JP2611964B2 - Magnetic recording media - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a magnetic recording medium, and more particularly, to a coating type high-density magnetic recording medium using ultrafine hexagonal ferrite particles.

[Technical background of the invention and its problems]

The magnetic recording medium is composed of a flexible non-magnetic substrate such as polyethylene terephthalate and a magnetic layer mainly formed of magnetic fine particles and a binder provided on the substrate. As magnetic fine particles, conventionally, γ-Fe ₂ O ₃ , Cr
Acicular magnetic particles such as O ₂ and Co-γFeO ₃ are used. On the other hand, in recent years, a recording medium capable of perpendicular magnetic recording has been strongly demanded in order to greatly improve the magnetic recording density, and a magnetic recording medium using hexagonal ferrite ultrafine particles as magnetic particles suitable for this purpose has been developed. Has been studied.

The present inventors have formed a magnetic layer formed by coating ultrafine particles of hexagonal ferrite with a binder on a flexible and insulating substrate, and forming the magnetic layer formed by coating the needle-shaped magnetic particles together with the binder on the substrate. It has been found that a magnetic recording medium having a higher density than that of the magnetic layer obtained can be obtained. However, the magnetic layer of such a magnetic recording medium has a drawback that it is easily charged due to its high surface resistance of 10 ¹² Ω or more. Conventionally, as a means for lowering the surface resistance to prevent charging, a method of incorporating a conductive powder such as carbon black into a magnetic layer has been widely adopted. However, when such a method is applied to a coating medium of hexagonal ferrite ultra-fine particles, the reproduction output decreases due to the need for a large amount of conductive powder and the noise increases due to the decrease in dispersibility. There is a drawback that tends to cause such problems.

On the other hand, as another means for lowering the surface resistance of a magnetic recording medium, a method of providing a conductive layer between a substrate and a magnetic layer is known. However, when this method is applied to a coating medium of hexagonal ferrite ultrafine particles, for example, a magnetic tape, the adhesion of the magnetic tape back surface (substrate back surface) due to charging is remarkable,
In particular, the sticking between the tape layers wound on the reel is more remarkable than in the case where there is no conductive layer.

[Object of the invention]

An object of the present invention is to provide a magnetic recording medium suitable for high-density recording which prevents charging without impairing the recording and reproducing characteristics and has no troubles due to charging.

[Summary of the Invention]

The present inventors have conducted intensive studies to prevent electrification of a magnetic recording medium having a magnetic layer containing hexagonal ferrite fine particles and a binder as a main component. As a result, a flexible insulating substrate and the magnetic layer A conductive layer mainly composed of a conductive substance and a binder is provided between them, and a conductive layer mainly composed of a conductive substance and a binder is further provided on the back surface of the base, and the surface resistance of the magnetic layer and the conductivity of the back surface are provided. By making the surface resistance of the layer substantially equal, it is possible to prevent the charging of the magnetic layer surface while maintaining the high density recording performance by using the magnetic layer of hexagonal ferrite fine particles, and also prevent the charging of the back surface of the substrate. A magnetic recording medium that can avoid the sticking phenomenon has been found.

The flexible and insulating substrate is not particularly limited, and for example, a polyester film such as polyethylene terephthalate can be used.

Examples of the hexagonal ferrite fine particles include barium ferrite, strontium ferrite, lead ferrite, calcium ferrite, and ion substitutes thereof having a crystal structure of M type or W type. These fine particles have a particle size of 0.01 to 0.2 μm, more preferably 0.02 to 0.1 μm, and a coercive force (Hc) of 200 to 2000O.
e, more preferably 300 to 1500 Oe. The condensing agent used for forming the magnetic layer is not particularly limited, and a conventionally used thermoplastic resin, thermosetting resin, or reactive resin is used.

As the conductive layer interposed between the base and the magnetic layer,
For example, there may be mentioned a coated layer which leads to a polymer binder to which a conductive substance such as carbon black is added. The surface resistance of these conductive layers from the surface resistance of the magnetic layer is 5 × 10 ¹¹ Ω or less antistatic is made, selected so that the surface resistivity of the magnetic layer is 5 × 10 ¹¹ Ω or less More specifically, it is preferably 1 × 10 ¹¹ Ω or less.

As the conductive layer provided on the back surface of the base, a layer coated with a conductive substance such as carbon black or graphite using a polymer binder can be used. At this time, by simultaneously mixing and applying inorganic particles such as alumina, α-hematite, titanium dioxide, calcium carbonate, etc. together with the conductive material, it is possible to form a conductive film having excellent coating film strength and friction resistance. The conductivity given to the back surface of the magnetic recording medium is preferably 10 ¹¹ or less in surface resistance value, and is preferably substantially equal to the surface resistance of the magnetic layer.

(Example of the invention)

Next, examples of the present invention will be described. In the examples, parts by weight are simply indicated as parts.

First, 30 parts of carbon black, 60 parts of a urethane resin and 10 parts of a vinyl chloride-vinyl acetate copolymer were mixed and kneaded with 180 parts of methyl ethyl ketone, 180 parts of toluene and 180 parts of cyclohexanone, and then dispersed, followed by 20 parts of a curing agent. In addition, a conductive paint was prepared. Then, apply this conductive paint to a thickness of 11μ.
m was applied on a polyethylene terephthalate film having a dry thickness of 0.3 μm, and then dried to form a conductive layer. The surface resistance of the conductive layer thus formed is determined by JIS
It was 3 × 10 ⁷ Ω when measured according to —C-6240.

