JPH04263116A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To enable electromagnetic conversion characteristic and running property to be improved by using a non-magnetic support and a plurality of magnetic layers on it and containing a ferromagnetic allay powder on an upper layer and an oxide containing cobalt on a lower layer. CONSTITUTION:A plurality of magnetic layers which are equal to or more than two layers where a ferromagnetic powder is dispersed within a connecting agent are provided on a non-magnetic support. Then, an iron oxide powder containing cobalt, where an amount of adsorbed stearic acid is 3X10<-6>-6X10<-6>mol/m<3>, is contained at a lower magnetic layer. Also, a ferromagnetic metal or an alloy where the amount of adsorbed stearic acid is 6X10<-6>mol/m<2> or more is contained as a ferromagnetic powder of an upper magnetic layer and the above upper magnetic layer includes at least one type of organic phosphor compound which is expressed by general expressions I-III. Dispersion is improved by using the above organic phosphor compound, electromagnetic conversion characteristics are improved, and running property is improved.

Description

Detailed Description of the Invention [0001] [Industrial Application Field] The present invention consists of a non-magnetic support and a plurality of magnetic layers, and the upper layer contains a ferromagnetic metal or alloy powder (hereinafter abbreviated as ferromagnetic metal powder). ), relates to a magnetic recording medium containing cobalt-containing iron oxide in the lower layer, and particularly relates to a magnetic recording medium with improved electromagnetic conversion characteristics and runnability. [0002] Conventionally, as magnetic recording media for video, audio, or computers, a magnetic layer in which ferromagnetic iron oxide powder, ferromagnetic alloy powder, etc. is dispersed in a binder is used as a non-magnetic support. A magnetic recording medium coated on top is used. In particular, ferromagnetic metal/alloy powders have larger coercive force and saturation magnetization than iron oxide magnetic powders, and are suitable for high-density recording. Generally, when the coercive force is increased, the output in the short wavelength range increases, but on the contrary, the output in the long wavelength range decreases. In order to obtain good output over a wide band, it has been proposed to have a multilayer magnetic layer, with a ferromagnetic metal/alloy powder in the upper layer and an iron oxide magnetic powder in the lower layer. By having the lower layer take charge of recording signals in the long wavelength range, it is possible to improve output over a wide band by using ferromagnetic powder with high coercive force in the upper layer. On the other hand, in order to obtain good electromagnetic conversion characteristics, it is necessary to improve the surface properties of the magnetic layer and reduce the spacing loss between the magnetic head and the tape. In particular, in the case of ferromagnetic metal/alloy powders, their saturation magnetization is large, making them difficult to disperse due to magnetic interaction between magnetic particles, and even once dispersed, they tend to aggregate, making it difficult to obtain good surface properties. For this reason, various dispersion methods have been proposed, and dispersants and
Binders have been proposed. Furthermore, after coating and drying, it has been proposed that the surface be smoothed between metal rolls, elastic rolls, or between metal rolls. On the other hand, such a magnetic recording medium must have both excellent electromagnetic conversion characteristics and excellent running durability. In particular, as mentioned above, the smoother the magnetic layer surface becomes, the more difficult it becomes to provide excellent running durability. For this reason, it has generally been proposed to include carbon black in the magnetic layer or add an abrasive such as corundum, silicon carbide, or chromium oxide. However, in order to improve running durability using these powders, it is necessary to add a considerable amount, which reduces the degree of filling of the ferromagnetic powder and deteriorates the surface properties of the magnetic recording medium. , good electromagnetic conversion characteristics cannot be obtained. A method has also been proposed in which a fatty acid or an ester of a fatty acid and a fatty acid alcohol is contained as a lubricant in the magnetic layer to reduce the coefficient of friction. however,
In order to keep the coefficient of friction low with a smoother magnetic layer, it is necessary to use more of the above lubricant. Since a lubricant generally has a much smaller molecular weight than a binder, if a large amount is used, the magnetic layer will become plasticized and, for example, still durability may deteriorate. [0007] JP-A-2-206020 discloses a multilayer structure in which both the upper layer and the lower layer use iron oxide magnetic powder, the amount of stearic acid adsorbed by the ferromagnetic powder is specified, and the upper layer is made of ferromagnetic powder with a low amount of stearic acid adsorbed. It is stated that powder is used. The purpose of this is that even if the amount of fatty acid added to the magnetic layer is small, it will not be adsorbed to the ferromagnetic powder, but will come out onto the tape surface and effectively act as a lubricant. However, in the system of upper layer metal/lower layer cobalt-containing iron oxide magnetic powder, the range of stearic acid adsorption in the invention described in JP-A-2-206020 is that the friction coefficient of the magnetic layer is high and further increases after repeated running. This turned out to be extremely problematic in practice. [0008] The present invention consists of a non-magnetic support and a plurality of magnetic layers thereon, with a ferromagnetic alloy powder in the upper magnetic layer and a cobalt-containing iron oxide in the lower magnetic layer. It is an object of the present invention to provide a magnetic recording medium containing improved electromagnetic conversion characteristics and running properties. Means for Solving the Problems [0009] The above object of the present invention is to provide a magnetic material in which two or more magnetic layers each made of ferromagnetic powder dispersed in a binder are provided on a non-magnetic support. In the recording medium, the lower magnetic layer contains cobalt-containing iron oxide powder having a stearic acid adsorption amount of 3 x 10-6 to 6 x 10-6 mol/m2 as the ferromagnetic powder, and the upper magnetic layer has a The magnetic powder contains a ferromagnetic metal or alloy powder having an adsorption amount of stearic acid of 6 x 10-6 mol/m2 or more, and the upper magnetic layer contains at least one of the following general formulas (1) to (3). This is achieved by a magnetic recording medium characterized by containing one type of organic phosphorus compound. (1) (R-O)nP0(OM)3-n(2)
(R-O)nP(OM)3-n(3) (R)nP0
(OM)3-n (where R represents a substituted or unsubstituted alkyl group, alkenyl group, or aryl group, M represents a hydrogen atom, an alkali metal, or -N(R1)4, and R
1 represents an alkyl group, and n represents 1 or 2. [0010] Also, the above object of the present invention is to provide a magnetic recording medium in which a plurality of two or more magnetic layers each made of a ferromagnetic powder dispersed in a binder are provided on a non-magnetic support. The magnetic layer contains a ferromagnetic powder in which the silicon content in the cobalt-containing iron oxide magnetic powder is 0.2 to 4.0 at% Si/Fe, and the upper magnetic layer contains a ferromagnetic metal or alloy powder. The aluminum content is Al/Fe and 5.
