JPS59124023A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To produce high output in a wide zone by forming a magnetic layer contg. magnetic powder with uniaxial anisotropy and magnetic powder with isotropic anisotropy by which the powder is not oriented but is magnetized in any direction and having specified squareness in each of the vertical and horizontal directions and a specified orientation ratio. CONSTITUTION:Magnetic powder with uniaxial anisotropy such as gamma-Fe2O3 or Co powder is mixed with magnetic powder with isotropic anisotropy such as spheroidal or needlelike powder of iron oxide contg. solubilized Co. The former powder is easily oriented by applying a magnetic field, and by applying the magnetic field in the horizontal direction, the powder is oriented in the horizontal direction to produce high output in a low frequency zone. The latter powder is hardly oriented even by applying a magnetic field in any direction, but the powder is easily magnetized in any direction, so it contributes to the increase of output especially in a high frequency zone. A magnetic layer contg. said mixture and having 500-2,000 Oe coercive force, >=0.3 squareness in the vertical direction, >=0.6 squareness in the horizontal direction and 0.3-<1.0 squareness ratio, that is, orientation ratio is formed. Thus, high output is produced in both of low and high frequency zones.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetic recording medium, and its object is to provide a magnetic recording medium that has high output in low frequency and high frequency bands and can perform both recording over a wide range of recording wavelengths and high density recording. Our goal is to provide the following.

Generally, the magnetic properties of magnetic recording media such as magnetic tapes are improved by orienting the acicular magnetic powder in the magnetic layer in the longitudinal direction. Although they can provide high output in a low frequency band, they have a limit to high-density recording, and recording at a recording wavelength of 1.0 μm or less is extremely difficult.

For this reason, in recent years, as magnetic recording media suitable for high-density recording, magnetic powders with isotropic anisotropy are used to utilize their perpendicular components, or magnetic powders with -axis anisotropy are used. A method has been proposed in which the magnetic layer is non-oriented and uses its perpendicular component, but a method using magnetic powder with isotropic anisotropy provides high output in the high frequency band, but on the other hand, it produces a high output in the low frequency band. In addition, if magnetic powder with -axis anisotropy is not oriented in the magnetic layer, the squareness in all directions becomes low and high output cannot be obtained. .

As a result of various studies in view of the current situation, the inventors of the present invention discovered that magnetic powder having -axis anisotropy and magnetic powder having isotropic anisotropy were mixed and used in the perpendicular direction of the magnetic layer. The square shape is 0.3 or more, and the horizontal square shape is 0.6 or more, and the vertical to horizontal orientation ratio (vertical square/horizontal square) is 0.3. or more and 1.0
If it is within the range below, high output can be obtained in low frequency and high frequency bands, high density recording is possible up to a recording wavelength of 1.0 μ or less, and both long wavelength recording and high density recording can be performed well. It was discovered that a magnetic recording medium could be obtained, and this invention was made.

The magnetic powder having uniaxial anisotropy used in this invention is easily oriented by applying a magnetic field, and when a horizontal magnetic field is applied, it is oriented in the horizontal direction and the output in the low frequency band becomes high. In addition, magnetic powder with isotropic anisotropy is hardly oriented when a magnetic field is applied from any direction, but because it has the property of being easily magnetized in any direction, it is particularly useful for increasing output in high frequency bands. Make a contribution.

Therefore, when a magnetic powder having -axis anisotropy and a magnetic powder having isotropic anisotropy are mixed and used, and a magnetic paint containing these mixed magnetic powders is applied onto a substrate, the substrate When a magnetic field is applied in a direction parallel to the magnetic field, the magnetic powder with uniaxial anisotropy is oriented in the horizontal direction, and the magnetic powder with uniaxial anisotropy oriented in the horizontal direction and the magnetic powder with isotropic anisotropy are oriented in the horizontal direction. The horizontal component of the powder is effectively used to improve the output in the low frequency band, and the vertical component of the magnetic powder, which has isotropic anisotropy, is effectively used to obtain high output even in the high frequency band. .

