JPS629535B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to magnetic iron oxide used in magnetic recording media such as magnetic tapes, magnetic disks, and magnetic sheets. In particular, the present invention relates to magnetic iron oxide, which has few pores, high coercive force, and excellent dispersibility and orientation. This relates to a method for producing magnetic iron oxide. The production of high-density magnetic recording bodies requires magnetic materials with high coercive force, excellent acicular squareness ratio, and good dispersibility. As is well known, ferromagnetic iron oxide is iron oxyhydroxide [α-FeOOH (goethite)]
Obtained by dehydrating, reducing, and oxidizing β-FeOOH, γ-FeOOH (lepidocrocite). Regarding the above technology, please refer to Special Publication No. 26-7776, No. 31
-No. 3292, No. 44-14090, No. 47-25959, No. 47
-39477, JP-A No. 47-40097, JP-A No. 49-15699
No. 2,127,907, and US Pat. No. 2,388,659 are known. In order to increase the coercive force of iron oxide magnetic powder,
It is effective to dissolve Co as a solid solution, and this method includes U.S. Patent No. 3117333, U.S. Patent No. 3671435, U.S. Patent Publication No. 41-6538, U.S. Pat.
No. 48-10994, No. 48-15759, No. 49-4264,
JP-A No. 47-22707, No. 48-1998, 48-51297
No. 48-54497, No. 48-76097, No. 48-
Issues such as No. 87397 and No. 48-101599 are known. Co-containing magnetic iron oxide has pressure demagnetization, heating demagnetization, changes in coercive force over time, uneven coercive force, erasing properties,
There are problems such as deterioration of the SP ratio, and improvements are being made in these areas. 〓〓〓〓
In addition, ferromagnetic iron oxide has many vacancies as a result of water loss, but the presence of vacancies causes a decrease in the apparent magnetization per unit volume of ferromagnetic iron oxide. This produces several magnetic domains within the particles and causes ferromagnetic iron oxide aggregation in the magnetic film. The following four methods are known to reduce the number of pores during dehydration, reduction, and oxidation steps. (1) Coating particles with an inorganic substance prior to dehydration, reduction, and oxidation. (Special Publication No. 38-26278, No. 40-
No. 22055, JP-A No. 47-42396, JP-A No. 48-83100
No. 48-67197, No. 49-14400, US Patent
No. 3652334 etc. are known. ) (2) Coating particles with organic matter prior to dehydration, reduction, and oxidation. (U.S. Patent Nos. 3394142 and 3498748)
No., JP-A-47-40097, JP-A-49-8496, JP-A-41-18786, etc. are known. ) (3) Add ions that are effective against dehydration, reduction, and oxidation. [Al ion (Special Publication No. 38-26278,
Cr ion (Unexamined Japanese Patent Publication No. 1973-59137, etc.)
43899, 49-43900, etc.), Ca ion (Japanese Patent Publication No. 47-31195), and other examples include
- No. 30477, Special Publication No. 48-23752, No. 48-23753
No. 48-23754, No. 49-7313, Japanese Unexamined Patent Publication No. 1973
- There are issues such as 97800. ] (4) Use special dehydration, reduction, and oxidation conditions.
(Special Publications No. 26-7776, No. 38-26156, No. 39-
No. 5009, No. 39-16612, No. 42-24661, Japanese Unexamined Patent Publication No. 49-43900, and US Patent No. 2689168 are known. ) The above measures have been taken to reduce the number of pores. When particles are covered with inorganic substances or metal ions are added, these particles become solid solutions in magnetic iron oxide during heat treatment, or the surface properties of iron oxide change, causing sintering to proceed. In order to obtain high coercive force with few holes, α
-500~ ₈₀₀ ℃ at _Fe2O3 stage, 300 _℃ at _Fe3O4 stage
It is necessary to perform heat treatment at a high temperature of ~500°C, and such heat treatment promotes sintering of the magnetic iron oxide. It is difficult and requires a long dispersion time to disperse the magnetic iron oxide whose surface properties have changed due to the progress of sintering to create a magnetic coating liquid. The present invention improves these drawbacks. An object of the present invention is to provide a method for producing a ferromagnetic iron oxide having a small number of first pores, a high coercive force, and excellent acicularity. The second object is to provide a method for producing ferromagnetic iron oxide in which the coercive force decreases little when the iron oxide is highly filled. Thirdly, it is an object of the present invention to provide a method for producing ferromagnetic iron oxide, which has excellent dispersibility and short dispersion time to prepare a magnetic coating liquid. Fourth, it is an object of the present invention to provide a method for producing ferromagnetic iron oxide with excellent orientation. Fifth, it is an object of the present invention to provide a magnetic recording body using the above-mentioned ferromagnetic iron oxide, which has an excellent squareness ratio and orientation, and is suitable for high-density recording. In recent years, research on the state of atomic nuclei has been progressing using resonance absorption of gamma rays. This phenomenon is called the Mössbauer effect, and various research is progressing on it, including iron compounds and tin compounds. More information about the Mössbauer effect can be found in the following books: Γ H. H. Frauenfelder, “Mössbauer Effect”, (Davrieux, A., Benjamin, New York, 1962) [H.Frauenfelder
Author, “The Mossbaner Effect”, (WA
Benjamin, New York, 1962)]. Γ G., K., Beltime, “Mössbauer Effect: Principles and Applications” (Academic Press,
New York, 1964) [GKWertheim,
“Mossbaner Effect: Principles and
Applications” (Academic Press, New
York, 1964)]. Γ “Mössbauer spectroscopy” by Hirotoshi Sano, (Kodansha, 1972). When the Mössbauer effect was measured for the magnetic recording material according to the present invention, it was completely unexpected that a peak corresponding to a super paramagnetic material was present. A superparamagnetic material is a ferromagnetic or antiferromagnetic material that becomes fine particles and exhibits the behavior of a paramagnetic material due to thermal motion.