Then, 100 parts of hexagonal barium ferrite CoTi-substituted ultrafine particles (average particle size 0.08 μm, holding power He: 800 Oe), 10 parts of vinyl chloride-vinyl acetate copolymer, 10 parts of urethane resin and 2 parts of aluminum oxide lubricant ( 1 part of myristic acid and butyl palmitate), 60 parts of methyl ethyl ketone,
After sufficiently kneading and dispersing with 60 parts of toluene and 60 parts of cyclohexanone, 6 parts of a curing agent was added to prepare a magnetic paint. Subsequently, the magnetic paint was applied on the conductive layer, dried, and then subjected to a surface smoothing treatment to form a magnetic layer having a thickness of 3.5 μm. The surface resistance of this magnetic layer is 5 × 10 ⁹ Ω
Met.

Next, 20 parts of carbon black, 40 parts of αFe ₂ O ₃ , 15 parts of a urethane resin and a vinyl chloride-vinyl acetate copolymer,
After thoroughly kneading and dispersing with 120 parts of methyl ethyl ketone, 120 parts of toluene and cyclohexanone, a curing agent 8
The resultant was added to prepare a conductive coating for a back coat. Subsequently, this paint was applied to the back surface of the polyethylene terephthalate film so as to have a dry thickness of 0.7 μm,
After drying, a conductive layer was formed. The surface resistance of the conductive layer thus formed was 5 × 10 ⁹ Ω.

Then, after the curing treatment, it was cut with a slitter to produce a 1 / 2-inch wide magnetic tape sample.

Comparative Example 1 A conductive layer having a dry thickness of 0.3 μm was formed on a polyethylene terephthalate film having a thickness of 11 μm and a magnetic layer having a thickness of 3.5 μm was further formed on the conductive layer in the same manner as in Example. Thereafter, the back surface of the polyethylene terephthalate film was subjected to a curing treatment as it was without applying a conductive coating material for a back coat, and further cut with a slitter to the same size and width as in the example to produce a magnetic tape sample.

Comparative Example 2 A magnetic paint similar to that of the example was directly applied to a polyethylene terephthalate film having a thickness of 11 μm so as to have a thickness of 3.5 μm, dried, and then subjected to a surface smoothing treatment to form a magnetic layer. Subsequently, the same conductive paint for back coating as in the example was applied to the back surface of the polyethylene terephthalate film so as to have a dry thickness of 0.7 μm. After performing the hardening treatment, the sample was cut with a slick to produce a magnetic tape sample having the same size and width as the example.

Comparative Example 3 First, 100 parts of ultrafine hexagonal barium ferrite CoTi-substituted particles (average particle size 0.08 μm, coercive force He: 800 Oe), 10 parts of vinyl chloride-vinyl acetate copolymer, 10 parts of urethane resin, 5 parts of carbon black And 2 parts of aluminum oxide, 60 parts of methyl ethyl ketone, 60 parts of toluene, cyclohexanone
After sufficiently kneading and dispersing together with 60 parts, 6 parts of a curing agent was added to prepare a magnetic paint. Next, apply this paint to the thickness
After directly applying on a 11 μm polyethylene terephthalate film to a dry thickness of 3.5 μm and drying,
The surface was subjected to a surface smoothing treatment to form a conductive magnetic layer. Next, after a hardening treatment, it was cut with a slitter to produce a magnetic tape sample having a width of 1/2 inch. The surface resistance of the magnetic layer of this magnetic tape sample was 3 × 10 ⁹ Ω.

Thus, the magnetic tape samples obtained in this example and Comparative Examples 1 to 3 were wound into a β-format VTR cassette, and the β-type VTR was modified so that the relative speed between the tape heads was reduced to half of the standard. Recording and reproduction were performed, and the electromagnetic conversion characteristics and running properties were examined. The results are shown in the table below.

As is clear from the above table, the magnetic tape according to the present invention has good electromagnetic conversion characteristics in high-density recording, and has no charging and troubles associated therewith.

〔The invention's effect〕

As described above in detail, according to the present invention, a conductive layer is interposed between a flexible and insulating substrate and a magnetic layer containing hexagonal ferrite fine particles and a binder as main components. By providing a conductive layer on the surface of the base material with a surface resistance value approximately equal to the surface resistance of the magnetic layer, high-performance magnetic recording that eliminates charging and troubles associated with it without impairing the characteristics of high-density recording. Media can be provided.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Ryoichi Sato, Inventor Ryoichi Sato, Kobayashi-ku, Kawasaki 1st Tokyo Shibaura Electric Co., Ltd. (72) Inventor Yoshihito Tsugane 1st institution, Komukai Toshiba-cho, Saiwai-ku, Kawasaki-shi Tokyo Shibaura Electric Co., Ltd. (56) References JP-A-58-205928 (JP, A) JP-A-55-55432 (JP, A) JP-A-59-94231 (JP, A)

Claims (1)

(57) [Claims] 1. A flexible insulating substrate, a magnetic layer mainly containing hexagonal ferrite fine particles and a binder, and a conductive material and a binder provided between the substrate and the magnetic layer. A first conductive layer having a main component; a second conductive layer having a conductive material and a binder provided on a back surface of the base as a main component; a surface resistance of the magnetic layer and a second conductive layer; A magnetic recording medium characterized by having substantially the same surface resistance.