JPH0685213B2 - Method of manufacturing magnetic recording medium - Google Patents

Description

The present invention relates to a magnetic recording medium such as a video tape, an audio tape, a computer tape or the like.

[Prior art]

The method for producing a magnetic recording medium which is widely used at present is to apply a magnetic coating liquid on a non-magnetic support, dry it, and then smooth the coating layer with a calendar consisting of a mirror-finish metal roll and an elastic roll. After that, the binder is cross-linked by means such as heating. However, this manufacturing method requires a smoothing step in addition to the coating and drying steps,
For this reason, the method has a high manufacturing cost. Further, in recent years, magnetic recording media have been required to have high electromagnetic conversion characteristics and running durability, but conventional manufacturing methods have not been able to meet these requirements.

As one proposal for preventing the above-mentioned drawbacks, it is possible to cure by radiation irradiation using a radiation-polymerizable compound as a binder instead of a thermosetting system such as a polyisocyanate compound and the like. 122802, 56
However, even if a radiation-polymerizable compound is used as a binder, the above problems cannot be solved.

[Problems to be solved by the invention]

Symposium as a technology to improve the surface smoothness of the coating layer
on Magnetic Media Manufacturing Methods (198
Dr. Nab proposed Transfer Coating in May 3rd, Honolulu)
(PAPER No.B-4), but the technology disclosed here cannot increase the concentration of the ferromagnetic fine powder (so-called pigment-vehicle ratio), and thus manufactures a magnetic recording medium. The method was unusable. That is, D
The r.Nablo method cannot secure a sufficient electromagnetic conversion characteristic and cannot be adopted as a method for manufacturing a magnetic recording medium.

An object of the present invention is, firstly, a method of manufacturing a magnetic recording medium having a high degree of electromagnetic conversion characteristics, a second method of manufacturing a magnetic recording medium having good durability, and a third method of magnetic recording having a low manufacturing cost. A fourth object is to provide a method for manufacturing a medium, and fourthly, a method for manufacturing a magnetic recording medium having a magnetic surface having good smoothness.

[Means for solving problems]

In order to solve the above problems, the present inventors have made earnest studies and as a result, the above object is to provide a magnetic coating liquid comprising a ferromagnetic fine powder, a binder containing at least a radiation-polymerizable compound and an organic solvent as a non-magnetic support. After applying a magnetic layer on the body, when the solvent content of the magnetic layer is 0.05 to 10 wt% by drying, the surface of the magnetic layer is brought into contact with a mirror-finished roll or strip at a contact pressure of 1 to 50 kg / cm. It has been found that this can be achieved by a method for producing a magnetic recording medium, characterized in that the roll or the strip and the magnetic layer are peeled off after being brought into contact with each other.

In the method of the present invention, the magnetic layer can be stripped and then irradiated with radiation. In yet another embodiment, the magnetic layer surface is contacted with a mirror-finished roll or strip, and then the roll or strip is contacted. Irradiation can be performed during the process of separating the magnetic layer and the magnetic layer.

As the ferromagnetic powder used in the present invention, ferromagnetic iron oxide fine powder, Co-doped ferromagnetic iron oxide fine powder, ferromagnetic chromium dioxide fine powder, ferromagnetic alloy powder, barium ferrite, etc. can be used. The acicular ratio of ferromagnetic iron oxide and chromium dioxide is about 2/1 to 20/1, preferably 5/1 or more and the average length is 0.2 to
A range of about 2.0 μm is effective. The ferromagnetic alloy powder has a metal content of 75 wt% or more, and a metal content of 80 wt% or more is a ferromagnetic metal (that is, Fe, Co, Ni, Fe-Co, Fe-Ni, Co-Ni, Fe-Co-
Ni) with a major axis of about 1.0 μm or less.

