JPH04319523A - Magnetic recording medium and production thereof - Google Patents

Abstract

PURPOSE:To improve electromagnetic conversion characteristics and durable traveling property by specifying the respective pore volumes after a calender treatment in the case of provision of a lower magnetic layer and an upper magnetic layer respectively alone and the pore volumes after a calender treat ment of a magnetic layer consisting of the lower magnetic layer and the upper magnetic layer. CONSTITUTION:This magnetic recording medium is formed by providing the magnetic layer consisting of the lower magnetic layer and the upper magnetic layer by applying a magnetic coating material contg. ferromagnetic powder and binder on a nonmagnetic base and subjecting the layer to drying and orienting, then to the calender treatment. The pore volume V1 of the lower magnetic layer after the calender treatment in the case of provision of the lower magnetic layer alone is specified to <=0.02ml/g. The pore volume V2 of the upper magnetic layer after the calender treatment in the case of provision of the upper magnetic layer alone is specified to 0.03 to 0.07ml/g. Further, the pore volume V3 after the calender treatment of the magnetic layer consisting of the lower magnetic layer and the upper magnetic layer is specified to 0.01 to 0.05ml/g and is specified to the relation V2>V3>V1.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a magnetic recording medium, and in particular a magnetic recording medium with excellent electromagnetic conversion characteristics and running durability in high-density recording (short wavelength recording). Regarding recording media. 2. Description of the Related Art Recently, magnetic recording media have been widely used as audio tapes, video tapes, computer magnetic tapes, and the like. Magnetic recording media are required to have excellent properties in various properties such as electromagnetic conversion properties and running durability. In particular, excellent electromagnetic conversion characteristics and good running characteristics are extremely important requirements, and it is necessary to achieve both of the above characteristics so that they are both excellent. In order to satisfy both of these required characteristics, in magnetic disks, the average pore area of the magnetic layer is 6 x 10-5 by random orientation of the magnetic layer.
~7 x 10-1 μm2 (pore diameter: 86 Å ~ 9560 Å
) A magnetic disk has been proposed in which the pores are impregnated with a lubricant to prevent output caused by surface properties and improve durability at the same time (
JP 62-137718). In addition, the pore size distribution contained in the coating layer is 0.01 to 0.1 μm (100 to 1000 μm).
A magnetic recording medium with a pore diameter of 1.55 Å) has been proposed and is said to have improved durability (Japanese Patent Application Laid-Open No. 167416/1983). However, in recent years, high image quality and high sound quality systems such as S-VHS and Hi-Eight have been studied, as well as systems such as high-definition and high-density floppy disks, and the demand for higher density has increased. . In order to achieve such high density, it is necessary to make the surface of the magnetic layer ultra-smooth, for example, with a center line average roughness (Ra) of 10 nm or less, preferably 5 nm or less. and,
Since such an ultra-smooth surface has a high coefficient of friction, it is necessary to further improve running durability. [0004] In response to such requests, the above-mentioned Japanese Patent Application Laid-Open No. 1983
The average pore area of No.-137718 and JP-A No. 63-167416 is very large, and sufficient smoothness cannot be obtained, and the entrance diameter of the pores is large, so the lasting effect of the lubricant is low. In other words, in conventional magnetic recording media, the surface of the magnetic layer is not very smooth, so the sliding area between the magnetic head and the magnetic layer is small, and there is no problem with the sliding characteristics. Because it is not a smooth surface,
The S/N ratio at short wavelengths was not improved and excellent electromagnetic conversion characteristics were not obtained. Furthermore, since the entrance diameter of the pores is relatively large, the lubricant immediately seeps out, resulting in a disadvantage that the effect does not last long. Furthermore, in JP-A No. 62-22239, the magnetic layer contains fatty acids, and the amount of fatty acids extracted from the surface of the magnetic layer by a nonpolar hydrocarbon solvent is 5 to 5 per volume of the magnetic layer.
It is disclosed that running stability and running durability can be improved by adjusting the amount to 30 mg/cm3. However, in the case of a magnetic recording medium for high-density recording having an ultra-smooth surface, sufficient running stability and running durability could not be obtained even if such a so-called free fatty acid was present inside the magnetic layer. Furthermore, JP-A No. 63-167416 states that fluorine-based lubricants such as perfluoropolyether can also be used, but ether bonds are preferable because they have relatively low polarity and the entrance diameter of the pores is large. It was not possible to obtain adequate running stability and running durability. In such a single magnetic layer, when the pore volume is increased, the degree of filling of the ferromagnetic powder decreases, and the electromagnetic conversion characteristics, especially the output in long wavelength recording, decrease.
