JP2799221B2 - Magnetic recording media - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium, and particularly to a special copolymer mainly composed of vinyl chloride, which exhibits excellent performance as a binder for a ferromagnetic fine powder. The present invention relates to an improved magnetic recording medium using coalescence.

[Prior Art] A magnetic recording medium such as a magnetic tape is generally produced by providing a coating film composed of a magnetic powder and a binder (synthetic resin) on the surface of a support such as a polyester film. In recent years, high signal density and high reproduction output in single-wavelength recording have been required due to higher performance of video tapes and audio tapes. To cope with these trends, magnetic powders are more finely divided than before, and because of their very large magnetic moment, the particles tend to agglomerate with each other, resulting in uniform dispersion in the binder resin. Are becoming more difficult than ever.

Also, when dispersing the ferromagnetic fine powder, a method of applying a high shearing force to disperse the powder is used. In this case, a vinyl chloride binder is used due to the viscosity increase of the paint and the temperature rise, and the temperature rise when using a magnetic recording tape. There is a drawback that the thermal decomposition of the resin is induced to deteriorate the magnetic powder due to the hydrogen chloride gas, the durability of the magnetic recording medium is reduced, and the magnetic head is corroded.

As a means of preventing this thermal decomposition, a method of adding a stabilizer for vinyl chloride resin has been well known. However, since these are low molecular weight compounds, if they are present in a large amount in a magnetic recording medium, they will bleed from the magnetic recording medium. In order to cause the phenomenon and to reduce the durability and cause the magnetic head to be stained, the amount of its use is naturally limited, and its effect is also limited.

With respect to such technical problems, extensive studies have been made from the viewpoint of improving the affinity for magnetic powder as a binder resin. For example, as disclosed in JP-A-57-128711, vinyl chloride- Carboxylic acid vinyl ester-unsaturated carboxylic acid and unsaturated carboxylic acid anhydride-based copolymers have been proposed, but they are useful for various magnetic powders, including ultra-fine Co-containing γ-Fe ₂ O ₃ which is important as a magnetic powder. The dispersibility is poor, and the reactivity with the urethane resin is poor, so that when a magnetic paint using the same is applied to a substrate, the coating film peels off, making the magnetic recording medium impractical. They also have poor thermal stability.

In JP-A-61-117729 and JP-A-61-243934, vinyl chloride copolymers having a hydroxyl group, a carboxyl group, etc. introduced into the molecular structure have been proposed. The content of γ-Fe ₂ O ₃ and dispersibility in metal powder is not sufficient, and the solution viscosity is high, so that a large amount of organic solvent is required at the time of preparing the magnetic paint. It has the disadvantage that the magnetic head is corroded by the separated hydrogen chloride. In addition, JP-A-61-19
The copolymer disclosed in Japanese Patent No. 9220 discloses an improvement in dispersibility in magnetic powder, but is insufficient in thermal stability.

[Problems to be Solved by the Invention] Accordingly, the present invention is intended to produce a magnetic coating material having excellent Co-containing γ-Fe ₂ O ₃ of ultrafine particles, excellent dispersibility in metal powder and thermal stability, and low viscosity. It was made to develop a possible binder resin and provide a high performance magnetic recording medium.

[Means for Solving the Problems] The present invention relates to a magnetic recording medium which solves such problems, and comprises a non-magnetic support having the following structural units, (a) a vinyl chloride unit, B) Expression (Wherein R ¹ represents a hydrogen atom or a methyl group, R ² represents a monovalent hydrocarbon group), (c) a hydroxyl group-containing unit or a vinyl alcohol unit, (d) an epoxy group-containing unit, (E) Formula (F) a magnetic layer in which a ferromagnetic fine powder is dispersed in a copolymer comprising a carboxyl group-containing unit represented by (n = 1 to 8) and (f) an amine-modified vinyl unit; Magnetic recording medium.

