JPS60113319A - Vertical magnetic recording medium - Google Patents

Abstract

PURPOSE:To make S/N (db) ratio the same on the front and rear and to decrease defects such as wrinkle, flaw, etc. by forming vertical magnetic recording layers each consisting of a thin magnetic metallic material film having <=1.5mu thickness on both surfaces of a base constituted by forming coated films dispersed with a lubricant on both surfaces of a high polymer film. CONSTITUTION:Since a high polymer film on which coated films dispersed with a lubricant is used as a base, there are no problems in handling at all such as transfer, taking up, etc. of the film even if the surface of the film itself is extremely smooth; moreover, there is no difference in the characteristics of the vertical magnetic recording layers provided on both surfaces and the vertical magnetic recording medium having a substantial output level of said layers is obtd. The thickness of the vertical magnetic recording layers, i.e., the thin magnetic metallic material films forming said layers is made <=1.5mum. Polyolefin such as PE, PP or the like, polyamide such as nylon-6, etc., polyester such as polyethylene terephthalate, polyethylene-2,6-naphthalate, etc. and other thermoplastic resin films are applicable to the high polymer film to be used as the base.

Description

Detailed Description of the Invention [Field of Application 1] The present invention relates to a thin film type perpendicular magnetic recording medium in which perpendicular magnetic recording layers are provided on both sides of a support, and more specifically, to solve problems in production when providing perpendicular magnetic recording layers. The present invention relates to a perpendicular magnetic recording medium suitable for use as a flexible disk, which has a structure with a small number of magnetic disks and has uniform characteristics on both sides.

[Prior Art and Problems] In recent years, high-density magnetic recording media have been developed in which a thin metal film is formed as a magnetic recording layer on a polymer film by a vacuum deposition method such as vacuum thermal bonding or sputtering, or by a plating method without using a binder. Therefore, it has been proposed to use this ferromagnetic metal thin film as a magnetic recording layer. For example, Co vapor deposition tape
JP-A-54-147010@), perpendicularly magnetized films made of Go--Cr alloy (Japanese Patent Publication No. 58-91, Japanese Patent Publication No. 58-10764), and the like have been disclosed. Metal thin films formed by such thin film forming means such as vapor deposition, sputtering, or ion blating have a thickness of 1.5 μm or less and have performance superior to that of conventional coated recording media in which the magnetic layer has a thickness of 3 μm or more. can get.

However, if the metal thin film formed is thin, the surface condition (surface irregularities) of the non-magnetic support will directly appear as irregularities on the magnetic film, which is said to have the disadvantage of causing spacing loss and dropouts. Ta. That is, from the viewpoint of reproduction output value and error characteristics, it is preferable that the surface condition of the substrate be as flat as possible.

However, it has been found that when an inexpensive polyester film is used as a support, the surface roughness of the film causes a spacing loss between the medium and the head, resulting in a large reduction in reproduction output. These problems can be solved by using a film with a small surface roughness, but such a film is expensive and usually has a large coefficient of friction due to its smooth surface. From the viewpoint of handling properties such as winding and transport, and running properties, the surface of the nonmagnetic support of a magnetic recording medium is required to be rough, and magnetic recording media have had contradictory problems. In other words, if the surface of the film is smooth, the sliding property between the films is poor and a blocking phenomenon occurs. It has also been found that since the slipperiness between the film and the roll is poor, if a magnetic film is formed while continuously winding the film, defects such as wrinkles and scratches will occur during the formation of the magnetic film.

Therefore, when such a film is used, the magnetic film must be formed on a sheet-by-sheet basis, which poses a problem in terms of productivity.

As mentioned above, from the viewpoint of handling the film, it is required that the surface of the film be moderately large, and from the viewpoint of electromagnetic conversion characteristics, a film with as smooth a surface as possible is required. One of the inventors of the present invention previously proposed in Japanese Patent Application Laid-Open No. 113418/1983 that the surface roughness (CLA) and the number of protrusions on the surface were specified as a non-magnetic support for a magnetic recording medium. It was proposed to use a non-magnetic support with a range of . Although the above-mentioned problems were solved by this proposed magnetic recording medium, in some cases the S/N ratio during high-density recording decreased, the running performance deteriorated, and further performance improvements were required for practical use. I was in a situation where I needed it. From these viewpoints, a polyester film coated with a smooth coating has been proposed as a support that satisfies the contradictory demands of both ministries at the same time (Japanese Patent Application Laid-Open No. 124620/1983). Such films are particularly used as base films for magnetic tapes. In other words, by applying a smooth coating to only one side of the support base film and using this side as the running surface, problems during film handling do not occur, and by providing a magnetic recording layer on the smooth surface, it has excellent electromagnetic characteristics. Magnetic tape and vines.

