JPH0877542A - Magnetic recording medium and its production - Google Patents

Abstract

PURPOSE: To form a protective layer having high preservability, running performance and durability not imparted by the conventional lubricant by using both of an alkylsilane compd. and a fluorine-contg. carboxylic ester compd. CONSTITUTION: A surface layer contg. an alkylsilane compd. and a fluorinecontg. carboxylic ester compd. is formed on a protective film laminated on a ferromagnetic metallic thin film. Since the alkylsilane compd. is formed on the protective film especially under heating, the bonding property of the alkylsilane compd. to the protective film is improved. By the combination of the alkylsilane compd. with the fluorine-contg. carboxylic ester compd., the objective magnetic recording medium having superior characteristics even in an environment at low temp. and humidity is obtd.

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 having a ferromagnetic metal thin film as a magnetic layer. The chemical structure and composition of a lubricant present on the protective film of the magnetic recording medium are specified. The present invention relates to manufacturing a ferromagnetic metal thin film type magnetic recording medium excellent in runnability, durability and storability.

[0002]

2. Description of the Related Art In a magnetic recording medium such as a magnetic tape or a floppy disk, a lubricant is applied to the surface of the magnetic layer to improve the lubricity and running durability between the magnetic recording medium and the head. Has been done. In particular,
In the magnetic recording medium, the surface of the magnetic layer becomes smoother due to the higher recording density, the magnetic recording medium is used in various environments, and the recorded information is stored for several years to several decades. Therefore, running durability and storage stability under various environments are required, and conventional lubricants cannot exhibit sufficient effects. Further, a camcorder, that is, a video tape recorder with a built-in camera and a small video tape recorder such as an 8 mm video are often used outdoors, and a magnetic recording medium is required to have a performance to withstand a wide range of environmental conditions. ing. In addition, in order to improve the magnetic recording density on a video tape in response to future high definition and digitalization of television, a metal thin film type magnetic recording using a ferromagnetic metal thin film as a magnetic layer, which is advantageous for high density recording. A medium is expected, but since the magnetic layer is only protected by an extremely thin metal oxide layer, the ferromagnetic metal thin film type magnetic recording medium only guarantees runnability and durability. Instead, it is required to provide a material for the lubricating layer that can significantly improve the storage stability. In particular, in a ferromagnetic metal thin film type magnetic recording medium, the surface is smoothed and the composition of the magnetic layer is CoNi in order to enable higher density recording.
Although improvements from -O system in the direction of the high B _m of mainly composed of Co, such as Co-Fe containing Co-O system or Co-O is being performed, stable ones with many content of these cobalt It was difficult to obtain good running property, durability and corrosion resistance.

As a lubricant for a metal thin film type magnetic recording medium, hydrocarbon-based and fluorine-based lubricants having various structures and excellent in lubrication performance have been studied. In particular, organic compounds having a hydrophilic functional group in the molecule have been investigated. It is known that a fluorine compound can greatly improve running durability. However, even if a lubricant with excellent characteristics is used, in a smooth metal thin film magnetic recording medium with improved electromagnetic conversion characteristics, the lubricant adhered to the magnetic layer is gradually lost due to repeated sliding, and the characteristics There was a problem of deterioration.

Therefore, the properties have been improved by using a lubricant having various polar groups in the molecule. For example, carboxylic acid, ester, phosphoric acid ester and the like are disclosed in JP-A-59-119537 and Japanese Patent Publication No.
Although disclosed in Japanese Patent No. 50644, there is a problem that durability against repeated running at low temperature is poor. There 2
Many studies have been made to improve the characteristics by using more than one kind of lubricant. It is also possible to use a carboxylic acid and a fluorine-containing ester in combination.
No. 25, it is possible to remarkably improve the repeated running durability at low temperatures as compared with the case where each lubricant is used alone, but the corrosion resistance, especially the storage stability under high temperature and high humidity environment There was a problem of being scarce. Further, JP-A-62-112213 describes the use of a silane coupling agent and a perfluoroalkylcarboxylic acid, but a silane coupling agent having a relatively short hydrocarbon chain is itself lubricated. Therefore, the effect of improving running durability was small.

Japanese Unexamined Patent Publication (Kokai) No. 4-205712 proposes a method of forming a layer composed of two kinds of lubricants to regulate the amounts of the lubricants on the magnetic layer side and the back coat layer side. However, sufficient lubricity has not been obtained.
Further, there is a method in which a lubricant is applied to the backcoat layer provided on the surface of the magnetic recording medium opposite to the surface on which the magnetic layer is formed, and the lubricant on the surface of the magnetic layer lost by sliding is supplied from the backcoat layer at any time. , JP-A-57-29767, JP-A-58-188326, JP-A-60-63711, JP-A-60-63712, and JP-A-62-2.
It is described in Japanese Patent Application Laid-Open No. 09718 and Japanese Patent Application Laid-Open No. 1-211215. Although repeated running durability is improved by such a coating method, it is difficult to secure durability when a lubricant is applied only to the backcoat layer side, and it is applied to both the backcoat layer and the magnetic layer. In this case, there was a problem that the lubricant was excessively present on the magnetic layer, the coefficient of static friction increased, and sticking occurred.

