JPH06111281A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a magnetic recording medium having excellent surface properties and electromagnetic conversion characteristics. CONSTITUTION:A magnetic layer is formed on a nonmagnetic base through a nonmagnetic layer containing nonstructural carbon having a mean particle size of 10-50nm, a specific surface area of 150m<2>/g or less by a BET method, and a DBP oil absorption of 100ml/100g or less. The nonmagnetic layer has a weight ratio of nonstructural carbon/resin binder of 100/50-100/25. The nonmagnetic layer is formed of coating solution containing nonstructural carbon of 10-20wt.%. The nonmagnetic layer, the magnetic layer are coated by a wet- on-wet coating method.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coating type magnetic recording medium.

[0002]

2. Description of the Related Art In magnetic recording media represented by high-performance audio cassette tapes, various video tapes, DAT, various magnetic disks and the like, there is a strong demand for higher recording density.

In order to realize this, it has been proposed to use metal magnetic powder using magnetic metal or hexagonal plate-shaped barium ferrite powder as the magnetic powder material, which has been put to practical use.

On the other hand, in order to increase the recording density, it is necessary to consider the thickness loss and self-demagnetization loss of the medium. From this viewpoint, it is desired to make the magnetic layer thinner.

However, when the magnetic layer is thinned, the surface properties of the support are reflected on the surface of the magnetic layer, and the electromagnetic conversion characteristics are deteriorated. Therefore, conventionally, it has been proposed to provide a non-magnetic layer using, for example, a thermosetting resin as a binder on the surface of the support, and to provide the magnetic layer via the non-magnetic layer.

However, such a non-magnetic layer has problems such as insufficient durability.

Further, when the non-magnetic layer and the magnetic layer are coated, a method is employed in which the non-magnetic layer is once coated, dried and then formed to form the magnetic layer. In some cases, the surface property of the non-magnetic layer may deteriorate the surface property of the magnetic layer.

From the above, Japanese Patent Laid-Open No. 63-191
Nos. 315 and 63-191318, a non-magnetic lower layer in which a non-magnetic powder is dispersed in a thermoplastic resin binder is applied, and the lower layer and the magnetic layer are wetted with a coating solution for each layer. So-called wet coating
It is disclosed that it is provided by an on-wet method.

The nonmagnetic powder used in the examples is α-Fe ₂ O ₃ , which is considered to be needle-shaped.

It is also described that this improves electromagnetic conversion characteristics, durability and head wear.

However, in magnetic recording media such as digital recording type video tapes and floppy disks (FD), thinning of the magnetic layer is required more and more in accordance with higher recording density, and therefore disclosed in the above publication. Even if such a non-magnetic layer is used, the surface properties of the medium surface are not sufficient, and further improvement is desired.

[0012]

SUMMARY OF THE INVENTION The main object of the present invention is to provide a magnetic recording medium having excellent surface properties and good electromagnetic conversion characteristics.

[0013]

Such an object is achieved by the following constitutions (1) to (4). (1) In a magnetic recording medium having a magnetic layer containing a magnetic powder and a resin binder on a non-magnetic support via a non-magnetic layer, the non-magnetic layer has an average particle size of 10 to 60 nm.
With a BET specific surface area of 150 m ² / g or less, DB
The non-magnetic carbon having a P oil absorption of 100 ml / 100 g or less is contained, and the non-magnetic layer and the magnetic layer are applied by a wet-on-wet method. A coating solution containing structural carbon and a resin binder, (non-structural carbon / resin binder) having a weight ratio of 100/50 to 100/25, and a non-structural carbon content of 10 to 20 wt%. A magnetic recording medium formed by using. (2) The non-structural carbon has a BET specific surface area of 20 to 150 m ² / g and a DBP oil absorption of 20.
The magnetic recording medium according to the above (1), which is -100 ml / 100 g. (3) The magnetic recording medium according to (1) or (2), wherein the magnetic layer has a thickness of 2.5 μm or less. (4) The magnetic recording medium according to any one of (1) to (3), wherein the magnetic powder contained in the magnetic layer is an oxide magnetic powder or a metal magnetic powder.

[0014]

Specific Structure The specific structure of the present invention will be described in detail below.

