JPS6316415A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve thermal stability, durability and runnability by providing a magnetic layer contg. a vinyl chloride resin having an epoxy group and carboxylic acid compd. or sulfonic acid compd. having a perfluoroalkyl group to a titled medium. CONSTITUTION:This recording medium has the magnetic layer contg. the vinyl chloride resin having the epoxy group and the carboxylic acid compd. or sulfonic acid compd. having the perfluoroalkyl group. The improvement in the thermal stability is obtd. as the hydrogen chloride generated by the thermal decomposition of the vinyl chloride resin is captured by the epoxy group in the molecular chain to prevent the chain reaction of the decomposition. Since the perfluoroalkyl group having lubricating performance exists in and on the magnetic layer in the form of being fixed to the resin, the runnability, wear resistance and durability are improved.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an improved magnetic recording medium, and more particularly to a magnetic recording medium with excellent dispersibility, thermal stability, and durability.

(Prior Art) Magnetic recording media such as magnetic tapes and magnetic cards are generally manufactured by applying a magnetic paint containing magnetic powder and its binder as a magnetic layer onto a substrate such as a polyester film. In recent years, in order to increase the coercive force and maximum saturation magnetization, and improve the signal-to-noise ratio and recording density, miniaturized magnetic powders with a large specific surface area have come to be used as the above-mentioned magnetic powders.

However, as a binder for such fine magnetic powder,
Magnetic properties are obtained using vinyl chloride copolymer resins such as vinyl chloride-vinyl acetate-vinyl alcohol copolymer resins, vinyl chloride-vinyl acetate-maleic acid copolymer resins, and vinyl chloride-vinyl acetate-maleic acid-vinyl alcohol copolymer resins. When a paint is prepared, there are drawbacks such as thickening of the paint and insufficient dispersibility.

For this reason, a method of increasing the dispersibility of magnetic powder is to apply high shearing force during dispersion, but this method is difficult to avoid due to the heat of the vinyl chloride copolymer resin due to the thickening of the paint and the rise in temperature. This has the disadvantage 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, one of the conventionally well-known methods for preventing thermal decomposition of vinyl chloride copolymer resins is a method of adding a so-called stabilizer for vinyl chloride resins. Typical examples of these include 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 organotin compound such as dibutyltin laurate or dibutyltin maleate. There is.

However, if a large amount of low-molecular-weight epoxy compounds exist in a magnetic recording medium, it will cause a bleed phenomenon from the magnetic recording medium, resulting in decreased durability and head stains, so the amount of low-molecular-weight epoxy compounds used is naturally limited, and therefore its effectiveness is limited. There are also limits. Additionally, when an organic tin compound is added, the organic tin compound acts as a catalyst for the crosslinking reaction of the isocyanate compound that is generally added to the binder, which dramatically shortens the bit life of the magnetic paint and stabilizes the paint. The viscosity increases significantly during coating, resulting in decreased dispersibility and impaired surface smoothness of the magnetic layer.

On the other hand, in response to the increasing recording density and high S/N of magnetic recording media, magnetic tapes have a magnetic layer with a smooth surface obtained by highly dispersing fine and highly coercive magnetic powder. teeth,
This creates a problem in that the frictional resistance between the head guide and the tape increases and the tape runs poorly.

In order to solve these problems, conventional methods have included lubricants such as silicone oil, fluororesin, fatty acids or their ethers, esters, amides, and their fluorides, as well as fine particles such as carbon black and alumina, in the magnetic layer. It has been practiced more than ever. However, the former lubricant is
Problems such as bleeding phenomenon after being left for a long time, instability of the dispersion of the magnetic paint, and resulting non-uniformity of the magnetic layer after coating are likely to occur. Especially when perfluoroalkyl sulfonic acid or carboxylic acid is used as a lubricant, the strength of the acid may destabilize the magnetic paint, soak the magnetic layer, or damage the head or guide. It has also been introduced that these lubricants are used as a component of backcoat paints, but they cause similar problems due to the bleed phenomenon after being left for a long time.On the other hand, the latter fine particles As a result, the filling properties of the magnetic powder in the magnetic layer are reduced, and there is a natural limit to the use of large amounts.