Also in terms of corrosion resistance, which is a problem in practical use of a magnetic recording medium having a ferromagnetic metal thin film as a magnetic layer, a fluorine-based lubricant having a polar group in its molecule is insufficient, and a rust preventive agent Although the combined use has been proposed, it has been difficult to secure the corrosion resistance with the commonly known combined use of the lubricant and the rust preventive. Therefore, in recent years, attempts have been made to improve durability and corrosion resistance by providing a protective film on the magnetic layer not only in the magnetic disk but also in the magnetic tape. Among them, a carbon film typified by a diamond-like carbon film has a high hardness and is hard to seize on a sliding member in any environment, and is therefore the most watched protective film. However, even in such a carbon protective film, the friction coefficient increases due to repeated sliding with only the carbon protective film, and the film breaks. Therefore, it is common to apply a lubricant having a polar group on the protective film. For example, JP-A-5-151559 describes a magnetic recording medium in which a long-chain alkylsilane compound is provided on a carbon protective film, and JP-A-5-174373 describes a long-chain alkylsilane compound on a carbon protective film. After applying the compound, it is dried at a temperature of 80 to 100 ° C., and then left to stand in an atmosphere having a humidity of 50% or more to anneal. However, in a low temperature and low humidity environment, the long-chain alkylsilane compound alone lacks the lubrication performance, and the film of the protective film is easily broken due to the increase of the friction coefficient.

[0007]

DISCLOSURE OF THE INVENTION The present invention provides a magnetic recording medium which has a low friction coefficient and is stable, is excellent in still durability and repeated running durability, and is particularly excellent in corrosion resistance capable of high density magnetic recording. Is provided.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to provide a magnetic recording medium in which a magnetic layer made of a ferromagnetic metal thin film is provided on at least one surface of a non-magnetic support, and a protective film is provided on the magnetic layer. And an alkylsilane compound having an alkyl group having 6 or more carbon atoms and a fluorine-containing carboxylic acid ester compound are present on the protective film,
On the surface of the non-magnetic support opposite to the surface on which the magnetic layer is provided,
This is achieved by a magnetic recording medium characterized by being provided with a back coat layer containing a non-magnetic powder and a binder resin. In the magnetic recording medium of the present invention, an alkylsilane compound is likely to be reactively adsorbed on a protective film such as a carbon film and is considered to form a strong lubricating film, and durability and corrosion resistance can be improved. Further, by additionally using the above-mentioned fluorine-containing carboxylic acid ester, fluid lubricity due to the behavior of non-adsorbed molecules on the adsorbed film of the alkylsilane compound can be obtained. This effect is particularly remarkable in low temperature and low humidity environments.

As described above, in the magnetic recording medium of the present invention, by using the alkylsilane compound and the fluorine-containing carboxylic acid ester compound together, the advantages thereof can be sufficiently exerted as compared with the case where each of them is used alone. . Further, the present invention is greatly characterized in that it is possible to greatly improve the still durability and the repeated running durability, which cannot be expected from the characteristics of both of them alone. In the magnetic recording medium of the present invention, a backcoat layer is further provided on the surface opposite to the surface provided with the magnetic layer, and the fluorine-containing carboxylic acid ester is present in the backcoat layer or on the surface thereof. As a result, the lubricant that gradually disappears due to the sliding of the magnetic head or the guide pole on the medium surface can be replenished by transferring the lubricant from the back coat when the tape-shaped medium is wound up. The repeated running durability can be improved. Therefore, when the magnetic recording medium of the present invention is a tape-shaped medium, its characteristics can be effectively utilized.

Further, when the alkylsilane compound and the fluorine-containing carboxylic acid ester constituting the present invention have the following structures, particularly excellent running durability and corrosion resistance can be achieved. Alkylsilane compound R ¹ -SiX ₃ (1) However, R ¹ is a hydrocarbon group having 6 to 26, X is any one selected from an alkoxyl group, a hydroxyl group and halogen.

The fluorine-containing carboxylic acid ester is
It is at least one compound represented by the following chemical formula. ^{R 2 -COO-R 3 ... (} 2) R 4 -COO- (R 6 O) n -R 5 ... (3) Rf-COO-R 7 ... (4) R 7 -COO-CH 2 -Rf ... ( 5) However, R ² and R ³ may be the same or different,
A hydrocarbon group having 8 to 26 carbon atoms or a fluorinated hydrocarbon group in which some or all of hydrogen atoms are replaced by fluorine atoms, and at least one of R ² and R ³ contains a fluorine atom. Is. R ⁴ is a hydrocarbon group having 8 to 26 carbon atoms, R ⁵ is a hydrocarbon group having 2 to 18 carbon atoms, or a fluorinated hydrocarbon group obtained by substituting a part or all of hydrogen atoms with fluorine atoms. Further, R ⁶ has 1 to 4 carbon atoms.
Is a linear or branched alkylene group, n is 1 to 18, Rf is a perfluoropolyether group having a molecular weight of 1000 to 3000, and R ⁷ is a hydrocarbon group having 8 to 26 carbon atoms. Further, in the magnetic recording medium of the present invention, since a protective film such as a carbon protective film is formed on the magnetic layer, it may be difficult for the alkylsilane compound to be adsorbed. It is possible to improve running durability by heating the surface of the protective film to 100 to 300 ° C. and fixing the alkylsilane compound onto the protective film after applying the alkylsilane compound to the protective film.

