JPH07169042A - Magnetic recording medium and its manufacture - Google Patents

Abstract

PURPOSE:To improve the corrosion-resistance, abrasion durability and weather- resistance. CONSTITUTION:An undercoating layer 2, a magnetic layer 3 and a protective layer 4 are successively built up on a nonmagnetic substrate 1 to obtain a multi-layer unit. In this multilayer unit, the undercoating layer 2 is made of a silicon oxide which is expressed by a general formula: SiOx wherein 1.8<=x<=1.95. The magnetic layer 3 is made of cobalt or a cobalt alloy and formed in the existence of a silicon compound and oxygen. The protective film 4 is composed of a hydrogen-containing carbon film whose refractive index is not less than 1.9 and whose contact angle is less than 80 degrees.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium such as a magnetic tape or a magnetic disk and a manufacturing method thereof. More specifically, the present invention relates to a magnetic recording medium having excellent corrosion resistance, friction durability, and weather resistance, and a method for manufacturing the same.

[0002]

2. Description of the Related Art A magnetic recording medium used in a magnetic recording device such as a magnetic tape or a magnetic disk is generally formed on a non-magnetic substrate such as plastic on an oxide of iron or chromium, cobalt or nickel. It is configured by providing a magnetic film made of a metal or an alloy thereof.
This magnetic film is usually formed in an oxygen atmosphere, but the magnetic film formed in this way lacks corrosion resistance and cannot be used as it is in a corrosive environment, for example, near a coast or a volcano, and has a frictional effect. Since the durability is low, a protective layer is provided on the surface.

Hitherto, as such a protective layer, fluorine-containing organic compounds such as fluorinated hydrocarbons, fluorinated ketones and fluorinated ethers (JP-A-57-135442), vinylidene fluoride, and tetrafluoroethylene. Polymers of monomers such as ethylene, vinyl chloride and styrene (JP-A-57-135443), composite layers of polycarbonate and higher fatty acid or its ester (JP-A-57-164432), various low molecular weights Although plasma polymers of compounds (JP-A-59-72653, JP-A-59-171028) and the like have been proposed, these protective layers are made of an organic material, and therefore, have excellent friction durability. The point was not always satisfactory.

On the other hand, in order to improve friction durability, when forming the magnetic layer by vapor deposition, a silicon compound gas is introduced together with oxygen gas to cause a chemical reaction between the surface of the magnetic particles, oxygen and silicon. As a result, each magnetic column is surrounded by a protective film so that the end face of the magnetic material is not directly exposed to the atmosphere during slitting (Japanese Patent Laid-Open No. 62-54828), or a strong monomer gas is introduced. It has also been proposed to coat the surface of a ferromagnetic metal with a polymer by vapor deposition, ion plating or sputtering of a magnetic metal (Japanese Patent Publication No. 5-18173), but these magnetic recording media have excellent durability. I cannot avoid getting lower.

[0005]

SUMMARY OF THE INVENTION The present invention overcomes the above-mentioned drawbacks of conventional magnetic recording media, has sufficient corrosion resistance even in a corrosive environment, is excellent in friction durability, and has excellent weather resistance. The purpose of the invention is to provide a good magnetic recording medium.

[0006]

The present inventor has conducted extensive studies to improve the characteristics of a magnetic recording medium, and as a result, formed a magnetic layer in the presence of a silicon compound and oxygen and used it as an undercoat layer. By using a silicon oxide with a specific composition to improve the adhesion between the substrate surface and the magnetic layer, and by using a protective layer consisting of a hydrogen-containing carbon film to improve corrosion resistance and lubricity, rust is maintained even in a corrosive environment. It has been found that an ideal magnetic recording medium having high friction durability can be obtained without causing the above phenomenon, and the present invention has been completed based on this finding.

That is, according to the present invention, in a multilayer structure constituted by sequentially laminating an undercoat layer, a magnetic layer and a protective layer on a non-magnetic substrate, (a) the undercoat layer has the general formula SiO _x (where 1.8 ≦ x ≦ 1.95), (b) the magnetic layer is composed of a cobalt compound or a cobalt alloy formed in the presence of a silicon compound and oxygen, and (c) ) The protective layer is composed of a hydrogen-containing carbon film and has a refractive index of 1.9 or more and a contact angle of 80.
A magnetic recording medium characterized by having a magnetic recording medium of less than 100 degrees.

