JPH10255259A - Manufacturing method of magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a magnetic layer coating material for improving the dispersion stability, to improve the smoothness of the surface of the magnetic layer, to improve the magnetic characteristics, and to improve the electromagnetic conversion characteristics. An object of the present invention is to provide a method for manufacturing a medium. SOLUTION: A step of preparing a magnetic layer coating by dispersing ferromagnetic powder particles 1 such as metal magnetic powder and a binder 2 such as polyester polyurethane in a solvent, and applying the magnetic layer coating to a non-magnetic material such as a polyethylene terephthalate film. In the method for producing a magnetic recording medium having a step of forming a magnetic layer by coating on a support, a main component of a solvent for uniformly dispersing the ferromagnetic powder particles 1 and the binder 2 is a poor solvent for the binder 2 There is a feature. Desirably, the amount of the poor solvent is 50 parts by weight or more and 95 parts by weight or less with respect to 100 parts by weight of the solvent, and the preferable poor solvent is toluene.

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 magnetic recording medium that improves the smoothness and magnetic properties of a magnetic layer surface and improves electromagnetic conversion characteristics.

[0002]

2. Description of the Related Art In a magnetic recording / reproducing apparatus using a magnetic recording medium such as a tape or a disk, high-density recording by short-wavelength recording is performed. There is a need for further improvement in electromagnetic conversion characteristics. Generally, the general manufacturing process of a magnetic recording medium uniformly disperses a ferromagnetic powder or a binder in a solvent such as an organic solvent,
This is filtered to remove foreign substances and agglomerates to form a magnetic layer coating. This magnetic layer coating is applied on a non-magnetic support, dried after magnetic orientation treatment, cured after calendering, and cured to form a magnetic layer. It is completed through a process of forming and cutting to a predetermined size. An ideal magnetic layer coating material maintains a state in which ferromagnetic powder, binder, and the like are uniformly dispersed in a solvent, and smoothes the magnetic layer surface, improves magnetic characteristics, and improves electromagnetic conversion characteristics. It is effective to repeat the calendar process in the calendar process for improving the calendar process.

However, calendering is a process performed under severe conditions, and repetition of calendering may damage the magnetic recording medium and requires many man-hours. In order to solve these problems, various studies have been made to adjust the material and the content ratio of each of the ferromagnetic powder and binder contained in the magnetic layer coating material, but no effective means has yet been found. Is the actual situation. In addition, if the dispersion stability of the ferromagnetic powder and the binder contained in the prepared magnetic layer paint is small, the magnetic layer paint may be agglomerated before being filtered and applied on the non-magnetic support. There is a possibility that the smoothness of the magnetic layer surface may be deteriorated.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for producing a coating material for a magnetic layer which improves the dispersion stability, to improve the smoothness of the surface of the magnetic layer and to improve the magnetic characteristics, and to improve the electromagnetic conversion characteristics. It is an object of the present invention to provide a method of manufacturing a magnetic recording medium for improving the quality.

[0005]

In order to solve the above-mentioned problems, in a method for manufacturing a magnetic recording medium according to the present invention, at least a ferromagnetic powder such as a metal magnetic powder and a binder such as a polyester polyurethane are mixed with a solvent such as an organic solvent. A method for producing a magnetic layer paint by dispersing the same in a magnetic layer, and a step of applying the magnetic layer paint to a non-magnetic support such as a polyethylene terephthalate film to form a magnetic layer. The main component of the solvent for uniformly dispersing the powder and the binder is a poor solvent for the binder.

[0006] A preferred embodiment of the present invention is a solvent 100
The poor solvent is 50 parts by weight or more and 95 parts by weight or less with respect to parts by weight, and a desirable poor solvent is toluene.

[0007] According to the above-mentioned means, the dispersion stability of the prepared magnetic layer paint is good, and the surface of the magnetic layer formed by applying this to a non-magnetic support can be made a smooth surface. Therefore, the process of the present invention makes it possible to provide a magnetic recording medium having good electromagnetic conversion characteristics corresponding to shorter wavelength recording.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a magnetic layer paint prepared by dispersing a ferromagnetic powder, a binder and the like in a solvent.
FIG. 2 is a schematic model sectional view showing a state of ferromagnetic powder particles 1. On the entire circumference surrounding the ferromagnetic powder particles 1, an adsorption layer 3 is formed by the binder 2 and the solvent adsorbed on the ferromagnetic powder particles 1. The thickness of the adsorption layer 3 and the density of the binder 2 change depending on the compatibility of the binder 2 and the solvent with the ferromagnetic powder particles 1. And each ferromagnetic powder particle 1
Attraction force acts in the direction indicated by arrow A in the drawing due to magnetic energy, and between the ferromagnetic powder particles 1 depends on the thickness of the adsorption layer 3 and the density of the binder 2 in the drawing. Repulsive forces in the direction indicated by arrow B act on each other. The repulsion becomes smaller as the layer thickness of the adsorption layer 3 and the density of the binder 2 become smaller, and conversely, becomes larger as the layer thickness and the density of the binder 2 become larger.

