JPS639015A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve the film strength of a magnetic layer by providing thin ferromagnetic metallic film layers consisting of an upper layer and lower layer essentially consisting of Co on a plastic film having a prescribed thickness and specifying the ratio of the thickness between the upper and lower layers to 0.2-0.9. CONSTITUTION:The lower layer part 3 and upper layer part 4 of the thin ferromagnetic metallic film are formed on a substrate 2 formed of the plastic having <=8mum thickness. These layers are so formed that the direction of the inclination of the lower layer crystal grains 5 in the lower layer part 3 is different from the direction of inclination of the upper crystal grains 6 in the upper layer part 4. The thin ferromagnetic metallic film layers 3, 4 are decreased in the length of the columnar crystal grains by forming the same into the two-layered constitution. The film strength of the thin film layers 3, 4 is, therefore, improved. The ratio of the thickness between the upper layer 3 and the lower layer 4 is specified to 0.2-0.9, by which the signal of about 5MHz having a relatively shallow magnetic field is held in the upper layer 3 having the relatively small layer thickness and the signal of about 0.75MHz having the relatively deep magnetic field is effectively held by the lower layer 4 having the larger layer thickness and having the structure in which the columnar crystal grains are more erected with respect to the main plane of the substrate 1.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium, particularly a metal thin film type magnetic recording medium.

Prior art and its problems As magnetic recording media for video, audio, etc., media having a metal thin film type magnetic layer are being actively developed because of their compactness when wound into tapes.

The magnetic layer of such a metal thin film type medium is made of Co-based, Co-Ni-based, etc., formed by the so-called oblique evaporation method, which is performed at a predetermined angle of inclination to the normal to the substrate due to its characteristics. A vapor deposited film is preferred.

For such media, research has been progressing on media using films of, for example, 10 F or higher in order to achieve miniaturization and long-term recording, but there are issues with running performance, durability, and the strength of ferromagnetic metal thin films. Problems arise in terms of strength, etc.

Therefore, in order to eliminate these inconveniences, a proposal was made to provide a metal thin film reinforcing layer on the back side of the film (Japanese Unexamined Patent Publication No. 56-1
No. 6939, No. 58-97131, No. 57-7862
7, No. 57-37737) or a proposal to improve the head touch and running surface by disposing fine particles on the film surface (Japanese Patent Application Laid-open No. 58-68227, No. 58-1002).
No. 21) etc. have been made.

In addition, various proposals have been made to divide the ferromagnetic metal thin film layer into two layers in order to improve durability and electromagnetic conversion characteristics (Japanese Patent Application Laid-open No. 54-141608, Japanese Patent Publication No. 56-26
No. 892, JP-A-57-130228, etc.).

However, the technique described in the above-mentioned publication does not completely solve the problems in media using films of 10- or less.

Furthermore, today, in order to realize longer recording times, there is a growing demand for media with a film thickness of 8 μm or less that combines good running performance, durability of the magnetic layer, and stability of magnetic properties. , it has not been adequately addressed.

■ Purpose of the Invention The purpose of the present invention is to use a film support with a film thickness of 8 mm or less, to provide good running properties of the medium, to reduce cracks and scratches in the magnetic layer due to running, and to reduce head wear and dropouts. It is an object of the present invention to provide a magnetic recording medium of a thin metal film type with a small amount of metal.

■Disclosure of invention Such objects are achieved by the invention described below.

That is, the present invention has a ferromagnetic metal thin film layer mainly composed of Co on a plastic film having a thickness of 8 mm or less,
This magnetic recording medium is characterized in that the ferromagnetic metal thin film layer has an upper layer and a lower layer, and the ratio of the thickness of the upper layer to the thickness of the lower layer is 0.2 to 0.9.

■Specific structure of the invention Hereinafter, a specific configuration of the present invention will be explained in detail.

The ferromagnetic metal thin film layer as the magnetic layer in the present invention is C
The main component is o, including 0, and further N as necessary.
It has a composition containing i and/or Cr.

That is, in a preferred embodiment, it may be made of Co alone, or it may be made of Co and Ni. When Ni is included, the weight ratio of Co/Ni is preferably 1.5 or more.

Furthermore, Cr may be contained in the ferromagnetic metal thin film layer.

In such cases, Cr/Co or Cr/(Co
+Ni) weight ratio is 0.1 or less, especially 0.001 to 0.
1, more preferably 0.005 to 0.05.

Furthermore, the ferromagnetic metal thin film contains zero.

The average amount of oxygen in a ferromagnetic metal thin film is determined by the atomic ratio, especially O/(
The atomic ratio of Co or Co+Ni is preferably 0.5 or less, more preferably 0.05 to 0.5.