It is characterized in that it contains 0 to 15.0 atom % of ferromagnetic powder, and the upper magnetic layer contains at least one organic phosphorus compound represented by the following general formulas (1) to (3). Achieved by magnetic recording media. That is, the present inventors investigated the running performance of a magnetic recording medium in which the upper layer is a metal/alloy powder and the lower layer is a cobalt-containing iron oxide magnetic powder, and investigated the surface properties of the ferromagnetic powder and the lubricant. The present invention was developed by focusing on the interaction with fatty acids. For this kind of multilayer configuration,
Based on the idea that short wavelength signals are handled by the upper layer and long wavelength signals are handled by the lower layer, the thickness of the upper layer is generally 0.1 to 1.5 μm, which is less than half of the total thickness. Therefore, when considering the interaction between the ferromagnetic powder and the lubricant, it is thought that the lower layer has a larger contribution, so the present inventors first studied the ferromagnetic powder in the lower layer. As a result, by setting the adsorption amount of stearic acid in the cobalt-containing iron oxide magnetic powder used for the lower layer within the above range, it is possible to appropriately control the adsorption of fatty acids, which are lubricants, to the cobalt-containing iron oxide magnetic powder. We were able to lower the initial coefficient of friction to a level that poses no problem for practical use. That is, by containing silicon, the ferromagnetic powder becomes acidic, the amount of stearic acid adsorbed becomes low, and fatty acids are more likely to come out to the upper layer, producing the above-mentioned effect. If the amount of stearic acid adsorbed is greater than the above range, the fatty acid as a lubricant will be adsorbed more to the cobalt-containing iron oxide magnetic powder, the amount of fatty acid on the tape surface will decrease, and good running properties cannot be obtained. On the other hand, if the stearic acid adsorption amount is less than this range,
When dispersing magnetic powder, the polymer also becomes difficult to adsorb, reducing dispersibility and filling degree, resulting in a decrease in low-frequency output, and poor surface properties, which also decreases high-frequency output. I found out that it does. Although the initial coefficient of friction was lowered in this way, the coefficient of friction after repeated running remained high, so the surface characteristics of the metal/alloy powder in the upper layer were then investigated. As a result, it was found that by setting the amount of stearic acid adsorbed by the metal/alloy powder in the upper layer within the above range, it was possible to suppress the increase in the coefficient of friction after repeated running. That is, it was found that by containing aluminum, the ferromagnetic powder becomes alkaline, the amount of stearic acid adsorbed increases, the fatty acid retention ability increases, and the increase in the coefficient of friction after repeated running is suppressed. However, in this case, the dispersion decreased and the electromagnetic conversion characteristics were insufficient. It has been found that the use of the above-mentioned organic phosphorus compound is effective in improving this dispersibility. Regarding a magnetic recording medium having a single magnetic layer using ferromagnetic metal/alloy powder, the use of the above-mentioned organic phosphorus compound is known from JP-A-1-189025, but the lower layer contains cobalt. In the case of a multilayer structure using iron oxide magnetic powder, good electromagnetic conversion characteristics and runnability cannot be obtained simply by using the above-mentioned organic phosphorus compound in the upper layer. If the amount of stearic acid adsorbed by the ferromagnetic metal/alloy magnetic powder used in the upper layer is smaller than the above range, the friction coefficient of the magnetic layer after repeated running increases as described above, which is a practical problem. In this way, it has been found that by regulating the amount of stearic acid adsorbed by the magnetic materials in the upper and lower layers and by using the above-mentioned organic phosphorus compound in the upper layer, it is possible to achieve both good electromagnetic conversion characteristics and runnability. The amount of stearic acid adsorbed by the ferromagnetic powder in the present invention was measured by the following method, and the unit is mol/m2. 5g of ferromagnetic powder, 2w of stearic acid
The mixture was added to a 100 ml Erlenmeyer flask containing 50 ml of a methyl ethyl ketone solution containing t%, the flask was tightly stoppered, and the mixture was stirred with a magnetic stirrer at 25° C. for 25 hours. Then, solid-liquid separation was performed using a centrifuge, and the stearic acid concentration C (wt%) in the supernatant was measured using gas chromatography. The amount of stearic acid adsorbed per unit area of the ferromagnetic powder is determined by the following formula. Stearic acid adsorption amount (mol/m2) = (1-50xC)
/(5×SSA×MA) However, SSA: Specific surface area of ferromagnetic powder MA: Molecular weight of stearic acid (284) The magnetic recording medium of the present invention contains a nonmagnetic support and ferromagnetic powder. The basic structure is that a multilayer magnetic layer is provided on this nonmagnetic support. Examples of nonmagnetic supports used in the present invention include various synthetic resin films such as polyethylene terephthalate, polypropylene, polyethylene naphthalate, polycarbonate, polyamide, polyimide, and polyamideimide, and metal foils such as aluminum foil and stainless steel foil. I can list them. The thickness of the nonmagnetic support is generally 2.5 to 100 μm, preferably 3 to 70 μm. Further, the nonmagnetic support may be provided with a back layer on the side where the magnetic layer described below is not provided. The magnetic recording medium of the present invention has a multilayer magnetic layer containing ferromagnetic powder provided on a nonmagnetic support as described above. The total thickness of the magnetic layer is 1.5 mm in total for the upper and lower layers.
