JPS58159227A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a magnetic recording medium with superior magnetic characteristics and durability by forming a magnetic layer contg. metallic magnetic powder, alpha-type ferric oxide powder and polyurethane resin having a specified mol.wt. or more. CONSTITUTION:Metallic magnetic powder (A) of a metal such as Fe, Co or Ni or an alloy thereof is mixed with alpha-Fe2O3 powder (B) having about 0.3-3mum particle size by >= about 0.1wt% of the amount of the component A and polyurethane resin (C) having >=5,000mol.wt. The mixture may be further mixed with a binder resin D other than the component C such as polyvinyl butyral resin, a dispersant, an antistatic agent, etc. The resulting magnetic coating is applied to a substrate such as a polyester film and dried to obtain the desired magnetic recording medium. This medium has superior wear resistance because of the presence of the component B.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetic recording medium that uses four magnetic powders in gold as magnetic powders, and the object thereof is to provide a magnetic layer that has excellent dispersibility of the magnetic powder and is durable. The object of the present invention is to provide a magnetic recording medium having the following characteristics.

Magnetic recording media are usually made by spreading a magnetic paint consisting of magnetic powder, a binder component, an organic solvent, and other necessary components onto a substrate such as a polyester film and drying it.
When high performance is required, metal magnetic powders such as iron and cobalt are used.

However, since these gold-magnetic powders have a very large magnetic moment, they tend to aggregate between particles, and there are wax points that are difficult to disperse uniformly in the binder resin. For this reason, efforts have been made to improve the dispersibility and durability by selecting binder resins that are highly durable and can absorb the dispersibility of metal magnetic powder. Polyurethane resins having a molecular weight of 5,000 or more are used as relatively good materials, but the abrasion resistance of the magnetic layer is still not fully satisfactory.

Therefore, in a magnetic layer containing such a polyurethane resin with a molecular weight of 5000 or more as a binder component, Cr is roughly added.
Attempts have been made to improve the wear resistance of the magnetic layer by mixing hard non-magnetic powders such as Os powder, but the combined use of such hard Cr z OS powders does not improve the wear resistance. Although the abrasion resistance is improved, there is a problem in that the dispersibility of the metallic magnetic powder is reduced.

As a result of extensive research in view of the current situation, the inventors used α-type ferric oxide powder (α-FezO@ powder) as a non-magnetic powder to be mixed into the magnetic layer, and this α-Fe
, O, powder in combination with a polyurethane resin having a molecular weight of 5,000 or more and incorporated into the magnetic layer together with the metal magnetic powder, the dispersibility of the metal magnetic powder is improved and the wear resistance of the magnetic layer is also sufficiently improved. The present inventors have discovered that a magnetic recording medium with excellent magnetic properties and durability can be obtained, leading to the present invention.

The polyurethane resin used as a binder component in this invention preferably has a molecular weight of 5000 or more, and specific examples include Takeratsuta E-5517 manufactured by Narita Pharmaceutical Co., Ltd., TU201 manufactured by Sanyo Chemical Co., Ltd.,
Examples include Handettus T5205, Bandettus T5201, and Pandexf 5250 manufactured by Dainippon Ink and Chemicals.

This type of polyurethane resin has good affinity with metal magnetic powder and disperses metal magnetic powder well. It also has good compatibility with other bonding systems and fats, such as vinyl chloride-vinyl acetate co-electrolyte, l-vinyl petitral resin, cellulose, @resin,
10 for the total number of fats such as isocyanate compounds.
It is preferable to use the amount in the range of ~80 II. If it is too small, the dispersibility of the metal magnetic powder will be reduced, and if it is too large, the magnetic layer will become hard and calcification will easily occur.

