JPH0516085B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a magnetic recording medium suitable for short wavelength recording and reproduction, and a method for manufacturing the same. [Conventional structure and its problems] Magnetic recording media are generally produced by preparing a magnetic paint in which oxide-based magnetic powder or metal magnetic powder is dispersed in a binder solution, and applying this to a support such as a polymer film. Apply it on the body to form a magnetic layer, align it with a magnetic field, dry it,
Manufactured through cutting and other finishing operations. Video tapes, whose usage has been rapidly increasing in recent years, are
Since it comes into sliding contact with the magnetic head at a high relative speed of 4m/sec to 6m/sec, there is a demand for improved durability of the magnetic layer, and improvements in the binder have been made mainly from the viewpoint of materials.
It has become known that magnetic layers using binders made from polymerized compounds having unsaturated bonds that can be polymerized by electron beam irradiation have excellent durability, and efforts are being made to put them into practical use. However, structures with a polymer substrate as a support and a coated magnetic layer on top of which the binder is a polymer polymerized by electron beam irradiation suffer from dimensional changes over time and durability. However, there was a drawback in that the properties were insufficient in the usage environment, especially under high humidity. [Object of the Invention] The present invention has been made in view of the above-mentioned circumstances, and it is an object of the present invention to provide a magnetic recording medium with little dimensional change and excellent durability, and a method for manufacturing the same. [Structure of the Invention] The magnetic recording medium of the present invention is characterized in that a metal thin film layer is interposed between a polymer substrate and a coated magnetic layer whose binder is a polymer polymerized by electron beam irradiation. shall be. The method for manufacturing a magnetic recording medium of the present invention involves forming a metal thin film on a polymer substrate by vacuum evaporation, and bonding a compound having an unsaturated bond that can be polymerized by electron beam irradiation onto the metal thin film. The method is characterized in that after applying a magnetic paint as a coating agent, electron beam irradiation is performed from the coated surface side to polymerize the compound having the unsaturated bond. [Description of Examples] FIG. 1 is an enlarged cross-sectional view of a magnetic recording medium of the present invention, in which a metal thin film layer 2 is arranged on a polymer substrate 1, and a coated magnetic layer 3 is arranged thereon. . The coated magnetic layer 3 uses as a binder a polymer obtained by polymerizing a compound having an unsaturated bond that can be polymerized by electron beam irradiation. Polymer substrates that can be 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,
Examples include polyimide. Those that can be used as the metal thin film layer formed on the above substrate include Cu, Pb, Zn, Sn, Si,
Examples include single substances or alloys of Ti, Ni, W, Mo, Ta, B, etc. Polymers that can be used as the binder of the present invention are those obtained by polymerizing a compound having an unsaturated bond that can be polymerized by electron beam irradiation, and typically include an acryloyl group, an acrylamide group, an allyl group, Examples include polymerized compounds containing vinylthioether groups and unsaturated polyesters. The molecular weight is preferably in the range of 1,000 to 20,000. The magnetic powder that can be used in the present invention is γ-
Fe ₂ O ₃ , Co-doped γ-Fe ₂ O ₃ , Fe ₃ O ₄ ,
Oxide magnetic powder such as CrO ₂ and barium ferrite,
Metal magnetic powders such as Co, Fe, Co-Ni, Co-Fe, etc., non-magnetic powders, organic materials, etc. added to the binder can be appropriately selected depending on the purpose. Next, the outline of the method for manufacturing the magnetic recording medium of the present invention will be explained. First, a metal thin film layer is formed on a polymer substrate by vacuum evaporation. The thickness of the metal thin film is 0.1 μm to 2 μm, preferably 0.3 μm to 1 μm, to obtain the effects described later, so electron beam evaporation or ion plating is more suitable than sputtering. . Next, a coated magnetic layer is formed by applying the magnetic paint using a coating method selected from air doctor coating, squeeze coating, air knife coating, impregnation coating, reverse roll coating, gravure coating, kiss coating, spray coating, spin coating, etc. After coating and drying the organic solvent used during coating, electron beam irradiation is performed. Alternatively, calendering can be combined, but it is of course possible to incorporate other finishing operations as appropriate without departing from the gist of the present invention. Electron beam irradiation requires an electron beam accelerator, but
A single-stage acceleration curtain beam type electron beam accelerator is suitable. Of course, other types of accelerators may be used, and it is possible to select as appropriate whether the electron beam passed through a thin metal is irradiated in the atmosphere or in a vacuum. FIG. 2 is an enlarged sectional view of a magnetic recording medium schematically showing the pattern of electron beam irradiation. Since a magnetic recording medium is constructed by interposing a metal thin film layer 2 between a polymer substrate 1 and a coated magnetic layer 3, when an electron beam 4 is irradiated from the coated surface side, the electron beam 4 loses energy and The electron beam 5 passes through the coated magnetic layer 3 consisting of a binder 3a, magnetic powder 3b, and other components (not shown) and reaches the interface with the metal thin film layer 2, and a portion also passes through this metal thin film layer 2. The electron beam 7 is then separated into an electron beam 7 that advances toward the polymer substrate 1 and an electron beam 6 that is partially reflected and acts on the coated magnetic layer 3 again. Energy selection of electron beam 4 per 1 μm coating thickness
40KeV to 80KeV, preferably from 55KeV
By using the 65KeV standard, the amount of electron beam 7 acting on the polymer substrate 1 can be almost eliminated.
In addition, since the reflected electron beam 6 effectively contributes to the polymerization of the binder 3a of the coated magnetic layer 3, the dispersion of the magnetic powder is improved in a configuration in which the metal thin film layer 2 is not interposed between the polymer substrate 1 and the coated magnetic layer 3. Polymerization can be sufficiently carried out even in regions that are not affected by the electron beam due to local disturbance and agglomeration, thereby improving durability. In addition, as the polymerization progresses, internal distortion remains in the coated magnetic layer 3, but this is mainly due to compressive stress, and stress relaxation causes dimensional changes over time, especially so-called cutting, where the magnetic recording medium curves. There were problems in inducing and proceeding with high-density recording. In the product of the present invention, the metal thin film layer has the same internal strain, and this strain is due to the opposite tensile stress to the coated magnetic layer, so that both are balanced.
Dimensions can be kept stable. The present invention will be explained in more detail with reference to specific examples, but the present invention is not limited to the following examples and is limited to the description as a magnetic tape, but it can also be used in magnetic disks and magnetic sheets. Of course, the types of signals to be recorded and reproduced are not limited. Example 1 A polyethylene terephthalate substrate with a thickness of 8.5 μm was subjected to surface treatment using glow discharge at 500 V and 2 A for 2 seconds in argon at 0.1 Torr, and then a cooling can (diameter 50 cm) was prepared in which the surface temperature was maintained at 10°C.
0.3μm of Ti was electron beam evaporated while winding along the . Next, the magnetic paint was applied using a reverse roll coater so that the film thickness after evaporating the solvent was 2 μm. The magnetic paint contains cobalt-containing γ-
Fe ₂ O ₃ 80 parts by weight (hereinafter expressed as "parts"), urethane acrylate 14 parts, diethylene glycol diacrylate 6 parts, methyl isobutyl ketone 100 parts,
A paint component consisting of 3 parts of stearyl stearate was mixed and dispersed in a ball mill for 72 hours. After coating and drying, an electron beam with an acceleration voltage of 120 KV was irradiated for 1 second at a current density of 20 μA/cm ² from the surface side of the coated magnetic layer. This was cut into 8 mm width to obtain magnetic tape A. Example 2 A polyethylene terephthalate substrate with a thickness of 8.5 μm was subjected to surface treatment using glow discharge at 500 V and 2 A for 2 seconds in argon at 0.1 Torr, and then treated along a cooling can (diameter 50 cm) that maintained the surface temperature at 10°C. Cr was deposited by electron beam to a thickness of 0.35 μm while winding the film. Next, among the constituent materials of the coated magnetic layer, magnetic powder is
Magnetic tape B was obtained under the same conditions as in Example 1 except that 80 parts of Co75%Fe25% alloy fine particles were used. [Comparative Example] A polyethylene terephthalate substrate having a thickness of 8.5 μm was subjected to surface treatment using glow discharge at 500 V and 2 A for 2 seconds in argon at 0.1 Torr, followed by coating drying and electron beam irradiation. The same magnetic paint was used as in Example 1 and Example 2, and the electron beam irradiation conditions were also the same. Tape C was a comparative example corresponding to Example 1, and Tape D was a comparative example corresponding to Example 2. The above tapes were evaluated for dimensional stability and durability. The deck used was a prototype deck with a cylinder diameter of 4cm, a magnetic head with a ferrite head with a track width of 20μm and a gap length of 0.3μm, a dropout of 15μsec, and signal output drops of -16dB or more were counted and expressed as a count value for 1 minute. . The dimensional stability was evaluated in a curved state with the magnetic layer 8 on the inside as shown in FIG. 3, using h as a parameter. When h shows a negative value, it represents a state of being curved with the substrate 9 on the inside. Table 1 shows the stability of dimensions over time, and Table 2 shows the results of durability in terms of dropout changes.

