JPH0685215B2 - Method of manufacturing magnetic recording medium - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a magnetic recording medium, and more particularly to a method of manufacturing a magnetic recording medium having an improved degree of orientation.

2. Description of the Related Art In recent years, high density recording has been required for magnetic recording media. However, in the in-plane magnetic recording method in which the direction of magnetization, which has been widely used in the past, lies in the plane of the recording medium, the magnetizations repel each other, and it is impossible to achieve a higher density than a certain level.

Therefore, a perpendicular magnetic recording system, which does not repel the magnetization because the direction of the magnetization is perpendicular to the surface of the recording medium, has been attracting attention.

Among them, in a magnetic recording medium using a coating type recording layer, generally, a magnetic paint is applied on a base film, and this is passed through a magnetic field in an undried state, and the easy axis of magnetization of magnetic particles is perpendicular to the perpendicular direction. A manufacturing method is used in which the film is orientated and then dried.

In this case, as the orientation magnetic field, a method using an N-S facing magnet can be mentioned, but in this method, the coating film is exposed to the orientation magnetic field for a short time, the orientation is disturbed by the influence of the demagnetizing field, and drying is performed. Since it takes a long time, there is a drawback that the magnetic particles once oriented are disturbed again during that time.

In order to solve these drawbacks, tabular ferromagnetic particles are used as magnetic particles, and a plurality of NS facing magnets 21 and 22 as shown in FIG. And a method of drying while allowing it to pass through such a magnetic field (Japanese Patent Laid-Open Nos. 58203631, 58-203632 and 58-203633), and an NS side facing the outlet side as shown in FIG. Auxiliary magnet 33,34
A method in which an N-S facing main magnet 31, 32 with a magnetic field is applied to form an orientation magnetic field, and the magnetic particles are oriented and then dried (Japanese Patent Laid-Open No. Sho 61-206).
59-139142) and the like have been proposed.

However, even these methods are still insufficient in terms of the degree of vertical orientation, surface roughness, etc., and further improvement is required.

II Object of the Invention An object of the present invention is to provide a method for producing a magnetic recording medium having an improved degree of vertical orientation and a good surface roughness.

III DISCLOSURE OF THE INVENTION Such an object is achieved by the present invention described below.

That is, according to the present invention, a magnetic coating material is applied onto a support, and the magnetic coating material is applied between N-S facing main magnets in which a plurality of ferromagnetic materials are arranged with a gap on at least one of the main magnet facing surfaces. The magnetic recording medium is characterized in that the easy axis of magnetization of the magnetic particles in the coating film is oriented substantially perpendicular to the film surface, and the coating film is dried.

IV Specific Structure of the Invention Hereinafter, the specific structure of the present invention will be described in detail.

The method for producing a magnetic recording medium of the present invention comprises applying a magnetic coating material on a support and allowing it to pass through a magnetic field as shown below so that the easy axis of magnetization of the magnetic particles in the coating film is almost the same as the film surface. It is oriented vertically and dried.

As the magnetic field, an N-S facing main magnet in which a ferromagnetic material as a minute yoke is arranged with a gap on at least one main magnet facing surface of the N-S facing main magnet is used. And, the NS having the ferromagnetic material arranged with such a gap
One or more sets of opposing main magnets may be arranged. FIG. 1 shows an embodiment in which ferromagnetic bodies are arranged with a gap on both main magnet facing surfaces of the N-S facing main magnet.

Next, description will be made with reference to FIG.

The magnets used in the present invention are NS facing main magnets 11 and 12, and the ferromagnetic bodies 13 and 12 have a gap between the facing surfaces of the main magnets 11 and 12.
14 are arranged.

It is preferable to arrange about 2 to 100 such ferromagnetic bodies 13 and 14 on the facing surfaces of the main magnets 11 and 12, respectively. Further, the gap is 0.5 to 20 mm, preferably about 1 to 10 mm. And the length of one of the ferromagnets 13 and 14 is 0.5-
20mm, the height of each piece is about 1-10mm.

