JP2000173053A - Manufacture of magnetic recording medium and magnetic redording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the electromagnetic conversion characteristics of a magnetic recording medium such as a video tape or an audio tape while improving both dispensability till media dispersion and dispersibility during media dispersion, in a method of manufacturing a magnetic coating for producing a magnetic recording medium. SOLUTION: The method of manufacturing a magnetic recording medium 1 in this invention comprises a first step of kneading a magnetic coating material including magnetic particles and a binder and dispersing the magnetic material in advance after kneading, a second step of highly dispersing the magnetic coating by media dispersion after the first step. A filtering is performed in the pre-dispersion of the first step or during the first or second steps. Preferably, the filter diameter in the filtering is more than 1% and less than 20% of the media diameter used for the media dispersion.

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 a magnetic recording medium for use in video equipment, audio equipment, and computers, and more particularly, to a magnetic paint used for manufacturing a magnetic recording medium. The present invention relates to a method for manufacturing a magnetic recording medium and a magnetic recording medium characterized by the method for manufacturing a magnetic recording medium.

[0002]

2. Description of the Related Art A magnetic coating material used for producing a magnetic recording medium is produced by mixing and dispersing magnetic particles, a binder, and various additives to be added as necessary with a dispersion medium such as an organic solvent. By applying this magnetic paint to a non-magnetic support such as a polyester film,
A magnetic recording medium such as a magnetic tape or a magnetic disk is manufactured. In recent years, as recording wavelengths have become shorter and higher densities seen in VTRs and the like, in order to improve the characteristics of magnetic recording media such as video tapes and audio tapes, fine particles of magnetic particles and various dispersants and additives have been added. Is being considered. On the other hand, in order to convert magnetic particles into a paint and obtain a magnetic recording medium having excellent electromagnetic conversion characteristics, a technique of dispersing and mixing the magnetic particles is important.

[0003] Generally, the above magnetic paint is kneaded with a kneader,
After the first step of kneading with a high-viscosity kneading device such as a twin-screw kneader such as an extruder, a manufacturing method having a second step of dispersing using a media disperser such as a sand mill or an attritor, and a kneading device are used. Without disperser, high-speed disperser, etc., having a first step of pre-dispersing and pre-dispersing with relatively low viscosity, and then a second step of dispersing using the above-mentioned media disperser. Manufacturing methods are used. In the dispersion using the above kneading machine, generally, after kneading, together with an organic solvent for dissolving a high-viscosity paste, pre-dispersion treatment with a high-speed disperser or the like, and then using a media disperser such as a sand mill. Mixed and dispersed.

In a media disperser, the size of agglomerates in various kinds of premixed pigments greatly affects dispersion efficiency. It is known that the stress from the dispersing medium applied to the agglomerate in the media disperser is almost proportional to the ratio of the cross-sectional area of the dispersing medium to the cross-sectional area of the agglomerate. Cannot be obtained, or it takes a considerable time to obtain the desired dispersion. Therefore,
The selection of the size of the dispersion media used in the media disperser and the control of the pigment agglomerates in the premixed paint provided to the disperser to the smallest possible obtain a highly dispersed magnetic paint, This is an important point for obtaining a magnetic recording medium having good electromagnetic conversion characteristics.

For example, as disclosed in Japanese Patent Application Laid-Open No. 5-36067, a method is disclosed in which a solvent is introduced stepwise into a kneader and the paste is diluted and dissolved in the kneader to realize high dispersibility. are doing. Also in this method, a premix process such as a high-speed disperser is performed before a media disperser such as a sand mill. By these manufacturing methods, magnetic particles and various additives are dispersed before media dispersion.
Although the dispersion progresses considerably, it is difficult to remove undispersed agglomerates in the premix and pastes insoluble in the organic solvent, which hinder the dispersion in the media disperser.

