JP2852773B2 - Manufacturing method of magnetic disk - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetic disk and a method for manufacturing the same.

B. 2. Description of the Related Art For example, in a magnetic disk such as a video floppy disk for an electronic still camera, when a magnetic layer is formed by binding a metal magnetic powder on a support with a binder resin, this type of magnetic layer becomes conductive. The sex is not so good,
Easily charged due to relatively high surface electrical 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.) or a surfactant (natural, nonionic, anionic, cationic, amphoteric) may be added to the magnetic layer to lower the surface electric resistance. , Tokiko 46-22726
No. 47-24881, No. 47-26882, No. 48-15440,
Nos. 48-26761, U.S. Pat.Nos. 2,227,223 and 2,240,472
No. 2288226 No. 2676122 No. 2676924 No.
No. 2676975, No. 2691566, No. 2727860, No. 2
No. 730498, No. 2742379, No. 2739891, No. 306810
No. 1, No. 3158484, No. 3201253, No. 3210191,
No. 3294540, No. 3415649, No. 3441413, No. 3
No. 442654, No. 3475174 and No. 3545974. However, in these conventional techniques, the addition of conductive powder to the magnetic layer (more than the magnetic tape) reduces the packing density and dispersibility of the metal magnetic powder, resulting in lower output and lower noise. Disadvantageously increases. In addition, the addition of a surfactant has a small effect of lowering the surface electric resistance, and when the addition amount is increased, the durability of the magnetic layer deteriorates.

On the other hand, Japanese Patent Publication No. 1-20488 discloses an attempt to improve the above disadvantage by providing a conductive layer containing carbon black between a support and a magnetic layer. However,
In the case of this prior art, the conductive layer is coated on a support,
Forming the magnetic layer after drying, because it is by the so-called wet-on-dry multi-layer coating method,
Adhesion between the magnetic layer and the conductive layer is reduced, and in particular, in a magnetic disk using metal magnetic powder, durability problems such as film peeling occur. In the so-called wet-on-dry multi-layer 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, high output, Low noise is required), there is a disadvantage that the output decreases and the noise increases.

C. OBJECTS OF THE INVENTION An object of the present invention is to provide a metal powder having a high packing density, good dispersibility, high output, low noise, high durability, low dropout, and durability especially at high temperatures. An object of the present invention is to provide an excellent magnetic disk.

It is another object of the present invention to provide a method of manufacturing a magnetic disk capable of improving durability, smoothing the surface, and realizing high output and low noise.

D. The purpose of the present invention is to provide a non-magnetic support having a particle size of 10 to 50 μm.
In applying the conductive layer paint containing carbon black, and the magnetic layer paint containing a metal magnetic powder having a specific surface area of 40 m ² / g or more and carbon black having a particle size of 40 to 300 mμ in this order, extruding. This is achieved by a method for manufacturing a magnetic disk, in which the coating for a magnetic layer is applied while the coating for the conductive layer applied is in an undried state using a coater.

The magnetic disk according to the present invention has a magnetic layer containing a metal magnetic powder as a magnetic layer, and usable metal magnetic powders include Fe, Ni, Co, Fe-Al,
-Al-Ni, Fe-Al-Co, Fe-Ni-Si, Fe-Al-Zn
System, Fe-Ni-Co system, Fe-Mn-Zn system, Fe-Ni system, Fe-Ni-
Al system, Fe-Ni-Zn system, Fe-Ni-Mn system, Fe-Co-Ni-P
Powders, ferromagnetic powders such as metal magnetic powders containing Fe, Ni, Co or the like as a main component. Among them, particularly in terms of corrosion resistance and dispersibility, Fe-Al, Fe-Al-Ni, Fe-Al-Zn, Fe-
Al-Co, Fe-Ni, Fe-Ni-Al, Fe-Ni-Zn, Fe-Ni-Al
-Si-Zn, Fe-Ni-Al-Si-Mn-based metal magnetic powders are preferred.

Such metal magnetic powders have high saturation magnetization and coercive force,
Excellent for high density recording. In addition, when a metal magnetic powder having a specific surface area of 40 m ² / g or more is used, high-density recording can be performed, and a medium having an excellent S / N ratio can be provided.

The magnetic layer has a particle size of 40 in addition to the metal magnetic powder.
It should be noted that ~ 300mμ of carbon black is contained. By containing such carbon black, not only durability at normal temperature but also durability under high temperature conditions are improved.

