JPS5856231A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a magnetic recording medium having an excellent reproducing output in all bands with a low level of noise, by setting the specific surface area, the reluctance force, the residual magnetic flux density, etc. within a specific range respectively for the oxide or the metallic magnetic powder of each of two magnetic layers. CONSTITUTION:The powder of oxide magnetic material having 18-30m<2>/g specific surface and obtained by a BET process is coated on a nonmagnetic substrate 1 to obtain the 1st magnetic layer 4 which has 350-700 oersted reluctance force HC1 and 1,600-2,000G residual magnetic flux density. Then the metallic magnetic powder having 35-80m<2>/g specific area and obtained by the BET process to obtain the 2nd magnetic layer 5 which has 550-900 oersted reluctance force HC2. The HC2 of the layer 5 is set larger than or equal to the HC1 of the layer 4.

Description

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

Conventional magnetic recording media, for example, magnetic tapes with a single magnetic layer coated with γ-Fe203 magnetic powder (specific surface area of magnetic powder 2
(approximately 0 m2/g) has a large coercive force and a large residual magnetic flux density, and has the drawback that although the reproduction output becomes large over the entire band, the bias noise also becomes large.

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.

Based on experiments and research carried out in various buildings, the present inventor has found that in magnetic recording media, when metal magnetic powder with a large specific surface area is distributed on the surface of the magnetic layer, bias noise is reduced, and the inside of the magnetic layer (
In other words, oxide magnetic material powder with a small specific surface area (r Fe2O3 magnetic powder, γ-Fe2
It has been found that the best results can be obtained by increasing the reproduction output over the entire band by distributing the magnetic particles (O3-Co magnetic powder, etc.).

Therefore, based on the results of this research, the present invention provides a magnetic recording medium with a two-layer structure of oxide magnetic material powder and metal magnetic powder of iron oxide magnetic powder to which Co is deposited as a magnetic layer.
Specific surface area of each magnetic powder in both the upper and lower magnetic layers, coercive force 11
c, residual magnetic flux density Br, etc. are selected respectively, and the bias noise is reduced while maintaining high reproduction output in the entire band.

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

Example 1, γF with specific surface area 20 mg and coercive force 4200e
e2O3Co magnetic powder: 400 parts by weight Thermoplastic polyurethane resin: 50 parts by weight (Nistan 5702 Ii, manufactured by F1 Gutdrich) Vinyl chloride-vinyl acetate copolymer (VAGHlU, manufactured by C, C) )...50 parts by weight Lecithin...■ 4 streetcar parts Methyl ethyl ketone -φ...-700ii parts Cyclohexano/#I+9-50 heavy lid parts The above composition was added and after dispersion treatment in a ball mill for 24 hours, 1 part of polyincyanate (Desmodicol-75, manufactured by Bayer A, Q) was added and subjected to high-speed dispersion for 2 hours to obtain a magnetic paint. This was called magnetic paint (A). do.

2. Specific surface area 20m, anti-corrosion power 4200e r
Fe2O5-Co magnetic powder...400 parts by weight Thermoplastic polyurethane resin...33.3m1t
Part Vinyl chloride-vinyl acetate copolymer...-33.3 parts by weight Lecithin...4 parts by weight Methyl ethyl ketone...Φ650 i Part Cyclohexanone -■ Contention 5o parts by weight In addition to the above composition, the following A magnetic paint was obtained by the same process as the magnetic paint body of the first example. This is called magnetic paint (BJ).

3. γ-Fe with specific surface area of 20 m and coercive force of 42 ooe
2O3-Co magnetized powder - 400 parts by weight Thermoplastic polyurethane resin 253 parts vinyl chloride-vinyl acetate copolymer 25 parts by weight Lecithin - Skewers @ 4 mJ [methyl ethyl ketone] 625 parts by weight cyclohexanone 50 parts by weight The above composition was added and a magnetic paint was obtained by following the same steps as the magnetic paint (A) of the first example. This is called magnetic paint (C).

4. Magnetic paint of the third example (1-Fe2O3-C of q
o The magnetic powder has a specific surface area of 20m and a coercive force of 5200e.
, 6200e, and 7200e (other things being the same), magnetic paints were obtained by the same process as the magnetic paint (A) of the first example. These are referred to as magnetic paints (I), (E), and (F), respectively.

