JPH0443326B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a method of manufacturing a magnetic recording medium suitable for wideband signal recording and reproduction. [Constitution of Conventional Example and Problems thereof] The technique of recording and reproducing audio images using a helical scanning method using a rotating magnetic head is one of the most advanced types of magnetic recording in terms of high-density recording. In order to further increase the recording density as an extension of this technology, a magnetic recording medium that not only has a smaller minimum recording wavelength but also has wavelength characteristics with a wide band is desired. On the other hand, in conventional magnetic recording media, as the recording wavelength becomes shorter, the self-demagnetizing field inside the medium increases, and the magnetization vector rotates to minimize the energy inside the medium, which causes a rapid reproduction output. In order to minimize the effect of the self-demagnetizing field, the coercive force of the medium has been increased to overcome the self-demagnetizing field. However, this method works to reduce the penetration of magnetization in the direction of the medium thickness, resulting in a decrease in long wavelength output, so the amount of magnetization must be increased, but the ferrite head in practical use is not magnetically saturated. Because a phenomenon occurs,
It is necessary to develop an alloy head. Therefore, a first magnetic layer having a relatively low coercive force, such as a layer in which acicular particles of γ-Fe ₂ O ₃ are coated and oriented and dried together with a binder, is formed on the support, and a second magnetic layer, such as γ- A two-layer magnetic recording medium in which Fe ₂ O ₃ acicular particles are replaced with CrO ₂ has been devised and is already in practical use. Another two-layer structure has been proposed, in which a ferromagnetic layer is arranged in the form of a metal thin film on a coated magnetic layer.
For example, powder magnetic materials such as oxide magnetic powders such as γ-Fe ₂ O ₃ , Co-doped γ-Fe ₂ O ₃ , Fe ₃ O ₄ , CrO ₂ or ferromagnetic alloy powders are coated on a support with vinyl chloride. - Vacuum deposition, sputtering, electroless plating, etc. on the first magnetic layer obtained by dispersing and coating in an organic binder such as vinyl acetate copolymer, styrene-butadiene copolymer, or polyurethane resin, and drying. So, Co, Co−Ni, Co−Mo, Co−Cr, Co
There is a medium in which a second magnetic layer is formed by forming a ferromagnetic metal thin film such as -Ni-Mg. This configuration is suitable for recording and reproducing wideband signals, but when recording and reproducing are repeated using a mechanism modified from a commercially available video tape recorder (hereinafter referred to as VTR), the signal-to-noise ratio (hereinafter expressed as S/N) ) occurs rapidly. This S/N reduction phenomenon is mainly due to cracks and partial peeling of the second magnetic layer, and although there are differences depending on the constituent materials, it occurs between 30 and 60 passes, and in practice, 200 passes are required under various environments. Stable performance was required and improvements were desired. [Object of the Invention] The present invention has been made in view of the above circumstances, and an object thereof is to provide a method for manufacturing a magnetic recording medium suitable for recording and reproducing broadband signals by improving the coated magnetic layer. [Structure of the Invention] The method for producing a magnetic recording medium of the present invention involves coating a support with a magnetic paint containing as a binder a compound having an unsaturated bond that can be polymerized by electron beam irradiation, and forming a coated magnetic layer. After forming, a ferromagnetic metal thin film is formed on the coated magnetic layer by a vacuum evaporation method, and then electron beam irradiation is performed through the ferromagnetic metal thin film in a vacuum to polymerize the compound having the unsaturated bond. Features. [Description of Examples] FIG. 1 is an enlarged sectional view of a magnetic recording medium obtained by the manufacturing method of the present invention. That is, support 1
A coated magnetic layer 2 for fixing a powder magnetic material 2a using a polymer polymerized by electron beam irradiation as a binder 2a is disposed thereon, and a ferromagnetic metal thin film layer 3 and a lubricant layer 4 are disposed thereon. 2c is an intermediate layer formed between the ferromagnetic metal thin film layer 3 and the coated magnetic layer by the manufacturing method of the present invention. Examples of compounds having unsaturated bonds that can be polymerized by electron beam irradiation that can be used in the present invention include compounds containing acryloyl groups, acrylamide groups, allyl groups, vinyl thioether groups, etc., and unsaturated polyesters. etc. The molecular weight of the polymerized polymer is preferably in the range of 1,000 to 20,000. The magnetic powder used in the present invention is γ-Fe ₂ O ₃ , Co
γ- _Fe2O3 , _Fe3O4 , _{CrO2 , barium} ferrite and other oxide magnetic powders containing
Additives such as metal magnetic powders such as Fe and Co-Ni can be appropriately selected and used. The ferromagnetic metal thin film that can be used in the present invention is
Fe, Co, Fe-Co, Co-Ni, Co-P, Co-B,
Co-Si, Co-V, Co-Ru, Co-Cr, Co-Cu,
Co-Ti, Co-Mo, Co-W, Co-Ni-Cr, Co
Examples include -Fe-Cr, Co-Si-Sm, Co-Ni-Mg, and partial oxide films and partial nitride films thereof. Supports used in the present invention include polyesters such as polyethylene terephthalate, polyolefins such as polypropylene, cellulose derivatives such as cellulose diacetate and nitrocellulose, polyvinyl chloride, aromatic polyamides, polyimides, and the like. The manufacturing method of the present invention for manufacturing a magnetic recording medium made of the above-mentioned constituent materials involves preparing a magnetic paint made of magnetic powder, an organic solvent, etc. using a compound that can be polymerized by electron beam irradiation as a binder, and applying the magnetic paint to the magnetic recording medium. It is coated on the support in advance by a coating method selected from air doctor coat, air knife coat, squeeze coat, impregnation coat, reverse roll coat, gravure coat, kiss coat, spray coat, spin coat, etc., dried and rolled up. The wound roll is attached to an apparatus for carrying out the method of manufacturing a magnetic recording medium of the present invention, which is a modified take-up vapor deposition machine described later, and a ferromagnetic metal thin film is formed on the coated magnetic layer. For this purpose, a thin film forming method such as an electron