JP2615574B2 - 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, -SO ₃ M group in the molecule of the polyurethane resin used as the binder of the coating type magnetic recording medium, -OSO ₃ M
Base, (Wherein M represents a hydrogen atom or an alkali metal atom, and M ′ represents a hydrogen atom, an alkali metal atom or a hydrocarbon group) to obtain a dispersibility in magnetic powder. , Providing a binder that has excellent properties in terms of the properties of the coating film when formed as a magnetic layer, workability in forming the coating film, etc., has excellent surface properties and durability, and has excellent magnetic properties and electromagnetic conversion properties. It is intended to provide a good magnetic recording medium.

[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, 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 have found that by introducing a --COOM group into the side chain as a polar group, it exhibits a high affinity for magnetic powder and improves dispersibility, drastically improves powder drop, and further improves polar group -SO ₃ M group, -OSO ₃ M group, It is effective to improve the workability that is introduced into the side chain, has led to the completion of the present invention by focusing on the like, ferromagnetic powder and binder on a non-magnetic support In the magnetic recording medium in which a magnetic layer mainly composed of is formed, the binder has -SO ₃ M group as a polar group in the molecule, -OSO ₃ M
Group, A polyurethane resin having at least one selected from the group consisting of -COOM group (where M represents a hydrogen atom or an alkali metal atom, and M 'represents a hydrogen atom, an alkali metal atom or a hydrocarbon group), and The total amount of the polar group contained in the polyurethane resin is 0.01 to 1.0 mmol /
g, of which the amount of -COOM groups introduced is 0.01 to 0.5 mmol /
g, the amount of other polar groups introduced is 0.001 mmol / g or more.

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 adducts or propylene oxide adducts of bisphenol A and ethylene oxide adducts 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 2-propanol and diethanolamine propionate adducts 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. Furthermore, -COOM group and -SO ₃ M group as the hydrophilic polar group in the polyurethane resin, -OSO ₃ M group, (However, M represents a hydrogen atom or an alkali metal atom,
M 'represents a hydrogen atom, an alkali metal atom or a hydrocarbon group. ) Is introduced. Here, the COOM group is very effective in improving the dispersibility of the magnetic powder, and when used as a magnetic recording medium, the effect of reducing powder drop is particularly large.
In the case of a binder into which a COOM group is introduced alone, the viscosity becomes extremely large when formed into a coating material, which is not practical. Therefore, the above-mentioned hydrophilic polar group is introduced.

According to the experiments of the present inventors, having a COOM group in the molecule,
And, by using the polyurethane resin having the hydrophilic polar group, it is possible to obtain a paint having good viscosity characteristics without impairing the powder drop reduction effect of the COOM group, COOM
It is possible to obtain a magnetic recording medium having more excellent dispersibility than the case where the group is contained alone.

By the way, these COOM group or a group -SO ₃ M, -OSO ₃ M group, -P
In order to introduce a hydrophilic polar group such as _two O (OM ') groups into the polyurethane resin, the following method may be used.

(1) A method in which the hydrophilic polar group 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 a terminal or a side chain of a polyurethane resin, and the OH group is modified with the compound having a hydrophilic polar group.

Examples of the diisocyanate or polyol having a hydrophilic polar group introduced therein used in the method (1) include a diol containing a hydrophilic polar group and an organic diisocyanate containing a hydrophilic polar group. 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 the hydrophilic polar group-containing diol, COOM group-containing diol, PO (OM ') ₂ group-containing diol, SO ₃ M group-containing diol, an OSO ₃ group-containing diols.

Examples of the COOM group-containing diol include, for example, dimethylolpropionic acid and these COOM groups in a NaOH methanol solution, K
Compounds neutralized using an OH methanol solution or the like are exemplified. By synthesizing a polyurethane resin using the compound as a chain extender, a COOM group is introduced into the molecule.

PO (OM ') ₂ group-containing diol has the general formula (Wherein, R ₁ is an alkylene group having 2 to 6 carbon atoms or a substituent thereof, R ₂ is an alkylene group having 1 to 6 carbon atoms or a substituent thereof, R ₃ and R ₄ are alkyl groups having 1 to 6 carbon atoms. The compound shown by these is mentioned.

