JPH03120613A - Magnetic disk and its production - Google Patents

Abstract

PURPOSE:To obtain a magnetic disk having high packing density of meal magnetic powder, good dispersion state, high output, low noise, high durability and little dropout by successively forming a conductive layer containing carbon black and a magnetic layer containing metal magnetic powder on a nonmagnetic supporting body in this order. CONSTITUTION:A coating material containing carbon black and a coating material containing metal magnetic powder are successively applied in this order on a nonmagnetic supporting body 1 with an extrusion coater to form the conductive layer 2 and the magnetic layer 4. respectively. In this procedure, the coating material for the magnetic layer 4 is applied while the coating material of conductive layer 2 is not dried. By this method, surface electric resistance of the magnetic layer 4 is enough reduced to prevent noise and dropout. Moreover, the obtd. magnetic layer 4 is excellent in high-density recording because of improved packing density and dispersion state of metal magnetic powder, and show high output and low noise. The obtd. medium is free from peeling since adhesion property of the two layers is enough and thus, durability of the medium is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to a magnetic disk and a method of manufacturing the same.

Conventional technology For example, when a magnetic disk such as a video floppy disk for an electronic still camera has a structure in which a magnetic layer is formed by bonding metal magnetic powder onto a support with a binder resin, this type of magnetic layer does not have very good conductivity and has a relatively high surface electrical resistance, so it is easily charged. As a result, noise may be generated when the charged charges are discharged, and dust may adhere, causing dropouts.

To this end, conductive powders (carbon black, graphite, silver powder, nickel powder, etc.) and surfactants (natural, nonionic, anionic, cationic, amphoteric) can be added to the magnetic layer to lower the surface electrical resistance. , Special public official 1977-227
No. 26, No. 47-24881, No. 47-26882, No. 48-15440, No. 48-26761, U.S. Pat. 267
No. 6924, No. 2676975, No. 269156
No. 6, No. 2727860, No. 2730498,
Same No. 2742379, Same No. 2739891, Same No. 3
No. 068101, No. 3158484, No. 3201
No. 253, No. 3210191, No. 3294540
No. 3415649, No. 3441413, No. 3442654, No. 3475174, No. 35
It is described in No. 45974, etc. However, in these conventional technologies, by adding conductive powder to the magnetic layer (in a larger amount than in the magnetic tape), the packing density and dispersibility of the metal magnetic powder decrease, resulting in a decrease in output.
The disadvantage is that noise increases. Moreover, the addition of a surfactant has a small effect on lowering the surface electrical resistance, and when the amount added is increased, the durability of the magnetic layer deteriorates.

On the other hand, an attempt has been made to improve the above drawbacks by providing a conductive layer containing carbon black between the support and the magnetic layer, as described in Japanese Patent Publication No. 1-20488. However, this conventional technology uses a so-called wet-on-dry multilayer coating method in which the conductive layer is coated on a support and the magnetic layer is formed after drying. Adhesion with the layer decreases, and durability problems such as film peeling occur, especially in magnetic disks using metal magnetic powder. And the so-called wet
In the on-dry multilayer method, the surface roughness of the conductive layer
It tends to affect the magnetic layer, and especially in magnetic disks using metal magnetic powder (high output and low noise are required for high-density recording), the disadvantage is that the output decreases and the noise increases. There is.

An object of the present invention is to provide a magnetic disk with high packing density of metal magnetic powder, good dispersibility, high output, low noise, high durability, and less dropout. .

Another object of the present invention is to provide a method for manufacturing a magnetic disk that eliminates film peeling, improves durability, and smoothes the surface to achieve high output and low noise.

20 Structure of the Invention That is, the present invention relates to 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 non-magnetic support. be.

In addition, the present invention includes applying a conductive logging paint containing carbon black and a magnetic layer paint containing metal magnetic powder in this order onto a non-magnetic support using an extrusion coater,
At this time, the present invention also provides a method for manufacturing a magnetic disk in which the magnetic layer paint is applied when the conductive logging paint is in an undried state.

The magnetic disk according to the present invention has a magnetic layer containing metal magnetic powder, and usable metal magnetic powders include Fe, Ni, and C.

Including Fe-Aj! system, Fe-Al2-Ni system, F
e-Al2-Co system, Fe-Ni-3i system, Fe-Al
2-Zn system, Fe-Ni-Co system, Fe-Mn-Zn system, Fe-Ni system, Fe-N1-Al system, Fe-Ni-Z
n-based, Fe-Ni-Mn-based, Fe-Co-N1-P-based,
Co-Ni system, Fe, Ni.

