JPH11126325A - Magnetic record medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic record medium having good electromagnetic conversion characteristics for high-density recording and excellent travelling stability and durability. SOLUTION: This magnetic record medium is produced by forming an intermediate layer containing at least a magnetic powder/or nonmagnetic powder and a binder and forming a magnetic layer as the outermost layer containing at least a ferromagnetic metal powder, binder and nonmagnetic inorg. powder in this order on a nonmagnetic supporting body. In such a case, the specific surface area of the ferromagnetic metal powder is >=50 m<2> /g. The nonmagnetic inorg. powder contains alumina. The alumina is present as primary particles and particle groups of aggregation of plural particles after the coating film is formed. When the average particle size of the primary particle size is expressed by (d), the average particle size of the particle groups is 1.2 d to 10 d, and the abundance ratio of the primary particles to particle groups ranges 1:1 to 10:1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium of a multilayer coating type, and more particularly to a magnetic recording medium in which the presence of an abrasive on the surface of a coating film is improved.

[0002]

2. Description of the Related Art In recent years,
Magnetic recording media are required to have high recording density as well as miniaturization, and attempts have been made to reduce the size of magnetic powder in order to meet the demand. However, along with this, there is a problem that the hardness of the coating film is reduced, and the surface of the coating film is smoothed and the friction coefficient is increased. In addition, as the recording density increases, the relative speed between the recording / reproducing head and the medium tends to increase, and a higher level of durability of the medium is required.

With respect to the running durability of a magnetic recording medium, a ferromagnetic fine powder, a binder, and the like are used for the purpose of improving the surface coating hardness of a magnetic recording layer and reducing the surface friction coefficient between the medium and a magnetic recording head or a guide roll. It is widely known that containing a non-magnetic abrasive together with an abrasive, and that specifying the particle size, shape, hardness, etc., is effective for durability, and various abrasives have been proposed. .

In order to improve the recording density, the reproduction output is stabilized, the reproduction output is increased, the reproduction noise is reduced, etc. by super-smoothing the surface of the magnetic recording medium. In addition, the relative speed between the recording / reproducing head and the medium has also become faster due to the need to increase the speed of writing and reading to the magnetic recording medium, and to reduce the shortest recording wavelength, in order to prevent wear of the recording / reproducing head. Hardening of the recording / reproducing head material is progressing.

[0005] Further, as an improvement in the medium, the running durability has been improved by increasing the amount of the non-magnetic abrasive added, or increasing the particle diameter of the abrasive. However, the above method reduces the surface smoothness of the medium, resulting in a decrease in recording / reproducing output. For this reason, in addition to abrasives, lubricants and the like are added and used to improve running durability.However, if a sufficient amount of lubricant is added, the filling property of the magnetic recording layer is reduced and the output is reduced. Decrease. Further, the magnetic coating film may be softened due to a plasticizing effect by adding a lubricant to the coating film, which may cause abrasion of the coating film in running durability.

That is, if the abrasive is reduced in particle size, a coating film having excellent surface smoothness and excellent electromagnetic conversion characteristics can be obtained, but sufficient characteristics in running durability and friction coefficient cannot be obtained. Also, by increasing the particle size of the abrasive, good characteristics can be obtained in terms of running durability, but the electromagnetic conversion characteristics are deteriorated due to head wear and a decrease in surface smoothness. In the prior art, one of the characteristics has to be sacrificed for the above problem, and it is difficult to balance the characteristics, and sufficient characteristics have not been obtained.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a magnetic recording medium having excellent electromagnetic conversion characteristics for high-density recording and excellent running stability and durability.

[0008]

Means for Solving the Problems As a result of repeated studies, the present inventors have achieved the above object by causing alumina particles having a fixed average particle size to coexist with primary alumina particles in a magnetic layer. I knew that I could get it.

