JPS6035732B2 - magnetic recording medium - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a magnetic recording medium, and particularly to a method for manufacturing a magnetic recording medium with a low noise level.

Conventionally, ferromagnetic materials used for magnetic recording media such as audio tapes, video tapes, memory tapes, magnetic sheets, and magnetic cards include ferromagnetic iron oxide, cobalt ferrite, ferromagnetic chromium dioxide, or fine powder of ferromagnetic metals. and ferromagnetic metal thin films. The field of application of magnetic recording media now covers an extremely wide range of technical fields, including recording and reproducing electrical or magnetic signals, and recently emphasis has been placed on methods for recording short-wavelength signals in particular at high density. . Along with this, ferromagnetic materials are required to have magnetic recording properties suitable for high-density recording, such as considerably high coercive force and high residual magnetic flux density. Also, there is a demand for magnetic cards that are less likely to be demagnetized by heating or pressure. Metallic magnetic materials are considered to be the most promising ferromagnetic materials that are less susceptible to such demagnetization and can be adapted to high-density recording. On the other hand, the recording wavelength for videotape is shorter than that for recording (home-use 4-inch VTRs and the like must record short wavelengths up to a minimum wavelength of about 2).
Particularly recently, VTRs that use recording wavelengths with a minimum wavelength of about 0.6 to 1 French are being developed. However, the above-mentioned oxide magnetic material has a short recording wavelength and is not suitable for magnetic recording of signals (approximately two peaks or less). This is because the magnetic properties of the above-mentioned oxide magnetic material, such as shape, particle size, coercive force, and residual magnetic flux density, were insufficient for use as a high-density magnetic recording material. Ferromagnetic metal powder is being actively developed as a material that satisfies these characteristics and enables high-density recording.

There are various methods for obtaining powdered metal magnetic materials, but the following six methods are generally known. 1
A method of thermally decomposing organic acid salts of ferromagnetic metals and reducing them with reducing gas.

[For example, Special Publication No. 36-11412, No. 36-222
No. 30, No. 38-1480y, No. 39-3807,
40-806, 40-8027, 40-15
No. 167, No. 40-16899 (U.S. Patent No. 31868)
No. 2y), No. 41-12096, No. 41-14818
No. (U.S. Patent No. 3190748), No. 42-24032
No. 43-3221, No. 43-22394, No. 4
No. 3-292368, No. 44-4471, No. 44-2
No. 7942, No. 46-38755, No. 47-3841
No. 7, No. 47-41158, No. 48-29280, etc.]. 2. A method for reducing acicular oxyhydroxides, those containing other metals, or acicular iron oxides obtained from these oxyhydroxides.

[For example, Special Publication No. 35-3862, No. 37-115
No. 20, No. 39-20335, No. 39-20939, No. 46-24833, No. 47-29706, No. 4
No. 7-30477, (U.S. Patent No. 3598563), No. 47-39477, No. 48-24952, Tokuseki Sho 4
No. 6-5057, No. 46-7153, No. 48-791
No. 53, No. 48-82695, U.S. Patent No. 3607
No. 22, Specification No. 370227, etc.]. 3. A method of vaporizing ferromagnetic metals in a low-pressure inert gas.

[For example, Tokuseki No. 46-2562, No. 47-41
No. 31, No. 47-27718, No. 48-25662, No. 48-25663, No. 48-25664, No. 4
No. 8-25665, No. 48-31166, No. 48-5
No. 5400, Publication No. 48-81092, etc.]. 4. A method of thermally decomposing metal carbonyl compounds.

[For example, Tokuseki No. 39-1004, No. 40-341
No. 5, No. 45-16868, U.S. Patent No. 29839
No. 97, No. 3172776, No. 3200007, Specification No. 3228882, etc.]. 5. A method in which ferromagnetic metal powder is broken down into a haze using a mercury cathode and then separated from mercury.

[For example, Special Publication No. 35-1291, No. 36-386
No. 0, No. 36-5513, No. 39-787, No. 39
-15525, 40-8123, 40-960
No. 5, (U.S. Pat. No. 3,198,717), 45-196
No. 61 (U.S. Patent No. 315665), U.S. Patent 3
262812 specification, etc.]. 6 A method of reducing a solution containing a ferromagnetic metal salt by adding a reducing agent.

