JPH07296365A - Magnetic recording medium and production thereof - Google Patents

Abstract

PURPOSE:To obtain a magnetic recording medium excellent in the electrode conversion characteristics by providing a magnetic support, a nonmagnetic layer formed thereon, and a magnetic layer formed on the nonmagnetic layer. CONSTITUTION:In the magnetic recording medium, a magnetic layer has a thickness d2 (after a magnetic paint is applied and dried) in the range of 0.05-1.5mum, preferably in the range of 0.05-1.2mum and more preferably in the range of 0.1-1mum. A nonmagnetic layer has a thickness d1 (after a nonmagnetic paint is applied and dried) in the range of 0.5-4mum, preferable in the range of 0.5-3.5mum and more preferable in the range of 0.5-3mum, and a magnetic body has a thickness d. in the range of 1-10mm, preferably in the range of 1-100mum, wherein a relationship d0>d2 is preferably satisfied.

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.

[0002]

BACKGROUND OF THE INVENTION Conventional magnetic recording media such as magnetic tapes have been obtained by applying a magnetic coating material onto a non-magnetic support. That is, it can be obtained by coating a non-magnetic support such as a polyester film with a magnetic coating material obtained by kneading a magnetic powder, a binder, other necessary additives, and a solvent, and drying.

In the field of magnetic tapes for VTRs and floppy disks, the demand for high density recording is increasing. And research has been actively conducted to answer such requests. For example, proposals have been made to improve coercive force and saturation magnetization. It has also been proposed to reduce the thickness of the magnetic layer. The technique proposed in Japanese Patent Laid-Open No. 62-92132 is known for reducing the thickness of the magnetic layer. In this technique, a magnetic coating liquid is applied to a running non-magnetic support to form a magnetic layer, and a magnetic layer is applied to the magnetic layer while the magnetic layer is still undried, and then the magnetic recording medium is dried. In the manufacturing method of 1., the magnetic layer is provided by simultaneous multi-layer coating together with a non-magnetic undercoat layer, and both layers are subjected to a magnetic field while they are undried.

According to this, it is said that the magnetic layer can be made thin and the degree of orientation can be improved. Further, a non-magnetic support containing a non-magnetic layer containing non-magnetic particles and a magnetic layer formed on the non-magnetic support is disclosed in, for example, JP-A-62-2.
The technique of Japanese Patent No. 14514 has been proposed. This publication proposes a magnetic recording medium having a nonmagnetic layer having a specific surface roughness and a magnetic layer formed on the nonmagnetic layer. Further, JP-A-62-231417 proposes a magnetic recording medium having a non-magnetic layer containing a lubricant and a magnetic layer containing a lubricant. In addition, JP-A-3-21
In Japanese Patent No. 4417 and Japanese Unexamined Patent Publication No. 3-214422,
A magnetic recording medium has been proposed in which a smooth non-magnetic layer is provided on a relatively inexpensive non-magnetic support having a poor surface state, and a magnetic layer is provided on the smooth non-magnetic layer. Further, Japanese Patent Application Laid-Open No. 5-73883 proposes a magnetic recording medium in which the interface state between the non-magnetic layer and the magnetic layer is defined.

However, there is an ever-increasing demand for higher density.

[0006]

DISCLOSURE OF THE INVENTION An object of the present invention is to provide a magnetic recording medium having an excellent squareness ratio. Another object of the present invention is to provide a magnetic recording medium having excellent output characteristics. An object of the present invention is to provide a magnetic recording medium comprising a magnetic support, a non-magnetic layer provided on the magnetic support, and a magnetic layer provided on the non-magnetic layer. To be achieved.