The present invention has been made on the basis of the above findings. An intermediate layer containing at least a magnetic powder and / or a nonmagnetic powder and a binder on a nonmagnetic support, a ferromagnetic metal powder, a binder and In a magnetic recording medium comprising, in this order, a magnetic layer as an outermost layer containing at least a nonmagnetic inorganic powder, the ferromagnetic metal powder has a specific surface area of 50 m
² / g or more, and contains alumina as the nonmagnetic inorganic powder, and the alumina exists as a group of particles obtained by assembling primary particles and a plurality of particles after the coating film is formed, and the average particle diameter of the primary particles is d. When the average particle size of the particle group is 1.2
d to 10d, and an abundance ratio between the primary particles and the particle group is in the range of 1: 1 to 10: 1.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail.
The magnetic recording medium of the present invention is provided with an intermediate layer containing at least a magnetic powder and / or a nonmagnetic powder and a binder on a nonmagnetic support, on which a ferromagnetic metal powder, a binder and a nonmagnetic inorganic powder are provided. It is provided with a magnetic layer as an uppermost layer including at least. Further, a back coat layer is provided on the back surface of the nonmagnetic support as necessary. Further, in the magnetic recording medium of the present invention, in addition to the non-magnetic support, the intermediate layer, the magnetic layer and the back coat layer, a primer further provided between the non-magnetic support and the intermediate layer or the back coat layer Layers,
Another layer such as another magnetic layer provided for recording a servo signal or the like corresponding to a hard system using a long wavelength signal may be provided.

First, the magnetic layer will be described. The magnetic layer is usually the uppermost layer of the magnetic recording medium, that is, a layer existing on the surface of the magnetic recording medium.
It contains at least a binder and a nonmagnetic inorganic powder. This magnetic layer can be formed using a magnetic paint containing ferromagnetic metal powder, a binder, a non-magnetic inorganic powder and a solvent as main components.

In the present invention, the ferromagnetic powder contained in the magnetic layer has a specific surface area (S _BET ) of 50 m ² / g or more, preferably 50 m ² / g, in order to achieve high density recording.
７０70 m ² / g, more preferably 52 to 65 m ² / g
It is.

The ferromagnetic metal powder contained in the magnetic paint used for forming the magnetic layer has a metal content of 50%.
% Or more, and 60% by weight or more of the metal component is iron. Specific examples of the ferromagnetic metal powder include, for example, Fe, Fe-Co, Fe-Ni,
Fe-Al, Fe-Ni-Al, Fe-Co-Ni, F
Powders of alloys such as e-Ni-Al-Zn and Fe-Al-Si are given.

In the above ferromagnetic metal powder mainly composed of iron,
The shape must be needle-like. The major axis length is preferably 0.05 to 0.25 μm, and more preferably 0.05 to 0.2 μm. The preferred needle ratio is 2 to 20, and the preferred particle size is 130 to 250 ° as measured by an X-ray method.

The coercive force of the ferromagnetic metal powder is 120 to
It is preferably 210 kA / m, especially 125 to 2 kA / m.
It is preferably 00 kA / m. Within the above range, the RF output in all wavelength regions can be obtained without excess and deficiency, and the overwrite characteristics are also good.

The saturation magnetization of the ferromagnetic metal powder is
It is preferable that it is 100-180 Am < ² > / kg, and it is especially preferable that it is 110-160 Am < ² > / kg.
Within the above range, a sufficient reproduction output can be obtained.

Further, the ferromagnetic metal powder contained in the magnetic paint used for forming the magnetic layer may contain a rare earth element or a transition metal element as required.

In the present invention, the ferromagnetic metal powder may be subjected to a surface treatment in order to improve the dispersibility and the like of the ferromagnetic metal powder. The above-mentioned surface treatment is referred to as “Characteriza
tion of Powder Surfaces "(Academic Press), and the like.
For example, a method of coating the surface of the above ferromagnetic metal powder with an inorganic oxide is described, and can be suitably employed. At this time, as the inorganic oxide that can be used, Al ₂ O ₃ , SiO ₂ , TiO ₂ , ZrO ₂ , S
Examples thereof include nO ₂ , Sb ₂ O ₃ , and ZnO. These may be used alone or in combination of two or more. The surface treatment can be performed by an organic treatment such as a silane coupling treatment, a titanium coupling treatment, and an aluminum coupling treatment, in addition to the above-described methods.

The magnetic paint for forming the magnetic layer contains a non-magnetic inorganic powder. As such a non-magnetic inorganic powder, the same non-magnetic inorganic powder as used in the intermediate layer described later is used, and specific examples thereof include alumina and carbon black. The mixing ratio of these non-magnetic inorganic powders is 0.5 to 100 parts by weight of the ferromagnetic metal powder.
It is preferably from 50 to 50 parts by weight, more preferably from 1 to 20 parts by weight.