Examples include ferromagnetic powder such as metal magnetic powder containing Co or the like as a main component. Among them, Fe-
Al2, Fe-Al2-Ni, Fe-A1-Zn5Fe
-Al2-Co, Fe-N15Fe-Ni-Al, Fe
-Ni-Zn, Fe-Ni -Al-3i-Zn, ,F
Metal magnetic powder of eFe-Ni-Al-3i- system is preferred.

These metal magnetic powders have large saturation magnetization and coercive force, and are excellent for high-density recording. In addition, the specific surface area is 40rrf/
By using metal magnetic powder with a particle size of more than g, high-density recording is possible and a medium with excellent S/N ratio etc. can be provided! Wear.

In addition to the metal magnetic powder described above, the magnetic layer contains lubricants (e.g. silicone oil, graphite, molybdenum disulfide, tungsten disulfide, monobasic fatty acids having 12 to 20 carbon atoms (e.g. stearic acid) and carbon atoms. Number is 3~
fatty acid ester consisting of 26 monohydric alcohols, etc.)
etc. may be added.

Non-magnetic abrasive particles may also be added, including alumina (such as α-AlzOs (corundum)), artificial corundum, fused alumina, silicon carbide, chromium oxide, diamond, artificial diamond, garnet, emery ( Main ingredients: corundum and magnetite) etc. are used. The content of this abrasive material is preferably 20 parts by weight or less based on the magnetic powder, and the average particle thread size is preferably 0.5 μm or less, and 0.4
Even better is less than μm.

Furthermore, at least polyurethane can be used as the binder resin for the magnetic layer, which can be synthesized by reacting polyol and polyisocyanate. If a phenoxy resin and/or a vinyl chloride copolymer is contained together with polyurethane, the dispersibility of the magnetic powder will be improved when applied to a magnetic layer, and its mechanical strength will be increased. However, if only the phenoxy resin and/or the vinyl chloride copolymer is used, the layer becomes too hard, but this can be prevented by containing polyurethane, and the adhesion to the support or base layer is improved.

In addition to the above, cellulose resins, thermoplastic resins, thermosetting resins, reactive resins, and electron beam curable resins may be used as the binder resin.

There is no need to add an antistatic agent such as carbon black 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 surface electrical resistance of the magnetic layer is sufficiently reduced by this conductive layer. Because you can. In addition, the magnetic layer has improved packing density and dispersibility of the metal magnetic powder.

As the carbon black used for such a conductive layer, for example, Conductex 975 (specific surface area 250 r) manufactured by Columbia Carbon Japan Co., Ltd.
rf/g, particle size 24 mμ), Conductex 900
(specific pressure area 125rd/g, particle size 27mμ), Conductex 40-220 (particle size 20mμ), Conductex SC (particle size 20mμ), Cabot Vulcan X C-72 (specific surface area 254mμ) /g, particle size 30 mμ), Palcan P (particle size 20 mμ), Raven 1040.4201 Black Pearls 2000 (particle size 15 mμ), # manufactured by Mitsubishi Kasei ■
There are conductive carbon blacks such as No. 44. This carbon black has an oil absorption of 90d (DBP)/100
If it is more than g, it is desirable because it is easy to form a stracture structure and exhibits higher conductivity.

This conductive layer is made by fixing the above-mentioned carbon black with the same binder resin as above, and may further include the above-mentioned lubricant and the like. The carbon blank in this layer has an average particle size of 10 to 50 mμ (and even 20 to 40 mμ).
), the amount added is 10 to 100 parts by weight of the binder resin.
It is preferably 300 parts by weight (more preferably 50 to 150 parts by weight).

Further, in the magnetic disk according to the present invention, the dry film thickness of the magnetic layer is preferably 0.5 to 4.0 μm, and 1
．． 0 to 3.0 μm is even better. Further, the dry film thickness of the above conductive layer is preferably 0.5 to 4.0 μm, and 1.0 to 3.0 μm.
μm is even better.

The magnetic disk of the present invention, for example, as shown in FIG.
A conductive layer 2 containing the above-mentioned carbon black, a magnetic layer 4 containing the above-mentioned metal magnetic powder, and an overcoat layer (not shown) if necessary are arranged on both sides of the non-magnetic support 10 in this order. They are provided in a stacked manner.

The magnetic recording medium shown in FIG. 1 includes a conductive layer 2 and a support 1.
An undercoat layer (not shown) may be provided between the two, or an undercoat layer may not be provided (the same applies hereinafter).

Further, the support may be subjected to a discharge treatment.

