JPH0334127B2 - - Google Patents

Description

Detailed Description of the Invention [Field of Application] 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, as a high-density magnetic recording medium, a metal thin film has been formed as a magnetic recording layer on a polymer film by a vacuum deposition method such as vacuum evaporation or sputtering, or 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-deposited tape
147010), perpendicular magnetization film made of Co-Cr alloy (Japanese Patent Publication No. 58-91, Japanese Patent Publication No. 58-10764)
etc. are disclosed. The metal thin film formed by such thin film forming means such as vapor deposition, sputtering or ion plating has a thickness of 1.5 μm.
In the following, performance superior to conventional coated recording media in which the thickness of the magnetic layer is 3 μm or more can be obtained. However, if the thin metal film formed is thin, the surface condition (surface irregularities) of the non-magnetic support directly manifests as irregularities in the magnetic film, which has the disadvantage of causing spacing loss and dropouts. . 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 significant reduction in the 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 properties between the films are poor and a blocking phenomenon occurs. It has also been found that if a magnetic film is formed while continuously winding the film because the slipperiness between the film and the roll is poor, defects such as wrinkles and scratches will occur during the formation of the magnetic film. Therefore, when using such a film, the magnetic film must be formed on a single sheet, 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 appropriately rough, and from the viewpoint of electromagnetic conversion characteristics, the film must have a surface as smooth as possible. One of the inventors of the present invention previously proposed in Japanese Patent Application Laid-Open No. 57-113418 that the surface roughness (CLA) and the number of protrusions on the surface of a non-magnetic support for a magnetic recording medium are It was proposed to use a certain range of non-magnetic supports. 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 it was necessary. From these viewpoints, a polyester film coated with an easy-sliding coating has been proposed as a support that satisfies both contradictory requirements at the same time (Japanese Unexamined Patent Publication No. 124620/1983). Such films are particularly used as base films for magnetic tapes. In other words, by applying an easy-sliding coating to only one side of the support base film and using this surface as a running surface, problems during film handling will not occur, and by providing a magnetic recording layer on the smooth surface, a magnetic recording layer with excellent electromagnetic conversion characteristics can be created. Can be used as tape. 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 of 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 playback using flexible disks with different characteristics on the front and back surfaces, it is necessary to design the head and input and output impedances to match each surface in order to make the interface between the medium and the head the same. However, there were problems in that the equipment became complicated and expensive, and there were problems in practical use. Therefore, it is not practical to use a polyester film coated with an easy-sliding coating 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, perpendicular magnetic recording layers are continuously formed on both sides of a polyester film in the same vacuum chamber by a physical deposition method using vacuum, such as sputtering, vapor deposition, or ion plating. In such a method,
During the transfer from the unwinding shaft to the winding shaft, the film comes into contact with a cooling drum or cooling plate and moves with the rotation of the cooling drum, or it moves while sliding on the cooling plate, during which time it is deposited by a physical deposition method. The particles thus formed fly through the 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 layer 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, the film formation rate is usually about 0.01 to 1 μ/min, so 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 plating, 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, and the amount of heat received by the film is faster than sputtering. big. For this reason, the film undergoes heat shrinkage.
Thermal deformation such as thermal expansion occurs. Thermal deformation causes relative movement with the cooling drum or cooling plate, causing wrinkles,
This may cause scratches, etc. It has also been found that poor contact with the cooling drum or cooling plate sometimes causes problems in film formation, such as melting of the film. Such problems can be solved if the surface of the film is rough and has good sliding properties with the cooling drum or cooling plate, and deformation such as wrinkles can be solved by the film sliding smoothly on the cooling drum or cooling plate. Problems such as scratches and scratches rarely occur. 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 such defects due to thermal deformation of the film can be avoided by using a film coated with easy slip coating on only one side. It was unavoidable. Furthermore, using films with different sliding properties on both sides cannot be used as a perpendicular magnetic recording medium for double-sided flexible disks in which films with different properties on the front and back sides are used as a support from the viewpoint of each drum or cooling plate. [Object of the present invention] The present invention was made in view of the current situation, and provides a double-sided flexible disk in which the running properties of the support during the production of the magnetic recording layer are excellent on both the front and back sides, and the characteristics of the front and back sides are uniform and the reproduction output value is large. The purpose of this invention is to provide a magnetic recording medium. [Configuration and effects of the present invention] The above objects are achieved by the present invention as described below.