The thickness of the magnetic layer is 0 to 5.0 μm, and the thickness of the upper magnetic layer is 0.1 to 1.5 μm. If the upper magnetic layer is thinner than the above range, the output in the short wavelength region will decrease. Further, if the upper magnetic layer is thicker than the above range, the effect of multilayering will not be sufficiently exhibited, and the output in the long wavelength region will decrease, which is not preferable. As long as the effects of the present invention are exhibited,
It is also possible to provide a non-magnetic intermediate layer between the upper and lower magnetic layers, a subbing layer between the lower layer and the support, and furthermore a thin protective layer on the upper layer. The cobalt-containing iron oxide used in the lower layer is Co
Co-modified iron oxides such as tofu or Co solid solution iron oxide, and Co-coated iron oxide are included, and examples of the iron oxide include FeOx (preferably 1.33≦X≦1.50). The C
The specific surface area of the o-containing iron oxide magnetic powder by the BET method is 3
It is preferably 5 m2/g or more and 70 m2/g or less. 35m2
/g or less, the surface of the magnetic tape will not be sufficiently smoothed,
Moreover, if it exceeds 70 m2/g, dispersion becomes difficult, which is not preferable. For the same reason, it is preferable that the average major axis length is 0.25 μm or less and the crystallite size is 35 nm or less. Although it is preferable that σs be as high as possible, it is practically difficult to exceed 80 emu/g. [0019] The coercive force of the lower layer is 500 Oe or more and 1500 Oe or more.
The range is preferably Oe or less, and 650 Oe or more and 900 Oe or more.
A range of Oe is particularly preferred. More or less than this,
The electromagnetic conversion characteristics in the long wavelength region are poor, which is not preferable. In the present invention, the amount of stearic acid adsorbed in the cobalt-containing iron oxide magnetic powder used in the lower layer is 3 x 10-6 to 6 x 10-6 mol/
Let it be m2. Cobalt-containing iron oxide magnetic powder, Si, A
By performing surface treatment with a compound of L, Ca, Sn, Zr, and Ti, the amount of stearic acid adsorbed can be brought into this range. The above surface treatment can be carried out, for example, by mixing cobalt-containing iron oxide ferromagnetic powder and water glass in an alkaline solution and heating the mixture. The pH of the alkaline solution is 8-13, preferably 8-11. Processing temperature is 40-250°C, preferably 50-200°C
℃, and the treatment time is preferably 0.5 to 5 hours. These methods are specifically described in JP-A-2-206020 and the like. In order to make it particularly acidic, it is preferable to include silicon, and examples of these silicon compounds include silicic acid and metal silicate salts described in JP-A-2-257419. By setting the amount of silicon in the range of 0.2 to 4.0 atomic % (Si/Fe), the amount of stearic acid adsorbed can be within the above range. The ferromagnetic metal or alloy powder used in the upper layer has a metal content of 75% by weight or more, and 8% of the metal content is 75% by weight or more.
0% by weight or more of at least one ferromagnetic metal or alloy (e.g., Fe, Co, Ni, Fe-Co, Fe-Ni,
Co-Ni, Co-Ni-Fe), and contains other components (e.g., Al, Si, S) within a range of 20% by weight or less of the metal component.
, Ti, Cr, Mn, Cu, Zn, W, Sn, B, P,
Examples include alloys containing Bi, Nd). Furthermore, the metal/alloy powder may contain a small amount of water, hydroxide, or oxide. In order to make the ferromagnetic powder alkaline,
It is preferable to add an aluminum compound, and for example, aluminum oxide, aluminum chloride, aluminum hydroxide, etc. described in JP-A-2-257419 are added. [0022] The specific surface area of the metal or alloy powder measured by the BET method is preferably 45 m2/g or more and 80 m2/g or less. If it is less than 45 m2/g, the surface of the magnetic tape will not be sufficiently smoothed, particle noise will increase, and electromagnetic conversion characteristics will deteriorate. Moreover, if it exceeds 80 m2/g, dispersion becomes difficult, which is not preferable. For the same reason, the average major axis length is 0.25
The crystallite size is preferably 25 nm or less. It is preferable that σs be as high as possible, but 180 emu/
It is actually difficult to exceed g. [0023] The coercive force of the upper layer is 900 Oe or more and 2200
The range is preferably Oe or less, and 1400 Oe or more and 200
A range of 0 Oe is particularly preferred. Below 900 Oe, the electromagnetic conversion characteristics in the short wavelength range are poor, and above 2200 Oe, the magnetic head becomes saturated and recording becomes difficult. In the present invention, the stearic acid adsorption amount of the ferromagnetic metal or alloy powder is set to be 6×10 −6 mol/m 2 or more. Controlling the amount of stearic acid adsorbed is not preferable because post-treatment in an aqueous system, such as that applied to the cobalt-containing iron oxide magnetic powder used in the lower layer, will lead to oxidation and corrosion of the metal/alloy powder, resulting in a decrease in saturation magnetization. . A preferred method is to add a compound of a metal (eg, Al) that easily forms an alkaline oxide during or after the formation of goethite (α-FeOOH). The amount of Al added is Al/Fe, 5
．． It is preferable to set it as 0-15.0 atomic%. If the amount of Al added is larger than this, the saturation magnetization will be lowered, Bm will be lowered when it is made into a tape, and the electromagnetic conversion characteristics will be lowered, which is not preferable. Note that elements other than Al, such as Ni and C, may be added as necessary.
