JPH0740348B2 - Magnetic recording medium - Google Patents

Description

TECHNICAL FIELD The present invention relates to an improved magnetic recording medium, and more particularly to a magnetic recording medium excellent in dispersibility, thermal stability and durability.

(Prior Art) A magnetic recording medium such as a magnetic tape or a magnetic card is generally manufactured by coating a base material such as a polyester film with a magnetic paint containing a magnetic powder and a binder thereof as a magnetic layer. In recent years, in order to increase the coercive force and the maximum saturation magnetization, and improve the SN ratio and recording density, finely divided magnetic powder having a large specific surface area has been used as the above magnetic powder.

However, as a binder for such fine magnetic powder,
Vinyl chloride-vinyl acetate-vinyl alcohol copolymer resin, vinyl chloride-vinyl acetate-maleic acid copolymer resin,
When a magnetic paint is prepared using a vinyl chloride-based copolymer resin such as a vinyl chloride-vinyl acetate-maleic acid-vinyl alcohol copolymer resin, there are problems that the paint thickens and the dispersibility is insufficient.

For this reason, as a method of improving the dispersibility of magnetic powder, a method of applying high shearing force at the time of dispersion has been adopted. There is a drawback that it induces decomposition, deteriorates the magnetic powder due to hydrogen chloride gas, reduces the durability of the magnetic recording medium, and impairs reliability.

On the other hand, there is a method of adding a so-called stabilizer for vinyl chloride resin to a well-known method as a method for preventing thermal decomposition of vinyl chloride copolymer resin. Typical examples of these are a method of adding a low molecular weight epoxy compound such as epoxidized soybean oil or n-butyl glycidyl ether, or a method of adding a liquid organic tin compound such as dibutyltin laurate or dibutyltin malate. is there.

However, when a large amount of low molecular weight epoxy compound is present in the magnetic recording medium, the bleeding phenomenon occurs from the magnetic recording medium, the durability is deteriorated, and the head is soiled. Is limited. Also, when an organotin compound is added, this organotin compound serves as a catalyst for the crosslinking reaction of the isocyanate compound generally added to the binder, so the pot life of the magnetic paint becomes extremely short, and the paint stability is improved. As a result, the viscosity is greatly increased during coating, the dispersibility is lowered, and the surface smoothness of the magnetic layer is impaired.

On the other hand, in response to higher recording density and higher S / N of magnetic recording media, a magnetic tape having a magnetic layer with a smooth surface obtained by highly dispersing magnetic powders that have been made finer and have higher coercive force. Is
The frictional resistance between the head guide and the tape increases, which causes a problem that the tape travels poorly.

In order to solve these problems, it has been conventionally practiced to add lubricants typified by silicone oil, fluororesins, fatty acids or ethers, esters, amides and fluorides thereof, and fine particles such as carbon black and alumina into the magnetic layer. Has been done more. However, the former lubricant is
Problems such as bleeding after standing for a long time, instability of magnetic coating dispersion, and non-uniformity of the magnetic layer after coating are likely to occur, leading to deterioration of tape storage stability and electromagnetic conversion characteristics. There is danger. In particular, when perfluoroalkylsulfonic acid or carboxylic acid is used as the solvent, the strength of the acid may cause the magnetic coating to become unstable, attack the magnetic layer, or stain the head or guide. . It is also introduced that these lubricants are used as one component of the back coat paint, but the same problem occurs due to the bleeding phenomenon after standing for a long time. On the other hand, the latter fine particles, as a result, reduce the filling property of the magnetic powder in the magnetic layer, so that the use of a large amount is naturally limited.

(Problems to be Solved by the Invention) The inventor of the present invention prevents thermal decomposition of a vinyl chloride-based copolymer resin that occurs during the production of such a high-density magnetic recording medium, and thus reduces the durability of the high-density magnetic recording medium. As a result of intensive research to solve the drawbacks such as, and to achieve both excellent surface property and running property, a vinyl chloride resin and an epoxy group-containing resin are used as the binder of the magnetic powder, and a specific acid compound It was found that a high density magnetic recording medium excellent in thermal stability at the time of preparing a coating, and excellent in durability and running property can be obtained by combining the above, and thus completed the present invention.

