JPH077499B2 - Magnetic recording medium - Google Patents

Description

The present invention relates to a magnetic recording medium such as a magnetic tape or a magnetic disk for high density magnetic recording.

[Outline of Invention]

The present invention provides a magnetic recording medium comprising a non-magnetic support and a magnetic layer containing a hexagonal ferrite magnetic powder and a binder as main components. 0.03
〜0.1μm, plate ratio 3 ~ 6, and the product of specific surface area and plate ratio less than 200m ² / g, especially to improve both short wavelength output and long wavelength output simultaneously. Is.

[Conventional technology]

Conventionally, in magnetic recording media, magnetic properties have been improved by orienting needle-like magnetic powder in the magnetic layer in the horizontal longitudinal direction.

However, in the longitudinal recording using the magnetization component in the longitudinal direction of the magnetic layer as described above, although a high reproduction output can be obtained in the low frequency band (long wavelength band), as the frequency becomes the high frequency band (short wavelength band), The demagnetizing field inside the magnetic layer is increased, and the self-demagnetization loss is increased, so that the recording / reproducing characteristics are deteriorated.

Therefore, in recent years, by using a plate-like hexagonal ferrite magnetic powder whose easy axis of magnetization is perpendicular to the plate surface and positively utilizing the magnetization component in the direction perpendicular to the magnetic layer surface, At the same time, there are many attempts to solve the problem and to achieve high density recording.

[Problems to be solved by the invention]

However, in a magnetic recording medium using this type of hexagonal ferrite magnetic powder, the magnetic properties of the magnetic layer, particularly the saturation magnetic flux density and the vertical orientation, depend on the grain size, plate ratio, specific surface area, etc. of the hexagonal ferrite magnetic powder. It has the drawbacks of drastically changing the degree of output, low long-wavelength output compared to improvement of short-wavelength output, etc., and has sufficient magnetic characteristics and electromagnetic conversion characteristics from the short-wavelength band to the long-wavelength band. There was a difficulty that it could not be improved.

For example, when magnetically transferring a video signal, a digital audio signal, or the like, the electromagnetic conversion characteristics of the slave medium, which is the medium to be transferred, is high in output and high in a wide frequency band.
SN is preferable, and if the reproduction output in either the short wavelength band or the long wavelength band is insufficient, the recording quality such as image quality and sound quality deteriorates.

Therefore, the present invention has been proposed in view of the above circumstances, and is capable of simultaneously improving both short-wavelength output and long-wavelength output, and has a higher density than the hexagonal ferrite magnetic recording media proposed so far, An object is to provide a magnetic recording medium capable of high quality recording.

[Means for solving problems]

As a result of intensive investigations by the inventors of the present invention, the magnetic recording medium having a hexagonal ferrite magnetic powder having a particle size, a plate ratio, and a specific surface area within a predetermined range has good magnetic characteristics. The present invention has been completed to find out that, in a magnetic recording medium comprising a non-magnetic support, a magnetic layer comprising a hexagonal ferrite magnetic powder and a binder as main components is formed, The above hexagonal ferrite magnetic powder is characterized by having an average particle size of 0.03 to 0.1 μm, a plate ratio of 3 to 6, and a product of specific surface area and plate ratio of 200 m ² / g or less. Is.

The magnetic powder used in the magnetic recording medium of the present invention is
Hexagonal ferrite magnetic powder represented by the general formula MO · n (Fe ₂ O ₃ ), where M represents at least one of Ba, Sr, and Ca, and n = 5 to 6. Is.
In this case, in order to control the coercive force, Co, Ti, Ni, Mn, Cu, Z
At least one of n, In, Ge, and Nb may be added to replace a part of Fe in the above hexagonal ferrite magnetic powder with these elements. For example, in Ba-ferrite, when a part of Fe is replaced by the above additive element, its composition is represented by the general formula BaO.n (Fe ₁ -mXm) ₂ O ₃ (I) (where X is Co, Ti, Ni, Mn, Cu, Zn, In, Ge, Nb represents at least one kind, m represents a number of 0 to 0.2, and n represents a number of 5 to 6, respectively.).

