JPH03120618A - Production of magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a high-quality coating state of the uppermost layer by incorporating urethane resin as a binder into the coating material for lower magnetic layers, incorporating vinyl chloride resin and urethane resin both containing polar groups as a binder into the coating material for the uppermost magnetic layer, and kneading the coating material for specified time. CONSTITUTION:The recording medium is produced by successively or simultane ously applying coating materials in a wet state on a traveling flexible body to form several magnetic layers, and then drying and calendering the layers. The coating material for a lower magnetic layer contains urethane resin as the binder and is applied by the amt. <=30cm<3>/m<2>. Vinyl chloride resin and polyurethane resin each containing polar groups are incorporated as the binder into the coating material for the uppermost magnetic layer. The coating material is kneaded for 5 minutes to 2 hours under the actual load of >=0.1 kw/kg- magnetic powder on the motor of the kneader, and then applied by the amt. <=25cm<3>/m<2>. By this method, coating property for the uppermost layer is signifi cantly improved and troubles in the coating process can be largely reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a magnetic recording medium, and particularly to a magnetic layer structure.

[Background of the invention]

Magnetic recording has become indispensable for social activities and private life today, and demands for high performance, low cost, and reliable quality are increasing.

The magnetic recording layer of magnetic tape, which has the most widespread demand, can be made by coating a support with magnetic paint in which magnetic powder is suspended in a binder solution, by vapor deposition of magnetic material without using a binder, by sputtering, etc. Although there are a so-called thin film type that is densely deposited on a support and a plating type that is laminated by plating, the coating type is the mainstream because of its high degree of technological integration, technical reliability, and cost.

Coating-type magnetic recording media are usually made by coating a moving support with a magnetic coating containing ferromagnetic powder and various additives as necessary in a binder solvent solution, and then drying the coating. , followed by calendering.

In recent years, there has been an increasing demand for higher densities in magnetic recording media, and in particular, for videotapes, with the demand for higher recording frequencies, it has become necessary to perform extremely high-density recording. Various types of laminated magnetic layer structures have been proposed in which two or three or more layers consisting of an upper layer and a lower layer are coated on a support.

Conventionally, methods such as roll coating, gravure coating, and extrusion coating have been commonly used to apply the magnetic paint in multiple layers. Wet on Dry
Wet on Wet (WOD) method is a method in which the next layer is applied sequentially or simultaneously on top of the undried wet layer, which is called Wet on Wet (WOW). The multilayer coating method is superior.

Prior art regarding multilayer coating includes, for example, Japanese Patent Application Laid-open No. 6
No. 3-164022, No. 63-164023, No. 62
-214524, 62-124631, 62-
Examples include techniques described in Japanese Patent Publication No. 92132 and Japanese Patent Publication No. 57-'17291.

In addition, prior art related to the equipment process of the coating method for magnetic recording media is disclosed in Japanese Patent Application Laid-open No. 63-164022 and No. 63-164022.
-164023, No. 62-124631, etc.

However, these techniques cannot be said to be good in terms of the coatability of the magnetic paint for multilayer coating.

When an extrusion coater is used to apply a magnetic paint onto a 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.

Regarding this point, JP-A-62-214524 discloses the mutual solubility of a solvent and a binder, but in this technology, the relationship between the uppermost layer magnetic paint and the lower layer magnetic paint is clearly defined. However, especially when the uppermost layer is a magnetic layer, the above-mentioned degree of dispersion is important but unclear.

In addition, in multilayer coating using the conventional WOW method, the coating condition of the top layer fluctuates due to uneven tension, fluctuations, and other fluctuations in the tape-shaped flexible support, making it difficult to coat the top layer with uniform coating quality. In particular, various coating failures such as failure to change the thin top layer have become a problem.

In particular, if the magnetic particles are small (for example, the major axis length is 0.1
This tendency is remarkable when the thickness of the top layer becomes as thin as 1.0 μm or less after calendering.

[Purpose of the invention]

In view of these circumstances, an object of the present invention is to provide a magnetic recording medium in which the coating quality of the magnetic layer, especially the top layer, is good when a plurality of magnetic paints are coated sequentially or simultaneously in layers on a moving support using the WOW method. The purpose of this invention is to provide a method for manufacturing the same.