As the non-magnetic inorganic powder, alumina as an abrasive is used. The alumina is present as a particle group in which primary particles and a plurality of particles are aggregated after forming a coating film, and the average particle diameter of the particle group is 1.2d to 10d when the average particle diameter of the primary particles is d. It is necessary to be. In addition, the ratio of the primary particles to the particle group is 1: 1.
To 10: 1, preferably 2: 1 to 8: 1.

In the present invention, alumina consisting of a group of primary particles and a plurality of particles is intentionally made to exist on the surface of the coating film, and the particle size ratio and the existence ratio are defined. When (S _BET ) is used in combination with a ferromagnetic powder of 50 m ² / g or more, good electromagnetic conversion characteristics and running durability can be obtained. Since the primary particles and the particle group are present, the contact area with the magnetic head is equal to that of the case where two types of alumina having different particle diameters are included, but the contact points are increased, so that the running durability is excellent. Further, the aggregate state of the particle groups spreads in the coating direction, and the ratio in the depth direction is extremely low. On the other hand, in the case of including alumina having a primary particle diameter the same as the alumina particle group in the present invention, the area occupied by alumina also increases in the depth direction, so that the occupation amount of the ferromagnetic powder decreases, Hinder the transformation. Also, since the calendering property is poor, it is difficult to obtain good surface smoothness. On the other hand, according to the present invention, the calendering property is excellent, the surface property can be easily controlled, a smoother surface can be obtained, the output is high, and the electromagnetic conversion characteristics are excellent.

However, when the particle size of the particle group exceeds 10 times the particle size of the primary particles, or when the abundance ratio of the particle group increases, noise increases and output decreases, resulting in good electromagnetic conversion characteristics. Not only will it not be obtained, but the wear of the head will increase and the running durability will deteriorate. Also, if the particle size of the particle group is less than 1.2 times the primary particle size or the abundance ratio is too low, the effect is weakened and the desired characteristics cannot be obtained.

In order to obtain the particle diameter and the abundance ratio of the particle group, for example, after sufficiently dispersing alumina together with the ferromagnetic metal powder in the paint dispersion step, the coating step is carried out after the final preparation of the paint. By controlling the time and storage conditions.

Specific storage conditions include, for example, stirring at about 5 to 10 rpm after the final preparation of the paint. At this time 10r
If the stirring is performed at a rotation speed exceeding pm, it is difficult to form particles. In addition, the magnetic powder aggregates in the stationary state. The time until the coating step is optimally in the range of 2 to 5 hours, and the particle size and the abundance ratio of the particle group can be controlled within the time within the range.

The mixing ratio of the alumina is preferably 2 to 20 parts by weight, more preferably 5 to 15 parts by weight, based on 100 parts by weight of the ferromagnetic metal powder.

Carbon black is also preferably used as the nonmagnetic inorganic powder. The carbon black desirably has an average particle diameter of less than 1/2 of the average primary particle diameter of the alumina. If the average particle size of the carbon black is at least の of the average primary particle size of the alumina, the surface smoothness deteriorates, and good electromagnetic conversion characteristics cannot be obtained. The primary particles of alumina preferably have a particle size of 0.05 to 0.8 μm, particularly 0.1 to 0.5 μm.

Examples of such carbon black include furnace for rubber, thermal for rubber, black for color,
Examples thereof include acetylene black and ketchen black, and details thereof are described in “Carbon Black Handbook” (edited by Carbon Black Association). The amount of the carbon black is preferably from 0.1 to 10 parts by weight, more preferably from 0.2 to 5 parts by weight, based on 100 parts by weight of the ferromagnetic metal powder. The carbon black preferably has an average primary particle size of 10 to 100 nm, particularly preferably 20 to 60 nm.

The binder used in the magnetic coating material for forming the magnetic layer includes a thermoplastic resin, a thermosetting resin,
And a reactive resin. When used, they can be used alone or in combination. Specific examples of the binder include vinyl chloride resins, polyesters, polyurethanes, nitrocellulose, epoxy resins, and the like. In addition, JP-A-57-162128, page 2, upper right column, line 19 , Page 2, lower right column, line 19, and the like. Further, the binder may contain a polar group for improving dispersibility and the like.

The compounding ratio of the binder is preferably 5 to 200 parts by weight, more preferably 5 to 70 parts by weight, based on 100 parts by weight of the ferromagnetic metal powder.

