JPH08104834A - Magnetic coating - Google Patents

Abstract

PURPOSE: To provide a magnetic coating which contains a specific low- molecular-weight polyurethane resin and a low-molecular-weight vinyl chloride polymer as a binder for the magnetic powder, thus provides a magnetic recording medium having excellent magnetic characteristics and high durability because fine particles of the magnetic powder disperses stably in the coating. CONSTITUTION: This coating contains (A) a polyurethane resin of 2,000-10,000 number-average molecular weight, containing, in one molecule, (i) 2.2-7.0 terminal epoxy groups and (ii) 0.1-5.0wt.% of sulfonate base as SO<-> 3 , 0.05-3.0wt.% of carboxylate base as COO<-> or 0.02-1.0wt.% of quaternary ammonium base as N<+> , and (B) a vinyl chloride copolymer having 0.1-20wt.% of epoxy groups and 100-330 average polymerization degree as a binder for the magnetic powder where the intrinsic viscosity of the solution of this binder is 0.13-0.45dl/g. The component B preferably contains further carboxyl groups and anionic hydrophilic groups selected from acids and salts containing S and P.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a magnetic coating material containing magnetic powder, a binder and a solvent.

[0002]

2. Description of the Related Art In recent years, higher recording densities of magnetic recording media have been demanded. For example, even in a magnetic tape, the surface area of a magnetic recording medium has a high saturation magnetic flux density Bm and a high squareness ratio Rs (residual magnetic flux density Br / saturated magnetic flux density Bm). A material having a small roughness and excellent flexibility and abrasion resistance is required. In response to demand for high S / N ratio, specific surface area using a large fine magnetic powder and 30m ² / g~70m ² / g, in order to firmly bonded by uniformly dispersing this binding It is required that the agent has both excellent dispersion performance and strong binding strength.

Polyurethane resins have been widely used as binders because of their excellent wear resistance, and vinyl chloride polymers because of their ease of forming the surface of the magnetic layer and their strength. In order to impart the dispersion performance of the magnetic powder to these vinyl chloride polymer and polyurethane resin, a hydroxyl group,
Introducing hydrophilic groups such as a carboxyl group, a sulfonic acid group, a sulfuric acid group, a phosphoric acid group, an amino group and a quaternary ammonium salt group has also been carried out. On the other hand, in order to increase the strength of the magnetic layer, it is necessary to increase the strength of the binder, and it is effective to increase the molecular weight of the binder as a method.
When the molecular weight is increased, the viscosity of the coating material in which the magnetic powder is dispersed is increased and the dispersibility is reduced. Further, the finer the magnetic powder, the more easily the viscosity of the coating material increases, so a method for improving strength that does not depend on an increase in molecular weight is required. Cross-linking of binders with polyisocyanate compounds is widely used as a means therefor. Then, in order to enable cross-linking by the polyisocyanate compound, introduction of a group having active hydrogen capable of reacting with an isocyanate group represented by a hydroxyl group into the binder has been carried out.

However, in order to develop sufficient strength by using a binder having a small molecular weight in order to improve the dispersibility, it is necessary to introduce a large amount of hydroxyl groups into the binder as a crosslinking point. Then, in a magnetic coating material containing a fatty acid or its ester which is usually used as a lubricant, the binder is also adsorbed to the lubricant and the dispersion stability of the magnetic powder is lowered, so that a magnetic recording medium having good characteristics can be obtained. Can no longer be manufactured. In addition, it has been proposed to introduce an epoxy group into a polyurethane resin and utilize it for crosslinking (Japanese Patent Publication No. 55-40927 and Japanese Patent Application Laid-Open No. 1-109523).
However, since these binders have a small dispersive force, it is not possible to sufficiently disperse the fine magnetic powder, and satisfactory strength cannot be obtained in terms of durability.

[0005]

DISCLOSURE OF THE INVENTION The inventors of the present invention have diligently studied various problems in the past with respect to the demands for higher recording density and higher durability of the magnetic recording medium as described above, and as a result, have an end epoxy group. By combining a specific low molecular weight polyurethane resin and a low molecular weight vinyl chloride polymer having an epoxy group as a binder for magnetic powder, and using a solvent in which the molecules of these binders can be dissolved with a certain spread, A magnetic coating material of low viscosity in which various magnetic powders are stably dispersed can be obtained, and the magnetic recording medium obtained by coating this coating on a non-magnetic substrate and crosslinking it has excellent magnetic characteristics, durability and running. The present invention has been completed after confirming that the present invention can exert its properties.

[0006]

Thus, according to the present invention, the average of (a) terminal epoxy groups is 2.2 to 2 in one molecule.
7.0, (b) sulfonate group as SO ₃ ⁻ is 0.1 to 5.0% by weight, carboxylate group as COO ⁻ is 0.05 to 3.0% by weight, or quaternary ammonium salt group is N. ^{+ With} 0.02 to 1.0% by weight of any one of them, a polyurethane resin having a number average molecular weight of 2,000 to 10,000, and 0.1 to 20% by weight of an epoxy group,
A vinyl chloride copolymer having an average degree of polymerization of 100 to 330 is used as a binder for the magnetic powder, and the intrinsic viscosity of the binder is 0.13.
A magnetic coating material is provided which is characterized by using a solvent of about 0.45 dl / g. According to the present invention, the vinyl chloride-based copolymer further comprises an anionic hydrophilic group or -N ⁺ R ¹ R ² R selected from the group consisting of a carboxyl group and an acid containing sulfur or phosphorus and salts thereof. ³ X ^-,
-NR ¹ R ² · HX ¹ is a magnetic coating material having at least one of cationic hydrophilic groups (provided that
R ¹ , R ² and R ³ represent an alkyl group, an allyl group, an alkenyl group or an alkoxy group, and X and X ¹ are a halogen or a residue of sulfuric acid, phosphoric acid or nitric acid, a carboxylic acid, an acidic sulfuric acid ester or an acidic phosphoric acid. (Representing an organic acid residue such as an ester) is provided.

The polyurethane resin used in the present invention is
In one molecule, (a) an average of 2.2 to 7.0 terminal epoxy groups and (b) a sulfonate group as SO ₃ ^— are 0.1 to 0.1.
5.0% by weight, carboxylate group as COO ⁻ 0.0
5 to 3.0% by weight or 0.02 to 1.0% by weight as N ⁺ of a quaternary ammonium salt group, having a number average molecular weight of 2,000 to 10,000. The molecular weight of the polyurethane resin used in the present invention was measured by gel permeation chromatography, and was calculated by using polystyrene having a known molecular weight as a standard.
The number average molecular weight of the polyurethane resin used in the present invention is in the range of 2,000 to 10,000, and preferably in the range of 2,500 to 8,000. When the number average molecular weight is less than 2,000, the strength is low and a good binder cannot be obtained. When the number average molecular weight exceeds 10,000, the viscosity of the coating material in which the magnetic powder is dispersed is increased and the dispersibility is lowered. The number of terminal epoxy groups of the polyurethane resin used in the present invention needs to be 2.2 to 7.0 per molecule, and preferably 2.3 to 5.0.
When the number is less than 2.2, the cross-linking of the polyurethane resin cannot form a sufficient network structure, and satisfactory mechanical properties and abrasion resistance cannot be obtained. If it is more than 7.0, the solubility in the solvent will decrease.