Further, in the above-mentioned media dispersing machine, for example, as disclosed in Japanese Patent Application Laid-Open No. 1-290121, zirconia beads having a smooth surface roughness are used as a dispersing medium to improve dispersibility. Similarly, a method of improving the dispersibility by using engineering plastic beads having a low specific gravity as a dispersion medium has been proposed, as in JP-A-3-6267. In these cases, the dispersibility of the media disperser can be improved,
Similarly to the above, agglomerates of the magnetic paint before media dispersion disturb the dispersion. As described above, in the manufacturing method of the magnetic paint, there are many studies on the improvement of the dispersibility up to the dispersion of the media and the studies on the improvement of the dispersibility in the dispersion of the media, but efficient studies utilizing both of them are being conducted. I wasn't.

[0007]

SUMMARY OF THE INVENTION Accordingly, the present invention has been made in view of the above-mentioned problems, and is directed to a method of manufacturing a magnetic coating material for manufacturing a magnetic recording medium, the method comprising the steps of: An object of the present invention is to provide a method of manufacturing a magnetic recording medium and a magnetic recording medium that improve the electromagnetic conversion characteristics of a magnetic recording medium such as a video tape and an audio tape while improving both.

[0008]

According to a first aspect of the present invention, there is provided a method for manufacturing a magnetic recording medium, comprising: a first step of kneading a magnetic paint containing magnetic particles and a binder, and pre-dispersing the magnetic paint after the kneading; A method for producing a magnetic recording medium, comprising a second step of performing a high dispersion of a magnetic paint by media dispersion after the step, wherein a filtration treatment is performed in the pre-dispersion of the first step, or Or a filtration process between the two. The filtration diameter in the filtration treatment is desirably not less than 1% and not more than 20% of the diameter of the medium used for dispersion of the medium.

According to a third aspect of the present invention, there is provided a magnetic recording medium manufacturing method comprising:
A method for producing a magnetic recording medium, comprising: a step of, after the first step, performing a high dispersion of the magnetic paint by media dispersion, wherein a filtration treatment is performed in the first step;
The present invention is characterized in that either one of the first step and the second step is subjected to a filtration treatment. The filtration diameter in the filtration treatment is 1% or more of the media diameter used for media dispersion.
Desirably, it is 0% or less.

A magnetic recording medium according to a fifth aspect is manufactured by the method for manufacturing a magnetic recording medium according to the first aspect.

A magnetic recording medium according to a sixth aspect is manufactured by the method for manufacturing a magnetic recording medium according to the third aspect.

According to the method for manufacturing a magnetic recording medium and the magnetic recording medium of the present invention, the magnetic paint before being subjected to media dispersion is subjected to a filtration treatment so that the aggregates of pigments in the paint are controlled to a minimum. In addition, the effect of media dispersion can be maximized, and a magnetic coating medium with high dispersibility can be easily obtained. By using this magnetic coating, a magnetic recording medium with excellent electromagnetic conversion characteristics can be obtained. .

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of a method for manufacturing a magnetic recording medium and an embodiment of a magnetic recording medium according to the present invention will be described with reference to FIG. FIG. 1 is a schematic sectional view of a magnetic recording medium according to the present invention.

As shown in FIG. 1, a magnetic recording medium 1 generally has a magnetic layer 3 formed on a non-magnetic support 2, a top coat layer 4 formed on the magnetic layer 3, The back coat layer 5 is formed on the main surface opposite to the surface on which the magnetic layer 3 is formed.

The present invention relates to a method for producing a magnetic paint, which is a mixture of magnetic particles, a binder and various additives, for forming the magnetic layer 3 on the magnetic recording medium 1 described above. The method for manufacturing the above will be described in detail below. First, in the first step, kneading of the magnetic paint and pre-dispersion after kneading or only pre-dispersion are performed. In the kneading step, a kneader, a twin-screw kneader such as a continuous kneader or an extruder or a roll mill is used, and the magnetic particles of the magnetic paint and various additives are kneaded with a binder and an organic solvent. The kneaded paste is usually diluted and dissolved with a binder and an organic solvent in a premix tank or the like and subjected to pre-dispersion. When there is no kneading step, the magnetic particles and various additives are pre-dispersed in a premix tank having a dissolver, a high-speed dissolver, etc. together with a binder and an organic solvent.

