JPH0682454B2 - Radiation-curable magnetic recording medium - Google Patents

Description

TECHNICAL FIELD The present invention relates to a magnetic recording medium having excellent magnetic properties and mechanical properties.

(Prior Art) A general-purpose magnetic tape is prepared by dispersing needle-shaped magnetic particles having a major axis of 1 μm or less in a binder solution together with an appropriate additive (dispersant, lubricant, antistatic agent, etc.) to prepare a magnetic paint. Is applied to a polyethylene terephthalate film.

A magnetic recording medium is required to have a high density of magnetic recording and a high reproduction output. For that purpose, it is necessary to highly pack and orient the magnetic particles having a high coercive force. In order to achieve high packing and high orientation, magnetic particles must be dispersed up to primary particles. The dispersion of magnetic particles is greatly influenced by the binder,
Even if a disperser having high dispersion efficiency is used, the magnetic particles are not dispersed in the coating material if the dispersibility of the binder is low. Although magnetic particles having a high coercive force have been developed, the magnetic particles become difficult to disperse as the coercive force increases.

Conventionally, vinyl chloride / vinyl acetate copolymers, vinyl chloride / vinyl acetate / vinyl alcohol copolymers, vinyl chloride / vinylidene chloride copolymers, thermoplastic polyurethane resins, thermosetting polyurethane resins, polyesters have been used as magnetic binders. Resin, acrylonitrile-butadiene copolymer, nitrocellulose, cellulose state butyrate, epoxy resin, acrylic resin, etc. are used. On the other hand, as radiation-curable binders, vinyl chloride / vinyl acetate copolymers having acrylic double bonds, epoxy resins, polyester resins, polyurethane resins, acrylic resins, etc. have been proposed, but for video tapes and electronic computers. In the current situation, the magnetic properties are not sufficient, especially for applications requiring high performance such as tapes. It is known to use a surfactant as a dispersant for improving magnetic properties,
Due to the presence of a low molecular weight surfactant in the magnetic coating film, there are drawbacks such as deterioration of physical properties and aging.

Magnetic tape has not only excellent magnetic properties, but also wear resistance,
It must have excellent mechanical properties such as runnability, flexibility, and adhesion to a support. Magnetic tapes using polyester resin and polyurethane resin as binders are available in Japanese Patent Publications No. 44-17947, No. 44-18222, No. 45-24900,
JP-B-44-23500, JP-B-45-24902, JP-B-49-4812
6, JP-B-48-31611, JP-B-48-31610, JP-B-42-154
32, Japanese Patent Publication No. 51-6522, it has excellent mechanical properties and is useful as a magnetic tape binder.

(Problems to be Solved by the Invention) It is disclosed in JP-B-54-28603 and JP-B-58-41565 that the dispersibility of magnetic particles is dramatically improved by introducing a metal salt of sulfonic acid into a polyester resin or a polyurethane resin. Although disclosed in the official gazette, the effect of the metal salt of sulfonic acid is due to its hydrophilicity, and the metal salt of a phosphorus compound such as phosphinic acid and phosphonic acid can be expected to have the same effect. Similar effects are expected in resins. However, metal salts of phosphorus compounds, such as phosphinic acid and phosphonic acid, may cause deactivation of catalysts during the production of polyester resins, polyurethane resins, polyester acrylate resins, acrylate compounds, etc., or physical properties of polymers obtained by forming ether bonds. May be reduced, or the polarity may be different, resulting in separation without uniform reaction. Polyurethane resin, polyurethane acrylate resin, epoxy acrylate resin, etc.
Since metal salts of phosphorus compounds such as phosphonic acid are highly inorganic, they can be reacted in a general-purpose solvent or in the absence of solvent to form a resin,
It was impossible to introduce this hydrophilic group.

