JPH0457213A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obviate the generation of curling and to improve wear resistance by forming a carbon protective layer on the rear surface side of a substrate to the thickness of a range 0.5 to 2.0 times the thickness of the carbon protective layer on the front surface of a magnetic recording layer. CONSTITUTION:The inside of a vacuum chamber 5 of an electron beam vapor deposition device is evacuated and thereafter metals essential consisting of cobalt are evaporated while the flexible high-polymer substrate 16 is made to travel at a prescribed speed by a traveling system and while prescribed gases are supplied. After a specified vacuum is broken, graphite carbon is evaporated and the carbon protective layer is laminated on the magnetic recording layer. An ion source 25 is used at need at this time. After the vacuum is broken again, the carbon protective layer is stuck on the rear surface side of the substrate. The carbon protective layer which consists of the carbon of the same quality as the quality of the carbon formed on the front surface of the magnetic recording layer and has the thickness of the range of 0.5 to 2.0 times the thickness of the carbon protective layer on the front surface of the magnetic recording layer is provided.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a magnetic recording medium, and more particularly to a thin-film perpendicular magnetic recording medium suitably used in magnetic tapes and the like.

[Prior art] Vacuum deposition method 1. Thin-film magnetic recording media manufactured by physical vapor deposition methods such as sputtering are suitable for high-density recording because their magnetic recording layers are thin, and some have already been put into practical use as vapor-deposited magnetic tapes. . Among these, perpendicular magnetic recording media are expected to be the next generation high-density magnetic recording media. However, these thin-film magnetic recording media have thinner magnetic recording layers than coated magnetic recording media, and it is difficult to incorporate lubricant inside the magnetic recording layer, so they do not have sufficient wear resistance. I'm not getting sex. Attempts have been made to stack various protective layers and lubricant layers on the magnetic recording layer in order to improve wear resistance.

Among the protective layers, carbon protective layers are hard and have a large effect of improving wear resistance, so they have been widely used.

[Problem to be solved by the invention] When the magnetic recording medium is used for a magnetic disk with a rigid substrate or a floppy disk where the medium configuration is the same on both sides of the substrate, deformation and curling are not a particular problem. When applying the magnetic recording medium to a magnetic tape, if the magnetic recording layer and the carbon protective layer are simply laminated in this order on one side of a flexible polymer substrate as in the past,
There was often a problem that the internal stress of these laminated thin films caused the formation of culls on the entire magnetic tape with the carbon protective layer on the inside. Due to this curling, the running properties of the magnetic tape deteriorate, or the tape contact becomes poor, resulting in an inability to record or a significant drop in playback output, which makes it difficult to put it to practical use, which is a big problem. It was a dot.

The present invention was devised in view of the various drawbacks of the prior art, and its purpose is to eliminate the curling that is seen in vapor deposited tapes using conventional magnetic recording media.
Another object of the present invention is to provide a magnetic recording medium for a vapor-deposited magnetic tape that also has excellent wear resistance.

[Means for Solving the Problems] An object of the present invention is to provide a partial oxide perpendicular magnetic recording layer mainly composed of cobalt with a thickness of 0.5 μm or less and a carbon protective layer on a flexible polymer substrate. in this order, and further comprising a carbon protective layer on the back side of the flexible polymer substrate, wherein the thickness of the carbon protective layer on the back side of the substrate is equal to or greater than the surface of the magnetic recording layer. carbon protective layer thickness of 0. This is achieved by a magnetic recording medium characterized in that it is in the range of 5 to 2.0 times.

As the flexible polymer substrate used in the present invention, organic polymer materials are suitable, and among them, polyesters such as polyethylene terephthalate, polyethylene naphthalate, and polyethylene dicarboxylate, polyphenylene sulfide, and aromatic polyamides are suitable. There is. In particular, a biaxially stretched film of the organic polymer material is most suitable because of its excellent flatness and dimensional stability.

The thickness of the base is not particularly limited, but the workability 2
In terms of mechanical strength, the thickness is preferably in the range of 2 μm to 100 μm, particularly preferably in the range of 3 μm to 40 μm.