In the present invention, the particle size of the hexagonal ferrite magnetic powder is
The plate ratio is 0.03 to 0.1 μm and the plate ratio is 3 to 6.

When the particle size is smaller than 0.03 μm, the porosity of the magnetic layer becomes high, it is difficult to secure the saturation magnetic flux density Bm when used as a magnetic recording medium, and the output decreases in the entire wavelength region.
Cause inconvenience. On the contrary, when the particle size is larger than 0.1 μm, the saturation magnetic flux density Bm can be increased to some extent,
The surface roughness increases, which is disadvantageous for high density recording.

On the other hand, if the plate ratio is less than 3, it becomes difficult to increase the squareness ratio in the vertical direction to 0.5 or more even if the vertical alignment treatment is performed, the magnetization of the vertical component is reduced, and the short wavelength output can be improved. Disappear. If the plate ratio exceeds 6, it is not possible to obtain a plate ratio x specific surface area of 200 m ² / g as described below for any particle size, and to increase the output in the entire wavelength range. Will be difficult. In addition, the particles tend to aggregate, and the dispersibility deteriorates.

Here, the particle diameter means the average particle diameter of the particles, and the plate ratio is D / when the particle diameter is D and the average thickness of the particles is t.
It is a value represented by t.

In the present invention, the product of the plate ratio and the specific surface area of the hexagonal ferrite magnetic powder used is an important factor.

That is, even when the magnetic powder having a particle size of 0.03 to 0.1 μm and a plate ratio of 3 to 6 is used, the plate ratio and the specific surface area (BET
Method)) (plate ratio x specific surface area) exceeds 200 m ² / g, the porosity of the magnetic layer increases, resulting in a saturation magnetic flux density Bm
However, both short-wavelength output and long-wavelength output cannot be increased. As described above, the saturation magnetic flux density of the magnetic layer cannot be determined by individual values such as the specific surface area, the plate-like ratio, and the particle size, but depends on the change in the porosity of the magnetic layer.

The above porosity is And the plate-like ratio x, as shown in FIG.
It increases in proportion to the value of the specific surface area. From this equation (1) as well, it is understood that an increase in the porosity causes a decrease in the saturation magnetic flux density Bm of the obtained magnetic recording medium. Therefore, when the relationship between the value of (plate ratio × specific surface area) and the saturation magnetic flux density of the obtained magnetic recording medium is examined, as shown in FIG. 2, the saturation gradually increases as the plate ratio × (specific surface area) increases. It can be seen that the magnetic flux density decreases, making it difficult to secure output in either the short wavelength band or the long wavelength band. When the value of (plate ratio × specific surface area) is 200 m ² / g or less, the saturation magnetic flux density is about 1600 gauss or more, which is not a practical problem.

From the above experimental results, a suitable range of the hexagonal ferrite magnetic powder used in the magnetic recording medium of the present invention is shown in FIG.

In Fig. 3, the horizontal axis represents the plate-like ratio and the vertical axis represents the specific surface area, and the regions where the particle size D is 0.03 μm, 0.05 μm, 0.1 μm, 0.2 μm are straight lines D ₁ , D ₂ , D _{3 respectively.} is a representation in D _4. The curve a in FIG. 3 represents the plate ratio × specific surface area 200 m ² / g. Therefore, the range of the hexagonal ferrite magnetic powder used in the magnetic recording medium of the present invention is the area surrounded by the diagonal lines in FIG.