(Problems to be Solved by the Invention) The present inventor aims to prevent the thermal decomposition of the vinyl chloride copolymer resin that occurs during the production of the high-density magnetic recording medium, and to reduce the durability of the high-density magnetic recording medium. (As a result of extensive research, we have found that a vinyl chloride resin with an epoxy group is used as a binder for magnetic powder, and a vinyl chloride resin with a perfluoroalkyl group is used as a binder for the magnetic powder.) They discovered that by combining a carboxylic acid compound or a sulfonic acid compound, it is possible to obtain a high-density magnetic recording medium that has excellent thermal stability during paint preparation, as well as excellent durability and running properties, leading to the completion of the present invention. .

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

The vinyl chloride resin having an epoxy group is composed of (1) vinyl chloride, a radically polymerizable monomer having an epoxy group that can be copolymerized with vinyl chloride, and, if necessary, a monomer that can be copolymerized with these monomers. (2) Polyvinyl chloride or a copolymer resin containing vinyl chloride as a main component is partially dehydrochlorinated by heating or contacting with a dehydrochlorination agent. It can be obtained by epoxidation using an epoxidizing agent such as percarboxylic acid. The chlorinated polyvinyl chloride resin having an epoxy group can be obtained by the method (2) using a chlorinated polyvinyl chloride resin or a chlorinated polyvinyl chloride copolymer resin as a starting material.

Examples of monomers having epoxy groups used in the production of vinyl chloride resins having epoxy groups include glycidyl ethers of unsaturated alcohols such as allyl glycidyl ether and methallyl glycidyl ether, glycidyl acrylate, glycidyl methacrylate, Glycidyl
Glycidyl esters of unsaturated acids such as p-vinyl benzoate, methylglycidyl itaconate, glycidyl ethyl maleate, glycidyl vinyl sulfonate, glycidyl (meth)allylsulfonate, butadiene monoxide, vinylcyclohexene monooxide, 2-
Examples include epoxide olefins such as methyl-5,6-epoxyhexene.

In addition, examples of monomers having an epoxy group and monomers used as necessary other than vinyl chloride include carboxylic acid vinyl esters such as vinyl acetate and vinyl propionate; methyl vinyl ether, inbutyl vinyl ether;
Vinyl ethers such as cetyl vinyl ether; vinylidenes such as vinylidene chloride and vinylidene fluoride; diethyl maleate, butylbenzyl maleate, c-2-hydroxyethyl maleate, dimethyl itaconate, methyl (meth)acrylate, (meth)acrylic acid Unsaturated carboxylic acid esters such as ethyl, lauryl (meth)acrylate, and 2-hydroxypropyl (meth)acrylate; olefins such as ethylene and furopylene + unsaturated nitriles such as (meth)acrylonitrile; styrene, α-methylstyrene and aromatic vinyl such as p-methylstyrene. These monomers are used not only to improve the solubility of the resin by controlling the compatibility and softening point of the resin of the present invention and other resins when mixed, but also to improve the properties of the coating film and the coating properties. Appropriate selection is made depending on the need for process improvement, etc.

Note that, as a vinyl chloride resin having an epoxy group, one into which a hydrophilic group is introduced for the purpose of improving the dispersibility of magnetic powder is more suitable as a binder. The hydrophilic groups used are C00M and SO3M.

504M, PO3M2 and PO4M2 (M is hydrogen, an alkali metal or ammonium), and the like.

The weight fraction of epoxy groups in the vinyl chloride resin in the present invention is preferably in the range of 0.1 to 20% by weight. If it is less than 0.1% by weight, it is difficult to achieve the object of the present invention, and 20% by weight.
When the amount is larger, the amount of vinyl chloride is relatively reduced, and the physical properties of the resin are deteriorated. The proportion of vinyl chloride in this resin is usually 20% by weight or more, preferably 50 to 95% by weight.

If the ratio is less than this, the physical properties of the resin will deteriorate and the strength of the coating film will be too weak to be used as a binder. Moreover, it is preferable that the average degree of polymerization of this resin is 100 to 10,000. If it is less than 100, the coating strength and thermal stability of the magnetic layer will be poor, and if it exceeds 1000, the dispersibility of the magnetic powder and the solubility of the resin will be reduced.

