JPH08138229A - Binder and magnetic recording medium - Google Patents

Abstract

PURPOSE: To improve surface smoothness and durability by incorporating a resin having a thiosulfuric acid or thiosulate group represented by the general formula -S-SO3 X (where X is H, an alkali metal or org. amine) in each molecule. CONSTITUTION: This binder contains the resin (A), e.g. polyurethane resin produced by bringing polyester polyol having a thiosulfuric acid or thiosulfate group or this polyester polyol and known other glycol and polycarboxylic acid into a polycondensation reaction or bringing polycarboxylic acid having a thiosulfuric acid or thiosulfate group and other polycarboxylic acid and glycol into a polycondensation reaction.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a binder used for manufacturing a magnetic recording medium such as a magnetic tape or a magnetic disk, and a magnetic recording medium using the binder.

[0002]

2. Description of the Related Art Polyurethane resins, polyester resins, nitrocellulose, vinyl chloride-vinyl acetate copolymers, vinyl chloride-vinyl acetate-vinyl alcohol copolymers, etc. have been used as binders for magnetic recording media. . However, in recent years, as the performance of magnetic recording media has become higher, fine particles of magnetic powder and higher magnetic force have been achieved, and the above-mentioned binders are in a situation where sufficient dispersibility, surface smoothness, and durability are not obtained. . Therefore, in order to deal with making the magnetic powder into fine particles, a polyester resin containing a metal sulfonate group (Japanese Patent Publication No. 57-3134) and a polyurethane resin containing a metal sulfonate group (Japanese Patent Publication No. 58-415).
No. 65) is used as a binder.

[0003]

However, the binder containing such a metal sulfonate group has improved dispersibility of the magnetic powder as compared with a binder having no polar group due to the effect of the hydrophilic polar group. However, I haven't got enough satisfaction yet.

[0004]

Means for Solving the Problems The present inventors arrived at the present invention as a result of extensive studies on a binder that provides a magnetic recording medium having good dispersibility of magnetic powder and excellent surface smoothness and durability. did.

That is, the present invention has the general formula -S in the molecule.
A binder for a magnetic recording medium containing a resin (A) having a thiosulfate (salt) group represented by —SO ₃ X (wherein X represents hydrogen, an alkali metal or an organic amine);
And a magnetic recording medium having a magnetic layer containing the binder.

The resin (A) containing the functional group in the present invention is not particularly limited as long as it is a resin containing a thiosulfate (salt) group in the molecule, and the polyurethane resin (a)
1), polyester resin (a2), polyamide resin (a
3), polyacrylic resin (a4), vinyl chloride resin (a5) and the like. You may use these resins individually or in combination of 2 or more types. Of these resins, (a1) and (a2) are particularly preferable.

The thiosulfate (salt) group in the present invention is represented by the general formula —S—SO ₃ X, where X is hydrogen, alkali metal (potassium, sodium, lithium, etc.) or organic. Represents an amine (amine, alkanolamine, etc.). Preferred as X is potassium and sodium.

The content of thiosulfate (salt) group in (A) is
The amount is usually 1 to 1000 equivalents, preferably 5 to 500 equivalents, and more preferably 10 to 300 equivalents per 10 ⁶ g of (A). If it is less than 1 equivalent, the dispersibility in magnetic powder becomes insufficient, and if it exceeds 1000 equivalents, the viscosity of the magnetic coating becomes high and the workability deteriorates.

(A1) among those exemplified as (A)
Examples thereof include those obtained by reacting a polyol with a polyisocyanate. By using a thiosulfate (salt) group-containing polyol as a part or all of the polyol, a thiosulfate (salt) group is added to (a1). Can be introduced. Examples of thiosulfate (salt) group-containing polyols include halogen group-containing polyols [4- (chloroacetyl) catechol, 3,5-dichloro-4,4′-
Dihydroxydiphenylamine or an alkylene oxide (ethylene oxide, propylene oxide, etc.) adduct of these compounds, etc.] and a reaction product of sodium thiosulfate and the like.

The thiosulfate (salt) group-containing polyol can be synthesized, for example, by reacting the halogen group-containing polyol with alcohol (ethanol or the like) at a temperature of about 60 to 150 ° C. with sodium thiosulfate to obtain the desired product. It can be illustrated.

