JP2576102B2 - 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]

According to the present invention, a -COOM group (where M represents a hydrogen atom or an alkali metal atom) and a sulfonic acid tertiary amine salt are contained in a molecule of a polyurethane resin used as a binder of a coating type magnetic recording medium. Introducing a binder with excellent properties in terms of dispersibility in magnetic powder, properties of a coating film formed as a magnetic layer, workability in forming a coating film, etc. It is an object of the present invention to provide a magnetic recording medium having excellent magnetic properties and electromagnetic conversion properties.

[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, a polyurethane resin, or the like is mentioned.
With the above-mentioned demands for an increase in packing density and further improvement in durability, various problems have occurred with these binders, and it is presently difficult to sufficiently 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 metal sulfonic acid salt or the like is introduced into a polyurethane resin, and an attempt has 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 was completed by focusing on the fact that the introduction of a tertiary amine salt of a sulfonic acid as a polar group into the side chain is effective in improving workability. In a magnetic recording medium in which a magnetic layer mainly composed of a ferromagnetic powder and a binder is formed on a body, the binder is a -COOM group (where M represents a hydrogen atom or an alkali metal atom) in the molecule. ) (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 About 500-5000 long-chain diol, molecular weight about 5
It is preferable to use 0 to 500 short-chain diols and 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 polyesterdiols or ε-caprolactone obtained by reacting hexane glycol, diethylene glycol, neopentyl glycol, or an ethylene oxide adduct of bisphenol A, or a mixture thereof; And the like 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,
Triols such as 1,2,6-hexanetriol, 1-bis (2-hydroxyethyl) amino-2-propanol, and propylene oxide adduct of 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, 4,4'-diisocyanate diphenyl ether, 1,5
Aromatic diisocyanates such as naphthalene diisocyanate, 2,4-naphthalene diisocyanate, 1,3-diisocyanatomethylcyclohexyne, 1,4-diisocyanatomethylcyclohexane, 4,4′-diisocyanate Alicyclic diisocyanates such as natodicyclohexylmethane 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 sulfonic acid tertiary amine 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 tertiary amine sulfonic acid salt is used in combination, because the particle size becomes very large and the practicability is poor.

According to experiments performed by the present inventors, by using a polyurethane resin having a -COOM group in a molecule and having a tertiary amine salt of sulfonic acid, it is possible to obtain a favorable without impairing the powder dust reduction effect of the -COOM group. A coating material having a particle size characteristic was obtained, and a magnetic recording medium having more excellent dispersibility than in the case of containing only the -COOM group was obtained.

By the way, in order to introduce these -COOM groups and sulfonic acid tertiary amine salts into the polyurethane resin, the following method may be used.

(1) A method in which the above-mentioned -COOM group or sulfonic acid tertiary amine salt is previously introduced into a part of diisocyanate or polyol which is a raw material of polyurethane.

(2) A method in which an OH group is left at the terminal or side chain of the polyurethane resin, and the OH group is modified with a compound containing a -COOM group-containing compound and a sulfonic acid tertiary amine salt.

Examples of the diisocyanate or polyol into which a -COOM group or a sulfonic acid tertiary amine salt is introduced as a hydrophilic polar group used in the method (1) include a -COOM group-containing diol, a sulfonic acid tertiary amine salt-containing diol, −
COOM group-containing organic diisocyanates and sulfonic acid tertiary amine salt 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 -COOM 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 sulfonic acid tertiary amine salt-containing diol is obtained by reacting a carboxylic acid component having no sulfonic acid tertiary amine salt, a glycol component, and a dicarboxylic acid component having a sulfonic acid tertiary amine salt.

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

As the above-mentioned 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 sulfonic acid tertiary amine salt include the following.

(However, R ₁ , R ₂ , and R ₃ each represent an alkyl group having 1 to 6 carbon atoms.) Therefore, a part of the long-chain diol is converted to the sulfonic acid 3
A tertiary amine salt of sulfonic acid is introduced into the molecule by synthesizing a polyurethane resin by replacing the diol with a diol containing a tertiary amine salt.