As the ferromagnetic material, iron, cobalt, nickel, permalloy, sendust, so-called amorphous alloy, ferrite, silicon steel plate and the like are preferable.

It should be noted that the number of main magnets may be not limited to one, and a plurality of main magnets may be used. At this time, at least one of the main magnets should have a ferromagnetic material with a gap, and the main magnets should be connected without a gap. Various arrangements are possible, such as arranging with a gap.

In this case, it is preferable to use a main magnet having a magnetic field strength of about 1000 to 6000G.

The main magnet may be a permanent magnet, an electromagnet, a solenoid or the like, and the opposing magnetic pole gap is about 5 to 30 mm and the length of the magnetic pole is about 100 to 5000 mm.

With such a structure, the magnetic field oscillates, and the effect of this oscillating magnetic field improves the vertical orientation degree and the surface roughness.

The length of one of the ferromagnetic materials and the range of the gap between them are the range of the region where this oscillating magnetic field preferably acts.

Although FIG. 1 shows an example in which the ferromagnetic bodies 13 and 14 are provided on the facing surfaces of both the main magnets 11 and 12, the ferromagnetic body may be provided only to one of the main magnets.

In this case, when using a plurality of N-S facing main magnets in which a ferromagnetic material is placed with a gap on one of the main magnet facing surfaces, there is no particular limitation on the way of placement.

For example, a method of arranging the ferromagnetic material on the coating surface side, a method of arranging it on the support side, a method of alternately or periodically arranging the ferromagnetic material on the coating surface side or the support side can be mentioned.

To apply magnetic paint on the support, gravure code,
Any coating method such as reverse roll coating, air knife coating, air doctor coating, blade coating, kiss coating or spray coating may be used.

The speed at which the above-mentioned coated material passes through the above-mentioned magnetic field is 2 to
About 500 m / min is preferable.

Drying after the orientation treatment is preferably performed at 30 to 150 ° C. and at a speed of about 2 to 500 m / min with a heater source such as hot air or a far infrared lamp.

The magnetic powder used in the magnetic coating material of the present invention is α-Fe ₂ O ₃ , Fe ₃ O ₄ , Co-doped α-Fe ₂ O ₃ , Co-doped α-Fe ₂ O.
₃ -Fe ₂ O ₃ solid solution, CrO ₂ , Co-based compound-adhered α-Fe ₂ O ₃ , Co-based compound-adhered Fe ₃ O ₄ , Ba ferrite, etc. granular, needle-shaped, plate-shaped,
Although it has a polyhedral shape and the like, Ba ferrite is particularly preferable.

As the Ba ferrite, a hexagonal plate-shaped ferrite system is preferable, and further, in order to improve the degree of vertical orientation, it is preferable that the plate-shaped ratio (average grain size / average thickness) is 6 or more. The plate ratio can be controlled up to about 30.

As Ba ferrite, Ba ferrite such as BaFe ₁₂ O ₁₉ or a part of Ba and Fe of Ba ferrite is Ca, Sr, Pb, C ₀ , Ni, Ti, Cr, Zn, In, Mn, Cu,
Examples include Ge, Nb, Zr, and those substituted with other metals.

The binder used in the magnetic paint may be various binders, but a binder obtained by curing a radiation curable compound is preferable.

Specific examples of the radiation-curable compound include acrylic double bonds such as acrylic acid, methacrylic acid, or ester compounds thereof having an unsaturated double bond having radical polymerizability, and an allyl double bond such as diallyl phthalate. It is a resin containing or introducing into a molecule of a thermoplastic resin a group such as a heavy bond, an unsaturated bond such as maleic acid or a maleic acid derivative, which is crosslinked or polymerized by irradiation with radiation. In addition, any compound having an unsaturated double bond that undergoes cross-linking polymerization upon irradiation with radiation can be used.