When an organic solvent mainly composed of a good solvent having excellent solubility in the binder 2 is used, the solubility of the binder 2 adsorbed on the ferromagnetic powder particles 1 increases, and the binder 2 Dissolution in the organic solvent is preferentially performed rather than adsorption to the ferromagnetic powder particles 1, and the density of the binder 2 adsorbed to the ferromagnetic powder particles 1 is reduced. This tendency becomes more remarkable as the dissolving power of the organic solvent increases. vice versa,
When an organic solvent containing a poor solvent as a main component is used, the solubility becomes small, and the adsorption to the ferromagnetic powder particles 1 is preferentially performed rather than the dissolution of the binder 2. The density of the binder 2 adsorbed on the particles 1 increases, and the thickness of the adsorption layer 3 and the density of the binder 2 increase.

That is, if the repulsive force is smaller than the attractive force between the ferromagnetic powder particles 1, aggregation occurs in the magnetic layer paint, and conversely, the repulsive force is larger than the attractive force between the ferromagnetic powder particles 1. When there is, there is no possibility that agglomeration occurs in the magnetic layer coating material, and the dispersion stability of the magnetic layer coating material can be increased. Hereinafter, the manufacturing process of the magnetic recording medium of the present invention will be described with reference to specific examples.

Example 1 First, the following composition was kneaded with a twin-screw extrusion kneader, dispersed using a sand mill, and filtered through a filter having an average diameter of 3.5 μm to prepare a magnetic layer coating material. Ferromagnetic powder: Metal magnetic powder 50 parts by weight (specific surface area BET value = 54.0 m ² / g) Binder: Polyester polyurethane 10 parts by weight (trade name N-2304, manufactured by Nippon Polyurethane Co.) Vinyl chloride vinyl acetate copolymer 5 Parts by weight (VAGH, manufactured by Union Carbide Co.) Additives: 5 parts by weight of α-Al ₂ O ₃ (AKP-30, manufactured by Sumitomo Chemical Co., Ltd.) Lubricant: 1 part by weight of butyl stearate Organic solvent: 50 parts by weight of toluene Parts methyl ethyl ketone 5 parts by weight methyl isobutyl ketone 45 parts by weight

Next, as an example, the following composition was dispersed using a ball mill for 48 hours, and filtered through a filter having an average diameter of 1.5 μm to prepare a back coat layer paint. Non-magnetic powder: 100 parts by weight of carbon black (trade name RAVE-1255, manufactured by Colombian Carbon Co.) Binder: 20 parts by weight of polyester polyurethane (trade name: UR-8300, manufactured by Toyobo Co., Ltd.) 5 parts by weight of phenoxy resin (trade name: YP Organic solvent: Toluene 220 parts by weight Methyl ethyl ketone 220 parts by weight Methyl isobutyl ketone 220 parts by weight

Next, 10 parts by weight of a curing agent (Coronate L) was added to the prepared back coat layer coating material, and this was added to 9 μm
It was applied to a thick polyethylene terephthalate film so that the layer thickness after drying was 0.7 μm, to form a back coat layer.

Next, 1 part by weight of myristic acid as a lubricant and 10 parts by weight of a curing agent (Coronate L) are added to the prepared magnetic layer paint, and a polyethylene terephthalate film on the side opposite to the side where the back coat layer is formed is formed. Coating is performed so that the layer thickness after drying becomes 3.5 μm, a magnetic layer is formed through a calendering process and a curing process, and this is cut into a 1/2 inch width to complete a 1/2 inch width magnetic tape. Was.

