JP2000030247A - Production of magnetic disk - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a process for production capable of producing a coating type magnetic disk which produces less curling. SOLUTION: A lower layer coating film is formed by applying a nonmagnetic coating material contg. nonmagnetic powder on a nonmagnetic base, and thereafter an upper layer coating film is formed by applying a magnetic coating material contg. the ferromagnetic powder on this lower layer coating film. A raw sheet roll is manufactured by subjecting this nonmagnetic base to a calender treatment and is then taken up again, while the raw sheet roll is held on a heating roll in a direction reverse from the winding direction of the roll. The raw sheet roll is blanked to a prescribed size after a curing treatment. At this time, a temp. T of the heating roll 28 is set at Tg<=T<=Tg+30 deg.C, when the glass transition point of the nonmagnetic base is defined as Tg. The temp. of the calender treatment and the temp. of the curing treatment are set lower by 5 deg.C or more than the temp. of the heating roll. The raw sheet roll of the magnetic disk is taken up again, while the roll is held around the heated roll in the direction reverse from the winding direction, as a result of which curling is drastically improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a magnetic recording medium, and more particularly, to a method for manufacturing a multilayer-coated magnetic disk, and to a technique for preventing curling.

[0002]

2. Description of the Related Art Conventionally, as a magnetic medium such as a magnetic tape or a magnetic disk, a magnetic coating prepared by dispersing a ferromagnetic powder in a binder is applied to a non-magnetic support to form a magnetic layer. A so-called coating type magnetic recording medium in which is formed is widely used.

[0003] In recent years, in the field of magnetic recording, high-density recording and shorter wavelength have been progressing, and the above-mentioned coating type magnetic recording medium has characteristics corresponding to such high-density recording and shorter wavelength. It is required to have.

Here, in a coating type magnetic recording medium, as a method of improving the electromagnetic conversion characteristics even in a high density recording area,
Thinning of the magnetic layer may be mentioned. Thereby, the self-demagnetization loss at the time of recording and the thickness loss at the time of reproduction are reduced, and the electromagnetic conversion characteristics are effectively improved.

However, by making the magnetic layer thinner, the surface depends on the surface properties on the nonmagnetic support.
If the surface of the nonmagnetic support is rough, the surface of the magnetic layer becomes rough according to its shape. As a result, the electromagnetic conversion characteristics are deteriorated or a dropout is induced due to the spacing loss.

Therefore, in a coating type magnetic recording medium, a relatively thick lower non-magnetic layer is interposed between the magnetic layer and the non-magnetic support, so that the magnetic layer does not follow the surface shape of the non-magnetic support. There has been proposed a multilayer coating type structure in which a layer surface can be freely designed. Therefore, in a multilayer coating type magnetic recording medium, excellent electromagnetic conversion characteristics can be obtained in a short wavelength region.

[0007]

By the way, due to the increase in track density and the like accompanying the recent increase in capacity of magnetic disks,
The electrical, mechanical, and physical properties required of media have become more stringent. In coating magnetic disks, in order to obtain excellent characteristics, the design of the disk shape is also an important factor in addition to the surface design described above.

[0008] In the case of a coating type magnetic disk, since it is cut out to a predetermined size from the rolled material, it is manufactured.
The curl remains on the sheet. Alternatively, when the non-magnetic support roll before the coating layer is formed has a large curl, the curl is further increased.

When a disk having such a distortion (curl) is used, the followability of the head is deteriorated, causing a fluctuation, and as a result, the electromagnetic conversion characteristics are deteriorated. In particular, at the time of low-speed rotation, such a recovery of the distortion of the magnetic sheet cannot be obtained, and when the distortion is large, the surface deflection occurs even at the time of high-speed rotation. Further, the contact with the head becomes strong, which results in damaging the magnetic sheet and deteriorating durability. In addition, problems arise when incorporating into a shell. In particular, the defect rate when attaching the center plate is increased.

Accordingly, the present invention has been proposed in view of such a conventional situation, and has as its object to provide a manufacturing method capable of manufacturing a coating type magnetic disk with less curl.

