JPS62159338A - magnetic disk - Google Patents

Abstract

PURPOSE:To improve durability by providing an undercoating layer contg. nonmagnetic powder having a specific average particle size on a substrate and providing a thin magnetic layer on the undercoating layer. CONSTITUTION:The magnetic layer to be formed via the undercoating layer on the substrate is specified to <=5mum thickness to permit good high-density recording. A demagnetization loss increases and the satisfactory high-density recording is not possible if the layer is made thicker than said value. The nonmagnetic powder having 0.1-3Xm average particle size is incorporated into the undercoating layer to be provided between the substrate and the magnetic layer. The layer thickness is preferably made 0.1-3mum at which the above- mentioned nonmagnetic powder can be thoroughly incorporated into the undercoating layer. The internal stress generated by sliding with a magnetic head is dispersed and the durability is thoroughly improved if the undercoating layer incorporated with the nonmagnetic powder having 0.1-3mum average particle size and having 0.1-3mum layer thickness is provided between the magnetic layer and the substrate.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a magnetic recording medium suitable for high-density recording in which the thickness of the magnetic layer is 5 μm or less, and more specifically to the above-mentioned magnetic recording medium with excellent durability. Regarding.

[Conventional technology]

The magnetic layer of a magnetic recording medium is usually made by applying 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. In order to improve the adhesion of the magnetic layer to the substrate and reduce the surface electrical resistance,
An undercoat layer mainly made of polyester resin is formed between the magnetic layer and the substrate, or an undercoat layer is provided in which conductive powder such as carbon blank is uniformly dispersed. (Unexamined Japanese Patent Publication No. 55-84040) [Problems to be Solved by the Invention] However, in response to the increasing density of magnetic recording, the thickness of the magnetic layer is reduced as much as possible (which reduces demagnetization loss). On the other hand, the amount of filler contained in the magnetic layer gradually decreases, and the mechanical strength of the magnetic layer decreases, making it impossible to obtain sufficient durability. Especially 10℃
In the case of a low temperature below, the influence of the sliding stress of the magnetic head on the magnetic layer is large, and the magnetic layer may be destroyed in a short period of time, resulting in a significant decrease in durability.

[Means for solving problems]

This invention was made as a result of various studies in view of the current situation, and includes a base body and a thickness of 5.5 mm formed on the base body.
The average particle diameter is 0.1 to 3 μm between the magnetic layer and the magnetic layer of μm or less.
By providing an undercoat layer containing m non-magnetic powder,
The durability of the magnetic layer, which is extremely thin, has been sufficiently improved to enable high-density recording to be performed satisfactorily.

In this invention, the magnetic layer formed on the substrate via the undercoat layer is preferably 5 μm or less in order to enable good high-density recording; if it is thicker than this, demagnetization loss increases and Density recording cannot be performed well.

Further, in the present invention, the undercoat layer provided between the substrate and the magnetic layer contains non-magnetic powders having an average particle diameter of 0.1 to 3 μm, and the layer thickness is set to 0.00000000000000000000000000000, which is sufficient to contain these non-magnetic powders. The thickness of the undercoat layer is preferably 0.01 to 3 μm and contains nonmagnetic powder with an average particle size of 0.1 to 3 μm. When provided between the layers, the non-magnetic powder contained in the undercoat layer can disperse the internal stress caused by the sliding of the magnetic head, sufficiently reinforcing the mechanical strength of the magnetic layer, and increasing the strength of the magnetic layer. Even when the thickness is as thin as possible, the magnetic layer can be sufficiently reinforced and durability can be sufficiently improved.

As the non-magnetic powder contained in such an undercoat layer, an oxide powder with an average particle size of 0.1 to 3 μm is preferably used, and one with an average particle size of 0.3 to 1.0 μm is more preferably used. Ru. As such non-magnetic powder,
For example, A12o3 powder, αF e 203 powder, C
aCO3 powder, MgO powder, Cr2O3 powder, BaSO
4 powder, BaCO3 powder, ZnO powder, Cu2O powder,
CuO powder, Tio2 powder, etc. are preferably used. The amount used is 20% based on the total solid components of the undercoat layer.
It is preferable to use it within the range of ~80% by weight; if it is less than this, the desired effect will not be obtained, and if it is too much, the surface roughness of the undercoat layer will increase, causing increased noise in the magnetic layer. .

An undercoat layer containing such non-magnetic powder is usually prepared by mixing and dispersing these non-magnetic powders with a binder resin, an organic solvent, etc. to prepare an undercoat paint, and applying this onto a substrate such as a polyester film. It is formed by applying and drying. The thickness of the undercoat layer formed in this way is set to 0.
．． Preferably, the thickness is within the range of 1 to 3 μm.

Here, the binder resin used for the undercoat layer includes vinyl chloride-vinyl acetate copolymer, polyvinyl butyral resin, cellulose resin, polyurethane resin, polyester resin, epoxy resin, and polyether resin. , isocyanate compounds, radiation-curable resins, and other binder resins that have been widely used in the past are all suitably used.

