JP2576101B2 - Magnetic recording media - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a magnetic recording medium such as a magnetic tape, and more particularly, to a binder contained in a magnetic layer formed on a non-magnetic support. It is related to the improvement of.

[Summary of the Invention]

The present invention introduces a —COOM group (where M represents a hydrogen atom or an alkali metal atom) and a quaternary ammonium salt into the molecule of a polyurethane resin used as a binder of a coating type magnetic recording medium. By providing a binder that has excellent properties in terms of dispersibility in magnetic powder, properties of the coating film when formed as a magnetic layer, workability in forming a coating film, surface properties and durability It is an object of the present invention to provide a magnetic recording medium which is excellent in magnetic characteristics and electromagnetic conversion characteristics.

[Prior Art] In recent years, magnetic recording media, especially magnetic recording media for VTRs (Video Tape Recorders), have been developed to have high magnetic characteristics and electromagnetic characteristics so that high reproduction output can be obtained even when short-wavelength recording is performed. There is a demand for improved conversion characteristics. As a countermeasure, the fineness of the magnetic powder is increased and the magnetic force is increased, and the packing density of the magnetic powder in the magnetic layer, that is, the so-called packing density, tends to increase.

On the other hand, as a binder for a magnetic recording medium conventionally used, a binder mainly composed of a vinyl chloride-vinyl acetate copolymer or a polyurethane resin can be mentioned. Various problems have occurred with these binders in response to demands for improved properties and the like, and it is currently difficult to adequately address them.

For example, with the increase in specific surface area due to micronization of magnetic powder and the increase in cohesive force due to high magnetizing force, satisfactory dispersibility and surface properties cannot be obtained with the above-mentioned binder, and the packing density of magnetic powder increases. It is also difficult. Therefore, the durability, the magnetic characteristics, and the electromagnetic conversion characteristics are also insufficient. In particular, the performance with respect to a magnetic powder that has been made into ultrafine particles or a magnetic powder having a high magnetization amount in order to cope with an increase in recording density has been insufficient. In this case, for example, a method of using a surfactant as a dispersant is conceivable. However, since the surfactant is a low molecule, blooming or the like due to powder falling or aging changes occurs, and mechanical strength and durability are increased. Etc. will cause problems.

Therefore, for example, Japanese Patent Publication No. 58-41565 discloses a binder in which a sulfonic acid metal base is introduced into a polyurethane resin, and attempts have been made to improve the dispersibility of the magnetic powder. For example, when a magnetic recording medium is used, powder fall occurs, and there is still a point to be improved in terms of durability.

[Problems to be solved by the invention]

Thus, the binders containing vinyl chloride copolymers and polyurethane resins, which are widely used in the past, as well as the binders containing metal sulfonate groups, have problems such as dispersibility in magnetic powders, physical properties of coatings, and handling in manufacturing. There are many points to be solved in terms of the point, and it has been difficult to secure predetermined durability, magnetic characteristics, and electromagnetic conversion characteristics.

Therefore, the present invention has been proposed to solve the above-mentioned drawbacks in the technical field, and has been proposed to disperse magnetic powder, properties of a coating film formed as a magnetic layer, and workability in forming a coating film. It is an object of the present invention to provide a binder having excellent characteristics in such points as to provide a magnetic recording medium having excellent surface properties and durability, and excellent magnetic characteristics and electromagnetic conversion characteristics.

[Means for solving the problem]

The present inventors show that by introducing a carboxylic acid and its metal base to the side chain as a polar group, exhibit high affinity for magnetic powder and improve dispersibility, dripping is greatly improved, Further, the present invention has been completed by paying attention to the fact that the introduction of a quaternary ammonium salt as a magnetic group into the side chain is effective in improving workability. In a magnetic recording medium having a magnetic layer mainly composed of a ferromagnetic powder and a binder formed thereon,
The binder has a —COOM group in the molecule (where M represents a hydrogen atom or an alkali metal atom). (Wherein, R ₁ , R ₂ , and R ₃ each represent an alkyl group having 1 to 6 carbon atoms).