[0011]

In order to achieve the above-mentioned object, the present invention provides a method for applying a non-magnetic paint containing a non-magnetic powder on a non-magnetic support to form a lower coating film. An upper coating film is formed by applying a magnetic paint containing a ferromagnetic powder on the lower coating film, and then calendered to produce a raw roll, which is then heated in a direction opposite to the winding direction of the raw roll. Rewind it while holding it in a roll, and after curing,
It is characterized by punching into a predetermined size.

Curling is greatly improved by rewinding the original roll of the magnetic disk while holding it on a roll heated in a direction opposite to the winding direction.

[0013]

Embodiments of the present invention will be described below.

In order to prepare a multi-layer type magnetic disk, a lower layer non-magnetic paint prepared by dispersing a non-magnetic powder and a binder together with a solvent on a non-magnetic support is applied to the lower layer coating film. Is formed, the upper layer coating film is formed by applying an upper layer magnetic paint prepared by dispersing a magnetic powder and a binder together with a solvent on the lower layer coating film. Means for forming these two layers include a so-called wet-on-wet coating method in which an upper layer coating is formed in a lower layer coating while the lower layer coating is in a wet state, or a method in which the lower layer coating is applied and dried. After that, a wet-on-wet coating method in which an upper layer coating film is formed on the lower layer coating film may be mentioned, but any method may be used.

Specific materials for the upper magnetic layer in the present invention include the following.

First, the upper magnetic layer is mainly composed of a ferromagnetic powder and a binder. As the ferromagnetic powder, any conventionally known ferromagnetic powder can be used, and an oxide magnetic powder may be used. Metal magnetic powder may be used. Examples of the oxide magnetic powder include γ-Fe ₂ O ₃ and Co-containing γ-Fe ₂
O ₃ , Fe ₃ O ₄ , Co-containing γ-Fe ₃ O ₄ , Co-deposited-F
e ₃ O ₄ , CrO ₂ , and the like. Examples of the metal magnetic powder include Fe, Co, Ni, Fe-Co, and Fe-
Ni, Fe-Co-Ni, Co-Ni, Fe-Co-
B, Fe-Co-Cr-B, Mn-Bi, Mn-Al,
Fe-Co-V and the like. Further, for the purpose of improving these various properties, Al, Si, Ti, Cr, Mn,
A metal component such as Cu or Zn may be added. Of these, Fe-based magnetic powders have excellent electrical characteristics. At the time of corrosion resistance and dispersibility, Fe-Al
System, Fe-Al-Ca system, Fe-Al-Zn system, Fe-
Al-Co system, Fe-Ni-Si-Al-Zn system, Fe
Fe-Al alloy powders such as -Ni-Si-Al-Mn are preferred. The shape of these ferromagnetic powders has an average major axis length of 0.5 μm or less, preferably 0.01 to 0.4 μm.
m, more preferably 0.01 to 0.3 μm, and an axial ratio (average major axis length / average minor axis length) of 12 or less, preferably 10 or less.

In each case, the saturation magnetization (σs) is 70
It is preferably at least emu / g. 7 saturation magnetization
If it is less than 0 emu / g, sufficient electromagnetic conversion characteristics may not be obtained.

Further, in view of enabling recording and reproduction in a high-density recording area, the specific surface area by the BET method is 45 m ² / g.
It is preferable that it is above. Also, hexagonal ferrites such as barium ferrite, iron nitride, and the like can be used.

The barium ferrite is a barium ferrite in which a part of Fe is replaced by at least Co and Zn, and has an average grain size (diagonal length of the plate surface of hexagonal ferrite) of 300 to 900 angstroms. The plate ratio (value obtained by excluding the length of the diagonal line of the plate surface of hexagonal ferrite by the plate thickness) is 2.0 to 10.0, and the coercive force is 450 to 1
500 Oe is preferred.

Typical examples of the binder include a polyurethane resin, a polyester resin, and a vinyl chloride resin such as a vinyl chloride copolymer.

These resins include -SO ₃ M, -OSO ₃ M,
—COOM, —PO (OM ′) ₂ (where M represents a hydrogen atom or an alkali metal, and M ′ represents a hydrogen atom or an alkali atom or an alkali group) and has at least one polar group selected from a sulfopetine group. It preferably contains a repeating unit. These polar groups have the effect of improving the dispersibility of the ferromagnetic powder, and the content is.
It is preferably from 1 to 8.0 mol%, more preferably from 0.2 to 6.0 mol%. When the content of the polar group is less than 0.1 mol%, the dispersibility of the magnetic powder is reduced. Conversely, the content is 8.
If it exceeds 0 mol%, the magnetic paint tends to gel. The weight average molecular weight of the resin is 15,000 to 50.
It is preferably in the range of 000.