The material of the support 1 may be plastics such as polyethylene terephthalate or polypropylene, or AfSZn.
Metals such as, glass, BNSSi carbide, ceramics such as porcelain, earthenware, etc. are used.

Next, an example of a method for manufacturing the above-mentioned medium based on the present invention will be explained with reference to FIG.

In this manufacturing apparatus, when manufacturing the medium shown in FIG. 1, the film-like support 1 fed out from the supply roll 32 is first transferred to the above-mentioned other magnet 33 by an extrusion type extrusion coater 10. It is introduced into a dryer 34 equipped with a non-orientation magnet 35, where it is dried by blowing hot air from nozzles arranged above and below. Next, the dried support 1 with each coated layer is transferred to a super calender device 37 consisting of a combination of calender rolls 38.
After being guided there and calendered there, it is wound onto a winding roll 39. Thereafter, the conductive layer 2 and the magnetic layer 4 are coated on the other side of the support 1 in the same manner as described above, dried, and calendered.The thus obtained magnetic film has a diameter of 2 An electronic still video floppy is manufactured by punching out an inch disc and storing it in a cassette.

In the above method, each paint may be fed to the extrusion coater 10.11 through an in-line mixer, not shown. In addition, in the figure, the arrow indicates the conveyance direction of the nonmagnetic base film. The extrusion coaters 10.11 are each provided with a reservoir 13.14 to deposit the paint from each coater in a wet-on-wet manner. That is, immediately after applying the conductive paint (in an undried state), the magnetic layer paint is applied in a multilayer manner.

In multilayer coating using this wet-on-wet method, since the upper magnetic layer is applied while the lower conductive layer is wet, the surface of the lower layer (i.e., the interface with the upper layer) is smooth and the surface of the upper layer is smooth. The surface properties of the layer are improved, and the adhesion between the upper and lower layers is also sufficient. As a result, a magnetic disk using metal magnetic powder, which requires high output and low noise for high-density recording, meets the performance requirements, and unlike magnetic tape, it has high dust resistance. Even when performance is required, film peeling is eliminated, film strength is improved, and durability is sufficient. Regarding durability, since the magnetic disk of the present invention does not require the addition of conductive powder to the magnetic layer, the durability of the separable layer is improved.

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

In addition to cases in which there is substantially a clear boundary between the upper and lower layers formed by multilayer coating using the wet-on-wet method described above, there is a boundary formed by a mixture of components of both layers at a certain thickness. Although there may be regions, the upper or lower layer excluding such boundary regions is the above-mentioned magnetic layer and conductive layer. Either case is within the scope of the present invention.

In addition, when forming the above-mentioned magnetic layer, etc., solvents that can be used in the paint include ketones (e.g., methyl ethyl ketone, cyclohexanone), ethers (e.g., diethyl ether), esters (e.g., ethyl acetate), and aromatic solvents. (for example, toluene), alcohols (for example, methanol), and these can be used alone or in combination.

E, Example The present invention will be explained in detail below.

The components, proportions, order of operations, etc. shown below may be changed in various ways without departing from the spirit of the invention. In addition, in the following examples, all "parts" are parts by weight.

The ingredients shown below are thoroughly kneaded and dispersed using a niegu and ball mill, and then, just before coating, 5 parts of a polyisocyanate compound (Coronate: manufactured by Nippon Polyurethane) is added to form a magnetic layer. A magnetic paint (1) and a conductive carbon black paint (n) were prepared.

Magnetic paint [■]: 100 parts of iron-nickel ferromagnetic alloy powder, Kickel content = 3% by weight, BET specific surface area: 43nf/g,
Coercive force (Hc) = 13500e) Polyurethane resin
5 parts of Tuboran 2304 (manufactured by Nippon Polyurethane) vinyl chloride-vinyl acetate-vinyl alcohol copolymer
8 parts (VAG) I: manufactured by U, C, C, USA) α-alumina 7 parts myristic acid
2-part butyl stearate
1 part cyclohexanone
200 parts toluene
30 parts methyl ethyl ketone 3
0 parts carbon black paint [■]: Carbon black 100 parts (Conductex 975 (C-975): manufactured by Columbian Carbon Japan ■) Polyurethane resin 60 parts and Tubolan 2304: manufactured by Nippon Polyurethane ■) Vinyl chloride -
Vinyl acetate-vinyl alcohol copolymer
60 copies (VAGH: US U, C,
Manufactured by Company C) Myristic acid 5 parts Butyl stearate 5 parts Cyclohexanone 600 parts Toluene
200 parts methyl ethyl ketone
200 parts Next, on a polyethylene terephthalate base film having a thickness of 32 μm, the above carbon black paint [■] and magnetic paint (1) were sequentially applied as shown in Table 1 below. After that, each paint (II
) and m were applied sequentially, and after drying, calendering was performed.

