Coating processes – Magnetic base or coating – Magnetic coating
Reexamination Certificate
1999-07-21
2001-03-27
Cameron, Erma (Department: 1762)
Coating processes
Magnetic base or coating
Magnetic coating
C427S132000, C427S412100, C427S412500, C427S365000
Reexamination Certificate
active
06207223
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for producing a magnetic recording medium, in particular, a producing method of a magnetic recording medium which is excellent in surface properties and capable of achieving high output.
2. Description of the Related Art
With the trend of the increase of density of magnetic recording media in recent years, recording wavelength has become narrow. As a result, the thickness of a magnetic layer has become thinner. On the other hand, separately from main recording, tracking signal recording such as servo signals has become necessary. Therefore, a multilayer magnetic recording medium having a plurality of magnetic recording layers has been proposed. As producing methods and producing apparatuses therefor, e.g., JP-A-5-212337 (the term “JP-A” as used herein means an “Unexamined Japanese patent Publication (kokai)”) suggests simultaneous multilayer coating methods and apparatuses.
The techniques disclosed in JP-A-5-212337 has elaborated to discharge a coating solution from a plurality of slits for effectively preventing generation of uneven colors and vertical streaks in multilayer coating of thin layers, and preventing the reduction of orientation properties to manufacture good magnetic recording media stably. Further, at least a coating solution for the lowermost layer is made nonmagnetic solution and a coating unit the edge shape of which is contrived is used for coating.
However, in such a multilayer simultaneous coating method, it is very difficult to select optimal viscosity of a coating solution of each layer to obtain a desired coating thickness of each layer while preventing the turbulence in the interface between each layer, at the same time, ensuring the surface properties of the uppermost layer. Further, a coating unit becomes complicated because at least three feeding pipe and slits are required. In addition, when a magnetic recording medium comprises a plurality of magnetic layers, control and insurance of the thickness of each layer during production are difficult.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a method for producing a magnetic recording medium capable of preventing the turbulence in the interface between each layer and ensuring the surface properties of the uppermost layer.
The above object of the present invention can be achieved by the following constitution.
(1) A method for producing a multilayer magnetic recording medium having at least three layers on the side of a support on which a magnetic recording layer is provided, comprises forming all the coating layers on the magnetic layer side using a monolayer coating step and a simultaneous multilayer coating step.
(2) In the method for producing a magnetic recording medium as described in the above item (1), said two times of layer formation include at least one time of simultaneous multilayer coating of two layers.
(3) The method for producing a magnetic recording medium as described in the above item (1) or (2), further comprises performing calendering process after all the coating layers on the magnetic recording layer side have been formed.
That is, in the method for producing a magnetic recording medium according to the present invention, in order to produce a required multilayer medium, a monolayer coating and two-layer simultaneous multilayer coating are preferably used in combination for satisfying the desired coating thickness of each layer. Thus, a magnetic recording medium capable of preventing the turbulence in the interface between each layer and ensuring the surface properties of the uppermost layer can be obtained.
For example, when a magnetic recording medium having an upper magnetic layer, an intermediate magnetic layer and a lower nonmagnetic layer is produced, it is preferred that a lower nonmagnetic layer is coated on a support in the first stage, then an upper magnetic layer and an intermediate magnetic layer are simultaneously multilayer-coated to form a three layer structure medium. Alternatively, in the first stage, an intermediate magnetic layer and a lower nonmagnetic layer are coated on a support by simultaneous multilayer coating, then an upper magnetic layer is coated by monolayer coating.
The technique disclosed in JP-A-5-104054 can be preferably used in two-layer simultaneous multilayer coating.
Further, the technique disclosed in JP-A-7-287843 can be preferably used in thin layer monolayer coating.
For improving the surface properties of the uppermost layer which are most important in electromagnetic characteristics, it is effective to perform calendering process after all the layers have been coated.
That is, it has been found that when calendering process is performed after one or a plurality of lower layers have been formed and then, an upper layer is coated thereon, the surface properties of the uppermost layer are not improved even if calendering process is performed after that.
Three layers in the present invention do not include a thin undercoating layer for the improvement of the adhesion of the magnetic layer, or a thin overcoating lubricating layer for imparting running property and durability to the magnetic recording medium.
REFERENCES:
patent: 4927665 (1990-05-01), Chino et al.
patent: 5069934 (1991-12-01), Chino et al.
patent: 5474814 (1995-12-01), Komatsu et al.
patent: 5-104054 (1993-04-01), None
patent: 5-212337 (1993-08-01), None
patent: 7-129947 (1995-05-01), None
patent: 7-287843 (1995-10-01), None
patent: 9-212861 (1997-08-01), None
Kasahara Seiji
Komatsu Kazunori
Cameron Erma
Fuji Photo Film Co. , Ltd.
Sughrue Mion Zinn Macpeak & Seas, PLLC
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