o, Cr, Si, Zn, Mn, etc. may be added. Ferromagnetic metal or alloy powders are usually subjected to slow oxidation treatment on the surface to avoid spontaneous combustion in the air. In this slow oxidation step, when slow oxidation is performed using an organic solvent, a modified product of the solvent is generated due to the catalytic activity on the surface of the metal powder, which is adsorbed to the surface of the metal/alloy powder and changes the surface characteristics to the acidic side. For this reason, it is preferable to perform gradual oxidation by gradually increasing the concentration of the oxidizing gas in an inert gas without using an organic solvent. The organic phosphorus compound contained in the upper layer is at least one compound represented by the following general formulas (1) to (3). (1) (R-O)nP0(OM)3-n(2)
(R-O)nP(OM)3-n(3) (R)nP0
(OM)3-n (where R represents a substituted or unsubstituted alkyl group, alkenyl group, or aryl group, M represents a hydrogen atom, an alkali metal, or -N(R1)4, and R
1 represents an alkyl group, and n represents 1 or 2. ) Specific examples of M include hydrogen atom, sodium, potassium, and tetraethylammonium ion. Specific examples of R include the following. The straight chain or branched alkyl group preferably has 1 to 22 carbon atoms, such as methyl group, ethyl group, propyl group, butyl group, hexyl group, heptyl group, octyl group, nonyl group, decyl group, Dodecyl group, tetradecyl group, octadecyl group, etc.: Straight chain or branched alkenyl groups include, for example, vinyl group,
Propenyl group, isopropenyl group, butenyl group, pentenyl group, allyl group, oleyl group, etc. Aryl groups include phenyl group, naphthyl group, anthryl group, diphenyl group, diphenylmethyl group, p-ethylphenyl group, tolyl group, Xylyl group, etc.: Examples of alkyl groups, alkenyl groups, and aryl groups having substituents other than hydrocarbon groups include 2-aminoethyl group, 2-butoxyethyl group, p-nitrophenyl group, etc.; may contain a ring other than a benzene ring, such as indene or tetralin. Examples of the organic phosphorus compound represented by the above general formula include α-naphthyl phosphoric acid, phenyl phosphoric acid, diphenyl phosphoric acid, n-butyl phosphate, di-n phosphate,
- Mono- and diesters of phosphoric acid such as butyl, di(2-ethylhexyl) phosphate, isopropyl phosphate, diisopropyl phosphate, and salts thereof;
- mono- and diesters of phosphorous acid, such as butyl, diethyl phosphite, dioleyl phosphite, diphenyl phosphite, and salts thereof; phosphonic acids, such as p-ethylbenzenesulfonic acid, phenylphosphonic acid, and salts thereof; ; Examples include phosphinic acids such as phenylphosphinic acid and salts thereof. Among the above examples, organic phosphorus compounds having an aryl group are preferred, and organic phosphorus compounds having a phenyl group are particularly preferred. All the compounds described in JP-A-1-189025 can be used as the organic phosphorus compound of the present invention. In the upper magnetic layer of the present invention, it is preferable that the organic phosphorus compound is contained in an amount of 0.03 to 10 parts by weight based on 100 parts by weight of the ferromagnetic metal or alloy powder. Even more preferably, the amount is 0.05 to 7 parts by weight. If the content is less than this, the effect of the organic phosphorus compound will not be effectively exhibited, and if the content is more than this, the dispersion state will deteriorate or free organic phosphorus compounds will be generated, resulting in deterioration of running durability. When using the above-mentioned organic phosphorus compound in the upper magnetic layer, the organic phosphorus compound is dissolved or dispersed in a low boiling point organic solvent, ferromagnetic powder is added to this solution and mixed, and then the organic solvent is mixed. A method for preparing a pretreated ferromagnetic powder by removing ferromagnetic powder, and manufacturing a magnetic recording medium using this ferromagnetic powder, and a method for preparing a magnetic paint using the above-mentioned organic phosphorus compound, preferably for preparing a magnetic paint. It is possible to use a method in which the material is added in a dissolved or dispersed state to a part of the solvent and then kneaded and dispersed. As the binder used for the upper and lower magnetic layers of the present invention and the back layer provided as necessary, a commonly used binder is usually used in an amount of 10 parts by weight per 100 parts by weight of ferromagnetic powder.
-40 parts by weight (preferably 15 to 30 parts by weight) can be used. Examples of resins used include cellulose derivatives, vinyl chloride copolymers (eg, vinyl chloride/vinyl acetate copolymers containing a third component such as vinyl chloride/vinyl acetate/maleic anhydride copolymers) vinyl chloride/vinyl acetate copolymer), vinylidene chloride copolymer, polyester resin, acrylic resin, polyvinyl acetal resin, polyvinyl butyral resin, phenoxy resin,
Examples include epoxy resins, butadiene/acrylonitrile copolymers, polyurethane resins, and urethane epoxy resins, and these can be used alone or in combination in the present invention. Among the above, it is preferable to use a polyurethane resin and a vinyl chloride copolymer together. moreover,
When using a polyurethane resin and a vinyl chloride copolymer, it is particularly preferred that at least one of these resins is a resin containing a repeating unit having a polar group. Examples of repeating units having polar groups included in the vinyl chloride copolymer include -COOM, -SO3M, -OSO3
M and -PO(OM)2 (M represents a hydrogen atom or an alkali metal atom) can be mentioned. Even if the vinyl chloride copolymer contains these repeating units alone, 2
It may contain more than one species. Among these -SO3N
It is preferable to use a vinyl chloride copolymer containing a repeating unit having a and/or a repeating unit having -COOH. The content of repeating units having polar groups in the copolymer is usually in the range of 0.001 to 5.0 mol% (preferably 0.05 to 3.0 mol%). Content of repeating units with polar groups is 0.001 mol%
If it is lower, the dispersion state of the ferromagnetic powder tends to deteriorate, and if it is higher than 5.0 mol %, the copolymer becomes hygroscopic and the weather resistance of the magnetic tape tends to deteriorate. [0034] The above vinyl chloride copolymer preferably further contains a repeating unit having an epoxy group. The epoxy group in the vinyl chloride copolymer mainly acts to stabilize the vinyl chloride copolymer and suppress the dehydrochlorination reaction of the copolymer that progresses over time. [0035] When a repeating unit having an epoxy group is contained, the content of the repeating unit having an epoxy group in the copolymer is preferably in the range of 1 to 30 mol%, and the content of the repeating unit having an epoxy group in the copolymer is preferably in the range of 1 to 30 mol%. The ratio of repeating units having an epoxy group to 1 mole of vinyl chloride repeating units is 0.01 to 0.5 mole (particularly preferably 0.01 to 0.5 mole).