In this case, oxygen forms an oxide with the ferromagnetic metal (Co, Ni) on the surface of the ferromagnetic metal thin film layer.

That is, in the surface area, particularly in the thickness range of 50 to 500, more preferably 50 to 200, from the surface, a peak indicating an oxide is observed by Auger spectroscopy. The oxygen content of this oxide layer is about 0.5 to 160 in atomic ratio.

Furthermore, in such a ferromagnetic metal thin film, there are other!
Quantitative components, especially transition elements such as Fe, Mn, V, Zr
, Nb, Ta, Ti, Zn, Mo, W, Cu, etc. may be included.

In a preferred embodiment, such a ferromagnetic metal thin film layer is composed of an aggregate of the above-mentioned patent crystal grains characterized by Co.

In this case, the total thickness of the ferromagnetic metal thin film layer is 0.05
~0.5-1, preferably 0.07-0.3-.

Such a ferromagnetic metal thin film layer of the present invention has two layers, an upper layer and a lower layer.
It is composed of layers.

The thickness of the upper layer is smaller than that of the lower layer.

In this case, the ratio of the thickness of the upper layer to the thickness of the lower layer is between 0.2 and 0.
．． 9, more preferably in the range of 0.4 to 0.9.

The columnar crystal grains have a length spanning almost the entire thickness direction of each layer, and there is no particular restriction on the angle at which the longitudinal direction is inclined with respect to the normal to the main surface of the base body.

In this case, the direction of inclination of the crystal grains in the lower layer and the crystal grains in the upper layer may be in the same direction in the length direction of the medium with respect to the normal to the main surface of the substrate, but preferably they are in opposite directions. It is preferable that

FIGS. 1 and 2 schematically illustrate the direction of the inclination of crystal grains.

1 and 2, a magnetic recording medium 1 includes a ferromagnetic metal thin film lower layer 3 and a ferromagnetic metal thin film upper layer 4 on a base 2. As shown in FIGS. Then, the ferromagnetic metal thin film lower layer part 3
The direction of inclination of the lower layer crystal grains 5 in the ferromagnetic metal thin film upper layer section 4 and the direction of inclination of the upper layer crystal grains 6 in the ferromagnetic metal thin film upper layer section 4 are opposite directions in the longitudinal direction a of the medium in FIG. In the figure, the length direction a of the medium is the same direction.

In the present invention, the crystal grains may have either the crystal grain inclination shown in FIG. 1 or FIG. 2, but those having the crystal grain inclination shown in FIG. 1 are preferable.

Note that oxygen exists in the form of a compound on the surface of the columnar crystal grains in the surface portion, as described above.

Further, there is no particular restriction on the oxygen concentration gradient of the ferromagnetic metal thin film layer.

Moreover, it is preferable that the short axis of the crystal grain has a length of about 50 to 500 grains.

In this way, by forming the ferromagnetic metal thin film layer into a two-layer structure, the length of the columnar crystal grains becomes small, so that the film strength of the ferromagnetic metal thin film layer is improved. In addition, because the ratio of the thickness of the upper layer to the thickness of the lower layer is 0.2 to 0.9, a signal of about 5 MHz with a relatively shallow magnetic field is retained in the thin upper layer, and a relatively deep magnetic field is retained in the thin upper layer. with 0,75MH
A signal of about z is effectively held in the lower layer, which has a thick layer and has a structure in which the columnar crystal grains stand more vertically with respect to the main surface of the substrate.

The substrate on which such a ferromagnetic metal thin film layer is formed is not particularly limited as long as it is non-magnetic, but flexible substrates, especially plastic films such as polyester films, polyamide films, and polyimide films, may be used. That's good.

Further, the thickness thereof is preferably 8 or less, particularly about 5 to 7.

If the thickness exceeds 8 mm, the objectives such as miniaturization of the medium and long-term recording cannot be achieved. In addition, if this thickness becomes too thin, the effect of improving the film strength by forming the magnetic layer with a two-layer structure as described above will be canceled out, resulting in a decrease in running performance and output.
Problems such as head wear occur.

In the case of a conventional single-layer ferromagnetic metal thin film layer, if the base thickness is 8 mm or less, the output, especially the output in the high frequency range of about 5 MHz, will be significantly reduced, making it impractical.

On the other hand, when the base thickness is greater than 8 -, if the 8 ferromagnetic metal layers are made into a two-layer structure, the output and durability will be improved as has been proposed in the past.

Even if the base thickness is 8 mm or less, if the two-layer structure is used, the output and durability will be similarly improved.