The polyurethane resin used in the present invention has excellent coating strength and is obtained by a reaction between a polyhydroxy compound and a polyisocyanate. The polyhydroxy compound and polyisocyanate which are the main components of the resin have a molecular weight of It is preferred to use about 500-5000 long-chain diols and short-chain diols with a molecular weight of about 50-500, organic diisocyanates.

The long-chain diol is, for example, polyester diol,
It is roughly classified into polyether diol and polyether ester glycol. As polyester diol,
Specifically, for example, succinic acid, adipic acid, sebacic acid,
Aliphatic dicarboxylic acids such as azelaic acid, terephthalic acid,
An aromatic dicarboxylic acid such as isophthalic acid or a lower alcohol ester thereof, and ethylene glycol 1,3-propylene glycol, 1,4-butylene glycol, 1,6-
Lactones obtained by ring-opening polymerization of lactones such as polyester diols or ε-caprolactone obtained by reacting hexane glycol, diethylene glycol, neopentyl glycol, or an ethylene oxide adduct of bisphenol A or a mixture thereof, or the like. And polyester diols. Examples of the polyether diol include polyethylene glycol, polypropylene ether glycol, polytetramethylene ether glycols, and copolymerized polyether glycols thereof. Examples of the polyetherester glycol include polyester glycols obtained by reacting the above polyalkylene ether glycol as a polyol component with an aliphatic or aromatic dicarboxylic acid. If the molecular weight of this long-chain diol is too small, the resulting polyurethane resin will have too high a urethane group concentration, resulting in poor flexibility of the resin, and poor solubility in solvents, and will be used as a binder for magnetic recording media. It is not so good. When the molecular weight of the long-chain diol is too large, the content of the long-chain diol in the resin becomes too large and the urethane group concentration becomes relatively small, so that the abrasion resistance and heat resistance of the resin decrease. I do.

The short-chain diol is, for example, ethylene glycol, propylene glycol, 1,4-butylene glycol, 1,6-
There are aliphatic glycols such as hexane glycol and neopentyl glycol, and aromatic diols such as ethylene oxide adduct or propion oxide adduct of bisphenol A and ethylene oxide adduct of hydroquinone. These may be used alone depending on the properties of the polyurethane resin. Alternatively, they can be mixed and used in various quantitative ratios.

Further, glycerin, ethylene oxide adduct of glycerin, 2-methylpropane-1,2,3-triol,
4- [bis (2-hydroxyethyl)]-2-hydroxypentane, 3-methylpentane-1,3,5-triol, 1,2,6-hexanetriol, 1-bis (2-hydroxyethyl) amino- Triols such as propylene oxide adduct of 2-propanol and diethanolamine can also be used in combination.

As the organic diisocyanate, an aliphatic diisocyanate such as tetramethylene diisocyanate, hexamethylene diisocyanate, m-phenylene diisocyanate, p-phenylene diisocyanate, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, diphenylmethane diisocyanate, 3,3-dimethoxy-4,4'-biphenylene diisocyanate, 3,3'-
Dimethyl-4,4'-biphenylene diisocyanate, 4,
Aromatic diisocyanates such as 4'-diisocyanate diphenyl ether, 1,5-naphthalenediisocyanate, 2,4-naphthalenediisocyanate, 1,3-diisocyanatomethylcyclohexane, 1,4-diisocyanate Examples include alicyclic diisocyanates such as methylcyclohexane, 4,4'-diisocyanatodicyclohexylmethane, and isophorone diisocyanate.

The reaction method employed in the production of the polyurethane resin includes melt polymerization to be carried out in a molten state, and dissolving the above-described raw materials in an inert solvent such as ethyl acetate, methyl ethyl ketone, acetone, toluene or the like alone or in a mixed solvent. Solution polymerization is performed, but solution polymerization is preferred for the production of polyurethane resins that are often dissolved and used in a solvent such as a binder for magnetic recording media. It is more preferable to perform the solution polymerization by adding the above inert solvent before performing the extension reaction.

At the time of the reaction, an organometallic compound such as stannous octylate or an organic tin compound such as dibutyltin dilaurate, or a tertiary amine such as N-methylmorpholine or triethylamine may be added as a catalyst. Also, to increase the stability of the product, antioxidants, UV absorbers,
A hydrolysis inhibitor or the like may be added in an amount of about 5% or less based on the solid content.

