JPS60209928A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a magnetic recording medium which has large reproduced output and permits high-density recording by using fine magnetic material particles of which the average particle size is of a limited length and the volumetric packing rate of the fine magnetic material particles in the magnetic layer is specific % or above. CONSTITUTION:The particle size of fine magnetic material particles consisting of hexagonal ferrite is made 0.02-0.15mum and the volumetric packing rate of the fine magnetic material particles in a magnetic layer contg. said particles is made >=42% in a magnetic recording medium provided with said magnetic layer on a substrate. The fine magnetic material particles consisting of hexagonal ferrite are exemplified by, for example, M type (magneto-plumbite type), W type hexagonal barium ferrite, strontium ferrite, lead ferrite, orcium ferrite or the solid soln. thereof or ion substituted matter thereof. The fine magnetic material particles consisting of hexagonal ferrite having 200-2,000Oe coercive force are mainly used.

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 magnetic recording medium is composed of a support such as polyethylene terephthalate, and a magnetic layer provided on the support and containing magnetic fine particles and a binder resin as main components. Conventionally, as magnetic particles, γFe1OB, C
Acicular magnetic particles such as r01 and Co-γFe2O3 are widely used. Recently, in order to greatly improve magnetic recording density, a magnetic recording medium capable of perpendicular magnetization recording has been strongly desired. Things have been studied and it has been found that high-density recording is possible.

Incidentally, the demand for high-density recording is not limited to simply the longitudinal direction of the recording track, but is also directed toward narrowing the track width and increasing the track density, and a magnetic recording medium that can meet this demand is desired.

Therefore, even in the case of magnetic recording media using ultrafine hexagonal ferrite particles, it is required to obtain sufficient reproduction output even when the track width becomes narrow in high-density recording, and this point is an important development issue. Met. Possible methods for increasing the reproduction output include a method of increasing the saturation magnetization of the magnetic fine particles, a method of increasing the coercive force, and a method of increasing the volume filling rate of the magnetic fine particles. However, increasing the saturation magnetization of fine magnetic particles cannot be expected to significantly improve unless ultrafine hexagonal ferrite particles are used, and increasing the coercive force is difficult in magnetic recording, which is mainly perpendicular recording. Not effective.

Next, we will discuss the volumetric optical density of magnetic particles in a magnetic recording medium. In conventional coated magnetic recording media using acicular magnetic particles, the volumetric optical density of the magnetic particles is 30 to 40%.
It is. In media used with high recording density, such as recent VTR technos, the diameter of the major axis is 0.3 to 0.4μ.
Because magnetic particles with small particle diameters such as m are used, a large amount of binder is required to bind them well, and in order to prevent charging of the medium, ultrafine particles of caden black are used. is added, and therefore the volumetric optical density of the magnetic particles cannot be made very high.

To give a specific example, in a standard grade VTR Chif (for β or VH8), the volume optical density of magnetic particles is approximately 38.
In some high-performance VTR systems that use magnetic powder with a much smaller particle size, the volumetric optical density of the magnetic particles is as low as about 32 inches. In order to increase the volume optical density of magnetic particles in such magnetic recording media, it is necessary to reduce the amount of binder or the amount of carzen black, but reducing the amount of binder causes a decrease in coating strength and This results in a decrease in durability, and a decrease in kerptic density leads to the generation of medium charging, both of which are undesirable results for a magnetic recording medium.

[Purpose of the invention]

The present invention aims to provide a magnetic recording medium that has a large reproduction output and is capable of high-density recording.

[Summary of the invention]

As a result of various studies on magnetic recording media using hexagonal ferrite fine particles, the present inventors have found that using macrogonal ferrite crystal fine particles of a predetermined size, the volume filling rate of hexagonal heptagonal ferrite fine particles is 42% or more. They discovered that the reproduction output can be significantly improved by setting the volume filling factor beyond the conventional range, and have developed the magnetic recording medium of the present invention. In particular, when plate-shaped macrogonal ferrite particles are used, unlike the case of conventional needle-shaped hexagonal ferrite particles, it becomes possible to significantly reduce the amount of binder resin. The volume filling rate of fine particles can be increased, and the strength of the coating film can also be maintained at a sufficient value.