As an example of the carboxylic acid compound having a perfluoroalkyl group in the present invention, perfluorododecanoic acid [C
! F3 (C!F2 ) 10 C0OH], perfluoroalkylcarphonic acids such as perfluorooctanoic acid (ay3 (cy2>6cooa), perfluoropropionic acid (02F5COOH)), perfluorooctylhydromethylenecarboxylic acid (ap3 (cF2 ) 7-
CF3 0F3 oloalkyl polyether from perfluoroalkylhydroalkylcarboxylic acids such as cH2cooa), W-monohydroperfluoroalkylcarboxylic acids such as W-monohydroperfluoroundecanoic acid, and perfluoro-1,2-epoxypropane. Examples include carboxylic acids that have Examples of sulfonic acid compounds having a perfluoroalkyl group include perfluoroalkyl sulfonic acids such as perfluorooctyl sulfonic acid CCF'3 (C! 1!
C! made from perfluoroalkenyl(alkyl)aryl needlesulfonic acids such as c+F170(06E4)SO3M), perfluoro-1,2-epoxypropane! 2F5 (OCF20F) 30C! 2F4S
There are sulfonic acids with CF3 barfluoroalkyl polyether such as ○3H.

The amount of the carboxylic metal oxide or sulfonic acid compound having a perfluoroalkyl group is preferably an amount containing an acid chemical equivalent of 0.05 to 3.00 times the chemical equivalent of the epoxy group in the epoxy group-containing vinyl chloride resin. . If the chemical equivalent is less than 0.05 times, it is difficult to improve the durability of the magnetic layer, which is the objective of the present invention, and if the chemical equivalent is more than 3.00 times, the dispersibility of the magnetic powder decreases and the durability also decreases descend.

In the present invention, in addition to the vinyl chloride resin having an epoxy group, a flexible resin such as a polyurethane resin, a polyester resin, or an acrylonitrile-butadiene copolymer resin is used as a binder for the purpose of improving adhesiveness and imparting durability. There is no problem even if it is included. Note that these flexible resins may contain epoxy groups, and for the purpose of improving the dispersibility of magnetic powder, C00M, 803M,
804M, PO3M2.

It may contain a functional group such as PO4M2 (M is hydrogen, an alkali metal, or ammonium).

Magnetic powders that can be used in the present invention include Fe and Go.

Fe alloy system, Co-containing 1-Fe2O3 system, CO-containing Fe
3O4 series! Any powder such as -1'e203 type, Fe3O4 type, barium-ferrite type etc. may be used.

Also, if necessary, conventional materials such as lubricants, dispersants, antistatic agents and abrasives, as well as conventional magnetic coating resins such as phenoxy resins, cellulose resins, amino resins, butyral resins and acrylic resins, can be added. It is also possible to use it within a range that does not impair achievement of the purpose of the invention. Furthermore,
There is no problem even if a commonly used polyisocyanate compound is added within the usual range and a crosslinking reaction based on the incyanate reaction is also carried out.

Vinyl chloride resin having an epoxy group in the present invention,
By appropriately mixing the acid compound, magnetic powder, and the desired components described above, a magnetic paint can be obtained as a dispersion in any organic solvent. The magnetic recording medium of the present invention is obtained by applying this paint as a magnetic layer on a substrate such as a polyester film by any arbitrary means such as spraying or roll coating, and drying to form a magnetic layer.

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

The improvement in thermal stability in the present invention is achieved by the epoxy group in the molecular chain capturing hydrogen chloride generated by thermal decomposition of the vinyl chloride resin to prevent a chain reaction of decomposition. This effect can also be obtained by adding an epoxy group-containing compound to the binder system, but compared to the conventional method of adding a low-molecular compound such as epoxidized soybean oil. Therefore, the present invention is free from problems such as head contamination due to bleeding onto the surface of the magnetic layer and a decrease in tape runnability due to increased tape adhesive pressure, and can exhibit extremely excellent improvement effects.

Further, according to the present invention, both components react in the dispersion, coating, surface molding, and crosslinking curing steps 8 of the magnetic paint, and the perfluoroalkyl group having lubricating properties is fixed to the resin and becomes magnetic. Since it exists in the layer and on the surface, it is thought that improvements in runnability, abrasion resistance, and durability are also achieved.

