JP2975922B2 - Manufacturing method of magnetic disk - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a method for manufacturing a magnetic disk.

[0002]

2. Description of the Related Art For example, in a magnetic disk such as a video floppy disk for an electronic still camera, a magnetic layer is formed by binding metal magnetic powder on a support with a binder resin. In the case of a structure, this kind of magnetic layer is not so good in conductivity, and is easily charged due to relatively high surface electric resistance. As a result, noise is generated at the time of discharging the charged electric charges, and dust adheres to the liquid, causing dropout.

For this purpose, a conductive powder (carbon black, graphite, silver powder, nickel powder, etc.) and a surfactant (natural, nonionic, anionic, cationic, amphoteric) are added to the magnetic layer to reduce the surface electric resistance. It is possible to lower it.
No. 6-22726, No. 47-24888, No. 47-26882, No. 48-15440,
No. 48-27661, U.S. Pat. No. 2,271,623
No. 2,224,472, No. 228822
No. 6, specification 2676122, specification 267669
No. 24, No. 2676975, No. 2691
Nos. 566 and 2727860 and 273
Nos. 0498 and 2742379 and 27
No. 39891, No. 3068101, No. 3
158484, 32020153, 3202101, 3294540,
Nos. 3,415,649, 3,441,413, 3,442,654, 3,475,174, 3,545,974, and the like.

However, in these prior arts, the addition of a conductive powder to the magnetic layer (more than a magnetic tape) reduces the packing density and dispersibility of the metal magnetic powder, resulting in lower output. However, there is a disadvantage that noise increases. In addition, the addition of a surfactant has a small effect of lowering the surface electric resistance, and when the amount is increased, the durability of the magnetic layer deteriorates.

On the other hand, an attempt to improve the above-mentioned drawback by providing a conductive layer containing carbon black between a support and a magnetic layer is described in Japanese Patent Publication No. 1-20488. However, in the case of this prior art, the conductive layer is coated on a support, dried and then the magnetic layer is formed. This is a so-called wet-on-dry multi-layer coating method. Adhesion with the conductive layer is reduced, and in particular, a magnetic disk using metal magnetic powder causes a problem of durability such as film peeling.

[0006] In the wet-on-dry multi-layer coating method, the surface roughness of the conductive layer easily affects the magnetic layer. In particular, a magnetic disk using metal magnetic powder (for high density recording, Output, low noise required)
, There is a drawback that the output decreases and the noise increases. Therefore, the first problem to be solved by the present invention is:
An object of the present invention is to provide a magnetic disk having a high filling density of metal magnetic powder, good dispersibility, high output, low noise, high durability, and low dropout.

A second object of the present invention is to provide a method of manufacturing a magnetic disk capable of eliminating film peeling, improving durability, smoothing the surface, and realizing high output and low noise. To provide.

[0008]

An object of the present invention is to provide a magnetic disk in which a conductive layer containing carbon black and a magnetic layer containing metal magnetic powder are laminated in this order on a nonmagnetic support . The manufacturing method , wherein the metal magnetic powder
Is an iron-nickel-based metal magnetic powder having a specific surface area of 40 m ² / g or more , and the carbon black has an average particle size.
The conductive layer and the magnetic layer are coated with a conductive layer coating material containing the carbon black and a magnetic layer coating material containing the metal magnetic powder by an extrusion coater. when, paint the conductive layer can be solved by a manufacturing method of a magnetic disk, wherein said that the magnetic layer coating material Ru is applied when undried.

[0009]

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION In the method for manufacturing a magnetic disk of the present invention, a conductive layer containing carbon black and a magnetic layer containing metal magnetic powder are laminated in this order on a nonmagnetic support. a manufacturing method of a magnetic disk, the magnetic metal powder has a specific surface area of 40 m ² / g or more iron - a nickel-based metal magnetic powder, the carbon black
Has an average particle diameter of 20 to 40 μm, and the conductive layer and the magnetic layer are each composed of a conductive layer paint containing the carbon black and a magnetic layer containing the metal magnetic powder. use paint is applied by extrusion coaters, this time, paint the conductive layer is Ru said magnetic layer coating is applied when the undried state.