In the production of (a1) in the present invention, a polyester polyol containing a thiosulfate (salt) group can be used as a polyol component. The thiosulfate (salt) group-containing polyester polyol is a polycondensation reaction of a thiosulfate (salt) group-containing polyol obtained by the above reaction and other publicly known glycols and polyvalent carboxylic acid as necessary, or thiosulfate (salt) ) It is obtained by a polycondensation reaction of a group-containing polyvalent carboxylic acid and optionally other known polyvalent carboxylic acid with glycol.

The thiosulfuric acid (salt) group-containing polycarboxylic acid includes halogen group-containing polycarboxylic acid (4,5-dichlorophthalic acid, 2,5-dichloroterephthalic acid, 4-bromoisophthalic acid, etc.) and thiol. Examples include reaction products with sodium sulfate and the like.

The thiosulfate (salt) group-containing polyvalent carboxylic acid can be synthesized by, for example, halogen-group-containing polyvalent carboxylic acid in alcohol (ethanol or the like) at a temperature of about 60 to 15.
An example is a method of reacting with sodium thiosulfate at 0 ° C. to obtain the desired product.

Other glycols used in the polycondensation reaction include alkylene glycols (ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, 1,4-butanediol, 1,3-butanediol, neopentyl glycol, 1,6-hexanediol, 1,8-octanediol, 1,10-decanediol, etc.); low-molecular diols having a cyclic group (cyclohexanediol, glycols such as cyclohexanedimethanol, and JP-B-4)
Those described in 5-1474 [bis (hydroxymethyl)
Cyclohexane, xylylene glycol, bis (hydroxyethyl) benzene, 1,4-bis (2-hydroxyethoxy) benzene, 4,4'-bis (2-hydroxyethoxy) -diphenylpropane (ethylene oxide adduct of bisphenol A) Etc.]}; and these two
Examples include a mixture of two or more species. If necessary, a trihydric or higher polyhydric alcohol such as trimethylolethane, trimethylolpropane, glycerin, pentaerythritol may be used in combination.

Other polyvalent carboxylic acids include aromatic dicarboxylic acids (terephthalic acid, isophthalic acid, phthalic acid,
1,5-naphthalic acid, etc.); aromatic oxycarboxylic acid [P
-Oxybenzoic acid, P- (hydroxyethoxy) benzoic acid, etc.]; aliphatic dicarboxylic acids (succinic acid, adipic acid,
Azelaic acid, sebacic acid, dimer acid, dodecanedicarboxylic acid, etc.); trivalent or higher carboxylic acids (trimellitic acid, trimesic acid, pyromellitic acid, etc.); and mixtures of two or more thereof.

(A1) essentially contains the above-mentioned thiosulfate (salt) group-containing polyol or polyester polyol, and if necessary, other polymer polyol (number average molecular weight is usually 500 to 5000, preferably 500 to 4500).
And / or low molecular weight polyol (typically 500
It can be obtained by reacting a polyol component consisting of less than 50, preferably 60 to 450) with an organic polyisocyanate by a known method.

Examples of the other polymer polyols include polyester polyol, polyether polyol, polycarbonate polyol and the like.

Examples of polyester polyols include polyester polyols obtained by polycondensation reaction of polyhydric alcohols (ethylene glycol, 1,4-butanediol, etc.) and polyhydric carboxylic acids (adipic acid, phthalic acid, etc.),
Examples thereof include polylactone-based polyols obtained by ring-opening polymerization of lactone using a polyhydric alcohol (ethylene glycol, trimethylolpropane, etc.) as an initiator.

Examples of the polyether polyol include polyethylene ether polyol, polypropylene ether polyol, polytetramethylene ether, and copolymerized (random or floc) polyether polyols thereof.

Polycarbonate polyol is 1,6-
Examples thereof include a polycarbonate polyol obtained by a polycondensation reaction of hexanediol and diethyl carbonate or diphenyl carbonate.

