JP2000173054A - Manufacturing method of magnetic recording medium - Google Patents

Abstract

(57) Abstract: In a method for manufacturing a magnetic recording medium having a lower magnetic layer and an upper magnetic layer having different coercive forces, each of the lower magnetic layer and the upper magnetic layer is magnetically isotropic. An alignment process is performed. SOLUTION: A first magnetic paint mainly composed of at least a first ferromagnetic powder and a binder is applied on a non-magnetic support 2 to form first magnetic layers 3a and 3b. While the magnetic layers 3a and 3b are in a wet state, a second magnetic paint mainly composed of a second ferromagnetic powder having a higher coercive force than the first ferromagnetic powder and a binder is applied to form a second magnetic layer. 4a and 4b are formed and a first alignment process is performed using an AC magnetic field.
The second alignment process is performed with an alternating magnetic field having a lower magnetic field intensity than the first alignment process.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a method of manufacturing a magnetic recording medium having a lower magnetic layer capable of recording a predetermined signal, wherein the upper and lower magnetic layers having different coercive forces are both non-oriented. It relates to a manufacturing method.

[0002]

2. Description of the Related Art As a magnetic recording medium, a magnetic layer is formed by applying a magnetic paint prepared by dispersing a ferromagnetic powder, a binder and various additives together with an organic solvent onto a nonmagnetic support and drying. A so-called coating type magnetic recording medium is known. Such coated magnetic recording media include:
For the purpose of high-density recording, there is a type in which metal fine particle powder is used as a ferromagnetic powder.

A magnetic recording medium coated with metal powder using such metal fine particle powder is used not only in various formats for audio and video, but also in computer peripheral devices such as a large-capacity floppy disk or a data cartridge for backup. Have been.

[0004] Some magnetic recording media are disk-shaped. This disc-shaped magnetic recording medium must be non-oriented in the in-plane direction in order to keep the output in the circumferential direction constant. As a method for non-orienting a disk-shaped magnetic recording medium, there is a method using magnetism. The non-alignment treatment using magnetism is roughly classified into a method of performing a non-alignment treatment by a combination of permanent magnets and a method of performing a non-alignment treatment by applying an AC magnetic field.

[0005] The non-orientation treatment of a disc-shaped magnetic recording medium by applying an alternating magnetic field requires 80% of the coercive force that a ferromagnetic powder normally has in the case of a disc-shaped magnetic recording medium having a single magnetic layer.
It is performed by applying the following magnetic field. This is due to a mechanism in which the ferromagnetic powder is magnetized with an external magnetic field lower than the coercive force that the ferromagnetic powder normally has, and the magnetization of the ferromagnetic powder is randomized by a magnetic torque with the external magnetic field.

On the other hand, as a metal powder-coated magnetic recording medium, a single-layer coated magnetic recording medium having a storage capacity of about 20 MB has been widely used in the past.
Multilayer coated magnetic recording media having a storage capacity of MB to 200 MB have been widely used.

The multi-layer coated magnetic recording medium includes a substrate having a non-magnetic layer and a magnetic layer formed in this order on a substrate;
There is a structure in which a first magnetic layer and a second magnetic layer are formed on a substrate in this order.

In a multilayer coating type magnetic recording medium having a lower layer as the first magnetic layer and an upper layer as the second magnetic layer, the coercive force of the ferromagnetic powder contained in the lower layer is reduced by the coercive force of the ferromagnetic powder contained in the upper layer. With a lower coercive force, information such as an identification signal and a servo signal is recorded in the lower layer. In other words,
In this multilayer coating type magnetic recording medium, generally, a high-coercivity metal fine-particle powder is used in an upper layer having a high recording density to store a short-wavelength signal, and a low-coercivity iron oxide powder is used in a lower layer, and a long-wavelength signal is used. Is recorded.

A method of manufacturing such a multi-layer coating type magnetic recording medium includes a simultaneous multi-layer coating method (also referred to as a wet-on-wet method) in which an upper layer is coated on a lower layer in a wet state that has not been dried. Or a successive multi-layer coating method (also referred to as a wet-on-dry method) in which the lower layer is dried after being applied, and then the upper layer is applied and dried.