The vinyl chloride copolymer containing a dendritic group is an addition reaction between a copolymer having a hydroxyl group such as a vinyl chloride-vinyl alcohol copolymer and a compound having a polar group and a chlorine atom. It can be synthesized more.

The polyester is synthesized by reacting a polyol with a polybasic acid. Polyesters having other polar groups introduced can also be synthesized by known methods.

Polyurethane is synthesized by a reaction between a polyol and a polyisocyanate. As this polyol, a polyester polyol obtained by reacting a polyol with a polybasic acid is generally used. When a polyester polyol having a polar group is used as a raw material, a polyurethane having a polar group can be synthesized.

These resins may be used alone or in combination of two or more. For example,
When a mixture of polyurethane and / or polyester and a vinyl chloride resin is used, the weight ratio is 90: 1.
The range is from 0 to 10:90, preferably from 70:30 to 30:70.

Further, the following resin is added to 50% by weight of the total binder.
The following usage amount may be used together.

That is, the resin used in combination is a vinyl chloride-vinyl acetate copolymer, a vinyl chloride-vinylidene chloride copolymer, a vinyl chloride-acrylonitrile copolymer, a butadiene acrylonitrile copolymer having a weight average molecular weight of 10,000 to 200,000. Coalesce, polyamide resin, polyvinyl butyral, cellulose derivative, styrene-butadiene copolymer, phenol resin, epoxy resin, urea resin, melamine resin, phenoxy resin, silicone resin,
Acrylic resins, urea formamide resins, various synthetic rubber resins, and the like are included.

As the binder, the above-mentioned resins are used. The amount of the binder to be mixed in the upper magnetic layer is preferably 8 to 25 parts by weight per 100 parts by weight of the ferromagnetic metal powder. And preferably 10 to 20 parts by weight.

In order to improve the running durability and the like of the medium, additives such as abrasives, lubricants, dispersants, antistatic agents and the like usually used in this type of magnetic recording medium are added to the upper magnetic layer. May be added.

The abrasive has an average particle diameter of 0.05 to
The thickness is 0.6 μm, preferably 0.05 to 0.3 μm.

The addition amount is suitably 3 to 20 parts by weight, preferably 5 to 10 parts by weight, based on 100 parts by weight of the magnetic powder.

As the lubricant, fatty acids and fatty acid esters are used alone or in combination. The fatty acid may be a monobasic acid or a dibasic acid and has 6 to 6 carbon atoms.
30 is preferable, and it is more preferable that it is 12-22.

The addition amount of these fatty acids and fatty acid esters is preferably from 0.2 to 10% by weight, more preferably from 0.5 to 5% by weight, based on the magnetic powder.

When the amount of the fatty acid is less than 0.2% by weight, the running property of the medium is not sufficiently improved.
If it exceeds 0% by weight, the fatty acid tends to exude to the surface of the magnetic layer or to lower the output.

On the other hand, if the amount of the fatty acid ester is less than 0.2% by weight, the still durability is particularly insufficient.

If it exceeds 100% by weight, the fatty acid ester is likely to exude to the surface of the magnetic layer or to lower the output. The ratio between the fatty acid and the fatty acid ester is preferably from 10:90 to 90:10 by weight.

A known lubricant may be used in combination with the above fatty acids and fatty acid esters. Examples of the lubricant used in combination include silicone oil, carbon fluoride, fatty acid amide, olefin oxide and the like.

As the curing agent, a polyisocyanate or the like is used. Examples of the polyisocyanate include an aromatic polyisocyanate such as an adduct of tolylene diisocyanate (TDI) and an active hydrogen compound, and a fatty acid polyisocyanate such as an adduct of hexamethylene diisocyanate (HMDI) and an active hydrogen compound. Can be The weight average molecular weight of these polyisocyanates is 100 to 3
000 is desirable.

As the dispersant, for example, JP-A-4-214
Compounds as described in JP-A-218 can be used.
These dispersants are 0.5 to 5% by weight based on the magnetic powder.
It is appropriate to use within the range.