The magnetic recording layer used in the present invention is preferably a perpendicular magnetic recording medium made of a partial oxide mainly containing cobalt and having a columnar structure oriented approximately perpendicular to the substrate surface, but is not limited thereto. Any known magnetic recording layer can be used.

Since the columnar structure increases the reproduction output, it is desirable that the columnar structure can be clearly observed in a transmission electron micrograph of a cross section of the magnetic layer, and that gaps exist between the columnar structures. Further, it is preferable that the metallic cobalt, which is a permanent component of the magnetic recording layer, be crystalline, since the reproduction output can be increased.

The thickness of the magnetic recording layer is required to be 0.5 μm or less in order to relieve the internal stress of the magnetic layer and reduce curl. Further, in order to maintain good magnetic properties and increase output, a thickness of 0.1 μm or more is preferable. The magnetic recording layer has magnetic anisotropy in the perpendicular direction, and the value of the perpendicular anisotropy magnetic field (Hk) is 2 Oersted or more.

The perpendicular magnetic recording layer may contain iron and/or nickel and oxides thereof in addition to the above-mentioned main components.

In the present invention, the carbon protective layer laminated on the magnetic recording layer and the carbon protective layer laminated on the back surface of the flexible polymer substrate can be formed by vacuum evaporation, sputtering, plasma CVD, etc., but are not particularly limited. It is formed by a vacuum thin film forming method, and from an industrial manufacturing point of view, it is preferably formed by a vacuum evaporation method, which has a high film forming speed.
Furthermore, since carbon is a high melting point material, it is most desirable to form it by electron beam evaporation.

In addition, there are various types of carbon protective layer, and there are no particular limitations, but graphite capo 2. Although a mixture of graphite carbon and amorphous carbon can be used, it is preferable to use a mixed layer of graphite carbon and amorphous carbon, since appropriate hardness and lubricity can be obtained.

The thickness of the carphone protective layer laminated on the surface of the perpendicular magnetic recording layer is preferably thin in order to keep the spacing with the magnetic head small and to reduce the drop in playback output as much as possible. The range of 70A to 250A is desirable because the effect of improving properties is small.

Furthermore, in terms of improving wear resistance, the carbon formed on the surface of the magnetic recording layer is a mixed layer of graphite components and amorphous carbon, and the closer you get to the magnetic recording layer side, the more graphite components are. It is preferable that there is a compositional gradient such that the amorphous component increases as it approaches the side. The carbon protective layer having a gradient in composition can be obtained by performing ion irradiation with a light element gas such as helium or nitrogen obliquely to the flexible polymer substrate from the rear in the running direction of the flexible polymer substrate during vacuum deposition of carbon. I can do it.

Furthermore, the purpose is to improve the running properties of the magnetic tape between the carbon protective layer on the back side of the plastic substrate and the flexible polymer substrate, or between the magnetic recording layer and the flexible polymer substrate, or between the substrate and the carbon protective layer, or between the substrate and the magnetic recording layer. In order to improve the adhesion between the layers, an intermediate layer is provided or the substrate surface is treated with plasma.

Surface treatment such as ion irradiation treatment may also be applied.

It is preferable to apply a liquid or solid lubricant onto these carbon protective layers, which are laminated for the purpose of improving the running properties and abrasion resistance of the magnetic tape.

In the present invention, a carbon protective layer is laminated on both the surface of the magnetic recording layer and the back surface of the flexible polymer substrate, and the thickness of the carbon protective layer on the back surface of the substrate is determined by the thickness of the carbon protective layer on the surface of the magnetic recording layer. 0. It is important to set it within a range of 5 to 2.0 times, and thereby the curl of the entire vapor-deposited magnetic tape can be reliably reduced. If it is less than 0.5 times, the curl reduction effect will be small, and if it exceeds 2.0 times, curling may occur in the opposite direction, that is, with the back side of the substrate inside. More preferably 0. 5-1.5
This is twice the range.

In addition, both the carbon protective layer laminated on the surface of the magnetic recording layer and the carbon protective layer laminated on the back side of the flexible polymer substrate must be made of the same quality carbon obtained by the same manufacturing method except for the film thickness. is preferable, and thereby a great curl reduction effect can be exhibited.