The magnetic recording medium of the present invention has a magnetic layer formed on a non-magnetic support via a non-magnetic layer.

This non-magnetic layer has an average particle size of 10 to 60 n.
m, preferably 15 to 40 nm and having a BET specific surface area of 150 m ² / g or less, preferably ²⁰ to 150 m ² / g, more preferably 25 to 150 m ² / g, particularly preferably 60.
~ 150m ² / g, DBP oil absorption is 100ml / 100g or less,
It further preferably contains 20 to 100 ml / 100 g, particularly preferably 30 to 80 ml / 100 g of non-structural carbon.

The non-structural carbon generally means an undeveloped structure.

By using such non-structured carbon, high dispersibility can be obtained and the carbon filling rate in the non-magnetic layer can be increased. Therefore, the surface property of the non-magnetic layer itself is improved, and the surface property of the magnetic layer is improved, and the effect of the present invention is achieved.

Conventionally, when carbon is used as an undercoat, carbon has been mainly used for the purpose of antistatic effect, and generally, structural carbon has been developed, and structural carbon excellent in conductivity is mainly used. . Structural carbon generally means a specific surface area of 140 to 15 by the BET method.
00m ² / g, DBP oil absorption amount is in the range of 100 to 400 ml / 100g.

With such structured carbon, a coating film having a good surface property can be obtained by selecting carbon having a small particle size, but since the specific surface area and the DBP oil absorption are large, a highly filled coating material should be used. It is difficult to prepare, and it is not particularly suitable for coating the magnetic layer by the wet-on-wet method described later.

Therefore, the effect of the present invention is obtained only by using so-called non-structural carbon having the above-mentioned characteristics, and is not obtained by using so-called structural carbon.

The average particle size of the non-structured carbon is set within the above range because the surface property is deteriorated when the average particle size exceeds 60 nm and the dispersibility is deteriorated when the average particle size is less than 10 nm. This is because the surface property is also deteriorated.

The average particle size is determined by a transmission electron microscope (T
It may be determined by EM) observation.

When the specific surface area exceeds 150 m ² / g,
Since it becomes difficult to disperse carbon and it is difficult to prepare a high filling amount, it becomes difficult to apply the magnetic layer particularly when the magnetic layer is applied by a wet-on-wet method described later.

Even if the DBP oil absorption exceeds 100 ml / 100 g, the same thing can be said as in the case of the specific surface area. However, when the specific surface area and the DBP oil absorption are small, the surface properties are poor in both cases.

There are no particular restrictions on the properties other than the above-mentioned properties of the non-structured carbon, such as shape, pH and volatile matter.

As the non-structural carbon of the present invention, a commercially available product may be used as it is.
5B, MA8B, # 45L, # 52B, CF9B [all manufactured by Mitsubishi Kasei Co., Ltd.] and the like.

Further, in the present invention, the non-magnetic layer contains the above-mentioned non-structural carbon and the resin binder, but the ratio of the non-structural carbon and the resin is a weight ratio, and the non-structural carbon is not. / Resin = 100 / 50-100 /
25, and the amount of non-structural carbon in the coating solution may be appropriately determined depending on the affinity with the magnetic layer coated on the non-magnetic layer, the handleability, etc., and is usually 10 to 20 wt.
It is about%.

When the amount of carbon is less than the above range, it becomes difficult to apply the magnetic layer by the wet-on-wet method described later. When the amount exceeds the above range, the viscosity is too high and the application is difficult. become.

A resin may be used as the binder of the non-magnetic layer, and may be an electron beam curable resin, a thermoplastic resin, a thermosetting or reactive resin, or a mixture thereof, and the film strength obtained. Therefore, it is preferable to use a thermosetting resin or an electron beam curable resin.