The relationship with the Mössbauer effect is explained in pages 238 to 239 of the above-mentioned "Mössbauer Spectroscopy", which states, ``When a ferromagnetic material or an antiferromagnetic material becomes fine particles, a significant change is observed in the Mössbauer spectrum. There are magnetic domains of a certain size in the body, but when they become fine particles, there are even
There is only one magnetic domain, and the magnetic field acting on the position of the nucleus within it fluctuates with a relaxation time r given by r = roexp [KV/KT] (5.26). Here, K is an asymmetry constant and V is the particle size. As can be seen from this, when kT<KV, the magnetic field is oriented in a fixed direction for a long time at that temperature, indicating magnetic splitting, but when kT>KV, the magnetic field at the core position is averaged due to thermal motion, and the magnetic field is The division will no longer be visible. This latter state is similar to the phenomenon in which the magnetic field at the core is averaged out due to the thermal motion of molecules in paramagnetic materials, and is called a superparamagnetic phenomenon. From the relationship in equation (5.26), it is also possible to estimate the particle size using the superparamagnetic phenomenon (in terms of Mössbauer, the disappearance of magnetic splitting). ” is stated. The superparamagnetic material used in the present invention does not refer to fine particles that are said to contribute to the transfer effect in magnetic recording materials, but rather to substances that give a peak corresponding to super paramagnetism when measuring the Mössbauer effect. means. In other words, the superparamagnetic material of the present invention is physically considered to be iron oxide. Although it is not clear how the superparamagnetic iron oxide is distributed in Example 1, it is clear from the difference with the comparative example that the diameter of one particle (long axis 0.5μ) is
It is thought that superparamagnetic iron oxides with a diameter of 100 Å or less exist near the surface, and when these superparamagnetic iron oxides are made into paint, they promote dispersion into single particles, resulting in excellent squaring as shown in Table 1. high saturation magnetic flux density,
This is thought to be the cause of the low modulation noise. The proportion of the superparamagnetic substance in the magnetic iron oxide is confirmed from the area of the absorption peak of the magnetic iron oxide and the area of the absorption peak due to the superparamagnetic substance in the Mössbauer spectrum. In addition, it should be determined by precisely measuring the saturation magnetization (os), but in this case there is also the influence of non-magnetic impurities, so the relationship between the presence of the superparamagnetic component and the improvement of the characteristics of the magnetic recording medium according to the present invention is not clear. This was done for the first time using the Bauer spectrum. That is, the present invention is a method for producing ferromagnetic iron oxide, which is characterized in that the ferromagnetic powder whose main component is iron oxide contains a superparamagnetic component. In the present invention, ferromagnetic powders containing iron oxide as a main component include maghemite (γ-Fe ₂ O ₃ ), magnetite (Fe ₃ O ₄ ), and bertolide compounds (FeOx,
1.33 < Co is particularly preferred as the metal ion. Specifically, Codoped maghemite, Co and
Mndoped maghemite, Co and Crdoped maghemite, Co, Mn and Crdoped maghemite,
Codoped magnetite, Co and Mndoped magnetite, Co and Crdoped magnetite, Co, Mn
and Crdoped magnetite, Codoped beltrite iron oxide, Co and Mndoped beltrite iron oxide, Co, Mn and Crdoped beltrite iron oxide, etc. The effective range of the superparamagnetic material in the magnetic recording medium is 0.01 to 30 wt.%, based on the magnetic iron oxide, and the generally preferred range is 0.1 to 15 wt.%. but,
If the amount of binder can be reduced, this range can be expanded. It is known that the coercive force (Hc) of an iron oxide magnetic material can be increased by containing Co. The amount of Co added is within a range of 0.5% or more and 20% or less, which is useful in the field of magnetic recording. ), the amount of Co is preferably 1 to 10%. Even in the case of magnetic recording materials using such iron oxide magnetic materials containing Co, the effective range of superparamagnetic materials is 0.01 to 30 wt.%.