Further, a -COOM group (where M represents a hydrogen atom or an alkali metal atom) and a quaternary ammonium salt are introduced into the polyurethane resin as a hydrophilic polar group. Here, the -COOM group is very effective in improving the dispersibility of the magnetic powder, and the effect of reducing powder dropout is particularly large when used as a magnetic recording medium. In this case, the particle size becomes very large and the practicability is lacking. Therefore, a quaternary ammonium salt is used in combination.

According to the experiments of the present inventors, by using a polyurethane resin having a -COOM group in a molecule and having a quaternary ammonium salt, a good particle size without impairing the powder drop reduction effect of the -COOM group. Paints with properties can be obtained,
-It was found that a magnetic recording medium having more excellent dispersibility than in the case of containing only the -COOM group can be obtained.

Incidentally, the following method may be used to introduce these -COOM groups and quaternary ammonium salts into the polyurethane resin.

(1) A method in which the -COOM group or the quaternary ammonium salt is introduced in advance into a part of diisocyanate or polyol which is a raw material of polyurethane.

(2) An OH group is allowed to remain at the terminal or side chain of the polyurethane resin, and the OH group is added to the -COOM group-containing compound and the fourth group.
A method of modifying with a compound containing a quaternary ammonium salt.

The —COOM group or the fourth group used in the method (1) above;
Examples of the diisocyanate or polyol having a quaternary ammonium salt introduced as a hydrophilic polar group include a diol containing a -COOM group, a diol containing a quaternary ammonium salt, and -COOM.
Group-containing organic diisocyanates and quaternary ammonium salt-containing organic diisocyanates are exemplified. These compounds polymerize with other raw materials to form a part of the polymer molecular chain of the polyurethane resin, and as a result, a hydrophilic polar group is introduced into the polyurethane resin.

Examples of -COOM group-containing diols include dimethylolpropionic acid and compounds obtained by neutralizing these -COOH groups with a NaOH methanol solution, a KOH methanol solution, or the like. By synthesizing a polyurethane resin using the compound as a chain extender, a -COOM group is introduced into the molecule.

The quaternary ammonium salt-containing diol is obtained by reacting a carboxylic acid component having no quaternary ammonium salt, a glycol component, and a dicarboxylic acid component having a quaternary ammonium salt.

Examples of the carboxylic acid component having no quaternary ammonium salt include aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, orthophthalic acid and 1,5-naphthalic acid, p-oxybenzoic acid, and p- (hydroxyethoxy) benzoic acid. Aromatic oxycarboxylic acids such as acids, aliphatic dicarboxylic acids such as succinic acid, adipic acid, azelaic acid, sebacic acid and dodecanedicarboxylic acid; tri- and tetracarboxylic acids such as trimellitic acid, trimesic acid, and pyromellitic acid; No.

As the glycol component, ethylene glycol,
Propylene glycol, 1,3-propanediol, 1,4-
Butanediol, 1,5-pentanediol, 1,6-hexanediol, neopentyl glycol, diethylene glycol, dipropylene glycol, 2,2,4-trimethyl-1,3-pentanediol, 1,4-cyclohexanedimethanol, Examples thereof include an ethylene oxide adduct and a propylene oxide adduct of bisphenol A, polyethylene glycol, polypropylene glycol, polytetramethylene glycol, and the like. Further, tri- and tetraols such as trimethylolethane, trimethylolpropane, glycerin and pentaerythritol may be used in combination.

Examples of the dicarboxylic acid component having the quaternary ammonium salt include those shown below.

(However, R ₁ , R ₂ , and R ₃ each represent an alkyl group having 1 to 6 carbon atoms.) Therefore, a polyurethane resin is obtained by replacing a part of the long-chain diol with the quaternary ammonium salt-containing diol. Is synthesized to introduce a quaternary ammonium salt into the molecule.

In addition, the above-mentioned organic diisocyanate containing -COOM group and
The quaternary ammonium salt-containing diisocyanate can be added to a tri- or higher functional polyisocyanate compound by adding a -COOM group or a quaternary
It can be obtained by reacting a compound having a quaternary ammonium salt.

As the polyisocyanate compound, trifunctional trade names such as Desmodur L (manufactured by Bayer) and Coronate L (manufactured by Nippon Polyurethane) are known.
Generally, a polyfunctional polyisocyanate compound is obtained by performing an addition reaction between a polyol and a diisocyanate.

