JPS6166224A - Production of magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a magnetic recording having low DC noise by treating a dispersion obtd. by dispersing magnetic powder with alcohol with a solvent which can be mixed with the alcohol and mixing and dispersing the same with a binder resin soluble in the solvent replacing the dispersion to prepare a magnetic paint. CONSTITUTION:The magnetic powder is dispersed with the alcohol which is most miscible with the powder and has good affinity therewith. The resultant alcohol dispersion of the magnetic powder is treated with the solvent which can be mixed with the alcohol and the dispersion medium of the magnetic powder is replaced with the solvent which can be mixed with the alcohol from the alcohol; thereafter, the magnetic powder is mixed and dispersed with the binder resin soluble in the solvent replacing the magnetic paint. Such magnetic paint is coated on a substrate and is dried to form the magnetic layer. The magnetic powder is thereby uniformly dispersed into the magnetic paint, by which the dispersibility of the magnetic powder in the magnetic layer and the surface smoothness are improved and the electrical characteristic is improved.

Description

[Detailed explanation of the invention] [In industrial use field] This invention is more detailed in the manufacturing method of magnetic recording media, which has excellent diversification of magnetic powder, has good surface smoothness, and has excellent electrical characteristics. The present invention relates to a method of manufacturing a magnetic recording medium having a layer.

[Conventional technology]

Magnetic recording media are usually produced by dissolving a binder resin in a solvent that can dissolve the binder component, and mixing and dispersing magnetic powder and other necessary components in this solution to prepare a magnetic paint. Coating onto a substrate such as polyester film,
It is required that the magnetic layer is dry and has good surface smoothness and excellent electrical properties.

Therefore, it is desirable to prepare a magnetic paint in which the magnetic powder to be used is dispersed as uniformly as possible in a binder resin, and to disperse the magnetic powder as uniformly as possible in the magnetic layer.

[Problem that the invention seeks to solve]

However, in the conventional method, it is difficult to use lipophilic organic solvents that are difficult to get on the surface of hydrophilic magnetic powder, or water, etc. that are easy to get on the surface of hydrophilic magnetic powder but do not have sufficient affinity for the magnetic powder. is used as a solvent to dissolve the binder resin from the beginning and to disperse the magnetic powder, etc., and with these solvents, the magnetic powder is mixed and dispersed with the binder resin soluble in these solvents to form a magnetic paint. However, since the magnetic powder is not sufficiently uniformly dispersed, the surface smoothness of the magnetic layer cannot be improved sufficiently to improve the electrical properties.

[Means for solving problems]

This invention was made as a result of various studies in view of the current situation, and consists of dispersing magnetic powder in alcohol that is most compatible with the magnetic powder and having good affinity, and then dispersing the obtained magnetic powder in alcohol. After treating the magnetic powder with a solvent that is miscible with alcohol to replace the dispersion medium of the magnetic powder from alcohol with a solvent that is miscible with alcohol, this is treated with a binder resin that is soluble in the replaced solvent and a binder resin that is the same as the replaced solvent. Prepare magnetic paint by mixing and dispersing with a solvent.
By applying this magnetic paint onto a substrate and drying it to form a magnetic layer, the magnetic powder is uniformly dispersed in the magnetic paint, and the dispersibility of the magnetic powder in the magnetic layer is sufficiently improved. The surface smoothness of the magnetic layer is improved and the electrical characteristics are further improved.

In this invention, lower alcohols having 1 to 5 carbon atoms such as methanol, ethanol, propatool, isopropanol, butanol, and pentanol are used as the alcohol for dispersing the magnetic powder. Since these alcohols are easily compatible with the surface of hydrophilic magnetic powder and have extremely good affinity with the magnetic powder, the magnetic powder is dispersed extremely well when these alcohols are used. Dispersion of magnetic powder with these alcohols is
This is carried out using various conventionally known dispersing machines such as a kneader, ball mill, sand mill, disperser, and ultrasonic wave.

In addition, replacing the dispersion medium of the magnetic powder from alcohol to a solvent that is miscible with alcohol is performed by treating the alcohol dispersion of the magnetic powder obtained in this way with a solvent that is miscible with alcohol. After the alcohol dispersion is filtered, before the magnetic powder on the filter dries, a solvent that can be mixed with alcohol is poured into the filter to wash the magnetic powder. Therefore, agglomeration of the magnetic powder, which tends to occur when a dispersion medium such as alcohol is once dried, does not occur at all, and the dispersibility of the magnetic powder is further improved. Examples of solvents that can be mixed with alcohol include ketone solvents such as cyclohexanone, methyl ethyl ketone, and methyl isobutyl ketone, ester solvents such as ethyl acetate and butyl acetate, and aromatic hydrocarbon solvents such as benzene, toluene, and xylene. One or more solvents selected from hydrocarbon solvents such as hexane and heptane, acid amide solvents such as dimethylformamide, sulfoxide solvents such as dimethyl sulfoxide, and ether solvents such as tetrahydrofuran and dioxane. Mixed organic solvents or water are used.

