JP2001110033A - Magnetic disk - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic disk wherein damage is hardly generated on the surface even if the disk collides with a head while rotating at a high speed at the time of recording or reproducing by a magnetic disk recording and reproducing device. SOLUTION: In the magnetic disk having a non-magnetic substrate 2, a non- magnetic layer 3 formed by applying a non-magnetic paint consisting of a non- magnetic powder and a curing agent which are dispersed in a bonding agent onto the non-magnetic substrate 2 and a magnetic layer 4 formed by applying a magnetic paint onto the non-magnetic layer 3, the non-magnetic paint contains >=10 wt.% vinyl chloride based copolymer having >=0.2 wt.% hydroxyl group concentration to the non-volatile component of the non-magnetic paint as the bonding agent as >=35 wt.% polyisocyanate compound having >=30 wt.% isocyanate group concentration to the total weight of the bonding agent as the curing agent.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic disk having at least one nonmagnetic layer and a magnetic layer.

[0002]

2. Description of the Related Art Conventionally, magnetic recording media such as video tapes, audio tapes, magnetic disks and the like include non-magnetic supports such as polyethylene terephthalate film, ferromagnetic iron oxide, Co-modified iron oxide, CrO ₂ , and ferromagnetic alloys. A so-called coating type magnetic recording medium including a magnetic layer formed by applying a magnetic paint prepared by dispersing a ferromagnetic powder such as a powder and a binder together with a solvent, is widely used.

In recent years, studies have been made on high-density recording of magnetic recording media, such as shortening the recording wavelength. For this reason, even in a coating type magnetic recording medium, in order to realize high-density recording, improvement in electromagnetic conversion characteristics with respect to a short recording wavelength is required.

[0004] In a coating type magnetic recording medium, thinning of a magnetic layer has been studied in order to improve electromagnetic conversion characteristics in a high recording density region. This means that by reducing the thickness of the magnetic layer, self-demagnetization loss during recording and thickness loss during reproduction can be reduced, and electromagnetic conversion characteristics can be effectively improved.

However, when the thickness of the magnetic layer is reduced, for example, when the thickness of the magnetic layer is reduced to 1 μm or less, the surface shape of the nonmagnetic support is more likely to emerge on the surface of the magnetic layer, so that the surface smoothness of the magnetic layer is improved. I can't let it. For this reason, there has been a problem that the electromagnetic conversion characteristics are deteriorated due to spacing loss, and dropout frequently occurs.

Therefore, as a coating type magnetic recording medium, a multilayer coating type magnetic recording medium in which a nonmagnetic layer is interposed between a magnetic layer and a nonmagnetic support has been proposed. In this multilayer coating type magnetic recording medium, since the thin magnetic layer has a smooth surface property, excellent electromagnetic conversion characteristics can be obtained in a short wavelength region.

[0007] In such a multilayer coating type magnetic recording medium, there are problems such as that the coating process is complicated and it is difficult to obtain a thin and uniform magnetic layer. The above problem has been solved to some extent by the proposal of a so-called wet-on-wet coating method in which a magnetic layer is applied simultaneously or sequentially.

[0008]

Such a multilayer coating type magnetic recording medium has excellent electromagnetic conversion characteristics in a short wavelength region, and is processed into a disk-shaped magnetic disk.
It has been used in a so-called magnetic disk recording / reproducing apparatus that performs recording / reproducing while rotating it at high speed.

In the magnetic disk recording / reproducing apparatus, since the magnetic disk rotates at a very high speed of, for example, 2400 rpm or more, there is a problem that the magnetic disk surface is scratched by collision with the head, and the still durability is improved. It has been demanded.

As a method of suppressing the scratch on the surface of the magnetic disk, for example, a method of increasing the amount of abrasive particles added to the magnetic layer can be mentioned. However, since only a very small amount of the added abrasive particles is located on the surface of the magnetic disk and acts effectively, a large amount of abrasive must be added to suppress damage to the magnetic disk surface. .
However, when a large amount of abrasive is added, the nonmagnetic component in the magnetic layer becomes too large, so that as a magnetic recording medium,
There is a possibility that the magnetic characteristics may be deteriorated.

Further, for example, there is a method in which a resin having a high glass transition temperature is blended to improve the strength of the coating film. However, the properties required for the resin include various properties in addition to the strength of the coating film, such as particle dispersibility, adhesion, paint stability, and ease of application. For this reason, it is extremely difficult to improve only the coating film strength while maintaining these properties in the resin.

Therefore, the present invention has been proposed in view of such a conventional situation. When recording or reproducing by a magnetic disk recording / reproducing apparatus, even if the magnetic disk collides with a head while rotating at high speed, An object of the present invention is to provide a magnetic disk whose surface is hardly damaged.