A method of manufacturing a magnetic recording medium comprising a magnetic support, a non-magnetic layer provided on the magnetic support, and a magnetic layer provided on the non-magnetic layer. ,
The magnetic layer is applied before drying the applied non-magnetic layer, which is achieved by a method of manufacturing a magnetic recording medium. In the present invention, the magnetic layer has a thickness d ₂ (thickness after applying the magnetic coating and drying) of 0.05 to 1.
5 μm, preferably 0.05 to 1.2 μm, more preferably 0.1 to 1 μm, and the thickness d ₁ of the non-magnetic layer (the thickness after applying the non-magnetic coating material and drying). ) Is 0.5 to 4 μm, preferably 0.5 to 3.5 μ
m, more preferably 0.5 to 3 μm, and the thickness d ₀ of the magnetic support is 1 μm to ₁₀ mm, preferably 1 to 100 μm, and d ₀ > d ₂ is preferable. . Here, it is preferable that the thickness of the magnetic layer or the non-magnetic layer is as described above, because the thinner the magnetic layer is, the higher the recording density can be supported.
If the thickness of the non-magnetic layer is too small, the provision of the non-magnetic layer has little meaning. Therefore, the thickness is preferably 0.5 μm or more. That is, considering the degree of orientation and the output characteristics, it is preferable that the thickness of the nonmagnetic layer is 0.5 μm or more.

The present invention is particularly applicable to a coating type magnetic recording medium. Of course, the present invention is not limited to this, but is generally applied to the case of a coating type. The magnetic layer may be of a single-layer type or a multi-layer type of two or more layers. When two or more layers are coated, it is preferable that the upper layer is provided before the lower layer is dried, as in simultaneous multi-layer coating.

A non-magnetic layer is provided between the magnetic support and the magnetic layer used for recording and reproduction. This non-magnetic layer is preferably provided on the magnetic support by means such as simultaneous multilayer coating. That is, the magnetic layer is preferably provided before the non-magnetic layer provided on the magnetic support is dried. This non-magnetic layer may not contain non-magnetic powder, but preferably contains non-magnetic powder.

In the magnetic recording medium of the type of magnetic support / non-magnetic layer / magnetic layer or magnetic support / magnetic layer / non-magnetic layer / magnetic layer as in the present invention, at least the uppermost magnetic layer is used. Layers are used for recording / playback. By the way, the support itself has magnetism. Therefore, it is possible to use this support itself for recording and reproduction depending on its magnetic characteristics. And while this is not something that is not actively excluded, magnetic recording media are usually used for recording and
It is not used for reproduction. Therefore, the magnetic characteristics of the uppermost magnetic layer are not required. From this, there is a high degree of freedom in selecting the magnetic material for forming the magnetic support.

The present invention will be described below. A technique for forming a support with a magnetic material is disclosed in JP-A-3-173.
It was proposed in Japanese Patent Publication No. 920. That is, in this publication, 20 magnetic particles having an average particle diameter of 0.05 to 10 μm are used.
Layer composed of a thermoplastic resin (A layer)
There has been proposed a magnetic recording medium comprising a base film having a magnetic field and a magnetic layer laminated on the A layer side of the base film. Here, the magnetic layer laminated on the A layer of the base film is for recording image signals, and the A layer of the base film is for recording audio signals. It is described that the base film may be composed of only the A layer. That is, there is disclosed a technical idea in which all of the magnetic recording medium including the support is composed of a magnetic layer, and the magnetic layer is entirely used as a recording layer.

Therefore, the present invention is also disclosed in Japanese Patent Laid-Open No. 17392/1993.
The technique disclosed in Japanese Patent Publication No. 0 seems to be similar in that the support is composed of a magnetic layer, but the basic position is different. That is, the present invention has a special structure in that the non-magnetic layer is provided between the magnetic support and the recording / reproducing magnetic layer. In this respect, the invention of the present application and the technology of Japanese Patent Laid-Open No. 3-173920 are completely different. Then, due to this difference, the characteristics such as the output are significantly different. That is, the technique disclosed in Japanese Patent Application Laid-Open No. 3-173920 has a feature that cannot be fully achieved, and a nonmagnetic layer is provided between the magnetic support and the recording / reproducing magnetic layer. The idea is not recognized in JP-A-3-173920.