The preferred range is 0.1 to 15 wt.%. In addition, the stability of iron oxide magnetic materials (including iron oxide magnetic materials containing Co), pressure demagnetization,
Bertolide compounds (FeOx, 1.33<x<1.5) in an oxidation state intermediate between magnetite and maghemite are used to improve thermal demagnetization, but in the case of magnetic recording materials using these compounds, the effective The range is 0.01 to 30 wt.%, and the preferred range is 0.1 to 20 wt.%. When dehydrating, reducing, and oxidizing iron oxide-based magnetic materials, the surface of iron oxyhydroxide is coated with various substances in advance to reduce the number of pores.
It is known. The amount of material covering the surface is γ-Fe ₂ O ₃
0.1-20wt.% is effective, but the preferred range is
It is 0.5-10wt.%. Material ions that coat the surface of iron oxyhydroxide include phosphates (for example, H ₃ PO ₄ ; Na ₄ P ₂ O ₇・10H ₂ O; NaPO ₃
12H ₂ O ₂ (NH ₄ ) ₃ PO ₄・3H ₂ O; (NH ₄ ) ₂ HPO ₄ ;
K ₂ HPO ₄ ; Na ₂ HPO ₄ ; Na ₂ HPO ₄・12H ₂ O;
NH ₄ H ₂ PO ₄ ; KH ₂ PO ₄ ; NaH ₂ PO ₄・H ₂ O;
NaH ₂ PO ₄・2H ₂ O; L: H ₂ PO ₄ , etc.; Borate (H ₃ BO ₃ , NaBO ₄・4H ₂ O, etc.); SiO ₂ sol, Al
(OH) ₃ , Fe(OH) ₃ AlCl ₃ , KCl, ZnCl ₂ , titanium chloride, sodium sulfate, aluminum sulfate, Ca
(OH) ₂ , silver ions, platinum metal ions, water-soluble fatty acids (stearic acid, balmitic acid, oleic acid, etc.) and their alkali salts, higher alcohols, higher alcohol esters, amides and other derivatives, morpholin, hydrophobic fatty acids These include monocarboxylic acids and coconut oil fatty acids. In this way, in the case of a magnetic recording medium using surface-treated magnetic iron oxide, the effective range of superparamagnetic material is 0.01 to 30 wt.%, and the preferable range is 0.1%.
~10wt.%. If the superparamagnetic component exceeds the effective range, the sensitivity and output of a magnetic tape will be low, and the surface resistance of the magnetic layer will be high, causing noise. As methods for producing magnetic iron oxide used in the present invention, the following two methods are preferred. (1) Disperse α-FeOOH in water, add iron () salt solution, and then add oxalic acid or alkali oxalate to form an iron oxalate layer on α-FeOOH. This is washed with water, dried, dehydrated at 300-700°C, and reduced to Fe ₃ O ₄ at 300-500°C. Fe ₃ O ₄
is partially oxidized to form a bertholed compound of FeOx (1.33<x<1.5). Or Fe ₃ O ₄ 200
It is oxidized to γ-Fe ₂ O ₃ at ~400℃. When an iron () salt solution is added and Co is present, an iron oxalate layer containing Co can be formed. In these cases, an iron oxalate layer may be formed by coexisting a surface coating of iron oxyhydroxide and adding oxalic acid or an alkali oxalate. (2) α-Fe ₂ O ₃ (acicular α-Fe ₂ O ₃ is particularly preferred) is dispersed in water, and an iron oxalate layer is provided on the surface in the same manner as in (1 _). Get O ₃ , 300-500
Reduce at °C. Partially oxidize the obtained Fe ₃ O ₄ ,
Obtain FeOx (1.33<x<1.5). or
Oxidize Fe ₃ O ₄ at 200 to 400°C to form γ-Fe ₂ O ₃ . By coexisting iron() salt and Co salt,
An iron oxalate layer containing Co can be provided. As the iron salt used in the above method, any water-soluble ferrous salt can be used. Similarly, any water-soluble salt can be used as the Co salt, and NaOH, KOH, NH ₄ OH, LiOH, etc. can be used as the alkali. In Example 2, an example of a magnetic recording body using only the magnetic material according to the present invention is described, but other magnetic recording materials [for example, ordinary γ-Fe ₂ O ₃ ,
A magnetic recording body may be formed by mixing Fe ₃ O ₄ , FeOx (1.33<x<1.5), Co-containing iron oxide magnetic material, CrO ₂ , alloy]. Furthermore, it is suitable for use in magnetic recording bodies coated in multiple layers, and can be used as either the upper layer or the lower layer. When applying multilayer coating, it may be mixed with other magnetic materials and used in the same manner as above. The ferromagnetic iron oxide of the present invention obtained by the above method is dispersed with a binder, coated on a substrate (support) using an organic solvent, and dried to form a magnetic layer to obtain a magnetic recording medium. Regarding the manufacturing method of the magnetic paint used in the present invention, please refer to Japanese Patent Publications Nos. 43-186, 47-28043, 47-28045, 47
