JPS5870429A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To increase the output in the whole band by forming an upper layer contg. Co deposited iron oxide powder and a lower layer contg. metallic magnetic powder while regulating the specific surface area, coercive force and residual magnetic flux density of each of magnetic powders, in the upper and lower magnetic layers and the thickness of each of the layer. CONSTITUTION:A nonmagnetic substrate 1 is coated with ferromagnetic metallic powder having 20-50m<2>/g specific surface area according to the BET method to form the 1st magnetic layer 4 having 500-1,200 Oe coercive force, 2,000-4,000 G residual magnetic flux density and 2-6mum thickness. The layer 4 is coated with magnetic powder of Co deposited iron oxide having 35-50m<2>/g specific surface area according to the BET method to form the 2nd magnetic layer 5 having 600-1,200 Oe coercive force and 0.2-2mum thickness. The coercive force of the 2nd layer is made higher than that of the 1st layer.

Description

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

Conventional magnetic recording media, e.g. single layer γ-Fe 203-
C.

Magnetic tape using magnetic powder (specific surface area of magnetic powder 2
0 rn'/f), both the coercive force and the residual magnetic flux density are large, and the reproduced output becomes sharp over the entire band, but conversely the noisy 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 in all bands.

Based on various experiments and researches, the present inventor has found that in magnetic recording media, when iron oxide magnetic powder with a large specific surface area is distributed on the surface of the magnetic layer, noise is reduced, and We have found that if metal magnetic powder with a small specific surface area is distributed in the lower layer below, the reproduction output becomes sharper over the entire waveband. C has a large specific surface area, especially in the upper layer.

It has been found that good results can be obtained by distributing deposited iron oxide magnetic powder and distributing metal ferromagnetic powder with a small specific surface area in the lower layer.

Therefore, based on the research results of this invention, the magnetic layer of a magnetic recording medium is made of a lower layer using metal ferromagnetic powder and a CO2.
'# It has a two-layer structure with an upper layer using shaped iron oxide magnetic powder, and the specific surface area, coercive force Hc, residual magnetic flux density Br, layer thickness, etc. of each magnetic powder in both the upper and lower magnetic layers are selected respectively. It is designed to maintain a high reproduction output in the entire band while reducing harsh noise.

The CO#-shaped acid-form iron oxide magnetic powder used in the present invention can be obtained by the following method.

That is, acicular iron oxide magnetic powder, such as γ-Fe2O3 or iron oxide magnetic powder in an oxidation state intermediate between γ-Fe2O3 and Fe304, is mixed into a water-soluble copolymer in a strong alkaline aqueous solution.
2 Mix with rut salt or metal co-malt particles and heat 1υ
The surface of the acicular acid iron magnetic powder is adsorbed on the iron hydroxide particles by stirring, washed with water, dried, and sized out, and heat-treated in an empty package or with N2, etc. to improve the surface of the acicular acid iron magnetic powder. cobalt compounds (e.g. cobalt intoxicants)
Wait for the iron oxide magnetic powder that has adhered to 111 □At this time, heat treatment after taking it out of the solution, e.g. 80°C to 200°C.
The specific surface area of the Co (compound)-adhered iron oxide B magnetic powder produced by this method, the coercive force HC is the specific surface area of the acicular iron oxide magnetic powder as the starting material, Axial ratio and deposited Co
It can be controlled by the season of (compound) and heat treatment temperature.

A method for producing CO-adhered iron oxide magnetic powder is disclosed, for example, in the specifications of Japanese Patent Application No. 52-79645, Japanese Patent Application No. 53-67490, or Japanese Patent Application No. 54-57374.
Further, it is also possible to use a ferric oxide magnetic powder in which not only a COO compound but also a compound of Co and Fe is deposited on the surface of acicular iron oxide particles.