(Means for Solving the Problems) In view of the above circumstances, the present inventors have found that the cured coating film retains the mechanical properties of the polyester resin, polyurethane resin, epoxy resin, acrylic resin and the like. , For the purpose of improving the dispersibility of magnetic particles,
As a result of diligent studies, stable production of polyurethane resin, polyurethane acrylate resin, polyester acrylate resin, epoxy acrylate resin, etc. can be achieved by using a specific phosphorus compound, and the desired dispersibility of magnetic particles is significantly improved. I found that

That is, the present invention is a magnetic recording medium in which a magnetic material in which a ferromagnetic powder is dispersed in a binder is applied and cured on a non-magnetic support, and the following formulas (I) to (I) are used as components in the binder.
A magnetic recording medium comprising a phosphorus-containing polyurethane acrylate resin having at least one acrylic double bond in the molecule, which has been reacted with at least one compound represented by formula (III).

(In the formula (I), (II) or (III), X and Y are ester-forming functional groups, R ₁ and R ₂ are lower alkylene groups having 1 to 6 carbon atoms, and R ₃ is 1 carbon atom. Is an alkyl group of 10 to 10, and m and n can take any numerical values of 0 to 10. M is an alkali metal atom, a hydrogen atom, or 1 to 10 carbon atoms.
6 represents a lower alkyl group. The radiation-curable resin of the present invention has at least one acrylic double bond in the molecule and is a phosphorus-containing radiation obtained by reacting at least one of the phosphorus compounds represented by the formulas (I) to (III). It is a curable resin. Specifically, it is a polyurethane acrylate resin bonded to the acrylic double bond-containing compound (A) via a urethane bond.

The acrylic double bond contained in the binder of the present invention refers to residues (acryloyl group or methacryloyl group) of acrylic acid, acrylic acid ester, acrylic acid amide, methacrylic acid, methacrylic acid ester, methacrylic acid amide and the like.

The acrylic double bond-containing compound (A) is (meth)
Acrylic acid and other carboxyl group-containing acrylic compounds (A-1), ethylene glycol, diethylene glycol, hexamethylene glycol and other glycol mono (meth) acrylates, trimethylolpropane, glycerin, trimethylolethane and other triol compound mono ( Mono (meth) acrylates of tetravalent or higher valent polyols such as (meth) acrylate and di (meth) acrylate, pentaerythritol, dipentaerythritol,
Di (meth) acrylate, tri (meth) acrylate,
Hydroxy group-containing acrylic compounds such as glycerin monoallyl ether and glycerin diallyl ether (A-
2), glycidyl group-containing acrylic compound (A-3) such as glycidyl (meth) acrylate, amino group-containing acrylic compound (A-4) such as (meth) acrylamide, monomethylol (meth) acrylamide, cyanoethyl (meth) ) An isocyanate group-containing acrylic compound (A-5) such as acrylate.

It is necessary that at least one of these acrylic double bonds is present in the molecule of the binder. If the number is less than one, the crosslinking density will not be sufficiently high and the film will have poor mechanical strength, which is not preferable.

The polyurethane acrylate resin is generally obtained by reacting a hydroxyl group-containing resin and a hydroxyl group-containing acrylic compound (A-2) with a polyisocyanate-containing compound. Examples of the hydroxyl group-containing resin include polyalkylene glycols such as polyethylene glycol, polybutylene glycol, and polypropylene glycol, alkylene oxide adducts of bisphenol A, various glycols, and polyester polyol (B) having a hydroxyl group at the molecular chain end. To be Among these, polyester polyol (B)
Polyurethane acrylate resin obtained as one component is preferable.

As the carboxylic acid component of the polyester polyol (B), terephthalic acid, isophthalic acid, orthophthalic acid, 1,
Aromatic dicarboxylic acids such as 5-naphthalic acid, p-oxybenzoic acid, aromatic oxycarboxylic acids such as p- (hydroxyethoxy) benzoic acid, succinic acid, adipic acid, azelaic acid, sebacic acid, dodecanedicarboxylic acid, etc. Unsaturated aliphatic and alicyclic dicarboxylic acids such as aliphatic dicarboxylic acids, fumaric acid, maleic acid, itaconic acid, tetrahydrophthalic acid, hexahydrophthalic acid, trimellitic acid, trimesic acid, pyromellitic acid and other tri and tetra A carboxylic acid etc. can be mentioned.

