JPH0740349B2 - Magnetic recording medium - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a magnetic recording medium having a magnetic layer coated on a base fabric, and more specifically, fine magnetic powder is well dispersed and oriented. The present invention relates to a coating type magnetic recording medium having a magnetic layer and having excellent magnetic properties and durability.

(Prior Art) A magnetic recording medium such as a magnetic tape or a magnetic card is generally manufactured by applying a magnetic paint containing a magnetic powder and a binder thereof as a magnetic layer on a substrate such as a polyester film. In order to increase the coercive force and the maximum saturation magnetization, and to improve the SN ratio and recording density, fine magnetic powders with large coercive force and large specific surface area have been used as the above magnetic powders. Came.

However, such fine magnetic powder is a vinyl chloride-vinyl acetate-vinyl alcohol terpolymer, vinyl chloride-
When a magnetic coating material is prepared with an ordinary binder such as a vinyl acetate-maleic acid terpolymer or nitrocellulose, the coating material has a problem in that it thickens and the dispersibility is still insufficient. A low molecular weight surfactant is used as a dispersant for improving dispersibility. However, if a large amount of these dispersants is used, durability of the magnetic recording medium, head stains, etc. may occur. There are naturally limits.

On the other hand, in order to improve the durability and reliability of the magnetic recording medium,
Flexible materials such as polyurethane resin, polyester resin, acrylonitrile-butadiene rubber, etc. are used together as a binder component, and a crosslinking agent that reacts with some or all of these binders to form a crosslinking bond is added to the magnetic coating material to make it magnetic. It is common practice to form a cross-linked coating on a layer, especially in a magnetic recording tape for recording. Therefore, it is required for the binder to have appropriate reactivity with the crosslinking agent.

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. 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 present inventor has conducted diligent studies to develop a binder capable of improving the performance of such a magnetic recording medium. As a result, the use of a specific hydroxyl group-containing resin results in high dispersibility. The magnetic recording medium obtained by using the coating material retains the viscosity, prevents thickening, and has excellent reactivity with the cross-linking agent, and has a surface smoothness and durability of the coating film. The inventors have found that they are good and have excellent running properties, magnetic properties, and electromagnetic conversion properties, and have reached the present invention.

(Means for Solving Problems) Thus, according to the present invention, a resin having an epoxy group-containing resin having a hydroxyl group content of 0.5% by weight or more obtained by reacting a carboxylic acid or a sulfonic acid having a perfluoroalkyl group is used. There is provided a magnetic recording medium characterized by being used as a binder component.

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

The epoxy group-containing vinyl chloride resin has a degree of polymerization of 200 to 900.
And vinyl chloride homo- or copolymer resins and chlorinated vinyl chloride resins. If the degree of polymerization is less than 200, the durability of the magnetic tape will be insufficient, and if it exceeds 900, the viscosity of the magnetic coating will be high and the dispersibility of the magnetic powder will be poor. These vinyl chloride resins are (1) vinyl chloride, a radically polymerizable monomer having an epoxy group which is copolymerizable with vinyl chloride, and other monomers which are copolymerizable with these monomers as necessary. In the presence of a radical generator, or (2) heating vinyl chloride or a vinyl chloride-based copolymer (these may be chlorinated) or contacting it with a dehydrochlorination agent. Thus, the resin obtained by partial dehydrochlorination is obtained by a method of epoxidizing the resin with an epoxidizing agent such as percarboxylic acid.