In this magnetic recording medium, for example, a silicon compound gas and an oxygen gas are chemically vapor-deposited by plasma on the surface of a non-magnetic substrate to form SiO _x (provided that 1.8).
≦ x ≦ 1.95), and then under pressure 1 in the presence of a silicon compound gas and oxygen gas.
A magnetic layer was formed from cobalt or a mixture of cobalt and a metal capable of forming an alloy with cobalt under the condition of 0 ^-3 to 10 ^-7 Torr, and then applied power source frequency in the presence of hydrocarbon and hydrogen. It can be manufactured by discharging at 50 to 400 kHz and forming a protective layer made of a hydrogen-containing carbon film.

There is known a method in which a magnetic tape having a magnetic layer made of a ferromagnetic metal thin film is wound and a high frequency is applied in the presence of a monomer so that only both end surfaces are brought into contact with a plasma polymerization atmosphere. No. 62-54828),
The magnetic recording medium obtained by such a method has low friction durability and weather resistance, and is not necessarily satisfactory for practical use.

[0010]

[Structure] Next, the structure of the present invention will be described in more detail.

FIG. 1 is an enlarged cross-sectional view showing an example of the magnetic recording medium of the present invention. An undercoat layer 2 is applied in contact with the surface of a non-magnetic substrate 1, which is provided thereon. The magnetic layer 3 is interposed between the magnetic layer 3 and the substrate surface 1 and acts as a moisture barrier layer for the magnetic layer and also serves as an adhesive layer between them. Also, by providing a moisture barrier layer on the surface of the substrate, it is possible to prevent external moisture from passing through the substrate to corrode the magnetic substance, and to prevent the moisture contained in the substrate, which is observed when the magnetic layer is directly formed. It has the effect of preventing the deterioration of magnetic properties. The surface of the magnetic layer 3 is covered with the protective layer 4.

The material of the non-magnetic substrate 1 is not particularly limited as long as it has appropriate flexibility and hardness and can be used as a video tape or a video disk. Examples of such materials include polyethylene terephthalate (PET), polyethylene naphthalate (PEN),
Examples thereof include polyphenylene sulfide (PPS), polyether ether ketone (PEEK), polyimide, polyimine imide, and aramid resin, and engineering plastics and super engineering plastics whose surface properties can be controlled to some extent are preferable. The thickness of this substrate is usually selected in the range of 4 to 75 μm, and the thickness of the substrate is appropriately determined according to the specifications of the magnetic recording medium.

Next, the undercoat layer 2 to be applied thereon
Is composed of a silicon oxide represented by the general formula SiO _x , and serves both as a moisture barrier layer and as an adhesive layer between the substrate surface and the magnetic layer, where x in the formula is from 1.8 It must be in the range 1.95. x
Those having a composition deviating from this range have a low moisture barrier property and do not show a sufficient protective effect.

This product is formed on the surface of the substrate by a plasma polymerization method by sending a mixed gas of a silicon compound and oxygen to the reaction chamber. At this time, the inside of the vapor deposition chamber should be 10
^The chamber is evacuated to about ^-6 Torr, a mixed gas of a silicon compound and oxygen is introduced into the chamber, and plasma discharge is started after reaching a predetermined pressure. The discharge frequency in this case is used in the order of kHz to MHz, and in particular kH
The z order is preferred. When a high frequency of 13.56 MHz band is used, the generated ions stay in the space and do not reach the substrate, which is not suitable for forming the protective layer.

The silicon compound used at this time is 10
There is no particular limitation as long as it can be gasified under a pressure of about ^-3 Torr, preferably about 10 ^-5 Torr, but it is preferably one having a boiling point of 200 ° C. or less in view of easy handling. Examples of such substances include silane, trimethylsilane, tetramethylsilane, trimethoxysilane, tetramethoxysilane, and tetraethoxysilane.