(Means for Solving Problems) Thus, according to the present invention, a magnetic layer containing a vinyl chloride resin, an epoxy group-containing resin, and a carboxylic acid compound or a sulfonic acid compound having a perfluoroalkyl group is provided. A magnetic recording medium is provided.

The vinyl chloride resin used in the present invention is a vinyl chloride homopolymer or a copolymer of vinyl chloride and another monomer, and a reaction product thereafter. Examples of other monomers include vinyl acetate, vinyl propionate, and other carboxylic acid vinyl esters; methyl vinyl ether, isobutyl vinyl ether, cetyl vinyl ether, and other vinyl ethers; vinylidene chloride, vinylidene fluoride, and other vinylidene; diethyl maleate, malein. Butylbenzyl acidate,
Unsaturated carvone such as maleic acid-di-2-hydroxyethyl, dimethyl itaconate, methyl (meth) acrylate, ethyl (meth) acrylate, lauryl (meth) acrylate, and 2-hydroxypropyl (meth) acrylate. Acid esters; olefins such as ethylene and propylene;
Unsaturated nitriles such as (meth) acrylonitrile; aromatic vinyls such as styrene, α-methylstyrene, p-methylstyrene and the like. These monomers are used to improve the compatibility between the resin of the present invention and other resins when mixed with each other, control the softening point of the resin, improve the solubility of the resin, the characteristics of the coating film and the coating process. Is appropriately selected according to the need for improvement of

As the vinyl chloride resin, one having a hydrophilic group introduced for the purpose of improving the dispersibility of the magnetic powder is more suitable as the binder. The hydrophilic group used is COOM, S
O ₃ M, SO ₄ M, PO ₃ M ₂ and PO ₄ M ₂ (M is hydrogen, alkali metal or ammonium) and the like can be mentioned.

The proportion of vinyl chloride in vinyl chloride resin is usually 20% by weight
The above is preferably 50 to 95% by weight. If it is less than this ratio, the physical properties of the resin are deteriorated, the coating film strength is weak, and it cannot be used as a binder. The average degree of polymerization of this resin is preferably 100 to 1000. When it is less than 100, the coating strength and thermal stability of the magnetic layer are poor, and when it exceeds 1000, the dispersibility of the magnetic powder and the solubility of the resin decrease.

Examples of the epoxy group-containing resin in the present invention include epoxy group-containing polyurethane resin, epoxy group-containing polyester resin, epoxy group-containing acrylonitrile-butadiene copolymer resin and epoxy resin.

Epoxy group-containing polyurethane resin has a molecular weight of 1,000-20
The one of 0,000 is used. When the molecular weight is less than 1,000, the durability of the coating film is insufficient, and when it exceeds 200,000, the viscosity of the coating becomes too high, which causes a practical problem. The epoxy-modified polyurethane resin is an epoxy polyol obtained by amine-modifying an epoxy resin or an epoxy resin having a bifunctional or higher hydroxyl group per molecule, for example, bisphenol A.
Group, an epoxy group-containing polyester obtained by reacting an epoxy resin of a halogenated bisphenol type, a resorcin type, a bisphenol F type with a dibasic acid such as adipic acid, phthalic acid, dimerized linoleic acid, maleic acid, etc., Further, it can be synthesized by reacting a polyfunctional isocyanate with an epoxy group-containing polyester resin described later. Alternatively, an epoxidizing agent such as a percarboxylic acid is allowed to act on a polyurethane resin synthesized from an unsaturated polyester resin obtained by the reaction of an unsaturated fatty acid such as maleic acid, fumaric acid or itaconic acid with a polyhydric alcohol. It can also be synthesized.