In the method (1), examples of the monomer having an epoxy group copolymerizable with vinyl chloride include glycidyl ethers of unsaturated alcohols such as allyl glycidyl ether and methallyl glycidyl ether, glycidyl acrylate, and glycidyl methacrylate. , Glycidyl-p-
Vinyl benzoate, methyl glycidyl itaconate,
Glycidyl ethyl malate, glycidyl vinyl sulfonate, glycidyl esters of unsaturated acids such as glycidyl (meth) allyl sulfonate, butadiene monooxide, vinyl cyclohexene monooxide, epoxide olefins such as 2-methyl-5,6-epoxyhexene, etc. Can be given. Further, examples of the monomer having an epoxy group and the monomer used as necessary other than vinyl chloride include vinyl acetate, carboxylic acid vinyl ester such as vinyl propionate; methyl vinyl ether, isobutyl vinyl ether, cetyl vinyl ether, etc. Vinyl ethers; vinylidene chloride, vinylidene fluoride, etc .; dimethyl maleate, diethyl maleate, butylbenzyl maleate, maleic acid-di-2-
Unsaturated carboxylic acid esters such as hydroxyethyl, dimethyl itaconate, methyl (meth) acrylate, ethyl (meth) acrylate, lauryl (meth) acrylate, and 2-hydroxypropyl (meth) acrylate; ethylene, propylene, etc. Olefins; unsaturated nitriles such as (meth) acrylonitrile; aromatic vinyls such as styrene, α-methylstyrene and p-methylstyrene. These monomers are used for the purpose of improving the solubility of the resin while controlling the compatibility and softening point of the resin of the present invention and the other resin when mixed, and the characteristics of the coating film and the coating. It can be appropriately selected depending on needs such as process improvement.

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 group-containing polyurethane resin is an epoxy polyol obtained by modifying an epoxy resin with an amine, or an epoxy resin having a bifunctional or higher hydroxyl group per molecule, for example, bisphenol A type, halogenated bisphenol type, resorcin type, bisphenol F type, etc. An epoxy group-containing polyester obtained by reacting an epoxy resin with adipic acid, phthalic acid, dimerized linoleic acid, dibasic acid such as maleic acid, or the like,
Furthermore, it can be synthesized by reacting an epoxy group-containing polyester resin described later with a polyfunctional polyisocyanate such as tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, hexamethylene diisocyanate, and metaxylylene diisocyanate.
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 a transesterification reaction is used as a starting material. Good.

As the epoxy group-containing acrylonitrile-butadiene resin, the acrylonitrile content is generally 12 to 50.
Weight% and molecular weight of 5,000 to 500,000 are used. When the content of acrylonitrile is less than 12%, the compatibility with vinyl chloride resins generally used in magnetic recording media and other binders such as nitrocellulose is poor, and the content is 50% by weight.
If the amount is larger, the solvent solubility is lowered, and the dispersibility of the magnetic powder is greatly lowered. 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. Epoxy group-containing acrylonitrile-
Butadiene-based resin, together with acrylonitrile, butadiene, a radical copolymerizable monomer containing an epoxy group,
It can be obtained by copolymerizing with other monomers, if necessary, in the presence of a radical generator. 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. If the molecular weight is less than 500, the durability of the coating film is low, and unreacted substances may bleed to the surface of the magnetic layer, making it difficult to use. If 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

It is necessary that these epoxy group-containing resins contain 1.5% by weight or more of epoxy groups. Otherwise, it will not be possible to add sufficient amounts of hydroxyl groups to achieve the objects of the invention.

Among the epoxy group-containing resins in the present invention, the vinyl chloride resin has a low coating viscosity, good magnetic powder dispersibility, and an appropriate hardness, and the polyester resin and polyurethane resin are good base films and Has the adhesiveness of
Further, the acrylonitrile-butadiene-based resin imparts flexibility to the coating film, and has a good use property of the magnetic tape particularly at low temperatures.

The carboxylic acid or sulfonic acid having a perfluoroalkyl group used for producing the resin used in the present invention is preferably a monobasic acid. The polybasic acid is apt to cause gelation when it reacts with a resin containing an epoxy group, because it causes a crosslinking reaction at the same time.

Examples of carboxylic acids having a perfluoroalkyl group that can be used 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-monohydroperfluoroundecanoic acid, etc.
-Monohydroperfluoroalkylcarboxylic acids, made from perfluoro-1,2-epoxypropane And carboxylic acids having a perfluoroalkyl polyether such as Examples of the sulfonic acid 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 ) SO ₃ H)
Made from perfluoroalkenyl (alkyl) aryl ether sulfonic acids, such as perfluoro-1,2-epoxypropane Sulfonic acids having perfluoroalkyl polyethers such as

The reaction between the epoxy group-containing resin and the carboxylic acid or sulfonic acid having a perfluoroalkyl group can proceed in a suspension (emulsification) state or a solution state using water or a non-aqueous medium, mixing roll, pressurization. It is also possible to proceed in a molten state by using a kneader or a resin mixer such as an extruder. The amount of the carboxylic acid or sulfonic acid having a perfluoroalkyl group used here is preferably equal to or less than the equivalent amount of the epoxy group in the resin, and if it is used in excess of this, a great deal of labor is required to remove the excess acid.

