JPH0251463B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a magnetic recording medium in which a ferromagnetic layer is formed on a polymer molded product, particularly a polymer film, by vapor deposition, sputtering, or the like. In recent years, increasing the density of magnetic recording has attracted attention as a requirement of the times, but conventional oxide magnetic powders such as γ-Fe ₂ O ₃ and alloy magnetic powders such as cobalt and nickel are combined with suitable organic polymer binders. Mix and apply evenly. In contrast to so-called coating type magnetic recording, a ferromagnetic layer consisting of a ferromagnetic metal thin film that does not contain a polymeric binder such as cobalt is directly formed on the substrate using techniques such as vacuum evaporation or sputtering. Media have been developed in a form that is extremely advantageous for high-density recording. The biggest problem when putting into practical use a magnetic recording medium provided with such a ferromagnetic layer is the adhesion strength between the base material and the ferromagnetic layer. This ferromagnetic layer generally has a thickness of around 1000 angstroms, and the surface smoothness of the base material is required to have conditions that are incomparably more severe than those of conventional coating types. An anchor effect cannot be expected at all. Furthermore, since the ferromagnetic layer is made of a single metal or metal compound, it itself has poor elongation, and unlike the coated type, it does not have the buffering effect of a binder, making it brittle against external forces. Furthermore, since the base material is generally made of organic polymers, conventional coating methods use an organic binder to improve compatibility with the base material, but this method has the fundamental problem of adhesion between organic and inorganic materials. . Various methods have been used to improve the adhesion of such ferromagnetic layers. For example, in the case of vapor deposition, electron beam vapor deposition conditions may be varied to select the optimum conditions for adhesion, or polyethylene terephthalate film, the most commonly used base material, may be subjected to glow discharge treatment or buffing immediately before vapor deposition. Many efforts have been made to apply so-called surface treatments such as surface treatment. However, it is difficult to substantially improve adhesion using such methods. First of all, adhesion is not just a simple cellophane tape peel test, but also a magnetic recording medium, especially when the magnetic tape comes into contact with the head or the roll of the running system, causing chips or scratches. There is a background in which adhesion in a broad sense, such as whether it sticks or not, becomes a practical problem. For example, in video tapes, etc., contact with the head at high relative speeds, repeated contact at the same point during stills,
Furthermore, they are exposed to extremely harsh conditions, including contact with posts. It is required that the adhesion is so good that there is almost no dropout even after 50 or 100 runs. Secondly, the rigidity and toughness of the ferromagnetic layer itself are important for adhesion in a practical sense, and even if the surface of the base material is sufficiently treated, it may affect the properties of the deposits. would be small. Third, physical surface treatment may have a fatal adverse effect on the surface smoothness of the base material, which is most important for magnetic recording media provided with a ferromagnetic layer, as described above. In addition to this adhesion, the following durability is required in order to obtain a magnetic recording medium that is comprehensively excellent. (1) High mechanical properties. In other words, it has excellent tensile modulus in addition to strength and elongation. (Dimensional stability against external forces) (2) Excellent dimensional stability at high temperatures. (3) Excellent dimensional stability against environmental changes such as temperature and humidity. The present inventors have conducted intensive studies to solve these various problems, and as a result, they have arrived at the present invention. That is, an object of the present invention is to provide a magnetic recording medium that has practical adhesion between a ferromagnetic layer and a base material and has high overall durability against severe use. In order to achieve the above object, the present invention has the following configuration:
That is, in a magnetic recording medium in which a polymer molded product is provided with at least one ferromagnetic layer made of a metal or a metal compound, the tensile modulus in at least one in-plane direction is 500 Kg/mm ² or more, and the polymer molded product is the general formula The present invention is characterized by a magnetic recording medium having a structure containing 50 mol% or more of the basic structural unit represented by (where m and n are integers of 0 to 3). The polymer molded article in the present invention is a film or sheet having a structure containing 50 mol% or more of a wholly aromatic polyamide or a chloro-substituted wholly aromatic polyamide whose composition is as described above and whose bonds are para-para bonds. , superior in mechanical properties, heat resistance properties, etc., compared to those bonded at the meta position. Examples of monomers constituting a base material mainly composed of a wholly aromatic polyamide or a chlorine-substituted wholly aromatic polyamide having this structure include terephthalic acid chloride, 2 -Chlorterephthalic acid chloride, 2,
5-dichloroterephthalic acid chloride, 2,6-dichloroterephthalic acid chloride, etc. and p-phenylene diamine, 2-chloro p-phenylene diamine,
2,5-dichloro-p-phenylenediamine,
Examples include 2,6-dichloro-p-phenylenediamine. It is essential that the basic structural unit represented by the above general formula accounts for 50 mol% or more of the base polymer used in the present invention. It is more desirable that the basic structure is an aromatic polyamide, and more preferably that it has a chlorine substituent. When the basic structural unit content is less than 50 mol%, the adhesion of the ferromagnetic layer decreases, and at the same time, the original characteristics as a supporting substrate of a magnetic recording medium, the original characteristics as a supporting substrate of a magnetic recording medium, etc. The physical properties and moisture absorption dimensional stability deteriorate, and the present invention is not satisfied. The composition of less than 50 mol% is not particularly limited as long as it is a wholly aromatic polyamide unit, but the following structural units can be cited as representative examples. That is, Here, X is _-CH3 , _-NO2, or a halogen other than Cl, and p and q are integers from 0 to 3, and cannot be 0 at the same time. moreover, Here, Y is absent, -O-, -SO ₂ -, -S-,

[Formula] −CH ₂ −,

【formula】

[Formula], S is an integer from 0 to 3. These wholly aromatic polyamides or chloro-substituted wholly aromatic polyamides do not have industrially usable melting points (the decomposition temperature of the polymer is lower than the theoretical melting temperature, or the two are very close to each other). , cannot be melt-molded, and is made into a film by solution casting, and the resulting film has excellent heat resistance and is sufficiently stable against heat generated during post-processing such as vapor deposition. Further, the polymer molded article of the present invention has a shape of a film or a sheet and a thickness of 1 micron or more.
millimeter or less, preferably 3 microns or more,
Less than 500 microns. This polymer molding has 200
It is desirable that the heat shrinkage rate at 10% at 100° C. is 0% or more and 10% or less, preferably 0% or more and 2% or less under substantially no-load conditions. Furthermore, since the ferromagnetic layer of the magnetic recording medium is a metal layer, it has virtually no elongation, so it is inconvenient that the base material deforms due to external force. Furthermore, since this field aims at unprecedented high-density recording, it is difficult to deform the tape body due to, for example, tension while the tape is running. Therefore, the polymer molded article constituting the present invention has a tensile modulus of 500 in at least one direction.
Kg/mm ² or more, preferably 5000
Kg/ ^mm2 or less. These characteristics of the substrate are in the state in which it is configured as a magnetic medium, and can be measured by removing the ferromagnetic layer using an appropriate method, but the thickness of the magnetic layer is so thin that its effects can be ignored. Since it is as small as possible, it can be considered to be a characteristic of the entire magnetic recording medium. Such a base material is manufactured as follows.
That is, the polymer is synthesized by low-temperature solution polymerization in an organic polar solvent such as N-methylpyrrolidone, dimethylacetamide, or γ-butyrolactone, or by interfacial polymerization using an aqueous medium. The polymer solution is an acid as a monomer, and when chloride and diamine are used, hydrogen chloride is produced as a by-product, so an inorganic neutralizing agent such as calcium hydroxide or an organic neutralizing agent such as ethylene oxide is added to neutralize this. do. This polymer solution may be used as it is as a film-forming stock solution for forming a base material, that is, a film, or the polymer may be isolated once and then redissolved in the above-mentioned solvent to prepare a film-forming stock solution. In some cases, inorganic salts such as calcium chloride, magnesium chloride, etc. are added to the film-forming stock solution as a solubilizing agent, but the amount and type of addition vary depending on the amount of basic structural units and the type of copolymerized units. In order to obtain a film with practical strength, the intrinsic viscosity of the polymer must be 0.5 or higher.