5. γFe2O3Co of the magnetic paint (13) of the second example
The magnetic powder has a specific surface area of 20r and a coercive force of 4200o.

γ-Fe2O3, CO-doped, Co-Fe3O4,
and replaced with CrO2 magnetic powder (other things being the same)
A unique paint was obtained by the same process as magnetic paint 4 of the first example. These are magnetic paints O), (I]), (I) and (
J).

6. Alloy powder red paper with a specific surface area of 40m and coercive force of 6000e... @ 300 parts by weight Thermoplastic polyurethane resin Work... 25 parts by weight Vinyl chloride-vinyl acetate copolymer - 25 parts by weight Olein Acid ψ・・・6*tj
ki((methyl ethyl ketone...e@0440
m! Okibe cyclohexanone II work...
Adding 44,040 parts by weight of the above ingredients, a magnetic coating material was obtained by following the same process as in the magnetic coating material of the first example. This is called magnetic paint σ〈).

7. Replace the alloy powder of the magnetic paint of the sixth example with alloy powder of specific surface area 40 m, i, anti-magnetic cuff 000e and 10000e (other things being the same) and the magnetic paint body of the first example). A magnetic paint was obtained by the same process. This is referred to as magnetic paint (L) and (2).

8. The same as the magnetic paint of Example 1, except that the alloy powder of the magnetic paint of Example 6 was replaced with the alloy powder of anti-magnetic cuffs of 000e and 100006 with a specific surface area of 5 om31 (assuming everything else was the same). A magnetic paint was obtained through the process. These will be referred to as magnetic paints (f) and (o).

9. The same as magnetic paint 4 of Example 1, except that the alloy powder of the magnetic paint of Example 6 was replaced with alloy powder of specific surface area som and anti-magnetic cuffs of 000e and 10000e (assuming other things were the same). A magnetic paint was obtained through the process. These are called magnetic paints (P) and Q.

The characteristics of each of the above-mentioned magnetic paints (A) to @ are summarized in the table below. However, frost indicates the ratio of binder B to magnetic powder P.

Using each of the above magnetic paints (N-0), as shown in Figure 1, the magnetic paint was applied onto a non-magnetic substrate (for example, a 12 μm thick polyethylene terephthalate film) (1), and subjected to magnetic field orientation treatment. After drying, a super calender roll treatment is performed to form a crushed magnetic layer (2) to produce a magnetic recording medium (3).

In addition, as shown in FIG. 2, a first magnetic/m (lower layer) (4) is formed in the same process as above using the same magnetic paint.
After this first magnetic layer (4) is sufficiently hardened, a second magnetic layer (upper layer) (5) is formed in the same process as above to produce a two-layer magnetic recording medium (6) according to the present invention.

The magnetic properties (residual magnetic flux density Br, coercive force Hc), reproduction output (MOL), bias noise, etc. of the magnetic recording media (3) and (6) produced as described above were measured.

The results are shown in FIGS. 3 to 6.

Figures 3A and 3B show the characteristics of the magnetic recording medium (3) of the single magnetic layer (2) with each magnetic coating material (A) to 0 (single layer example (1) to (
3I) Figure 4 shows the characteristics of the two-layer magnetic recording medium (6) according to the present invention (Examples (1) to (13) of the present invention), and Figure 5 shows the magnetic properties of the upper layer in the two-layer magnetic RT recording medium (6). Characteristics when changing the thickness t2 of layer (5) (same example (14) to (2)
, and FIG. 6 similarly show the characteristics when the thickness tl of the lower magnetic layer (4) was changed (Countries C to C of the same example).

The magnetic recording medium (magnetic tape) used for the measurement was 1
This is an audio tape cut into inch width pieces. Also,
The measurement method for each characteristic is as follows.

1. The residual magnetic flux density Br is the residual magnetic flux density when measured with an external magnetic field of 20000e. The unit is gauss
).

2. The coercive force Hc is the coercive force when measured with an external magnetic field of 20000e. The unit is Oersted (Oe).

3. For MOL (maximum output level: playback output), the reference frequency (315Hz) and high frequency (10KHz) are used. This is the maximum saturation output level.

4. Bias noise is measured using auditory correction filter fi-A (JI
This is the noise when using S). The unit is decibel (d
b).

5. Tape speed is 4-8x.

The MOL (315Hz, l0KI(z) and bias noise are based on the single layer example (1) in Figure 3 (Qd
b) is expressed as a relative value (db).