beam evaporation method, an ion plating method, or a sputtering method may be used. Next, an electron beam is irradiated from the surface side of the ferromagnetic metal thin film to wind it up. The electron beam accelerator used for electron beam irradiation is preferably a single-stage acceleration curtain beam type accelerator. Of course, other types of accelerators may be used, but considering the irradiation in a vacuum, the effective emission of bremsstrahlung X-rays from the ferromagnetic metal thin film layer, and the thickness of the coated magnetic layer, it is necessary to It is necessary to optimize the energy for polymerization and curing. The manufacturing method of the present invention does not form a ferromagnetic metal thin film after polymerizing and hardening the coated magnetic layer, but forms a ferromagnetic metal thin film with the coated magnetic layer in an uncured state, so that some of the deposited atoms are removed. , diffuse into the coated magnetic layer, and form an intermediate layer with the atoms as nuclei. In addition, these atoms are active and can catalyze polymerization, and some energy is lost while the electron beam passes through the ferromagnetic metal thin film.
Since it emits so-called bremsstrahlung X-rays, the X-ray source is in close contact with the coated magnetic layer, which increases the degree of polymerization and makes the coated magnetic layer harder than with electron beam irradiation alone, making it more durable. This is something that can improve sexual performance. The present invention will be explained in more detail by examples.
The present invention is not limited to the following examples. Prior to describing the embodiments, a winding vapor deposition apparatus used to carry out the method for producing a medium of the present invention will be outlined with reference to FIG. A web (hereinafter simply referred to as a web) 5 is coated on a support with so-called magnetic paint in which magnetic powder is dispersed in a compound that can be polymerized by electron beam irradiation. Then, it is configured to move from the sending shaft 7 to the winding shaft 8. First, a ferromagnetic metal thin film is formed on the coating surface side of the web 5 along the cooling can 6 using a limited vapor flow 11 . Next, electron beam irradiation is performed along the cooling can 6 in order to polymerize the binder. This situation is schematically illustrated by filament 9 and electron beam 10. The limited vapor flow 11 is, for example, vapor generated when the evaporation material 13 charged in the evaporation source container 12 reaches the evaporation temperature heated by the electron beam 15 emitted from the heating electron source 14 and is emitted. In this case, the flow is limited by a mask 16 that determines the minimum angle of incidence for oblique deposition. The above configuration is arranged in a vacuum container 18 that is maintained in a vacuum by an exhaust system 17. 19 is a free roller, and 20 is an electron beam shielding plate. Example 1 A magnetic paint was prepared by mixing and dispersing paint components consisting of 80 parts by weight (hereinafter expressed as "parts") of CrO ₂ , 14 parts of urethane acrylate, 6 parts of diethylene glycol diacrylate, and 100 parts of methyl ethyl ketone in a ball mill for 72 hours. This magnetic paint has a thickness of 8.5μ
After the solvent was evaporated, the film was coated on a polyethylene terephthalate film with a reverse roll coater to a film thickness of 2.5 μm, and then dried. This film was mounted on the apparatus shown in Fig. 2, and Co-Ni-Cr (Co70, Ni15,
Co-Ni-Cr thin film with a thickness of 0.13μ
m was formed. The degree of vacuum was 2 × 10 ^-6 Torr, the minimum angle of incidence was 40°, and a cooling canister with a diameter of 1 m was used.
The treatment was carried out while moving at 30 m/min. Next, in a state along the same cooling can, the accelerating voltage
It was irradiated with a 110 KV electron beam at a current density of 20 μA/cm ² and wound up. The film in this state was taken out into the atmosphere, and myristic acid was dissolved in methyl isobutyl ketone.
A 200ppm solution was applied using the same reverse roll coater to form a lubricant layer with a dry thickness of approximately 40 mm.
A magnetic tape A having a width of 1.5 mm was manufactured. Example 2 A magnetic paint was prepared by mixing and dispersing paint components consisting of 80 parts of Co--Ni (20 parts of Ni) alloy fine powder, 14 parts of urethane acrylate, 6 parts of pentaerythritol tetraacrylate, and 100 parts of cyclohexanone in a ball mill for 72 hours. This magnetic paint was applied onto a 7 μm thick polyethylene terephthalate film using a reverse roll coater so that the film thickness after evaporating the solvent was 2 μm. The film thus obtained was moved at a speed of 60 m/min using the device shown in Figure 2, and was
A Co--Ni (20 parts Ni) thin film was formed to a thickness of 0.14 μm by electron beam evaporation in oxygen at 10 ⁻⁵ Torr. A cooling can with a minimum incident angle of 37° and a diameter of 1 m was used. Next, along the same cooling cann, it was irradiated with an electron beam at an accelerating voltage of 130 KV at a current density of 30 μA/cm ² and wound up. The film in this state was taken out into the atmosphere, and myristic acid was applied in the same manner as in Example 1 to produce a magnetic tape B having a width of 8 mm. Comparative Example 1 80 parts of CrO ₂ , 12 parts of vinyl chloride-vinyl acetate-vinyl alcohol copolymer, 8 parts of acrylonitrile-butadiene copolymer, methyl isobutyl ketone
A magnetic paint was prepared by mixing and dispersing 100 parts of paint components in a ball mill for 72 hours. Using this, magnetic tape C was manufactured in the same manner as in Example 1 except that electron beam irradiation was not performed. Comparative Example 2 Magnetic tape D was manufactured in the same manner as in Example 2 except that the order of electron beam irradiation and Co--Ni thin film formation was reversed. Evaluation V. which prototyped magnetic tapes A to D.
Changes in S/N with repeated use of TR were investigated. Measurement is 5℃80%RH, 25℃55%RH, 30℃80
%RH and 40°C and 80%RH, but the results at 40°C and 80%RH, which was the worst condition, are summarized in the following table. S/N is the ratio of the signal output of the luminance signal to the noise output. A signal with a center frequency of 5.5 MHz is measured using an amorphous head (track width 20 μm, gap length 0.3 μm) at a magnetic head/tape relative speed of 3.5 m/sec. This is a relative comparison value with the initial value as 0dB. S/
The number of passes where N decreased by 3 dB and the results of repeated running are shown. In addition, the cause of the decrease in S/N and the surface observation results after the final test are also listed.