The modified resin thus obtained has a hydroxyl group due to the addition of an acid to the epoxy group, but it is necessary that the content of the hydroxyl group is 0.5% by weight or more. If the amount of hydroxyl groups is less than 0.5% by weight, the dispersibility of the magnetic powder is insufficient and the crosslinking performance with the isocyanate compound is insufficient.

Acid-modified resins may be combined with each other in the present invention, or other commonly used binder resins such as nitrocellulose, cellulose acetate and other fibrin-based resins, polyvinyl butyral resins, phenoxy resins, chlorides. It may be used in combination with a hard binder such as vinyl resin or a soft binder such as polyester resin, polyurethane resin, acrylonitrile butadiene rubber or epichlorohydrin rubber.

The magnetic powder used in the magnetic recording medium of the present invention includes Fe
Γ-Fe including metallic magnetic powders such as powder and Co powder
₂ O ₃ , Fe ₃ O ₄ , Co-containing γ-Fe ₂ O ₃ , Co-containing Fe ₃ O ₄ , iron oxide powders such as barium ferrite, and CrO ₂ powders.

The magnetic powder, the binder, the abrasive, the antistatic agent, and in some cases, the dispersant and the lubricant are mixed and dispersed in a solvent by a sand mill or the like, and then a cross-linking agent represented by a polyisocyanate compound is mixed to obtain a polyester. It is coated on a base film represented by a film. Next, the coating film, which has been subjected to an orientation treatment and then dried, and which has been surface-formed, is subjected to cross-linking aging and cut, and is used as a magnetic tape or disk.

(Effects of the Invention) The binder for a magnetic recording medium of the present invention provides excellent magnetic powder dispersibility, and provides a smooth coating film surface due to moderate crosslinkability and little deterioration of the resin due to mildness of the modification step. In addition, it has low frictional resistance, is hard to be scratched, and is hard to deteriorate. Therefore, it becomes possible to manufacture a magnetic tape, a floppy disk, or the like that can stably maintain excellent electromagnetic conversion characteristics and running performance even when used for a long period of time.

(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. The amount of hydroxyl groups in the modified product was determined by infrared absorption analysis.

Reference Example 1 100 parts of vinyl chloride resin (a) obtained by copolymerizing vinyl chloride and allyl glycidyl ether having an average degree of polymerization of 300 and an epoxy group content of 3.7% was dissolved in 400 parts of tetrahydrofuran, Add 25 parts of perfluorooctylic acid for 30 minutes
After stirring at 50 ° C., the mixture was poured into a large amount of methanol, the precipitated resin was recovered, washed with a large amount of water and dried to obtain a modified product (A). The amount of hydroxyl groups was 1.1%.

Reference Example 2 Obtained by post-chlorinating polyvinyl chloride having an average degree of polymerization of 380,
Chlorinated vinyl chloride resin with a chlorine content of 68% was dehydrochlorinated in a nitrogen stream at 160 ° C and then epoxidized with perbenzoic acid in benzene to give a chlorinated chloride with an epoxy group content of 3%. A vinyl resin (b) was obtained. 100 parts of this epoxidized chlorinated vinyl chloride resin and 30 parts of perfluorooctyl sulfonic acid were reacted in 300 parts of methyl ethyl ketone at 45 ° C. for 60 minutes to obtain a modified resin solution (B). The amount of hydroxyl groups is
It was 0.7%.