The above-mentioned hexagonal ferrite magnetic powder is a hexagonal tabular particle, and the plate surface of this particle tends to be parallel to the recording medium surface,
Moreover, since the axis of easy magnetization is perpendicular to the plate surface, it is easy to perform vertical orientation by magnetic field orientation processing or mechanical orientation processing.
It can be non-oriented (omnidirectional orientation). in this case,
Squareness ratio in the vertical direction (meaning the remanent magnetization / saturation magnetization ratio obtained by demagnetizing the magnetization curve measured in the direction perpendicular to the medium surface.) If R _s is less than 0.5, the magnetization of the vertical component decreases. However, this causes a problem that the short wavelength output is reduced. On the contrary, when the squareness ratio R _s in the vertical direction becomes larger than 0.75, the short-wavelength output increases, but the long-wavelength output remarkably decreases as a result of the decrease in the longitudinal magnetization component. Further, since the surface roughness also increases, there is a drawback that the rate of improvement in short wavelength output is not necessarily large compared with the rate of increase in the perpendicular magnetization component.

Therefore, in the magnetic recording medium of the present invention, it can be said that the squareness ratio R _s in the vertical direction is preferably within the range of 0.5 ≦ R _s ≦ 0.75. The squareness ratio R _{s in the} vertical direction can be easily controlled by changing the alignment treatment conditions.

These hexagonal ferrite magnetic powders are dissolved and dispersed in an organic solvent together with a resin binder and applied as magnetic paint on the base film. The coercive force in the magnetic direction is 600 to 1500 (O
e) is preferred.

Furthermore, when using as a slave medium for magnetic transfer, 600 (O
e) to 800 (Oe) is required.

The resin binder and organic solvent to be used may be any as long as they are generally used in this kind of magnetic recording medium, and the magnetic layer further contains a dispersant, a lubricant, an abrasive, an antistatic agent. You may add rust preventives.

Examples of usable resin binders are vinyl chloride-vinyl acetate copolymers, vinyl chloride-vinylidene chloride copolymers, vinyl chloride-acrylonitrile copolymers, acrylate-acrylonitrile copolymers, thermoplastic polyurethanes. Elastomer, polyvinyl fluoride, vinylidene chloride-acrylonitrile copolymer, butadiene-acrylonitrile copolymer, polyamide resin, polyvinyl butyral, cellulose derivative, polyester resin, synthetic rubber resin such as polybutadiene, phenol resin, epoxy resin, polyurethane curing type Resin, melamine resin, alkyd resin, silicone resin, acrylic reaction resin, epoxy-polyamide resin, nitrocellulose-melamine resin, mixture of high molecular weight polyester resin and isocyanate prepolymer Mixture of methacrylate copolymer and diisocyanate prepolymer, mixture of polyester polyol and polyisocyanate, urea formaldehyde resin, mixture of low molecular weight glycol / high molecular weight diol / triphenylmethane triisocyanate, polyamine resin and these And the like.

Materials for the base film include polyesters such as polyethylene terephthalate, polyolefins such as polyethylene and polypropylene, cellulose derivatives such as cellulose triacetate, cellulose diacetate and cellulose acetate butyrate, and vinyl resins such as polyvinyl chloride and polyvinylidene chloride. , Plastics such as polycarbonate, polyimide, polyamide-imide,
Examples include light alloys such as aluminum alloys and titanium alloys, and ceramics such as alumina glass. The form of the base film may be a film, a sheet, a disc, a card, a drum, or the like.

[Action]

By setting the particle size, plate ratio, plate ratio × specific surface area of the hexagonal ferrite magnetic powder within the range of the present invention, the porosity of the obtained magnetic recording medium is suppressed and the saturation magnetic flux density is secured. In addition, since the hexagonal ferrite magnetic powder has vertical orientation, a high reproduction output can be achieved from the short wavelength region to the long wavelength region.

〔Example〕

Hereinafter, specific examples of the present invention will be described, but the present invention is not limited to these examples.

