JPS60171630A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a high-density recording medium having an improved temp. characteristic by using fine particles of a hexagonal ferrite crystal having a prescribed size and shape for the fine particles of a magnetic material. CONSTITUTION:Fine particles of a magnetic material consists of a hexagonal ferrite crystal having uniaxial anisotropy and has <=2.3 ratio D/t between the average value D of the C-face diameter of the crystal particles and the average value (t) of the thickness in the C-axis direction. The average value D is limited to 0.02-0.2mum. The reason for limiting said ratio lies in that if the value D is below 0.02mum the magnetization and coercive force decrease and the reproduced output of a recording medium decreases and that if said value exceeds 0.2mum the coercive force decreases and the noise during reproducing in high-density recording increases considerably. If the ratio D/t exceeds 2.3, the change of the coercive force with temp. increases and therefore said ratio is limited in the above-mentioned range.

Description

[Detailed description of the invention] [Technical field of invention] The present invention relates to improvements in magnetic recording media.

[Technical background of the invention and its problems]

A coated magnetic recording medium is composed of a nonmagnetic support such as polyethylene terephthalate, and a magnetic layer provided on the support and containing magnetic fine particles and a binder as main components. Conventionally, 7 Fe2 is used as magnetic fine particles.
Acicular magnetic particles such as O3, CrO2, Co-γ'Fe2O3 are widely used. Recently, in order to significantly improve magnetic recording density, there has been a strong desire for a magnetic recording medium that can perform perpendicular magnetization recording, and a magnetic recording medium that uses ultrafine hexagonal ferrite particles is a suitable magnetic recording medium for this purpose. has been studied and found to be capable of high-density recording.

Incidentally, even in a magnetic recording medium using the above-mentioned hexagonal ferrite as magnetic particles, the magnetic properties thereof need to be stable against temperature changes. -1l
l) If the magnetic properties change significantly with temperature, the recording and reproducing properties of the magnetic recording medium will vary significantly with changes in the ambient temperature during use, causing a practical problem. A magnetic recording medium using hexagonal ferrite exhibits a characteristic temperature characteristic in which the value of coercive force (He) increases as the temperature rises even at around room temperature, and is a medium that is relatively stable against temperature changes. However, from a practical standpoint, even greater temperature stability has been desired.

[Purpose of the invention]

The present invention seeks to provide a high-density magnetic recording medium with improved temperature characteristics.

[Summary of the invention]

As a result of extensive research into improving the temperature characteristics of coercive force of magnetic recording media using hexagonal ferrite fine particles, the present inventors found that by using hexagonal ferrite crystal fine particles with a predetermined size and shape, the temperature characteristics can be improved. They found that the magnetic recording medium of the present invention can be improved and developed the magnetic recording medium of the present invention.

That is, the present invention provides a magnetic recording medium in which a magnetic layer having magnetic fine particles is provided on a support, wherein the magnetic fine particles are made of a macrogonal ferrite crystal having uniaxial anisotropy.
The ratio D/l of the average value of the zero diameter of the crystal grains to the average value t of the thickness in the C-axis direction is 2.3 or less, and D is 0.02 to 0.
．． It is characterized by its length of 211 m.

As the hexagonal ferrite crystal used in the present invention, for example, M type (Magneto-plumbite type)
), W-type hexagonal barium ferrite, strontium ferrite, lead ferrite, calcium ferrite, or solid solutions or ion-substituted products thereof. Such hexagonal ferrite crystals mainly have a coercive force of 200 to 20,000 e.

The reason for limiting the average value of the diameter of the zero plane of the -axis anisotropic hexagonal ferrite crystal is that if D is less than 0.02 μm, the magnetization and coercive force will decrease, and the reproduction output of the magnetic recording medium will decrease. On the other hand, when D exceeds 0.2 μm, the coercive force decreases and noise during reproduction becomes significant in high-density recording.