When the polyurethane resin used in the present invention has a sulfonate group, its amount must be 0.1 to 5.0% by weight as SO ₃ ⁻ , preferably 0.3 to ₃ . It is 0% by weight. When the polyurethane resin has a carboxylic acid group, the amount thereof is required to be 0.05 to 3.0% by weight, preferably 0.2 to 2.0% by weight, as COO ⁻ . When the polyurethane resin has a quaternary ammonium salt group, its amount is N ⁺
0.02 to 1.0% by weight, preferably 0.05 to
It is 0.5% by weight. In each case, if it is less than the required lower limit amount, sufficient magnetic powder dispersibility is not exhibited, and if it is more than the required upper limit amount, solvent solubility is impaired and the magnetic powder dispersibility is rather deteriorated. The polyurethane resin having such a sulfonate group is prepared by preparing a prepolymer having a terminal isocyanate group from a mixture of an organic polyisocyanate, a high molecular weight polyol having two or more hydroxyl groups and a compound having a hydroxyl group and a sulfonate group. A method of adding a compound having both a hydroxyl group and an epoxy group,
Alternatively, it can be obtained by adding a compound having both a hydroxyl group and a double bond to the prepolymer and then epoxidizing it with an epoxidizing agent such as percarboxylic acid. Further, the polyurethane resin having a carboxylate group, a method of introducing into a prepolymer in the same manner as in the case of a sulfonate group, a compound having both a hydroxyl group and an epoxy group in the prepolymer having a terminal isocyanate and a hydroxyl group and a carboxylate group. It can be obtained by a method of adding a compound having both of them. The polyurethane resin having a quaternary ammonium salt group is preferably prepared by epoxidizing the terminal and then adding a tertiary amine and a counterionic acid component to chlorinate the quaternary ammonium salt. In either case, it is preferable to use a low molecular weight polyol having two or more hydroxyl groups as a polyol component in the prepolymer synthesis. By interposing the low molecular weight polyol in the polyol component, a low molecular weight prepolymer is formed to form a hard segment, so that a polyurethane resin having high strength as a whole can be obtained. However, the molar ratio of the high molecular weight polyol to the low molecular weight polyol is preferably 1/1 to 8/1, and more preferably 2/1 to 6/1. When it is less than 1/1, non-uniformity is likely to occur due to the difference in reaction rate during polyurethane synthesis, and the polyurethane resin may lack flexibility. On the other hand, if it exceeds 8/1, the rigidity of the polyurethane resin may be insufficient. In order to produce the polyurethane resin of the present invention, first, an organic polyisocyanate and a polyol are reacted in an NCO / OH molar ratio of 1.2 / 1 to 2/1, and the terminal isocyanate group is on average 2.2 per molecule. A prepolymer having more than one prepolymer is obtained. At that time, a polyol having a slow reaction rate with respect to polyisocyanate, such as a polyol having a high molecular weight or a low activity hydroxyl group, is first charged, and then the polyols are sequentially added and reacted in the order of slow reaction rate to uniformly form a polyurethane. It is preferable to proceed.
Next, an epoxy group is added to the end of the prepolymer. To add an epoxy group to the terminal, a compound having at least one hydroxyl group and at least one epoxy group is reacted with the isocyanate group at the terminal, or a compound having at least one hydroxyl group and a double bond at the molecular end. After the reaction, the double bond portion is oxidized and epoxidized.

As the organic polyisocyanate, 2,4
-Tolylene diisocyanate (hereinafter abbreviated as 2,4-TDI), 2,6-tolylene diisocyanate (hereinafter 2,6)
-TDI), 4,4'-diphenylmethane diisocyanate (hereinafter abbreviated as MDI), p-phenylene diisocyanate, m-phenylene diisocyanate, 1,5-
Naphthylene diisocyanate, isophorone diisocyanate, hexamethylene diisocyanate, lysine diisocyanate, xylene diisocyanate, cyclohexane diisocyanate, hydrogenated MDI, benzene triisocyanate, lysine ester triisocyanate, 1,
6,11-undecane triisocyanate, 1,3,6
-Hexamethylene triisocyanate, bicycloheptane triisocyanate and the like and mixtures thereof. Of these, MDI, 2,4-TDI and mixtures thereof are preferred.

Examples of the high molecular weight polyol having two or more hydroxyl groups include polyether polyol and polyester polyol having a molecular weight of 500 to 3,000. Examples of the polyether polyol include ethylene glycol, 1,2-propylene glycol, 2,3-butylene glycol, 1,4-butylene glycol, 2,2-
Dimethyl-1,3-propanediol (neopentyl glycol), diethylene glycol, 1,5-pentamethylene glycol, 1,6-hexamethylene glycol, 3-methyl-1,5-pentanediol, cyclohexane-1,4-diol , Cyclohexane-1,4-
Examples thereof include polycondensation of glycols such as methanol alone or in a mixture. In addition, polyether polyols such as polyethylene ether polyol, polypropylene ether polyol, and polybutylene ether polyol obtained by adding ethylene oxide, propylene oxide, or butylene oxide to these polyether polyols, and ε-caprolactone are present in the presence of the glycols. Polycaprolactone diols which have been subjected to ring-opening addition polymerization below can also be used. As the polyester polyol, succinic acid, maleic acid, adipic acid, glutaric acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, phthalic acid, isophthalic acid, terephthalic acid, hexahydroterephthalic acid may be used alone or as a mixture of the above glycols. Acid, dibasic acid such as hexahydroisophthalic acid,
Examples thereof include those obtained by polycondensing these dibasic acid esters or acid halides. Further, a polyol having three or more hydroxyl groups in the molecule, such as trimethylolethane, trimethylolpropane, glycerin, pentaerythritol, triethanolamine and other low molecular weight tri- and tetraols, and the low-molecular weight glycol in a mixed system, Examples are polyester polyols obtained by polycondensation of dibasic acids and their acid esters and acid halides.

