JP3071310B2 - Magnetic recording media - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium such as a magnetic tape, a magnetic card and the like, and more particularly to a method of copolymerizing a special monomer having excellent performance as a binder for a ferromagnetic fine powder. The present invention relates to an improved magnetic recording medium using the obtained acrylic copolymer.

[0002]

2. Description of the Related Art Magnetic recording media such as magnetic tapes and magnetic cards are generally produced by providing a coating (magnetic layer) comprising a magnetic powder and a binder (synthetic resin) on the surface of a support such as a polyester film. ing. In recent years, magnetic powders have been made finer and more coercive with the demand for improvement in recording density of magnetic recording media and improvement in S / N and C / N ratios. In order to form a smooth magnetic layer having a high degree of filling and to improve the performance as a magnetic recording medium, the dispersion performance of the binder is a critical factor.

[0003] Such ferromagnetic powder materials are transferred from iron oxide to iron oxide to which cobalt ions are adsorbed or doped, and furthermore, ferromagnetic metals such as iron, nickel and cobalt or alloys containing these. Is being used. On the other hand, as a synthetic resin binder for the purpose of improving the dispersibility of ferromagnetic powder, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinylidene chloride copolymer,
Are known acrylic copolymers, -OH these _{polymers, -COOH, -SO 3 M, -OSO} 3 M, -P
By having at least one hydrophilic functional group such as O ₃ M ₂ , -OPO ₃ M ₂ , -N <, -CON <(where M is a hydrogen atom or an alkali metal), it is advantageous for dispersion of magnetic powder. Is disclosed in the prior art.

However, even if these good binders are selected, dispersion becomes more difficult as the particle size of the ferromagnetic powder is made finer for high-density recording. The dispersion process takes a long time. In this kneading and dispersing step, a high shearing force is applied to the ferromagnetic powder and the synthetic resin binder, and the ferromagnetic powder is exposed to severe conditions for a long time, so that the properties of the ferromagnetic powder may be impaired. In the case of products such as vinyl chloride copolymers, hydrochloric acid generated by dehydrochlorination causes deterioration of the magnetic powder.

[0005] Polyacrylates which do not have the above-mentioned drawbacks of the vinyl chloride copolymers,
Acrylic copolymer resins such as a (meth) acrylate-acrylonitrile copolymer and a carboxyl group-containing (meth) acrylate copolymer are disclosed in
648, JP-B-56-23211, JP-B-56-12935, JP-B-56-15047, JP-B-56-37608, and JP-B-58-42.
No. 524, JP-A-54-46512, JP-A-60-35321, JP-A-60-219628, JP-A-61-278019, and JP-A-62-269.
No. 139118 has been proposed.

However, these resins have insufficient dispersibility with respect to fine magnetic powder and have poor compatibility with the polyurethane resin used in producing the magnetic coating liquid. Since the viscosity is high and the change of the viscosity with time is large, there are many problems in terms of work. JP-B-2-35366 proposes a magnetic recording carrier containing a single or copolymer of N-vinylpyrrolidone. However, this copolymer does not show a role as a binder, It merely provides the magnetic layer with uniformity and surface properties as an additive.

[0007]

SUMMARY OF THE INVENTION The present invention does not have the above-mentioned problems of the prior art, has good dispersibility in fine magnetic powder, has good compatibility with polyurethane resin, and has good coating properties. The purpose of the present invention is to develop a binder resin that provides a magnetic coating material that is easy to work with and to provide a magnetic recording medium having a magnetic layer with excellent characteristics.

[0008]

SUMMARY OF THE INVENTION The present invention has solved the above-mentioned problems, and is directed to a magnetic recording medium having a magnetic layer in which a ferromagnetic fine powder is dispersed in a binder on a non-magnetic support. The binder is 1 to 50% by weight of nitrogen in all monomers
Having no atom, not having an ether bond of 5 to 30% by weight with an ether compound monomer having a radical polymerizable group ,
The main component is an acrylic copolymer obtained by copolymerizing a nitrogen-containing monomer having a radical polymerizable group with an acrylic monomer having no ether bond and no nitrogen atom in the presence of a persulfate polymerization initiator. The gist of the present invention is a magnetic recording medium. That is, the inventors of the present invention have conducted intensive studies to solve the above-described problems, and have found that nitrogen derived from an ether bond and a nitrogen-containing monomer and sulfonic acid groups derived from a sulfuric acid group or a monomer derived from a polymerization initiator. It has been found that the use of an acrylic copolymer having the above as the main component of the binder improves the dispersibility of the ferromagnetic fine powder and the compatibility with the polyurethane resin, thereby improving the properties.

Hereinafter, the present invention will be described in detail. Examples of the ether compound-based monomer having no nitrogen atom and no sulfonic acid group and having a radical polymerizable group used in the present invention include ethylenically unsaturated groups such as an allyl group, a vinyl group, and a (meth) acryl group. The following can be given. Allyl-2-hydroxyethyl ether, allyl-2-hydroxypropyl ether, allyl-3-hydroxypropyl ether, allyl-2-hydroxybutyl ether, allyl-3-hydroxybutyl ether,
Allyl-4-hydroxybutyl ether, allyl-6
Monoallyl ethers of alkylene glycol such as hydroxyhexyl ether, diethylene glycol monoallyl ether, monoallyl ethers of polyoxyalkylene glycol such as dipropylene glycol monoallyl ether, glycerin monoallyl ether, allyl glycidyl ether,

Alkyl vinyl ethers such as methyl vinyl ether, ethyl vinyl ether, isobutyl vinyl ether, n-butyl vinyl ether, 2-ethylhexyl vinyl ether, n-octyl vinyl ether, lauryl vinyl ether, cetyl vinyl ether, stearyl vinyl ether, hydroxyethyl vinyl ether, hydroxybutyl vinyl ether, etc. Hydroxyalkyl vinyl ethers,

Alkoxyalkyl (meth) acrylates such as methoxyethyl (meth) acrylate and butoxyethyl (meth) acrylate, and polyoxyalkylene glycol mono (meth) acrylates such as polyethylene glycol mono (meth) acrylate and polypropylene glycol mono (meth) acrylate ) Acrylates, glycidyl (meth) acrylate,

The ether compound monomer may be used alone or in combination of two or more. When the amount is too small, the dispersibility decreases, and when the amount is too large, the dispersibility decreases. In addition, the physical strength is reduced and the durability is deteriorated. Therefore, this ether compound-based monomer is used in an amount of 1 to 50% by weight, preferably 2 to 30% by weight of the total monomers.

The ether bond and sulfo used in the present invention
Examples of the nitrogen-containing monomer having no acid group and having a radical polymerizable group include N-vinyl-2-pyrrolidone, N-vinylcarbazole, vinyl cyanide, 2-vinyl-4,
6-diamino-5-triazine, 2-vinylpyridine,
4-vinylpyridine, acrylonitrile and (meth) acrylamide, diacetone (meth) acrylamide,
(Meth) such as N-methylol (meth) acrylamide
Acrylamides may be mentioned.

Even if only one kind of the nitrogen-containing monomer is used,
More than one kind may be used in combination, but if the amount is too small, the compatibility with the polyurethane resin decreases, and if the amount is too large, the compatibility decreases. Therefore, the content of the nitrogen-containing monomer is 5 to 30% by weight of the total monomer, preferably 3 to 2% by weight.
0% by weight.

The ether bond and the nitrogen source used in the present invention
Examples of the sulfonic acid group monomer having no radical and having a radical polymerizable group include the following. CH ₂ = CHSO ₃ M, CH ₂ = CHCH ₂ SO ₃ M, CH ₂ = CHC ₆ H ₄ SO ₃ M,

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The sulfonic acid group-containing monomer may be used alone or in combination of two or more. If the amount is too small, the dispersibility decreases. If the amount is too large, the coating viscosity becomes high. Become. Therefore, the content of the sulfonic acid group-containing monomer is 0.05 to 5% by weight based on the total amount of the monomer.
5 to 3% by weight.

The acrylic monomer used in the present invention includes both acryl and methacryl, and examples thereof include the following. Methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, isobutyl (meth) acrylate, pentyl (meth) acrylate, hexyl (meth) acrylate, octyl (meth) acrylate, 2- Alkyl (meth) acrylates such as ethylhexyl (meth) acrylate, lauryl (meth) acrylate, stearyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate,
2-hydroxypropyl (meth) acrylate, (meth) acrylic acid,

The acrylic monomer may be used alone or in combination of two or more. A more preferable combination for achieving the effects of the present invention is an ether compound monomer or a combination thereof. At least one of the acrylic monomers to be polymerized has a hydroxyl group. However, the amount of the monomer having a hydroxyl group is preferably 1 to 50% by weight.

When the above-mentioned ether compound-based monomer, nitrogen-containing monomer, acrylic monomer or sulfonic acid-containing monomer is used, if necessary, the monomer to which it has been added may be used. And other radically polymerizable monomers can be copolymerized. Examples of such monomers include styrene,
α-methylstyrene, vinyl acetate, vinyl propionate, maleic anhydride, crotonic acid, itaconic acid and the like. These monomers can be used in an amount of 10% by weight or less as long as the effects of the present invention are not impaired.
The type and amount of the monomer used in the present invention are other resins used for the glass transition temperature and the magnetic recording medium of the obtained copolymer, generally a polyurethane resin, a polyester resin,
Considering the compatibility with the acrylonitrile-butadiene copolymer or the like, it is selected according to the physical properties of the coating film.

If the molecular weight of the copolymer composed of the above-described monomers is too low, the magnetic coating film becomes brittle and the physical strength decreases, and the durability of the magnetic tape and the like also decreases. On the other hand, if the molecular weight is too high, the viscosity of the paint at a predetermined concentration becomes high, and the workability becomes poor and the handling becomes difficult. Therefore, the average molecular weight is from 5,000 to
It is preferably 100,000, and more preferably in the range of 10,000 to 60,000. For adjusting the molecular weight, a molecular weight modifier such as n-dodecyl mercaptan, thioglycol, trichloroethylene and the like can be used.

Examples of the persulfate polymerization initiator used in the present invention include potassium persulfate, sodium persulfate, and ammonium persulfate. The amount of the polymerization initiator is usually 0.1 to 10.0% by weight based on the monomer,
Preferably it is 0.5 to 5.0% by weight. In the present invention, when the copolymer component contains a sulfonic acid group-containing monomer, it is not always necessary to use a persulfate polymerization initiator. In this case, hydrogen peroxide or t- Organic peroxide-based polymerization initiators such as butyl hydroperoxide, benzoyl peroxide, cumene hydroperoxide, dibutyl peroxide or the like may be used alone, or they may be used together with sodium acid sulfite, Rongalit, L-ascorbic acid, saccharides, Polymerization can be carried out by a conventional method using a reducing agent such as an amine in combination.

This copolymer can be produced by a known emulsion polymerization method. It is economically advantageous to obtain a copolymer resin by a known salting-out method after the polymerization. Examples of the emulsifier include anionic emulsifiers such as alkyl or alkyl allyl sulfate, alkyl or alkyl allyl sulfonate, and dialkyl sulfosuccinate; cationic emulsifiers such as alkyltrimethylammonium chloride and alkylbenzylammonium chloride; and polyoxyethylene alkylphenyl ether. And nonionic emulsifiers such as polyoxyethylene alkyl ether and polyoxyethylene carboxylate. At the time of polymerization, the monomers described above, the polymerization initiator, the emulsifier, the molecular weight modifier and the like may be added to the polymerization system at a time at the start of the polymerization, or may be added separately during the polymerization. .
The polymerization is usually carried out at a temperature of 35 to 80 ° C. with stirring.
After polymerization, according to a known salting-out method, sodium sulfate, an aqueous solution of an inorganic salt such as calcium chloride, or a water-soluble organic solvent or the like is added to aggregate the particles,
What is necessary is just to filter, wash and dry.

When the above copolymer is used as a binder resin in the production of a magnetic coating liquid, other resins may be used in equal amounts or less if necessary. , Nitrocellulose, polyester resin, epoxy resin, polyamide resin, phenolic resin,
Various polymers such as polymers or copolymers such as alkyd resins and polyvinyl butyral resins are exemplified. Among these, a polyurethane resin is particularly preferable.

In addition, it is desirable to use a polyisocyanate-based curing agent in combination. Examples of the curing agent include Coronate L (trade name, manufactured by Nippon Polyurethane Industry Co., Ltd.) and Dismodur L (trade name, manufactured by Bayer AG). And the like, and urethane prepolymers having isocyanate groups at both terminals. In addition,
The amount of these curing agents used is 5 per 100 parts by weight of the binder resin.
It is preferable to set it to 40 parts by weight.

The ferromagnetic powder used in the present invention includes:
γ-Fe ₂ O ₃ , Fe ₃ O ₄ and those in which cobalt ions are adsorbed or doped, CrO ₂ , and needle-like fine particles of metals or alloys containing Fe, Co, Fe—Co, Ni, etc. First, other various known magnetic powders are exemplified. The mixing ratio of the ferromagnetic fine powder and the binder resin is desirably 8 to 50 parts by weight of the binder resin per 100 parts by weight of the ferromagnetic fine powder.

In order to uniformly disperse the ferromagnetic powder and the binder, a lubricant, an abrasive, an antistatic agent, a dispersing aid, a rust inhibitor, etc., which are conventionally used, are added.
Further, the use of various organic solvents other than methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, toluene and the like as the coating medium may be the same as in the prior art, and there is no particular limitation on these points.

As the support, synthetic resins such as polyester, polyolefin, cellulose acetate, polycarbonate and the like, non-magnetic metals, ceramics and the like are used, and forms such as films, tapes, sheets, and plates are used.

As a coating means for forming a magnetic layer on a support, a conventionally known method may be used, and a smoothing treatment such as a calendering treatment may be appropriately performed to obtain a high-performance magnetic recording medium of the present invention. A recording medium is obtained.

[0029]

EXAMPLES Next, examples of the synthesis of a binder resin, specific examples using the binder resin and comparative examples will be given, but the present invention is not limited to these examples. Parts and% in Examples are parts by weight and% by weight, respectively.

Synthesis Example 1 (Synthesis of Polymer 1) 750 parts of deionized water, 5 parts of potassium persulfate, and 1.6 parts of sodium carbonate were charged into a polymerization vessel equipped with a stirrer, a condenser, a thermometer, and a nitrogen gas inlet. , After nitrogen substitution 57
The temperature was raised to ° C. Meanwhile, 500 parts of deionized water in advance,
270 parts of methyl methacrylate, 120 parts of butyl methacrylate, allyl-2-hydroxyethyl ether 70
Parts, N-vinyl-2-pyrrolidone 40 parts, sodium lauryl sulfate 10 parts, n-dodecyl mercaptan 1.25
The mixture was homogenously mixed and emulsified with a homomixer, and the mixture was uniformly dropped into the polymerization vessel in 9 hours, and further reacted at 57 ° C. for 2 hours to complete the polymerization. Then, 500 parts of methanol and 10 parts of sodium sulfate were added. Then, the polymer was precipitated. The precipitated polymer was washed twice with 5000 parts of methanol and then four times with 5000 parts / time of deionized water, filtered and dried to obtain Polymer 1. The average molecular weight of this polymer is 2
It was 9,000.

Synthesis Example 2 (Synthesis of Polymer 2) The procedure of Synthesis Example 1 was repeated except that 5 parts of sodium persulfate was used instead of 5 parts of potassium persulfate, and the types and amounts of the monomers shown in Table 1 were used. Copolymerization was carried out in the same manner, and salting out was carried out in the same manner to obtain polymer 2.

Synthesis Examples 3, 4, 5, 8, and 10 (Synthesis of Polymers 3, 4, 5, 8, and 10) In the same manner as in Synthesis Example 1, copolymerization was performed using the types and amounts of monomers shown in Table 1. And salted out in the same manner to polymer 3, 4,
5, 8, and 10 were obtained.

Synthesis Example 6 (Synthesis of Polymer 6) In a polymerization vessel equipped with a stirrer, a condenser, a thermometer and a nitrogen gas inlet, 750 parts of deionized water, 7.8 parts of L-ascorbic acid, 1.6 parts of sodium carbonate were added. Then, the temperature was increased to 57 ° C. after nitrogen replacement. On the other hand, deionized water 5
00 parts, 275 parts of methyl methacrylate, 25 parts of butyl acrylate, 150 parts of hydroxybutyl vinyl ether
Parts, N-methylolacrylamide 35 parts, sodium vinyl sulfonate 15 parts, sodium lauryl sulfate 10
And 1.25 parts of n-dodecyl mercaptan mixed and emulsified with a homomixer and 10 parts of 30% hydrogen peroxide diluted with 50 parts of deionized water in parallel into the polymerization vessel for 9 hours. , And the mixture is dropped evenly at 57 ° C.
For 2 hours to complete the polymerization, then methanol 500
And 10 parts of sodium sulfate were added to precipitate a polymer. The precipitated polymer is twice with 5000 parts of methanol,
Then, it is washed four times with 5000 parts / time of deionized water, filtered,
After drying, polymer 6 was obtained. The average molecular weight of this polymer was 28,000.

Synthesis Example 7 (Synthesis of Polymer 7) Synthesis was performed except that 5 parts of benzoyl peroxide was used in place of 10 parts of 30% hydrogen peroxide and monomers of the type and amount shown in Table 1 were used. Polymer 7 was obtained in the same manner as in Example 6.

Synthesis Example 9 (Synthesis of Polymer 9) Polymer 9 was obtained by copolymerizing in the same manner as in Synthesis Example 2 with the types and amounts of monomers shown in Table 1 and salting out in the same manner. Synthesis Example 11 (Synthesis of Polymer 11) In the same manner as in Synthesis Example 6, copolymerization was performed using the types and amounts of monomers shown in Table 1, and polymer 11 was obtained by salting out in the same manner. Synthesis Example 12 (Synthesis of Polymer 12) In the same manner as in Synthesis Example 7, copolymers were copolymerized with the types and amounts of the monomers shown in Table 1, and salted out by the same method to obtain Polymer 12.

[0036]

[Table 1]

Examples 1-7, Comparative Examples 1-5 Liquid A Binder resin (Polymer 1-12) 18 parts Metal magnetic powder 100 parts Polyurethane resin (N-2304: 7 parts Nippon Polyurethane Industry Co., Ltd.) Carbon Black 5 parts Lecithin 2 parts Methyl ethyl ketone 75 parts Cyclohexanone 75 parts Toluene 75 parts The above components were mixed for 90 minutes with a laboratory mixer, and further kneaded with an Eiger mill containing glass beads for 3 hours to obtain a coating A liquid.

Liquid B Liquid A 355 parts Polyisocyanate (Coronate L: 5 parts Nippon Polyurethane Industry Co., Ltd.) Cyclohexanone 30 parts
A liquid was obtained.

The above coating solution B was applied to a thickness of 6 μm on a polyester film, subjected to a magnetic field orientation treatment, dried, and then subjected to a surface treatment with a super calender to produce a magnetic tape. The viscosity stability of the coating liquid A obtained as described above,
The coating properties and magnetic properties of the magnetic tape were examined. Also,
The compatibility of the binder resin (Polymers 1 to 12) with the polyurethane resin was examined. The results were as shown in Table 2.

[0040]

[Table 2]

The characteristics were measured as follows. a. Viscosity stability of coating solution A The viscosity of the kneaded solution A was measured with an E-type viscometer (initial viscosity). The evaluation was made in four steps based on the ratio of the viscosity after 48 hours when the initial viscosity was 100. ◎: almost no change in viscosity (110% or less) ○: slightly thickened (120 to 200%) △: large thickened (200% or more) ×: gelation

B. Gloss A 60-degree reflectance before calendering was compared with a standard glass plate using a gloss meter (manufactured by Murakami Color Research Laboratory). c. Residual magnetic flux density (Br) and squareness ratio Measured using a vibrating sample magnetometer (Toei Kogyo).

D. Durability After leaving the created magnetic tape in a constant temperature and humidity room at 65 ° C. and a relative humidity of 90% for 168 hours, a load of 100 g was applied thereto, and the magnetic tape was rotated 1000 times at 150 rpm by contact with a rotating drum on which abrasive paper was stuck. The degree to which the magnetic coating film adhered to the polishing paper was visually evaluated on a four-point scale. ◎: No stain on the abrasive paper ○: Very slight stain △: Slight stain ×: Many stains

E. Runability The force generated between the coating film and the rotating drum was measured by a U gauge in an atmosphere of 65 ° C. and a relative humidity of 80% in the same manner as in the evaluation of the durability, and evaluated in four steps in ascending order of running resistance. ◎: extremely low, ○: low, Δ: medium, ×: high

F. Compatibility with polyurethane resin 100 parts of a 20% solution of each of polymers 1 to 12 using a mixed solvent of methyl ethyl ketone / methyl isobutyl ketone / toluene = 1/1/1 and various polyurethane resins 5
After stirring for 1 hour with a stirrer, the mixture was coated on a glass plate and dried, and the compatibility was visually evaluated on a 4-point scale based on the presence or absence of bumps and haze of the coating film. ◎: Excellent, ○: Good, △: Acceptable, ×: Not Acceptable

[0046]

According to the present invention, there has been provided a magnetic recording medium having a magnetic layer having excellent properties using a newly developed binder resin. The newly developed binder resin has excellent dispersibility in magnetic powders, has improved compatibility with polyurethane resins, and the viscosity of the resulting magnetic paint is suitable for coating operations. The change over time is also small. Improved dispersibility of magnetic powder and improved compatibility with polyurethane resin improve coating film surface smoothness, improve abrasion resistance, and excel in durability and running performance of magnetic recording media It became something.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G11B 5/702 C09D 5/23 C09D 133/04

Claims (2)

(57) [Claims] 1. A magnetic recording medium comprising a magnetic layer in which a ferromagnetic fine powder is dispersed in a binder on a non-magnetic support, said binder comprising 1 to 50% by weight of nitrogen in all monomers. atom
And a nitrogen-containing monomer having a radically polymerizable group and having no ether bond of 5 to 30% by weight with an ether compound monomer having a radically polymerizable group and a persulfate polymerization initiator. A magnetic recording medium comprising, as a main component, an acrylic copolymer obtained by copolymerizing with an acrylic monomer having no ether bond and no nitrogen atom in the presence. 2. A magnetic recording medium comprising a magnetic layer in which a ferromagnetic fine powder is dispersed in a binder on a non-magnetic support, said binder comprising 1 to 50% by weight of nitrogen in all monomers. atom
And it does not have a sulfonic acid group, an ether compound-based monomer and 5 to 30 wt% of the ether formation having a radical polymerizable group
And a nitrogen-containing monomer having no radically polymerizable group having no sulfonic acid group and 0.05 to 5% by weight of an ether bond and
A sulfonic acid group monomer having a radical polymerizable group having no nitrogen atom and a nitrogen atom by an ether bond, a nitrogen atom and a sulfo group.
A magnetic recording medium comprising, as a main component, an acrylic copolymer obtained by copolymerizing with an acrylic monomer having no acid group .