Solvents contained in the magnetic paint used for the magnetic layer include ketone solvents, ester solvents, ether solvents, aromatic hydrocarbon solvents and chlorinated hydrocarbon solvents. Specifically, the solvents described on page 3, lower right column, line 17 to page 4, lower left column, line 10 of JP-A-57-162128 can be used. The mixing ratio of the solvent is preferably 80 to 500 parts by weight, more preferably 100 to 350 parts by weight, based on 100 parts by weight of the ferromagnetic metal powder.

The magnetic coating material used for forming the magnetic layer may be formed of a general material such as a lubricant, an abrasive, a dispersant, an antistatic agent, a rust inhibitor, a fungicide, a fungicide, and a curing agent. Additives used in magnetic recording media can be added as needed. Specific examples of the additives include the above-mentioned JP-A-57-
No. 162128, page 6, lower left column, line 6 to page 2, lower right column, line 10 and page 3, lower left column, line 6 to page 3, upper right column first
Various additives described in line 8 and the like can be mentioned.

The thickness of the magnetic layer is preferably 0.4 μm or less, more preferably 0.05 to 0.4 μm. Within the above range, the balance between durability and output stability is excellent and preferable.

In order to prepare a magnetic paint, for example, the above-mentioned ferromagnetic metal powder, binder and non-magnetic inorganic powder are put into a Nauta mixer or the like together with a part of the solvent and premixed to obtain a mixture. The mixture is kneaded with a continuous pressure kneader or the like, then diluted with a part of the solvent, and dispersed using a sand mill or the like, and then mixed with additives such as a lubricant, filtered, and further cured. A method of mixing the remaining solvent can be used.

Next, the intermediate layer provided on the nonmagnetic support will be described. The intermediate layer is a layer containing at least a magnetic powder and / or a nonmagnetic powder and a binder, and may be a magnetic layer or a nonmagnetic layer. The intermediate layer is formed using a coating mainly composed of a magnetic powder and / or a non-magnetic powder, a binder and a solvent (hereinafter also referred to as an intermediate coating). The purpose of providing the intermediate layer is to improve magnetostatic characteristics and surface smoothness.

As the magnetic powder, a ferromagnetic powder is preferably used, and as the ferromagnetic powder, both a soft magnetic powder and a hard magnetic powder are preferably used. The kind of the soft magnetic powder is not particularly limited, but is preferably used for a so-called weak electric device such as a magnetic head or an electronic circuit. (Shokabo, 1984) Soft magnetic materials (soft magnetic materials) described on pages 368 to 376, and specifically, oxide soft magnetic powder can be used.

The coercive force of the oxide soft magnetic powder is usually 0.008 to 12.0 kA / m, and the saturation magnetization is usually 30 to 90 Am ² / kg. The coercive force of the metal soft magnetic powder is usually 0.0016 to 8.0 kA / m,
Saturation magnetization is usually 50~500Am ² / kg.

The shape of the soft magnetic powder is not particularly limited, but may be spherical, plate-like, needle-like or the like, and the size is preferably 5 to 800 nm.

As the hard magnetic powder, for example,
γ-Fe_TwoO_Three, Co-coated γ-Fe _TwoO_ThreeSuch as iron oxide
Magnetic powder, iron alone or ferromagnetic metal powder mainly composed of iron,
And hexagonal ferrite powder. Above strong magnetic
As the conductive metal powder, the one used for forming the magnetic layer was used.
The same one as described above is used.

The ferromagnetic metal powder mainly composed of iron oxide and iron is preferably in the shape of a needle or a spindle. And the major axis length is preferably 0.05 to
It is 0.25 μm, more preferably 0.05 to 0.2 μm. The preferred needle ratio is 3 to 20, the preferred particle size is 130 to 250 ° as measured by an X-ray method, and the preferred specific surface area is 30 to 70 m ² / g.

Further, as the hexagonal ferrite,
Barium ferrite and strontium ferrite in the form of microplates and part of their Fe atoms are Ti, Co,
Examples include magnetic powders substituted with atoms such as Ni, Zn, and V. The hexagonal ferrite powder has a preferable plate diameter of 0.02 to 0.09 μm, a preferable plate ratio of 2 to 7, and a preferable specific surface area of 30 to 60 m ² / m.
g.

The coercive force of the hard magnetic powder is 120 to 21.
0 kA / m, preferably 125 to 200
It is preferably kA / m. Within the above range, the RF output in all wavelength regions can be obtained without excess and deficiency, and the overwrite characteristics are also good.