(Structure and Effects of the Invention) The object of the present invention described above is to provide a magnetic recording medium in which a plurality of magnetic layers are coated sequentially or simultaneously in a wet state on a moving flexible support, dried, and calendered. (a) The binder of the lower magnetic layer coating should contain at least urethane resin, and the coating amount should be 30 cm
(b) The binder of the uppermost magnetic layer paint contains a vinyl chloride resin and a polyurethane resin each having a polar group,
Magnetic recording characterized in that the actual load applied to the kneading machine motor is 0.1 KW/, 9-magnetic powder or more is kneaded for 5 minutes to 2 hours, and the amount of application is suppressed to 25 cm"/m" or less. This is achieved by the method of manufacturing the media.

Note that the actual load in this case is the value obtained by subtracting the current value when the kneader is not loaded from the current value during kneading.

In the embodiment of the present invention, the polar groups of the vinyl chloride and urethane resins are preferably negative functional groups, and the thickness of the top layer after calendering is determined by adjusting the evaporated component ratio of the top magnetic layer paint and by calendering. Application amount 25cm+ by adjusting the pressure
It is preferable to set the dry thickness to 1 μm or less by setting the dry thickness to 1 μm or less.

Further, to explain the present invention, examples of magnetic materials used in the present invention include γ-Fez03 and G.

SS type γ containing as a solid solution Fe, O, or G
The core/shell (c/s) deposited with o as the shell is γ
-F+I! Oxide magnetic materials such as ZOS, Fe50 and Crow; Others, such as Fe1Nls Fe-Ni alloy,
Fe-Co alloy, Fe-N'i-P alloy, Fe-Ni-
Co alloy, Fe-IJn-Zn alloy, Fe-Ni-Zn
alloy, Fe-Go-Ni-Cr alloy, Fe-Go-Ni
-Fe of P alloy, Co-P alloy, Go-Cr alloy, etc.
Examples include various ferromagnetic materials (powders) such as metal magnetic powders containing Ni and Co as main components.

As an additive to these metal magnetic materials, 5i1Cu
%Zn1AQ, PlMn, Cr, or other elements or compounds thereof may be included.

Furthermore, various natural or synthetic resins have been proposed as binders for use in the magnetic layer of magnetic recording media, and polyurethane resins are preferred.

The polyurethane resin according to the present invention has strong adhesion to other substances, is mechanically strong to withstand repeated stress or bending, and has good abrasion resistance and weather resistance.

In addition to the polyurethane resin, a vinyl chloride copolymer is also used in combination to improve the dispersibility of the magnetic powder in the magnetic layer and increase its mechanical strength.

However, if the vinyl chloride copolymer alone is used, the layer becomes too hard, 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. Preferable examples of the vinyl chloride copolymer include a copolymer containing vinyl chloride-vinyl acetate or a copolymer containing vinyl chloride-vinyl acetate-vinyl alcohol.

Furthermore, modified resins obtained by adding polar groups, such as negative functional groups, to polyurethane, vinyl chloride homopolymers, vinyl chloride-vinyl acetate copolymers, etc., in order to improve dispersibility and physical properties, are It is particularly suitable for use as a binder for magnetic recording media. 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, such as a copolymer of vinyl chloride and vinyl acetate. Refers to a resin made by introducing polar groups into. Such resins include, for example, vinyl chloride homopolymers, vinyl chloride-vinyl acetate copolymers, and C(2-CH,CHffSO,M, CI2-CH205
03M, C12-H, C00M or OM.

CQ-CH2-P=O (Ml and M2 are each OM.

Hail alkali metals like lithium, sodium, and potassium. ), etc., can be easily obtained by condensing a compound containing a negative functional group and chlorine in the molecule through a dehydrochloric acid reaction.

Furthermore, the polyurethane resin having a polar group is a resin obtained by introducing a polar group into a polyurethane resin, and as in the case of the above-mentioned vinyl chloride resin having a polar group, for example, polyurethane resin and Cf2-CH2CF12S03
M%C(2-CH20SOsM1G+2-CHxCOO
M or P=CQ-CH,-P=O (where Ml and M2 are
Each is OM.

Hail alkali metals like thium, sodium, and potassium. It can be easily obtained by condensing a compound containing a negative functional group and chlorine in the molecule with a dehydrochloric acid reaction, such as chlorine.

Typical polar groups in such condensates include, for example, sulfonic acid groups and carboxyl groups, but are not limited to these.

As long as the effects of the present invention are not impaired, the lower layer and the uppermost layer may contain various commonly used resins 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, the magnetic paint can contain various hardening agents such as incyanate.

Examples of aromatic incyanates include tolylene diisocyanate (TDI) and adducts of these isocyanates with active hydrogen compounds, and the preferred average molecular weight is usually in the range of 100 to 3,000. It is.

Examples of aliphatic incyanates include hexamethylene diisocyanate (HMDI) 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. Among the aliphatic incynates, non-alicyclic incynates and adducts of these compounds with active hydrogen compounds are preferred.