[0013]

In order to achieve the above-mentioned object, a magnetic disk according to the present invention comprises a non-magnetic support, a non-magnetic powder and a binder which are dispersed together with a solvent and cured into a prepared coating material. A magnetic layer having a non-magnetic layer formed by applying a non-magnetic paint obtained by adding an agent to a magnetic support, and a magnetic layer formed by applying a magnetic paint to the non-magnetic layer. The magnetic paint contains a vinyl chloride copolymer having a hydroxyl group concentration of 0.2% by weight or more as a binder in an amount of 10% by weight or more based on the non-volatile component of the nonmagnetic paint, and an isocyanate group concentration of 30% as a curing agent. It is characterized by containing 35% by weight or more of the polyisocyanate compound in an amount of 35% by weight or more based on the total weight of the binder.

The magnetic disk according to the present invention configured as described above has a nonmagnetic layer formed by applying a nonmagnetic paint between the magnetic layer and the nonmagnetic support. This non-magnetic paint contains a vinyl chloride copolymer having a hydroxyl group concentration of 0.2% by weight or more as a binder in an amount of 10% by weight or more based on a nonvolatile component of the non-magnetic paint, and an isocyanate group as a curing agent. A non-magnetic layer formed by applying a polyisocyanate compound having a concentration of 30% by weight or more to the binder in an amount of 35% by weight or more based on the total weight of the binder has a significantly improved coating film strength. Becomes

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The embodiments of the magnetic disk according to the present invention will be described below with reference to the drawings.

A magnetic disk 1 to which the present invention is applied has a structure shown in FIG.
As shown in (1), a non-magnetic support 2, a non-magnetic layer 3 formed on the non-magnetic support 2, and a magnetic layer 4 formed on the non-magnetic layer 3.

Examples of the nonmagnetic support 2 include polyesters such as polyethylene terephthalate and polyethylene-2,6-naphthalate; polyolefins such as polypropylene; cellulose derivatives such as cellulose triacetate and cellulose diacetate; polyamides;
Plastics such as aramid resin and polycarbonate are exemplified.

These nonmagnetic supports 2 may have a single-layer structure or a multilayer structure. Further, for example, surface treatment such as corona discharge treatment may be performed,
An organic layer such as an easy-adhesion layer may be formed on the surface.

The thickness of the nonmagnetic support 2 is not particularly limited.
It is preferably 100 μm.

The non-magnetic layer 3 is formed by applying a non-magnetic coating obtained by adding a hardener to a coating prepared by dispersing a non-magnetic powder, a binder and the like together with a solvent.

As the non-magnetic powder, conventionally known non-magnetic powders such as acicular iron oxide such as α-Fe ₂ O ₃ , TiO ₂ , Cr ₂ O ₃ , α-FeOOH, CaO,
SiO ₂ or the like can be used. In particular, it is preferable to use α-Fe ₂ O ₃ which has excellent dispersibility as compared with other non-magnetic powder particles. By using α-Fe ₂ O ₃ , the surface smoothness of the non-magnetic layer 3 is further improved, so that the surface smoothness of the magnetic layer 4 formed on the non-magnetic layer 3 is further improved.

The major axis length of the nonmagnetic powder is 0.2 μm
It is preferable to set the following. The axial ratio (major axis length / single axis length) of the nonmagnetic powder is preferably 2 to 20, more preferably 5 to 15, and most preferably 5 to 10. The specific surface area of the non-magnetic powder is preferably 10 to 250 m ³ / g,
１５０150 m ³ / g, more preferably 30 to 1
Most preferably, it is 00 m ³ / g.

As a binder used in the non-magnetic paint, a vinyl chloride copolymer having a hydroxyl group concentration of 0.2% by weight or more is used so as to be 10% by weight or more with respect to a nonvolatile component of the non-magnetic paint.

The vinyl chloride copolymer preferably has an average degree of polymerization as small as 100 to 200. If the average degree of polymerization is less than 100, sufficient strength may not be obtained even when a curing agent is used in combination, and durability may be poor. On the other hand, when the average degree of polymerization is larger than 200, the wettability to powder components such as non-magnetic powder becomes poor, and this powder component may not be sufficiently dispersed.

