JP2635596B2 - Magnetic recording media - Google Patents

Description

The present invention relates to a magnetic recording medium having a magnetic layer formed on a non-magnetic support, and particularly to a low-temperature, low-temperature suitable for a perpendicular magnetic recording medium. The present invention relates to a magnetic recording medium having excellent durability in high-temperature and low-temperature to high-temperature cycle tests.

(Prior art) Recently, magnetic recording media have come to be used as recording media for recording a large amount of information in a wide range of fields such as audio, video, and computers, and accordingly, high-density recording is possible. Therefore, a magnetic recording medium having excellent durability, which is hardly worn by a magnetic head or a magnetic pad which slides at a high speed, is being developed.

In order to improve the durability and also the surface smoothness to improve the electromagnetic conversion characteristics, a method of including carbon or graphite in the magnetic layer has been studied.

However, the use of such conventional carbon,
It is added for the purpose of imparting conductivity, and has little effect on improving the durability of a magnetic recording medium for high-density recording.

(Problems to be Solved by the Invention) As described above, the conventional magnetic recording medium has a problem that the durability, particularly in the case of high-density recording, is insufficient.

The present inventor, in order to solve such conventional difficulties, considering the surface area of carbon, the relationship between the particle size and these properties, as a result of intensive research, if the surface area of carbon, the particle size is in a specific range, The inventors have found that the above problems are solved, and have accomplished the present invention.

Accordingly, it is an object of the present invention to provide a magnetic recording medium having excellent surface smoothness and durability in low-temperature, high-temperature, and low-temperature to high-temperature cycle tests.

[Constitution of the Invention] (Means for Solving the Problems) The magnetic recording medium of the present invention is a magnetic recording medium comprising a magnetic layer having a magnetic powder, a binder and carbon on a non-magnetic support. The carbon has a number average particle size of 100
~ 800nm carbon and a mixture of carbon with number average particle size of 20 ~ 80nm, and weight average particle size of 100 ~ 280nm
Wherein at least 95% by weight of the particles have a particle size in the range of 5 to 950 nm.

The carbon used in the present invention has a specific surface area by BET method (hereinafter simply referred to as surface area) of 5 to 1600 m ² / g,
A mixture of a plurality of types of carbon is used, particularly carbon having a number average particle size of 100 to 800 nm and a number average particle size of 20 to 80 nm.
Mixtures with carbon are suitable.

As described above, when a mixture of coarse-grained carbon and fine-grained carbon is used, the fine-grained carbon enters between the magnetic powders to improve dispersibility and to increase the conductivity. , And carbon having a large particle size protrudes from the surface to improve lubricity and act to improve durability.

In the present invention, the range of the number average particle diameter and the weight average particle diameter of carbon contained in the magnetic layer is limited as described above, because the effect of the present invention cannot be obtained outside the above range.

The above carbon is used per 100 parts by weight of magnetic powder in the magnetic layer.
It is blended in a ratio of 2.5 to 10 parts by weight. If the amount is too large, it adversely affects the surface of the magnetic layer, resulting in poor electromagnetic conversion characteristics. If the amount is too small, the durability is impaired.

Commercially available carbons that can be used in the present invention include Ketjen Black EC (Lion), STERLING N, BLACK PE
RLS 1000, BLACK PERLS 2000 (Cabot), RAVEN
2000, RAVEN 3500, RAVEN MTP, RAVEN 1255, RAVEN 45
0, Conductex 40-220, Conductex SC (Columbia Carbon), THERMA XN-990 (Can Curve) and the like.

As the binder used for the magnetic layer of the present invention, a curable resin, particularly a polyurethane resin, is suitable. Examples of such a polyurethane resin include N-2301 and N-2304 manufactured by Nippon Polyurethane Industry, and Essen 5703 manufactured by BF Goodrich. It is preferable to use a nitrocellulose resin together with these polyurethane resins. As such nitrocellulose resin, for example, FM-200 manufactured by Daicel Corporation can be mentioned. As a curing agent used for these curable resins, an isocyanate-based curing agent is preferable. Coronate L manufactured by Nippon Polyurethane Industry Co., Ltd.
Takeda XL-10007 manufactured by Takeda Pharmaceutical Co., Ltd. can be mentioned. The binder used in the present invention is not limited to such a curable resin, and an electron beam-curable, ultraviolet-curable, or non-curable resin may be used as necessary.