That is, the present invention provides a magnetic recording medium in which a magnetic layer containing hexagonal 7E2ite magnetic particles is provided on a support, wherein the magnetic particles have a particle diameter of 0.02 to 0.15μ.
m, and the volume filling factor of the magnetic fine particles in the magnetic layer is 42
- or more.

Magnetic particles of hexagonal 7-elite used in the present invention include M type (Magn@to-plumbit), for example.

type), W-type hexagonal barium 7-elite, strontium 7-elite, lead ferrite, orcilla 4-ferrite, or solid solutions or ion-substituted products thereof.

These macrogonal hepteralite magnetic fine particles mainly have a coercive force of 200 to 20,000 e.

The reason for limiting the size of the magnetic fine particles is that if the particle size is less than 0.02 μm, the magnetization value will decrease and the output will decrease during high-density recording and reproduction as a recording medium. This is because if the thickness exceeds 0.15 μm, noise during high-density recording and reproduction increases.

In the present invention, the reason why the volume filling rate of the magnetic fine particles in the magnetic layer is limited is that if the volume filling rate is less than 42 gb, it becomes impossible to improve the reproduction output during high-density recording and reproduction.

In the present invention, examples of the binder resin constituting the magnetic layer together with the magnetic fine particles include vinyl chloride-vinyl acetate copolymer, vinylidene chloride copolymer, acrylic ester copolymer, polyvinylzotyral resin, Polyurethane resins, terester 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.

In the present invention, the volume optical content of the magnetic powder can be increased to 4 parts or more by controlling the amount of additives other than the magnetic powder. In the magnetic layer of a magnetic recording medium, carbon black as an antistatic agent has a large volume ratio other than magnetic powder, and a desired volumetric optical transmittance can be easily obtained by controlling the amount of carbon black. In this way, among the additives in the magnetic layer, carbon black for antistatic purposes is completely removed, or only a small amount is added, and the carbon black-containing undercoat layer or backcoat layer (
Alternatively, by providing it as an undercoat υ layer and puncture coat layer), antistatic measures are taken. In this way, in a magnetic recording medium using hexagonal hexagonal heptagonal light magnetic particles, the volume optical density of the magnetic particles can be increased by significantly reducing the amount of binder resin, and the coating film The strength can be maintained at a sufficient value. The reason why the present invention is able to obtain high volume optical density and coating film strength of magnetic particles with a small amount of binder is not yet fully clear, but since hexagonal ferrite is plate-shaped particles, the particles touch each other's plate surfaces. It is thought that the major difference from conventional acicular particles is that they can overlap in layers while being in contact with each other.

It has been found that by increasing the volumetric optical density of the magnetic particles in the magnetic layer of a magnetic recording medium to 4 parts or more, the reproduction output can be significantly improved. The improvement in reproduction output obtained in this manner significantly exceeds the value estimated from the relationship between the volumetric light transmittance and the reproduction output in the low volumetric light transmittance region.

[Embodiments of the invention]

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

Example 1 First, hexagonal barium ferrite in the amount shown in Table 1 below.
CoTi substituted material (average particle size 0.08 μm 1 coercive force 8
000e), vinyl chloride-vinyl acetate copolymer and polyurethane, 2 parts of aluminum oxide, 1.5 parts of lubricant,
Six kinds of magnetic paints were prepared consisting of 760 parts of methyl ethyl keto, 60 parts of toluene, 60 parts of cyclohexanone, and 6 parts of a hardening agent.

Next, each magnetic paint was applied onto a polyethylene terephthalate film having a thickness of 1.5 μm, and calendering and slitting were performed to produce six types of magnetic chips each having a magnetic layer approximately 3.5 μm thick.

Comparative Example First, hexagonal nororium 7-elite Co Tl-substituted product (average particle size 0.08 μm 1, magnetic force 8000@), vinyl chloride-vinyl acetate copolymer, polyurethane and carbon were used in the amounts shown in Table 2 below. Four kinds of magnetic paints were prepared, each consisting of black, 2 parts of aluminum oxide, 1.5 parts of lubricant, 60 parts of methyl ethyl ketone, 60 parts of toluene, 60 parts of cyclohexanone, and 6 parts of hardener.

Next, each of the magnetic paints was applied onto a 1.5 μm thick positive ethylene terephthalate film, and calendering and slitting were performed to produce four types of magnetic tapes each having a magnetic layer about 3.5 μm thick. .

