JP2531158B2 - Magnetic recording media - Google Patents

Description

TECHNICAL FIELD The present invention relates to a magnetic recording medium such as a magnetic tape, and more specifically, a binder contained in a magnetic layer formed on a non-magnetic support. Related to the improvement of.

[Outline of Invention]

The present invention introduces a --COOM group (where M represents a hydrogen atom or an alkali metal atom) and a tertiary amine into the molecule of a polyurethane resin used as a binder for a coating type magnetic recording medium. Provides a binder with excellent properties in terms of dispersibility in magnetic powder, coating film properties when formed as a magnetic layer, workability during coating film formation, and excellent surface properties and durability. An object of the present invention is to provide a magnetic recording medium having good magnetic characteristics and electromagnetic conversion characteristics.

[Conventional technology]

In recent years, magnetic recording media, especially magnetic recording media for VTRs (Video Tape Recorders), have been improved in magnetic characteristics and electromagnetic conversion characteristics so that high reproduction output can be obtained even when short wavelength recording is performed. Requested. 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 can be mentioned. Various problems have occurred with these binders in accordance with demands for improvement in durability and the like, and it is difficult to sufficiently cope with them at present.

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, magnetic characteristics, and electromagnetic conversion characteristics were 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 can be considered. However, since the surfactant has a low molecular weight, powdering or blooming due to aging may occur, resulting in mechanical strength or durability. 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 problems]

The present inventors show that by introducing a carboxylic acid or a metal base thereof into the side chain as a polar group, the dispersibility is improved by exhibiting a high affinity with respect to the magnetic powder, and powder falling is significantly improved. Furthermore, the present invention has been completed by paying attention to the fact that introducing a tertiary amine into a side chain as a polar group is effective in improving workability. In a magnetic recording medium in which a magnetic layer mainly composed of ferromagnetic powder and a binder is formed, the binder has a --COOM group (where M represents a hydrogen atom or an alkali metal atom) in the molecule, and (R ₁ and R ₂ each represent a hydrocarbon group.).

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,
They are roughly classified into polyether diols and polyether ester glycols. As polyester diol,
Specifically, for example, succinic acid, adipic acid, sebacic acid,
Aliphatic dicarboxylic acids such as azelaic acid, terephthalic acid,
Aromatic dicarboxylic acids such as isophthalic acid or their lower alcohol esters, ethylene glycol, 1,3-
Propylene glycol, 1,4-butylene glycol, 1,6
-Polyester diols obtained by reacting hexane glycol, diethylene glycol, neopentyl glycol, an ethylene oxide adduct of bisphenol A, or the like, or a lactone obtained by ring-opening polymerization of a lactone such as ε-caprolactone The polyester diols of 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 concentration of urethane groups in the resulting polyurethane resin will be too high and the flexibility of the resin will be poor, and the solubility in solvent will be poor, and it will be used as a binder for magnetic recording media. Is not very desirable for 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 the abrasion resistance and heat resistance of the resin decrease. To do.

Examples of the short-chain diol include 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.

Furthermore, 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.

Examples of the organic diisocyanate include tetramethylene diisocyanate, aliphatic diisocyanates such as 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-naphthalene diisocyanate, 2,4-naphthalene diisocyanate, 1,3-diisocyanato methylcyclohexane, 1,4-diisocyanate Examples thereof include alicyclic diisocyanates such as methylcyclohexane, 4,4'-diisocyanate dicyclohexylmethane, 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.

Furthermore, a -COOM group (wherein M represents a hydrogen atom or an alkali metal atom) and a tertiary amine are introduced into the polyurethane resin as hydrophilic polar groups. Here, the --COOM group is very effective in improving the dispersibility of the magnetic powder, and the effect of reducing the powder drop when used as a magnetic recording medium is particularly large. In that case, the particle size becomes so large that it becomes impractical, so a tertiary amine is used in combination.

According to the experiments of the present inventors, by using a polyurethane resin having a -COOM group and a tertiary amine in the molecule, good particle size characteristics can be obtained without impairing the powder falling reduction effect of the -COOM group. It was found that it is possible to obtain a coating material having the above, and it is possible to obtain a magnetic recording medium having excellent dispersibility as compared with the case of containing the —COOM group alone.