As the low molecular weight polyol, alkylene glycols (ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol,
1,4-butanediol, 1,3-butanediol, neopentyl glycol, 1,6-hexanediol,
1,8-octamethylenediol, 1,10-decanediol, etc.); low-molecular diols having a cyclic group {cyclohexanediol, glycols such as cyclohexanedimethanol, and those described in Japanese Patent Publication No. 45-1474 [bis ( Hydroxymethyl) cyclohexane, xylylene glycol, bis (hydroxyethyl) benzene,
1,4-bis (2-hydroxyethoxy) benzene,
4,4′-bis (2-hydroxyethoxy) -diphenylpropane (ethylene oxide adduct of bisphenol A) and the like]; and a mixture of two or more thereof. If necessary, a trihydric or higher polyhydric alcohol such as trimethylolethane, trimethylolpropane, glycerin, pentaerythritol may be used in combination.

As the organic polyisocyanate, aromatic diisocyanates (1,3- and / or 1,4-phenylene diisocyanate, 2,4- and / or 2,6-tolylene diisocyanate, 4,4'- or 2, 4'-diphenylmethane diisocyanate etc.); Aliphatic diisocyanate (hexamethylene diisocyanate, tetramethylene xylylene diisocyanate etc.);
Examples thereof include alicyclic diisocyanates (isophorone diisocyanate, dicyclohexylmethane diisocyanate, etc.); modified polyisocyanates (burettes of hexamethylene diisocyanate, trimerization of isophorone diisocyanate, etc.); and mixtures of two or more thereof.

In the production of (a1), the equivalent ratio of the polyol and the organic polyisocyanate in reacting the polyol and the organic polyisocyanate is usually 0.6.
˜1.5, preferably 0.8 to 1.2. If the equivalent ratio is less than 0.6 or exceeds 1.5, the molecular weight of the obtained polyurethane resin becomes low, and the resin strength, abrasion resistance, scratch resistance, and hydrolysis resistance decrease.

The above reaction can be carried out in the presence or absence of a solvent inert to the isocyanate group. Examples of the solvent include ester solvents (ethyl acetate, butyl acetate, etc.), ether solvents (dioxane, tetrahydrofuran, etc.), ketone solvents (cyclohexanone, methyl ethyl ketone, methyl isobutyl ketone, etc.), aromatic hydrocarbon solvents (toluene). , Xylene, etc.), a mixed solvent of two or more of these, and the like.

As the urethanization reaction method, a known method can be used. For example, a method in which a polyol and an organic polyisocyanate are put together in a reaction vessel and reacted, or an active hydrogen group-containing compound and an organic polyisocyanate are separated. And a multistage reaction, and a method in which a premixed polyol and an organic polyisocyanate are passed through a heated multi-screw extruder to react. The reaction temperature is usually 30 to 180 ° C., preferably 60
~ 120 ° C. In the reaction, a catalyst used in a usual urethanization reaction may be used to accelerate the reaction. Examples of the catalyst include tin catalysts (trimethyltin laurate, trimethyltin hydroxide, dimethyltin dilaurate, dibutyltin dilaurate, stannas octoate, etc.), lead catalysts (red oleate, red 2-ethylhexoate, etc.). Etc.

The number average molecular weight of (a1) is usually 3,000.
0 to 200,000, preferably 5,000 to 100,
000. When the number average molecular weight is less than 3,000, the physical properties of the resin are deteriorated and the durability of the magnetic tape is deteriorated.
If it exceeds 000, the viscosity of the coating composition increases and the dispersibility of the magnetic powder deteriorates.

Examples of (a2) in the present invention include polycondensation reaction of the above-mentioned thiosulfate (salt) group-containing polyol and other glycol with polyvalent carboxylic acid, or thiosulfate (salt) group-containing polyvalent carboxylic acid. And polycondensation reactions of other polycarboxylic acids with glycols.

The thiosulfate (salt) group-containing polycarboxylic acid includes halogen group-containing polycarboxylic acid (4,5-dichlorophthalic acid, 2,5-dichloroterephthalic acid, 4-bromoisophthalic acid, etc.) and thiol. Examples include reaction products with sodium sulfate and the like.

As the other glycols, alkylene glycols (ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, 1,4-butanediol, 1,3-butanediol, neopentyl glycol, 1,6-hexanediol) are used. , 1,8-octamethylene diol, 1,10-decane diol, etc.); low molecular weight diols having a cyclic group {cyclohexane diol, glycols such as cyclohexane dimethanol, and those described in JP-B-45-1474 [bis (Hydroxymethyl) cyclohexane, xylylene glycol, bis (hydroxyethyl) benzene, 1,4-bis (2-hydroxyethoxy) benzene, 4,4'-bis (2-hydroxyethoxy) -diphenylpropane (bispheno Ethylene oxide adduct of A), etc.]}; and a mixture of two or more thereof. Also, if necessary, trimethylolethane,
You may use together trivalent polyhydric alcohols, such as trimethylol propane, glycerin, and pentaerythritol.