Further, the saturation magnetization of the iron oxide magnetic powder and the ferromagnetic metal powder is preferably 100~180Am ² / kg, it is preferable that particularly 110~160Am ² / kg. The saturation magnetization of the hexagonal ferrite powder is preferably 30~70Am ² / kg, it is preferable that particularly 45~70Am ² / kg. Within the above range, a sufficient reproduction output can be obtained.

The nonmagnetic powder preferably has a Mohs hardness of 5 or more and an average particle size of 1.5 times or less the average particle size of the alumina particles in the magnetic layer. If the average particle size exceeds 1.5 times the average particle size of the alumina particles in the magnetic layer, the surface smoothness is poor, and good electromagnetic conversion characteristics cannot be obtained.

As such a non-magnetic powder, for example,
Graphite, titanium oxide, barium sulfate, zinc sulfide,
Magnesium carbonate, calcium carbonate, zinc oxide, calcium oxide, magnesium oxide, magnesium dioxide, tungsten disulfide, molybdenum disulfide, boron nitride, tin dioxide, silicon dioxide, nonmagnetic chromium oxide, alumina,
Silicon carbide, cerium oxide, corundum, artificial diamond, non-magnetic iron oxide, garnet, garnet, quartzite,
Examples include silicon nitride, molybdenum carbide, boron carbide, tungsten carbide, titanium carbide, diatomaceous earth, dolomite, and resinous powder. Among these, non-magnetic iron oxide,
Titanium oxide, alumina, silicon oxide, silicon nitride, boron nitride and the like are preferably used. These non-magnetic powders may be used alone or in combination of two or more.

The shape of the non-magnetic powder may be spherical, plate-like, needle-like, or amorphous. The size of the non-magnetic powder is 5 to 200 nm in the case of spherical, plate-like or amorphous. Preferably, the needle-shaped one has a major axis length of 20.
It is preferable that the needle ratio is 3 to 20 at ~ 300 nm.

The above magnetic powder or non-magnetic powder may contain a rare earth element or a transition element as necessary. Further, in order to improve the dispersibility and the like of the magnetic powder or the non-magnetic powder, the powder may be subjected to the same surface treatment as the ferromagnetic metal powder contained in the magnetic paint used for forming the magnetic layer. .

It is desirable that the above intermediate paint contains carbon black. As such carbon black, those similar to the carbon black used for the magnetic layer are used.

The binder and solvent contained in the intermediate paint are the same as the binder and solvent contained in the magnetic paint used for forming the magnetic layer. The mixing ratio of the binder is 1% of the magnetic powder and / or non-magnetic powder.
5 to 200 parts by weight, preferably 5 to 200 parts by weight,
~ 70 parts by weight is more preferred. The mixing ratio of the solvent is preferably 80 to 500 parts by weight, and more preferably 100 to 3 parts by weight, based on 100 parts by weight of the magnetic powder and / or nonmagnetic powder.
50 parts by weight are more preferred.

[0049] The above intermediate paint may, if necessary,
Additives that are added to the magnetic paint used to form the magnetic layer can be added.

The thickness of the intermediate layer is preferably 0.5 to 3 μm. Within the above range, sufficient bending rigidity can be obtained in the magnetic recording medium.

In order to prepare the intermediate coating, for example, the magnetic powder and / or the nonmagnetic powder and the binder are put into a Nauta mixer or the like together with a part of the solvent and premixed to obtain a mixture. The mixture is kneaded with a continuous pressure kneader or the like, then diluted with a part of the solvent, and dispersed using a sand mill or the like, and then mixed with additives such as a lubricant, filtered, and further cured. A method of mixing the remaining solvent can be used.

As the non-magnetic support used in the magnetic recording medium of the present invention, any known non-magnetic support can be used without any particular limitation. Specifically, a flexible film made of a polymer resin, Discs: Films, discs, cards, and the like made of nonmagnetic metals such as Cu, Al, and Zn, ceramics such as glass, porcelain, and ceramics can be used.

Examples of the polymer resin for forming a flexible film or disk include polyesters such as polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polycyclohexylene dimethylene terephthalate and polyethylene bisphenoxycarboxylate, polyethylene, polypropylene and the like. Polyolefins, cellulose derivatives such as cellulose acetate butyrate, cellulose acetate propionate, vinyl resins such as polyvinyl chloride and polyvinylidene chloride, or polyamides, polyimides, polycarbonates, polysulfones, polyether ether ketones, polyurethanes, etc. When used, they can be used alone or in combination of two or more.

