JP2779663B2 - Manufacturing method of magnetic recording medium - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a magnetic recording medium, and more particularly to a magnetic layer structure.

[Background of the Invention]

Magnetic recording has become indispensable for social activities and personal life today, and increasingly requires high performance, low cost, and reliability of quality.

The magnetic recording layer of magnetic tape, which has the most widespread demand, is a coating type in which magnetic powder is suspended in a binder solution and a magnetic paint is applied on a support.The magnetic material is deposited without using a binder by vapor deposition, sputtering, etc. There are a so-called thin film type which is densely deposited on a support and a plating type which is laminated by plating. However, a coating type is dominant in terms of high technical integration and technical reliability and cost.

The coating type magnetic recording medium is usually prepared by applying a ferromagnetic powder and, if necessary, a magnetic paint to which various additives are added to a running support in a solvent solution of a binder,
It is manufactured by drying and then calendering.

In recent years, there has been an increasing demand for high-density magnetic recording media. In particular, for example, video tapes have been required to perform very high-density recording in response to a demand for a higher recording frequency. Various types of laminated magnetic layers in which two or three or more layers composed of an upper layer and a lower layer are coated on the body in multiple layers have been proposed.

Conventionally, methods such as roll coating, gravure coating, and extrusion coating (extrusion) have been generally used as a method of applying the magnetic paint in a multi-layered manner.・ Dry (We
A method in which the next layer is successively or simultaneously superimposed on a layer in a wet state that is less dry than the method of “t on Dry; WOD”, so-called “wet on wet”.
t; WOW) is superior.

As a prior art relating to multi-layer coating, for example,
63-164022, 63-164023, 62-214524, 62
The techniques described in JP-A-124631, JP-A-62-92132 and JP-B-57-17291 are exemplified.

Further, prior art relating to an apparatus-like process of a coating method of a magnetic recording medium is disclosed in JP-A-63-164022 and JP-A-63-164023.
And Nos. 62-124631.

However, these techniques are not satisfactory in terms of coatability of the magnetic paint for performing multilayer coating.

When an extrusion coater is used to apply the magnetic paint on the support, the formulation of the magnetic paint and the degree of dispersion of each component in the magnetic paint are important factors in terms of coatability.

In this regard, Japanese Patent Application Laid-Open No. 62-214524 discloses the mutual solubility of a solvent and a binder. In this technique, however, the prescription relationship between the uppermost magnetic paint and the lower magnetic paint is clear. However, when the uppermost layer is a magnetic layer, it is unclear even though the degree of dispersion is important.

In addition, in the conventional multi-layer coating by the WOW method, the coating state of the uppermost layer fluctuates due to non-uniform tension, run-out, and other fluctuations of the tape-like flexible support, and the uppermost layer of uniform coating quality is obtained. In particular, there is a problem that various coating failures occur, for example, a thin top layer cannot be obtained.

In particular, when the magnetic particles are small (for example, the major axis length is 0.18
This tendency is remarkable when the thickness of the uppermost layer becomes as thin as 1.0 μm or less after the calendar processing.

[Object of the invention]

In view of such circumstances, an object of the present invention is to provide a magnetic recording medium having a good coating quality of a magnetic layer, particularly the uppermost layer, when a plurality of magnetic paints are sequentially or simultaneously coated on a running support by a WOW method. It is to provide a manufacturing method of.

[Structure and operation and effect of the invention]

An object of the present invention is to provide a magnetic recording medium in which a plurality of magnetic layers are sequentially or simultaneously wet-coated on a running flexible support, dried and calendered; The binder of the layer paint contains at least a urethane resin and the coating amount is suppressed to 30 cm ³ / m ² or less. (B) The binder of the uppermost magnetic layer paint is a vinyl chloride resin having a polar group, a polyurethane, respectively. Containing resin,
When the actual load applied to the kneader motor is 0.1 kw / kg-magnetic powder or more, kneading is performed for 5 minutes to 2 hours, and the applied amount is 25 cm ³ / m ^2.
This is achieved by a method of manufacturing a magnetic recording medium characterized by the following.

The actual load in this case is a value obtained by subtracting the current value of the kneading machine when there is no load from the current value during kneading.

In the embodiment of the present invention, the polar group of the vinyl chloride-based resin and the urethane-based resin is preferably a negative functional group, and the thickness of the uppermost layer after calendering is adjusted by adjusting the evaporation component ratio of the uppermost magnetic layer paint and calendering. Application amount 25cm ³ / m ² by adjusting pressure
It is preferable that the dry thickness be 1 μm or less.