In the magnetic disk of the present invention, the magnetic powder of the magnetic layer is a metal magnetic powder. There are various types of metal magnetic powder. For example, there are iron-based metal magnetic powder, nickel-based metal magnetic powder, cobalt-based metal magnetic powder, and the like. But,
The metal magnetic powder used in the present invention is an iron-nickel metal magnetic powder. For example, Fe-Ni metal magnetic powder, Fe
-Ni-Al-based metal magnetic powder, Fe-Ni-Si-based metal magnetic powder, Fe-Ni-Co-based metal magnetic powder, Fe-N
i-Zn-based metal magnetic powder, Fe-Ni-Mn-based metal magnetic powder, Fe-Ni-Co-P-based metal magnetic powder, Fe-N
i-Al-Si-Zn-based metal magnetic powder, Fe-Ni-A
Ferromagnetic powders such as l-Si-Mn-based metal magnetic powders are exemplified. In particular, iron-nicke having a specific surface area of 40 m ² / g or more
Metal powder.

The iron-nickel metal magnetic powder has a large saturation magnetization and a large coercive force, and is excellent in high density recording. In particular, when an iron-nickel-based metal magnetic powder having a specific surface area of 40 m ² / g or more is used, higher density recording can be performed, and S / N
This provides a magnetic recording medium excellent in quality. In the magnetic layer, in addition to the magnetic powder, a lubricant (eg, silicone oil, graphite, molybdenum disulfide, tungsten disulfide, a monobasic fatty acid having 12 to 20 carbon atoms (eg, stearic acid) and a carbon atom number) 3-26 monohydric alcohol fatty acid ester, etc.) may be added. Also, alumina (α-Al ₂ O ₃ (corundum), etc.), artificial corundum, fused alumina, silicon carbide, chromium oxide, diamond, artificial diamond, garnet, emery (main component:
Non-magnetic abrasive particles selected from corundum and magnetite) may be added. The content of the abrasive is 10
It is preferably 20 parts by weight or less based on 0 parts by weight. The size of the abrasive is 0.5 μm or less, especially 0.1 μm.
Those having a size of 4 μm or less are preferred.

As the binder resin for the magnetic layer, at least polyurethane can be used. It can be synthesized by reacting a polyol with a polyisocyanate. If a phenoxy resin and / or a vinyl chloride-based copolymer is included together with the polyurethane, the dispersibility of the magnetic powder is improved, and the mechanical strength is increased. However, phenoxy resin and / or
Alternatively, the layer becomes too hard with the vinyl chloride copolymer alone, but this can be prevented by the combined use of polyurethane.
In addition, the adhesion to the support and the underlayer is improved. In addition to the above, as the binder resin, a fibrous resin, a thermoplastic resin, a thermosetting resin, a reactive resin, or an electron beam irradiation curable resin may be used.

An antistatic agent such as carbon black may not be added to the magnetic layer. That is, according to the present invention, since the conductive layer containing carbon black is provided between the magnetic layer and the nonmagnetic support, the conductive layer sufficiently lowers the surface electric resistance of the magnetic layer. It is not necessary to add an antistatic agent such as carbon black to the magnetic layer. When no antistatic agent such as carbon black is added to the magnetic layer, the packing density of the metal magnetic powder increases and the dispersibility also improves.

As the carbon black used for the conductive layer having the above-mentioned features, for example, Conductex 975 (specific surface area 250 m ²⁾ manufactured by Columbia Carbon Co., Ltd.
/ G, particle size 24mμ), Conductex 900 (specific surface area 125m ² / g, particle size 27mμ), Conductex 40-220 (particle size 20mμ), Conductex S
C (particle diameter 20mμ), Vulcan XC- manufactured by Cabot Corporation
72 (specific surface area 254 m ² / g, particle size 30 mμ), Vulcan P (particle size 20 mμ), Raven 1040, 420,
There is a conductive carbon black such as # 44 manufactured by Mitsubishi Kasei. This carbon black has an oil absorption of 90 ml
(DBP) / 100 g or more is preferable because the structure can be easily formed and higher conductivity is exhibited.

[0016] Carbon black used in the conductive layer has an average particle size of from 20～40Emumyu. The content is 10 to 300 parts by weight, particularly 50 to 150 parts by weight, based on 100 parts by weight of the binder resin. The conductive layer is obtained by fixing the above carbon black with the same binder resin as described above. Further, it may contain the above-mentioned lubricant and the like.