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 in which a lubricant is 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 with 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 0.008μm
It is in the range of 0.02 μm or less, and more preferably, the height h (unit: μm) of the protrusions on the surface and the number N (unit: ke/mm ² ) of the protrusions on the surface are 0.27<h≦0.54, N10, 0.54< This is a perpendicular magnetic recording medium suitable as a flexible disk, characterized in that h satisfies N0.2. 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 various studies, it was found that the reduction in reproduction output is not so large and is at a sufficiently practical level when a support is formed by forming a coating film in which a lubricant is dispersed in a smooth polymer film. 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, even though the surface of the film itself is very smooth, there are no problems in handling such as transporting or winding the film as described above. A perpendicular magnetic recording medium with no difference in the characteristics of the perpendicular magnetic recording layers provided on both sides and a sufficient output level can be obtained. Note that the thickness of the perpendicular magnetic recording layer and the magnetic metal thin film that forms it are determined as described above.
It should be 1.5μm or less. If the thickness exceeds 1.5 μm, its surface characteristics may differ from those of the support, and desired reproduction characteristics may not be obtained. By the way, when the surface roughness CLA of the support is less than 0.008 μm, the runnability decreases, making continuous production of magnetic metal thin films difficult, while when the CLA is 0.020 μm or more, the electromagnetic conversion characteristics deteriorate. The decrease is particularly large during high-density recording. Therefore, the surface CLA is
It needs to be in the range of 0.008 to 0.020 μm, more preferably in the range of 0.008 to 0.015 μm. Further, protrusions on the surface of the medium are not directly related to the average value (envelope) of the reproduction output, but are related to dropout (D/O), which is important in practice, and the influence differs depending on the track width of a flexible disk or the like. Because it is a thin film type and has a high track density,
For the protrusions on the substrate, the protrusion height h (unit: μm) and the number N (pieces/m ² ) of the protrusions must satisfy the following formula: 0.27<h0.54 is N10 0.54<h is N0.2. Further, it is preferable that the following formula 0.27h<0.54 satisfies N5 0.54<h N=0. Note that microprotrusions with h<0.27 or less are included in CLA and evaluated regardless of D/O. In addition, the polymer film serving as the support of the present invention mentioned above includes polyolefins such as polyethylene and polypropylene, polyamides such as nylon 6, polyethylene terephthalate, polyethylene-2,6-
Polyester and other thermoplastic resin films such as naphthalate can be used. Among them, polyethylene terephthalate and polyethylene-2,6-naphthalate are low cost and have good dimensional stability, surface properties,
It is preferable because it has excellent heat resistance, mechanical properties, etc. In the present invention, in order to impart slipperiness to the polymer film and adjust the surface roughness to obtain the support described above, a solution in which a lubricant is dispersed in water or a solvent is applied to both surfaces of the polymer film. This is done by applying. All conventionally known methods can be used to impart slipperiness by applying a solution. For example, a method may be used in which an aqueous or solvent solution of (lubricant + polymeric binder + surfactant) is applied during film formation. Examples of the lubricant include organic lubricants such as sorbitan, 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. Generally, a thickness of about 50 to 5000 Å can be used, and more preferably a thickness of about 100 to 1500 Å. The amount added is preferably in the range of 0.02 to 2 wt% relative to the coating liquid. Examples of the polymeric binder include copolyurethane, nylon, and melamine. especially,