Example 2 First, the following composition was kneaded with a twin-screw extrusion kneader, dispersed using a sand mill, and filtered through a filter having an average diameter of 3.5 μm to prepare a magnetic layer coating material. Ferromagnetic powder: Metal magnetic powder 50 parts by weight (specific surface area BET value = 54.0 m ² / g) Binder: Polyester polyurethane 10 parts by weight (trade name N-2304, manufactured by Nippon Polyurethane Co.) Vinyl chloride vinyl acetate copolymer 5 Parts by weight (VAGH, manufactured by Union Carbide Co.) Additives: 5 parts by weight of α-Al ₂ O ₃ (AKP-30, manufactured by Sumitomo Chemical Co., Ltd.) Lubricant: 1 part by weight of butyl stearate Organic solvent: 50 parts by weight of toluene Parts 25 parts by weight of methyl ethyl ketone 25 parts by weight of methyl isobutyl ketone

Hereinafter, through a step of forming a back coat layer using a back coat layer paint similar to the case shown in Example 1 or a step of forming a magnetic layer using the magnetic layer paint prepared in this embodiment, the width is reduced to 1/2 inch. It was cut to complete a 1/2 inch wide magnetic tape.

Example 3 First, the following composition was kneaded with a twin-screw extrusion kneader, dispersed using a sand mill, and filtered through a filter having an average diameter of 3.5 μm to prepare a magnetic layer paint. Ferromagnetic powder: Metal magnetic powder 50 parts by weight (specific surface area BET value = 54.0 m ² / g) Binder: Polyester polyurethane 10 parts by weight (trade name N-2304, manufactured by Nippon Polyurethane Co.) Vinyl chloride vinyl acetate copolymer 5 Parts by weight (VAGH, manufactured by Union Carbide Co.) Additives: 5 parts by weight of α-Al ₂ O ₃ (AKP-30, manufactured by Sumitomo Chemical Co., Ltd.) Lubricant: 1 part by weight of butyl stearate Organic solvent: 50 parts by weight of toluene Parts Methyl ethyl ketone 45 parts by weight Methyl isobutyl ketone 5 parts by weight

Hereinafter, through a step of forming a back coat layer using the same back coat layer paint as in the case shown in Example 1 or a step of forming a magnetic layer using the magnetic layer paint prepared in this embodiment, the width is reduced to 1/2 inch. It was cut to complete a 1/2 inch wide magnetic tape.

Example 4 First, the following composition was kneaded with a twin-screw extrusion kneader, dispersed using a sand mill, and filtered through a filter having an average diameter of 3.5 μm to prepare a magnetic layer paint. Ferromagnetic powder: Metal magnetic powder 50 parts by weight (specific surface area BET value = 54.0 m ² / g) Binder: Polyester polyurethane 10 parts by weight (trade name N-2304, manufactured by Nippon Polyurethane Co.) Vinyl chloride vinyl acetate copolymer 5 Parts by weight (trade name VAGH, manufactured by Union Carbide Co.) Additive: 5 parts by weight of α-Al ₂ O ₃ (brand name: AKP-30, manufactured by Sumitomo Chemical Co., Ltd.) Lubricant: 1 part by weight of butyl stearate Organic solvent: 60 parts by weight of toluene Parts methyl ethyl ketone 5 parts by weight methyl isobutyl ketone 35 parts by weight

Hereinafter, through a step of forming a back coat layer using the same back coat layer paint as in the case shown in Example 1 or a step of forming a magnetic layer using the magnetic layer paint prepared in this embodiment, the width is reduced to 1/2 inch. It was cut to complete a 1/2 inch wide magnetic tape.

Example 5 First, the following composition was kneaded with a twin-screw extrusion kneader, dispersed using a sand mill, and filtered through a filter having an average diameter of 3.5 μm to prepare a magnetic layer paint. Ferromagnetic powder: Metal magnetic powder 50 parts by weight (specific surface area BET value = 54.0 m ² / g) Binder: Polyester polyurethane 10 parts by weight (trade name N-2304, manufactured by Nippon Polyurethane Co.) Vinyl chloride vinyl acetate copolymer 5 Parts by weight (trade name VAGH, manufactured by Union Carbide Co.) Additive: 5 parts by weight of α-Al ₂ O ₃ (brand name: AKP-30, manufactured by Sumitomo Chemical Co., Ltd.) Lubricant: 1 part by weight of butyl stearate Organic solvent: 60 parts by weight of toluene Parts methyl ethyl ketone 20 parts by weight methyl isobutyl ketone 20 parts by weight

Hereinafter, through a step of forming a back coat layer using a back coat layer paint similar to the case shown in Example 1 or a step of forming a magnetic layer using the magnetic layer paint prepared in this embodiment, the width is reduced to 1/2 inch. It was cut to complete a 1/2 inch wide magnetic tape.