．． It is preferably within the range of 0.01 to 0.3 mol). The number average molecular weight of such a vinyl chloride copolymer is usually 10,000 to 100,000 (preferably 15,000 to 100,000).
00 to 60,000). When the polyurethane resin contains a repeating unit having a polar group, examples of the repeating unit having a polar group include -COOM, -SO3M, -OSO3M and -PO(OM)2 [M is a hydrogen atom or an alkali represents a metal atom]. These repeating units may be contained alone, or two or more types thereof may be contained. Among these, repeating units having -SO3Na and/
Alternatively, it is preferable to use a polyurethane resin containing a repeating unit having -COOH. The content of repeating units having polar groups in the polyurethane resin is usually in the range of 0.001 to 5.0 mol% (preferably 0.01 to 2.0 mol%). The content of repeating units with polar groups is 0.00
If it is less than 1 mol %, the dispersion state of the ferromagnetic powder tends to deteriorate, and if it is higher than 5.0 mol %, the polyurethane resin becomes hygroscopic and the weather resistance of the magnetic tape tends to deteriorate. The number average molecular weight of the polyurethane resin is 10.0
00-200,000 (preferably 15,000-60
,000). In the present invention, when the above-mentioned vinyl chloride copolymer and polyurethane resin are used together as a binder,
The ratio of both is preferably in the range of 35:65 to 80:20 (particularly preferably 40:60 to 70:30) by weight. Further, the binder is preferably a cured product obtained by adding a polyisocyanate compound in addition to the vinyl chloride copolymer/polyurethane resin. In this case, common polyisocyanate compounds can be used, and specific examples include 3 mol of diisocyanate such as diphenylmethane-4,4'-diisocyanate, tolylene diisocyanate, xylylene diisocyanate, etc. and 1 mole of trimethylolpropane, a biuret adduct compound of 3 moles of hexamethylene diisocyanate, an isocyanurate adduct compound of 5 moles of tolylene diisocyanate, an isocyanurate adduct compound of 3 moles of tolylene diisocyanate and 2 moles of hexamethylene diisocyanate, and Mention may be made of polymers of diphenylmethane diisocyanate. The lubricant contained in the magnetic layer of the magnetic recording medium of the present invention includes silicone oil, fatty acid-modified silicone oil, graphite, fluorinated alcohol, polyolefin (polyethylene wax, etc.), polyglycol (polyethylene oxide wax, etc.). , tetrafluoroethylene oxide wax, polytetrafluoroglycol, perfluoro fatty acid, perfluoro fatty acid ester,
Perfluoroalkyl sulfate, perfluoroalkyl phosphate, alkyl phosphate, polyphenyl ether, fatty acid, fatty acid ester, fatty acid amide,
and fatty alcohols. [0041] Among these, it is preferable that fatty acids are contained. When containing fatty acids, the content thereof is preferably 0.1 to 5 parts by weight (particularly preferably 0.3 to 4 parts by weight) based on 100 parts by weight of the magnetic powder. If the amount of fatty acid added is less than this, the lubricating effect will not be sufficient,
The coefficient of friction becomes high and the running of the tape becomes unstable. Furthermore, if the amount added is greater than the above range, the magnetic layer will become plasticized and may become brittle if used repeatedly. [0042] Examples of fatty acids used in the present invention include:
Examples include capric acid, undecylic acid, lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, montanic acid, oleic acid, elaidic acid, linoleic acid, linolenic acid, and stearolic acid. Furthermore, it is preferable to use a fatty acid ester in addition to the fatty acid. The content of the fatty acid ester is preferably 0.1 to 5 parts by weight (particularly preferably 0.3 to 4 parts by weight) based on 100 parts by weight of the magnetic powder. When fatty acids and fatty acid esters are used together, the weight ratio is 1:9 to 9:
It is preferable to use it within the range of 1. Examples of fatty acid esters used in the present invention include butyl myristate, methyl myristate, butyl stearate, ethyl palmitate, butoxyethyl palmitate, butoxyethyl stearate, and the like. The magnetic layer of the magnetic recording medium of the present invention preferably contains inorganic particles having a Mohs hardness of 5 or more. Examples of inorganic particles are not particularly limited as long as they have a Mohs hardness of 5 or more. For example, Al2O3 (Mohs hardness 9
), TiO (6), TiO2 (6.5), SiO2
(7), SnO2 (6.5), Cr2O3 (9)
and α-Fe2O3 (5.5). These can be used alone or in combination. Among these, inorganic particles having a Mohs hardness of 8 or more are preferred in order to improve running durability. The content of the inorganic particles is preferably in the range of 0.1 to 20 parts by weight, particularly preferably 1 to 15 parts by weight, based on 100 parts by weight of the ferromagnetic powder. In addition to the above-mentioned inorganic particles, the magnetic layer of the magnetic recording medium of the present invention contains carbon black (particularly, an average particle size of 10