The present inventors have conducted intensive studies on a binder resin for a magnetic recording medium consisting of a copolymer of a monomer containing vinyl chloride and an ester unit and a hydroxyl group-containing vinyl monomer in order to solve the above-mentioned problems. A specific dibasic acid half-ester is used as a component for copolymerization of a specific amount among the group-containing monomers, and a specific monomer is selected from a monomer containing a vinyl chloride and an ester unit and a carboxyl group-containing monomer. A half-ester of a dibasic acid copolymerized in a specific amount is dissolved in an organic solvent, and an amine compound is added to the solution to carry out a saponification reaction to effect amine modification, thereby obtaining ultrafine Co-containing γ-Fe ₂ particles. The dispersibility of O ₃ and metal powder is remarkably improved, and the viscosity of magnetic paint is reduced because these copolymer resins have extremely good solubility in various organic solvents used as a coating medium. Was found, and the coating property was able to be greatly improved.

The present inventors have further found that by using an epoxy group-containing monomer as a component for copolymerization, the thermal stability can be improved over a long period of time without causing a bleeding phenomenon of a stabilizer for vinyl chloride resin, and completed the present invention. It was made.

 Hereinafter, the present invention will be described in more detail.

In the present invention, a copolymer produced by a different method as described above can be used.

The first method for producing the copolymer is based on copolymerization alone. (A) Vinyl chloride, (b) Formula (Wherein R ¹ represents a hydrogen atom or a methyl group, and R ² represents a monovalent hydrocarbon group), and (c) a vinyl monomer having a hydroxyl group-containing monovalent organic group in the side chain. (D) Vinyl monomer having epoxy group, (E) Formula (Where n is an integer of 1 to 8), and (f) amino-modified vinyl units are those obtained by saponification / amine modification, for example, (a) vinyl chloride units, (b) formulas (Wherein R ¹ represents a hydrogen atom or a methyl group, and R ² represents a monovalent hydrocarbon group); (d) a vinyl monomer unit having an epoxy group; )formula (Where n is an integer of 1 to 8), and a saponification reaction is carried out in an organic solvent by adding an amine compound to a copolymer comprising a monomer unit represented by the following formula:

The copolymer as a binder resin obtained by these production methods and used in the present invention is characterized by being composed of the above-described units. About degree, vinyl chloride unit 60-95
%, Ester unit 0.1 to 15% by weight, hydroxyl group-containing unit or vinyl alcohol unit 3 to 15% by weight, epoxy group-containing unit 0.1 to 8% by weight, carboxyl group-containing unit 0.1 to 10%
It is preferable that the composition has a weight percentage of 0.05 to 5% by weight of an amine-modified vinyl unit and has an average degree of polymerization of 200 to 500.

 Next, each copolymerized unit will be described.

(A) The vinyl chloride unit, which is a unit, imparts physical strength. If the amount is too small, the physical strength decreases. On the other hand, if the amount is too large, the solubility decreases, which is disadvantageous in use. . It is preferably from 60 to 95% by weight, but a particularly preferred range is from 65 to 88% by weight.

The ester unit (b) is used to improve the solubility, flexibility and the like of the copolymer.
As the monomer corresponding to the unit, Is mentioned. R ¹ in the formula is a hydrogen atom or a methyl group, R ²
Is a monovalent hydrocarbon group.

Desirable vinyl esters corresponding to the above formula [I] include vinyl acetate, vinyl propionate, vinyl versatate (manufactured by Ciel Chemical Co., Ltd.), vinyl stearate,
Examples thereof include vinyl benzoate. Further, desirable (meth) acrylates corresponding to the formula [II] include:
Ethyl acrylate, butyl acrylate, acrylic acid 2-
Examples include ethylhexyl and propyl methacrylate.

As the ester unit (b), any of the above-mentioned formulas [I] to [II] may be used alone or in combination of two or more thereof, but the polymerization ratio in the copolymer is high. If the amount is too large, the resin becomes soft and the durability of the magnetic recording medium (magnetic tape or the like) decreases, so that the content is in the range of 0.1 to 15% by weight, particularly 3 to 7% by weight as described above. Is desirable.