The alkylsilane compound in the magnetic recording medium of the present invention has a molecular structure represented by the above chemical formula (1) and has a hydrocarbon group R ¹ which is a hydrophobic group thereof. Has 6 to 26 carbon atoms, and preferably 10 to 20 carbon atoms. The hydrocarbon group is preferably a linear saturated hydrocarbon group, but may be an unsaturated hydrocarbon group-containing group, a side chain, or a branched chain hydrocarbon group having a connecting group introduced therein. If the number of carbon atoms is less than this, a good protective effect cannot be obtained, and conversely, if it is too large, the crystallinity increases, it becomes difficult to form a uniform coating film, and the lubricating effect deteriorates, which is not preferable. Further, X is selected from an alkoxyl group, a hydroxyl group and halogen. Alkoxyl groups are most preferred in consideration of corrosion resistance and hydrolyzability.

Alky usable in the magnetic recording medium of the present invention
Specific examples of the rusilane compound include C₁₂H_{twenty five}Si
(OC₂H_Five)₃, C₁₆H₃₃Si (OC₂H_Five)₃, C₁₈H
₃₇Si (OC₂H_Five)₃, C₁₈H₃₅Si (OC₂H_Five)₃,
C₁₈H₃₇Si (OCH₃)₃, C ₁₈H₃₇Si (OC₃H₇)
₃, C₁₈H₃₇Si (OH)₃, C₁₈H₃₇SiCl₃Etc.
Can be mentioned.

On the other hand, the fluorine-containing carboxylic acid ester compound used in combination with the alkylsilane compound is an ester of carboxylic acid and alcohol, and is a compound containing a fluorine atom in the molecule. In particular, it has a molecular structure represented by the chemical formulas (2) to (5). In particular, compounds having a perfluoropolyether chain represented by (4) to (5) have the best lubricity and are preferable. Each fluorine-containing carboxylic acid ester will be described below. In the compound R ² —COO—R ³ of the general formula (2), R ² and R ³ may be the same or different and may be a hydrocarbon group having 8 to 26 carbon atoms or a part or all of the hydrocarbon group. It is a fluorinated hydrocarbon group in which a hydrogen atom is replaced by a fluorine atom, and at least one of R ² and R ³ contains a fluorine atom. This can be expected to lower the melting point and improve the fluid lubricity. The carbon chain length is preferably 8 to 2
It is 0, more preferably 8-18. If the number of carbon atoms of R ² and R ³ is less than 8, good lubricity cannot be obtained, and if the number of carbon atoms is too large, the crystallinity increases and uniform coating cannot be achieved, which is not preferable.

Further, in order to suppress the volatility of the lubricant and obtain a good lubricating effect, at least one of the two carbon chains in the molecule preferably has 10 or more carbon atoms. Further, a fluorinated product of a saturated hydrocarbon is preferable, but the carbon chain may have an unsaturated bond or a branched structure. The fluorine-containing carboxylic acid ester is specifically C ₈ F ₁₇ COOC ₁₈ H ₃₇ C ₈ F ₁₇ (CH ₂ ) ₂ COOC ₁₈ F ₃₇ C ₁₇ F ₃₅ COO (CH ₂ ) ₂ C ₈ F ₁₇ C ₁₇ F _{33 COO (CH 2) 2 C} 8 F 17 C 17 F 31 COO (CH 2) 2 C 8 F 17 C 8 F 17 (CH 2) 10 COO (CH 2) 10 C 8 F 17 , and the like.

The compound of the chemical formula (3) R ⁴ --CO
In _{^{O- (R 6 O) n -R}} 5, R 4 is a carbon number 8 to 26
R ⁵ is a hydrocarbon group having 2 to 18 carbon atoms, at least one of which is a fluorinated hydrocarbon group in which some or all of hydrogen atoms are replaced by fluorine atoms, R 5
⁶ is a linear or branched alkylene group having 1 to 4 carbon atoms,
n is 1-18. This compound is a compound obtained by introducing an alkylene oxide group into the compound represented by the chemical formula (2). The alkylene oxide group lowers the melting point, improves the uniformity of the coating film, and at the same time improves the running durability at low temperatures. Further, in the compound of the chemical formula (2), a compound in which an unsaturated bond is introduced into the carbon chain improves durability at low temperature similarly to the compound of the chemical formula (3), while the compound of the chemical formula (3) is hydrolyzed. It is characterized by being hard to receive and good storability.

The compound represented by the chemical formula (3) includes C ₈ F ₁₇ COO (CH ₂ CH ₂ O) ₂ C ₁₂ H ₂₅ C ₆ F ₁₃ C ₈ H ₁₆ COO (CH ₂ CH ₂ O) ₆ C ₂ H ₄ C. ₄ F ₉ C ₈ F ₁₇ C ₁₄ H ₂₉ COO (C ₆ H ₁₂ O) C ₈ H ₁₇ C ₈ F ₁₇ COO (C ₄ H ₈ O) C ₄ H ₈ CH (CH ₃ ) C ₈ H
_{17 (CF 3) 2 CFC 10} H 20 COO (C 6 H 12 O) 4 C 14 H 29 C 8 F 17 C 2 H 4 COO (C 8 H 16 O) 2 C 5 H 10 CF (CF
₃ ) ₂ .