~300 mμ) is preferably contained. Next, a method for manufacturing the magnetic recording medium of the present invention will be explained. When producing the magnetic layer of the magnetic recording medium of the present invention, a magnetic coating material is prepared by kneading and dispersing ferromagnetic powder, a binder, and, if necessary, an abrasive, carbon black, a lubricant, and others, usually together with a solvent. As the solvent used during kneading and dispersion, solvents such as methyl ethyl ketone, toluene, butyl acetate, and cyclohexanone, which are usually used in the preparation of magnetic paints, can be used. The method of kneading and dispersing is not particularly limited as long as it is a method normally used for preparing magnetic paints, and the order of addition of each component can be set as appropriate. However, in the present invention, when preparing the magnetic paint for the upper layer, the magnetic powder treated with an organic phosphorus compound is used as described above, or the organic phosphorus compound is added during kneading and dispersion. , the organic phosphorus compound is contained in the magnetic layer. [0046] For preparing the magnetic paint, conventional kneading machines such as two-roll mills, three-roll mills, ball mills, sand grinders, attritors, high-speed impeller dispersers, high-speed stone mills, high-speed impact mills, dispersers, kneaders, High-speed mixers, homogenizers, ultrasonic dispersers, etc. are used. For details on the technology related to kneading and dispersion, please refer to
T. C. PATTON ”Paint Flow an
d Pigment Dispersion” (Joh
n Wiley & Sons, 1964) and Shinichi Tanaka, Kogyo Materials, Vol. 25, 37 (1977). It is also described in US Pat. No. 2,581,414 and US Pat. No. 2,855,515. In the present invention, a magnetic coating material can also be prepared by kneading and dispersing according to the method described in the above cited document. The magnetic paint thus prepared is coated on the non-magnetic support described above. These supports are subjected to corona discharge treatment, plasma treatment,
Undercoat treatment, heat treatment, dust removal treatment, metal vapor deposition treatment, and alkali treatment may be performed. The following can be proposed as an example of an apparatus and method for coating the multilayer magnetic layer on the support. ■After coating and drying the lower layer using gravure coating, roll coating, blade coating, extrusion coating equipment, etc. commonly used in magnetic coating coating, the coating method is applied as described in Japanese Patent Publication No. 1-46186 and Japanese Patent Application Laid-Open No. 1983-1989. The upper layer is coated using a support pressure type extrusion coating device disclosed in Japanese Patent Application Laid-open No. 238179 and Japanese Patent Application Laid-Open No. 2-265672. [0050] First, a lower layer is applied using gravure coating, roll coating, blade coating, extrusion coating equipment, etc., which are generally used for applying magnetic paint, and while the lower layer is wet, it is coated with Japanese Patent Publication No. 1-46186 and Japanese Patent Application Laid-open No. 1-46186. 1986-2
The upper layer is coated using a support pressurizing type extrusion coating device disclosed in Japanese Patent Publication No. 38179 and Japanese Patent Application Laid-Open No. 2-265672. [0051] With one coating head having two built-in coating liquid passage slits as disclosed in JP-A-63-88080, JP-A-2-17971, and JP-A-2-265672. , apply the upper and lower layers almost simultaneously. (2) Upper and lower layers are coated almost simultaneously using an extrusion coating device equipped with a backup roll disclosed in Japanese Patent Application Laid-Open No. 2-174965. In addition, in order to prevent deterioration of the electromagnetic conversion characteristics of the magnetic recording medium due to agglomeration of magnetic particles, the coating method is It is desirable to apply shear to the coating liquid inside the head. The magnetic layer coated on the support by such a method is treated, if necessary, to orient the magnetic powder in the layer in a desired direction while immediately drying, and then the formed magnetic layer is dried. . The conveying speed of the support at this time is 10 to 1000 m/min, and the drying temperature is 20 to 13 m/min.
Controlled at 0°C. Furthermore, a back layer can be provided if necessary. After this, surface smoothing treatment is performed. Furthermore, a magnetic recording medium can be obtained by cutting into a desired shape. The present invention will be explained below using examples. Note that "parts" in Examples and Comparative Examples indicate "parts by weight." Preparation of surface-treated Co-containing iron oxide magnetic powder C
o Modified acicular ferromagnetic iron oxide powder (Co-FeOx: x=1
．． 45, coercive force = 800Oe, specific surface area = 48m2/g
, crystallite size = 25 nm, average major axis length = 0.15 μ
Add 500 g of Co.
A slurry of modified iron oxide magnetic powder was prepared. Add 0.0% water-soluble water glass to this slurry so that the amount of Fe in the Co-containing ferromagnetic iron oxide powder is 1.5 atomic % in terms of Si.
It was dissolved in 2 liters of pure water and added in its entirety to the above slurry. After that, carbon dioxide gas is bubbled through to adjust the pH of the slurry to 7.
0, filtered, dried at 40°C and surface treated Co
A magnetic powder containing iron oxide (magnetic powder B) was obtained. Magnetic powder A and magnetic powder C were obtained by changing the amount of Si in the same manner. Table 1 shows the measurement results of the Si/Fe content and stearic acid adsorption amount of these magnetic powders. Table 1 Number Si/
Fe stearic acid adsorption amount
(atom%)
(mol/m2) Magnetic powder A
5.5
1.0×10-6 Magnetic powder B 1.5
4.0×10-6 Magnetic powder C 0.1
8.0×10-6
Preparation of magnetic paints F-1 to F-3 (lower layer liquid)
The above magnetic powder A
100
Part Vinyl chloride copolymer (MR-110 manufactured by Nippon Seion) 15
Part: Polyester polyurethane (Toyobo UR-8600) 5 parts
Polyisocyanate (Coronate L manufactured by Nippon Polyurethane) 6.7 parts
Stearic acid (industrial)
2
Part Butyl Stearate (Industrial)
1
Part Methyl ethyl ketone

350 parts cyclohexanone

150 parts Of the above composition, components other than polyisocyanate and stearic acid were dispersed for 3 hours using a sand grinder. After that, polyisocyanate and stearic acid were added and dispersed for 15 minutes, and then filtered using a filter with an average pore size of 1 μm to form magnetic paint F-1.