Examples of the support in the present invention include a film in which magnetic powder is dispersed. As the magnetic powder to be dispersed, metal magnetic powder or oxide-based magnetic powder can be used. For example, γ-iron oxide, or C
γ − to which a divalent metal such as r, Mn, Co or Ni is added
Iron oxide, chromium dioxide, or Na, K, Fe, Mn
And the like, semiconductors such as P, and chromium dioxide to which oxides of these metals are added are used. In addition, barium ferrite in the form of a small flat plate and some of its Fe atoms are T
Magnetic powders substituted with atoms such as i, Co, Zn, and V can also be used. Furthermore, Fe-Co, Fe-N
i, Fe-Al, Fe-Ni-Al, Co-Ni, Fe
-Co-Ni, Fe-Ni-Al-Zn, Fe-Al-
Metal magnetic powder such as Si can also be used.

Then, the support of the present invention can be obtained by dispersing the magnetic powder having a size of 0.01 to 1 μm in the film at a ratio of about 1 to 90 wt%. Examples of the film include polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polycyclohexylene dimethylene terephthalate,
Polyesters such as polyethylene bisphenoxycarboxylate, polyolefins such as polyethylene and polypropylene, cellulose derivatives such as cellulose acetate butyrate and cellulose acetate propionate,
A vinyl resin such as polyvinyl chloride or polyvinylidene chloride, polyamide, polycarbonate or the like is used. Of course, it is not limited to these.

The magnetic support is obtained by kneading the above resin material with the magnetic powder in a molten or solution state and extruding this mixture using an extruder. Of course, the support may be a single layer having magnetism, and may be a composite layer such as a magnetic layer / nonmagnetic layer, a magnetic layer / nonmagnetic layer / magnetic layer or a nonmagnetic layer / magnetic layer / nonmagnetic layer. It may have a layered structure. After this extrusion molding, a stretching process or the like is performed if necessary. For example, biaxial stretching treatment may be performed in the longitudinal direction or the width direction. Further, various surface treatments are performed as necessary. For example, surface treatment by corona discharge or other appropriate means is performed in order to improve the adhesion with the coating film provided on the support. Further, polyester, polyurethane, oligomer or the like may be applied for improving the adhesiveness. That is, a usual treatment is performed as the support.

The thickness of the magnetic support depends on the application. For example, 1 to 100 μ when used in a film form
m (preferably 2 to 50 μm), and a thickness of 30 μm to 10 mm when used in a disk shape or a card shape.
A magnetic layer used for recording / reproduction is formed on the magnetic support as described above by a coating means. That is, the magnetic layer used for recording and reproduction is formed by applying the magnetic paint. As the magnetic powder used in this magnetic paint, ferromagnetic iron oxide, ferromagnetic chromium dioxide, ferromagnetic metal powder, etc. can be used. A divalent metal may be added to the ferromagnetic iron oxide. As the divalent metal, Cr, Mn,
There are Co, Ni and the like. As the ferromagnetic chromium dioxide, CrO ₂ and a metal such as Na, K, Fe, Mn, a semiconductor such as P, or an oxide of these metals added thereto can be used. The ferromagnetic metal powder has a metal content of 75% by weight or more, and 80% by weight or more of the metal content is at least one ferromagnetic metal (for example, Fe, Co, Ni). As the ferromagnetic metal powder, For example, Fe-Co, Fe-N
i, Fe-Al, Fe-Ni-Al, Co-Ni, Fe
-Co-Ni, Fe-Ni-Al-Zn, Fe-Al-
Si or the like. If necessary, rare earth elements and transition metal elements may be contained. Moreover, barium ferrite in the form of a small flat plate and a part of its Fe atoms are
Magnetic powders substituted with atoms such as Zn and V can also be used.

As the binder used in the magnetic paint,
A thermoplastic resin, a thermosetting resin, a reactive resin, or a mixture thereof can be used together. For example, vinyl chloride resin and the like can be mentioned. In addition, JP-A-57-
The resins described in Japanese Patent No. 162128 are listed. These binder resin components are used in an amount of about 5 to 100 parts by weight, preferably 10 to 30 parts by weight, based on 100 parts by weight of the magnetic powder.