[0018] In the chemical formula (4) and (5) Rf-COO-R 7 ... (4) a compound of _{^{R 7 -COO-CH 2 -Rf ...}} (5), Rf has a molecular weight of 1000 to 3000
Perfluoropolyether group, R ⁷ has 8 to 2 carbon atoms
6 hydrocarbon groups. When the molecular weight is less than this range, the excellent fluid lubricity unique to perfluoropolyether cannot be obtained, and when it is more than this range, the static friction coefficient is increased, and running stoppage or head crash is likely to occur. Rf is perfluoromethylene oxide polymer (CF ₂ O) _n , perfluoroethylene oxide polymer (CF ₂ CF ₂ O) _n , perfluoro-n-propylene oxide polymer (CF ₂ CF ₂ CF ₂ O) _n. , Perfluoroisopropylene oxide polymer (CF (C
Examples thereof include F ₃ ) CF ₂ O) _{n and} copolymers thereof. Specifically, KRYTOX manufactured by DuPont, FOMBLIN manufactured by Montefluos, and Demnum manufactured by Daikin can be used. The compound (4) is an esterified product of a perfluoropolyether having a carboxyl group at the terminal and an aliphatic alcohol, and the compound (5) is an esterified product of a fatty acid and a perfluoropolyether having a hydroxyl group at the terminal. From the viewpoint of production costs and environmental protection, the above-mentioned esters are preferably dissolved in an ordinary organic solvent. For that purpose, a compound having a fluorine-free hydrocarbon chain on one of the ester bonds is used, or a fluoroalkyl group is used. The ratio of the alkyl part of the group to the perfluoroalkyl group may be adjusted to increase the solubility. Further, when an ester having high crystallinity and a high melting point is used, precipitation may occur on the surface of the magnetic layer or the back coat layer. Therefore, considering the lubricity at a lower temperature, the melting point of the ester should be 30 ° C. or less. desirable.

In the magnetic recording medium of the present invention, in order to allow the lubricant compound to be present on the protective film, a solution of an alkylsilane compound used as a lubricant and a fluorine-containing carboxylic acid ester compound in an organic solvent is applied. A mixed coating method or a sequential coating method in which an alkylsilane compound is coated and then a mixture of fluorine-containing carboxylic acid ester compounds is coated can be used. However, since the alkylsilane compound is closely aligned on the surface of the protective film, the alkylsilane compound is used. It is preferable to form the lubricant layer of the fluorine-containing carboxylic acid ester compound after forming the lubricant layer of.

Further, an alkylsilane compound dissolved in an organic solvent is applied on the magnetic layer and dried, and then a backcoat layer containing a fluorine-containing carboxylic acid ester compound is formed and wound to form a fluorine-containing carboxyl group of the backcoat layer. The most preferred method is to transfer the acid ester compound to the surface of the protective film. This is because it is advantageous to retain more lubricant in the backcoat layer, which usually has much more voids than the ferromagnetic metal thin film, and at the same time, the lubricant lost by sliding can be replenished at the time of winding. This is done. Further, when a fluorine-containing compound is applied on the magnetic layer, even if the compound is soluble in an organic solvent,
Although fine coating unevenness and compound precipitation sometimes occurred when dried after coating, in the method of transferring from the back coat layer, a lubricant containing a fluorine-containing fatty acid ester compound is mixed or coated in the back coat layer to form a back coat layer. Since it is transferred from the layer to the magnetic layer side by contact during winding,
Since uneven coating is less likely to occur and lubricant is less likely to be deposited than when directly coated on the magnetic layer, there is an advantage that the number of types of lubricant that can be used is increased.

The back coat layer comprises a non-magnetic powder and a binder resin. As the non-magnetic powder, various inorganic pigments and carbon black can be used, and as the binder resin, nitrocellulose and phenoxy resin can be used. Various materials used as a binder resin for the coating type magnetic layer such as vinyl chloride resin and polyurethane can be used.

The lubricant compound of the present invention is soluble in an organic solvent containing a hydrocarbon solvent selected from acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, methanol, ethanol and isopropanol as a main component. A magnetic recording medium can be manufactured by applying and drying without using a system organic solvent. As described above, since it can be dissolved in a hydrocarbon-based solvent, it has a very practical feature that it does not cause the environmental problem of ozone layer destruction due to the use of a fluorine-based solvent unlike conventional fluorine-based compounds. .

The alkylsilane compound used in the present invention reacts and adsorbs with the protective film by coating it on the protective film. However, when the protective film has a hydrophobic surface such as a carbon film, coating and drying are sufficient. The characteristics may not be fully exhibited. In such a case, the alkylsilane compound can be firmly adhered to the protective film by applying the alkylsilane compound and then heating the surface at 100 ° C. to 300 ° C. This temperature is not the temperature of the entire magnetic recording medium, but the instantaneous reaching temperature of the surface portion. Processing temperature is 100 ° C
The following is not preferable because it requires a long treatment,
When the temperature is 300 ° C. or higher, the plastic film used as the support of the magnetic recording medium is apt to be deteriorated by heat, which is not preferable. Further, the steps from the application of the alkylsilane compound to the heat treatment are preferably performed in an atmosphere containing water in order to accelerate the hydrolysis reaction. In particular, the heat treatment step has a relative humidity of 30-80.
%, It is preferable to raise the temperature from 20 to 30 ° C. under the environment. As this heating method, the back surface of the support is brought into close contact with a cooling roller or the like to be conveyed while being cooled, and a method of heating only the medium surface portion with a heating device such as an infrared heater is preferable. When used, only the surface portion can be heated in a short time, deterioration of the support due to heat and the like can be minimized, and the processing time can be shortened.