In order to improve the dispersibility of powder components such as non-magnetic powder in the non-magnetic paint, a sulfonate group and / or a quaternary ammonium base are introduced into the vinyl chloride copolymer. Is preferred. Further, the content of the sulfonic acid group and / or the quaternary ammonium group is 0.1.
Preferably it is 3 to 3% by weight. When the content is less than 0.3% by weight, the dispersibility of the powder components such as the non-magnetic powder becomes low, so that the surface of the non-magnetic layer 3 cannot be smoothed, and the surface smoothness of the magnetic layer 4 is reduced. There is a risk of deterioration. On the other hand, if the content exceeds 3.0% by weight, the vinyl chloride-based copolymer may have poor solubility in a solvent used for forming a nonmagnetic paint.

The quaternary ammonium base serves as a catalyst when the hydroxyl groups of the vinyl chloride copolymer react with isocyanate added as a curing agent. This catalytic action is sufficiently exhibited when the content of the quaternary ammonium base is 0.3% by weight or more.

Further, a vinyl chloride copolymer containing a polar group can be obtained by an addition reaction of a copolymer having a hydroxyl group such as a vinyl chloride-vinyl alcohol copolymer with a compound having a polar group and a chlorine atom. Can be synthesized.

As the binder used for the non-magnetic paint, conventionally known resins such as a polyurethane resin, a polyether resin and a cellulose derivative can be used in combination with the vinyl chloride copolymer. The mixing amount of these binders in the non-magnetic paint is preferably 15 to 100 parts by weight based on 100 parts by weight of the non-magnetic powder.

As a solvent for converting the non-magnetic paint, for example, methyl ethyl ketone, toluene, etc., which are used for preparing a normal non-magnetic paint, can be used. These solvents may be used alone or as a mixture of two or more.

Further, carbon black may be added to the non-magnetic paint for the purpose of imparting conductivity and light shielding properties.
When imparting conductivity, it is preferable to use carbon black having a dibutyl phthalate oil supply amount of 100 ml / 100 g or more.

Further, a lubricant may be added for the purpose of improving the running durability of the magnetic disk 1. As the lubricant, a conventionally known lubricant can be used, and examples thereof include silicone oil, carbon fluoride, fatty acid amide, and olefin oxide. These lubricants may be used alone or in combination of two or more.

It is also possible to use a fatty acid or a fatty acid ester alone or as a mixture as a lubricant. The fatty acid may be a monobasic acid or a dibasic acid. Further, the carbon number is preferably 6 to 30, and 1
More preferably, it is 2 to 22. When a fatty acid and a fatty acid ester are used in combination, the weight ratio between the fatty acid and the fatty acid ester is preferably from 10:90 to 90:10.

As described above, in preparing a coating material obtained by dispersing a nonmagnetic powder and a binder in a solvent,
Kneading may be performed as needed.

Examples of the kneader (not shown) for performing the kneading include a two-roll mill, a three-roll mill, an open kneader, a continuous twin-screw kneader, and a pressure kneader.
Both can be used. In particular, 0.05 to 0.5 kW
A pressure kneader, an open kneader, a continuous twin-screw kneader, a two-roll mill, and a three-roll mill are suitable because they can provide a power consumption load (per kg of powder). A continuous twin-screw kneader that can be diluted is more preferable.

When kneading with this kneader, a dispersant may be added. Examples of the dispersant include a silane coupling agent. This dispersant is suitably used in the range of 0.5 to 5% by weight based on the ferromagnetic powder.

A curing agent is added to the paint prepared as described above to obtain a non-magnetic paint. As a curing agent, a polyisocyanate compound having an isocyanate group concentration of 30% by weight or more is used in an amount of 35% by weight based on the total weight of the binder of the nonmagnetic layer 3.
It is added so as to be at least% by weight.

When the polyisocyanate compound has an isocyanate group concentration of less than 30% by weight, the curing effect is not sufficient. If the amount is less than 35% by weight based on the total weight of the binder in the non-magnetic layer 3, the curing effect is not sufficient.

Examples of the polyisocyanate compound include aromatic polyisocyanates such as adducts of tolylene diisocyanate and active hydrogen compounds, and aliphatic polyisocyanates such as adducts of hexamethylene diisocyanate and active hydrogen compounds. Can be The weight average molecular weight of these polyisocyanates is preferably from 100 to 3,000.

The magnetic layer 4 is formed by applying a magnetic paint prepared by dispersing a ferromagnetic powder and a binder together with a solvent.

