JPS62208421A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve thermal stability and durability by providing a magnetic layer contg. a vinyl chloride resin, resin having an epoxy group and carboxylic acid compd. having <=4 pka. CONSTITUTION:The magnetic layer contg. the vinyl chloride resin, the resin having the epoxy group and the carboxylic acid compd. having <=4.0 pka is provided. The resin having the epoxy group is exemplified by an epoxy-modified polyurethane resin, epoxy-modified polyester resin, epoxy-modified acrylonitrile/ butadiene copolymer resin and epoxy resin, etc. The epoxy-modified polyurethane resin and epoxy-modified polyester resin having 1,000-200,000mol.wt. are used, and the epoxy-modified acrylonitrile/butadiene copolymer resin having 12-50wt% content of acrylonitrile and 5,000-500,000mol.wt. is used. The epoxy resin having 500-200,000mol.wt. is used. The magnetic recording medium having the excellent thermal stability, dispersibility and durability is thus obtd.

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 the maximum saturation magnetization i, and to improve the signal-to-noise ratio and recording density, miniaturized magnetic powders with a large specific surface area have been 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, a well-known method for preventing thermal decomposition of vinyl chloride copolymer resins is the addition of 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. be.

However, if a large amount of low-molecular-weight epoxy compounds exist in a magnetic recording medium, they will cause a bleed phenomenon from the magnetic recording medium, resulting in decreased durability and head stains, so the amount used is naturally limited, and therefore its effectiveness is limited. There are also limits. In addition, when an organic tin compound is added, the organic tin compound becomes a catalyst for the crosslinking reaction of the incyanate compound added to a general binder, so the pot life of the magnetic paint is not extremely short. The stability of the paint decreases, and the viscosity increases significantly during coating, resulting in decreased dispersibility and loss of surface smoothness of the magnetic layer.

Furthermore, with the aim of creating magnetic recording media with excellent durability and no pot life problems, it has been proposed to crosslink magnetic coatings with electron beams, but binders and additives do not necessarily provide sufficient performance. Currently, the desired magnetically coordinated media cannot be obtained because the requirements are not met.

(Problems to be Solved by the Invention) The present inventor aims to prevent thermal decomposition of the vinyl chloride copolymer resin that occurs during the production of such high-density magnetic recording media, and thereby reduce the durability of the high-density magnetic recording media. As a result of intensive research to solve these drawbacks, we have found that by using a vinyl chloride resin and a resin with an epoxy group as a binder for magnetic powder, and by combining this with a specific carboxylic acid compound, the heat during paint preparation can be reduced. It was discovered that a high-density magnetic recording medium with excellent stability and durability can be obtained, and the present invention was completed.

(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, a resin having an epoxy group, and a carboxylic acid compound having a pKa of 4.0 or less. A magnetic recording medium is provided.

The chlorinated beer resin used in the present invention is a vinyl chloride homopolymer or a copolymer of vinyl chloride and other monomers, and a subsequent reaction product. Examples of other monomers include vinyl acetate, vinyl carbinate of vinyl globionate, methyl vinyl ether, imbutyl vinyl ether, cetyl vinyl ether, tonovinyl z-
TeA/: [vinylidene such as vinylidene chloride and vinylidene fluoride; diethyl maleate, butylbenzyl maleate, di-2-and-droxyethyl maleate, dimethyl itaconate, methyl (meth)acrylate, ethyl (meth)acrylate , (meth)lauryl acrylate, (meth)
Unsaturated carbo/acid esters such as 2-hydroxypropyl acrylate; olefins such as ethylene, glopyrene; unsaturated nitrites such as (meth)acrylonitrile;
Examples include aromatic vinyls such as styrene, α-methylstyrene, and 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 necessity such as process improvement.

Note that vinyl chloride resins into which hydrophilic groups have been introduced for the purpose of improving the dispersibility of magnetic powder are suitable as binders. The hydrophilic group used is C00
Examples thereof include M, 803M, 304M, PO, M2 and 204M2 (M is hydrogen, alkali metal or ammonium).

The proportion of vinyl chloride in vinyl chloride resin is usually 20ft.
% or more, preferably 50 to 95% by weight
It is b. 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 1000. 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.