Further, when only the treatment which is stored in a low temperature and high humidity environment of 100 ° C. or less is performed, a long treatment time is required, so that not only the productivity is lowered but also in a tape-shaped magnetic recording medium. Since it is necessary to perform the treatment in a wound state, the effect of modifying the surface of the magnetic recording medium is small, and the back coat surface having a large surface roughness deteriorates the surface roughness of the magnetic layer, which is not preferable. Further, even when an infrared heater is used, if the far infrared heater is used, the temperature rise of the support is large and the support is likely to be deteriorated by heat.

In the magnetic recording medium of the present invention, the protective film provided on the ferromagnetic metal thin film is silica, alumina, titania, zirconia, oxides such as cobalt oxide, nitrides such as titanium nitride, carbides such as chromium carbide, It is a protective film made of carbon such as graphite and amorphous carbon.
In the magnetic recording medium of the present invention, the effect of the lubricating layer in the present invention is further added to the protective action of these protective films, and the magnetic recording medium can sufficiently withstand sliding with the magnetic head under severe conditions. It is possible to provide a magnetic recording medium having a low surface friction and capable of maintaining the surface lubricity for a long period of time.

Therefore, as the protective film, a film having a hardness equal to or higher than that of the head material and having a high hardness is preferable, and further, it is most preferable that seizure hardly occurs during sliding and the effect is stable and lasts. As such a protective film, there is a hard carbon film. The hard carbon film is
A carbon film made of an amorphous, graphite, diamond structure, or a mixture thereof formed by a plasma CVD method, a sputtering method, or the like, and particularly preferably a hard carbon film generally called diamond-like carbon. This carbon film has a Vickers hardness of 1000 kg
/ Mm ² or more, preferably 2000 kg / mm ² or more of a hard carbon film. Further, its crystal structure is an amorphous structure and is non-conductive. And, when the structure of the diamond-like carbon film in the present invention is measured by Raman spectroscopic analysis, it is 1520 to 1560 ^-1 c
This can be confirmed by detecting the peak at m. When the structure of the carbon film deviates from the diamond-like structure, the peak detected by Raman spectroscopic analysis deviates from the above range, and the hardness of the carbon film also decreases, making it difficult to achieve the object of the present invention. come.

The structure of the diamond-like carbon film according to the present invention is not limited to Raman spectroscopy but may be X-ray electron spectroscopy (ESC).
It can also be identified by A). In particular, ESCA
When the plasmon loss energy of C-1s is 26 ± 1 eV, a better carbon film is obtained. The plasmon loss energy referred to here is an X-ray electron spectroscopic device (for example, manufactured by Perkin Elmer Co., Ltd., which is a deviation of a peak caused by plasmon loss from a main peak of a C-1s spectrum measured by irradiating a carbon film with X-rays.
PHI-560). When the hardness of the carbon protective film is reduced, the friction characteristics are improved, but the wear resistance is insufficient and desired running durability cannot be obtained.
In particular, the still durability is greatly reduced. These diamond-like carbon protective films are used for sputtering and CVD.
Although it can be produced by CVD, it is preferable to produce it by CVD from the viewpoints of productivity, stability of quality, and good wear resistance even with an ultrathin film having a thickness of 10 nm or less. It is preferable to apply a bias voltage to the magnetic recording medium to accelerate the magnetic recording medium.

There are no particular restrictions on the carbon compound that is turned into plasma, which is the material for the carbon protective film.
Examples include hydrocarbon-based, ketone-based, and alcohol-based compounds. In particular, it is preferable to form a hard carbon protective film by plasma CVD using a carbon-containing compound such as alkanes such as methane, ethane, propane, butane, alkenes such as ethylene and propylene, or alkynes such as acetylene as raw materials. . These film-forming substances are generally introduced into the plasma generator at a partial pressure of 13.3 to 0.133 N / m ² , preferably 6.67 to 2.67 N / m ² . In addition to the raw material gas, an inert gas such as hydrogen or argon can be introduced at the same time. In this case, a desirable mixed gas includes a hydrocarbon such as methane and argon. In this case, the mixing ratio is generally hydrocarbon: argon = 6:
1 to 2: 1 is desirable. If the hard carbon protective film is thick, the electromagnetic conversion characteristics are deteriorated and the adhesion to the magnetic layer is deteriorated. If the hard carbon protective film is thin, abrasion resistance is insufficient.
5 to 20 nm is preferable, and 5 to 10 n is particularly preferable.
m. Further, the surface of the hard carbon protective film may be surface-treated with an oxidizing or inert gas for the purpose of further improving the adhesion with the lubricant applied on the hard carbon protective film.