As the ferromagnetic powder, γ-Fe ₂ O ₃ , Co
Containing γ-Fe ₂ O ₃ , Co-coated γ-Fe ₂ O ₃ , CrO ₂ ,
Ferrites represented by magnetite, that is, Fe ₃ O ₄ , Co-containing Fe ₃ O ₄ , Co-coated Fe ₃ O _{4, and the} like can be given. Further, as the ferromagnetic powder, F
e, metal powder such as Co, Fe-Al-based, Fe-Al-
Ni-based, Fe-Al-Zn-based, Fe-Al-Co-based, F
e-Al-Ca system, Fe-Ni system, Fe-Ni-Al
System, Fe-Ni-Co system, Fe-Ni-Si-Al-M
n-based, Fe-Ni-Si-Al-Zn-based, Fe-Al-
Si-based, Fe-Ni-Zn-based, Fe-Ni-Mn-based, F
e-Ni-Si system, Fe-Mn-Zn system, Fe-Co-
Metal magnetic powders such as Ni-P-based, Ni-Co-based, and alloy powders containing Fe, Ni, Co, or the like as a main component can be used.

Of these, Fe-based metal powders have excellent electrical characteristics. Further, from the viewpoint of corrosion resistance and dispersibility, F
e-Al system, Fe-Al-Ca system, Fe-Al-Ni
System, Fe-Al-Zn system, Fe-Al-Co system, Fe-
Ni-Si-Al-Zn system, Fe-Ni-Si-Al-
Fe-Al alloy powder such as Mn alloy is preferable.

The ferromagnetic powder preferably has an average major axis length of 0.5 μm or less,
To 0.4 μm, more preferably 0.01 to 0.4 μm.
Most preferably, it is 0.3 μm. Further, the axial ratio (average major axis length / average minor axis length) is preferably 12 or less, more preferably 10 or less.

As for the magnetic properties of the ferromagnetic powder, it is preferable that the saturation magnetization (σs) is 70 emu / g or more. If the saturation magnetization is less than 70 emu / g, sufficient electromagnetic conversion characteristics may not be obtained. In addition, it is preferable that the specific surface area by the BET method is 45 m ² / g or more from the viewpoint of enabling recording and reproduction in a high density recording area.

Examples of the binder used in the magnetic paint include polyurethane resins, polyester resins, and vinyl chloride resins such as vinyl chloride copolymers.

These resins include -SO ₃ M, -OSO ₃ M,
—COOM, —PO (OM) ₂ (where M represents a hydrogen atom or an alkali metal such as Na, K, Li, and M represents a hydrogen atom or an alkali atom such as Na, K, Li, or an alkyl group); It preferably contains a repeating unit having at least one kind of polar group selected from sulfobetaine groups. These polar groups have the effect of improving the dispersibility of the ferromagnetic powder, and the content is preferably 0.1 to 8.0 mol%, more preferably 0.2 to 6.0 mol%. preferable. If the content of the polar group is less than 0.1 mol%, the dispersibility of the ferromagnetic powder may be reduced.
On the other hand, when the content of the polar group exceeds 8.0 mol%,
There is a possibility that the magnetic paint tends to gel. Further, the weight average molecular weight of the resin is preferably in the range of 10,000 to 50,000.

In particular, as the binder used in the magnetic paint,
It has a sulfonate group and / or a quaternary ammonium group, a hydroxyl group and an epoxy group, and has an average degree of polymerization of 10
A vinyl chloride copolymer having 0 to 200 is preferable.

One of these resins may be used alone, or two or more thereof may be used in combination. For example, when a mixture of polyurethane and / or polyester and a vinyl chloride resin is used, the weight ratio is 90:
The ratio is preferably 10 to 10:90, and 70:30 to
The ratio is more preferably 30:70.

Further, the following resins may be used in combination within the range of 50% by weight or less of the total binder content contained in the magnetic paint.

The resins used in combination are vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, butadiene-acrylonitrile copolymer having a weight average molecular weight of 10,000 to 200,000. , Polyamide resin, polyvinyl butyral, cellulose derivative (such as nitrocellulose), styrene-butadiene copolymer, phenol resin, epoxy resin, urea resin, melamine resin, phenoxy resin, silicone resin, acrylic resin, urea formamide resin, various Synthetic rubber-based resins and the like can be mentioned.

As the binder to be contained in the magnetic paint, the above-mentioned resins are used, and the amount of the binder to be mixed is 8 to 25 parts by weight with respect to 100 parts by weight of the ferromagnetic metal powder. More preferably, it is 10 to 20 parts by weight.

As the solvent for converting the magnetic coating material into a coating material, there can be mentioned those usually used in the production of magnetic recording media, for example, methyl ethyl ketone, toluene and the like. These solvents may be used alone or as a mixture of two or more.

For the purpose of improving the running durability and the like, the magnetic paints usually include abrasives used in magnetic recording media,
An additive such as a lubricant may be added.