Furthermore, to describe the present invention, the core as the magnetic material used in the present invention, for example, where the γ-Fe ₂ O _3, Co deposited the SS-type γ-Fe ₂ O ₃ or Co containing as a solid solution as a shell / Shell (c / s) type γ-Fe ₂ O ₃ , Fe ₂ O ₄ , CrO ₂
Oxide magnetic materials such as Fe; Ni, Fe-Ni alloy, Fe-Co alloy, Fe-Ni-P alloy, Fe-Ni-Co alloy, Fe
-Mn-Zn alloy, Fe-Ni-Zn alloy, Fe-Co-Ni-Cr alloy,
Fe-Co-Ni-P alloy, Co-P alloy, Fe such as Co-Cr alloy,
Various ferromagnetic substances (powder) such as metal magnetic powder containing Ni or Co as a main component are exemplified.

Additives for these metallic magnetic materials include Si, Cu,
Elements such as Zn, Al, P, Mn, and Cr or compounds thereof may be contained.

Further, as a binder used for the magnetic layer of the magnetic recording medium, various natural or synthetic resins have been proposed so far, and a preferable one is a polyurethane resin.

The polyurethane resin according to the present invention has a strong adhesive force to other substances, is mechanically tough against repeated stress or bending, and has good wear resistance and weather resistance.

Further, in addition to the polyurethane resin, a vinyl chloride copolymer is generally used in combination, so that the dispersibility of the magnetic powder in the magnetic layer is improved and the mechanical strength is increased. However, the layer becomes too hard with the vinyl chloride copolymer alone, but this can be prevented by the presence of the above-mentioned polyurethane resin.

The above polyurethane resin and vinyl chloride copolymer may be partially hydrolyzed. As the vinyl chloride copolymer, preferably, a copolymer containing vinyl chloride-vinyl acetate or a copolymer containing vinyl chloride-vinyl acetate-vinyl alcohol is used.

Furthermore, polyurethane for improving dispersibility and physical properties,
A modified resin obtained by adding a polar group, for example, a negative functional group, to a homopolymer of vinyl chloride, a vinyl chloride-vinyl acetate copolymer, or the like is particularly preferably used as a binder for this type of magnetic recording medium. . The vinyl chloride resin having a polar group used in the present invention is a homopolymer of vinyl chloride or a copolymer of vinyl chloride and a monomer copolymerizable with vinyl chloride, for example, a copolymer of vinyl chloride and vinyl acetate. Refers to a resin obtained by introducing a polar group into the polymer.
Such resins, for example, homopolymers or vinyl chloride vinyl chloride - vinyl acetate _{copolymer, Cl-CH 2 CH 2 SO} 3 M, Cl-CH 2 OSO 3 M, Cl-H 2 COOM or (However, M ₁ and M ₂ each represent an alkali metal such as lithium, sodium and potassium.) And condensate with a compound containing a negative functional group and chlorine in the molecule by a dehydrochlorination reaction. It is easily obtained by

Further, the polyurethane resin having a polar group is a resin obtained by introducing a polar group into the polyurethane resin. For example, similarly to the case of the vinyl chloride resin having the polar group, for example, a polyurethane resin and Cl-CH ₂ CH ₂ SO ₃ M, Cl-CH ₂ OSO
₃ M, Cl-CH ₂ COOM or (However, M ₁ and M ₂ each represent an alkali metal such as lithium, sodium and potassium.) And condensate with a compound containing a negative functional group and chlorine in the molecule by a dehydrochlorination reaction. It is easily obtained by

Representative examples of the polar group in such a condensate include, for example, a sulfonic acid group and a carboxyl group, but are not limited thereto.

As long as the effects of the present invention are not impaired, the lower layer and the uppermost layer may contain various resins that are already commonly used as a binder in addition to the above-mentioned essential components.

In the present invention, in order to improve the durability of the magnetic layer of the magnetic recording medium, various hardeners, for example, isocyanate can be contained in the magnetic paint. As the aromatic isocyanate, for example, tolylene diisocyanate (TD
I) and the like, and adducts of these isocyanates with active hydrogen compounds, and the like.
A range of 3,000 is preferred.

Examples of the aliphatic isocyanate include hexamethylene diisocyanate (HMDI) and the like, and adducts of these isocyanates and active hydrogen compounds. Among these aliphatic isocyanates and adducts of these isocyanates and active hydrogen compounds, those having a molecular weight in the range of 100 to 3,000 are preferred. Of the aliphatic isocyanates, non-alicyclic isocyanates and adducts of these compounds with active hydrogen compounds are preferred.

The magnetic paint used for forming the magnetic layer may contain a dispersant and, if necessary, additives such as a lubricant, an abrasive, a matting agent, and an antistatic agent.