Examples of the polyol include propylene glycol, glycerol, trimethylolpropane, pentaerythritol, sorbitol and the like. Examples of the diisocyanate include tolylene diisocyanate, 4,4-diphenylmethane diisocyanate, naphthylene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, xylene diisocyanate, and lysine diisocyanate. Can be

-COOM to the trifunctional or higher polyisocyanate compound
To introduce a group, one molecule has a -COOM group, and-
A compound having active hydrogen capable of reacting with an NCO group may be reacted with a tri- or higher functional polyisocyanate compound. Thus, two or more -NCs in one molecule
A compound having an O group and having a -COOM group (an organic diisocyanate containing a -COOM group) is obtained.

Examples of the compound having a -COOM group in one molecule and having an active hydrogen capable of reacting with the -NCO group include the following.

These compounds undergo an addition reaction with a tri- or higher functional polyisocyanate compound, for example, as shown in the following reaction formula.

(In the reaction formula, R-NCO represents a tri- or higher functional polyisocyanate compound.) In order to introduce a quaternary ammonium salt, a quaternary ammonium salt is contained in one molecule, and -NCO group is added. A compound having an active hydrogen capable of reacting with the polyisocyanate may be reacted with a polyisocyanate compound having three or more functional groups. Thus, a compound having two or more —NCO groups in one molecule and having a quaternary ammonium salt (a quaternary ammonium salt-containing organic diisocyanate) is obtained.

A quaternary ammonium salt in one molecule, and
Examples of the compound having an active hydrogen capable of reacting with the NCO group include the following.

[(CH ₃ ) ₃ N ⁺ CH ₂ CH ₂ OH)] X ^- [(CH ₃ ) ₃ N ⁺ CH ₂ CH ₂ OOCNH ₂ )] X ^- [(CH ₃ ) ₃ N ⁺ CH ₂ CH (CH ₃ ) OH] ^{_{X - H 2 NC 6 H 4}} N - (CH 3) 3 X - · HCl ^{_{[HOCH 2 CH 2 N + (C}} 2 H 5) 3 ] X ^- (where, X represents a Cl, Br or I These compounds are subjected to an addition reaction with a tri- or higher functional polyisocyanate compound, for example, as shown in the following reaction formula.

R-NCO + ^{_{[(CH 3) 3 N + CH}} 2 CH 2 OH) ] ^{X - → R-NHCOO-CH} 2 CH 2 N + (CH 3) 3 X - ...... (iii) ( in the reaction formulas, R -NCO represents a tri- or higher functional polyisocyanate compound.) On the other hand, the method (2) is based on the OH group present at the terminal or side chain of the polyurethane resin which has been chain-extended to a predetermined molecular weight by a polymerization reaction. , -COOM group or a compound having a quaternary ammonium salt.
In this case, a compound having an OH group and a -COOM group, or a compound having an OH group and a quaternary ammonium salt is synthesized, and is reacted with the diisocyanate compound in an equimolar manner. Group or a quaternary ammonium salt, and the remaining -NCO group and -OH of the polyurethane resin are introduced.
When reacted with a group, a polyurethane resin into which a -COOM group or a quaternary ammonium salt is introduced is obtained. The reaction equation is as follows.

(2-1) OCN-R-NCO + HOCH 2 COOM → OCN-R-NCOOCH 2 COOM R PU -OH + OCN-R-NCOOCH 2 COOM → R PU -OCONH-R-NCOOCH 2 COOM ( In the formula R is a divalent Represents a hydrocarbon group, and R _PU represents a polyurethane resin.) (Wherein, R and R ′ represent a divalent hydrocarbon group, R ″ represents a monovalent hydrocarbon group such as an alkyl group, and R _PU represents a polyurethane resin.) As described above, the —COOM group And each of the quaternary ammonium salts can be introduced into the polyurethane resin.

The magnetic recording medium according to the present invention is obtained by introducing a quaternary ammonium salt together with a -COOM group into a polyurethane resin used as a binder for a magnetic paint. Therefore, the introduction of two types of hydrophilic polar groups consisting of a -COOM group and a quaternary ammonium salt may be carried out as follows.

