JPH0517606B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to a magnetic recording medium such as a magnetic tape for recording and reproducing audio and video.

Structures of conventional examples and their problems Polyester films are made by forming thin films of cobalt, nickel, iron, alloys containing these as main components, or their oxides using vacuum deposition methods such as vacuum evaporation, sputtering, and ion plating. A ferromagnetic thin film magnetic recording medium formed on a base material is
Since it has a high recording density, it is suitable as a recording medium for 8mm video. However, in an 8 mm video system, it is necessary to reduce the thickness of the film base material in order to enable long-term recording on the same level as the current VHS system. The mechanical strength of a magnetic recording medium is expressed by the combination of the strength of the film base material and the strength of the ferromagnetic thin film, but since the thickness of the ferromagnetic thin film is about 0.1 to 0.2 μm, most of the strength comes from the film. Depends on the base material. At this time, the magnetic recording medium must withstand a tension of about 100 g that is applied during the running of the video deck, especially when the video deck suddenly stops. Furthermore, since a ferromagnetic thin film cracks and increases noise when elongated by less than 0.5%, it is necessary that it does not elongate at 100 g. Furthermore, the magnetic recording medium is required to have stiffness in the width direction so that the magnetic recording medium does not break at the end of the width regulating cut in the guide post or cylinder during traveling. When a polyethylene terephthalate film or the like is used as the film base material, the thickness of the film is approximately 8 μm even if it is stretched and strengthened in the longitudinal direction in order to satisfy the above-mentioned mechanical strength constraints. Further, for high-density recording, it is necessary to finely control the surface properties of the film, but in reinforced and stretched films, scratches and the like are likely to occur on the surface and the surface is likely to be rough. For example, Japanese Patent Publication No. 48-34161 discloses a method in which a metal magnetic layer is provided on a base layer of a polymeric material in which a non-magnetic pigment is dispersed.
In this case, the optimum value of the average particle size of the inorganic pigment is 0.1~
The recording density was 0.5 μm, and the recording density was low. Furthermore, JP-A-56-13518 discloses a magnetic recording medium in which a non-magnetic polymer layer containing non-magnetic solid lubricating powder is formed on a support, and a metal magnetic layer is provided on this. However, the average particle size of the lubricating powder was set to 3μ or less, and the recording density was also low in this case.

Purpose of the Invention The present invention uses a thin film base material such as a polyester film to have excellent mechanical strength, and
The purpose of the present invention is to provide a magnetic recording medium that enables high-density recording.

Structure of the Invention The magnetic recording medium of the present invention has an undercoat layer on a film base material, and a ferromagnetic metal thin film is provided on the undercoat layer. It is a layer having a thickness of 0.2 μm or more containing parts by weight, and is characterized in that the inorganic fine particles are ultrafine particles with an average particle diameter of 0.003 to 0.05 μm.

The drawing is an enlarged sectional view showing a magnetic recording medium of the present invention, and in the drawing, 1 is a film base material, 2 is a film base material, and 2 is a film base material.
3 indicates an undercoat layer, and 3 indicates a ferromagnetic metal thin film.

As the film base material 1, for example, polyethylene terephthalate or a copolymer or mixture thereof,
Furthermore, a biaxially stretched, preferably reinforced biaxially stretched polyester film made of polyethylene naphthalate or a copolymer or mixture thereof is suitable.

The undercoat layer 2 contains inorganic fine particles uniformly dispersed in a resin. As the inorganic fine particles, inorganic ultrafine particles with an average particle diameter of 0.003 to 0.05 μm are suitable, and in particular, it is preferable that the particles be in a state of dispersion almost close to the average particle diameter during use, that is, in the coating liquid. Organosols of silica, alumina, titanium oxide, iron oxide, zirconia, etc. can be easily obtained in such a state. Organosilica sol is described, for example, in US Pat.
It can be obtained by the method described in Publication No. 126594 and the like. Further, organosols of alumina, titanium oxide, iron oxide, etc. are described, for example, in the Abstracts of the Color Materials Association of Japan, pages 3-4 (November 11, 1982).
Organosols of metal oxides or hydroxides such as zirconia and barium titanate obtained by hydrolysis of metal alkoxides can also be used. In addition, as a primary particle, the particle diameter is 0.003
Even if the particle size is within the range of ~0.05 μm, because it has been dried or produced by a dry method, the aggregate particles are considerably larger than that and it is difficult to monodisperse them in the state of primary particles in a solution. For example, color carbon black, dry silica sol fine powder, etc. are not preferred.