Epoxy group-containing polyester resin has a molecular weight of 1.000 to 2
The one of 00,000 is used. If the molecular weight is less than 1,000,
The durability of the coating film is insufficient, and if it exceeds 200,000, the viscosity of the coating material becomes too high, which causes practical problems. Epoxy group-containing polyester resins include unsaturated dibasic acids such as maleic acid, fumaric acid and itaconic acid or saturated dibasic acids such as phthalic acid, adipic acid and terephthalic acid, and 1,4-butanediol and 1,5-pentane. Epoxidation of unsaturated polyester resin obtained by heat condensation with polyols such as diol, 1,6-hexanediol, 1,10-decanediol, and butadiene oligomer having hydroxyl groups at both ends with an epoxidizing agent such as percarboxylic acid Obtained by
Incidentally, instead of the unsaturated polyester resin, even if a modified unsaturated polyester resin obtained by melt-mixing this with a polycarbonate resin or a saturated polyester resin in the presence of a catalyst, and carrying out an ester conversion reaction is used as a starting material. Good.

The epoxy group-containing acrylonitrile-butadiene copolymer resin generally has an acrylonitrile content of 12
-50 to 50% by weight and molecular weight of 5,000 to 500,000 are used. When the content of acrylonitrile is less than 12%, compatibility with polyvinyl chloride generally used in magnetic recording media and other binders such as nitrocellulose is poor, and when it is more than 50% by weight, solvent solubility is reduced, resulting in magnetic powder. Greatly disperses the dispersibility of. When the molecular weight is less than 5,000, the durability of the coating film is low, and when it is more than 500,000, the viscosity of the coating is too high to be practical. The epoxy group-containing acrylonitrile-butadiene resin is a copolymer of acrylonitrile and butadiene, a radical copolymerizable monomer containing an epoxy group, and optionally other copolymerizable monomer in the presence of a radical generator. Obtained. It can also be obtained by partially epoxidizing the double bond in the acrylonitrile-butadiene resin using an epoxidizing agent such as percarboxylic acid.

The epoxy resin used in the present invention has a molecular weight of 50.
Those of 0 to 200,000 are used. When the molecular weight is less than 500, the durability of the coating film is low, and unreacted may bleed to the surface of the magnetic layer, making it difficult to use. When it exceeds 200,000, the viscosity of the coating is too high to be practical. Specific examples of the epoxy resin include bisphenol A-epichlorohydrin type, those using halogenated bisphenol, resorcin, bisphenol F, tetrahydroxyphenylethane and the like in place of the bisphenol A, and novolak type epoxy resin. To be

Incidentally, the epoxy group-containing resin in the present invention, CO in the resin having an epoxy group for the purpose of improving the dispersibility of the magnetic powder.
It may contain functional groups such as OM, SO ₃ M, SO ₄ M, PO ₃ M ₂ and PO ₄ M ₂ (M is hydrogen, alkali metal, ammonium).

In order to achieve the effect of the present invention, the ratio of the epoxy group-containing resin is preferably in the range of 5 to 70% by weight based on the total amount of the vinyl chloride resin, and the weight ratio of the epoxy group is
It is required to be 0.1% by weight or more based on the vinyl chloride resin.

Examples of the carboxylic acid compound having a perfluoroalkyl group in the present invention include perfluorododecanoic acid [CF
₃ (CF ₂ ) ₁₀ COOH], perfluorooctanoic acid (CF ₃ (CF ₂ ) ₆ C
OOH], perfluoropropionic acid [C ₂ F ₅ COOH] and other perfluoroalkylcarboxylic acids, perfluorooctylhydromethylenecarboxylic acid [CF ₃ (CF ₂ ) ₇ CH ₂ COOH] and other perfluoroalkylhydroalkylcarboxylic acids , Ω-monohydroper-fluoroundecanoic acid, etc.
-Monohydroperfluoroalkylcarboxylic acid, made from perfluoro-1,2-epoxypropane And carboxylic acids having a perfluoroalkyl polyether such as Examples of the sulfonic acid compound having a perfluoroalkyl group include perfluoroalkyl sulfonic acids such as perfluorooctyl sulfonic acid [CF ₃ (CF ₂ ) ₇ SO ₃ H], perfluorodiisopropylpropenyl phenyl ether sulfonic acid [C ₉ F ₁₇ O (C ₆ H ₄ )
Made from perfluoroalkenyl (alkyl) aryl ether sulfonic acids, such as SO ₃ H], perfluoro-1,2-epoxypropane Sulfonic acids having perfluoroalkyl polyethers such as