The method for manufacturing the partial oxide perpendicular magnetic recording layer containing cobalt as the main component of the present invention includes, for example, the method described in JP-A-58-36653, in which oxygen gas is supplied substantially perpendicularly to the substrate surface while supplying oxygen gas into a vacuum chamber. Alternatively, a method of evaporating cobalt as described in JP-A-61-94237 by the present inventors, or supplying oxygen and a gas with low chemical activity such as nitrogen or argon into a vacuum chamber, Methods such as increasing the pressure (to evaporate cobalt) can be used, but
The latter method, in which cobalt and the like are evaporated by supplying oxygen and a gas with low chemical activity such as nitrogen or argon, is preferred because the resulting magnetic recording layer will have fewer cracks and curls.

An example of the method for manufacturing the magnetic recording medium of the present invention will be explained with reference to FIG. FIG. 1 shows an example of an electron beam evaporation apparatus, which is used for forming a magnetic recording layer and a carbon protective layer. In FIG. 1, 5 is a vacuum chamber, and a partition wall 8
It is divided into an upper tank 6 and a lower tank 7. Each type is provided with exhaust ports 9 and 10, and can be evacuated to a predetermined degree of vacuum by an exhaust system (not shown). There is an unwinding shaft 11 inside the upper layer. Nip roll 12. Drum 13. A substrate conveyance system consisting of a nip roll 141 and a take-up shaft 15 is provided. Reference numeral 8'8' denotes a shielding plate-forming extension portion extending from the tip of each partition wall 8 by a predetermined length along a predetermined width of the lower tank side circumferential surface of the drum 13, and the tip of the extension portion is for forming a shielding plate. A shielding plate 22 is formed to regulate the angle of incidence. In order to form a perpendicular magnetic recording layer, the shielding plate must have an angle of incidence (
The arrangement is preferably such that the angle between the evaporated vapor and the normal to the substrate surface is 45 degrees or less. Reference numeral 17 denotes an enclosure for forming a gas supply chamber which is branched and extended from each middle part of the extension part 8', and is located between the drum 13 and the electron beam evaporator 21 disposed opposite to the drum. A gas supply chamber 26 surrounded by the enclosure 17 and the shielding plate 22 is formed. A gas supply pipe 18 is provided in the gas supply chamber 26, and the valve 1
By adjusting 9, a predetermined flow rate of gas can be supplied.

Reference numeral 20 denotes a concave portion of the electron beam evaporator 21, which is filled with a metal containing cobalt as a main component when forming a magnetic recording layer, and filled with, for example, graphite carbon when forming carbon. Reference numeral 25 indicates an ion source used as necessary during carbon formation, and reference numeral 24 indicates a gas supply pipe to be supplied to the ion source.

To form the magnetic recording layer, after evacuating the vacuum chamber of the electron beam evaporation apparatus shown in FIG. Evaporates metals whose main component is cobalt. Next, after breaking the vacuum once, the graphite carbon is evaporated and a carbon protective film is laminated on the magnetic recording layer. At this time, 25 ion sources are used as necessary.

Next, after the vacuum is broken again, a carbon protective film is deposited on the back side of the substrate using the same manufacturing method as the carbon protective film laminated on the magnetic recording layer.

In addition, although we have described an example in which a magnetic recording layer and a carbon protective layer were sequentially laminated while breaking the vacuum using a vacuum evaporation apparatus equipped with one electron beam evaporator in one vacuum chamber, for example, three electron beam evaporators could be used. Of course, it is also possible to sequentially stack the magnetic recording layer, the carbon protective layer on the magnetic recording layer, and the carbon protective layer on the back surface of the substrate without breaking the vacuum in a vacuum evaporation apparatus equipped with the following.

[Function] Even if a magnetic recording layer alone is laminated on one side of a flexible polymer substrate and the surface is flat without any curling, the internal stress of the carbon film is quite strong and the surface of the flat magnetic recording layer is For example, if a carbon protective film with a thickness of several tens of OA is laminated thereon, a fairly severe curl will occur. A carbon protective film of the same quality as that formed on the surface of the magnetic recording layer and having a thickness in the range of 0.5 to 2.0 times the thickness of the carbon protective layer on the surface of the magnetic recording layer is formed on the back surface of the substrate. It is thought that by providing this, the stress of the entire magnetic tape can be balanced and curling can be reduced.