As the thermosetting resin, for example, vinyl chloride-vinyl acetate (including carboxylic acid-containing), vinyl chloride-
Vinyl alcohol-vinyl acetate (including carboxylic acid-containing), vinyl chloride-vinylidene chloride, chlorinated vinyl chloride, vinyl chloride-acrylonitrile, vinyl butyral, vinyl formal, and other vinyl copolymer resins and cross-linking agent mixtures, polyurethane resins A mixture of a fibrous resin such as polyester resin, nitrocellulose, and cellulose acetobutyrate and a crosslinking agent, a mixture of a synthetic rubber such as butadiene-acrylonitrile and a crosslinking agent, and a mixture thereof are preferable. These are -SO ₃ M, -
COOM, -N (R) ₂ , -N (R) ₃ (where M represents a monovalent metal such as H or Na, and R represents a hydrogen atom or a monovalent hydrocarbon group such as an alkyl group). ) Or the like. Furthermore, phenol resin, epoxy resin, urea resin, butyral resin, formal resin, melamine resin, alkyd resin, silicone resin,
Acrylic reaction resin, polyamide resin, epoxy-polyamide resin, polycondensation resin such as urea-formaldehyde resin or a mixture of high molecular weight polyester resin and isocyanate prepolymer, mixture of methacrylate copolymer and diisocyanate prepolymer, polyester polyol And a polyisocyanate, a mixture of low molecular weight glycol / high molecular weight diol / triphenylmethane triisocyanate, and the like, and a mixture of the above-mentioned polycondensation resin and a crosslinking agent such as an isocyanate compound.

As the cross-linking agent for curing the binder resin, various polyisocyanates, especially diisocyanate, can be used, and particularly tolylene diisocyanate,
One or more of hexamethylene diisocyanate and methylene diisocyanate are preferable. Crosslinking agent content is resin 1
It is preferably 10 to 30 parts by weight with respect to 00 parts by weight. In order to cure such a thermosetting resin, generally, it may be heated at 50 to 70 ° C. for 12 to 48 hours in a heating oven.

As the binder, a binder obtained by curing an electron beam curable compound, that is, a binder using an electron beam curable resin is also suitable. Specific examples of the electron beam-curable compound include acrylic double bonds such as acrylic acid, methacrylic acid, or their ester compounds showing an unsaturated double bond having radical polymerizability, and an allyl series such as diallyl phthalate. It is a resin in which a group of a double bond, an unsaturated bond such as maleic acid or a maleic acid derivative, which is crosslinked by electron beam irradiation or polymerized and dried is contained or introduced in the molecule of the thermoplastic resin. In addition, any compound having an unsaturated double bond that undergoes cross-linking polymerization by electron beam irradiation can be used.

Examples of thermoplastic resins that can be modified into electron beam curable resins include vinyl chloride copolymers, vinyl chloride-vinyl acetate, vinyl alcohol copolymers, vinyl chloride-
Examples thereof include acrylic copolymers, saturated polyester epoxy resins, phenoxy resins, and fibrin derivatives. These may be subjected to acrylic modification by a known method.

The dry film thickness of the non-magnetic layer is 0.5 μm.
Or more, preferably 1.0 μm or more. When the film thickness is too small, the surface property of the non-magnetic support is reflected on the surface of the non-magnetic layer, which in turn deteriorates the surface of the magnetic layer and deteriorates the electromagnetic conversion characteristics. However, if the film thickness is too large, the thickness loss becomes large, which makes it unsuitable for high-density recording. Therefore, the upper limit is preferably about 2.5 μm.

The non-magnetic layer in the present invention is formed by using a coating solution containing a resin or the like in which non-structural carbon is dispersed.

In this case, the solvent used is not particularly limited, and various solvents such as a ketone system such as cyclohexanone and isophorone, an alcohol system such as isopropyl alcohol and butyl alcohol, a cellosolve system such as ethyl cellosolve and cellosolve acetate, and an aromatic system such as toluene. The solvent may be selected according to the purpose.

On the other hand, the magnetic layer coated on the non-magnetic layer is
It contains a magnetic powder and a binder.

The magnetic powder in this case is γ-Fe ₂
O _3, Co-containing _{γ-Fe 2 O 3, Fe} 3 O 4, Co -containing Fe ₃ O _4, CrO _2, barium ferrite, and oxide magnetic powder such as strontium ferrite, Fe, C
Metals such as o and Ni, alloy fine powders thereof, iron carbide and the like can be mentioned.

These magnetic powders may be appropriately selected according to the type of medium to be applied, but barium ferrite, metal or alloy, iron carbide and the like are preferable. Further, these magnetic powders may be used alone or in combination of two or more kinds. As the iron carbide magnetic powder, those whose surface is mainly carbon and / or iron carbide are preferable. Further, as the metal magnetic powder, a powder containing iron as a main component and further containing a rare earth element containing Y is also preferable. Furthermore, iron nitride may be partially included.