In particular, in a still video system, there are many uses in which seek reproduction is repeated for a long time, and at this time, the temperature of the set may increase, and it is desired to improve durability under high temperature conditions. This requirement can be sufficiently achieved by the above carbon black. This is presumably because the carbon black reduces friction of the magnetic layer and increases its durability.

Examples of such slippery carbon black having a particle size of 40 to 300 mμ include R-14 (specific surface area 45 m ² / g, particle size 68 mμ) and R-420 (specific surface area 25 m ² /
g, particle size 68mμ), R-450 (specific surface area 33m ² / g, particle size 62m)
μ), R-MT-P (specific surface area 8 m ² / g, particle size 280 mμ), Sterling V manufactured by Cabot (specific surface area 35 m ² / g, particle size 50 m)
μ), SterlingNS (specific surface area 25m ² / g, particle size 75mμ), Ste
rlingSO (specific surface area 42 m ² / g, particle size 41 mμ), # 22B manufactured by Mitsubishi Kasei Corporation (specific surface area 55 m ² / g, particle size 40 mμ), # 20
B (specific surface area 56m ² / g, particle size 40mμ), CF-9 (specific surface area 60
m ² / g, particle size 40mμ), # 3500 (specific surface area 47m ² / g, particle size 40m)
μ), Denka Corporation's HS-100 (specific surface area 32 m ² / g, particle size 53 mμ), ASAHI HS-500 (specific surface area 37 m ² / g, particle size 76 m
μ) etc. are used.

If the particle size of the slippery carbon black is less than 40 mμ, the particle size is too small, resulting in poor dispersibility and increased friction on the surface of the magnetic layer. Conversion characteristics are deteriorated. The particle size range is more preferably from 50 to 200 mμ, and still more preferably from 60 to 100 mμ. The amount of addition is 0.1 to 2.
0 parts by weight is preferred, and 0.3 to 1.0 parts by weight is more desirable. If the addition amount is too small, the effect of addition is poor, and if it is too large, the electromagnetic conversion characteristics tend to deteriorate.

The magnetic layer further includes a lubricant (eg, silicone oil, graphite, molybdenum disulfide, tungsten disulfide, a monobasic fatty acid having 12 to 20 carbon atoms (eg, stearic acid) and 3 to 26 carbon atoms). Fatty acid esters of monohydric alcohols, etc.) may be added. Non-magnetic abrasive particles may also be added, including alumina (α-Al ₂ O ₃ (corundum), etc.), artificial corundum, fused alumina, silicon carbide, chromium oxide, diamond, artificial diamond, garnet , Emery (main components kolangmu and magnetite) and the like are used. The content of the abrasive is preferably 20 parts by weight or less based on the magnetic powder, and the average particle system is preferably 0.5 μm or less, more preferably 0.4 μm or less.

Further, at least polyurethane can be used as a binder resin for the magnetic layer, and can be synthesized by a reaction between a polyol and a polyisocyanate. When a phenoxy resin and / or a vinyl chloride-based copolymer is contained together with the polyurethane, the dispersibility of the magnetic powder is improved when applied to a magnetic layer, and the mechanical strength is increased. However, the layer becomes too hard with only the phenoxy resin and / or the vinyl chloride copolymer, but this can be prevented by the inclusion of polyurethane, and the adhesion to the support or the underground layer becomes good. In addition to the above, a cellulose resin, a thermoplastic resin, a thermosetting resin, a reactive resin, and an electron beam irradiation curable resin may be used as the binder resin.

Furthermore, according to the present invention, a conductive layer containing carbon black having a particle size of 10 to 50 μm is provided between the magnetic layer and the nonmagnetic support. The electric resistance can be sufficiently reduced. As a result, in the magnetic layer, the amount of conductive carbon black added can be reduced, so that the magnetic layer improves the packing density and dispersibility of the metal magnetic powder.