[For example, Special Publication No. 38-2052, No. 38-265
No. 55, No. 43-20116, No. 45-986y,
No. 45-14934, No. 47-7820, No. 47-
No. 16052, No. 47-41718, No. 47-417
No. 19 (US Patent No. 3,607,218), JP-A-47-11
No. 353 (U.S. Patent No. 375 Total No. 66), No. 47-136
No. 3, No. 47-42252, No. 47-42253,
No. 48-44194, No. 48-79754, No. 48
US Pat. No. 182396, US Pat. No. 49-41899, US Patent No. 3206338, US Patent No. 3494760, US Pat.
No. 04, No. 3567525, No. 3661556, No. 3663318, No. 3669643, No. 36728
No. 67, Specification No. 3726664, etc.]. However, in tapes in which the ferromagnetic powder obtained by the above method is kneaded and dispersed with a binder, a dispersant, etc. and coated on a support, the noise level is high due to the low dispersibility of the ferromagnetic powder. This was a major obstacle to the practical application of magnetic recording media using ferromagnetic metal powder.

This is thought to be due to the fact that the surface of the ferromagnetic metal powder is active and hydrophilic, and that it is difficult to mix with the binder. In particular, ferromagnetic metal powder obtained by reduction with a phosphinic acid compound or a borohydride compound in an aqueous solution has very poor compatibility with a binder, which makes it difficult to use magnetic recording media with high output and low noise level. It was difficult to make. The present inventors have conducted extensive research in order to provide a magnetic recording medium using ferromagnetic metal powder with low noise level and high output.

That is, the present inventors investigated various methods to improve the dispersibility of wave phase reduction type alloy fine powder, and found that when dispersing ferromagnetic fine powder, the ferromagnetic fine powder has a methyl group on the surface and a diameter of 7. ~5
The inventors discovered that a magnetic recording material obtained by coating a support with a magnetic paint containing 0h1 colloidal silica and drying it had a significantly low noise level, leading to the present invention. That is, the present invention provides a magnetic recording material comprising a magnetic layer in which fine ferromagnetic powder is dispersed in a binder on a non-magnetic support, the magnetic recording material containing colloidal silica in the magnetic layer. It is. Examples of adding colloidal silica to the magnetic layer include JP-A-49-1190 and JP-A-49-12802, but these inventions require a step of mixing a binder and colloidal silica in advance. Moreover, in these inventions, the purpose is to strengthen the binder.

Furthermore, it has been found that the intended effects of the present invention cannot be obtained if a reinforcing binder prepared by mixing a binder and colloidal silica in advance is used. This is thought to be because the binder is partially crosslinked by colloidal silica during this step, resulting in a decrease in the dispersion performance of the binder. The colloidal silica used in the present invention is silicic anhydride with a diameter of 7 to 5 mm, preferably 10 to 3 mm. These colloidal silicas are made by burning silicon tetrachloride and have silanol groups on the surface, but in the present invention, the silanol on the surface is removed by treating it with methanol, trimethylmonochlorosilane, dimethyldichlorosilane, etc. Colloidal silica having a reduced proportion of groups and having methyl groups on its surface is used. Specifically, this methyl group substitution is performed by heating colloidal silica in methanol to its boiling point or treating it in methanol vapor for 30 minutes to 6 hours, or treating colloidal silica and tetrachlorosilane with methanol vapor for 30 minutes to 6 hours. Most preferably, colloidal silica is heated and reacted with dimethyldichlorosilane and water vapor at about 400 qo in a fluidized bed using an inert gas such as nitrogen gas as a carrier. In the colloidal silica thus obtained, about 70% or more of the silanol groups on the surface are substituted with methyl groups. These silanol groups and methyl groups are analyzed using an infrared spectrometer. It is not clear why colloidal silica having a methyl group is preferable, but it is probably because its surface is hydrophobic and it is compatible with the binder. The colloidal silica used in the present invention is added at the time of kneading and dispersing the ferromagnetic fine powder and the binder.

Addition after dispersion is not preferred because the desired effect of the present invention cannot be obtained. The amount added is 2 to 20 parts by weight, preferably 3 to 1 part by weight, based on 10 parts by weight of the ferromagnetic fine powder.
Particularly preferably 4 to 8 parts by weight. If the amount added is less than 2 parts by weight, the desired effect of the present invention cannot be obtained, and if it is more than 2 parts by weight, not only will the magnetic flux density of the obtained magnetic recording medium be low, but also the adhesion between the magnetic recording layer and the support will be reduced. This is not preferable because it deteriorates the properties and makes the magnetic recording layer more likely to fall off. The method for manufacturing the magnetic paint used in the present invention is Hakama Kosho No. 43-186,
No. 47-28043, No. 47-28045, No. 47
No. 128046, No. 47-28048, No. 47-31
This method is similar to the method described in detail in Publication No. 445 and the like.