Examples of the abrasive include α-alumina, fused alumina, chromium oxide, titanium oxide, α-iron oxide, silicon oxide, silicon nitride, tungsten carbide, molybdenum carbide,
Examples include boron carbide, corundum, zinc oxide, cerium oxide, magnesium oxide, and boron nitride.
The average particle size of the abrasive is preferably 0.05
μm to 0.6 μm, more preferably 0.05 μm
0.5 μm, more preferably 0.05 μm
0.3 μm. The amount of the abrasive added is preferably 3 to 20 parts by weight, more preferably 5 to 15 parts by weight, and still more preferably 5 to 10 parts by weight with respect to 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 a carbon number of 6 to
30 is preferable, and it is more preferable that it is 12-22.
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.

Further, a paint additive may be used if necessary. As a paint additive, for example,
Any of those described in JP-A-18985, JP-B-48-4367, and JP-B-53-20530 can be used.

In preparing the magnetic paint by dispersing the magnetic powder and the binder together with the solvent as described above, kneading may be performed as necessary.

Examples of the kneader (not shown) for performing the kneading include a two-roll mill, a three-roll mill, an open kneader, a continuous twin-screw kneader, a pressure kneader, and the like.
Both can be used. In particular, 0.05 to 0.5 kW
A pressure kneader, an open kneader, a continuous twin-screw kneader, a two-roll mill, and a three-roll mill are suitable because they can provide a power consumption load (per kg of powder). A continuous twin-screw kneader that can be diluted is more preferable.

When kneading with this kneading machine, a dispersant may be added. Examples of the dispersant include a silane coupling agent. This dispersant is suitably used in the range of 0.5 to 5% by weight based on the ferromagnetic powder.

A hardener may be added to the magnetic paint prepared as described above when it is applied on the nonmagnetic support 2. As the curing agent, any of those exemplified as the curing agent contained in the nonmagnetic paint can be used. Further, the types and amounts of the curing agents added to the magnetic layer 4 and the non-magnetic layer 3 may be different or the same.

Next, a method of applying the non-magnetic paint and the magnetic paint prepared as described above to the non-magnetic support 2 will be described.

A non-magnetic support and a non-magnetic support 2
When applied on the top, when the non-magnetic coating formed by applying the non-magnetic coating is in a wet state, a so-called wet-on-wet method is used in which the magnetic coating is applied to form a magnetic coating. . The non-magnetic layer 3 may be composed of a plurality of layers as necessary. In this case, at least the non-magnetic layer 3 and the magnetic layer 4 adjacent to the magnetic layer 4 are wet-on-wet. It is to be applied in a multi-layered manner.

Specifically, the non-magnetic layer 3 on the non-magnetic support 2
When the magnetic layer 4 is formed by a wet-on-wet method, for example, a coating film forming apparatus 10 is used as shown in FIG.

The coating film forming apparatus 10 is provided with a winding roll 12 and a supply roll 13, which are formed by winding the non-magnetic support 2 formed in a long shape and extending the non-magnetic support 2 around the non-magnetic support 2.
A coating device 14 for coating a non-magnetic paint and a magnetic paint on the non-magnetic support 2 pulled out from the supply roll 13;
An orientation magnet 15 for determining the magnetization direction of the magnetic layer 4, a dryer 16 for drying the paint, and a calendar device 17 for performing a calendar process are provided.

That is, in the coating film forming apparatus 10, the non-magnetic support 2 is transported from the supply roll 13 to the take-up roll 12, and the coating device 14 is oriented along the transport direction. Magnet 15, dryer 16,
The calendar devices 17 are arranged in this order.

In such a coating film forming apparatus 10, first, a non-magnetic coating material and a magnetic coating material are applied in multiple layers on the non-magnetic support 2 by the coating device 14. This coating device 14 is shown in FIG.
As shown in FIG. 1, a first extruder coater 18 for applying a non-magnetic paint and a second extruder coater 19 for applying a magnetic paint are provided. Further, in the coating apparatus 14, the second extrusion coater 19 is arranged so as to be on the sending side of the nonmagnetic support 2, and the first extrusion coater 18 is arranged on the introduction side of the nonmagnetic support 2.

The first extrusion coater 18 and the second
The extruder coater 19 has slit portions 20 and 21 formed at the tip thereof for extruding the paint, and paint pools 22 and 23 for supplying the paint on the back side of the slit portions 20 and 21, respectively. I have. In the first extrusion coater 18 and the second extrusion coater 19, the non-magnetic paint and the magnetic paint supplied to the paint reservoirs 22 and 23 are respectively pushed out to the tip of the coater through the slits 20 and 21. It is.

Then, the non-magnetic support 2 to which the paint is applied
Is transported along the distal end surfaces of the first extrusion coater 18 and the second extrusion coater 19 in the direction of arrow D in FIG.

