was 138, the linear absorption coefficient was 1.48 cm ⁻¹ , and the surface electric resistance was 1.3 × 10 ⁸ Ω / sq.

[0147]

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 surface of any one of the acicular magnetic particle powders coated with at least one compound is coated with an organosilane compound generated from alkoxysilane, and the organosilane compound coating has an average particle diameter of 0.002. ~ 0.0
Acicular black composite magnetic particle powder having an average particle diameter of 0.051 to 0.72 μm to which 5 μm carbon black fine particle powder is adhered, wherein the carbon black fine particle powder is based on 100 parts by weight of the acicular magnetic particle powder. 0.5-1
The acicular black composite magnetic particle powder attached at a ratio of 0 parts by weight has excellent dispersibility in a vehicle due to a small amount of carbon black fine particle powder detached from the particle surface, and has high blackness. It is the fact that it has a low volume resistivity.

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 fine particles powder uniformly and densely adhered to the surface of the acicular magnetic particles. This is considered to be because the color of the core particle powder is canceled by the above, and the original color of the carbon black fine particle powder is exhibited.

Regarding the reason why the acicular black composite magnetic particle powder according to the present invention has a low volume resistivity, the present inventor concluded that carbon black fine particles having excellent conductivity were formed on the surface of the acicular black composite magnetic particle powder. It is considered that the powder was able to be uniformly and densely attached.

Regarding the reason why the carbon black fine particles desorbed from the particle surface of the acicular black composite magnetic particles according to the present invention is so small, the present inventor has argued that the carbon black fine particles contained in the inside or the surface of the acicular magnetic particles were not contained. A metallosiloxane bond (≡Si—OM (where M is an integer) between a metal element such as Si, Al, and Fe and an alkoxy group of the alkoxysilane to which the carbon black fine particle powder is attached.
Is a metal atom contained in iron-based black particles such as Si, Al, and Fe. It is considered that the formation of)) causes the organosilane compound to which the carbon black fine particles are adhered to be strongly bonded to the particle surface of the magnetic iron oxide particles.

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 considers that the acicular black composite magnetic particle powder has Dispersion in the system is not hindered by the carbon black fine particle powder due to the small amount of carbon black fine particles to be detached, and the carbon black fine particle powder adheres to the particle surface of the acicular magnetic particle powder. It is considered that irregularities are generated on the surface and contact between particles is suppressed.

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 can be obtained by reducing the amount of carbon black in the magnetic recording layer as much as possible. This is the fact that the light transmittance is small, the surface electric resistance value 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 reported that carbon black fine particle powder which usually behaves as an aggregate due to the fact that it is a fine particle is used in the present invention. In the case of the acicular black composite magnetic particles according to the present invention, the particles are uniformly and densely adhered to the particle surface of the acicular magnetic particles, so that they exist in a state of being dispersed to near primary particles, I believe that each is functioning more effectively.

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.

[0156]

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 above embodiment of the present invention. Was.

Table 1 shows the properties of the acicular magnetic particles.

[0159]

[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 in which agglomeration of core particles 1 was disentangled and 150 l of water. 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 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 acicular cobalt-coated maghemite particles powder) 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 acicular cobalt-coated maghemite particles having a particle surface coated with aluminum hydroxide.

Table 2 shows the main production conditions at this time, and Table 3 shows the properties of the obtained acicular cobalt-coated maghemite particles coated with aluminum hydroxide on the surface of the particles.

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

[0163]

[Table 2]

[0164]

[Table 3]

Core Particles 7 to 10 Surface-treated needle-like magnetic particle powders were obtained in the same manner as for 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 processing conditions at this time are shown in Table 2, and various properties of the obtained surface-treated needle-like magnetic particles are shown in Table 3.

Examples 1 to 10, Comparative Examples 1 to 5 Types of core particle powder, presence / absence, type and amount of alkoxysilane in coating step with organosilane compound,
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. The needle-shaped black composite magnetic particles obtained in each of Examples 1 to 10 showed almost no carbon black particles as a result of electron microscopic observation. It was confirmed that it adhered to the organosilane compound coating generated from the above.

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.

[0170]

[Table 4]

[0171]

[Table 5]

[0172]

[Table 6]

Electron micrograph (× 3000) of the surface-treated spindle-shaped cobalt-coated maghemite particles of core particles 7
FIG. 5 is an electron micrograph (× 30) of the spindle-shaped black composite magnetic particle powder of Example 7 obtained by using the surface-treated spindle-shaped cobalt-coated maghemite particles powder of the core particles 7.
000) is shown in FIG.

For reference, without coating with methyltrimethoxysilane, the surface-treated spindle-shaped cobalt-coated maghemite particles of the core particles 7 and the carbon black particles were obtained by mixing and stirring with an edge runner. FIG. 7 shows an electron micrograph (× 30000) of the treated particles obtained.
Shown in As shown in the electron micrograph of FIG. 7, it was confirmed that the carbon black fine particle powder did not adhere to the surface of the surface-treated spindle-shaped cobalt-coated maghemite particle powder, and that both particle powders were mixed separately. Was done.

<Manufacture of Magnetic Recording Medium> Examples 11 to 23 and Comparative Examples 6 to 20 Embodiments of the invention described above, except that the type of the acicular magnetic particles and the amount of the carbon black particles added were variously changed. A magnetic recording medium was obtained in the same manner as described above.

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

[0177]

[Table 7]

[0178]

[Table 8]

[0179]

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 particles have excellent blackness and low volume resistivity, and Low surface electrical resistance, and
Since the surface is smooth due to the fact that the amount of carbon black added to the magnetic recording layer can be reduced as much as possible and the dispersibility of the acicular black magnetic particle powder itself is improved, the magnetic recording for high density recording is performed. It is preferable as a 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.

[0182]

[Brief description of the drawings]

[0183]

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.

[0184]

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).

[0185]

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).

[0186]

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.

[0187]

FIG. 5 is an electron micrograph (× 30000) showing a particle structure of a surface-treated spindle-shaped cobalt-coated maghemite particle powder obtained by core particles 7;

[0188]

FIG. 6 is an electron micrograph (× 30000) showing the particle structure of the spindle-shaped black composite magnetic particles obtained in Example 7.
It is.

[0189]

FIG. 7 is an electron micrograph (×) showing a particle structure of a mixed powder of a surface-treated spindle-shaped cobalt-coated maghemite particle powder and a carbon black fine particle powder shown for comparison.
30,000).

 ──────────────────────────────────────────────────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 (3)

[Claims] An organosilane compound formed from alkoxysilane is coated on the particle surface of a needle-shaped magnetic particle powder, and the organosilane compound coating has an average particle diameter of 0.1 μm.
A needle-like black composite magnetic particle powder having an average major axis diameter of 0.051 to 0.72 μm to which carbon black fine particle powder of 002 to 0.05 μm is attached, wherein the carbon black fine particle powder is the needle-like magnetic particle powder A needle-shaped black composite magnetic particle powder for a magnetic recording medium, wherein the powder is attached at a ratio of 0.5 to 10 parts by weight with respect to 100 parts by weight. 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. An organosilane compound generated from alkoxysilane is coated as an upper layer, and the organosilane compound coating has an average particle size of 0.002 to 0.002.
Acicular black composite magnetic particle powder having an average major axis diameter of 0.051 to 0.72 μm to which 0.05 μm carbon black fine particle powder is adhered, wherein the carbon black fine particle powder is 100% by weight of the acicular magnetic particle powder 0.5 per part
A needle-shaped black composite magnetic particle powder for a magnetic recording medium, wherein the powder is attached at a ratio of 10 to 10 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.