Further, magnetic powder subjected to hot isostatic pressing (HIP) may be used. The metal or alloy magnetic powder includes a part (surface etc.) of carbide or nitride.

The binder used for the magnetic layer may be the same as the binder used for the non-magnetic layer, and it is also preferable to use the same binder resin for both layers.

The content of the magnetic powder in the magnetic layer is 5% of the total.
The content is 0 to 85 wt%, preferably 55 to 75 wt%.

The dry film thickness of the magnetic layer is 2.5 μm or less, preferably 0.15 to 1.5 μm. High recording density can be realized with such a film thickness.

If necessary, the magnetic layer may contain various additives such as inorganic fine particles and lubricants.

The magnetic layer is formed by using a magnetic paint. The solvent used at this time may be the same as that for forming the non-magnetic layer.

The content of the magnetic powder in the magnetic paint is 10 to 10.
50 wt%, preferably 15-45 wt%.

In the present invention, after the magnetic layer is formed,
It is preferable to apply a magnetic field to orient the magnetic particles in the layer. The orientation direction may be the longitudinal direction, the vertical direction, or the licking direction with respect to the running direction of the medium.

The non-magnetic support used in the magnetic recording medium of the present invention is not particularly limited, and a material selected from various flexible materials and various rigid materials according to the purpose is prescribed in tape form according to various standards. The shape and size may be used. For example,
Examples of the flexible material include polyester such as polyethylene terephthalate.

In the present invention, the nonmagnetic layer and the magnetic layer are preferably applied by a so-called wet-on-wet method. This is because the surface property can be remarkably improved. However, it may be applied by a wet-on-dry method in some cases because it is advantageous for application work because it is not affected by the physical properties of the magnetic paint.

In the wet-on-wet system, a non-magnetic layer is applied and then the next magnetic layer is applied in a wet state where this layer is not dried. The dry method is one in which a non-magnetic layer is once applied, dried and then the magnetic layer is applied.

Among these, in the wet-on-wet system, the non-magnetic layer may be applied and then the magnetic layer may be applied, or both layers may be applied simultaneously.

The coater used in such a coating method is not particularly limited, but for example, JP-A-63-191315,
The one disclosed in Japanese Patent Laid-Open No. 63-191318 can be used.

In this case, one having a plurality of coating ports or one having a plurality of coater heads may be used.

In such a wet-on-wet coating method, the non-magnetic layer may be formed before the magnetic layer is formed, or both layers may be formed at the same time.

The magnetic recording medium of the present invention may be provided with a back coat layer or the like, if necessary. Further, not only one having a magnetic layer on one side but also one having a magnetic layer on both sides may be used.

The magnetic recording medium of the present invention is preferably used for a digital recording type video tape, floppy disk or the like.

In the digital recording method, the shortest recording wavelength is 0.3 to 1.5 μm, and the recording depth of the medium at this time is 0.15 to 0.75 μm. It is known that good output, resolution and overwrite characteristics can be obtained by making the film thickness of the magnetic layer the same as the medium recording depth at the shortest recording wavelength.

Of these, the film thickness of the magnetic layer when used as a video tape is often as thin as 0.15 to 0.3 μm, and the magnetic powder at this time is mainly metal powder.

The film thickness of the magnetic layer in the case of a floppy disk is 0.30 to 1.00 μm, and barium ferrite powder is mainly used as the magnetic powder at this time.

[0061]

EXAMPLES The present invention will be specifically described below with reference to examples. Example 1 Preparation of Magnetic Paint A magnetic paint was prepared with the following composition.