Examples of carbon black used in such a conductive layer include Conductex 975 (specific surface area 250 m ² / g, particle diameter 24 mμ) of Columbia Carbon Japan,
Conductex 900 (specific surface area 125m ² / g, particle size 27m
μ), Conductex 40-220 (particle size 20mμ), Conductex SC (particle size 20mμ), Cabot Vulcan XC-72 (Cabot Vulcan) XC-72 (specific surface area 254m ² / g, particle size 30m)
μ), Vulcan P (particle size 20mμ), Raven 1040, 420,
Black Pearls 2000 (particle size 15mμ), Mitsubishi Kasei Corporation
And conductive carbon black such as # 44. When the carbon black has an oil absorption of 90 ml (DBP) / 100 g or more, it is desirable because it easily has a structure structure and exhibits higher conductivity.

The particle size of this carbon black should be 10 to 50 mμ, but if it is less than 10 mμ, it is too small to cause poor dispersion and the like,
If it exceeds 50 μm, conductivity will not be obtained. The particle size is more preferably 15 to 40 mμ, and more preferably 20 to 30 mμ. The addition amount is 10 parts by weight with respect to 100 parts by weight of the binder resin.
The amount is preferably 300 to 300 parts by weight (more preferably 50 to 150 parts by weight).

This conductive layer is obtained by fixing the above-described carbon black with the same binder resin as described above, and may further include the above-described lubricant and the like.

The “particle size” of the carbon black described above refers to an average particle, and a cross section of the medium is taken with an electron micrograph (70,000 times).
Means the number average particle size measured for 100 carbon blacks.

In the magnetic disk according to the present invention, the dry thickness of the magnetic layer is preferably 0.5 to 4.0 μm, and 1.0 to 3.0 μm.
Is even better. The dry thickness of the conductive layer is also 0.5 to
It is preferably 4.0 μm, more preferably 1.0 to 3.0 μm.

As shown in FIG. 1, for example, a magnetic disk according to the present invention has a conductive layer 2 containing the above-described carbon black and a magnetic layer containing the above-described metal magnetic powder and carbon black on both surfaces of a non-magnetic support 1. The layer 4 and, if necessary, an overcoat layer (not shown) are provided by laminating in this order.

The magnetic recording medium shown in FIG. 1 may be provided with an undercoat layer (not shown) between the conductive layer 2 and the support 1, or may not be provided with an undercoat layer. (The same applies hereinafter). The support may be subjected to corona discharge treatment.

Further, as a 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, an example of a method for manufacturing the above-described medium according to the present invention will be described with reference to FIG.

In this manufacturing apparatus, in manufacturing the medium shown in FIG. 1, first, the film-like support 1 fed from the supply roll 32 is formed by an extrusion-type extrusion coater.
Each of the above-mentioned paints for the conductive layer 2 and the magnetic layer 4 was applied in multiple layers by wet-on-wet method according to steps 10 and 11, and then a pre-stage non-oriented magnet 33 and a post-stage non-oriented magnet 35 were provided. It is introduced into the dryer 34, where it is dried by blowing hot air from nozzles arranged above and below. Next, the dried support 1 with each coating layer is guided to a super calender device 37 composed of a combination of calender rolls 38, where it is calendered, and then wound up by a take-up roll 39. Thereafter, the conductive layer 2 and the magnetic layer 4 are applied to the other surface of the support 1 in the same manner as described above, 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 may be supplied to the extrusion coaters 10 and 11 through an inline mixer (not shown). Note that, in the figure, the arrow D indicates the transport direction of the non-magnetic base film. Extruder coaters 10 and 11 respectively
Liquid reservoirs 13 and 14 are provided, and the paint from each coater is overlaid in a wet-on-wet manner. 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 this wet-on-wet multi-layer coating, since the lower conductive layer is wet and the upper magnetic layer is coated, the surface of the lower layer (that is, the interface with the upper layer) is formed.
Is smooth, the surface property of the upper layer is good, the adhesion between the upper and lower layers is sufficient, and the film is not peeled off. As a result, a magnetic disk using metal magnetic powder, which requires high output and low noise, especially for high-density recording, satisfies the required performance and, unlike magnetic tape, has high durability performance. Even if required, 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 it is not necessary to add conductive powder to the magnetic layer, the durability of the magnetic layer is improved accordingly.

The extrusion coater is not limited to the one described above, and may have a one-head structure, for example.

The upper and lower layers formed by the wet-on-wet multi-layer coating described above have a certain thickness, except when there is a substantial boundary. Although a region may exist, 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.

