JPH0442436A - Production of disk shape magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve surface property and to obtain high electromagnetic conversion characteristics by carrying out a burnishing process after a punching process in the production process including lubricant impregnation, punching into a disk form, curing of the magnetic layer and burnishing. CONSTITUTION:In the process including lubricant impregnation, punching into a disk form, curing of the magnetic layer, and burnishing, burnishing is carried out after the punching process. By burnishing the magnetic layer after the medium is punched into a disk form, the disk which is very small in size compared to a film can be polished under enough pressure, for example, while being rotated. Thereby, the magnetic layer of the medium can be adequately polished and the desired surface roughness can be easily obtained with good workability. Thus, the obtd. medium has improved electromagnetic conversion characteristics.

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to a method of manufacturing a disk-shaped magnetic recording medium.

BACKGROUND ART Conventionally, as a disk-shaped magnetic recording medium for still videos, computers, etc., there has been a magnetic recording medium in which a magnetic layer in which ferromagnetic alloy powder is dispersed in a binder is coated on a non-magnetic support. It is used.

Such a disk-shaped magnetic recording medium, such as an electronic still video floppy disk, is usually manufactured as follows. That is, after preparing a magnetic paint containing magnetic powder (ferromagnetic metal powder), this magnetic paint was filtered to remove poorly dispersed components, and a polyethylene terephthalate film (thickness: 2328 mm) was prepared.
(m) is coated on both sides using a reverse roll coater so that the dry thickness of each layer becomes 3.5 μm, and after removing the solvent under heating, calendering is performed. Then heat curing for the polyisocyanate compound in the magnetic layer (
After performing a lubricant impregnation process on the magnetic layer, the magnetic layer is punched out into a disk shape of 2 inches in diameter to produce an electronic still video floppy. Before the above punching process (after the lubricant impregnation process), a burnishing (surface polishing) process is performed.

However, as a result of the inventor's studies on the above-mentioned manufacturing method, he discovered that there are the following drawbacks. That is, in the conventional method, in the burnishing process before the punching process, the media of the film-like semi-finished product is run and polished in the width direction with a polishing tape, but at this time, the film is pressed against the polishing tape. If the air pressure for polishing is increased, the film will shake in the same width direction, making it impossible to obtain a uniform pressing force, and polishing will become uneven in places. Therefore, polishing can only be performed with weak air pressure, which may result in insufficient polishing, resulting in poor workability such as a decrease in the surface properties of the intended magnetic layer (as a result, electromagnetic conversion characteristics), or a longer polishing time. Become.

It is an object of the present invention to provide a manufacturing method capable of obtaining a disk-shaped magnetic recording medium with conversion characteristics with high productivity.

21 Constitution of the Invention That is, the present invention has a lubricant impregnation step for the magnetic layer, a punching step into a disk shape, a curing step for the magnetic layer, and a burnishing step, and after the punching step, the The present invention relates to a method for manufacturing a disk-shaped magnetic recording medium that performs a burnishing process.

The method for manufacturing a disk-shaped magnetic recording medium according to the present invention basically includes, for example, applying a magnetic paint, drying, and then calendering, followed by at least a lubricant impregnation step, a punching step into a disk shape, and a curing step for the magnetic layer. When performing the burnishing process, the burnishing process is performed after the punching process.

That is, the above-mentioned coating, drying, and calendering may be performed in a known order and by a known method, but in the subsequent steps, burnishing is performed after punching into a cheesecloth shape, so the size is much smaller than that of a film. For example, a small disk medium can be polished while rotating and applying sufficient pressure.

FIG. 4 shows a state after punching, in which the disk medium 10 is rotated upward and air 31 is blown from the bottom side to press the medium 10 against the polishing tape 30, and the medium 10 is polished in the radial direction by the polishing tape 30. It shows. The tape 30 is fed out from the feed roll 32 to the take-up roll 33, guided and supported by the guide means 34, and moved as a whole in the radial direction, while air 31 is ejected by the ejection means 35 having a slit-shaped air ejection port. Ru.

In FIG. 5, the polishing area 36 for the medium 10 is shown in phantom lines.