The low molecular weight polyol having two or more hydroxyl groups has a molecular weight of 60 to 300, and examples thereof include glycols used in the production of the high molecular weight polyether polyol. Also, diols obtained by adding 2 to 4 mol of ethylene oxide, propylene oxide, butylene oxide, etc. to hydroquinone can be used. Furthermore, low molecular weight tri and tetraols can be used. Examples of the compound having both a hydroxyl group and a sulfonate group include a molecular weight of 3000 obtained by polycondensation of 5-sodium sulfoisophthalic acid or its diester with a low molecular weight glycol or other dibasic acid.
The following polyester diols, molecular weight 3 at both terminal hydroxyl groups
It is preferable to use an unsaturated polyester of 000 or less in which sodium bisulfite is added to the internal double bond to introduce a sulfonate group.

The compounds having at least one hydroxyl group and at least one epoxy group include 2,3-epoxy-1-propanol, 3,4-epoxy-1-butanol, and 5,6-.
Epoxy-1-hexanol, 7,8-epoxy-1-
Compounds having one hydroxyl group and one epoxy group at the terminal such as octanol, diglycidyl ether of glycerin,
Examples thereof include compounds having one hydroxyl group and two or more epoxy groups such as trimethylolpropane diglycidyl ether, diglycerol polyglycidyl ether and sorbitol polyglycidyl ether.

Examples of the compound having one or more hydroxyl groups and a double bond at the molecular end include α-olefin alcohols such as 3-buten-1-ol and 5-hexen-1-ol, 2-hydroxyethyl vinyl ether, 2 -Vinyl ethers such as hydroxypropyl vinyl ether;
(Meth) allyl-2-hydroxyethyl ether, (meth) allyl-2-hydroxypropyl ether, (meth) allyl-3-hydroxypropyl ether, (meth) allyl-2-hydroxybutyl ether, (meth)
Allyl-3-hydroxybutyl ether, (meth) allyl-4-hydroxybutyl ether, (meth) allyl-
Alkylene glycol mono (meth) allyl ethers such as 6-hydroxyhexyl ether; and polyoxyalkylene glycol mono (meth) allyl ethers such as diethylene glycol mono (meth) allyl ether and dipropylene glycol mono (meth) allyl ether. . As an epoxidizing agent for epoxidizing a compound having one or more of these hydroxyl groups and a double bond at the molecular end with a terminal isocyanate of a prepolymer, percarboxylic acids such as perbenzoic acid and peracetic acid are used. Known materials such as these can be used.

Compounds having two hydroxyl groups and a carboxylate group in the molecule for introducing a carboxylate group into the prepolymer in advance include sodium 2,4-dioxybenzoate, sodium dimethylolpropionate, 4,4 −
Examples thereof include sodium bishydroxyphenylbutyrate. Examples of the compound having one hydroxyl group and carboxylate group in the molecule for addition to the terminal isocyanate prepolymer include sodium salicylate, sodium glycolate, sodium p-aminobenzoate and the like. As an example of the tertiary amine used for adding the quaternary ammonium salt group after epoxidizing the terminal, tertiary amines such as pyridine, dimethyllaurylamine, dimethylstearylamine, triethylamine and diethylmethoxyethylamine can be used. In addition, a saturated acid such as acetic acid, lactic acid or chloroacetic acid can be used for the addition of the amine.

Further, in producing the polyurethane resin used in the present invention, a method of injecting the reaction mixture into an extruder in the presence of a catalyst after sufficiently mixing the reactants, if desired, and dimethylformamide, toluene, xylene,
Benzene, dioxane, cyclohexane, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone,
An ordinary production method of a solution reaction method in which the reaction is performed in an organic solvent such as ethyl acetate or butyl acetate or a mixed solvent organic solvent can be used.

As will be described later, in the magnetic coating material of the present invention, the solvent used must be a single type or a composite type so that the intrinsic viscosity of the binder falls within a specific range. The amount of the solvent used during the production of the polyurethane is 1 to 10% by weight of the amount of the solvent used for the magnetic paint,
Since it exists in the magnetic paint, it is necessary to select it in consideration of the influence on the intrinsic viscosity.

Examples of the catalyst include organometallic compounds such as dibutyltin dilaurate. Further, in order to increase the stability and the like of the resin, an antioxidant, an ultraviolet absorber, a hydrolysis inhibitor and the like may be added. The synthesis reaction of a prepolymer having an isocyanate group at the end is usually 60 to 12
Perform at 0 ° C. The reaction of adding a compound having one hydroxyl group and one or more epoxy group to the terminal isocyanate group is performed at 80 ° C. or lower, preferably 40 to 60 ° C. to prevent ring opening of the epoxy group.

Next, the vinyl chloride copolymer used in the present invention has an epoxy group of 0.1 to 20% by weight and an average degree of polymerization of 10 to 330. Such a vinyl chloride-based polymer is a radical generator containing a compound having an epoxy group and a polymerizable double bond (epoxy group-containing monomer) together with vinyl chloride and, if necessary, a monomer copolymerizable therewith. It is obtained by a method such as copolymerization in the presence or a method in which a vinyl chloride polymer is partially dehydrochlorinated by heating or contact with a dehydrochlorination agent and then epoxidized with an epoxidizing agent such as percarboxylic acid. . Examples of the epoxy group-containing monomer include glycidyl ethers of unsaturated alcohols such as allyl glycidyl ether and methallyl glycidyl ether; glycidyl (meth) acrylate, glycidyl-p-vinylbenzoate, methylglycidyl itaconate and glycidyl ethyl. Malate,
Examples thereof include glycidyl esters of unsaturated acids such as glycidyl vinyl sulfonate and glycidyl (meth) acryl sulfonate; butadiene monooxide, vinyl cyclohexene monooxide, and epoxy olefins such as 2-methyl-5,6-epoxyhexene. The amount of the epoxy group in the vinyl chloride-based copolymer of the present invention introduced by these is required to be 0.1 to 20% by weight, preferably 1.0 to 15% by weight. If it is less than 0.1% by weight, the object of the present invention is difficult to achieve, and if it is more than 20% by weight, the amount of vinyl chloride is relatively reduced and the physical properties of the resin are deteriorated.