The magnetic paints described in these documents mainly contain ferromagnetic fine powder, binder, and coating solvent, and may also contain additives such as dispersants, lubricants, and abrasives. As the ferromagnetic powder used in the present invention, in addition to ferromagnetic alloy fine powder, ferromagnetic iron oxide, ferromagnetic chromium dioxide, etc. can be used. A fine ferromagnetic alloy powder is preferable, and among these, one obtained by the method 6 above is particularly preferable. The "metal salt capable of producing a ferromagnetic material" used in this method includes iron, cobalt, nickel, iron-cobalt, iron-nickel, cobalt-nickel, or iron-cobalt-nickel as a main component, and has magnetic properties and Means containing trace amounts of metal salts of various elements such as lanthanum, cerium, neodymium, samarium, aluminum, sulfur, chromium, manganese, copper, tin, zinc, etc., as necessary, to improve oxidation stability, etc. . Specifically, these metals include sulfates, chlorides, nitrates, formates, acetates, sulfamates, and pyrophosphates. As a reducing substance for performing a reduction reaction,
The above-mentioned acids and salts containing hypophosphite ions: Boron hydride compounds such as sodium borohydride, borane, borazane, and their derivatives: One or more combinations of hydrazine and derivatives, or hydrogen Gases such as carbon monoxide, carbon monoxide, and mixtures thereof are generally available.

The metal salt is reduced by these reducing substances to precipitate a single substance or a composition (alloy) of ferromagnetic metal atoms. The concentration of the borohydride compound or its derivative used as a reducing agent is preferably within the range of 0.0002 to 10 mol. In particular, the reaction is preferably carried out at a reducing agent/metal ion molar ratio of 0.1 to 5. desirable.

The reaction conditions in this method are not particularly limited, but the effective range is that the reaction stress is 0.5 to 5 atm, and the reaction temperature and pH vary depending on the reducing substance used.

For example, with hypophosphorous acid, the temperature is 65-9 pi○, the pH is 8-9
12: Temperature -5 to 60 0 for borohydride compound system,
pHI ~ 12: Temperature 60 ~ 10 picC for hydrazine type,
The pH range is preferably 7.5 to 12. Moreover, the action of the magnetic field is effective if it is several tens of degrees or more, and a direct current magnetic field, an alternating current magnetic field, and a pulsed magnetic field are effective. It is effective if the metal ion concentration is below a level that does not result in supersaturation. However, if the concentration is too high, the properties of the powder obtained will deteriorate, the reaction yield will decrease,
Problems arise such as the necessity of increasing the size of the reaction apparatus due to foaming and the like. Furthermore, if the metal ion concentration is too low, the yield of powder will be low, resulting in poor efficiency in mass production. Therefore, countermeasures such as increasing the size of the reactor are required. In this method, it is desirable that the metal ion concentration be in the range of 0.002 to 4 mol/part, particularly preferably in the range of 0.01 to 2 mol/part.

As the binder used in the present invention, conventionally known thermoplastic resins, thermosetting resins, reactive resins, and mixtures thereof are used.

The thermoplastic resin has a softening temperature of 150 oo or less, an average molecular weight of 10,000 to 200,000, and a degree of polymerization of about 2.
00 to 200 degrees Fahrenheit, such as 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 Coalescence, ester acrylate styrene copolymer, ester methacrylate acrylonitrile copolymer, ester methacrylate vinylidene chloride copolymer, ester methacrylate styrene copolymer, urethane elastomer, polyvinyl fluoride, vinylidene chloride Acri.

Nitrile copolymers, polyamide resins, polyvinyl phthyral, cellulose derivatives (cellulose acetate butylate, cellulose diacetate, cellulose triacetate, cellulose propionate, nitrocellulose, etc.), styrene acrylonitrile copolymers, polyester resins, amino resins, various Synthetic rubber-based thermoplastic resin (
polybutadiene, polychloroprene, polyisoprene,
Styrene-butadiene copolymers, butadiene-acrylonitrile copolymers, etc.) and mixtures thereof are used. Examples of these resins are listed in Japanese Patent Publications No. 37-1 Iso No. 77 and No. 39
-12528, 39-19282, 40-53
4zu No. 40-20907, No. 41-9463,
No. 41-1405, No. 41-16985, No. 42
No. 16428, No. 42-111621, No. 43-462
No. 3, No. 43-15206, No. 44-2 No. 9, No. 4
No. 4-17947, No. 44-18232, No. 45-1
No. 402, No. 45-1450, No. 47-1857
No. 3, No. 47-22063, No. 47-22064,
47-220 Iso No. 47-22069, 47-
No. 2207, No. 48-27886, U.S. Patent 3
No. 144352: No. 3419420: No. 349978
No. 9: Described in the specification of 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, for example, phenol formalin novolac resin, phenol formalin resol resin,
Phenol. Furfural resin, xylene/formaldehyde resin, urea resin, melamine resin, drying oil-modified alkyd resin, carbonic acid resin-modified alkyd resin, maleic acid resin-modified alkyd resin, unsaturated polyester resin,
Epoxy resins and curing agents (polyamines, acid anhydrides, polyamide resins, etc.), terminal isocyanate polyester moisture-curing resins, terminal isocyanate polyether moisture-curing resins, polyisocyanate prepolymers (diisocyanate and 1 obtained by reacting with a low molecular weight triol
Compounds having 3 or more isocyanate groups in the molecule,
diisocyanate trimer, tetofumer and pentamer), polyisocyanate prepo IJ mer and resin containing active hydrogen (polyester polyol, polyether polyol, acrylic acid copolymer, maleic acid copolymer,
2-hydroxyethyl methacrylate copolymer, rose hydroxystyrene copolymer, etc.), and mixtures thereof. Examples of these resins are given in Japanese Patent Publication No. 39-81
No. 03, No. 40-977, No. 41-7192, No. 41-8016, No. 41-14275, No. 42-1
817 shout number, 43-12081, 44-2802
No. 3, No. 45-14501, No. 45-24902,
No. 46-13103, No. 47-22065, No. 47
-22066, 47-22067, 47-22
No. 072, No. 47-22073, No. 47-28045
US Pat. No. 47-28048, US Pat. No. 47-28922, US Pat. No. 3144353: US Pat. No. 3320090; US Pat.
No. 1; described in the specification of No. 3781211.