As the glycol component of the polyester polyol (B), ethylene glycol, propylene glycol, 1,
3-propanediol, 1,4-butanediol, 1,5-pentadiol, 1,6-hexanediol, neopentyl glycol, diethylene glycol, dipropylene glycol, 2,2,4-trimethyl-1,3-pentanediol ,
1,4-cyclohexanedimethanol, bisphenol A
Ethylene oxide adduct and propylene oxide adduct of hydrogenated bisphenol A, ethylene oxide and propylene oxide adduct of hydrogenated bisphenol A, polyethylene glycol, polypropylene glycol, and polytetramethylene glycol. Further, tri- and tetraols such as trimethylolethane, trimethylolpropane, glycerin and pentaerythritol may be used in combination. Other polyester polyols include lactone polyester diols obtained by ring-opening polymerization of lactones such as ε-caprolactone.

The polyisocyanate (C) used in the present invention is
2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, p-phenylene diisocyanate, biphenyl methane diisocyanate, m-phenylene diisocyanate, hexamethylene diisocyanate, tetramethylene diisocyanate, 3,3'-dimethoxy-4, 4'-
Biphenylene diisocyanate, 2,4-naphthalene diisocyanate, 3,3'-dimethyl-4,4'-biphenylene diisocyanate, 4,4'-diphenylene diisocyanate, 4,4'-diisocyanate-diphenyl ether, 1,5'-naphthalene diisocyanate, p-xylylene diisocyanate, m-xylylene diisocyanate, 1,3-diisocyanate methylcyclohexane, 1,4
-Diisocyanate methylcyclohexane, 4,4'-diisocyanate dicyclohexane, 4,4'-diisocyanate cyclohexylmethane, isophorone diisocyanate, or other diisocyanate compound, or 3 mol% or less of 2,4-tolylene diisocyanate in all isocyanate groups. Examples of the triisocyanate compound include trimers and hexamethylene diisocyanate trimers.

The specific phosphorus compound that characterizes the radiation-curable resin of the polyurethane acrylate resin used in the present invention is the phosphorus compound represented by the above formulas (I) to (III). The structural formulas of typical examples of these phosphorus compounds are shown below.

Examples of the compound represented by the formula (I) are as follows.

Examples of the compound represented by the formula (II) are as follows.

Examples of the compound represented by the formula (III) include the following.

These specific phosphorus compounds can be reacted through various processes. For example, polyester polyol (B),
It can be used as one component when producing a raw material resin such as polyalkylene glycol or epoxy resin. In particular, when the polyester polyol (B) is produced, the phosphorus compounds represented by the formulas (I) to (III) can be added and reacted at any stage before the completion of the polymerization of the polyester polyol (B). From the viewpoint of operation during production, it is preferably added after the transesterification reaction or after the esterification reaction.

Further, these specific phosphorus compounds can be used as one component of the raw material of the polyurethane acrylate resin. For example, it contains a hydroxyl group. The phosphorus compound can be directly reacted with the isocyanate compound (C), the polyester polyol (B) or the acrylate compound (A) to produce a polyurethane acrylate resin.

The radiation-curable resin of the present invention is prepared by a known method using a solvent containing an acrylic double bond-containing compound (A) and a specific phosphorus compound and / or a raw material containing a raw material resin reacted with the specific phosphorus compound. It can be obtained by reacting in medium or without solvent. The obtained resin has a molecular weight of 500 to 100,0.
00 is desirable.

The phosphorus compounds represented by the general formulas (I) to (III) are appropriately used so that the resin contains 200 ppm to 50,000 ppm of phosphorus atoms. If the phosphorus compound is less than the above range, the dispersibility in the magnetic particles is low. On the other hand, if it exceeds the above range, the hygroscopicity is increased, the physical properties are deteriorated, the adhesion to the non-magnetic support is deteriorated, and the practicality is reduced.