The SO ₃ M group-containing diol is obtained by reacting a carboxylic acid component having no —SO ₃ M group, a glycol component, and a dicarboxylic acid component having a —SO ₃ M group.

As the carboxylic acid component having no the -SO ₃ M group, terephthalic acid, isophthalic acid, orthophthalic acid, aromatic dicarboxylic acids such as 1,5-naphthalic acid, p- oxybenzoate, p- (hydroxyethoxy) benzoic Aromatic oxycarboxylic acids such as acids, 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 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, Bisphenol A ethylene oxide adduct and propylene oxide adduct, hydrogenated bisphenol A
And propylene oxide adducts, polyethylene glycol, polypropylene glycol, polytetramethylene glycol and the like. Also, trimethylolethane, trimethylolpropane,
Tri and tetraols such as glycerin and pentaerythritol may be used in combination.

The dicarboxylic acid component having the above-mentioned -SO ₃ M group, 5
-Sodium sulfoisophthalic acid, 5-potassium sulfoisophthalic acid, 2-sodium sulfoterephthalic acid, 2
-Potassium sulfoterephthalic acid and the like.

Therefore, by replacing a part of the long-chain diol with this SO ₃ M group-containing diol to synthesize a polyurethane resin, the SO ₃ M group is introduced into the molecule.

Further, the above-mentioned organic diisocyanate containing a hydrophilic polar group can be obtained by reacting a compound having a hydrophilic polar group with a polyisocyanate compound having three or more functional groups.

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 polyisocyanate.

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

In order to introduce a COOM group into the trifunctional or higher polyisocyanate compound, a compound having a -COOM group in one molecule and having an active hydrogen capable of reacting with the -NCO group can be introduced into a trifunctional or higher polyisocyanate compound. What is necessary is just to make it react with an isocyanate compound. As a result, a compound having two or more -NCO groups in one molecule and having a -COOM group (COOM group-containing diol) 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.) To introduce an SO ₃ M group, one molecule has a —SO ₃ M group,
A compound having an active hydrogen capable of reacting with the -NCO group may be reacted with a tri- or higher functional polyisocyanate compound. Thereby, having two or more -NCO groups per molecule and a compound having a -SO ₃ M group (SO ₃ M
Group-containing diol) is obtained.

Examples of the compound having a —SO ₃ M group in one molecule and 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.) To introduce an -OSO ₃ M group, a reaction product of a tri- or higher functional polyisocyanate compound and H ₂ SO ₄ May be neutralized with NaOH, KOH or the like. As a result, two or more-
Having an NCO group, and the resulting compound having an -OSO ₃ M group (OSO ₃ M group-containing diol) is, for example, as shown in the following reaction scheme.

R-NCO + H ₂ SO ₄ → R-NHCO-OSO ₃ H R-NHCO-OSO ₃ H + NaOH → R-NHCO-OSO ₃ Na + H ₂ O (iv) (In the reaction formula, R-NCO has three or more functional groups. In order to introduce _two PO (OM ') groups, the reaction product of a tri- or higher functional polyisocyanate compound with H ₂ PO ₃ is converted to NaOH, KOH
And the like. Thereby, for example, it is obtained as shown by the following reaction formula.

(In the reaction formula, R-NCO represents a tri- or more functional polyisocyanate compound.) On the other hand, specific examples of the above method (2) include: (A) ClCH ₂ COOM, ClCH ₂ CH ₂ SO ₃ M, ClCH ₂ CH ₂ OSO ₃ M, (Where M represents a hydrogen atom or an alkali metal atom, and M ′ represents a hydrogen atom, an alkali metal atom or a hydrocarbon group), and a compound containing a hydrophilic polar group and chlorine in the molecule, and a polyfunctional compound. A polyurethane resin having an -OH group is dissolved in a solvent such as dimethylformamide or dimethylsulfoxide, in which both components are soluble, and amines such as pyridine, picoline and triethylamine: epoxy compounds such as ethylene oxide and propylene oxide; There is a method of introducing a hydrophilic polar group by a dehydrochlorination reaction between -OH group and chlorine in the presence of a dehydrochlorinating agent. The reaction equation is as follows.