Other polycarboxylic acids include aromatic dicarboxylic acids (terephthalic acid, isophthalic acid, phthalic acid,
1,5-naphthalic acid, etc.); aromatic oxycarboxylic acid [P
-Oxybenzoic acid, P- (hydroxyethoxy) benzoic acid, etc.]; aliphatic dicarboxylic acids (succinic acid, adipic acid,
Azelaic acid, sebacic acid, dimer acid, dodecanedicarboxylic acid, etc.); trivalent or higher carboxylic acids (trimellitic acid, trimesic acid, pyromellitic acid, etc.); and mixtures of two or more thereof.

As a method for producing (a2), a known method can be used. For example, after polycondensing glycol and polyvalent carboxylic acid at a temperature of about 170 to 250 ° C., further 0.5 to 1.0 mmHg. Under vacuum temperature of about 150-2
A method of completing the polycondensation reaction at 50 ° C. can be exemplified.

The number average molecular weight of the above (a2) is usually 3,
000 to 200,000, preferably 5,000 to 1
It is 10,000. When the number average molecular weight is less than 3,000, the physical properties of the resin are deteriorated, the durability of the magnetic tape is deteriorated, and 2
If it exceeds 0,000, the viscosity of the coating composition becomes high and the dispersibility of the magnetic powder becomes poor.

(A3) in the present invention can be obtained by a polycondensation reaction of the above-mentioned polyvalent carboxylic acid containing a thiosulfate (salt) group and, if necessary, another polyvalent carboxylic acid with a polyamine.

Other polycarboxylic acid components include aromatic dicarboxylic acids (terephthalic acid, isophthalic acid, phthalic acid, 1,5-naphthalic acid, etc.); aromatic oxycarboxylic acids [P-oxybenzoic acid, P- (Hydroxyethoxy) benzoic acid, etc.]; Aliphatic dicarboxylic acid (succinic acid, adipic acid, azelaic acid, sebacic acid, dimer acid, dodecanedicarboxylic acid, etc.); Trivalent or higher carboxylic acid (trimellitic acid, trimesic acid, pyro Meritic acid, etc.) and the like; and mixtures of two or more thereof.

Examples of polyamines include aliphatic polyamines [alkylene (C ₂ -C ₄ ) diamines (ethylenediamine, propylenediamine, etc.)]; polyalkylenepolyamines (diethylenetriamine, dipropylenetriamine, triethylenetetramine, etc.); alicyclic polyamines ( Cyclohexylenediamine, isophoronediamine, diaminodicyclohexylmethane, dimethyldiaminodicyclohexylmethane, etc.); heterocyclic polyamines [piperazine, aminoalkyl-substituted piperazine (aminoethylpiperazine, etc.)]; and mixtures of two or more thereof.

As a method for producing (a3), a known method can be used, for example, polycondensation of polyvalent carboxylic acid and polyamine at a temperature of about 170 to 250 ° C., and then 0.5 to 1.0 mmHg. Under vacuum temperature of about 150-2
A method of completing the polycondensation reaction at 50 ° C. can be exemplified.

The number average molecular weight of the obtained (a3) is usually 3,000 to 200,000, preferably 5,000 to.
It is 10,000. When the number average molecular weight is less than 3,000, the physical properties of the resin are deteriorated, the durability of the magnetic tape is deteriorated, and 2
If it exceeds 0,000, the viscosity of the coating composition becomes high and the dispersibility of the magnetic powder becomes poor.

Examples of (a4) in the present invention include those obtained by radical copolymerization using a vinyl monomer having a thiosulfate (salt) group copolymerizable with (meth) acrylic acid esters as an essential constituent component. Can be mentioned.

As the thiosulfate (salt) group-containing vinyl monomer copolymerizable with (meth) acrylic acid esters, halogen group-containing vinyl monomers (2-chloroethyl vinyl ether, 3,4-dichloro-1-butene, 2-bromo-2-butene and the like) and a reaction product of sodium thiosulfate and the like.

