JPS6166227A - Production of magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve the surface smoothness and then the electrical characteristics of a magnetic recording medium by dispersing the magnetic powder with a prescribed dispersant to obtain a dispersion solution which is replaced with a solvent that can be mixed with the dispersant and forming a magnetic layer with a magnetic coating material which is obtained by mixing a binder resin soluble in the replaced solvent and a solvent equal to the replaced solvent. CONSTITUTION:The magnetic powder of 1g which is dried through a 80-mesh sifter is dispersed into a dispersion solution of 20ml by means of a dispersion medium with the sedimentation volume of the magnetic powder is set at <=10cc after two weeks from an ultrasonic dispersion mode of 8 hours. A solvent soluble in the dispersant is used to replace the dispersion medium of the magnetic powder with a solvent soluble in said dispersion medium. This solvent is mixed with the binder resin soluble in the replaced solvent and a solvent equal to the replaced solvent and then dispersed for control of a magnetic coating material. This coating material is applied and dried on a substrate to obtain a magnetic layer.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for manufacturing a magnetic recording medium, and more specifically, the present invention relates to a method for manufacturing a magnetic recording medium, and more specifically, it relates to a method for manufacturing a magnetic recording medium, and more specifically, a magnetic powder having excellent properties, good surface smoothness, and excellent electrical properties. The present invention relates to a method of manufacturing a magnetic recording medium having a magnetic 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 made by drying, and requires a magnetic layer with 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 the binder component, and to disperse the magnetic powder in the magnetic layer as uniformly as possible.

[Problem that the invention seeks to solve]

However, in the conventional method, a lipophilic solvent that is difficult to blend on the surface of hydrophilic magnetic powder is used, or a water solution that is easy to blend on the surface of hydrophilic magnetic powder but does not have sufficient affinity with the magnetic powder is used. etc., from the beginning with binder 1
4. A magnetic paint is prepared by dissolving the resin and using it as a solvent to disperse magnetic powder, etc., and using these solvents, the magnetic powder is mixed and dispersed with a binder resin that is soluble in these solvents. Therefore, the magnetic powder cannot be sufficiently uniformly dispersed, and the surface smoothness of the magnetic layer cannot be improved to sufficiently improve the electrical characteristics.

[Means for Solving the Problems] This invention was made as a result of various studies in view of the current situation, and it is possible to pass 1 g of magnetic powder sufficiently dried through an 80 sieve sieve into 20 ml! After 8 hours of ultrasonic dispersion in a dispersion medium of
The magnetic powder is dispersed in a dispersion medium that has a dispersion medium of less than or equal to After substituting the solvent with a suitable solvent, a magnetic paint is prepared by mixing this with a binder 1 cedar fat soluble in the substituted solvent and the same solvent as the substituted solvent to prepare a magnetic paint. By applying it 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 to form a magnetic layer. It has improved surface smoothness and further improved electrical characteristics.

In this invention, the dispersion medium for dispersing the magnetic powder is such that 1 g of the magnetic powder, which has been thoroughly dried through an 80-mesh sieve, is
It is preferable that the sedimentation volume of the magnetic powder after 2 weeks is 10 cc or less when ultrasonically dispersed in 0 ml of dispersion medium for 8 hours.
A small solvent of 0 cc or less has excellent affinity for the magnetic powder, and when this type of solvent is used, the magnetic powder is dispersed extremely well. On the other hand, the sum of the magnetic powder sediments is 10c
If a solvent larger than c is used, the affinity for the magnetic powder will not be good, and even if the magnetic powder is dispersed using this solvent, the dispersibility of the magnetic powder will not be sufficiently improved.

When 1 g of such magnetic powder that has been thoroughly dried through an 80-mesh sieve is subjected to ultrasonication for 8 hours in a dispersion medium of 20 mA, the sedimentation volume of the magnetic powder after 2 weeks is 1.
Examples of solvents that are less than occ include lower alcohols with 1 to 5 carbon atoms such as methanol, ethanol, propatool, isopropanol, butanol, and pentanol, and ether solvents such as dioxane and tetrahydrofuran. A solvent selected from the following or a mixture of two or more of them is preferably used, and the magnetic powder molecule i & with a solvent whose sedimentation volume of the magnetic powder is 10 cc or less is processed by a kneader, a ball mill, a sand mill, a dispersion machine, etc. This is carried out using various conventionally known dispersers such as , ultrasonic, and the like.