It is described in detail in publications such as No. 28046, No. 47-28048, and No. 47-31445. The magnetic paints described in these documents mainly consist of ferromagnetic powder, binder, and coating solvent, and also include dispersants, lubricants,
It may also contain additives such as abrasives and antistatic agents. As the binder used in the present invention, conventionally known thermoplastic resins, thermosetting resins, reactive resins, and mixtures thereof are used. As a thermoplastic resin, the softening temperature is 150℃ or less, the average molecular weight is 10,000 to 200,000, and the degree of polymerization is approximately 200 to 2,000.
For example, vinyl chloride vinyl acetate copolymer, vinyl chloride vinylidene chloride copolymer, vinyl chloride acrylonitrile copolymer, acrylic acid ester acrylonitrile copolymer, acrylic acid ester vinylidene chloride copolymer, acrylic acid ester copolymer, 〓〓〓〓
Stealth styrene copolymer, methacrylic acid ester acrylonitrile copolymer, methacrylic acid ester vinylidene chloride copolymer, methacrylic acid ester styrene copolymer, urethane elastomer, polyvinyl fluoride, vinylidene chloride acrylonitrile copolymer, butadiene acrylonitrile copolymer combination, polyamide resin, polyvinyl butyral, cellulose derivatives (cellulose acetate butyrate, cellulose diacetate, cellulose triacetate, cellulose propionate, nitrocellulose, etc.), styrene-butadiene copolymer,
Polyester resins, chlorovinyl ether acrylate copolymers, amino resins, various synthetic rubber-based thermoplastic resins, and mixtures thereof are used. Examples of these resins are given in Japanese Patent Publication No. 37-6877, 39-
No. 12528, No. 39-19282, No. 40-5349, No. 40-20907
No. 41-9463, 41-14059, 41-16985, 42
- No. 6428, No. 42-11621, No. 43-4623, No. 43-15206
No. 44-2889, 44-17947, 44-18232, 45
-No. 14020, No. 45-14500, No. 47-18573, 47-
No. 22063, No. 47-22064, No. 47-22068, No. 47-22069
No. 47-22070, No. 48-27886, U.S. Patent
No. 3144352; No. 3419420; No. 3499789; No. 3499789;
Described in No. 3713887. The thermosetting resin or reactive resin has a molecular weight of 200,000 or less in the state of a coating solution, but when added after coating and drying, the molecular weight becomes infinite due to reactions such as condensation and addition. Also, among these resins, those that do not soften or melt before the resin is thermally decomposed are preferred. Specifically, examples include phenolic resins, epoxy resins, polyurethane curable resins, urea resins, melamine resins, alkyd resins, silicone resins, acrylic reaction resins, epoxy-polyamide resins, mixtures of high molecular weight polyester resins and isocyanate prepolymers, and methacrylic resins. Mixture of acid salt copolymer and diisocyanate prepolymer, mixture of polyester polyol and polyisocyanate, urea formaldehyde resin, low molecular weight glycol/high molecular weight diol/
These include mixtures of triphenylmethane triisocyanate, polyamine resins, and mixtures thereof. Examples of these resins are given in Japanese Patent Publication No. 39-8103, 40-
No. 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-
No. 22065, No. 47-22066, No. 47-22067, No. 47-22072
No. 47-22073, No. 47-28045, No. 47-28048,
No. 47-28922, US Patent No. 3144353; US Patent No. 3320090
No. 3437510; No. 3597273; No. 3781210;
It is described in No. 3781211. These binders may be used alone or in combination, and other additives may be added. The mixing ratio of the ferromagnetic powder and the binder is 10 to 400 parts by weight of the binder to 100 parts by weight of the ferromagnetic powder, preferably 10 to 400 parts by weight.