The ferromagnetic metal thin film to be the magnetic layer in the magnetic recording medium of the present invention is formed by a vacuum film forming method such as a vacuum vapor deposition method, an ion plating method, a sputtering method and a CVD method. The film is formed by a single layer, a parallel type multilayer, a non-parallel type multilayer, or the like. Examples of the metal material used include, in addition to metals such as iron, cobalt, and nickel, cobalt-nickel alloys, cobalt-chromium alloys, cobalt-platinum alloys, cobalt-based alloys such as iron-cobalt alloys, and the like. . When a ferromagnetic metal thin film is formed by a vacuum oblique vapor deposition method in a slight amount of oxygen atmosphere, 90% or more of the metal atoms constituting the magnetic layer are cobalt in order to improve electromagnetic conversion characteristics. Co-O, Co- Co-Fe containing O and the like are preferable. Further, 95% or more of the metal atoms is preferably cobalt, and more preferably 97% or more. The thickness of the magnetic layer is preferably 100 to 300 nm, more preferably 120 to 200 nm.

The ferromagnetic metal thin film may have a multi-layered structure or may have a non-magnetic underlayer or an intermediate layer in order to improve electromagnetic conversion characteristics. The ferromagnetic metal thin film in which most of the metal atoms constituting the magnetic layer is cobalt has excellent magnetic properties, but has poor weather resistance, and has problems in practical use in terms of running property and durability. However, by using the lubricating layer as in the present invention, even if the composition is 90% or more of cobalt as described above, it is excellent in terms of corrosion resistance, running property and durability, and is a magnetic recording that can withstand practical use. It can be a medium.

As the non-magnetic support used in the present invention,
A film made of polyethylene terephthalate, polyethylene naphthalate, polyimide, polyamide, polyamide-polyimide or the like having a thickness of 3 to 10 μm is preferable, and a film having an inorganic filler having a particle diameter of 5 to 20 nm applied to the surface thereof is preferable in order to improve runnability. Further, the non-magnetic support may contain a filler to form irregularities on the surface of the non-magnetic support.

Further, by providing a back coat layer consisting of a coating film mainly composed of non-magnetic powder and a binder resin on the surface of the non-magnetic support opposite to the surface on which the magnetic layer is formed, the magnetic recording according to the present invention. The running property and durability of the medium can be further improved. Since the ferromagnetic metal thin film has a small amount of lubricant that can be retained on the surface or inside thereof, it is possible to supply the insufficient lubricant from the backcoat layer side by previously including the lubricant in the backcoat layer. This is advantageous because it can. That is, the lubricant is replenished to the magnetic layer by bringing the backcoat layer and the magnetic layer into contact with each other in a state where the tape-shaped magnetic recording medium is wound, so that the effect can be sufficiently exhibited. As the non-magnetic powder of the back coat layer, various inorganic pigments and carbon black can be used, and as the binder resin, nitrocellulose, vinyl chloride resin, binder resin for coating type magnetic layer such as polyurethane, etc. Various materials used as can be used.

In the magnetic recording medium of the present invention, a perfluoropolyether may be used in combination as a lubricant compound. The perfluoropolyether that can be used in the present invention includes perfluoromethylene oxide, perfluoroethylene oxide polymer, perfluoro-n-
Propylene oxide polymer (CF ₂ CF ₂ CF ₂ O) _n , perfluoroisopropylene oxide polymer (CF (CF
₃ ) CF ₂ O) _n or copolymers thereof, and the like,
It may contain polar groups such as alcohol and methyl ester groups. Specifically, CRYTOX143A manufactured by DuPont
Z, 157SL, FOMBLIN made by Montefluos
Z-DOL, Z-DEAL, etc. can be used.

When a perfluoropolyether is used, it may be mixed in the liquid for the back coat layer in the same manner as the fluorine-containing carboxylic acid ester compound, or the fluorine-containing carboxylic acid ester may be formed on the back coat layer prepared in advance. When the compounds are applied, they may be mixed and applied.

In the present invention, it is also possible to use in combination a fluorinated hydrocarbon compound obtained by substituting a part of hydrogen atoms of a hydrocarbon having no adsorptive functional group with fluorine atoms, whereby a low temperature and low humidity environment is used. The running durability can be further improved. This fluorinated hydrocarbon has 14 to 40 carbon atoms, preferably 16 to 28 carbon atoms, more preferably 18 to 24 carbon atoms, and some of the hydrogen atoms thereof are replaced with fluorine atoms. If the carbon number is too large, the crystallinity will increase and the still durability and the repeated running durability will deteriorate. On the other hand, if the amount is too small, the volatility becomes high and the characteristics may deteriorate over time, which is not preferable.

The ratio of fluorine atoms in the carbon chain is preferably 3: 1 to 1: 2 in terms of the number ratio of hydrogen atoms to fluorine atoms. If the proportion of fluorine is too high, the solubility or coatability in a usual hydrocarbon solvent containing no fluorine atom may be impaired. Further, the fluorinated hydrocarbon is one in which one or both of the linear saturated hydrocarbons are substituted with fluorine, or a branched one,
Various materials such as those having an unsaturated bond can be used. Specifically, CF ₃ (CF ₂ ) ₉ (CH ₂ ) ₁₅ CH ₃ , CF
₃ (CF ₂ ) ₇ (CH ₂ ) ₁₇ CH ₃ , CF ₃ (CF ₂ ) ₇ (C
_{H 2) 6 (CF 2)} 7 CF 3, (CF 3) 7 CF (CF 2)
₄ (CH ₂ ) ₁₅ CH ₃ , (CF ₃ ) ₂ CF (CF ₂ ) ₄ (C
_{H 2) 8 (CF 2)} 4 CF (CF 3) 2 and the like.