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

(Example) The present invention will be described in more detail with reference to Examples below. In addition, in Examples and Reference Examples, Parts and Excellent are based on superimposition standards unless otherwise specified.

Reference Example 1 Emulsion polymerization of allyl glycidyl ether, vinyl chloride and 2-hydroxypropyl methacrylate with potassium persulfate revealed that the epoxy group was 3.5% and -day 0.
4 is 0.7%, hydroxyl group is 0.7%, vinyl chloride is 84%
A vinyl chloride copolymer resin (A) was obtained.

Reference Example 2 Vinyl cyclohexene monooxide, vinyl chloride and vinyl arsenate were suspension polymerized with 2,2'-azobisisobutyronitrile to obtain a polymer containing 5% epoxy groups, 5% vinyl acetate, and 87% vinyl chloride. Vinyl chloride copolymer resin (B)
I got it.

Reference Example 3 By emulsion polymerizing vinyl chloride, allyl glycidyl ether, sodium styrene sulfonate, and vinyl acetate with potassium persulfate, the epoxy group was 1.5%, -
A vinyl chloride copolymer resin (C) containing 8O3Na of 1.04 and vinyl chloride of 87% was obtained.

Examples (Thermal Stability Test) Vinyl chloride copolymer resin 1F and polyurethane resin (Nipporan 2304 manufactured by Nippon Polyurethane Kogyo ■) shown in the table
1 f was taken, dissolved in tetrahydrofuran, and the acid compound shown in the table was added thereto in an amount of 0.8 times the chemical equivalent of the epoxy group in the vinyl chloride copolymer resin, and then polyisocyanate (manufactured by Nippon Polyurethane Industries, Ltd.) was added. Coronate I,
) After adding 0.45F, coating was performed using a doctor blade, and the solvent was evaporated to create a cast film. This cast film 1y- is placed in a 15 cc test tube, the opening of which is plugged with absorbent cotton sandwiched with Congo red paper, and placed in a 150 t:' oil bath, and the Congo red test paper changes color due to the generated hydrochloric acid. Thermal stability was evaluated by measuring the time until

(Glossiness test) 400 parts of cobalt magnetic iron oxide powder, 70 parts of the vinyl chloride copolymer resin shown in the table, 30 parts of the same polyurethane resin used in the thermal stability test, and the carboxylic acid compound shown in the table A mixture consisting of 8 times the chemical equivalent of the epoxy group in the copolymer resin, 300 parts of methyl ethyl ketone, 500 parts of methyl isobutyl ketone, and 500 parts of toluene was dispersed under high speed shear for 90 minutes, and then subjected to a thermal stability test. 20 parts of the same polyisocyanate was added and mixed and dispersed for 10 minutes to prepare a magnetic paint. The obtained magnetic paint was applied onto a polyester film to a film thickness of 5 μm, subjected to magnetic field orientation treatment, and then dried. The reflectance of the magnetic coating film at a human reflection angle of 60 degrees was measured using a glossy needle. The larger the number, the better the dispersibility of the magnetic powder.

(Durability Test) The magnetic coating film used in the glossiness test was smoothed using a calendar roll, and then crosslinked and cured in a constant temperature bath at 65C for 40 hours. This magnetic coating was brought into contact with a 40 m diameter rotating drum covered with abrasive paper under a load of 1001,
After rotating at 150 rpm for a predetermined period of time, the degree of staining on the abrasive paper was evaluated in five grades: ◯ (no stain), Δ (slight stain), and x (severe stain).

(Runability test) The magnetic coating used in the glossiness test was smoothed and cross-linked in the same manner as in the durability test, and the sample was brought into contact with a mirror-like rotating drum plated with hard chrome, and a sample was placed between the drum and the sample. The force generated was measured using a U gauge in an atmosphere of 65C and relative humidity of 80 degrees, and the running resistance was expressed in the following three levels.

○: Low resistance Δ: Medium resistance ×: High resistance (bleed test) The magnetic coating used for the gloss test was brought into contact with an aluminum plate, and after being left in a constant temperature and humidity chamber of 45CX95%RH for 7 days, the magnetic coating was removed. ○ Changes in the aluminum plate surface that was in contact with the surface
Judgment was made using (no change) and x (change).

The above test results are shown in the table.

Claims (1)

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