As an antistatic agent, for example, JP-A-4-24-2
Surfactants such as those described in 14218 can be used. The addition amount of these antistatic agents is preferably in the range of 0.01 to 40% by weight based on the binder. Any of conventionally known materials can be used as these additives, and the additives are not limited at all.

On the other hand, the lower nonmagnetic layer mainly comprises a nonmagnetic powder,
It is composed of a binder.

First, non-magnetic powders include carbon black, graphite, TiO ₂ , barium sulfate, Zn
S, MgCO ₃ , CaCO ₃ , ZnO, CaO, tungsten disulfide, molybdenum disulfide, MgO, SnO ₂ , S
iO ₂ , Cr ₂ O ₃ , α-Al ₂ O ₃ , α-Fe ₂ O ₃ , Si
C, cerium sulfide, silicon nitride, silicon carbide, molybdenum carbide, titanium carbide and the like. Of these,
Carbon black, TiO ₂ , barium sulfate, α-Al ₂
Inorganic powders such as O ₃ , α-Fe ₂ O ₃ and Cr ₂ O ₃ are preferred.

These non-magnetic powders may be surface-treated with a Si compound or an Al compound. The surface treatment is preferably performed such that the content of Si and Al is 0.1 to 10% by weight based on the nonmagnetic powder.

The shape of the above-mentioned nonmagnetic powder may be acicular or spherical, and preferably acicular. By using the acicular nonmagnetic powder, the smoothness of the surface of the nonmagnetic layer is improved, and as a result, the surface of the upper magnetic layer laminated thereon is also smooth. The major axis diameter, minor axis diameter and axial ratio (major axis diameter / minor axis diameter) of the nonmagnetic powder are preferably in the following ranges.

That is, the major axis of the non-magnetic powder is 0.5 μm or less, preferably 0.30 μm or less.

The minor axis diameter is preferably 0.1 μm or less, more preferably 0.06 μm or less. Further, the axial ratio (major axis diameter / minor axis diameter) is suitably 2 to 20, preferably 5 to 10. The specific surface area is 10 to 250 m ² / g, preferably 30 to 100 m ² / g. When the nonmagnetic powder having the major axis diameter, the minor axis diameter, the axial ratio, and the specific surface area as described above is used, the surface of the upper magnetic layer laminated thereon is also in a good state.

The mixing amount of the nonmagnetic powder in the lower nonmagnetic layer is as follows:
50 with respect to the total amount of the prime of the non-magnetic layer
Suitably, it is set to ~ 99% by weight. By setting the mixing amount of the magnetic powder in this range, the surface properties of the lower non-magnetic layer and the upper non-magnetic layer are improved.

As the binder, any of the resins exemplified for the upper magnetic layer can be used. The mixing amount of the binder is 5 to 150 parts by weight, preferably 10 to 120 parts by weight, based on 100 parts by weight of the nonmagnetic powder.

Using the above materials, a lower non-magnetic layer,
To form the upper non-magnetic layer, first, the lower non-magnetic paint,
Adjust the upper layer magnetic paint.

The paint for the upper layer is the ferromagnetic powder exemplified above,
It is prepared by kneading various additives such as a binder and a dispersant, a lubricant, an abrasive, and an antistatic agent together with a solvent to prepare a high-concentration magnetic paint, and then diluting and dispersing the high-concentration magnetic paint. . In addition, the non-magnetic paint for the lower layer of the present invention was prepared by kneading various additives such as the binder and dispersant, lubricant, abrasive, and antistatic agent described above together with a solvent to prepare a high-concentration magnetic paint. Thereafter, the high-concentration magnetic paint is prepared by diluting and dispersing the same.

As the organic medium for the coating, those usually used in this type of magnetic recording medium, for example, ketones such as acetone, methyl ethyl ketone, diisobutyl ketone and cyclohexanone, benzene, toluene, xylene and chlorobenzene Any of aromatic hydrocarbons, hexane and the like can be used. These organic solvents may be used alone or in combination of two or more.

As the kneading and dispersing machine, for example, any of those described in JP-A-4-214218 can be used. Especially 0.05 to 0.5 kW (magnetic powder 1
A pressure kneader, an open kneader, a continuous kneader, a roll mill, and a three-roll mill are suitable because they can provide a power consumption load of (per kg).