Further, in the present invention, if the α-FelO@ powder used in combination with the polyurethane fiiIwI has a particle size of 0.3 to 3 μ and is added to the metal magnetic powder at 0.1 times IS or more, excellent wear resistance can be obtained. As the amount added increases, the wear resistance improves without reducing the dispersibility of the metal magnetic powder, but when it is added by more than 30% by weight to the metal magnetic powder, the metal magnetic powder decreases relatively. If the metal magnetic powder is
It is preferable to use it within the range of 1 to 30% by weight.

Examples of metal magnetic powders include metal powders such as iron, cobalt, and iron, as well as various alloy powders of these materials or iron with AI.
, Crs 111% Si, 1m, and other known metal magnetic powders are widely included.

In addition, various additives commonly used in magnetic paints,
For example, a fractional agent, a lubricant, a band preventive agent, etc. may be optionally added.

The magnetic recording medium of the present invention can be produced by a conventional method, for example, α-Fe is added to an organic bath solution containing a polyurethane resin having a molecular weight of 5,000 or more and other binder resins together with a metal magnetic powder. , 0. The powder may be added and sufficiently dispersed using a ball mill or the like to prepare a magnetic coating material, which may be coated onto a substrate such as a 1-ester film by any means and dried.

Next, a practical example of this invention will be explained.

Example α-Fei 13 powder 80 parts VA
GH (manufactured by U, C, C, USA, 14N vinyl chloride-vinyl acetate-vinyl alcohol copolymer) Takelac E-551T (Bu 1) 5 #manufactured by Yakuhin Kogyo Co., Ltd., urethane prepolymer, molecular weight 6000) Coronate Japan Polyurethane (1 part by weight, manufactured by Kogyo Co., Ltd., king-functional low-molecular-weight isocyanate compound) α-Fe, O, powder, 1.6 r toluene 60 #Methyl isobutyl ketone 60 l A mixture was mixed and dispersed in a ball mill for 72 hours. A magnetic paint was prepared. This magnetic paint was applied to a polyester film with a thickness of 12 μm to a dry thickness of 4 μm, dried, and then cut to a predetermined width to form a magnetic tape.

Ratio S Example 1 In the composition of the magnetic paint in the example, --Fe20
．． A magnetic tape was made in the same manner as in the example except that the powder was omitted.

Comparative Example 2 In the composition of the magnetic paint in the example, Tanalak E
-5517 in place of Tanane) L -1O07 (Take■
Manufactured by I Yakuhin Kogyo Co., Ltd., urethane prepolymer, molecular weight 250
A magnetic tape was made in the same manner as in the actual example except that the same amount of 0) was used.

Comparative Example 3 In the composition of the magnetic paint in the actual example, α-Fc10
A magnetic tape was produced in the same manner as in Example except that the same amount of Cr1O@ powder was used in place of Cr3 powder.

Regarding the magnetic tapes obtained in Examples and Comparative Examples,
Coercive force (Hc), 8 magnetic flux density (Br), squareness ratio (Br
/B-) and the surface thickness of the magnetic layer were measured to test durability. The surface roughness of the magnetic layer was measured using a stylus-type surface roughness needle, and the numerical value of the surface roughness was calculated using the centerline average (C,
L, A). In addition, durability tests were carried out on each magnetic tape using Tablet+ (Rhody D-E9G manufactured by Hitachi).
The same number of runs was carried out until the output decreased by 0.5 dB from the initial output, with tIA fixed.

The table below shows the results.

As is clear from the above table, the magnetic tape obtained by this invention (Execution M) is different from the conventional magnetic tape (Comparison 941-3).
Compared to the above, the residual magnetic flux density and squareness ratio are high, the surface roughness is small, and the durability is improved. Therefore, the magnetic recording medium obtained by the present invention has excellent dispersibility of magnetic powder, and It can be seen that it has excellent durability.

Patent applicant Hitachi Maxell Co., Ltd.

Claims (1)

[Claims] 1. ftH magnetic recording medium having a magnetic layer made of gold containing 4 magnetic powder, α-type ferric powder, and polyurethane mb having a molecular weight of 5000 or more.