Since such burnish polishing is performed on the disk medium 10, even if the pressure of the air 31 is sufficient (for example, 1 kg), the disk 10 will be pressed against the tape 30 without wobbling. Become. As a result, the surface of the magnetic layer of the medium is sufficiently polished, and the desired surface roughness can be obtained with good workability, so that it is possible to improve the IT electromagnetic conversion characteristics, and the polishing efficiency is also good. This greatly improves productivity.

The main steps of the method according to the invention are illustrated in Figures 1 to 3.
There are combinations of steps illustrated in the figure. FIG. 1 shows a method in which a lubricant impregnation step (for example, lubricant overcoat→drying) is performed, followed by curing, and then burnishing is performed after punching into a disk shape.

FIG. 2 shows a method in which curing is performed after punching in FIG. 1, and FIG. 3 shows a method in which punching is performed in FIG. 2 before lubricant impregnation.

Both methods have the order of punching and burnishing according to the present invention, and as described above, sufficient polishing is possible, and it is possible to improve electromagnetic conversion characteristics by improving surface properties. Note that if the lubricant impregnation is performed before curing, the binder in the magnetic layer is in an uncured state and has not yet formed a crosslinked structure. Therefore, the lubricant can penetrate into the magnetic layer in sufficient quantity and will be properly retained within the crosslinked structure upon subsequent curing. In other words, the crosslinked structure holds the lubricant molecules, and when a shortage occurs on the surface of the magnetic layer, the lubricant oozes out from inside the magnetic layer, resulting in good durability. becomes. Furthermore, if the punching step is performed after the lubricant impregnation step, the lubricant impregnation work (overcoating) will be easier and mass productivity will be improved.

Next, in the above, lubricants used in the lubricant impregnation step include fatty acid esters (e.g. isooctyl palmitate), -basic fatty acids (e.g. stearic acid),
silicone oil, graphite, molybdenum disulfide,
Examples include tungsten disulfide, but fatty acid esters are preferred.

The lubricant can be impregnated into the magnetic layer by dissolving the lubricant in a solvent to a predetermined concentration, applying this solution by roll coating, etc., and drying it at a predetermined temperature. This impregnation amount is 20 to 60
■/d is even better (30 to 50 ■/d is better. Also, the impregnation of the lubricant after punching may be performed using a spin cord that applies the lubricant while rotating the disk body.

Further, the burnishing process is performed by polishing the surface of the magnetic layer with a polishing tape, for example, as shown in FIG. 4, but other methods (eg, diamond foil) may be used. The polishing amount by burnishing is as follows: After burnishing, the surface roughness of the magnetic layer is 0.001 in Ra.
It is preferable to make it smaller by about 0.002.

(Before burnishing) (After burnishing) Ra 0.01
2-0. O05Ra O,011 to 0.004 (more preferably (more preferably Ra O,010
~0.008) RaO,009~0.00
7) For example, the burnish conditions are as follows.

Linear pressure: 3 kg/ci + Rotation speed: 250 Orpm Burnishing: 2 hours: 1 second Polishing tape: G C10000 (manufactured by Micro Coating Co., Ltd.) In addition, the above punching process is performed by punching with a die while transporting the medium semi-finished product. The method itself is known.

Furthermore, the above-mentioned curing is a heating step to completely react the unreacted curing agent in the magnetic layer with the binder to form a crosslinked structure.
It is preferable to carry out the heating for 2 hours, preferably at 65 to 70°C for 48 to 60 hours.

Further, the application, drying, and calendering of the magnetic paint described above can be performed by known methods.

Here, as the magnetic powder of the magnetic layer, F e -Aj! It is preferable to use metal magnetic powders (ferromagnetic alloy powders) such as Fe, Ni, Co, Fe-Aj! system, Fe-Al2-Ni system, Fe-Af
-Co system, Fe-Ni-3i system, Fe-Al2-Zn system, Fe-Ni-Co system, FeMn-Zn system, Fe-Ni
system, Fe-Ni-At system, Fe-Ni-Zn system, Fe
-Ni-Mn system, Fe-Co -N i-P system, Co
-Ni-based, Fe.

Examples include ferromagnetic powder such as metal magnetic powder containing Nj, Co, etc. as a main component. Among them, Fe-Al5Fe-Al2-Ni is particularly preferred in terms of corrosion resistance and dispersibility.