Here, in a multi-layer coating type magnetic recording medium manufactured by using a sequential multi-layer coating method in which coating and drying are performed one by one, the lower layer which is already the first magnetic layer is coated at the stage of coating the upper layer which is the second magnetic layer. Are dried and the surface is hardened. Therefore, at the stage where the upper layer as the second magnetic layer is subjected to the non-orientation treatment, the ferromagnetic powder already contained in the lower layer as the first magnetic layer is fixed. For this reason, in the multilayer coating type magnetic recording medium using the sequential multilayer coating method, good surface properties cannot be obtained. Therefore, high-density recording cannot be achieved with a multilayer coating type magnetic recording medium using a sequential multilayer coating method.

On the other hand, when the simultaneous multilayer coating method is used, a coating film having a uniform thickness with few coating defects and coating streaks can be formed. Therefore, in the multilayer coating type magnetic recording medium using the simultaneous multilayer coating method, the upper magnetic layer has excellent surface properties.

[0012]

By the way, in the above-described multilayer coating type magnetic recording medium, when the sequential multilayer coating method is used, it is possible to perform the non-alignment treatment in the circumferential direction. That is, in this case, the first magnetic layer is subjected to the non-orientation treatment and dried at the stage of applying the second magnetic layer as the upper layer. The ferromagnetic powder contained in the lower layer, which is the first magnetic layer, is fixed. Therefore, in the multilayer coating type magnetic recording medium using the sequential multilayer coating method, even if the non-alignment treatment is performed with the magnetic field strength optimized for the upper layer of the high coercive force, the ferromagnetic powder contained in the lower layer is not affected. .

However, it has been difficult to perform a non-orientation treatment on a multilayer-coated magnetic recording medium having a first magnetic layer and a second magnetic layer manufactured by using the simultaneous multilayer coating method. This is because there is a difference between the coercive force of the ferromagnetic powder contained in the first magnetic layer and the coercive force of the ferromagnetic powder contained in the second magnetic layer.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances, and provides a method of manufacturing a magnetic recording medium having a lower magnetic layer and an upper magnetic layer having different coercive forces. It is an object of the present invention to provide a method of manufacturing a magnetic recording medium in which each layer has been subjected to a magnetically isotropic non-alignment treatment.

[0015]

In order to achieve the above-mentioned object, a method of manufacturing a magnetic recording medium according to the present invention comprises the steps of: providing at least a first ferromagnetic powder and a binder on a non-magnetic support; After forming a first magnetic layer by applying a first magnetic paint, the second ferromagnetic powder having a higher coercive force than the first ferromagnetic powder while the first magnetic layer is in a wet state. A second magnetic coating mainly composed of a magnetic material and a binder, forming a second magnetic layer, performing a first alignment process using an alternating magnetic field, and then applying a magnetic field lower than the first alignment process. The second alignment treatment is performed with a strong alternating magnetic field.

In this method of manufacturing a magnetic recording medium, the second magnetic layer is made non-oriented by performing the first orientation treatment using an AC magnetic field, and the first magnetic layer is kept in a state where the magnetization of the second magnetic layer does not move. The first magnetic layer is made non-oriented by performing the second orientation process at a lower magnetic field strength than the orientation process.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, specific embodiments of a method for manufacturing a magnetic recording medium according to the present invention will be described with reference to the drawings.

The magnetic recording medium 1 manufactured by the method described in the present embodiment is a magnetic recording medium formed in a substantially disk shape and having magnetic layers on both main surfaces. As shown in FIG. 1, the magnetic recording medium 1 includes a non-magnetic support 2, first magnetic layers 3a and 3b formed on both main surfaces 2a and 2b of the non-magnetic support 2, respectively. First magnetic layers 3a, 3
b and second magnetic layers 4a and 4b respectively formed on the second magnetic layer 4b.

In the magnetic recording medium 1, the first magnetic layers 3a and 3b have a lower coercive force than the second magnetic layers 4a and 4b.

First, the first magnetic layers 3a and 3b will be described. The first magnetic layers 3a and 3b are formed by applying a magnetic paint mainly composed of a ferromagnetic powder and a binder.

The ferromagnetic powder used for the first magnetic layers 3a and 3b includes, for example, iron oxide powder such as γ-iron oxide, magnetite, Co-modified γ-iron oxide, and Co-modified magnetite, chromium oxide, iron nitride, and iron carbide. And fine metal particles.

For example, Fe,
Co, Ni, Fe-Co, Fe-Ni, Fe-Al, F
e-Ni-Al, Fe-A1-P, Fe-Ni-Si-
Al, Fe-Ni-Si-Al-Mn, Fe-Mn-Z
n, Fe-Ni-Zn, Co-Ni, Co-P, Fe-
Co-Ni, Fe-Co-Ni-Cr, Fe-Co-N
i-P, Fe-Co-B, Fe-Co-Cr-B, Mn
Alloys such as -Bi, Mn-Al, and Fe-Co-V.