The average degree of polymerization of the vinyl chloride copolymer used in the present invention is 100 based on JIS K 6721.
It is necessary to be ˜330, and especially 100 to 200 is preferable in a magnetic paint using fine magnetic powder. If it is less than 100, the strength will be insufficient even if it is crosslinked,
When it exceeds 330, the dispersibility of the magnetic powder is deteriorated. In the conventional vinyl chloride binder, when the average degree of polymerization is set to 200 or less in order to improve the dispersibility of the magnetic powder, the strength is insufficient and the abrasion resistance is poor. In addition, if it is combined with a high-molecular-weight binder to supplement it, the adsorption form on the surface of the magnetic powder may collapse, possibly leading to aggregation of the magnetic powder and lowering the dispersibility. However, even if it is a vinyl chloride-based copolymer having an average degree of polymerization of 100 to 330 by combining the above-mentioned vinyl chloride-based copolymer with the polyurethane resin used in the present invention to crosslink the epoxy groups possessed by both, In addition to the unprecedented high degree of magnetic powder dispersibility, sufficient wear resistance is realized. The vinyl chloride-based copolymer used in the present invention comprises an anionic hydrophilic group selected from the group consisting of a carboxyl group and an acid containing sulfur or phosphorus and salts thereof in addition to the above epoxy group, or -N ⁺ R ¹ A polymer having one or more cationic hydrophilic groups selected from R ² R ³ X ⁻ and —NR ¹ R ² · HX ¹ is more suitable for dispersing fine magnetic powder. However, R ¹ , R ² and R ³ represent an alkyl group, an allyl group, an alkenyl group or an alkoxy group, and X and X ¹
Represents a residue of halogen or sulfuric acid, phosphoric acid or nitric acid, an organic acid residue such as carboxylic acid, acidic sulfuric acid ester or acidic phosphoric acid ester. As a first method of introducing the above-mentioned anionic hydrophilic group or cationic hydrophilic group into the vinyl chloride-based copolymer used in the present invention, a monomer having these functional groups such as monobutyl maleate, There is a method in which vinyl sulfonic acid, propyl-3-chloro-2-phosphate acrylate, diallyldimethylammonium stearate or the like is used as a comonomer of vinyl chloride and an epoxy group-containing monomer to perform copolymerization.

As a method for producing a vinyl chloride copolymer having an anionic hydrophilic group used in the present invention, when an epoxy group-containing monomer is copolymerized with vinyl chloride, the process of the copolymerization reaction is carried out. It is also possible to employ a method of adding an alkali metal salt or ammonium salt of a carboxylic acid or an acid containing sulfur or phosphorus to an epoxy group site in an aqueous system or a non-aqueous system before or after the reaction. In that case, examples of the alkali metal salt of an acid containing sulfur or phosphorus, or an ammonium salt include potassium sulfite, sodium thiosulfate, ammonium hydrogensulfate, disodium hydrogenphosphate,
Ammonium hydrogen phosphite, potassium sulfanilate,
Examples thereof include potassium persulfate and sodium perphosphate. A method for adding a strong acid salt containing sulfur or phosphorus in the copolymerization of this epoxy group-containing monomer and vinyl chloride is disclosed in JP-A-6-96.
No. 0-238306, JP-A-60-238371 and JP-A-61-53367. There is also a method of reacting a vinyl chloride copolymer containing an epoxy group with a tertiary amine in the presence or absence of an acid (second
the method of). This method is described in JP-A-63-12111.
It is described in detail in No. 7. The amount of these anionic hydrophilic groups is preferably in the range of 4,000 to 40,000 as the molecular weight of vinyl chloride-based copolymerization per hydrophilic group, that is, the equivalent, and when the equivalent is less than 4,000, the moisture resistance of the medium is low. If it is more than 40,000, the dispersibility of the magnetic powder is poor. Further, the content of the cationic hydrophilic group is preferably in the range of 0.02 to 0.5% by weight as the nitrogen content. 0.02% by weight
Below, the dispersibility of the magnetic powder is poor, and if it exceeds 0.5% by weight, the moisture resistance is impaired.

In the vinyl chloride-based copolymer used in the present invention, examples of the monomer optionally used together with the epoxy group-containing monomer include carboxylic acids such as vinyl acetate and vinyl propionate. Vinyl ester; vinyl ether such as methyl vinyl ether, isobutyl vinyl ether and cetyl vinyl ether; vinylidene such as vinylidene chloride and vinylidene fluoride; unsaturated carboxylic acid anhydride such as maleic anhydride and itaconic anhydride; diethyl maleate, dibutyl maleate, itacone Diethyl acid,
Unsaturated carboxylic acid alkyl esters such as methyl (meth) acrylate and ethyl (meth) acrylate; unsaturated nitriles such as acrylonitrile; aromatic vinyl monomers such as styrene, α-methylstyrene, p-methylstyrene, etc. Can be mentioned. The proportion of vinyl chloride monomer units in the vinyl chloride copolymer used in the present invention is usually 20% by weight or more, preferably 50 to 95% by weight. If it is less than 20% by weight, the strength of the copolymer is lowered and durability is lost.

The vinyl chloride copolymer used in the present invention can be produced by any known polymerization method. From the viewpoint of the operation of dissolving the copolymer in a solvent, it is preferable to use a suspension polymerization method using a lower alcohol such as methanol or ethanol alone or a combination thereof with deionized water as a medium for solution polymerization or a polymerization reaction. . Emulsion polymerization is convenient when water-soluble salts such as strong acid salts containing sulfur or phosphorus are used in the reaction. Examples of the polymerization initiator used in the production of the copolymer include lauroyl peroxide, diisopropyl peroxydicarbonate, di-2-ethylhexyl peroxydicarbonate, t-butyl peroxypivalate, 3, 5, 5 -Organic peroxides such as trimethylhexanoyl peroxide; azo compounds such as α, α'-azobisisobutyronitrile; ammonium persulfate,
Examples thereof include persulfates such as potassium persulfate. Suspension materials for suspension polymerization include polyvinyl alcohol, partially saponified products of polyvinyl acetate, cellulose derivatives, polyvinylpyrrolidone, maleic anhydride-vinyl acetate copolymers, synthetic high molecular substances such as polyacrylamide; starch, gelatin, etc. Natural polymer substances of Examples of the emulsifier used in emulsion polymerization include anionic surfactants such as sodium alkylbenzene sulfonate, sodium lauryl sulfate and sodium stearate; nonionic surfactants such as polyoxyethylene alkyl ether and polyoxyethylene sorbitan fatty acid partial ester. Can be mentioned. The average degree of polymerization of the vinyl chloride copolymer is 100 to
330, preferably 100-200, trichloroethylene, t-dodecyl mercaptan,
It is necessary to add a molecular weight modifier such as mercaptoethanol or a method of copolymerizing a comonomer having a large chain transfer to vinyl chloride. The polymerization reaction for producing the vinyl chloride-based copolymer is usually carried out at 35 to 80 ° C. under stirring.