Solvents that can be used in the coating when forming the magnetic layer and the like include ketones (eg, methyl ethyl ketone, cyclohexanone), ethers (eg, diethyl ether), esters (eg, ethyl acetate), and aromatic solvents. (E.g., toluene), alcohols (e.g., methanol), and the like. These can be used alone or in combination.

E. Examples Hereinafter, examples of the present invention will be described.

The components, ratios, operation orders, and the like shown below can be variously changed without departing from the spirit of the present invention. In the following examples, "parts" are all parts by weight.

Examples 1 to 5 The components shown below were sufficiently kneaded and dispersed by a kneader and a ball mill, and then immediately before coating, a polyisocyanate compound (Coronate L: manufactured by Nippon Polyurethane Co., Ltd.)
Five parts were added and mixed to prepare a magnetic coating [I] for the magnetic layer and a carbon black coating [II] for the conductive layer.

Magnetic paint [I]: iron-nickel ferromagnetic alloy powder 100 parts (nickel content: 3% by weight, BET specific surface area: 43 m ² / g, coercive force (Hc): 1350 Oe) Carbon black 0.5 part (Columbia Carbon Japan) R-14, 45
m ² / g, particle size 68 mμ) Polyurethane resin 5 parts (Nipporan 2304: manufactured by Nippon Polyurethane Co., Ltd.) Vinyl chloride-vinyl acetate-vinyl 8 parts Alcohol copolymer (VAGH: manufactured by UCC USA) α-alumina 7 parts Myristic acid 2 parts Butyl stearate 1 part Cyclohexanone 200 parts Toluene 30 parts Methyl ethyl ketone 30 parts Carbon black paint [II]: Carbon black 100 parts (Conductex 975 (C-975): manufactured by Columbia Carbon Japan Co., Ltd., specific surface area 250 m ² / g, particle size 24mμ) Polyurethane resin 60 parts (Nipporan 2304: manufactured by Nippon Polyurethane Co., Ltd.) Vinyl chloride-vinyl acetate-vinyl 60 parts Alcohol copolymer (VAGH: manufactured by UCC USA) 5 parts butyl steer Rate 5 parts Cyclohexanone 600 parts Toluene 200 parts Methyl ethyl ketone 200 parts Next, polyethylene of 32 μm thickness Lev tallate base film, the above carbon black paint [II],
As shown in Table 1 below, the magnetic paint [I] was wet-on-coated with an extrusion-type extrusion coater.
Various coatings were applied by a wet method, and a calender treatment was performed after drying. Thereafter, on the opposite side of the polyethylene terephthalate base film, similarly, each paint (II),
[I] was sequentially applied, and after drying, calendering was performed.

The magnetic film obtained in this manner was punched into a disk having a diameter of 2 inches and housed in a cassette to produce an electronic still video floppy.

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 and calendered to obtain an electron having the same dry film thickness as in Example-2. A still video floppy was prepared.

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 coater of the extrusion method was changed to a gravure roll coater.

Comparative Example-3 A magnetic paint [I] was applied on a polyethylene terephthalate base film having a thickness of 32 μm, dried, and calendered to prepare an electronic still video floppy having a magnetic layer dry thickness of 4.0 μm and a single layer application. .

Comparative Example-4 Carbon black (C-975:
A magnetic paint [III] having the same composition as the magnetic paint [I] was obtained except that 7 parts of Columbia Carbon Japan Co., Ltd. was added. This magnetic paint [III] was applied in a single layer in the same manner as in Comparative Example-3 to prepare an electronic still video floppy.

Comparative Example-5 An electronic still video floppy was prepared in the same manner as in Example 1, except that carbon black R-140.5 parts was removed from the magnetic paint [I].

Example-6 The addition amount of carbon black R-14 in the magnetic paint [I] was
An electronic still video floppy was produced in the same manner as in Example 1, except that 3.0 parts were used.

Examples -7 to 14 and Comparative Examples -6 to 9 In Example 1, the particle size and amount of carbon black in the magnetic coating [I], and the carbon black coating [II]
The particle size and addition amount of carbon black in the following Table-
The electronic still video floppy was manufactured in the same manner as in Example 1 except for changing as in Example 2.

The following performance evaluation was performed for each of the above video floppies, and the results are shown in Table 3 below.