The thus obtained magnetic film was punched out into a disk shape of 2 inches in diameter and placed in a cassette to produce an electronic still video floppy.

Table 1 Carbon black paint (U) was applied with an extrusion coater, dried, and then magnetic paint [[] was applied as an upper layer, dried, and calendered to produce an electronic still with the same dry film thickness as Example 2. I made a video floppy.

Comparison 1: 2: An electronic still video floppy film having the same dry film thickness was prepared in the same manner as in Example 2, except that the extrusion type extrusion coater was replaced with a gravure roll coater.

This W21 Magnetic paint (1) was coated on a polyethylene terephthalate base film with a thickness of 32 μm, dried, and calendered to produce an electronic still video syrup coated in a single layer with a magnetic layer dry film thickness of 4.0 μm. Created.

A magnetic paint (111) having the same composition as the magnetic paint (2) was obtained except that 7 parts of carbon black (C975: manufactured by Columbian Carbon Japan) was added to the composition of the magnetic paint (H).

A single layer of this magnetic paint (I[I) was applied in the same manner as in Comparative Example 3 to produce an electronic still video floppy.

The following performance evaluations were performed on each of the above video floppies, and the results are shown in Table 2 below.

(The following is a blank space) (1) RF output A 7 MHz sine wave signal was recorded using an MVP-5500 manufactured by Calany ■, and the reproduced RF output was measured.

The measured reproduction RF outputs are listed in Table 2 as relative values when the reproduction RF output of the electronic still video floppy manufactured in Example 1 is expressed as O, OdB. The larger the RF specific output value, the better the electronic still video floppy.

(2) Noise level ■ Using a spectrum analyzer manufactured by Avantest, the 6 MHz noise level of the sample whose RF specific output was measured was measured. The measured noise level is shown in Example-
Table 2 shows the relative values when the noise level of the electronic still video floppy manufactured in 1 is 0.0 dB. The smaller the noise level value, the better the electronic still video floppy.

(3) Surface electrical resistivity The surface electrical resistivity was measured by placing 10 mm wide electrodes 10 mm apart and sandwiching the measurement material between them, and the surface electrical resistivity was recorded in Table 2.

The larger the value, the larger the surface electrical resistivity.

(4) Driving durability Using Hitachi's VX-SO, an electronic still video floppy with image signals recorded on 25 tracks was continuously played back in still mode, and the playback output was 3D.
The time taken for B to decrease was measured. The results are shown in Table-2.

(5) Dropout Using a dropout measuring machine manufactured by Konica ■, the length is 15 μm.
sec or more, dropout of 12dB or more in depth is 1
When an electronic still video floppy with 3 or more floppy disks is considered a dropout N0 product (defective product), it shows the pass rate (%) when 100 disks are measured.The higher the pass rate, the less dropouts. .

(The following is a blank space) From these results, by configuring and manufacturing a magnetic disk based on the present invention, it is possible to provide a magnetic disk with high output, low noise, high durability, and few dropouts.

As described above, the present invention provides a conductive layer containing carbon black between the magnetic layer and the non-magnetic support, so that the surface electrical resistance of the magnetic layer can be sufficiently reduced. In addition, the magnetic layer has improved packing density and dispersibility of the metal magnetic powder, resulting in excellent high-density recording, high output, and low noise.

In addition, since the magnetic layer paint is applied to the conductive footwear paint when it is still wet, the surface of the conductive layer (i.e., the interface with the magnetic layer) is smooth and the magnetic layer is smooth. The surface properties are good, and the adhesion between both layers is also sufficient. As a result, high output and low noise can be achieved, and film peeling is eliminated.
Improves durability.

[Brief explanation of drawings]

The drawings are for explaining the present invention by way of example, and FIG. 1 is a sectional view of an example of a magnetic disk, and FIG. 2 is a schematic diagram of a magnetic disk manufacturing apparatus. In addition, in the symbols shown in the drawings, 1......Nonmagnetic support 2......Conductive layer 4...Magnetic layer 10.11 ......Extrusion coater 34.
. . . Dryer 37 . . . It is a super calender device.

Claims (1)

[Claims] 1. 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 non-magnetic support. 2. On a non-magnetic support, a conductive layer paint containing carbon black and a magnetic layer paint containing metal magnetic powder are extruded in this order and coated with a coater, and at this time, the conductive layer paint A method of manufacturing a magnetic disk, wherein the magnetic layer coating material is applied when the magnetic disk is in an undried state.