Further, the above-mentioned organic diisocyanate containing -COOM group or organic diisocyanate containing tertiary amine salt of sulfonic acid reacts a compound having -COOM group or tertiary amine salt of sulfonic acid with a polyisocyanate compound having three or more functional groups. Can be obtained by:

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 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 (COOM group-containing organic diisocyanate) 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 polyisocyanate compound having three or more functional groups.) To introduce a tertiary amine salt of sulfonic acid, a tertiary amine salt of sulfonic acid is contained in one molecule, and an NCO group is used. A compound having an active hydrogen capable of reacting with a polyisocyanate compound having three or more functional groups may be reacted. Thus, a compound having two or more —NCO groups in one molecule and having a tertiary amine salt of sulfonic acid (sulfonic acid 3
An organic diisocyanate containing a tertiary amine salt) is obtained.

Examples of the compound having a sulfonic acid tertiary amine salt in one molecule and having an active hydrogen capable of reacting with a -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 polyisocyanate compound having three or more functional groups.) On the other hand, the method (2) is present at a terminal or a side chain of a polyurethane resin which has been chain-extended to a predetermined molecular weight by a polymerization reaction. The OH group is reacted with a compound having a COOM group or a tertiary amine salt of sulfonic acid.
In this case, a compound having an OH group and a COOM group, or a compound having an OH group and a tertiary amine salt of sulfonic acid is synthesized, and one of the NCO groups of the diisocyanate to be subjected to an equimolar reaction with the diisocyanate compound has a COOM group or When a sulfonic acid tertiary amine salt is introduced and the remaining NCO groups are reacted with OH groups of the polyurethane resin, a polyurethane resin into which a COOM group or a sulfonic acid tertiary amine salt is introduced can be obtained. The reaction equation is as follows.

(2-1) OCN-R-NCO + HOCH ₂ COOM → OCN-R-NHCOOCH ₂ COOM R _PU -OH + OCN-R-NHCOOCH ₂ COOM → R _PU -OCONH-R-NHCOOCH ₂ COOM (where R is divalent Represents a hydrocarbon group, and R _PU represents a polyurethane resin.) (Where R represents a divalent hydrocarbon group, R ₁ , R ₂ , and R ₃ represent an alkyl group having 1 to 6 carbon atoms, and R _PU represents a polyurethane resin). ClCH ₂ COOM as a compound containing a -COOM group and chlorine in the molecule, and a polyurethane resin having an OH group, dimethyl formamide both components is soluble, dissolved in a solvent such as dimethyl sulfoxide,
Amines such as pyridine, picoline and triethylamine;
It can also be introduced by a dehydrochlorination reaction between an OH group and chlorine in the presence of a dehydrochlorinating agent such as an epoxy compound such as ethylene oxide or propylene oxide.
The reaction equation is as follows.

(2-3) R _PU -OH + ClCH ₂ COOM → P _PU -OCH ₂ COOM + HCl (where R _PU represents a polyurethane resin) Further, the tertiary amine salt of sulfonic acid is a terminal or side chain of the polyurethane resin. Can be introduced by reacting a tertiary amine with a compound containing a sulfonic acid group with respect to the OH group present in the compound. The reaction equation is as follows.

(In the formula, R _PU represents a polyurethane resin, and R ₁ , R ₂ , and R ₃ each represent a hydrocarbon group having 1 to 6 carbon atoms.) (In the formula, _RPU represents a polyurethane resin.) In this case, specific examples of the sulfonic acid tertiary amine salt to be introduced include the following.

As described above, each of the -COOM group and the sulfonic acid tertiary amine salt can be introduced into the polyurethane resin.