The non-magnetic support 2 conveyed in this manner
On the upper side, when passing through the first extrusion coater 18, the non-magnetic paint extruded from the slit portion 20 is applied to form a non-magnetic coating film 24. Then, when passing through the second extrusion coater 19, the magnetic paint extruded from the slit portion 21 is applied on the wet non-magnetic coating film 24, and the magnetic coating film 25 is formed.

The first extrusion coater 18
The supply of the paint to the second extrusion coater 19 may be performed via an inline mixer.

As described above, the non-magnetic coating film 24 and the magnetic coating film 2
5 is formed on the non-magnetic support 2,
It is sequentially conveyed to the dryer 16 and the calender 17.

In the magnet 15 for orientation, the magnetic coating film 25 to be the magnetic layer 4 is subjected to a magnetic field orientation treatment. In addition, the magnet for orientation 15
The magnet for longitudinal orientation or the magnet for vertical orientation, or the magnet for random orientation is used in the case of manufacturing the magnetic disk 1 or the like.

In the dryer 16, the non-magnetic coating film 24 is heated by hot air from nozzles arranged above and below the dryer 16.
And the magnetic coating film 25 is dried. As drying conditions at this time, the temperature is about 30 to 120 ° C., and the drying time is about 0.1.
It is preferably for about 10 to 10 minutes.

The non-magnetic support 2 that has passed through the dryer 16 is further guided to a calender 17 and subjected to a surface smoothing process. In the surface smoothing process by the calendar device 17, the temperature, the linear pressure, the transport speed, and the like are important. That is, the temperature is 50 as the surface smoothing condition.
１４０140 ° C., the linear pressure is preferably 50-1000 kg / cm ² , and the transfer speed is preferably 20-1000 m / min. If these conditions are not satisfied, the surface properties of the magnetic layer 4 may be impaired.

In the coating film forming apparatus 10, the non-magnetic paint and the magnetic paint are applied by separate coaters, but the present invention is not limited to the coating apparatus 14. That is, as shown in FIG. 4, a coating apparatus 27 including an extrusion coater 26 in which a first extrusion coater 18 and a second extrusion coater 19 are integrated.
It may be.

Further, in the above-described coating film forming apparatus 10, the coating devices 14 and 27 in which the non-magnetic paint and the magnetic paint are sequentially applied are used. However, the present invention is not limited to this. An application device that applies the paint simultaneously may be used. That is, as shown in FIG. 5, a coating device 29 having an extrusion coater 28 in which two slits are formed close to each other may be used, and the non-magnetic paint and the magnetic paint may be simultaneously applied by the extrusion coater 28. .

The coating apparatus 29 is provided with the extrusion coater 2
The first slit portion 30 through which the paint is extruded at the tip of
A first paint reservoir 32 to which a non-magnetic paint is supplied and a second paint to which a magnetic paint is supplied are formed on the back side of these two slits 30 and 31. Each of the pools 33 is provided.

In the coating device 29, the non-magnetic paint supplied to the first paint reservoir 32 is applied from the first slit portion 30 onto the non-magnetic support 2, and the non-magnetic coating film 24 is formed. Then, the magnetic paint supplied to the second paint reservoir 33 is applied from the second slit portion 31 to the non-magnetic coating film 24 in a wet state almost simultaneously, and the magnetic coating film 25 is formed.

Further, the above-mentioned coating apparatuses 14, 27, 29
In, an extrusion coater was used, but a reverse roll, a gravure roll, an air doctor coater, a blade coater, an air knife coater, a squeeze coater, an impregnation coater, a transfer roll coater, a kiss coater, a cast coater, a spray coater, and the like may be used. good. At this time, the method of applying the non-magnetic paint and the method of applying the magnetic paint may be the same or different. Therefore,
For example, it is also possible to apply a magnetic paint and a non-magnetic paint by combining a reverse roll and an extrusion coater, or combining a gravure roll and an extrusion coater.

The thickness of the magnetic layer 4 is preferably 0.5 μm or less, more preferably 0.1 to 0.3 μm. With this thickness, the electromagnetic conversion characteristics in the high-density region are improved. When the thickness of the magnetic layer 4 is 0.
If the thickness is more than 5 μm, the electrical characteristics of the magnetic disk 1 may be degraded and may have insufficient characteristics as a recording medium applied to, for example, a digital recording method.

After the non-magnetic layer 3 and the magnetic layer 4 are formed on one main surface of the non-magnetic support 2 as described above, the other main surface of the non-magnetic support 2 is also An original magnetic film is obtained by forming the layer 4 in the same manner as described above.

