JPH04311813A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To provide the metallic thin-film type magnetic recording medium having excellent traveling durability and more particularly electromagnetic conversion characteristics. CONSTITUTION:This magnetic recording medium is constituted by forming a protective layer consisting of a resin which includes a copolymer formed of at least tetrafluoroethylene and vinylidene fluoride as monomer compsn., is easily soluble in org. solvents and can be uniformly applied on the magnetic layer of the magnetic recording medium formed with the magnetic layer consisting of a ferromagnetic metallic thin film on a nonmagnetic base.

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 comprising a ferromagnetic metal thin film as a magnetic layer, and more particularly to a metal thin film type magnetic recording medium that has excellent running durability under a wide range of temperature and humidity conditions.

0002

[Prior Art] Conventionally, coating-type magnetic recording media have been widely used, in which a magnetic material in the form of ferromagnetic powder dispersed in an organic polymer binder is coated on a non-magnetic support and dried. It's coming. In recent years, due to the need for high-density recording as typified by high-band 8mm video and digital video, it has been formed using vapor deposition methods such as vacuum evaporation, sputtering, and ion plating, or plating methods such as electroplating and electroless plating. A so-called metal thin film magnetic recording medium, which uses a ferromagnetic metal thin film as a magnetic layer and does not use a binder, has been intensively studied and partially put into practical use. In particular, the method using vacuum evaporation has great advantages because it does not require waste liquid treatment as in the case of plating, the manufacturing process is simple, and the deposition rate of the film can be increased. A method for manufacturing a magnetic film having coercive force and squareness desirable for magnetic recording media by vacuum deposition is disclosed in US Pat. No. 33,426.
The oblique vapor deposition method disclosed in No. 32, US Pat. No. 3,342,633, etc. is known. Further, major problems concerning magnetic recording media made of ferromagnetic metal thin films include weather resistance and running durability. In other words, the magnetic recording medium is subjected to high-speed relative motion with the magnetic head during the process of recording, reproducing, and erasing magnetic signal information, but at this time, the running must be smooth and stable, and at the same time, the head and the magnetic recording medium must move smoothly and stably. No contact, abrasion or destruction shall occur. Providing a lubricating layer or a protective layer has been considered as a method of improving such running durability. Thermoplastic resin,
There are products in which a thermosetting resin, a fatty acid, a metal salt of a fatty acid, a fatty acid ester, an alkyl phosphate, a perfluoropolyether compound, etc. are dissolved in an organic solvent and applied. (For example, JP-A No. 60-69824, JP-A No. 60-60
It is disclosed in Japanese Patent No.-85427. ) Also, recently, technology has been developed to improve running durability by using compounds with branched perfluoroalkenyl groups. (JP-A-61-107528) However, the running durability of the metal thin film magnetic recording medium thus obtained is insufficient under harsh conditions such as low humidity and high humidity. In particular, there is a problem in that sticking occurs due to friction against mechanical parts, magnetic heads, and guide members of recording/reproducing machines such as VTRs. In addition, there is a problem in that electromagnetic conversion characteristics deteriorate due to spacing loss between the head and the tape due to the thickness of the protective/lubricant layer provided to solve these problems, and improvements have been desired. especially,
It has been difficult to fully meet the requirements for maintaining running durability over a wide range of running speeds, from low to high speeds, as with VTRs. That is, fluorine-based resins such as tetrafluoroethylene, vinylidene fluoride, and the copolymer of vinylidene fluoride and trifluoroethylene disclosed in JP-A-60-69824 are effective in reducing the coefficient of friction. Although this has been shown to be true, it has been confirmed that the electromagnetic conversion characteristics are insufficient under severe conditions as described above, and that the durability is particularly poor during high-speed running. The reason for this is that these fluorine-based resins have poor solubility due to the lack of suitable solvents, which makes it difficult to provide uniform protection and protection.
This is thought to be because a lubricating layer is difficult to form.

0003

SUMMARY OF THE INVENTION An object of the present invention is to provide a metal thin film type magnetic recording medium that has excellent running durability, particularly excellent electromagnetic conversion characteristics.

