JPS5860431A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To reduce bias-noise while keeping all bands in high reproducing output, by choosing and providing specific surface areas of magnetic powder of the first and second magnetic layers and anti-magnetic force of each magnetic layer etc. on a non-magnetic substrate and thereon by forming >=1 layers of magnetic metallic thin films. CONSTITUTION:After the first magnetic layer 4 contg. metallic (including alloy) magnetic powder having 30-40m<2>/g specific surface area by BET method and which have 2-6mu thickness t1, is formed on a nonmagnetic substrate 1 such as polyethylene terephthalate, the second magnetic layer 5 contg. metallic (alloy) magnetic powder having 35-150m<2>/g specific surface area is formed so as to have 0.2-2mu thickness t2. Further, each of anti-magnetic forces Hc1, Hc2 of the layers 4, 5 is arranged to be Hc1<Hc2. Above one layer e.g. one layer of a magnetic metallic thin film 7, for which its anti-magnetic force Hc3 is chosen to be equal to or more than the anti-magnetic force Hc2 of the layer 5, is formed so as to have 500-1,500Angstrom thickness t3 on the layer 5. By this way, high reproducing output is kept over all band and bias-noise is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetic recording medium having multiple magnetic layers.

Conventional magnetic recording media, such as single-layer metal tapes using alloy powder (the specific surface area of alloy magnetic powder is about 305), have large coercive force and residual magnetic flux density, resulting in large reproduction output over the entire band, but conversely bias noise It also had the disadvantage of being dog-like.

Therefore, various studies have been made to improve this shortcoming.
It has been found that bias noise can be reduced by distributing alloy magnetic powder with a large specific surface area in the magnetic layer of a magnetic tape. However, when increasing the specific surface area of the alloy magnetic powder, the bias noise is reduced due to a decrease in the residual magnetic flux density due to the decrease in the magnetic properties of the alloy magnetic powder, and a deterioration in the dispersibility when dispersed with a binder. The disadvantage is that the desired playback output cannot be obtained.

In view of the above points, the present invention provides a magnetic recording medium having excellent reproduction output and low noise (bias noise) in all bands.

That is, the present invention forms a magnetic layer in a magnetic recording medium by forming first and second magnetic layers by distributing metal magnetic powder (including alloys), and forming at least one magnetic metal thin film layer thereon. The multilayer structure, the specific surface area of the magnetic powder of the first and second magnetic layers, the coercive force ILc of each columnar layer, etc. were selected [7
This is designed to reduce bias noise while maintaining a high reproduction output of all outputs.

Hereinafter, the magnetic recording medium according to the present invention will be described in detail with reference to Examples.

Example 2 1. Alloy magnetic powder with specific surface area 30/g and coercive force '10 (l Oe)
...3 F2O city part thermoplastic polyurethane ・
...251nJt part (Nistan 5702H
Vinyl chloride-vinyl acetate copolymer...25 parts by volume (VAGHU, C,
(Manufactured by Company C) Oleic acid ・・・・・・・・−6 Methyl ethyl cutone ・・・・・・・・・・・4
・1fldi-i part cyclohexanone...
・・・・・・・50 parts by weight In addition to the above composition, after fractional treatment for 24 hours in a ball mill, polyisocyanate (Desmodur) ”-75 bar (manufactured by +-L Co., Ltd.)
A portion of 201 was added and subjected to high-speed shear dispersion for 2 hours to obtain magnetic paint. This is referred to as magnetic coating R(A).

2 2. Alloy magnetic powder with specific surface area 30/g and anti-magnetic cuff 000e 3
00 parts by weight thermoplastic polyurethane resin...
・15 heavy electrical parts vinyl chloride-vinyl acetate copolymer...
...15-layer lid oleic acid ...
・・・・・・・・・・・・・・・6 parts by weight Methyl ethyl ketone ・Mountain・・・・・・・・・250
mt part cyclohexanone・・・・・・・・・25
A magnetic paint was obtained by adding the above composition and following the same process as the magnetic paint (A) of the first example. This is referred to as magnetic paint (B).

3. Alloy magnetic powder with specific surface area 30") and anti-magnetic cuff 000e 300 parts by weight Thermoplastic polyurethane resin 10 parts by weight Vinyl chloride-vinyl acetate together Polymer, 10 parts by weight Oleic acid ・・・
6 parts by weight methyl ethyl ketone ・・・・・・・・・
・・240 m It part cyclohexanone・・
240'1ilEt part The above composition was added and the same process as for the magnetic paint (A,) of the first example was carried out to obtain a magnetic paint. This is called magnetic paint (C).

4. The alloy magnetic powder of the magnetic paint (A) of the first example has a specific surface area of 60"/g, anti-magnetic cuffs 000C and Q (1 (1
Replaced with alloy magnetic powder of (')e (other things being the same) (-
) Magnetic paint 4 was made using the same process as magnetic paint (A).