As a method for synthesizing a thiosulfate (salt) group-containing monomer, for example, the above thiosulfate (salt) group-containing vinyl monomer is placed in an alcohol (ethanol or the like) at a temperature of about 60-.
An example is a method of obtaining the desired product by reacting with sodium thiosulfate at 150 ° C.

As the (meth) acrylic acid esters,
Methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth)
Acrylate, 2-hydroxyethyl (mer) acrylate, 2-hydroxy (meth) propyl acrylate,
Glycidyl (meth) acrylate and the like; and mixtures of two or more thereof can be used. Also, if necessary (Mare)
Monomers other than acrylic acid esters [styrene, maleic acid, maleic anhydride, (meth) acrylic acid, methacrylic acid, fumaric acid, dibutyl fumarate, etc.] can be used in combination.

As the method for producing (a4), a known method can be used. For example, one or more of the above (meth) acrylic acid esters and a thiosulfate (salt) group-containing vinyl monomer are mixed in an organic solvent. An example is a method of obtaining a polyacrylic resin by copolymerization using a polymerization initiator such as benzoyl peroxide.

The number average molecular weight of the obtained (a4) is usually 3,000 to 200,000, preferably 5,000 to.
It is 100,000. If the number average molecular weight is less than 3,000, the physical properties of the resin are deteriorated and the durability of the magnetic tape is deteriorated.
If it exceeds 200,000, the viscosity of the coating material increases and the dispersibility of the magnetic powder deteriorates.

As (a5) in the present invention, for example, vinyl chloride and the above-mentioned vinyl monomer having a copolymerizable thiosulfate (salt) group are used as essential constituents, and other copolymerizable monomers are copolymerized as necessary. There are some.

Other copolymerizable monomers include vinyl acetate, vinyl propionate, vinylidene chloride, acrylonitrile, (anhydrous) maleic acid, (meth) acrylic acid, 2
-Hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, glycylyl (meth) acrylate and the like; and mixtures of two or more thereof.

The resin (A) used in the binder for a magnetic recording medium of the present invention may contain other resin, if necessary. As the other resin, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl acetate-vinyl alcohol copolymer, vinyl chloride-vinylidene chloride copolymer, acrylic ester-acrylonitrile copolymer, polyvinyl fluoride, Examples thereof include vinylidene chloride-acrylonitrile copolymer, polyamide resin, polyvinyl butyral, cellulose derivative, polyurethane resin, polyester resin, and synthetic rubber thermoplastic resin such as polybutadiene.

These other resins may have a functional group such as a carboxyl group, a metal sulfonate group, a sulfobetaine, a phosphoric acid ester group, an amino group or a quaternary ammonium salt group as a polar group in the resin. .

In the magnetic recording medium of the present invention, the binder, magnetic powder, solvent and additive of the present invention are mixed and dispersed, and the resulting magnetic coating material is applied onto a non-magnetic support to form a magnetic layer. can get. The binder for magnetic recording media of the present invention can also be used as a binder for the back coat layer on the side opposite to the magnetic layer.

The magnetic powder used in the magnetic recording medium of the present invention includes iron oxide [γ-Fe ₂ O ₃ (γ-hematite)].
Etc.], CrO ₃ (chromium trioxide), alloy-based magnetic substance [C
o-γ-Fe ₂ O ₃ (cobalt ferrite, cobalt-doped γ-iron oxide and the like), Fe-Co-Cr and the like], barium ferrite, pure iron Fe (metal powder), iron carbide, iron nitride and the like.

Further, in addition to the binder and the magnetic powder, a dispersant, a lubricant, an abrasive, an antistatic agent, a rust preventive, a cross-linking agent, etc. may be added to the magnetic layer.

Examples of the dispersant include fatty acids having 12 to 18 carbon atoms (caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid, elaidic acid, linoleic acid, linolenic acid, stearolic acid). Etc.); metal soaps [alkali metal (potassium, sodium, etc.) salts and alkaline earth metal (magnesium, calcium, barium, etc.) salts of the above fatty acids] and the like.