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

First, regarding the --COOM group, for example, (1) a method in which the --COOM group is previously introduced into a part of the raw material of polyurethane, such as diisocyanate or polyol.

(2) A method of leaving an OH group at the terminal or side chain of the polyurethane resin and modifying the OH group with a -COOM group-containing compound.

And so on.

Examples of the diisocyanate or polyol introduced with the -COOM group as a hydrophilic polar group used in the above method (1) include a -COOM group-containing diol and a -COOM group-containing organic diisocyanate. These compounds polymerize with other raw materials to form a part of the polymer molecular chain of the polyurethane resin, and as a result, —COOM groups are 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.

Further, the above-mentioned organic diisocyanate containing a -COOM group has 3
It can be obtained by reacting a functional or higher polyisocyanate compound with a compound having a —COOM group.

As the above-mentioned polyisocyanate compound, trifunctional trade name Desmodur L (manufactured by Bayer), trade name Coronate L (manufactured by Nippon Polyurethane Co.) and the like 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 (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.

etc.

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.) On the other hand, the method (2) is present at the terminal or side chain of a polyurethane resin chain-extended to a predetermined molecular weight by a polymerization reaction. The compound having a COOM group is reacted with the OH group. In this case, a compound having an OH group and a COOM group is synthesized, and a COOM group is introduced into one NCO group of the diisocyanate by reacting it equimolar with the diisocyanate compound, and the remaining NCO group and the OH group of the polyurethane resin. By reacting, a polyurethane resin having a COOM group introduced is obtained. The reaction equation is as follows. (2-1) OCN-R-NCO + HOCH ₂ COOM → OCN-R-NHCOOCH ₂ COOMR _{PU
-OH + OCN-R-NHCOOCH 2} COOM → R PU -OCONH-R-NHCOOCH 2 COOM ( wherein R represents a divalent hydrocarbon group, R _PU represents a polyurethane resin.) In addition, -COOM group , A compound containing a --COOM group and chlorine in the molecule, such as ClCH ₂ COOM, and a polyurethane resin having an OH group, both components are dissolved in a solvent such as dimethylformamide, dimethylsulfoxide,
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 shown below. (2-2) R _PU- OH + ClCH ₂ COOM → R _PU -OCH ₂ COOM + HCl (However, R _{PU in} the formula represents a polyurethane resin.) On the other hand, the tertiary amine is the following tertiary amino group-containing diol. By being used as a part of the chain extender, it is introduced into the main chain of the polyurethane resin.

Examples of the tertiary amino group-containing diol include, for example, Etc.

As described above, the --COOM group and the tertiary amine can be introduced into the polyurethane resin.

The magnetic recording medium according to the present invention comprises a polyurethane resin used as a binder for a magnetic paint, together with a --COOM group.
A primary amine is introduced. Therefore, −CO
In order to introduce two kinds of hydrophilic polar groups consisting of an OM group and a tertiary amine, the following may be done.

(I) A method of incorporating a compound having a --COOM group and a compound having a tertiary amine into a raw material of a polyurethane resin, and introducing the --COOM group and the tertiary amine at the same time when the polyurethane resin is produced.

(II) A method of incorporating a compound containing a tertiary amine into the raw material of the polyurethane resin, and modifying the OH group at the terminal or side chain of the resulting tertiary amine-containing polyurethane resin to introduce a -COOM group.

For example, in the case of the method (I), a polyurethane resin may be synthesized by using a short chain diol containing a tertiary amine and a short chain diol containing a --COOM group (for example, dimethylolpropionic acid) as a chain extender. .

The -COOM group and the tertiary amine 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 0.01 to 1.0 mmol / g, more preferably 0.01 to 0.5 mmol, of the sum of -COOM group and tertiary amine. The range is / g. Where −C
The amount of OOM group introduced is 0.01 to 0.5 mmol / g, and the amount of tertiary amine 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 number average molecular weight of the polyurethane resin according to the present invention is preferably in the range 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 in the production of paint, mixing, transfer,
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, acrylic ester-acrylonitrile copolymer, acrylic ester-vinylidene chloride copolymer, methacrylic acid Ester-vinylidene chloride copolymer, methacrylic acid 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 them in combination with those 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, examples of the ferromagnetic powder that can be used include ferromagnetic iron oxide particles, ferromagnetic chromium dioxide, ferromagnetic alloy powder, hexagonal barium ferrite fine particles, and iron nitride.