However, when such a film is used to make a magnetic recording medium for a flexible disk, since the surface properties of the front and back sides are different, if a magnetic recording layer is provided on both sides, a defect occurs in that the electromagnetic conversion characteristics, especially the output on the front and back sides, are different. Various difficulties have arisen in using such recording and reproducing devices. In other words, in order to perform recording and reproduction using a flexible disk with different characteristics on the front and back sides, the head and the output impedance must be set together on each side in order to make the interface between the medium and the head the same. However, there were problems in that the device became complicated and expensive, which caused problems in practical use. Therefore, it has been impractical to use a polyester film coated with lubrication on only one side as a magnetic recording medium for a double-sided flexible disk.

Furthermore, when using such a film and providing perpendicular magnetic recording layers on both sides, another production problem has arisen. Normally, the perpendicular magnetic recording layer is continuously formed on both sides of the polyester film in the same vacuum chamber by a physical deposition method using a vacuum such as sputtering, vapor deposition, or ion blating.

In such a method, the film comes into contact with a cooling drum or cooling plate while being transferred from the unwinding shaft to the winding shaft, and moves with the rotation of the cooling drum, or slides on the cooling plate, and during that time, the film is moved by physical contact. Particles formed by the deposition method fly through a vacuum and are deposited on the film. During deposition, the film is cooled by a cooling drum or plate to prevent radiant heat from the sputtering source, evaporation source, or heat from the plasma. The thickness of the perpendicular magnetic recording tank to be deposited is usually on the order of 0.1 to 1.5 microns, and in order to form a thin film of such thickness, the film is necessarily subjected to considerable heat. That is, in the case of sputtering, since the film formation rate is usually about 0.01 to 1 μ/min, the time the film stays in the plasma space where particles fly is required to be several tens of seconds or more, usually one minute or more. In addition, in the case of vapor deposition and ion blating, the film formation rate is 0.
1 μ/min or more, usually 1 μ/min or more, which is faster than sputtering, but the radiant heat from the evaporation source is large.
The amount of heat received by the film is greater than that of the subverting. For this reason, the film undergoes thermal deformation such as thermal contraction and thermal expansion.

Thermal deformation causes relative movement with the cooling drum or cooling plate, causing wrinkles, scratches, etc. In addition, it has been found that poor contact with the cooling drum or cooling plate sometimes causes film-forming problems such as fusing of the film. This problem arises because if the surface of the film is rough and has good sliding properties with the cooling drum or cooling plate, deformation such as wrinkles will cause the film to slide smoothly on the cooling drum or cooling plate.
It also eliminates problems such as scratches and scratches.

When a perpendicular magnetic recording layer is provided on both sides, one side of the film will inevitably come into contact with the cooling drum, so defects caused by thermal deformation of the film can be avoided by easily coating only one side. This was unavoidable when a modified film was used.

Furthermore, using films with different slipperiness on both sides,
From the viewpoint of each drum or cooling plate, it has not been possible to create a perpendicular magnetic recording medium for double-sided flexible disks that uses films with different properties on the front and back sides as a support.

[Objective of the present invention] The present invention has been made in view of the current situation, and has the following characteristics: the support has excellent runnability on the front and center during production of the magnetic recording layer, and has the characteristics ↑9 on the front and back that have a large reproduction output value. The object is to provide a magnetic recording medium for double-sided flexible disks.

[Configuration and effects of the present invention] The above objects are achieved by the invention as follows.

That is, the present invention relates to a perpendicular magnetic recording medium having recording layers made of magnetic metal thin films on both the front and back sides of a non-magnetic support, in which a support is formed by forming a coating film with a lubricant dispersed on both sides of a polymer film. A perpendicular magnetic recording medium characterized in that a perpendicular magnetic recording layer made of a magnetic metal thin film having a thickness of 1.5 μm or less is formed on each side of the support, and preferably has a surface roughness [CLA ( unit μm)]
is o, oog μm or more 0.02 μm or more 0 Box 02 et al. Preferably, the height h (unit: μm) of the protrusions on the surface and the number N (unit: ke/-) of the protrusions on the surface are 0.27 <h≦0654
N;, 10, 0.54<h, N≦0.2
This is a perpendicular magnetic recording medium suitable as a flexible disk, which satisfies the following.

The above-mentioned present invention was made as follows.

In other words, in perpendicular magnetic recording media, since magnetization is recorded in the direction perpendicular to the film surface, the surface roughness of the support greatly affects the reproduction output, and as mentioned above, in the case of magnetic metal thin films, the surface characteristics of the support This directly appears as unevenness on the surface of the recording layer, which greatly affects the reproduction output. However, after conducting various tests, it was found that with a support made of a smooth polymer film coated with a lubricant dispersed therein, the reduction in recyclability was not so great and was at a sufficiently practical level. The present invention has been made based on this knowledge.

Since the support is a polymer film on which a coating film with a lubricant dispersed on both sides is formed, there is no problem in handling such as transporting or winding the film, as mentioned above, even though the surface of the film itself is very smooth. In addition, a perpendicular magnetic recording medium with a sufficient output level without any difference in the characteristics of the perpendicular magnetic recording layers provided on both sides can be obtained. The thickness of the perpendicular magnetic recording layer, and therefore the magnetic metal 7iI film forming it, is set to 1.5 μm or less as described above. If the thickness exceeds 1.5 μm, the surface characteristics may differ from those of the support, and desired reproduction characteristics may not be obtained.

By the way, if the surface roughness CLA of the support is less than 0.008 μm, running properties will be reduced and continuous production of magnetic metal thin films will be difficult, while if CLA is 0.020 μm or more, electromagnetic conversion characteristics will be deteriorated. The decrease is particularly large during high-density recording. Therefore, the CLA of the surface is 0.008-0.
It needs to be in the range of 0.020 μm, more preferably,
It is in the range of 0.008 to 0.015μ tiles.

In addition, protrusions on the surface of the medium are not directly related to the average playback output (1t4 (envelope)), but are related to dropout (Dlo), which is important in practice, and the influence differs depending on the track width of flexible disks, etc. Since the track density is also increased by N demolding, the protrusions on the substrate have a protrusion height h
(unit 2 μm) and the number N (pieces/m) must satisfy the following formula % formula %. Further, it is preferable that the following formula 0.27 h < 0.54 satisfies NA3 0.54 < h N=0. Note that microprotrusions with h<0.27 or less are included in CLA and evaluated regardless of Dlo.

In addition, the polymer film serving as the support of the present invention described above includes:
Polyolefins such as polyethylene and polypropylene, polyamides such as nylon 6, polyesters such as JC'JJ ethylene terephthalate, polyethylene-2,6-naphthalate, and other thermoplastic resin films can be used.

Among them, polyethylene terephthalate, polyethylene
2,6-naphthalate is low cost, dimensionally stable and has a surface of 9.

It is preferable because it has excellent heat resistance and mechanical properties.

In the present invention, in order to provide the above-mentioned polymer film with slipperiness and adjust the surface roughness to obtain the above-mentioned support, a solution in which a lubricant is dispersed in water or a solvent is applied to both sides of the polymer film. This is done by applying. All conventionally known methods can be used to apply a solution to provide slipperiness (=l).For example, a water-based or solvent-based solution of (lubricant + polymeric binder + surfactant) is used to form a film. Sometimes methods such as coating are used.

Examples of the lubricant include organic lubricants such as Tsurujitan, organic polymer lubricants such as polytetrafluoroethylene and polyethylene, and inorganic lubricants such as alumina, kaolin, silica, and molybdenum sulfide.

The average particle size of the lubricant used needs to be large in order to impart slipperiness, but needs to be small from the viewpoint of electromagnetic conversion characteristics, and is determined by taking both factors into account. Usually, about 50 to 5000 people can be used, but more preferably about 100 to 1500 people. The amount added is preferably in the range of 0.02 to 2 wt% based on the coating liquid.

Examples of the polymeric binder include copolyurethane, nylon, and melamine. In particular, for example Ti (
A metal salt such as CH2=CHC00)4 and a water-soluble, water-swollen, oil-based or water-dispersible film-forming polymer compound such as a water-soluble silicone resin or polyvinyl alcohol, its monomer, or a mixture thereof are dissolved or dispersed in water. A liquid is preferred.

Furthermore, a surfactant is preferably added for the purpose of improving the wettability with the film and the dispersibility of the coating liquid. Further, there is no problem in adding ultraviolet absorbers, antistatic agents, etc.