As the lubricant, dialkyl polysiloxane (alkyl has 1 to 5 carbon atoms), dialkoxy polysiloxane (alkoxy has 1 to 4 carbon atoms), monoalkyl monoalkoxy polysiloxane (alkyl has 1 carbon atoms).
~ 5, alkoxy has 1 to 4 carbon atoms, phenyl polysiloxane, fluoroalkyl polysiloxane, silicon oil, conductive fine powder (graphite etc.), inorganic powder (molybdenum disulfide, tungsten disulfide etc.), plastic fine powder , Fatty acid esters, fluorocarbons and the like.

Examples of the abrasive include alumina, silicon carbide, chromium oxide, corundum, artificial corundum, diamond and artificial diamond.

As the antistatic agent, conductive powder (carbon black, carbon black graft polymer, etc.),
Natural surfactants (saponins, etc.), nonionic surfactants (alkylene oxide, glycerin, glycidol, etc.), cationic surfactants (higher alkylamines, quaternary ammonium salts, pyridine and other heterocycles) , Phosphoniums, etc.), anionic surfactants (carboxylic acid type, sulfonic acid type, phosphoric acid type, sulfuric acid ester group type, phosphoric acid ester group type, etc.), amphoteric surfactants (amino acids,
Amino sulfonic acids, amino alcohol sulfuric acid or phosphoric acid esters, etc.) and the like.

As the rust preventive agent, phosphoric acid, sulfide, guanidine, pyridine, amine, urea, zinc chromate,
Examples thereof include calcium chromate and strontium chromate. Further, in particular, vaporizable rust preventives such as dicyclohexylamine nitrite, cyclohexylamine chromate, diisopropylamine nitrite, diethanolamine phosphate, cyclohexyl ammonium carbonate, propylenediamine stearate, guanidine carbonate, triethanolamine nitrite, morpholine stearate ( Inorganic or organic acid salts of amines, amides or imides) are used to improve the anticorrosion effect.

In order to improve the strength of the magnetic layer of the magnetic recording medium, polyisocyanate can be incorporated as a cross-linking agent in the magnetic paint.

Preferred polyisocyanates include, for example, modified MDI (eg, "Millionate ME",
Hodogaya Chemical Co., Ltd .; 3,3'-dimethoxy-4,4'-diisocyanate) and NCO group-terminated prepolymer {polyisocyanate (TDI, MDI, etc.) and active hydrogen compound (low molecular weight polyol, polyamine, polyether polyol, polyester polyol) Etc.) and NCO group-terminated prepolymers [for example, “Desmodur L” (manufactured by Bayer), “Coronate HL” (manufactured by Nippon Polyurethane), etc.]}.

The blending ratio of the binder and the crosslinking agent is not particularly limited, but the crosslinking agent is usually 3 to 80 parts by weight with respect to 100 parts by weight of the binder. Further, in order to accelerate the crosslinking reaction, the catalyst used in the production of the above-mentioned polyurethane resin may be appropriately added.

Solvents used for the magnetic paint include ester solvents (ethyl acetate, butyl acetate, etc.), ether solvents (dioxane, tetrahydrofuran, etc.), ketone solvents (cyclohexanone, methyl ethyl ketone, methyl isobutyl ketone, etc.), aromatic solvents. Hydrocarbon solvents (toluene, xylene, etc.); and mixed solvents of two or more of these. Among these, preferred is a mixed solvent of a ketone solvent and an aromatic hydrocarbon solvent.

Materials for the non-magnetic support used in the magnetic recording medium include polyesters (polyethylene terephthalate, polyethylene-2,6-naphthalate, etc.); polyolefins (polyethylene, polypropylene, etc.);
Cellulose derivatives (cellulose triacetate, cellulose diacetate, cellulose diacetate, cellulose acetate butyrate, cellulose acetate propionate, etc.); vinyl resins (polyvinyl chloride, polyvinylidene chloride, etc.); plastics (polycarbonate, polyimide, polyamideimide, etc.) ); Non-magnetic metals (aluminum, copper, tin, zinc or non-magnetic alloys containing these); Ceramics (glass, pottery, porcelain, etc.); Olefins (baryta, polyethylene, ethylene-butene copolymer, etc.) Examples include paper coated or laminated with. Further, the form of the non-magnetic support may be any of film, tape, sheet, disk, card, drum and the like.