From FIGS. 3 to 6, it can be seen that the upper second magnetic layer (5)
A two-layer magnetic recording medium (6) according to the present invention in which the specific surface area of the magnetic powder is larger than that of the lower first magnetic layer (4).
produces a high reproduction output of the conventional single-layer magnetic recording medium (3),
Furthermore, it is recognized that bias noise can be significantly reduced.

The specific surface area of the oxide magnetic material powder in the lower first magnetic layer (4) is preferably in the range of 18 to aom%; if it deviates from this range, the low frequency reproduction output will decrease, and the upper second magnetic layer (5)
The specific surface area of the metal magnetic powder is preferably in the range of 35 to som%, and if it is outside this range, bias noise will not be reduced. On the other hand, the coercive force Hc1 and residual magnetic flux density Br+ of the first magnetic layer (4) are 350 to 700 engineering A/stead and 1
A value of 600 to 2000 Gauss is good, and for Br+, if it is out of this range of 1600 to 2000 Gauss, the low-frequency output decreases. The coercive force Hc2 of the second magnetic layer (5) is preferably 500 to 900 oersted; if it is out of this range, the high frequency range will not be extended, and recording bias erasure will be subject to restrictions on the recording/reproducing apparatus side. In addition, the coercive force Hc1 of the first magnetic layer (4) and the coercive force Hc1 of the second magnetic layer (5)
The relationship with c2 is l-1cl (Hc2 is preferred.

The thickness of the first magnetic layer (4) is 2.0 μm or more and 6.0 μm thick.
The thickness is preferably 0μ or less; if it is thinner than 2.0μ, the low-frequency reproduction output will decrease; if it is thicker than 6.0μ, only the low-frequency reproduction output will increase too much, and the balance between low and high frequencies will be poor. The thickness of (5) should be in the range of 0.2 to 2.0μ; if it is thinner than 0.2μ, bias noise will not be reduced
If it is thicker than 2°0μ, the low frequency reproduction output will decrease.

As described above, in the present invention, based on the characteristic results shown in FIGS. 4 to 6, the first magnetic M (4) and the second magnetic Wt ( 5), the first magnetic layer (4) is formed by applying an oxide magnetic material powder having a specific surface area of 18 to aom% by the BET method, and its resistance is Magnetic force Hc
1 to 350 to 700 oersted, residual magnetic flux density Br (
1600 to 2000 Gauss, and the second magnetic layer (
5) is formed by coating a metal magnetic powder with a specific surface area of 35 to 80" d by the BET method, and its coercive force Hc2 is 55
0 to 900 oersted and the coercive force Hc1 (coercive force HC2 is selected).

According to the present invention, it is possible to reduce bias noise while maintaining high reproduction output over the entire band, and it has superior magnetic properties compared to conventional single-layer magnetic recording media (for example, metal tape). A recording medium can be provided.

[Brief explanation of drawings]

FIG. 1 is an enlarged sectional view of a conventional magnetic recording medium, FIG. 2 is an enlarged sectional view of a magnetic recording medium according to the present invention, and FIGS. 3A and 3B show characteristics of each side of a single-layer magnetic recording medium. Figure, 4th
The figure is a table showing the characteristics of each embodiment of the two-layer magnetic recording medium according to the present invention, FIG. 5 is a table showing the relationship between the thickness of the upper layer of the two-layer magnetic recording medium and the characteristics, and FIG. FIG. 3 is a table showing the relationship between the thickness and characteristics of the lower layer of a layered magnetic recording medium. In the figure, (1) is a nonmagnetic substrate, (4) is a first magnetic layer (lower layer), and (5) is a second magnetic layer (upper layer). Figure 1 Figure 2

Claims (1)

[Claims] It consists of a non-magnetic substrate, a first magnetic layer on the substrate, and a second magnetic layer on the first magnetic layer, and the first magnetic layer is made of B.
It is formed by applying oxide magnetic material powder with a specific surface area of 18 to 30 m2/g by the ET method, and its coercive force HC1 is 3.
50 to 700 oersted, residual magnetic flux density Br 160
0 to 2000 gauss, and the second magnetic layer is formed by coating metal magnetic powder with a specific surface area of 35 to 80 m2/g by the BET method, and its coercive force HC2 is 500 to 900 gauss.
1. A magnetic recording medium which is Oersted and is characterized in that coercive force HC1 < coercive force HC2.