The magnetic paint used to form the magnetic layer contains a dispersant,
Further, additives such as a lubricant, an abrasive, a matting agent, and an antistatic agent may be included as necessary.

Dispersants used in the present invention include phosphoric acid esters, amine compounds, alkyl sulfates, fatty acid amides, higher alcohols, polyethylene oxides, sulfosuccinic acids, sulfosuccinic esters, known surfactants, and salts thereof. , and also a negative organic group (e.g. -〇〇OH)
It is also possible to use salts of polymeric dispersants having . These dispersants may be used alone or in combination of two or more.

In addition, as lubricants, silicone oil, graphite, carbon black graft polymer molybdenum disulfide, tungsten disulfide, lauric acid, myristic acid,
Fatty acid esters (so-called waxes) consisting of a monobasic fatty acid having 12 to 16 carbon atoms and a monohydric alcohol having 21 to 23 carbon atoms in total can also be used. These lubricants are usually added in an amount of 0.2 to 20 parts by weight per 100 parts by weight of the binder.

As the abrasive, commonly used materials include fused alumina, various aluminas such as a-alumina, silicon carbide, chromium oxide, corundum, artificial corantum, artificial diamond,
Garnet, emery (main ingredients: corundum and magnetite), etc. are used. These abrasives usually have an average particle size of 0.
A size of 0.05 to 5 μm is used, particularly preferably 0.1 to 2 μm. These abrasives are generally used in an amount of 1 to 20 parts by weight based on 100 parts by weight of the binder.

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

The organic powder used in the present invention is preferably powder of acrylic resin, styrene resin, benzoguanamine resin, melamine resin, phthalocyanine pigment, etc., but powder of polyolefin resin, polyester resin, polyamide resin, polyimide resin, etc. is preferable. Powders such as resins and polyfluoroethylene resins can also be used, and inorganic powders include silicon oxide, titanium oxide, aluminum oxide, calcium carbonate, barium sulfate, zinc oxide, tin oxide, aluminum oxide, chromium oxide, silicon carbide, Calcium carbide, a-Fe, O,
, talc, kaolin, calcium sulfate, boron nitride, zinc fluoride, molybdenum dioxide, and other powders.

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

Solvents to be added to the above paint or diluting solvents during application of this paint include ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; alcohol a such as methanol, ethanol, propatool, and butanol; 8-methyl vinegar , ethyl acetate, butyl acetate, ethyl lactate, ethylene glycol monoacetate, and other esters; glycol dimethyl ether, glycol monoethyl ether, dioxane, tetrahydro-7rane, and other ethers; benzene, toluene, xylene, and other aromatic hydrocarbons ; Halogenated hydrocarbons such as methylene chloride, ethylene chloride, carbon tetrachloride, chloroform, and dichlorobenzene can be used.

In the present invention, among the magnetic paints composed of the above-mentioned components, the magnetic paint for the top layer in particular is placed in a kneading machine, and the actual load of the motor of the kneading machine is Q, 1Kw/Kg-
The mixture is kneaded for 5 minutes to 2 hours under conditions higher than those for magnetic powder.

By performing multilayer coating using the WOW method after such treatment, the coating properties of the uppermost layer can be improved and a homogeneous coating film can be formed.

Even if the processing time in this case is too short from the point of view of effectiveness,
Further, it is not preferable if the time is too long, and it is usually 5 minutes to 2 hours, and particularly preferably 10 minutes to 1.5 hours.

The flexible support to which the magnetic paint is applied includes polyesters such as polyethylene terephthalate and polyethylene-2,6-naphthalate, polyolefins such as polypropylene, cellulose derivatives such as cellulose triacetate and cellulose diacetate, polyamide, polycarbonate, etc. One example is plastic.

The thickness of these flexible supports is about 3 to 1100 P in the case of a film or sheet, preferably 5 to 50 μm, and about 30 μm to 10 μm in the case of a disk or card.

Conventional coating methods for forming the magnetic layer on the support include air knife coating, blade coating, air knife coating, squeeze coating, impregnation coating, reverse roll coating, transfer roll coating, Tarabia coating, kiss coating, and cast coating. , spray coat, extrusion coat, etc. are used. Although any method can be used in the present invention, it is particularly preferable to employ the extrusion coating method.

By such a method, the magnetic layer coated on the support is optionally treated to orient the ferromagnetic particles in the layer, and then the formed magnetic layer is dried.

In this case, the orientation magnetic field is approximately 500 to 50° with alternating current or direct current.
oo Gauss, and the drying temperature is approximately 50-1200C
The drying time is approximately 0.1 to 10 minutes.