This silicon compound and oxygen are used as a mixed gas having a ratio of 3 equivalents or more of oxygen per one atom of silicon. Such a mixed gas keeps a tank containing a liquid silicon compound at a constant temperature, for example. It is advantageous to prepare it by bubbling oxygen through it. The mixing ratio of silicon and oxygen can be adjusted by changing the temperature of the tank at this time. Further, a gaseous substance such as silane at room temperature can be supplied in appropriate amounts by using a mass flow controller. Even liquids can be controlled and supplied separately by using a vaporizer. The thickness of the undercoat layer 2 is usually 0.02 to 0.1 μm.
It is selected in the range of.

Cobalt or a cobalt alloy is used for the magnetic layer 3 formed on the undercoat layer 2 formed in this manner. The cobalt alloy has a poor crystal anisotropy of cobalt. It is preferable that the cobalt content is such that it is not lost, usually 70% by weight or more.
Examples of the cobalt alloy include Co-Fe, Co-Ni,
Co-Cr, Co-Ni-Cr, Co-Cu, Co-
B, Co-Bi, Co-P, Co-Pt, Co-Sm, etc. can be mentioned. The structure of the magnetic layer may be a single layer or multiple layers, and is appropriately selected according to the required characteristics.

The formation of this magnetic layer is carried out by vacuum vapor deposition, chemical vapor deposition, ion plating, sputtering or the like, and a silicon compound gas and an oxygen gas are simultaneously introduced in an atmosphere of 10 ^-5 Torr to 10 ^-4 Torr. It is necessary to. At this time, the silicon compound and the oxygen gas are supplied according to the case of forming the undercoat layer, but the flow rate ratio of the silicon gas and the oxygen gas is also used for controlling the magnetic layer. Use a large ratio. This oxygen has the function of controlling the magnetic properties and hardening the surface to improve durability, and the silicon compound has the function of increasing the protective effect. At this time, as the silicon compound, those shown in the case of forming the undercoat layer can be used. The thickness of this magnetic layer is 0.02 to 0.5 μm,
It is preferably selected in the range of 0.05 to 0.2 μm.

In the present invention, it is necessary to use a plasma-polymerized hydrogen-containing carbon film, a so-called diamond-like carbon film (DLC film), as the protective layer 4 provided on the magnetic layer. To form this film, the reaction chamber was previously
After evacuating to about ^-6 Torr, the hydrocarbon gas and hydrogen gas are in a molar ratio (carbon number / H ₂ ratio) of 1: 3 to 3:
1 preferably introduced in a ratio of 1: 2 to 2: 1 and 10
Discharge starts when the pressure reaches ^-2 Torr or 1 Torr. If excess molar ratio of 1: 3 or more is used, the film is softened and the yield is lowered. Conversely, if the molar ratio of hydrocarbon is 1: 3 or more, carbon powder is generated to lower the yield. The discharge frequency at this time is preferably in the range of 50 to 400 kHz. If it is lower than this, it is difficult to continue the discharge in a stable state and the damage to the substrate is large, and if it is higher than this, ions are confined in the electrode space and ion bombardment does not occur. No diamond-like carbon film is formed.

In this case, the hydrocarbon gas used is methane, ethane, propane, butane, hexane,
Aliphatic hydrocarbons such as petroleum ether and aromatic hydrocarbons such as benzene and toluene are preferable. These are also 10 ^-3
There is no particular limitation as long as it is gasified at Torr.

The protective layer must have a refractive index of 1.9 or more and a contact angle of less than 80 degrees, and the film thickness is 30.
Since it is preferably in the range of 150 Å, the discharge is continued until such a protective layer is formed. This protective layer not only provides corrosion resistance but also lubricity and improves friction durability. When the refractive index is less than 1.9, the film becomes soft and the durability is not improved, and when the contact angle is 80 degrees or more, the durability and still properties are deteriorated. Further, if the film thickness is less than 30 Å, the desired effect cannot be obtained, and if it exceeds 150 Å, a drawback in electromagnetic conversion characteristics occurs.

In the magnetic recording medium of the present invention, a liquid lubricant can be further coated on the protective layer 4 if desired. As such a liquid lubricant, for example, polar perfluoropolyether, perfluorocarboxylic acid, phosphazene, polyacrylate and the like are used.