Used in a range of 30-200 parts by weight. In addition to the above-mentioned binder and fine ferromagnetic powder, additives such as a dispersant, a lubricant, an abrasive, and an antistatic agent may be added to the magnetic recording layer. Dispersants include caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid, elaidic acid, linoleic acid,
Fatty acids with 12 to 18 carbon atoms such as linolenic acid and stearolic acid (R ₁ COOH, R ₁ is an alkyl group with 11 to 17 carbon atoms); Alkali metals of the above fatty acids (Li.
Na, K, etc.) or alkaline earth metals (Mg, Ca,
Metal soap consisting of Ba); lecithin, etc. are used. In addition, higher alcohols having 12 or more carbon atoms and sulfuric esters can also be used. These dispersants are added in an amount of 1 to 20 parts by weight per 100 parts by weight of the binder. Lubricants include silicone oil, carbon black, graphite, carbon black graft polymer, molybdenum disulfide, tungsten disulfide, monobasic fatty acids with 12 to 16 carbon atoms and 3 carbon atoms.
Fatty acid esters consisting of ~12 monohydric alcohols, monobasic fatty acids having 17 or more carbon atoms, and monohydric alcohols having 21 to 23 carbon atoms in total with the number of carbon atoms in the fatty acids etc. can be used. These lubricants are added in an amount of 0.2 to 20 parts by weight per 100 parts by weight of the binder. Regarding these, please refer to Special Publication No. 23889 (1973), Special Application No. 23889 (1977),
28647, specifications of Japanese Patent Application No. 1983-81543, U.S. Patent No. 3470021; U.S. Patent No. 3492235; U.S. Pat.
No. 3523086; No. 3625760; No. 3630772; No. 3630772;
No. 3634253; No. 3642539; No. 3687725; “IBM
Technical Disclosure Bulletin”Vol.9.No.7.Page
〓〓〓〓
779 (December 1966); “ELEKTRONIK” 1961
It is listed in 2015, No. 12, Page 380, etc. Commonly used abrasive materials include fused alumina, silicon carbide chromium oxide, corundum, artificial corundum, diamond, artificial diamond, garnet, and emery (main components: corundum and magnetite). These abrasives have an average particle size of 0.05 to 5μ,
Particularly preferably, it is 0.1 to 2μ. These abrasives are added in an amount of 7 to 20 parts by weight per 100 parts by weight of the binder. Regarding these, please refer to the special application filed in 1973
No. 26749, US Patent No. 3007807; US Patent No. 3041196
No. 3293066; No. 3630910; No. 3687725;
British Patent No. 1145349, West German Patent (DT-PS)
Described in No. 853211. Natural surfactants such as sabonin as antistatic agents; nonionic surfactants such as alkylene oxide, glycerin, and glycidol; higher alkylamines, quaternary ammonium salts, pyridine and other heterocycles, phosphonium or sulfonium. Cationic surfactants such as; anionic surfactants containing acidic groups such as carboxylic acid, sulfonic acid, phosphoric acid, sulfuric acid ester groups, and phosphoric ester groups;
Ampholytic activators such as amino acids, aminosulfonic acids, sulfuric acid or phosphoric acid esters of amino alcohols, etc. are used. Some examples of surfactant compounds that can be used as antistatic agents are U.S. Pat.
No. 2288226, No. 2676122, No. 2676924,
Same No. 2676975, No. 2691566, No. 2727860, Same No.
No. 2730498, No. 2742379, No. 2739891, No.
No. 3068101, No. 3158484, No. 3201253, No. 3201253, No.
No. 3210191, No. 3294540, No. 3415649, No. 3210191, No. 3294540, No. 3415649, No.
No. 3441413, No. 3442654, No. 3475174, No. 3441413, No. 3442654, No. 3475174, No.
No. 3545974, West German Patent Publication (OLS) 1942665
No. 1077317, British Patent No. 1198450, etc., "Synthesis of Surfactants and Their Applications" by Ryohei Oda et al. (Maki Shoten 1964 edition); "Surface Active Agents" by A.W. Bayley) (Interscience Publications) corporate
1958 edition); TP Sisley, “Encyclopedia of Surf-Eighth Active Agents Volume 2” (Chemical Publishing Company, 1964 edition); “Surfactant Handbook”, 6th edition (Sangyo Tosho Co., Ltd., December 20, 1966) It is written in books such as Japan). These surfactants may be added alone or in combination. Although these are used as antistatic agents, they are sometimes applied for other purposes, such as dispersion, improving magnetic properties, improving lubricity, and as coating aids. To form the magnetic recording layer, the above-mentioned composition is dissolved in an organic solvent and applied as a coating solution onto a support. The thickness of the support is about 5 to 50 μm, preferably 10 to 50 μm.
The diameter is preferably around 40 μm, and materials include polyesters such as polyethylene terephthalate and polyethylene-2,6-naphthalate, polyolefins such as polypropylene, cellulose derivatives such as cellulose triacetate and cellulose diacetate,
Polycarbonate or the like is used. The above-mentioned support may be coated with a so-called backcoat on the side opposite to the side on which the magnetic layer is provided for the purpose of preventing static electricity, preventing transfer, and the like. Regarding back coats, for example, the US patent
No. 2804401, No. 3293066, No. 3617378, No. 3617378, No. 3293066, No. 3617378, No.
No. 3062676, No. 3734772, No. 3476596, No.
No. 2643048, No. 2803556, No. 2887462, No. 2887462, No.
No. 2923642, No. 2997451, No. 3007892, No.
It is shown in No. 3041196, No. 3115420, No. 3166688, etc. In addition, the form of the support is tape, sheet, card,
It may be a disk, a drum, etc., and various materials are selected depending on the form as necessary. Methods for coating the magnetic recording layer on the support include air doctor coating, plate coating,
Air knife coat, squeeze coat, impregnated coat, reverse roll coat, transfer roll coat, gravure coat, kiss coat, cast coat, spray coat, etc. can be used, and other methods are also possible. Specific explanations of these are published by Asakura Shoten. It is described in detail in "Coating Engineering", pages 253 to 277 (published on March 20, 1972). Organic solvents used during coating include ketones such as acetone, methylethylketone, methylimptylketone, and cyclohexanone; alcohols such as methanol, ethanol, propanol, and butanol; methyl acetate, ethyl acetate, butyl acetate, and lactic acid. Ethyl, glycol acetate monoethyl ethyl
Ester systems such as ether; glycol ether systems such as ether, glycol dimethyl ether, glycol monoethyl ether, and dioxane; tar systems (aromatic hydrocarbons) such as benzene, toluene, and xylene; methylene chloride, ethylene chloride, carbon tetrachloride, chloroform , ethylene chlorohydrin, dichlorobenzene, and other chlorinated hydrocarbons can be used. By such a method, the magnetic layer coated on the support is optionally treated to orient the magnetic powder in the layer, and then the formed magnetic layer is dried. Further, the magnetic recording body of the present invention is manufactured by subjecting it to surface smoothing processing and cutting it into a desired shape, if necessary. In this case, the orientation magnetic field is approximately 500 AC or DC
~2000 gauss or so, and the drying temperature is approximately 50~100 gauss
℃, and the drying time is about 3 to 10 minutes. These are, for example, Special Publication No. 39-28368, No. 40-
No. 23625, US Pat. No. 3,473,960, etc.
Furthermore, the method disclosed in Japanese Patent Publication No. 13181/1973 is considered to be a basic and important technique in this field. 20 mCi of 57Co was used as a source and a NaI detector was used. The Mössbauer effect measuring device is an AME-30 model manufactured by Elsinto, and the wave height analyzer is an NS-710 manufactured by Northern Scientific Corporation.