[Characteristics evaluation method, evaluation criteria] ■ Curl evaluation method Prepare a sample cut into 30 mm square pieces vertically and horizontally as an evaluation sample. As shown in FIG. 2, with this sample placed on a flat surface with the curled inner surface facing up, the height of this sample is measured using a hide gauge and is defined as h. During such measurements,
For example, if the height varies depending on the location, the arithmetic mean value of the highest and lowest heights is set as the height h. Next, as shown in Figure 2, the width (W) of the sample in the curl direction is
Measure with a caliper. The height and width are measured in this way, and the value of height (h) and width (w) is taken as the curl index. The measurement was performed three times as n number of samples, and the average value was taken as the curl index of the measurement sample. Samples with such a curl index of 0.5 or less were accepted.

(2) Evaluation method of abrasion resistance A magnetic recording medium for evaluation was slit into a width of 8 mm, and the slit was placed in a commercially available 8 mm tape cassette as an evaluation sample. It was recorded in a still state using a commercially available 8mm VTR deck, and the output was observed by continuously reproducing it. A sample with no fluctuation in reproduction output for 10 minutes was considered to be a pass.

■ How to observe the envelope A 50% white video signal was generated using a television signal generator (manufactured by Shibaku ■, TG-7) into a commercially available 8 mm VT.
Input to R deck (manufactured by Sony ■, EV-8900),
Recording was performed on a sample having the same shape as that used in the abrasion resistance evaluation method (2), and the envelope, which is the reproduced output waveform, was observed.

(2) Structural analysis of carbon protective layer Ultra-thin sections of the samples were prepared and analyzed by energy loss spectroscopy (EELS) using an ultra-high resolution analytical electron microscope as described below. The structure of the carbon protective layer can be identified by comparison with the spectra of standard samples of amorphous carbon and graphite carbon.

Ultra-high resolution analytical electron microscope: HB501 manufactured by VG, Energy loss spectrometer: ELS80 manufactured by G, measurement conditions: acceleration voltage 100 KV, sample absorption current: 10-9 A,
Counting time = 50 to 150 seconds [Example] The present invention will be explained in more detail using Examples below.

Example 1. 2. 3 Using the apparatus shown in Figure 1, a biaxially stretched polyethylene terephthalate film with a thickness of 10 μm is set as a flexible polymer base in the running system inside the apparatus, and the gas supply chamber is
After exhausting the air until the temperature is below X10-5 Torr, a mixed gas of oxygen and nitrogen at a mixing ratio of 15:85 is introduced into the waste supply chamber for 3.
Cobalt/nickel/iron (weight ratio 90
1515) Evaporate the alloy and run the substrate to a thickness of 3
A 500A magnetic recording layer was formed. Further, when forming the magnetic recording layer, the position of the shielding plate was adjusted so that the angle of incidence of the evaporated vapor flow onto the substrate was 20 degrees or less. In this method, the substrate with the magnetic recording layer formed on one side is again mounted on the unwinding shaft of the traveling system, and the concave part of the electron beam evaporator is filled with gelaphytocarbon with a purity of 99.9%. After evacuating the gas supply chamber to below 1 x 10-5 Torr, a carphone protective film of a desired thickness is formed on the previously formed magnetic recording layer by electron beam evaporation by adjusting the power and running speed. .

A magnetic recording medium of the present invention was obtained by using the same manufacturing method, but changing the film thickness to a desired thickness, and laminating a carbon protective layer on the opposite side of the substrate (the side without the magnetic recording layer).

Example 1 is a combination of carbon protective layer thickness on the magnetic recording layer and carbon protective layer thickness on the back side of the substrate, or a combination of 70A/100A, Example 2 is a combination of 100A/150A, and 20OA/100A. Example 3 is a combination of 300A.

Example 4.5 The ion source 25 shown in FIG. 3 was used only when forming the carbon protective layer on the surface of the magnetic recording layer.

The procedure was the same as in Examples 1 and 2.3, except that nitrogen gas was supplied to the ion source at a rate of 0.05 1/min, and a carbon protective layer was formed while ion irradiation was performed under the conditions of an ion acceleration voltage of IKeV and an ion current of 200 mA. A magnetic recording medium of the present invention was obtained.

