JPH0359487B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a magnetic recording medium and aims to provide a recording medium with excellent dispersibility. Prior Art and Problems In general, magnetic recording media include magnetic tape, magnetic sheet, magnetic card, magnetic disk, magnetic drum, etc., and each is widely used for audio, video, or computer purposes.
Recently, remarkable developments have been observed. Generally, magnetic recording media are made by kneading ferromagnetic particles, which serve as a magnetic material, with a binder composition.
It is coated on a non-magnetic support. With the expansion of applications, the emergence of high-density magnetic recording media has become increasingly desirable. Requirements to enable high-density recording include the following points. (1) The coercive force of the ferromagnetic particles is high; (2) The saturation magnetization (Is) of the ferromagnetic particles is large; (3) The diameter of the ferromagnetic particles is, for example, 0.4 μm or less in major axis diameter. (4) The ferromagnetic particles must be uniformly dispersed in the binder composition; (5) The magnetic coating film must be smooth and have good contact with the magnetic head. There is no spacing loss, etc. Of the above requirements (1) to (3), the requirements for (1) to (3) can be achieved through the development of improved acicular iron oxide, acicular iron oxide coated with cobalt, or acicular alloy magnetic particles containing iron as the main component. There is a high possibility that you will be satisfied. However, it is extremely difficult to uniformly disperse ferromagnetic particles in a binder composition, a problem that remains largely unsolved or insufficiently solved in the prior art. Problems to be Solved by the Invention This invention was made to solve these problems, and it has a high coercive force and a large saturation magnetization, and furthermore, contains very fine acicular ferromagnetic particles in the binder composition. Even during the process of uniformly dispersing the magnetic particles and coating them on the support, reaggregation of the magnetic particles is difficult to occur, and the ferromagnetic particles are uniformly dispersed in the resulting magnetic coating layer. Moreover, the object is to obtain a coating film with excellent surface smoothness. Normally, the means for dispersing ferromagnetic particles in a binder composition requires selection of a dispersant, selection of a binder composition, selection of a kneading machine, etc., but in the present invention, ferromagnetic particles are dispersed in a binder composition. The present invention relates to a high-performance dispersant for uniformly dispersing the composition. In the present invention, the dispersant is selected from the viewpoint of improving the uniformity and stability of the magnetic material composition before and during the coating process. Traditionally, dispersants for ferromagnetic particles include natural surfactants such as lecithin,
Alkylbenzene sulfonic acids, fatty acid salts, fatty acid esters, phosphoric acid esters, etc. are widely used, but these known dispersants have high coercivity, large saturation magnetization, and ferromagnetic materials with fine particle diameters. There has been no one that can satisfy the requirements of dispersing particles in a binder composition and maintaining the resulting highly dispersed composition in a highly dispersed state for a long period of time. Although conventionally used dispersants are effective when dispersing ferromagnetic particles in a binder composition by mechanical kneading, they do not change the obtained dispersion state for a long time (from storage state to It is difficult to sustain the dispersion stably (up to the coating process), and therefore, although it was highly dispersible immediately after kneading, it was found that the dispersion state was poor in the magnetic layer of the magnetic recording medium. I was getting used to it. Therefore, as a result of intensive research aimed at improving dispersion stability, by using high molecular weight polyethylene oxide in combination with the above dispersant, excellent dispersibility was expressed, and the resulting highly dispersible composition The present invention was achieved based on the finding that the magnetic layer is stable even during the drying process of coating the magnetic layer without causing non-uniformity. Components of the Invention Namely, by coexisting high molecular weight polyethylene oxide with a dispersant as described above in a magnetic particle dispersion composition, ferromagnetic particles are highly dispersed by a dispersion treatment such as mechanical kneading. This not only reduces the change in properties over time, making it possible to store the above-mentioned dispersion composition for a long time, but also eliminates non-uniform dispersion of the magnetic particles during the coating and drying process, resulting in smoother coatings. In addition to improving the squareness ratio and orientation ratio, electromagnetic conversion characteristics such as the S/N ratio are improved. The polyethylene oxide used in the present invention has a molecular weight of 100,000 or more, but