In the present invention, in addition to the resins obtained by reacting the phosphorus compounds represented by the general formulas (I) to (III), the flexibility of the magnetic tape can be adjusted, the heat resistance and cold resistance can be improved, and the wear resistance can be improved. It is desirable to add another compatible resin for the purpose or to mix a compound which reacts with the resin of the present invention to crosslink.

Examples of the resin compatible with the resin of the present invention include vinyl chloride resin, polyester resin, cellulose resin, acrylic resin, epoxy resin, phenoxy resin, polyvinyl butyral, acrylonitrile-butadiene copolymer and the like. Further, compounds that crosslink with the radiation-curable resin of the present invention include epoxy-based acrylic oligomers, spirane ring-containing acrylic-based oligomers, ether-acrylic-based oligomers, acrylic-based polyhydric alcohols, and other acrylic-based oligomers having a molecular weight of 200 to 10,000. .

The ferromagnetic particles used in the present invention include γ-Fe ₂ O
₃ , mixed crystal of γ-Fe ₂ O ₃ and Fe ₃ O ₄ , CrO ₂ , cobalt ferrite, cobalt adsorbed iron oxide, barium ferrite, Fe-C
Examples thereof include ferromagnetic alloy powders such as o and Fe-Co-Ni.

The magnetic recording medium of the present invention may optionally contain a flexibilizer such as dibutyl phthalate, triphenyl phosphate, dioctyl sulfo sodium succinate, t-butyl phenol-polyethylene ether, ethyl naphthalene-sodium sulfonate, dilauryl succinate. A lubricating oil such as nate, zinc stearate, soybean oil lecithin, and silicone oil, and various antistatic agents can also be added.

A magnetic material in which ferromagnetic powder is dispersed in a binder generally uses a solvent, and the solvent includes acetone, methyl ethyl ketone, methyl isobutyl ketone, ketones such as cyclohexanone, alcohols such as methanol, methyl acetate, acetic acid. Esters such as ethyl, butyl acetate, ethyl butyrate, ethylene glycol dimethyl ether, ethylene glycol monoethyl ether, glycol ethers such as dioxane, aromatic hydrocarbons such as benzene, toluene, xylene, and aliphatic carbonization such as hexane and heptane. Hydrogen or a mixture thereof can be used.

In the radiation curable magnetic recording medium of the present invention, the above magnetic material is coated on a non-magnetic support. As the material of the non-magnetic support that can be used, for example, polyester such as polyethylene terephthalate, polyolefin such as polypropylene,
Examples thereof include cellulose derivatives such as cellulose triacetate and cesulose diacetate, polycarbonate, polyvinyl chloride, polyimide, metals such as aluminum and copper, and paper.

The magnetic material is coated on a non-magnetic support by a conventional method and dried, and then the coating film is subjected to calendering treatment and radiation treatment if necessary. A calendar process can also be performed after the radiation process. In particular, as irradiation radiation, ionizing radiation such as neutron rays and γ rays can be used in addition to electron beams,
The radiation amount is preferably about 1 to 10 Mrad, and particularly preferably about 2 to 8 Mrad.

(Function) In the present invention, the radiation-cured coating film obtained by using a resin obtained by reacting a phosphorus compound as at least one component of the binder retains the mechanical properties of the polyester resin or polyurethane resin, while maintaining the magnetic particles. The dispersibility can be improved, and the properties resulting from the dispersibility, such as the filling properties of the magnetic particles, the orientation, and the smoothness of the magnetic layer, are excellent, and the powder has less dust and has good durability.

(Examples) Hereinafter, the present invention will be specifically described with reference to Examples. In the examples, "parts" means "parts by weight".

Example of production of raw material polyester In an autoclave equipped with a thermometer and a stirrer, 485 parts of dimethyl terephthalate and 485 of dimethyl isophthalate
, Ethylene glycol 409 parts, neopentyl glycol 458 parts and tetrabutoxy titanate 0.68 parts were charged and heated at 150 to 230 ° C. for 120 minutes for transesterification,
Then, 23.6 parts of the phosphorus compound (F) was charged, and the temperature was 220 to 230 ° C.
The reaction was carried out for 1 hour. Then the reaction system is 25
Raise the temperature to 0 ° C and gradually reduce the system pressure, and after 45 minutes 10mmHg
The reaction was continued for another 60 minutes under these conditions. The raw material polyester A obtained has a molecular weight of 2,000 and a phosphorus content of 3,300 pp.
It was m.