Initial running performance is good, but repeated running performance deteriorates. [0007] Furthermore, when the pore volume is reduced in a single magnetic layer, the degree of filling of the ferromagnetic powder increases, and the surface properties improve, resulting in improved electromagnetic conversion characteristics and improved repeatability. Driving performance deteriorated and problems such as wow and flutter occurred. SUMMARY OF THE INVENTION Accordingly, the present invention provides a magnetic recording medium which has particularly excellent electromagnetic conversion characteristics and has improved running stability and running durability, especially running durability under high temperature and high humidity conditions. The purpose is to provide [Means for Solving the Problems] That is, the above object of the present invention is to form a magnetic layer consisting of a lower magnetic layer and an upper magnetic layer by coating a magnetic paint containing ferromagnetic powder and a binder on a non-magnetic support. In a magnetic recording medium obtained by calendering after drying and orientation, when a lower magnetic layer closer to the non-magnetic support is provided alone, the pore volume V1 of the lower magnetic layer after calendering is 0.02 ml/g or less, and when the upper magnetic layer is provided alone, the pore volume V2 of the upper magnetic layer after calendering is 0.03 to 0.07 ml/g, and The pore volume V3 of the magnetic layer consisting of the lower magnetic layer and the upper magnetic layer after calendering is 0.01 to 0.05 ml/
g, and the relationship of V2 > V3 > V1 is satisfied. Two types of magnetic coatings containing ferromagnetic powder and a binder are coated on a non-magnetic support to obtain a magnetic layer consisting of a lower magnetic layer and an upper magnetic layer, and after drying and orientation,
In a method for manufacturing a magnetic recording medium that undergoes calendering,
The amount of binder per 100 parts by weight of ferromagnetic powder in the magnetic paint used for the lower magnetic layer closer to the non-magnetic support is 10 parts by weight.
~30 parts by weight, and when the lower magnetic layer is provided alone, the pore volume V1 after calendering is 0.02
ml/g or less, and the amount of the binder is 15 to 100 parts by weight of the ferromagnetic powder of the magnetic paint used for the upper magnetic layer.
50 parts by weight, and when the upper magnetic layer is provided alone, the pore volume V2 after calendering is 0.03 to
0.07 ml/g, and the magnetic paints for the lower magnetic layer and the upper magnetic layer are applied simultaneously or sequentially by a wet coating method to obtain the magnetic layer consisting of the lower magnetic layer and the upper layer, and after drying and orientation, By calendering, the pore volume V3 of the entire magnetic layer after calendering is 0.01
~0.05ml/g, and V2 > V3 > V1
A method for manufacturing a magnetic recording medium characterized by obtaining a magnetic layer having the following relationship. That is, in the present invention, the lower magnetic layer has a small pore volume, a high degree of filling of ferromagnetic powder, and has good surface properties, so that the upper magnetic layer also has good surface properties, and the spacing and spacing for the magnetic head are improved. Loss is eliminated. Therefore, the electromagnetic conversion characteristics, especially by short wavelength recording, are improved. Furthermore, since the lower magnetic layer has a high degree of filling and is thick, the degree of filling of all layers can be increased, and the electromagnetic conversion characteristics due to long wavelength recording are improved. Regarding running properties, since the pores in the upper magnetic layer remain intact, the rate at which the lubricant oozes out is higher than in normal cases. This makes it possible to improve running performance under high temperature, high humidity environments, which were previously quite severe conditions. In particular, lubricant is added at a slow speed from the lower magnetic layer to compensate for the lack of lubricant in the upper magnetic layer, making it possible to maintain good running performance. [0011] Furthermore, in the case of a multilayer tape, it is known that calendering increases the filling degree on the surface of the upper magnetic layer and between the upper magnetic layer and the lower magnetic layer. For this reason, if the pore volume of the multilayer tape is smaller than 0.01ml/g, the pores from which the lubricant on the upper layer surface seeps out are small, and the amount of surface lubricant is insufficient, resulting in poor initial running performance. If the pore volume of the multilayer tape is larger than 0.05 ml/g, the pores from which the lubricant oozes out on the surface of the upper magnetic layer are too large, and the lubricant oozes out too much, resulting in too much lubricant existing on the surface. For this purpose, the tape surface was plasticized, and it was found that the tape surface was scraped during running, making the tape surface smooth and sticking to the sliding object. The following methods can be used to control the pore volume in the magnetic recording medium of the present invention. ■A method of controlling the specific surface area of the ferromagnetic powder contained in the magnetic layer using the BET method. These relationships are such that when the particle size of the ferromagnetic powder is large, the pore volume becomes large because the gap between the ferromagnetic powders becomes large, and when the particle size is small, the pore volume also becomes small. ■Method of controlling the amount of binder present in the magnetic layer. If there is too much binder, the pores will be clogged. In other words, the pore volume becomes smaller. On the other hand, if the amount of binder is too small, the pore volume will increase. ■How to control calendar processing conditions. Calendering is a process in which tape is compressed under high temperature and pressure using elastic rolls and metal rolls. At high temperatures, plastic deformation of the binder increases, improving formability and reducing pore volume. Furthermore, even in the case of high pressure, the pore volume tends to decrease due to the increase in plastic deformation. ■Method of controlling the glass transition temperature (Tg) of the magnetic layer. When the Tg of the magnetic layer is high, it becomes difficult to plastically deform the coating film at the calender temperature. Therefore, the pore volume is increased. Conversely, if the Tg is lowered, the pore volume increases, but the durability decreases. ■How to improve the performance of the kneading machine. Since the ferromagnetic powder and the binder are difficult to mix, they are forcibly kneaded using a kneader that applies high pressure. Therefore, when a large pressure is applied, the degree of filling increases and the pore volume decreases. The magnetic recording medium of the present invention can be obtained by appropriately selecting and combining the methods (1) to (2) above. The magnetic recording medium of the present invention eliminates the above-mentioned drawbacks by controlling the pore volume of the upper magnetic layer, the lower magnetic layer, and the pore volume of the entire layer, and improves electromagnetic conversion characteristics and running stability. Therefore, it is possible to create a magnetic recording medium that has excellent running durability and resistance to running environments. A particularly effective combination in the present invention is that the specific surface area of the ferromagnetic powder in the upper magnetic layer is: 33
~48m2/g, specific surface area of ferromagnetic powder of lower magnetic layer:
21-31 m2/g, amount of binder: 16-26 parts by weight (100 parts by weight of ferromagnetic powder), calender temperature: 80-90
°C, pressure: 250-350 kg/cm, Tg of magnetic layer:
This is a combination of a kneader that applies a small pressure to the upper magnetic layer and a kneader that applies a large pressure to the lower magnetic layer at a temperature of 55 to 65°C. The pores in the magnetic layer of the present invention were measured by the nitrogen gas adsorption method described below. Autosorb-1 (manufactured by Canterchrome, Inc., USA) was used as a measuring device, and the sample tape had a width of 8 mm and a length of about 10 m. The sample is 2×10-3t in advance.
