JPH0685214B2 - 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, is in the plane of the recording medium, the magnetizations repel each other, and it becomes impossible to achieve a high density above 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 coating 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 the magnetic particles is set in the perpendicular direction. A manufacturing method is used in which the film is orientated and then dried.

In this case, a method using an N-S facing magnet as a magnetic field can be mentioned. 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 the time for drying is increased. Therefore, there is a defect that the orientation of the magnetic particles once oriented during that period is disturbed again.

In order to solve these drawbacks, tabular ferromagnetic particles are used as magnetic particles, and a plurality of N-S facing magnets as shown in FIG. 2 are used.
A system in which 21,22 are arranged at intervals to form an orientation magnetic field, and a method of drying while passing through such a magnetic field and performing orientation (Japanese Patent Laid-Open Nos. 58-203631, 58-203632 and 58) No. 203633), and an N-S facing auxiliary magnet 33, 34 on the outlet side as shown in FIG.
A method has been proposed in which magnetic fields are oriented by using N-S facing main magnets 31 and 32 to which magnets arranged at intervals are attached and magnetic particles are oriented and then dried (Japanese Patent Laid-Open No. 59-139142). .

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 paint is applied on a support, and this is an N-S opposing main magnet, and an auxiliary magnet in which a plurality of magnetic poles of the same pole are arranged with a gap on the inlet side of one main magnet. The method for producing a magnetic recording medium is characterized in that the magnetic particles in the coating film are allowed to pass through between the ones having rows so that the easy axis of magnetization is oriented substantially perpendicular to the film surface and 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 passing it through a magnetic field as shown below,
The axis of easy magnetization of the magnetic particles in the coating film is oriented almost perpendicular to the film surface and the film is dried.

As the magnetic field, an N-S facing main magnet having auxiliary magnet rows of the same pole on the inlet side or the inlet side and the outlet side of one of the N-S facing main magnets is used. The reason why the auxiliary magnet array is provided at least on the inlet side of the main magnet is to improve the degree of orientation and surface roughness. And, it is sufficient that one or more sets of N-S facing main magnets having such an auxiliary magnet array are arranged.

FIG. 1 shows an embodiment in which an auxiliary magnet array is provided on the inlet side of the 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 one of the main magnets (the magnet 12 in FIG. 1) has an auxiliary magnet of the same pole on the inlet side in the running direction a of the magnetic recording medium. Row 14 is provided.

The auxiliary magnet array 14 has a plurality of magnetic poles 141 arranged with a gap 142 therebetween.

Although the number of such magnetic poles 141 is five in the illustrated example, it is preferable that the number is about 2 to 50. The gap is 0.5-10m
m, preferably 1 to 5 mm. The length of one magnetic pole is about 0.5 to 10 mm.

Further, although FIG. 1 shows an example in which the auxiliary magnet array 14 is integrated, it is not limited to this mode.

Specific examples of such an auxiliary magnet array include (1) one in which the auxiliary magnet array is multi-polarized with a gap on the magnet surface, and (2) the auxiliary magnet array is a laminated body of an auxiliary magnet and a non-magnetic material. (3) Auxiliary magnet array in which a plurality of auxiliary magnets are embedded in a non-magnetic material, (4) Auxiliary magnet array in which a magnet material having a plurality of recesses is surface magnetized, (5) The auxiliary magnet array may be a permanent magnet such as a gap in the magnet row, but other electromagnets or solenoids may be provided.

It should be noted that the main magnet is not limited to one, and a plurality of main magnets may be used. At this time, at least one of the main magnets only needs to be provided with an auxiliary magnet array, and the main magnets may be arranged continuously without a gap, Various embodiments are possible.

In this case, it is preferable that the main magnet has a central magnetic field of about 1000 to 6000 G, and the auxiliary magnet has a central magnetization of about 1000 to 5000 G.

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

With such a configuration, the magnetic field vibrates each time it passes through the auxiliary magnet, and the effect of this oscillating magnetic field improves the vertical orientation degree and the surface roughness. The effect of this magnetic field vibration is effective when performed before passing through the main magnet, and does not occur only after passing through the main magnet. However, also in the present invention, it is possible to apply magnetic field vibration before passing through the main magnet and then pass through the auxiliary magnet array after passing through the main magnet.

The magnetic pole length of the auxiliary magnet array, the range of its gap, the magnetic field strength, and the like are the range of regions in which this oscillating magnetic field preferably acts.

Further, when a plurality of N-S facing main magnets having the above-mentioned auxiliary magnet array are used, there is no particular limitation on the arrangement method. For example, a method of arranging the auxiliary magnet array on the coating surface side, a method of arranging the auxiliary magnet array on the support side, a method of alternately or periodically arranging the auxiliary magnet row on the coating surface side and the support side can be mentioned.

To apply magnetic paint on the support, gravure coat,
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 using a hot air source or a heater source such as a far infrared ray 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, Cr
O ₂ and Co-based compound-adhered α-Fe ₂ O ₃ and Co-based compound-adhered Fe ₃ O ₄ are polyhedral, but 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.