(I) A compound having a -COOM group and a compound having a quaternary ammonium salt are contained in a raw material of the polyurethane resin, and these -COOM groups,
A method of introducing a quaternary ammonium salt.

(II) A method in which a —COOM group and a quaternary ammonium salt are introduced by modifying a —OH group present on the side chain or terminal of the already synthesized polyurethane resin.

(III) A method in which a compound having a -COOM group is contained in the raw material of the polyurethane resin, whereby the terminal or side chain OH group of the -COOM group-containing polyurethane resin is modified to introduce a quaternary ammonium salt.

(IV) The raw material of the polyurethane resin contains a compound having a quaternary ammonium salt, and the terminal or side chain OH group of the resulting quaternary ammonium salt-containing polyurethane resin is modified to form a -COOM group. How to introduce.

For example, in the case of the method (I), a long-chain polyester diol containing a quaternary ammonium salt is used as a part of the long-chain diol, and a short-chain diol containing a -COOM group (for example, dimethylolpropionic acid) is used. A polyurethane resin may be synthesized by using it as a chain extender.

In the case of the method (II), a -COOM group is first introduced into a part of the -OH group existing on the side chain or terminal of the already synthesized polyurethane resin, and then a second -OH group is introduced into the remaining -OH group. What is necessary is just to introduce a quaternary ammonium salt.

The -COOM group and the quaternary ammonium salt can be easily introduced into the polyurethane resin by the method described above.

The amount of the hydrophilic polar group introduced into the polyurethane resin used as the binder is preferably the sum of the -COOM group and the quaternary ammonium salt is 0.01 to 1.0 mmol / g, more preferably 0.01 to 1.0 mmol / g. It is in the range of 0.5 mmol / g.
Here, the introduction amount of the -COOM group is 0.01 to 0.5 mmol / g, and the introduction amount of the quaternary ammonium salt is 0.001 mmol / g or more. When the introduction amount of the hydrophilic polar group is less than 0.01 mmol / g, a sufficient effect on the dispersibility of the ferromagnetic powder is not recognized, and when the introduction amount of the hydrophilic polar group exceeds 1.0 mmol / g, Not only does intermolecular or intramolecular aggregation tend to occur, which adversely affects the dispersibility, but also causes selectivity to the solvent, making it impossible to use a general-purpose solvent.

The polyurethane resin according to the present invention preferably has a number average molecular weight of 10,000 to 100,000, more preferably 10,000 to 60,000. When the number average molecular weight is less than 10,000, the coating film forming ability of the resin becomes insufficient, and when the number average molecular weight exceeds 60,000, the paint is mixed, transferred,
There is a possibility that a problem may occur in a process such as coating.

The polyurethane resin according to the present invention is other thermoplastic resin,
It can be used in combination with a thermosetting resin or a reactive resin.

As the thermoplastic resin, the softening temperature is 150 ° C. or less,
It has an average molecular weight of 10,000 to 200,000 and a degree of polymerization of about 200 to 20,000. For example, a vinyl chloride-vinyl acetate copolymer,
Vinyl chloride-vinyl acetate-vinyl alcohol copolymer,
Vinyl chloride-vinyl acetate-maleic acid copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, acrylate-acrylonitrile copolymer, acrylate-vinylidene chloride copolymer, methacrylic acid Ester-vinylidene chloride copolymer, methacrylic ester-styrene copolymer, thermoplastic polyurethane resin, polyvinyl fluoride, vinylidene chloride-acrylonitrile copolymer, butadiene-acrylonitrile copolymer, acrylonitrile-butadiene-methacrylic acid copolymer , Polyamide resin, polyvinyl butyral, cellulose derivative, styrene-butadiene copolymer, polyester resin polybutadiene, and other synthetic rubber resins. Examples of the thermosetting resin or the reactive resin include, for example, phenol resin, epoxy resin, thermosetting polyurethane resin, urea resin, melamine resin, alkyd resin, urea-formaldehyde resin silicon resin, acrylic reaction resin, epoxy-polyamide Resin, nitrocellulose-melamine resin, mixture of high molecular polyester resin and isocyanate prepolymer, mixture of polyester polyol and polyisocyanate, urea formaldehyde resin, mixture of low molecular weight glycol / high molecular weight diol / triphenylmethane triisocyanate, Examples thereof include polyamine resins and mixtures thereof. Of these, it is desirable to use in combination with one having good dispersibility in ferromagnetic powder.