Vacuum degassing was carried out for 4 hours or more at a vacuum degree of about orr. Helium gas is used as a carrier gas, nitrogen gas is used as an adsorption gas, a mixed gas of nitrogen + helium is used, and the partial pressure of nitrogen gas is gradually increased from 0 to 1 to measure the adsorption isotherm. The pressure was gradually lowered from 1 to 0, and the desorption isotherm was measured. The measurement data was analyzed using the BJH method (E.P.
．． Barrett, L. G. Joyner a
nd P. P. Halenda; Journa
l of American Chemical So
73, 373 (1951)), the pore internal diameter was determined from the adsorption isotherm, and the pore entrance diameter and its distribution were determined from the desorption isotherm. In addition, the total volume of the pores was determined from the integrated value of the amount of adsorbed gas. The measurement device orthotobe 1 is a device that fully automatically measures nitrogen adsorption/desorption isotherms at liquid nitrogen temperature using the “constant volume method”. The present invention has a basic configuration in which two magnetic layers are provided on a nonmagnetic support. Examples of materials forming the non-magnetic support include various synthetic resin films such as polyethylene terephthalate, polypropylene, polycarbonate, polyethylene naphthalate, polyamide, polyamideimide, and polyimide, and metal foils such as aluminum foil and stainless steel foil. can be mentioned. There is also no particular limit to the thickness of the non-magnetic support, but it is generally 2.5
~100 μm, preferably 3 to 80 μm. Also,
The surface roughness (Ra: optical interference type surface roughness) of the support is 0.
．． 0.05 μm or less, preferably 0.02 μm or less, more preferably 0.015 to 0.004 μm, especially 0.05 μm or less.
Excellent effects can be achieved when a support with an excellent surface smoothness of 0.02 μm or less is used. As the ferromagnetic powder in the present invention, conventionally known ferromagnetic powders such as
Hexagonal crystals such as γ-iron oxide ferromagnetic powder, cobalt γ-iron oxide ferromagnetic powder, ferromagnetic chromium dioxide fine powder, ferromagnetic metal or alloy fine powder, iron nitride ferromagnetic powder, barium ferrite, strontium ferrite, etc. Ferrite-based ferromagnetic powder or the like can be used. Such ferromagnetic powder can be produced by a method known per se. In the present invention, the specific surface area according to the BET method is 35 m
2/g or more, preferably 45 m2/g or more, and the crystallite size is 300 angstroms or less, preferably 25 m2/g or more.
It is preferred to use ferromagnetic powders that are less than 0 angstroms. There are no particular restrictions on the shape of the ferromagnetic powder, but needle-like, granular, dice-like, rice-grain-like, and plate-like shapes can usually be used. The particle diameter (major axis diameter) of the ferromagnetic powder contained in the magnetic layer of the present invention is 0.30 μm or less, preferably 0.2 μm or less.
It is 0 μm or less, more preferably 0.15 μm or less. The ratio of the short axis diameter to the long axis diameter, that is, the acicular ratio is 2
~20. The long axis here means the longest axis of the three axes of the particle, and the short axis means the shortest axis. It is preferable that the particle size of the ferromagnetic powder in the upper magnetic layer is smaller than that in the lower layer.
The specific surface area of the upper magnetic layer is preferably 25 to 80 m<2>/g when expressed by the T method, and the specific surface area of the upper magnetic layer is preferably larger than that of the lower magnetic layer. The crystallite size of the ferromagnetic powder of the present invention is 450 to 100 angstroms, preferably 3
It is 5 to 150 angstroms. Preferably, the upper magnetic layer is smaller. The ferromagnetic powder of the present invention has an Hc of 200 to 18
00 Oe, preferably 500 to 1000 Oe. It is preferable that the upper magnetic layer has a higher Hc. The saturation magnetization (δs) of the ferromagnetic powder of the present invention is 50 emu/g or more, preferably 70 emu/g or more, and preferably 100 emu/g or more when the ferromagnetic powder is a fine metal powder. When the ferromagnetic powder of the present invention is cobalt-modified iron oxide, the ratio of divalent iron to trivalent iron is preferably 0.