As the binder for the magnetic powder of the magnetic layer of the magnetic recording medium of the present invention, the above-mentioned polyurethane resins 80 to 2 are usually used.
0% by weight and the above vinyl chloride copolymer 20 to 80% by weight are used in combination. The amount of the total binder is usually 10 to 30 parts by weight, preferably 1 to 100 parts by weight of the magnetic powder.
4 to 24 parts by weight. If it is less than 10 parts by weight, it is difficult to disperse the magnetic powder and the strength of the coating becomes weak, and if it is more than 30 parts by weight, the magnetic characteristics of the magnetic recording medium deteriorate. Further, 5 to 50% by weight of the total amount of the above binders used may be applied to other binders. Other binders include polyurethane resins other than the polyurethane resin used in the present invention, polyester resins, vinyl chloride-vinyl acetate copolymers, vinyl chloride-vinyl acetate-maleic acid and / or (meth) acrylic acid copolymers. , Vinyl chloride
Vinyl propionate copolymer, saponified vinyl chloride-carboxylic acid vinyl ester copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, epoxy group- and sulfate group-containing vinyl chloride copolymer , (Meth) acrylic acid ester-acrylonitrile copolymer, (meth) acrylic acid ester-vinylidene chloride copolymer, (meth) acrylic acid ester-styrene copolymer, nylon-silicone resin, nitrocellulose-
Polyamide resin, polyvinyl fluoride, vinylidene chloride-
Acrylonitrile copolymer, butadiene-acrylonitrile copolymer, styrene-butadiene copolymer, styrene-butadiene-acrylonitrile copolymer, polyamide resin, polyvinyl butyral, cellulose derivative (cellulose acetate butyrate, cellulose acetate propionate, cellulose dye) Acetate, cellulose triacetate, nitrocellulose, etc.), polyester resin, chlorovinyl ether acrylate copolymer, thermoplastic resin such as various synthetic rubbers; phenol resin, phenoxy resin, urea resin, melamine resin, alkyd resin, silicone resin, acrylic Examples include thermosetting resins such as system reaction resins, epoxy-polyamide resins, and nitrocellulose-melamine resins.

In the present invention, the above polyurethane resin having a terminal epoxy group and the above vinyl chloride polymer having an epoxy group are used in combination as a binder for the magnetic powder, but the magnetic paint of the present invention is nonmagnetic. When coated on a substrate to form a magnetic layer, these binders are cross-linked mainly via epoxy groups. This cross-linking is between polyurethane resins,
It may occur between the polyurethane resin and the vinyl chloride-based polymer or between the vinyl chloride-based polymer, and it is considered that they occur in various ways. In the crosslinking reaction used in the present invention, a known crosslinking agent for epoxy crosslinking, that is, an amine compound, a thiol compound, an organic acid, an acid anhydride, an aminosilane compound, or the like can be used. As the amine-based cross-linking agent, aliphatic polyamines such as ethylenediamine, diethylenetriamine, triethylenetetramine, and tri (methylamino) hexane; metaphenylenediamine,
Aromatic polyamines such as 4,4'-diaminodiphenylmethane are mentioned. Examples of thiol-based cross-linking agents include mercaptopropionate and polyepoxide SH.
And triazine polythiols such as dibutylaminotriazinedithiol and triazinetrithiol. Examples of the acid anhydride-based cross-linking agent include aliphatic succinic anhydrides such as alkylsuccinic anhydride and polyadipic anhydride; alicyclic acid anhydrides such as methyltetrahydrophthalic anhydride and methylhexahydrophthalic anhydride; Examples thereof include aromatic acid anhydrides such as mellitic acid and pyromellitic dianhydride. As other crosslinking agents, polyamide-based crosslinking agents, phenol-based crosslinking agents, substituted imidazoles, aminosilanes such as γ-aminopropyltriethoxysilane, etc. can be used. When these accelerators and catalysts such as tertiary amines are used together with these crosslinking agents, the crosslinking can be further effectively promoted. Further, with the above-mentioned epoxy cross-linking agent, for the purpose of cross-linking the hydroxyl group generated when the epoxy group is ring-opened and cross-linking, and for the purpose of cross-linking the hydroxyl group when other binder having a hydroxyl group is used in combination. You may use together the polyisocyanate crosslinking agent of. The magnetic coating material of the present invention is a dispersion obtained by mixing the binder of the above-mentioned polyurethane resin and vinyl chloride-based copolymer, the crosslinking agent and the magnetic powder together with a solvent. The solvent used in the present invention dissolves both the above-mentioned binders and has an intrinsic viscosity [η] of 0.
It is necessary to select a material having a density of 13 to 0.45 dl / g, and a material having a density of 0.14 to 0.35 dl / g is preferably used. . A single solvent or a mixed solvent of a plurality of types may be used as long as it has these properties.

For the intrinsic viscosity [η], a dilute solution of several points is prepared within the range of 0.2 to 0.8 g / dl in the use ratio of the polyurethane resin and the vinyl chloride copolymer used in the magnetic paint. Then, the reduced viscosity is plotted against the binder concentration on the figure, and the concentration is extrapolated to 0 for determination. Intrinsic viscosity [η] can be seen as an index showing the state of spread of binder molecules in the solution. If this falls within the range of the above numerical values, polyurethane resin and vinyl chloride copolymer are compared to conventional products. It was found that even with a much lower molecular weight, the adsorption thickness on the surface of the magnetic powder is sufficient for stabilizing the dispersion of the magnetic powder. Based on this finding, it is possible to utilize a low-molecular weight binder having good dispersibility even for fine high-performance magnetic powder. As the solvent, toluene, acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, tetrahydrofuran or the like is used, and a single or mixed composition is determined depending on the above-mentioned polyurethane resin and vinyl chloride copolymer used as the binder. To prepare the magnetic coating material of the present invention, the polyurethane resin and the vinyl chloride-based copolymer, which are binders, are usually dissolved or mixed in the solvent, and the magnetic powder is optionally mixed with the dispersant used in the solvent. Disperse, add additives such as a crosslinking agent, a lubricant, an antistatic agent, and an abrasive, and mix. In particular, since both the polyurethane resin, which is the binder used in the present invention, and the vinyl chloride-based copolymer contain epoxy groups, addition of a cross-linking agent between epoxy groups has an effect on the magnetic characteristics of the magnetic recording medium. It is preferable from the viewpoint of improving durability and running property. The magnetic coating thus obtained is applied onto a non-magnetic substrate represented by a polyester film, subjected to magnetic field orientation treatment and surface formation treatment, and then subjected to heat treatment for cross-linking and surface polishing by use, cutting, assembling, etc. A magnetic recording medium can be manufactured by adopting the process of.

As the magnetic powder used in the present invention, particularly fine ones are preferable, and they are γ-Fe ₂ O ₃ and γ-F.
e ₃ O ₄ , ferromagnetic iron oxide powder such as γ-FeOx (1.33 <x <1.5), Co-doped ferromagnetic iron oxide powder,
In addition to barium ferrite, iron carbide powder such as Fe ₅ C ₂ powder, iron nitride powder, and the like, ferromagnetic metal powder containing iron, cobalt, or nickel can be used. As an example of the ferromagnetic metal powder, the metal content in the ferromagnetic metal powder is 75% by weight or more, and 80% by weight or more of the metal content is at least one kind of ferromagnetic metal or alloy (eg, Fe, Co, Ni, Fe-
Co, Fe-Ni, Co-Ni, Co-Ni-Fe), and other components (eg, Al, Si, S, Sc, Ti, V, Cr) within the range of 20% by weight or less of the metal content. , Mn,
Cu, Zn, Y, Mo, Rh, Pd, Bi, La, C
e, Pr, Nd, B, P) may be included. Methods for preparing these ferromagnetic powders are already known, and magnetic powders according to the present invention prepared by these known methods can be used. The shape of the magnetic powder used in the present invention is not particularly limited, but normally needle-shaped, dice-shaped, or plate-shaped particles can be used.