As a method for producing a magnetic recording medium (magnetic tape, etc.), for example, a binder, magnetic powder, a solvent and, if necessary, additives are mixed in advance with a premixer or the like, and then a mixing / dispersing machine (ball mill, paint conditioner, sand, etc.). A magnetic coating is prepared by dispersing magnetic powder with a grinder, sand mill, plastomill, etc., and then this magnetic coating is applied to a non-magnetic support by doctor blade method, transfer printing method (gravure method, reverse roll method, etc.). A method for producing a magnetic recording medium can be exemplified by applying the composition to the magnetic recording medium, and then performing steps such as orientation, drying, surface processing, cutting and winding. The dry thickness of the magnetic layer coated on the non-magnetic support is usually 0.1 to 50 μm.

The magnetic recording medium generally comprises a non-magnetic support and a magnetic layer (magnetic powder, binder, etc.), but an intermediate layer (undercoat layer; between the non-magnetic support and the magnetic layer).
Undercoat layer), a nonmagnetic support having magnetic layers on both sides, a stack of magnetic layers having different magnetic properties, a protective layer provided on the magnetic layer, a nonmagnetic support The back coat layer may be provided on the back surface.

[0063]

EXAMPLES The present invention will be further described below with reference to examples, but the present invention is not limited thereto. In the following, “part” indicates “part by weight” and “%” indicates “% by weight”.

Example 1 A reaction vessel equipped with a stir bar, a thermometer and a reflux condenser was used.
4- (chloroacetyl) catechol (1 mol), sodium thiosulfate (1 mol) and 70% ethanol 250
ml was charged and the reaction was carried out by refluxing for about 4 hours. The obtained mixed solution was desolvated to obtain the desired crystalline substance (B). The structure of (B) is (HO) ₂ C ₆ by NMR analysis or the like.
It was confirmed to be H ₃ COCH ₂ SSO ₃ Na. In a similar reaction vessel, 1 mol of adipic acid, 1 mol of isophthalic acid, 1.5 mol of ethylene glycol, 1.5 mol of neopentyl glycol and 0.017 mol of the above (B) were charged, and esterification was carried out at 160 to 220 ° C. Then, a polyester polyol (C) having a hydroxy value of 113 was obtained. In a similar reaction vessel, the above polyester polyol (C) 1
Mol, neopentyl glycol 1 mol and diphenylmethane diisocyanate (MDI) 2 mol were charged and reacted at about 80 ° C. During the reaction, it was diluted with methyl ethyl ketone to obtain a polyurethane resin (I) solution having a final solid content of 30%. The content of thiosulfate group in the obtained polyurethane resin was 20 equivalents per 10 ⁶ g of the resin, and the number average molecular weight was 15,500. Using the obtained polyurethane resin solution (I) as a binder, a mixture having the following composition was dispersed and mixed in a ball mill for 70 hours, followed by filtration and defoaming to obtain a magnetic coating material. Co-γ-Fe ₂ O ₃ fine powder 100 parts Polyurethane resin (I) 10 parts (solid content conversion value) Vinyl chloride-vinyl acetate copolymer 10 parts Stearic acid 1 part Butyl stearate 1 part Methyl ethyl ketone 75 parts Toluene 75 parts To the obtained magnetic paint, 5 parts of a curing agent (trimethylolpropane tolylene diisocyanate 3 mol adduct) was added and mixed for 30 minutes. This magnetic paint was applied to a polyester film (dry film thickness: 5 μm) and oriented by applying a magnetic field of 1,000 Oe to obtain a tape. Further, this tape was treated with a calendar roll to obtain a magnetic tape (I-1).

Example 2 A reaction vessel equipped with a stirrer, a thermometer and a backed column was charged with 0.45 mol of terephthalic acid and 0.43 mol of isophthalic acid.
Mol, adipic acid 0.12 mol, ethylene glycol 0.73 mol, neopentyl glycol 0.75 mol, and the crystal substance (B) 0.02 mol used in Example 1 were charged together with 0.1 part of dibutyltin oxide, Under stirring 14
Esterification reaction at 0 to 220 ° C., then 0.1 part of antimony trioxide is added and 220 to 2 under reduced pressure of 1 mmHg or less.
The polyester resin (II) finally obtained by condensation at 60 ° C. had a thiosulfate content of 80 equivalents per 10 ⁶ g of resin and a number average molecular weight of 12,200.
A magnetic tape (II-1) was obtained in the same manner as in Example 1 except that the polyester resin (II) was used instead of the polyurethane resin (I) in Example 1.