The magnetic powder in which the dispersion medium has been replaced with a solvent that is miscible with alcohol is used as it is before the dispersion medium such as the above-mentioned organic solvent or water is volatilized, and the dispersion of the replaced dispersion is carried out. A magnetic paint is prepared by mixing and dispersing the same solvent as the medium and a binder resin soluble in this solvent. In this way, magnetic powder is used after being replaced with the same dispersion medium as the organic solvent or water used to dissolve the binder resin and prepare the magnetic paint. Furthermore, since the alcohol in which the magnetic powder is dispersed is not dried once, there is no agglomeration of the magnetic powder due to drying, and therefore the dispersibility of the magnetic powder is further improved. When the resulting magnetic paint is applied onto a substrate and dried, a magnetic recording medium with even better surface smoothness of the magnetic layer and better electrical properties can be obtained.

In this way, magnetic powder is first dispersed in alcohol that has the best affinity for magnetic powder, and then this alcohol dispersion of magnetic powder is treated with a solvent that is miscible with alcohol to form a dispersion medium for magnetic powder. When a magnetic paint is prepared by replacing alcohol with a solvent that is miscible with alcohol and mixing and dispersing this with the same solvent as the replaced solvent and a binder resin that is soluble in the replaced solvent, the magnetic property in the magnetic paint increases. The dispersibility of the powder is sufficiently improved, but if an alcohol-soluble surface modifier is added to the alcohol dispersion of the magnetic powder, this type of surface modifier will be well coated on the particle surface of the magnetic powder. This film further improves the affinity between the solvent that replaces the alcohol and the magnetic powder, and at the same time prevents the particles from approaching each other and agglomerating, improving the dispersibility and dispersion of the magnetic powder. The stability is further improved, the surface smoothness of the magnetic layer is further improved, and the electrical properties are further improved.

Examples of such alcohol-soluble surface modifiers include polyvinyl butyral having a molecular weight of 2000 to 8000, alkylamine salts of polyacrylic acid, polyacrylates, polyacrylic esters, and alkylamine salts of polymaleic acid. , polymaleic acid ester, polymaleic acid polyether, and sodium dialkyl sulfosuccinate with a molecular weight of 2000 or less, higher alcohol phosphoric acid ester, alkylamine salt, sorbitan monolaurate, silane coupling agent, titanium coupling agent, aluminum coupling agent Coupling agents such as are preferably used. The amount to be used is 0.00% based on the magnetic powder.
It is preferably used within the range of 1 to 10% by weight; if it is too small, the dispersibility of the magnetic powder will not be sufficiently improved, and if it is too large, the surface smoothness of the magnetic layer will deteriorate.

Examples of the magnetic powder used in this invention include r-F
e203 powder, Fe3O4 powder, Go-containing-Fe20
3 powder, Fe3O4 powder with Goo, barium ferrite, strontium ferrite, and other iron oxide magnetic powders, and metal magnetic powders such as Fe powder, CO powder, and Fe-Ni powder that have undergone corrosion-resistant treatment by pre-oxidizing the particle surface. is preferably used.

In addition, as the binder resin, vinyl chloride-vinyl acetate copolymer, polyvinyl butyral resin, cellulose resin,
Conventional binder resins such as polyester resins, polyurethane resins, and isocyanate compounds are all used. As the solvent a, any of the solvents used in the solvent replacement described above may be used alone or in a mixture of two or more.

In addition, various additives commonly used in magnetic paints,
For example, lubricants, abrasives, antistatic agents, and the like may be added as appropriate.

〔Example〕

Next, embodiments of the invention will be described.