Examples of the resin include saturated polyester resins, polyurethane resins, cellulose resins, vinyl chloride resins, vinyl acetate resins, acrylic resins, styrene resins, polyamide resins, epoxy resins, etc. alone or in mixtures; Copolymers thereof, etc. can be used. The organosol of the inorganic ultrafine particles is added to these resins, and other additives are added as necessary, and the resultant is coated on at least one side of the film base material 1 to form the undercoat layer 2. Inorganic ultrafine particles are resin
It is appropriate to add it in a proportion of 50 to 300 parts by weight, more preferably 100 to 250 parts by weight per 100 parts by weight. When the amount of inorganic ultrafine particles is less than 50 parts by weight, it is difficult to obtain the mechanical strength of the undercoat layer 2, and
When the amount exceeds 300 parts by weight, the flexibility of the undercoat layer 2 decreases, causing practical problems. Further, the effect of improving mechanical strength is reduced in both cases when the average particle diameter of the inorganic ultrafine particles is smaller than 0.003 μm or larger than 0.05 μm. Further, as other additives, various surfactants, various silicones, various rust preventive agents, etc. can be used for the purposes of dispersion stabilization, surface property improvement, rust prevention of the magnetic film, etc. The thickness of the undercoat layer 2 is suitably at least 0.2 μm, more preferably 0.5 μm or more, and the upper limit is suitably 3 μm or less from a practical standpoint. The effects obtained by containing inorganic ultrafine particles include not only improving the mechanical strength of the undercoat layer 2, but also enabling fine control of the surface shape of the undercoat layer 2, and further improving the adhesive strength between the undercoat layer 2 and the film base material 1. Also, the adhesion strength of the ferromagnetic metal film 3 to the undercoat layer 2 is improved. In particular, the surface shape can be arbitrarily controlled by varying the particle size, amount added, etc. of the inorganic ultrafine particles. The surface shape has a height of 0.003 to 0.05 μm and a protrusion density of 1×14 ⁴ to 1×
It is desirable to have ¹⁰⁹ protrusions/ ^mm2 .

The ferromagnetic metal thin film 3 may be a metal thin film mainly made of Co, Ni, Fe, etc., or a metal thin film mainly made of an alloy thereof (for example, Co- A perpendicularly magnetized Cr film) can be used, but vapor deposition is performed in an atmosphere dominated by oxygen gas in order to improve the adhesion strength with the undercoat layer or to improve the corrosion resistance and abrasion resistance of the ferromagnetic metal thin film itself. It is preferable to use an oxygen-containing ferromagnetic metal thin film obtained in the following manner. In this case, the appropriate oxygen content is at least 3% or more, preferably 5% or more in terms of atomic ratio to the ferromagnetic metal.

A thin layer made of an inorganic or organic material can be provided on the surface of the ferromagnetic metal thin film for purposes such as improving lubricity, corrosion resistance, and durability.

If necessary, an undercoat layer (not shown) similar to that on the magnetic surface side can be formed on the surface (back surface) of the film base material 1 opposite to the surface on which the ferromagnetic metal thin film 3 is formed. It is desirable to apply a back layer to the material 1 directly or through various undercoating layers to improve running properties.

Description of Examples Example 1 A reinforced biaxially stretched polyethylene terephthalate film with a thickness of 5.5 μm was calendered in advance to suppress large protrusions existing on the surface, and then a solution with the following composition was applied to the surface and dried. thickness
A 1.3 μm undercoat layer was formed. The surface of the undercoat layer has granular protrusions with a protrusion height of 100 to 300 Å per ¹ mm2.
There were 5 million of them.