those that are more suitable for the purpose of the present invention have a molecular weight of 150,000 or more, particularly preferably 200,000 or more. At such a high molecular weight, the shape of the molecular terminal has little effect; it may be a hydroxyl group or may be blocked by another organic group, but it is usually a hydroxyl group, an alkyl group, or an alkoxy group. It is convenient to use this as a raw material source. In general, the smaller the amount of materials other than ferromagnetic particles used, the better for the electrical output of the medium, but the amount of high molecular weight polyethylene oxide used is 0.01 to 5 parts by weight per 100 parts by weight of ferromagnetic particles. By doing so, the object of the present invention can be achieved. If the content of polyethylene oxide is less than 0.01 part by weight, the improvement in dispersion stability that is the objective of the present invention can hardly be expected. Further, even if 5 parts by weight or more is used, not only the dispersibility is no longer improved, but also undesirable adverse effects such as a decrease in running durability of the magnetic recording medium occur. Next, manufacturing of the magnetic recording medium of the present invention will be explained. The magnetic paint for producing the magnetic medium of the present invention contains ferromagnetic particles, a binder, a coating solvent and a dispersant, a lubricant, an abrasive, an antistatic agent, and the high molecular weight polyethylene oxide referred to in the present invention. . A magnetic coating is prepared by dissolving or dispersing all or part of the above composition in an organic solvent, either simultaneously or sequentially, and then coated on a support to form a magnetic recording layer (magnetic layer). . The manufacturing method of general magnetic paints is well known. In the present invention, the magnetic paint further contains high molecular weight polyethylene oxide, and this dispersion improver is
Due to its nature, it can be added after the dispersion process, but if it is added to the magnetic paint before or during the dispersion process, the effect of improving dispersion will be even greater. The magnetic particles used in the present invention include γ-
Fe ₂ O ₃ , Co containing - γ - Fe ₂ O ₃ , Co deposited - γ -
Oxide-based ferromagnetic particles such as Fe ₂ O ₃ , Fe ₃ O ₄ , Co-containing -Fe ₃ O ₄ , CrO ₂ , Co-Ni-Fe alloy, Fe-Mn
-Zn alloy, Fe-Ni-Zn alloy, Fe-Co-Ni-Cr
Alloy, Fe-Co-Ni-P alloy, Fe-Co-Ni-Cr
alloy, Fe-Co-Ni-P alloy, Ni-Co alloy, Fe,
Examples include metal-based magnetic powders such as Ni and Co. As the binder used in the present invention, conventionally known thermoplastic resins, thermosetting resins, reactive resins, and mixtures thereof can be used. As a thermoplastic resin, a softening temperature of 150℃ or less, a molecular weight of 10,000 to 200,000, a degree of polymerization of about 200 to 2,
000, such as vinyl chloride (vinyl chloride)-vinyl acetate (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-acrylonitrile copolymer, methacrylic acid ester-styrene copolymer, urethane elastomer, polyvinyl fluoride, vinyldene chloride-acrylonitrile copolymer, acrylonitrile-butadiene copolymer, polyamide, borivinyl petyral, cellulose Derivatives (cellulose acetate ptylate, cellulose diacetate, cellulose triacetate, nitrocellulose, etc.), styrene-butadiene copolymers, polyester resins, amino resins, various synthetic rubber thermoplastic resins, and mixtures thereof are used. As a thermosetting or reactive resin, it has a molecular weight of 200,000 or less in the coating liquid state, and after coating and drying,
The molecular weight becomes infinite due to reactions such as condensation and addition. Specifically, for example, phenolic resins, epoxy resins, polyurethane curable resins, urea resins, melamine resins, alkyd resins, silicone resins, acrylic reaction resins, mixtures of high molecular weight polyester resins and isocyanate prepolymers,
These include mixtures of methacrylate copolymers and diisocyanate prepolymers, mixtures of polyester polyols and polyisocyanates, urea formaldehyde resins, mixtures of low molecular weight glycols/high molecular weight diols/triphenylmethane triisocyanate, polyamine resins, and mixtures thereof. These binders may be used alone or in combination, and magnetic powder may be used alone or in combination as required. The mixing ratio of the ferromagnetic powder and the binder is 10 to 200 parts by weight, preferably 15 to 100 parts by weight, per 100 parts by weight of the ferromagnetic powder. If the amount of binder is too large, the recording density of the magnetic recording medium will be lowered, and if it is too small, the strength of the magnetic layer will be poor, and defects such as reduced durability and powder falling will easily appear. In addition to the above-mentioned binder and ferromagnetic powder, the magnetic paint forming the magnetic layer contains additives such as a dispersant,
Coupling agents, lubricants, abrasives, and antistatic agents are added. Dispersants used include those having 12 or more carbon atoms, such as caprylic acid, capric acid, stearic acid, oleic acid, elaidic acid, linoleic acid, and linolenic acid.