[0023]

EXAMPLES The present invention will be described in more detail with reference to Examples and Comparative Examples.

The refractive index of the protective layer, the contact angle and the physical properties of the magnetic recording tape in each example were measured by the following methods. (1) Refractive index; measured using an ellipsometer (manufactured by Mizojiri Optical Co., Ltd.). (2) Contact angle; using a contact angle meter (Kyowa Interface Science Co., Ltd.),
The measurement was performed using water (ion-exchanged water) as droplets. (3) Initial friction: 1 with a pin friction tester with a 180 ° wrap angle
The coefficient of friction of the pass was measured. The test pin is made of stainless steel (SUS304) with a diameter of 3 mm and has a surface roughness of 0.15 μm.
I used the one. (4) Durability friction: The friction coefficient after 200 passes was measured by the same method as in the case of initial friction. (5) Still; 7M under the environment of temperature 40 ° C and humidity 20%
The signal of Hz was recorded, and the time until the output became -5 dB was measured. (6) Weather resistance: It was stored for 1 week in an environment of temperature 60 ° C. and humidity 90%, and the reduction rate of saturation magnetic flux density was measured. (7) Square; measured by VSM. (8) Electromagnetic conversion characteristics: 95 wt% cobalt and 5 nickel on a polyethylene terephthalate film having a thickness of 7 μm
The electromagnetic conversion characteristics measured with an output of 7 MHz were set to 0 dB for a sample on which a magnetic layer of an alloy consisting of wt. ◯: 0 to less than -1 dB Δ: -1 dB to less than -2 dB X: -2 dB or more

Examples 1 to 6 and Comparative Example 1 A mixed gas in which trimethylsilane and oxygen were mixed at a ratio of 4 equivalents of oxygen per 1 atom of silicon was sent onto a polyethylene terephthalate film having a thickness of 7 μm, and a pressure of 10 P was applied.
a, a temperature of 25 ° C. and a discharge frequency of 100 kHz were used to perform plasma polymerization to form an undercoat layer of SiO _{1.9 with a} thickness of 200 Å.
The silane compound and oxygen were separately introduced by the Myflow controller.

Then, on the undercoat layer thus obtained, 95% by weight of cobalt and 5% of nickel were formed by a conventional method.
A weight% alloy was vacuum-deposited under a pressure of 5 × 10 ⁻⁵ Torr and a CAN temperature of −10 ° C. to form a magnetic layer having a thickness of 0.1 μm. At this time, the silicon compound and oxygen shown in Table 1 were simultaneously introduced while bubbling oxygen into the silicon compound at a ratio of 10 equivalents of oxygen per atom of silicon.
The silicon compound changes its holding temperature depending on the boiling point,
The range was 90 ° C.

A gas obtained by mixing methane and hydrogen at a ratio of 1 equivalent of hydrogen to 1 atom of carbon of methane was used in the laminate thus obtained, pressure was 10 Pa, temperature was 20 ° C., and frequency was 1
A discharge treatment was performed under the condition of 00 kHz to form a protective layer made of a diamond-like carbon film having a refractive index of 1.95, a contact angle of 75 degrees and a thickness of 100Å on the magnetic layer.

Table 1 shows the physical properties of the magnetic recording tape thus obtained. For comparison, the physical properties of a magnetic recording tape obtained by only applying a magnetic layer of an alloy of 95% by weight of cobalt and 5% by weight of nickel to a thickness of 0.2 μm on a polyethylene terephthalate film are also shown.

[0029]

[Table 1]

Examples 7, 8 and Comparative Examples 2, 3 After forming an undercoat layer on a polyethylene terephthalate film in the same manner as in the above Examples, tetraethoxysilane was used as a silicon compound gas and the pressure was 5 ×. The magnetic layer was formed under the same conditions as in Example 3 except that the range was changed from 10 ⁻⁴ Torr to 5 × 10 ⁻⁷ Torr. However, the protective layer thickness of Comparative Example 2 was 30Å, Comparative Example 3
The protective layer thickness was 200Å.