Examples of the dispersant used in the present invention include phosphate esters,
Amine compounds, alkyl sulfates, fatty acid amides,
There are higher alcohols, polyethylene oxide, sulfosuccinic acid, sulfosuccinate, known surfactants and the like, and salts thereof, and use of a salt of a polymer dispersant having a negative organic group (for example, -COOH). Can also. These dispersants may be used alone or in combination of two or more.

As the lubricant, silicone oil, graphite, carbon black graft polymer, molybdenum disulfide, tungsten disulfide, lauric acid, myristic acid, a monobasic fatty acid having 12 to 16 carbon atoms and the number of carbon atoms of the fatty acid Fatty acid esters (so-called waxes) composed of monohydric alcohols having a total of 21 to 23 carbon atoms can also be used. These lubricants are usually added in the range of 0.2 to 20 parts by weight based on 100 parts by weight of the binder.

As abrasives, commonly used materials include fused alumina, various aluminas such as α-alumina, silicon carbide, chromium oxide, corundum, artificial corundum, artificial diamond, garnet, emery (main components: corundum and magnetite)
Etc. are used. These abrasives usually have an average particle size
Those having a size of 0.05 to 5 μm are used, and particularly preferably 0.1 to 2 μm. These abrasives are available in binder 100
It is usually used in the range of 1 to 20 parts by weight with respect to parts by weight.

As the matting agent, an organic powder or an inorganic powder may be used alone or in a mixture.

The organic powder used in the present invention is preferably an acrylic resin, a styrene resin, a benzoguanamine resin, a melamine resin, a powder of a phthalocyanine pigment or the like, but is preferably a polyolefin resin, a polyester resin, a polyamide resin, or a polyimide resin. Resins and powders such as polyfluoroethylene resins can also be used. As inorganic powders, silicon oxide, titanium oxide, aluminum oxide, calcium carbonate,
Barium sulfate, zinc oxide, tin oxide, aluminum oxide,
Chromium oxide, silicon carbide, calcium carbide, α-Fe ₂ O ₃ ,
Examples include powders of talc, kaolin, calcium sulfate, boron nitride, zinc fluoride, molybdenum dioxide, and the like.

Examples of antistatic agents include conductive powders such as carbon black, graphite, tin oxide-antimony oxide compounds, titanium oxide-tin oxide-antimony oxide compounds, natural surfactants such as saponins, alkylene oxides, and glycerin. Nonionic surfactants such as glycidol-based, higher alkylamines, quaternary ammonium salts, pyridine, other heterocycles, cationic surfactants such as phosphonium or sulfonium, carboxylic acid, sulfonic acid, phosphoric acid, sulfuric acid Examples include anionic surfactants containing acidic groups such as esters and phosphates, and amphoteric surfactants such as amino acids, aminosulfonic acids, and sulfuric acid or phosphate esters of amino alcohols.

Examples of the solvent to be blended in the above coating material or a diluting solvent at the time of applying this coating material include ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone;
Alcohols such as methanol, ethanol, propanol and butanol; esters such as methyl acetate, ethyl acetate, butyl acetate, ethyl lactate and ethylene glycol monoacetate; ethers such as glycol dimethyl ether, glycol monoethyl ether, dioxane and tetrahydrofuran; , Toluene and xylene; and halogenated hydrocarbons such as methylene chloride, ethylene chloride, carbon tetrachloride, chloroform and dichlorobenzene.

In the present invention, among the magnetic paints composed of the components described above, especially the magnetic paint for the uppermost layer in the kneader, the actual load of the motor of the kneader is 0.1 kw / kg-magnetic powder or more conditions. Kneading for 5 minutes to 2 hours.

After such treatment, by applying a multi-layer coating by the WOW method, the coatability of the uppermost layer can be improved, and a uniform coating film can be formed.

The processing time at this time is not preferably too short or too long from the viewpoint of the effect, and is usually 5 minutes to 2 minutes.
The time is preferably 10 minutes to 1.5 hours.

As a flexible support to which the magnetic paint is applied, polyethylene terephthalate, polyesters such as polyethylene-2,6-naphthalate, polyolefins such as polypropylene, cellulose triacetate, cellulose derivatives such as cellulose diacetate, polyamides, polycarbonates and the like Plastics.

The thickness of these flexible supports is about 3 to 100 μm, preferably 5 to 50 μm in the case of a film or sheet, and about 30 to 10 mm in the case of a disk or card.

As a coating method for forming the magnetic layer on the support, conventionally, an air doctor coat, a blade coat, an air knife coat, a squeeze coat, an impregnation coat, a reverse roll coat, a transfer roll coat, a gravure coat, a kiss coat, a cast coat , A spray coat, an extrusion coat and the like are used. In the present invention, any method can be used, but it is particularly preferable to employ an extrusion coating method.

According to such a method, the magnetic layer coated on the support is subjected to a treatment for orienting the ferromagnetic particles in the layer if necessary, and then the formed magnetic layer is dried.