When the volume filling factor of the magnetic fine particles in the magnetic layer of each of the magnetic tapes of Example 1 and Comparative Example 1 was investigated, the results shown in Table 3 below were obtained. Furthermore, the recording and reproducing output was measured for each magnetic tape. The results are shown in the same third column.
Shown in the table. The recording and reproducing output was measured under the conditions of a head chive relative speed of 3.75 m/sec, a recording and reproducing signal frequency of 4 MHz, and a recording head (Gatsu 7' 0.3 μm, a ring head with a track width of 35 μm and a number of turns of 18). .

On the other hand, the relationship between the volume filling rate of the magnetic fine particles of Example 1 and Comparative Example 1 and the reproduction output is shown in the illustrated characteristic diagram.

Table 3 As is clear from the above Table 3 and the illustrated characteristic diagram, hexagonal barium ferrite) CoT1 substituted product (magnetic fine particles)
It can be seen that the magnetic tape of the present invention, in which the volume filling factor in the magnetic layer is 42% or more, has significantly increased reproduction output compared to the comparative example.

Example 2 Five types of hexagonal barium ferrite Co Ti substituents with average particle diameters in the range of 0.02 μrIL to 0.15 μm were selected, and magnetic fine particles were used in the same manner as in Example 1 to make them magnetic. A coating material was prepared, a magnetic layer with a volume filling rate controlled to 47% was formed on a polyethylene terephthalate film, and five types of magnetic chips were produced.

Comparative Example 2 Hexagonal barium ferrite CoTi substituted materials with average particle diameters of 0.01511 m and 0.20 fim were selected, and magnetic paint was prepared using these magnetic fine particles in the same manner as in Example 1, and polyethylene Two types of magnetic tapes were produced by forming a magnetic layer on a terephthalate film with a controlled volumetric filling rate of 47 cm.

However, when we investigated the reproduction output and modulation noise for each magnetic tape of Example 2 and Comparative Example 2, we found that
The results shown in the table were obtained.

As is clear from Table 4 above, the magnetic tape of Example 2 exhibits good performance in terms of reproduction output and modulation noise. On the other hand, the reproduction output of Magnetic Chee 76 (Hllll 6), which uses magnetic fine particles with an average particle size of 0.015 μm, is extremely low;
It can be seen that the modulation noise increases significantly in a magnetic tape using magnetic fine particles as large as μm.

〔Effect of the invention〕

As detailed above, according to the present invention, the reproduction output is high and the S
It is possible to provide a magnetic recording medium that is capable of high-density recording with a high A ratio and has durability such as high coating film strength.

[Brief explanation of the drawing]

FIG. 3 is a characteristic diagram showing the relationship between the volume filling rate of magnetic fine particles in the magnetic layer and the reproduction output in a drawing magnetic tape. Applicant's representative Patent attorney Takehiko Suzue 1. His Majesty's Honshan Kazuko f) Katsutaka Ito (0mu) Procedural amendment 61 Todoroki, 1o, 58 Commissioner of the Patent Office Manabu Shiga 1, Indication of the case Japanese Patent Application No. 59-63574 2, Name of the invention Magnetic recording medium 3, Person making the amendment Relationship to the case Patent applicant (307) Toshiba Corporation 6 Specification to be amended 7, Contents of the amendment (1) ) In box 4, line 18 of the specification, the phrase "volume filling rate range" is corrected to "volume filling rate range." (2) Box 5, lines 17 and 188 of the specification. Correct "Olsium ferrite" to "Orsium ferrite". (3) In the specification box, page 6, lines 18 and 199. "Cellulose derivative engineering I xy resin" has been corrected to "cellulose derivative, epoxy resin." (4) In box 8, line 19 of the specification, correct the statement ``Show in Table 1-1'' instead of ``Show in Table 1.'' (5) In the 5th line from the bottom of box 9 in the specification and the 1st line from the bottom of page 10, the correction is made to ``rl, 5 μm''.

Claims (1)

[Claims] A magnetic recording medium comprising a magnetic layer containing hexagonal ferrite magnetic fine particles on a support, wherein the magnetic fine particles have an average particle diameter of 0.02 to 0.15 μm, and the magnetic layer includes a magnetic layer. A magnetic recording medium characterized in that the volume filling rate of fine particles is 42 inches or more.