Example 4 is a combination of the thickness of the carbon protective layer on the magnetic recording layer and the thickness of the carbon protective layer on the back side of the substrate of 100 A/100 A, and Example 5 is a combination of 100 A/80 A.

Comparative Examples 1 and 2 Comparative Example 1 is a magnetic recording medium obtained in the same manner as in Example 2 except that a carbon protective layer was not laminated on the back side of the substrate. (In Comparative Example 1, 100% was applied only to the surface side of the magnetic recording layer.
It has a carbon protective layer with a thickness of A. ) Comparative Example 2 is a magnetic recording medium obtained in the same manner as in Example 2, except that no carbon protective layer was laminated on the surface of the magnetic recording layer. (Comparative Example 2 has a carbon protective layer with a thickness of 150A only on the back side of the substrate.) When the curl and abrasion resistance of the magnetic recording layers obtained in Examples 1 to 5 were measured, the curl was small in all cases. , and had an acceptable level of wear resistance.

Further, when the magnetic recording layers of Comparative Examples 1 and 2 were measured for curl, curling was observed in both of them and they were rejected. In Comparative Example 2, cull was generated in the opposite direction with the carbon protective film on the back surface of the substrate facing inside. Furthermore, when the abrasion resistance was evaluated, both Comparative Examples 1 and 2 showed large fluctuations in reproduction output and were inferior in abrasion resistance.

Analysis revealed that the carbon protective layer was a mixed layer of graphite carbon and amorphous carbon. The carbon protective layer formed on the surface of the magnetic recording layer in Example 4.5 is a mixed layer of graphite carbon and amorphous carbon, and the closer it gets to the magnetic recording layer side, the more the graphite component is, and the closer it gets to the surface of the carbon protective layer, the more amorphous the layer is. It had a gradient composition with many components.

Note that the anisotropic magnetic field (Hk) of the magnetic recording media of Examples 1 to 5 and Comparative Examples 1 and 2 was perpendicular magnetic recording media exceeding 2 Oersteds.

The envelopes of Examples 1 to 5 were all stable with no fluctuation force, but the envelope output of Comparative Example 1 was small and unstable, and the envelope output of Comparative Example 2 could not be recorded.

Examples 1 to 5 that satisfy the conditions stipulated by the present invention have small curls, enable stable recording and reproduction, and exhibit excellent abrasion resistance, and can be used as vapor-deposited magnetic tapes for practical use. Met.

A carbon protective film similar to that on the surface of the recording layer is provided, and the thickness of the carbon protective layer on the back side of the substrate is 0.5 to 2.0 times the thickness of the carbon protective layer on the front side of the magnetic recording layer. Because of this structure, curling of the entire magnetic recording medium is reduced, and it also has excellent wear resistance, so stable running performance and playback output can be obtained, making it a practical magnetic recording suitable for magnetic tape. I was able to provide the medium. Further, the magnetic recording medium of the present invention is a perpendicular magnetic recording medium that can be manufactured by electron beam evaporation, and can be provided as a high-density magnetic tape suitable for mass production.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram illustrating an example of a magnetic recording medium manufacturing apparatus of the present invention, and FIG. 2 is a schematic diagram illustrating a method for evaluating curl of a magnetic recording medium. 5: Vacuum chamber, 8: Partition wall, 16: Flexible polymer substrate 17: Gas supply chamber formation enclosure, 18. 23 + gas supply pipe, 21: Electron beam evaporator 22: Shielding plate, 25: Ion source

Claims (1)

[Claims] 1 A partial oxide perpendicular magnetic recording layer mainly composed of cobalt having a thickness of 0.5 μm or less and a carbon protective layer are provided on a flexible polymer substrate in this order, and further, a carbon protective layer is provided on a flexible polymer substrate. A magnetic recording medium including a carbon protective layer on the back side of the substrate, wherein the thickness of the carbon protective layer on the back side of the substrate is 0.5 to 2.0 of the thickness of the carbon protective layer on the surface of the magnetic recording layer.
A magnetic recording medium characterized by a double range.