In this case, a compound of iron and cobalt is deposited on the surface of the acicular iron oxide particles by thermally stirring the acicular iron oxide in a strong alkaline aqueous solution together with a conosite salt and an iron salt, and then the same heat treatment as described above is carried out. It can be obtained by applying An example of this method is disclosed, for example, in the specification of Japanese Patent Application No. 130918/1982.

The above method for producing magnetic powder is used only in the present invention (:
These are merely examples of the method for producing 0 compound adhesion or CO and Fe compound ferric oxide, and it goes without saying that the magnetic powder used in the present invention is not limited to these production methods. do not have.

゛Hereinafter, Co-adhered acid iron oxide magnetic powder is γ-Fe20
The magnetic recording medium according to the present invention will be described in detail with reference to an example using 3-CO magnetic powder. Note that the specific surface area of the magnetic powder is determined by the B E 'I' method.

Example 1, specific surface area 20 d/y-1 anti-magnetic cuff 200e) γ-
F'8203-Co magnetic powder ・・・・・・・・・
400 parts by weight lecithin
・・・・・・・・・・・・ 4 parts by weight Methyl ethyl ketone ・・・・・・・・・・・・・・・ 625 parts by weight Cyclohexanone ・・・・・・・・・・・・・・・
・・・・・・ 50 parts by weight of the above composition was added, and after dispersion treatment in a Zeel mill for 24 hours, 20 parts by weight of polyisocyanate (Desmodicol L-75, manufactured by Inil A, G) was added and high-speed shearing was performed for 2 hours. Dispersion was performed to obtain magnetic paint.

This is called magnetic paint (A).

2 Body surface area 20rr? /l-1 anti-magnetic cuff 200e (
7) γ-Fe203-Co magnetic powder...
...400 parts by weight thermoplastic polyurethane resin ・
・・・・・・・・・ 50 parts by weight Vinyl chloride-vinyl acetate copolymer ・・・・・・・・・ 50 parts by weight Lecithin
・・・・・・Track 4 fiJ 1 part Methyl ethyl ketone ・・・・・・・・・700 parts by weight Cyclohexanone ・・・・・・・・・ 50 parts by weight The above composition was added, and the magnetic paint of Example 1 (A ,
) A magnetic paint was obtained using the same process. Add this to magnetic paint (
A').

3. r-Fe203- of magnetic cylinder 1 (A) of the first embodiment
Co magnetized powder with a specific surface area of 20 rr? /? -Magnetic paint (as a magnetic powder rotating between γ-Fe203-Co magnetic powders with coercive force of 9200e and 12000e)
A magnetic paint was obtained by the same process as A). These are referred to as magnetic paints (B) and (C), respectively.

4. Specific surface area 30rr? /? , alloy magnetic powder with coercive force of 6000e 300 parts by weight thermoplastic polyurethane resin 2
5 parts by weight Vinyl chloride-vinyl acetate copolymer...
25 parts by weight oleic acid...
... 6 parts by weight methi, ethyl ketone ...
- 440 parts by weight of curved parts cyclohexanone - 440 parts by weight of concave parts The above composition was added, and a magnetic paint 'ff: was obtained by following the same process as the magnetic paint (A) of the first example. This is called a magnetic paint (D).

5 The alloy magnetic powder of the magnetic paint (D) of the fourth example has a specific surface of 8 [30th'/), a coercive force of 8000e, 10
A magnetic paint was obtained by the same process as the magnetic paint (A) of the first example except that alloy magnetic powders of 000e and 13000e were substituted (other things being the same). Apply this to resistant paint (E)
, (one and (G).

6 γ-IF with specific surface area 40m/P and antimagnetic cuff 200e
”e203-Co magnetic powder ・・・・・・・・・4
00 weight department plastic gold polyurethane resin ・・・・・・
... 5 parts by weight Vinyl chloride-vinyl acetate copolymer 50 parts by weight Lecithin
・・・・・・・・・ 4 iJi parts quantum methyl ethyl ketone ・・・・・・・・・700Mr
Quantity part cyclohexanone... Song... In addition to the composition for the 50-weight INN part, the following magnetic paint of Example 1 (
A magnetic paint was obtained by the same process as A). This is called magnetic paint (H).