Example 1 Ba-ferrite magnetic iron oxide powder 100 parts by weight Particle size ・ ・ ・ ・ ・ ・ 0.07 μm Plate ratio ・ ・ ・ ・ ・ ・ ・ ・ 3 Specific surface area ・ ・ ・ ・ ・ 29 (m ² / g ) Plate ratio x specific surface area ··· 87 (m ² / g) Polyurethane resin 15 parts by weight Vinyl chloride-vinyl acetate copolymer 10 parts by weight Abrasive 5 parts by weight Carbon black 5 parts by weight Lecithin 1 part by weight Methyl ethyl ketone 100 parts by weight Toluene 50 parts by weight Cyclohexane 50 parts by weight After kneading the above composition in a ball mill for 20 hours, a curing agent
2.5 parts by weight was added and the mixture was filtered through a filter having an average pore size of 1 μm to prepare a magnetic paint.

Next, this magnetic paint was applied onto a polyester film having a thickness of 15 μm, subjected to vertical alignment treatment, and then dried. Further, the surface of the magnetic layer was processed by using a super calendar device to prepare a wide sheet having a magnetic layer thickness of 4 μm, which was cut into 1/2 inch width to obtain a sample tape.

The magnetic properties of the obtained sample tape are magnetic flux density Bm1800.
The squareness ratio R _s was 0.65 in the thickness direction of the magnetic layer and Gauss.

Example 2 Particle size as magnetic powder ・ ・ ・ ・ ・ ・ 0.06 μm Plate ratio ・ ・ ・ ・ 4 Specific surface area ・ ・ ・ 34 (m ² / g) Plate ratio × Specific surface area A sample tape was prepared in the same manner as in Example 1 except that Ba-ferrite magnetic iron oxide powder having a density of 136 (m ² / g) was used.

The magnetic properties of the obtained sample tape are shown by the magnetic flux density B _m 1710
The squareness ratio R _s was 0.68 in the thickness direction of the Gauss and magnetic layers.

Comparative Example 1 Particle size as magnetic powder ・ ・ ・ ・ ・ ・ 0.1μm Plate-like ratio ・ ・ ・ ・ 8 Specific surface area ・ ・ ・ ・ 38 (m ² / g) Plate-like ratio × specific surface area A sample tape was prepared in the same manner as in Example 1 except that Ba-ferrite magnetic iron oxide powder of 304 (m ² / g) was used.

The magnetic properties of the obtained sample tape are as follows: magnetic flux density B _m 1400
The squareness ratio R _s 0.70 in the thickness direction of the magnetic layer was Gauss.

Comparative Example 2 As magnetic powder, particle size: 0.03 μm Plate ratio: 6 Specific surface area: 104 (m ² / g) Plate ratio x Specific surface area A sample tape was prepared in the same manner as in Example 1 except that Ba-ferrite magnetic iron oxide powder having a particle size of 624 (m ² / g) was used.

The magnetic properties of the obtained sample tape are as follows: magnetic flux density B _m 1080
The squareness ratio R _s was 0.65 in the thickness direction of the magnetic layer and Gauss.

The frequency characteristics of the reproduction output were measured for each of the above sample tapes. Measurement was performed using a metal-based head with a track width of 20 μm and a gap length of 0.25 μm, and the relative speed
A square wave of 250 kHz to 6 MHz was recorded and reproduced at 3 m / sec, and the fundamental wave output level of each frequency was measured using a spectrum analyzer. The band width was 10 kHz. Results are shown in FIG.

From FIG. 4, in Comparative Example 1 and Comparative Example 2 in which the plate-like ratio × specific surface area was 200 m ² / g or more, the magnetic flux density of the magnetic layer was small, and both short wavelength output and long wavelength output were obtained in Example 1, Example 1. It can be seen that it is lower than in Example 2.

Next, sample tapes in which the grain shape, the plate ratio, and the specific surface area × plate ratio were respectively within the range of the present invention were prepared, and the influence of the squareness ratio R _{s on} the reproduction output was examined.