-20%, more preferably 5-10%. The amount of cobalt atoms relative to iron atoms is 0 to 15%, preferably 3 to 8%. It is preferable to optimize the pH of the ferromagnetic powder depending on the combination with the binder used. The range is 4-12, preferably 6-10. At least one of the ferromagnetic powders can be made of Al, Si,
Surface treatment may be performed with P or an oxide thereof. As the binder for the upper magnetic layer and the lower magnetic layer in the present invention, known thermoplastic resins, thermosetting resins, radiation curable resins, and reactive type resins that have been conventionally used as binders for magnetic recording media can be used. It may be a resin or a mixture thereof. More preferably, the binder contains a substance that can be crosslinked or polymerized by radiation irradiation. The thermoplastic resins include acrylic acid ester acrylonitrile copolymer, acrylic acid ester vinylidene chloride copolymer, acrylic acid ester styrene copolymer, methacrylic acid ester acrylonitrile copolymer, and methacrylic acid ester vinylidene chloride copolymer. , methacrylate styrene copolymer, vinyl chloride copolymer (details below), polyurethane resin (details below), urethane elastomer, nylon-silicon resin, nitrocellulose-polyamide resin, polyvinyl fluoride, chloride Vinylidene acrylonitrile copolymer, butadiene acrylonitrile copolymer, polyamide resin, polyvinyl butyral, cellulose derivatives (cellulose acetate butyrate, cellulose diacetate, cellulose triacetate, cellulose propionate, nitrocellulose, etc.), styrene butadiene copolymer, polyester Examples include resins, chlorovinyl ether acrylate copolymers, amino resins, and various synthetic rubber-based thermoplastic resins. [0021] The above thermosetting resin or reactive resin has a molecular weight of 200,000 or less in the state of a coating liquid, and its molecular weight becomes extremely large when heated after coating and drying. , phenolic resin, phenoxy resin, epoxy resin, polyurethane curable resin,
Urea resin, melamine resin, alkyd resin, silicone resin, acrylic reactive resin, epoxy-polyamide resin,
Nitrocellulose melamine resins, mixtures of high molecular weight polyester resins and isocyanate prepolymers, mixtures of methacrylate copolymers and diisocyanate prepolymers, mixtures of polyester polyols and polyisocyanates, urea formaldehyde resins, low molecular weight glycols/high molecular weight diols /triphenylmethane triisocyanate mixtures, polyamine resins, and mixtures thereof. Furthermore, as the radiation-curable resin, a resin having at least one carbon-carbon unsaturated bond in its molecule that can be cured by radiation irradiation can be used. Examples of radiation-curable resins include using a compound having at least one carbon-carbon unsaturated bond in the molecule as a copolymerization component in the vinyl chloride copolymer or polyurethane resin, or using the copolymer as a copolymer component during polymerization. Examples include those manufactured by reacting with a resin or the like. As a compound having at least one carbon-carbon unsaturated bond, a compound containing at least one (meth)acroyl group in the molecule is preferable, and such a compound may further contain a glycidyl group or a hydroxyl group. Furthermore, a compound that can be polymerized by radiation irradiation may be added to the binder. Such compounds include (meth)acrylic acid esters, (meth)acrylamides, allyl compounds, vinyl ethers, vinyl esters, vinyl heterocyclic compounds, N-vinyl compounds, styrenes, acrylic acid, methacrylic acid. , crotonic acids, itaconic acids, olefins, and the like. Particularly preferred compounds among these are compounds containing two or more (meth)acryloyl groups in one molecule;
For example, diethylene glycol di(meth)acrylate, triethylene glycol (meth)acrylate, trimethylolpropane tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, reaction products of polyisocyanate and poly(meth)acrylate, etc. can be mentioned. As the vinyl chloride copolymer, those having a softening temperature of 150° C. or less and an average molecular weight of about 10,000 to 300,000 can be used. Specific examples of preferred vinyl chloride copolymers include vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl acetate-maleic acid copolymer, vinyl chloride-vinyl acetate-vinyl alcohol copolymer, and vinyl chloride-acetic acid copolymer. Vinyl-maleic acid, vinyl alcohol copolymer, vinyl chloride-vinyl propionate-maleic acid copolymer, vinyl chloride-vinyl propionate-vinyl alcohol copolymer, vinyl chloride-vinyl acetate-acrylic acid copolymer, chloride Examples include vinyl-vinyl acetate-acrylic acid-vinyl alcohol copolymers, and oxidized versions of these copolymers. In particular, vinyl chloride copolymers having polar groups such as carboxylic acid groups or their salts, sulfonic acid groups or their salts, phosphoric acid groups or their salts, amino groups, and hydroxyl groups are used to improve the dispersibility of magnetic materials. preferable. [0025] As the above-mentioned polyurethane, a polyurethane produced from a polyol, a diisocyanate, and, if necessary, a chain extender, by a method known per se for producing polyurethane can be used. The above polyols are, for example, compounds such as polyether diol, polyester diol, polycarbonate diol, and polycaprolactone diol. Typical examples of the polyether polyol include polyalkylene glycols such as polyethylene glycol and polypropylene glycol. [0026] The above polyester polyol is, for example,
Polycondensation of dihydric alcohol and dibasic acid, lactones,
For example, it can be totalized by ring-opening polymerization of caprolactone. The polyisocyanate used to react with the above polyol to form polyurethane is not particularly limited, and commonly used polyisocyanates can be used. For example, hexamethylene diisocyanate, toridine diisocyanate, isophorone diisocyanate, 1,3-xylylene diisocyanate, 1,4-
Xylylene diisocyanate cyclohexane diisocyanate, toluidine diisocyanate, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, p