The magnetic recording medium according to the present invention is obtained by introducing a sulfonic acid tertiary amine salt together with a -COOM group into a polyurethane resin used as a binder for a magnetic paint. Therefore, the following method may be used to introduce two types of hydrophilic polar groups consisting of a -COOM group and a sulfonic acid tertiary amine salt.

(1) A method in which a compound having a -COOM group and a compound having a sulfonic acid tertiary amine salt are contained in the raw material of the polyurethane resin, and the -COOM group and the sulfonic acid tertiary amine salt are introduced simultaneously with the production of the polyurethane resin.

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

(III) A compound having a -COOM group is contained in the raw material of the polyurethane resin, and the terminal or side chain OH group of the resulting -COOM group-containing polyurethane resin is modified to introduce a tertiary amine salt of sulfonic acid. how to.

(IV) A compound containing a sulfonic acid tertiary amine salt is contained in the raw material of the polyurethane resin, and the terminal or side chain OH group of the resulting sulfonic acid tertiary amine salt-containing polyurethane resin is modified to form -COOM How to introduce groups.

For example, in the case of the method (I), a long-chain polyester diol containing a sulfonic acid tertiary amine salt is used as a part of the long-chain diol, and a short-chain diol containing a -COOM group (for example, dimethylolpropionic acid) May be used as a chain extender to synthesize a polyurethane resin.

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 sulfone is substituted into the remaining —OH group. An acid tertiary amine salt may be introduced.

The -COOM group and the sulfonic acid tertiary amine salt can be easily introduced into the polyurethane resin by the above method.

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 sulfonic acid tertiary amine salt is 0.01 to 1.0 mmol / g, more preferably 0.01 to 1.0 mmol / g. 0.50.5 mmol / g. Here, the introduction amount of the -COOM group is 0.01 to 0.5 mmol /
g, the amount of the tertiary amine salt of sulfonic acid introduced 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 a phenol resin, an epoxy resin, a thermosetting polyurethane resin, a urea resin, a melamine resin, an alkyd resin, a urea-portaldehyde resin silicone resin, an acrylic reaction resin, and an epoxy resin. 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 , 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 ≦ X1.50, that is, maghemite (γ-Fe ₂ O ₃ , X = 1.50), magnetite (Fe _Three
O ₄ , X = 1.33) and their solid solutions (FeOx, 1.33 <X <1.5
0). 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, balmitic 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 its metal salts, fatty acid amides, fatty acid alcohols or alkoxides thereof, fatty acid 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 glycol ethers such as glycol dimethyl ether, glycol monoethyl ether and dioxane; aromatics such as benzene, toluene, and xylene Examples thereof include hydrocarbons, 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 and 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 sulfonic acid tertiary amine salt are introduced into the molecule as a binder, the affinity for the magnetic powder is greatly improved, and the ultrafine magnetic powder is used. Even if the magnetic powder has a large amount of magnetization, it is well dispersed and the durability is improved by the effect of reducing powder dropping of the -COOM group.

Particularly, by introducing both a -COOM group and a sulfonic acid tertiary amine salt, 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 sulfonic acid tertiary amine 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 Example 1 to Comparative Example 6 In the composition of Example 1, instead of binder 1, binder 8 to
A sample tape was prepared in the same manner as in Example 1 except that the binder 13 was used.

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 °. In addition, the amount of powder falling was evaluated by visually observing the amount of powder falling onto a head drum, a guide or the like after running the shaft 100 times for 60 minutes, and evaluated by the deduction method (−5 to 0). 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. .

〔The invention's effect〕

As is clear from the above description, in the present invention, since a -COOM group is introduced into the molecule of the polyurethane resin and a tertiary amine salt of sulfonic acid is further introduced and used as a binder, the magnetic powder It exhibits high affinity for, and even if it is a magnetic powder that is made into ultrafine particles 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, and a magnetic recording medium having extremely excellent durability, surface properties, and electromagnetic conversion characteristics is obtained.

Further, since the paint containing the above 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).