In addition, 1k liquid of the magnetic powder obtained in this manner was separated with the dispersion medium and mixed with the dispersion medium for 1!7 minutes.
To replace the dispersion medium of magnetic powder by treating it with a solvent, after filtering the dispersion of magnetic powder with a filter, add a solvent that can be mixed with the dispersion medium to the filter while the magnetic powder on the filter does not dry. This is done while washing the magnetic powder. Therefore, the agglomeration of the magnetic powder, which tends to occur when the dispersion medium of the magnetic powder 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 the dispersion medium for magnetic powder include ketone solvents such as cyclohexanone, methyl ethyl ketone, and methyl isobutyl ketone, ester solvents such as ethyl acetate and butyl acetate, and aromatic solvents such as benzene, toluene, and xylene. Group hydrocarbon solvents, hydrocarbon solvents such as hexane and heptane, alcohol solvents such as isopropyl alcohol, acid amide solvents such as dimethylformamide, sulfoxide solvents such as dimethyl sulfoxide, ether solvents such as tetrahydrofuran and dioxane, etc. Any one selected from, or a mixture of two or more selected from
A solvent or water is used.

In this way, the magnetic powder in which the dispersion medium can be mixed with the dispersion medium of the magnetic powder is used as is before the dispersion medium such as the organic solvent or water that has been replaced is volatilized. Then, a binder resin soluble in the substituted solvent and the same solvent as the substituted solvent are mixed and dispersed to prepare a magnetic paint. In this way, the magnetic powder is used after being replaced with the same dispersion medium as the organic solvent or water used to melt the binder resin and prepare the magnetic paint. Furthermore, since the dispersion medium in which the magnetic powder is dispersed is not once dried, there is no agglomeration of the magnetic powder due to drying, which further improves the dispersibility of the magnetic powder. When the magnetic paint thus obtained is spread on a substrate and dried, a magnetic recording medium with improved surface smoothness of the two magnetic layers and even better electrical properties is obtained.

In this way, the magnetic powder is first dispersed in a dispersion medium in which the sedimentation volume of the magnetic powder is 10 cc or less, which has the best affinity with the magnetic powder, and then this dispersion of the magnetic powder is mixed with this dispersion medium. The dispersion medium of the magnetic powder is replaced with a solvent that is miscible with the dispersion medium, and this is mixed and dispersed with a binder resin soluble in the replaced solvent and the same solvent as the replaced solvent. If the magnetic paint is made of steel, the dispersibility of the magnetic powder in the magnetic paint will be sufficiently improved.
When a surface modifier that is soluble in the magnetic powder dispersion is added to the dispersion, this kind of surface modifier adheres well to the surface of the magnetic powder particles, forming a film. The affinity between the solvent to be substituted and the magnetic powder is further improved, and at the same time, the particles are prevented from approaching each other and agglomerating, so the dispersibility and minute ttt stability of the magnetic powder are further improved.
The surface smoothness of the magnetic layer is further improved, and the electrical characteristics are further improved.

Such surface modifiers soluble in the above-mentioned dispersion include:
For example, polyvinyl butyral, polyacrylates, alkylamine salts of polyacrylic acid, polyacrylic esters, alkylamine salts of polymaleic acid, polymaleic esters, polymaleic acid polyethers with a molecular weight of 2000 to 8000, and polymaleic acid polyethers with a molecular weight of 2000 or less. Sodium dialkyl sulfosuccinate, higher alcohol phosphate ester, alkylamine salt, sorbitan monolaurate, silane coupling agent, titanium coupling agent,
Coupling agents such as aluminum coupling agents are preferably used. The amount used is 0 for 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, Co-containing r-Fe20
3 powder, iron oxide magnetic powder such as CO-containing Fe5Q4 powder, barium ferrite, and strontium ferrite, and metalworking magnetic powder such as Fe powder, Co powder, and Fe-Ni powder whose particle surfaces have been pre-oxidized and subjected to anti-corrosion treatment are suitable. used as something.

In addition, as the binder resin, vinyl chloride-vinyl acetate copolymer, polyvinyl butyral resin, fiber cord resin,
Conventionally widely used binder resins such as polyester resins, polyurethane resins, and isocyanate compounds are all used, and the organic solvents used in the solvent replacement described above can be used alone or in combination of two or more. used.