0004

[Means for Solving the Problems] 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 formed on a non-magnetic support, in which at least tetrafluoroethylene and fluoride are added on the magnetic layer. This is achieved by a magnetic recording medium characterized by forming a protective layer made of a resin containing a copolymer formed of vinylidene as a monomer composition. The present inventor has provided a resin containing a copolymer formed of at least tetrafluoroethylene and vinylidene fluoride as monomer compositions on the magnetic layer, thereby achieving a magnetic head and a guide under severe conditions such as low humidity and high humidity. It was discovered that the coefficient of friction against members such as poles is reduced, and the present invention was developed. In other words, the resin constituting the protective layer in the present invention has excellent solubility in solvents, so it can be easily and uniformly coated on a ferromagnetic metal thin film, so that it can be coated uniformly and mechanically. Able to form an excellent film. Uniformity here means
The surface of the magnetic layer can be completely covered, and the arrangement of molecules within the protective layer is amorphous and uniform as a whole, with no coexistence of crystalline portions, oriented portions, and amorphous portions. Therefore, it is considered that the protective effect is large and peeling at the interface with the magnetic head is less likely to occur. The resin used for the protective layer of the present invention (hereinafter referred to as the resin of the present invention) has a monomer composition of at least tetrafluoroethylene (i.e., CF2 = CF2) and vinylidene fluoride (i.e., CH2 = CF2). It consists of a resin containing a copolymer (hereinafter referred to as the copolymer of the present invention). The copolymer of the present invention is not particularly limited as long as it is synthesized from a monomer containing at least tetrafluoroethylene and vinylidene fluoride, and any other copolymerizable monomer may be added to the monomer composition. It can be done. Therefore, the copolymers of the present invention include copolymers of tetrafluoroethylene and vinylidene fluoride, copolymers of tetrafluoroethylene and vinylidene fluoride, and other copolymerizable monomers, such as copolymers of tetrafluoroethylene and vinylidene fluoride with other copolymerizable monomers. Examples include trifluoroethylene, vinylidene chloride, vinyl chloride, and styrene. The resin of the present invention may be composed only of the copolymer of the present invention, or may be a blend of the copolymer of the present invention as a main component and any other resin. When the monomer composition of the copolymer of the present invention is composed of tetrafluoroethylene and vinylidene fluoride, the copolymerization ratio (weight ratio) is preferably tetrafluoroethylene:vinylidene fluoride=20:80 to 99:1. , when other monomers are added, tetrafluoroethylene: vinylidene fluoride: other monomers = 10:40:50 to 99:1
:1 is preferable. When the copolymerization ratio is out of this range, the solubility decreases and it becomes impossible to form a protective layer with a uniform structure. Further, the specific arrangement structure of the monomer components of the copolymer of the present invention is arbitrary, and may be either a random type or a graft type, but preferably a random type. The weight average molecular weight of the copolymer of the present invention is 10,000 to 200,000, preferably 10,000 to 100,000. If it is too large, it will affect the solubility and the uniformity of the protective layer, and if it is too small, it will affect the running durability. This is a problem in terms of gender. Specifically, the copolymers of the present invention include the Kynar series sold by Pennwalt.