Examples of lubricants that can be used in the present invention are:
Fatty acids having 8 to 18 carbon atoms, higher alcohols, amides, fatty acid esters and the like can be used. For example, caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid, elaidic acid, linoleic acid , Linolenic acid, stearolic acid, stearyl alcohol, palmityl alcohol, lauryl amide, dimethyl stearyl amide, butyl lauryl amide, butyl stearate, octyl stearate, sorbitan oleate and the like. In addition, silicon oil, fluorinated oils such as polyperfluoroalkylene oxide and perfluoroalkane, paraffin wax, polyethylene oxide and the like can also be used. Further, solid lubricants such as carbon black, graphite, molybdenum disulfide, and tungsten disulfide can be used. These lubricants are used in the range of 1 part to 6 parts per 100 parts of the magnetic powder.

Further, as the polishing agent, TiO ₂ , Ti
O, ZnO, CaO, SnO ₂ , SiO ₂ , α-Fe ₂
O ₃ , Cr ₂ O ₃ , α-Al ₂ O ₃ , ZnS, Mo
_{S 2, BaSO 4, CaSO 4} , MgCO 3, BN, S
iC etc. can be mentioned. These abrasives may be used alone or in combination of two or more. Further, as the antistatic agent, conductive fine powder such as carbon black and carbon black graft polymer;
Natural surfactants such as saponins; nonionic surfactants such as alkylene oxide-based, glycerin-based and glycidol-based; higher alkylamines, quaternary ammonium salts, salts of pyridine and other heterocyclic compounds, phosphonium or sulfonium compounds, etc. Anionic surfactant containing an acidic group such as carboxylic acid, sulfonic acid, phosphoric acid, sulfuric acid ester group, phosphoric acid ester group; amino acid, aminosulfonic acid, amino alcohol sulfuric acid or phosphoric acid Examples thereof include amphoteric activators such as esters. If desired, a dispersant can be used in the magnetic recording medium of the present invention. Examples of the dispersant that can be used in the present invention include fatty acids having 10 to 22 carbon atoms (eg, caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid,
Elaidic acid, linoleic acid, linolenic acid, stearolic acid), a metal soap consisting of the above fatty acid and an alkali metal (eg, lithium, sodium, potassium) or an alkaline earth metal (eg, magnesium, calcium, barium), Esters of fatty acids and compounds obtained by substituting a part or all of hydrogen atoms of the compounds with fluorine atoms, amides of the above fatty acids, aliphatic amines, higher alcohols, polyalkylene oxide alkyl phosphates, alkyl phosphates, alkyl borates. Examples thereof include known dispersants such as sarcosinates, alkyl ether esters trialkylpolyolefinoxy quaternary ammonium salts, and lecithin.

(1) A terminal epoxy group (a) is included in one molecule.
An average of 2.2 to 7.0 and (b) sulfonate group SO
₃ ^-0.1 to 5.0% by weight and a carboxylic acid group as C
OO^-0.05 to 3.0% by weight or quaternary ammonium
Um base to N⁺0.02 to 1.0% by weight
Number average molecular weight of 2,000 to 10,000 having heel
0.1 to 20 weight of polyurethane resin and epoxy group
% Vinyl chloride copolymer having an average degree of polymerization of 100 to 330
Polymer is used as a binder for magnetic powder, and
Use a solvent having a viscosity of 0.13 to 0.45 dl / g
Magnetic paint characterized by (2) Polyurethane resin has terminal epoxy groups in one molecule
The above (1) description, which has 2.3 to 5.0 on average.
Magnetic paint. (3) Polyurethane resin has a number average molecular weight of 2,500 to
The magnetic coating material according to (1) or (2) above, which has a thickness of 8,000. (4) Polyurethane resin has a sulfonate group of 0.3-
The above items (1) to (3) having 3.0% by weight.
A little magnetic paint. (5) The vinyl chloride copolymer has an epoxy group of 1.0 to 1
Any of the above (1) to (4) having 5% by weight.
That magnetic paint. (6) The above (1), wherein the intrinsic viscosity is 0.14 to 0.35.
A magnetic coating material according to any one of (5) to (5). (7) The vinyl chloride-based copolymer is more like a carboxyl group
And a group of acids containing sulfur or phosphorus and their salts.
Anionic hydrophilic group or -N selected from⁺R¹ R²R³
X^-, -NR¹R²・ HX¹More preferred cationic parents
The compound according to claim 1, which has one or more aqueous groups.
Magnetic paint. However, R¹, R²And R³Is alkyl
Represents a group, an alkenyl group or an alkoxy group, and X and X¹
Is an inorganic acid residue such as halogen, sulfuric acid, phosphoric acid or nitric acid.
Group, or carboxylic acid, acidic sulfate or acidic phosphoric acid
Represents an organic acid residue such as ester. (8) Vinyl chloride-based copolymer is a carboxyl group, sulfur
Or an acid selected from the group consisting of phosphorus-containing acids and salts thereof.
It has 4,000 to 40,000 equivalents of a nonionic hydrophilic group.
Or -N⁺R¹R²R³X^-, -NR¹R²・ H
X¹One or more of the cationic hydrophilic groups selected from
It has 0.02 to 0.5% by weight as a nitrogen content.
The magnetic paint according to (7) above. (9) Polyurethane resin has terminal epoxy groups in one molecule
The above (7) or having an average of 2.3 to 5.0
(8) Magnetic paint. (10) The polyurethane resin has a number average molecular weight of 2,500 to
The magnetic coating composition according to any one of (7) to (9) above, wherein the magnetic coating composition is 8,000. (11) The polyurethane resin has a sulfonate group of 0.3 to
Of the above (7) to (10), which has 3.0% by weight.
Either magnetic paint. (12) The vinyl chloride copolymer has an epoxy group of 1.0 to
The above items (7) to (11) having 15% by weight.
A little magnetic paint. (13) The above having an intrinsic viscosity of 0.13 to 0.35
The magnetic coating material according to any one of (7) to (12).