Example 6 First, the following composition was kneaded with a twin-screw extruder, dispersed using a sand mill, and filtered with a filter having an average diameter of 3.5 μm to prepare a magnetic layer coating material. Ferromagnetic powder: Metal magnetic powder 50 parts by weight (specific surface area BET value = 54.0 m ² / g) Binder: Polyester polyurethane 10 parts by weight (trade name N-2304, manufactured by Nippon Polyurethane Co.) Vinyl chloride vinyl acetate copolymer 5 Parts by weight (trade name VAGH, manufactured by Union Carbide Co.) Additive: 5 parts by weight of α-Al ₂ O ₃ (brand name: AKP-30, manufactured by Sumitomo Chemical Co., Ltd.) Lubricant: 1 part by weight of butyl stearate Organic solvent: 60 parts by weight of toluene Parts methyl ethyl ketone 35 parts by weight methyl isobutyl ketone 5 parts by weight

Hereinafter, a process of forming a back coat layer using a back coat layer paint similar to the case shown in Example 1 or a process of forming a magnetic layer using the magnetic layer paint manufactured in this embodiment is performed to reduce the width to 1/2 inch. It was cut to complete a 1/2 inch wide magnetic tape.

Example 7 First, the following composition was kneaded with a twin-screw extruder, dispersed using a sand mill, and filtered through a filter having an average diameter of 3.5 μm to prepare a magnetic layer coating material. Ferromagnetic powder: Metal magnetic powder 50 parts by weight (specific surface area BET value = 54.0 m ² / g) Binder: Polyester polyurethane 10 parts by weight (trade name N-2304, manufactured by Nippon Polyurethane Co.) Vinyl chloride vinyl acetate copolymer 5 Parts by weight (trade name VAGH, manufactured by Union Carbide Co.) Additives: 5 parts by weight of α-Al ₂ O ₃ (trade name: AKP-30, manufactured by Sumitomo Chemical Co., Ltd.) Lubricant: 1 part by weight of butyl stearate Organic solvent: 70 parts by weight of toluene Parts methyl ethyl ketone 5 parts by weight methyl isobutyl ketone 25 parts by weight

Hereinafter, through a process of forming a back coat layer using a back coat layer paint similar to the case shown in Example 1 or a process of forming a magnetic layer using the magnetic layer paint produced in this embodiment, the width is reduced to 1/2 inch. It was cut to complete a 1/2 inch wide magnetic tape.

Example 8 First, the following composition was kneaded with a twin-screw extrusion kneader, dispersed using a sand mill, and filtered through a filter having an average diameter of 3.5 μm to prepare a magnetic layer coating material. Ferromagnetic powder: Metal magnetic powder 50 parts by weight (specific surface area BET value = 54.0 m ² / g) Binder: Polyester polyurethane 10 parts by weight (trade name N-2304, manufactured by Nippon Polyurethane Co.) Vinyl chloride vinyl acetate copolymer 5 Parts by weight (trade name VAGH, manufactured by Union Carbide Co.) Additives: 5 parts by weight of α-Al ₂ O ₃ (trade name: AKP-30, manufactured by Sumitomo Chemical Co., Ltd.) Lubricant: 1 part by weight of butyl stearate Organic solvent: 70 parts by weight of toluene Parts 25 parts by weight methyl ethyl ketone 5 parts by weight methyl isobutyl ketone

Hereinafter, a process of forming a back coat layer using a back coat layer paint similar to the case shown in Example 1 or a process of forming a magnetic layer using the magnetic layer paint produced in this embodiment is performed to reduce the width to 1/2 inch. It was cut to complete a 1/2 inch wide magnetic tape.