At that time, the polymer concentration in the film forming stock solution is 2 to 40 wt%.
degree is preferred. Here, the intrinsic viscosity of the polymer is represented by measuring 0.5 g of the polymer in 100 ml of N-methylpyrrolidone solution containing 2.5 wt% of lithium bromide at 30°C. The film-forming stock solution prepared as described above is formed into a film by a so-called solution film-forming method. A thin film is formed by casting and extruding the film-forming stock solution from a die onto a drum or an endless belt, and after removing the solvent or solvent and inorganic salt by dry, wet, dry-wet, etc. processes, it is thermally solidified to form the final film. The process and manufacturing conditions for obtaining a film should be determined based on the characteristics of the polymer and the desired physical properties of the film. For example, at an appropriate stage of the process, the area magnification is 1.0 or more simultaneously or sequentially.
Stretching by 9.0 not only improves the mechanical properties of the film, but also greatly contributes to making the film uniform in its flatness and thickness. Also, care must be taken as heat setting or generally preferred heat treatment temperatures for film dimensional stability at high temperatures are too high, as this may lead to polymer deterioration and relaxation of orientation, and conversely worsen the mechanical and thermal properties of the final film. It is. The ferromagnetic layer of the present invention refers to a so-called thin film type magnetic layer, and is a ferromagnetic layer made of metal or a metal compound, specifically, Ni, Co, Cr, Fe, γ-Fe ₂ O ₃
It is a layer formed by a dry method, consisting mainly of a single substance or an alloy of . Further, it is desirable that this ferromagnetic layer has a thickness of 0.01 to 1μ, preferably 0.01 to 0.5μ, more preferably 0.05 to 0.20μ. The method for forming the ferromagnetic layer is the vapor deposition method, in which the metal alloy is heated and evaporated in vacuum and deposited on the substrate.
Furthermore, well-known dry methods such as the sputtering method, in which molecules of the target metal or metal compound are driven out using ionized argon activated by electric discharge in a high vacuum, and adhered to the substrate, and other well-known dry methods such as the ion plating method are used. It can be formed using In forming the ferromagnetic layer, cobalt is the single element with the best magnetic properties and good adhesion, and a small amount of nickel is added to improve the corrosion resistance, and chromium is added to improve the corrosion resistance in the vertical direction. It is possible to create a film that is easily magnetized. The vapor deposition method uses electron beam heating to generate a vapor flow of ferromagnetic material, and deposits the film to a thickness of 0.01~
It is desirable to form a controlled thin film of 0.5μ, preferably 0.05-0.20μ. Here, the degree of vacuum is generally 10 ^-7 to 10 ^-2 mmHg, and a gas such as oxygen, nitrogen, or argon may be actively introduced from the outside into the deposition atmosphere in relation to magnetic properties. In the present invention, as a pretreatment for vapor deposition, an atmosphere of argon or oxygen, for example, a vacuum degree of 10 ^-2 to several mm is used.