-phenylene diisocyanate, m-phenylene diisocyanate, 1,5-naphthylene diisocyanate, 4
, 4-diphenylmethane diisocyanate, 3,3-dimethylphenylene diisocyanate, dicyclohexylmethane diisocyanate, and the like. Examples of the chain extender include the aforementioned polyhydric alcohols, aliphatic polyamines, alicyclic polyamines, and aromatic polyamines. The above polyurethane is, for example, -COOM, -SO3 M, -OPO3
It may contain a polar group such as M, -OM (where M represents a hydrogen atom, sodium, or potassium). [0029] The binder may further contain a compound having two or more isocyanate groups (polyisocyanate). Examples of such polyisocyanates include tolylene diisocyanate, 4,4'-
Isocyanates such as diphenylmethane diisocyanate, hexamethylene diisocyanate, xylylene diisocyanate, naphthylene-1,5-diisocyanate, o-toluidine diisocyanate, isophorone diisocyanate, triphenylmethane triisocyanate,
Examples include reaction products of these isocyanates and polyalcohols, and polyisocyanates produced by condensation of these isocyanates. The above polyisocyanates include, for example, Coronate L, Coronate HL, Coronate H, Coronate EH, Coronate 2030, Coronate 2031, Coronate 2036, and Coronate 301 from Nippon Polyurethane Industry Co., Ltd.
5. Coronate 3041, Coronate 2014, Millionate MR, Millionate MTL, Daltosec 135
0, Daltosec 2170, Daltosec 2280, Takenate D-102, Takenate D-110N, Takenate D-200, Takenate D-202, Sumidur N from Sumitomo Bayer Co., Ltd.
75, from West German Bayer, Desmodule L, Desmodule L, Desmodule IL, Desmodule N,
Desmodur HL is sold by Dainippon Ink and Chemicals Co., Ltd. under trade names such as Burnock D850 and Burnock D802. [0030] The binder used in the present invention is used in the upper magnetic layer,
5 to 50wt for the ferromagnetic powder in each layer for both the lower magnetic layer and
%, preferably 10 to 30 wt%. 5 to 30 wt% when using vinyl chloride resin
, 2 to 20 wt% when using a polyurethane resin compound,
It is preferable to use a combination of polyisocyanates in a range of 2 to 20 wt%. In the present invention, when polyurethane is used, the glass transition temperature is -50 to 100°C and the elongation at break is 1.
00-2000%, breaking stress 0.05-10kg/c
m2 and yield point are preferably 0.05 to 10 kg/cm2. When the magnetic layer is calendered during production of the magnetic recording medium of the present invention, the glass transition temperature Tg (peak temperature of E'') of the magnetic layer before calendering is 30° C. or more higher than the calendering temperature; Preferably, it is maintained at a lower value of 50°C or more.Generally, the above T
It is preferable that g is 60°C or less, particularly 40°C or less. In order to maintain the above Tg under the above conditions, the type and amount of the binder used may be appropriately selected, or the amount of solvent remaining in the magnetic layer may be adjusted. In particular, as the bonding agent,
If a substance that can be crosslinked or polymerized by radiation irradiation is used, the above-mentioned Tg can be easily adjusted. In addition to the above-mentioned ferromagnetic fine powder, binder, and fluorine-containing ester compound, the upper magnetic layer and the lower magnetic layer of the magnetic recording medium of the present invention contain various other additives, such as carbon black and filler. It may contain abrasives, abrasives, dispersants, antistatic agents, lubricants, etc. The content of these various additives is preferably lower than the content of the binder. As the carbon black, any known carbon black such as furnace black, color black, acetylene black, etc. can be used. Carbon black whose surface is partially grafted may also be used. It is preferable to use carbon black having an average particle size of about 30 to 1000 μm, and fine-particle carbon black and coarse-particle carbon black may be used in combination. There are no particular restrictions on the filler, and for example, the average particle size is in the range of 0.01 to 0.8 μm, preferably 0.01 μm to 0.8 μm.
Commonly used particulate fillers in the range 0.06 to 0.4 μm can be used. Examples of the above-mentioned fillers include particles of tungsten disulfide, calcium carbonate, titanium dioxide, magnesium oxide, zinc oxide, calcium oxide, lithopone and talc, which may be used alone or in mixtures. be able to. The abrasive contained in the magnetic layer in the present invention includes:
For example, α-alumina, fused alumina, silicon carbide, chromium oxide, cerium oxide, corundum, artificial diamond, α-iron oxide, garnet, emery (main components: corundum and magnetite), garnet, silica, silicon nitride, nitride Typical examples include boron, molybdenum carbide, boron carbide, tungsten carbide, titanium carbide, tripoly, diatomaceous earth, and dolomite from the viewpoint of durability of the magnetic layer of the magnetic recording medium. In particular, it is preferable to use a combination of one to four types of abrasives having a Mohs hardness of 6 or more. Preferably, the average particle size of the abrasive is between 0.005 and 5 microns, particularly between 0.05 and 2 microns. Dispersants include fatty acids having 9 to 22 carbon atoms (eg, caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid, elaidic acid, linoleic acid, linolenic acid, stearol). acid)
, metal soaps consisting of the above fatty acids and alkali metals (e.g. lithium, sodium, potassium) or alkaline earth metals (e.g. magnesium, calcium, barium), esters of the above fatty acids and some or all of the hydrogen in their compounds. Compounds substituted with fluorine atoms, amides of the above fatty acids, aliphatic amines, higher alcohols, polyalkylene oxide alkyl phosphates, alkyl phosphates, alkyl borates, sarcosinates, alkyl ether esters, trialkyl polyolefin oxy Known dispersants such as quaternary ammonium salts and lecithin can be mentioned. When using a dispersant, it is usually 0.0 parts by weight per 100 parts by weight of the binder used.