(A-1) R'-OH + ClCH 2 COOM → R'-OCH 2 COOM + HCl (A-2) R'-OH + ClCH 2 CH 2 SO 3 M → R'-OCH 2 CH 2 SO 3 M + HCl (A-3) R _{'-OH + ClCH 2 CH 2 OSO} 3 M → R'-OCH 2 CH 2 OSO 3 M + HCl (A-4) (However, R 'represents a polyurethane resin.) Although some by-products are produced, they can also be synthesized by the following method. (B) HOCH ₂ COOM, HOCH ₂ CH ₂ SO ₃ M, HOCH ₂ CH ₂ OSO ₃ M, And diisocyanate compounds such as 4,4'-diphenylmethane diisocyanate, tolylene diisocyanate,
Hexamethylene diisocyanate is reacted equimolarly,
One -NCO group of the diisocyanate and -O in the above compound
The reaction product with the H group is obtained. Next, by reacting the remaining —NCO group with the —OH group of the polyurethane resin, a polyurethane resin having a hydrophilic polar group introduced can be obtained. The reaction equation is as follows.

(B-1) OCN-R "-NCO + HOCH 2 COOM → OCN-R" -NHCOOCH 2 COOM R'-OH + OCN-R "-NHCOOCH 2 COOM → R'-OCONH-R" -NHCOOCH 2 COOM (B-2) _{OCN-R "-NCO + HOCH 2} CH 2 SO 3 M → OCN-R" -NHCOOCH 2 CH 2 SO 3 M R'-OH + OCN-R "-NHCOOCH 2 CH 2 SO 3 M → R'-OCONH-R" -NHCOOCH _{2 CH 2 SO 3 M (B} -3) OCN-R "-NCO + HOCH 2 CH 2 OSO 3 M → OCN-R" -NHCOOCH 2 CH 2 OSO 3 M R'-OH + OCN-R "-NHCOOCH 2 CH 2 OSO 3 M → R'-OCONH-R "-NHCOOCH ₂ CH ₂ OSO ₃ M (However, R ′ represents a polyurethane resin, and R ″ represents a divalent hydrocarbon group.) As described above, the —COOM group, the —SO ₃ M group, and the —OSO ₃ M
Base, Each of them can be introduced into a polyurethane resin.

The magnetic recording medium according to the present invention contains -COOM groups together with -COOM groups in a polyurethane resin used as a binder for magnetic paint.
SO ₃ M group, -OSO ₃ M group, Is introduced. -COOM group and -SO ₃ M group, -OSO ₃ M group, In order to introduce two kinds of hydrophilic polar groups consisting of any one of the above, the following method may be used. For example, -COOM group and-
Taking the case where an SO ₃ M group is introduced as an example, (I) a compound having a COOM group in a raw material of a polyurethane resin and any one of a SO ₃ M group, an OSO ₃ M group, and a PO (OM ′) ₂ group A method comprising introducing a COOM group, an SO ₃ M group, an OSO ₃ M group or a PO (OM ′) ₂ group simultaneously with the production of a polyurethane resin.

(II) By modifying the OH group present on the side chain or terminal of the already synthesized polyurethane resin, the COOM group and SO ₃ M
Group, OSO ₃ M group, or PO (OM ') ₂ group.

(III) A compound containing a COOM group is mixed 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 form SO ₃ M
Group, OSO ₃ M group, or PO (OM ') ₂ group.

(IV) SO ₃ M group, OSO ₃ M group, PO
A compound containing any one of (OM ') ₂ groups is mixed, and the resulting SO ₃ M group, OSO ₃ M group or PO (OM') ₂
A method of modifying a terminal or side chain OH group of a group-containing polyurethane resin to introduce a COOM group.