These binders may be used alone or in combination;
Other additives may be added. The mixing ratio of the ferromagnetic fine powder and the binder is 10 to 40 parts by weight, preferably 15 to 20 parts by weight, particularly preferably 15 to 20 parts by weight, of the binder to 10 parts by weight of the ferromagnetic fine powder. A range of 10 parts by weight is used. In addition to the binder and ferromagnetic fine powder described above, 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,
Fatty acids with 12 to 18 carbon atoms such as myristic acid, palmitic acid, stearic acid, oleic acid, elaidic acid, linoleic acid, linolenic acid, stearolic acid (R, COO, R, is a fatty acid with 11 to 17 carbon atoms) alkyl or alkenyl group): alkali metal (Li, Na, K
etc.) or metal soaps consisting of alkali metals (Mg, Ca, Ba); fluorine-containing compounds of the above fatty acid esters; amides of the above fatty acids: polyalkylene oxide alkyl phosphate esters; lecithin; Alkyl polyolefin oxy quaternary ammonium salts (alkyl having 1 to 5 carbon atoms, olefin being ethylene, propylene, etc.) are used.

In addition, higher alcohols having 1 or more carbon atoms and sulfuric acid esters can also be used. These dispersants are added in an amount of 0.5 to 2 parts by weight based on 10 parts by weight of the binder. Regarding these, special public relations
No. 836y, No. 44-17945, No. 48-7441
No. 48-15001, No. 48-15002, No. 48-16363, No. 50-4121, US Pat. No. 3,387,993; US Pat. Even when the additive according to the present invention is used in combination with these dispersants, the effect of the dispersants is not impaired in any way. Lubricants include inorganic powders such as molyptene disulfide and tungsten disulfide; fine plastic powders such as polyethylene, polypropylene, polyethylene vinyl chloride copolymers, and polytetrafluoroethylene; and Q-olefin polymers: unsaturated fats that are liquid at room temperature. Group hydrocarbons (compounds in which an n-olefin double bond is bonded to the terminal carbon, approximately 20 carbon atoms); carbon number 1
Fatty acid esters consisting of 2 to 2 hard monobasic fatty acids and alcohols having 3 to 12 carbon atoms can be used.

These lubricants are used in amounts of 0.2 to 100 parts by weight of binder.
It is added in an amount of 20 parts by weight. Regarding these, Special Publications No. 41-18064, No. 43-23889, No. 46
-40461, 47-15621, 47-18
No. 482, No. 47-28043, No. 47-32001
No. 50-5042, U.S. Patent No. 3470021
No. 3492235; No. 3497411, No. 35
No. 23086: No. 362576; No. 3630772
No. 3642539; “BMTechnic
aI Disclosure Bulletin''V
ol. 9, No. 7, Pa bag 779 (December 1966); “ELEK-TRONIK” 1961, No. 1
2, 38 beats connected to Pa, etc. are described. Commonly used abrasive materials include fused alumina, silicon carbide,
Chromium oxide, corundum, artificial corundum, diamond, artificial diamond, garnet, emery (main ingredients;
corundum and magnetite) etc. are used. These abrasives have a Mohs hardness of 5 or more and an average particle size of 0.05 to
A size of 5 Buddha is used, particularly preferably 0.1
~2 Buddhas. These abrasives are added in an amount of 0.5 to 2 parts by weight based on 10 parts by weight of the binder. Regarding these, Mochiko No. 47-18572, No. 41-1500
No. 3, No. 48-15004 (US Pat. No. 3,617,378)
U.S. Patent No. 49-39402, U.S. Patent No. 50-9401, U.S. Pat.
No. 5: British Patent No. 114534y; West German Patent (DT
- PS) No. 853211: Described in the specification of PS No. 1101000. The additive according to the present invention, when used in combination with these abrasives, reduces head wear caused by the abrasives.
Antistatic agents include conductive fine powders such as carbon black, graphite, and carbon black graft polymers;
Natural surfactants such as saponins; nonionic surfactants such as alkylene oxides, glycerols, and glycidols; cationic surfactants such as higher alkylamines, quaternary ammonium salts, pyridine and other heterocycles, and phosphoniums or sulfoniums. Anionic surfactants containing acidic groups such as carboxylic acid, sulfonic acid, phosphoric acid, sulfuric acid ester groups, and phosphoric acid ester groups; Ampholytic surfactants such as amino acids, aminosulfonic acids, and sulfuric acid or phosphoric acid esters of amino alcohols etc. are used.

The above conductive fine powder is 0.00 parts by weight of the binder.
2 to 20 parts by weight are added, while surfactants are added in the range of 0.1 to 1 part by weight.

Some examples of conductive fine powders and surfactant compounds that can be used as antistatic agents include Japanese Patent Publication Nos. 46-122726, 47-24881, 47-26882, and 4
No. 8-15440, US Pat. No. 48-26761, US Pat. No. 2271623, US Pat. No. 2240472, US Pat. No. 2288
No. 226, No. 2676122, No. 2676924,
No. 2676975, No. 2691566, No. 2727
No. 860, No. 2730498, No. 2742379,
No. 2739891, No. 3068101, No. 31 4
No. 84, No. 3201253, No. 3210191, No. 3294540, No. 3415649, No. 34414
No. 13, No. 3442654, No. 3475174, No. 3545974, West German Patent Publication (OLS) 194
No. 2665, British Patent No. 1077317, British Patent No. 11984
5bi specification, "Synthesis of surfactants and their applications" by Ryohei Oda et al. (Yokoshoten 1964 edition): A. M. Schwall & J. W. "Surf S Active Agents" by IJ Bay (Interscience Publications, Inc. 1958 main edition): J. P. Sisley, "Encyclopedia of Surf S Active Engineering, Volume 2" (Chemical Publishing Company 196 French edition); "Surfactant Handbook" 6th edition (Sangyo Tosho Co., Ltd., December 2, 1960) It is written in books such as

These surfactants may be added alone or in combination.

These are used as antistatic agents, but are sometimes used for other purposes, such as dispersion, improving magnetic properties,
It may also be used to improve lubricity and as a coating aid.
The magnetic recording layer of the present invention is formed by dissolving the above-mentioned composition in an organic solvent, kneading and dispersing, and coating each coating solution on a non-magnetic support and drying.

After coating this magnetic layer and before drying, a treatment can be performed to orient the magnetic powder in each magnetic layer.
Further, the surface of each magnetic layer can be smoothed after drying. Materials for this non-magnetic 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, plastics such as polycarbonate, Cu, and A. Non-magnetic metals such as Zn, ceramics such as glass, porcelain, and earthenware are used.

In addition, the form of the non-magnetic support is film, tape, sheet,
It may be a disk, a drum, or the like, and various materials are selected as necessary depending on the form. The thickness of these non-magnetic supports is approximately 2 to
It is about 50 mm, preferably 3 to 25 mm.

Further, in the case of a disk or card shape, the thickness is about 0.5 to 10 degrees, and in the case of a drum shape, it is cylindrical, and the shape is determined depending on the recorder used. In the case of a flexible support such as a film, tape, sheet, or thin flexible disk, the above-mentioned non-magnetic support should be placed on the opposite side of the magnetic layer for the purpose of preventing static electricity, preventing transfer, preventing wow and flutter, etc. The surface may also be provided with a so-called backcoat.

Regarding the back coat, for example, US Patent No. 280,440
No. 1, No. 3293066, No. 3617378, No. 3
No. 062676, No. 3734772, No. 347659
No. 6, No. 2643048, No. 2803556, No. 2
No. 887462, No. 2923642, No. 299745
No. 1, No. 3007892, No. 3041196, No. 3
No. 115420, No. 3166688, No. 376131
This is shown in the Specification No. 1, etc.

The magnetic powder, the above-mentioned binder, colloidal silica, dispersant, lubricant, abrasive, antistatic agent, solvent, etc. are mixed and loosened 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 solvent containing a dispersant and then kneaded for a predetermined period of time to form a magnetic paint.
Various kneaders are used to disperse the magnetic coating liquid into the slurry.

For example, two roll mill, three roll mill, ball mill,
Bepul mill, thoron mill, sand grinder, Sze
gvarl attritor, high speed invera disperser,
These include high-speed stone mills, high-speed impact mills, dispersers, kneaders, high-speed mixers, homogenizers, and ultrasonic dispersers. The technology regarding kneading and dispersion is described by T. C. PATT
“PaintFlowandPigmentD” by ON
John Wile (1964)
(Published by Y & Sone).