It is preferable to perform glow discharge treatment under Hg, and a clear significant difference in adhesion is observed compared to the case without treatment. In addition, since the magnetic recording medium of the present invention is based on a polymer molded product containing 50 mol% or more of a specific basic structural unit, it has good thermal stability at high temperatures and can withstand the heat generated during vapor deposition. Therefore, there are a number of constraints during vapor deposition, such as the introduction of a means to cool the substrate to below 80°C, and conditions that reduce thermal deformation of the substrate, which sacrifices magnetic properties and durability. Not only does it not have to be removed, but the base material can be further heat-treated during or after vapor deposition, and the adhesion can be significantly improved by this treatment. This is considered to be because the cohesive force of the metal film increases and the molecular conformity of the interface with the base material is strengthened. Note that this treatment temperature is desirably within a range of 100° C. or higher and 400° C., preferably 120° C. or higher and 250° C., so that the characteristics of the ferromagnetic layer do not deteriorate. Furthermore, the effects of this method are further enhanced when heat treatment not only improves adhesion but also changes the chemical properties, crystal structure, and crystal morphology of the thin film and improves magnetic recording characteristics. As described above, the magnetic recording medium of the present invention has superior performance compared to conventional coating-type magnetic recording media, which are thin film magnetic recording media based on polyester films and existing heat-resistant films (for example, DuPont's "Kapton"). In other words, it is a high-performance, high-density magnetic recording medium that has excellent comprehensive properties such as high adhesion, dimensional stability at high temperatures, dimensional stability against external forces, and dimensional stability under the environment in which it is used. Specific uses of the present invention include video tape,
It provides a material suitable for audio tapes and various types of floppy disks. Furthermore, the present invention can be applied to the field of all kinds of magnetic recording materials such as electronic cameras and video discs. Further, the magnetic recording method does not matter whether horizontal magnetization or perpendicular magnetization is used. Note that a protective layer may be provided on the magnetic layer of the present invention,
It is often preferable to provide a back coat layer on the back surface of the film substrate for running properties, antistatic properties, and other purposes since this improves the performance of the magnetic recording material as a whole. The evaluation of the magnetic recording medium of the present invention and the film as a base material was determined based on the following criteria. (1) Intrinsic viscosity Calculated using the following formula. ηinh=ln(ηrel)/C where ηrel is the relative viscosity measured at 25℃, and C is
The value obtained when 0.5 gr of polymer was dissolved in a solution of 100 ml of N-methylpyrrolidone and 2.5 gr of lithium bromide was used. (2) Strength and elongation, tensile modulus Measured according to JIS L-1073 at 20°C and 75% RH using "Tensilon". (3) Heat shrinkage rate A film of approximately 25 cm in width was cut out to a width of 5 mm, marks were made at 20 cm intervals, and the film was hung in an oven at a predetermined temperature, with a load of 5 gr applied to the lower end. After 10 minutes, the sample was taken out, the distance between the marks was determined, and the heat shrinkage rate was calculated. (4) Humidity expansion coefficient A tape-shaped sample cut out to a width of 5 mm and a length of 20 cm was left at 20°C and 70% RH for 24 hours, then the conditions of the constant temperature and humidity chamber were changed to 90% RH, and the tape length was continuously The humidity expansion coefficient was calculated from the value after equilibrium was reached. (5) Adhesion Although various methods were considered to test the adhesion between the film substrate and the metal thin film, results with good reproducibility were mainly obtained using an actual test using a video device. For the actual machine, we used a commercially available "Betamax" to cut out samples into tapes 1 m to 10 m long, and then repeatedly fed the tape to observe how the thin film was damaged. Similar observations were also made after leaving the sample in a still state for a long time. Next, embodiments of the present invention will be described based on Examples. Example 1 100 ml of dry N-methylpyrrolidone was placed in a 200 ml stirring tank, and 8 kg of lithium chloride, 2-
Dissolve 2.42Kg of chlor p-phenylenediamine and 0.60Kg of 4,4'-diaminodiphenyl ether at 0℃.