However, in the case of the saponification / amine modification method, since the ester unit [I] is converted into a vinyl alcohol unit by the saponification reaction, an amount for obtaining a desired vinyl alcohol unit content% by weight after saponification is obtained. It is necessary to copolymerize the ester unit [I]. In the case of this saponification / amine modification method, it is optional to copolymerize the hydroxyl group-containing unit and use both units together.

Examples of the monomer corresponding to the hydroxyl group-containing unit (c) include the following.

If the weight ratio in the copolymer of the hydroxyl group-containing units introduced by these monomers is too small, not only does the dispersibility of the ferromagnetic powder deteriorate, but also the compatibility with the polyurethane resin and the like used as appropriate. On the other hand, if the amount is too large, the viscosity increases greatly when the isocyanate prepolymer is blended, which causes a problem in pot life, lowers the physical strength and decreases the durability of the magnetic recording medium (such as a magnetic tape). As described above, the content is preferably in the range of 3 to 15% by weight, particularly preferably in the range of 7 to 10% by weight.

Examples of the monomer corresponding to the epoxy group-containing unit (d) include glycidyl ethers of unsaturated alcohols such as allyl glycidyl ether and methallyl glycidyl ether, glycidyl acrylate, glycidyl methacrylate, methyl glycidyl itaconate, and glycidyl ethyl. Glycidyl esters of unsaturated acids such as malate and the like can be mentioned. The ratio of these polymerizations in the copolymer is desirably in the range of 0.1 to 8% by weight, particularly preferably in the range of 1 to 5% by weight. If the amount is too small, the dehydrochlorination property upon heating is remarkable. If it is too much, the resin will not be soluble in various organic solvents used as a coating medium.

The monomer corresponding to the carboxyl group-containing unit (e) is a half-ester of a polymerizable unsaturated dibasic acid, such as a monoalkyl maleate or a monoalkyl fumarate (both are methyl as an alkyl group). ,
Ethyl, propyl, butyl, hexyl, octyl, etc.)
Is mentioned.

The polymerization ratio in the copolymer is desirably in the range of 0.1 to 10% by weight, particularly preferably in the range of 0.5 to 5% by weight. If the amount is too small, the dispersibility decreases. Would.

(F) In order to introduce an amine-modified vinyl unit by a saponification / amine-modification method, various amine compounds such as an aliphatic amine, an alicyclic amine, and an aromatic amine are added to a copolymer in an organic solvent. , And simultaneously with saponification.

Examples of these amine compounds include ethylamine, propylamine, butylamine, cyclohexylamine, ethanolamine, naphthylamine, aniline,
O-toluidine, diethylamine, dioctylamine,
Diisobutylamine, diethanolamine, N-methylaniline, trimethylamine, triethylamine, tributylamine, triisobutylamine, tridecylamine, N-methyldiphenylamine, triethanolamine, dimethylbenzylamine, tetramethylethyldiamine, tetramethyl-1, 3-diaminopropane, pentamethyldiethylenetriamine, hexamethylenetetramine, pyridine, α-picoline, β-picoline, γ-picoline, 2.4-lutidine, quinoline, morpholine and the like.

The amine-modified vinyl unit in this production method is considered to be formed by the reaction of the amine compound with the chlorine atom of the vinyl chloride component to be introduced into the side chain at the same time as the saponification reaction.

Although this has not been confirmed structurally, the fact that it does not exist as a mere mixture but binds to the resin means that nitrogen atoms can be quantified even in a resin washed with a large amount of organic solvent after the saponification reaction. It is based on facts.

That is, the term "amine-modified vinyl unit" in the present invention is defined based on the above-mentioned purpose, and the amount is determined by nitrogen atom analysis by the termulene method on the assumption that one amine compound is added to one vinyl chloride molecule. It is calculated from the value.

The proportion of amine-modified vinyl units in the resin is 0.05 to
It is desirable to be in the range of 5% by weight, particularly in the range of 0.05 to 2% by weight. If the amount is too small, the viscosity of the magnetic paint becomes too high, and further improvement in dispersibility in metal powder cannot be expected. On the other hand, if the amount is too large, the solubility of the resin is lowered, and the crosslinking reaction with the isocyanate compound is too fast to be usable, which is not preferable.

If the average degree of polymerization of the copolymer composed of such unit components is too low, the physical strength of the magnetic layer decreases, and the durability of the magnetic tape or the like also decreases. If the concentration is too high, the solution viscosity at a predetermined concentration becomes high and the workability deteriorates remarkably, so that the average polymerization degree is preferably in the range of 200 to 500.

In addition, this copolymer can be generally produced by a suspension polymerization method, an emulsion polymerization method, a solution polymerization method, a bulk polymerization method, or the like.

On the other hand, in the saponification / amine modification method, the copolymer is dispersed or dissolved in alcohol or another organic solvent, an amine compound is added thereto, and an alkali such as KOH, NaOH, sodium alcoholate is used as a catalyst, 30
Heat to ~ 80 degrees to perform the saponification reaction.

As the alcohol in this case, any alcohol can be used as long as the above object can be achieved. Usually, methyl alcohol, ethyl alcohol, butyl alcohol, and isopropyl alcohol are used. Other organic solvents include hydrocarbons such as hexane, heptane, benzene, toluene and xylene; esters such as methyl acetate, ethyl acetate and butyl acetate; ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone and cyclohexanone; There are ethers such as ethyl ether and tetrahydrofuran, and other solvents may be mixed and used.

When the above copolymer is used as a binder resin, other resins may be used in equal amounts or less as necessary, and the resins that can be used in combination include polyurethane resins, nitrocellulose, epoxy resins, and polyamides. Examples include resins, phenolic resins, and various polymers such as polymers or copolymers of acrylates, methacrylates, styrene, acrylonitrile, butadiene, ethylene, propylene, vinylidene chloride, acrylamide, vinyl ethers and the like. Among these, polyurethane resin and nitrocellulose are particularly preferable.

It is desirable to use another polyisocyanate-based curing agent in combination, and as the curing agent, tolylene diisocyanate, diphenylmethane diisocyanate,
Bifunctional isocyanates such as hexane diisocyanate,
Examples include trifunctional isocyanates such as Coronate L (trade name, manufactured by Nippon Polyurethane Industry) and Disel Module L (trade name, manufactured by Bayer AG), and urethane prepolymers containing isocyanate groups at both terminals.

As the ferromagnetic powder used in the present invention, γ-Fe
₂ O ₃ , Fe ₃ O ₄ and those adsorbed or doped with these cobalt ions, or CrO ₂ etc., further Fe, Co,
Other conventionally known various magnetic powders such as a needle-shaped fine particle metal material containing Fe-Co or optionally Ni or the like are exemplified. The mixing ratio of the ferromagnetic powder and the binder resin is desirably 8 to 30 parts by weight of the binder resin per 100 parts by weight of the ferromagnetic powder.

In order to uniformly disperse the ferromagnetic powder and the binder resin, conventionally used lubricants, abrasives,
The addition of antistatic agents, dispersing aids, rust inhibitors, etc., and the use of various other organic solvents such as methyl ethyl ketone, methyl isobutyl ketone, and toluene as the coating medium may be the same as in the past. There are no restrictions.

As the support, synthetic resins such as polyester, polyolefin, cellulose acetate, and polycarbonate, other non-magnetic metals, and ceramics are used. The form is a film, tape, sheet, plate, or the like.

As a coating means for forming a magnetic layer on a support, a conventionally known method may be used, and a high-performance magnetic recording medium aimed at by the present invention is obtained by appropriately performing a smoothing treatment such as a calendering treatment. Is obtained.

[Examples] Next, the present invention will be specifically described based on examples. All parts in the examples are parts by weight, and all parts are percentages by weight.

Example 1 After autoclave equipped with a stirrer was replaced with nitrogen, 280 parts of methanol, 375 parts of pure water, 200 parts of vinyl chloride, 75 parts of vinyl acetate, 3 parts of allyl glycidyl ether, mono (2-ethylhexyl) maleate were used. 3 parts, as a polymerization initiator, 5 parts of di (2-ethylhexyl) peroxydicarbonate, and 1 part of methylcellulose were charged and heated to 63 ° C. with stirring to start the reaction, and the internal pressure was maintained at 6 kg / cm ² . While adding 200 parts of vinyl chloride and 114 parts of a mixture (7 parts of mono (2-ethylhexyl) maleate, 7 parts of allyl glycidyl ether, 100 parts of methanol) to 8 parts each.
It took a long time to perform continuous press-fitting to cause a copolymerization reaction.

After the internal pressure of the autoclave became ² kg / cm ² after 10 hours, the residual pressure was released, the mixture was cooled, filtered, washed, dehydrated and dried to obtain a copolymer powder (polymer A).

The thus obtained polymer A (160 parts) was treated with methanol.
430 parts, acetone 40 parts, sodium hydroxide 16 parts, dimethylethanolamine 2.4 parts together with a reactor (stirrer,
After the reaction at 45 ° C for 8 hours,
It was washed three times with 1000 parts of methanol and further twice with 1000 parts of pure water, filtered and dehydrated to obtain 130 parts of powder (polymer).

As a result, vinyl chloride unit 88.7%, ester unit 0.4
%, Vinyl alcohol unit 7.3%, epoxy group containing unit
A copolymer having 1.5%, a carboxyl group-containing unit 1.8%, an amine-modified vinyl unit 0.3%, and an average degree of polymerization of 400 was obtained.

<Comparative Example 1> After nitrogen replacement in an autoclave equipped with a stirrer, 280 parts of methanol, 375 parts of pure water, 115 parts of vinyl chloride, 5 parts of vinyl acetate, 15 parts of 2-hydroxypropyl acrylate, and mono (2-ethylhexyl) maleate were used. ) 3 parts of an ester, 5 parts of di (2-ethylhexyl) peroxydicarbonate as a polymerization initiator, and 1 part of methylcellulose were charged and heated to 60 ° C. with stirring to start the reaction. 300 parts of vinyl, 20 parts of vinyl acetate, 2
-Hydroxypropyl acrylate 35 parts, maleic acid mono (2-ethylhexyl) ester 7 parts, methanol 10
0 parts) 462 parts were continuously press-fitted for 7 hours to carry out a copolymerization reaction.

After the internal pressure of the autoclave reached 2 kg / cm ² after 11 hours, the residual pressure was released, the mixture was cooled, filtered, washed, dehydrated and dried to obtain 470 parts of a copolymer powder (polymer).

As a result, vinyl chloride unit 84.4%, ester unit 4.6
%, Hydroxyl group-containing unit 9.3%, carboxyl group-containing unit 1.7
%, An average degree of polymerization of 430 was obtained.

<Comparative Example 2> Under the same polymerization conditions as in Comparative Example 1, the following polymerization was carried out.

Initial charge Additional mixture Methanol 280 parts 100 parts Pure water 375-Vinyl chloride 105 300 Vinyl acetate 5 20 2-Hydroxypropyl acrylate 15 35 Allyl glycidyl ether 3 7 Maleic acid mono (2-ethylhexyl) ester 3 7 440 parts of a polymer powder (polymer) were obtained.

<Comparative Example 3> 160 parts of polymer A was converted to 430 parts of methanol, 40 parts of acetone,
Charge it in a reactor (with a stirrer and jacket) with 16 parts of sodium hydroxide and react at 45 ° C for 4 hours.
Wash three times with one part methanol and two more with 1000 parts pure water.
Washing and filtration and dehydration were repeated 140 times to obtain 140 parts of powder (polymer).

As a result, vinyl chloride unit 89.2%, ester unit 0.8
%, Vinyl alcohol unit 6.9%, epoxy group containing unit
1.5%, carboxyl group-containing unit 1.6%, average polymerization degree 390
Was obtained.

A sample was prepared by the following method using the composition analysis result, average polymerization degree analysis result, and each polymer of the copolymer powder (polymer to) obtained above, and various physical properties (solution viscosity, heat stability, dispersibility). , Magnetic paint viscosity and magnetic performance) are shown in Table 1.

(1) Solution viscosity 40 parts of the copolymer resin was dissolved in 160 parts of a solvent (methyl ethyl ketone / methyl isobutyl ketone / toluene = 1/1/1), and the viscosity of the solution adjusted to 25 ° C. was measured using a B-type viscometer. Measured.

(2) Thermal stability 1 g of the copolymer resin was precisely weighed in a 15 cc test tube, and the opening was plugged with absorbent cotton sandwiched with Congo Red test paper.
The sample was placed in an oil bath at 0 ° C., and the time required for the Congo Red test paper to change its color due to the generated hydrochloric acid was measured.

(3) Dispersibility 10 parts of copolymer resin is put into a solvent composed of 30 parts of methyl ethyl ketone, 30 parts of methyl isobutyl ketone, and 30 parts of toluene.
After dissolving at 50 ° C. for 1 hour, 5 parts of polyurethane resin N-2304 (manufactured by Nippon Polyurethane Industry Co., Ltd.) and 40 parts of the following magnetic powders A to C were added while mixing with an Eiger mill, and kneaded for 1 hour. Further, 2 parts of Coronate L (manufactured by Nippon Polyurethane Co., Ltd.) was added and kneaded for 5 minutes to obtain a magnetic paint. This was applied on a 21 micron thick polyester film to a thickness of 6 μm, subjected to a magnetic field orientation treatment, and dried.

Magnetic powder A: 45.0 m ² / g Co-containing γ-Fe ₂ O ₃ magnetic powder B: 50.0 m ² / g Co-containing γ-Fe ₂ O ₃ magnetic powder C: 67.5 m ² / g metal powder (Si System, gas phase) The gloss (%) of the magnetic tape thus produced was measured. The gloss was measured using a gloss meter (manufactured by Murakami Color Research Institute) and the reflectance at 60 ° was compared with that of a standard glass plate. This value represents the dispersibility of the magnetic powder in the magnetic coating,
It is determined that the larger the numerical value, the better the dispersibility.

(4) Viscosity of magnetic paint The viscosity of the magnetic paint obtained above was measured using an E-type viscometer.

(5) Magnetic Performance Using the magnetic tape prepared above, the squareness ratio was measured using a vibrating sample magnetometer (manufactured by Toei Kogyo).

[Effects of the Invention] The binder resin forming the magnetic recording medium of the present invention has excellent dispersibility in ultrafine Co-containing γ-Fe ₂ O ₃ and metal powder and solubility in various organic solvents used as a coating medium. Is extremely good, and the viscosity of the magnetic paint is low, so the coating performance is very good.Moreover, it shows excellent thermal stability, so that a high-performance magnetic recording medium with good durability and excellent stability over time can be obtained. The practical value is great.

In addition, the binder resin used in the present invention has an advantage that it has sufficient compatibility with a polyurethane resin or the like used in combination as appropriate, and is easy to react and crosslink with an isocyanate group-containing urethane polymer or the like. Therefore, by using this as a binder, a high-performance magnetic recording medium with improved long-term durability can be obtained.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-1-292621 (JP, A) JP-A-62-181310 (JP, A) JP-A-64-39624 (JP, A) (58) Investigation Field (Int.Cl. ⁶ , DB name) G11B 5/702

Claims (2)

(57) [Claims] 1. A non-magnetic support comprising the following structural units: (a) a vinyl chloride unit; (Wherein R ¹ represents a hydrogen atom or a methyl group, and R ² represents a monovalent hydrocarbon group), (c) a hydroxyl group-containing unit or a vinyl alcohol unit, and (d) an epoxy group-containing unit. , (E) (Where n is an integer of 1 to 8) and a magnetic layer in which a ferromagnetic fine powder is dispersed in a copolymer comprising a carboxyl group-containing unit represented by (f) an amine-modified vinyl unit Magnetic recording medium. 2. A copolymer for dispersing a ferromagnetic fine powder,
(A) unit 60-95% by weight, (B) unit 0.1-15% by weight,
(C) unit 3 to 15% by weight, (d) unit 0.1 to 8% by weight,
(E) Unit 0.1-10% by weight, (F) Unit 0.05-5% by weight
The magnetic recording medium according to claim 1, wherein the magnetic recording medium has an average degree of polymerization of 200 to 500.