The resin containing or introduced into the molecule of the thermoplastic resin a group to be crosslinked or polymerized and dried by irradiation with radiation is one containing maleic acid, fumaric acid or the like in the resin, the content of which is crosslinked during production, It is 1 to 40 mol%, preferably 10 to 30 mol% in the acid component due to radiation curability and the like.

As an example of the thermoplastic resin that can be modified into a radiation curable resin, the following vinyl chloride copolymers are particularly suitable.

Vinyl chloride-vinyl acetate-vinyl alcohol copolymer, vinyl chloride-vinyl alcohol copolymer, vinyl chloride-vinyl alcohol-vinyl propionate copolymer, vinyl chloride-vinyl acetate-maleic acid copolymer, vinyl chloride-acetic acid Vinyl-vinyl alcohol-maleic acid copolymer, vinyl chloride-vinyl acetate-terminal OH side chain alkyl group copolymer, for example VRO manufactured by UCC
H, VYNC, VYEGX, VERR, VYES, VMCA, VAGH and the like.

Then, an acrylic double bond, a maleic acid double bond, and an allyl double bond are introduced into this to perform radiation-sensitive modification.

These may contain a carboxylic acid.

In addition, saturated polyester resin, polyvinyl alcohol resin, epoxy resin, phenoxy resin, fibrin derivative and the like are also suitable.

Other resins that can be used for radiation-sensitive modification include polyfunctional polyester resins, polyetherester resins, polyvinylpyrrolidone resins and derivatives (PVP olefin copolymers), polyamide resins, polyimide resins, phenolic resins, spiroacetal resins, An acrylic resin containing at least one of a hydroxyl group-containing acrylic ester and a methacrylic ester as a polymerization component is also effective.

And these are used individually or in combination of 2 or more types.

Elastomers or prepolymers can also be used, suitable examples being polyurethane elastomers or prepolymers.

The use of polyurethane is abrasion resistant and base film,
For example, it is particularly effective in that it has good adhesion to a PET film. As an example of the urethane compound, as the isocyanate, 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, 1,3-xylene diisocyanate, 1,4
-Xylene diisocyanate, 1,5-naphthalene diisocyanate, m-phenylene diisocyanate, p-phenylene diisocyanate, 3,3'-dimethyl-4,4'-
Diphenylmethane diisocyanate, 4,4'-diphenylmethane diisocyanate, 3,3'-dimethylbiphenylene diisocyanate, 4,4'-biphenylene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, dicyclohexylmethane diisocyanate, Desmodur L, Desmodur N, etc. Polyvalent isocyanate and linear saturated polyester (ethylene glycol, diethylene glycol, glycerin, trimethylolpropane, 1,4-butanediol,
Polyhydric alcohols such as 1,6-hexanediol, pentaerythritol, sorbitol, neopentyl glycol, 1,4-cyclohexanedimethanol and phthalic acid, isophthalic acid, terephthalic acid, succinic acid, adipic acid, sebacic acid Such as polycondensation with saturated polybasic acid),
Polyurethane elastomers and prepolymers made of polycondensation products such as linear saturated polyethers (polyethylene glycol, polypropylene glycol, polytetramethylene glycol), caprolactam, various polyesters such as hydroxyl-containing acrylic acid ester and hydroxyl-containing methacrylic acid ester are effective. is there.

By reacting a terminal isocyanate group or hydroxyl group of these urethane elastomers with a monomer having an acrylic double bond or an allyl double bond,
Radiation-sensitive modification is very effective. It also includes those containing OH, COOH or the like as a polar group at the terminal.

Further, a monomer having an unsaturated double bond having an active hydrogen that reacts with an isocyanate group and having a radiation-curable unsaturated double bond, such as a mono- or diglyceride of a long-chain fatty acid having an unsaturated double bond, is also included.