Among them, compounds having a fluorinated hydrocarbon group at both ends or a branched fluorinated hydrocarbon group at one or both ends, which are excellent in fluid lubricity, are preferable.

Although the magnetic recording medium of the present invention is excellent in corrosion resistance, the use of a heterocyclic rust preventive can further improve the corrosion resistance. Examples of rust preventives that can be used in the present invention include benzotriazole, benzimidazole, purine,
Nitrogen-containing heterocycles such as pyrimidine and derivatives in which an alkyl side chain is introduced into their mother nucleus, benzothiazole,
Examples thereof include nitrogen- and sulfur-containing heterocycles such as 2-mercapton benzothiazole, tetrazaindene ring compound, and thiouracil compound, and derivatives thereof. Examples of the tetrazaindene ring compound that can be used for such a purpose include those shown below.

[0039]

Embedded image

Here, R is a hydrocarbon group selected from an alkyl group, an alkoxy group and an alkylamido group.
Particularly preferably, the number of carbon atoms is 3 or more and 20 or less, and in the case of an alkoxy group, R of ROCOCH ₂ − is C ₃ H.
_{7 -, C 6 H 13 -} , phenyl, also in the case of alkyl _{groups, C 6 H 13 -, C} 9 H 19 -, C 17 H 35 - , and the like, in the case of an alkylamide group RNHCOCH ₂ - of R is a phenyl group, C ₃ H ₇ - and the like. Further, examples of the thiouracil ring compound include those shown below.

[0041]

Embedded image

Here, R is a hydrocarbon group having 3 or more carbon atoms. The amount of rust preventive agent applied is 1.0 to 50 m for lubricants.
respect ^{g / m 2, 0.01~5.0mg / m} 2 is preferred. Particularly preferably, the lubricant is 3 to 30 mg / m ² and the rust preventive is 0.1 to 10 mg / m ² .

[0043]

The magnetic recording medium of the present invention has a magnetic layer comprising a ferromagnetic metal thin film on one surface of a non-magnetic support and a protective film laminated on the magnetic layer. An alkylsilane compound having 6 or more alkyl groups and a fluorine-containing carboxylic acid ester compound are present, and on the other surface of the nonmagnetic support, a backcoat layer mainly composed of nonmagnetic powder and a binder resin is provided. Therefore, the alkylsilane compound sufficiently functions as a lubricant as well as binding to the protective film, has little deterioration in running durability, can obtain high reliability, and is particularly remarkable in low temperature and low humidity environments. The characteristics are obtained.

[0044]

EXAMPLES The present invention will be described in more detail below by showing Examples and Comparative Examples of the present invention. Examples and Comparative Examples On a polyethylene terephthalate film having a thickness of 10 μm and having a spherical silica filler having a particle diameter of 13 nm on the surface thereof, an angle of incidence of a magnetic metal vapor flow on the polyethylene terephthalate film was 45 ° in an oxygen-containing atmosphere. Then, cobalt was vapor-deposited twice with a thickness of 70 nm to obtain a magnetic layer made of a ferromagnetic metal having a total thickness of 140 nm and having a two-layer structure. In addition, the inclinations of the columnar crystals of magnetic metal constituting the thin films of both layers were set to be the same. After that, heat treatment was performed to correct the curl and the like, and then a carbon protective film was formed on the magnetic layer by the plasma CVD method described below.

Methane was supplied as a raw material at a flow rate of 150 sccm, and argon was supplied as a carrier gas at a flow rate of 50 sccm, high-frequency power of 600 W was applied, and -4 was applied to the surface of the magnetic layer through a pass roller.
A direct current voltage of 00 V is applied, and a direct current voltage of +500 V is applied to the anode installed in the gas introduction part to accelerate the generated plasma to accelerate the generated plasma to a diamond-like carbon on the magnetic layer surface at a temperature of 20 ° C. at a transport speed of 5 m / min. A hard carbon protective film made of was formed. The obtained carbon protective film had a thickness of 8 nm, and it was confirmed by Raman spectroscopy that the carbon protective film was diamond-like carbon. The Vickers hardness of the obtained protective film was 2,200 kg / mm ² .

On the side of the film opposite to the surface on which the magnetic recording medium was formed, a coating solution for a back coat layer having the following composition was applied to form a back coat layer having a thickness of 0.5 μm. (Backcoat layer coating liquid) Carbon black Kancarb N-990 3 parts by weight (Cancarb Co., Ltd. average particle diameter 270 nm) Black Pearl 800 97 parts by weight (Cabot Co., Ltd. average particle diameter 17 nm) Nitrocellulose (DAICEL RS1 / 2H) 60 parts by weight Polyurethane (N-2304 manufactured by Nippon Polyurethane Co., Ltd.) 60 parts by weight Polyisocyanate (Coronate L manufactured by Nippon Polyurethane Co., Ltd.) 20 parts by weight Methyl ethyl ketone 1000 parts by weight Then, a mixed ethanol solution of an alkylsilane compound and a fluorine-containing carboxylic acid ester is wire. The coating amount and coating surface shown in Table 1 were coated by the bar method and dried.