7. Magnetic paint of the sixth example (1-Fe2O5 of I-()
-Co magnetic powder with a specific surface area of 40i/? , coercive force 92
00e.

1-Fe2O3C(l
Replace the tuna with M
It is reminiscent of the LTB paint made by the same process as the magnetic paint (A) of the first embodiment. These are referred to as magnetic paints (I), (J) and (K), respectively.

8 γ-Fe203-C of the magnetic paint (H) of the sixth example
o The specific surface area of the magnetic powder is 50d/? , anti-magnetic cuff 200
e.

r of 9200e, 12200e and 1420(')e
Fe203-C.

A magnetic paint was obtained by the same process as the magnetic paint of the first example (A,) except that the magnetic paint was replaced with cedar magnetic powder (assuming that the diameter was the same). These were used as magnetic paints (L) and (M), respectively.

(N) and (0).

Each of the above-mentioned magnetic paints (A), (A'), (B) ~
The characteristics of (0) are summarized and shown in the table below. However, the ratio of No.zeta.inder B to P/B magnetic powder P is shown.

Therefore, each of the above magnetic paints (A), (A'),
Using (LJ) to (0), as shown in Figure 1, a magnetic paint is applied on a non-magnetic substrate (for example, a polyethylene terephthalate film with a thickness of 12 μm) (1), and Funaba orientation treatment is performed. After drying, the suit is subjected to one calender roll treatment to form a single magnetic layer (2) to produce a magnetic recording medium (3).

Using similar magnetic paints (D), (I), etc.
As shown in the figure, a first filtration layer (lower layer) (4) is formed in the same process as above, and after this first magnetic layer (4) is sufficiently hardened, a second magnetic layer (upper layer) is formed in the same process as above. ) (5) A two-layer magnetic pointing medium (6) according to the present invention is produced.

The magnetic properties (residual magnetic density IFBr, coercive force 11c), reproduction output (MOL), bias noise, etc. of the magnetic recording bodies (3) and (6) produced as described above were measured.

The results are shown in Figures 3, 2p and 4.

Figure 3 shows each radial muscle (#4 (A'), (A), (
Characteristics of the magnetic recording medium (3) of the m-magnetic layer (2) according to l() to (0) (single layer example m to (+e), m4 Figure 1tim property, elf (D) to (G), (I), (J
), (K)(M) ~ Characteristics of the two-layer magnetic recording body (6) according to the present invention according to (0) (Example (1) of the present invention)
~α61,).

The magnetic recording medium (aluminum tape) used in the measurements was an audio tape cut into 1z 8 inch pieces.

Moreover, the measurement method of each characteristic is as follows.

1. The residual magnetic flux density Br is the residual magnetic flux density when measured at a magnetic field of 20,000 e.The unit is Gauss (gauss).
ss).

2 Coercive force I- (C is the coercive force measured in an external magnetic field of 20000e. The unit is Oersted (Oe).

3. MOL (maximum output level: reproduction output) is the standard frequency (3151-Iz) and high frequency (1,0k'Hz).
) is used, the former is 315) Iz output signal is 3%
The output level that causes distortion, the latter of which is a 10kHz signal, is “
This is a large saturation output level.

4 Noζ ear noise is filtered using auditory divine filter A (JIS
) is used. The unit is decibel (db)
).

5 The tape speed is 4.8u'sec.

And to 40 L (3151-1z, 10kHz
z) and 6ias noise are shown as relative values (db) with the single layer example (1) in FIG. 3 as the reference (Odb).