Raw material polyesters B to F obtained by the same manufacturing method
Is shown in Table 1. The resin composition was analyzed by NMR. First
The starting polyester F in the table did not show an increase in viscosity during polymerization. The raw material polyester E was completely separated from the resin by agglomeration of the sodium salt of the phosphorus compound into particles.

The constituent units of the raw material polyesters E and F represent the molar ratio of the acid component and the glycol component when the raw material was charged.

Method for producing polyurethane acrylate resin After dissolving 72 parts of toluene, 72 parts of methyl ethyl ketone and 100 parts of polyester diol A in a reaction vessel equipped with a thermometer, a stirrer and a reflux condenser, 10.8 parts of 2,4-tolylene diisocyanate and dibutyl After charging 0.05 part of tin dilaurate and reacting at 70-80 ° C for 3 hours, 33 parts of pentaerythritol triacrylate was further added and reacted at 70-80 ° C for 10 hours to obtain a polyurethane acrylate resin solution having a solid content concentration of 50% by weight. Got The solvent was evaporated from the reaction solution.
Polyurethane acrylate resin A had a molecular weight of 2700 and a phosphorus content of 2300 ppm.

By the same manufacturing method, polyester diols B to D,
Polyurethane acrylate resins BF were obtained from GH. The resulting polyurethane acrylate resin is shown in Table 2.

Examples 1 to 4 Comparative Examples 1 and 2 Magnetic powder (Cobalt-coated γ-Fe ₂ O ₃ ) 60 parts Polyurethane acrylate resin A solution 30 parts (solid content concentration 50%, solvent methyl ethyl ketone / toluene = 1/1 weight ratio) methyl ethyl ketone 25 parts Toluene 25 parts Methyl isobutyl ketone 25 parts The above composition was mixed in a ball mill for 24 hours, and then this magnetic paint was applied onto a 25 μm polyethylene terephthalate film so that the thickness after drying would be 6 μm. Then 0.
A magnetic field orientation treatment was carried out in the length direction of the film by a direct current magnetic field of 2500 gauss for 05 seconds, followed by hot air drying at 100 ° C. for 1 minute, calendering treatment and radiation treatment of 5 Mrad.

Urethane-modified acrylate resin (B) shown in Table 2
(F) Methyl ethyl ketone / toluene (1/1 weight ratio)
The solution was used to form a magnetizable layer on a polyethylene terephthalate film in a similar manner.

The measurement results of each magnetizable layer are shown in Table 3.

As is clear from Table 3, the magnetic recording media obtained from polyurethane acrylate resins A, B, E and F had Br / Bm values,
Excellent adhesion, smoothness and solvent resistance.

(Effects of the Invention) As is clear from the examples and comparative examples, conventionally, it was difficult to introduce a metal base of a phosphorus compound such as phosphinic acid and phosphonic acid into a resin. Not only can a group be introduced, it is effective for the dispersibility of the magnetic powder, and the characteristics of the base resin forming the basic skeleton are not compromised at all.

Claims (1)

[Claims] 1. A magnetic recording medium comprising a non-magnetic support coated with a magnetic material in which a ferromagnetic powder is dispersed in a binder and cured. The following formulas (I) to (III) are used as components in the binder.
A radiation-curable magnetic recording medium containing a phosphorus-containing polyurethane acrylate resin having at least one acrylic double bond in the molecule, which is obtained by reacting at least one of the phosphorus compounds represented by (In the formula (I), (II) or (III), X and Y are ester-forming functional groups, R ₁ and R ₂ are lower alkylene groups having 1 to 6 carbon atoms, and R ₃ is 1 to 6 carbon atoms. Is a lower alkyl group, and m and n can take any numerical values from 0 to 10.
M represents an alkali metal atom, a hydrogen atom or a lower alkyl group having 1 to 6 carbon atoms. )