(Ingredients) (Parts by weight) Organosilica sol (Silica content 30% by weight)
300 Saturated polyester resin (Byron 200, Toyobo
Co., Ltd.) 100 Methyl ethyl ketone 200 Toluene 200 Cyclohexanone 100 The above organosilica sol has a particle size of
After ion exchange with 0.01μm aqueous colloidal silica,
Most of the alcohol in the sol obtained by heating with isopropyl alcohol and distilling off excess water is replaced with methylinobutyl ketone.

Next, an oxygen-containing Co-Ni ferromagnetic metal thin film (Ni content 20% by weight, film thickness 1200 Å) was formed on the undercoat layer by continuous vacuum oblique evaporation while introducing a small amount of oxygen gas. The oxygen content in the magnetic layer was 5% in terms of atomic ratio to the metal.

The following composition liquid was applied to the back side of the film to form a back layer having a thickness of 0.3 μm, and the film was slit to a predetermined width to obtain a magnetic tape.

(Ingredients) (Parts by weight) Polyester resin (Vylon 200, manufactured by Toyobo Co., Ltd.)
80 Nitrocellulose 20 Carbon Black (Ketsutien Black, manufactured by Lion Akzo Co., Ltd.)
80 Organosilica sol (same as above) 100 Methyl ethyl ketone 200 Toluene 200 Cyclohexanone 200 Attach this magnetic tape to a video deck and record.
After repeated rewinding (fast forwarding) and playback 100 times, a stable output was obtained, and no problems such as running abnormalities, tape edges breaking, or running scratches occurred.

Example 2 A magnetic tape was obtained in the same manner as in Example 1 except that the composition of the undercoat layer forming solution was changed as shown below and the thickness of the undercoat layer was 0.5 μm. No abnormalities were observed with this product even after 100 runs. In this case, on the surface of the undercoat layer, about 1 million granular protrusions with a protrusion height of 200 to 400 Å were present per 1 mm ² .

(Ingredients) (Parts by weight) Polyvinyl butyral resin 100 Organozirconia sol (zirconia content 50% by weight) 300 Methyl ethyl ketone 300 Cyclohexanone 300 The above organozirconia sol is made of tetraisopropyl zirconate (manufactured by Daiichi Kigenso Co., Ltd.). Isopropyl alcohol solution (10% by weight) at 80℃
Most of the alcohol in the organozirconia sol obtained by heating the sol and blowing water vapor into it to hydrolyze tetraisopropyl zirconate and precipitate zirconia particles is obtained by replacing and concentrating most of the alcohol with cyclohexanone. Particle size
It is an organosol in which 0.04μm zirconia particles are dispersed.

Effect of the invention According to this invention, the average particle diameter is 0.003 to 0.05 μm.
By providing a ferromagnetic metal thin film on an undercoat layer containing ultrafine inorganic particles, it is possible to finely control the surface shape and enable high-density recording. The effect is that it is possible to realize a magnetic recording medium that is thin, with a diameter of about 7 μm or less, and has excellent mechanical strength.

[Brief explanation of the drawing]

The drawing is an enlarged cross-sectional view of the magnetic recording medium of the present invention. 1...Film base material, 2...Undercoat layer, 3...Ferromagnetic metal thin film.

Claims (1)

[Scope of Claims] 1. A magnetic recording medium comprising a film base material, an undercoat layer provided on the film base material and containing inorganic fine particles, and a ferromagnetic metal thin film provided on the undercoat layer, The thickness of the undercoat layer containing 50 to 300 parts by weight of inorganic fine particles to 100 parts by weight of resin.
1. A magnetic recording medium characterized in that the layer has a thickness of 0.2 μm or more, and the inorganic fine particles are ultrafine particles with an average particle diameter of 0.003 to 0.05 μm.