In the magnetic recording medium of the present invention, the back coat layer provided on the back surface of the non-magnetic support as necessary can be formed using a known back coat paint without any particular limitation.

The magnetic recording medium of the present invention can be applied as a magnetic recording medium such as a magnetic tape such as an 8 mm video tape or a DAT tape or a floppy disk.

Next, an outline of a method for manufacturing a magnetic recording medium of the present invention will be described. First, an intermediate paint for forming the intermediate layer and a magnetic paint for forming the magnetic layer are prepared. Here, in order to set the particle size and the abundance ratio of the alumina particle group in the magnetic layer to a predetermined range,
In the dispersion step of the magnetic paint, after sufficiently dispersing the alumina together with the magnetic powder, the time and storage conditions from the final preparation of the paint to the coating step are controlled. The storage conditions are set by applying stirring at about 5 to 10 rpm after the final preparation of the paint, and the time until the coating step is 2 to 5 hours.

Next, an intermediate paint and a magnetic paint are simultaneously applied on a non-magnetic support by a wet-on-wet method so that the dry thicknesses of the intermediate layer and the magnetic layer become the above-mentioned thicknesses. And forming a coating film of the magnetic layer. That is, the magnetic layer is preferably applied and formed when the intermediate layer is wet. The coating speed at this time is 50-100.
It is desirable to set it to 0 m / sec.

Next, the obtained coating film is subjected to a magnetic field orientation treatment, followed by a drying treatment and winding. Thereafter, after performing a calendering treatment, a back coat layer is further formed as necessary. In some cases, the back coat layer may be formed before performing the calendering treatment, and thereafter, the magnetic layer and the back coat layer may be calendered together. Next, if necessary, for example, when obtaining a magnetic tape, aging treatment is performed at 40 to 70 ° C. for 3 to 72 hours, and slits are formed to have a desired width.

The above simultaneous multi-layer coating method is described in JP-A-5-73.
No. 883, column 42, line 31 to column 43, line 31, etc., which is a method of applying a magnetic paint for forming a magnetic layer before the intermediate paint for forming the intermediate layer dries. Since the interface between the intermediate layer and the magnetic layer is smooth and the surface properties of the magnetic layer are good, the dropout is small, high density recording is possible, and the coating film (intermediate layer and magnetic layer) is durable. A magnetic recording medium having excellent properties can be obtained.

The magnetic field orientation treatment is performed before the intermediate paint and the magnetic paint are dried. For example, when the magnetic recording medium of the present invention is a magnetic tape, the magnetic paint is applied in a direction parallel to the magnetic paint application surface. About 40 kA / m or more, preferably about 80 to
It can be performed by a method of applying a magnetic field of 800 kA / m, a method of passing an intermediate paint and a magnetic paint through a solenoid of 80 to 800 kA / m in a wet state, or the like.

The drying treatment can be performed, for example, by supplying a heated gas. At this time, the degree of drying of the coating film can be controlled by controlling the temperature of the gas and the amount of the supplied gas. As the drying conditions, for example, the temperature of hot air is set to 3
It is preferable that the temperature is 0 to 120 ° C., the wind speed is 5 to 35 m / sec, and the drying time is 1 to 60 seconds.

The calendering treatment can be performed by a super calendering method in which a metal roll and a cotton roll or a synthetic resin roll, a metal roll and a metal roll are passed between two rolls.

In the production of the magnetic recording medium of the present invention, a finishing step such as a polishing or cleaning step of the surface of the magnetic layer can be performed, if necessary. Further, the application of the intermediate paint and the magnetic paint can also be carried out by a generally known sequential multilayer coating method.

[0064]

EXAMPLES Hereinafter, the present invention will be specifically described based on examples and the like.