In addition, various additives commonly used in magnetic paints,
For example, dispersants, 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 dioxane 2001 Higher alcohol phosphate ester 1O The above ingredients were mixed in a ball mill for about 100 hours to prepare a solution in minutes 11, After that, 800 parts by weight of dioxane was added to the liquid and heated in a homomixer for 10 hours.
A dilute 17/liquid solution was prepared with 8IFlI. Next, this dispersion was poured into a filter and filtered, and before the dioxane dried, 500 parts by weight of methyl isobutyl ketone and 50 parts by weight of methyl isobutyl ketone were added.
A mixed solvent with 0 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 dioxane with a mixed solvent of methyl isobutyl ketone and toluene. Acicular Co-containing γ-Fe2 obtained in this way
03 magnetic powder was used before the mixed solvent volatilized, and 100 parts by weight of acicular Co-containing γ-Fe203 magnetic powder VAGH (American U,C,C company, chloride 18 vinyl-vinyl acetate-vinyl alcohol copolymer) was prepared. ) Takerac E-551T7 (Take 1) 12μ manufactured by Yakuhin Kogyo Co., Ltd., polyurethane elastomer) Desmodur Shikku manufactured by Bayer AG, 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 8°C in a ball mill at a time of about 80°C. 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-Fe203 was prepared in the same manner as in Example 1 except that the higher alcohol phosphate ester was omitted in the preparation of the dioxane dispersion of the acicular Co-containing γ-p' 6203 magnetic powder in Example 1. A dioxane dispersion of magnetic powder was prepared and a magnetic tape was made.

Example 3 Same as Example 1 except that polyalkylene oxide silane was used instead of higher alcohol phosphate ester in the preparation of dioxane content tik'/(l) of the acicular Co-containing r-Fe203 magnetic powder in Example 1. A dioxane dispersion of acicular Co-containing γ-FezOavt powder was prepared and a magnetic tape was made.

Example 4 In the preparation of the dioxane dispersion of needle-like Co-containing r-Fe203 magnetic powder in Example 1, needle-like Co-containing γ-
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.
In the same manner as in Example I, a dioxane-containing liquid of α-Fe magnetic powder was prepared and a magnetic tape was applied.

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 dioxane and the solvent was not replaced with the mixed solvent from dioxane.

Comparative Example 2 Example 4 was carried out in the same manner as in Example 4, except that α-Fe magnetic powder whose particle surface had been oxidized in advance and subjected to anti-corrosion treatment was not dispersed in dioxane and the solvent was not replaced from dioxane to a mixed solvent. and made magnetic tape.

Regarding the magnetic tapes obtained in each example and comparative example,
The output, DC noise, and surface roughness of the magnetic layer were measured at 15 KIlz. 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 center line aperage (C, L, A).

The table below shows the results.

〔Effect of the invention〕

As is clear from the table above, the magnetic tapes obtained by the present invention (Examples 1 to 4) have higher output and lower DC noise than conventional magnetic tapes (Comparative Examples 1 and 2). The surface roughness is small, and 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. When 1 g of magnetic powder that has been thoroughly dried through an 80 mesh sieve is ultrasonically dispersed in 20 ml of dispersion medium for 8 hours, the sedimentation volume of the magnetic powder after 2 weeks is 10 cc or less. Dispersing the magnetic powder in a dispersion medium, and then treating the resulting dispersion of the magnetic powder with a solvent that is miscible with the dispersion medium, so that the dispersion medium of the magnetic powder can be mixed with the dispersion medium. This is mixed and dispersed with a binder resin soluble in the substituted solvent and the same solvent as the substituted solvent to prepare a magnetic paint, and this magnetic paint is applied onto a substrate and dried. A method for manufacturing a magnetic recording medium characterized by forming a magnetic layer 2, wherein the dispersion medium for dispersing the magnetic powder is selected from lower alcohols having 1 to 5 carbon atoms and ether solvents such as dioxane and tetrahydrofuran. 3, a method for producing a magnetic recording medium according to claim 1, wherein the solvent is one or a mixture of two or more of them. 4, the method for manufacturing a magnetic recording medium according to claim 1, which is carried out using a dispersing machine such as Claim No. 1, which is an organic solvent selected from solvents, hydrocarbon solvents, alcohol solvents, acid amide solvents, sulfoxide solvents, and ether solvents, or a mixture of two or more thereof, or water. 5. A method for manufacturing a magnetic recording medium according to claim 1, wherein the magnetic powder is iron oxide magnetic powder or metal working magnetic powder whose particle surface has been oxidized in advance and subjected to anti-corrosion treatment. The magnetic recording medium according to claim 1. 6. A method 7 for producing a magnetic recording medium according to claim 1, in which a surface modifier soluble in a dispersion medium is contained in a dispersion of magnetic powder. The method for manufacturing a magnetic recording medium according to claim 1, in which a substitution treatment of replacing the solvent with a solvent that is miscible with the medium is performed during filtration.