Comparative Example 1 In a reaction vessel equipped with a stirrer, a thermometer and a reflux condenser,
Adipic acid 1 mol, isophthalic acid 1 mol, ethylene glycol 1.5 mol, 5-sodium sulfoisophthalic acid 0.017 mol and neopentyl glycol 1.5 mol were charged and esterification was carried out at 160 to 220 ° C. to obtain a hydroxy value. 112 polyester polyols (D) were obtained. Polyester polyol (D) 1 in the same reaction vessel
Mol, neopentyl glycol 1 mol and MDI 2 mol were charged and reacted at about 80 ° C. During the reaction, it was diluted with methyl ethyl ketone to obtain a polyurethane resin (III) solution having a final solid content of 30%. The sodium sulfonate group content of the obtained polyurethane resin was 22 equivalents per 10 ⁶ g of the resin, and the number average molecular weight was 16,300. A magnetic tape (III-1) was obtained in the same manner as in Example 1 except that the polyurethane resin (III) was used instead of the polyurethane resin (I) in Example 1.

Comparative Example 2 0.45 mol of terephthalic acid and 0.43 mol of isophthalic acid were placed in a reaction vessel equipped with a stirrer, a thermometer and a backed column.
Mol, adipic acid 0.12 mol, 5-sodium sulfoisophthalic acid 0.02 mol, ethylene glycol 0.7
3 mol and neopentyl glycol 0.75 mol were charged together with 0.1 part of dibutyltin oxide, and the mixture was stirred with stirring 1
Esterification reaction at 40-220 ° C., then add 0.1 part of antimony trioxide, and under reduced pressure of 1 mmHg or less 220-
Polyester resin (IV) obtained by condensation at 260 ° C. has a sodium sulfonate group content of 82 equivalents per 10 ⁶ g of resin and a number average molecular weight of 13,000.
It was 0. A magnetic tape (IV-1) was obtained in the same manner as in Example 1 except that the polyester resin (IV) was used instead of the polyurethane resin solution (I) of Example 1.

Performance Test Example 1 The gloss of the magnetic layer of the magnetic tapes obtained in Examples 1 and 2 and Comparative Examples 1 and 2 was measured. Table 1 shows the results. The gloss was measured using a gloss meter [manufactured by Nippon Denshoku Industries Co., Ltd.] (incident angle / reflection angle = 60 ° / 60 °).

[0069]

[Table 1]

Performance Test Example 2 The squareness ratios of the magnetic tapes obtained in Examples 1 and 2 and Comparative Examples 1 and 2 were measured. The results are shown in Table 2. The squareness ratio is the ratio of the saturation magnetization Bm to the residual magnetization Br (Br / Bm)
It was shown by the value of. The squareness ratio was measured using a vibrating sample magnetometer [manufactured by Riken Denshi Kogyo Co., Ltd.].

[0071]

[Table 2]

[0072]

The binder for magnetic paint of the present invention has the following effects as compared with the conventional ones. (1) A magnetic recording medium having good dispersibility of magnetic powder and excellent surface smoothness and electromagnetic conversion characteristics can be obtained. (2) Since the paint viscosity is low, it has excellent workability during application. (3) Excellent adhesion to a non-magnetic support. Since the binder of the present invention exerts the above effects, for example, an audio tape, a video tape, a computer tape, a data recorder tape, a video sheet,
It can be suitably used for manufacturing magnetic recording media such as metal tapes, metal disks, and magnetic cards.

Claims (4)

[Claims] 1. A compound represented by the general formula —S—SO ₃ X (wherein
X represents hydrogen, an alkali metal or an organic amine. ) A binder for a magnetic recording medium, which comprises a resin (A) having a thiosulfate (salt) group represented by 2. The magnetic recording medium according to claim 1, wherein (A) is at least one resin selected from the group consisting of polyurethane resins, polyester resins, polyamide resins, polyacrylic resins and vinyl chloride copolymers. Binder. 3. The binder according to claim 1, wherein the content of the thiosulfate (salt) group in (A) is 1 to 1000 equivalents per 10 ⁶ g of (A). 4. A magnetic recording medium having a magnetic layer containing the binder according to claim 1.