For example, a metal salt such as Ti(CH ₂ =CHCOO) ₄ and a water-soluble, water-swollen, oily or water-dispersible film-forming polymer compound such as a water-soluble silicone resin or polyvinyl alcohol, a monomer thereof, or a mixture thereof. An aqueous solution or aqueous dispersion is preferred. Further, 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 liquid 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 slipperiness. For example, when coating a biaxially oriented polyethylene terephthalate film, the coating process is one of a series of continuous film manufacturing processes in which molten polyethylene terephthalate resin is extruded through a slit using an extruder to form an unstretched film, then uniaxially stretched, and then biaxially stretched. An in-line coating method that can be carried out without disturbing the flow of the film is industrially advantageous. Particularly preferably, the coating is applied to both surfaces of the running film immediately before biaxial stretching, since the resulting coating film is an aggregate of many microprotrusions, which is good for the purpose of imparting slipperiness. Further, by incorporating a lubricant into the coating liquid, the form of the coating film described above can be made more preferable. The perpendicular magnetic recording layer of the present invention may be any layer made of a continuous thin film of magnetic metal with a thickness of 1.5 μm or less that enables perpendicular magnetic recording, and may have a multilayer structure, with an intermediate layer such as an adhesive layer between the layers. It may have layers. Alternatively, a protective layer may be provided. Coating film (magnetic recording layer) used for such purpose
For example, there is a perpendicularly magnetized film known in Japanese Patent Publication No. 1983-91, among others, a double layer consisting of a Co-Cr alloy film with an axis of easy magnetization perpendicular to the film surface and a low coercive force layer. A film structure is preferable as a double-sided recording medium from the viewpoint of reproduction surface and the like. As a means for forming the metal thin film of the recording layer, conventionally known vacuum evaporation methods, ion plating methods, physical vapor deposition methods such as sputtering methods, and electroless plating methods can be applied. Among them, the magnetron sputtering method is used to form the above-mentioned perpendicular magnetic recording layer on a polyester 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 opposed target sputtering method disclosed in Publication No. 158380 and the like is preferred. The method for measuring surface properties is shown below. 1 CLA [Center Line Average (Center Line Average)]
Obtained according to JIS B 0601. In other words, a commercially available stylus type surface roughness meter (for example, manufactured by Tokyo Seimitsu Co., Ltd.)
SURFCOM 30B), needle diameter 2μm needle load
0.07g, cutoff 0.25mm, measuring length approximately 2mm.
Asked for CLA. 2. Protrusion height and number of surface protrusions: Observe the medium surface using a visible monochromatic light multiple interference microscope [for example, using a thallium lamp (input = 535 nm) manufactured by Carl Zeiss JENA. ] was used to photograph and observe at a magnification of 100 to 200 times, and the height and number of protrusions were determined from the interference draft. Usually, 10 arbitrary locations were photographed and converted to ^1mm2 . Examples and Comparative Examples 1 and 2 Zinc acetate was added as a catalyst to 100 parts by weight of dimethyl terephthalate and 70 parts by weight of ethylene glycol.
Adding 0.023 parts by weight (0.020 mol% to dimethyl terephthalate), transesterification was carried out at 150 to 240°C for 4 hours while distilling methanol off, and then the stabilizer (glycol solution of phosphorus compound) was cooled once to room temperature. Add 0.014 parts by weight in terms of trimethyl phosphate. Next, 0.04 parts by weight of antimony trioxide was added as a polycondensation catalyst, and the polycondensation reaction was carried out for 4 hours in a high vacuum of 1 mmHg or less [η] = 0.65 (O
- chlorophenol solution, measured at 25°C) of polyethylene terephthalate was obtained. Furthermore, this polyethylene terephthalate was extruded to produce an unstretched film with a thickness of 650 μm, and the film was stretched 3.5 times in the longitudinal direction at 90°C.