Example 3 Particle size as magnetic powder ・ ・ ・ ・ ・ ・ 0.09 μm Plate ratio ・ ・ ・ ・ ・ ・ ・ ・ 4 Specific surface area ・ ・ ・ ・ 27 (m ² / g) Plate ratio × Specific surface area A sample tape was prepared in the same manner as in Example 1 except that Ba-ferrite magnetic iron oxide powder of 108 (m ² / g) was used.

The magnetic properties of the obtained sample tape have a magnetic flux density B _m 1770.
The squareness ratio R _s was 0.65 in the thickness direction of the magnetic layer and Gauss.

Example 4 As magnetic powder Particle size: 0.1 μm Plate ratio: 6 Specific surface area: 31 (m ² / g) Plate ratio × Specific surface area A sample tape was prepared in the same manner as in Example 1 except that Ba-ferrite magnetic iron oxide powder having a size of 186 (m ² / g) was used.

The magnetic properties of the obtained sample tape are shown by the magnetic flux density B _m 1620
Gauss, the squareness ratio R _s 0.82 in the thickness direction of the magnetic layer.

Example 5 Particle size of magnetic powder: 0.04 μm Plate ratio: 3 Specific surface area: 50 (m ² / g) Plate ratio x Specific surface area A sample tape was prepared in the same manner as in Example 1 except that Ba-ferrite magnetic iron oxide powder having a particle size of 150 (m ² / g) was used and the orientation treatment was longitudinal orientation.

The magnetic properties of the obtained sample tape are as follows: magnetic flux density B _m 1680
The squareness ratio R _s 0.40 in the thickness direction of the magnetic layer was Gauss.

FIG. 5 shows the reproduction output frequency characteristics of the sample tapes produced in Examples 3 to 5. The measuring method was according to the method described above.

From FIG. 5, it can be seen that the sample tape obtained in Example 3 exhibits a high reproduction output from the short wavelength band to the long wavelength band, while the squareness ratio R _{s in} the thickness direction of the magnetic layer is 0.75
It was found that in the sample tape of Example 4 which exceeded the above range, since the squareness ratio R _s was too high, the magnetization in the longitudinal direction was small and the long wavelength output was lowered. Also, in Example 5, it is shown that the squareness ratio R _s in the thickness direction of the magnetic layer is too low, and as a result, the magnetization of the perpendicular component decreases, resulting in a decrease in short wavelength output.

〔The invention's effect〕

As is clear from the above description, the magnetic recording medium of the present invention is excellent in dispersibility, has a high saturation magnetic flux density of the magnetic layer, and has a suitable degree of vertical orientation. It is a magnetic recording medium capable of simultaneously improving output, and has excellent characteristics as a medium for high density magnetic recording.

Further, when the magnetic recording medium of the present invention is used as a magnetic transfer medium for video signals, digital audio signals, etc., efficient transfer is possible over a wide wavelength range, and magnetic transfer with good quality such as image quality and sound quality. Is possible.

[Brief description of drawings]

FIG. 1 is a characteristic diagram showing the relation between plate ratio × specific surface area and porosity, and FIG. 2 is a characteristic diagram showing relation between plate ratio × specific surface area and saturation magnetic flux density of the magnetic layer. FIG. 3 is a characteristic diagram showing a preferable range of the hexagonal ferrite magnetic powder used in the present invention. FIG. 4 is a characteristic diagram showing the frequency characteristics of the reproduction output of the sample tape manufactured according to the embodiment of the present invention in comparison with that of the comparative example, and FIG. 5 shows the squareness ratio in the vertical direction to the frequency characteristics of the reproduction output. It is a characteristic view which shows the influence which gives another example of this invention as an example.

Claims (1)

[Claims] 1. A magnetic recording medium comprising a non-magnetic support and a magnetic layer comprising a hexagonal ferrite magnetic powder and a binder as main components, wherein the hexagonal ferrite magnetic powder has an average grain size. Is 0.03 ~
A magnetic recording medium characterized in that the product of the specific surface area and the plate ratio is 200 m ² / g or less, with 0.1 μm and a plate ratio of 3 to 6.