Further, as in the case of the sample of Sample No. 6, after coating the protective film with the alkylsilane compound, the back surface of the support was brought into close contact with a water-cooled cooling roller, and the support was conveyed at a speed of 5 m / min. The surface was heated to about 100 ° C., about 200 ° C., and about 250 ° C. by a near infrared heater (manufactured by Hibeck Co., Ltd.) to fix the alkylsilane compound on the protective film to obtain sample numbers 14, 15 and 16. The temperature at this time is obtained by measuring the highest temperature reached on the surface of the magnetic recording medium using a non-contact type surface thermometer. Sample number 14,
In the magnetic recording media of Nos. 15 and 16, a back coat layer similar to the above is formed on the back surface of the film of the support, and the ethanol solution of the fluorine-containing carboxylic acid ester shown in Table 1 is applied onto the back coat layer and dried, The width of the original is 8
The sample was cut into 8 mm and incorporated in a cassette for 8 mm VTR. The ratio described in the sample number indicates that the sample number is a comparative example.

[0048]

[Table 1]

The friction coefficient, the still durability, the repeated running durability and the corrosion resistance of the samples of the respective magnetic recording media obtained as described above were measured under the following conditions, and the results are shown in Table 2. [Evaluation method] Measurement of friction coefficient (μ value) A magnetic recording medium and a stainless steel rod (material SUS420J) were brought into contact with each other at a winding angle of 180 ° with a tension (T ₁ ) of 20 g in an environment of 23 ° C. and 70% RH, and a magnetic tape was used. Was measured at a tension (T ₂ ) required to run at a speed of 3.3 cm / sec, and the friction coefficient μ of the magnetic tape was obtained by the following calculation formula. μ = 1 / π · ln (T ₂ / T ₁ ) Still durability measurement (A condition) 8 mmV in 23 ° C. 10% RH environment
After recording a color bar image with a running tension of 20 g using TR (FUJIX-M6 manufactured by Fuji Photo Film Co., Ltd.), the image is reproduced in the still state without operating the still limit mechanism, and the output is -6 dB at the initial stage. It evaluated by measuring the time until it became. (Condition B) In an environment of -10 ° C, a color bar signal is recorded and reproduced by an 8 mm VTR (FUJIX V-88 manufactured by Fuji Photo Film Co., Ltd.), and an image is reproduced in a still state without activating the still limit mechanism. And the output is
The time required to reach 6 dB was measured and evaluated. (C condition) 8 mm under the environmental condition of 5 ° C. and 10% RH
Using a VTR (EV-S700 manufactured by Sony Corp.), the color bar signal is recorded and reproduced after the number of rotations of the cylinder of the recording head is twice the normal number of rotations, and the still limiter mechanism is activated. Without playing the still image,
The time required for the output to reach the initial -6 dB was measured and evaluated.

Repeated running durability 8 mm VTR under the environmental condition of 23 ° C. and 10% RH
(Sony Corporation EV-S1500) was used.
After recording a 6MHz single wave signal for 60 minutes,
After continuous continuous reproduction, the output change and the head stain after 100 times were examined. Head stains were evaluated as ◯ when no stains were observed on the sliding and non-sliding parts, as x when stains were clearly observed on the sliding part, and as Δ for other cases. Corrosion resistance Visual evaluation After storing the surface of the magnetic recording medium for 72 hours in the environment of 27 ° C, 80% RH, and 1 ppm of sulfurous acid gas, visually observe the tape surface after storage. What was not seen was marked with ◯, while the metallic luster on the entire surface of the tape was observed but corrosion was observed, it was marked with Δ, and when part or all of the magnetic layer was dissolved by corrosion was marked with x.

[0051]

[Table 2]

[0052]

EFFECTS OF THE INVENTION A technology of a protective layer having a high degree of storability, running property and durability, which cannot be obtained by a conventional lubricant, has been obtained, and a high density magnetic recording medium has been realized. A protective film laminated on a ferromagnetic metal thin film is formed with a surface layer on which an alkylsilane compound and a fluorine-containing carboxylic acid ester compound are present. In particular, since the alkylsilane compound is formed on the protective film under heating. In addition, the binding property between the alkylsilane compound and the protective film is enhanced, and by further using the fluorine-containing carboxylic acid ester in combination, it is possible to obtain a magnetic recording medium having excellent characteristics even in a low temperature and low humidity environment.

Claims (2)

[Claims] 1. A magnetic recording medium in which a magnetic layer made of a ferromagnetic metal thin film is provided on at least one surface of a non-magnetic support, and a protective film is formed on the magnetic layer, and the protective film is further formed. A magnetic recording medium, wherein an alkylsilane compound having an alkyl group having 6 or more carbon atoms and a fluorine-containing carboxylic acid ester compound are present thereon. 2. A magnetic layer comprising a ferromagnetic metal thin film is formed on at least one surface of a non-magnetic support, a protective film is then formed on the magnetic layer, and then the protective film has 6 carbon atoms.
After applying the above alkylsilane compound having an alkyl group, the applied surface is heat-treated at a temperature of 100 ° C. or higher and 300 ° C. or lower, and then a fluorine-containing carboxylic acid ester compound is further applied to the surface. Recording medium manufacturing method.