(Example 1) [Blending of paint] <Blending of intermediate paint> ・ 50 parts by weight of hexagonal ferromagnetic powder (coercive force: 138 kA / m, saturation magnetization: 75 Am ² / kg, plate diameter: 0.03 μm) , BET specific surface area: 39 m ² / g) ・ Acicular α-Fe ₂ O ₃ powder 50 parts by weight (major axis length: 0.15 μm) ・ Alumina powder (average particle diameter 0.3 μm) 5 parts by weight ・ Carbon black ( 5 parts by weight ・ Sulfonate group / epoxy group-containing vinyl chloride resin 15 parts by weight (sulfonic acid group content: 1.5 × 10 ⁻⁴ eq / g, epoxy group content: 3.5%) (GPC number average molecular weight: 17000)-2 parts by weight of butyl stearate-2 parts by weight of myristic acid-3 parts by weight of a polyisocyanate compound (trade name: Coronate L, manufactured by Nippon Polyurethane Industry Co., Ltd.)-Methyl ethyl keto 80 parts by weight Toluene 80 parts by weight Cyclohexanone 40 parts by weight

<Formulation of Magnetic Coating> 100 parts by weight of acicular ferromagnetic powder mainly composed of iron Fe: Al: Co: Ca (weight ratio) = 85: 4: 2: 8: 1 (coercive force: 145 kA / m, saturation magnetization: 136 Am ² / kg, BET specific surface area: 58 m ² / g, major axis length: 0.11 μm, X-ray particle size: 15 nm) 10 parts by weight of alumina powder (average particle size: 0.1 μm) 0.5 parts by weight of carbon black (average particle size: 30 nm) 15 parts by weight of sulfonic acid group / epoxy group-containing vinyl chloride resin (sulfonic acid group content: 1.5 × 10 ⁻⁴ eq / g, epoxy group content) : 3.5%, GPC number average molecular weight: 17000)-3 parts by weight of butyl stearate-2 parts by weight of myristic acid-3 parts by weight of polyisocyanate compound (trade name: Coronate L, manufactured by Nippon Polyurethane Industry Co., Ltd.) Ethyl ketone 120 parts Toluene 120 parts Cyclohexanone 50 parts by weight

[Preparation of Magnetic Recording Medium] A magnetic paint having the above composition and an intermediate paint were applied on a polyethylene terephthalate support having a thickness of 6 μm so that the thickness of the intermediate layer was 1.8 μm and the thickness of the magnetic layer was 0.3 μm. Simultaneous multilayer coating was performed with a die coater. Next, while the magnetic layer was changed from a wet state to a dry state, a magnetic field orientation treatment was performed using a 0.5 T solenoid. Further, in a drying oven, hot air of 80 ° C. was blown for 10 minutes.
The coating film was dried by spraying at a speed of m / min. After drying and calendering, it was slit into a width of 8 mm to obtain a magnetic recording medium. After the final adjustment of coating, stirring was performed at 5 to 10 rpm until coating (2 hr).

The measurement of the particle group diameter / primary particle diameter and their abundance ratio was carried out according to the following method. <Measurement method> A particle group in which a plurality of alumina particles were aggregated was examined with a secondary electron scanning microscope (SEM) on the coating film surface.
Observation was performed using photographs taken at a magnification of 0000 to 50,000. The primary particle diameter and the particle group particle diameter were measured based on the visual field diameter of the photograph. As for the particle group particle diameter, the diameter of the particle group in the major axis direction was defined as the particle group particle diameter. The abundance ratio between the primary particles and the particle group was similarly measured from this photograph.

(Examples 2 to 6) As the alumina of the magnetic layer, the average primary particle diameter was 0.1 μm, 0.2 μm or 0.1 μm.
3 μm each was blended, and the storage conditions and time from the final preparation of the paint to the coating process were adjusted, and the particle group particle size / primary particle size and their abundance ratio were changed as shown in Table 1. In the same manner as in Example 1, a magnetic recording medium was obtained.

Example 7 Example 1 was repeated except that alumina having an average primary particle diameter of 0.3 μm was additionally added, and the particle group particle diameter / primary particle diameter and their abundance ratio were changed as shown in Table 1. A magnetic recording medium was obtained in the same manner as described above.

(Comparative Examples 1 to 3) As the alumina of the magnetic layer, those having an average primary particle diameter of 0.1 μm or 0.3 μm, respectively, were blended. Was adjusted, and the magnetic recording medium was obtained in the same manner as in Example 1 except that the particle group particle diameter / primary particle diameter and their abundance ratio were changed as shown in Table 2.

(Comparative Example 4) An alumina having an average primary particle diameter of 0.2 μm and 0.6 μm was used in combination, and the particle diameter of the particle group /
A magnetic recording medium was obtained in the same manner as in Example 1, except that the primary particle diameter and the proportion of the primary particles were changed as shown in Table 2.