In this case, the orientation magnetic field is about 500-5000 AC or DC.
The drying temperature is about 50 to 120 ° C., and the drying time is about 0.1 to 10 minutes.

After drying, the film is usually subjected to a calendering treatment. However, in the magnetic recording medium of the present invention, the coating thickness of the uppermost layer is not preferably made too thick from the viewpoint of the properties and effects of the magnetic recording medium, and is usually 1 μm or less. It is desirable to do.

The magnetic recording medium after the calendar processing is cut into a desired shape.

〔Example〕

Next, the present invention will be described with reference to examples, but it goes without saying that the present invention is not limited to these examples.

Example 1 Kneading Effect <Preparation of Magnetic Coating for Lower Layer> The components for magnetic coating except for the diluting liquid described in Table 1 were charged in a kneading machine, and kneaded with an actual load of 0.3 kwh / kg of magnetic powder for 1.5 hours. The liquid was added, and 5 parts by weight of Coronate L "(manufactured by Nippon Polyurethane Industry Co., Ltd.) was added by a sand mill to prepare a lower layer magnetic paint.

<Preparation of Magnetic Coating for Top Layer> The components for magnetic coating described in Table 2 were charged into a kneading apparatus and kneaded for a predetermined time, and then each of methyl ethyl ketone, cyclohexanone and toluene was added to (100-
X) After the addition by weight, 5 parts by weight of the above-mentioned Coronate L was added to prepare a magnetic coating material for the uppermost layer.

Various values of X were varied to prepare various magnetic paints of the present invention (Examples) and magnetic paints of the present invention (Comparative Examples).

 Table 3 shows the production conditions for these magnetic paints.

Next, for each of the magnetic paints A to F, Table 4 shows the classification of the magnetic paint (Example) of the present invention and the magnetic paint (Comparative Example) outside the present invention when the kneading time was variously changed.

In Table 4, the numbers in parentheses are Comparative Example No., and the Example No. is shown naked. The sections of the present invention are surrounded by dotted lines.

<Application of magnetic paint> The magnetic paint for the lower layer prepared as described above was applied to a thickness of 14 μm.
m on a polyethylene terephthalate support, using an extrusion-type coating head to form a lower layer, and then using another extrusion-type coating head, apply the magnetic coating for the uppermost layer of the above Examples and Comparative Examples. By the WOW method, a multilayer coating was performed on the wet thickness of the lower layer 30 cm ³ / m ² and the uppermost layer 25 cm ³ / m ^{2 at} a coating speed of 200 m / min.

 The dry thickness of the uppermost layer after calendering was 1.0 μm.

The applicability of the uppermost layer was visually evaluated in five stages.

 Table 5 shows the obtained results.

Judgment Criteria Evaluation point 5 has extremely good coating properties, has no problem in production, and has improved electromagnetic characteristics. 3 is the lower limit of the applicability, and 1 is the practically unacceptable level in both the applicability and the properties. 4 and 2 are given an intermediate rating above.

Example 2 Effect of Film Thickness Example 1 A mixture obtained by kneading the lower layer paint and the magnetic paint A for one hour to obtain a wet thickness shown in Table 6 and a WOW method of 200 m / mi.
n was applied in multiple layers.

 The applicability was evaluated on a 5-point scale, and the results are shown in Table 6.

The range surrounded by the dotted line is the defined range of the present invention, and all of the evaluations 5 are given. Deterioration is apparent outside the specified range.

[Effects of the Invention] According to the present invention, when a magnetic recording medium is produced by applying a plurality of magnetic paints on a flexible support in a multi-layered manner by a WOW coating method, the applicability of the uppermost layer is significantly improved. In addition, it is possible to drastically reduce coating failures as conventionally seen.

Claims (3)

(57) [Claims] 1. A method for producing a magnetic recording medium comprising a plurality of magnetic layers successively or simultaneously coated on a running flexible support in a wet state, followed by drying and calendering; (b) paint for a lower magnetic layer a binder, is contained at least urethane resin and suppressing the coating amount to 30 cm ³ / m ² or less, (b) a binder of the uppermost magnetic layer coating material, a vinyl chloride resin having a respective polar groups, the polyurethane resin Containing
When the actual load of the motor applied during kneading is 0.1 kw / kg-magnetic powder or more, kneading is performed for 5 minutes to 2 hours, and the applied amount is 25 cm ³ /
A method for manufacturing a magnetic recording medium, characterized in that the magnetic recording medium is suppressed to m ² or less. 2. The method according to claim 1, wherein the polar group is a negative functional group. 3. The method according to claim 1, wherein the thickness of the uppermost layer is 1 μm after the calendering process.
3. The method for manufacturing a magnetic recording medium according to claim 1, wherein: