JPH0332884B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a surface-treated ferromagnetic metal powder and a method for producing a magnetic recording medium, and the present invention relates to an improvement in a surface treatment method for modifying the surface properties of a ferromagnetic metal powder, and a method for producing a magnetic recording medium using a ferromagnetic metal powder. This invention relates to an improved method of manufacturing a recording medium. BACKGROUND OF THE INVENTION Magnetic recording media such as magnetic tapes and magnetic sheets are widely used in the audio and video fields. For example, magnetic tapes are made of a coated type in which ferromagnetic powder is dispersed in a binder, but as the demand for high-density recording has recently increased, there has been an increase in the use of oxide magnetic powder, which has a low saturation magnetization of the magnetic powder itself. Instead, metal magnetic powders with large saturation magnetization have come to be used. In recent years, various techniques using metal magnetic powders containing iron as a main component have been proposed and put into practical use as metal magnetic powders for increasing the recording density. This metal magnetic powder has large saturation magnetization and coercive force, and has excellent properties as a high-density recording material. but,
On the other hand, due to its high surface activity, the following two main
It has two problems. Oxidation resistance stability of metal magnetic powder in air If metal magnetic powder is left in the air, its magnetic properties will gradually deteriorate due to the progress of oxidation. heat,
Spontaneous combustion occurs due to impact, etc. Dispersibility in Binder When metal magnetic powder is dispersed in a binder, it has poor dispersibility due to its high surface activity, making it difficult to disperse, and in extreme cases, the binder resin may gel in the paint. Therefore, in order to improve these problems, for example, the following measures have been attempted. (1) A method in which metal magnetic powder is immersed in an organic solvent and then the organic matter is gradually volatilized (Japanese Patent Application Laid-open Nos. 49-97738 and 52-54998). (2) A method of stirring and mixing metal magnetic powder and higher fatty acid salt powder in an organic solvent to form a film containing higher fatty acid groups on the particle surface (Japanese Patent Laid-Open No. 49-97738). (3) A method of processing metal magnetic powder in an atmosphere with adjusted oxygen partial pressure (Japanese Patent Application Laid-open No. 7153/1983). (4) A method in which metal magnetic powder is immersed in an aqueous solution and then the particle surface is forcibly oxidized with an oxidizing agent (KMnO ₄ etc.) (Japanese Patent Application Laid-open Nos. 56-30707 and 52-69859). (5) Immerse metal magnetic powder in a solvent (water, organic matter),
A method of bubbling treatment with oxygen-containing gas (Japanese Patent Application Laid-open Nos. 52-85054 and 56-16601). (6) A method of vapor phase oxidation of the surface with water vapor (Japanese Patent Publication No. 35-3862, Japanese Patent Application Laid-open No. 19301/1983). (7) A method of cleaning or treating with water or an aqueous solution of ammonium hydroxide or a surfactant (JP-A-46-
No. 5057, No. 50-104903, No. 51-33758, No. 50-104903, No. 51-33758, No.
54-136696, 56-51029, 57-85206). However, all of these methods have the following drawbacks. Method (1) can overcome the above drawbacks, but
There is a problem in terms of dispersibility. Method (2) is somewhat satisfactory in the above points, but since it uses a metal salt that is poorly soluble in organic solvents, the reaction becomes non-uniform and it is difficult to obtain metal magnetic powder with a uniform surface texture. Trying to get it takes time and effort. Method (3) is possible at the laboratory level, but
Adjustment of the oxygen partial pressure is difficult in terms of experimental production and production, and the above points have not been sufficiently improved. Method (4) is good in terms of the above points, but it is difficult to control the reaction, and since the process is carried out in an aqueous system, the magnetic properties are significantly degraded. In method (5), bubbling with gas is
It is difficult to obtain uniformity of oxidation, it is difficult to control the product, and the method is unsatisfactory in the above points. Method (6) is a gas phase reaction, making it difficult to control the system and resulting in large variations in the product. In method (7), the method of cleaning with water or ammonium hydroxide can overcome the disadvantage of If it is dry, it can be dangerous and cause a fire. In addition, when ferromagnetic metal powder is immersed in water and surfactant, unless the pH control and the amount of dissolved oxygen are controlled, the saturation magnetization of the ferromagnetic metal powder will drop significantly. 20-30
% saturation magnetization value decreases, and although it looks better in terms of , the property of high saturation magnetization, which is a characteristic of magnetic powder, may be lost. As mentioned above, none of the conventional processing methods for ferromagnetic metal powder can improve the above-mentioned drawbacks, or there are problems in manufacturing, and improvements have been desired. OBJECT OF THE INVENTION An object of the present invention is to provide a method for surface treatment of ferromagnetic metal powder that can avoid problems such as heat generation and poor dispersion in a binder due to the surface activity of ferromagnetic metal powder. Another object of the present invention is to provide an industrially simple method for processing ferromagnetic metal powder. Still another object of the present invention is to provide a magnetic recording medium of good quality and easy to manufacture by using the above-mentioned surface-treated ferromagnetic metal powder. Structure of the Invention The object of the present invention is to provide an aqueous solution containing a polycarboxylic acid surfactant represented by the general formula below, and a solution that is miscible with the aqueous solution and that is
This is achieved by immersing ferromagnetic metal powder in an organic solvent containing more than 50% by weight, and drying under reduced pressure after the immersion to obtain surface-treated ferromagnetic metal powder. Another object of the present invention is to provide an aqueous solution containing a polycarboxylic acid surfactant represented by the general formula below, and an organic compound that is miscible with the aqueous solution and that is more than 50% by weight based on the total amount of the aqueous solution. A surface-treated ferromagnetic metal powder is produced by immersing a ferromagnetic metal powder in a solvent and drying under reduced pressure after the immersion, and a magnetic layer consisting of the surface-treated ferromagnetic metal powder and at least a binder resin is made into a non-magnetic layer. This is achieved by coating a support and manufacturing a magnetic recording medium. Next, the present invention will be explained in detail. In the present invention, ferromagnetic metal powder is immersed in an aqueous solution of a polycarboxylic acid surfactant represented by the general formula below and an organic solvent. The proportion is greater than 50% by weight. If the amount of organic solvent is less than this, the amount of aqueous solution increases, which is undesirable because it lowers the saturation magnetization value of the ferromagnetic metal powder, for example. Furthermore, if the amount of organic solvent is too large, the dispersibility of the ferromagnetic powder in the binder cannot be improved, as in the case of the conventional method (1) above, for example. From this, the above proportion of organic solvent is 55% by weight.
A range of 97% by weight is preferred. To immerse ferromagnetic metal powder in an aqueous solution and organic solvent containing a polycarboxylic acid surfactant represented by the general formula below, ferromagnetic metal powder is immersed in a mixture of an aqueous solution containing these surfactants and an organic solvent. Alternatively, the organic solvent may be added after immersing the ferromagnetic metal powder in an aqueous solution containing a surfactant. In the latter case, the timing of adding the organic solvent is important so that the saturation magnetization value of the ferromagnetic metal powder does not decrease. Moreover, on the contrary, after immersing the ferromagnetic metal powder in an organic solvent, an aqueous solution containing a surfactant may be added. In any of these cases, the immersion of the ferromagnetic metal powder is
This may be used alone, but it may also be combined with stirring after or during immersion. The ferromagnetic metal powder immersed in or stirred in the aqueous solution and organic solvent containing the surfactant is dried under reduced pressure. For example, dry at 5 mmHg and 80°C until no distillate remains, then blow in an inert gas such as nitrogen, evacuate several times at 5 mmHg and 80°C, and then return to room temperature. By drying under reduced pressure in this manner, water and organic solvents can be volatilized even at low temperatures, and the oxygen concentration can also be lowered, so rapid oxidation reactions of the ferromagnetic metal powder can be suppressed, and temperature rise and ignition can be prevented. The above polycarboxylic acid surfactant is represented by the following general formula. general formula (In the formula, R is a vinyl compound, M ¹ and M ² are monovalent metals, hydrogen atoms, NH ₄ or organic ammonium ions, and k is an integer from 2 to 1000). The vinyl compound represented by R in the polycarboxylic acid compound represented by the above general formula includes styrene, methylstyrene, propylene, butylene, isobutylene, vinyl acetate, vinyl methyl ether, vinyl methyl ketone, N- Examples include vinylpyrrole, and preferred examples include styrene, isobutylene, and vinyl acetate. Examples of monovalent metals for M ¹ and M ² include Na, K, Li, etc.
Preferred examples include Na, K, and the like. Examples of the organic ammonium ion include tetramethylammonium ion, propyltrimethylammonium ion, etc., and preferably tetramethylammonium ion. As specific examples of compounds represented by this general formula, the trade names are Orotane 731SD, Orotane 731SD, Orotane 731SD, Orotane 731SD,
7313D, Primal 850, Orotan 901, Orotan
960, Orotan 165 (manufactured by Rohm and Haas), Nopkozant R Nopkozant RFA,
SN Dispersant 5020, SN Dispersant
5033 (manufactured by San Nopco Co., Ltd.), Demol P, Demol ST, Demol EP (all manufactured by Kao Soap Co., Ltd.), and the like. The amount of the above polycarboxylic acid surfactant used is:
The amount is preferably 1.0 to 10 parts by weight, more preferably 1.0 to 5 parts by weight per 100 parts by weight of the magnetic powder.
The amount of this polycarboxylic acid surfactant added is 1.0
When the amount is less than 10 parts by weight, the dispersibility of the magnetic powder in the paint and magnetic layer using these materials and the effect on the wear resistance of the magnetic layer are not noticeable, and when it exceeds 10 parts by weight, blooming occurs on the surface of the magnetic layer. This may cause problems or cause excessive plasticization of the coating film of the magnetic layer, reducing its strength. The organic solvent used in the present invention includes:
Alcohols are preferred, and methanol, ethanol, propyl alcohol and the like are particularly preferred, but cellosolves such as methyl cellosolve and ethyl cellosolve, and water-miscible organic solvents such as diacetone alcohol can also be used. In addition, the organic solvent used in the present invention includes not only the above-mentioned individual organic solvents but also a mixed solvent. Organic solvents that are miscible with water when mixed with other solvents can also be used. For example, trichlorethylene, perchlorethylene, etc. can also be used, and since these are nonflammable, it is preferable for safety to use them together with ferromagnetic metal powders that have the risk of igniting. The ferromagnetic metal powder used in the present invention includes:
Fe, Ni, Co, Fe-Ni alloy, Fe-Al alloy, Fe-
Ni-P alloy, Fe-Ni-Co alloy, Fe-Mn-Zn alloy, Fe-Ni-Zn alloy, Fe-Co-Ni-Cr alloy,
Examples include various ferromagnetic powders such as metal magnetic powders containing Fe, Ni, and Co as main components, such as Fe-Co-Ni-P alloys, Co-Ni alloys, and Co-P alloys. Additives to these metal magnetic powders include Si, Cu, Zn, Al,
Elements such as P, Mn, and Cr or compounds thereof may be included. The ferromagnetic metal powder in the present invention also includes ferromagnetic powder produced in a non-oxidizing atmosphere and immersed in an organic solvent for transportation purposes. To manufacture the magnetic recording medium according to the present invention,
A magnetic layer containing at least the surface-treated ferromagnetic metal powder dispersed in a binder resin is coated on a support. Examples of such binder resins include thermoplastic resins, thermosetting resins, reactive resins, electron beam curable resins, and mixtures thereof. Thermoplastic resins used as binder resins have a softening temperature of 150℃ or less and an average molecular weight of 10,000~
200,000, with a degree of polymerization of about 200 to 2,000, such as vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, acrylic ester-acrylonitrile copolymer, Acrylic acid ester
Vinylidene chloride copolymer, acrylic ester
Styrene copolymer, methacrylic ester-acrylonitrile copolymer, methacrylic ester-
Vinylidene chloride copolymer, methacrylic acid ester-styrene copolymer, urethane elastomer, polyvinyl fluoride, vinylidene chloride-acrylonitrile copolymer, acrylonitrile-butadiene copolymer, polyamide resin, polyvinyl butyral,
Cellulose derivatives (cellulose acetate butyrate, cellulose diacetate, cellulose triacetate, cellulose propionate, nitrocellulose, etc.), styrene-butadiene copolymer, polyester resin, chlorovinyl ether
Acrylic ester copolymers, amino resins, various synthetic rubber-based thermoplastic resins, and mixtures thereof are used. These resins are disclosed in Japanese Patent Publications No. 37-6877 and No. 39-
No. 12528, No. 39-19282, No. 40-5349, No. 40-
No. 20907, No. 41-9463, No. 41-14059, No. 41-
No. 16985 No. 42-6428, No. 42-11621, No. 43-
No. 4623, No. 43-15206, No. 44-2889, No. 44-
No. 17947, No. 44-18232, No. 45-14020, No. 45
-14500, 47-18573, 47-22063, 47-22063, 47-18573, 47-22063,
No. 47-22064, No. 47-22068, No. 47-22069,
Publications No. 47-22070 and No. 48-27886, U.S. Patent No. 3144352, U.S. Patent No. 3419420, U.S. Patent No. 3499789,
It is described in the specification of the same No. 3713887. As the thermosetting resin or reactive resin, one is used that has a molecular weight of 200,000 or less in the state of a coating solution and becomes insolubilized by a reaction such as condensation or addition after coating and drying. Among these resins, those that do not soften or melt before the resin is thermally decomposed are preferred. Specifically, for example, phenolic resin, phenoxy resin, epoxy resin, polyurethane curable resin, urea resin, melamine resin, alkyd resin, silicone resin, acrylic reaction resin, vinyl chloride-vinyl acetate resin, methacrylate copolymer. and diisocyanate polymer mixtures, mixtures of high molecular weight polyester resins and isocyanate prepolymers, urea formaldehyde resins, mixtures of polyester polyols and isocyanates, polycarbonate-type polyurethanes, polyamide resins,
These include mixtures of low molecular weight glycols, high molecular weight diols, triphenylmethane triisocyanate, polyamine resins, and mixtures thereof. These resins are listed in Special Publication No. 39-8103 and No. 40-9779.
No. 41-7192, No. 41-8016, No. 41-14275,
No. 42-18179, No. 43-12081, No. 44-28023,
No. 45-14501, No. 45-24902, No. 46-13103,
No. 47-22067, No. 47-22072, No. 47-22073,
No. 47-28045, No. 47-28048, No. 47-28922,
58-4051, Japanese Patent Publications No. 57-31919, 58-60430, Japanese Patent Application No. 58-151964, 58-120697
No. 58-120698, U.S. Patent No. 3144353
No. 3320090, No. 3437510, No. 3437510, No. 3320090, No. 3437510, No.
It is described in the specifications of No. 3597273, No. 3781210, and No. 3731211. Examples of electron beam irradiation-curable resins include unsaturated prepolymers such as maleic anhydride type, urethane acrylic type, polyester acrylic type,
Polyether acrylic type, polyurethane acrylic type, polyamide acrylic type, etc., and polyfunctional monomers include ether acrylic type, urethane acrylic type, phosphate ester acrylic type, aryl type, hydrocarbon type, etc. Among these, phenoxy resins, epoxy resins, and polyurethane resins are preferable for use with the ferromagnetic metal powder.
Phenoxy resin is suitable as a dispersion medium for metal magnetic powder, for example, high molecular weight polyhydroxy ether made from bisphenol A and epichlorohydrin. To explain, this material is chemically stable and does not easily decompose even with metallic magnetic powder. Furthermore, since it has a high concentration of hydroxyl groups along the main chain, it has excellent dispersibility of magnetic powder and excellent crosslinking properties. In addition, when it is included as a binder in a magnetic layer, it can provide appropriate softness, and the liquid phase does not change suddenly to a solid phase even with a slight temperature change, so the mechanical properties of the surface do not change. It is possible to provide a magnetic layer with excellent surface properties. It is particularly preferable to use phenoxy resin in combination with polyurethane. Furthermore, in order to improve the durability of the magnetic layer of the magnetic recording medium according to the present invention, the magnetic layer can contain various hardening agents, for example, isocyanate. Aromatic isocyanates that can be used include, for example, tolylene diisocyanate (TDI), 4,4'-diphenylmethane diisocyanate (MDI), xylylene diisocyanate (XDI), metaxylylene diisocyanate (MXDI), and combinations of these isocyanates with active hydrogen compounds. There are adducts of
The average molecular weight is preferably in the range of 100 to 3000. On the other hand, examples of aliphatic isocyanates include hexamethylene diisocyanate (HMDI), lysine isocyanate, trimethylhexamethylene diisocyanate (TMDI), and adducts of these isocyanates with active hydrogen compounds. Among these aliphatic isocyanates and adducts of these isocyanates and active hydrogen compounds, those having a molecular weight in the range of 100 to 3,000 are preferred.
Among the aliphatic isocyanates, non-alicyclic isocyanates and adducts of these compounds with active hydrogen compounds are preferred. In addition, as alicyclic isocyanate among aliphatic isocyanates, for example, methylcyclohexane-2,4-diisocyanate (structural formula) 4,4'-methylenebis(cyclohexyl isocyanate (structural formula) Examples include isophorone diisocyanate and adducts of active hydrogen compounds thereof. Examples of the adduct of the above-mentioned isocyanate and an active hydrogen compound include an adduct of a diisocyanate and a trivalent polyol. Polyisocyanates can also be used as curing agents, including, for example, a pentamer of diisocyanate, a decarboxylation compound of 3 moles of diisocyanate and water, and the like. Examples of these include an adduct of 3 moles of tolylene diisocyanate and 1 mole of trimethylolpropane, an adduct of 3 moles of metaxylylene diisocyanate and 1 mole of trimethylolpropane, a pentamer of tolylene diisocyanate, and 3 moles of tolylene diisocyanate. and a pentamer consisting of 2 moles of hexamethylene diisocyanate, which can be obtained industrially in large quantities. From the viewpoint of the film properties of the magnetic layer, it is preferable to use these isocyanates in combination, for example, aromatic isocyanates and aliphatic isocyanates. In order to form the magnetic layer of the magnetic recording medium of the present invention using these isocyanates, a coating material is prepared by mixing and dispersing the above-exemplified binder resin and, if necessary, various additives described later in an organic solvent. This is coated with the above-mentioned isocyanate (aromatic isocyanate and aliphatic isocyanate may be used in combination) on a support such as a polyester film, and dried if necessary.
In this case, the amount of isocyanate added is preferably 5 to 60% by weight based on the binder. If it is less than 5% by weight, the coating film tends to be insufficiently cured, and if it is more than 60% by weight, the coating film becomes too hard, which is undesirable. The magnetic paint forming the magnetic layer may contain additives such as a dispersant, a lubricant, an antistatic agent, and an abrasive, if necessary. Examples of dispersants include lecithin; fatty acids (R R represented by -COOH is a saturated or unsaturated alkyl group having 7 to 17 carbon atoms); alkali metals of the above fatty acids (Li, Na, K
etc.) or alkaline earth metals (Mg, Ca, Ba, etc.)
Examples include metal soaps made of. In addition, higher alcohols having 12 or more carbon atoms, sulfuric esters, and the like can also be used. Moreover, commercially available general surfactants can also be used. Further, combinations of sulfonic acid salts of succinic acid esters (including ethylene glycol esters), polycarboxylic acids of maleic acid copolymers, amine surfactants, and polyoxyalkylene glycols can also be used. These dispersants may be used alone or in combination of two or more. These dispersants are added in an amount of 1 to 20 parts by weight per 100 parts by weight of the magnetic powder. These dispersants are described in Japanese Patent Publications No. 39-28369 and No. 44-
Publication No. 17945, Publication No. 48-15001, U.S. Patent No.
It is described in specifications such as No. 3587993 and No. 3470021. A coupling agent may also be used, and known titanate coupling agents, silane coupling agents, etc. may be used in combination. Among titanium-based coupling agents, hexacoordinated titanate-based coupling agents are preferred;
Furthermore, it is a coupling agent with six coordinations,
A compound whose general formula is (R-0)- ₄ Ti[P(OR') ₂ OH] ₂ (R and R' are linear or branched saturated alkyl groups, or R is a linear or branched saturated alkyl group) An alkyl group in which R' represents an aryl group is preferred. Examples of this compound include the following (1) and (2). (1) Tetraisopropylbis(dioctylphosphite) titanate ( _{2) Tetraoctylbis(ditridecylphosphite) titanate (C8H17O)-4Ti[P(-OC13H27 ) 2OH ] 2As a lubricant} , aliphatic dibasic carboxylic acid, Aromatic carboxylic acid, silicone oil, graphite, molybdenum disulfide, tungsten disulfide, fatty acid esters consisting of a monobasic fatty acid with 12 to 16 carbon atoms and a monohydric alcohol with 3 to 12 carbon atoms, carbon number Fatty acid esters made of 17 or more monobasic fatty acids and a monohydric alcohol with a total carbon number of 21 to 23 carbon atoms are used. These lubricants are added in an amount of 0.2 to 20 parts by weight based on 100 parts by weight of the binder.
These are described in Japanese Patent Publication No. 43-23889. In addition, commonly used abrasive materials include fused alumina, silicon carbide, chromium oxide, corundum, artificial corundum, diamond, artificial diamond, garnet, emery (main ingredients are corundum and magnetite), titanium dioxide, etc. be done.
These abrasives have an average particle diameter of 0.05 to 5μ, particularly preferably 0.1 to 2μ. These abrasives are added in an amount of 1 to 20 parts by weight per 100 parts by weight of the magnetic powder. These abrasives are disclosed in Japanese Unexamined Patent Publication No. 115510/1984 and US Patent No.
Publication No. 3007807, Publication No. 3041196, Publication No. 3041196, Publication No.
3687725, British Patent No. 1145349, and West German Patent (DT-PS) No. 853211. In addition, carbon black is used as an antistatic agent.
Conductive powders such as graphite, tin oxide-antimony oxide compounds, titanium oxide-tin oxide-antimony oxide compounds, carbon black graft polymers; natural surfactants such as saponin; alkylene oxide-based, glycerin-based, glycidol-based, etc. Nonionic surfactants; cationic surfactants such as pyridine and other heterocycles, phosphoniums or sulfoniums; carboxylic acids, sulfonic acids,
Examples include, but are not limited to, anionic surfactants containing acidic groups such as phosphoric acid, sulfuric ester groups, and phosphoric ester groups; amphoteric surfactants such as amino acids, aminosulfonic acids, and sulfuric or phosphoric esters of amino alcohols. These surfactants that can be used as antistatic agents are US Pat. Nos. 2271623, 2240472,
No. 2288226, No. 2676122, No. 2676924, No. 2676924, No.
No. 2676975, No. 2691566, No. 2727860, No. 2730498, No. 2742379, No. 2739891, No. 3068101, No. 3158484, No. 3201253,
Same No. 3210191, Same No. 3294540, Same No. 3415649,
3441413, 3442654, West German Patent Publication (OLS) 1942665, British Patent No. 1077317,
1198450, etc., Ryohei Oda et al., ``Synthesis of Surfactants and Their Applications'' (Maki Shoten 1964 edition); AW Peiri, ``Surf S Active Agents'' (Interscience Publications Inc. 1958) 2009 edition): "Encyclopedia of Surf S Active Agents Volume 2" by TR Sisley (Chemical Publishing Company - 1964 edition): "Surfactant Handbook" 6th edition (Sangyo Tosho Co., Ltd. December 20, 1964)
It is written in books such as Japan). These surfactants may be added alone or in combination. These are used as antistatic agents, but may also be used for other purposes, such as dispersion, improving magnetic properties, improving lubricity, and as coating aids. Solvents blended in the above paint or diluting solvent when applying this paint include ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; alcohols such as methanol, ethanol, propanol, butanol; methyl acetate, ethyl acetate. , esters such as butyl acetate, ethyl lactate, and ethylene glycol monoacetate; ethers such as glycol dimethyl ether, glycol monoethyl ether, dioxane, and tetrahydrofuran; aromatic hydrocarbons such as benzene, toluene, and xylene; methylene chloride, ethylene chloride, Halogenated hydrocarbons such as carbon tetrachloride, chloroform, and dichlorobenzene can be used. The magnetic powder, the above-mentioned binder resin, dispersant, lubricant, abrasive, antistatic agent, solvent, etc. are kneaded to form a magnetic paint. During kneading, the magnetic powder and each of the above-mentioned components are fed into a kneading machine either simultaneously or sequentially. For example, there is a method in which magnetic powder is first added to a solution containing a dispersant and kneaded for a predetermined period of time, and then the remaining components are added and kneaded continuously to obtain a magnetic paint. Various kneaders are used for kneading and dispersing. For example, two-roll mill, three-roll mill, ball mill, pebble mill, sand grinder,
Szegvari attritor, high speed impeller disperser,
These include high-speed stone mills, high-speed impact mills, disper kneaders, high-speed mixers, homogenizers, and ultrasonic dispersers. The technology related to kneading and dispersion is written by TCPATTON.
Paint Flow and Pigment Despersion 2nd Ed.
(published by John Willey & Sons in 1979). Also, U.S. Patent No. 2581414;
It is also described in each specification of No. 2855156. The above-mentioned magnetic paint is composed of magnetic powder, binder resin, organic powder used in the above-mentioned present invention, and the above-mentioned various additives and solvents as required. 15
No. 39-26794, No. 43-186, No. 47-28043
No. 47-28045, No. 47-28046, No. 47-
No. 28048, No. 47-31445, No. 48-11162, No. 48
-21331, 48-33683, West German patent publications
Those described in detail in the specification of No. 2060655 etc. can also be used. Examples of the support include polyesters such as polyethylene terephthalate and polyethylene-2,6-naphthalate, polyolefins such as polypropylene, cellulose derivatives such as cellulose triacetate and cellulose diacetate, and plastics such as polyamide and polycarbonate. Metals such as Cu, Al, Zn, glass,
Ceramics such as BN, Si carbide, porcelain, and ceramics can also be used. The thickness of these supports is approximately 3 to 100 μm in the case of a film or sheet, preferably 5 to 50 μm.
and 30 μm to 10 in the case of disks and cards.