The upper magnetic layer and the lower non-magnetic layer of the present invention comprise:
The magnetic paint for the upper layer and the non-magnetic paint for the lower layer thus prepared are applied to a non-magnetic support and dried.

Here, as the non-magnetic support, for example,
Polyethylene terephthalate, polyethylene-2,6-
Examples include polyesters such as naphthalate, polyolefins such as polypropylene, cellulose derivatives such as cellulose triacetate and cellulose diacetate, and plastics such as polyamide, aramid resin and polycarbonate. These nonmagnetic supports may have a single-layer structure or a multilayer structure. Further, for example, a surface treatment such as a corona discharge treatment may be performed.

The thickness of the nonmagnetic support is preferably about 30 μm to 10 mm in the case of a magnetic disk.

As a method of applying the magnetic paint for the upper layer and the non-magnetic paint for the lower layer to the non-magnetic support, a gravure coating method,
A blade coating method, a paint extruding method, etc. may be mentioned, but any conventionally known coating method may be used. Further, any of the following multilayer coating methods may be used as the multilayer coating method.

A. After applying and drying the non-magnetic paint on the non-magnetic support, a calender treatment is performed as necessary, and the magnetic paint is applied to the lower non-magnetic layer having been subjected to the drying,
So-called dry-on-wet coating method.

B. For example, as described in JP-A-63-191315, a so-called wet-on-wet coating method in which an upper coating film is formed in a lower coating film while the lower coating film is in a wet state.

As a method of forming a multilayer coating film, for example, a coating film forming system as shown in FIGS. 1 and 2 can be mentioned.

That is, in this coating film forming system, the non-magnetic support 3 on which the coating film is formed is conveyed from the supply roll 1 to the take-up roll 2, and along the conveyance direction. The coating device 4, the magnet for orientation 5, the dryer 6, and the calender device 7 are arranged in this order.

In such a coating film forming system, first, the magnetic coating material 10 for the upper layer and the non-magnetic coating material 11 for the lower layer are applied in multiple layers on the non-magnetic support by the coating device 4. An extruder coater 8 for lower layer paint for applying the lower layer paint and an extruder coater 9 for upper layer paint for applying the upper layer paint are arranged in the application device.

Each of the extrusion coaters has a slit 12 formed at the tip thereof for extruding the paint, and a paint pool 13 for supplying the paint is provided on the back side. The paint supplied to the paint reservoir 13 is supplied to the slit 12
Through the coater tip.

On the other hand, the support 3 to which the coating material is applied is conveyed from the lower layer extrusion coater 8 to the upper layer extrusion coater 9 in the direction of the arrow along the tip of the extrusion coater.

The non-magnetic support conveyed in this manner is coated with a lower layer coating material extruded from the slit portion of the lower layer extrusion coater 8 to form a lower layer coating film. The lower-layer paint extruded from the portion is applied in the form of a lower-layer coating film in a wet state, and two layers of coating films are sequentially formed.

The lower coating film and the upper coating film formed as described above are provided with an orientation magnet 5, a drier 6, a calender
Are sequentially transported.

In this coating system, the lower layer paint and the upper layer paint are applied by separate coaters. As shown in FIG. 3, a lower layer extrusion coater and an upper layer extrusion coater are integrated. Extrusion coater 14
May be used. Further, in addition to the extrusion coater, a gravure roll, a blade coater, an air doctor coater, an impregnated coater, or the like may be used.

Further, in the above configuration, the lower layer non-magnetic paint and the upper layer magnetic paint are sequentially applied. However, an extrusion coater having two slits formed in close proximity is used. The paint and the upper layer paint may be applied simultaneously.

That is, as shown in FIG. 4, the extrusion coater 15 used in the simultaneous multi-layer coating method has two slit portions 12 (a lower layer slit portion and an upper layer slit portion) at the tip end of which are extruded. A lower layer paint reservoir 16 and an upper layer paint reservoir 17 to which each paint is supplied are provided on the back surface of the two slit portions. In this extrusion coater, the lower layer paint and the upper layer paint supplied to the paint pool are extruded to the tip of the coater through a slit. On the other hand, the support 3 to which the coating material is applied is conveyed along the tip of the extrusion coater from the lower layer slit to the upper layer slit in the direction of the arrow in the figure.