When a metal powder is used, one having a lower coercive force than that used in the second magnetic layers 4a and 4b is selected.

The specific surface area of these ferromagnetic powders is 20 to
90 m ² / g, preferably 25 to 70 m ² / g
Is more preferable. When the specific surface area is in the above range, high-density recording becomes possible with the formation of fine particles of the ferromagnetic powder, and a magnetic recording medium having excellent noise characteristics can be obtained. One type of ferromagnetic powder can be used, but two or more types may be used in combination.

On the other hand, examples of the binder include a thermoplastic resin, a thermosetting resin, and a reactive resin. These binders preferably have an average molecular weight of 5,000 to 100,000.

The thermoplastic resin includes, for example, vinyl chloride,
Vinyl chloride copolymer, vinyl acetate, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinylidene chloride copolymer,
Vinyl chloride-acrylonitrile copolymer, acrylate-acrylonitrile copolymer, acrylate-vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, acrylate-acrylonitrile copolymer, acrylate -Vinylidene chloride copolymer, methacrylic acid ester-vinylidene chloride copolymer, methacrylic acid ester-vinyl chloride copolymer, methacrylic acid ester-ethylene copolymer, polyvinyl fluoride, vinylidene chloride-acrylonitrile copolymer , Acrylonitrile-butadiene copolymer, polyamide resin, polyvinyl butyral, cellulose derivatives (cellulose acetate butyrate, cellulose diacetate, cellulose triacetate, cellulose propionate, nitrose) Loin), styrene-butadiene copolymer, polyurethane resin, polyester resin, amino resin, there is a synthetic rubber.

Examples of the thermosetting resin include phenol resin, epoxy resin, polyurethane curable resin, urea resin, melamine resin, alkyd resin, silicone resin,
Examples include polyamine resins and urea-formaldehyde resins.

These binders include, for example, -SO ₃ M, -OSO ₃ M,
A polar functional group such as -COOM, P = O (OM) ₂ may be introduced. Here, M is a hydrogen atom or
It is an alkali metal such as lithium, potassium and sodium. Further, polar functional groups include, for example, -NR ₁ R ₂ ,-
NR ₁ R ₂ R ₃ ⁺ X ⁻ side chain type having a terminal group, NR ₁
There is a main chain type of R ₂ ⁺ X ⁻ . Where R ₁ ,
R ₂ and R ₃ are a hydrogen atom or a hydrocarbon group;
^- is fluorine, chlorine, bromine, a halogen element ion or an inorganic or organic ion of iodine. Also, -OH,-
There are also polar functional groups such as SH, -CN, and epoxy groups. The amount of these polar functional groups is preferably 10 ^-1 to 10 ^-8 mol / g, and more preferably 10 ^-2 to 10 ^-6 mol / g. Note that these binders may be used alone, or a plurality of binders may be used as a mixture.

At this time, the ferromagnetic powder and the binder are kneaded in a conventionally known solvent to form a coating.

Examples of the solvent used in this coating include ketone solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone and cyclohexanone, alcohol solvents such as methanol, ethanol and propanol, methyl acetate and ethyl acetate. , Butyl acetate, propyl acetate, ethyl lactate, ester solvents such as ethylene glycol acetate, diethylene glycol dimethyl ether, 2-ethoxyethanol, ether solvents such as tetrahydrofuran, dioxane, aromatic hydrocarbon solvents such as benzene, toluene, xylene, Methylene chloride, ethylene chloride, carbon tetrachloride, chloroform,
There are halogenated hydrocarbon solvents such as chlorobenzene. These solvents are appropriately mixed and used.

Next, the second magnetic layers 4a and 4b will be described. The second magnetic layers 4a and 4b are formed by applying a magnetic paint mainly composed of a ferromagnetic powder and a binder.

The fine metal powder used in the second magnetic layers 4a and 4b includes, for example, Fe, Co, Ni, Fe-
Co, Fe-Ni, Fe-Al-Fe-Ni-Al, F
e-Al-P, Fe-Ni-Si-Al, Fe-Ni-
Si-Al-Mn, Fe-Mn-Zn, Fe-Ni-Z
n, Co-Ni, Co-P, Fe-Co-Ni, Fe-
Co-Ni-Cr, Fe-Co-Ni-P, Fe-Co
-B, Fe-Co-Cr-B, Mn-Bi, Mn-A
1, alloys such as Fe-Co-V, iron nitride, iron carbide and the like.