Next, the magnetic paint predispersed in the first step is subjected to a filtration treatment by a filter treatment. As the filter, a commonly used surface filtration type filter and a depth type filter can be used. As the surface filtration type, a metal mesh type or the like can be used. As a depth type, S
A series or a pleated type by Paul Corporation can be used. What is important in the filter used is the filtration accuracy and the life of the filter depending on the filtration diameter. If the filtration diameter is too small, the dispersion efficiency in the media disperser can be expected to be improved, but the filtration life is short and undesirable in terms of productivity may occur. Also, if the filtration diameter is too large,
There is no filtration effect and the original purpose cannot be achieved. Such a filtration treatment may be performed during the pre-dispersion treatment in the premix tank in the first step or during the transfer from the premix tank to the media disperser in the second step described below.

Next, in the second step, media dispersion for the purpose of high dispersion is performed. As a media dispersion machine used for media dispersion, a sand mill, a dyno mill,
A known disperser such as a pin mill can be used. Well-known dispersing media can be used, for example, glass beads, alkali-less beads, zirconia beads, titania, beads coated with alumina, etc., steel balls, etc. It is desirable to use media that has been used.
As the size of the dispersion medium, a generally used medium having a size of about 0.5 to 2.0 mm can be used.

The magnetic material to be provided to the magnetic particles contained in the magnetic paint is a ferromagnetic material γ-FeOx (x =
1.33 to 1.5), Co-modified γ-FeOx (x = 1.
33-1.5), known ferromagnetic materials such as a ferromagnetic alloy containing Fe, Ni or Co as a main component (70% or more), barium ferrite, and strontium ferrite. In addition to these atoms, these ferromagnetic materials include Al, Si, S, Sc, Ti, V, Cr, C
u, Y, Mo, Rh, Pd, Ag, Sn, Sb, Te,
Ba, Ni, Ta, W, Re, Au, Hg, Pb, B
It may contain atoms such as i, La, Ce, P, Mn, Zn, Co, Sr, and B.

In addition, in the magnetic recording medium 1 according to the present invention, a binder other than a magnetic material, a dispersant used as necessary, As the agent, antistatic agent, rust preventive, or solvent used for preparing the magnetic paint, any of conventionally known ones can be applied, and there is no particular limitation.

As a material of the nonmagnetic support 2, for example,
What is generally used for magnetic recording media can be used, for example, polyethylene terephthalate, polyesters such as polyethylene naphthalate, polyethylene,
Polyolefins such as polypropylene, cellulose derivatives such as cellulose triacetate, cellulose diacetate, cellulose acetate butyrate, vinyl resins such as polyvinyl chloride and polyvinylidene chloride, polycarbonate, polyimide, polyamide imide, other plastics, aluminum and copper Metals, aluminum alloys, light alloys such as titanium alloys, ceramics, single crystal silicon, and the like.

As the binder, any known materials can be used, for example, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl acetate-vinyl alcohol copolymer, vinyl chloride-vinylidene chloride copolymer. Copolymer, vinyl chloride-acrylonitrile copolymer, vinyl chloride-vinyl acetate-maleic acid copolymer, acrylate-vinylidene chloride copolymer, acrylate-acrylonitrile copolymer, methacrylic acid-vinylidene chloride copolymer, Methacrylic acid ester-styrene copolymer, thermoplastic polyurethane resin, phenoxy resin, polyvinyl fluoride, vinylidene chloride-acrylonitrile copolymer, butadiene-acrylonitrile copolymer, acrylonitrile-butadiene-methacrylic acid copolymer, polyvinyl butyral, cellulose Conductor, styrene - butadiene copolymer, polyester resin, phenol resin, epoxy resin, thermosetting polyurethane resins, urea resins, melamine resins, alkyd resins, urea - formaldehyde resins, polyvinyl acetal resin or a mixture thereof, and the like.

Of these, polyurethane resins, polyester resins, acrylonitrile-butadiene copolymers and the like, which impart flexibility, and cellulose derivatives, phenol resins, epoxy resins, etc., which impart rigidity, are preferred. The binder may be one having improved durability by crosslinking an isocyanate compound as a curing agent, or one having an appropriate polar group introduced.