Fe-Al-Zn, Fe-Al2-Co, Fe-Ni.

Fe-N1-Al2, Fe-Ni-Zn5Fe-NiA
Metal magnetic powders of the f-3i-Zn and Fe-N1-Al2-3i-Mn systems are preferred.

These metal magnetic powders have high saturation magnetization and coercive force, and are excellent for high-density recording. In addition, the specific surface area is 40rrf/
Specific surface area (BET value) of g or more, especially 42rd/g or more
By using the above-mentioned ferromagnetic alloy powder, the electromagnetic conversion characteristics are greatly improved. In addition, the coercive force (coercive force) of the ferromagnetic metal powder is usually 10,000e or more (preferably 1
2000 e or higher).

Further, there is no particular restriction on the shape of the magnetic powder that can be used in the present invention, and for example, acicular, spherical, etc. can be used.

Since the above magnetic powder is a metal magnetic powder, it is difficult to disperse it sufficiently, but this can be sufficiently prevented by using the following polyurethane resin as a binder in the magnetic layer, which improves dispersibility. be able to.

That is, the polyurethane resins used are 505M, O5OzM, PO(OM')! ,−
0PO(OM')ffi (where M is hydrogen or an alkali metal such as lithium, potassium, sodium, etc., M' is an alkali metal such as hydrogen, lithium, potassium, sodium, etc.) (Il aqueous polar group) These polar groups in the molecule, which are preferably contained one or more, improve the compatibility between the resin and the magnetic powder, thereby improving the dispersibility of the magnetic powder and preventing agglomeration of the magnetic powder. By preventing this, the stability of the coating liquid can be further improved, and the durability of the medium can also be improved.

Regarding the synthesis of such a polyurethane resin, a reaction between a polyol and a polyisocyanate, which is a commonly used method, can be used. As the polyol component, generally used is a polyester polyol obtained by the reaction of a polyol and a polybasic acid. Therefore, by using the above polyester polyol having a polar group as a raw material, a polyurethane having a polar group can be synthesized.

Polyols that can be used include organic dibasic acids such as phthalic acid, adipic acid, trimerized lyluic acid, and maleic acid;
Glycols such as ethylene glycol, propylene glycol, butylene glycol, diethylene glycol, trimethylolpropane, hexanetriol,
Polyester polyol synthesized by reaction with polyhydric alcohols such as glycerin, trimethylolethane, pentaerythritol, or any two or more polyols selected from these glycols and polyhydric alcohols; or S - Lactone polyester polyols synthesized from lactams such as caprolactam, α-methyl-1-caprolactam, S-methyl-S-caprolactam, and γ-butyrolactam; or polyethers synthesized from ethylene oxide, propylene oxide, butylene oxide, etc. These polyols include tolylene diisocyanate (TDI), hexamethylene diisocyanate (HMDI), methylene diisocyanate, metaxylylene diisocyanate, diphenylmethane-4,4-diisocyanate (MDI), etc.
), 1,5-naphthalene diisocyanate (NDI)
, tolisine diisocyanate (TODI), and lysine isocyanate methyl ester (LDI), thereby synthesizing urethanized polyester polyurethane, polyether polyurethane, and polycarbonate polyurethane carbonated with phosgene or diphenyl carbonate. These polyurethanes are usually produced primarily by the reaction of polyisocyanates and polyols and are also in the form of urethane resins or urethane prepolymers containing free isocyanate groups and/or hydroxyl groups, or containing reactive end groups of these. (for example, in the form of a urethane elastomer).

Since the methods for producing polyurethane, urethane prepolymers, urethane elastomers, curing and crosslinking methods, etc. are well known, detailed explanation thereof will be omitted.

Alternatively, for example, a polyurethane resin into which polyfunctional -OH has been introduced is produced, and this polyurethane resin is reacted with a compound containing a polar group and chlorine described below (dehydrochloric acid reaction) to impart a polar group to the polyurethane resin. You can use the method of introduction.

CfCH,CH,SOs M, C1,CH,CH,050,M, CIGHzCOOM CI CHz PO(OM') t, The weight average molecular weight of this polyurethane resin is generally 1 to 15.
It is preferable to set the reaction conditions so that the amount is within the range of 20,000 to 60,000 (preferably 20,000 to 60,000).