[0030]

EXAMPLES The present invention will be described in more detail with reference to the following examples. In addition, parts and% in the examples and comparative examples are based on weight unless otherwise specified. Polyurethane Synthesis Example 1 500 g of methyl ethyl ketone and poly (1,4-butylene / neopentyl) / (adipic acid / 5-500) having a molecular weight of 1500 were placed in a temperature-adjustable reactor equipped with a stirring propeller, a thermometer and a condenser and having a temperature-adjustable capacity of 5 liters. 300 g of sodium sulfoisophthalic acid dimethyl ester (0.
2 mol), 191.4 g (1.1 mol) of 2,4-TDI and 225 g (0.9 mol) of MDI were charged to 80.
After reacting for 2 hours at ℃, add 2000 g of polybutylene adipate 40% methyl ethyl ketone solution having a molecular weight of 1000 (0.8 mol as polybutylene adipate) and further add 2
Allowed to react for hours. Then 10 of trimethylol propane
% Methyl ethyl ketone solution (130 g (0.1 mol as trimethylolpropane)) was added and reacted for 6 hours to prepare a terminal isocyanate prepolymer. To this polymer solution, 253 g of 50% methyl ethyl ketone solution of 2,3-epoxy-1-propanol (1.71 mol as 2,3-epoxy-1-propanol) was added and reacted at 40 ° C. for 15 hours to prepare a sample (A ) Got. In the same manner, the prepolymer prepared by adding trimethylolpropane in methyl ethyl ketone solution as 400 and 520 g is added with 50% methyl ethyl ketone solution in 2,3-epoxy-1-propanol at 164 and 1 respectively.
37 g was reacted to obtain samples (B) and (C). The composition of each polyurethane sample is shown in Table 1.

Polyurethane Synthesis Example 2 Methyl ethyl ketone (500 g) and 2,4-TDI (208.8 g) were charged in a temperature-adjustable reactor having a capacity of 5 liters equipped with a stirring propeller, a thermometer and a condenser.
2 mol), 225 g (0.9 mol) of MDI and 750 g (1.25) of polybutylene adipate having a molecular weight of 600.
(Mole) and reacted at 80 ° C. for 2 hours, 320 g of a 10% methylethylketone solution of trimethylolpropane (0.24 mole as trimethylolpropane) was added, and the mixture was further reacted for 6 hours to prepare a terminal isocyanate prepolymer. Glycidol 63. in which 20 g (0.13 mol) of sodium salicylate was dissolved in this polymer solution.
4 g (0.86 mol) was added and reacted at 40 ° C. for 15 hours to obtain a sample (D).

Polyurethane Synthesis Example 3 Using the same equipment as in Synthesis Example 1, methyl ethyl ketone 50
0 g, 208.8 g of 2,4-TDI (1.2 mol),
After 225 g (0.9 mol) of MDI and 750 g (1.25 mol) of polybutylene adipate having a molecular weight of 600 were charged and reacted at 80 ° C. for 2 hours, 320 g of a 10% methylethylketone solution of trimethylolpropane (0.3% as trimethylolpropane). 24 mol) was added and the reaction was further continued for 6 hours to prepare a terminal isocyanate prepolymer. 228.2 g (1.0 mol) of glycerol diglycidyl ether was added to this polymer solution, and the mixture was added at 40 ° C. for 15
The reaction was carried out for a time to obtain a polyurethane resin having terminal epoxy groups. Dimethyl stearylamine 11 was added to this polymer solution.
After adding 0 g and 25 g of acetic acid and reacting at 60 ° C. for 20 hours, reprecipitation and purification were performed in methanol to obtain a sample (E).

Polyurethane Synthesis Example 4 Using the same apparatus as in Synthesis Example 1, 300 parts of methyl ethyl ketone was added.
0 g, 73.1 g of hexamethylene diisocyanate
(0.435 mol), molecular weight 3600 poly (1,4-
Butylene / ethylene / bisphenol A) / (adipic acid / 5-sodium sulfoisophthalate ester 900
g (0.25 mol) and 800 g of polyethylene (isophthalic acid / sebacic acid) ester having a molecular weight of 3200
(0.25 mol) was charged and reacted at 80 ° C. for 8 hours,
A sample (F) was obtained. The composition of the obtained sample is as shown in Table 1.

[0034]

[Table 1]

Note * 1 Molar ratio of high molecular weight polyol and low molecular weight polyol in prepolymer synthesis reaction. "High only" refers to the high molecular weight polyol alone. * 2 The content of hydrophilic groups is S for sulfonate groups.
It was determined as O ₃ ⁻ , COO ^{− in} the case of a carboxylate group, and N ^{+ in} the case of a quaternary ammonium salt group. * 3 Sample (F) does not have a terminal epoxy group, but has two terminal hydroxyl groups.

Vinyl Chloride Copolymer Synthesis Example 1 A polymerization vessel was charged with 200 parts of deionized water, 1 part of sodium lauryl sulfate, 1 part of potassium hydrogen carbonate and 6 parts of potassium persulfate, and after degassing, allyl glycidiether. 30 parts and 70 parts of vinyl chloride were charged and the temperature was raised to 60 ° C. to start polymerization. When the internal pressure of the polymerization vessel dropped to 3.5 kg / m ² G, unreacted vinyl chloride was recovered, and a polyaluminum chloride aqueous solution was added to the polymerization solution to solidify the polymer particles.
Recovered. The recovered polymer was thoroughly washed with warm water, dehydrated and dried to obtain a sample (a).

Vinyl chloride copolymer synthesis example 2 In a degassed polymerization vessel, 50 parts of vinyl chloride, 2 parts of monobutyl maleate, 20 parts of vinyl acetate, 3 parts of vinylcyclohexene monooxide, 2.5 parts of trictalethylene, Charge 1 part of sodium hydrogen carbonate, 150 parts of deionized water, 2 parts of azobisisobutyronitrile, 1 part of polyoxyethylene stearyl ether, 0.2 part of methyl cellulose,
Polymerization was started at 60 ° C., and 25 parts of vinyl chloride was continuously injected into the polymerization vessel for 7 hours from the third hour after the initiation of polymerization, and when the internal pressure of the polymerization vessel reached 4 kg / m ² G, The reaction vinyl chloride was recovered, dehydrated, washed with deionized water and dried to obtain a sample (a).

Vinyl Chloride Copolymer Synthesis Example 3 In a polymerization vessel, 21 parts of allyl glycidyl ether, 3 parts of sodium lauryl sulfate, 2 parts of t-butyl hydroperoxide, 1 part of sodium sulfite and 1.
5 parts and 300 parts of deionized water were charged, and after degassing, 79 parts of vinyl chloride were charged and the polymerization was started at 55 ° C. When the internal pressure of the polymerization vessel reached 3 kg / m ² G, unreacted vinyl chloride was recovered, charged with 30 parts of dipotassium hydrogen phosphate, 15 parts of tetrabutylammonium chloride, and 30 parts of ethylene glycol dimethyl ether, and heated at 6 ° C at 70 ° C.
After stirring and mixing for a time, it solidified. The recovered polymer was thoroughly washed with warm water, dehydrated and dried to obtain a sample (c).