These second magnetic layers have a higher coercive force than the first magnetic layer described above. For this reason, the ferromagnetic powder used for the second magnetic layer needs to be appropriately selected in consideration of the coercive force of the first magnetic layer.

As the binder or solvent used in the second magnetic layers 4a and 4b, those exemplified for the first magnetic layers 3a and 3b can be used.

The first magnetic layers 3a and 3b and the second magnetic layers 4a and 4b may contain, for example, a lubricant, non-magnetic reinforcing particles, and the like, if necessary.

Examples of the lubricant include graphite, molybdenum disulfide, tungsten disulfide, silicone oil, fatty acids having 10 to 22 carbon atoms, fatty acid esters of alcohols having 2 to 26 carbon atoms, and terpenes. And the like, oligomers thereof, and fluorine-based lubricants. Since the lubricant is insufficient in absolute amount to be used for adding only the second magnetic layers 4a and 4b, it is preferable to add the lubricant also to the first magnetic layers 3a and 3b.

Further, the non-magnetic reinforcing particles are used in the second magnetic layer 4.
a, 4b are added to improve the magnetic characteristics, particularly to improve the coercive force.

The non-magnetic reinforcing particles include, for example, aluminum oxide (α, β, γ), chromium oxide, silicon carbide, diamond, garnet, emery, boron nitride, titanium carbide, silicon carbide, titanium carbide, titanium oxide ( Rutile, anatase) and the like. The addition amount of the nonmagnetic reinforcing particles is 20 parts by weight or less, preferably 10 parts by weight or less, more preferably 100 parts by weight of the ferromagnetic powder.
5 parts by weight or less is preferred. The Mohs hardness of the non-magnetic reinforcing particles is 4 or more, preferably 5 or more, and more preferably 6 or more.
The above is good. Furthermore, the specific gravity of the nonmagnetic reinforcing particles is 2 to
6, preferably in the range of 3-5. Further, the average primary particle size of the non-magnetic reinforcing particles is 1.0 μm or less, preferably 0.5 μm or less.

The first magnetic layers 3a and 3b and the second magnetic layers 4a and 4b may be used in combination with a polyisocyanate for crosslinking and curing the binder. The polyisocyanate includes toluene diisocyanate and its adduct, alkylene diisocyanate and its adduct. The amount of the polyisocyanate to be added to the binder is 5 to 80 parts by weight based on 100 parts by weight of the binder.
Parts by weight, preferably 10 to 50 parts by weight, are good. These polyisocyanates may be used for both the first magnetic layers 3a and 3b and the second magnetic layers 4a and 4b, or may be used only for the second magnetic layers 4a and 4b. First magnetic layers 3a, 3
When used for both the b layer and the second magnetic layers 4a and 4b, the compounding amount may be added to each layer in an equal amount or may be changed at an arbitrary ratio.

Next, a method for manufacturing the above-described magnetic recording medium will be described.

First, the first magnetic layers 3a and 3b and the second magnetic layers 4a and 4a are mainly composed of the above-described ferromagnetic powder and binder.
A magnetic paint for b is prepared. At this time, the ferromagnetic powder and the binder are kneaded using a conventionally known kneader such as a continuous twin-screw kneader, a continuous twin-screw kneader capable of being diluted in multiple stages, a kneader, a pressure kneader, and a roll kneader. Is done. Then, the ferromagnetic powder and the binder, etc., in the paint preparation process and dispersion process, roll mill, ball mill, horizontal sand mill, vertical sand mill, spike mill,
It is dispersed using a pin mill, a tower mill, an agitator, a homogenizer, an ultrasonic disperser, or the like.

When manufacturing the magnetic recording medium 1,
The first and second magnetic layers 3a and 3b and the second magnetic layers 4a and 4 are simultaneously coated on the non-magnetic support 2 with the magnetic paints for the first and second magnetic layers produced as described above.
b is formed. When the magnetic paints for the first magnetic layer and the second magnetic layer are simultaneously applied on the non-magnetic support 2 in a multilayer manner, for example, a die coater is used. The lip configuration of the die coater includes a two-lip system, a three-lip system, and a four-lip system.