Further, as the organic solvent, conventionally commonly used organic solvents such as acetone, methyl isobutyl ketone, methyl ethyl ketone, cyclohexanone, toluene, ethyl acetate, tetrahydrofuran, and dimethyl formamide can be used alone or in a mixture of two or more kinds. .

The magnetic layer on the undercoat layer is formed using γ-Fe203 powder,
Fe3O4 powder, CO-containing r-Fe203 powder, CO-containing Fe3O4 powder, Fe powder, C.

A magnetic paint was prepared by mixing and dispersing various conventionally known magnetic powders such as powder, Fe-Ni powder, barium ferrite, and strontium ferrite together with a binder resin and an organic solvent, and this magnetic paint was formed on a substrate. It is formed by coating and drying on the undercoat layer.

At this time, the binder resin and organic solvent used are preferably the same as those used in forming the undercoat layer.

In addition, various commonly used additives such as lubricants, dispersants, polishing agents, antistatic agents, etc. may be appropriately added to the magnetic paint.

〔Example〕

Next, embodiments of the invention will be described.

Example 1 Polyester resin 100 parts by weight Al2
O3 powder (particle size 0.7 to 100〃μm) Cyclohexanone 400〃Toluene
400〃This composition was mixed in a ball mill for 24 hours to prepare a paint required for undercoating, and this was applied to both sides of a 75 μm thick polyester film so that the dry thickness was 3 μm, and dried. An undercoat layer was formed by calendering.

Next, on the undercoat layer on both sides of this polyester film, a magnetic paint having the following composition was applied to a dry thickness of 0.7 μm, dried, and calendered at 50° C. and 10 kg/cnl to form a magnetic layer. . Thereafter, it was punched into a disk shape to produce a magnetic disk A in which an undercoat layer 2 and a magnetic layer 1ii3 were laminated on both sides of a polyester film 1, as shown in FIG.

Magnetic paint - α-Fe magnetic powder 500 parts by weight Vinyl chloride-vinyl acetate-vinyl 50//alcohol copolymer) Polyurethane resin 30 Isocyanate compound 20 Oley oleate
15〃Cyclohexanone
650〃Toluene 650〃Example 2 In the composition of the undercoat paint in Example 1, Al
CaCO3 powder (average particle size 0.-
A magnetic disk A was produced by forming an undercoat layer in the same manner as in Example 1, except that the same amount of 1 μm) was used.

Example 3 In the composition of the undercoating paint in Example 1, Al
An undercoat layer was formed in the same manner as in Example 1, except that the same amount of (X-Fe203 powder (average particle size: 0.3 μm) was used instead of 2O2 powder, and magnetic disk A was prepared.

Comparative Example 1 Same as Example 1 except that in the composition of the undercoating paint in Example 1, the same amount of Al2O3 powder with an average particle size of 0.07 μm was used instead of the Al2O3 powder with an average particle size of 0.7 μm. Then, an undercoat layer was formed and a magnetic disk was manufactured.

Comparative Example 2 Same as Example 1 except that in the composition of the undercoating paint in Example 1, the same amount of Al2O3 powder with an average particle size of 4.0 μm was used instead of the Al2O3 powder with an average particle size of 0.7 μm. Then, an undercoat layer was formed and a magnetic disk was manufactured.

Comparative Example 3 In the composition of the undercoating paint in Example 1, Al
An undercoat layer was formed in the same manner as in Example 1, except that the same amount of carbon black having an average particle size of 0.2 μm was used in place of 2O3 powder, and a magnetic disk was produced.

Comparative Example 4 In the composition of the undercoating paint in Example 1, Al
An undercoat layer was formed in the same manner as in Example 1, except that the 2O3 powder was omitted, and a magnetic disk was produced.

The durability of the magnetic disks obtained in each example and comparative example was examined. Durability was examined by mounting the magnetic disk in a magnetic disk drive and measuring the time until scratches appeared on the magnetic disk at a relative speed of 3 m/sec and a head pressure of 20 g.

Table 1 below shows the results.

Table 1 - [Effects of the Invention] As is clear from the above Table 1, the magnetic disks (Examples 1 to 3) obtained by the present invention are the same as those of Comparative Examples 1 to 4.
Compared to the magnetic disk obtained by the present invention, it takes a longer time for scratches to occur (This shows that the magnetic recording medium obtained by the present invention has sufficiently improved durability.

[Brief explanation of drawings]

FIG. 1 is a partially enlarged sectional view of a magnetic disk obtained by the present invention. 1... Polyester film (substrate), 2... Undercoat layer, 3... Magnetic layer, A... Magnetic disk (magnetic recording medium)

Claims (1)

[Claims] 1. An undercoat layer containing non-magnetic powder with an average particle size of 0.1 to 3 μm is provided on the substrate, and a layer with a thickness of 5 μm is provided on this undercoat layer.
A magnetic recording medium characterized by having a magnetic layer having a thickness of m or less.