Known compounds such as 18 fatty acids, metal compounds made of alkali metals or alkaline earth metals of these fatty acids, natural surfactants such as lecithin, salts of alkylbenzene sulfonic acids, salts of sulfosuccinates, etc. can be used. In addition, higher alcohols having 12 or more carbon atoms and sulfuric acid ester salts thereof are also used, and these dispersants are added in an amount of 0.1 to 10 parts by weight per 100 parts by weight of the ferromagnetic powder. Coupling agents may be used as desired,
In this case, a known titanate coupling agent,
A silane coupling agent or the like is used, but is not necessarily an essential component. Lubricants include graphite, molybdenum disulfide, tungsten disulfide, fatty acid esters consisting of monobasic fatty acids with 12 to 16 carbon atoms, monohydric alcohols with 3 to 16 carbon atoms, ether alcohols, and hydrocarbons. silicone oil, fluorinated polyethers, etc. are used. These lubricants are added in an amount of 0.5 to 15 parts by weight per 100 parts by weight of the magnetic powder. As the abrasive, commonly used materials may be used, such as fused alumina, silicon carbide, chromium oxide, corundum, artificial diamond, artificial corundum, garnet, silica/alumina, iron dioxide, and emery (main components: corundum and magnetite). etc. are used. These abrasives have an average particle size of 0.05-5μm
size is used. Especially preferably
These abrasives having a diameter of 0.1 to 2 μm are added in an amount of 0.5 to 10 parts by weight per 100 parts by weight of the ferromagnetic powder. Antistatic agents include conductive powders such as graphite, carbon black, and carbon black graft polymers, natural surfactants such as saponin, nonionic surfactants such as alkylene oxide, glycerin, and glycidol, and higher alkyl amines. , quaternary ammonium salts, pyridine, other heterocycles, cationic surfactants such as phosphonium or sulfonium, anions containing acidic groups such as carboxylic acid, sulfonic acid, phosphoric acid, sulfate ester group, phosphoric ester group, etc. Ampholytic surfactants such as surfactants, amino acids, aminosulfonic acids, sulfuric acid or phosphoric acid esters of amino alcohols, and the like are used. These surfactants may be added alone or in combination. Although these agents are used as antistatic agents, they may also be used 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. Organic solvents used during coating include ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone, esters such as methyl acetate, ethyl acetate, butyl acetate, and cellosolve acetate, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, Ethers such as dioxane; aromatic hydrocarbons such as benzene, toluene, and xylene; and halogenated hydrocarbons such as methylene chloride, ethylene chloride, carbon tetrachloride, chloroform, and dichlorobenzene can be used. Support materials include polyesters such as polyethylene terephthalate and polyethylene-2,6-naphthalene dicarboxylate; polyolefins such as polypropylene; cellulose derivatives such as cellulose triacetate and cellulose diacetate; polycarbonate and polyphenylene sulfide polysulfone. , polyether sulfone, etc., metals such as copper, aluminum, zinc, ceramics, etc. may be used. The thickness of these supports is about 3 to 200 μm, preferably 5 to 100 μm when they are in the form of a film or sheet.
m, and 0.5 to 10 in case of disk/card type.