The amount of the carboxylic acid compound or sulfonic acid compound having a perfluoroalkyl group is preferably an amount containing a chemical equivalent of 0.05 to 3.00 times the chemical equivalent of the acid of the epoxy group in the epoxy group-containing resin. If it is less than 0.05 times the chemical equivalent, it is difficult to improve the durability of the magnetic layer, which is the object of the present invention.
If it exceeds twice the chemical equivalent, the dispersibility of the magnetic powder is lowered and the durability is also lowered.

In the present invention, as the binder, in addition to the vinyl chloride resin and the epoxy group-containing resin, a conventional flexible resin such as a known polyurethane resin, polyester resin, acrylonitrile-butadiene copolymer resin, etc. is provided with improved adhesion and durability. It may be contained for the purpose of. In addition, these flexible resins are used in order to improve the dispersibility of the magnetic powder.
O ₃ M, SO ₄ M, PO ₃ M ₂ , PO ₄ M ₂ (M is hydrogen, alkali metal,
It may contain a functional group such as ammonium).

Magnetic powder that can be used in the present invention, Fe, Co, Fe alloy system,
Co-containing γ-Fe ₂ O ₃ system, Co-containing Fe ₃ O ₄ system, γ-Fe ₂ O ₃ system, Fe ₃
Any powder such as O ₄ system or barium-ferrite system may be used.

Also, if necessary, ordinary materials such as lubricants, dispersants, antistatic agents and abrasives, and ordinary magnetic paint resins such as phenoxy resin, fibrin resin, amino resin, butyral resin and acrylic resin can be used. It can also be used within a range that does not impair the achievement of the object of the invention. Furthermore, there is no problem even if a commonly used polyisocyanate compound is added within the usual range and the crosslinking reaction due to the isocyanate reaction is also carried out.

The vinyl chloride resin, the epoxy group-containing resin, the carboxylic acid compound or the sulfonic acid compound, the magnetic powder and the above-mentioned desired components in the present invention are appropriately mixed to obtain a magnetic coating material as an arbitrary organic solvent dispersion liquid. This coating material is applied as a magnetic layer to a substrate such as a polyester film by a conventional method by any means such as blade coating, bar coding, gravure roll coating or roll coating, and dried to form a magnetic layer, thereby forming a magnetic layer of the present invention. A recording medium is obtained.

(Effects of the Invention) Thus, according to the present invention, it is possible to obtain a magnetic recording medium which is superior in thermal stability, dispersibility, durability and running property as compared with the prior art.

Incidentally, the improvement of the thermal stability in the present invention is to prevent the generation of hydrogen chloride due to the thermal decomposition of the vinyl chloride-based resin by the epoxy group in the molecular chain of the epoxy group-containing resin to prevent the chain reaction of the decomposition. Estimated to be achieved.
According to the present invention, a conventionally known compound,
Compared with the method of adding a low molecular weight compound such as epoxidized soybean oil, there are no problems such as head stains due to bleeding on the magnetic layer surface and deterioration of tape running property due to increased adhesiveness of the tape. The improvement effect can be exhibited.

Further, according to the present invention, in each step of dispersion, coating, surface molding, and crosslinking curing of the magnetic paint, both components of the epoxy group-containing resin and the carboxylic acid compound or sulfonic acid compound having perfluoroalkyl react with each other to lubricate. Since the perfluoroalkyl group having performance is fixed to the resin in the magnetic layer and on the surface, it is considered that the running property, abrasion resistance and durability are also improved.

In addition, a coating film using a vinyl chloride resin, an epoxy-containing resin, and a carboxylic acid compound or sulfonic acid compound having a perfluoroalkyl group as a binder, which is used in the present invention, is intended to improve the running property of a magnetic recording medium. It is also effective as a back coating film.

(Example) Hereinafter, the present invention will be described more specifically with reference to Examples. The parts and% in the examples and reference examples are based on weight unless otherwise specified.