Examples of barium ferrite include barium ferrite such as BaFe ₁₂ O ₁₉ and Ba, which is part of barium ferrite, and Ca.
Examples thereof include those substituted with Sr, Pb, Co, Ni, Ti, Cr, Zn, In, Mn, Cu, Ge, Nb and 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-based 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 resins, polyvinyl alcohol resins, epoxy resins, phenoxy resins, fibrin derivatives and the like are preferable.

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 of various polyesters such as linear saturated polyethers (polyethylene glycol, polypropylene glycol, polytetramethylene glycol), caprolactam, hydroxyl-containing acrylic acid ester, hydroxyl-containing methacrylic acid ester, etc. 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,
Modification to radiation sensitivity 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 polyptadiene elastomer are also suitable.

Also cyclized polybutadiene, CBR-M90 made by Japan Synthetic Rubber
1 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, a support coated with a magnetic coating has an auxiliary magnet array of the same pole on the inlet side or the inlet side and the outlet side of one of the N-S opposing main magnets. By passing between the N-S facing main magnets and aligning the easy axis of magnetization of the magnetic particles in the coating film almost perpendicularly to the film surface and drying, the vertical orientation degree is improved and the surface roughness is good. A method of manufacturing a magnetic recording medium 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 μm) 10 parts by weight Solvent (MEK / toluene: 50/50) 100 parts by weight The above composition is ball milled. The mixture was mixed for 3 hours in a well-wetted barium ferrite.

Next, as a binder, vinyl chloride-vinyl acetate-vinyl alcohol copolymer (maleic acid-containing; MW40,000) 6 parts by weight (in terms of solid content), acrylic double bond-introduced vinyl chloride-vinyl acetate copolymer (maleic acid) Acid-containing; MW20,000) 12 parts by weight (based on solid content), acrylic double bond-introduced polyether urethane elastomer (MW40,000) 9 parts by weight (based on solid content), pentaerythritol triacrylate 3 parts by weight, solvent (MEK / toluene; 50/50) 200 parts by weight 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. The magnetic coating material thus obtained was gravure-coated on a 75 μ 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, 12 having an auxiliary magnet 141 row of the same pole on the inlet side of one main magnet as shown in FIG.
(Central magnetic field of main magnet 3000G, central magnetic field of one auxiliary magnet 150
0 G) at a speed of 30 m / min, and was vertically aligned while being dried. Then, it dried with the far-infrared lamp.
The main magnet is composed of 10 magnets each having a magnetic pole length of 50 mm arranged without a gap.

This is designated as Sample B.

In this case, the length of the magnetic poles of the auxiliary magnet array was 3 mm, the gap between the magnetic poles was 3 mm, and 20 auxiliary magnets were embedded between nonmagnetic materials (brass plates).

Next, the sample A is used as the SN facing magnets 21 and 22 as shown in FIG.
(Central magnetic field 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.

Further, the exit side auxiliary magnet array of Sample D was added to the magnet of Sample B to prepare Sample E.

In this case, the main magnetic field of the main magnetic field is 3000G, 10 magnetic field lengths of 50 mm are arranged side by side, the central magnetic field of the auxiliary magnet is 1500 G, and 20 auxiliary magnets of the magnetic field length of 3 mm are used. .

The characteristics of samples B, C, D and E 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) 0.73 0.05 μm C (comparison) 0.68 0.07 μm D (comparison) 0.68 0.07 μm E (invention) 0.74 0.05 μm From the above, the effect of the present invention is clear.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an explanatory view showing one embodiment of an NS facing main magnet having an auxiliary magnet array of the same pole on the inlet side of one main magnet in the present invention. The arrow a indicates the direction in which the coating material passes. FIG. 2 is an explanatory view showing an example of the conventional N-S facing magnets which are arranged at intervals. The arrow a indicates the direction in which the coating material passes. FIG. 3 is an explanatory view showing an example of a conventional N-S facing main magnet with an N-S facing auxiliary magnet mounted on the exit side. The arrow a indicates the direction in which the coating material passes. Explanation of symbols 11,12 ... NS facing main magnet, 14 ... auxiliary magnet array, 141 ... magnetic pole, 142 ... gap, 21,22 ... NS facing magnet, 31,32 ... N- S facing main magnet, 33,34 ... NS facing auxiliary magnet, a ... Direction of passing coating material

Claims (3)

[Claims] 1. A magnetic coating material is applied onto a support, which is applied with N-
The S-opposing main magnet is passed through a main magnet having an auxiliary magnet array in which a plurality of magnetic poles having the same poles are arranged with a gap on the inlet side of one main magnet, and the easy axis of magnetization of the magnetic particles in the coating film is set. A method of manufacturing a magnetic recording medium, which comprises orienting the film substantially perpendicularly to a film surface and drying. 2. The method for manufacturing a magnetic recording medium according to claim 1, wherein the gap is 0.5 to 10 mm. 3. The method for manufacturing a magnetic recording medium according to claim 1, further comprising an auxiliary magnet array having the same pole on the outlet side of the main magnet.