The magnetic layer of the magnetic disk of the present invention comprises:
The thickness after drying is preferably from 0.5 to 4.0 μm. In particular, it is preferably from 1.0 to 3.0 μm.
The conductive layer in the magnetic disk of the present invention preferably has a thickness after drying of 0.5 to 4.0 μm. In particular, it is preferably from 1.0 to 3.0 μm. As shown in FIG. 1, the magnetic disk of the present invention has a conductive layer 2 containing carbon black on both sides of a non-magnetic support 1.
And a magnetic layer 4 containing the above-described iron-nickel-based metal magnetic powder and, if necessary, an overcoat layer (not shown), which are laminated in this order.

The magnetic recording medium of FIG. 1 may be provided with an undercoat layer (not shown) between the conductive layer 2 and the support 1, or may be provided with no undercoat layer. (The same applies hereinafter). Further, the support may be subjected to a corona discharge treatment. As the material of the support 1, plastics such as polyethylene terephthalate and polypropylene, metals such as Al and Zn, glass, BN, Si carbide, ceramics such as porcelain and ceramics are used.

Next, a manufacturing method will be described with reference to FIG. In this manufacturing apparatus, when manufacturing the medium of FIG. 1, first, the film-like support 1 fed from the supply roll 32 is extruded by the extrusion type coaters 10 and 11 to form the conductive layer 2 and the magnetic layer. 4
Are applied in a wet-on-wet manner and then introduced into a dryer 34 in which a pre-stage non-orientation magnet 33 and a post-stage non-orientation magnet 35 are arranged, where the nozzles are arranged vertically. Dry with hot air. Next, the dried support 1 with each coating layer was calender roll 3
It is guided to a super calender device 37 composed of eight combinations, where it is calendered, and then wound up by a winding roll 39. Thereafter, the other coatings for the conductive layer 2 and the magnetic layer 4 are applied on the other surface of the support 1 in the same manner as described above by a wet-on-wet method, dried and calendered. The magnetic film obtained in this way is punched into a disk having a diameter of 2 inches and is housed in a cassette to manufacture an electronic still video floppy.

In the above method, each paint is extruded through an in-line mixer (not shown).
11 may be supplied. Note that, in the figure, the arrow D indicates the transport direction of the non-magnetic base film. Extrusion coater 1
Liquid pools 13 and 14 are provided at 0 and 11 respectively, and paints from the respective coaters are overlapped by a wet-on-wet method. That is, immediately after the application of the coating material for the conductive layer (when it is in an undried state), the coating material for the magnetic layer is applied in multiple layers.

In the wet-on-wet multi-layer coating, the lower magnetic layer is applied in a wet state of the lower conductive layer, so that the lower layer has a smooth surface (that is, a boundary surface with the upper layer). As a result, the surface properties of the upper layer are improved, and the adhesion between the upper and lower layers is also sufficient. As a result,
In particular, for high-density recording, a magnetic disk using metal magnetic powder, which requires high output and low noise, satisfies the required performance, and unlike a magnetic tape, high durability performance is required In this case, film peeling is eliminated, film strength is improved, and durability is sufficient. As for the durability, in the magnetic disk of the present invention, since the conductive powder is not added to the magnetic layer, the durability of the magnetic layer is improved accordingly.

The extrusion coater is not limited to the one described above, but may be a single head structure. Between the upper and lower layers formed by the above-mentioned wet-on-wet multi-layer coating, in addition to the case where a clear boundary substantially exists, there is a boundary region where the components of both layers are mixed with a constant thickness. Although it may be present, the upper or lower layer excluding such a boundary region is referred to as the magnetic layer or the conductive layer. Either case is included in the scope of the present invention.

When the magnetic layer or the like is formed by coating, the solvent usable for the coating includes ketones (eg, methyl ethyl ketone, cyclohexanone), ethers (eg, diethyl ether), and esters (eg, ethyl acetate). ), Aromatic solvents (eg, toluene), alcohols (eg, methanol), and the like.
These can be used alone or as a mixture.