Examples of the curing agent include aromatic polyisocyanates and aliphatic polyisocyanates.
Further, active hydrogenated products thereof are desirable. Examples of the aromatic polyisocyanate include toluene diisocyanate (TDI), 1,3-xylene diisocyanate,
Examples thereof include 4-xylene diisocyanate, 4-4'-diphenylmethane isocyanate, p-phenyl diisocyanate, m-phenyl diisocyanate, 1,5-naphthyl diisocyanate, and the like. Examples of the aliphatic polyisocyanate include hexamethylene isocyanate (HDI), dicyclohexylmethane diisocyanate, and cyclohexane diisocyanate. Examples of active hydrogen compounds that form adducts with these include ethylene glycol, 1,4-butanediol, 1,3-butanediol, neopentethyl glycol, diethylene glycol, trimethylolpropane, and glycerin. 100 ~
Those in the range of 5,000 are preferred.

As the lubricant, silicone oil, fatty acid-modified silicone, fluorine-containing silicone or other fluorine-based lubricant, polyolefin, polyglycol, alkyl phosphate and metal salt, polyphenyl ether, fluorinated alkyl ether, carbon number 12 to 24 alcohols (each of which may be unsaturated or branched), 12 to 24 carbon atoms of higher fatty acids and fatty acid esters (each of which may be unsaturated or branched) ), Amine-based lubricants such as alkylcarboxylic acid amine salts and fluorinated alkylcarboxylic acid amine salts, and the like. Specific examples of higher fatty acids and fatty acid esters include lauric acid, myristic acid, palmitic acid, stearic acid, isostearic acid, arachiic acid, oleic acid, eicoic acid, elaidic acid, hebenic acid, linoleic acid, linoleic acid, and stearic acid. Examples include octyl, isooctyl stearate, octyl myristate, isooctyl myristate, butoxyethyl stearate, butyl stearate, and heptyl stearate. Further, the lubricant may be mixed with a plurality of lubricants.

As the abrasive, for example, α-alumina,
β-alumina, fused alumina, silicon carbide, chromium oxide, cerium oxide, α-iron oxide, corundum, diamond, silica, garnet, garnet, silicon nitride, boron nitride, molybdenum carbide, boron carbide, tungsten carbide, titanium oxide Known materials having a Mohs' hardness of 6 or more are used alone or in combination with the above as a main component.
The average particle size of these abrasives is preferably from 0.01 to 2 μm. However, if necessary, abrasives having different particle sizes may be combined, or a single abrasive may be used with an expanded particle size distribution.

As the carbon black used for the magnetic layer 3 or the non-magnetic layer such as the top coat layer 4 and the back coat layer 5, any known carbon black can be used. For example, acetylene black, furnace black, black for color and the like can be used. Can be used for Further, in order to improve the handling during the manufacturing process, a granular material may be used. The average particle size of the carbon black is 10 to 1,000.
It is preferable to use one in the range of nm.

Examples of the dispersant include metal soaps composed of fatty acids having 5 to 25 carbon atoms and alkali metals or alkaline earth metals thereof, fatty acid esters, fatty acid amides, fatty acid amines, quaternary ammonium salts, phosphate esters and boric acid. Known dispersants such as esters can be used.

Similarly, as the antistatic agent, the above-mentioned car
In addition to Bon Black, known antistatic agents such as natural surfactants, anionic surfactants and cationic surfactants can be used.

Examples of the solvent for preparing the above magnetic paint include ketone solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone and cyclohexanone, and ester solvents such as methyl acetate, butyl acetate, ethyl lactate and ethyl acetate monoethyl ether. , Glycol ether solvents such as glycol monoethyl ether and dioxane, aromatic hydrocarbon solvents such as benzene, toluene and xylene, meterene chloride, ethylene chloride, carbon tetrachloride, chloroform, ethylene chlorohydrin, dichlorobenzene, etc. And a chlorine-containing solvent. In addition, other conventionally known organic solvents can be used.