A magnetic recording tape was obtained by coating the thus obtained laminate with a protective layer in the same manner as in the above-mentioned Examples. The physical properties of this product are shown in Table 2.

[0032]

[Table 2]

As is clear from this table, when the pressure at the time of forming the magnetic layer is lower than 10 ^-3 Torr, friction durability and weather resistance are deteriorated.

Examples 9 and 10, Comparative Examples 4 to 6 Magnetic recording tapes were manufactured in the same manner as in Example 3 except that the x value of SiO _x was changed by changing the formation conditions of the undercoat layer. The physical properties of this product are shown in Table 3. The X value was adjusted by adjusting the amount of oxygen contained in the silicon compound to 3 equivalents or less.

[0035]

[Table 3]

As is clear from this table, SiO _x forming the undercoat layer having an x value outside the range of 1.8 to 1.95 has low friction durability and weather resistance.

Examples 11 and 12, Comparative Examples 6 to 8 Magnetic recording tapes were prepared in the same manner as in Example 3 except that the protective layer formation conditions were changed to change the refractive index and contact angle of the DLC film. Manufactured. The physical properties of this product are shown in Table 4.
When the discharge frequency is increased, the refractive index becomes smaller, and when the flow rate is increased, the contact angle becomes 80 ° or more.

[0038]

[Table 4]

As is apparent from this table, when the refractive index of the protective layer is less than 1.9 and the contact angle is 80 degrees or more, the friction durability and weather resistance are deteriorated.

Comparative Examples 8 to 10 A magnetic recording tape was produced in the same manner as in Example 3, except that the undercoat layer and / or the protective layer were omitted. Table 5 shows their physical properties.

[0041]

[Table 5]

As is clear from this table, even when a magnetic layer is formed while introducing a mixed gas of a silicon compound and oxygen, those lacking an undercoat layer or a protective layer have poor friction durability and weather resistance. Is insufficient.

Comparative Examples 12 to 16 According to the method described in JP-A-62-54828, the magnetic recording tape obtained in Comparative Example 1 was wound, and only the edge portion was subjected to plasma treatment using various organic compounds, and then liquid. Lubricant AM2001 (manufactured by Montedison Co., Ltd.) was applied and the physical properties were measured. The results are shown in Table 6.

[0044]

[Table 6]

[0045]

According to the present invention, there is provided a magnetic recording medium having remarkably improved corrosion resistance, friction durability and weather resistance as compared with the conventional magnetic recording medium.

[Brief description of drawings]

FIG. 1 is an enlarged sectional view of a magnetic recording medium of the present invention.

[Explanation of symbols]

 1 non-magnetic substrate 2 undercoat layer 3 magnetic layer 4 protective layer

Claims (3)

[Claims] 1. In a multilayer structure constituted by sequentially laminating an undercoat layer, a magnetic layer and a protective layer on a non-magnetic substrate, (a) the undercoat layer has the general formula SiO _x (where
1.8 ≦ x ≦ 1.95), (b) the magnetic layer is composed of cobalt or a cobalt alloy formed in the presence of a silicon compound and oxygen, and (c) The protective layer is composed of a hydrogen-containing carbon film and has a refractive index of 1.
A magnetic recording medium having a contact angle of 9 or more and a contact angle of less than 80 degrees. 2. The magnetic recording medium according to claim 1, wherein the protective layer has a film thickness of 30 to 150 Å. 3. An undercoat represented by the general formula SiO _x (where 1.8 ≦ x ≦ 1.95) is obtained by chemically vapor-depositing a silicon compound gas and an oxygen gas on a surface of a non-magnetic substrate by plasma. Layers, and then in the presence of silicon compound gas and oxygen gas at a pressure of 10 ⁻³ to 10 ⁻⁷ Tor.
After forming a magnetic layer from cobalt or a mixture of cobalt and a metal capable of forming an alloy with cobalt under the condition of r, an applied power supply frequency of 50 is applied in the presence of hydrocarbon and hydrogen.
A method of manufacturing a magnetic recording medium, comprising forming a protective layer made of a hydrogen-containing carbon film by discharging at ~ 400 kHz.