The binder used in the present invention is a thermoplastic resin such as vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl acetate-malenic acid copolymer, vinyl chloride-vinyl acetate-acrylic acid copolymer, vinyl chloride- Vinyl propionate-
Maleic acid copolymer, vinyl chloride-vinyl propionate-butenoic acid copolymer, vinylidene chloride-vinyl acetate-maleic acid copolymer, vinyl chloride-vinyl acetate-vinyl alcohol copolymer, vinyl chloride-vinyl propionate-
Vinyl acetate copolymers such as vinyl alcohol copolymers,
Cellulose nitrate, cellulose acetate propionate, cellulose diacetate, fibrin resin such as cellulose propionate, polyvinyl formal, polyvinyl acetal, polyvinyl butyral and other acetal resin, phenoxy resin, urethane resin, vinyl chloride- Vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, acrylic ester-acrylonitrile copolymer, vinylidene chloride-acrylonitrile copolymer, butadiene acrylonitrile copolymer, polyester resin, polyisocyanate compound, a radiation-polymerizable compound Polyester type urethane acrylate,
Acrylic and methacrylate oligomers such as polyether type urethane acrylate, polyester ether type urethane acrylate, epoxy acrylate, polyester acrylate, and polyether acrylate. Specific examples of these are A. Vrancken “Fa
Cited by the fipec Congress " 11 19 (1972). Is. Other radiation-polymerizable compounds include ethylene glycol diacrylate, diethylene glycol diacrylate, triethylene glycol diacrylate, trimethylolpropane triacrylate, pentaerythritol tetraacrylate, dipentaerythritol hexaacrylate, dipentaerythritol heptaacrylate, bis-2. -Acryloyloxyethyl-hydroxyethyl isocyanurate, tris (β-acryloyloxyethyl) isocyanurate and other polyfunctional acrylate compounds, and polyfunctional methacrylate compounds thereof, and further acrylic acid, methyl acrylate and their homologs Body acrylic acid alkyl ester, methacrylic acid alkyl ester, styrene, α-methylstyrene,
1 carbon-carbon unsaturated bond such as acrylonitrile, acrylamide, vinyl acetate, vinyl propionate in the molecule
It is a compound having more than one.

The above binders can be used as a mixture of two or more kinds.
It is also possible to add a thermoplastic resin to the radiation-polymerizable compound.

Among the above, a particularly preferable binder is a fibrin type or
It is a three-component system of a vinyl chloride-vinyl acetate copolymer, urethane acrylate and a polyfunctional acrylate compound. In this case, a preferable ratio is a ratio of fibrous resin or vinyl chloride-vinyl acetate copolymer to urethane acrylate is 4/1 to 1/2, and a ratio of the sum of these and polyfunctional acrylate is 8/2 to 1/1. is there.

In the present invention, radiation is applied in a state (process) in which the mirror-finished roll or strip, the magnetic layer and the non-magnetic support have a Sangertian structure or after peeling from the roll or strip. It is particularly preferable to irradiate in the state in which the above-mentioned Saint-Gerchi structure is formed, and it is easiest to peel the magnetic layer from a mirror-finished roll or strip. When the irradiation is performed with the Saint-Gerache structure, the irradiation is performed from the non-magnetic support side, but when the irradiation is performed after peeling from the roll or the strip, the irradiation may be performed from the magnetic layer side.

As the solvent used, acetone, methyl ethyl ketone,
Ketones such as methyl isobutyl ketone, methyl isobutyl ketone and cyclohexanone; ester systems such as methyl acetate, ethyl acetate, butyl acetate, ethyl lactate and glycol monoethyl ether acetate; glycols such as ether, glycol dimethyl ether, glycol monoethyl ether and dioxane Ether type; benzene, toluene,
Aromatic hydrocarbons such as xylene; chlorinated hydrocarbons such as methylene chloride, ethylene chloride, carbon tetrachloride, chloroform, ethylene chlorohydrin, dichlorobenzene, and tetrahydrofuran can be selected and used.
The ratio of ferromagnetic support to binder and solvent in the magnetic coating liquid is by weight.
It can be adjusted arbitrarily within the range of 2/1/6 to 6/1/15.