It was created. Similarly, using magnetic powder B, magnetic paint F
Magnetic paint F-3 was prepared using Magnetic Powder C. Preparation of ferromagnetic metal powder (D) α-FeOO
H (Ni/Fe=3 atomic%, specific surface area=86 m2/g,
500 g of α-FeOOH (average long axis length = 0.23 μm) was added to 5 liters of pure water and dispersed with a homomixer to create a slurry of α-FeOOH. An aqueous solution of water-soluble water glass was added to this slurry at 10.0 atomic % in terms of Si in α-FeOOH.
It was dissolved in 0.5 liters of pure water so as to give the following amount, and the entire amount was added to the above slurry. Thereafter, carbon dioxide gas was bubbled through to adjust the pH of the slurry to 7.0, and the slurry was stirred at 30°C for 30 minutes. This slurry was filtered, washed with water, and dried to form an α-
FeOOH powder was obtained. This Si-containing α-FeOOH was dehydrated by heating at 500° C. for 1 hour in a nitrogen stream, and then subjected to a reduction treatment at 490° C. for 6 hours in a hydrogen stream. After reduction, the inside of the container was replaced with nitrogen, and after cooling to room temperature, oxygen gas was gradually added to the nitrogen gas to increase the oxygen concentration, and the oxygen concentration was brought to the same level as air over a period of 6 hours. A ferromagnetic metal powder mainly composed of Fe was obtained. The obtained ferromagnetic metal powder has a saturation magnetization of 124 emu/g and a coercive force of 1600.
Oe, specific surface area = 59 m2/g, crystallite size = 19
nm, average major axis length = 0.17 μm, and stearic acid adsorption amount was 4.0×10 −6 mol/m 2 . Preparation of ferromagnetic metal powder (E) α-FeOO
H (Ni/Fe=3 atomic%, specific surface area=86 m2/g,
500 g of α-FeOOH (average long axis length = 0.23 μm) was added to 5 liters of pure water and dispersed with a homomixer to create a slurry of α-FeOOH. To this slurry, an aqueous solution of aluminum sulfate was dissolved in 0.5 liters of pure water so that the amount of aluminum sulfate was 10.0 atomic % based on α-FeOOH in terms of Al, and the entire amount was added to the slurry. Thereafter, an aqueous solution of sodium hydroxide was added to adjust the pH of the slurry to 9.0, and the mixture was stirred at 30° C. for 30 minutes. This slurry was filtered, washed with water, and dried to obtain α-FeOOH powder containing Al. This Al-containing α-FeOOH was dehydrated by heating at 500° C. for 1 hour in a nitrogen stream, and then subjected to a reduction treatment at 490° C. for 6 hours in a hydrogen stream. After reduction, the inside of the container was replaced with nitrogen, cooled to room temperature, and then oxygen gas was gradually added to the nitrogen gas to increase the oxygen concentration. Over 6 hours, the oxygen concentration was the same as that of air, and Al and N
A ferromagnetic metal powder containing i and mainly consisting of Fe was obtained. The obtained ferromagnetic metal powder has a saturation magnetization of 122 emu/g
, coercive force=1570Oe, specific surface area=55m2/g, crystallite size=20.5nm, average major axis length=0.15μ
m, stearic acid adsorption amount is 8.0 x 10-6 mol/m2
Met. Preparation of magnetic paints G-1 to G-4 (upper layer liquid) Metal magnetic powder E
100 copies
phenylphosphonic acid
2nd part
Vinyl chloride copolymer (MR-11 manufactured by Nihon Seion)
0) 15 copies
Polyester polyurethane (Toyobo UR-8600)
5 parts Polyisocyanate (Coronate L manufactured by Nippon Polyurethane)
6.7 parts stearic acid (industrial use)
Part 2 Butyl stearate (industrial use)
1 part α-alumina (average particle size 0
．． 2μm)
5 parts carbon (oil absorption 63ml/g
, average particle size゛80mμ)
1 part methyl ethyl ketone

350 parts cyclohexanone

150 parts Of the above composition, components other than polyisocyanate and stearic acid were dispersed for 3 hours using a sand grinder. After that, polyisocyanate and stearic acid were added and dispersed for 15 minutes, and the average pore size was 1.
The mixture was filtered using a μm filter to prepare magnetic paint G-4. Magnetic paints G-1 to G-3 were created in the same manner. Table 2 shows the ferromagnetic powder (magnetic material) used at this time and the amount of phenylphosphonic acid added. Shown below. Table 2. Magnetic paint Magnetic material Phenylphosphonic acid number of the magnetic material used
Addition amount of stearic acid adsorption amount

(mol/m2)
G-1 D
4.0×10-6 None G-2
D 4.0
×10-6 2 parts G-3
E 8.0×10-
6 None G-4 E
8.0×10-6
2 parts In Table 2, the amount of phenylphosphonic acid added indicates the weight relative to 100 parts of the ferromagnetic powder. Furthermore, in Tables 1 and 2, the stearic acid adsorption amount of the ferromagnetic powder was measured by the following method, and the unit is mol/m2. 5g of ferromagnetic powder,
Added to a 100 ml Erlenmeyer flask containing 50 ml of methyl ethyl ketone solution containing 2 wt% stearic acid,
Seal the flask and stir with a magnetic stirrer for 25 minutes.
The mixture was stirred at ℃ for 25 hours. Then, solid-liquid separation was performed using a centrifuge, and the stearic acid concentration C (wt.%) in the supernatant was determined.
was measured using gas chromatography. The amount of stearic acid adsorbed per unit area of the ferromagnetic powder was determined using the following formula. Stearic acid adsorption amount (mol/m2) = (1-50xC)
/(5 x SSA x MA) However, SSA: Specific surface area of ferromagnetic powder MA: Molecular weight of stearic acid (284) Using the obtained magnetic paint, an extrusion type coating head having two slits in one head was used. On a polyethylene terephthalate support with a thickness of 10 μm, an upper layer with a dry thickness of 0.5 μm,
Simultaneous multilayer coating was carried out at a coating speed of 100 m/min so that the thickness of the lower layer was 3.0 μm, and magnetic field orientation and drying treatment were performed. Thereafter, the surface was smoothed and slit to a width of 8 mm to obtain samples of Examples and Comparative Examples 1 to 4. The following measurements were performed on these samples, and the results are shown in Table 2. (1) Surface glossiness Measure the incident angle of 4 using a standard glossmeter (manufactured by Suga Test Instruments Co., Ltd.).