【table】

[Table] Regarding the durability of the magnetic recording medium of the present invention, in terms of the stability of the playback output in still mode on a video tape recorder, at 40°C and 80%RH, the playback output drops by 3 dB from the initial value. The products of the present invention were superior in terms of time of 72 minutes, 81 minutes, 21 minutes, and 19 minutes for tapes A, B, C, and D, respectively, and in conjunction with Tables 1 and 2,
The manufacturing method of the product of the present invention and the medium obtained thereby can be said to be a magnetic recording medium with greatly improved practical performance. [Effects of the Invention] The present invention provides a magnetic recording medium in which the binder used in the magnetic layer is a polymer polymerized by electron beam irradiation, in which a metal thin film layer is interposed between the support and the magnetic layer, By balancing the internal stress of the magnetic layer and metal thin film layer, we prevent dimensional changes and
The electron beam reflected from the metal thin film layer during electron beam irradiation creates a magnetic layer with no end-polymerized portion of the binder, so there is almost no increase in dropout with repeated use and still durability is achieved, making it highly durable for practical use. It can provide an excellent medium for

[Brief explanation of the drawing]

FIG. 1 is an enlarged cross-sectional view of the magnetic recording medium of the present invention;
FIG. 2 is an enlarged sectional view of the magnetic recording medium of the present invention schematically showing the state of electron beam irradiation, and FIG. 3 is a schematic diagram showing dimensional changes of the magnetic recording medium. 1... Polymer substrate, 2... Metal thin film layer, 3...
Coated magnetic layer, 3a...binder, 3b...magnetic powder, 4, 5, 6, 7...electron beam.

Claims (1)

[Scope of Claims] 1. A magnetic recording medium characterized in that a metal thin film layer is interposed between a polymer substrate and a coated magnetic layer whose binder is a polymer polymerized by electron beam irradiation. 2. After forming a metal thin film on a polymer substrate by vacuum evaporation, and applying a magnetic paint containing as a binder a compound having an unsaturated bond that can be polymerized by electron beam irradiation on the metal thin film, A method for producing a magnetic recording medium, characterized in that the compound having an unsaturated bond is polymerized by irradiating an electron beam from the coated surface side.