These are referred to as magnetic paints (I) and (1!;).

5. The alloy magnetic powder of the magnetic paint (A) of the first example was coated with a specific surface area of 100''/jjr anti-magnetic cuff 000e and 9 (10
(Replaced with Je alloy magnetic powder (other things being the same)
A magnetic paint was obtained using the same process button as the magnetic paint (A).

This includes magnetic paint (F) and ((i) and -1''.

6. The alloy of the magnetic paint (A,) of the first example also contains female powder with a specific surface of 40-7g + anti-magnetic cuff 000e and 900
Replaced with 0e alloy magnetic powder (other things being the same)
Same process as magnetic paint (A,): Iromagnetic paint was used.

n2 7, specific surface; Pjr4+1 7. , coercive force 6200e
Nor-Fe2U3-C.

Magnetized powder ・・・・・・・・・・・・・・・
...400 heavy storm part heat jil plastic polyurethane resin ・
・・・・・・－・50 parts by weight Vinyl chloride/face/vinyl acid copolymer ・・・・・・50 parts by weight Lecithin ・・
・・・・・・・・・・・・・・・・・・・・・・・・
・・・・・・・・・4-m IM part Methyl ethyl ketone ・・・・・・・・・・・・・・・・・・700 Heavy part Cyclohexanone ・・・・・・・・・・・・・・・
- 50-layer lid part A magnetic paint was obtained by adding the above composition and following the same process as the magnetic paint (A) of the first example. This is referred to as magnetic paint σ1).

8. Magnetic paint (H) of the seventh example (1) r Fe2
A magnetic paint was obtained by placing an O5-Co magnetically magnetic powder on a γ-Fe203-Co magnetic powder having a specific surface area of 407 np and a coercive force of 8200 e. This is referred to as magnetic paint (I).

The specific surface area and coercive force of the above-mentioned magnetic powder (IC) are the specific surface area, axial ratio, and amount of the compound subjected to N of the acicular magnetic powder as the starting material;
It can be controlled by heat treatment temperature, etc.

Further, the specific surface area of the magnetic powder is determined by the 13 E'l' method.

The characteristics are summarized in the table below. However, B indicates the ratio of binder (E) to magnetic powder (average).

Therefore, each magnetic paint (A,) (
Using A, ), (A), (H) to (1), apply a magnetic paint onto a non-magnetic substrate (for example, a polyethylene terephthalate film with a thickness of 12 μm) (1) as shown in FIG. A magnetic recording medium (3) is prepared by performing magnetic field orientation treatment, drying, and supercalender roll treatment to form a single magnetic layer (2).

Using the same process as above, as shown in Figure 2, the first
A magnetic layer (4) is formed, and after this first magnetic layer (4) is sufficiently cured, a second magnetic layer (5) is formed using a different magnetic paint in the same process to produce an intermediate (6). , this intermediate (6) is heated to a vacuum degree of H1-4 to 10-6 Torr, for example.
A metal magnetic material (for example, Co loo %) is heated and evaporated by a Y electron beam in this vacuum container, and is incident on the second magnetic layer (5) of the intermediate (6). A multilayer magnetic recording medium (8) according to the present invention shown in FIG. 3 is fabricated by forming a magnetic metal thin film layer (7) having an average thickness of 100X by oblique vapor deposition at an angle of 65°.

In addition, gold maple Kobal) (010%) is directly applied to the non-magnetic support.
The magnetic properties when deposited by the above process are coercive force Hc
= 10000e, residual magnetic flux density Br = 10(
100 gauss.

The squareness ratio 1'ts = 90%.

Magnetic properties (residual magnetic flux density Br) of the single-layer magnetic recording medium (3) and multilayer magnetic recording medium (8) produced as described above.

Coercive force Ic), reproduction output (MOL), bias noise, etc. were measured. The results are shown in FIGS. 4 to 6.

The performance of the magnetic recording medium (3) with a single magnetic layer (2) according to
Single layer examples (1) to (231), FIG. 5 shows the characteristics (Example (231)
1)~f121).

Figure 6 shows the characteristics when changing the thickness tl of the lower magnetic layer (4) and the thickness tl of the middle magnetic layer (51) in the multilayer magnetic recording medium (8) (Example α□□□~(23″rC :be.

The magnetic recording medium (magnetic tape) used in the measurement was
This is audio tape cut to inch width. Also,
The measurement method for each characteristic is as follows.

1.8r is the residual magnetic flux density when measured with an external magnetic field of 60,000e. The unit is gauss.

2. l-1c is the coercive force when measured with an external magnetic field of 60000e. The unit is Oersted (Ue).