In the magnetic recording medium of the present invention, the magnetic layer is formed, for example, by applying a magnetic paint prepared by dispersing a ferromagnetic powder in the above-mentioned binder and dissolving it in an organic solvent to the surface of the non-magnetic support.

Here, as the ferromagnetic powder used in the present invention, any ordinary magnetic powder can be used.
Therefore, usable ferromagnetic powders include ferromagnetic iron oxide particles, ferromagnetic chromium dioxide, ferromagnetic alloy powder, hexagonal barium ferrite fine particles, iron nitride and the like.

When the ferromagnetic iron oxide particles are represented by the general formula FeOx, those having a value of X in the range of 1.33 ≦ X ≦ 1.50, that is, maghemite (γ-Fe ₂ O ₃ , X = 1.50), magnetite (F
e ₃ O ₄ , X = 1.33) and their solid solutions (FeOx, 1.33 <X <
1.50). Further, cobalt may be added to these ferromagnetic iron oxides for the purpose of increasing coercive force. Cobalt-containing iron oxides are roughly classified into two types: a doped type and an adhered type.

Examples of the ferromagnetic chromium dioxide include CrO ₂ or Ru, Sn, Te, Sb, Fe, Ti, V, Mn for the purpose of improving coercive force.
And the like can be used.

As ferromagnetic alloy powders, Fe, Co, Ni, Fe-Co, Fe-Ni, F
e-Co-Ni, Co-Ni, Fe-Co-B, Fe-Co-Cr-B, Mn-Bi, Mn
-Al, Fe-Co-V or the like can be used, and a metal component such as Al, Si, Ti, Cr, Mn, Cu, Zn or the like may be added thereto for the purpose of improving various characteristics.

Further, in addition to the binder and the ferromagnetic powder, a dispersant, a lubricant, an abrasive, an antistatic agent, a rust inhibitor, and the like may be added to the magnetic layer.

Examples of the dispersant (pigment wetting agent) include caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid,
Fatty acids having 12 to 18 carbon atoms (R ₇ COOH, R ₇ is an alkyl or alkenyl group having 11 to 17 carbon atoms) such as stearic acid, oleic acid, elaidic acid, linoleic acid, linolenic acid, and stearolic acid; Fatty acid alkali metals (Li, Na,
K) or an alkaline earth metal (Mg, Ca, Ba) metal soap, amides of the above-mentioned fatty acids, polyalkylene oxide alkyl phosphates, trialkyl polyolefin oxyquaternary ammonium salts (alkyl has 1 to 1 carbon atoms)
5, olefins such as ethylene and propylene) are used. In addition, higher alcohols having 12 or more carbon atoms, sulfates, and the like can also be used. These dispersants are added in the range of 0.5 to 20 parts by weight based on 100 parts by weight of the binder.

Examples of the lubricant include dialkyl polysiloxane (alkyl has 1 to 5 carbon atoms), dialkoxy polysiloxane (alkoxy has 1 to 4 carbon atoms), monoalkyl monoalkoxy polysiloxane (alkyl has 1 to 5 carbon atoms).
Silicon, oil such as phenylpolysiloxane, fluoroalkylpolysiloxane (alkyl has 1 to 5 carbons), conductive fine powder such as graphite, molybdenum disulfide, tungsten disulfide Inorganic fine powders such as polyethylene, polypropylene, polyethylene vinyl chloride copolymer, plastic fine powders such as polytetrafluoroethylene, α-olefin polymer,
Unsaturated aliphatic hydrocarbons that are liquid at room temperature (compounds in which an n-olefin double bond is bonded to a terminal carbon, having about 20 carbon atoms),
Fatty acid esters composed of fatty acids having 12 to 22 carbon atoms and alcohols having 3 to 22 carbon atoms (which may be any of monoesters, diesters, and triesters, and may be polyfunctional polyesters of higher molecular weight), fatty acids, or Metal salts, fatty acid amides, fatty acid alcohols or alkoxides thereof, aliphatic amines, polyhydric alcohols, sorbitan esters, mannittan esters, sulfurized fatty acids, aliphatic mercaptans, perfluoroalkylethylene oxides, perfluoropolyethers, higher alkyl sulfones Acids or metal salts thereof, perfluoroalkylsulfonic acids or ammonium salts or metal salts thereof, perfluoroalkylcarboxylic acids or metal salts thereof, fluorocarbons and the like can be used. These lubricants are binders
It is added in the range of 0.2 to 20 parts by weight based on 100 parts by weight.