Vinyl Chloride Copolymer Synthesis Example 4 In a polymerization vessel, 35 parts of allyl glycidyl ether, 3 parts of sodium lauryl sulfate, 2 parts of t-butyl hydroperoxide, 1 part of sodium sulfite and 1.
5 parts and 300 parts of deionized water were charged, and after deaeration, 65 parts of vinyl chloride were charged and the polymerization was started at 55 ° C. When the internal pressure of the polymerization vessel reached 6 kg / m ² G, 2 parts of dimethylstearylamine was press-fitted, the temperature was raised to 70 ° C. and the reaction was carried out for 6 hours. Then, unreacted vinyl chloride was recovered and an aqueous polyaluminum chloride solution was added. Was added to solidify. The recovered polymer was thoroughly washed with warm water, dehydrated and dried to obtain a sample (D). The composition of these samples was compared with the commercially available resins MR-110 and VAGH which were conventionally used as binders.
The results are shown in Table 2 together with (sample names are (e) and (f), respectively).

[0040]

[Table 2]

Note MR-110 manufactured by Nippon Zeon Co., Ltd., vinyl chloride copolymer containing -SO ₄ K group, epoxy group and hydroxyl group VAGH Union Carbide Co., vinyl chloride-
Vinyl acetate-vinyl alcohol copolymer

Using these samples, magnetic paints were prepared by the following method. Example of preparation of magnetic paint 100 parts of ferromagnetic metal powder (Hc: 1640 oersted, σs: 122 emu / g, specific surface area 60 m ² /
g), a mixture of 12 parts of a vinyl chloride copolymer shown in Table 3, 8 parts of a polyurethane resin and 16 parts of a mixed solvent having the composition shown in Table 3 is kneaded in a pressure kneader for 60 minutes, and then the same mixed solvent composition is obtained. After diluting to a solid content concentration of 70% in a kneader, 100 parts of the same mixed solvent is added and subjected to high speed shear dispersion for 3 hours, then 78 parts of the same mixed solvent is added and dispersed for 1 hour,
Further, 20 parts of a mixed solvent was added and dispersed for 10 minutes to obtain a magnetic paint.

[0043]

[Table 3]

Note: Unit is weight%

Examples 1 to 7 and Comparative Examples 1 to 6 The resins thus synthesized, the magnetic coatings prepared and the magnetic tapes produced using them were evaluated by the following methods. The results are shown in Table 4.

[0046]

[Table 4]

1) Glossiness The magnetic coating material obtained by the above method was coated on a polyester film, subjected to magnetic field orientation treatment, and dried. The magnetic coating film is set to 60 ° using a gloss meter specified in JIS K5400.
The reflectance at the reflection angle was measured. The surface of glass having a refractive index of 1.567 is used as a reference surface, and the glossiness is 100%. The higher the reflectance, the more uniformly the magnetic powder is dispersed. However, the value changes depending on the particle size of the magnetic powder. 2) Dispersion stability The paint used for gloss evaluation was allowed to stand for 3 days, then coated on a polyester film, subjected to magnetic field orientation treatment and dried, and the magnetic coating film was measured at a 60 ° reflection angle using a gloss meter. Was measured. If the magnetic powder aggregates after standing for 3 days, the value will decrease. 3) Solvent Separation The paint used for gloss evaluation was placed in a 100 ml graduated cylinder and allowed to stand for 3 days, and then the amount of the supernatant solvent layer was measured. A paint with little separation is good. A: d = 0 ml B: 0 <d ≦ 2 ml C: 2 <d ≦ 10 ml D: 10 <d ≦ 20 ml (d is the amount of the supernatant) 4) Magnetic properties The magnetic coating used for gloss evaluation was 6 mm × It was cut into 6 mm, and the saturation magnetic flux density (Bm) and the squareness ratio (RS) were measured by a magnetic property measuring machine (VSM).

When the polyurethane according to the present invention and the vinyl chloride polymer are used as a binder, the intrinsic viscosity of the polymer is 0.13 to 0.19, even though they have a low molecular weight as a polymer.
By selecting a solvent system that gives 0.45 dl / g, a magnetic paint with good stability in which the solvent hardly separates can be obtained, and the magnetic tape made using this has a good surface gloss and saturation magnetic flux. It was excellent in density and squareness ratio (Examples 1 to 7). However, if a solvent system having a small intrinsic viscosity is used, an unstable magnetic coating composition in which magnetic powder easily aggregates is obtained (Comparative Example 1 and Example 1, Comparative Example 2 and Example 2, Comparative Example 3 and Example 6). Contrast). Even if the same vinyl chloride copolymer and the same solvent system are used, the dispersion stability of the magnetic coating material and the magnetic properties of the tape can be judged to be good or bad depending on whether or not the polyurethane resin satisfies the requirements of the present invention. Comparison between Example 1 and Comparative Example 4 and Example 7 and Comparative Example 5). Also, using the same polyurethane resin and the same solvent that meet the same requirements,
Depending on whether or not the vinyl chloride-based copolymer satisfies the requirements of the present invention, the surface gloss and magnetic properties of the tape will be different (comparison between Example 7 and Comparative Example 6).

[0049]

As described above, according to the present invention, a magnetic paint in which fine magnetic powder is stably dispersed can be obtained. The magnetic coating material of the present invention can provide a magnetic recording medium having excellent magnetic properties, durability and running properties.

Claims (2)

[Claims] 1. A 1 and average 2.2 to 7.0 pieces of (a) terminal epoxy group in the molecule, a (b) sulfonate SO ₃ ^-
0.1 to 5.0% by weight as a COO
A polyurethane resin having a number average molecular weight of 2,000 to 10,000, having 0.05 to 3.0% by weight as ⁻ or 0.02 to 1.0% by weight as a quaternary ammonium salt group as N ⁺ , A vinyl chloride-based copolymer having an epoxy group of 0.1 to 20% by weight and an average degree of polymerization of 100 to 330 is used as a binder for the magnetic powder, and the solution of the binder has an intrinsic viscosity of 0.13 to 0.45 dl. A magnetic coating material characterized by using a solvent having an amount of / g. 2. An anionic hydrophilic group selected from the group consisting of a carboxyl group and an acid containing sulfur or phosphorus and salts thereof, or --N ⁺ R ¹
The magnetic coating composition according to claim 1, which has at least one cationic hydrophilic group selected from R ² R ³ X ⁻ and —NR ¹ R ² · HX ¹ . However, R ¹ , R ² and R ³ represent an alkyl group, an alkenyl group or an alkoxy group, and X and X ¹ are an inorganic acid residue such as halogen, sulfuric acid, phosphoric acid or nitric acid, or a carboxylic acid, an acidic sulfuric acid ester or Represents an organic acid residue such as acidic phosphoric acid ester.