The Mössbauer spectrum was measured using the mold. FIG. 1 shows an example of the magnetic recording material of Example 1, in which a peak 29 of superparamagnetic material is observed. Fe(), Fe
Complex peak group 21-29 due to the coexistence of ()
was gotten. Figure 2 is the Mössbauer spectrum of γ-Fe ₂ O ₃ (Comparative Example 1) prepared by the usual method. In Figure 2, peak 29 does not exist, and it is clear that no superparamagnetic material exists. be. Effects and advantages of the present invention are as follows: (1) Magnetic iron oxide with few pores, high coercive force, and good acicularity was obtained. (2) Magnetic iron oxide was obtained with little decrease in coercive force even when the degree of filling was increased. (3) Magnetic iron oxide with excellent dispersibility and short dispersion time for making a magnetic coating solution was obtained. (4) Magnetic iron oxide with excellent orientation was obtained. (5) When such magnetic iron oxide was used, a magnetic recording medium with excellent squareness ratio and orientation was created. The magnetic recording medium using magnetic iron oxide of the present invention has low modulation noise, excellent sensitivity and frequency characteristics,
It is an excellent magnetic recording material that can be used for broadcasting video tapes, home video tapes, computer memory tapes, memory cassette tapes, digital cassette tapes, high quality sound tapes, etc. The present invention will be explained in more detail below using Examples. Those skilled in the art will readily understand that the components, proportions, order of operations, etc. shown herein may be modified without departing from the spirit of the invention. Therefore, the invention should not be limited to the examples below. In addition, in the following examples, all parts indicate parts by weight. Example 1 150g of goethite (particle size 0.5μ) and 1.5g of water
dispersed into _FeSO4・_7H2O100g and _CoSO4・
A solution of 12 g of 7H ₂ O dissolved in 0.5 of water was added to the goethite slurry. 55g of sodium oxalate in water
1.5 was added to the above slurry and stirred to obtain iron oxalate containing Co on goethite. After washing with water and drying, the yield was 203 g. Goethite with an iron oxalate layer containing Co was dehydrated at 350°C for 2 hours and then reduced at 400°C for 2 hours to obtain magnetite. After the firing furnace had cooled down, the surface of the magnetite was slowly oxidized with air, and after being allowed to adapt to the air, it was taken out and kept in a constant temperature bath at 60°C for 48 hours. A bertride iron oxide magnetic material was obtained which had a coercive force (Hc) of 590 Oe, a saturation magnetization (σs) of 81 emu/g, an oxidation degree of M=1.39, and a Co content of 1.95 atomic%. Here, M is defined by the following formula. M=1/2 × {2 × (atomic% of divalent metal ions) +3 × (atomic% of trivalent metal ions)} ×1/100 When the obtained particles were observed with an electron microscope, the average particle size was has a long axis of 0.5μ and a needle ratio of 1:10.
〜1:13, and the number of vacancies in the particles is one particle on average〓〓〓〓
There was one for. Comparative example 1 Put 62g of NaOH in a beaker of 5 and add 1 of water.
Added and dissolved. 500 g of FeSO ₄ .7H ₂ O was dissolved in 1.5 g of water and added to the NaOH solution. The liquid temperature was maintained at 40°C, and the mixture was oxidized while stirring and blowing air at a rate of about 10 min., and the reaction continued until the liquid turned yellow and the pH stabilized around 4. Next, the temperature of the above reaction solution was raised to 80°C, and 82g of NaOH was added.
was dissolved in 1 part of water, added while adjusting the pH to 4.5, and further air oxidized. After the reaction was completed, the mixture was further stirred for 30 minutes, washed with water, and dried to obtain 157 g of goethite. This goethite was dehydrated at 380°C for 2 hours, then reduced at 410°C for 2 hours, and oxidized at 280°C for 2 hours to obtain maghemite. Magnetic property is coercive force (Hc)
was 375 Oe, and the saturation magnetization (σs) was 74.6 emu/g. When the obtained particles were observed with an electron microscope, the average particle size was 0.6μ on the long axis, and the acicular ratio was 1:
The ratio was 7 to 1:10, and there were an average of 7 pores in each particle. The magnetic iron oxide obtained in Example 1 and Comparative Example 1 was uniformly sprinkled on cellophane tape, and cellophane tape was further placed on top of the powder and adhered to prepare a measurement sample.
The Mössbauer spectrum of this sample was measured at room temperature. 57Co (20mCi) was used as a radiation source, and a NaI detector was used as a detector. The Mössbauer effect measurement device used was AME-30 model manufactured by Elsinto (Israel), and the wave height analyzer was NS-710 manufactured by Northern Scientific Corporation (USA). The Mössbauer spectra obtained for Example 1 and Comparative Example 1 are shown in FIG. 1 and FIG. 2, respectively. In FIG. 1, there is a peak 29 in the center indicating superparamagnetism. Because Fe() and Fe() coexist, it is complex and some peaks are split. 2
1-28. Figure 2 is the Mössbauer spectrum of Comparative Example 1.