Examples of the resin having an epoxy group in the present invention include epoxy-modified polyurethane resin, epoxy-modified I-lyester resin, niboxy-modified acrylonitrile-butadiene copolymer resin, and polyurethane resin. Examples include xylene resin and the like.

The engineering 4xy modified polyurethane resin has a molecular weight of t, ooo~
200,000 are used. Molecular weight is 1.00
If it is less than 0, the durability of the coating film is insufficient, and 200.0
If it exceeds 00, the viscosity of the paint becomes too high, causing a practical problem. Engineering I Ki degeneration? The urethane resin is an epoxy resin having two or more functional hydroxyl groups per molecule;
By reacting with dibasic acids such as adipic acid, phthalic acid, dimerized sulfuric acid, and maleic acid, a terminal hydroxyl group type 4? It can be synthesized by synthesizing a polyester resin and reacting it with a polyfunctional polyisocyanate.

Alternatively, an epoxidizing agent such as percarboxylic acid is applied to a polyurethane resin synthesized from an unsaturated polyester resin obtained by reacting an unsaturated fatty acid such as maleic acid, dimalic acid, or itaconic acid with a polyhydric alcohol. It can also be synthesized by

Epoxy modified polyester resin has a molecular weight of 1.000
~200,000 are used. Molecule 1 is 1,0
If it is less than 200.00, the durability of the coating film is insufficient.
If it exceeds 000, the viscosity of the paint becomes too high, causing a practical problem. Epoxy-modified polyester resin is made by combining 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 with 1,4-butanediol and 1,5-bentanediol. , 1,6-hexanediol, 1,10-decanediol, and an unsaturated polyester resin obtained by thermal condensation with polyols such as butadiene oligomers with hydroxyl groups at both ends are epoxidized using an epoxidizing agent such as percarboxylic acid. obtained by In addition, instead of the above-mentioned unsaturated polyester resin, this and a polycarnate resin or a saturated polyester resin are melt-mixed in the presence of a catalyst,
A modified unsaturated polyester resin obtained by transesterification may be used as a starting material.

Furthermore, as an epoxy-modified acrylonitrile-butanoene copolymer resin, the acrylonitrile content is generally 12
~50 weight ratio and a molecular weight of 5,000 to 500,000 are used. If the content of acrylonitrile is less than 12 parts, it is generally not compatible with other binders such as polyvinyl chloride or nitrocellulose used in magnetic recording media, and if it is more than 50 parts fk, the solubility in solvents decreases, and the solubility of magnetic particles decreases. This greatly reduces dispersibility. Also, the molecular weight is 5
If it is less than 500,000, the durability of the coating film is low;
If it is larger than 0, the viscosity of the paint is too high to be practical.

Epoxy-modified acrylonitrile-butadiene copolymer resin is made by copolymerizing a radical copolymerizable monomer containing an epoxy group with acrylonitrile and butadiene, if necessary, in the presence of a radical generator along with other copolymerizable monomers. While it can be obtained by polymerization, it can also be obtained by partially epoxidizing the double bonds within the acrylonitrile-butadiene copolymer resin using an epoxidizing agent such as percarboxylic acid.

The epoxy resin used in the present invention has a molecular weight of 5
00 to 200,000 is used. molecular weight is 5
If it is less than 0.00, the durability of the coating film will be low, and unreacted substances may lead to the surface of the magnetic layer.
,000, the viscosity of the paint is too high to be practical. Specific examples of epoxy resin include bisphenol A-
Examples include epichlorohydrin type, those using halodanated bisphenol, resorcinol, bisphenol F, tetrahydroxyphenylethane, etc. in place of the bisphenol A, and tumelac type epoxy resin.

In addition, the resin having an epoxy group in the present invention contains C00M, SO3M, 504M + P03M in the resin having an epoxy group for the purpose of improving the dispersibility of magnetic powder.
It may contain a functional group such as 2°204M2 (M is hydrogen, an alkali metal, or ammonium).

In order to achieve the effects of the present invention, the ratio of the resin containing M epoxy groups is 5 to 7 per the total amount of the vinyl chloride resin.
A range of 0% by weight is desirable, and the weight ratio of the epoxy group is required to be 0.1% by weight or more based on the vinyl chloride resin.