However, the effect of improving the characteristics, especially improving the electronic conversion characteristics, by forming the ferromagnetic metal thin film layer into a two-layer structure with a predetermined film thickness ratio in the present invention is extremely large when the substrate thickness is made as thin as 8 mm or less. This is something that appears significantly and critically.
This was something that could not have been predicted previously.

More specifically, for example, when the thickness of the substrate is 10 -, the ferromagnetic metal thin film layer is changed from the conventional single layer structure to 2 as in the present invention.
The extent of improvement in electromagnetic conversion characteristics due to the layered structure is 0.
Approximately +2 (dB) for signals in the low frequency region of 75 MHz, 5
It is approximately +2 (dB) for a signal in the high frequency region of MHz.

On the other hand, when the substrate thickness is 7%, the improvement is 0.7
The signal in the low frequency region of 5M) Iz is about +2 (dB), which is equivalent to the case with a substrate thickness of 10-, but the signal in the high frequency region of 5MHz significantly increases to about +4 (dB).

in this way,! 〇-The reason why the electronic conversion characteristics of the 7-thick substrate is significantly improved compared to that of the 10-thick substrate is that
By changing from - to 7-, the head touch due to insufficient board rigidity deteriorates rapidly, and this effect is even greater in a high frequency region such as 5 MHz, and it is in such cases that the effects of the present invention are manifested. .

Therefore, by using a base thickness of 8 mm or less, which has hitherto been impractical in terms of output, especially in high frequencies, a medium with output and durability that is sufficiently suitable for practical use can be realized.

A backing layer may be provided on the other side of the plastic film on which the magnetic layer is not provided.

When installing a backing layer, the backing layer is Afl, Cu, W%M
single metals such as o, Cr, Ti or alloys containing these;
Alternatively, it is preferable to use a thin film of an oxide thereof.

Among the above-mentioned metals, it is particularly preferable to use non-magnetic ones. The reason for this is, for example, when the backing layer is made of magnetic metal and the magnetic surface is wound up in a magnetized state,
If the lining layer is magnetized by magnetic flux leakage from the magnetic layer, or if the lining layer is magnetized and the magnetic surface is re-recorded and re-wound, the magnetization state of the magnetic surface will be disturbed due to the influence of the magnetism of the lining layer. This is because problems such as increased noise occur.

The forming method of the backing layer includes, for example, vacuum thin film forming methods such as vapor deposition, sputtering, and ion blating, and various CV methods.
A vapor phase growth method such as D, a plating method, or the like may be used.

The film thickness of the lining layer formed in this way is 0.05 to 1.
5-1, more preferably 0607 to 0.9-1, and even more preferably 0.07 to 0.7-.

If the film thickness exceeds 1.5 -, cracks in the magnetic layer or scratches on the magnetic surface occur due to running. Further, the amount of head wear increases. And dropouts increase. In addition, when the film thickness is less than 0.05 μm, running stability decreases, head touch failure occurs, output decreases, and envelope failure occurs.

Fine protrusions may be provided at a predetermined density on the surface of the magnetic recording medium of the present invention.

The fine protrusions are 30 to 300 people, more preferably 50 to 300 people.
It has a height of 250 people.

That is, the protrusions of the present invention cannot be observed with an optical microscope and measured with a stylus type surface roughness meter, but can be observed with a scanning electron microscope.

If the height of the protrusions exceeds 300 and becomes observable with an optical microscope, the electromagnetic conversion characteristics deteriorate and the running stability deteriorates.

Moreover, when it is less than 50λ, there is no effective improvement in physical properties.

And its density is on average 10 per mm2! ' or more, more preferably 105 to 109, especially 106 to 1
It is 08.

When the protrusion density is less than 10 5 /mm 2 , noise increases, still characteristics deteriorate, and other physical properties deteriorate, making it unsuitable for practical use.

Moreover, if the number exceeds 109 pieces/a+m2, the effect on physical properties will decrease.

Note that the diameter of the projection is generally about 200 to 1000 people.

In order to provide such protrusions, it is usually sufficient to arrange fine particles on the substrate. The diameter of the fine particles may be 30 to 1000, thereby forming fine protrusions corresponding to the diameter of the fine particles.

The fine particles used are those commonly known as colloidal particles, such as 5in2 (colloidal silica), An203 (alumina sol), MgO.
, T i 02, Zno, Fe2O3, Zirconia, C
d01N i O, CaWO4, CaCo3, BaCo
3. Coco, BaTiO3, Ti (titanium black), Au, Ag, Cu, Ni, Fe, various hydrosils, resin particles, etc. can be used. In this case, it is particularly preferable to use inorganic substances.