After drying, calendering is usually performed, but in the magnetic recording medium of the present invention, it is not preferable to make the top layer coating too thick in terms of the characteristics and effects of the magnetic recording medium, and it is usually 1 μm or less. It is desirable to do so.

After calendering, the magnetic recording medium is cut into a desired shape.

〔Example〕

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

Example 1: Adjustment of magnetic paint for lower layer with kneading effect> The components for magnetic paint other than the diluent listed in Table 1 were charged into a kneader, and the strength of the magnetic powder was 1 at an actual load of 0.3 Kwh/Kg.
．． The mixture was kneaded for 5 hours, a diluent was added, and 5 parts by weight of Coronate L'' (manufactured by F1 Polyurethane Industry Co., Ltd.) was added using a sand mill to prepare a magnetic paint for the lower layer.

Table 1 <Magnetic paint for lower layer> Adjusted the paint.

Magnetic paint of the present invention (Examples) by varying the value of X
Various magnetic paints (comparative examples) other than those of the present invention were also prepared.

Table 3 shows the manufacturing conditions for these magnetic paints.

Table 2 <Magnetic paint for the top layer> Preparation of the magnetic paint for the top layer> The components for the magnetic paint listed in Table 2 were charged into a kneading device and kneaded for a predetermined time, and then methyl ethyl ketone, cyclohexanone, and toluene were added to each of the components. (100-x
) After adding 5 parts by weight of Coronate L, magnetic for the top layer Table 3 <Manufacturing conditions of magnetic paint for the top layer> Table 4 <Categories of Example ゛ and Comparative Example 7> ☆ Above table The actual current consumption value is the difference between the value during kneading and the current consumption during no-load.

Next, Table 4 shows the classification of the magnetic paints of the present invention (example) and the magnetic paints other than the present invention (comparative examples) when the kneading time was varied for each of the magnetic paints A to F.

In Table 4, the numbers in parentheses are comparative example numbers.

, and Example No. is shown naked. Application of the magnetic paint according to the present invention> The magnetic paint for the lower layer prepared as described above was applied to a thickness of 14 mm.
The magnetic paint for the uppermost layer of the above Examples and Comparative Examples was coated onto a μm polyethylene terephthalate support using an extrusion type coating head to form a lower layer, and then coated using another F-Buntruzimin type coating head. WO
By W method, bottom layer 30am'/m", top layer 25cm
Multi-layer coating was carried out to a wet thickness of "/m" at a coating speed of 200 m/min.

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

The coatability of the top layer was visually judged on a five-point scale.

The results obtained are shown in Table 5.

The range surrounded by the dotted line is the defined range of the present invention, and is given a rating of 5 for all. And deterioration is obvious outside the specified range.

Judgment Criteria Evaluation score 5 means that the coating properties are extremely good and there are no problems with production.
Electromagnetic properties are also improved. 3 is the lower limit of allowable applicability, and l
Both coating properties and properties are at a level that is unacceptable for practical use.

4 and 2 are given intermediate evaluations.

Example 2 Film thickness effect Example 1 Lower layer paint and magnetic paint A were kneaded for 1 hour and then mixed with WOW method 200 to the wet thickness shown in Table 6.
Multilayer coating was performed at m/min.

The coating properties were evaluated on the above five scales and are also listed in Table 6.

〔Effect of the invention〕

According to the present invention, when manufacturing a magnetic recording medium by coating a plurality of magnetic paints in multiple layers on a flexible support using the WOW coating method, the coating properties of the top layer are significantly improved, unlike conventional coatings. Application failures can be drastically reduced.

Claims (3)

[Claims] (1) In the production of magnetic recording media in which multiple magnetic layers are coated sequentially or simultaneously in a wet state on a moving flexible support, dried and calendered; (a) Binder for paint of lower magnetic layer; contains at least urethane resin, and the coating amount is 30cm^3/m
(b) The binder of the uppermost magnetic layer paint contains a vinyl chloride resin and a polyurethane resin each having a polar group,
A magnetic product characterized in that the actual load applied to the motor during kneading is 0.1 Kw/Kg or more, and the kneading is performed for 5 minutes to 2 hours with magnetic powder or more, and the amount of application is suppressed to 25 cm^3/m^2 or less. A method for manufacturing a recording medium. (2) The method for manufacturing a magnetic recording medium according to claim 1, wherein the polar group is a negative functional group. (3) The method for manufacturing a magnetic recording medium according to claim 1, wherein the thickness of the uppermost layer is 1 μm or less after calendering.