As other components added to the magnetic paint, a dispersant, a lubricant, an abrasive, an antistatic agent, a rust preventive, a fungicide and the like may be added. For example, JP-A-57-162128
Various additives described in the publication may be added. As the solvent used for producing the magnetic paint, a ketone solvent, an ester solvent, an ether solvent, an aromatic hydrocarbon solvent, or a chlorinated hydrocarbon solvent can be appropriately selected and used. For example, various solvents described in JP-A-57-162128 can be used.

The magnetic powder, the binder and the like are kneaded to form a magnetic coating material. At the time of kneading, the magnetic powder and the above-mentioned components are all introduced into the kneading machine at the same time or individually. In kneading and dispersing the magnetic coating material, various kneading machines, for example, the kneading machine described in JP-A-57-162128 can be used. A nonmagnetic layer is provided between the magnetic support and the recording / reproducing magnetic layer.

Such a non-magnetic layer may be formed by applying a coating material containing a binder and a solvent as described in the section of the magnetic coating material. Further, a non-magnetic powder may be added, that is, a coating containing a non-magnetic powder, a binder and a solvent may be applied. Examples of the non-magnetic powder include carbon black, graphite, titanium oxide, barium sulfate, zinc sulfide, magnesium carbonate, calcium carbonate, zinc oxide, calcium oxide, magnesium oxide, tungsten disulfide, molybdenum disulfide, boron nitride, tin dioxide, and dioxide. Silicon, chromium oxide, alumina, silicon carbide, cerium oxide, corundum, artificial diamond, iron oxide,
Garnet, garnet, silica stone, silicon nitride, molybdenum carbide, boron carbide, tungsten carbide, titanium carbide, diatomaceous earth, dolomite, and other resin powders are used. Among these, carbon black, titanium oxide, barium sulfate, calcium carbonate, alumina and iron oxide are preferable. Moreover, these non-magnetic powders are S
It may be surface-treated with i or Al. The size of these non-magnetic powders is 0.001 to 3 μm, preferably 0.005 to 1 μm, and more preferably 0.005 to 0.
It is preferably 5 μm. And, these nonmagnetic powders are contained in the nonmagnetic layer in an amount of 5 to 99 wt%, preferably 30%.
˜95 wt%, and more preferably 50 to 95 wt%.

The magnetic layer and the lower non-magnetic layer are preferably provided by simultaneous multilayer coating. That is, it is preferable to employ simultaneous multilayer coating in which the magnetic layer is coated before the lower non-magnetic layer is dried. For this simultaneous multilayer coating, the means described in JP-A-5-73883 can be used. In addition, in the multi-layer coating by the wet-on-wet method, since the upper layer is applied in a wet state in the lower layer of the uppermost layer, the boundary surface becomes smooth and the surface property of the upper layer is also improved. Get better As a result, there are few dropouts, high density recording is possible, and the durability of the film is also excellent.

After the magnetic paint is applied, an orientation treatment is performed in the undried state. For example, in the case of a magnetic tape, an orientation treatment is performed in which a magnetic field of about 1000 G or more, preferably about 2000 to 10000 G is applied in a direction parallel to the coated surface. After this magnetic field action operation, for example, a drying operation is performed by supplying hot air heated to 30 to 120 ° C. The degree of drying of the magnetic coating film is controlled by controlling the temperature and the heat supply amount.

If necessary, the surface of the magnetic recording medium may be smoothed or cut into a desired shape to obtain a magnetic recording medium. For the calendering treatment of the magnetic coating film, a super calendering method in which two rolls such as a metal roll and a cotton roll, a synthetic resin roll, or a metal roll and a metal roll are used is used. If necessary, the surface of the magnetic layer is polished or cleaned, and the back coat layer is formed.

The present invention will be described below with reference to specific examples.

[0025]

【Example】

[Magnetic support A] Granules of polyethylene terephthalate having an intrinsic viscosity of 0.70 and acicular α-Fe magnetic powder are adjusted so that the magnetic powder is 20 wt% and melt-mixed using an extruder. A mixture of granules was obtained, which was dried under reduced pressure (3 Torr) at 180 ° C. for 3 hours.

