JPH04364221A - Disk type magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve reliability by making film thickness of a magnetic layer thin and by making film thickness of an under coating layer thick enough for durability. CONSTITUTION:A coating layer consists of two layers, the under coating layer 2 and the magnetic layer 3. An under coating material which is obtained by mixing and dispersing alpha-iron oxide powder with a solution having a composition of 100 pts.wt. alpha-iron oxide, 75 pts.wt. each of MEK and toluene, 25 pts.wt. cyclohexanon and other carbon black, MR-110, polyurethane resin, oleyl oleate, and 'Desmodule L (R)' with a sand mill for 3hrs is applied on the non-magnetic supporting body 1 having 62mum film thickness as the under coating layer 2 having 2.5mum film thickness. And a magnetic coating material which is obtained by mixing and dispersing a strong magnetic particulate of metallic pure iron with 100 pts.wt. metallic pure iron, 210 pts.wt. each of MEK and toluene and other carbon black, alumina, MR-110, polyurethane resin, oleyl oleate, cyclohexanon, and 'Desmodule L (R)' with the sand mill for 3hrs is applied on the layer 2 as the magnetic layer having 0.5mum film thickness. In this way, high density and durability is improved and high reliability is attained.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coated type medium using ferromagnetic fine powder, particularly a disk-shaped magnetic recording medium which has high recording density and excellent durability due to improved linear recording density.

0002

2. Description of the Related Art Coating type disk-shaped magnetic recording media such as floppy disks and hard disks are made to have higher densities in order to increase their capacity. In addition, there are two methods for achieving higher density: improving linear recording density and improving track density. As the recording density increases, the reproduction output tends to decrease, so in order to obtain a sufficient reproduction output, the ferromagnetic fine powder in the magnetic layer is made to have a high Hc, to be made fine, and to be highly packed. In addition to the composition of the magnetic layer, smoothness of the medium surface is also required in order to reduce air gap loss with the magnetic head.

[0003] In order to increase the linear recording density, it is necessary to shorten the recording wavelength. As a result, the magnetized region of the medium becomes shallower, so in so-called R/W dual-purpose heads, where the same head is used for both writing and reading, there is a tendency to make the magnetic layer of the medium thinner in order to satisfy resolution and overwrite characteristics. .

0004

[Problems to be Solved by the Invention] It is already known that in order to increase the density, it is necessary to make the ferromagnetic fine powder in the magnetic layer finer and more densely packed, to make the surface of the medium smoother, and to make the magnetic layer thinner. Stated. When the ferromagnetic fine powder is made finer and more highly filled, the amount of binder decreases, so the strength of the coating film tends to decrease and the durability tends to deteriorate. When the surface of the medium is made smooth, contact resistance increases, which tends to increase rotational torque and deteriorate durability. Further, even when the magnetic layer is made thinner, the strength of the coating film tends to decrease and the durability tends to deteriorate.

Since durability depends on the thickness of the magnetic layer, it can be improved by increasing the thickness of the magnetic layer. However, increasing the thickness of the magnetic layer causes deterioration in resolution and overwriting characteristics. A pre-erase method has been proposed to improve the overwrite characteristics of a thick magnetic layer, but it complicates the head structure and makes it difficult to achieve high density.

[0006] For the above reasons, it has been difficult to increase capacity while simultaneously satisfying high density and durability.

[0007]

[Means for solving the problem] The coating film on the non-magnetic support has a two-layer structure, and the upper layer is a magnetic layer suitable for short wavelength recording.
The lower layer is an undercoat layer that provides the necessary thickness for the durability of the coating as a whole and does not affect the electromagnetic conversion characteristics of the upper layer.

[0008]

[Operation] By increasing the Hc of the magnetic layer, making it thinner and flattening it, sufficient resolution and overwriting characteristics can be obtained even with a so-called R/W head, and high density recording by short wavelength recording can be realized. Furthermore, by providing an undercoat layer, the coating film as a whole can have a thickness necessary and sufficient for durability.

With the above configuration, the present invention makes it possible to simultaneously satisfy high density and durability, which have been difficult in the past, and to realize a large capacity of a disk-shaped magnetic recording medium.