It is also described in US Patent Nos. 2, 1414 and 2,855,156. Methods for applying the magnetic recording layer onto the support include air doctor coating, plaid coating, air knife coating, squeeze coating, impregnation coating, reverse roll coating, transfer roll coating, gravure coating, kiss coating, cast coating,
Soubray coat, etc. can be used, and other methods are also possible, and detailed explanations of these methods are given in "Coating Engineering", pages 253 to 277, published by Asakura Shoten (published on March 2, 1977). There is.

The magnetic paint of the present invention is prepared by coating a magnetic layer on a non-magnetic support by the coating method described above and drying it.

Alternatively, two magnetic layers may be provided by repeating this step and performing a continuous coating operation. Also, JP-A-48-98803 [
West German Published Patent (DT-OS) No. 2309159],
No. 48-99233 [West German Published Patent (DT-AS)
) 23091] As described in the publication, two magnetic layers may be simultaneously provided by a multilayer simultaneous coating method. Organic solvents used during coating include ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; alcohols such as methanol, ethanol, propanol, and butanol; methyl acetate, ethyl acetate, butyl acetate, ethyl lactate, and acetic acid. Ester types such as glycol monoethyl ether; glycol ether types such as ether, glycol dimethyl ether, glycol monoethyl ether, and dioxane; tar types (aromatic hydrocarbons) such as benzene, toluene, and xylene; methylene chloride Edo, echlenk.

Chlorinated hydrocarbons such as Ride, carbon tetrachloride, chloroform, ethylene chlorohydrin, and dichlorobenzene 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 as described above, 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 particular, in the present invention, it has been found that by subjecting the magnetic recording layer to surface smoothing treatment, a magnetic recording body with a smooth surface and excellent wear resistance can be obtained. In this case, the orientation magnetic field is about 50 to 2000 Gauss in alternating current or direct current.

The drying temperature of the magnetic layer is approximately 50 to 12,000°C, preferably 70 to 10,000°C, particularly preferably 80 to 90°C.
The air flow rate is 1 to 1 minute per minute, preferably 2 to 1 minute per minute, and the drying time is about 3 minutes to 1 minute, preferably 1 to 5 minutes. The saddle direction of the magnetic material is determined by its use.

That is, in the case of sound tape, small video tape, memory tape, etc., it is parallel to the length direction of the tape, and in the case of broadcast video tape, etc., it is parallel to the length direction.
It is oriented with an inclination of 00 to 90 degrees. Methods for orienting magnetic powder are also described in the following patents:

For example, US Pat. No. 194984; US Pat. No. 2,796,359; US Pat.
No. 6949: No. 347396; Specification No. 3681138; Special Publication No. 32-3427; No. 39-28368
No. 40-23624: No. 40-23625; No. 41-13181; No. 48-13043: No. 48-
Publication No. 39722, etc.

Furthermore, as described in West German Patent Publication (DT-AS) No. 1190985, the upper and lower layers may be oriented in different directions. As the surface smoothing treatment of the coating film before drying of each of the magnetic layers described above, a method such as a magnetic smoother, a smoothing coil, a smoothing blade, a smoothing blanket, etc. is used as necessary.

These are Special Publication No. 47-38802 and Special Publication No. 48-11
No. 336, Special Publication No. 49-53631, British Patent 1
It is shown in the specification of No. 191424, etc. The surface smoothing treatment after drying each magnetic layer is performed by calendering,
etc. In the case of calendering, it is preferable to carry out the supercalendering method in which the material is passed between two rolls such as a metal roll and a cotton roll or a synthetic resin (for example, nylon) roll. The conditions of the supercalender are about 25-100k9/fox, preferably 30-70k9/fox, with an inter-roll pressure of about 35-100k9/fox.
It is preferable to carry out the treatment at a temperature of 40 to 8,000 °C, preferably at a processing speed of 5 to 12 h/min. Temperature and pressure above these upper limits have an adverse effect on the magnetic layer and non-magnetic support. Moreover, if the processing speed is less than about 8 h/min, the surface smoothing effect cannot be obtained, and the processing speed is about 12 h/min.
If it is more than in, processing operation becomes difficult. These surface smoothing treatments are described in U.S. Pat. No. 2,688,567;
No. 8325: No. 3783023: West German published patent (DT
-OS) 2405222 specification; JP-A-49-536
No. 31, No. 50-10337, etc. By adding the colloidal silica according to the present invention into a magnetic paint at the time of its dispersion, a low-noise magnetic recording medium can be produced without impairing the characteristics of a magnetic recording medium using a magnetic material, especially a ferromagnetic alloy fine powder. I was able to get it.

