JPH07262549A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a magnetic recording medium with a back coat layer excellent in characteristics. CONSTITUTION:A binder for forming a back coat layer is based on a (meth) acrylic copolymer obtd. by copolymerizing 1-50wt.% radical-polymerizable ether compd. monomer and 1-30wt.% radical-polymerizable nitrogen-contg. monomer with 20-98wt.% (meth)acrylic monomer having neither ether bond nor nitrogen.

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, and in particular, it is obtained by copolymerizing a special monomer having excellent performance as a binder for forming a back coat layer. The present invention relates to an improved magnetic recording medium using the resulting acrylic copolymer.

[0002]

2. Description of the Related Art Magnetic recording media such as magnetic tapes for audio, video or computers have a relatively large electric resistance and their surfaces are smooth, so that they are electrically charged when they are wound or unwound at high speed. It may cause dropout and output fluctuation. Therefore, various attempts have been made such as coating a support film on the side opposite to the magnetic layer with carbon black, glycol or the like together with a binder to provide a back coat layer having good conductivity. As the binder for the back coat layer, the same one as for the magnetic layer, for example, vinyl chloride resin such as vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl acetate-vinyl alcohol copolymer, nitrocellulose or the like is used. Has been done.

However, even if these resins are used, the average particle size of carbon black is very small, about 10 to 300 μm, and usually 40 to 4 per 100 parts by weight of the binder.
It is extremely difficult to disperse in the paint for forming the backcoat layer because it is mixed in a large amount of about 00 parts by weight, and the surface roughness of the backcoat layer becomes large due to the poor dispersion, and the magnetic tape is wound up. In this state, the unevenness of the back coat layer is transferred to the magnetic layer, which adversely affects the electromagnetic conversion characteristics, increases the friction coefficient of the surface and reduces durability, is damaged by pinch rollers and guide pins, and runs many times. If the binder is vinyl chloride resin when the back coat layer contacts the magnetic layer, hydrochloric acid, which is a decomposition product, deteriorates the magnetic powder in the magnetic layer. There was a problem.

[0004]

The present invention does not have the problems that the above-mentioned prior art has, and has a good dispersibility in a conductive non-magnetic powder such as fine carbon black and is used in combination. The purpose is to develop a binder resin that has good compatibility with polyurethane resin, which is often used, and does not generate decomposition products that deteriorate magnetic powder, and to provide a magnetic recording medium having a backcoat layer with excellent characteristics. It is a thing.

[0005]

DISCLOSURE OF THE INVENTION The present invention has solved the above-mentioned problems and has a magnetic recording medium having a magnetic layer on one surface and a back coat layer on the other surface of a non-magnetic support. In, the binder of the backcoat layer is 1 to 50% by weight of an ether compound monomer having a radical polymerizable property, 1 to 30% by weight of a nitrogen-containing monomer having a radical polymerizable property, and both an ether bond and nitrogen. A magnetic recording medium characterized by using as a main component a (meth) acrylic copolymer obtained by copolymerizing a (meth) acrylic monomer which does not have 20 to 98% by weight. Is. Hereinafter, the radically polymerizable ether compound-based monomer is abbreviated as an ether compound-based monomer, and the radically polymerizable nitrogen-containing monomer is abbreviated as a nitrogen-containing monomer.

That is, the inventors of the present invention have made earnest studies to solve the above-mentioned problems, and as a result, (meth) acrylic co-polymer having an ether bond and nitrogen derived from an ether compound-based monomer and a nitrogen-containing monomer The present invention was found to find that a backcoat layer having improved dispersibility of non-magnetic powder and compatibility with a polyurethane resin, and improved durability and runnability can be obtained by using a coalescent as a main component of a binder. It was In addition,
(Meth) acrylic is a general term for acrylic and methacrylic. The present invention will be described in detail below.

Examples of the ether compound type monomer used in the present invention include the following compounds having an ethylenically unsaturated group such as an allyl group, a vinyl group and a (meth) acryl group. 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-hydroxyhexyl ether and other alkylene glycol monoallyl ethers; diethylene glycol mono (meth) allyl ether , Mono (meth) allyl ethers of polyoxyalkylene glycols such as dipropylene glycol mono (meth) allyl ether; glyceryl mono (meth) allyl ether; allyl glycidyl ether; 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, suture Alkyl vinyl ethers such as allyl vinyl ether; hydroxyalkyl vinyl ethers such as hydroxyethyl vinyl ether and hydroxybutyl vinyl ether; alkoxyalkyl (meth) acrylates such as methoxyethyl (meth) acrylate and butoxyethyl (meth) acrylate; polyethylene glycol mono (meth ) Acrylate, polyoxyalkylene glycol mono (meth) acrylates such as polypropylene glycol mono (meth) acrylate; N-butoxymethyl (meth) acrylamide, N-
N-alkoxymethyl (meth) acrylamides such as methoxymethyl (meth) acrylamide

The ether compound-based monomer may be used alone or in combination of two or more kinds, but if the amount is too small, the dispersibility of the non-magnetic powder having conductivity is lowered,
If the amount is too large, the dispersibility is reduced and the physical strength is reduced, resulting in poor durability. Therefore, the amount of the ether compound-based monomer is 1 to 50% by weight, preferably 2 to 30% by weight, based on all the monomers.

Examples of the nitrogen-containing monomer used in the present invention include N-vinyl-2-pyrrolidone, N-vinylcarbazole, 2-vinyl-4,6-diamino-5-triazine, 2-vinylpyridine, Cyclic compounds such as 4-vinylpyridine; (meth) acrylamides such as (meth) acrylamide, diacetone (meth) acrylamide, N-methylol (meth) acrylamide; maleimide, N
-Phenylmaleimide, (meth) acrylonitrile and the like.

Even if only one type of this nitrogen-containing monomer is used, it is 2
Although more than one type may be used in combination, if the amount is too small, the compatibility with the polyurethane resin will decrease, and if it is too large, the viscosity of the coating will increase. Therefore, the amount of this nitrogen-containing monomer is 1 to 30% by weight based on the total amount of monomers, but preferably 3 to 20%.
% By weight.

Examples of the (meth) acrylic monomer having neither an ether bond nor nitrogen used in the present invention are methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate and butyl. (Meth) acrylate, isobutyl (meth) acrylate, pentyl (meth) acrylate, hexyl (meth)
Acrylate, octyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, lauryl (meth)
Alkyl (meth) acrylates such as acrylate, stearyl (meth) acrylate, cyclohexyl (meth) acrylate; (meth) acrylates of aromatic alcohol such as benzyl (meth) acrylate; 2-
Examples thereof include hydroxyalkyl (meth) acrylates such as hydroxyethyl (meth) acrylate and 2-hydroxypropyl (meth) acrylate; glycidyl (meth) acrylate, (meth) acrylic acid and the like.

The (meth) acrylic monomer having neither ether bond nor nitrogen may be used alone or in combination of two or more kinds, but the characteristics such as strength of the back coat layer are obtained. In order to achieve this, the amount is 20 to 98% by weight based on the total monomers. It is preferably 50 to 95% by weight. Further, a more preferable combination for exerting the effect of the present invention is at least one of an ether compound-based monomer or an (meth) acrylic-based monomer having neither an ether bond nor a nitrogen copolymerized therewith. It has a hydroxyl group.
However, the amount of the monomer having a hydroxyl group is 5 to 30 in all the monomers.
It is preferably set to wt%.

In addition to the above-mentioned ether compound-based monomer, nitrogen-containing monomer, and (meth) acrylic-based monomer having neither ether bond nor nitrogen, other radical-polymerizable monomer may be added, if necessary. The body can be copolymerized. Examples of such a monomer include styrene, α-methylstyrene, vinyl acetate, vinyl propionate, maleic anhydride, crotonic acid, and itaconic acid. As long as these monomers do not impair the effects of the present invention,
It can be used in the range of 30% by weight or less based on the total monomers.

The copolymer composed of a combination of the above-mentioned monomers has a low physical weight such that the backcoat layer becomes brittle when the molecular weight is too low, and the durability of a magnetic tape or the like also deteriorates. However, on the contrary, if the molecular weight is too high, the viscosity of the paint at a predetermined concentration becomes high and the workability becomes poor, making it difficult to handle. Therefore, the average molecular weight is 5,000 to 100,000 as measured by the GPC method. The range is preferably 10,000 to 60,000. For adjusting the molecular weight, a molecular weight adjusting agent such as n-dodecyl mercaptan, thioglycol or trichloroethylene may 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. Polymerization initiators used in the production of the copolymer include ammonium persulfate, potassium persulfate, sodium persulfate, and other persulfates and hydrogen peroxide; diisopropyl peroxydicarbonate, t-butyl hydroperoxide, and benzoyl. Organic peroxide initiators such as peroxides, cumene hydroperoxide, dibutyl peroxide; nitrogen-containing initiators such as azobisisobutyronitrile and azobisisovaleronitrile are exemplified, and are these used alone? Alternatively, if necessary, a reducing agent such as acidic sodium sulfite, Rongalit, L-ascorbic acid, saccharides, amines and the like may be used in combination to carry out polymerization by a conventional method.

In the case of solution polymerization, examples of the reaction solvent include ketones such as acetone, methyl ethyl ketone and methyl isobutyl ketone, and esters such as methyl acetate, ethyl acetate and butyl acetate. As the reaction solvent in the case of precipitation polymerization, , Alcohols such as methanol, ethanol and isopropanol, and hydrocarbons such as hexane and pentane. 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 methyl cellulose, hydroxypropyl cellulose and carboxymethyl cellulose; polyvinyl pyrrolidone, polyacrylamide and malein. Examples thereof include synthetic polymers such as acid-styrene copolymers and maleic acid-methyl vinyl ether copolymers, and natural polymers such as starch and gelatin. Further, as an emulsifier in the case of emulsion polymerization, anionic emulsifiers such as alkyl or alkylallyl sulfate, alkyl or alkylallyl sulfonate, alkylallyl sulfosuccinate; polyoxyethylene alkyl phenyl ether, polyoxyethylene alkyl ether, Examples include nonionic emulsifiers such as polyoxyethylene carboxylic acid esters.

In the polymerization, the above-mentioned monomers, polymerization initiator, suspension stabilizer, emulsifier and the like may be added to the polymerization system all at once at the start of the polymerization, or may be dividedly added during the polymerization. You can also do it. In the case of emulsion polymerization, particles are aggregated by adding an aqueous solution of an inorganic salt such as sodium chloride, calcium chloride or sodium sulfate or a water-soluble organic solvent according to a known salting-out method after polymerization. After that, it may be filtered, washed with water and dried.

When the above copolymer is used as a binder resin in the production of a back coat coating composition, other resins may be used in an amount equal to or less than an equal amount, if necessary. Examples include various resins such as resins, nitrocellulose, polyester resins, epoxy resins, polyamide resins, phenol resins, alkyd resins, polyvinyl butyral resins, and other polymers or copolymers. Among these, polyurethane resin is preferable.
In addition to this, it is desirable to use a polyisocyanate-based curing agent together, and as this curing agent, Coronate L
Examples include trifunctional isocyanates such as [trade name of Nippon Polyurethane Industry Co., Ltd.], Dismodur L (trade name of Bayer Co.), urethane prepolymers having isocyanate groups at both ends, and the like. The amount of these curing agents used is preferably 5 to 40 parts by weight based on 100 parts by weight of the binder resin including the resins used in combination.

As the non-magnetic powder used in the present invention, in addition to carbon black, conductive powders such as graphite, tin oxide, antimony oxide type compounds, titanium oxide-tin oxide-antimony oxide type compounds and carbon black graphite polymer are used. can give. These may be used alone or in combination of two or more.

When the non-magnetic powder and the binder resin are dispersed, a lubricant, an abrasive, an antistatic agent, a dispersion aid, a rust preventive, etc., which have been conventionally used, are added.
Further, various organic solvents other than methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, toluene, etc. may be used as the coating medium in the same manner as in the past, and there is no particular limitation in these points.

As the support, synthetic resins such as polyester, polyolefin, cellulose acetate and polycarbonate, non-magnetic metals and the like are used, and the form is used as a film, tape, sheet or the like. As a means for forming a backcoat layer on a support, a known method may be used. A backcoating coating material comprising the above-mentioned components is prepared, and the coating material is used after forming a magnetic layer on the surface side. ,
Alternatively, it may be applied on the back side of the non-magnetic support before being formed and dried.

The magnetic layer of the magnetic recording medium of the present invention is not particularly limited, and as is well known, various types of magnetic powder and binder resin are mainly used as a lubricating oil, an abrasive, an antistatic agent, a dispersion aid, and the like. It is obtained by using a magnetic paint containing an additive. As the above magnetic powder, γ-Fe ₂ O ₃ , Fe ₃ O ₄ and those in which cobalt ions are adsorbed or doped, CrO ₂ , and
Examples thereof include needle-like fine particles of metal or alloy containing Fe, Co, Fe—Co, Ni and the like. Further, as the binder resin, conventionally known vinyl chloride resins, the (meth) acrylic copolymer according to the present invention, and various resins listed as the combined resin can be used. Furthermore, any of the curing agents can be used.

[0023]

EXAMPLES Next, synthesis examples of (meth) acrylic copolymers for binders and specific examples and comparative examples using the copolymers will be given, but the present invention is limited to these examples. Not a thing. In addition, the part in an example shows a weight part.

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 75 parts of deionized water, 1 part of potassium persulfate and 0.3 part of sodium carbonate were added. Was charged, and the temperature was raised to 60 ° C. with stirring under a nitrogen gas atmosphere. On the other hand, 75 parts of deionized water, 14 parts of allyl-2-hydroxyethyl ether, 8 parts of N-vinyl-2-pyrrolidone, 54 parts of methyl methacrylate, 24 parts of butyl methacrylate, 2 parts of sodium lauryl sulfate and 0.25 of n-dodecyl mercaptan.
What was mixed and emulsified with a homomixer was uniformly added dropwise to the above polymerization vessel over 5 hours, and the reaction was continued at 60 ° C for 2 hours to complete the polymerization, and then 100 parts of methanol and 2 parts of sodium sulfate were added. The polymer was added to precipitate. The precipitated polymer was washed twice with 1,000 parts / methanol of methanol and then 4 times with 1,000 parts / m of deionized water, filtered and dried to obtain a polymer 1. The average molecular weight of this polymer by the GPC method (the same applies hereinafter) 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 replaced with nitrogen, and then 260 parts of deionized water, 0.2 part of benzoyl peroxide, and partially saponified polyvinyl. 1 part alcohol, 8 parts allyl-2-hydroxyethyl ether, 6 parts allyl glycidyl ether, N-vinyl-2
-Pyrrolidone (10 parts), methyl methacrylate (60 parts) and butyl acrylate (16 parts) were charged, and the temperature was raised to 70 ° C with stirring under a nitrogen gas atmosphere. After reacting for 5 hours, it was cooled to room temperature, washed twice with 1,000 parts / deionized water, filtered and dried to obtain a polymer 2. The average molecular weight of this polymer is 35,000
Met.

Synthetic Example 3 (Synthesis of Polymer 3) In Synthetic Example 1, 7 parts of n-butyl vinyl ether, 19 parts of 2-vinyl pyridine, 61 parts of methyl methacrylate and 13 parts of hydroxypropyl acrylate were used as a comonomer. Polymer 3 was obtained in the same manner as in Synthesis Example 1 except that the temperature was 50 ° C. The average molecular weight of this polymer is
It was 50,000.

Synthesis Example 4 (Synthesis of Polymer 4) A polymerization vessel equipped with a stirrer, a condenser, a thermometer and a nitrogen gas inlet was replaced with nitrogen, and then 150 parts of methanol, 15 parts of allyl-2-hydroxyethyl ether and allylglycidyl were used. 15 parts ether, 10 parts N-vinyl-2-pyrrolidone,
30 parts methyl methacrylate, 20 parts butyl acrylate,
2-Hydroxyethyl methacrylate (10 parts) and diisopropyl peroxydicarbonate (5 parts) were charged, the temperature was raised to 45 ° C. with stirring under a nitrogen gas atmosphere, and the reaction was carried out for 20 hours. The resulting slurry is 3 parts with 1,000 parts / methanol
It was washed twice with 1,000 parts / deionized water, filtered, and dried to obtain Polymer 4. The average molecular weight of this polymer is 2
It was 0,000.

Synthetic Example 5 (Synthesis of Polymer 5) In Synthetic Example 1, 15 parts of allyl glycidyl ether, 8 parts of 2-vinylpyridine, 47 parts of methyl methacrylate, 15 parts of hydroxypropyl acrylate as a comonomer,
Polymer 5 was obtained in the same manner as in Synthesis Example 1 except that 15 parts of styrene was used and the reaction temperature was 55 ° C. The average molecular weight of this polymer was 40,000.

Synthetic Example 6 (Synthesis of Polymer 6) In Synthetic Example 1, 14 parts of allyl-2-hydroxyethyl ether and 62% of methyl methacrylate were used as copolymerizable monomers.
Example 1 except that 24 parts of butyl methacrylate was used
Polymer 6 was obtained by performing the same operation as above. The average molecular weight of this polymer was 30,000.

Synthesis Example 7 (Synthesis of Polymer 7) N-vinyl-2- as a comonomer in Synthesis Example 2
Pyrrolidone 8 parts, methyl methacrylate 54 parts, butyl methacrylate 24 parts, hydroxypropyl acrylate 14
Polymer 7 was obtained by performing the same operation as in Synthesis Example 2 except that parts were used. The average molecular weight of this polymer was 35,000.

Examples 1 to 4, Comparative Examples 1 to 2 Copolymer (Polymer 1) 18 parts Co-γ-Fe ₂ O ₃ 100 parts with specific surface area 35 m ² / g Polyurethane resin [N-2304: 7 parts Japan Polyurethane Industry Co., Ltd. product name] Carbon black [MA-7B: Mitsubishi Kasei Co., Ltd. product name] 5 parts Lecithin 2 parts Methyl ethyl ketone 75 parts Cyclohexanone 75 parts Toluene 75 parts are mixed with a lab mixer for 90 minutes, and The mixture was kneaded for 3 hours with an Eiger mill containing glass beads, and 5 parts of polyisocyanate [Coronate L: trade name of Nippon Polyurethane Industry Co., Ltd.] was added to the obtained paint to prepare a magnetic paint, and the paint was 13 μm thick. The polyester film was coated on one surface of the polyester film to a dry thickness of 4.5 μm, dried, and calendered to form a magnetic layer.

Next, the following components were blended, and copolymer (polymers 1-4, 6-7) 20 parts polyurethane resin (N-2304: supra) 20 parts carbon black (MA-7B: supra) 45 parts Alumina [AKP-20: trade name manufactured by Sumitomo Chemical Co., Ltd.] 2 parts Methyl ethyl ketone 90 parts Cyclohexanone 90 parts Toluene 90 parts Obtained by kneading with a lab mixer for 90 minutes and with an Eiger mill containing glass beads for 3 hours. 5 parts of polyisocyanate (Coronate L: described above) was added to the paint and mixed to prepare a back coat paint. Apply this coating to the surface on the opposite side of the polyester film with the above magnetic layer to a dry thickness.
A back coat layer was formed by coating so as to have a thickness of 0.7 μm and then dried to form a magnetic tape by slitting into a 1/2 inch width. The coating properties of the magnetic tape obtained as described above were examined. The results are as shown in Table 1.

Example 5 Same as Example 1 except that nitrocellulose was used as the binder resin for the magnetic coating material for forming the magnetic layer and polymer 5 was used as the binder resin for the coating material for forming the backcoat layer. Then, a magnetic tape was produced. The results of examining the coating properties of the obtained magnetic tape are as shown in Table 1. In addition, the copolymer (polymer 1
The compatibility with the polyurethane resin of 7) was investigated and the results are shown in Table 1.
It was shown to.

[0034]

[Table 1]

The characteristics were measured as follows. a. Friction coefficient of the back coat layer The test tape was hooked on a stainless rod having a diameter of 3 mmφ by 180 degrees (half circumference), and the load on the entrance side and the exit side when the tape was slid at 5 cm / sec was measured. However, the load on the entry side is 2
It was set to 0.0 g. Also, the measurement was performed on each test tape after 100 running tests were completed in an environment of 40 ° C. and 80% RH. b. Powder drop The amount of powder drop on the head drum and guides after 100 runs of the 60-minute shuttle 100 times was visually observed and evaluated by the deduction method. The larger the absolute value, the larger the powder falling. c. Scratchability The scratches on the back coat layer after 100 minutes of shuttle travel of the sample tape having a length of 10 minutes were visually evaluated in four grades. ⊚: Very good, ◯: Good, Δ: Slightly scratched, ×: Severely scratched d. Surface roughness Using a stylus type surface roughness meter, the centerline average roughness R of the backcoat layer surface was measured under the conditions of stylus speed of 0.06 mm / sec and cutoff of 0.08 mm. e. Amount of generated hydrogen chloride In accordance with JIS K-7217, a 3 mm square sample cut from a test tape is burned in the air, and the combustion gas is absorbed in an aqueous solution of sodium hydroxide so that chlorine ions in the absorbing liquid are silver nitrate / ferric ammonium sulfate. / Quantified by the ammonium thiocyanate method. f. Compatibility with polyurethane resin 100 parts of each 20% solution of polymers 1 to 7 using a mixed solvent of methyl ethyl ketone / methyl isobutyl ketone / toluene = 1/1/1 and 50 parts of polyurethane resin (N-2304: supra) Were mixed with each other, stirred for 1 hour with a stirrer, and then coated and dried on a glass plate, and the compatibility was visually evaluated on a 4-grade scale based on the presence or absence of lumps in the coating film and the degree of haze. ◎: excellent, ◯: good, △: acceptable, ×: not acceptable

[0036]

INDUSTRIAL APPLICABILITY The present invention provides a magnetic recording medium having a back coat layer having excellent characteristics, which uses a newly developed copolymer for a binder. This newly developed copolymer for binder exhibits excellent dispersibility in non-magnetic powder such as fine carbon black, improved compatibility with polyurethane resin, and deteriorates magnetic powder in the magnetic layer. No decomposition products are generated. Since the dispersibility is improved, the smoothness of the surface of the back coat layer is improved and the coefficient of friction is small and stable. Therefore, the running resistance on the device is small and the magnetic tape is less damaged even after repeated running.

Claims (1)

[Claims] 1. A magnetic recording medium having a magnetic layer on one surface and a backcoat layer on the other surface of a non-magnetic support, wherein the binder of the backcoat layer is an ether compound based on radical polymerization. Ratio of 1 to 50% by weight of monomer, 1 to 30% by weight of nitrogen-containing monomer having radical polymerizability, and 20 to 98% by weight of (meth) acrylic monomer having neither ether bond nor nitrogen. A magnetic recording medium comprising a (meth) acrylic copolymer obtained by copolymerization as a main component.