Example 9 First, the following composition was kneaded with a twin-screw extrusion kneader, dispersed using a sand mill, and filtered with a filter having an average diameter of 3.5 μm to prepare a magnetic layer coating material. Ferromagnetic powder: Metal magnetic powder 50 parts by weight (specific surface area BET value = 54.0 m ² / g) Binder: Polyester polyurethane 10 parts by weight (trade name N-2304, manufactured by Nippon Polyurethane Co.) Vinyl chloride vinyl acetate copolymer 5 Parts by weight (trade name VAGH, manufactured by Union Carbide Co.) Additive: 5 parts by weight of α-Al ₂ O ₃ (brand name: AKP-30, manufactured by Sumitomo Chemical Co., Ltd.) Lubricant: 1 part by weight of butyl stearate Organic solvent: 80 parts by weight of toluene Parts methyl ethyl ketone 5 parts by weight methyl isobutyl ketone 15 parts by weight

Hereinafter, a process of forming a back coat layer using a back coat layer paint similar to the case shown in Example 1 or a process of forming a magnetic layer using the magnetic layer paint prepared in this embodiment is performed to reduce the width to 1/2 inch. It was cut to complete a 1/2 inch wide magnetic tape.

Example 10 First, the following composition was kneaded with a twin-screw extruder, dispersed using a sand mill, and filtered through a filter having an average diameter of 3.5 μm to prepare a magnetic layer coating material. Ferromagnetic powder: Metal magnetic powder 50 parts by weight (specific surface area BET value = 54.0 m ² / g) Binder: Polyester polyurethane 10 parts by weight (trade name N-2304, manufactured by Nippon Polyurethane Co.) Vinyl chloride vinyl acetate copolymer 5 Parts by weight (trade name VAGH, manufactured by Union Carbide Co.) Additive: 5 parts by weight of α-Al ₂ O ₃ (brand name: AKP-30, manufactured by Sumitomo Chemical Co., Ltd.) Lubricant: 1 part by weight of butyl stearate Organic solvent: 80 parts by weight of toluene Parts methyl ethyl ketone 15 parts by weight methyl isobutyl ketone 5 parts by weight

Hereinafter, a process of forming a back coat layer using a back coat layer paint similar to the case shown in Example 1 or a process of forming a magnetic layer using the magnetic layer paint prepared in this embodiment is performed to reduce the width to 1/2 inch. It was cut to complete a 1/2 inch wide magnetic tape.

Example 11 First, the following composition was kneaded with a twin-screw extrusion kneader, then dispersed using a sand mill, and filtered through a filter having an average diameter of 3.5 μm to prepare a magnetic layer paint. Ferromagnetic powder: Metal magnetic powder 50 parts by weight (specific surface area BET value = 54.0 m ² / g) Binder: Polyester polyurethane 10 parts by weight (trade name N-2304, manufactured by Nippon Polyurethane Co.) Vinyl chloride vinyl acetate copolymer 5 Parts by weight (VAGH, manufactured by Union Carbide Co.) Additives: 5 parts by weight of α-Al ₂ O ₃ (AKP-30, manufactured by Sumitomo Chemical Co., Ltd.) Lubricant: 1 part by weight of butyl stearate Organic solvent: 90 parts by weight of toluene Parts methyl ethyl ketone 5 parts by weight methyl isobutyl ketone 5 parts by weight

Hereinafter, through a step of forming a back coat layer using the same back coat layer paint as in the case shown in Example 1 or a step of forming a magnetic layer using the magnetic layer paint prepared in this embodiment, the width is reduced to 1/2 inch. It was cut to complete a 1/2 inch wide magnetic tape.

Example 12 First, the following composition was kneaded with a twin-screw extrusion kneader, dispersed using a sand mill, and filtered through a filter having an average diameter of 3.5 μm to prepare a magnetic layer coating material. Ferromagnetic powder: Metal magnetic powder 50 parts by weight (specific surface area BET value = 54.0 m ² / g) Binder: Polyester polyurethane 10 parts by weight (trade name N-2304, manufactured by Nippon Polyurethane Co.) Vinyl chloride vinyl acetate copolymer 5 Parts by weight (trade name VAGH, manufactured by Union Carbide Co.) Additives: 5 parts by weight of α-Al ₂ O ₃ (trade name: AKP-30, manufactured by Sumitomo Chemical Co., Ltd.) Lubricant: 1 part by weight of butyl stearate Organic solvent: 95 parts by weight of toluene Parts methyl ethyl ketone 0 parts by weight methyl isobutyl ketone 5 parts by weight

Hereinafter, through a step of forming a back coat layer using a back coat layer paint similar to the case shown in Example 1 or a step of forming a magnetic layer using the magnetic layer paint prepared in this embodiment, the width is reduced to 1/2 inch. It was cut to complete a 1/2 inch wide magnetic tape.