The thickness of the protective layer in the magnetic recording medium of the present invention is preferably 0.5 nm to 20 nm, more preferably 1 nm to 10 nm. If the thickness is less than 0.5 nm, it is difficult to form a uniform film, and the runnability
Not durable enough. Further, if the thickness is 20 nm or more, there is a problem that electromagnetic conversion characteristics deteriorate due to spacing loss between the head and the tape. In order to improve the adhesion of the ferromagnetic metal thin film of the protective layer of the magnetic recording medium of the present invention to the magnetic layer, the surface of the ferromagnetic metal thin film may be activated by glow discharge or energy beam before forming the protective layer. It can also be modified with surfactants such as fatty acids and various coupling agents. Further, the protective layer of the present invention may have any structure as long as it contains at least the resin of the present invention. For example, the protective layer may be a single layer made of the resin of the present invention, or may be made of a plurality of layers made of different types of resins of the present invention. Furthermore, the protective layer of the present invention may be composed of the resin of the present invention mixed with other lubricants, or may be formed on the resin layer of the present invention or between the resin layer and the surface of the magnetic layer (inside the resin layer, Alternatively, any lubricant may be laminated on the surface of the magnetic layer (including under the resin layer). Examples of lubricants that can be mixed or layered include fatty acids, metal soaps, fatty acid amides, fatty acid esters, higher aliphatic alcohols, monohydrocarbyl phosphates, dihydrocarbyl phosphates,
Trihydrocarbyl phosphate, paraffins, silicone oil, animal and vegetable oils, mineral oil, higher aliphatic amines;
Inorganic fine powders such as graphite, silica, molybdenum disulfide, tungsten disulfide; polyethylene, polypropylene, polyvinyl chloride, ethylene-vinyl chloride copolymer,
Examples include fine resin powders such as polytetrafluoroethylene; α-olefin polymers; unsaturated aliphatic hydrocarbons that are liquid at room temperature. Among these, in order to further enhance the effects of the present invention, it is desirable to use it in combination with a fluorine-based lubricant. Among fluorine-based lubricants, lubricants that are liquid at room temperature and have a melting point of 20° C. or lower are preferred. Examples of the fluorine-based lubricant include modified or unmodified perfluoropolyethers having a molecular weight of 1,500 to 15,000. Specifically, DuPont's Krytox 143 series (polyfluoropropylene oxide), Montefluos' Fomblin Y series (perfluoropropylene oxide/perfluoromethylene oxide copolymer)
, Fomblin Z series (perfluoroethylene oxide/perfluoromethylene oxide copolymer) and functional groups (for example, -C
OOH, -OH, -CONH2, etc.) are introduced, or compounds in which a plurality of perfluoropolyether chains extend from a central atomic group are used. Among these, compounds with a plurality of perfluoroether chains extending from a central atomic group have a low coefficient of friction and are extremely durable. Examples of specific molecular structures thereof include those described in Chemical Formulas 1 to 3. In either formula, n is typically 6 to 30.

[0006]

[Chemical formula 1]

[Chemical 2]

embedded image These lubricants can be used as they are or dissolved in an organic solvent. The same organic solvent used for dissolving the resin of the present invention can be used.

[0007] In the present invention, the method for forming the protective layer is to mix materials (resin of the present invention, lubricant, etc.) with acetone,
Organic solvents such as methyl ethyl ketone (MEK) or special fluorine solvents (fluorine such as Freon 113, chlorine-substituted alkanes, fluorine-substituted alcohols, fluorine-substituted ethers, etc.)
A method of dissolving the material and coating or spraying it on the substrate and then drying it, a method of rubbing an object impregnated with the material on the surface of the substrate (metal thin film magnetic recording medium), a method of immersing the magnetic recording medium in a solution of the material dissolved in an organic solvent. Examples include a method in which the material is adsorbed onto the surface of the magnetic layer, a method in which a monomolecular film of the material is formed on the surface of the magnetic layer by Langmuir-Blodgett method, and the like.

The ferromagnetic metal thin film of the magnetic recording medium of the present invention may be formed by electroplating, electroless plating, vapor phase plating,
It is a ferromagnetic metal thin film formed by methods such as sputtering, vapor deposition, and ion plating. Materials for the ferromagnetic metal thin film include iron, cobalt, nickel, and other ferromagnetic metals, or Fe-Co, Fe-Ni, and Co.
-Ni, Fe-Rh, Co-P, Co-B, Co-Y,
Co-La, Co-Ce, Co-Pt, Co-Sm, C
o-Mn, Co-Cr, Fe-Co-Ni, Co-Ni
-P, Co-Ni-B, Co-Ni-Ag, Co-Ni
-Nd, Co-Ni-Ce, Co-Ni-Zn, Co-
Examples include ferromagnetic alloys such as Ni-Cu, Co-Ni-W, and Co-Ni-Re, and a ferromagnetic metal thin film is formed on a nonmagnetic support by the above method. When used as a magnetic recording medium, the film thickness is in the range of 0.02 to 2 μm, particularly preferably in the range of 0.05 to 1.0 μm. The above ferromagnetic metal thin films include O, N, Cr, Ga, As, Sr,
Zr, Nb, Mo, Rh, Pd, Sn, Sb, Te, P
It may contain m, Re, Os, Ir, Au, Hg, Pb, Bi, etc. Although the surface shape of the above-mentioned magnetic layer is not particularly limited, when it has protrusions with a height of 1 to 100 nm, it is particularly excellent in runnability and durability.