The carboxylic acid compound used in the present invention must have a pKa (in the case of a polybasic carboxylic acid, pKa hereinafter means pKa 1 unless otherwise specified) of 4 or less; If it is larger than 4, durability cannot be improved. Carboxylic acid compounds with a pKa of 4 or less include saturated and unsaturated aliphatic and polyvalent carboxylic acid compounds, and aromatic monovalent and polyvalent carboxylic acid compounds, and specific examples thereof include formic acid, Monochloroic acid, dichloroacetic acid, trichloroacetic acid, α-chlorobutyric acid, monofluoroacetic acid, monobromoacetic acid, nofluoroacetic acid, α-chloroacrylic acid, p-nitrobenzoic acid, m-nitrobenzoic acid, O
-Nitrobenzoic acid, m-chlorobenzoic acid, 0-chlorobenzoic acid, 0-toluic acid, 3.5-dinitrobenzoic acid,
Salicylic acid, sialic acid, malonic acid, maleic acid, fumaric acid, phthalic acid, isophthalic acid, terephthalic acid, hemimellitic acid, trimellitic acid, trimesic acid, brenidic acid, merofanic acid, pyromellitic acid, benzenepentacardic acid, mellitic acid, Phenylpropiolic acid %Q-phenylenediacetic acid, glyoxylic acid, pyruvic acid, acetoacetic acid, glycolic acid, (to)-lactic acid, (to)-Mandel fi 2,
(→-malic acid, (to)-malic acid, (+)-tartaric acid.

(→-tartaric acid, tartaric acid, tartaric acid, citric acid, etc.)

The amount of the carboxylic acid compound is preferably in the range of 0.1 to 20 parts by weight per 100 parts by weight of the magnetic powder.

If the amount is less than 0.1 parts by weight, it is difficult to achieve the object of the present invention, and if it is more than 20 parts by weight, the dispersibility of the magnetic powder is rather reduced, unreacted products remain, and durability is also reduced.

In the present invention, in addition to vinyl chloride resins and resins having epoxy groups, known polyurethane resins, polyester resins, acrylic resins, and acrylic resins can be used as binders.
A common flexible resin such as Tagene copolymer resin may be included for the purpose of improving adhesion and imparting durability. Note that these flexible resins are C00M for the purpose of improving the dispersibility of magnetic powder.

803M, 804M, PO3M2. PO4M
2 (M is hydrogen, an alkali metal, or ammonium).

The magnetic powder that can be used in the present invention is Fe + Co
+Fe alloy system, Co-based -Fe 20. Any powder such as Co-containing W Fe3O4 type, γ-FeO type, Fe, 04 type, barium-ferrite type, etc. may be used.

In addition, if necessary, common materials such as lubricants, dispersants, antistatic agents and abrasives, and common resins for calming paints such as 7-enoxy resins, cellulose resins, amino resins, butyral resins and acrylic resins. It is also possible to use them within a range that does not impair achievement of the objectives of the present invention. Furthermore, there is no problem even if a commonly used polyincyanate compound is added within the usual range (and a crosslinking reaction using incyanate anti-FaK is also carried out).

If an unsaturated ruby/acid compound is used as the carboxylic acid compound having a pKa of 4 or less, the resulting coating film can be crosslinked and cured by electron beam irradiation.

In this case, it is also possible to use in combination resins, oligomers, monomers, etc. that are curable with IL radiation and have one or more unsaturated bonds in one molecule.

The vinyl chloride resin according to the present invention has an epoxy group-containing resin, a carboxylic acid compound, a magnetic powder, and the above-mentioned desired components are appropriately mixed to obtain a magnetic paint as a dispersion in any organic solvent. This coating material can be applied as a magnetic layer on a substrate such as a polyester film by any means such as 7" radar coating, per coating, gravure roll coating, or roll coating, and dried to form a mother layer. A magnetic recording medium of the invention is obtained.

(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, and durability compared to the prior art.

It is presumed that this is achieved by trapping the epoxy groups in the molecular chains of the resin having epoxy groups and preventing chain reactions of decomposition. According to the present invention, compared to the conventional method of adding various low-molecular-weight compounds such as epoxidized soybean oil, it is possible to prevent head stains due to bleeding on the surface of the magnetic layer and increase tape stickiness. There are no problems such as a decrease in tape runnability due to this, and an extremely excellent improvement effect can be exhibited.