Comparative Example 1 In this comparative example, the compounding ratio of the organic solvent added to the coating material for the magnetic layer is normal. First, the following composition was kneaded with a twin-screw extrusion kneader, dispersed using a sand mill, and filtered through a filter having an average diameter of 3.5 μm to prepare a magnetic layer paint. Ferromagnetic powder: Metal magnetic powder 50 parts by weight (specific surface area BET value = 54.0 m ² / g) Binder: Polyester polyurethane 10 parts by weight (trade name N-2304, manufactured by Nippon Polyurethane Co.) Vinyl chloride vinyl acetate copolymer 5 Parts by weight (trade name VAGH, manufactured by Union Carbide Co.) Additives: α-Al ₂ O ₃ 5 parts by weight (trade name: AKP-30, manufactured by Sumitomo Chemical Co., Ltd.) Lubricant: 1 part by weight butyl stearate Organic solvent: 30 parts by weight toluene Parts Methyl ethyl ketone 35 parts by weight Methyl isobutyl ketone 35 parts by weight

Hereinafter, through a step of forming a back coat layer using a back coat layer paint similar to the case shown in Example 1 or a step of forming a magnetic layer using a magnetic layer paint prepared in this comparative example, the width is reduced to 1/2 inch. It was cut to complete a 1/2 inch wide magnetic tape.

Comparative Example 2 First, the following composition was kneaded with a twin-screw extruder, dispersed using a sand mill, and filtered with a filter having an average diameter of 3.5 μm to prepare a magnetic layer paint. Ferromagnetic powder: Metal magnetic powder 50 parts by weight (specific surface area BET value = 54.0 m ² / g) Binder: Polyester polyurethane 10 parts by weight (trade name N-2304, manufactured by Nippon Polyurethane Co.) Vinyl chloride vinyl acetate copolymer 5 Parts by weight (trade name VAGH, manufactured by Union Carbide Co.) Additives: α-Al ₂ O ₃ 5 parts by weight (trade name: AKP-30, manufactured by Sumitomo Chemical Co., Ltd.) Lubricant: 1 part by weight butyl stearate Organic solvent: 30 parts by weight toluene Parts methyl ethyl ketone 5 parts by weight methyl isobutyl ketone 65 parts by weight

Hereinafter, through a step of forming a back coat layer using a back coat layer paint similar to the case shown in Example 1, or a step of forming a magnetic layer using the magnetic layer paint prepared in this comparative example, the width is reduced to 1/2 inch. It was cut to complete a 1/2 inch wide magnetic tape.

Comparative Example 3 First, the following composition was kneaded with a twin-screw extruder, dispersed using a sand mill, and filtered with a filter having an average diameter of 3.5 μm to prepare a magnetic layer coating material. Ferromagnetic powder: Metal magnetic powder 50 parts by weight (specific surface area BET value = 54.0 m ² / g) Binder: Polyester polyurethane 10 parts by weight (trade name N-2304, manufactured by Nippon Polyurethane Co.) Vinyl chloride vinyl acetate copolymer 5 Parts by weight (trade name VAGH, manufactured by Union Carbide Co.) Additives: α-Al ₂ O ₃ 5 parts by weight (trade name: AKP-30, manufactured by Sumitomo Chemical Co., Ltd.) Lubricant: 1 part by weight butyl stearate Organic solvent: 30 parts by weight toluene Parts Methyl ethyl ketone 65 parts by weight Methyl isobutyl ketone 5 parts by weight

Hereinafter, through a step of forming a back coat layer using a back coat layer paint similar to the case shown in Example 1, or a step of forming a magnetic layer using the magnetic layer paint prepared in this comparative example, the width is reduced to 1/2 inch. It was cut to complete a 1/2 inch wide magnetic tape.

Comparative Example 4 First, the following composition was kneaded with a twin-screw extruder, dispersed using a sand mill, and filtered with a filter having an average diameter of 3.5 μm to prepare a magnetic layer coating material. Ferromagnetic powder: Metal magnetic powder 50 parts by weight (specific surface area BET value = 54.0 m ² / g) Binder: Polyester polyurethane 10 parts by weight (trade name N-2304, manufactured by Nippon Polyurethane Co.) Vinyl chloride vinyl acetate copolymer 5 Parts by weight (trade name VAGH, manufactured by Union Carbide Co.) Additives: 5 parts by weight of α-Al ₂ O ₃ (trade name: AKP-30, manufactured by Sumitomo Chemical Co., Ltd.) Lubricant: 1 part by weight of butyl stearate Organic solvent: 45 parts by weight of toluene Parts methyl ethyl ketone 5 parts by weight methyl isobutyl ketone 50 parts by weight

Thereafter, through a step of forming a back coat layer using a back coat layer paint similar to the case shown in Example 1 or a step of forming a magnetic layer using the magnetic layer paint prepared in this comparative example, the width was reduced to 1/2 inch. It was cut to complete a 1/2 inch wide magnetic tape.