When untreated colloidal silica is added, the magnetic layer becomes hygroscopic, which causes deterioration of magnetic flux density due to oxidation in magnetic recording materials using fine ferromagnetic alloy powder. I found out that using . \The present invention will be explained in more detail below using Examples and Comparative Examples.

It will be readily understood by those skilled in the art 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 and Comparative Examples, all parts indicate parts by weight.

Example 1 Ferrous sulfate 0.685 in a 1000 Gauss DC magnetic field
A fine alloy powder was obtained by adding 1 mole of sodium borohydride to an aqueous solution containing 0.305 mole of cobalt sulfate/0.010 mole of chloralum/alum.

The obtained alloy fine powder has a shape in which 10 to 19 particles with a diameter of about 400 A are tightly linked on average, and Fe:Co:C
It had a composition of r±69:30:1 and also contained about 3% B. Using 300 parts of the obtained alloy fine powder, in addition, 4 parts of polyester polyurethane polyethylene adibate were used.
, 4-diphenylmethane diisocyanate, average molecular weight: approximately 130,000 in terms of styrene equivalent weight.Two-part synthetic non-drying oil-modified alkyd resin.Reaction product of glycidyl ester of glycerin, phthalic anhydride and fatty acid synthesized by the Koch method. MmK/xylene mixed solution with 70% solid content Oil length: 29%, hydroxyl value: about 130 25 parts Oleic acid 3 parts Silicone oil (dimethylpolysiloxane) 3 parts Colloidal silica (Additional amounts are shown in Table 1.

) Average flea length of approximately 16 m, approximately 70% of the silanol groups on the surface have been replaced with methyl groups Manufactured by Nippon Aerosil Co., Ltd. (product name): Narrow R side L R-972 MIBK (methyl isobutyl ketone) From 60 anchors The above composition was put into a ball mill, kneaded and dispersed for 24 hours, and 2 parts of polyisocyanate compound (
After adding Desmodur L-75% ethyl acetate solution of an adduct of 75.3 mol of tolylene diisocyanate and 1 mol of trimethylolpropane), high-speed traversal dispersion was carried out for 1 hour.

After the above treatment, a magnetic coating solution was obtained which was suitable for use in a furnace with a filter having an average diameter of 3 Buddhas. Apply the above magnetic coating liquid to a thickness of 22 mm.
The film was coated with a doctor coat onto a polyethylene terephthalate film to a dry thickness of 3 cm.

This was subjected to magnetic field orientation for 0.02 seconds in a DC magnetic field of 2,500 gauss, and dried for 2 minutes at an air flow rate of 10,000 gauss/min. A super calender roll treatment was carried out at a speed of 10 min to obtain a Hironaka magnetic recording film. This was slit to obtain a 1/2 inch videotape. Table 1 below shows the amount of colloidal silica used (weight percent relative to the ferromagnetic fine powder) and the characteristics of the resulting videotape. (C No. is a comparative example) Table 1 The relationship between the amount of colloidal silica added and the output and noise is shown in the attached drawing, where the broken line indicates the output and the solid line indicates the noise.

Methods for measuring the properties shown in Table 1.

(a) Maximum magnetic flux density: The obtained videotape was measured in an external magnetic field of 3000 oersted.

Measuring device: Toei Kogyo KK VSM-m 'b' Squareness ratio: Ratio between residual magnetic flux density and maximum magnetic flux density when measured in an external magnetic field of 3000 Oersted.

[c) Output: Playback video output when the reference signal of Insect Day 2 was recorded at the optimum recording current value using a unified type 1 VTR.
It is shown as a relative value based on the cro2 tape.
Measuring device: SONY Corp. Manufactured by AV-8700. 'd}
/Z: When the SMHZ reference signal was reproduced, the output of the noise modulated to mountain MHZ and reproduced was measured using a frequency spectrum analyzer.

The values are shown as relative values based on tape C.

Measuring device: FSA-IB manufactured by Ando Electric KK. 'e} Durability: The time until an abnormality appears on the monitor TV screen when a test pattern is drawn in green and played back in still mode. [f} Thio powder: magnetic layer and 2. A tape recorder equipped with a mock-fixing head with a dovetail length can be used to record 5 plate lengths of tape. The weight of the magnetic layer attached to or scraped off by the head after main recovery at a speed of 10 h/sec.

From Table 1 and the attached figures, the noise level of the magnetic recording material in which colloidal silica according to the present invention is added to the magnetic paint is almost the same as that without the addition of colloidal silica, but the noise level is significantly reduced. I understand things.