Generally, the first magnetic layer 3 is formed on the non-magnetic support 2.
a and 3b and the second magnetic layers 4a and 4b are formed by a sequential multi-layer coating method in which coating and drying are performed one by one, and the second magnetic layer is formed on the first magnetic layers 3a and 3b which are not dried and wet.
There is a simultaneous multi-layer coating method in which the magnetic layers 4a and 4b are applied in an overlapping manner. In the present invention, the first magnetic layers 3a and 3b and the second magnetic layers 4a and 4b are formed using the simultaneous multilayer coating method. By performing the simultaneous multi-layer coating method, the uniformity of the coating film, the adhesiveness of the upper and lower interfaces, and the productivity can be improved.

As shown in FIG. 2, an extrusion coater 17 of an extrusion method is used in the simultaneous multilayer coating method. The extrusion coater 17 includes a first magnetic layer liquid reservoir 11 for storing the first magnetic layer paint and a second magnetic layer liquid reservoir 12 for storing the second magnetic layer paint.
And a first magnetic layer slit 13 connected to the first magnetic layer liquid reservoir 11, and a second magnetic layer slit 14 connected to the second magnetic layer liquid reservoir 12. ing.

In the simultaneous multi-layer coating method, the film-shaped non-magnetic support 2 is run in the direction of arrow B,
A traveling system in which the film-shaped non-magnetic support 2 is brought into contact with the extrusion coater 17 at a predetermined pressure is used.

First, the non-magnetic support 2 in the form of a film is fed in the direction of arrow B while being in contact with the extrusion coater 17 of the extrusion method. And the extrusion coater 17
Applies a coating material for the first magnetic layer on one main surface of the running nonmagnetic support 2 through the slit portion 13 for the first magnetic layer to form a first magnetic layer coating film 15.

Thereafter, while the first magnetic layer coating film 15 formed on the film-like non-magnetic support 2 is in a wet state, a magnetic coating for the second magnetic layer coating film 16 It is applied through the layer slit 14. Thus, the extrusion coater 17 forms the second magnetic layer coating 16 by applying the magnetic coating for the second magnetic layer on the first magnetic layer coating 15 in a wet state.

In the magnetic recording medium using such a simultaneous multi-layer coating method, the first magnetic layers 3a and 3b are in a wet state and the second magnetic layers 4a and 4b are coated.
The interface between the magnetic layers 3a, 3b and the second magnetic layers 4a, 4b is smooth, the surface properties of the second magnetic layers 4a, 4b are good, and the adhesion between the layers is improved.
As a result, the magnetic recording medium using the simultaneous multilayer coating method
In particular, it satisfies the required performance as a magnetic recording medium that requires high output and low noise for high density recording,
Film peeling is eliminated and film strength is improved. In addition, the magnetic recording medium using the simultaneous multilayer coating method has reduced dropout and improved reliability.

In addition to the case where a clear boundary substantially exists between the upper and lower layers formed by using the simultaneous multilayer coating method, there is a boundary region formed by mixing the components of both layers with a certain thickness. Although it may be present, the upper layer portion excluding such a boundary region is used as the first magnetic layers 3a and 3 in the present invention.
b, and the lower layer portion is the second magnetic layer 4a, 4a in the present invention.
b.

Next, non-alignment treatment in an alternating magnetic field using a unit alignment apparatus will be described.

For example, as shown in FIG.
Thereby, the above-described first magnetic layer coating film 15 and second magnetic layer coating film 16 are subjected to a non-orientation treatment.

As shown in FIG. 3, the alignment processing section 20 includes a first unit alignment device 21, a drying device 22,
Are arranged in parallel in this order. The magnetic recording medium 1 moves between the devices thus arranged in the direction of arrow A, that is, from the first unit orientation device 21 to the second unit orientation device 23.

As shown in FIG. 4, the first unit orienting device 21 is composed of a magnet 31 which is a solenoid coil formed by winding a plurality of conductors around the magnetic recording medium 1. That is, the magnet 31 is used for the magnetic recording medium 1.
And a solenoid coil formed in a size capable of running around the center. Further, the magnet 31 has a length capable of completing the non-alignment treatment of the ferromagnetic powder contained in the second magnetic layers 4a and 4b while the magnetic recording medium 1 travels between the first unit alignment devices 21. Is configured.

A drying device 22 is arranged on the side of the magnet 31 in the direction in which the magnetic recording medium 1 advances. Also,
Although not shown, a DC power supply for supplying a DC current and a cooling water supply port for cooling heat generated in the magnet 31 are provided at both ends of the magnet 31.