Examples of the abrasive include commonly used materials such as fused alumina, silicon carbide, chromium oxide (Cr ₂ O ₃ ), corundum, artificial corundum, diamond, artificial diamond, garnet, and emery (main components: corundum and magnetite). Is used. These abrasives have a Mohs hardness of 5
As described above, those having an average particle diameter of 0.05 to 5 μm are used, and particularly preferably 0.1 to 2 μm. These abrasives are added in the range of 0.5 to 20 parts by weight based on 100 parts by weight of the binder.

Examples of the antistatic agent include conductive fine powders such as carbon black and carbon black graft polymer, natural surfactants such as saponin, nonionic surfactants such as alkylene oxide, glycerin and glycidol, higher alkylamines, Cationic surfactants such as quaternary ammonium salts, pyridine and other heterocycles, and phosphoniums; anionic surfactants containing acidic groups such as carboxylic acids, sulfonic acids, phosphoric acids, sulfate groups, and phosphate groups; Ampholytic agents such as amino acids, aminosulfonic acids, and sulfuric acid or phosphoric acid esters of amino alcohol are used. The conductive fine powder is in the range of 0.2 to 20 parts by weight based on 100 parts by weight of the binder, and the surfactant is 0.1 to 10 parts by weight.
It is added in the range of parts by weight. These surfactants may be added alone or as a mixture. These are used as antistatic agents, but are sometimes applied for other purposes such as dispersion, improvement of magnetic properties, improvement of lubricity, and application aids.

As the rust preventive, phosphoric acid, sulfamide, guanidine, pyridine, amine, urea, zinc chromate, calcium chromate, strontium chromate, etc. can be used. Vaporizable rust inhibitors such as phosphate, cyclohexyl ammonium carbonate, hexamethylene diamine carbonate, propylene diamine stearate, guanidine carbonate, triethanolamine nitrite, morpholine stearate (inorganic acid salts such as amine, amide or imide or organic acids) When salt is used, the rust prevention effect is improved. These rust inhibitors are used in the range of 0.01 to 20 parts by weight based on 100 parts by weight of the ferromagnetic fine powder.

The constituent material of the magnetic layer described above is prepared as a magnetic paint by dissolving it in an organic solvent, and applied on a non-magnetic support. As a solvent for the magnetic paint, acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone and the like are used. Ketones, esters such as methyl acetate, ethyl acetate, butyl acetate, ethyl lactate, and glycol monoethyl ether; glycol ethers such as glycol dimethyl ether, glycol monoethyl ether, and dioxane; and aromatic carbonization such as benzene, toluene, and xylene Examples include hydrogen, aliphatic hydrocarbons such as hexane and heptane, and chlorinated hydrocarbons such as methylene chloride, ethylene chloride, carbon tetrachloride, chloroform, ethylene chlorohydrin, and dichlorobenzene.

The material of the non-magnetic support to which these constituent materials are applied may be any material which is generally used for this type of magnetic recording medium, for example, polyethylene terephthalate, polyethylene-2,6-naphthalate. Polyesters such as polyethylene, polypropylene, etc., cellulose derivatives such as cellulose triacetate, cellulose diacetate, cellulose acetate butyrate, cellulose acetate propionate, vinyl resins such as polyvinyl chloride, polyvinylidene chloride, polycarbonate, Plastics such as polyimide, polyamide, polyamide-imide, etc., non-magnetic metals such as aluminum, copper, tin, zinc or non-magnetic alloys containing them, light alloys such as aluminum alloys and titanium alloys, ceramics, ceramics, Ceramics such as vessels, single crystal silicon, paper, baryta or polyethylene, polypropylene, ethylene - 2 carbon atoms, such as butene copolymer
Papers such as paper coated or laminated with 10 α-polyolefins can be used. The form of these nonmagnetic supports may be any of films, tapes, sheets, disks, cards, drums and the like.