Hereinafter, the present invention will be described with reference to specific examples. In addition, the components, ratios, operation order, etc. shown below are
Various changes can be made without departing from the spirit of the present invention. Further, "parts" in the following examples means "parts by weight".

[0025]

Examples 1 to 5 The following components were sufficiently kneaded and dispersed by a kneader and a ball mill, and immediately before coating, 5 parts of a polyisocyanate compound (Coronate L; manufactured by Nippon Polyurethane Co., Ltd.) was added and mixed to form a magnetic layer. Magnetic paint [I] and carbon black paint [II] for conductive layer
Was adjusted.

Magnetic paint [I] Iron-nickel ferromagnetic alloy powder (nickel content: 3% by weight, BET ratio surface area: 43 m ² / g, coercive force Hc: 1350 Oe) 100 parts Polyurethane resin (Nipporan 2304; Japan) Polyurethane) 5 parts Vinyl chloride-vinyl acetate-vinyl alcohol copolymer (VAGH; manufactured by U.C.C. USA) 8 parts α-alumina 7 parts Myristic acid 2 parts Butyl stearate 1 part Cyclohexanone 200 parts Toluene 30 Part methyl ethyl ketone 30 parts carbon black paint [II] carbon black (Conductex 975 (C-975); manufactured by Columbia Carbon Japan) 100 parts polyurethane resin (Nipporan 2304; manufactured by Nippon Polyurethane) 60 parts vinyl chloride-vinyl acetate-vinyl Alcohol copolymer (V GH: manufactured by U.C.C., USA) 60 parts Myristate 5 parts Butyl stearate 5 parts Cyclohexanone 600 parts Toluene 200 parts Methyl ethyl ketone 200 parts Next, the above carbon black paint is applied on a polyethylene terephthalate base film having a thickness of 32 μm. [I
I] and the magnetic paint [I] were sequentially wet-coated with an extrusion-type extrusion coater as shown in Table 1 below.
It was applied by an on-wet method, and calendered after drying. Thereafter, the same paint (I) was applied to the opposite side of the polyethylene terephthalate base film.
[I] and [I] were sequentially applied by a wet-on-wet method, dried, and then calendered.

The magnetic film thus obtained was punched into a disk having a diameter of 2 inches and housed in a cassette to produce an electronic still video floppy. Table 1 Carbon black dry film thickness Magnetic layer dry film thickness Example 1 1.0 μm 3.0 μm Example 2 2.0 μm 2.0 μm Example 3 3.0 μm 1.0 μm Example 4 0.4 μm 3.6 μm Example 5 3.6 μm 0.4 μm

[0028]

COMPARATIVE EXAMPLE 1 After coating and drying a carbon black paint [II] with an extrusion coater, a magnetic paint [I] was applied as an upper layer, dried, calendered, and dried in the same thickness as in Example 2. A still video floppy was prepared.

[0029]

Comparative Example 2 An electronic still video floppy having the same dry film thickness was produced in the same manner as in Example 2 except that the extrusion-type extrusion coater was changed to a gravure roll coater.

[0030]

Comparative Example 3 A magnetic paint [I] was applied on a polyethylene terephthalate base film having a thickness of 32 μm and dried.
An electronic still video floppy having a single layer of a magnetic layer having a dry film thickness of 4.0 μm was prepared by calendering.

[0031]

Comparative Example 4 A magnetic paint [III] was prepared by adding 7 parts of carbon black (C-975; manufactured by Columbia Carbon Japan) to the composition of the magnetic paint [I].
I) was applied in a single layer in the same manner as in Comparative Example 3 to produce an electronic still video floppy.

[0032]