In addition, the above polyurethane resin usually has a content of repeating units having polar groups in the copolymer from 0.01 to
The content is preferably within the range of 5 mol% (preferably 0.1 to 2.0 mol%).

Regarding the introduction of polar groups into polyurethane, please refer to Japanese Patent Publication No. 58-41565, Japanese Patent Publication No. 57-92422, Japanese Patent Publication No. 57-92423, Japanese Patent Publication No. 59-8127, Japanese Patent Publication No. 59-5.
No. 423, No. 59-5424, No. 62-121923
There are descriptions in publications such as No., and these can also be used in the present invention.

The above-mentioned polyurethane resin can further improve the abrasion resistance of the magnetic layer and provide appropriate flexibility. and,
When a vinyl chloride resin is used in combination with this polyurethane resin, it is possible to improve the dispersion of the magnetic powder and improve the mechanical strength of the magnetic layer. The weight ratio of the resin is 80:20 to 20:80 (preferably 70
: 30 to 40 : 60).

Usable vinyl chloride resins can be synthesized by adding to a copolymer containing an OH group, such as a vinyl chloride-vinyl alcohol copolymer, by reaction with a compound containing a polar group and a chlorine atom, as shown below. can do.

Cj!　CHz　CHz　S　Os　M.

CfCHtCHt050. M.

Cj! CHt P O(OM') z, CjIC
H,C00M From these, CjICHz CH,SO* Na is shown as an example: (CHzCH) -10Cj2 (C1lz)t 5
OJaH → −(CHz−CH) + IC120(C
Hz)z-SOsNa.

Alternatively, there is a method of copolymerizing all of them as copolymerizable monomers. That is, a predetermined amount of a reactive monomer having an unsaturated bond into which a repeating unit containing a polar group is introduced is injected into a reaction vessel such as an autoclave, and a suitable polymerization initiator such as BPO (benzoyl peroxide), AIBN (
Polymerization can be carried out using a radical polymerization initiator such as azobisisobutyronitrile), a redox polymerization initiator, an anionic polymerization initiator, a cationic polymerization initiator, etc. For example, sulfonic acid or its salt is introduced. Specific examples of reactive monomers include unsaturated hydrocarbon sulfonic acids such as vinylsulfonic acid, allylsulfonic acid, methacrylsulfonic acid, p-styrenesulfonic acid, and salts thereof.

Furthermore, sulfoalkyl esters of acrylic acid or methacrylic acid such as 2-acrylamido-2-methylpropanesulfonic acid, (meth)acrylic acid sulfoethyl ester, (meth)acrylic acid sulfopropyl ester, salts thereof, or acrylic acid. -2-ethyl sulfonate, etc. can be mentioned.

When introducing carboxylic acid or its salt (introduction of COOM), (meth)acrylic acid, maleic acid, etc. are used, and when phosphoric acid or its salt is introduced, (meth)acrylic acid-2-phosphate ester is used. good.

Further, it is preferable that an epoxy group is introduced into the vinyl chloride copolymer.The introduction of the epoxy group improves the thermal stability of the vinyl chloride copolymer. When introducing an epoxy group, the content of repeating units having an epoxy group in the copolymer is preferably 1 to 30 mol% (more preferably 1 to 20 mol%).The monomer for introducing is glycidyl. Acrylates are preferably used.

Regarding the introduction of polar groups into vinyl chloride copolymers, please refer to JP-A Nos. 57-44227, 5B-108052, 59-8127, 60-101161, 6
No. 0-235814, No. 60-238306, No. 60
-238371, 62-121923, 62-
There are descriptions in publications such as No. 146432 and No. 62-146433, and these can also be used in the present invention.

In the present invention, in addition to the binder described above, conventionally used unmodified vinyl chloride resins, polyurethane resins, or polyester resins can be used in combination or alone, and textile resins, phenoxy resins, etc. Resins, thermoplastic resins, thermosetting resins, reactive resins, electron beam curable resins, etc. that have a specific usage method may be used in combination.