Reference Example 1 4,4′-diphenylmethane diisocyanate was added to an epoxy polyol obtained by amine-modifying a bisphenol A type epoxy resin and heated to obtain an epoxy group-containing polyurethane resin having a molecular weight of about 17,000 and an epoxy group content of 10%. Obtained.

Reference Example 2 Unsaturated polyester resin obtained by heating and condensing maleic anhydride, mixed phthalic acid, and 1,4-butanediol as raw materials was epoxidized with peracetic acid in toluene to give a molecular weight.
An epoxy group-containing polyester resin having 9,000 epoxy groups and 6% was obtained.

Reference Example 3 Acrylonitrile-butadiene copolymer resin having an acrylonitrile content of 30% and an average molecular weight of 30,000 was partially epoxidized with peracetic acid to obtain an epoxy group-containing acrylonitrile-butadiene copolymer resin having an epoxy group content of 8%. .

Example (Thermal stability test) 1 g of vinyl chloride resin shown in the table and 1 g of epoxy group-containing resin shown in the table were taken, dissolved in tetrahydrofuran, and 0.2 g of the acid compound shown in the table and polyisocyanate (Japan Polyurethane Industry ( After adding 0.4 g of Coronate L) manufactured by K.K. Co., Ltd., coating was carried out with a doctor blade and the solvent was volatilized to prepare a cast film. Take 1 g of this cast film in a 15 cc test tube, plug the opening with absorbent cotton sandwiched with Congo red paper, put it in an oil bath at 150 ° C, until the Congo red test paper discolors due to the generated hydrochloric acid. The time was measured to evaluate the thermal stability.

(Glossiness test) 400 parts of cobalt-coated magnetic iron oxide powder, 70 parts of vinyl chloride resin shown in the table, 30 parts of the same epoxy group-containing resin used in the thermal stability test, 8 parts of acid compound shown in the table, methyl ethyl ketone 300 parts, methyl isobutyl ketone 300 parts, toluene 300
A mixture consisting of 10 parts was subjected to high-speed shear dispersion for 90 minutes, 20 parts of the same polyisocyanate as used in the thermal stability test was added, and mixed for 10 minutes to prepare a magnetic paint. The obtained magnetic coating material was applied onto a polyester film so that the coating film thickness would be 5 μm, subjected to magnetic field orientation treatment, and then dried. The reflectance of the magnetic coating film at a 60 ° reflection angle was measured using a gloss meter. The larger the value, the better the dispersibility of the magnetic powder.

(Durability Test) The magnetic coating film used in the gloss test was smoothed with a calendar roll, and then cross-linked and cured in a constant temperature bath at 65 ° C. for 40 hours. This magnetic coating was brought into contact with a 40 mm diameter rotary drum with a sandpaper attached under a load of 100 g and rotated at 150 rpm for a predetermined time, after which the degree of dirt adhered to the sandpaper was evaluated.
(No dirt) Δ (somewhat dirty) × (severe dirt)

(Running test) The magnetic coating used in the gloss test was smoothed and cross-linked in the same way as in the durability test, and the sample was brought into contact with a hard chrome-plated mirror surface rotating drum, and between the drum and the sample. The force generated was measured with a U gauge in an atmosphere of 65 ° C. and 80% relative humidity, and the running resistance was displayed in the following three stages.

○: Small resistance △: Medium resistance ×: Large resistance (bleeding test) The magnetic coating used in the gloss test was brought into contact with an aluminum plate, and left in a constant temperature and humidity chamber at 45 ° C × 95% RH for 7 days. The change of the surface of the aluminum plate which was in contact with the surface of the magnetic coating film was evaluated by ◯ (no change) and X (change).

The above test results are shown in the table.

As is apparent from the table, according to the present invention, a magnetic recording medium having excellent characteristics shown in the table can be obtained.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location G11B 5/708 8721-5D

Claims (1)

[Claims] 1. A magnetic recording medium having a magnetic layer containing a vinyl chloride resin, an epoxy group-containing resin, and a carboxylic acid compound or sulfonic acid compound having a perfluoroalkyl group.