The thickness of the support is preferably 4 to 50 μm. Further, an underlayer may be provided on the support in order to improve the adhesion and magnetic properties of the ferromagnetic thin film. An example of such an underlayer is a filler-containing resin layer in which fine particles of SiO2 or CaCO3 are uniformly dispersed. As the support used in the present invention, a plastic base such as polyethylene terephthalate, polyimide, polyamide, polyvinyl chloride, cellulose triacetate, polycarbonate, polyethylene naphthalate, polyphenylene sulfide, or Al, Ti, stainless steel, etc. is used. The magnetic recording medium of the present invention may have any shape such as tape, sheet, card, or disk, but tape and disk shapes are particularly preferred.

0010

EXAMPLES Next, the present invention will be explained in detail with reference to Examples, but the present invention is not limited thereto. Example 1 A cobalt-nickel magnetic film (thickness: 150 nm) was obliquely deposited on a polyethylene terephthalate film having a thickness of 113 μm to prepare a raw material for a magnetic recording medium. An electron beam evaporation source is used as the evaporation source, and a cobalt-nickel alloy (Co: 80 wt%, Ni: 20 wt%) is charged to it, and the incident angle is 50 degrees in a vacuum of 5 x 10-5 Torr. Oblique deposition was performed in an oxygen stream. Samples were prepared by coating and drying various resin materials dissolved or dispersed in various solvents on the magnetic metal thin film of the obtained magnetic recording medium. #
Nos. 1 to 4 and 8 are Examples, and Nos. 5 to 7 and 9 are Comparative Examples).

Table 1 Continuation of Table 1 *: mg/m2 **: Perfluoro(butyltetrahydrofuran)

Conditions (A) of the obtained magnetic tape: 25°C
, 10% relative humidity and condition (B): The friction coefficient, ie μ value, against the stainless steel rod at 40°C and 80% relative humidity, and the repeated running durability and still durability with an 8 mm VTR under condition (A) are as follows. When investigated by the method, the results were as shown in Table 2. The coefficient of friction is 50g between the magnetic layer surface of the magnetic tape sample and the stainless steel pole.
The tension (T1) and the tension (T2) required to run the magnetic tape at a speed of 3.3 cm/sec were measured by making contact with the magnetic tape at a wrapping angle of 180°, and from this measurement value, the friction was calculated based on the following formula. The coefficient μ was calculated. μ=(1/π)·ln(T2/T1) Furthermore, the low-speed friction coefficient was measured by running at a speed of 0.1 cm/sec under the condition (A). Here, repeated running durability is 50
A m-long tape was repeatedly played on an 8 mm VTR (FUJIX-8 M6 model manufactured by Fuji Photo Film Co., Ltd.).
This is the number of replays until the screen becomes distorted due to unstable running or the running stops due to an increase in the coefficient of friction. Further, still durability was evaluated by pressing the pause button during image playback using a VTR of the same type (however, the function to limit still playback time was removed) and measuring the time until the image stopped appearing. Thus the general formula: -(CF2 -CF2
)n-(CH2-CF2)m-, etc., on the surface of the metal thin film type magnetic recording medium, which is excellent in μ value, repeated running durability, and still durability, and has the following characteristics: It is clear that this has been achieved under a wide range of conditions from high humidity to low humidity.

Table 2

[0014]

[Effects of the Invention] A metal thin film type magnetic recording medium comprising a ferromagnetic metal thin film and a resin represented by the above general formula provided on the surface thereof is as follows:
Compared to conventionally studied lubricants as shown in the comparative example,
It is clear that it has extremely excellent adaptability to temperature and humidity, running performance, and durability.

Claims (3)

[Claims] 1. A magnetic recording medium comprising a magnetic layer made of a ferromagnetic metal thin film formed on a non-magnetic support, wherein a copolymer comprising at least tetrafluoroethylene and vinylidene fluoride as monomer composition is formed on the magnetic layer. A magnetic recording medium characterized by forming a protective layer made of a resin. [Claim 2] The weight average molecular weight of the copolymer is 10.
00 to 200,000, and the copolymerization ratio of tetrafluoroethylene and vinylidene fluoride is 20:80 to 99: by weight.
2. The magnetic recording medium according to claim 1, wherein the magnetic recording medium is 3. The magnetic recording medium according to claim 1, wherein the protective layer contains a fluorine-based lubricant having a melting point of 20° C. or less.