In the present invention, as a method for applying to a non-magnetic support, air doc coat, blade coat, air knife coat, squeeze coat, impregnation coat, reverse roll coat, transfer roll coat, gravure coat, kiss coat, cast coat, Spray coat, etc. can be used, and other methods are also possible, and specific explanations for these can be found in "Coating Engineering" pp. 253-277 (March 20, 1972)
Published by Hiasakura Shoten).

The thickness of the magnetic layer is applied so that the dry thickness is in the range of 1 to 10 μm.

As the non-magnetic support, polyethylene terephthalate,
Polyesters such as polyethylene-2,6-naphthalate; Polyolefins such as polyethylene and polypropylene; Cellulose derivatives such as cellulose triacetate, cellulose diacetate, cellulose acetate butyrate, cellulose acetate propionate; polyvinyl chloride, polyvinylidene chloride, etc. Vinyl resin; non-magnetic metals such as aluminum, copper, tin, zinc, or non-magnetic alloys containing these, in addition to plastics such as polycarbonate, polyimide, and polyamide-imide;
Alternatively, a support in which these nonmagnetic metals are provided as a thin layer on a plastic support by a method such as vacuum deposition can be used. These supports are preferably subjected to physical treatment such as undercoat layer coating or corona treatment before coating the magnetic layer. A back coat layer may be provided on these supports before use. After coating the magnetic layer, a back coat layer may be provided on the side opposite to the magnetic layer.

Radiation irradiation in the present invention means ultraviolet rays, electron beams, γ-
Rays, β-rays, X-rays, etc., but electron beams are more preferable. Scanning method as electron beam irradiation device,
Gubble skinning method or curtain beam method Broad beam curtain method can be adopted.

As electron beam characteristics, the acceleration voltage is 100 to 1000 kV, preferably 150 to 300 kV, and the absorbed dose is 1.0 to 20 megarads, preferably 2 to 10 megarads. Acceleration voltage
When the voltage is 100 kV or less, the amount of energy transmitted is insufficient and 1000 kV
If it exceeds V, the energy efficiency used for polymerization is reduced and it is not economical. If the absorbed dose is 1.0 mega rad or less, the curing reaction is insufficient and the magnetic layer strength cannot be obtained, and if it is 20 mega rad or more, the energy efficiency used for curing is reduced, and the irradiated object heats up, especially non-magnetic. The support is deformed, which is not preferable.

Drying after coating the magnetic layer is preferably 0.5 to 8 wt% when the amount of residual solvent is 0.05 to 10 wt% of the magnetic layer due to hot air.
More preferably, when it reaches 1.5 to 5 wt%, the mirror-finished roll or strip comes into contact. The contact pressure at this time is 1 to 50 kg / cm, preferably 5 to 30 kg / cm. After contact 0.1
The magnetic layer is peeled off from the support band in about 5 seconds. If necessary, the mirror roll or the belt-like material may be heated to about 40 ° C to 100 ° C. When using radiation irradiation, peeling is easy if irradiation is performed before the peeling after contact, and the smoothness of the magnetic layer can be maintained. It is also possible to provide a drying zone once even after peeling from the roll or strip. Further, after drying, it may be heat-cured or irradiated with radiation if necessary.

If necessary, magnetic field orientation can be easily applied after coating. In this case, a solenoid, electromagnet, or permanent magnet can be used.

Further, additives such as lubricity, abrasives, dispersants, antistatic agents and rust preventives may be added to the magnetic coating liquid of the present invention.
In particular, the lubricant includes saturated and unsaturated higher fatty acids, fatty acid esters, higher fatty acid amides, higher alcohols, silicone oils, mineral oils, vegetable oils, and fluorinated compounds,
These may be added at the time of preparing the coating liquid, or may be dissolved in an organic solvent after being peeled from the roll or the strip, or may be directly applied or sprayed on the surface of the magnetic layer.

Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples. In the following examples and comparative examples, all "parts" indicate "parts by weight".