The combined use of these urethane elastomers with the above-mentioned acrylic modified vinyl chloride copolymer is particularly suitable for improving the degree of orientation and surface roughness.

In addition, acrylonitrile-butadiene copolymer elastomer and polybutadiene elastomer are also suitable.

In addition, cyclized polybutadiene, CBR-M901 made by Japan Synthetic Rubber
Also has excellent properties when combined with a thermoplastic resin.

Other suitable thermoplastic elastomers and prepolymers thereof include styrene-butadiene rubber, chlorinated rubber, acrylic rubber, isoprene rubber and cyclized products thereof (CIR701 manufactured by Japan Synthetic Rubber), epoxy-modified rubber, internal Elastomers such as plasticized saturated linear polyester (Toyobo Byron # 300) can also be effectively used by subjecting them to radiation-sensitive modification treatment.

In addition, oligomers and monomers having various radiation-curable unsaturated double bonds are also preferably used.

The weight ratio of binder to magnetic powder is about 1: 1 to 1: 9.

Further, the magnetic paint may contain a solvent, an inorganic pigment, a dispersant, a lubricant and the like.

As the support to be used, various resins such as polyester, polyamide and polyimide can be used.

Further, the support may be subjected to a base layer or a base treatment.

After forming the magnetic layer, various back coat layers and top coat layers can be formed.

V. Specific Actions and Effects of the Invention According to the present invention, at least one N-S facing main magnet having a magnetic coating applied on a support is provided with a ferromagnetic material on the facing surface of the N-S facing main magnet with a gap. By passing between magnets, the magnetic particles in the coating film are oriented with the easy axis of magnetization almost perpendicular to the film surface and dried, so that the degree of perpendicular orientation is improved and the surface roughness of magnetic recording media is improved. A manufacturing method is obtained.

VI Specific Examples of the Invention Hereinafter, the present invention will be described in more detail by showing specific examples of the invention.

Example Using a hexagonal barium ferrite having an average particle size of 0.1 μm and a plate ratio of 8 (BaFe ₁₂ O ₁₉ partially substituted with Ba and Fe was synthesized by a hydrothermal synthesis method), magnetic properties were obtained as follows. Paint created.

Barium ferrite (Hc = 800) 120 parts by weight α-Al ₂ O ₃ (0.5 μ powder) 2 parts by weight Carbon black (20 mμ) 10 parts by weight Solvent (MEK / toluene: 50/50) 100 parts by weight The above composition The mixture was mixed in a ball mill for 3 hours to thoroughly wet the barium ferrite.

Next, as a binder, vinyl chloride-vinyl acetate-vinyl alcohol copolymer (maleic acid-containing; MW40,000) 6 parts by weight (solid component conversion), acrylic double bond-introduced vinyl chloride-vinyl acetate-vinyl alcohol copolymer Combined (maleic acid-containing; MW20,000) 12 parts by weight (solid component equivalent), acrylic double bond-introduced polyether urethane elastomer (MW40,000) 9 parts by weight (solid component equivalent), pentaerythryl triacrylate 3 parts by weight, 200 parts by weight of solvent (MEK / toluene: 50/50), 4 parts by weight of stearic acid, and 2 parts by weight of butyl stearate were mixed and dissolved.

This was placed in a ball mill containing the magnetic powder mixture, and mixed and dispersed again for 42 hours. Using the magnetic coating material thus obtained, gravure coating was performed on a 75 μm polyester film.

The sample thus prepared is referred to as sample A.

This sample A is used as an N-S facing main magnet 11 and 12 (a magnetic field strength of the main magnet is 3000 G) in which ferromagnetic bodies 13 and 14 are arranged with a gap between both main magnet facing surfaces as shown in FIG. Speed between 30m /
It was passed in minutes and vertically aligned while drying. Then, it was dried from a far infrared lamp. Main magnet is magnetic pole length
It is an array of 10 pieces of 50 mm without a gap.

This is designated as Sample B.