Example 1 Acicular Co-containing r-Fe203 magnet 100 parts by weight Powdered ethanol 200 Higher alcohol phosphate ester 10 The above components were mixed and dispersed in a ball mill for about 100 hours to prepare a dispersion, and then this dispersion 800 parts by weight of ethanol was added to the mixture and mixed and dispersed for 10 hours using a homomixer to prepare a dilute dispersion.Next, this dispersion was poured into a filter and filtered, and before the ethanol dried, 500 parts by weight of ethanol was added. A mixed solvent of methyl isobutyl ketone and 500 parts by weight of toluene was poured into the filter to wash the magnetic powder, and at the same time, the dispersion medium was replaced from ethanol with a mixed solvent of methyl isobutyl ketone and toluene. The thus obtained acicular Co-containing γ-Fe203 magnetic powder was used before the mixed solvent was volatilized, and 100 parts by weight of the acicular Co-containing T-Pe20 dimagnetic powder was prepared by VAGH (US company U, C, C). 18 Vinyl-vinyl acetate-vinyl alcohol copolymer) Takelac E-5517 (Take 1) 12μ Yakuhin Kogyo Co., Ltd., polyurethane elastomer) Desmod Shikki Bayer, 3 Trifunctional low molecular weight isocyanate compound) Valmitic acid 2 Methyl isobutyl ketone 80 Toluene
A magnetic paint was prepared by mixing and dispersing a mixture having a composition of 80% in a ball mill for about 100 hours. This magnetic paint was applied onto a 12 μm thick polyester film to a dry thickness of about 3 μm, dried, surface treated, and then cut to a predetermined width to produce a magnetic tape.

Example 2 Acicular Co-containing γ-Fe2O, magnetic An ethanol dispersion of the powder was prepared and a magnetic tape was made.

Example 3 In the preparation of the ethanol dispersion of the acicular Co-containing r-Fe203 magnetic powder in Example 1, the acicular Co-containing r-
Except that instead of Fe203 magnetic powder, α-Fe magnetic powder whose particle surface had been oxidized and subjected to anti-corrosion treatment was used.
An ethanol dispersion of α-Fe magnetic powder was prepared in the same manner as in Example 1 to produce a magnetic tape.

Comparative Example 1 A magnetic tape was produced in the same manner as in Example 1, except that the acicular CO-containing r-Fe203 magnetic powder was not dispersed in ethanol and the solvent was not replaced with the mixed solvent.

Comparative Example 2 The same procedure as in Example 3 was carried out except that in Example 3, α-Fe magnetic powder whose particle surface had been oxidized in advance and subjected to anti-corrosion treatment was not dispersed in ethanol and the solvent was not replaced from ethanol to a mixed solvent. and made magnetic tape.

Regarding the magnetic tapes obtained in each example and comparative example,
The output at 15 KHz, DC noise, and surface roughness of the magnetic layer were measured. The surface roughness of the magnetic layer was measured using a stylus type surface roughness meter, and the numerical value of the surface roughness was expressed as a center line average (C, L, A).

The table below shows the results.

Table [Effects of the Invention] As is clear from the above table, the magnetic tapes obtained by the present invention (Examples 1 to 3) have higher output than the conventional magnetic tapes (Comparative Examples 1 and 2). Furthermore, the DC noise is low and the surface roughness is small. Therefore, according to the manufacturing method of the present invention, the dispersibility of the magnetic powder is sufficiently improved.
It can be seen that a magnetic recording medium with extremely good surface smoothness of the magnetic layer and even better electrical properties can be obtained.

Claims (1)

[Claims] 1. Disperse magnetic powder in alcohol, and then treat the obtained alcohol dispersion of magnetic powder with a solvent that is miscible with alcohol to change the dispersion medium of magnetic powder from alcohol to alcohol. After replacing the solvent with the obtained solvent, this is mixed and dispersed with a binder resin soluble in the replaced solvent and the same solvent as the replaced solvent to prepare a magnetic paint, and this magnetic paint is applied onto a substrate and dried. 2, a method for producing a magnetic recording medium characterized in that a magnetic layer is formed by
5. Method 3 for manufacturing a magnetic recording medium according to claim 1, in which the magnetic powder is dispersed in alcohol using a dispersing machine such as a kneader, ball mill, sand mill, dispersion machine, ultrasonic wave, etc. Method 4 for manufacturing a magnetic recording medium according to claim 1, wherein the solvent that can be mixed with alcohol is a ketone solvent, an ester solvent, an aromatic hydrocarbon solvent, a hydrocarbon solvent, an acid amide solvent, The method 5 for producing a magnetic recording medium according to claim 1, wherein the magnetic powder is an organic solvent selected from sulfoxide solvents and ether solvents, or a mixture of two or more thereof, or water. 6. A method for producing a magnetic recording medium according to claim 1, which is iron oxide magnetic powder or metal magnetic powder whose particle surface has been oxidized in advance and subjected to anti-corrosion treatment. A method 7 for manufacturing a magnetic recording medium according to claim 1, in which a soluble surface modifier is contained, and a patent claim in which a process of replacing alcohol in the dispersion medium of the magnetic powder with a solvent that is miscible with alcohol is performed during filtration. A method for manufacturing a magnetic recording medium according to item 1 of the scope of