JPH07244832A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve the dispersibility of fine ferromagnetic powder in binder, avoid the deterioration in the kneading and dispersing process and obtain magnetic coating material having a satisfactory viscosity stability by a method wherein acrylic copolymer is cross-linked in the main component of the binder. CONSTITUTION:A magnetic layer made of material which is composed of binder and ferromagnitic fine powder dispersed in the binder is provided on a non- magnetic supporter. The main component of the binder is acrylic copolymer which contains acrylic monomer units which do not have both epoxy groups and carboxyl groups, monomer units having epoxy groups and monomer units having carboxyl groups (0.8-5.8wt.% of epoxy groups and 0.8--5.8-wt.% of carboxyl groups are contained). Further, by heating the magnetic layer, the acrylic copolymer in the binder is cross-linked.

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, a floppy disk, etc., and particularly when a fine ferromagnetic powder is used, it is dispersed in the fine ferromagnetic powder. Has good properties and does not use urethane prepolymer as a cross-linking agent for the binder, so it has excellent stability of the magnetic paint, can be cross-linked by heating, and the coating film obtained is durable, abrasion resistant and heat resistant. The present invention relates to an improved magnetic recording medium using an acrylic copolymer having excellent performance.

[0002]

2. Description of the Related Art Magnetic recording media such as magnetic tapes, magnetic cards, and floppy disks are prepared by mixing and dispersing a synthetic resin-based binder with magnetic powder and further adding a urethane prepolymer to prepare a magnetic paint. It is prepared by applying it on the body surface, drying it, and then heat-curing (crosslinking) it to provide a magnetic layer. In recent years, the recording density of magnetic recording media has been improved by the use of finely sized and highly coercive iron oxide or iron oxide having cobalt ions adsorbed or doped, and metals such as iron, nickel and cobalt or alloys containing these. On the other hand, the improvement of dispersibility, durability, heat resistance, and other coating properties of magnetic powders has been demanded, and the selection of binder has become an important factor for improving the above performance. ing.

Vinyl chloride-vinyl acetate copolymers, vinyl chloride-vinylidene chloride copolymers, etc. 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 these polymers have hydrophilic functional groups together, which is advantageous for the dispersion of magnetic powder. However, even if these good synthetic resins are selected, the dispersion of the magnetic powder becomes good, but high shearing force is applied to the magnetic powder and the binder in the kneading dispersion process and the magnetic powder is exposed to harsh conditions for a long time. The characteristics may be impaired, and the decomposition product from the synthetic resin, particularly in the vinyl chloride copolymer, hydrochloric acid generated by dehydrochlorination causes deterioration of the magnetic powder. Further, in order to improve the durability of the coating film, a urethane prepolymer is usually blended as a cross-linking agent at the time of preparing the magnetic paint, but since this urethane prepolymer reacts with moisture in the air, the viscosity of the paint is In some cases, a smooth coating film may not be obtained when such a paint is used. Therefore, the paint using the urethane prepolymer has a drawback that its pot life is limited.

[0004]

SUMMARY OF THE INVENTION The present invention does not have the problems of the above-mentioned prior art, has good dispersibility for fine ferromagnetic powder, and has no deterioration in the kneading and dispersing step.
It was made to develop a resin for a binder that gives a magnetic coating having good viscosity stability and to provide a magnetic recording medium having a magnetic layer having excellent characteristics.

[0005]

The present invention has solved the above-mentioned problems, and the present invention comprises a magnetic layer having ferromagnetic fine powder dispersed in a binder on a non-magnetic support. In a magnetic recording medium, the binder is an acrylic monomer unit having neither an epoxy group nor a carboxyl group,
Acrylic copolymer containing a monomer unit having an epoxy group and a monomer unit having a carboxyl group (provided that it contains 0.8 to 5.8% by weight of an epoxy group and 0.8 to 5.8% by weight of a carboxyl group). And a magnetic recording medium characterized in that the acrylic copolymer in the binder is crosslinked by heating the magnetic layer.
Further, the binder contains an acrylic monomer unit having neither an epoxy group nor a carboxyl group, and the content of the monomer unit having an epoxy group is higher than that of the acrylic copolymer described later. An acrylic copolymer which does not contain a monomer unit having a carboxyl group or has a small content, and an acrylic copolymer which contains an acrylic monomer unit having neither an epoxy group nor a carboxyl group. Acrylic copolymer that does not contain monomer units having epoxy groups or has a low content of monomer units having carboxyl groups compared to (combined weighted average after combination Containing 0.8 to 5.8% by weight of epoxy groups and 0.8 to 5.8% by weight of carboxyl groups as a main component), and the acrylic copolymer in the binder is crosslinked by heating the magnetic layer. And a magnetic recording medium characterized by the above.

That is, the inventors of the present invention have made extensive studies to solve the above-mentioned problems, and as a result, as a result, an acrylic copolymer having an epoxy group and a carboxyl group, an acrylic copolymer having an epoxy group, an acrylic copolymer having a carboxyl group. A type copolymer is used alone or in combination as the main component of the binder,
And by heating the magnetic layer to crosslink the acrylic copolymer, the dispersibility of the ferromagnetic powder is improved, the stability of the magnetic paint is excellent, and the durability and abrasion resistance of the magnetic coating film are improved. The present invention was completed by further investigating the ratio of various monomers, the temperature condition of heat crosslinking, and the like.
The present invention will be described in detail below.

The acrylic copolymer used as the main component of the binder in the present invention comprises a monomer unit having an epoxy group and / or a monomer unit having a carboxyl group and / or an epoxy group and a carboxyl group. Although it contains an acrylic monomer unit having neither of them, such an acrylic copolymer can be obtained by copolymerizing using a monomer corresponding to each monomer unit. In the present application, acrylic is a general term including methacrylic.

Examples of the monomer corresponding to the monomer unit having an epoxy group include glycidyl ethers of unsaturated alcohols such as allyl glycidyl ether and methallyl glycidyl ether; unsaturated acids such as glycidyl acrylate and glycidyl methacrylate. Glycidyl esters of butadiene monooxide, vinylcyclohexene monooxide, 2-methyl-5,6-epoxy-1-
Examples include epoxide olefins such as hexene. The monomer having an epoxy group may be used alone or in combination of two or more, but when used without combining the acrylic copolymer, the epoxy group in the acrylic copolymer is used. If the amount of is too small, the durability will decrease,
If it is too much, the flexibility of the coating film will be lost and it will become brittle and the durability will decrease.
%, But preferably 1.0 to 4.5% by weight.
It is necessary to adjust the introduction amount of the monomer unit having an epoxy group by the use amount of the monomer having an epoxy group so that the amount of the epoxy group in the copolymer falls within the above range.

Examples of the monomer corresponding to the monomer unit having a carboxyl group include:

[Chemical 1] (In the formula, X and Y represent a hydrogen atom or a monovalent hydrocarbon group, but at least one is a hydrogen atom.),

[0010]

[Chemical 2] And so on.

The monomer having a carboxyl group may be used alone or in combination of two or more kinds. However, when the monomer is used without combining the acrylic copolymer, in the acrylic copolymer If the amount of the carboxyl group is too small, the dispersibility of the ferromagnetic powder decreases and the durability also decreases, and if it is too large, the viscosity of the magnetic coating increases, so the amount of the carboxyl group is 0.8 to 5.8 in the copolymer. Although the weight% is
It is preferably 1.0 to 4.5% by weight. It is necessary to adjust the introduction amount of the monomer unit having a carboxyl group by the use amount of the monomer having a carboxyl group so that the amount of the carboxyl group in the copolymer falls within the above range.

Acrylic monomers corresponding to acrylic monomer units having neither an epoxy group nor a carboxyl group include both acryl and methacryl, examples of which include 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
-Ethylhexyl (meth) acrylate, lauryl (meth) acrylate, stearyl (meth) acrylate,
Alkyl (meth) acrylates such as cyclohexyl (meth) acrylate; aryl (meth) acrylates such as benzyl (meth) acrylate; (meth) acrylamide, diacetone (meth) acrylamide,
(Meth) acrylamides such as N-methylol (meth) acrylamide, N-methoxymethyl (meth) acrylamide and N-butoxymethyl (meth) acrylamide; hydroxyalkyl such as hydroxyethyl (meth) acrylate and hydroxypropyl (meth) acrylate (Meth) acrylates; methoxyethyl (meth)
Alkoxyalkyl (meth) acrylates such as acrylate and butoxyethyl (meth) acrylate; and (meth) acrylonitrile. The acrylic monomer may be used alone or in combination of two or more, but as the monomer unit, the above-mentioned epoxy group is combined with the monomer unit as an optional component described later. It occupies the rest of the monomer unit having and / or the monomer unit having a carboxyl group.

If desired, a polymerizable monomer other than the above-mentioned essential monomers can be copolymerized as an optional monomer. Examples of such a monomer include styrene and α-methyl. Styrene, vinyl acetate, vinyl propionate, methyl vinyl ether, hydroxyethyl vinyl ether,
Allyl hydroxyethyl ether and the like can be mentioned. These monomers can be used as a monomer unit in the range of 30% by weight or less based on the total monomer units of the copolymer as long as the effects of the present invention are not impaired.

The type and amount of the monomers used in the present invention are the glass transition temperature of the resulting copolymer and other resins used in magnetic recording media, generally polyurethane resin, polyester resin, polyamide resin, polysulfide resin. , The acrylonitrile-butadiene copolymer and the like are taken into consideration and selected according to the physical properties of the coating film.

The copolymer composed of a combination of the above-mentioned monomer units has a low physical strength such as a brittle magnetic coating film when the molecular weight is too low, and the durability of a magnetic tape or the like. On the contrary, if the molecular weight is too high, the viscosity of the coating material at a predetermined concentration becomes high, resulting in poor workability and difficulty in handling. Therefore, the average molecular weight is 10,000 to 100,000 as measured by the GPC method. It is preferably in the range of 20,000 to 60,000, more preferably. For adjusting the molecular weight, a molecular weight adjusting agent such as n-dodecyl mercaptan, thioglycol or trichloroethylene may be used.

The case where only one type is used alone without combining the acrylic copolymer used as the main agent has been described above. Furthermore, the acrylic copolymer used as the main agent of the binder has an epoxy group. A copolymer having a high content of monomer units having a carboxyl group or having a low content of monomer units, and the copolymer having a monomer unit having an epoxy group and a carboxyl group It may be a combination with a copolymer having an opposite content with respect to the monomer unit, and a weighted average value in the copolymer is 0.8 to 5.8.
It has also been found that the object of the invention can be achieved if it contains by weight of epoxy groups and 0.8-5.8% by weight of carboxyl groups. In the case of the combination of the copolymers, each of the copolymers used may be out of the range in the content of the epoxy group and the carboxyl group except that the copolymer is used in only one kind. It may be the same as the copolymer used in only one kind.

For the purpose of improving the durability of the magnetic layer of the magnetic recording medium, it is usual to use a urethane prepolymer as a crosslinking agent for the synthetic resin in the binder and treat it at 60 to 70 ° C. for 24 hours. A major feature of the present invention is that it is not necessary to use this type of crosslinking agent. In the present invention, since the acrylic copolymer or the combination thereof, which is the main component of the binder, contains an epoxy group and a carboxyl group, it crosslinks when heated to a certain temperature or higher, and durability and abrasion resistance are improved. To do. The thermal crosslinking is carried out with or without the use of a crosslinking accelerator.

Trialkylamine as a crosslinking accelerator,
Amines such as dimethylaminopropylamine, tetramethylguanidine, dimethylaminoethanol, triethanolamine, N, N′-dimethylpiperazine, N-methylmorpholine, hexamethylenetetramine, benzyldimethylamine, pyridine, pyrazine and salts thereof. An amine complex of boron trifluoride such as boron trifluoride monoethylamine, boron trifluoride piperidine, boron trifluoride aniline; an acid anhydride such as phthalic anhydride, maleic anhydride; p-toluenesulfonic acid, benzoic acid Examples include organic acids such as; phenol compounds such as phenol, bisphenol A, tris (dimethylaminomethyl) phenol; ketone-blocked polyamines; quaternary ammonium salts such as trimethylbenzylammonium salt; metal hydroxides such as caustic potash These are used alone or in combination in consideration of the pot life, heating temperature and crosslinking rate of the compounded paint.

The acrylic copolymer used in the present invention is
It can be produced by a general solution polymerization method, a precipitation polymerization method, a suspension polymerization method, an emulsion polymerization method or the like by a radical polymerization method. Polymerization initiators used in the production of copolymers include persulfates such as ammonium persulfate, potassium persulfate and sodium persulfate, and hydrogen peroxide; diisopropyl peroxydicarbonate, t-butyl hydroperoxide, benzoyl peroxide. Organic peroxide type initiators such as oxide, cumene hydroperoxide, dibutyl peroxide; nitrogen-containing initiators such as azobisisobutyronitrile and azobisisovaleronitrile are exemplified, and these are used alone or 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 solvent include ketones such as acetone, methyl ethyl ketone and methyl isobutyl ketone; esters such as methyl acetate, ethyl acetate and butyl acetate, and 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.

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 and poly. Examples thereof include synthetic polymers such as acrylamide, maleic acid-styrene copolymer and maleic acid-methyl vinyl ether copolymer; and natural polymers such as starch and gelatin.

As the 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 thereof include nonionic emulsifiers such as polyoxyethylene carboxylic acid ester.

In the polymerization, the above-mentioned monomer, 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 adding a water-soluble organic solvent according to a known salting-out method after the polymerization. After that, it may be filtered, washed, and dried.

When the above-mentioned copolymer is used as the main component of the binder during the production of the magnetic coating liquid, other resins may be used in an amount equal to or less than an equal amount, if necessary. Examples thereof include various polymers such as polyurethane resins, nitrocellulose, polyester resins, epoxy resins, polyamide resins, phenol resins, alkyd resins, polyvinyl butyral resins, polysulfide resins, and other polymers or copolymers. Among these, polyurethane resin is preferable.

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 on these, CrO ₂ , and further Fe, Co and Fe-C.
Examples thereof include needle-like fine particles of metal or alloy containing o, Ni, etc., and other various conventionally known magnetic powders. The mixing ratio of the ferromagnetic fine powder and the binder resin (the total of the resin used in combination with the main agent) is preferably 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 resin, a lubricant generally used in the past,
The addition of abrasives, antistatic agents, dispersion aids, rust preventives, etc., and the use of various organic solvents other than methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, toluene, etc. as the coating medium may be the same as the conventional one. ,
There are no particular restrictions on these points.

As the support, synthetic resins such as polyester, polyolefin, cellulose acetate and polycarbonate, non-magnetic metals, ceramics and the like are used, and the form is a film, tape, sheet, plate or the like. As a coating means for forming the magnetic layer on the support, a conventionally known method may be used, and after appropriately smoothing treatment such as calendering treatment, heating is performed to crosslink the acrylic copolymer. For example, the high-performance magnetic recording medium intended by the present invention can be obtained. The heating conditions are 60-130 ℃,
It may be 3 minutes to 5 hours, preferably 80 to 100 ° C,
It turns out that it should be 5 to 30 minutes.

[0028]

[Examples] Next, synthesis examples of an acrylic copolymer as a main component of a binder and specific examples and comparative examples using the obtained acrylic copolymer will be described. It is not limited to. The part and% in the examples
Indicates 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 purged with nitrogen, then 200 parts of deionized water, 0.5 part of diisopropyl peroxydicarbonate, partially saponified. Polyvinyl alcohol 1 part, n-dodecyl mercaptan
0.3 parts, 10 parts of glycidyl methacrylate, 6 parts of methacrylic acid, and 84 parts of methyl methacrylate were charged, and the temperature was raised to 57 ° C. with stirring under a nitrogen gas atmosphere. Subsequently, the mixture was reacted for 7 hours with stirring, cooled to room temperature, washed twice with 1,000 parts / deionized water, filtered and dried to obtain a polymer 1.
The amount of epoxy groups in this polymer was 3.0%, the amount of carboxyl groups was 3.1%, and the average molecular weight was 37,000. The amount of epoxy groups was determined by the hydrochloric acid-dioxane method, and the amount of carboxyl groups was determined by the neutralization titration method with a caustic soda-methanol standard solution. The same applies hereinafter.

Synthetic Example 2 (Synthesis of Polymer 2) After replacing the atmosphere in a polymerization vessel equipped with a stirrer, a condenser, a thermometer and a nitrogen gas inlet with nitrogen, 75 parts of deionized water, 0.11 part of 28% hydrogen peroxide solution, 1% 0.05 part of an aqueous ferrous sulfate solution was charged, and the temperature was raised to 50 ° C. with stirring under a nitrogen gas atmosphere. Meanwhile, 55 parts deionized water, 5 parts glycidyl acrylate, 3 parts acrylic acid, 46 parts methyl methacrylate,
Butyl methacrylate 46 parts, sodium lauryl sulfate 1
Parts, 0.1 parts of n-dodecyl mercaptan mixed and emulsified with a homomixer, and 0.18 parts of sodium bisulfite dissolved in 20 parts of deionized water were uniformly dropped into the above polymerization vessel under stirring for 5 hours. Then, the mixture was further reacted at 50 ° C. for 2 hours to complete the polymerization, and 100 parts of methanol and 10 parts of sodium sulfate were added to precipitate a polymer. The precipitated polymer was washed twice with 1,000 parts / methanol of methanol, then washed four times with 1,000 parts / time of deionized water, filtered and dried to obtain a polymer 2. The amount of epoxy groups in this polymer is
1.7%, the amount of carboxyl groups was 1.9%, and the average molecular weight was 27,000.

Synthesis Example 3 (Synthesis of Polymer 3) A polymerization vessel equipped with a stirrer, a condenser, a thermometer and a nitrogen gas inlet was replaced with nitrogen, and then 20 parts of deionized water and methanol were added.
80 parts and 1 part of diisopropyl peroxydicarbonate were charged and the temperature was raised to 50 ° C. with stirring under a nitrogen gas atmosphere. On the other hand, allyl glycidyl ether 3 parts in advance,
A mixture of 2 parts of methacrylic acid, 65 parts of methyl methacrylate, and 30 parts of butyl acrylate was uniformly added dropwise to the above polymerization vessel with stirring for 5 hours, and the mixture was further added at 50 ° C. for 2 hours.
Reacted for hours. The resulting slurry is deionized water 1,000
The polymer 3 was obtained by washing twice with parts / time, filtering and drying. The amount of epoxy groups in this polymer was 1.1%, the amount of carboxyl groups was 1.0%, and the average molecular weight was 30,000.
Met.

Synthesis Example 4 (Synthesis of Polymer 4) Same as Synthesis Example 2 except that 15 parts of glycidyl methacrylate, 7 parts of methacrylic acid, 58 parts of methyl methacrylate and 20 parts of styrene were used as the comonomer in Synthesis Example 2. Various operations were performed to obtain polymer 4. The amount of epoxy groups in this polymer was 4.5%, the amount of carboxyl groups was 3.7%, and the average molecular weight was 50,000.

Synthetic Example 5 (Synthesis of Polymer 5) The same operation as in Synthetic Example 2 was carried out except that 15 parts of glycidyl methacrylate, 65 parts of methyl methacrylate and 20 parts of butyl methacrylate were used as the comonomer in Synthetic Example 2. Polymer 5 was obtained. The amount of epoxy groups in this polymer was 4.3%, and the average molecular weight was 29,000.

Synthesis Example 6 (Synthesis of Polymer 6) In Synthesis Example 1, methacrylic acid 3 was used as a comonomer.
Part, methyl methacrylate 77 parts, butyl acrylate 20
Polymer 6 was obtained in the same manner as in Synthesis Example 1 except that parts were used. The amount of carboxyl groups in this polymer is 1.9
%, And the average molecular weight was 39,000.

Synthetic Example 7 (Synthesis of Polymer 7) Synthetic Example 2 except that 1.5 parts of allyl glycidyl ether, 1 part of acrylic acid, 82.5 parts of methyl methacrylate and 15 parts of hydroxypropyl acrylate were used as the comonomer in Synthesis Example 2. Polymer 7 was obtained by performing the same operation as in 2. The amount of epoxy groups in this polymer was 0.5%, the amount of carboxyl groups was 0.5%, and the average molecular weight was 27,000.
Met.

Examples 1 to 4 Main component (polymer 1, 2, 3 or 4) 18 parts Co-γ-Fe ₂ O ₃ 100 parts with specific surface area of 35 m ² / g Polyurethane resin [N-2304: Nippon Polyurethane Industry Co., Ltd. ) Product name] 7 parts Carbon black 5 parts Lecithin 2 parts Methyl ethyl ketone 75 parts Cyclohexanone 75 parts Toluene 75 parts The above components are mixed for 90 minutes with a lab mixer, and further kneaded with an Eiger mill containing glass beads for 3 hours and then obtained by filtration. 355 parts from the liquid, cyclohexanone 30 parts,
Add 1 part of dimethylaminoethanol and in a lab mixer
A coating liquid was obtained by mixing and dispersing for 90 minutes.

On the polyester film, 6 parts of the above-mentioned coating liquid were applied.
A magnetic tape was prepared by applying a coating having a thickness of μm, subjecting it to magnetic field orientation treatment, drying it, and then subjecting it to a surface treatment with a super calender, followed by heat crosslinking at 90 ° C. for 10 minutes. The viscosity stability of the coating liquid obtained as described above, the coating properties of the magnetic tape and the magnetic properties were examined. The results are as shown in Table 1.

Example 5 A magnetic tape was prepared in the same manner as in Example 1 except that 9 parts of Polymer 5 and 9 parts of Polymer 6 were used as the main components of the binder in Example 1. The results of examining the viscosity stability of the coating liquid, the coating properties of the magnetic tape and the magnetic properties are shown in Table 1.

Comparative Examples 1-2 Main agent (polymer 5 or 6) 18 parts Co-γ-Fe ₂ O ₃ 100 parts with specific surface area of 35 m ² / g Polyurethane resin (N-2304: above) 7 parts Carbon black 5 parts Lecithin 2 parts Methyl ethyl ketone 75 parts Cyclohexanone 75 parts Toluene 75 parts The above components are mixed for 90 minutes in a lab mixer, further kneaded in an Eiger mill containing glass beads for 3 hours, and then filtered to obtain 355 parts of polyisocyanate [polyisocyanate]. Coronate L: trade name of Nippon Polyurethane Industry Co., Ltd.] 5 parts Cyclohexanone 30 parts were added and mixed and dispersed for 90 minutes with a lab mixer to obtain a coating liquid.

On the polyester film, 6 parts of the above-mentioned coating liquid were applied.
A magnetic tape was prepared by applying a coating having a thickness of μm, subjecting it to magnetic field orientation treatment, drying, and then subjecting it to a surface treatment with a super calender, followed by heat crosslinking at 60 ° C. for 24 hours. Table 1 shows the results of examining the viscosity stability of the coating solution obtained as described above, the coating properties of the magnetic tape, and the magnetic properties.

Comparative Example 3 Polymer 7 was used as the main component of the binder, and the heating and crosslinking conditions were changed.
A magnetic tape was prepared in the same manner as in Comparative Example 1 except that the temperature was 90 ° C. for 10 minutes. The results of examining the viscosity stability of the coating liquid, the coating properties of the magnetic tape and the magnetic properties are shown in Table 1.

[0042]

[Table 1]

The respective characteristics were measured as follows. a. Stability of paint viscosity The viscosity of the kneaded and adjusted paint liquid was measured with an E-type viscometer (initial viscosity), and the residual liquid was allowed to stand at 25 ° C for 48 hours, and then the viscosity was measured again. The evaluation was performed in four stages based on the ratio of the viscosity after 48 hours when the initial viscosity was 100. ◎: Almost no change in viscosity (less than 110%) 〇: Slightly thickened (110 to 200%) △: Largely thickened (more than 200%) ×: Gelation

B. A gloss gloss meter (manufactured by Murakami Color Research Institute) was used to compare the 60-degree reflectance before calendaring with a standard glass plate. c. Square-type ratio Measurement was performed using a vibration sample type magnetometer (manufactured by Toei Industry Co., Ltd.).

D. Durability The created magnetic tape was left in a constant temperature and humidity room at 65 ° C and 90% relative humidity for 168 hours, then a load of 100 g was applied, and it was brought into contact with a rotating drum with abrasive paper and rotated 1,000 times at 150 rpm. The degree to which the magnetic paint adhered to the abrasive paper was visually evaluated on a 4-point scale. ⊚: No stain on abrasive paper, ◯: Slight stain, Δ: Slight stain, ×: Stain heavily e. Running property The force generated between the coating film and the rotary drum was measured by a U gauge in the atmosphere of 65 ° C. and 80% relative humidity in the same manner as the durability evaluation, and the running resistance was evaluated in three stages in order from the lowest one. ◯: Low, Δ: Medium, ×: High

[0046]

INDUSTRIAL APPLICABILITY The present invention provides a magnetic recording medium using a newly developed binder resin and having a magnetic layer having excellent characteristics. The newly developed binder resin exhibits excellent dispersibility in magnetic powder, the viscosity of the obtained magnetic coating is suitable for coating work, and the viscosity does not change with time. As a result, the smoothness of the coating film surface was improved, the wear resistance was improved, and the durability and running property of the magnetic recording medium were excellent. There is no phenomenon such as performance deterioration due to dehydrochlorination in the case of vinyl chloride resin.

Claims (2)

[Claims] 1. A magnetic recording medium comprising a magnetic layer having a ferromagnetic fine powder dispersed in a binder on a non-magnetic support, wherein the binder has neither an epoxy group nor a carboxyl group. Acrylic Copolymer Containing Acrylic Monomer Unit, Epoxy Group-Containing Monomer Unit, and Carboxyl Group-Containing Monomer Unit (However, 0.8 to 5.8 wt% of epoxy groups and 0.8 to 5.8 wt% of A magnetic recording medium containing a carboxyl group) as a main component, and the acrylic copolymer in the binder is crosslinked by heating the magnetic layer. 2. A magnetic recording medium comprising a magnetic layer having ferromagnetic fine powder dispersed in a binder on a non-magnetic support, wherein the binder has neither an epoxy group nor a carboxyl group. Acrylic containing a large amount of monomer units having an epoxy group and containing a small amount of monomer units having a carboxyl group, as compared with the following acrylic copolymer containing an acrylic monomer unit Copolymer, containing an acrylic monomer unit having neither an epoxy group nor a carboxyl group, and does not contain a monomer unit having an epoxy group as compared to the acrylic copolymer, or the content is A combination with an acrylic copolymer having a high content of monomer units having few carboxyl groups (provided that the weighted average value after combination is 0.8 to 5.8% by weight of epoxy groups and 0.8 to 5.8% by weight of Containing a carboxyl group.)
A magnetic recording medium characterized in that the acrylic copolymer in the binder is cross-linked by using as a main component and heating the magnetic layer.