Comparative Example 5 First, the following composition was kneaded with a twin-screw extrusion kneader, dispersed using a sand mill, and filtered through a filter having an average diameter of 3.5 μm to prepare a magnetic layer coating material. Ferromagnetic powder: Metal magnetic powder 50 parts by weight (specific surface area BET value = 54.0 m ² / g) Binder: Polyester polyurethane 10 parts by weight (trade name N-2304, manufactured by Nippon Polyurethane Co.) Vinyl chloride vinyl acetate copolymer 5 Parts by weight (trade name VAGH, manufactured by Union Carbide Co.) Additives: 5 parts by weight of α-Al ₂ O ₃ (trade name: AKP-30, manufactured by Sumitomo Chemical Co., Ltd.) Lubricant: 1 part by weight of butyl stearate Organic solvent: 45 parts by weight of toluene Parts Methyl ethyl ketone 20 parts by weight Methyl isobutyl ketone 35 parts by weight

Hereinafter, through a step of forming a back coat layer using a back coat layer paint similar to the case shown in Example 1, or a step of forming a magnetic layer using the magnetic layer paint prepared in this comparative example, the width is reduced to 1/2 inch. It was cut to complete a 1/2 inch wide magnetic tape.

Comparative Example 6 First, the following composition was kneaded with a twin-screw extrusion kneader, dispersed using a sand mill, and filtered through a filter having an average diameter of 3.5 μm to prepare a magnetic layer coating material. Ferromagnetic powder: Metal magnetic powder 50 parts by weight (specific surface area BET value = 54.0 m ² / g) Binder: Polyester polyurethane 10 parts by weight (trade name N-2304, manufactured by Nippon Polyurethane Co.) Vinyl chloride vinyl acetate copolymer 5 Parts by weight (trade name VAGH, manufactured by Union Carbide Co.) Additives: 5 parts by weight of α-Al ₂ O ₃ (trade name: AKP-30, manufactured by Sumitomo Chemical Co., Ltd.) Lubricant: 1 part by weight of butyl stearate Organic solvent: 45 parts by weight of toluene Parts Methyl ethyl ketone 35 parts by weight Methyl isobutyl ketone 20 parts by weight

Hereinafter, a process of forming a back coat layer using a back coat layer paint similar to the case shown in Example 1 or a process of forming a magnetic layer using the magnetic layer paint prepared in this comparative example is performed to reduce the width to 1/2 inch. It was cut to complete a 1/2 inch wide magnetic tape.

Comparative Example 7 First, the following composition was kneaded with a twin-screw extruder, dispersed using a sand mill, and filtered through a filter having an average diameter of 3.5 μm to prepare a magnetic layer coating material. Ferromagnetic powder: Metal magnetic powder 50 parts by weight (specific surface area BET value = 54.0 m ² / g) Binder: Polyester polyurethane 10 parts by weight (trade name N-2304, manufactured by Nippon Polyurethane Co.) Vinyl chloride vinyl acetate copolymer 5 Parts by weight (trade name VAGH, manufactured by Union Carbide Co.) Additives: 5 parts by weight of α-Al ₂ O ₃ (trade name: AKP-30, manufactured by Sumitomo Chemical Co., Ltd.) Lubricant: 1 part by weight of butyl stearate Organic solvent: 45 parts by weight of toluene Parts 50 parts by weight methyl ethyl ketone 5 parts by weight methyl isobutyl ketone

Hereinafter, a process of forming a back coat layer using a back coat layer paint similar to the case shown in Example 1 or a process of forming a magnetic layer using the magnetic layer paint prepared in this comparative example is performed to reduce the width to 1/2 inch. It was cut to complete a 1/2 inch wide magnetic tape.