Biaxial stretching was performed in the transverse direction by a factor of 4.0 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. 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 before the transverse stretching step. As Comparative Example 2, an uncoated film (support) was used. The composition of the coating liquid composition is as follows. ●Aluminum acrylate (Asada Chemical KK product name P-
3) 30wt%...60 parts by weight ●Polyethylene glycol (Molecular weight manufactured by NOF
20000Product name PEG 200)...20 parts by weight●Polyethylene glycol diglycidyl ether (trade name NEROIO, manufactured by Nagase Sangyo)...10 parts by weight●Molybdenum disulfide...5 parts by weight●Nonionic surfactant (NS 208.5)
...5 parts by weight or more of a coating composition with a total solids concentration of 2% by weight
It was diluted with water to make a coating solution. The coating amount was 4.1 g/m ² per side in wet form, and about 0.0286 g/m ² in solid content. The support obtained in this way had good slipperiness and could be wound up well without any blocking. Examples and Comparative Example 1 thus obtained
A low coercive force permalloy layer was applied to both sides of the support of Comparative Example 2 and the support of Comparative Example 2, and then the permalloy layer was coated with a low coercivity permalloy layer.
A Co--Cr perpendicular magnetization film was continuously formed using a continuous sputtering device under the following conditions. Mo-permalloy layer: 1mm thick Mo-permalloy target (Ni78%, Fe18%, Mo4%)
using the DC magnetron sputtering method.
A 0.4 μm thick film was prepared at a deposition rate of 500 Å/min in Ar (99.99%) at 10 ⁻² Torr. The coercive force in the in-plane direction of the obtained film was about 20e (Oersted) regardless of the difference in the surface of the support. Co-Cr layer: A 4 mm thick Co-Cr alloy target (Cr17wt%) was used, and ^a
A 0.3 μm thick Co-Cr alloy film was obtained at a deposition rate of Å/min. The C-axis dispersion angle (Δθ50: half-width of the rocking curve) of the hexagonal close-packed crystal lattice determined from the X-ray diffraction rocking curve of the obtained Co-Cr perpendicularly magnetized film was 5-6°. , magnetic M
The coercive force in the vertical direction determined from the -H curve was 610 to 660 Oe (Oersted), and the coercive force in the in-plane direction was 200 to 250 Oe.
The saturation magnetization was approximately 450 emu/cc. These values were constant regardless of the difference in the surface of the support. However, the supports of Comparative Examples 1 and 2 had poor slippage during sputtering, causing wrinkles on the cooling roll, and sputtering had to be frequently interrupted, making it impossible to obtain a continuous long medium. . Furthermore, in Comparative Example 2, the support was fused and cut during sputtering. The perpendicular magnetic recording medium obtained in this way was
As a 1/4" floppy disk, we evaluated the electromagnetic conversion characteristics (digital recording density characteristics) and the appearance of wrinkles, scratches, etc.The evaluation criteria for the electromagnetic conversion characteristics were the S/N (db ) ratio and
High-density recording characteristics were evaluated based on the rate of decrease in output during 50 KBPI recording and reproducing relative to the output during 2 KBPI recording and reproducing. In addition, the appearance of the obtained perpendicular recording medium, such as scratches and wrinkles, was visually observed. Table 1 summarizes the results.
Shown below. From the above results, it is understood that the S/N (db) ratio of the perpendicular magnetic recording medium of the present invention is the same on both sides, and there are few defects such as wrinkles and scratches. On the other hand, in Comparative Example 1, the difference in 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 between 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 have many wrinkles and cannot be used as magnetic recording media for flexible disks. Furthermore, in the comparative examples, the runability during sputtering was poor, and in particular, in comparative example 2, it was not possible to perform long sputtering. 【table】

Claims (1)

[Claims] 1. 1.5 μm on each side of a support formed by forming a coating film with a lubricant dispersed on both sides of a polymer film.
A perpendicular magnetic recording medium comprising a perpendicular magnetic recording layer made of a magnetic metal thin film having the following thickness: 2 The surface roughness [CLA (unit: μm)] of the support is
The perpendicular magnetic recording medium according to claim 1, wherein the perpendicular magnetic recording medium has a diameter of 0.008 μm or more and 0.02 μm or less. 3 The height h (unit: μm) of the protrusions on the surface of the support and the number N (unit: pieces/mm ² ) of the protrusions are as follows: 0.27<h≦0.54, N10; 0.54<h, N0.2. A perpendicular magnetic recording medium according to claim 2 which satisfies the scope of claim 2.