JPH0971739A - Magnetic coating material for magnetic recording medium applied with extrusion coating apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a magnetic coating material which forms a magnetic coating film with improved surface properties by kneading and dispersing the necessary ingredients in an org. solvent comprising methyl isobutyl ketone, toluene, and a specified amt. of methyl ethyl ketone. SOLUTION: A magnetic coating material M prepd. by kneading and dispersing a magnetic powder, a binder, additives, and a lubricant in an org. solvent comprising methyl isobutyl ketone, toluene, and 35wt.% or lower (based on the solvent) methyl ethyl ketone is supplied from a magnetic coating material supply source 4 through a magnetic coating material supply channel 3, extruded from a lip section 2, and continuously applied to the surface of a base film F, thus forming a magnetic coating film having an improved surface roughness. The coating film is subjected to surface treatments, e.g. drying, to give a magnetic recording medium having the magnetic film improved in surface properties.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic coating material for a magnetic recording medium (hereinafter, referred to as a magnetic coating material) containing a metal magnetic powder when a magnetic recording medium is manufactured using an extrusion coating device.
(Abbreviated as "magnetic paint").

[0002]

2. Description of the Related Art In recent years, magnetic recording and reproducing devices have been downsized,
In addition, high density recording has been promoted, and there is a strong demand for thinning of the magnetic layer of the magnetic recording medium and smoothing of the surface of the magnetic coating film. As a magnetic recording medium capable of high density recording, a metal type magnetic recording medium in which a magnetic coating material mixed with metal magnetic powder is applied to a base film has been developed. In this magnetic paint, metal magnetic powder is uniformly dispersed using an organic solvent composed of methyl ethyl ketone, methyl isobutyl ketone, toluene, etc. Usually, in this organic solvent, methyl ethyl ketone is mixed at a ratio of 40 wt% or more. There is.

[0003]

However, since the above-mentioned magnetic coating material has a high cohesive property, when it is applied using an extrusion coating device, the surface of the magnetic coating film formed by the magnetic coating material is a good surface. There is a problem that the properties are not obtained, the electromagnetic conversion characteristics are deteriorated as a result, and desired good magnetic recording and reproduction cannot be performed.

In order to improve the electromagnetic conversion characteristics of the magnetic recording medium, various experiments and studies have been carried out by changing the material and composition of metal magnetic powder, binder, carbon and the like used in magnetic paint. . However, in the present circumstances, such a method has not yet improved the above-mentioned problems, and an effective solution to the problem of the defect of the surface of the magnetic coating film during coating is desired. Therefore, in the present invention, even if the magnetic coating is applied onto the base film by using the extrusion coating device, a magnetic coating capable of obtaining a magnetic recording medium whose magnetic coating film surface of the formed magnetic layer has good surface properties is obtained. The purpose is to obtain.

[0005]

Therefore, the magnetic paint of the present invention contains the above-mentioned methyl ethyl ketone in an amount of 35 wt% or less among the organic solvents composed of methyl ethyl ketone, methyl isobutyl ketone, toluene and the like to be added to the magnetic paint. The above problems were solved by kneading and dispersing metal magnetic powder and the like with an organic solvent.

Accordingly, the cohesiveness of the magnetic coating material of the present invention becomes low, and the magnetic coating of the magnetic layer formed by applying this magnetic coating material without changing the material or composition of metal magnetic powder, binder, carbon and the like. The surface roughness of the film surface could be improved.

[0007]

EXAMPLES Examples of the magnetic coating material of the present invention will be described below. First, referring to FIG. 1, a method for applying a magnetic coating material using an extrusion coating device will be briefly described.
Reference numeral 1 indicates an extrusion die in the extrusion coating device. This extrusion die 1
Is a magnetic paint reservoir 3A in a part connected to the lip portion 2 facing the base film F and the pipe 5 of the magnetic paint supply source 4.
And a magnetic coating material supply path 3 in which is formed. When such an extrusion die 1 is used,
The magnetic paint M supplied from the magnetic paint supply source 4 through the magnetic paint supply passage 3 is discharged from the lip portion 2 and continuously applied to the surface of the base film F, and the magnetic paint film formed by the application is dried. A magnetic recording medium can be obtained by surface treatment such as.

In the present invention, a condition test for the mixing ratio of methyl ethyl ketone among the organic solvents consisting of methyl ethyl ketone, methyl isobutyl ketone and toluene to be mixed in the magnetic paint using the metal magnetic powder was carried out by the following procedure.