3. MOL (playback output) is based on the reference frequency (31511z
) and a high frequency (10 ktlz) are used, the former being the output level at which the 315 Hz output signal is 3% distorted, and the latter being the maximum saturated output level of the 10 kHz signal.

4. Bias noise is audible correction filter A (JIS)
This is the bias noise when using . The unit is decibel (db).

5. Tape speed is 4. B (Tn4.

and MOL (315Hz, 10kHz)
and bias noise are based on the single layer example (4) in Figure 4 (O
It is expressed as a relative value (db).

From these Figures 4 to 6, the specific surface area and coercive force of the magnetic powder of the middle second magnetic layer (5) are calculated from the lower first magnetic layer (4).
A multilayer magnetic recording medium (8
) is found to have lower bias noise and higher reproduction output over the entire low frequency band and mounting range than the single-layer magnetic recording medium (3).

In the above configuration, the specific surface area of the magnetic powder 2 of the first magnetic layer (4) is preferably in the range of 30 to 40 /y, and if it deviates from this range, the low frequency reproduction output decreases, and the second magnetic layer (5) The specific surface area of the magnetic powder is preferably in the range of 35 to 150''/.9, and if it deviates from this range, the bias noise will not be reduced.The thickness 11 of the first magnetic layer (4) is 2.0 g.
A value of 6.0μ or less is good; if it is thinner than 2.0μ, the reproduction output in the low range will decrease, and if it is thicker than 6.0μ, the reproduction output in the low frequency range will be too high, or the balance between low and high frequencies will be poor.

The thickness t2 of the second magnetic layer (5) is in the range of 02 to 20μ.If it becomes thinner than <0.2μ, the bias noise will not be reduced;
．． If it becomes thicker than 0 μ, the low-frequency 118 raw output decreases.

In addition, the coercive force 11c1 and residual magnetic flux density Br1 of the first m-th layer (4) are preferably 500 to 1000:L Rusted and 20 (lO to 5000 Gauss, respectively, and for 8r1, if outside this range, the low-frequency output will decrease. The coercive force Hc2 of the 24th fi layer +51 also decreases from 500 to 1000.
Oersted is preferable; if it is outside this range, the high range will not extend.

On the other hand, the coercive force 11c3 of the magnetic metal thin film layer (sword) should be equal to or greater than the coercive force He2 of the m24B layer (5), and the thickness of this magnetic metal thin film layer +7J t3 H 500-1500X, residual magnetic flux density Br
3:260Of) Gaussian is preferred.

Accordingly, in the present invention, based on the above characteristic results, etc., as shown in FIG. The second magnetic layer (5) has a specific surface area A determined by the BET method.
Magnetic powder containing an alloy of 35 to 150-7 g of 2 is formed by applying it in the relationship of specific surface area A1 (specific surface area A2), and the coercive force HCI of the first magnetic layer (4) and the second magnetic layer ( 5), the coercive force Hc 2 is selected to be Hcl (f-1c2), and at least one magnetic metal thin film layer is formed on the second magnetic layer (4), and the coercive force HcB is set to be Hcl (f-1c2). The magnetic force is selected to be equal to or greater than the magnetic force 11c2.

According to the present invention configured in this way, bias noise can be reduced while maintaining high reproduction output over the entire band, compared to conventional single-layer magnetic recording media (for example, metal tape, etc.). An excellent magnetic recording medium can be provided.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a conventional magnetic recording medium, and FIG. 2 is a cross-sectional view of a magnetic recording medium according to the present invention. 3 is a sectional view of the intermediate body in a state where the second magnetic layer is formed, FIG. 3 is a sectional view of the magnetic recording medium according to the present invention, and FIG. , FIG. 5 is a table showing the characteristics of each embodiment of the multilayer magnetic recording medium according to the present invention,
FIG. 6 is a table showing the relationship between the thickness and characteristics of the lower and middle layers of a multilayer magnetic recording medium. In the figure, (1) is the non-magnetic substrate, (4) is the first magnetic layer, (E)
) is the second magnetic layer, and (7) is the magnetic metal thin film layer. Figure 1 Figure 2

Claims (1)

[Claims] It consists of a non-magnetic substrate, a first magnetic layer on the substrate, a second magnetic layer on the first magnetic layer, and at least one magnetic metal thin film on the second magnetic layer, and the first magnetic layer is The second magnetic layer is formed by coating a metal magnetic powder containing an alloy with a specific surface area of 30 to 40 by the BET method, and the second magnetic layer is formed by coating a metal magnetic powder containing an alloy with a specific surface area of 35 to 150 or 9 by the BET method. The coercive forces of the first magnetic layer and the second magnetic layer have a relationship of Hc 1 (Hc 2), and the coercive force of the magnetic gold thin film and the coercive force of the second magnetic layer are Hc 3≧
A magnetic recording medium characterized by being Hc2.