In the application of the above magnetic paint, an undercoat layer such as an adhesive layer,
Pretreatment such as corona discharge treatment or electron beam irradiation treatment may be performed on the nonmagnetic support 2. The method of applying the magnetic paint on the non-magnetic support 2 includes air doctor coating, blade coating, rod coating, extrusion coating,
Examples of the method include an air knife coat, a squeeze coat, an impregnation coat, a reverse roll coat, a gravure coat, a transfer roll coat, and a cast coat. Other methods can also be used. Further, simultaneous multilayer coating by extrusion coating may be used.

[0031]

EXAMPLES Examples of the magnetic recording medium 1 to which the magnetic paint used for producing the magnetic recording medium 1 according to the present invention is applied are shown together with comparative examples. In Examples and Comparative Examples,
“Parts” represents “parts by weight”. First, the composition of the magnetic paint for forming the magnetic layer 3 of the magnetic recording medium 1 is shown below. [Magnetic paint composition] Co-containing Fe ₃ O ₄ 100 parts (Average particle size 0.2 μm, BET specific surface area 30 m ² / g) Nitrocellulose 8 parts (Asahi Kasei Corporation product name NC-110) Fluorine chloride-vinyl acetate-vinyl alcohol copolymer 6 parts (Nippon Seon Co., Ltd. Product name MR-110) Polyurethane resin 8 parts (Mw = 50,000, polar group SO ₃ Na = 0.1mmol / g) Carbon black (BP-L manufactured by Cahort) 6 parts Alumina (Product name AKP-30 manufactured by Sumitomo Chemical Co., Ltd.) ) 3 parts butyl stearate 1 part methyl ethyl ketone 80 parts methyl isobutyl ketone 80 parts toluene 80 parts

Hereinafter, the methods for manufacturing the magnetic recording media 1 of the embodiment and the comparative example will be described in detail. In Examples 1 to 3, in the first step, the composition of the magnetic paint was pre-dispersed with a high-speed disper, and then each had a filtration diameter of 10 μm.
Filtration treatment was performed with filters of m, 50 μm, and 200 μm, and in the above-mentioned second step, the mixture was dispersed in a sand mill using glass beads having a media diameter of 1.0 mm to prepare a magnetic paint. In Examples 4 to 6, in the first step, after kneading the composition mixture with a kneader, the paste was diluted and dissolved with a high-speed disper, and the filtration diameter was 10 μm each.
The resultant was filtered through a filter of m, 50 μm, or 200 μm, and dispersed in a sand mill using glass beads having a media diameter of 1.0 mm in the second step to prepare a magnetic paint.

In Comparative Example 1, after the composition of the magnetic coating composition was pre-dispersed with a high-speed disper in the first step, no filtration treatment was performed. It was dispersed by a sand mill using 0.0 mm glass beads to prepare a magnetic paint. In Comparative Examples 2 and 3, in the first step, the composition of the magnetic coating composition was pre-dispersed with a high-speed disper, and then each had a filtration diameter of 5 μm.
Filtration was performed with a 500 μm filter, and in the above-mentioned second step, the mixture was dispersed with a sand mill using glass beads having a media diameter of 1.0 mm to prepare a magnetic paint. In Comparative Example 4, in the first step, the composition was kneaded with a kneader, and then the paste was diluted and dissolved with a high-speed disper, and was not filtered. It was dispersed by a sand mill using 0 mm glass beads to prepare a magnetic paint. In Comparative Examples 5 to 6, in the first step, after kneading the composition mixture in a kneader, the paste was diluted and dissolved with a high-speed disper, and subjected to filtration with a filter having a filtration diameter of 5 μm and a filter of 500 μm, respectively. In the above-mentioned second step, the media diameters 1.
It was dispersed in a sand mill using 0 mm glass beads to prepare a magnetic paint.

To the magnetic paint prepared as described above, 4 parts of polyisocyanate and 1 part of myristic acid were added, and 3 μm
To obtain a magnetic paint. Next, the dispersed magnetic coating liquid was applied to the nonmagnetic support 2 of a polyethylene terephthalate film having a thickness of 14 μm by extrusion coating to a thickness of 3.0 μm, followed by drying and calendering. After the obtained wide magnetic film was cured, it was cut into 1/2 inch width to produce a video tape. With respect to the video tapes of the magnetic recording media 1 of the examples and the comparative examples manufactured by the above-described steps, each property of the dispersibility, the dispersion speed, and the filter life of the paint at the time of preparing the magnetic paint, and the video electromagnetic force when the video tape was used. The conversion characteristics were measured. These measurement conditions will be described below.