The ferromagnetic powder used in the magnetic layer of the present invention includes Co
Needle-like iron oxide such as -γ Fe ₂ O ₃ , CrO ₂ , metal powder such as Fe-Co can also be used, but in the form of a flat plate, and the plate ratio is in the range of 1 to 15, the particle size is 0.005 Coercive force (Hc) at ~ 0.3μm
However, a uniaxially anisotropic hexagonal ferrite powder of 200 to 2000 Oe is suitable, and has a general formula MO · n (Fe ₂ O ₃ ) (in the formula, M represents any one element of Ba, Sr, Pb and Ca, and n represents a number of 5 to 6, provided that part of Fe is Ti,
It may be substituted with a metal such as Co, Zn, In, Mn, Cu, Ge, Nb, Zr, V, Al, and Sn. The uniaxially anisotropic hexagonal ferrite powder represented by) is suitable. In addition, aluminum oxide, Cr ₂ O ₃
And a lubricant such as stearic acid and butyl stearate.

Further, as the non-magnetic support used in the present invention, various magnetic tapes, known materials used as a base of a floppy disk or the like can be used, for example, a polyester film or the like as a tape base,
A polyester sheet or an aluminum substrate is used as a floppy disk base.

The magnetic recording medium of the present invention is obtained by applying a magnetic paint containing the above-described carbon, binder, magnetic powder, etc. on a non-magnetic support and drying it, and then subjecting it to a predetermined shape after calendering if necessary. Molded manufactured.

(Function) The magnetic recording medium of the present invention has good dispersibility of the magnetic powder and carbon, and partially exposes carbon to the surface of the magnetic recording medium to reduce friction, thereby improving electromagnetic characteristics. And exhibit durability.

(Examples) Hereinafter, the present invention will be described more specifically with reference to Examples. In the examples below, "parts" indicates parts by weight.

Example 1 Ba ferrite (Co, Ti substitution) powder (average particle size 0.08 μm, H
c700Oe) 100 parts Nitrocellulose resin 6 parts Polyurethane resin 14 parts Alumina 4 parts Lecithin 2 parts Stearic acid 1.5 parts Butyl stearate 2.5 parts Carbon (weight average particle diameter 150 nm) * 1 5 parts Solvent (MEK / toluene / cyclohexanone) (1 / 1/1) 18
7.5 parts * 1: A 1: 1 mixture of carbon with a number average particle size of 280 nm (specific surface area 7 m ² / g) and carbon with a number average particle size of 30 nm (specific surface area 1300 m ² / g).

After kneading the above composition with a sand grinder to prepare a magnetic paint, the mixture is filtered, and 5 parts of a three-functional low molecular weight isocyanate compound is added and mixed as a curing agent.
A 75 μm thick polyethylene terephthalate was coated on both sides so that the thickness after drying was 2.5 μm, dried and cured to form a magnetic layer, mirror-polished with a calender, and punched into a disk to produce a magnetic disk. .

Example 2 Instead of the carbon used in Example 1, the weight average particle diameter was 10
0 nm (carbon having a number average particle size of 280 nm [specific surface area 7 m ² / g] and carbon having a number average particle size of 500 [specific surface area 200 m ² / g] are 1: 3.
A magnetic disk was produced in the same manner as in Example 1 except that the same amount of carbon as used in [weight] was used.

Example 3 Instead of the carbon used in Example 1, the weight average particle diameter was 20
0 nm (carbon having a number average particle diameter of 280 nm [specific surface area 7 m ² / g]) and carbon having a number average particle diameter of 60 nm [specific surface area 40 m ² / g] are 2: 1.
A magnetic disk was manufactured in the same manner as in Example 1 except that the same amount of carbon (by weight) was used.