〔Example〕

Examples 1 and 2, Comparative Examples 1 and 2 The coating material obtained by kneading the above components with a ball mill for 50 hours was applied onto a polyethylene terephthalate film 1 having a thickness of 10 μm so that the thickness of the coating liquid 2 was 20 μm, as shown in the accompanying drawing. After magnetic field orientation with a Co magnet, first
It was dried at 100 ° C. in the drying unit 5 and nipped on the mirror surface roll 7 (nip pressure 20 Kg / cm) and irradiated with an electron beam. Electron beam is accelerating voltage 1
Irradiation with 10 Mrad at 65 kV. Then, it was peeled off and the second drying was performed. The amount of residual solvent in the nip portion 6 was obtained as shown in Table 1 by controlling the roll and web speeds.

Example 3 In Example 1, the electron beam irradiation was not performed in the irradiation unit 9 in the attached figure, but the electron beam irradiation was performed under the same conditions immediately after the peeling. Sample No.5

Comparative Example 3 The magnetic coating liquid 2 of Example 1 was applied to a polyethylene terephthalate film 1 having a thickness of 10 μm, magnetic field was oriented with a Co magnet, dried at 100 ° C., smoothed with a calendar roll at 60 ° C., and then irradiated with electron beam. did. The irradiation conditions were 165 kV accelerating voltage and 10 Mrad. The residual solvent amount when smoothing with a calendar roll was 0.1 wt% or less.
Sample No.6

The amount of the residual solvent was measured by a gas chromatograph and determined by the weight% with respect to the magnetic layer.

Visually observe the state of the above samples after peeling,
The good ones carried out the following experiments.

Surface roughness of magnetic layer: The surface of the magnetic layer was measured with a surface roughness meter manufactured by Tokyo Seimitsu Co., Ltd. and shown by the center line average roughness defined by item 5 of JIS-B0601 (cutoff is 0.25 mm).

Video S / N: A gray signal of 50% set-up was recorded using an NV8200 video tape recorder manufactured by Matsushita Electric Co., Ltd., and noise was measured with a 925C type S / N meter manufactured by Shibasoku. Video S
/ N is the sample No. 1 for the samples No. 1 to 6
The values are shown as relative comparison values when OdB is set.

Still life: Record a constant video signal on a video tape (each sample) using a VHS video tape recorder (NV8200 manufactured by Matsushita Electric Industrial Co., Ltd.) until the reproduced still image loses sharpness. Indicates the time.

The following evaluation results are shown in Table 2.

In sample No. 4 of the comparative example, a good magnetic tape could not be obtained because a part of the magnetic layer did not peel well from the strip.

〔The invention's effect〕

From Table 2, it can be seen that the present invention shows how the surface of the magnetic layer is smooth, the electromagnetic characteristics are good, and the durability is good.

[Brief description of drawings]

The attached drawing is a side view of an embodiment explanatory drawing of the present invention. 1 ... Polyethylene terephthalate film, 2 ... Coating liquid, 3 ... Coating part, 4 ... Magnetic layer, 5 ... First drying part, 6 ... Nip part, 7 ... Mirror-finished roll, 8 ...
... Radiation irradiation device, 9 ... Irradiation unit, 10 ... Peeling unit, 11 ...
… Second drying section

Claims (3)

[Claims] 1. A magnetic coating liquid comprising a ferromagnetic fine powder, a binder containing at least a radiation-polymerizable compound, and an organic solvent is coated on a non-magnetic support to form a magnetic layer, and then the magnetic layer is dried. The magnetic layer surface is brought into contact with a mirror-finished roll or strip at a contact pressure of 1 to 50 kg / cm when the solvent content is 0.05 to 10 wt%, and then the roll or strip and the magnetic layer are peeled off. And a method for manufacturing a magnetic recording medium. 2. The method for producing a magnetic recording medium according to claim 1, wherein the magnetic layer is peeled off and then irradiated with radiation. 3. Radiation irradiation in the process from the step of contacting the surface of the magnetic layer with a mirror-finished roll or strip to the separation of the magnetic layer from the roll or strip. A method of manufacturing a magnetic recording medium according to item 1.