Furthermore, according to the present invention, in the dispersion step, the epoxy group acts as a thermal stabilizer and the carboxyl group acts as a dispersing agent.
It is believed that a magnetic coating material with excellent thermal stability and dispersibility can be obtained. In addition, in the steps after applying the magnetic paint and forming the surface, it is presumed that the reaction between both components proceeds, so that improvements in wear resistance and durability are also achieved.

(Example) The present invention will be described in more detail with reference to Examples below. Note that the parts and sections in Examples and Comparative Examples are based on the amount of Ti unless otherwise specified.

Synthesis example 1 “F”? A polyester resin is synthesized by reacting a bisphenol A type epoxy resin with a molecular weight of 182 to 194 and a molecule of 355 with adipic acid, and this reaction product is further treated with 4.
Add 4'-diphenylmethane soisocyanate and heat to obtain a molecular weight of approximately 17,000 mm. An epoxy-modified polyurethane resin having a total number of xyl groups of 10 was obtained.

Synthesis Example 2 Unsaturated oro-7? obtained by thermal condensation using maleic anhydride, mixed phthalic acid, and 1,4-butanol as raw materials. The polyester resin was epoxidized with peracetic acid in toluene to obtain a molecule of [9,000, an amount of 6 epoxy groups]. A xy-modified polyester resin was obtained.

Synthesis Example 3 Acrylonitrile content is 30%, average molecular weight is 30,
The acrylonitrile-butadiene copolymer resin No. 000 was partially epoxidized with peracetic acid to obtain an epoxy-modified acrylonitrile-butadiene copolymer resin having an epoxy group size of 8.

Practical Example (Thermal Stability Test) Take 1 g of the vinyl chloride resin 11 shown in the table and 1 g of the resin having an epoxy group shown in the table, dissolve it in THF, and add 0.2# of the carbic acid compound shown in the table and 1g of the carboxylic acid compound shown in the table. Isocyanate (Japan Polyurethane Kogyo (Keg Coronet) L) o, 4g
After adding , it was coated with a doctor blade and the solvent was evaporated to create a cast film. Place this cast film II in a 15cc test tube, plug the opening with absorbent cotton sandwiched with Congo red paper, and
Thermal stability was evaluated by placing the sample in an oil path at 50°C and measuring the time until Congo red test paper changed color due to the generated hydrochloric acid.

(Glossiness test) 400 parts of cobalt-coated magnetic iron oxide powder, 70 parts of the vinyl chloride resin shown in the table, 30 parts of the same epoxy group-carrying resin used in the thermal stability test, Cal shown in the table, +/ 9 parts of a mixture consisting of 8 parts of carbonic acid compound, 300 parts of methyl ethyl ketone, 300 parts of methyl imbutyl ketone, and 300 parts of toluene.
After high-speed shear dispersion for 0 minutes, 1.20 parts of the same polyisosilane used in the thermal stability test was added and mixed for 10 minutes to prepare a magnetic paint. However, among the examples in which an unsaturated acid was used as the carbic acid compound, in Experiment No. 9.1, no polyisocyanate was added.

The obtained magnetic paint was applied to a polyester film with a film thickness of 5
It was coated to a thickness of μm, subjected to magnetic field orientation treatment, and then dried.

The reflectance of the magnetic coating film at a reflection angle of 60 parts was measured using a gloss meter. 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 cross-linked and cured for 40 hours in constant temperature 4-carbonated soda at 65°C. However, for the example (experiment number 9.10) in which an unsaturated acid was used as the carboxylic acid compound and no polyisocyanate was added, an electron beam accelerator was used instead of heat curing at a constant temperature + n. conducted the RAD electron beam irradiation.

This omega-based coating film was brought into contact with a rotating drum of 7'C40rma diameter with a load of 1]floOg attached to it and rotated at 150 rpm for a predetermined period of time. The degree of staining was determined in three stages: ◯ (dirty (-)), △ (slightly stained) x (severely stained).

The above test results are shown in the table.

As is clear from the above, according to the present invention, a magnetic recording medium having excellent thermal stability, dispersibility, and durability can be obtained.

Claims (1)

[Claims] Vinyl chloride resin, resin with epoxy group and pKa
1. A magnetic recording medium comprising a magnetic layer containing a carboxylic acid compound having a carboxylic acid compound of 4 or less.