For example, in the case of the method (I), a long-chain polyester diol containing a SO ₃ M group, an OSO ₃ M group or a PO (OM ′) ₂ group is used as a part of the long-chain diol, and a COOM group is contained. A polyurethane resin may be synthesized using a short-chain diol (for example, dimethylolpropionic acid) as a chain extender.

In the case of the method (II), first, a -COOM group is introduced into a part of the -OH group existing on the side chain or terminal of the already synthesized polyurethane resin, and then, for example, the remaining -OH group is added to the remaining -OH group. it may be introduced -SO ₃ M group.

-COOM group and -SO ₃ M group by the method described above, -OSO ₃ M
Base, And two kinds of hydrophilic polar groups consisting of any one of them can be easily introduced into the polyurethane resin.

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 other polar group is 0.01 to 1.0 mmol / g,
More preferably, it is in the range of 0.01 to 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 another polar group 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 phenol resin, epoxy resin, thermosetting polyurethane resin, urea resin, melamine resin, alkyd resin, urea-formaldehyde resin silicon resin, acrylic-based 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 powder such as 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 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). Or a metal salt thereof, a fatty acid amide, an aliphatic alcohol or an alkoxide thereof, an aliphatic alcohol or an alkoxide thereof, an aliphatic amine, a polyhydric alcohol, a sorbitan ester, a mannitan ester, a sulfurized fatty acid, an aliphatic mercaptan, a perfluoroalkylethylene oxide, Perfluoropolyethers, higher alkyl sulfonic acids or metal salts thereof, perfluoroalkyl sulfonic acids or ammonium salts or metal salts thereof, perfluoroalkyl carboxylic acids or metal salts thereof, fluorocarbons and the like can be used. These lubricants are added in the range of 0.2 to 20 parts by weight based on 100 parts by weight of the binder.

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, COOM group and SO ₃ M group, OSO ₃ M group, P
By using a polyurethane resin with one of _two O (OM ') groups as the binder, the affinity for the magnetic powder is greatly improved, making it possible to use ultra-fine magnetic powder or magnetic powder with a large amount of magnetization. Even if it is present, it can be well dispersed and the durability can be improved by the effect of reducing powder drop of -COOM.

Particularly, by introducing a COOM group and any one of an SO ₃ M group, an OSO ₃ M group, and a PO (OM ′) ₂ group, 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, COOM group, SO ₃ M group, OSO ₃ M group, PO (O
M ') A polyurethane resin incorporating either of the _two groups was synthesized by the method described herein. 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 10 parts by weight of binder 1 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. The mixture was further mixed for 30 minutes. 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 10 In the composition of Example 1, instead of binder 1, binders 2
A sample tape was prepared in the same manner as in Example 1 except that the binder 10 was used.

Comparative Examples 1 to 6 In the composition of Example 1, binders 11 to
A sample tape was prepared in the same manner as in Example 1 except that the binder 16 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.

 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, a -COOM group is introduced into the molecule of the polyurethane resin, and any one of the SO ₃ M group, the OSO ₃ M group, and the PO (OM ′) ₂ group is used. Since it is introduced and used as a binder, it exhibits 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 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.

Continuation of front page (72) Inventor Yoshinobu Ninomiya 6-5-6 Kita-Shinagawa, Shinagawa-ku, Tokyo Inside Sony Magne Products Co., Ltd. (56) References Patent 2576101 (JP, C1) Patent 2576102 (JP, C1) ) Patent 2531158 (JP, C1)

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 -SO ₃ M group as a polar group in the molecule. , −OSO ₃
M groups, And a polyurethane resin having at least one selected from the group consisting of -COOM group (where M represents a hydrogen atom or an alkali metal atom, and M 'represents a hydrogen atom, an alkali metal atom or a hydrocarbon group), and The total amount of the polar groups contained in the polyurethane resin is 0.01 to 1.0 mmol / g, of which the amount of the -COOM group is 0.01 to 0.5 mmol / g, and the amount of the other polar groups is 0.001.
A magnetic recording medium characterized by being at least mmol / g.