[Action]

As described above, by using a polyurethane resin in which a -COOM group and a quaternary ammonium salt are introduced into the molecule as a binder, the affinity for the magnetic powder is greatly improved, and the magnetic powder or the ultrafine particles can be used. Even if the magnetic powder has a large amount of magnetization, it can be dispersed well and the durability can be improved by the effect of reducing powder dropping of the -COOM group.

In particular, by introducing both a -COOM group and a quaternary ammonium salt, the durability and the viscosity characteristics of the binder can be improved.

〔Example〕

Hereinafter, specific examples of the present invention will be described,
The present invention is not limited to these examples.

First, a polyurethane resin into which a -COOM group and a quaternary ammonium salt were introduced was synthesized by the method described in the present specification. Table 1 shows the characteristics of the synthesized polyurethane resin.

Example 1 Composition of magnetic paint 100 parts by weight of ferromagnetic powder (specific surface area 35 m ² / g, Co-γFe ₂ O ₃ ) 10 parts by weight of vinyl chloride-vinyl acetate copolymer Binder 1 10 parts by weight Lubricant (silicone oil) 0.5 parts by weight Dispersant (lecithin) 0.5 parts by weight Abrasive (Cr ₂ O ₃ ) 2 parts by weight Antistatic agent (carbon) 2 parts by weight Lubricant (butyl stearate) 0.5 parts by weight Methyl ethyl ketone 110 parts by weight Methyl isobutyl ketone 50 Parts by weight Toluene 50 parts by weight The above composition was mixed in a ball mill for 48 hours, filtered, and 3 parts by weight of a curing agent (trade name: Coronate L, manufactured by Nippon Polyurethane Co., Ltd.) was added. This was applied on a 16 μm thick polyethylene terephthalate film so that the film thickness after drying was 6 μm.
Next, after performing a magnetic field orientation treatment, the film was dried and wound up.
After calendering this, it was cut into 1/2 inch width to prepare a sample tape.

Examples 2 to 7 In the composition of Example 1, binder 2 was used instead of binder 1.
A sample tape was prepared in the same manner as in Example 1 except that the binder 7 was used.

Comparative Examples 1 to 6 In the composition of Example 1, a sample tape was prepared in the same manner as in Example 1, except that Binder 8 and Binder 13 were used instead of Binder 1.

With respect to each of the obtained sample tapes, the surface gloss, powder falling, and paint viscosity were measured.

The surface gloss was measured using a gloss meter (GLOSS METER) under the conditions of an incident angle of 60 ° and a reflection angle of 60 °. The powder drop was evaluated by the deduction method (−5 to 0) by visually observing the powder drop to the head drum, the guide and the like after running the shuttle 100 times for 60 minutes. The coating viscosity was a value measured at 30 rotations using a No. 4 rotor with a B-type rotational viscometer.

 Table 2 shows the measurement results.

As is clear from the results in Table 2, each sample tape according to the present invention is not only excellent in surface gloss and powder drop, but also low in paint viscosity and excellent in workability. .

[Effects of the Invention] As is clear from the above description, in the present invention, while introducing a -COOM group into the molecule of the polyurethane resin, a quaternary ammonium salt is further introduced, and this is used as a binder. Therefore, it shows a high affinity for the magnetic powder, and even if it is an ultrafine magnetic powder or a magnetic powder having a large amount of magnetization, the dispersibility becomes good.

Therefore, the properties of the coating film when formed as a magnetic layer are improved, resulting in a porcelain recording medium having extremely excellent durability, surface properties and electromagnetic conversion characteristics.

Further, since the paint containing the binder has a low viscosity and is easy to handle, it has excellent characteristics in terms of workability in forming a coating film.

Claims (1)

(57) [Claims] 1. A magnetic recording medium comprising a magnetic layer mainly composed of ferromagnetic powder and a binder formed on a non-magnetic support, wherein the binder has a —COOM group in the molecule (where M is hydrogen). Atom or alkali metal atom.) (Wherein R ₁ , R ₂ , and R ₃ each represent an alkyl group having 1 to 6 carbon atoms).