In this way, when a magnetic powder having -axis anisotropy and a magnetic powder having isotropic anisotropy are mixed and used, and a magnetic paint containing these mixed magnetic powders is applied onto a substrate, the substrate The magnetic layer formed by applying a magnetic field in a direction parallel to , has a square shape in the vertical direction of 0.3 or more and a square shape in the horizontal direction of 0.6.
In the above, it is preferable that the orientation ratio in the vertical direction and the horizontal direction (vertical direction square shape/horizontal direction square shape) is within the range of 0.3 or more and less than 1.0, and the vertical direction square shape is 0. If the horizontal square shape is smaller than 0.6 or the orientation ratio is 1.0 or more, the output in the high frequency band will not be high. The output cannot be made high enough. Therefore, it is preferable to adjust the blending ratio of these mixed magnetic powders so that the vertical square shape, horizontal square shape, and orientation ratio of the magnetic layer are within the above-mentioned ranges, and to orient the powder in the horizontal direction.

As the magnetic powder having uniaxial anisotropy that is mixed and used in this way, for example, γ-Fe20. Powder, Fe5
0. Powder, Co-containing r-Fe205 powder, Co-containing F
e y O4 powder, CrO2 powder, Fe powder, Co powder, Fe-Ni powder, etc. are preferably used, and as magnetic powders having isotropic anisotropy, granular and needle-shaped cobalt solid solution iron oxides are used. Magnetic powders are preferably used. It is preferable to use a mixture of these magnetic powders that have approximately the same or similar coercive force, and if the coercive force of the magnetic layer formed using these mixed magnetic powders is less than 500 oersteds, recording and reproduction will be good. Unable to go to 20
If it is larger than 00 Oersted, long wavelength recording becomes difficult, so it is preferably within the range of 500 to 2000 Oersted.

The magnetic recording medium of the present invention may be manufactured according to a conventional method, such as a mixed magnetic powder obtained by mixing a magnetic powder having -axis anisotropy and a magnetic powder having isotropic anisotropy. is mixed and dispersed with binder resin, organic solvent, etc. to prepare a magnetic paint, and this magnetic paint is applied onto a substrate such as a polyester film while performing horizontal orientation treatment using any coating means such as a roll coater. and dry it.

As the binder resin used here, conventionally widely used binder resins such as vinyl chloride-vinyl acetate copolymers, polyvinyl butyral resins, polyurethane resins, cellulose resins, and isocyanate compounds are widely used.

Further, as the organic solvent, methyl isobutyl ketone, methyl ethyl ketone, cyclohexanone, toluene, ethyl acetate, tetrahydrofuran, dimethyl formamide, etc. are used alone or in combination of two or more.

In addition, various additives commonly used in magnetic paints,
For example, dispersants, lubricants, abrasives, antistatic agents, and the like may be optionally added.

Next, embodiments of the invention will be described. .

Example 1 r-F with particle size (long axis) of 0.3μ and axial ratio (long axis/short axis) of 8
e20. After dispersing the powder 100 (l) in water ioj,
To this, 430 g of cobalt sulfate and 1280 g of ferrous sulfate were added and mixed and dissolved, and then 51 aqueous solution of caustic soda in which 1450 g of caustic soda was dissolved was added and reacted at 45° C. for 8 hours. After the reaction was completed, it was washed with water, filtered, and dried to obtain cobalt-containing iron oxide magnetic powder. The obtained cobalt-containing iron oxide magnetic powder has −axis anisotropy and has a coercive force (Hc)
is 1230 oersted, saturation magnetization (σS) is 77,
The squareness (σr/σs) was 0.50 at 2 emu/9.

Next, a part of this cobalt-containing iron oxide magnetic powder having -axis anisotropy was further heated and oxidized in air at a temperature of 450'C for 3 hours to obtain a cobalt solid solution iron oxide magnetic powder. The obtained cobalt solid solution iron oxide magnetic powder has isotropic anisotropy, has a coercive force (Hc) of 1180 oersteds, a saturation magnetization (σS) of 73.2 emu/q-, and a square shape (σr/ σ
S) was 0.78.