Such fine particles may be prepared by forming a coating liquid using various solvents, applying this onto a substrate, and drying it, or by applying a coating liquid containing a resin component such as various aqueous emulsions and drying it. Good too.

Note that, in some cases, these coating liquids may be provided as a top coat layer on the magnetic thin film layer instead of being provided on the substrate.

Further, when a resin component is used, gentle protrusions may be provided to overlap the microprotrusions based on these fine particles, but this is usually not necessary.

If necessary, a non-magnetic metal thin film layer may be interposed between the upper and lower ferromagnetic metal thin film layers.

In the present invention, the magnetic layer is preferably formed by a so-called oblique evaporation method.

In this case, there is no particular restriction on the minimum value of the incident angle of the vapor deposition substance with respect to the normal to the substrate.

Further, although the lower layer and the upper layer of the magnetic layer may be successively formed in one step, it is usually preferable that after forming the lower layer, the magnetic layer is passed through the vapor deposition process again to form the upper layer.

By dividing the formation of the magnetic layer into two steps, the lower layer formation and the upper layer formation, as described above, the direction of the inclination of the magnetic columnar crystal grains with respect to the normal to the substrate can be adjusted between the upper layer and the lower layer. They face each other in the length direction.

With such a magnetic layer configuration, the electromagnetic conversion characteristics are extremely good.

The vapor deposition atmosphere is usually an inert atmosphere such as argon, helium, or vacuum, and an atmosphere containing oxygen gas.
The pressure may be approximately -5 to 10'Pa, and the deposition distance, substrate conveyance direction, structure and arrangement of cans and masks, etc. may be the same as known conditions.

Then, a metal oxide film is formed on the surface by vapor deposition in an oxygen atmosphere. Note that the oxygen gas partial pressure at which metal oxides are formed can be easily determined through experiments.

Note that various oxidation treatments can be performed to form a metal oxide film on the surface.

Applicable oxidation treatments include the following.

Dry process a, energetic particle process As described in Japanese Patent Application No. 76,640/1982, oxygen is applied to the magnetic layer as energetic particles using an ion gun or a neutral gun in the latter stage of vapor deposition.

b. Glow treatment 02, using N20.0□+H20, etc. and an inert gas such as Ar, N2, etc., generates plasma by glow discharge, and exposes the surface of the magnetic film to this plasma.

C9 oxidizing gas Items that spray oxidizing gas such as ozone or heated steam.

d. Heat treatment: Oxidation is performed by heating. Heating temperature is 60-15
Around 0℃.

2) Wet treatment a, anodic oxidation, alkali treatment, C8 acid treatment, chromate treatment, permanganate treatment, phosphate treatment, etc. are used.

d. Oxidizing agent treatment H2O2 etc. are used.

The organic top coat layer of the present invention contains a radiation-curable compound, that is, one or more of radiation-curable polymers, monomers, and oligomers, an antioxidant, and, if necessary, a lubricant, and has a predetermined density. This is a layer formed on a ferromagnetic metal thin film having protrusions of the size of .

Furthermore, the running properties of the medium of the present invention can be further improved by providing a surface layer on the magnetic layer.

As the surface layer, various known materials can be applied, such as various polymeric substance coatings or coatings containing lubricants, antioxidants, surfactants, inorganic fine particles, etc.
There are various types of lubricant coatings or vapor phase deposits.

The thickness of the surface layer is approximately 5 to 300λ.

(2) Specific Effects of the Invention According to the present invention, since a substrate having a thickness of 8 mm or less is used, it is possible to miniaturize the medium and record for a long time.

Further, since the magnetic layer has a two-layer structure of an upper layer and a lower layer, the length of the magnetic columnar crystal grains becomes small, so that the film strength of the magnetic layer is improved. Therefore, the running stability is extremely high, the occurrence of cracks in the magnetic layer or scratching of the magnetic surface due to running is extremely small, and the amount of wear on the head is also extremely small.

Furthermore, the ratio between the thickness of the upper layer and the thickness of the lower layer of the magnetic layer is 0.
2 to 0.9, a signal of about 5 MHz with a relatively shallow magnetic field is retained in the thin upper layer, and a signal of about 0.75 MHz with a relatively deep magnetic field is effective in the thick lower layer. It is held in

(2) Specific Examples of the Invention Hereinafter, specific examples of the present invention will be shown and the present invention will be explained in more detail.

Example 1 A polyester (PET) film having the thickness shown in Table 1 below was moved along the circumferential surface of a cylindrical cooling can.
+Ar (volume ratio 1:1) was flowed at a rate of 800 cc per minute in a chamber with a vacuum level of 1.0 x lO-' Torr.