It can be seen that when the amount added is less than 2%, the effect of reducing the noise level is small, and when it is more than 20%, the saturation magnetic flux density decreases by 4.0%, resulting in a slight decrease in output and an increase in powder falling.
It can be seen that the squareness ratio is completely unrelated to the amount added and is constant, and the durability is also almost unrelated to the amount added. Comparative Example 1 Instead of the colloidal silica IJ used in Example 1, colloidal silica (manufactured by Nippon Aerosil Co., Ltd. (trade name): Aerosil 2), which does not have a methyl group on the surface and has an average length of about 12 hours, was used.
A videotape was obtained in the same manner as in Example 1 except that the following procedure was used: 00).

Table 2 shows the amount of colloidal silica used and the characteristics of the videotape obtained. For Table 2 a, b, c, d, e, f, see above explanation.

From Tables 1 and 2, it can be seen that colloidal silica that does not have methyl groups on its surface has a higher noise level than those that have methyl groups, even if the particle size is small. Comparative Example 2 A videotape was obtained in the same manner as in Example 1 except that in place of the colloidal silica used in Example 1, fine powder silica having an average particle size of 0.6 and having no methyl groups on the surface was used. .

Table 3 shows the amount of finely powdered silica used and the characteristics of the magnetic recording material obtained. For Table 3 a, b, c, d, e, f, see above explanation.

From Table 3, it can be seen that silica having a large particle size and not having a methyl group on its surface cannot achieve the desired effect of the present invention. Comparative Example 3 Instead of the colloidal silica used in Example 1, the particle size of fine powder silica having a methyl group on the surface was changed,
A videotape was obtained by operating the same machine as in Example 1.

Table 4 shows the particle size of the fine powder silica and the characteristics of the obtained magnetic recording material. Table 4 a, b, c, d, e, f 1st
See table.

It can be seen from Table 4 that when the particle size of the fine powder silica is large, noise becomes large even if the surface is made hydrophobic by methyl group substitution, and the desired effect of the present invention cannot be obtained.

Comparative Example 4 Polyester polyurethane (same as Example 1) 2 anchor parts Synthetic non-heron oil-modified alkyd resin 25 parts (Same as Example 1) MIBK I
Colloidal silica (types and amounts added are shown in Table 5).

) The above mixture was mixed using a kneader at a temperature of 60°C.
I watched the mixed lights for a minute.

After dispersing with a kneader, 40 parts of MIBK was added, and the mixture was dispersed twice with a three-roll mill. After dispersion, further Fe:Co
:Cr alloy fine powder (same as Example 1)
30 Xiaoguo oleic acid
3 parts silicone oil (dimethylpolysiloxane) 3 parts MIBK 55 were added and the same dispersion and coating steps as in Example 1 were carried out to obtain a videotape.

Table 5 shows the type (product name) of colloidal silica, the amount added, and the characteristics of the obtained videotape. Table 5 a'b, c
, d, e, f see the above explanation.

From Table 5, Ko. In the case where the silica is first mixed with a binder and then the ferromagnetic fine powder is added. Durability is improved compared to those without added silica, but the noise level is hardly improved. Well, it turns out. Comparative Example 5 The videotapes obtained in Example 1 and Comparative Example 1 were heated at 60°C for 9
It was stored in an atmosphere of 0% RH for one week, and the deterioration of saturation magnetic flux density due to temperature and humidity was measured.

The results obtained are shown in Table 6. Table 6 For a, see the above explanation.

From Table 6, it can be seen that even when R-972 having a methyl group on the surface is added, the deterioration of the magnetic properties due to temperature and humidity is almost the same as when no additive is added.

On the other hand, it can be seen that those without methyl groups on the surface show greater deterioration. From the above Examples and Comparative Examples, it can be seen that the magnetic recording material obtained from the magnetic paint by adding colloidal silica having a methyl group on the surface according to the present invention can be used with ferromagnetic powders, which have conventionally been difficult to lower the noise level. The noise level of magnetic recording media using liquid phase reduced alloy fine powder can be significantly lowered.

It is also seen that this magnetic recording medium shows no increase in deterioration over time under temperature and humidity conditions. It is also understood that the method and purpose of using colloidal silica according to the present invention are completely different from those described in JP-A-49-11909 and JP-A-49-12802. Further, the effect of reducing the noise level according to the present invention was almost the same when ferromagnetic iron oxide and ferromagnetic chromium dioxide were used.

[Brief explanation of drawings]

The attached drawing is a graph showing the relationship between the amount of colloidal silica added and the output and noise of the sample in Example 1.

Claims (1)

[Claims] 1. In a magnetic recording material having a magnetic layer formed by coating and drying a magnetic paint in which ferromagnetic fine powder is dispersed in a binder on a non-magnetic support, when the coating liquid of the ferromagnetic fine powder is dispersed, A magnetic recording body, characterized in that it has a methyl group on its surface and is doped with colloidal silica having a diameter of 7 to 50 mμ.