As shown in FIG. 4, the drying device 22 includes a hot air supply nozzle 32 to which hot air for drying the surface layer of the coating film of the magnetic recording medium 1 is supplied, and an outlet of the hot air to blow out. And a certain warm air outlet 33.

The hot air outlet 33 blows out hot air in a direction opposite to the traveling direction of the magnetic recording medium
Is dried.

The velocity of the warm air is preferably from 1 m per second to 60 m per second. More preferably, it is 5 m / sec to 40 m / sec. If the wind speed is lower than this, drying is not sufficiently performed, and if the wind speed is higher than this, the ripples of the paint become remarkable, and the surface properties rapidly deteriorate.

The temperature of the hot air is preferably 30 ° C. or more and 110 ° C. or less as measured at the hot air outlet 33. More preferably, it is 60 ° C. or more and 100 ° C. or less. If the temperature is too low, drying is not sufficiently performed, and if the temperature is too high, bumping of the solvent may occur, which is dangerous, and at the same time, the surface properties deteriorate, which is not preferable.

The second unit alignment device 23 is provided with the first unit
Is configured in the same manner as the unit alignment device 21 of FIG.

In the second non-orientation process performed by the second unit orienting device 23, the drying device 22 is not necessarily required, but may be provided. Further, the hot air outlet 33 shown in FIG. 4 is arranged on the opposite side so as to be symmetrical with respect to the magnet 31, and when hot air is blown in the same direction as the traveling direction of the magnetic recording medium 1, Warm air is directly applied to the low-viscosity paint when it is dried, so that the possibility of ripples is high, which is not preferable.

In FIG. 3, the second unit alignment device 23
The case where there is no drying device 22 is illustrated. Further, the first unit orienting device 21 and the second unit orienting device 23 have the same shape as the magnet 31 shown in FIG. Further, the DC power supply and the cooling system of each magnet 31 of the first unit orienting device 21 and the second unit orienting device 23 may use a common one in series or may be attached to each unit. .

Next, the non-orientation treatment in an alternating magnetic field will be specifically described.

First, the second magnetic layer coating film 1 of the magnetic recording medium 1
6 is subjected to a non-alignment treatment by the first unit alignment device 21.

In the first non-alignment treatment in the alternating magnetic field performed in the first unit alignment device 21, the high coercivity layer,
That is, since the purpose is to make the second magnetic layer 4a and the second magnetic layer 4b non-oriented, the second magnetic layer 4a and the second magnetic layer 4b
And preferably a magnetic field of 80% or less of the coercive force. The magnitude of the applied magnetic field is adjusted according to the paint viscosity and the like. The first magnetic layer 3a and the first magnetic layer 3b are slightly oriented in the longitudinal direction because the alternating magnetic field for non-orienting the second magnetic layer 4a and the second magnetic layer 4b is too large for itself. .

Then, by using the drying device 22, the second magnetic layer 4a and the second magnetic layer 4b are dried so that the magnetization direction does not easily move.

Next, the first magnetic layer coating film 1 of the magnetic recording medium 1
5 is subjected to a non-alignment treatment by the second unit alignment device 23.

That is, after performing the first non-alignment treatment in the AC magnetic field, the second unit alignment device 23 is used to optimize the AC magnetic field optimized for the first magnetic layer 3a and the first magnetic layer 3b. so,
The first magnetic layer 3a and the first magnetic layer 3b are non-oriented. At this time, the magnetic field strength is set to be equal to or less than the coercive force of the first magnetic layer 3a and the first magnetic layer 3b, and preferably equal to or less than 80% of the coercive force.

Here, since the coercive force of the second magnetic layers 4a and 4b is larger than the coercive force of the first magnetic layer, the second magnetic layer Is not changed. For this reason, the second unit alignment device 23 includes the first magnetic layer 3a,
Only 3b can be non-oriented.

In particular, in this method, since the surface of the second magnetic layers 4a and 4b is dried after the first non-orientation treatment, the magnetization directions of the second magnetic layers 4a and 4b must be fixed to some extent. Can be. Therefore, according to this method, even if the difference between the coercive force of the first magnetic layers 3a, 3b and the coercive force of the second magnetic layers 4a, 4b is small, the second unit alignment device 23 The second magnetic layer 4a,
There is no change in the magnetization direction of 4b.