Using the two types of magnetic powders obtained in this way, uniaxially anisotropic cobalt-containing iron oxide magnetism 450 parts by weight powder isotropic anisotropic cobalt solid solution iron oxide magnetism 300 parts VAGH powder (USA U, C, Manufactured by Company C, chloride 125
Vinyl-vinyl acetate-vinyl alcohol copolymer) Bandex T-5250 (Dainippon 80 (manufactured by Ink Co., Ltd., urethane elastomer) Coronate Shikuni Nippon Polyurethane 22.5//
A magnetic paint was prepared by mixing and dispersing a mixture consisting of 730 cyclohexanone and 730 methyl ethyl ketone in a ball mill for 3 days. This magnetic paint was applied to a polyester base film with a thickness of 12 μm to a dry thickness of 3 μm while performing an orientation treatment in a repulsive magnetic field, dried, and after surface treatment, it was cut into a predetermined width. I made magnetic tape.

Example 2 In Example 1, the amount of cobalt sulfate used was changed from 430g to 120g, and the amount of ferrous sulfate was changed to 1280g!
Coercive force 590 oersted, saturation magnetization ik 7
A cobalt-containing iron oxide magnetic powder having a uniaxial anisotropy of 6.8 emu/g and a square shape of 0.49 was obtained. In addition, a part of this cobalt-containing iron oxide magnetic powder was heated and oxidized in the same manner as in Example 1, resulting in a coercive force of 570 Oersted and a saturation magnetization of 7.
A cobalt solid solution iron oxide magnetic powder having an isotropy of 3.6 emu/9 and a square shape of 0.73 was obtained. Next, a magnetic tape was prepared in the same manner as in Example 1, except that the two types of magnetic powder thus obtained were used in the same amount in place of the two corresponding magnetic powders in Example I.

Example 3 In Example 1, the amount of the uniaxially anisotropic cobalt-containing iron oxide magnetic powder used in preparing the magnetic paint was changed from 450 parts by weight to 600 parts by weight, and the isotropically anisotropic cobalt solid solution iron oxide magnetic powder was changed from 450 parts by weight to 600 parts by weight. A magnetic tape was produced in the same manner as in Example 1 except that the amount of powder used was changed from 300 parts by weight to 150 parts by weight.

Example 4 In Example I, the amount of cobalt sulfate used was changed from 430 l to 3809 l, the amount of ferrous sulfate used was changed from 1280 l to 1130 l, and the amount of caustic soda used was changed from 145 l to 13007 l. Coercive force 1150 oersted, saturation magnetization Mk
A cobalt-containing iron oxide magnetic powder having a uniaxial anisotropy of 77.5 emu/L9 and a square shape of 0.49 was obtained. In addition, a part of this cobalt-containing iron oxide magnetic powder was heated and oxidized in the same manner as in Example 1 to obtain a coercive force of 1100 Oe, a saturation magnetization of 73.5 emu/r, and an isotropic anisotropy of square shape 0.76. A cobalt solid-soluted iron oxide magnetic powder having properties was obtained. Next, 500 parts by weight of the thus obtained cobalt-containing iron oxide magnetic powder having uniaxial anisotropy was used in place of the uniaxially anisotropic cobalt-containing iron oxide magnetic powder in Example IK,
In addition, the procedure was the same as in Example 1 except that 250 parts by weight of isotropic anisotropic cobalt solid solution iron oxide magnetic powder was used in place of the isotropic anisotropic cobalt solid solution iron oxide magnetic powder in Example 1. and made magnetic tape.

Example 5 In Example 4, the amount of cobalt sulfate used was changed from 380 g to 285 g, and the amount of ferrous sulfate was changed to 1130 g.
to 850g, and the amount of caustic soda used was changed to 1.
The coercive force was 960 oersted and the saturation magnetization was 77.2 in the same manner as in Example 4 except that 300 was changed to 9759.
A cobalt-containing iron oxide magnetic powder having a uniaxial anisotropy of emu/9 and a square shape of 0.49 was obtained. In addition, a part of this cobalt-containing iron oxide magnetic powder was heated and oxidized in the same manner as in Example 4, resulting in a coercive force of 930 Oersted and a saturation magnetization of 73.5.
emu/! 12. A cobalt solid solution melted iron magnetic powder having an isotropic anisotropy of 0.75 square shape was obtained. Next, a magnetic tape was prepared in the same manner as in Example 4, except that the two types of magnetic powder thus obtained were used in the same amount in place of the two corresponding magnetic powders in Example 4.