mm, and in the case of a drum shape, the shape is determined by the recorder used as it is cylindrical. The support may be coated with a so-called back coat 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. Further, the form of the support may be tape, sheet, card, disk, drum, etc., and various materials may be selected as necessary depending on the form. The magnetic powder, the above-mentioned binder, dispersant, high molecular weight polyethylene oxide, 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 kneader either simultaneously or individually one after another. For example, there is a method in which magnetic powder is first added to a solution of a portion of a binder 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 dispersion kneading. Examples include two-roll mills, three-roll mills, ball mills, pebble mills, sand grinders, high-speed impeller dispersers, high-speed stone mills, high-speed impact mills, dispensing kneaders, high-speed mixers, homogenizers, and ultrasonic dispersers. The technology related to kneading and dispersion was developed by TC Patton (TC
PATTON) ``Point Flow and Pigment Dispersion'' (Paint Flow
and Pigment Dispersion) published in 1964 by John Willey & Sons. Coating methods for coating the magnetic coating onto the support to form a magnetic recording layer include air doctor coating, blade coating, air knife coating,
Squeeze coat, impregnation coat, reverse roll coat, transfer roll coat, gravure coat, kiss coat, cast coat, spray coat, spin coat, etc. can be used, and other methods are also possible. "Coating Engineering" pp. 253-277 (March 1972)
(published on the 20th of May). By such a method, the magnetic recording layer coated on the support is optionally treated to orient or disorder the magnetic powder particles in the layer by coating, and then the formed magnetic recording layer is dried. The magnetic recording body of the present invention is manufactured by subjecting it to surface smoothing or cutting it into a desired shape, if necessary. The present invention will be explained in more detail below using Examples. It goes without saying that the component ratios, order of operations, etc. shown here may be changed without departing from the spirit of the present invention. Therefore, the invention should not be limited to the following examples. In the following examples, all "parts" indicate "parts by weight." Example 1 Co-adhesion γ-Fe ₂ O ₃ 100 parts by weight Vinyl chloride-vinyl acetate copolymer 25 (UCC VAGH) Carbon black 10 Thermoplastic polyurethane/urea resin 30 Dispersant: Lecithin 1.0 Lubricant: Silicone oil 1.0 parts by weight Abrasive: Cr ₂ O ₃ 10 Solvent: methyl ethylene ketone 100 methyl isobutyl ketone 50 Toluene 50 The above composition and 0.5 parts by weight of polyethylene oxide with a molecular weight of 1 million were kneaded in a ball mill for 48 hours.
Passed through a 3 μm filter. After applying the sample 1, 3, and 5 times, it was applied on a 75 μm polyethylene film so that the thickness after drying was approximately 2 μm.
After drying, the surface of the sample was observed under an electron microscope at a magnification of 10K to check the dispersion state. The sample after evaporation was processed in a centrifuge at 5000 rpm for 10 minutes, and the volume fraction of the separated solution was measured and used as a parameter for an accelerated test of dispersion stability. Add Oxide 100 to the composition that has been left for 3 days.
Add 10 parts by weight of Desmodyur L (manufactured by Bayer) as a hardening agent, mix for another 30 minutes, and apply this onto a 75 μm thick polyethylene terephthalate film so that the thickness after drying is approximately 2.0 μm. Magnetic field randomization processing was performed. This was calendered to create a 51/4 inch floppy medium. Comparative Example 1 The operation of Example 1 was carried out without adding polyethylene oxide having a molecular weight of 1 million. Result-1 Check of dispersion stability

[Table] Results - 2 Dispersion stability accelerated test example - 1 5% Comparative example with little solvent separation - 1 15% 〃 A lot...In the examples, it is understood that the pigment is stably dispersed. Ru. The N/S ratio was measured and the following results were obtained. S/N ratio difference result (in dB)

【table】

Claims (1)

[Claims] 1. A magnetic recording medium that is a laminate consisting of a non-magnetic support and a magnetic layer coated on the support, the magnetic layer containing a magnetic material and polyethylene oxide having a molecular weight of 100,000 or more. .