Reference Example 3 An acrylonitrile-butadiene resin having an acrylonitrile content of 30% and an average molecular weight of 30,000 was partially epoxidized with peracetic acid to obtain an epoxidized acrylonitrile-butadiene resin (c) having an epoxy group content of 8%. With 100 parts of this epoxidized resin 30 parts and 30 parts were heated and mixed in a pressure kneader having an internal volume of 1 at 80 ° C. for 2 hours to obtain a modified product (C). Addition of hydroxyl group is 1.1
%Met.

Reference Example 4 An unsaturated polyester resin obtained by heat-condensing maleic anhydride, mixed phthalic acid, and 1,4-butanediol as raw materials was epoxidized with peracetic acid in toluene to have a molecular weight of 9,00.
An epoxidized polyester resin (d) having an epoxy group content of 0 and 6% was obtained. This epoxidized polyester resin 100
C ₂ F ₅ OCF ₂ CF (CF ₃ ) OC ₂ F ₄ SO _{3 in} a mixture of 1 part and 200 parts toluene.
15 parts of H was added and mixed at room temperature for 20 minutes to obtain a modified product (D). The amount of hydroxyl groups added was 0.6%.

Reference Example 5 Obtained from an epoxy group-containing polyol and 4,4'-diphenylmethane diisocyanate, the average molecular weight was 50,00.
0, 20 parts of perfluorooctylic acid was added to a mixture of 100 parts of a polyurethane resin having an epoxy group content of 4%, 100 parts of cyclohexanone and 100 parts of methyl ethyl ketone, and mixed at 60 ° C. for 1 hour to obtain a modified product (E). . The amount of hydroxyl groups was 1.7%.

Reference Example 6 A modified product (A ′) was obtained by the same experiment as in Reference Example 1 except that 25 parts of perfluorooctylic acid used in Reference Example 1 was replaced with an equimolar amount of octylic acid. The amount of hydroxyl groups is
It was 0.2%.

Reference Example 7 Reference Example 3 except that the epoxy group content of the epoxidized acrylonitrile-butadiene resin used in Reference Example 3 was 0.5%.
The same experiment was conducted to obtain a modified product (F). The amount of hydroxyl groups is
It was 0.3%.

(Preparation of magnetic paint) Tables 1 and 2 were prepared using the acid-modified products obtained in Reference Examples 1 to 7.
A magnetic paint was prepared according to. Using a blade coater, dry this on a polyester film with a thickness of 20μ
It is coated so that it becomes μ, magnetic field orientation is performed, and after drying, the glossiness of the coated surface is measured, and then the surface is formed with a super calender and cross-linked for 48 hours in an atmosphere of 65 ° C and 90% relative humidity. After that, it was cut to a width of 12.65 mm to prepare a magnetic tape test piece.

Next, Table 3 shows the results of evaluating the characteristics of the obtained magnetic tape.
It was shown to. The evaluation method was as follows.

(1) Glossiness The reflectance at 60 ° reflection angle of the coating film before surface forming treatment was measured with a gloss meter.

(2) Crosslinking property A part of the sample was taken, and the degree of removal of the rubbing coating film was rubbed with absorbent cotton soaked with methyl ethyl ketone.

◯: No dropout or almost no dropout Δ: Slight dropout x: Large dropout (3) Orientation The sample was cut into 50 mm lengths and measured with a magnetic property measuring machine (Br / Bm).

(4) Durability A sample with a length of 50 cm is brought into contact with a rotating drum to which abrasive paper is attached with a load of 100 g, and it is rotated at 150 rpm, and the degree of dirt adhering to the abrasive paper is visually observed in the following three steps. displayed.

○: No dirt △: Some dirt X: Very dirty (5) Travelability The sample was brought into contact with a hard chrome-plated mirror surface rotating drum, and the force generated between the drum and the sample was 65 ° C and relative humidity 80.
%, The running resistance was displayed in the following three stages.

○: Small resistance △: Medium resistance ×: Large resistance

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location C09D 175/04 PHN

Claims (1)

[Claims] 1. A magnetic recording medium comprising a resin containing 0.5% by weight or more of hydroxyl groups as a binder component, which is obtained by reacting an epoxy group-containing resin with a carboxylic acid or sulfonic acid having a perfluoroalkyl group. .