JP3339958B2 - 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 a floppy disk. The present invention relates to an improved magnetic recording medium using an acrylic copolymer obtained by polymerization.

[0002]

2. Description of the Related Art A magnetic recording medium such as a magnetic tape, a magnetic card, and a floppy disk generally has a coating (magnetic layer) made of a magnetic powder and a binder (synthetic resin) provided on the surface of a support such as a polyester film. It is made by In recent years, improvement in recording density of magnetic recording media, S / N,
With the demand for improvement in the C / N ratio, magnetic powders have become finer and have higher coercive force, and their materials have also shifted from iron oxide to iron oxide to which cobalt ions have been adsorbed or doped. Ferromagnetic metals such as iron, nickel, and cobalt or alloys containing these have been used.

In order to uniformly disperse these magnetic powders in a paint and form a smooth and highly filled magnetic layer to improve the performance as a magnetic recording medium, it is necessary to disperse the binder and the solvent. Solubility and heat resistance are important factors. Vinyl chloride-vinyl acetate copolymers and vinyl chloride-vinylidene chloride copolymers are known as synthetic resins for binders for the purpose of improving the dispersibility of such magnetic powders. It has been disclosed in the prior art that the compound having a hydrophilic functional group is advantageous in dispersing the magnetic powder.

However, even if these good synthetic resins for a binder are selected, the finer the particle size of the ferromagnetic powder for high-density recording becomes, the more difficult it becomes to disperse, and a magnetic paint is prepared. In this case, the kneading and dispersing step requires a long time. In this kneading and dispersing step, the ferromagnetic powder and the binder are subjected to high shearing force and subjected to severe conditions for a long time, so that the properties of the ferromagnetic powder may be impaired, and decomposition products from the binder, especially In vinyl chloride copolymers, hydrochloric acid generated by dehydrochlorination causes deterioration of magnetic powder. Furthermore, magnetic recording media such as magnetic tapes and magnetic cards made using conventional vinyl chloride copolymers as binders have poor glass transition temperatures due to the low glass transition temperature of the copolymer, resulting in inferior durability and abrasion resistance. It has the disadvantage of not being able to withstand the use of

[0005]

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 heat resistance in the kneading step, and has good dehydrochlorination. Developing a binder resin that provides a magnetic coating with excellent coating durability and abrasion resistance, which is easy to apply and easy to apply, and provides a magnetic recording medium with a magnetic layer with excellent properties It was done for.

[0006]

The present invention has solved the above-mentioned problems, and the present invention comprises providing a magnetic layer having a ferromagnetic fine powder dispersed in a binder on a non-magnetic support. In a magnetic recording medium, the binder is (1) an (meth) acrylate having an aryl group, an alkoxyl group or a phenoxy group and / or N-substituted (meth) acrylamide 1 to 30% by weight (2) a radical having an epoxy group Polymerizable monomer 1 to 30% by weight (3) Radical polymerizable monomer having hydroxyl group 1 to 30% by weight (4) Other (meth) acrylic monomer 10 to 97% by weight copolymerized The main object is a (meth) acrylic copolymer obtained as a main component.

That is, the present inventors have conducted intensive studies to solve the above-mentioned problems, and as a result, have found that a (meth) acrylate having an aryl group, an alkoxyl group or a phenoxy group and / or an N-substituted (meth) acrylamide or an epoxy group have (Meth) acrylic copolymer obtained by copolymerizing a radical polymerizable monomer having a radical polymerizable monomer having a hydroxyl group and another (meth) acrylic monomer as an essential monomer. It has been found that, when used as a main component of a binder, the dispersibility of the ferromagnetic powder is improved as well as the durability, abrasion resistance, and heat resistance of the magnetic coating film are improved as features of the combination of the monomers. The present invention has been accomplished by examining the quantitative ratio of the monomer and the like. Note that (meth) acryl is a general term for acryl and methacryl. Hereinafter, the present invention will be described in detail.

Examples of the (meth) acrylate and / or N-substituted methacrylamide having an aryl, alkoxyl or phenoxy group used in the present invention include benzyl (meth) acrylate and phenyl (meth) acrylate.
Acrylate, methoxyethyl (meth) acrylate,
Ethoxyethyl (meth) acrylate, butoxyethyl (meth) acrylate, methoxypolyethylene glycol (meth) acrylate, methoxypolypropylene glycol (meth) acrylate, phenoxyethyl (meth) acrylate, phenoxypolyethylene glycol (meth) acrylate, N-methoxymethyl ( (Meth) acrylamide, N-ethoxymethyl (meth) acrylamide, N-propoxymethyl (meth) acrylamide,
Nn-butoxymethyl (meth) acrylamide, N-
iso-butoxymethyl (meth) acrylamide and the like. These monomers may be used alone or in combination of two or more. However, if the amount is too small, the dispersibility decreases, and if the amount is too large, the dispersibility decreases and the physical strength also decreases. It decreases and the durability deteriorates. Therefore, the content is 1 to 30% by weight, preferably 5 to 20% by weight of the total monomers.

Examples of the radical polymerizable monomer having an epoxy group used in the present invention include glycidyl ethers of unsaturated alcohols such as allyl glycidyl ether and methallyl glycidyl ether; and unsaturated monomers such as glycidyl acrylate and glycidyl methacrylate. Glycidyl esters of acids; epoxide olefins such as butadiene monooxide, vinylcyclohexene monooxide, and 2-methyl-5,6-epoxyhexene; The radical polymerizable monomer having an epoxy group may be used alone or in combination of two or more. However, if the amount is too small, the solvent solubility of the copolymer deteriorates, and the resulting magnetic property is reduced. The viscosity of the coating material increases and adversely affects the coating operation. Even if the amount is too large, the same phenomenon is exhibited. Therefore, the radical polymerizable monomer having this epoxy group accounts for 1 to 30% by weight of all monomers. %, But preferably 2 to 20% by weight.

Examples of the radical polymerizable monomer having a hydroxyl group used in the present invention include hydroxyethyl (meth)
Acrylate, hydroxypropyl (meth) acrylate, polyethylene glycol mono (meth) acrylate, polypropylene glycol mono (meth) acrylate, polyethylene glycol polypropylene glycol mono (meth) acrylate, glycerol mono (meth)
Acrylate, 3-chloro-2-hydroxypropyl (meth) acrylate, hydroxyethyl vinyl ether, hydroxypropyl vinyl ether, hydroxybutyl vinyl ether, hydroxyethyl mono (meth) allyl ether, hydroxypropyl mono (meth) allyl ether, hydroxybutyl mono (meth) ) Allyl ether, diethylene glycol mono (meth) allyl ether, dipropylene glycol mono (meth) allyl ether, glyceryl mono (meth) allyl ether, 3-chloro-2-hydroxypropyl (meth) allyl ether,
Vinyl alcohol, (meth) allyl alcohol, N-methylol (meth) acrylamide and the like can be mentioned. In addition, vinyl alcohol can be introduced by copolymerizing vinyl acetate and performing a saponification reaction with caustic alkali in a solvent. The radical polymerizable monomer having a hydroxyl group may be used alone or in combination of two or more.
If the amount is too small, the dispersibility decreases, and if the amount is too large, the increase in viscosity increases when an isocyanate prepolymer is blended. Therefore, the content of the hydroxyl polymerizable monomer having a hydroxyl group is 1 to 30% by weight, preferably 3 to 20% by weight of the total monomers.

Examples of other (meth) acrylic monomers used in the present invention include methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate and isobutyl (meth) acrylate. ) Acrylate, pentyl (meth) acrylate, hexyl (meth) acrylate, octyl (meth)
Alkyl (meth) acrylates such as acrylate, 2-ethylhexyl (meth) acrylate, lauryl (meth) acrylate, stearyl (meth) acrylate, and cyclohexyl (meth) acrylate; (meth) acrylamide, diacetone (meth) acrylamide, and the like. The (meth) acrylic monomer may be used alone or in combination of two or more.
10 to 10% of all monomers to obtain the properties of acrylic copolymer
97% by weight.

The above-mentioned essential monomer, an aryl group,
(Meth) acrylate and / or N-substituted methacrylamide having an alkoxyl group or a phenoxy group,
Radical polymerizable monomer other than the above-mentioned essential monomer, if necessary, with respect to the epoxy group-containing radical polymerizable monomer, the hydroxyl group-containing radical polymerizable monomer and other (meth) acrylic monomers. The body can be copolymerized. Examples of such monomers include alkyl vinyl ethers such as styrene, 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, and stearyl vinyl ether. Vinyl acetate, vinyl propionate and the like. These monomers can be used in a range of 30% by weight or less based on the total amount of the monomers as long as the effects of the present invention are not impaired.

The kind and amount of the monomer used in the present invention are determined by the glass transition temperature of the obtained copolymer and other resins used for the magnetic recording medium, generally, polyurethane resin, polyester resin, acrylonitrile-butadiene copolymer. It is selected according to the physical properties of the coating film in consideration of the compatibility with coalescence.

The copolymer composed of a combination of the above-described monomers serves as a main component of a binder.
If the molecular weight is too low, the physical strength such as the magnetic coating film becomes brittle and the durability of the magnetic tape decreases, and if the molecular weight is too high, the viscosity of the paint at a predetermined concentration increases and the workability increases. The average molecular weight was determined to be 5,000 by the GPC method.
~ 100,000, more preferably 10,000
The range is from 00 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.

Such a copolymer can be produced by a general solution polymerization method, precipitation polymerization method, suspension polymerization method, emulsion polymerization method or the like. Examples of the polymerization initiator used in producing the copolymer include persulfates such as ammonium persulfate, potassium persulfate, and sodium persulfate, and hydrogen peroxide; diisopropyl peroxydicarbonate, t-butyl hydroperoxide, and benzoyl peroxide. Oxides, cumene hydroperoxide, organic peroxide initiators such as dibutyl peroxide; azobisisobutyronitrile, nitrogen-containing initiators such as azobisisovaleronitrile are exemplified, whether these are used alone or Alternatively, if necessary, a reducing agent such as sodium acid sulfite, Rongalit, L-ascorbic acid, saccharide, amine or the like may be used in combination to carry out polymerization by a conventional method.

Examples of the solvent in the case of solution polymerization include ketones such as acetone, methyl ethyl ketone and methyl isobutyl ketone; esters such as methyl acetate, ethyl acetate and butyl acetate. Examples of the solvent in the case of precipitation polymerization include:
Examples thereof include alcohols such as methanol, ethanol, and isopropanol; and hydrocarbons such as hexane and pentane. Examples of suspension stabilizers in the case of suspension polymerization include polyvinyl alcohol-based polymers such as polyvinyl alcohol and partially saponified polyvinyl acetate; cellulose derivatives such as methylcellulose, hydroxypropylcellulose, and carboxymethylcellulose; polyvinylpyrrolidone, polyacrylamide, and maleic. Synthetic polymers such as acid-styrene copolymer and maleic acid-methylvinyl ether copolymer; and natural polymers such as starch and gelatin. Examples of the emulsifier in the case of emulsion polymerization include anionic emulsifiers such as alkyl or alkyl allyl sulfate, alkyl or alkyl allyl sulfonate, and alkyl allyl sulfosuccinate; polyoxyethylene alkylphenyl ether, polyoxyethylene alkyl ether, Nonionic emulsifiers such as polyoxyethylene carboxylate are exemplified.

In the polymerization, the monomers, polymerization initiators, suspension stabilizers, emulsifiers, etc. described above may be added to the polymerization system all at once at the start of the polymerization, or may be added separately during the polymerization. You can also. In the case of emulsion polymerization, after polymerization, according to a known salting-out method, an aqueous solution of an inorganic salt such as sodium chloride, calcium chloride, or sodium sulfate was added, or the particles were aggregated by adding a water-soluble organic solvent or the like. Then, it may be filtered, washed and dried.

When the above copolymer is used as a binder resin (main agent) in the production of a magnetic coating material, other resins may be used in equal amounts or less, if necessary. Various resins such as polymers or copolymers such as polyurethane resin, nitrocellulose, polyester resin, epoxy resin, polyamide resin, phenol resin, alkyd resin and polyvinyl butyral resin are exemplified.
Of these, polyurethane resins are preferred. 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). Examples thereof include functional isocyanates and urethane prepolymers having isocyanate groups at both terminals. The amount of these curing agents used is
It is preferable that the amount is 5 to 40 parts by weight per 100 parts by weight of the binder resin as a total of the above-mentioned main agent and the resin used in combination.

The ferromagnetic fine powder used in the present invention includes γ-Fe ₂ O ₃ , Fe ₃ O ₄ and those obtained by adsorbing or doping cobalt ions thereon, CrO ₂ , and also Fe, Co, Fe-C
and various other conventionally known magnetic powders, such as acicular fine particles of a metal or an alloy containing o, Ni or the like. The mixing ratio of the ferromagnetic fine powder and the binder resin (the total of the main resin and the resin used in combination) 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 fine powder and the binder resin, a lubricant, an abrasive, an antistatic agent, a dispersing aid, a rust inhibitor, etc., which are conventionally used in general, are added, and further coated. The use of various organic solvents other than methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, toluene and the like as the medium may be the same as the conventional one, and there is no particular limitation on these points. In the case of emulsion polymerization, a magnetic powder and a dispersing agent are added directly to the emulsified dispersion liquid after polymerization without using the above-mentioned known salting-out method after polymerization, and mixed and dispersed to form an aqueous emulsion-based magnetic paint. Is also possible.

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 the form is used as a film, tape, sheet, plate or the like. A known method may be used as a means for forming the magnetic layer on the support, and a high-performance magnetic recording medium of the present invention can be obtained by appropriately performing a smoothing process such as a calendering process. .

[0021]

EXAMPLES Examples of the synthesis of a copolymer as a main component of a binder, specific examples using the copolymer, and comparative examples will now be described. However, the present invention is not limited to these examples. Absent. Parts and% in Examples are parts by weight and% by weight, respectively.

Synthesis Example 1 (Synthesis of Polymer 1) A polymerization vessel equipped with a stirrer, a condenser, a thermometer and a nitrogen gas inlet was replaced with nitrogen, and then 50 parts of deionized water, 1.5 parts of L-ascorbic acid, and 0.5 parts of sodium carbonate were used. Was heated to 70 ° C. while stirring under a nitrogen gas atmosphere. On the other hand, 50 parts of deionized water, 22 parts of benzyl methacrylate, 15 parts of glycidyl acrylate, 15 parts of hydroxypropyl acrylate, 48 parts of methyl methacrylate, 1 part of sodium lauryl sulfate and 0.1 part of n-dodecyl mercaptan were previously mixed and emulsified with a homomixer. And 2 parts of 30% hydrogen peroxide solution diluted with 30 parts of deionized water are dropped in parallel into the above polymerization vessel in 5 hours, and further reacted at 70 ° C. for 2 hours to carry out polymerization. After completion, the polymer was washed twice with 1,000 parts / time of methanol and then four times with 1,000 parts / time of deionized water, filtered and dried to obtain Polymer 1. The average molecular weight of this polymer determined by the GPC method was 30,000.

Synthesis Example 2 (Synthesis of Polymer 2) A polymerization vessel equipped with a stirrer, a condenser, a thermometer and a nitrogen gas inlet was purged with nitrogen, and then 200 parts of deionized water, 0.5 part of benzoyl peroxide, and partially saponified polyvinyl alcohol were used. 1 part, ethoxyethyl acrylate 13 parts, glycidyl methacrylate 20 parts, hydroxypropyl acrylate 7 parts, hydroxyethyl monoallyl ether 20 parts,
40 parts of methyl methacrylate was charged and heated to 70 ° C. while stirring under a nitrogen gas atmosphere. After reacting for 7 hours, the mixture was cooled to room temperature, washed twice with 1,000 parts / time of deionized water, filtered and dried to obtain Polymer 2. The average molecular weight of this polymer determined by GPC was 40,000.

Synthesis Example 3 (Synthesis of Polymer 3) In a polymerization vessel equipped with a stirrer, a condenser, a thermometer and a nitrogen gas inlet, 100 parts of methanol and 1 part of diisopropyl peroxydicarbonate were charged after nitrogen substitution, and the mixture was placed in a nitrogen gas atmosphere. The temperature was raised to 50 ° C. while stirring. On the other hand, 7 parts of N-methoxymethylacrylamide, 11 parts of glycidyl methacrylate, 15 parts of allyl glycidyl ether
A mixture of 10 parts, 10 parts of hydroxybutyl vinyl ether, 30 parts of methyl methacrylate, and 27 parts of butyl methacrylate was uniformly dropped into the polymerization vessel over 5 hours, and further reacted at 50 ° C. for 2 hours. The obtained slurry was washed twice with 1,000 parts / time of deionized water, filtered and dried to obtain Polymer 3. The average molecular weight of this polymer determined by the GPC method was 15,000.

Synthesis Example 4 (Synthesis of Polymer 4) In Synthesis Example 1, 20 parts of benzyl methacrylate, 5 parts of ethoxyethyl acrylate, 10 parts of glycidyl acrylate, 18 parts of hydroxypropyl acrylate, 32 parts of methyl methacrylate, n Polymer 4 was obtained by performing the same operation as in Synthesis Example 1 except that 15 parts of -butyl vinyl ether was used. The average molecular weight of this polymer determined by GPC was 35,000.

Synthesis Example 5 (Synthesis of Polymer 5) Except that 18 parts of benzyl methacrylate, 5 parts of allyl glycidyl ether, 6 parts of hydroxyethyl monoallyl ether and 71 parts of methyl methacrylate were used as the comonomer in Synthesis Example 2. The same operation as in Synthesis Example 2 was performed to obtain Polymer 5. The average molecular weight of this polymer determined by GPC was 50,000.

Synthesis Example 6 (Synthesis of Polymer 6) In Synthesis Example 1, 17 parts of glycidyl acrylate and 25 parts of hydroxyethyl monoallyl ether were used as copolymer monomers.
Synthesis Example 1 except for using 1 part of methyl methacrylate and 58 parts of methyl methacrylate
By performing the same operation as described above, polymer 6 was obtained. The average molecular weight of this polymer determined by the GPC method was 30,000.

Synthesis Example 7 (Synthesis of Polymer 7) In Synthesis Example 1, 20 parts of benzyl methacrylate, 15 parts of hydroxypropyl acrylate, 3 parts of hydroxybutyl vinyl ether, 50 parts of methyl methacrylate, and 12 parts of butyl methacrylate were used as copolymer monomers. A polymer 7 was obtained in the same manner as in Synthesis Example 1 except for the above. The average molecular weight of this polymer determined by GPC was 35,000.

Synthesis Example 8 (Synthesis of Polymer 8) Synthesis Example 2 was the same as in Synthesis Example 2 except that 15 parts of ethoxyethyl acrylate, 10 parts of glycidyl methacrylate, 5 parts of allyl glycidyl ether, and 70 parts of methyl methacrylate were used as the comonomer. Perform the same operation as in Polymer 2
I got The average molecular weight of this polymer determined by GPC was 4
It was 0,000.

Examples 1-5, Comparative Examples 1-3 Liquid A Copolymer (Polymer 1-8) 18 parts Co-γ-Fe ₂ O ₃ having a specific surface area of 35 m ² / g 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 ingredients are mixed for 90 minutes with a laboratory mixer, and further 3 hours with an Eiger mill containing glass beads. The mixture was kneaded 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 The above components were mixed and dispersed by a laboratory mixer for 90 minutes to obtain a coating liquid B. 6μ of the above coating liquid B on a polyester film
It was applied to a thickness of m, subjected to a magnetic field orientation treatment, dried, and then surface-treated with a super calender to produce a magnetic tape. The viscosity stability of the coating solution A obtained as described above, and the coating properties and magnetic properties of the magnetic tape were examined. Table 1 shows the results
Was as shown in FIG.

[0032]

[Table 1]

The characteristics were measured as described below. a. Viscosity Stability of Coating A Solution The viscosity of the kneading-adjusted Coating A solution was measured with an E-type viscometer (initial viscosity), and the remaining solution was left at 25 ° C. for 48 hours to measure the reviscosity. The evaluation was made in four steps based on the ratio of the viscosity after 48 hours when the initial viscosity was 100. ：: little change in viscosity (less than 120%), 〇: slightly thickened (120 to 200%), Δ: large thickened (more than 200%), ×: gelled

B. Gloss A 60-degree reflectance before calendering was compared with a standard glass plate using a gloss meter (Murakami Color Research Institute). c. 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, apply a load of 100 g, contact the rotating drum with the abrasive paper on it, and rotate it 1,000 times at 150 rpm. The degree of adhesion of the magnetic paint to the abrasive paper was visually evaluated in four steps. ◎: no stain on abrasive paper, 〇: very slight stain, Δ: slight stain, ×: much stain e. Runnability 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 the three levels were evaluated in ascending order of running resistance. 〇: low, △: medium, ×: high

[0036]

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. This newly developed resin for a binder exhibits excellent dispersibility in magnetic powder, and the viscosity of the obtained magnetic paint is suitable for a coating operation, and the change in viscosity with time is small. As a result, the smoothness of the coating film surface was improved, the abrasion resistance was improved, and the durability and running properties of the magnetic recording medium were improved. It should be noted that there is no phenomenon such as a decrease in performance due to dehydrochlorination in the case of a vinyl chloride resin.

Claims (1)

(57) [Claims] 1. A magnetic recording medium comprising a nonmagnetic support and a magnetic layer in which ferromagnetic fine powder is dispersed in a binder, wherein the binder comprises (1) an aryl group, an alkoxyl group or a phenoxy group. (Meth) acrylate and / or N-substituted (meth) acrylamide having 1 to 30% by weight (2) radical polymerizable monomer having an epoxy group 1 to 30% by weight (3) radical polymerizable monomer having a hydroxyl group 1 to 30% by weight (4) Other (meth) acrylic monomers The main component is a (meth) acrylic copolymer obtained by copolymerizing at a ratio of 10 to 97% by weight. Magnetic recording medium.