Composition of Magnetic Paint Magnetic powder: Metal magnetic powder 100 parts by weight (specific surface area BET value = 54.0 m ² / g) Binder: Polyester polyurethane 20 parts by weight (Nippon Polyurethane Co., trade name N-2304) Bi-based polymer 10 parts by weight (Uniown Carbide Co., trade name VAGH) Additive: α-Al ₂ O ₃ 10 parts by weight (Sumitomo Chemical Co., trade name AKP-30) Lubricant: Butyl stearate 2 parts by weight Organic solvent: methyl ethyl ketone, methyl isobutyl ketone, toluene 210 parts by weight

Magnetic coating material After kneading the raw materials having the above composition with a biaxial extrusion type kneader,
The particles were dispersed using a sand mill and filtered with a filter having an average diameter of 4.0 μm to prepare a magnetic paint. In addition,
The blending ratio of methyl ethyl ketone, methyl isobutyl ketone, and toluene of the organic solvent to be blended was changed as in Examples 1 to 5 described in [Table 1].

Composition of coating for back coat Nonmagnetic powder: 210 parts by weight of carbon black (Colombyan Carbon Co., Ltd., product name RAVEN-1255) Binder: Polyester polyurethane 20 parts by weight (Toyobo Co., Ltd. product name UR-8300) Phenoxy resin 30 parts by weight (Toto Kasei Co., Ltd., trade name YP-50) Organic solvent: Methyl ethyl ketone 220 parts by weight Methyl isobutyl ketone 220 parts by weight Cyclohexanone 220 parts by weight

Coating material for back coat Disperse the raw materials of the above composition using a sand mill to obtain 3.0
A back coat paint was prepared by filtering with a filter having an average diameter of μm.

After adding 1 part by weight of a lubricant (myristic acid) and 10 parts by weight of a curing agent (Coronate L) to the magnetic coating material prepared as described above, the thickness is adjusted by using an extrusion die 1. A 9 μm polyethylene terephthalate base film F is applied so as to have a thickness of 3.5 μm, and a back coat coating composition obtained by adding 10 parts by weight of a curing agent (Coronate L) to the back surface of the base film F is 0.8 μm. It was applied so as to have a thickness of. The base film F coated on both sides was calendered and cured, and then cut into a width of 0.5 inch.

With respect to the surface properties of each sample magnetic tape thus prepared, the surface roughness under each condition (Examples 1 to 6) described in [Table 1] was measured, and the results are shown in [Table 1]. I wrote it. The surface roughness is a three-dimensional surface roughness SRa measured using a three-dimensional roughness meter. This 3
If the dimensional surface roughness SRa is 0.05 μm or less, it is determined that the surface properties of the sample magnetic tape are good, and desired electromagnetic conversion characteristics can be secured.

[0015]

[Table 1]

Also for the magnetic tapes of Comparative Examples 1 to 6 shown in [Table 2] for comparison, the three-dimensional surface roughness SRa of the magnetic coating film surface was measured in the same manner as the sample magnetic tape. The results are also shown in [Table 2].

[0017]

[Table 2]

From Table 1 and Table 2, Examples 1 to 6 are shown.
As described above, by setting the content of methyl ethyl ketone in the magnetic paint using metal magnetic powder to 35 wt% or less,
The effect of improving the surface quality was obtained when the coating was performed using the extrusion coating device. The compounding condition of the organic solvent that gives the most preferable surface property is when the compounding ratio of methyl ethyl ketone is 15 wt% or less.
The dimensional surface roughness SRa is 0.025 μm, and it is desirable to set this value or less.

[0019]

As described above, according to the magnetic paint of the present invention, the mixing ratio of methyl ethyl ketone among the organic solvents of methyl ethyl ketone, methyl isobutyl ketone, and toluene to be added to the magnetic paint using metal magnetic powder is 35
By adjusting the content to be not more than wt%, the cohesiveness of the magnetic coating material was lowered, and the surface texture (surface roughness) of the surface of the magnetic coating film when applied using an extrusion coating device could be improved. Therefore, the electromagnetic conversion characteristics of this magnetic recording medium could also be improved.

[Brief description of drawings]

FIG. 1 is a conceptual diagram for explaining a method of applying a magnetic coating material onto a surface of a base film by using an extrusion coating device.

[Explanation of symbols]

 1 Extrusion Die 2 Lip Part 3 Magnetic Paint Supply Path 3A Magnetic Paint Reservoir 4 Magnetic Paint Supply Source 5 Piping

Claims (1)

[Claims] 1. A metal magnetic powder or the like is kneaded with an organic solvent containing methylethylketone, methylisobutylketone, toluene or the like, which is added to a magnetic coating material in a proportion of 35 wt% or less, of the organic solvent.
A magnetic coating material for a magnetic recording medium, which is applied by using an extrusion coating device characterized by being dispersed.