It is used in a range of 5 to 20 parts by weight. As the antistatic agent, conductive fine powder such as carbon black graft polymer; natural surfactant such as saponin; nonionic surfactant such as alkylene oxide type, glycerin type and glycidol type; higher alkylamines; Cationic surfactants such as quaternary ammonium salts, salts of pyridine and other heterocyclic compounds, 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 Surfactant; amino acids,
Examples include amphoteric activators such as aminosulfonic acids, sulfuric acid or phosphoric acid esters of amino alcohols, and the like. When using the above conductive fine powder as an antistatic agent, for example, 0.2 to 2 parts by weight per 100 parts by weight of the binder.
It is used in a range of 0 parts by weight, and when a surfactant is used, it is used in a range of 0.1 to 10 parts by weight. Examples of lubricants that can be used in combination with the fluorine-containing compound of the present invention include the above-mentioned fatty agents, higher alcohols, butyl stearate, sorbitan oleate, and other lubricants containing 12 carbon atoms.
Fatty acid esters consisting of ~20 monobasic fatty acids and monohydric or polyhydric alcohols with 3 to 20 carbon atoms, mineral oil,
In addition to animal and vegetable oils, olefin low polymers, and α-olefin low polymers, known lubricants and plastic lubricants such as silicone oil, fine graphite powder, fine molybdenum disulfide powder, and fine Teflon powder can be mentioned. . The amount of lubricant added can be arbitrarily determined according to known techniques. [0038] There are no particular restrictions on the solvent used during kneading, and solvents commonly used in the preparation of magnetic paints can be used. There is no particular restriction on the kneading method, and the order of addition of each component can be set as appropriate. For the preparation of magnetic coatings, conventional kneading machines are used, such as two-roll mills, three-roll mills, ball mills, bevel mills, thoron mills, sand gliders, Szegvari attritors, high-speed impeller dispersers, high-speed stone mills, high-speed impact mills, dispers, Mention may be made of kneaders, high speed mixers, homogenizers and ultrasonic dispersers. [0039] The above-mentioned additives such as dispersants, antistatic agents, lubricants, etc. are not strictly limited to having only the above-mentioned effects; for example, dispersants, antistatic agents, lubricants, etc. may also act as a lubricant or antistatic agent. Therefore, it goes without saying that the effects of compounds etc. exemplified by the above classifications are not limited to those listed in the above classifications, and when using substances that have multiple effects, the amount of is preferably determined by considering the action and effect of the substance. In addition, a detergent dispersant, a viscosity index improver, a pour point depressant, a foam stopper, etc. can also be added. The viscosity of the magnetic paint thus prepared is usually in the range of 60 to 200 ps. [0040] Although it is possible to apply the magnetic paint directly onto the non-magnetic support, it is also possible to apply the magnetic paint via an adhesive layer or the like, or by applying physical treatment (for example, to the non-magnetic support).
It can also be coated onto a non-magnetic support after being subjected to corona discharge treatment, electron beam irradiation treatment). [0041] Examples of coating methods on non-magnetic supports include:
Air doctor coat, blade coat, rod coat, extrusion coat, air knife coat, squeeze coat,
Examples include methods such as impregnation coating, reverse roll coating, transfer roll coating, gravure coating, kiss coating, cast coating, spray coating, and spun coating, and methods other than these may also be used. In the present invention, it is preferable to use simultaneous multilayer coating (wet on wet method) as shown in JP-A No. 62-21933. The coating thickness is preferably such that the thickness of the magnetic layer of the finally obtained magnetic recording medium is within the range of 2 to 10 μm. Generally, the coating layer thus applied is subjected to a magnetic field orientation treatment in an undried state to orient the ferromagnetic fine powder contained in the magnetic layer. The magnetic field orientation treatment can be performed according to a conventional method. Next, the coated layer is subjected to a drying process and dried to form a magnetic layer. The drying process is usually 50
This is done by heating the coating layer at ~120°C. The heating time is generally 10 seconds to 5 minutes. After drying, the magnetic layer is usually subjected to surface smoothing treatment. The surface smoothing treatment is carried out by calendering. This calendering process preferably includes a step of heating and pressurizing using at least one pair (two stages), preferably three or more stages of rigid rolls. For example, the rigid roll has a center surface roughness (Ra:
Preferred are metal rolls having a cutoff value (0.25 mm) of less than or equal to about 20 nm, more preferably about 10 nm. Examples of rigid rolls include rolls made of various steels whose surfaces are coated with hard chrome or ceramics, rolls whose surfaces are made of cemented carbide, and the like. Before and/or after the step of using at least one pair of rigid rolls, a step of using a combination roll of a rigid roll and an elastic roll used in normal calendering may be provided. [0044] The above calender treatment is carried out at 50 to 110°C.