Thus, in this method, the first magnetic layer 3
a, 3b and the second magnetic layers 4a, 4b can be completely non-oriented.

In the above-described embodiment, the drying is performed in the magnetic field using the drying device 22 during the first non-orientation process, but the drying is performed using the drying device 22 after the first non-orientation process. Is also good.

As a result, the first magnetic layer 3a and the second magnetic layer 4a, each of which is non-oriented, are formed. Thereafter, the non-magnetic support 2 is carried into a dryer, dried, and wound up.

After the nonmagnetic support 2 is formed with the first magnetic layer 3b and the second magnetic layer 4b which are similarly non-oriented, the nonmagnetic support 2 is carried into a dryer, dried and wound up. After the first magnetic layers 3a and 3b and the second magnetic layers 4a and 4b are formed on both the main surfaces 2a and 2b,
It is carried into a calendar device and subjected to calendar processing,
Then, it is wound up on a winding roll. Finally, the disk is punched into a predetermined size to form a disk, thereby forming a disk-shaped magnetic recording medium.

It should be noted that the magnetic recording medium using the simultaneous multi-layer coating method is not subjected to the above-described manufacturing sequence, but is applied to one side, then carried into a dryer and wound up, and then carried into a calender and subjected to a flattening process. This time, after applying the opposite surface, it may be manufactured by being carried into a dryer and wound up, then carried into a calender device, subjected to a flattening treatment, and wound up by a take-up roll.

Finally, by punching the magnetic recording medium 1 having been subjected to the non-orientation processing into a disk having a predetermined size,
The disk-shaped magnetic recording medium 1 is obtained.

[0076]

EXAMPLES Hereinafter, specific examples and comparative examples of the present invention will be described, but it goes without saying that the present invention is not limited to these examples.

Example 1 First, paints for the first magnetic layer and the second magnetic layer were prepared based on the following compositions.
The needle ratio and long axis length of the magnetic powder were randomly selected from a transmission electron micrograph (50,000 or 100,000; appropriately selected according to the particle size).
The arithmetic mean value of the particles was used.

According to a conventional method, a magnetic powder, a binder, an additive, and a solvent are mixed and kneaded by a continuous kneader. The first magnetic layer paint is a sand mill for 3 hours, and the second magnetic layer paint is mixed. The mixture was dispersed in a sand mill for 5 hours.

<Coating Composition of First Magnetic Layer> 100 parts by weight of γ-iron oxide powder (average major axis length = 0.32 μ, needle ratio = 12, saturation magnetization = 72 Am ² / kg, coercive force = 25 kA / m 10 parts by weight of polyvinyl chloride resin (degree of polymerization: 300, containing potassium oxysulfonate as a polar functional group at 5 × 10 ⁻⁵ mol / g) 10 parts by weight of polyester polyurethane resin (sodium sulfonate as a polar functional group) 1 × 10 ^-4 mol / g) 3 parts by weight of stearic acid 3 parts by weight of heptyl stearate 150 parts by weight of methyl ethyl ketone 150 parts by weight of cyclohexanone

<Coating Composition of Second Magnetic Layer> 100 parts by weight of Fe-based metal ferromagnetic powder (average major axis length = 0.2 μ, needle ratio = 9, saturation magnetization = 130 Am ² / kg, coercive force = 135 kA) / M) Polyvinyl chloride resin 10 parts by weight (polymerization degree 300, containing potassium oxysulfonate 5 × 10 ⁻⁵ mol / g as a polar functional group) Polyester polyurethane resin 10 parts by weight (sodium sulfonate as a polar functional group) Additive 1 × 10 ^-4 mol / g) Additive 5 parts by weight (Primary particle size 0.20 μAl ₂ O ₃ ) Stearic acid 3 parts by weight Heptyl stearate 3 parts by weight Methyl ethyl ketone 150 parts by weight Cyclohexanone 150 parts by weight

After adding 4 parts by weight of polyisocyanate to the obtained paint, it was simultaneously and multi-layer coated on a 62 μm-thick polyethylene terephthalate film (surface roughness Ra = 8 nm) using a 4-lip die coater. The second alignment magnetic field is 32 kA / m, and the second alignment magnetic field is 4 kA.
/ M and the first unit alignment device 2 used for the first time
The drying device 22 from which warm air blows out was disposed only in the case 1.