0010

[Example] Specific examples will be described in detail below. (Figure 1
) shows a cross-sectional view of the disk-shaped magnetic recording medium of the present invention. In the case of a floppy disk, the nonmagnetic support 1 is a film made of cellulose diacetate, cellulose triacetate, polyvinyl chloride, polyethylene terephthalate, polyethylene naphthylate, polycarbonate, polyamide, or polyimide. In the case of a hard disk, the nonmagnetic support 1 is a circular plate made of aluminum, glass, polycarbonate, or the like. The subbing layer 2 consists of filler powder, carbon black, lubricant and binder. The magnetic layer 3 is composed of ferromagnetic fine powder, abrasive, carbon black, lubricant, and binder. Inorganic fine powders such as FeOOH, alumina, chromium oxide, α-iron oxide, titanium oxide, and silica are used as the filler powder and the polishing agent. Lubricants include fatty acids, fatty acid esters,
Phosphate esters, fluorocarbons, etc. are used in multiple combinations. As the binder, a system in which vinyl chloride-vinyl acetate-vinyl alcohol copolymer, nitrocellulose, polyurethane resin, and polyester resin are appropriately combined is used, and a low molecular weight isocyanate compound is used in combination as necessary. These materials are mixed with a mixed solvent of methyl ethyl ketone, methyl isobutyl ketone, toluene, xylene, cyclohexanone, and acetone in a pressure kneader, planetary mixer, ball mill, sand mill,
The magnetic paint is made into a paint using a dispersing machine such as a pebble mill, and the magnetic paint is applied to both sides of the non-magnetic support 1 and dried to form a magnetic recording medium.

[0011] In the present invention, in order to form a two-layer coating, the undercoat paint and the magnetic paint are applied twice.

(Example 1) As the undercoat layer 2 shown in FIG. 1, α-iron oxide fine powder (
BET specific surface area 45m2/g) was mixed and dispersed in the following composition solution using a sand mill for 3 hours, and then the undercoat paint was applied to a thickness of 62μ.
It was provided on a non-magnetic support 1 (polyethylene terephthalate film) with a film thickness of 2.5 μm.

α-Iron oxide
100
Weight part Carbon black

9 parts by weight MR-110 (manufactured by Nippon Zeon)
18 parts by weight Polyurethane resin
7 parts by weight Oleyl oleate
4
Weight part MEK

75 parts by weight Toluene

75 parts by weight cyclohexanone
25 parts by weight Desmodur L (manufactured by DuPont)
5 parts by weight Furthermore, metal pure iron ferromagnetic fine powder (Hc 1600 Oe,
σs 135 emu/g, BET specific surface area 40 m
A magnetic paint obtained by mixing and dispersing 2/g) in the following composition liquid using a sand mill for 3 hours was provided on the undercoat layer 2 to a thickness of 0.5 μm.

0014 Metal pure iron
100
Weight part Carbon black
3
Weight part Alumina

18 parts by weight MR-110 (manufactured by Nippon Zeon Co., Ltd.) 12
Weight part Polyurethane resin
12
Part by weight Oleyl oleate
10
Weight part MEK

210 parts by weight Toluene

210 parts by weight cyclohexanone
70 parts by weight Desmodur L (manufactured by DuPont)
5 parts by weight The magnetic sheet thus obtained was supercalendered and punched into 3.5 inch disks. Furthermore, the disk was polished for 10 seconds with a No. 10,000 polishing tape, and this was used as a sample.

(Example 2) The first magnetic layer 2 shown in FIG. 1 was made of γ-iron oxide ferromagnetic fine powder (Hc 370 Oe, σs 70 emu/g
, BET specific surface area 43 m2/g) was mixed and dispersed in the following composition liquid using a sand mill for 3 hours, and then the magnetic paint was mixed and dispersed to a thickness of 62 m2/g.
It was provided on a non-magnetic support 1 (polyethylene terephthalate film) with a film thickness of 2.5 μm.

γ-Iron oxide
100
Weight part Carbon black

5 parts by weight Alumina

4 parts by weight MR-110 (manufactured by Nippon Zeon Co., Ltd.) 1
4 parts by weight Polyurethane resin

14 parts by weight oleyl oleate

5 parts by weight MEK

90 parts by weight toluene

90 parts by weight cyclohexanone
30 parts by weight Desmodur L (manufactured by DuPont)
6 parts by weight Furthermore, as the magnetic layer 3 shown in (Fig. 1), the same magnetic paint used in (Example 1) was coated on a non-magnetic support 1 (polyethylene terephthalate film) with a thickness of 62 μm to a film thickness of 0.5 μm. It was established in

The magnetic sheet thus obtained was supercalendered and punched into a 3.5 inch disk. Furthermore, the disk was polished for 10 seconds with a No. 10,000 polishing tape, and this was used as a sample.

(Comparative Example I) As the magnetic layer 3 shown in (FIG. 2), the same magnetic paint used in (Example 1) was coated with a thickness of 0.5 μm on a non-magnetic support 1 (polyethylene terephthalate film) with a thickness of 62 μm. It was provided with a film thickness of .