The mixture was kept at a constant temperature and the whole was stirred gently. 4.07 Kg of granulated terephthalic acid chloride was added over approximately 30 minutes with continued stirring. Stirring was continued for 1 hour to obtain a viscous polymer solution. A large amount of water was placed in a large mixer, and the polymer solution was added thereto and reprecipitated to obtain a fibrous solid polymer. Wash this,
After drying, 2 kg of polymer, 1 kg of lithium bromide, N
A homogeneous solution was prepared by mixing 40 ml of methylpyrrolidone at room temperature. The intrinsic viscosity of this polymer was 4.57. This liquid was uniformly cast from a nozzle onto a stainless steel drum with a polished surface and heated in an atmosphere of 120°C for about 20 minutes. This film was peeled off from the drum and continuously immersed in a water bath for about 10 minutes. This film was heated in a tenter at 300° C. for about 5 minutes at a constant length to obtain a transparent film with a thickness of 16 μm and a smooth surface. This film has a strength of 40Kg/mm ² and a tensile modulus
Shows 1500Kg/mm ² and has minimal heat shrinkage at 250℃
It turned out to be a heat-resistant film with an extremely high strength of 0.3%. In addition, the temperature expansion coefficient near room temperature is 4 × 10 ^-6 mm/mm/℃, and the humidity expansion coefficient is 5 × 10 ^-6
It was also found that it has excellent environmental stability (mm/mm/RH%). This film was loaded into a vacuum chamber and subjected to ion bombardment in an Ar gas atmosphere of 10 ^-2 Torr. Next, the vacuum chamber was evacuated to a level of 10 ^-6 Torr, and while the film was running, a Co-Ni alloy (75% by weight of Co, 25% by weight of Ni) was deposited obliquely by electron beam evaporation at an incident angle of 70° or more. by law
A magnetic tape having a thin ferromagnetic metal layer was produced by vapor deposition to a film thickness of 0.15μ. The magnetic properties of the obtained film include a coercive force in the longitudinal direction of 720 Oe, a coercive force in the width direction of 480 Oe, and a squareness ratio of 0.92, making it suitable for audio and video tapes as a longitudinally oriented magnetic tape. have. This magnetic tape was run on a commercially available home video system, Betamax, and the results showed that the adhesion of the magnetic layer was extremely good, and there was hardly any fall-off of the magnetic layer or deformation of the tape, which was noticeable. It was confirmed that there was no increase in dropout. Comparative Example 1 A magnetic tape was produced in the same manner as in Example 1 using a polyethylene terephthalate film ("Lumirror" 16μ, manufactured by Toray Industries, Ltd.) and a polyimide film ("Kapton", 25μ, manufactured by DuPont, USA) as a base. In the case of polyethylene terephthalate, holes frequently occur due to heat during ion bombardment treatment or vapor deposition treatment, making it impossible to produce long tapes. In addition, as a result of running this with "Betamax", the magnetic layer was partially destroyed or fell off due to multiple runs or still running, resulting in insufficient adhesion with the magnetic layer such as polyethylene terephthalate. confirmed. In the case of ``Kapton,'' there was no heat loss during production, but it was not possible to obtain a tape with stable magnetic recording properties, probably due to poor surface smoothness. In addition, the tape's stiffness and dimensional stability against humidity are poor (humidity expansion coefficient: 32 x 10 ^-6 mm/mm/
RH%), it was not possible to obtain good tape properties. Example 2 Co-Cr was deposited on the 16μ thick film obtained in Example 1 using a magnetron type RF sputtering device.
A magnetic thin film made of the alloy was formed. First, a film is loaded into a vacuum chamber, the vacuum chamber is evacuated to 10 ^-6 Torr, and then Ar gas is introduced and 2×
Maintain pressure at 10 ^-2 Torr. Then, with a diameter of 150mm
A high frequency voltage of 13.56MHz was applied to a Co-Cr alloy target (81% by weight of Co, 19% by weight of Cr), and 200W
Sputtering was carried out for 30 minutes with the input power of 0.5 μm, and a strong thin film with a thickness of 0.5 μm was obtained. The coercive forces of this Co-Cr film in the directions perpendicular and parallel to the film surface are 1100 Oe and 1100 Oe, respectively.
It was 600 Oe. In addition, this magnetic thin film has characteristics that make it suitable as a perpendicular recording medium, as the residual magnetization in the direction perpendicular to the film surface is larger than the residual magnetization in the direction parallel to the film surface, and it has an axis of easy magnetization in the perpendicular direction. There is. As a result of testing the durability of this tape using a commercially available video device, it was found that the adhesion between the base film and the magnetic layer was sufficiently excellent. Example 3 Fe ₃ O ₄ was deposited on the 16μ film obtained in Example 1.