A coating solution in which (lubricant + polymeric binder surfactant) is dispersed in water or a solvent can be applied during or after film formation, and dried to obtain a support with pickling properties. For example, when coating a biaxially oriented polyethylene terephthalate film, the molten polyethylene terephthalate resin is extruded through a slit using an extruder to form an unstretched film, which is then uniaxially stretched and further biaxially stretched to form a series of continuous films. An in-line coating method that does not disrupt the flow of the film during the manufacturing process would be advantageous. Particularly preferably, this is applied to both surfaces of the running film immediately before biaxial stretching, since the resulting coating film will be an aggregate of a large number of microprojections, which is good for the purpose of imparting slipperiness. Further, by incorporating a lubricant into the coating liquid, the above-mentioned coating film can have a more preferable form.

The perpendicular magnetic recording layer of the present invention may be any layer made of a continuous magnetic metal thin film with a thickness of 1.5 μm or less that enables perpendicular magnetic recording, and may have a multilayer structure, and may have an adhesive layer or the like between the layers. It may also have an intermediate layer. Alternatively, a protective layer may be provided. As a coating film (!1 recording layer) used for this purpose, there is a perpendicularly magnetized film known, for example, from Japanese Patent Publication No. 1988-91, among others, Co which has an axis of easy magnetization perpendicular to the film surface. A double-layered recording medium comprising a -Cr alloy film and a low coercive force layer is preferable as a double-sided recording medium from the viewpoint of the reproduction surface and the like.

As a method for forming the metal thin film of the recording layer, conventionally known physical vapor deposition methods such as vacuum evaporation, ion blating, and sputtering, and electroless plating can be applied. Among them, the magnetron sputtering method is used to form a perpendicular magnetic recording layer using polyester as a substrate to obtain a perpendicular magnetic recording medium, since it is possible to form a film at a low temperature and to form a perpendicularly anisotropic film stably. Or JP-A-57-
The facing target sputtering method disclosed in Japanese Patent No. 158380 and the like is preferred.

The following methods of measuring surface properties are available.

1. ClAl center line average (Cent
er Line A Verage - center line average roughness)] Based on JrS B 0601. That is, a commercially available stylus type surface roughness meter (for example, 5URF manufactured by Tokyo Seimitsu IA Shusha)
COIVL 30B), needle diameter 2 μm, side load 0.07 g, cut 1-A 70.25 mm, measurement length approximately 2
CLA was measured in mm.

2. Protrusions of surface protrusions - height and number
iss JENA thallium lamp (input = 535 nm
)use. ] was photographed and observed at a magnification of about 10 to 20 times, and the height and number of protrusions were determined from the interference draft. Usually, the dancer dances at any 10 locations and exchanges money for 1-per.

[Examples and Comparative Examples 1 and 2] 1 ootm part of dimethyl terephthalate and 0 weight ω parts of ethylene glyco-Schiff were added with zinc acetate and 023 weight parts (0,020 mol% to dimedimethyl terephthalate, 150 to 240 mol%). A transesterification reaction is carried out while methanol is distilled off at ℃ for 4 hours, and then a stabilizer (a glycol solution of a phosphorus compound) is once cooled to room temperature, and then 0.014 parts by weight in terms of trimethyl phosphate is added.Next, polycondensation is carried out. Adding 0.04 parts by weight of antimony trioxide as a catalyst, the polycondensation reaction was carried out for 4 hours in a high vacuum of 1 mm H9 or less to obtain [η] = 0.65 (0-chlorophenol solution, measured at 25 °C). Polyethylene terephthalate was obtained. This polyethylene terephthalate was further extruded to produce an unstretched film with a thickness of 650 μm, and the film was stretched in the longitudinal direction by 9
Biaxial stretching was performed 3.5 times at 0° C. and 4.0 times in the transverse direction at 100° C., followed by heat setting at 205° C. for 30 seconds to create a biaxially stretched film with a thickness of 50 μm.

In addition, before the transverse stretching process, a coating liquid having the following composition was applied to both sides of the film \ in Examples, and to one side of Comparative Example 1.

As Comparative Example 2, an uncoated film (support) was used. The composition of the coating liquid composition is as follows.