As the above-mentioned ferromagnetic iron oxide particles, when represented by the general formula FeOx, those having an X value in the range of 1.33 ≦ X ≦ 1.50, that is, maghemite (γ-Fe ₂ O ₃ , X = 1.50) magnetite (Fe ₃
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 oxide is roughly classified into two types: a doped type and an adhered type.

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

As the ferromagnetic alloy powder, 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 preventive, etc. 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 such as stearic acid, oleic acid, elaidic acid, linoleic acid, linolenic acid and stearolic acid (R ₇ COOM, R ₇ is an alkyl or alkenyl group having 11 to 17 carbon atoms), Alkali metals of fatty acids (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).
, Alkoxy has 1 to 4 carbon atoms, silicon oil such as phenyl polysiloxane, fluoroalkyl polysiloxane (alkyl has 1 to 5 carbon atoms), conductive fine powder such as graffite, molybdenum disulfide, disulfide Inorganic fine powder such as tungsten, polyethylene, polypropylene, polyethylene vinyl chloride copolymer, plastic fine powder 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 ester consisting of fatty acid having 12 to 22 carbon atoms and alcohol having 3 to 22 carbon atoms (may be any of monoester, diester, triester, and further polyfunctional polyester), fatty acid Or metal salts thereof, fatty acid amides, fatty acid alcohols or alkoxides thereof, fatty acid amines, polyhydric alcohols, sorbitan esters, mannittan esters, sulfurized fatty acids, aliphatic mercaptans, perfluoroalkyl ethylene oxides, perfluoropolyethers, higher alkyl sulfones. An acid or a metal salt thereof, a perfluoroalkylsulfonic acid or an ammonium salt thereof or a metal salt thereof, a perfluoroalkylcarboxylic acid or a metal salt thereof, a fluorocarbon or 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 with respect to 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 inhibitor, phosphoric acid, sulfamide, guanidine, pyridine, amine, urea, zinc chromate, calcium chromate, strontium chromate, etc. can be used, but especially dicyclohexylamine nitrite, cyclohexylamine chromate, diisopropylamine nitrite, diethanolamine Vaporizing 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 acid) The use of (salt) improves the rust prevention effect. 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 having a --COOM group and a tertiary amine introduced in its molecule as a binder, the affinity for magnetic powder is significantly improved, and ultrafine magnetic powder and magnetized amount are used. Even if the magnetic powder has a large particle size, it can be dispersed well and the durability can be improved due to the powder falling reduction effect of -COOM.

In particular, the introduction of both the --COOM group and the tertiary amine can improve the viscosity characteristics of the binder.

〔Example〕

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

First, a polyurethane resin having a —COOM group and a tertiary amine introduced was synthesized by the method described in this specification. First
The characteristics of the synthesized polyurethane resin are shown in the table.

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, it was dried and wound.
This was calendered and then cut into a 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 produced 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 °. 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.

 The measurement results are shown in Table 2.

As is clear from the results shown in Table 2, the sample tapes according to the present invention are not only excellent in surface gloss and powder falling, but also have low paint viscosity and excellent workability. .

[Effects of the Invention] As is clear from the above description, in the present invention, a -COOM group is introduced into the molecule of the polyurethane resin, and a tertiary amine is further introduced, which serves as a binder. It has a high affinity for the magnetic powder, and even if it is made into ultrafine particles or has a large amount of magnetization, the dispersibility is 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 a ferromagnetic powder and a binder formed on a non-magnetic support, wherein the binder has a --COOM group (where M is hydrogen) in the molecule. Represents an atom or an alkali metal atom) and A magnetic recording medium comprising a polyurethane resin having (wherein R ₁ and R ₂ each represent a hydrocarbon group).