Comparative Example 8 First, the following composition was kneaded with a twin-screw extruder, dispersed using a sand mill, and filtered through a filter having an average diameter of 3.5 μm to prepare a magnetic layer coating material. Ferromagnetic powder: Metal magnetic powder 50 parts by weight (specific surface area BET value = 54.0 m ² / g) Binder: Polyester polyurethane 10 parts by weight (trade name N-2304, manufactured by Nippon Polyurethane Co.) Vinyl chloride vinyl acetate copolymer 5 Parts by weight (trade name VAGH, manufactured by Union Carbide Co.) Additive: 5 parts by weight of α-Al ₂ O ₃ (brand name: AKP-30, manufactured by Sumitomo Chemical Co., Ltd.) Lubricant: 1 part by weight of butyl stearate Organic solvent: 100 parts by weight of toluene Parts methyl ethyl ketone 0 parts by weight methyl isobutyl ketone 0 parts by weight

However, when the organic solvent was only 100 parts by weight of toluene as in this comparative example, dispersion was not possible, and a magnetic layer coating material could not be obtained. Therefore, 1
A 1/2 inch wide magnetic tape could not be completed.

The 1/2 inch width magnetic tapes produced in Examples 1 to 12 and Comparative Examples 1 to 7 except Comparative Example 8 were evaluated by the following items. The surface roughness was measured using a surface roughness meter (trade name SE-30H) manufactured by Kosaka Laboratory Co., Ltd. The measurement conditions are a magnification of 50,000 times, a measurement length of 2 mm, and a cutoff value of 0.08 mm. If the surface roughness Ra value exceeds 6.0 nm, the electromagnetic conversion characteristics deteriorate. Therefore, the surface roughness Ra value of 6.0 nm or less was regarded as a good product. Electromagnetic conversion characteristics 1/2 inch VTR manufactured by Matsushita Electric (product name: NV-820)
0) was used to record a 4 MHz luminance signal, and the 1/2 inch width magnetic tape produced in Comparative Example 1 was used as a reference (reference value 0d).
The difference in S / N ratio was measured as B). If this value is 0.
Samples with an improvement of 5 dB or more were regarded as good products. With respect to these results, Tables 1 and 2 show Examples 1 to 12, and Table 2 shows Comparative Examples 1 to 7 and Comparative Example 8 which could not be completed as a 1/2 inch width magnetic tape. FIG. 2 is a graph showing the results of the blending ratio (parts by weight) of toluene and the surface roughness Ra, and FIG. 3 is the result of the blending ratio (parts by weight) of toluene and the electromagnetic conversion characteristics. Is shown in the graph.

[0054]

[Table 1]

[0055]

[Table 2]

As is clear from Tables 1 and 2 and FIGS. 2 and 3, all of Examples 1 to 12 to which the present invention is applied have a surface roughness Ra value of 6.0 nm or less and an electromagnetic conversion characteristic. All were 0.5 dB or more, and all were good. In contrast, Comparative Examples 1 to 7 all had a surface roughness Ra value of 6.0.
nm, and all of the electromagnetic conversion characteristics were less than 0.5 dB. In particular, in the case of 100 parts by weight of toluene as an organic solvent as in Comparative Example 8, the solvent did not dissolve, and a magnetic layer coating material could not be obtained.

[0057]

According to the method for producing a magnetic recording medium of the present invention, a magnetic layer coating material having good dispersion stability can be obtained. And a magnetic recording medium having magnetic characteristics. Therefore, it is possible to provide a magnetic recording medium having good electromagnetic conversion characteristics corresponding to short wavelength recording.

[Brief description of the drawings]

FIG. 1 is a schematic model sectional view showing a state of ferromagnetic powder particles in a magnetic layer coating material of the present invention.

FIG. 2 is a graph showing the results of the blending ratio of toluene and the surface roughness Ra.

FIG. 3 is a graph showing the results of a blending ratio of toluene and electromagnetic conversion characteristics.

[Explanation of symbols]

 1: Ferromagnetic powder particles, 2: Binder, 3: Adsorption layer

Claims (4)

[Claims] 1. A magnetic layer comprising: a step of preparing a magnetic layer coating by dispersing at least a ferromagnetic powder and a binder in a solvent; and a step of applying the magnetic layer coating to a non-magnetic support to form a magnetic layer. A method for manufacturing a magnetic recording medium, wherein the main component of the solvent is a poor solvent for the binder. 2. The method according to claim 1, wherein the amount of the poor solvent is 50 parts by weight or more and 95 parts by weight or less based on 100 parts by weight of the solvent. 3. The method according to claim 1, wherein the poor solvent is toluene. 4. The method according to claim 1, wherein the ferromagnetic powder is a metal magnetic powder.