Aluminum acrylate (asada chemical, product name P-3)
30wt% solution・・・・・・・・・・・・・・・
・・・・60 Heavy Products Polyethylene Glycol (NOF 7.000 Product Name PEG200)・・・
・・Former ・・2o heavy suspension polyethylene glycol diglycidyl ether (product name manufactured by Nagase Sangyo: NEROIO>・・
・・・・・・・・・・・・・・・・・・・・・・・・
・・・・・・・・・・・・・・・・・・・・・10 Heavy State Capital Molybdenum Disulfide・・・・Old----------------------
------5 parts by weight of nonionic surfactant (N820
8.5)・・・・・・・・・・・・・・・・・・
・・・・・・・・・・・・・・・・・・・・・・・・
A coating solution was prepared by diluting 5 parts by weight or more of a coating composition with water so that the total solids concentration was 2% by weight. The coating set was 4.1 g/ni per side in wet form, and the solid content was approximately 0.0286! ? There is a button.

The support obtained in this way had good pickling properties and could be wound well without any blocking.

On both surfaces of the supports of Examples and Comparative Examples 1 and Comparative Example 2 obtained in this way, a low coercive coppermalloy layer was applied, and then a Co-Cr perpendicular magnetization film was continuously sputtered on the permalloy layers. The following strips '1' were formed continuously using a device.

■ MO-permalloy layer: Using a 1-thick MO-permalloy target (N+78%, FelB% 1MO4%), 1×10″2T o was formed by DC magnetron sputtering.
A 0.4 μι thick film was prepared at a deposition rate of 500 people/min in Ar (99,'19%). The coercive force in the in-plane direction of the obtained film was approximately 20, regardless of the difference in the surface of the support.
e (Oersted).

■ CO-Or II: Using a 4m thick Go-Cr alloy target l-<Cr17'tlft%), DC
1 x 1o-2T orr by magnetron sputtering method
A 0.3 μm thick Co-Cr alloy film was obtained at a deposition rate of 500 people/min in Ar (99,99%). The dispersion angle (Δθ50:
The half width of the rocking curve is 5-6'', and the coercive force in the perpendicular direction from the magnetic M-H curve is 610 to 6600e (Oersted).
The coercive force in the in-plane direction was 200 to 2500 e in all cases. The saturation magnetization was approximately 450011111/CC. These values do not depend on differences in the surface of the support;
It was constant.

However, the support of Comparative Example 1.2 had poor slippage during sputtering, and wrinkles occurred when rolling with a cold 1J roll, which often caused sputtering to be interrupted. Unavoidably, it was impossible to obtain continuous long media. Furthermore, comparative example 2
In this case, the support body of the sputtering ring 11,1 was also fused.

The perpendicular magnetic recording medium thus obtained was used as a 51" floppy disk, and the electromagnetic conversion characteristics (digital recording density characteristics) and appearance such as wrinkles and scratches were evaluated. As the evaluation criteria for the electromagnetic conversion characteristics, , 2KB
High-density single-route recording characteristics were evaluated based on the S/N (db) ratio during PI recording and playback and the rate of decrease in output during 50KB PI recording and playback relative to the output during 2KBP I recording and playback. The appearance of the obtained perpendicular recording medium, such as cracks and wrinkles, was also visually observed. The results are summarized in Table 1.

From the above results, the S/N (d
It is understood that the ratio i)) shows that the front and back sides are even and there are few defects such as wrinkles and scratches. On the other hand, in Comparative Example 1, the difference in the S/N ratio between the front and back sides is large and there are many flaws on the surface to which lubricant is not applied, and in Comparative Example 2, the S/N ratio on the front and back sides is the same and the output is large, but there are many flaws. There are many wrinkles on both the front and back sides, and both media cannot be used as magnetic recording media for flexible disks. Furthermore, in the comparative examples, the runnability during sputtering was poor, and in particular, in comparative example 2, it was not possible to perform long sputtering.

(Margin below)

Claims (1)

[Scope of Claims] 1) A perpendicular magnetic recording layer made of a magnetic metal thin film with a thickness of 1.5 μm or less is provided on both sides of a support made of a polymer film coated with a lubricant dispersed on both sides. A perpendicular magnetic recording medium characterized by the following: 2) Surface roughness of the support [CLA (unit μTrL)
)] is in the range of 0.008 μm or more and 0.02 μm or less. 3) Protrusion height h of the protrusion on the surface of the support (unit: μ
3. The perpendicular magnetic recording medium according to claim 2, wherein m) and the number N (unit side/-) satisfy the following formula.