The glossiness of the surface of the magnetic layer was measured at a reflection angle of 5 degrees and a reflection angle of 45 degrees. Note that the values shown are values when the glossiness of the sample obtained in Comparative Example 1 is taken as 100%. (2) Friction coefficient stainless steel pole (SUS420J, surface roughness 0.1s
, 5mmφ), the tension (T
2) was measured, and the coefficient of friction (μ) was calculated using the following formula. μ=1/π·ln (T2/T1) The environmental conditions for this measurement were a temperature of 23° C. and a relative humidity of 70%. Further, the coefficient of friction at the 100th pass was measured in the same way using a tape that had been run repeatedly for 99 passes on a video deck. (3) Record the Y output 50% white video signal with the standard recording current,
The average value of the envelope of the reproduced output was measured using an oscilloscope. (4) Recording the C output color (color signal) video signal at the standard recording current,
Reproduction output was measured in the same manner as above. (5) Y-S/N Use Shibasoku noise meter (925R), high-speed filter - 10KHz, low-speed filter 4
．． The noise level was measured at 2 MHz and the S/N ratio was determined. (6) C-S/N Use Shibasoku noise meter (925R), high-speed filter - 10KHz, low-speed filter 5
The noise level was measured at 00 KHz AM, and the S/N ratio was determined. In addition, for measurements (3) to (6), a SONY EV was used.
-S900 was used, and the sample of Comparative Example 1 was expressed as 0 dB. Table 3. Number Upper layer Lower layer Glossiness
Friction coefficient Y C Y- C
− Coating liquid Coating liquid
1st 100th Output Output
S/N S/N

(dB
) Example G-3 E-2 120
0.23 0.24 1.7 1.6
1.0 0.8 Comparative Example 1 G-3 E-
3 100 0.21 0.24
0.0 0.0 0.0 0.0 Comparative Example 2 G-3 E-1 115 0.37
0.42 0.8 1.0 0.
4 0.3 Comparative Example 3 G-1 E-2 1
27 0.22 0.63 1.9
1.4 0.9 0.6 Comparative Example 4 G-
2 E-2 92 0.17 0.5
9 -0.7 1.0 -0.5 -0
．． 3 Comparative Example 5 G-4 E-2 105
0.31 0.33 0.7 1.5
0.4 0.1 As shown in Table 3, it can be seen that the magnetic recording medium according to the present invention has a stable and low coefficient of friction both at the initial stage and after repeated running, and has excellent electromagnetic conversion characteristics. Effects of the Invention The present invention investigates the surface properties of the ferromagnetic powder and the running performance of a magnetic recording medium in which different materials are laminated, the upper layer being a metal/alloy powder and the lower layer being a cobalt-containing iron oxide magnetic powder. By focusing on the interaction with the fatty acid, which is a lubricant, and by setting the amount of stearic acid adsorbed in the cobalt-containing iron oxide magnetic powder used in the lower layer within the above specified range, the cobalt-containing iron oxide magnetic powder can be used as a lubricant. We were able to appropriately control the adsorption of the material and lower the initial friction coefficient to a level that poses no problem for practical use. It was also found that by setting the amount of stearic acid adsorbed by the metal/alloy powder in the upper layer within the above range, it was possible to suppress the increase in the coefficient of friction after repeated running. Furthermore, it has been found that by using a combination of the above-mentioned organic phosphorus compounds in the upper layer, both good electromagnetic conversion characteristics and running properties can be achieved.

Claims (2)

[Claims] [Claim 1] A magnetic recording medium comprising two or more magnetic layers formed by dispersing ferromagnetic powder in a binder on a non-magnetic support, wherein the lower magnetic layer contains the ferromagnetic powder as the ferromagnetic powder. Stearic acid adsorption amount is 3 x 10-6 to 6 x 10
-6 mol/m2 of cobalt-containing iron oxide powder;
The upper magnetic layer contains a ferromagnetic metal or alloy powder having an adsorption amount of stearic acid of 6 x 10-6 mol/m2 or more as the ferromagnetic powder, and the upper magnetic layer has the following general formula (1) to A magnetic recording medium comprising at least one organic phosphorus compound represented by (3). (1) (R-O)nP0(OM)3-n(2)
(R-O)nP(OM)3-n(3) (R)nP0
(OM)3-n (where R represents a substituted or unsubstituted alkyl group, alkenyl group, or aryl group, M represents a hydrogen atom, an alkali metal, or -N(R1)4, and R
1 represents an alkyl group, and n represents 1 or 2. ) 2. A magnetic recording medium in which a plurality of two or more magnetic layers each made of ferromagnetic powder dispersed in a binder are provided on a non-magnetic support, the lower magnetic layer having a cobalt-containing iron oxide magnetic layer. The silicon content in the powder is Si/Fe and is 0.
．． The upper magnetic layer contains a ferromagnetic metal or alloy powder containing ferromagnetic powder with an Al/Fe content of 5.0 to 15.0 at%. A magnetic recording medium comprising a magnetic powder and at least one organic phosphorus compound represented by the following general formulas (1) to (3) in the upper magnetic layer. (1) (R-O)nP0(OM)3-n(2)
(R-O)nP(OM)3-n(3) (R)nP0
(OM)3-n (where R represents a substituted or unsubstituted alkyl group, alkenyl group, or aryl group, M represents a hydrogen atom, an alkali metal, or -N(R1)4, and R
1 represents an alkyl group, and n represents 1 or 2. )