mm, and in the case of a drum, it is used in a cylindrical shape, and its shape is determined depending on the record used. Further, the support may be in any form such as a tape, sheet, card, disk, or drum, and various materials may be selected as necessary depending on the form. Application methods for applying the above paint onto the support include air doctor coating, blade coating, air knife coating, squeeze coating, impregnation coating, reverse roll coating, transfer roll coating, gravure coating, kiss coating, cast coating, Spray coats and the like can be used, but are not limited to these. Specific explanations of these are described in detail in ``Coating Engineering'' (published by Asakura Shoten in 1971). The orientation magnetic field used to orient the magnetic layer is approximately 500 to 3500 Gauss in alternating current or direct current, and the drying temperature when applying and drying the magnetic paint is approximately
The temperature is preferably about 50 to 100°C. Effects of the Invention According to the present invention, ferromagnetic metal powder is immersed in an aqueous solution containing a polycarboxylic acid surfactant represented by the above general formula and an organic solvent that accounts for 50% by weight or more of the entire liquid, and then dried under reduced pressure. As a result, the surface activity of the ferromagnetic metal powder can be reduced to prevent it from rising in temperature in the air or igniting, and it can also be dispersed with a binder resin to form a paint. Not only the dispersibility but also the dispersion stability can be maintained. Moreover, since the magnitude of saturation magnetization of the ferromagnetic metal powder is maintained as it is, it is suitable as a magnetic powder for high-density recording. If a magnetic recording medium is manufactured using such surface-treated ferromagnetic metal powder, it is not only easy to manufacture it, but also its quality can be maintained at a high level. ExamplesExample 1 Coercive force 1540Oe, σs145emu/g, specific surface area 53
m ² /g of acicular iron magnetic powder (impregnated with toluene 1.7 times the weight of the powder, Fe:Ni=89:
11) After drying 3,400 parts by weight by vacuum distillation and completely volatilizing toluene, 2 kg in a nitrogen atmosphere.
Collected. This raw material magnetic powder is designated as P-1. This raw material magnetic powder P-1 was mixed in nitrogen with the following composition. P-1 1000 parts by weight Orotane 7313D 120 parts by weight (25% aqueous solution manufactured by Rohm and Haas) Methanol 2000 parts by weight After this mixing, the mixture was taken out into the air and further stirred and mixed using a stirrer to prepare a slurry. Thereafter, this slurry was transferred to a vacuum distiller and dried until there was no distillate left, thereby producing the magnetic powder of Example 1. After the treated magnetic powder was cooled to room temperature, it was transferred from a vacuum to a nitrogen atmosphere, and then placed in an atmosphere with an oxygen concentration of 5%. No increase in temperature was observed even after 5 minutes had passed. Therefore, we tried to gradually increase the oxygen concentration, but no heat generation was observed even at the oxygen concentration of air, and we were able to extract it into the air. The coercive force (Hc) and saturation magnetization (σs) of the magnetic powder taken out were measured, and these results are shown in Table 2 along with the evaluation of the presence or absence of temperature rise and the presence or absence of heat generation. Note that Hc and σs were measured at a measurement magnetic field (Hm) of 10KOe. Examples 2 to 4 The same except that the formulations in the respective columns of Examples 2 to 5 in Table 1 were used instead of the above formulations used in Example 1 (same as the formulation in the Example 1 column in Table 1). Magnetic powders of Examples 2 to 5 were obtained respectively. Each of these magnetic powders was examined in the same manner as in Example 1 to determine whether there was a temperature increase or not and whether there was heat generation, and the results are shown in Table 2 similarly to the other measurement results of Example 1. Comparative Example 1 When 100 parts by weight of the above raw material magnetic powder P-1 was placed in an atmosphere with an oxygen concentration of 5%, the temperature rose to 25°C within 1 minute.
The temperature was raised from to 70℃. Then replace with nitrogen again.
After lowering the temperature of the raw magnetic powder to 25°C, when it was taken out into the air, it suddenly became red hot and changed color from black to reddish brown. These results are also shown in Table 2. Comparative Examples 2 to 4 Magnetic powders of Comparative Examples 2 to 4 were obtained in the same manner, except that the formulations in the Comparative Examples 2 to 4 columns of Table 1 were used in place of the above formulations used in Example 1. These magnetic powders were placed in an oxygen atmosphere in the same manner as in Comparative Example 1, and the temperature was raised from 25°C after 1 minute, and the presence or absence of red heat when taken out into the air in the same manner as in Comparative Example 1 was determined. The results are shown in Table 2 along with the other measurement items mentioned above. Comparative Example 9 Magnetic powder of Comparative Example 9 was obtained in the same manner as in Example 1, except that 30 parts by weight of sodium oleate, which is a monocarboxylic acid salt, was used in place of 120 parts by weight of Orotane 7313D. This magnetic powder was also examined in the same manner as in Example 1, and the results are shown in Table 2. Example 5 Raw material magnetic powder P- with the formulation used in Example 4
Example 5 was carried out in the same manner as in Example 4, except that raw magnetic powder P-2 having a coercive force (Hc) of 1510 Oe, a saturation magnetization (σ _s ) of 131 emu/g, and a specific surface area of 45 m ² /g was used in place of Example 1. Magnetic powder was obtained. Table 1 shows the formulation for magnetic powder treatment in Example 5, and Table 2 shows the results of evaluation in the same manner as in Example 1. From the results of Example 2 and Comparative Example 3, the amount of water is 50%
It can be seen that the smaller the amount, the less deterioration of characteristics such as saturation magnetization. Next, the magnetic powders of Examples 1 to 5 above and Comparative Example 1
The magnetic powders of Examples 6 to 10 corresponding to Examples 1 to 5 were prepared by dispersing the magnetic powders of Examples 1 to 4 and Comparative Example 9 to prepare paints using the following method. Magnetic tape and comparative examples 1 to 4
and Comparative Examples 5 to 8 corresponding to Comparative Example 9, respectively.