It is preferred to carry out at a temperature in the range of , and a linear pressure in the range of 50 to 1000 kg/cm, preferably 50 to 350 kg/cm. If the calendar processing conditions are outside the above range,
The magnetic recording medium of the present invention cannot be manufactured. If the above processing conditions are lower than the above range, a magnetic recording medium with excellent electromagnetic conversion characteristics and running characteristics cannot be manufactured, and if the above processing conditions are higher than the above range, the magnetic recording medium will be deformed. or the rigid roll may be damaged. After the surface smoothing treatment as described above,
After appropriately performing radiation irradiation treatment or heat treatment, the material is cut into a desired shape to obtain a magnetic recording medium. [0046] As the radiation irradiated in the above radiation treatment, electron beams, gamma rays, beta rays, ultraviolet rays, etc. can be used, but electron beams are preferable. Electron beam irradiation is performed using an electron beam accelerator. This electron beam irradiation causes a polymerization reaction in the binder component of the magnetic paint coated on the non-magnetic support and hardens it. The electron beam to be irradiated is generally 100
An accelerating voltage of ~500 kV, preferably 150-300 kV is used. In addition, the absorbed dose is generally 1.
0 to 20 megarads, preferably 2 to 10 megarads. If the accelerating voltage is less than 100 kV, there may be insufficient energy and the hardening reaction of the magnetic layer may not proceed completely, while if it exceeds 500 kV, the applied energy may be excessive than the energy used for the polymerization reaction. , may have an adverse effect on the magnetic layer and non-magnetic support. Furthermore, if the absorbed dose is less than 1.0 megarads, the curing reaction may not proceed sufficiently and the strength of the magnetic layer may not be sufficient. On the other hand, if it exceeds 20 megarads, the energy efficiency may decrease. Not only is this uneconomical, but the object to be irradiated may generate heat, and the heat generation may deform the nonmagnetic support. A known back layer may be provided on the surface of the non-magnetic support on which the magnetic layer is not provided. For example, the back layer may include carbon black,
It is a thin film layer having a thickness of 0.6 μm or less and made of a binder in which inorganic filler particles having a Mohs hardness of 5 or more are dispersed. [Example] Next, examples of the present invention and comparative examples will be shown. In each example, "parts" indicate "parts by weight." Example lower magnetic layer Cobalt-modified iron oxide

100 parts Hc Hc 350O
e Specific surface area 21 m2/g Crystallite size 450 angstrom Particle size (major axis diameter) 0.33 μm Acicular ratio 8 Vinyl chloride-vinyl acetate-vinyl alcohol copolymer
Total usage -NR4
Contains 5 x 10-6 eq/g of polar groups of X
3:1 is Table 2 - Table Composition ratio 86:
13:1 Polymerization degree 400
4 Description Polyester polyurethane resin Carbon black (particle size 50mμ)
1
Part α-Al2 O3 (particle size 0.3 μm
)
Part 1 Myristic acid modified silicone

1 part stearic acid

1
part lauric acid

1 part Butyl acetate


200 parts Upper magnetic layer Cobalt modified iron oxide

100 parts Hc 480Oe, specific surface area 33m2/g crystallite size 3
50 angstroms Particle size (major axis diameter) 0.30μ, needle ratio 10 Vinyl chloride-vinyl acetate-vinyl alcohol copolymer
Total amount used Composition ratio 91:3:
6 Polymerization degree 400 5:1 Table 1 and Table Polyester polyurethane resin

3 (carboxyl group 10-
(contains 4 mol/g)
α-Alumina (particle size 0.3μm)
2 parts carbon black (particle size 100mμ)
Part 3 Isostearic acid modified silicone
Part 1
myristic acid

2 parts Butyl acetate

200 parts of each of the above two paints were kneaded for the upper magnetic layer using an open kneader and for the lower magnetic layer using a continuous kneader, and then dispersed using a sand mill. To the resulting dispersion, 1 part of polyisocyanate was added to the coating solution for the lower magnetic layer, 3 parts to the coating solution for the upper magnetic layer, and 40 parts of butyl acetate was added to each, and a filter having an average pore size of 1 μm was added. Coating liquids for forming the lower magnetic layer and for forming the upper magnetic layer were prepared respectively. The obtained lower magnetic layer coating solution was dried to a thickness of 3.0 μm.
Immediately thereafter, the upper magnetic layer was coated in multiple layers on a polyethylene terephthalate support having a thickness of 7 μm and a centerline surface roughness of 0.02 μm so that the thickness of the upper magnetic layer was 2.0 μm. While both layers are still wet, a cobalt magnet with a magnetic force of 3000G and a 150G
After being oriented by a solenoid with 0G magnetic force and dried, it is heated to a temperature of 85% using a 7-stage calender consisting only of metal rolls.
The tape was processed at a temperature of 3.5 mm and slit to a width of 3.8 mm to produce an audio tape. Evaluation method Wow and flutter measurement method A 3kHz sine wave was recorded in advance at -20dB (OVU) using a SONY TC-K55ESR, and then heated to 25°C.