In addition to the magnetic powder and binder described above, the magnetic layer contains a lubricant (
For example, silicone oil, graphite, molybdenum disulfide, tungsten disulfide, -basic fatty acids (e.g. stearic acid), fatty acid esters, etc.) may be added.
In addition, alumina (α-A1.
z Os (corundum), etc.), artificial corundum, fused alumina, silicon carbide, chromium oxide, diamond,
α-Fe, 0° (hematite), artificial diamond, garnet, emery (main components: corundum and magnetite), etc. may also be used in small amounts.An antistatic agent such as carbon plaque may be added to the above magnetic layer. It's okay.

Solvents that can be used in magnetic paints include ketones (e.g. methyl ethyl ketone), ethers II (e.g. diethyl ether), esters (e.g. ethyl acetate), aromatic solvents (e.g. toluene), alcohols M (e.g. methanol). ), and these can be used alone or in combination.

The disk-shaped magnetic recording medium obtained by the method of the present invention is, for example, as shown at 10 in FIG. It is. If necessary, an overcoat layer (not shown) may be further provided on the magnetic layer.

The dry film thickness of the magnetic layer 24 is preferably 0.5 to 4.5 μm, more preferably 3.0 to 4.0 μm.

When the intermediate layer 22 is provided under the magnetic layer, a subbing layer may be formed by coating the various binders described above. It is provided for the purpose of improving adhesiveness, improving conductivity, etc.

Examples of materials for the support 21 include polyesters such as polyethylene terephthalate and polyethylene-2,6-naphthalate, polyolefins such as polypropylene, cellulose derivatives such as cellulose triacetate and cellulose diacetate, and plastics such as polycarbonate. be able to. Furthermore, Cu5
A7! , non-magnetic metals such as Zn, glass, so-called new ceramics, etc. can also be used.

The thickness of the support formed using these materials is usually 1
It is within the range of 0 to 80 μm.

A magnetic layer is provided on at least one surface of the support, but usually the other surface also has a magnetic layer as described above. By providing magnetic layers on both sides in this manner, deformation (curling) of the magnetic disk can be effectively prevented. However, it is also possible to prevent curling by providing a back coat layer on the back surface.

Note that the present invention may be applied to magnetic disks such as video floppies and data floppies for electronic still cameras, for example.

water, examples The present invention will be explained in detail below.

Various changes may be made to the ingredients, proportions, order of operations, etc. shown below without departing from the spirit of the present invention.

(Example 1) The components shown below were sufficiently mixed and dispersed using a disper kneader and a ball mill, and then, immediately before coating, a polyisocyanate compound (Coronate L: Nippon Polyurethane
Magnetic paint [1] was prepared by adding and mixing 5 parts by weight of Magnetic paint [1].

1 ■ - Ferromagnetic alloy powder 1 100 parts by weight of iron-aluminum ferromagnetic alloy powder (aluminum content: 4% by weight, specific surface area: 42 po/g, coercive force (Hc): 12500 e Polyurethane resin 6 parts by weight ( U made by Toyobo Co., Ltd.
R-8200: Vinyl chloride copolymer (contains So, Na group) 10 parts by weight (contains MRIIO Nippon Zeon So, Na group) Alumina oxide/1. Oyu 10 parts by weight (average particle size: 20.4 μm) Carbon black 0.5 parts by weight (
Average particle size: 55 nm BET specific surface area: 32 bo/g DBP oil equipment 180 d/lo Og) Oleic acid
1 part by weight isooctyl palmitate 】Part by weight cyclohexanone
100 parts by weight methyl ethyl ketone
100 parts by weight toluene
100 parts by weight of the obtained magnetic paint was filtered to remove poorly dispersed components, and coated on both sides of a polyethylene terephthalate film (thickness = 32 μm) using a reverse roll coater so that the dry thickness of each was 3.5 μm. After the solvent was removed under heating, calendering was performed.

Thereafter, a 1% solution of isooctyl palmitate (solvent: n-hexanone) was applied to the magnetic layer using a reverse roll coater, and dried at 90°C for 10 seconds. The polyisocyanate compound in the magnetic layer was then cured by heat treatment at 65° C. for 50 minutes. Thereafter, it was punched out into a disc shape with a diameter of 2 inches, and then burnished in the radial direction using a polishing tape. Polishing conditions are linear pressure:
3kg/cm, rotation speed = 250Orpm, burnish time: 1 second, polishing tape: G C10000 (
(manufactured by Micro Coating Co., Ltd.), and then placed in a cassette to produce an electronic still video floppy.