The reason why the ratio of D/l in the above-mentioned -axis anisotropic hexagonal nerite is limited is because if the D/l exceeds 2.3, the temperature change in coercive force becomes large. In addition, D/l
It is desirable that the lower limit of the ratio is set to 1. The reason for this is D
When /l is less than 1, the characteristic of the hexagonal ferrite crystal grains that the axis of easy magnetization of the hexagonal ferrite crystal in the magnetic layer can be oriented perpendicularly to the surface of the magnetic recording medium is likely to be lost, and the perpendicular magnetization component is There is a possibility that high-density recording using this method becomes difficult. In this way, by specifying the ratio D/l of the average value D1 of the diameter of the 0 face of hexagonal ferrite crystal particles and the average value t of the thickness in the C-axis direction, it is possible to reduce the amount of binder resin. It is also possible to achieve a higher packing density of hexagonal ferrite crystal particles and a higher magnetic flux density without reducing the strength of the coating film, resulting in improved reproduction output in high-density recording. In addition, such -axis anisotropic hexagonal ferrite crystal particles can be produced by, for example, the glass crystallization method disclosed in JP-A-56-67904 or JP-A-56-160.
It can be prepared by the coprecipitation method disclosed in No. 328.

In the present invention, examples of the binder resin that constitutes the magnetic layer together with the magnetic fine particles include vinyl chloride-vinegar, vinyl copolymer, vinylidene chloride copolymer, acrylic acid ester copolymer, polyvinyl butyral resin, and polyurethane. For example, resins such as polyester resins, cellulose derivative epoxy resins, or mixtures of two or more of these resins are used. Further, in addition to the magnetic fine particles and the binder resin, additives such as a dispersant, a lubricant, an abrasive, and an antistatic agent can be appropriately contained in the magnetic layer as necessary.

[Embodiments of the invention]

Next, the present invention will be explained in detail. Note that parts in the examples mean parts by weight.

Examples 1 to 5 First, five barium ferrite co-Ti substituted magnetic particles having different average particle diameters (D) in the zero plane and average thicknesses in the C-axis direction (1) shown in Table 1 below were prepared. .

Next, a magnetic paint having the following composition was prepared using the magnetic particles shown in Table 1 above.

Vinyl chloride-vinyl acetate copolymer 10 parts Polyurethane 10 parts Aluminum oxide 2 parts Lubricant 1.5 parts Dispersant (lecithin) 2 parts Methyl ethyl ketone 70 parts Toluene 70 parts Microhexanone 40 parts Hardening agent 5 parts The coating material was applied onto a polyethylene terephthalate film having a thickness of 15 μm, and calendering and slitting were performed to form a magnetic layer having a thickness of 3.5 μm, thereby producing a magnetic tape.

Comparative Examples 1 to 3 Three types of barium ferrite Co-Ti shown in Table 2 below
Paints having the same composition as in the example except that substituted magnetic particles were used were prepared, and magnetic tapes were manufactured using these paints.

However, for each of the magnetic tapes of this example and comparative example, the coercive force and the temperature coefficient (ΔHe/1(c)/AT) of the coercive force at 40°C to 60°C were measured.The results are shown in Table 3 below. It was shown to.

As is clear from Table 3 above, in the magnetic tape coated with hexagonal ferrite fine particles having -axis anisotropy, the average value of the diameter of the zero plane of the crystal grains and the average value of the thickness in the C-axis direction t
A magnetic tape with a ratio (D/l) of 2.3 or less has a temperature coefficient of coercive force (ΔHe/1(c)/IT of 2.3X10
It can be seen that it is very stable at -3/°C or less.

〔Effect of the invention〕

As described in detail above, according to the present invention, it is possible to provide a magnetic recording medium that is stable against temperature changes, has improved temperature characteristics, and is capable of high-density recording.

Applicant's representative Patent attorney Takehiko Suzue Continued from page 1 @ Inventor Tsugane Decline 1 Komukai Toshiba-cho, Saiwai-ku, Kawasaki City, Tokyo Shibaura Electric Co., Ltd. Research Center

Claims (1)

[Claims] In a magnetic recording medium in which a magnetic layer containing magnetic fine particles is provided on a support, the magnetic fine particles are made of hexagonal ferrite crystals having uniaxial anisotropy, and the crystal grains are 0.
Ratio D between the average value of the diameter of the surface and the average value t of the thickness in the C-axis direction
A magnetic recording medium characterized in that /l is 2.3 or less and D is 0.02 to 0.2 μm.