[Dispersibility] A magnetic coating liquid was applied on a polyethylene terephthalate film (14.0 μm thick) with a doctor blade 2MIL and dried, and the glossiness (gloss) of the coated surface was measured by Nippon Denshoku Kogyo Co., Ltd. Variable-angle gloss meter VG
It was measured at an incident angle of 45 degrees by -1D. [Dispersion speed] In the above-mentioned second step, at the time of media dispersion by a sand mill, the above-mentioned glossiness is measured every 30 minutes,
The time until the gloss reached 90% was measured. [Filter life] In the first step, when a fixed amount of magnetic paint pre-dispersed by a high-speed disperser is circulated and filtered by a gear pump having a fixed rotation speed, the differential pressure of the filter (from the filter inlet pressure to the outlet pressure) 400 kPa
The time to reach was measured. [Electromagnetic conversion characteristics] (1) RF-OUT (video output) For each video tape, a video signal was recorded using a VTR AG-6200 (manufactured by Matsushita Electric Industrial Co., Ltd.), and the reproduction level was compared with that of Comparative Example 1. The video tape is used as a reference tape, and is represented by a relative value when this is set to 0 dB. (2) YS / N (Video S / N) For each video tape, the S / N ratio of the video signal is represented by a relative value when the reference tape of Comparative Example 1 is 0 dB. Tables 1 and 2 show the measurement results of these characteristics of the examples and the comparative examples.

[0036]

[Table 1]

[0037]

[Table 2]

According to the results shown in Tables 1 and 2, after the pre-dispersion of the magnetic paint in the first step, the dispersion in the media was 1.0%.
1% (10 μm) to 20% (2
It can be seen that by performing a filtration treatment with a filter having a filtration diameter of (00 μm), the dispersibility after the media dispersion treatment in the second step is improved, and the electromagnetic conversion characteristics can be improved. When the filtration diameter is 1% or less of the dispersion medium, the dispersibility is good, but the filter life is remarkably inferior and not suitable for production. On the other hand, if the filtration diameter is 50% or more of the dispersion medium, filtration is not meaningful, dispersibility is poor, and sufficient electromagnetic conversion characteristics cannot be obtained.

[0039]

According to the method for manufacturing a magnetic recording medium and the magnetic recording medium of the present invention, a magnetic paint having a high degree of dispersibility can be easily obtained. Thus, a magnetic recording medium having excellent characteristics can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a magnetic recording medium according to the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Magnetic recording medium, 2 ... Non-magnetic support, 3 ... Magnetic layer, 4
… Top coat layer, 5… Back coat layer

Claims (6)

[Claims] 1. A kneading of a magnetic paint containing magnetic particles and a binder, a first step of predispersing the magnetic paint after the kneading, and a high dispersion of the magnetic paint by media dispersion after the first step. A method for producing a magnetic recording medium having a second step of performing a filtration treatment in the pre-dispersion of the first step;
A method for manufacturing a magnetic recording medium, wherein either one of a filtration process and a filtration process is performed between the first step and the second step. 2. The method for manufacturing a magnetic recording medium according to claim 1, wherein a filtration diameter in the filtration treatment is 1% or more and 20% or less of a media diameter used in the media dispersion. 3. A magnetic recording medium comprising: a first step of pre-dispersing a magnetic paint containing magnetic particles and a binder; and a second step of highly dispersing the magnetic paint by media dispersion after the first step. A method for producing a magnetic recording medium, comprising: performing either a filtration treatment in the first step or a filtration treatment between the first step and the second step. Method. 4. The method for manufacturing a magnetic recording medium according to claim 3, wherein a filtration diameter in the filtration treatment is 1% or more and 20% or less of a diameter of a medium used in the medium dispersion. 5. A magnetic recording medium manufactured by the method for manufacturing a magnetic recording medium according to claim 1. 6. A magnetic recording medium manufactured by the method for manufacturing a magnetic recording medium according to claim 3.