Then, the mixture was formed into a film by adjusting the discharge amount (thickness) using a biaxial stretching film forming machine equipped with a die capable of melt extrusion. It should be noted that a static electricity of 7 kV was applied during casting. Further, magnetic field orientation treatment was performed using a magnet of 800 G from the lip of the die to the cast drum so that the magnetic powder was along the longitudinal direction of the film. The cast film is stretched,
Then, calendering is performed, and then 3.3 in the longitudinal direction.
Doubled, stretched 3.3 times in the transverse direction, and heat-treated at 210 ° C. for 10 seconds.

The thickness of the magnetic support A thus obtained was 10 μm. [Magnetic support B] Mn-Zn ferrite powder was used instead of the α-Fe magnetic powder in [Magnetic support A], and the same operation was performed. The magnetic support B thus obtained
Had a thickness of 10 μm.

[Magnetic support C] Polycarbonate having an intrinsic viscosity of 0.70
Granules of ethylene terephthalate and acicular γ-Fe₂O ₃
Adjust magnetic powder and magnetic powder to 40wt%
And mix using an extruder to obtain a mixture of granules.
It was Then, a mixture of the above mixture and a magnetic material-free polyethylene
Co-extrusion is carried out by supplying renterephthalate granules,
A bilayer film was obtained. At this time, from the land in the base
Apply between cast lips between lips or base lip
Magnetic field orientation treatment using a magnet of 800G
So that the ends are along the length of the film
It was The cast film is first
Sequential biaxial stretching of 3.3 times and then 3.3 times in the transverse direction
Stretching and calendering were performed.

The magnetic support C thus obtained is
The total thickness is 10 μm and γ-Fe ₂O₃Including magnetic powder
The layer was 2.0 μm thick. [Magnetic paint] Needle-like metallic magnetic powder mainly composed of iron (Fe: Al: Ca: Si: Ni: Co = 92: 2: 1: 1: 2: 2, coercive force = 1730 Oe, saturation magnetization = 132 emu / g , Average long axis length = 0.13 μm, specific surface area = 56 m²/ G, moisture = 0.9%) 100 parts by weight Alumina (average particle size 0.3 μm) 7 parts by weight Carbon black (average particle size 20 nm) 3 parts by weight Vinyl chloride resin containing sulfonic acid group and epoxy group (molecular weight 20000) ) 8 parts by weight Sulfonic acid group-containing polyurethane (molecular weight 25000) 6 parts by weight Stearic acid 1 part by weight 2-Ethylhexyl oleate 2 parts by weight Polyisocyanate (Coronate L of Nippon Polyurethane Industry Co., Ltd.) 4 parts by weight Methyl ethyl ketone 92 parts by weight Toluene 46 Parts by weight cyclohexanone 92 parts by weight [non-magnetic paint] acicular α-iron oxide (average particle size 0.07 μm) 100 parts by weight carbon black (average particle size 17 nm) 8 parts by weight alumina (average particle size 0.2 μm) 3 parts by weight Part Vinyl chloride resin containing sulfonic acid group and epoxy group (molecular weight 2000 ) 8 parts by weight Sulfonic acid group-containing polyurethane (molecular weight 25,000) 6 parts by weight Oleyl oleate 1 part by weight Methyl ethyl ketone 80 parts by weight Toluene 40 parts by weight Cyclohexanone 120 parts by weight [Backcoat layer coating material] Carbon black (average particle size 0.02 μm) 32 parts by weight carbon black (average particle size 0.06 μm) 8 parts by weight Nipporan 2301 (polyurethane manufactured by Nippon Polyurethane Co., Ltd.) 20 parts by weight Nitrocellulose (made by Hercules Powder Co., viscosity display: 1/2 second) 20 Parts by weight D-250N (polyisocyanate manufactured by Takeda Pharmaceutical Co., Ltd.) 4 parts by weight stearic acid 1 part by weight methyl ethyl ketone 80 parts by weight toluene 40 parts by weight cyclohexanone 120 parts by weight In addition, the above paint is first powdered with a Nauta mixer. Component
And binder are premixed, then continuous pressure kneader
Pre-treatment with a solvent, then dilute with solvent and sand
It is distributed.