When the non-magnetic support conveyed in this way passes through the lower layer slit portion and the upper layer slit portion, the lower layer paint extruded from the lower layer slit portion is applied. The upper layer paint extruded from the upper layer slit is applied on the paint, and two layers of coating films are simultaneously formed.

Thus, the lower non-magnetic layer and the upper magnetic layer are formed, calendered, and wound up as a raw roll.

In the present invention, curling is suppressed by rewinding this raw roll while holding it on a heating roll in a direction opposite to the winding direction of the raw roll.

FIG. 5 shows a processing step using this heating roll. The raw magnetic disk 22 supplied from the raw roll 21 is transferred to guide rollers 23, 24, and 2.
The roll is guided by 5, 26, 27 and held so that the outer peripheral surface of the raw roll 21 is in contact with the peripheral surface of the heating roll 28, and is wound around the winding roll 29. After that, a hardening treatment is performed, and a predetermined size is punched.

At this time, the temperature T of the heating roll 28
It is preferable that Tg ≦ T ≦ Tg + 30 ° C. when the glass transition point of the nonmagnetic support is Tg.

The holding angle R of the magnetic disk material 22 to the heating roll 28 can be set arbitrarily, but is preferably 45 ° to 90 °, and is preferably 70 ° to 9 °.
More preferably, it is 0 °. In particular, the heating roll 28
Is preferably set to 2 seconds or more, and from such a viewpoint, it is preferable to set the diameter and the holding angle of the heating roll 28.

In the above series of steps, the temperature of the calendering treatment and the temperature of the curing treatment are preferably set at least 5 ° C. lower than the temperature of the heating roll.

[0076]

EXAMPLES Hereinafter, specific examples of the present invention will be described based on experimental results.

[0077] Example First, according to the following composition for the upper layer magnetic paint, weighed each component of lower layer non-magnetic coating for the upper layer magnetic paint by each kneading and dispersing using a kneader and a sand mill, a lower A non-magnetic paint was prepared.

Composition of magnetic coating for upper layer Ferromagnetic iron powder (specific surface area by BET method: 50 m ² / g, coercive force: 1600 Oe) 100 parts by weight Polyurethane resin containing sodium sulfonate group 6 parts by weight Vinyl chloride containing potassium sulfonate group Resin 14 parts by weight carbon black (trade name Asahi 50) 4 parts by weight α-alumina 8 parts by weight butyl stearate 2 parts by weight methyl ethyl ketone 200 parts by weight toluene 150 parts by weight cyclohexanone 200 parts by weight Non-magnetic paint composition for lower layer α-Fe ₂ O ₃ (specific surface area by BET method: 52 m ² / g) 100 parts by weight Polyurethane resin containing sodium sulfonate group 6 parts by weight Vinyl chloride resin containing potassium sulfonate group 14 parts by weight 2 parts by weight butyl stearate 100 parts by weight methyl ethyl ketone 100 parts by weight toluene 50 parts by weight Part cyclo Xanone 100 parts by weight A polyisocyanate compound (trade name: Coronate L, manufactured by Nippon Polyurethane Industry Co., Ltd.) was added to each of the upper magnetic coating material and the lower non-magnetic coating material thus prepared in an amount of 5 parts by weight. The coating material and the non-magnetic coating material for the lower layer are applied on a polyethylene terephthalate support having a thickness of 60 μm (glass transition temperature: 69 ° C.) using a coating device shown in FIG. The lower non-magnetic layer and the upper magnetic layer were formed by magnetic field orientation treatment. The dry film thickness of the lower non-magnetic layer was 1.
5 μm, and the upper magnetic layer was 0.4 μm.

Then, a lower nonmagnetic layer and an upper magnetic layer are similarly formed on the surface of the polyethylene terephthalate support opposite to the side on which the upper magnetic coating and the lower nonmagnetic coating are formed. After drying and performing a surface smoothing treatment using a calender, a wide original magnetic sheet was obtained. Here, the calendering temperature was 70 ° C.

As shown in FIG. 5, the raw roll obtained in this manner was run in a direction opposite to the winding direction so as to be in contact with a steel roll heated to 80 ° C.
It was sent at m / min and wound up again. Here, the holding angle between the steel roll and the raw sheet was 90 degrees.