As a ferromagnetic material, one piece is 5 mm long and one piece is 2 mm high.
A barium ferrite material was used, and the gap was set to 10 mm, and 30 main magnets 11 and 12 were arranged on the respective facing surfaces.

Next, the sample A is used as an N-S facing magnet 21,
(Magnetic field strength 3000 G, magnetic pole length 50 mm) 10 pieces were arranged at an interval of 10 cm and passed at a speed of 30 m / min, and were vertically aligned while being dried. Then, it was dried by a far infrared lamp.

This is designated as Sample C.

Further, the sample A was introduced between the N-S facing main magnets 31, 32 with the N-S facing auxiliary magnets 33, 34 mounted on the outlet side as shown in FIG. Then, it dried similarly to the sample B.

This is designated as Sample D.

In this case, the magnetic field strength of the main magnet is 3000G, and the magnetic field length of 50 mm is 10 pieces arranged side by side. The magnetic field strength of one auxiliary magnet is 1500 G, and the auxiliary magnet of 3 mm magnetic pole length is used. Magnet 20
Used individually.

In addition, the sample B in which the ferromagnetic material is not provided is referred to as E.

Further, in the sample B, F is a ferromagnetic material that is a continuous ferromagnetic material and that has no gap in the ferromagnetic material on the magnet surface.

Further, the magnet gaps of the samples B, C, D and E are 15 mm.

The characteristics of samples B, C, D, E and F were investigated.

The characteristics were evaluated as follows.

(1) Vertical orientation degree The squareness ratio Br / Bm in the vertical direction of the magnetic tape was measured and the demagnetizing field was corrected.

(2) Surface Roughness R ₂₀ Taristep (manufactured by TAYLOR-HOBSON) was used to obtain a 20-point average method from a chart obtained.

The cutoff was 0.17 mm and the needle pressure was 0.1 × 2.5 μ.

The results are shown below.

Sample No. Vertical orientation degree R ₂₀ B (Invention) 0.80 0.05 μm C (Comparison) 0.68 0.07 μm D (Comparison) 0.68 0.07 μm E (Comparison) 0.60 0.07 μm F (Comparison) 0.70 0.07 μm The effect is clear.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows one of the N-S facing main magnets in the present invention in which ferromagnetic materials are arranged with a gap on both main magnet facing surfaces.
It is a front view for explaining an example. FIG. 2 is a front view for explaining an example of a conventional N-S facing magnet arranged side by side with a gap. FIG. 3 is a front view for explaining an example of a conventional N-S facing main magnet with an N-S facing auxiliary magnet mounted on the exit side. Explanation of symbols 1 ... Coating material, 11,12 ... NS facing main magnet, 13,14 ... Ferromagnetic material, 21,22 ... NS facing magnet, 31,32 ... NS facing Main magnet, 33, 34 ... NS opposing auxiliary magnet, a ... Direction of passing coating material

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-57-58245 (JP, A) JP-A-58-203631 (JP, A) JP-A-59-139142 (JP, A)

Claims (4)

[Claims] Claim: What is claimed is: 1. A magnetic coating material is applied to a support, and the magnetic coating is applied between a plurality of N-S facing main magnets in which a plurality of ferromagnetic materials are arranged with a gap on at least one main magnet facing surface. A method for producing a magnetic recording medium, which comprises allowing the magnetic particles in the coating film to pass through, orienting the easy axis of magnetization of the magnetic particles substantially perpendicular to the film surface, and drying. 2. The method for producing a magnetic recording medium according to claim 1, wherein the gap between the ferromagnetic bodies arranged on the surface facing the main magnet is 0.5 to 20 mm. 3. The method of manufacturing a magnetic recording medium according to claim 1, wherein the ferromagnetic material is arranged on both main magnet facing surfaces. 4. The method of manufacturing a magnetic recording medium according to claim 1, wherein a plurality of N-S facing main magnets each having a ferromagnetic material are arranged.