[Characteristics] The following performance evaluation was performed on the video floppies of the respective examples, and the results are shown in Table-2. (1) RF Output Using a Sony MVR-5500, a 7 MHz sine wave signal was recorded, and the reproduced RF output was measured. The reproduction RF output of the electronic still video floppy of the first embodiment is set to 0.0 d.
The reproduced RF output of each example is indicated by a relative value when B is set. RF
The higher the output value, the better the electronic still video floppy. (2) Noise Level A 6 MHz noise level of the sample whose RF output was measured was measured using a spectrum analyzer manufactured by Advantest. The noise level of each example is shown by a relative value when the noise level of the electronic still video floppy of the first embodiment is 0.0 dB. The smaller the value of the noise level, the better the electronic still video floppy. (3) Surface Electric Resistivity An electrode having a width of 10 mm was separated by 10 mm, a measurement sample was sandwiched between the electrodes, and the surface electric resistivity was measured. The higher the value, the higher the surface electrical resistivity. (4) Running durability Using VX-50 manufactured by Hitachi, Ltd., continuous playback in the still mode of an electronic still video floppy in which image signals were previously recorded on 25 tracks was performed, and the playback output was 3d.
The time until B decreased was examined. (5) Dropout Use a dropout measuring device manufactured by Konica Corporation and measure 15μ in length.
1 sec or more, dropout with a depth of -12 dB or more
Three or more electronic still video floppies per sheet were determined to be defective, and the results were shown as a pass rate (%) when 100 sheets were measured. A high pass rate means less dropout.

Table 2 RF output Noise level Surface electrical resistivity Running durability Pass rate (dB) (dB) (Ω) (Hr) (%) Example 1 0.0 0.0 1.0 × 10 ⁸ > 100 95 Example 2 +0.5 −0.2 1.2 × 10 ⁷ > 100 97 Example 3 +0.3 −0.1 1.3 × 10 ⁶ > 100 98 Example 4 −0.5 +0.2 1.3 × 10 ⁹ 80 88 example ^{5 -0.8 +0.5 1.0 × 10 5 80} 97 Comparative example ^{1 -2.0 +1.0 1.2 × 10 7 50} 90 Comparative example 2-2. 5 +1.5 1.2 × 10 ⁷ 30 85 Comparative Example 3 0.0 −1.0 1.2 × 10 ¹¹ 50 80 Comparative Example 4 −3.5 −1.0 1.0 × 10 ⁶ 50 95 The results show that the magnetic disk of the present invention has high output, low noise, high durability, and low dropout.

[0034]

According to the present invention, a conductive layer containing carbon black and a magnetic layer containing metal magnetic powder are laminated in this order on a nonmagnetic support, and an iron-nickel metal magnetic powder is selected as the metal magnetic powder. The conductive layer and the magnetic layer,
The coating material for the conductive layer and the coating material for the magnetic layer are applied by an extrusion coater. At this time, when the coating material for the conductive layer is in an undried state, the coating material for the magnetic layer is applied. The disc has high output, low noise, high durability, and low dropout.

Further, a coating material for a conductive layer containing carbon black and a coating material for a magnetic layer containing magnetic powder of iron-nickel metal are applied in this order on a non-magnetic support by an extrusion coater. Since the coating for the magnetic layer is applied when the coating for the conductive layer is in an undried state, the obtained magnetic disk has high output, low noise, high durability, and low dropout. .

[Brief description of the drawings]

FIG. 1 is a sectional view of a magnetic disk.

FIG. 2 is a schematic diagram of a magnetic disk manufacturing apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Nonmagnetic support 2 Conductive layer 4 Magnetic layer 10,11 Extrusion coater

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Nobuyuki Sekiguchi 1 Konica Corporation, Sakura-cho, Hino-shi, Tokyo (72) Inventor Shozo Kikukawa 1 Konica Sakura-cho, Hino-shi, Tokyo (56 References JP-A-63-46621 (JP, A) JP-A-62-1115 (JP, A) JP-A-60-35323 (JP, A) JP-A-1-122024 (JP, A) JP-A 63-146210 (JP, A) JP-A-62-214524 (JP, A) JP-A-63-187418 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G11B 5/706 G11B 5/704 G11B 5/842

Claims (1)

(57) [Claims] 1. A method for manufacturing a magnetic disk comprising: a conductive layer containing carbon black and a magnetic layer containing metal magnetic powder laminated on a non-magnetic support in this order; The powder is an iron-nickel-based metal magnetic powder having a specific surface area of 40 m ² / g or more , and the carbon black has an average particle size of 20 to 40 μm.
Are those, wherein the magnetic layer and the conductive layer, the carbon black
Containing a coating for a conductive layer containing the metal magnetic powder
That the magnetic layer coating is applied by extrusion coaters, this time, paint the conductive layer is a magnetic disk, wherein said that the magnetic layer coating material Ru is applied when undried
Manufacturing method .