Example 4 Instead of the carbon used in Example 1, a weight average particle size of 25 was used.
0 nm (number average particle diameter 280 nm [specific surface area 7 m ² / g] carbon and number average particle diameter 70 nm [specific surface area 45 m ² / g] carbon 4: 1
A magnetic disk was manufactured in the same manner as in Example 1 except that the same amount of carbon (by weight) was used.

Comparative Example 1 A number average particle diameter of 75 nm was used instead of the carbon used in Example 1.
A magnetic disk was produced in the same manner as in Example 1 except that the same amount of carbon having a specific surface area of 45 m ² / g was used.

Comparative Example 2 Instead of the carbon used in Example 1, the number average particle size was 350 n.
A magnetic disk was produced in the same manner as in Example 1 except that the same amount of carbon having a specific surface area of 5 m ² / g was used.

Comparative Example 3 Co-Fe ₂ O ₃ was used in place of Ba-ferrite used in Example 1.
Is used in the same amount, and instead of the carbon used in Example 1,
A magnetic disk was prepared in the same manner as in Example 1 except that the same amount of carbon having a number average particle size of 150 nm (specific surface area 30 m ² / g) was used.

Comparative Example 4 The weight average particle diameter was 43 in place of the carbon used in Example 1.
nm (number average particle diameter of 75 nm [specific surface area 25 m ² / g]) and carbon having a number average particle diameter of 10 nm [specific surface area 1100 m ² / g]
A magnetic disk was manufactured in the same manner as in Example 1 except that the same amount of carbon (by weight) was used.

Comparative Example 5 In place of the carbon used in Example 1, the weight average particle size was 42.
0 nm (number average particle diameter 500 nm [specific surface area 2.5 m ² / g] carbon and number average particle diameter 270 nm [specific surface area 8.5 m ² / g] carbon
A magnetic disk was prepared in the same manner as in Example 1 except that the same amount of carbon (mixed at 2: 1 [weight]) was used.

Comparative Example 6 Instead of the carbon used in Example 1, the number average particle diameter was 500n.
A magnetic disk was manufactured in the same manner as in Example 1 except that the same amount of carbon having a specific surface area of 2.5 m ² / g was used.

The results of a durability test performed on the magnetic disks obtained in the above Examples and Comparative Examples are shown in the following table. Incidentally durability test is loaded each magnetic disk recording and reproducing apparatus, endurance running time until the reproduction output becomes 70% of the initial output while this is brought into sliding contact with the magnetic head pad pressure 40 g / cm ² Immediately after the creation of each magnetic disk (initial),
After storage at 50 ° C. for 5 weeks (high temperature storage), the test was performed under the conditions of low temperature (5 ° C.), high temperature (50 ° C.), and low to high temperature cycle (5 ° C. to 50 ° C.).

[Effects of the Invention] As is clear from the above embodiments, the magnetic disk of the present invention not only excels in the high-temperature preservability of the magnetic layer under a use environment from low temperature to high temperature, but also under high temperature. Even after storage for a long period of time, the initial state is favorably maintained, and excellent characteristics in high-temperature storage stability are obtained. In particular, when a uniaxial hexagonal ferrite powder is used as the magnetic powder, a more excellent durability is exhibited due to a synergistic effect of the shape and size of the magnetic powder and carbon.

Claims (3)

(57) [Claims] 1. A magnetic recording medium having a magnetic layer having a magnetic powder, a binder and carbon formed on a nonmagnetic support, wherein the carbon has a number average particle diameter of 100 to 800 nm and a number average particle diameter of 100 to 800 nm. Consists of a mixture with carbon with a diameter of 20-80 nm,
A magnetic recording medium having a weight average particle diameter of 100 to 280 nm and a particle diameter of at least 95% by weight falling within a range of 5 to 950 nm. 2. The magnetic powder according to claim 1, wherein the magnetic powder is a uniaxially anisotropic hexagonal ferrite powder having a tabular shape, a tabular ratio of 1 to 15 and a particle size of 0.005 to 0.3 μm. The magnetic recording medium according to claim 1, wherein 3. The coercive force (H) of said hexagonal ferrite powder.
3. The magnetic recording medium according to claim 2, wherein c) is 200 to 2000 Oe.