The magnetic sheet thus obtained was supercalendered and punched into a 3.5 inch disk. Furthermore, the disk was polished for 10 seconds with a No. 10,000 polishing tape, and this was used as a sample.

(Comparative Example II) As the magnetic layer 3 shown in (FIG. 2), the same magnetic paint used in (Comparative Example I) was coated on a 62 μm thick non-magnetic support 1 (polyethylene terephthalate film) with a thickness of 3.0 μm. It was provided with a film thickness of .

The magnetic sheet thus obtained was supercalendered and punched into a 3.5 inch disk. Furthermore, the disk was polished for 10 seconds with a No. 10,000 polishing tape, and this was used as a sample.

The physical and magnetic properties of the sample are shown in Table 1.

[0023]

[Table 1]

The above sample was assembled into a 3.5-inch floppy disk case, and electromagnetic conversion characteristics and continuous durability tests using FDD were measured. The measurement FDD has a head gap length of 0.3 μm and a track density of 542T.
PI, 1f is 0.5 MHz, 2f is 1 MHz, outermost recording wavelength: 1f is 4.96 μm, 2f is 2.48 μm,
Innermost recording wavelength: 1f is 2.90 μm, 2f is 1.45
μm, and the rotation speed of the disk is 600 rpm.

[0025] Overwriting (Comparative Example II) is 0 dB.
It is shown as a relative value. Durability is 50% of the initial output of the truck 40 at a temperature of 50°C and a relative humidity of 20%.
The time of decrease was defined as the durability time.

The electromagnetic characteristics and durability measurement results of the sample are shown in Table 2.

[0027]

[Table 2]

[0028] The recording wavelength of the innermost circumference 2f is 1.45 μm.
Therefore, the writing depth is shallow and there is no big difference in the magnetic properties and surface properties of the surface layer of each sample, so the 2f output is about the same.

Regarding resolution, the sample with a large surface magnetic layer thickness (Comparative Example II) has a large 1f output;
Resolution is 10% or more lower than other samples.

Since the surface magnetic layer of the samples other than (Comparative Example II) was a thin film, the residual 1
f becomes smaller. Even when the undercoat layer has magnetism like the sample in Example 2, Hc is low and Bm is 1800 Ga.
If it is less than uss, it will be 1f by overwriting 2f.
has been sufficiently erased.

Durability is correlated with coating film thickness, and a thin film like the sample of (Comparative Example I) is inferior in durability. The samples of (Example 1), (Example 2), and (Comparative Example II) have a total thickness of about 3 μm, including the surface magnetic layer and the undercoat layer, and thus exhibit sufficient durability for practical use.

[0032]

As described above, the present invention has a structure in which the magnetic layer suitable for short wavelength recording is made thin and the undercoat layer is set to a thickness sufficient for the durability of the entire media, thereby achieving high density. and durability at the same time. Therefore, by utilizing the present invention, a highly reliable large-capacity disk-shaped magnetic recording medium can be realized.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a disk-shaped magnetic recording medium in (Example 1) and (Example 2) of the present invention.

FIG. 2 is a cross-sectional view of a disk-shaped magnetic recording medium in (Comparative Example I) and (Comparative Example II).

[Explanation of symbols]

1 Non-magnetic support 2 Undercoat layer 3 Magnetic layer

Claims (4)

[Claims] 1. A disk-shaped magnetic recording medium comprising an undercoat layer and a magnetic layer provided in this order on both sides of a non-magnetic support, wherein the undercoat layer has an Hc of 800 Oe or less and a Bm of 2.
00 Gauss or less, the film thickness is within the range of 1.0 to 4.0 μm, the Hc of the magnetic layer is within the range of 1000 to 3000 Oe, and the film thickness is within the range of 0.1 to 1.0 μm. A disk-shaped magnetic recording medium. 2. A disk-shaped magnetic recording medium comprising an undercoat layer and a magnetic layer provided in this order on both sides of a non-magnetic support, wherein the undercoat layer has an Hc of 200 Oe or more and 800 Oe or more.
Bm is 200 Gauss or more 1800G within the following range
auss or less, the film thickness is within the range of 1.0 to 4.0 μm, the Hc of the magnetic layer is within the range of 1000 to 3000 Oe, and the film thickness is within the range of 0.1 to 1.0 μm. A disk-shaped magnetic recording medium characterized by: 3. The disk-shaped magnetic recording medium according to claim 1, wherein the undercoat layer contains an inorganic fine powder and carbon black. [Claim 4] The ferromagnetic fine powder contained in the magnetic layer is
4. The disk-shaped magnetic recording medium according to claim 1, 2, or 3, characterized in that it is metal pure iron or hexagonal barium ferrite.