There are only six peaks 31 to 36 indicating Fe() and no peak indicating superparamagnetism. Example 2 Each of the five magnetic iron oxides obtained in Example 1 and Comparative Example 1
The following composition was thoroughly kneaded and dispersed in 300 parts using a ball mill. Vinyl chloride vinyl acetate copolymer (molecular weight:
4000, copolymerization ratio: 87/13) 40 parts epoxy resin [mixture of bisphenol A and epichlorohydrin, hydroxyl group content: 0.16, molecular weight: 470, epoxy content: 0.36-0.44, specific gravity: 20°C) 1.181] 30 parts silicone oil (dimethylpolysiloxane) 5 parts toluenesulfonic acid ethylamide 7 parts ethyl acetate 250 parts methyl ethyl ketone 250 parts Dismodule L-75 (product name,
Manufactured by Bayer AG, polyisocyanate compound: 3
Add 20 parts of a 75 wt.% ethyl acetate solution of an adduct of 1 mol of toluene diisocyanate and 1 mol of trimethylolpropane, mix uniformly,
It was dispersed and made into a magnetic paint. This paint was applied to a polyethylene terephthalate base (thickness 25 mμ) to a dry thickness of 10 mμ, oriented in a magnetic field at 1000 Oe, dried, and slit to obtain a magnetic tape. The slit width was 1/2 inch. The magnetic properties of the obtained magnetic tape were investigated. In order to examine the uniformity of the coercive force distribution, a differential waveform of the BH curve was taken, and its half width (ΔHc) was determined (Table 1, Cf.1). The degree of orientation is determined by calculating the squareness ratio P (Br/Bm) when the magnetic field orientation and the applied magnetic field direction match and the squareness ratio V (Br/Bm) when the orientation direction and the magnetic field direction are perpendicular, and It was determined from (Br/Bm)/P(Br/Bm) (Table 1, Cf.2). Furthermore, using a frequency spectrum analyzer (manufactured by Ando Electric KK, FSA-1B type), the relative speed was measured.
Recording and reproduction were performed at 11 m/sec., frequency analysis was performed, noise levels were compared, and modulation noise and sensitivity were investigated. Sensitivity and modulation noise measurements are all expressed in OdB using a standard tape as a reference, and are expressed as relative values (Table 1, Cf.3). The above data are shown in Table 1 along with other characteristics. 〓〓〓〓

[Table] It can be seen that the magnetic tape using the magnetic material according to the present invention has extremely superior squareness ratio (Br/Bm) and degree of orientation compared to the comparative example. In addition, the saturation magnetic flux is extremely large, or in other words, the degree of filling is extremely high, but the coercive force decreases little. In general, iron oxide-based magnetic materials have shape anisotropy that increases their coercive force, so when the degree of filling is increased, the coercive force usually decreases.
From this result, it can be said that the magnetic iron oxide according to the present invention is a magnetic material with little decrease in coercive force even when it is highly filled. When considering the dispersion time, the magnetic iron oxide according to the present invention has a shorter dispersion time than the comparative example 75.
% of the time. The short dispersion time has great industrial advantages in the production of magnetic recording media. Looking at various properties when made into a magnetic tape, the magnetic recording material according to the present invention is characterized by high sensitivity corresponding to the ability to make a tape with a high degree of filling. Furthermore, considering modulation noise, compared to standard tape, it is 2.0 to 2.5 dB at 3.5 MHz, and
The noise level is 2.3 to 2.5 dB low, and this difference becomes even larger when compared with the comparative example. Due to its high sensitivity and low noise level, the magnetic recording medium according to the present invention is a magnetic recording medium with an extremely excellent signal-to-noise ratio. Furthermore, the modulation noise is approximately 3 to 4 dB inferior to the magnetic recording material according to the present invention, but this is thought to be due to the progress of sintering during the dehydration, reduction, and oxidation processes, which deteriorates the surface properties of the magnetic recording material. It will be done. The magnetic iron oxide according to the present invention containing a superparamagnetic material does not undergo much sintering, has excellent dispersibility, and has a good degree of orientation.

[Brief explanation of the drawing]

FIG. 1 shows a magnetic recording body according to the present invention (Example 1)
is a graph showing the Mössbauer spectrum at room temperature, and peaks 21 to 28 are Fe() and
This peak indicates the coexistence of Fe(),
Peak 29 is a peak indicating superparamagnetism. FIG. 2 is a graph showing the Mössbauer spectrum at room temperature of a magnetic recording medium manufactured by a conventional method, and peaks 31 to 36 are peaks indicating Fe(). 〓〓〓〓

Claims (1)

[Claims] 1. Acicular α-FeOOH, acicular Co-containing α-
By providing an iron oxalate layer on a type of surface selected from FeOOH, acicular α-Fe ₂ O ₃ , and acicular Co-containing α-Fe ₂ O ₃ , and then dehydrating and reducing it.
A method for producing ferromagnetic iron oxide containing superparamagnetic iron oxide, characterized in that it is Fe ₃ O ₄ or Co-containing Fe ₃ O ₄ . 2 Acicular α-FeOOH, acicular Co-containing α-
By providing an iron oxalate layer on a type of surface selected from FeOOH, acicular α-Fe ₂ O ₃ , and acicular Co-containing α-Fe ₂ O ₃ , and then dehydrating and reducing it.
A method for producing ferromagnetic iron oxide containing superparamagnetic iron oxide, characterized in that Fe ₃ O ₄ or Co-containing Fe ₃ O ₄ is further oxidized.