Comparative Example 5 An average primary particle diameter of 0.2 μm and an alumina having a diameter of 0.6 μm were combined and blended.
A magnetic recording medium was obtained in the same manner as in Example 1, except that the primary particle diameter and their abundance ratio were changed as shown in Table 2 and that titania having a particle diameter of 0.8 μm was used as the nonmagnetic powder of the intermediate layer. Was.

Comparative Example 6 Example 2 was repeated except that the magnetic layer had a particle size of 270 nm as carbon black.
A magnetic recording medium was obtained in the same manner as described above.

[Evaluation of Magnetic Recording Medium] With respect to the magnetic recording media obtained in Examples 1 to 7 and Comparative Examples 1 to 6,
The center line surface roughness (Ra), reproduction output, and durability were evaluated by the following methods. The results are shown in Tables 1 and 2, together with the particle group particle diameter / primary particle diameter of alumina and their abundance ratio.

<Center Line Surface Roughness (Ra)> Laser interference type surface roughness meter [Zygo, Laser Interf.
erometric Microscope Maxi
m 3D Model 5700] under the following conditions. Lens used: Fizeau 40x Remove: Cylinder Filter: off Sampling length: 180 nm Sampling number: 260

<Reproduction Output> A commercially available Hi8 deck was modified, a single wave of 9 Mhz was recorded, the output was measured with a spectrum analyzer, and the value of the magnetic tape of Comparative Example 1 was set to 1
The evaluation was made with an index of 00%.

<Durability (number of passes)> A commercially available Hi8 deck was modified, a single 9 MHz wave was recorded, and still durability was evaluated. The output was measured with an oscilloscope, and the initial output was set to 100%, and the number of passes up to 5% down was taken as durability.

[0079]

[Table 1]

[0080]

[Table 2]

As shown in Table 1, Examples 1 to 6
It can be seen that both the reproduction output and the durability are excellent. In addition, Example 7 has almost the same characteristics as Example 1, indicating that alumina having a different particle diameter may be mixed depending on the average particle diameter of alumina.

On the other hand, as shown in Table 2, Comparative Example 1
Indicates that the alumina particles are present in a low proportion and the reproduction output characteristics are excellent, but the durability is not sufficient. In Comparative Example 2, the reproduction output characteristics and durability were not sufficient because the abundance ratio of the particle groups was too high. In Comparative Example 3, it can be seen that the particle size of the particle group is large and the reproduction output and durability are not sufficient.

Comparative Example 4 contains alumina having different particle diameters and is almost the same as Example 3 by SEM observation, but it is found that the surface smoothness is poor and the reproduction output characteristics are not sufficient. In Comparative Example 5, the nonmagnetic powder in the intermediate layer had a particle diameter of 0.3.
Although 8 μm of titania was mixed, the content was more than 1.5 times that of the alumina particles in the magnetic layer, indicating that the surface smoothness was poor and the reproduction output was not sufficient. In Comparative Example 6, carbon black having a particle diameter of 270 nm was blended in the magnetic layer of Example 2, but the surface smoothness was poor and the reproduction output was not sufficient.

[0084]

As described above, the magnetic recording medium of the present invention has good electromagnetic conversion characteristics for high-density recording, and also has excellent running stability and durability.

Claims (3)

[Claims] 1. An intermediate layer containing at least a magnetic powder and / or a nonmagnetic powder and a binder and an outermost layer containing at least a ferromagnetic metal powder, a binder and a nonmagnetic inorganic powder on a nonmagnetic support. The ferromagnetic metal powder has a specific surface area of 50 m ² / g or more, contains alumina as the nonmagnetic inorganic powder, and forms a coating film on the magnetic recording medium. The primary particles and a plurality of particles later exist as a group of particles, and the average particle diameter of the particle group is 1.2d to 10d when the average particle diameter of the primary particles is d, and the primary particles A magnetic recording medium, wherein the abundance ratio between the particles and the particle group is in the range of 1: 1 to 10: 1. 2. The method according to claim 1, wherein the thickness of the magnetic layer is 0.4 μm or less, and the average particle diameter of the carbon black contained as the nonmagnetic inorganic powder is 1% of the average primary particle diameter of the alumina.
The magnetic recording medium according to claim 1, wherein the ratio is less than / 2. 3. The non-magnetic powder contained in the intermediate layer contains a non-magnetic powder having a Moh's hardness of 5 or more, and has an average particle size of 1.5 times the average particle size of the alumina particles in the magnetic layer.
3. The magnetic recording medium according to claim 1, wherein the ratio is not more than twice.