The raw magnetic film in which the non-magnetic layer 3 and the magnetic layer 4 are formed on both sides of the non-magnetic support 2 is punched into a disk having a desired diameter by a punching machine. Alternatively, the magnetic disk 1 is obtained by performing blade processing or the like.

The magnetic disk 1 manufactured as described above
Has a nonmagnetic layer 3 formed by applying a nonmagnetic paint. This non-magnetic paint has a hydroxyl group concentration of 0.2 as a binder.
A polyisocyanate compound containing 10% by weight or more of a vinyl chloride copolymer based on the nonvolatile component of the non-magnetic coating material and 30% by weight or more of an isocyanate group concentration as the curing agent; 35% by weight or more based on the total weight of the agent. As a result, the nonmagnetic layer 3 has a significantly improved coating film strength. Therefore,
When the magnetic disk 1 is recorded or reproduced by the recording / reproducing apparatus of the magnetic disk 1, even if it collides with the head while rotating at high speed, the surface of the magnetic disk 1 is hardly damaged.

Since the non-magnetic paint has dispersibility and applicability, it is possible to form a uniform non-magnetic coating film. Has a smooth coating surface. Therefore, the magnetic disk 1 has excellent electromagnetic conversion characteristics.

[0084]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, specific embodiments of the magnetic disk according to the present invention will be described. Further, a comparative example was prepared for comparison with this example, and characteristics of the example and the comparative example were evaluated.

Example 1 In accordance with the following composition, each component of the magnetic paint was weighed out and kneaded while performing multi-stage dilution using a continuous twin-screw kneader.
Subsequently, a solvent (a mixed solvent having a composition of methyl ethyl ketone: toluene: cyclohexanone (weight ratio) = 1: 1: 1) was added while performing a dispersion treatment using a sand mill to prepare a magnetic paint having a weight solid content of 28%. did.

<Magnetic paint> 100 parts by weight of ferromagnetic iron fine powder (manufactured by Dowa Mining Co., Ltd., coercive force Hc: 2200 Oe, specific surface area by BET method: 50 m ² / g, major axis length: 0.1 μm, Needle ratio: 3, saturation magnetization σs: 145 em u / g) Binder: 16 parts by weight of vinyl chloride resin (manufactured by Nippon Zeon Co., Ltd.) 4 parts by weight of polyurethane resin (manufactured by Toyobo Co., Ltd.) Parts: α-alumina (manufactured by Sumitomo Chemical Co., Ltd., basic particle size: 0.2 μm) 5 parts by weight ・ Myristic acid (manufactured by Kao Corporation) 1 part by weight ・ Butyl stearate (manufactured by Matsumoto Yushi Co., Ltd.) 1 part by weight-Polyisocyanate compound (manufactured by Nippon Polyurethane Co., Ltd.) 2 parts by weight Also, in accordance with the following composition, each component of the non-magnetic paint is weighed out, and multi-stage dilution is performed using a continuous twin-screw kneader. And then kneading, followed by a sand mill Using solvents while distributed processing to adjust the non-magnetic coating composition was 34% by weight solids by the addition of (methyl ethyl ketone: toluene: cyclohexanone (weight ratio) = 1:: 1 mixed solvent of 1 a composition).

<Non-magnetic paint> 100 parts by weight of α-Fe ₂ O ₃ (manufactured by Toda Kogyo KK, specific surface area by BET method: 52.6 m ² / g, major axis diameter: 0.15 μm, acicular) Ratio: 6.5) 24 parts by weight of carbon black (“PRINTEX 55” manufactured by Degussa Corp., average particle size: 25 nm, DBP oil absorption: 48 ml / 100 g) Binder: vinyl chloride resin (Nippon Zeon Co., Ltd. 20% by weight Polyurethane resin (manufactured by Toyobo Co., Ltd.) 8 parts by weight ・ Myristic acid (manufactured by Kao Corporation) 2 parts by weight ・ Heptyl stearate (Matsumoto Yushi Co., Ltd.) 3 parts by weight ・ Polyisocyanate compound 10 parts by weight (Nippon Polyurethane Co., Ltd., isocyanate concentration: 48 wt%)
By wet-on-wet application method, thickness 62
A multilayer coating is applied to both sides of a polyethylene terephthalate support having a thickness of 1.5 μm, and a magnetic field orientation treatment is performed while the coating is in an undried state, followed by drying and surface smoothing treatment using a calender to form a 1.5 μm thick lower layer. Magnetic layer, thickness 0.15μ
m upper magnetic layers were formed on both sides of a polyethylene terephthalate support.

The raw magnetic film thus obtained was punched into a circular shape having a diameter of 3.5 inches.
A magnetic disk was produced by heat treatment in an oven at 0 ° C. for 48 hours.