Magnetic paint Fe-Zn-Ni alloy 100 parts by weight Vinyl chloride-vinyl acetate copolymer 10 parts by weight Polyester polyurethane 10 parts by weight Polyisocyanate 4 parts by weight Stearic acid (industrial) 2 parts by weight Butyl stearate (industrial ) 2 parts by weight Methyl ethyl ketone / cyclohexanone / toluene (= 35/35/30) Suitable amount

Preparation of coating solution for non-magnetic layer (non-magnetic paint) Non-magnetic paint No. 1 # 45BZ (manufactured by Mitsubishi Kasei Co., Ltd.) [Average particle size 24 nm, BET 137 m ² / g, DBP oil absorption 53 ml / 100 g, pH 8] 100 parts by weight Vinyl chloride-vinyl acetate copolymer 20 parts by weight Polyester polyurethane 20 parts by weight Polyisocyanate 8 parts by weight Methyl ethyl ketone / cyclohexanone / toluene (= 35/35/30) 519 parts by weight

In the non-magnetic coating material No. 1, as shown in Tables 1 and 2, carbon-containing non-magnetic coating materials No. 2 to No.
15 was prepared. The carbons used are all manufactured by Mitsubishi Kasei. The non-magnetic paint No. is the sample No.
Is the same as.

The above magnetic coating material and non-magnetic coating material were applied onto a non-magnetic substrate made of polyethylene terephthalate having a thickness of 8 μm by the extrusion type simultaneous multilayer coating method and dried. At this time, a sample in which only the non-magnetic layer was applied was also prepared, and the glossiness and surface roughness (JISB
Ra) according to 0601 was also confirmed.

For samples coated with magnetic paint,
Further, calendar processing was performed to obtain a magnetic recording tape.
As mentioned above, sample N depends on the non-magnetic paint used.
o. 1 to No. 15 In addition, Sample No. 16 was obtained in the same manner as in Sample No. 1, except that the coating method was the wet-on-dry method.

The film thicknesses of the non-magnetic layer and the magnetic layer in these tape samples were respectively
It was set to 2.0 μm and 0.2 μm.

The glossiness and surface roughness of these tape samples were examined in the same manner as above. The output and C / N ratio were examined as follows.

(1) RF. Video Sensitivity The video sensitivity of 7 MHz measured with an amorphous head was obtained and evaluated.

(2) C / N C / N, which is the ratio of noise to RF at a distance of 0.3 and 1.0 MHz from 7 MHz, was obtained and evaluated.

The results are shown in Tables 1 and 2.

[0072]

[Table 1]

[0073]

[Table 2]

[0074]

According to the present invention, the surface property is excellent and the electromagnetic conversion characteristics are good.

[Procedure amendment]

[Submission date] October 4, 1993

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] 0027

[Correction method] Change

[Correction content]

As the non-structural carbon of the present invention, a commercially available product may be used as it is.
5B, MA8B, # 45L, # 52B, CF9B (all manufactured by Mitsubishi Kasei Co., Ltd.) and Raven 1060 (made by Colombian carbon).

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Akira Saito 1-13-1 Nihonbashi, Chuo-ku, Tokyo TDK Corporation (72) Inventor Yuko Mogi 1-13-1 Nihonbashi, Chuo-ku, Tokyo TDC Co., Ltd. (72) Inventor ▲ Muwa, Takayoshi Shima 13-1, Nihonbashi, Chuo-ku, Tokyo TDC Corporation

Claims (4)

[Claims] 1. A magnetic recording medium having a magnetic layer containing a magnetic powder and a resin binder on a non-magnetic support via a non-magnetic layer, wherein the non-magnetic layer has an average particle diameter of 10 to 60 nm. , BET specific surface area of 150 m ² / g or less, DBP oil absorption of 10
Containing non-structural carbon is 0ml / 100g or less, the non-magnetic layer and the magnetic layer is applied by a wet-on-wet method, the non-magnetic layer, the non-structural carbon and Containing a resin binder, (non-structural carbon / resin binder) in a weight ratio of 100/50 to 1
00/25 and the content of non-structural carbon is 10 to
A magnetic recording medium formed using a coating solution of 20 wt%. 2. The magnetic recording medium according to claim 1, wherein the non-structural carbon has a specific surface area according to the BET method of ²⁰ to 150 m ² / g and a DBP oil absorption of 20 to 100 ml / 100 g. 3. The magnetic recording medium according to claim 1, wherein the magnetic layer has a thickness of 2.5 μm or less. 4. The magnetic recording medium according to claim 1, wherein the magnetic powder contained in the magnetic layer is an oxide magnetic powder or a metal magnetic powder.