Then, the above coating materials were applied in the combinations shown in Table 1 below. The magnetic coating material and the non-magnetic coating material were applied by means of simultaneous multilayer coating. Then, while the magnetic layer was in a wet state, it was passed through a solenoid of 5000 Oe to perform magnetic field orientation treatment. After this, it was dried and calendered at 85 ° C. under conditions of 350 kg / cm.

After the magnetic layer was formed, the back coat layer coating material was applied to the other surface of the support so that the dry thickness was 0.5 μm, and the coating was kept at 50 ° C. for 24 hours. Then, a raw material having a magnetic layer on one surface side of the support and a back coat layer on the other surface side was slit into a width of 3.81 mm and loaded into a DAT cassette. Table-1 Support Thickness of Lower Layer Non-Magnetic Paint Upper Layer Thickness of Magnetic Paint Example 1 A 2.0 μm 0.5 μm Example 2 A 0.5 μm 1.5 μm Example 3 A 3.0 μm 1.0 μm Example 4 B 2.0 μm 0.5 μm Example 5 C 2.0 μm 0.5 μm Example 6 C 0.5 μm 1.5 μm Example 7 C 3.0 μm 0.2 μm Comparative Example 1 A 0 μm (none) 0.5 μm Comparison Example 2 B 0 μm (none) 0.5 μm Comparative Example 3 C 0 μm (none) 0.5 μm Comparative Example 4 D 2.0 μm 0.5 μm * Support D is 10 μm thick non-magnetic polyethylene terephthalate film The magnetic characteristics and reproducing characteristics of the magnetic tape for DAT obtained as described above were examined, and the results are shown in Table 2.

Table-2 Squareness Ratio Reproduction Output (dB) at 4.7 MHz Example 1 0.85 +0.8 Example 2 0.83 +0.5 Example 3 0.85 +1.2 Example 40 .86 +1.2 Example 5 0.85 +1.0 Example 6 0.86 +1.1 Example 7 0.83 +0.8 Comparative Example 1 0.76 -1.9 Comparative Example 2 0.77 -2 .7 Comparative Example 3 0.74-2.1 Comparative Example 4 0.810 * The squareness ratio is measured by peeling off the magnetic layer coating film.

* The reproduction output is represented by a relative value based on Comparative Example 4. According to this, compared with the magnetic tapes of Comparative Examples 1 to 3 having a magnetic support / magnetic layer structure and the magnetic tape of Comparative Example 4 having a non-magnetic support / nonmagnetic layer / magnetic layer structure. The magnetic tape of the present invention having a structure of magnetic support / non-magnetic layer / magnetic layer has a high squareness ratio and a large reproduction output.

[0034]

According to the present invention, a magnetic recording medium having excellent electromagnetic conversion characteristics can be obtained.

Claims (5)

[Claims] 1. A magnetic recording medium comprising a magnetic support, a non-magnetic layer provided on the magnetic support, and a magnetic layer provided on the non-magnetic layer. 2. The thickness of the magnetic layer is 0.05 to 1.5 μm,
2. The magnetic recording medium according to claim 1, wherein the non-magnetic layer has a thickness of 0.5 to 4 [mu] m and the magnetic support has a thickness of 1 [mu] m to 10 mm. 3. The magnetic layer provided on the non-magnetic layer is a recording layer.
The magnetic recording medium according to claim 1 or 2, wherein the magnetic support is used for reproduction and the magnetic support is not used for normal recording / reproduction. 4. The magnetic recording medium according to claim 1, wherein the magnetic layer is applied before drying the non-magnetic layer. 5. A method of manufacturing a magnetic recording medium comprising a magnetic support, a non-magnetic layer provided on the magnetic support, and a magnetic layer provided on the non-magnetic layer. The method for producing a magnetic recording medium, wherein the magnetic layer is applied before drying the applied non-magnetic layer.