Example 6 In Example 4, the amount of the uniaxially anisotropic cobalt-containing iron oxide magnetic powder used in preparing the magnetic paint was changed from 500 parts by weight to 375 parts by weight, and the amount of isotropic cobalt solid solution iron oxide was changed from 500 parts by weight to 375 parts by weight. A magnetic tape was produced in the same manner as in Example 4 except that the amount of magnetic powder used was changed from 250 parts by weight to 375 parts by weight.

Example 7 In Example 1, instead of the iron oxide magnetic powder containing -axis anisotropy
Short axis) 15, coercive force 1220 oersteds, saturation magnetization 'l 50 emu/l, and magnetization in the same manner as in Example 1 except that the same amount of uniaxially anisotropic metallic iron magnetic powder of square shape 0.50 was used. I made a tape.

Example 8 In Example 7, the amount of -axis anisotropic metal iron magnetic powder used was changed from 450 parts by weight to 250 parts by weight, and the amount of isotropic anisotropic cobalt solid solution iron oxide magnetic powder was changed to 300 parts by weight. A magnetic tape was produced in the same manner as in Example 7, except that the amount was changed from 1.0 parts to 500 parts by weight.

Comparative Example 1 In the magnetic coating composition in Example 1, the isotropic anisotropic cobalt solid solution iron oxide magnetic powder was omitted, and the amount of the -axis anisotropic cobalt-containing iron oxide magnetic powder was changed from 450 parts by weight to 750 parts by weight.
A magnetic tape was produced in the same manner as in Example 1 except that the parts by weight were changed.

Comparative Example 2 In the magnetic coating composition in Example 1, the -axis anisotropic cobalt-containing iron oxide magnetic powder was omitted, and the amount of the isotropic anisotropic cobalt solid solution iron oxide magnetic powder was changed from 300 parts by weight to 750 parts by weight.
A magnetic tape was produced in the same manner as in Example 1 except that the heavy background part was changed.

Comparative Example 3 A magnetic tape was produced in the same manner as in Example 1, except that in Comparative Example 1, the magnetic field orientation treatment was omitted and the -axis anisotropic cobalt-containing iron oxide magnetic powder was randomly distributed.

Regarding the magnetic tapes obtained in each example and each comparative example, the longitudinal coercive force (Hc), residual magnetic flux density (Br
), maximum magnetic flux density (Bs) and square type (Br/Bs)
, the coercive force (Hc) in the forward direction, and the residual magnetic flux density (Br
) and squareness (Br/Bs) were measured, and the orientation ratio (vertical squareness/longitudinal squareness) was measured. Furthermore, the maximum output level (M, 0.L) at various recording wavelengths was measured. The vertical square shape is 4πB in the vertical direction of the magnetic tape.
It was calculated by plotting on a hysteresis curve assuming that the demagnetizing field given by r acts, and correcting the demagnetizing field.

The table below shows the results.

As is clear from the above table, among the magnetic tapes obtained by the present invention, the tapes of Examples 1, 3, 7, and 8 have the same coercive force as the conventional tapes shown in Comparative Examples 1 to 3. Comparing the maximum output levels of the tapes of Comparative Examples 1 to 3, the magnetic tape obtained by the present invention exhibits higher values than the tape of Comparative Examples in all frequency ranges. The coercive force value of a tape can be set to an arbitrary value depending on the use of the tape, but the tape manufactured according to the present invention has a coercive force of the same level as that of conventional tapes, regardless of the coercive force. Compared to this, it shows high output in all frequency ranges. It has been confirmed that the tapes of Examples 2.4.5.6 also provide higher output than conventional tapes having the same coercive force. This shows that the magnetic recording medium obtained according to the present invention can obtain high output in all frequency ranges and can perform both long wavelength recording and high density recording well.

Claims (1)

[Claims] 1. The magnetic layer contains magnetic powder with uniaxial anisotropy and magnetic powder with isotropic anisotropy, and the square shape in the vertical direction is 0.
．． 3 or more and the horizontal square shape is 0.6 or more, and the vertical to horizontal orientation ratio (vertical square shape/horizontal square shape) is within the range of 0.3 or more and less than 1.0. A magnetic recording medium characterized by