JPH05298677A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To provide a magnetic recording medium having high recording density and excellent in recording characteristics in a wide wavelength band from short wavelength to long wavelength. CONSTITUTION:When a lower magnetic layer contg. acicular magnetic particles and a resin binder and an upper magnetic layer contg. magnetic powder for short-wavelength recording and a resin binder are formed on a nonmagnetic substrate to obtain a magnetic recording medium, the number of the acicular magnetic particles exposed to the surface of the upper magnetic layer is controlled to 0.1-10% of that of the magnetic powder for short-wavelength recording. By this control, characteristics in a long wavelength band are improved without deteriorating characteristics in a short wavelength band.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high recording density magnetic recording medium having excellent recording characteristics in a wide wavelength range from a short wavelength range to a long wavelength range.

[0002]

2. Description of the Related Art In recent years, magnetic recording media have been used for audio,
It has come to be widely used as a recording medium for recording a large amount of information in various fields such as video and computer, and accordingly, a demand for higher density recording is increasing.

Conventionally, a coating type magnetic recording medium is obtained by coating a support such as a polyester film with magnetic powder such as γ-ferrite or iron powder together with a resin binder. In order to significantly improve the magnetic recording density in such a magnetic recording medium, a perpendicular magnetic recording method using magnetization in a direction perpendicular to the coated surface of the support has been proposed.

As a magnetic recording medium suitable for perpendicular magnetic recording, a magnetic paint mainly composed of hexagonal ferrite ultrafine particles such as Ba ferrite and a resin binder, whose easy axis of magnetization is easily oriented in a direction perpendicular to the support, is supported. Magnetic recording media applied to the body are being researched and developed. However, the magnetic recording medium obtained by using such ultrafine particle hexagonal ferrite magnetic powder can obtain a high reproduction output in a short wavelength region of a recording wavelength of about 1 μm or less, while recording in a long wavelength region. It has been found to have a characteristic that a very high reproduction output cannot be obtained when used for.

Usually, in a magnetic recording medium, in addition to short wavelength recording, which makes good use of high density recording characteristics, relatively long wavelength recording is often performed simultaneously. For this reason, in addition to short wavelength recording characteristics, wide band recording characteristics including long wavelength recording characteristics are desired for magnetic recording media. In order to satisfy such recording characteristics, a magnetic recording layer having good recording characteristics at long wavelength is provided as a lower magnetic layer on a support, and a magnetic recording layer having excellent short wavelength recording characteristics is used as an upper magnetic layer on the support. Provided,
A magnetic recording medium having a multilayer structure has been proposed.

By the way, there are various methods for obtaining the above-mentioned magnetic recording medium having a multilayer structure. Among them, the simultaneous coating method (wet-on-wet method) is particularly noted because good surface smoothness can be obtained. Have been collected.
This simultaneous coating method is a method of coating the lower layer coating film using, for example, a slot die coater, and then coating the upper layer layer before the organic solvent of the coating film evaporates and does not finish drying. Even if some time passes during application, no inconvenience occurs. Therefore, it is not always necessary to combine the slot dies for simultaneous coating into one. Simultaneous coating is not limited to formation of the magnetic layer, but an underlayer containing carbon black or the like coated on the surface of the support can be formed simultaneously with the magnetic layer.

[0007]

However, even when the magnetic layers are multilayered, it is difficult to say that the effect of the multilayers is satisfactorily obtained in the actual recording / reproducing characteristics under the present circumstances. In order to bring out the effect of the lower magnetic layer sufficiently, the thickness of the upper magnetic layer is, for example, 0.2 to 0.5 μ.
This is because it is required to set in the submicron region of about m 2 or less, and this impairs the short wavelength recording characteristic which is an original feature of the upper magnetic layer.

The present invention has been made under the above circumstances, and provides a multi-layer magnetic recording medium capable of wide band recording by improving long wavelength characteristics without impairing short wavelength recording characteristics.

[0009]

According to the present invention, a lower magnetic layer containing acicular magnetic particles and a resin binder, and an upper magnetic layer containing magnetic powder for short wavelength recording and a resin binder are provided on a non-magnetic support. In the magnetic recording medium having the layer formed, the number ratio of the acicular magnetic particles found on the outermost surface of the upper magnetic layer to the magnetic powder for short wavelength recording is 0.1 to 10%.