From these figures 3 and 4, the specific surface area of the magnetic powder of the upper second magnetic layer (5) is set to be smaller than that of the lower first magnetic layer (4), and The dual-layer magnetic recording medium (6) according to the present invention, which has a large residual magnetic flux density (4), has a high reproduction output over the entire low and high frequencies compared to the conventional single-layer magnetic recording medium (3). The specific surface area of the metal ferromagnetic powder of the lower first magnetic layer (4) is preferably in the range of 20 to 50 G/N, and is 20 m2. If the residual magnetic flux density is less than /y-, the residual magnetic flux density becomes too large and the ear noise increases, and if it is more than 50rn'/y-, the residual magnetic flux density is so small that the low-frequency reproduction output decreases, and the upper layer The specific surface area of the CO-adhered oxidized iron oxide magnetic powder in the second magnetic layer (5) is preferably in the range of 35 to 50 m''/SI-; outside this range, noisy noise is not reduced.On the other hand, the second magnetic layer (5)
Coercive force Hc1 of magnetic layer 1 (4) and residual magnetic flux density B
rIH 500-1200 oersted and 2ooo respectively
~4000 Gauss is good, 2000 for 13r1
If it is less than Gauss, the low frequency output will decrease, and if it is more than 4000 Gauss, it will be difficult to eliminate.

The coercive force HCI of the first magnetic layer (4) and the second magnetic layer (5)
) is preferably I-(c1≦Hc2) with the coercive force l4c2.

60 when the thickness of the magnetic layer (4) of 1st grade 1 is 20μ or more
If it is thinner than 2.0μ, the low-frequency reproduction output will decrease, and if it is thicker than 60μ, only the low-frequency reproduction output will increase too much and the balance between low and high frequencies will be poor. The thickness t2 of the layer (5) is preferably in the range of 02 to 20μ,
If it becomes thinner than 0.2 μ, the bias noise will not be reduced, and 20
If it becomes thicker than μ, the low frequency reproduction output decreases.

As described above, in the present invention, based on the characteristic results shown in FIG. 4, as shown in FIG.
In a magnetic recording W body (6) comprising a magnetic layer (4) and a second magnetic layer (5) in one order, the first magnetic layer (
4) has a specific surface area of 20 to 50 m" by BFT method.
/? The coercive force H
C1 is 500 to 1200 oersted, residual magnetic flux density B
r is 2000 to 4000 Gauss, layer thickness t1 is 2 to 6 μm, and the second magnetic layer (5) is made of CO-coated acid iron oxide magnetic powder with a specific surface area of 35 to 50 m”/y− by BET method. It is formed by coating, and its coercive force HC2 is 600 to 1200.
The layer thickness t2 is set to 02 to 2μ, and the coercive force HCI≦coercive force HC2.

According to the present invention, it is possible to reduce noisy noise while maintaining a high p playback output over the entire band, and it is possible to reduce noise while maintaining a high p reproduction output over the entire band. 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, FIG. 3 is a table showing the characteristics of each side of the shore layer magnetic recording medium, and FIG. FIG. 4 is a table showing the characteristics of each embodiment of the two-layer magnetic recording medium according to the present invention. In the figure, (1) is a non-magnetic substrate, (4) is a first magnetic layer, and (5) is a non-magnetic substrate.
) is the second magnetic layer.

Claims (1)

[Claims] It consists of a non-magnetic gas, a first magnetic layer on the base, and a second magnetic layer on the first magnetic layer, and the first magnetic layer is made of B.
It is formed by coating metal ferromagnetic powder with a specific surface area of 20 to 50 d/y by the ET method, and its coercive force HCI is 500.
~1200 oersted, residual magnetic flux density Hr is 2000
~4000 Gauss and a layer thickness of 2 to 6μ, and the second
The magnetic layer has a specific surface area of 35 to 50 rr by BET method.
? /l- of Co-adhered acid iron oxide magnetic powder, the coercive force HC2 is 600 to 1200 Oe, the layer thickness is 02 to 2 μ, and the coercive force HCI≦coercive force H
A magnetically recorded ν body characterized by being c2.