Magnetron type RF targeting sintered bodies
An iron oxide thin film was formed using a sputtering device. First, the film is loaded into a vacuum device, which is evacuated to 10 ^-6 Torr, and then contains 6% by volume of oxygen gas.
Ar gas is introduced to maintain the pressure at 5×10 ⁻³ Torr. Next, a high frequency voltage of 13.56 MHz was applied to the target, and sputtering was performed for 15 minutes at an input power of 200 W to form a Fe ₃ O ₄ film with a thickness of 0.2 μm. Subsequently, this film was heated and oxidized in the atmosphere at 260° C. for 60 minutes to convert it into a γ-Fe ₂ O ₃ film. The obtained γ-Fe ₂ O ₃ film exhibited magnetic properties with a coercive force of 350 Oe, a residual magnetic flux density of 1500 G, and a squareness ratio of 0.81. This tape showed almost no deformation even after high-temperature treatment, and as in Examples 1 and 2, it was confirmed that the magnetic layer had sufficient durability for practical use. Example 4 In the same manner as in Example 1, 10 kg of lithium chloride, 2.00 kg of 2-chlorop-phenylenediamine, and 1.19 kg of 4,4-diaminodiphenylmethane were dissolved in 100 ml of dried N,N' dimethylacetamide and heated at 0°C. I kept it. Next, 4.08 kg of terephthalic acid chloride was added to obtain a solid polymer in the same manner as in Example 1. The intrinsic viscosity of this polymer was 2.89. Polymer 2Kg,
Calcium chloride 1Kg, N-methylpyrrolidone 25
A transparent film with a thickness of 16 μm and a smooth surface was obtained in the same manner as in Example 1. This film has a strength of 32Kg/mm ² and a tensile modulus
It showed a heat shrinkage rate of 950Kg/mm ² and a heat shrinkage rate of 1.2% at 250°C, indicating that it is a high-strength, heat-resistant film. The temperature expansion coefficient was 6 x 10 ^-6 mm/mm/°C, and the humidity expansion coefficient was 11 x 10 ^-6 mm/mm/RH%. A magnetic tape was prepared from the base film of this example in the same manner as shown in Examples 1 to 3, and although it was somewhat inferior to the film of Example 1, it was confirmed that it exhibited sufficient practical performance. Comparative Example 2 1.14 kg of 2-chloro-p-phenylenediamine and 4,4' diaminodiphenylmethane in 100 kg of N,N' dimethylacetamide dried as in the previous example.
2.38Kg was dissolved and kept at 0°C. Next, 4.07 kg of terephthalic acid chloride was added to obtain a solid polymer having an intrinsic viscosity of 2.52 in the same manner as in Example 1. Polymer 2Kg,
N-methylpyrrolidone 25, calcium chloride 0.5
Kg was mixed and a smooth film with a thickness of 15μ was obtained using the same process as in the previous example. This film had a high moisture absorption rate of 6.8% and a humidity expansion coefficient of 20×10 ^-6 mm/mm/RH%, making it unsuitable as a base film for magnetic tape. It also had poor heat resistance, exhibiting a heat shrinkage of approximately 5.3% at 200°C, resulting in frequent troubles due to heat loss during vapor deposition. Furthermore, the durability of the resulting magnetic tape was tested many times, and as a result, the magnetic layer often fell off, similar to the case with polyethylene terephthalate-based tapes.

Claims (1)

[Claims] 1. A magnetic recording medium in which at least one ferromagnetic layer made of a metal or a metal compound is provided on a polymer molding, which has a tensile modulus of elasticity in at least one in-plane direction of 500 Kg/mm ² or more. , the polymer molded product has the general formula 1. A magnetic recording medium comprising a wholly aromatic polyamide containing 50 mol% or more of basic structural units represented by (where m and n are integers of 0 to 3).