Next, the structure of the magnetic recording medium of the present invention will be described.

The lower magnetic layer of the present invention is a layer mainly composed of acicular magnetic particles dispersed in a resin binder. Examples of the acicular magnetic particles include Co-deposited γ-Fe ₂ O ₃ , Co-deposited-Fe ₃ O ₄ , or intermediates thereof, or Fe-A.
Various alloy magnetic particles such as l, Fe-Ni and Fe-Al-Ni can be used. The shape of these magnetic particles may be needle-like and may be rice-like, for example. The coercive force of these magnetic powders is 500 Oe or more, and the specific surface area is 30 m ² / g.
The above is desirable.

In the present invention, the lower magnetic layer may have a single layer structure or a multilayer structure.

The main magnetic particles for short wavelength recording contained in the upper magnetic layer of the present invention include, for example, the chemical formula BaO.n (Fe _{1 -m} M _m ) ₂ O ₃ (where M is Zn, Co, Ti, Ni, Mn, In, Cu, Ge, Nb,
1 selected from Sn, Mg, Ta, Cr, Mo, W, Zr, Hf, V
Hexagonal ferrite particles such as Ba ferrite, which represent one or more elements and represent the numbers 0 ≤ m ≤ 0.2 and 5 ≤ n ≤ 10, can be used. The shape of the magnetic particles is preferably a plate having a plate ratio (ratio of plate diameter to thickness) of 2 or more. The specific surface area of magnetic particles is
It is preferably 20 m ² / g or more, more preferably
It is 30 m ² / g or more. In the present invention, the number ratio of the needle-shaped magnetic particles found on the outermost surface of the upper magnetic layer to the short-wavelength recording magnetic powder is preferably 0.1 to 10%, more preferably 0.3 to 3%.

The above number ratio is the number ratio of particles having a major axis of 0.01 μm or more which can be easily counted when the surface of the magnetic recording medium is observed with a scanning electron microscope (SEM).

In the present invention, the number ratio of the acicular magnetic particles found on the outermost surface of the upper magnetic layer to the short-wavelength recording magnetic powder is set to 0.1 to 10% because the number of acicular magnetic particles is This is because if it is less than 0.1%, the improvement of the long wavelength characteristics, which is the effect of the present invention, becomes insufficient, and if it exceeds 10%, the deterioration of the short wavelength characteristics cannot be ignored.

The magnetic recording medium of the present invention is manufactured as follows according to a conventional method.

That is, first, the above-mentioned upper magnetic layer forming component mainly containing plate-like magnetic particles and a resin binder and the lower layer forming component containing needle-shaped particles and a resin binder are kneaded and dispersed in a solvent, respectively. A magnetic layer coating material and a lower magnetic layer coating material are prepared. Next, these magnetic paints are sequentially applied on a support, and then subjected to orientation treatment and drying treatment. The formed coating film is subjected to a smoothing treatment with a calendar to obtain the magnetic recording medium of the present invention.

[0018]

In the multi-layered magnetic recording medium of the present invention, the short wavelength characteristics of the upper magnetic layer are impaired by including an appropriate amount of a part of the magnetic particles contained in the lower magnetic layer in the upper magnetic layer. However, the wavelength characteristics are improved.

[0019]

EXAMPLES The details of the present invention will be described below based on examples. Prior to the examples, a general description will be given to the present invention.

Examples of the material constituting the non-magnetic support usable in the present invention include polyesters such as polyethylene terephthalate and polyethylene naphthalate, as well as polyolefins, cellulose derivatives and polycarbonate. Further, a support made of metal, glass, ceramic or the like can be used.

In the lower magnetic layer of the present invention, any resin commonly used as a resin binder may be used, for example, a thermoplastic resin, a thermosetting resin, a reactive resin, an electron beam curing resin, or the like. It is possible to mix even such a thing. Of these, resins such as vinyl chloride / vinyl acetate copolymers having functional groups such as metal sulfonate bases, polyurethanes and polyesters are particularly preferable.