And a magnetic tape of Comparative Example 10 was prepared. Preparation of paint Magnetic powder of each example or comparative example 500 parts by weight Salt-vinyl acetate copolymer 56 parts by weight (VAGH manufactured by Union Carbide Co.) Polyurethane (Estan 5701 manufactured by Gutudoritsu) 56 parts by weight Lecithin 13 parts by weight Lubricant 15 Parts by weight Cyclohexanone 655 parts by weight Methyl ethyl ketone 140 parts by weight Toluene 140 parts by weight These components were charged into a ball mill and dispersed to prepare a dispersion. After filtering this dispersion through a 1 μm filter, 10 parts by weight of polyfunctional isocyanate was added. A paint was prepared. Since the magnetic powder of Comparative Example 1 has high activity, the above mixing and dispersion were performed in a nitrogen-substituted system. Preparation of magnetic tape The above paint was coated and dried on a polyethylene terephthalate support using a reverse roll coater under an orienting magnetic field of 2500 Gauss to a dry film thickness of 3 μm, and further treated with a super calendar roll. Make it a tape. Regarding the magnetic tapes of the above examples and comparative examples,
Table 3 shows the coercive force (Hc), squareness ratio, C/N (carrier noise) (dB) at 5MHz, and demagnetization rate (%). In addition, the above Examples 6 to 10 and Comparative Examples 1 to
We sampled the magnetic tape paint in step 4 without a curing agent, and measured the differences in viscosity immediately after dispersion and after 1 day and night, the gloss (light selection) of the paint applied to a polyethylene terephthalate base with an applicator, and the magnetic field applied. A comparison was made based on the squareness ratio when The data are shown in Table 4. In addition, C/N is the value measured by wrapping a tape around a drum with a diameter of 40 mm and rotating at a rotation speed of 3.8 m/sec. The value measured is the ratio of decrease in , the gloss is the value of reflection by 60 degree constant angle reflection (ASTM compliant), and the viscosity is the value after 1 minute at 25°C with a B-type viscometer with No. 4 rotor (poise). From the results in Tables 2 to 4, it was found that the ferromagnetic metal powders of Examples 1 to 5 were superior to the ferromagnetic metal powders of Comparative Examples 1 to 4 and Comparative Example 9, and the performance of magnetic tapes using them was also improved. It can be seen that those using the ferromagnetic metal powders of Examples 1 to 5 are superior to those using the ferromagnetic metal powders of Comparative Examples 1 to 4 and Comparative Example 9.

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Claims (1)

[Scope of Claims] 1. An aqueous solution containing a polycarboxylic acid surfactant of the following general formula, and a ferromagnetic metal powder in an organic solvent that is miscible with the aqueous solution and that is more than 50% by weight based on the total amount of the aqueous solution. 1. A method for producing a surface-treated ferromagnetic powder, which comprises soaking the powder and drying it under reduced pressure to obtain a surface-treated ferromagnetic powder. general formula (In the formula, R is a vinyl compound, M ¹ and M ² are monovalent metals, hydrogen atoms, NH ₄ , or organic ammonium ions, and k is an integer from 2 to 1000) 2 Polycarboxylic acid-based surfactant of the following general formula A ferromagnetic metal powder surface-treated by immersing a ferromagnetic metal powder in an aqueous solution containing a chemical agent and an organic solvent that is miscible with the aqueous solution and in an amount greater than 50% by weight based on the total amount of the aqueous solution, and drying under reduced pressure after the immersion. 1. A method for producing a magnetic recording medium, which comprises producing a powder, and coating a nonmagnetic support with a magnetic layer made of the surface-treated ferromagnetic metal powder and at least a binder resin. general formula (In the formula, R is a vinyl compound, M ¹ and M ² are monovalent metals, hydrogen atoms, NH ₄ or organic ammonium ions, and k is an integer from 2 to 1000)