The magnetic sheet thus obtained was punched into a disk having a diameter of 3.5 inches, left in an oven at 60 ° C. (curing temperature) for 20 hours, and attached to a center plate.

The following evaluation was performed on the manufactured magnetic disk.

First, the curl amount was measured using a curl measuring device shown in FIG. That is, the magnetic disk D was mounted on the support shaft 31 of the curl measuring device 30, and the curl amount E was observed and measured with a microscope.

The amount of run-out was measured using a spindle motor capable of high-speed rotation up to 3600 rpm, and the run-out amount of the inner peripheral portion and the outer peripheral portion was measured.

Comparative Example 1 First, a magnetic paint for the upper layer and a non-magnetic paint for the lower layer were prepared in the same manner as in the example, and then a lower non-magnetic layer and a lower magnetic layer were formed.
A wide raw magnetic sheet was obtained.

Here, the calendering temperature was 70 ° C. A sample was prepared in the same manner as in the example except that the heating roll temperature was 120 ° C and the curing temperature was 60 ° C.

Then, this sample was evaluated in the same manner as in the example.

Comparative Example 2 A sample was prepared and evaluated in the same manner as in Comparative Example 1 except that the heating roll temperature was 60 ° C. and the curing temperature was 80 ° C.

Comparative Example 3 A sample was prepared and evaluated in the same manner as in Comparative Example 1 except that the heating roll temperature was set at 80 ° C. and the curing temperature was set at 80 ° C.

Comparative Example 4 A sample was prepared and evaluated in the same manner as in Comparative Example 1 except that the heating roll temperature was set at 80 ° C. and the calendering temperature was set at 100 ° C.

Table 1 shows the results.

[0092]

[Table 1]

In the example, it was found that the curl amount was very small, and the surface runout amount was also small on both the inner and outer circumferences.

On the other hand, in the comparative example, both the curl amount and the surface shake amount are large. For example, in Comparative Example 1, the heating roll temperature was lower than the glass transition temperature of the non-magnetic support by (50).
(Approximately ° C) was too high, causing thermal deformation. In Comparative Example 2, it is considered that the effect of removing the curl was not obtained because the heating roll temperature was equal to or lower than the curing temperature. In Comparative Example 4, almost no effect was obtained because the calendering temperature was too high than the hot roll temperature.

[0095]

As is clear from the above description, according to the present invention, it is possible to manufacture a multilayer coated magnetic disk having a small curl amount, and to provide a magnetic disk having excellent durability and electromagnetic conversion characteristics. Discs can be provided.

[Brief description of the drawings]

FIG. 1 is a schematic view showing a coating film forming system for forming a lower nonmagnetic layer and an upper magnetic layer by a wet-on-wet coating method.

FIG. 2 is a schematic view showing an example of an extrusion coater used in a multilayer coating method.

FIG. 3 is a schematic diagram showing another example of an extrusion coater used in a multilayer coating method.

FIG. 4 is a schematic diagram showing still another example of an extrusion coater used in a multilayer coating method.

FIG. 5 is a schematic diagram illustrating an example of a processing apparatus using a heating roll.

FIG. 6 is a schematic diagram showing a schematic configuration of a curl measuring device.

[Explanation of symbols]

21 material roll, 22 magnetic disk material, 28 heating roll

Claims (3)

[Claims] 1. A non-magnetic coating material containing a non-magnetic powder is applied on a non-magnetic support to form a lower coating film, and then a magnetic coating material containing a ferromagnetic powder is applied on the lower coating film. After forming the upper layer coating film, applying a calendering process to produce a raw roll, winding it again while holding it on a heating roll in the opposite direction to the winding direction of the raw roll, curing it, and then setting it to a predetermined size A method for manufacturing a magnetic disk, comprising punching. 2. The glass transition point of the nonmagnetic support is defined as Tg.
, Tg ≦ T ≦ T
2. The method for manufacturing a magnetic disk according to claim 1, wherein the temperature is set to g + 30 ° C. 3. The method according to claim 1, wherein a temperature of the calendering process and a temperature of the curing process are set to be lower than the temperature of the heating roll by 5 ° C. or more.