(1) RF output Using a Sony Corporation MVR-5500, a 7 MHz sine wave signal was recorded, and the reproduced RF output was measured. The measured reproduction RF output is shown in Table 3 as a relative value when the reproduction output RF output of the electronic still video floppy manufactured in Example-1 is 0.0 dB. The higher the RF 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 Avantest Corporation. Example 1
Table 3 shows relative values when the noise level of the electronic still video floppy manufactured in 1 was 0.0 dB.
The smaller the value of the noise level, the better the electronic still video floppy.

(3) Surface electrical resistivity An electrode having a width of 10 mm was separated by 10 mm, and a measurement sample was inserted between the electrodes, and the surface electrical resistivity was measured. The higher the value, the higher the surface electrical resistivity.

(4) Running durability-Using V # -50 manufactured by Hitachi, Ltd., reproduction of an electronic still video floppy in which the image signal was recorded in 25 tracks in advance in the still mode at 20 ° C. and 50% RH. The measurement was performed continuously below, and the time until the reproduction output decreased by 3 dB was measured. The results are shown in Table-3.

(5) Running durability-Measured in the same manner as (4) except that the environmental conditions were 40 ° C and 90% RH.

(6) Dropout Using a dropout measuring device manufactured by Konica Corporation,
The pass rate (%) when 100 pieces of electronic still video floppies each having three or more dropouts of 15 μsec or more and a depth of -12 dB or more were determined to be NG products (defective products) was measured. The higher the pass rate, the lower the dropout.

From these results, by constructing and manufacturing a magnetic disk according to the present invention, it is possible to provide a magnetic disk with high output, low noise, high durability under high temperature conditions, and low dropout.

F. Advantageous Effects of the Invention As described above, the present invention provides a method in which a magnetic layer containing a metal magnetic powder having a specific surface area of 40 m ² / g or more and carbon black having a particle diameter of 40 to 300 mμ and a non-magnetic support are provided with a particle. Diameter 10-50m
Since the conductive layer containing μ carbon black is provided, the surface electric resistance of the magnetic layer is sufficiently reduced to reduce the occurrence of noise and dropout, and the magnetic layer is filled with metal magnetic powder and dispersed. The recording performance is improved, high density recording is excellent, and high output and low noise can be obtained. Moreover, the particle size is 40 ~ 30
By including the carbon layer having a sliding property of 0 μm in the magnetic layer, it is possible to provide a magnetic disk having sufficient durability in a high-temperature environment.

Further, since the coating material for the magnetic layer is applied when the coating material for the conductive layer is not dried, the surface of the conductive layer (that is, the boundary surface with the magnetic layer) is smooth and the surface property of the magnetic layer is reduced. As a result, the adhesion between the two layers becomes sufficient, and as a result, high output and low noise can be realized, and the durability is improved.

[Brief description of the drawings]

BRIEF DESCRIPTION OF THE DRAWINGS The drawings are illustrative of the present invention, and FIG. 1 is a sectional view of an example of a magnetic disk, and FIG. 2 is a schematic view of a magnetic disk manufacturing apparatus. In the reference numerals shown in the drawings, 1 is a non-magnetic support 2 is a conductive layer 4 is a magnetic layer 10, 11 is an extruder coater 34 is a dryer 37 and is a super calender device.

──────────────────────────────────────────────────続 き Continuation of front page (72) Inventor Shozo Kikukawa 1 Sakura-cho, Hino-shi, Tokyo Konica Co., Ltd. Examiner Takuya Hayakawa (56) References JP-A-58-16201 (JP, A) JP-A-61-144727 (JP, A) JP-A-63-140421 (JP, A) JP-A-61-216116 (JP, A) JP-A-63-146210 (JP, A) JP-A-62-109228 (JP, A) , A) (58) Field surveyed (Int. Cl. ⁶ , DB name) G11B 5/704 G11B 5/708 G11B 5/842

Claims (2)

(57) [Claims] 1. A coating material for a conductive layer containing carbon black having a particle size of 10 to 50 μm on a non-magnetic support, and a specific surface area
When applying a magnetic layer paint containing metal magnetic powder of 40 m ² / g or more and carbon black having a particle size of 40 to 300 mμ in this order, using an extrusion coater, the applied paint for the conductive layer is not dried. A method for manufacturing a magnetic disk, wherein the magnetic layer coating material is applied in a state. 2. The method according to claim 1, wherein the metal magnetic powder is an iron-nickel ferromagnetic alloy powder.