In addition to the above, the lower magnetic layer of the present invention may contain a lubricant such as a fatty acid or a fatty acid ester, an abrasive such as alumina particles, and an antistatic agent such as carbon.

The resin binder used for the upper magnetic layer is
It is possible to select basically the same as that used for the lower magnetic layer. Therefore, the same resin binder can be used for the upper and lower magnetic layers. Alternatively, the types and types of upper and lower resin binders may be different depending on the purpose.

The types and kinds of other additives used in the upper magnetic layer can be selected similarly to the case of the resin binder.

Examples 1 to 10 First, the following material compositions were mixed as the <upper magnetic layer coating material> to obtain 10 kinds of magnetic coating materials having different acicular magnetic particle contents (X parts by weight). It was prepared according to a conventional method.

Ba ferrite powder 100-X parts by weight (Hc 1000 Oe, specific surface area d = 35 m ² / g, plate ratio 3.3) Co-containing iron oxide X parts by weight (Hc 770 Oe, specific surface area d = 45 m ² / g) Sulfonated vinyl chloride resin 10 parts by weight Sulfonated polyurethane 5 parts by weight Alumina (particle size 0.2 μm) 6 parts by weight Carbon 1 part by weight Myristic acid 1 part by weight Butyl stearate 1 part by weight Methyl ethyl ketone 100 parts by weight Cyclohexanone 100 parts by weight Parts Toluene 100 parts by weight After mixing the above materials, they were mixed and dispersed for 2 hours with a sand grinder. Next, to 100 parts by weight of the obtained coating material, 5 parts by weight of Coronate L (trade name of polyisocyanate-based curing agent, manufactured by Nippon Polyurethane Co., Ltd.) was further added and mixed. And

Next, as the <lower magnetic layer coating material> material, a composition having the same composition as the above <upper magnetic layer coating material> was prepared except that X = 100, and a coating material was prepared by the same method. Coating material for lower magnetic layer> was prepared.

The <upper magnetic layer coating material> and <lower magnetic layer coating material> thus obtained were applied on a polyethylene terephthalate film having a thickness of 9 μm by a wet-on-wet method, and then subjected to a magnetic field orientation treatment. The
Then, after drying, the surface was smoothed by a calendar. Further, the coating material for the bulk coat layer was applied on the back surface and dried.

The original fabric thus obtained is slit to 8 mm
A video tape was made. With respect to the obtained tape samples (Examples 1 to 10), a playback Y output (Y signal frequency 4.2 MHz to 5.4 MHz [carrier frequency 5 MHz]) and a C signal output (C signal frequency 0.75) were performed using an 8 mm video deck.
(MHz) was measured (Y signal was superimposed on C signal and recorded).
The evaluation results are shown in Table 1.

Comparative Examples 1 to 6 Tape samples of Comparative Examples 1 to 6 in which the content of the acicular magnetic particles was different from the range of the present invention were prepared in the same manner as in the Examples, and these are also the Examples. It evaluated similarly to.
The evaluation results are shown in Table 1.

[0031]

[Table 1]

[0032]

As is apparent from the above-described embodiments, the upper magnetic layer contains a part of the magnetic particles of the lower magnetic layer in an appropriate amount, so that the short wavelength recording characteristics of the upper magnetic layer are not impaired. The long wavelength characteristics are effectively improved.

[0033]

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Seiichi Tobizawa, 1 Sakura-cho, Hino-shi, Tokyo Konica stock company (72) Inventor Noriko Kawahara 1, Sakura-cho, Hino-shi, Tokyo Konica stock company

Claims (2)

[Claims] 1. A magnetic recording comprising a non-magnetic support, a lower magnetic layer containing acicular magnetic particles and a resin binder, and an upper magnetic layer containing short-wavelength recording magnetic powder and a resin binder. In the medium, the number ratio of the acicular magnetic particles found on the outermost surface of the upper magnetic layer to the short-wavelength recording magnetic powder is
A magnetic recording medium characterized by being 0.1 to 10%. 2. The magnetic powder for short wavelength recording has a coercive force Hc of 500 to
2. The magnetic recording medium according to claim 1, wherein the magnetic recording medium is hexagonal ferrite powder having a particle size of 3,000 Oe and a particle size of 0.01 to 0.1 .mu.m.