[Table] As is clear from the above table, the durability of the magnetic recording medium obtained by the manufacturing method of the present invention is at a practical level. [Effects of the Invention] The present invention provides a method for forming a coated magnetic layer by coating a magnetic coating containing a compound having an unsaturated bond as a binder that can be polymerized by electron beam irradiation on a support. Among two-layered media suitable for recording and reproducing broadband signals, a laminated type with a coated magnetic layer and a ferromagnetic metal thin film layer is produced by forming a ferromagnetic metal film on top and then performing electron beam irradiation in a vacuum. In the production of
It is possible to mass-produce media with durability at a practical level.

[Brief explanation of drawings]

FIG. 1 is an enlarged sectional view of a magnetic recording medium manufactured by the manufacturing method of the present invention, and FIG. 2 is an example of a configuration diagram of a main part of an apparatus for carrying out the manufacturing method of the present invention. DESCRIPTION OF SYMBOLS 1... Support, 2... Coated magnetic layer, 2a... Binder, 2b... Powdered magnetic material, 2c... Intermediate layer,
3...Ferromagnetic metal thin film layer, 10...Electron beam, 11
...Metal vapor flow.

Claims (1)

[Claims] 1. After forming a coated magnetic layer by coating a magnetic paint containing a compound having an unsaturated bond as a binder that can be polymerized by electron beam irradiation on a support, a ferromagnetic metal thin film is formed on the coated magnetic layer. 1. A method for manufacturing a magnetic recording medium, which comprises forming a compound having an unsaturated bond, and subsequently irradiating the compound with an unsaturated bond in a vacuum to polymerize the compound having an unsaturated bond.