After drying, the coating thickness of each layer was set to 1.5 μm for the first magnetic layer and 0.2 μm for the second magnetic layer. The orientation ratio is determined by the web traveling direction (MD) and the web width direction (TD).
And the orientation ratio OR = (M
The external magnetic field is 0.8 MA / m using a vibration sample magnetometer (D direction squareness ratio) / (TD direction squareness ratio) vibrating sample magnetometer (manufactured by Toei Kogyo).
(10 kOe).

Example 2 In Example 1, the magnetic powder of the first magnetic layer was changed from γ-iron oxide powder to Co-modified γ-iron oxide powder (average major axis length = 0.34 μ, needle ratio = 12, saturation A magnetic recording medium 1 was produced in the same manner as in Example 1, except that the magnetization amount was changed to 76 Am ² / kg and the coercive force was changed to 52 kA / m.

<Embodiment 3> In Embodiment 1, the hot air outlet 33 of the first unit orienting device 21 (hereinafter, referred to as the first unit orienting device 21) used for the first time is removed to allow air drying and natural drying. did.

<Embodiment 4> In Embodiment 2, the hot air outlet 33 of the first unit orienting device 21 was removed and air drying was performed.

<Comparative Example 1> In Example 1, the power supply of the second unit alignment device 23 (hereinafter referred to as the second unit alignment device 23) used for the second time was turned off.
The hot air outlet 33 using only the first unit orientation device 21
The magnetic recording medium 1 was produced while blowing warm air from the apparatus.

<Comparative Example 2> In Example 1, the power of the first unit orientation device 21 was turned off, and hot air was blown out of the hot air outlet 33 using only the second unit orientation device 23. A magnetic recording medium 1 was manufactured.

Table 1 summarizes the experimental parameters and measurement results of Example 1, Example 2, and Comparative Examples 1 to 4.

[0089]

[Table 1]

As is apparent from Table 1, in Examples 1 to 4, all the values of the orientation ratio OR were close to 100, and good results were obtained.

On the other hand, in Comparative Examples 1 and 2, the values of the orientation ratio OR greatly deviated from 100 were obtained.

Thus, after performing the first non-alignment treatment in the first unit alignment device 21, the second unit alignment device 2
3 to perform the second non-orientation treatment, whereby the first magnetic layer 3
a, 3b and the second magnetic layers 4a, 4b can be almost completely non-oriented.

On the other hand, as shown in Comparative Examples 1 and 2, when a single non-alignment treatment is performed, both the first magnetic layers 3a and 3b and the second magnetic layers 4a and 4b are formed. It cannot be made non-oriented.

Further, as is apparent from a comparison between Example 2 and Example 4, the second magnetic layer 4
By drying the surfaces of the first and second magnetic layers 3a and 4b,
The first magnetic layers 3a, 3b and the second magnetic layers 4a, 4b can be more reliably non-oriented even if the difference between the coercive forces of the magnetic layers a, 3b and the second magnetic layers 4a, 4b is small. Can be.

[0095]

As described above, according to the method for manufacturing a magnetic recording medium of the present invention, the lower magnetic layer and the upper magnetic layer having excellent surface properties and different coercive forces are provided. A magnetic recording medium in which each of the layer and the upper magnetic layer is magnetically isotropic and non-oriented can be manufactured.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view of a main part showing a configuration example of a magnetic recording medium to which the present invention is applied.

FIG. 2 is a schematic view showing a coating apparatus for applying a magnetic paint in a multi-layered manner on a non-magnetic support.

FIG. 3 is a configuration diagram of an alignment processing unit to which the present invention is applied.

FIG. 4 is a configuration diagram of a first unit alignment device and a drying device to which the present invention is applied.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Magnetic recording medium, 2 Non-magnetic support, 3 First magnetic layer, 4 Second magnetic layer

Claims (2)

[Claims] 1. A first magnetic layer comprising at least a first ferromagnetic powder and a binder as a main component is coated on a non-magnetic support to form a first magnetic layer. In a wet state, a second magnetic paint mainly composed of a second ferromagnetic powder having a higher coercive force than the first ferromagnetic powder and a binder is applied to form a second magnetic layer. An AC magnetic field is applied to perform a first alignment process, and then the second alignment is performed with an AC magnetic field having a lower magnetic field intensity than the first alignment process.
A method for producing a magnetic recording medium, comprising: 2. The magnetic recording medium according to claim 1, wherein drying is performed at least during the first alignment processing or before the second alignment processing, and then the second alignment processing is performed. Manufacturing method.