(Example 2) In Example 1, after calendering, a lubricant impregnation step was carried out in the same manner, and then a disk shape of 2 inches in diameter was punched out, and heat curing was performed for the polyisocyanate compound. , a burnishing process was performed to produce an electronic still video floppy.

(Example 3) In Example 1, after performing the calendering process, it was similarly punched into a disc shape with a diameter of 2 inches, followed by a lubricant impregnation step, and then heat curing (curing) for the polyisocyanate compound. Then, a burnishing process was performed to produce an electronic still video floppy.

(Comparative Example 1) In Example 1, after calendering, a lubricant impregnation process was performed, a burnishing process was performed, and then a disk shape with a diameter of 2 inches was punched, and then a polyisocyanate compound was A heat-cured electronic still video floppy was manufactured.

(Comparative Example 2) In Example 1, after calendering, a burnishing process was performed, followed by punching into a disc shape with a diameter of 2 inches, followed by a lubricant impregnation process, and heat curing for the polyisocyanate compound ( cure) to produce an electronic still video floppy.

(Comparative Example 3) In Example 1, after performing the calender treatment, a lubricant impregnation step was performed, followed by heat curing (curing) for the polyisocyanate compound, and a burnishing step.
Then, it was punched into a disk shape with a diameter of 2 inches to produce an electronic still video floppy.

(Comparative Example 4) In Example 1, after calendering, a burnishing process and a lubricant impregnation process were performed, followed by heat curing for the polyisocyanate compound, and then a 2-inch diameter disk was formed. An electronic still video floppy disk was manufactured by punching out a shape.

(Comparative Example 5) An electronic still video floppy was manufactured in the same manner as in Example 1 except that the burnishing process was not performed.

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

'-Seek commercially available electronic still video floppy recorder (AG8
00, manufactured by Matsushita Electric Industrial ■), the image signal is
0) In the still mode of the electronic still video floppy recorded on all the racks, playback of each track for 4 seconds is continuously repeated from 1 to 50 tracks, and the playback output is increased from the initial value to 3.
The time until the image quality decreased by dB or until image quality deterioration such as dropout occurred in the reproduced image was measured. The results are shown in the table below.

In the same table, 300 hours or more means that the reproduction output did not decrease by 3 dB and the image quality did not deteriorate even after 300 hours of reproduction.

A 7 MHz sine wave signal was recorded using an MVR-5500 manufactured by Yoshitomo Sony ■, and the reproduced RF output was measured. The measured reproduced RF outputs are listed in the table below as relative values to the gold reference values. The larger the RF small output value, the better the electronic still video floppy.

From this result, it can be seen that by manufacturing in the order of punching and burnishing according to the present invention, polishing can be performed sufficiently and the small RF output can be greatly improved. Moreover, durability can also be maintained satisfactorily. Those without burnishing have good durability, but have a small RF output drop.

Since burnishing is performed after extraction, the disk can be pressed with sufficient pressure against the polishing means without causing pre-cursions, and as a result, the magnetic layer of the medium is sufficiently polished to achieve the desired surface roughness. Therefore, the electromagnetic conversion characteristics can be improved, and the polishing efficiency is also good, and the productivity is greatly improved.

[Brief explanation of the drawing]

The drawings are for explaining the present invention, and include FIG.
Figures 2 and 3. 1 are charts showing the main flow of the manufacturing process for disk-shaped media, Figure 4 is a schematic side view during burnishing, Figure 5 is a schematic plan view during burnishing, and Figure 6 is a schematic plan view during burnishing.
The figure is a cross-sectional view of an example of a disk-shaped medium according to the present invention. In addition, in the symbols shown in the drawings, 10...Disk medium 21...Nonmagnetic support 22...Intermediate layer 24... . . . Magnetic layer 30 . . . Polishing tape 31 . . . Air. Figure 1

Claims (1)

[Claims] 1. A lubricant impregnation step for the magnetic layer, a punching step into a disk shape, and a curing step for the magnetic layer,
a burnishing step, and performing the burnishing step after the punching step.