80 and Ni20 (weight ratio) are melted, and the incident angle is set to 60° to 90° when the lower layer is laid, and 10° to 90° when the upper layer is laid.
°, and by oblique evaporation, Co-
A Ni-0 thin film was formed. For comparison, a single-layer Co--Ni-0 thin film of Jgo and ts- was formed by obliquely depositing only the portion at an incident angle of 30 to 90 degrees.

A large amount of oxygen was unevenly distributed at the interface between the lower layer and the upper layer with the base, and on the surface opposite to the base. Furthermore, the surface opposite to the base was covered almost exclusively with oxide.

Hc=10000e, and the average amount of oxygen in the film was 40% in terms of atomic ratio to Co and Ni.

The following measurements were performed on each of the samples shown in Table 1 below formed in this manner.

1) Durability A continuous running test was conducted under the conditions of a temperature of 20° C. and a humidity of 60% RH.

Deck used: 5ONY A-300 Head Varnish Batter Sendust Note that the running direction of the medium and the direction of inclination of the magnetic crystal grains with respect to the normal to the underlying substrate were made to be the same direction.

2) Electromagnetic conversion characteristics Outputs at center frequencies of 0.75 MHz and 5 MHz were measured, and values were determined when the output of sample No. 10 was set to 0 dB.

Deck used: 5ONY A-300 Head Varnish Batter Sendust mode: SP mode Samples No. 001 to 6 (base thickness near-1 magnetic layer structure: Table 1 shows the improvement in the output of the second layer)
It is written in parentheses.

The effects of the present invention are clear from the results shown in Table 1.

That is, 1. When the upper layer thickness/lower layer thickness is 0.2 to 0.9, an extremely high improvement in the 5 MHz output is observed especially when the base thickness is 8- or less, and the base thickness is not practical in terms of the 5 MHz output. It can be seen that even a thin material exhibits sufficient electromagnetic conversion characteristics for practical use.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of a cross section parallel to the medium direction of one embodiment of the magnetic recording medium of the present invention. FIG. 2 is a schematic diagram of a cross section parallel to the medium direction of another embodiment of the magnetic recording medium of the present invention. Explanation of symbols 1: Magnetic recording medium, 2: Substrate, 3: Lower layer of ferromagnetic metal thin film, 4: Upper layer of ferromagnetic metal thin film, 5: Lower crystal grain, 6: Upper layer Crystal grain, arrow a - Medium length direction Patent applicant TDC Co., Ltd. Representative Patent attorney Yo Ishii -', -・'' 5, °, - FIG, 1 FIG, 2 Procedure name formal text ( (Spontaneous) August 27, 1988 Patent Application No. 153179 2 Name of the invention Magnetic recording medium 3 Relationship with the person making the amendment case Patent applicant location
Nihonbashi-chome 13-1, Chuo-ku, Tokyo Name
(306) Representative of TDC Co., Ltd.
Hiroshi Otoshi 1, Agent 101 Address 4th floor, Chiyoda Iwamoto Building, 3-2-2 Iwamotocho, Chiyoda-ku, Tokyo 8864-4498 Fax: 864-6280
Name (8286) Patent attorney Yo Ishii
-6. Contents of amendment (1) Amend the power of attorney as shown in the attached sheet. (2) The column “3. Detailed Description of the Invention” of the specification is amended as follows. (i) "Improved electronic conversion characteristics" in the first line of page 11 of the specification is corrected to "improved electromagnetic conversion characteristics." (ii) In the specification, page 12, line 8 to page 13, line 11, the statement ``The magnetic layer of such a plastic film is...~0.7 μm'' has been changed to `` It is preferable to provide one of various known backing layers on the other side of the plastic film on which the magnetic layer is not provided. There are no particular restrictions on the material of the backing layer, but pigments and radiation curing are particularly preferred. The thickness of the lining layer is preferably 0.07 to 1.0 μm, more preferably 0.07 to 1.0 μm. (iii) On page 22 of the specification, line 6, after "it was 4θ%." 1. Add a new line and write, ``On the magnetic layer Nm, a surface layer of isopropyl myristate is formed with a thickness of 25 mm, and on the back side of the substrate, a layer of carbon, silica, and radiation is formed with a thickness of 0.5 μm. A backing layer containing a hardened resin was installed.'' is added.

Claims (1)

[Claims] (1) Co on a plastic film with a thickness of 8 μm or less
The ferromagnetic metal thin film layer has an upper layer and a lower layer, and the ratio of the thickness of the upper layer to the thickness of the lower layer is 0.2 to 0.9. A magnetic recording medium characterized by: