JP2001084565A - Magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a back coat for magnetic recording medium that has less transfer from the back coat and does not exert adverse influence on electromagnetic transducing characteristics. SOLUTION: This magnetic recording medium has a magnetic recording layer provided on one surface of a non-magnetic substrate and a back coat layer consisting essentially of non-magnetic powder radiation-curing type bonding agent resin on the other surface of the substrate. In this case, the radiation- curing type bonding agent resin in the back coat layer contains a radiation- curing type vinyl chloride based copolymer having an amino-modified vinyl unit and/or a vinyl unit which contains an acidic functional group in one molecule.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a magnetic material having a magnetic layer on one side of a non-magnetic support and a back coat layer mainly composed of a non-magnetic powder and a binder on the other side. The present invention relates to a recording medium, and particularly to a binder for a back coat layer.

[0002]

2. Description of the Related Art Several magnetic recording media in which a backcoat layer containing a radiation-curable binder resin is provided on one surface of a nonmagnetic support have been disclosed.

For example, Japanese Patent Publication No. 5-70206 states that in a magnetic recording medium having a magnetic recording layer provided on one side of a support and a back coat layer provided on the other side, the binder in the back coat layer is represented by ( A) Molecular weight of 5,000 to 1,000 having two or more unsaturated double bonds curable by radiation
(B) a molecular weight of at least one unsaturated double bond curable by radiation.
(C) a radiation-curable resin composition comprising a rubbery compound having a molecular weight of 200 to 3000 and having (C) one or more unsaturated double bonds curable by radiation; recoding media. Is disclosed. However, there is no description about the polar group of the radiation-curable binder resin, and it is difficult to prepare a backcoat layer coating material having good dispersibility, and as a result, the electromagnetic conversion characteristics of the magnetic recording medium tend to deteriorate. Was seen.

Japanese Patent Publication No. 5-7763 discloses that "a magnetic recording medium having a magnetic recording layer on one surface of a support, wherein the other surface contains a fatty acid or a mixture of a fatty acid and a fatty acid ester on the other surface. A magnetic recording medium comprising a back layer formed by dispersing a non-magnetic powder in a binder containing a radiation-sensitive curable resin is disclosed. However, there is no description regarding the polar group of the radiation-sensitive curable resin, and the dispersion of the coating material for the backcoat layer is insufficient.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems of the prior art, and it is an object of the present invention to provide a magnetic recording medium having less transfer from a back coat and having no adverse effect on electromagnetic conversion characteristics. To provide a back coat.

[0006]

The present invention has solved the above-mentioned problems, that is, (1) a magnetic recording layer on one side of a non-magnetic support and a non-magnetic powder on the other side. In a magnetic recording medium provided with a back coat layer containing a radiation-curable binder resin as a main component,
Magnetic recording characterized in that the radiation-curable binder resin in the back coat layer includes a radiation-curable vinyl chloride copolymer having an amine-modified vinyl unit and / or an acidic functional group-containing vinyl unit in one molecule. Medium. (2) The magnetic recording medium according to (1), wherein a center line average roughness (Ra) of the back coat layer surface of the magnetic recording medium is Ra ≦ 20.0 nm. (3) The radiation-curable vinyl chloride copolymer having an amine-modified vinyl unit and / or an acidic functional group-containing vinyl unit in one molecule has an average polymerization degree of 200 to 800. Magnetic recording medium. (4) The content of the amine-modified vinyl unit contained in the radiation-curable vinyl chloride-based copolymer having an amine-modified vinyl unit and / or an acidic functional group-containing vinyl unit in one molecule is 0.05 to 5.0% by weight. %, Wherein the content of the acidic functional group-containing vinyl unit is 0.05 to 2.5% by weight. It is.

Hereinafter, a specific configuration of the present invention will be described in detail.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS <Backcoat layer> The backcoat layer contains at least a nonmagnetic powder and a radiation-curable binder resin.

In the present invention, the binder resin is limited to a radiation-curable binder resin. With a conventionally used thermoplastic resin or thermosetting resin, in order to obtain sufficient coating film properties, the raw roll coated with the back coat layer is placed in an oven for a long time (for example, 70 ° C., 2 to 48 hours). It needs to be put in and cured. This is not only troublesome in the manufacturing process, but also causes a problem of transfer to the coating film of the magnetic layer due to tightening of the winding, and a problem of deterioration of the electromagnetic conversion characteristics. When the magnetic layer is a ferromagnetic metal thin film, cracks occur on the surface of the magnetic layer, and the function as a magnetic recording medium is lost. In order to avoid this, when a ferromagnetic metal thin film is formed after applying, drying, and curing the back coat layer, the non-magnetic support is damaged by heat during the film formation.

On the other hand, in the present invention, the dispersibility of the back coat layer forming paint is improved by introducing an amine-modified vinyl unit and / or an acidic functional group-containing vinyl unit into the radiation-curable binder resin. The surface roughness (Ra) of the back coat layer is improved. By thus smoothing the back coat layer, the electromagnetic conversion characteristics, dropout, and error rate of the magnetic recording medium are improved. Furthermore, if both the amine-modified vinyl unit and the acidic functional group-containing vinyl unit are introduced, the dispersibility of the paint is improved, and the dispersion stability of the paint is also improved, so that the stability in the paint production stage is improved.

The radiation-curable binder resin used in the present invention is a resin containing one or more unsaturated double bonds in a molecular chain, which generates a radical by radiation and cures by crosslinking or polymerization. Say.

The unsaturated double bond referred to herein means an acrylic double bond, which is a residue (acryloyl) of acrylic acid, acrylic ester, acrylic amide, methacrylic acid, methacrylic ester, methacrylamide, and the like. Group or methacryloyl group). Examples of the acrylic double bond-containing compound (A) include mono (meth) acrylates of glycols such as ethylene glycol, diethylene glycol and hexamethylene glycol, and mono (meth) acrylates of triol compounds such as trimethylolpropane, glycerin and trimethylolethane. And di (meta)
Hydroxy group-containing acrylic compounds such as mono (meth) acrylate and di (meth) acrylate, tri (meth) acrylate, glycerin monoallyl ether and glycerin diallyl ether of polyols having a valency of 4 or more such as acrylate, pentaerythritol and dipentaerythritol And the like are preferred. These acrylic double bonds have at least one, preferably 2 to 2, in the molecule of the binder.
There must be 20.

In the present invention, the radiation-curable binder resin contains, as an essential component, a radiation-curable vinyl chloride copolymer having an amine-modified vinyl unit and / or a vinyl unit having an acidic functional group in one molecule.

The acidic functional group-containing vinyl unit contained in the vinyl chloride copolymer of the present invention contains at least one functional group such as a carboxyl group, a sulfonic acid group, a sulfuric acid group, a phosphoric acid group and a phosphonic acid group. Is a vinyl unit. Any of these vinyl units may be used as long as it has the above functional group. For example, those having a carboxyl group include maleic acid, fumaric acid,
Examples include acrylic acid and methacrylic acid, and examples of those having a sulfonic acid group include sodium styrenesulfonate, sodium vinylsulfonate, sodium methacrylsulfonate, and sulfoethyl acrylate. Among these, maleic acid and fumaric acid having a carboxyl group, sulfoethyl acrylate and sodium methacrylsulfonate having a sulfonic acid group, 2-acid phosphooxyethyl methacrylate having a phosphoric acid group, and the like are particularly preferable. The content of the acidic functional group-containing vinyl unit is preferably 0.05 to 2.5% by weight, more preferably 0.1 to 2.0% by weight, particularly 0.5 to 1.5% by weight.
Is preferred. If there are too many acidic functional group-containing vinyl units,
The thixotropy of the paint tends to increase, and the surface smoothness of the applied magnetic layer tends to decrease. On the other hand, if the amount is too small, the stability of the coating material is deteriorated and aggregates are easily generated, and the surface property of the magnetic layer is deteriorated.

The amine-modified vinyl unit contained in the vinyl chloride copolymer used in the present invention contains an amino group. The amino group may be any of unsubstituted amino and substituted amino, for example, by adding various amine compounds described below to a vinyl chloride copolymer containing the acidic functional group-containing vinyl unit, And heating and stirring until the desired amine content is obtained for a certain period of time, in which case the amine is introduced into the side chain by the reaction between the chlorine atom of the vinyl chloride unit and the amine compound.

The amine compounds used include primary, secondary and tertiary amines such as aliphatic amines, alicyclic amines and aromatic amines, and specifically include ethylamine, propylamine, and the like. Butylamine, cyclohexylamine, ethanolamine, naphthylamine, aniline, O-toluidine, diethylamine, dioctylamine, diisobutylamine, diethanolamine, N, N '
-Dimethylethanolamine, N, N'-diethylethanolamine, N, N'-dibutylethanolamine, N-methylaniline, trimethylamine, triethylamine, triisobutylamine, tridecylamine, N-methyldiphenylamine, hexamethylenetetramine, trimethylamine Examples thereof include ethanolamine, tributylamine, pyridine, α-picoline, β-picoline, γ-picoline, 2,4-lutidine, quinoline, and morpholine.

The content of the amine-modified vinyl unit contained in the copolymer contained in the binder of the present invention is 0.03 to 0.03.
2.3% by weight is preferred, more preferably 0.05 to
2.0 wt%, especially 0.5 to 1.5 wt% is preferred.
If the content of the amine-modified vinyl unit is too large, the stability of the coating tends to deteriorate, and if it is too small, the dispersibility tends to deteriorate. The amount of the bound nitrogen is calculated from the nitrogen atom analysis value by the termulen method.

As other monomers used for producing the vinyl chloride copolymer, general monomers usually used for a vinyl chloride copolymer for paints can be used. These include, for example, vinyl acetate, vinyl propionate, vinyl monochloroacetate, vinyl carboxylate such as vinyl versatate, diethyl maleate,
Dibutyl maleate, di-2-hydroxyethyl maleate, dimethyl itaconate, methyl (meth) acrylate,
Glycidyl ethers of unsaturated alcohols such as ethyl (meth) acrylate, lauryl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, and allyl glycidyl ether and methallyl glycidyl ether; Glycidyl esters of unsaturated acids such as glycidyl (meth) acrylate, vinylidene halides such as vinylidene chloride and vinylidene fluoride, vinyl ethers such as methyl vinyl ether, isobutyl vinyl ether and cetyl vinyl ether, olefins such as ethylene and propylene, and (meth) acrylonitrile And unsaturated vinyl such as styrene and α-methylstyrene. These monomers can be used in a range of 5 to 50% by weight as long as the effects of the present invention are not impaired, and only one type may be used or two or more types may be used in combination.

In the copolymer described above, if the average degree of polymerization is too low, the coating film becomes brittle and the physical strength decreases, and if the average degree of polymerization is too high, the dispersion is insufficient. The average degree of polymerization is preferably in the range of 200 to 800, because the viscosity of the paint at a predetermined concentration becomes high and the workability becomes poor and handling becomes difficult.

As a method for radiation-modifying the above vinyl chloride resin (method of introducing an ethylenically unsaturated double bond), a vinyl chloride resin having a hydroxyl group or a carboxylic acid group is compared with a vinyl chloride resin having a (meth) acrylic group. And a compound having a carboxylic anhydride or a dicarboxylic acid for modification. A method of reacting and reacting a reaction product (adduct) of TDI with 2-HEMA for denaturation. A method comprising reacting a monomer having one or more ethylenically unsaturated double bonds and one isocyanate group in one molecule and having no urethane bond in the molecule. Is typical, but the method among them is excellent in the easiness of modification and the dispersibility and physical properties after modification, and it is preferable to modify by this method. Such monomers include:
Examples include isocyanate ethyl (meth) acrylate and methacryloyl isocyanate. The content of the acryl group or the methacryl group in the molecule is preferably 1 to 20 on the average, more preferably 2 to 15 in the molecule.

The above reaction is carried out by dissolving them in a known solvent, for example, toluene, cyclohexanone, methyl isobutyl ketone and the like, and combining with a urethanization reaction catalyst such as dibutyltin dilaurate and dibutyltin oxide and a radical polymerization inhibitor such as hydroquinone. Temperature 50-90 ° C
It should be done within the range. The ratio of reacting a monomer having one ethylenically unsaturated double bond and one isocyanate group in each molecule and having no urethane bond in the molecule is as follows:
In consideration of curability, the content is preferably 5 mol% or more of the hydroxyl group.

When the above copolymer is used as a binder resin in the production of a magnetic paint, another radiation-curable binder resin may be used in an amount equal to or less than an equal amount, if necessary. Examples thereof include various resins such as a polymer or a copolymer such as a polyurethane resin, a nitrocellulose, a polyester resin, an epoxy resin, a polyamide resin, a phenol resin, an alkyd resin, and a polyvinyl butyral resin. Of these, polyurethane resins are preferred.

The radiation-curable polyurethane resin is a urethane resin having at least one acrylic bond in the molecule, and is a polyurethane acrylate compound bonded to an acrylic double bond-containing compound via a urethane bond.

The term "acrylic double bond" as used herein means a residue (acryloyl group or methacryloyl group) such as acrylic acid, acrylic ester, acrylamide, methacrylic acid, methacrylic ester, and methacrylamide. Examples of the acrylic double bond-containing compound include glycol mono (meth) acrylates such as ethylene glycol, diethylene glycol, and hexamethylene glycol;
Mono (meth) acrylates and di (meth) acrylates of tri- or higher-valent polyols such as mono (meth) acrylate and di (meth) acrylate of triol compounds such as trimethylolpropane, glycerin and trimethylolethane, and pentaerythritol and dipentaerythritol Hydroxy group-containing acrylic compounds such as acrylate, tri (meth) acrylate, glycerin monoallyl ether and glycerin diallyl ether are preferred. These acrylic double bonds must be present in the binder molecule in at least one or more, preferably 2 to 20.

The polyurethane acrylate resin is generally obtained by reacting a hydroxyl group-containing resin with a hydroxyl group-containing acrylic compound and a polyisocyanate-containing compound. Examples of the hydroxyl group-containing resin include polyalkylene glycols such as polyethylene glycol, polybutylene glycol, and polypropylene glycol, alkylene oxide adducts of bisphenol A, various glycols, and polyester polyols having hydroxyl groups at the molecular chain terminals. Among these, a polyurethane acrylate resin obtained by using a polyester polyol as one component is preferable.

Examples of the carboxylic acid component of the polyester polyol include aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, orthophthalic acid and 1,5-naphthalic acid, p-oxybenzoic acid, p- (hydroxyethoxy) benzoic acid and the like. Aliphatic dicarboxylic acids such as aromatic oxycarboxylic acid, succinic acid, adipic acid, azelaic acid, sebacic acid, dodecanedicarboxylic acid, and unsaturated fatty acids such as fumaric acid, maleic acid, itaconic acid, tetrahydrophthalic acid, and hexahydrophthalic acid And tri- and tetracarboxylic acids such as alicyclic dicarboxylic acid, trimellitic acid, trimesic acid, and pyromellitic acid.

The glycol components of the polyester polyol include ethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol,
1,5-pentanediol, 1,6-hexanediol, neopentyl glycol, diethylene glycol, dipropylene glycol, 2,2,4-trimethyl-1,3-pentanediol, 1,4-cyclohexanedimethanol, bisphenol A, etc. Of ethylene oxide and propylene oxide of hydrogenated bisphenol A, ethylene oxide and propylene oxide of hydrogenated bisphenol A, polyethylene glycol, polypropylene glycol, and polytetramethylene glycol. Further, tri- and tetraols such as trimethylolethane, trimethylolpropane, glycerin and pentaerythritol may be used in combination. Examples of the polyester polyol include a lactone-based polyester diol chain obtained by ring-opening polymerization of a lactone such as caprolactone.

The polyisocyanates used include:
2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, p-phenylene diisocyanate, biphenylmethane diisocyanate, m-phenylene diisocyanate, hexamethylene diisocyanate, tetramethylene diisocyanate, 3,3'-dimethoxy 4,4'-biphenylene Diisocyanate, 2,4-naphthalenediisocyanate,
3,3'-dimethyl-4,4'-biphenylene diisocyanate,
4,4'-diphenylene diisocyanate, 4,4'-diisocyanate-diphenyl ether, 1,5-naphthalene diisocyanate, p-xylylene diisocyanate, m-xylylene diisocyanate, 1,3-diisocyanate methylcyclohexane, 1,4-isocyanate Diisocyanate compounds such as methylcyclohexane, 4,4'-diisocyanate dicyclohexane, 4,4'-diisocyanatecyclohexylmethane, isophorone diisocyanate, or trimers of 2,4-tolylene diisocyanate of 7 mol% or less of all isocyanate groups And triisocyanate compounds such as trimers of hexamethylene diisocyanate.

Further, in order to enhance the dispersibility,
J-SO_FourY, -SO_ThreeY, -POY, -PO_TwoY, -PO _ThreeY, -COOY (Y is hydrogen
Or alkali metal), -SR, -NR_Two, -NR_ThreeCl (R is hydrogen
Or hydrocarbons), phosphobetaines, sulfobetaines, e
Introduce polar groups such as sphamine and sulfamine by any method.
Is also preferable. Also, to increase thermal stability,
The introduction of an epoxy group is also preferred.

On the other hand, aside from the above radiation-curable urethane synthesis method, radiation-sensitive modification may be carried out using a thermosetting polyurethane resin as a raw material in the same manner as for a PVC-based resin.

If necessary, a radiation-curable monomer or oligomer may be used, and the use thereof can increase the degree of crosslinking of the coating film. The amount added is preferably not more than 30 parts by weight, more preferably not more than 20 parts by weight, based on the resin contained in the paint for forming the back coat layer. If the amount is more than 30 parts by weight, the shock applied to the paint is large, and conversely, the gloss is reduced. The radiation-curable monomer or oligomer may be added either at the time of dispersion after the paint is prepared.

The content of the binder resin is a total of 10
The amount is preferably 40 to 200 parts by weight, more preferably 50 to 180 parts by weight based on 0 parts by weight. If the content of the binder is too large, the friction with the medium sliding contact path becomes too large, the running stability is reduced, and a running accident is likely to occur. In addition, problems such as blocking with the magnetic layer occur. If the content of the binder is too small, the strength of the back coat layer is reduced, and the running durability tends to be reduced.

As the radiation used in the present invention, an electron beam, γ-ray, β-ray, ultraviolet ray or the like can be used, but an electron beam is preferable. The irradiation amount is preferably 1 to 10 Mrad, more preferably 3 to 7 Mrad, and the irradiation energy (acceleration voltage) is preferably 100 KV or more. Irradiation with radiation is preferably performed before winding after coating and drying, but may be performed after winding.

The back coat layer contains 30 to 80% by weight of carbon black. If the content of carbon black is too small, the antistatic effect tends to decrease, and the running stability tends to decrease. Also, since the light transmittance is likely to be high, there is a problem in a method of detecting the end of the tape by a change in the light transmittance. On the other hand, if the content of carbon black is too large, the strength of the back coat layer decreases, and running durability tends to deteriorate. Any carbon black may be used as long as it is commonly used, and the average particle size is preferably about 5 to 500 nm.
The average particle size is usually measured by a transmission electron microscope.

In the back coat layer, in addition to the carbon black, various non-magnetic powders may be contained in order to increase the mechanical strength. The content of the nonmagnetic powder is preferably 0.1 to 5 parts by weight, more preferably 0.5 to 2 parts by weight, based on 100 parts by weight of the carbon black. The average particle size of the nonmagnetic powder is preferably from 0.1 to 0.5 μm. If the content of such a nonmagnetic powder is too small, the mechanical strength of the back coat layer tends to be insufficient, and if it is too large, the amount of abrasion of the tape sliding path guide and the like tends to increase.

In addition, if necessary, a dispersant such as a surfactant, a lubricant such as a higher fatty acid, a fatty acid ester, and silicone oil, and other various additives may be added. Known lubricants such as fatty acids, esters, and saccharides may be used alone or as a mixture of two or more, regardless of whether they are saturated or unsaturated. Preferably, it is used. This is because it is necessary to continuously supply a lubricant corresponding to any temperature environment used for the magnetic recording medium to the medium surface. Specifically, as fatty acids, saturated linear chains such as stearic acid, palmitic acid, myristic acid, lauric acid, and erucic acid, and saturated side chains such as isocetyl acid and isostearic acid, oleic acid, linoleic acid, and linolenic acid An unsaturated fatty acid such as an acid can be used as appropriate. As the esters, butyl stearate, linear saturated fatty acid esters such as butyl palmitate, isocetyl stearate,
Saturated fatty acid esters with side chains such as isostearyl stearate, unsaturated fatty acid esters such as isostearyl oleate, fatty acid esters of unsaturated alcohol such as oleyl stearate, unsaturated fatty acids such as oleyl oleate and unsaturated alcohol Esters, esters of dihydric alcohols such as ethylene glycol distearate, esters of dihydric alcohols and unsaturated fatty acids such as ethylene glycol monooleate, ethylene glycol dioleate, neopentyl glycol dioleate,
Further, there are esters of saccharides such as sorbitan monostearate, sorbitan tristearate, sorbitan monooleate and sorbitan trioleate with saturated and unsaturated fatty acids. The lubricant content of the back coat layer is
It may be appropriately adjusted depending on the purpose, but 1 to 20% by weight based on the total weight of the carbon black and the inorganic powder.
Is preferred.

The organic solvent used for the back coat layer is not particularly limited, and one or more of various solvents such as ketone solvents such as methyl ethyl ketone, methyl isobutyl ketone and cyclohexanone and aromatic solvents such as toluene are used.
It may be appropriately selected and used. The addition amount of the organic solvent may be about 400 to 1300 parts by weight based on 100 parts by weight of the total of the solid content (various non-magnetic powders) and the binder.

The thickness (after calendering) of the back coat layer is 1.0 μm or less, preferably 0.1 to 1.0 μm.
m, more preferably 0.2 to 0.8 μm. If the back coat layer is too thick, the friction between the back coat layer and the medium sliding contact path becomes too large, and the running stability tends to decrease. On the other hand, if it is too thin, the surface properties of the backcoat layer will decrease due to the influence of the surface properties of the nonmagnetic support. For this reason, the roughness of the back coat layer surface is transferred to the magnetic layer surface, and high-frequency output, S /
N and C / N decrease. On the other hand, if the back coat layer is too thin, the back coat layer will be shaved during running of the medium. <Magnetic Layer> The structure of the magnetic layer formed on one surface of the non-magnetic support (the surface opposite to the surface on which the back coat layer is formed) is not particularly limited. For example, γ-Fe ₂ O ₃ , Co
Γ-Fe ₂ O ₃ , Fe ₃ O ₄ , Fe-containing oxides such as Co-containing Fe ₃ O ₄ , CrO ₃ , Fe, Co, Ni, or alloy fine powders of these, etc. And a continuous thin-film type magnetic layer formed by vacuum evaporation, sputtering or the like. As described above, the magnetic layer is formed on the opposite side of the nonmagnetic support from the surface on which the backcoat layer is formed. However, when the magnetic layer is a coating-type magnetic layer, any one of the magnetic layer and the backcoat layer is used. The layer may be formed first on the non-magnetic support. If necessary, a lower non-magnetic layer may be provided between the magnetic layer and the non-magnetic support. On the other hand, when the magnetic layer is a continuous thin film type magnetic layer, the back coat layer is usually formed after forming the magnetic layer. <Non-magnetic support> The material used as the non-magnetic support is not particularly limited, and is selected from various flexible materials and various rigid materials according to the purpose, and has a predetermined shape and dimensions such as a tape shape according to various standards. And it is sufficient. For example, examples of the flexible material include polyesters such as polyethylene terephthalate and polyethylene naphthalate, polyolefins such as polypropylene, and various resins such as polyamide, polyimide and polycarbonate.

The thickness of these nonmagnetic supports is 3.0 to 1
It is preferably 5.0 μm. The form of the non-magnetic support is not particularly limited, and may be any of a tape form and a sheet form, and various materials can be selected and used according to the form and as necessary.

The surface roughness of the nonmagnetic support used in the present invention is not more than 20 nm, preferably not more than 15 nm, as a center line average surface roughness Ra. The surface roughness of the non-magnetic support is
It can be freely controlled by the size and amount of the filler added to the non-magnetic support as needed. Examples of these fillers include oxides and carbonates such as Ca, Si, Ti, and Al,
An organic resin fine powder such as an acrylic resin is exemplified, and a combination of Al ₂ O ₃ and an organic resin fine powder is preferable.

[0041]

[Example] <Resin synthesis> ・ Synthesis 1 Electron beam-curable vinyl chloride-vinyl acetate-vinyl alcohol
Preparation of -N, N-dimethylethanolamine-modified vinyl unit-maleic acid copolymer Methanol, vinyl chloride, vinyl acetate, maleic acid, di (2-ethylhexyl) peroxydicarbonate and partial saponification in an autoclave equipped with a stirrer Polyvinyl alcohol was charged, the temperature was raised to 60 ° C. while stirring under a nitrogen gas atmosphere to start the reaction, and vinyl chloride was continuously injected to cause a copolymerization reaction. Release the autoclave residual pressure, cool, take out the copolymer slurry, and after filtration,
It was washed three times with methanol and twice with deionized water, filtered and dried to obtain a vinyl chloride-vinyl acetate-maleic acid copolymer powder. In a reactor equipped with a cooling pipe, the copolymer,
Methanol, N, N-dimethylethanolamine and sodium hydroxide were added, reacted at 40 ° C., cooled, and acetic acid was added to neutralize unreacted sodium hydroxide. This is washed three times with methanol, further twice with deionized water, filtered and dried to obtain vinyl chloride-vinyl acetate-vinyl alcohol-maleic acid-N, N-dimethylethanolamine-modified vinyl unit copolymer powder. Obtained. This copolymer powder was charged into a reaction vessel equipped with a stirrer, a condenser, a thermometer, and a dropping device. Toluene and methyl isobutyl ketone were added, and the temperature was raised to 60 ° C. to dissolve the resin. Subsequently, dibutyltin dilaurate and hydroquinone were added to this solution, and isocyanate ethyl methacrylate was dropped uniformly into the reaction vessel over 1 hour.
The temperature was raised to ° C., and stirring was continued for 6 hours to complete the reaction. Confirmation was made by eliminating the absorption of isocyanate groups in the IR absorption spectrum. After cooling to room temperature, methanol was gradually added to precipitate a polymer. After dewatering, the polymer was further washed twice with methanol and once with deionized water, and then dried and dried to obtain Polymer 1.

Table 1 Examples 2 to 7 having different monomer weight ratios and polymerization degrees were produced by changing the amount of each monomer unit or amine compound, and were used as polymers 2 to 7, respectively.・ Synthesis 2 Electron beam curing type vinyl chloride-vinyl acetate-vinyl alcohol
Production of -N, N-dimethylethanolamine-modified vinyl unit-sodium methacrylsulfonate copolymer In the above Synthesis 1, Polymer 8 was produced by using sodium methacrylsulfonate instead of maleic acid.・ Synthesis 3 Electron beam curing type vinyl chloride-vinyl acetate-vinyl alcohol
Production of -N, N-dimethylethanolamine-modified vinyl unit-2-acid phosphooxyethyl methacrylate copolymer In the above Synthesis 1, the polymer 9 was produced by using 2-acid phosphooxyethyl methacrylate instead of maleic acid. did.・ Synthesis 4 Electron beam curable vinyl chloride-vinyl acetate-vinyl alcohol
Production of -dibutylamine-modified vinyl unit-maleic acid copolymer Polymer 10 was produced in the above synthesis 1 using dibutylamine instead of N, N-dimethylethanolamine.
And・ Synthesis 5 Electron beam curable vinyl chloride-vinyl acetate-vinyl alcohol
-Production of morpholine-modified vinyl unit-maleic acid copolymer Polymer 11 was produced by using morpholine instead of N, N-dimethylethanolamine in Synthesis 1 described above.・ Synthesis 6 Electron beam curing type vinyl chloride-vinyl acetate-vinyl alcohol
-Production of maleic acid copolymer In an autoclave equipped with a stirrer, methanol, vinyl chloride, vinyl acetate, maleic acid, di (2-ethylhexyl) peroxydicarbonate and partially saponified polyvinyl alcohol are charged and stirred under a nitrogen gas atmosphere. While the temperature was raised to 60 ° C., the reaction was started, and vinyl chloride was continuously injected to cause a copolymerization reaction. Release the autoclave residual pressure, cool, take out the copolymer slurry, and after filtration,
The precipitate was washed three times with methanol and twice with deionized water, filtered and dried to obtain a vinyl chloride-vinyl acetate-maleic acid copolymer powder. The copolymer, methanol and sodium hydroxide were added to a reactor equipped with a cooling tube, reacted at 40 ° C. and cooled, and acetic acid was added to neutralize unreacted sodium hydroxide. This was washed three times with methanol, further twice with deionized water, and filtered and dried to obtain a vinyl chloride-vinyl acetate-vinyl alcohol-maleic acid copolymer powder. This copolymer powder was charged into a reaction vessel equipped with a stirrer, a condenser, a thermometer, and a dropping device. Toluene and methyl isobutyl ketone were added, and the temperature was raised to 60 ° C. to dissolve the resin. Subsequently, after adding dibutyltin dilaurate and hydroquinone to the solution, isocyanate ethyl methacrylate was uniformly dropped into the above-mentioned reaction vessel over 1 hour, and the temperature was further raised to 80 ° C. and stirring was continued for 6 hours to complete the reaction. I let it. Confirmation was made by eliminating the absorption of isocyanate groups in the IR absorption spectrum.
Then, after cooling to room temperature, methanol was gradually added to precipitate a polymer.
After washing once with deionized water, the solution is dried and dried to obtain polymer 12
I got・ Synthesis 7 Electron beam curing type vinyl chloride-vinyl acetate-vinyl alcohol
-Production of Sodium Methacryl Sulfonate Copolymer In the above Synthesis 6, polymer 13 was produced by using sodium methacrylsulfonate instead of maleic acid.・ Synthesis 8 Electron beam curing type vinyl chloride-vinyl acetate-vinyl alcohol
Production of 2-Acid Phosphooxyethyl Methacrylate Copolymer In the above Synthesis 6, Polymer 14 was produced using 2-acid phosphooxyethyl methacrylate instead of maleic acid.・ Synthesis 9 Electron beam curing type vinyl chloride-vinyl acetate-vinyl alcohol
Production of -N, N-dimethylethanolamine-modified vinyl unit copolymer In an autoclave equipped with a stirrer, methanol, vinyl chloride, vinyl acetate, di (2-ethylhexyl) peroxydicarbonate and partially saponified polyvinyl alcohol are charged. The reaction was started by raising the temperature to 60 ° C. while stirring under a gas atmosphere, and vinyl chloride was continuously injected to cause a copolymerization reaction. Release the autoclave residual pressure, cool,
The copolymer slurry is taken out, filtered, and then filtered with methanol.
Wash twice with deionized water, filter dry and wash with vinyl chloride
-A vinyl acetate copolymer powder was obtained. This copolymer, methanol, N, N-dimethylethanolamine and sodium hydroxide were added to a reactor equipped with a cooling pipe, reacted at 40 ° C., cooled, and acetic acid was added to remove unreacted hydroxylation. Sodium was neutralized. This is washed three times with methanol, twice with deionized water, filtered and dried, and
-A vinyl acetate-vinyl alcohol-N, N-dimethylethanolamine-modified vinyl unit copolymer powder was obtained. This copolymer powder was charged into a reaction vessel equipped with a stirrer, a condenser, a thermometer, and a dropping device. Toluene and methyl isobutyl ketone were added, and the temperature was raised to 60 ° C. to dissolve the resin. Subsequently, after adding dibutyltin dilaurate and hydroquinone to the solution, isocyanate ethyl methacrylate was uniformly dropped into the above-mentioned reaction vessel over 1 hour, and the temperature was further raised to 80 ° C. and stirring was continued for 6 hours to complete the reaction. I let it. Confirmation was made by eliminating the absorption of isocyanate groups in the IR absorption spectrum. After cooling to room temperature, methanol was gradually added to precipitate a polymer. After dewatering, the polymer was further washed twice with methanol and once with deionized water, and then dewatered and dried to obtain Polymer 15.・ Synthesis 10 Electron beam curing type vinyl chloride-vinyl acetate-vinyl alcohol
Production of -Dibutylamine-Modified Vinyl Unit Copolymer In the above Synthesis 9, polymer was produced by using dibutylamine instead of N, N-dimethylethanolamine.
And・ Synthesis 11 Electron beam curing type vinyl chloride-vinyl acetate-vinyl alcohol
-Preparation of morpholine-modified vinyl unit copolymer In the above Synthesis 9, Polymer 17 was prepared using morpholine instead of N, N-dimethylethanolamine.・ Synthesis 12 Production of electron beam-curable vinyl chloride-vinyl acetate-vinyl alcohol copolymer In an autoclave equipped with a stirrer, methanol, vinyl chloride, vinyl acetate, di (2-ethylhexyl) peroxydicarbonate and partially saponified polyvinyl alcohol were used. Was heated to 60 ° C. while stirring under a nitrogen gas atmosphere to start a reaction, and vinyl chloride was continuously injected to cause a copolymerization reaction. Release the autoclave residual pressure, cool,
The copolymer slurry is taken out, filtered, and then filtered with methanol.
Wash twice with deionized water, filter dry and wash with vinyl chloride
-A vinyl acetate copolymer powder was obtained. The copolymer, methanol and sodium hydroxide were added to a reactor equipped with a cooling tube, reacted at 40 ° C. and cooled, and acetic acid was added to neutralize unreacted sodium hydroxide. This was washed three times with methanol, further twice with deionized water, and filtered and dried to obtain a vinyl chloride-vinyl acetate-vinyl alcohol copolymer powder. This copolymer powder is charged into a reaction vessel equipped with a stirrer, a condenser, a thermometer, and a dropping device, and toluene and methyl isobutyl ketone are added thereto.
The temperature was raised to ° C. to dissolve the resin. Subsequently, after adding dibutyltin dilaurate and hydroquinone to the solution, isocyanate ethyl methacrylate was uniformly dropped into the above-mentioned reaction vessel over 1 hour, and the temperature was further raised to 80 ° C. and stirring was continued for 6 hours to complete the reaction. I let it. Confirmation was made by eliminating the absorption of isocyanate groups in the IR absorption spectrum. Then, after cooling to room temperature, methanol was gradually added to precipitate a polymer. After dewatering, the polymer was further washed twice with methanol and once with deionized water, and then dried and dried to obtain Polymer 18.・ Synthesis 13 Production of vinyl chloride-vinyl acetate-vinyl alcohol-N, N-dimethylethanolamine-modified vinyl unit-maleic acid copolymer In an autoclave equipped with a stirrer, methanol, vinyl chloride, vinyl acetate, maleic acid, di ( 2 Ethylhexyl) peroxydicarbonate and partially saponified polyvinyl alcohol were charged, the temperature was raised to 60 ° C. while stirring under a nitrogen gas atmosphere to start the reaction, and vinyl chloride was continuously injected to cause a copolymerization reaction. Release the autoclave residual pressure, cool, take out the copolymer slurry, and after filtration,
The precipitate was washed three times with methanol and twice with deionized water, filtered and dried to obtain a vinyl chloride-vinyl acetate-maleic acid copolymer powder. This copolymer, methanol, N, N-dimethylethanolamine and sodium hydroxide were added to a reactor equipped with a cooling pipe, reacted at 40 ° C., cooled, and acetic acid was added to remove unreacted hydroxylation. Sodium was neutralized. This was washed three times with methanol, further twice with deionized water, and filtered and dried to obtain polymer 19. <Coating for magnetic layer>-Preparation of binder solution Vinyl chloride resin (manufactured by Zeon Corporation: MR-110) 10 parts by weight Polyester polyurethane resin (manufactured by Toyobo Co., Ltd .: UR-8300) 7 parts by weight MEK 21 parts by weight Toluene 21 parts by weight Part 21 parts by weight of cyclohexanone The above composition was charged into a hypermixer, mixed and stirred to obtain a binder solution. -Kneading The following composition was put into a pressure kneader and kneaded for 2 hours. α-Fe magnetic powder 100 parts by weight (Hc = 1650 Oe, σs = 126 emu / g, BET = 57 m ² / g, major axis length = 0.10 μm) α-Al ₂ O ₃ (Sumitomo Chemical: HIT-50 average 5 parts by weight Cr ₂ O ₃ (manufactured by Nippon Chemical Industry Co., Ltd .: U-1 average particle size = 0.20 μm) 5 parts by weight Binder solution 40 parts by weight The following composition is added to the slurry after kneading. The viscosity was adjusted to be optimal for dispersion treatment. Binder solution 40 parts by weight MEK 15 parts by weight Toluene 15 parts by weight Cyclohexanone 15 parts by weight Dispersion The slurry was subjected to dispersion treatment by a sand mill.・ Viscosity adjusting liquid The following composition is put into a hyper mixer and mixed for 1 hour.
The mixture was stirred to obtain a viscosity adjusting liquid. The viscosity adjusting liquid was subjected to circulating filtration using a depth filter having a 95% cut filtration accuracy of 1.2 μm. 0.5 parts by weight of stearic acid 0.5 parts by weight of myristic acid 0.5 parts by weight of butyl stearate 100 parts by weight of MEK 100 parts by weight of toluene 100 parts by weight of viscosities ・ Adjustment of viscosity Was again subjected to a dispersion treatment to obtain a paint. The paint was circulated and filtered using a depth filter having a 95% cut filtration accuracy of 1.2 μm. -Final paint 0.8 parts by weight of an isocyanate compound (Coronate L, manufactured by Nippon Polyurethane) is added to 100 parts by weight of the filtered paint, followed by stirring and mixing. Was performed to obtain a final paint for the magnetic layer. <Coating for back coat layer> ・ Binder solution adjustment Electron beam-curable vinyl chloride resin (Polymer 1) 60 parts by weight Electron beam-curable polyester polyurethane resin 40 parts by weight (phosphorus compound-hydroxy-containing polyester polyurethane: number average molecular weight = 13000) Acrylic content = 6 / molecule, Tg = 10 ° C.) MEK 260 parts by weight Toluene 260 parts by weight Cyclohexanone 260 parts by weight The above composition was charged into a hyper mixer and stirred to obtain a binder solution. -Dispersion The following composition was charged into a ball mill and dispersed for 24 hours. Carbon black 70 parts by weight (Koronhi Bu Ankaho Bu emissions Co.: CoNductexSC average particle size ^{= 20nm, BET = 220m 2 /} g) Carbon black 10 parts by weight (Kyaho Bu Tsu preparative Co.: BLACK-PEARLS130 average particle size = 75nm, BET = 25m ² / g) α-Fe ₂ O ₃ (manufactured by Toda Kogyo Co., Ltd .: TF100 average particle size = 0.1 μm) 1 part by weight Binder solution 880 parts by weight ・ Viscosity adjusting solution The following composition is charged into a hyper mixer, stirred, and mixed with a viscosity adjusting solution. did. 1 part by weight of stearic acid 1 part by weight of myristic acid 1 part by weight of butyl stearate 2 parts by weight of MEK 210 parts by weight of toluene 210 parts by weight of cyclohexanone ・ Viscosity adjustment & final paint The dispersion treatment was performed for 3 hours. Apply the above paint 9
Circulation filtration was performed using a depth filter having a 5% cut filtration accuracy of 1.2 μm to obtain a backcoat paint. <Coating for back coat layer> ・ Binder solution preparation Vinyl chloride-vinyl acetate-vinyl alcohol-N, N-dimethylethanolamine-modified vinyl unit-maleic acid copolymer (Polymer 19) 60 parts by weight Polyester polyurethane resin (Toyobo Co., Ltd.) Manufacture: UR-8300) 40 parts by weight MEK 260 parts by weight Toluene 260 parts by weight Cyclohexanone 260 parts by weight The above composition was charged into a hypermixer and stirred to obtain a binder solution. -Dispersion The following composition was charged into a ball mill and dispersed for 24 hours. Carbon black 70 parts by weight (Koronhi Bu Ankaho Bu emissions Co.: CoNductexSC average particle size ^{= 20nm, BET = 220m 2 /} g) Carbon black 10 parts by weight (Kyaho Bu Tsu preparative Co.: BLACK-PEARLS130 average particle size = 75nm, BET = 25m ² / g) α-Fe ₂ O ₃ (manufactured by Toda Kogyo Co., Ltd .: TF100 average particle size = 0.1 μm) 1 part by weight Binder solution 880 parts by weight ・ Viscosity adjusting solution The following composition is charged into a hyper mixer, stirred, and mixed with a viscosity adjusting solution. did. 1 part by weight of stearic acid 1 part by weight of myristic acid 1 part by weight of butyl stearate 2 parts by weight of MEK 210 parts by weight of toluene 210 parts by weight of cyclohexanone ・ Viscosity adjustment Performed for 3 hours. Apply the above paint 9
Circulation filtration was performed using a depth filter with 5% cut filtration accuracy = 1.2 μm. -Final paint 1 part by weight of an isocyanate compound (manufactured by Nippon Polyurethane Co., Coronate-L) is added to 100 parts by weight of the paint after filtration, stirred and mixed, and 95% cut filtration accuracy = 1.2 µm
Was subjected to circulating filtration using a depth filter, to obtain a backcoat paint. <Preparation of magnetic tape><Continuous thin film type magnetic layer>-The polymers used in Examples 1-1 to 1-17 and Comparative example 1-1 are shown in the following table.

A continuous thin-film magnetic layer (composition: Co / Ni = 80/20% by weight, film thickness = 0.20 μm) was formed on the surface of a non-magnetic support (polyethylene terephthalate film having a thickness of 10.0 μm) by a vacuum evaporation method. Then, a fluorine-based lubricant was applied on the continuous thin-film type magnetic layer and dried. Further, a coating material for a back coat layer was applied to the back surface of the nonmagnetic support, dried, and then cured by irradiation with an electron beam in a nitrogen gas atmosphere.
The thickness of the back coat layer was 0.5 μm for all samples. The roll was cut into a width of 8 mm and assembled into a cassette to obtain a magnetic tape sample. Comparative Example 1-2 A continuous thin-film type magnetic layer (composition: Co / Ni = 80/20% by weight, film thickness = 0.0%) on the surface of a nonmagnetic support (a polyethylene terephthalate film having a thickness of 10.0 μm) by a vacuum evaporation method.
20 μm), a fluorine-based lubricant was applied on the continuous thin-film type magnetic layer, and dried. Further, a coating material for a back coat layer was applied to the back surface of the nonmagnetic support and dried. The thickness of the back coat layer was 0.5 μm for all samples. After leaving the roll at room temperature for 24 hours, it was cured in a heating oven at 60 ° C. for 24 hours. Observation of the cured magnetic layer surface with an optical microscope revealed that cracks had occurred and had lost its function as a magnetic recording medium. <Coating type magnetic layer>-The polymers used in Examples 2-1 to 2-17 and Comparative example 2-1 are shown in the following table.

A coating for a magnetic layer was applied to the surface of a non-magnetic support (polyethylene terephthalate film having a thickness of 8.3 μm), oriented, dried, calendered, and wound up. Magnetic layer thickness = 2.0 μm. After leaving this roll at room temperature for 24 hours, after curing in a heating oven at 60 ° C. for 24 hours, a back coat layer paint is applied to the back surface of the non-magnetic support, dried, calendered, and then placed in a nitrogen gas atmosphere. It was irradiated with an electron beam and cured. The thickness of the back coat layer was 0.5 μm for all samples. The roll was cut into a width of 8 mm and assembled into a cassette to obtain a magnetic tape sample. Comparative Example 2-2 A coating for a magnetic layer was applied to the surface of a non-magnetic support (a polyethylene terephthalate film having a thickness of 8.3 μm), and orientation was performed.
After drying, it was calendered and wound up. Magnetic layer thickness = 2.0 μm. The roll was allowed to stand at room temperature for 24 hours, cured in a heating oven at 60 ° C. for 24 hours, coated with a back coat layer coating on the back surface of the nonmagnetic support, dried, calendered, and wound up. The thickness of the back coat layer was 0.5 μm for all samples. This roll is 2
After leaving it at room temperature for 4 hours, 2
After curing for 4 hours, it was cut into 8 mm width and assembled into a cassette to obtain a magnetic tape sample. <Gloss> The gloss (%) at a measurement angle of 60 ° was measured using a digital gloss meter GM-3D manufactured by Murakami Color Research Laboratory. Optical conditions are JIS-Z-874
The method described in No. 1 was used. <Surface roughness Ra> Using a Taylor Hobson stylus type surface shape measuring instrument, TALYSTEP system, JI
The measured value is obtained by the method described in SB-0601. Measurement conditions were as follows: Filter conditions: 0.18 to 9 Hz Needle pressure: 2 mg Needle used: 0.1 × 2.5 μm special stylus Scan speed: 0.03 mm / sec. Scan length: 500 μm. Ra was determined from the obtained results. The surface roughness of the back coat layer after cutting was measured for both the continuous thin film type magnetic layer sample and the coating type magnetic layer sample. <7 MHz output> A 7 MHz signal was recorded on a tape sample, and the reproduced output of the 7 MHz signal when this signal was reproduced was measured with an oscilloscope. The continuous thin film type magnetic layer is a relative value when the 7 MHz output of Comparative Example 1-1 is 0 dB,
In addition, the coating type magnetic layer outputs the 7 MHz output of Comparative Example 2-1 at 0 d.
B was measured as a relative value.

Used deck: Sony EV-S900
(Hi8 format VTR) <Dropout> Dropout (DO) was measured for each sample. In this measurement, 16 dB
The output attenuation described above is 10 μsec. The case where the above was continued was determined as dropout. The measurement was performed for 10 minutes, and each table shows the dropout per minute.

Used deck: Sony EV-S900
(Hi8 format VTR) Dropout counter used: Shibasoku VH01
BZ

[0047]

[Table 1]

Comparative Example 1-1 When the radiation-curable vinyl chloride-based copolymer does not contain an amine-modified vinyl unit and an acidic functional group-containing vinyl unit, the dispersibility of the lower non-magnetic layer-forming paint is reduced. In addition, the surface properties are deteriorated, and the electromagnetic conversion characteristics are deteriorated. Dropout also increases.

[0049]

[Table 2]

Comparative Example 2-1 When the radiation-curable vinyl chloride copolymer did not contain an amine-modified vinyl unit and an acidic functional group-containing vinyl unit, the dispersibility of the lower non-magnetic layer coating material was reduced. In addition, the surface properties are deteriorated, and the electromagnetic conversion characteristics are deteriorated. Comparative Example 2-2 In a back coat layer using a thermosetting binder resin, the roughness of the back coat layer is transferred to the magnetic layer at the time of thermosetting, causing deterioration in electromagnetic conversion characteristics and deterioration in dropout.

[0051]

According to the present invention, there is provided a magnetic recording medium in which a magnetic recording layer is provided on one side of a non-magnetic support and a back coat layer mainly comprising a non-magnetic powder and a radiation-curable binder resin is provided on the other side. And a radiation-curable binder resin in the back coat layer comprising a radiation-curable vinyl chloride copolymer having an amine-modified vinyl unit and / or an acidic functional group-containing vinyl unit in one molecule. By the recording medium, a back coat for a magnetic recording medium can be obtained in which the transfer from the back coat is small and the electromagnetic conversion characteristics are not adversely affected.

Claims (4)

[Claims] 1. A magnetic recording medium comprising a magnetic recording layer provided on one surface of a non-magnetic support and a back coat layer comprising a non-magnetic powder and a radiation-curable binder resin as main components on the other surface. And a radiation-curable binder resin in the back coat layer comprising a radiation-curable vinyl chloride copolymer having an amine-modified vinyl unit and / or an acidic functional group-containing vinyl unit in one molecule. recoding media. 2. The magnetic recording medium according to claim 1, wherein the center line average roughness (Ra) of the back coat layer surface of the magnetic recording medium is Ra ≦ 20.0 nm. 3. A radiation-curable vinyl chloride copolymer having an amine-modified vinyl unit and / or an acidic functional group-containing vinyl unit in one molecule, having an average degree of polymerization of 200 to 800. Magnetic recording medium. 4. The radiation-curable vinyl chloride copolymer having an amine-modified vinyl unit and / or an acidic functional group-containing vinyl unit in one molecule has an amine-modified vinyl unit content of 0.05 to 5. 4. The magnetic recording medium according to claim 1, wherein the content is 0% by weight and the content of the acidic functional group-containing vinyl unit is 0.05 to 2.5% by weight.