Examples 2 to 3 and Comparative Examples 1 to 3 The ratio of the “vinyl chloride resin” used in the non-magnetic paint to the hydroxyl groups and the non-volatile components, the ratio of the “polyisocyanate compound” to the isocyanate and A magnetic disk was manufactured in the same manner as in Example 1, except that the ratio to the weight of the binder was changed to the contents specified in Tables 1 and 2.

[0090]

[Table 1]

[0091]

[Table 2]

Characteristics Evaluation Test Examples 1-3 and Comparative Examples 1-3 produced as described above
For each of the magnetic disks, surface roughness (Ra), electromagnetic conversion characteristics, and still durability were measured.

<Surface Roughness (Ra)> As the surface roughness (Ra), the center line average roughness (Ra) specified in JIS B0601 was measured. The surface roughness (Ra) was measured using a tally step roughness meter manufactured by Taylor Hopson. The measurement conditions were as follows: stylus: 2.5 × 0.1 μm, stylus pressure: 2 mg, cut-off filter: 0.33H
z, measurement speed 2.5 μm / s, reference length 0.5 m
m. In the roughness curve, irregularities of 0.01 μm or more were cut.

<Electromagnetic Conversion Characteristics (RF Output)> A magnetic disk drive (trade name: MPF-42B, manufactured by Sony Corporation) was modified so that the disk rotation speed was 3600 rpm, and a thin film head having a gap length of 0.2 μm was used as the magnetic head. make use of,
Each magnetic disk was run on the outermost track, and the output was evaluated by measuring the output component of 35 MHz generated in the magnetic head at that time. The measurement result was a relative value when the value for the magnetic disk of Example 1 was set to 0 dB.

<Still durability> Each magnetic disk is rotated at 3600 rpm on the magnetic disk drive,
The head was run on the outermost track of each magnetic disk. Then, the time until a scratch was confirmed on the surface of the magnetic disk was measured.

Table 3 shows the results of these characteristic evaluation tests.

[0097]

[Table 3]

As shown in Table 3, the magnetic disks of Examples 1 to 3 have good surface properties, excellent electromagnetic conversion characteristics, and extremely excellent still durability. Even at the time of high-speed rotation of 3600 rpm, It was found that the surface of the magnetic disk was hardly damaged.

On the other hand, when the hydroxyl group concentration was 0.2% by weight.
Comparative Example 1 in which a vinyl chloride-based resin less than the binder is used as the binder for the non-magnetic paint has poor still durability. In Comparative Example 2 in which the polyisocyanate compound having an isocyanate group concentration of 30% by weight or more was less than 35% by weight based on the total weight of the binder contained in the nonmagnetic paint, the desired electromagnetic conversion characteristics could not be obtained. And still durability is poor. Further, Comparative Example 3 in which the vinyl chloride copolymer having a hydroxyl group concentration of 0.2% by weight or more was less than 10% by weight with respect to the nonvolatile component of the non-magnetic paint, had a rough surface and poor electromagnetic conversion characteristics. , Still durability is very poor.

[0100]

As described in detail above, the magnetic disk according to the present invention has a non-magnetic layer whose coating film strength is greatly improved, so that it can be used when recording or reproducing by a magnetic disk recording / reproducing apparatus. Even if the head collides with the head while rotating at a high speed, the surface is hardly damaged.

[Brief description of the drawings]

FIG. 1 is a sectional view of a magnetic disk according to the present invention.

FIG. 2 is a schematic view showing a coating film forming apparatus for forming a lower nonmagnetic layer and an upper magnetic layer by a wet-on-wet coating method.

FIG. 3 is a schematic view illustrating an example of a coating apparatus of a coating film forming apparatus.

FIG. 4 is a schematic view showing another example of the coating apparatus.

FIG. 5 is a schematic view showing another example of the coating apparatus.

[Explanation of symbols]

1 magnetic disk, 2 non-magnetic support, 3 non-magnetic layer,
4 Magnetic layer

Claims (1)

[Claims] 1. A non-magnetic support, and a non-magnetic paint formed by dispersing a non-magnetic powder and a binder together with a solvent and adding a curing agent to the prepared paint is formed on the non-magnetic support by coating. A magnetic disk having a non-magnetic layer to be formed and a magnetic layer formed by applying a magnetic paint on the non-magnetic layer, wherein the non-magnetic paint has a hydroxyl group concentration of 0.2 as the binder.
A polyisocyanate compound containing 10% by weight or more of a vinyl chloride copolymer based on the nonvolatile component of the non-magnetic coating material and 30% by weight or more of an isocyanate group concentration as the curing agent; A magnetic disk comprising 35% by weight or more of the total weight of the agent.