SONY headphone stereo WM-71 at 60%RH
Repeat playback 20 times at 0C. The wow and flutter value and speed fluctuation value during that time were measured using a wow and flutter meter VP7751A manufactured by Matsushita Tsushin Kogyo. Running durability measurement method Samples were measured at 40°C and 80% RH for 100p using 10 SONY audio cassette decks TC-K555ESR.
I let it run. During this time, output fluctuations were measured, and dirt on various parts of the deck after running was evaluated. The results were evaluated based on how many of the six volumes the problem occurred in. Electromagnetic conversion characteristics MOL315 and MOL10k were measured by recording signals with a Nakamichi audio cassette deck type 582. M
OL315: This is the maximum output when the third harmonic of the 315Hz signal is 3%. The values listed are for audio cassette tape PS-IX manufactured by Fuji Photo Film Co., Ltd.
This is the value when C60 is 0 dB. MOL10k:
The saturated output of a 10kHz signal was investigated. The values listed are audio cassette tape P manufactured by Fuji Photo Film Co., Ltd.
S-IX C60 was set to 0 dB. For measurement, use HEW
Automatic made by LETT PACKARD
Spectrum Analyzer 3045A was used. Example Table 1 No. V1 V2 V
3 Upper layer thickness Lower layer thickness Upper layer binder (ml/g) (ml/g)
(ml/g) (μm) (μm) (
part) ■ 0.02 0.07
0.05 2.5 2.5
30 ■ 0.01≧
0.03 0.01 2
．． 5 2.5 15
■ 0.01 0.05
0.03 2.5 2.5
25 ■ 0.01
0.04 0.02
2.5 2.5 20
Table 2 No. Lower magnetic layer Calendar MOL
SOL wow flat running durability binder pressure
Tar 40℃80%
(part) (kg/m)
(dB) (dB) (dB) ■
20 250
1.7 0.5 0.2
O. K■ 12
250 2.0 1.
0 0.3 O. K■
15 250
1.9 0.8 0.1
O. K■ 15
250 1.9 0.6
0.2 O. K005
5] Comparative example Table 3 No. V1 V2 V
3 Upper magnetic layer Lower magnetic layer Upper magnetic layer
layer thickness layer thickness
Binder (ml/g) (ml/
g) (ml/g) (μm) (μm)
(Part) ■ 0.02 0
．． 07 0.01 2.5
2.5 30 ■
0.01 0.06 0
．． 06 2.5 2.5
25 ■ 0.03
0.05 0.04
2.5 2.5 3
5 ■ 0.01≧0.04
0.01≧2.5 2
．． 5 15 [0056] Table 4 No. Lower magnetic layer Calendar MOL
SOL wow flat running durability binder pressure
Tar 40℃80%
(part) (kg/m)
(dB) (dB) (dB) ■
20 250
1.9 0.7 0.7
1/6 ■ 18
250 2.1
0.9 0.9 2/6
■ 16 250
2.3 0.4 1
．． 2 2/6 ■ 14
250 2.5
1.2 0.9
1/6 [0057] The pore volume of the sample of the magnetic recording medium was determined by a nitrogen gas adsorption method. That is, as a measuring device, Autosorb 1 (Aut
osorb-1) was used. The sample of the 8 mm wide metal thin film magnetic recording medium was wound around a glass rod of about 4 m,
As a measurement sample, helium gas is used as a carrier gas, and nitrogen gas partial pressure (
The adsorption isotherm was first determined by gradually increasing the relative pressure (relative pressure) from 0 to 1, and then by gradually decreasing the nitrogen gas partial pressure (relative pressure) from 1 to 0. The total pore volume was determined from the amount of nitrogen adsorbed at a relative pressure of 1, assuming that the pores were filled with liquid nitrogen. As is clear from the results in the table, magnetic layers with pore volumes in the relationship V2 > V3 > V1 exhibit good MOL and SOL, and have remarkable improvements in wow and flutter and running durability. It can be seen that samples from ■ to ■ that deviate from the above relationship are MOL, S
It can be seen that OL, wow and flutter, and running durability deteriorate. Effects of the Invention According to the present invention, the lower magnetic layer has a small pore volume, a high degree of ferromagnetic powder filling, and has good surface properties, so that the upper magnetic layer also has good surface properties. There is no spacing loss for Therefore, the electromagnetic conversion characteristics, especially by short wavelength recording, are improved. Furthermore, since the lower magnetic layer has a high degree of filling and is thick, the degree of filling of all layers can be increased, and the electromagnetic conversion characteristics due to long wavelength recording are improved. Regarding running properties, since the pores in the upper magnetic layer remain intact, the rate at which the lubricant oozes out is higher than in normal cases. This makes it possible to improve running performance under high temperature, high humidity environments, which were previously quite severe conditions. In particular, lubricant is added at a slow speed from the lower magnetic layer to compensate for the lack of lubricant in the upper magnetic layer, making it possible to maintain good running performance.

Claims (4)

[Claims] Claim 1: A magnetic coating containing ferromagnetic powder and a binder is coated on a non-magnetic support to form a magnetic layer consisting of a lower magnetic layer and an upper magnetic layer, dried and oriented, and then calendered. In the magnetic recording medium, when the lower magnetic layer closer to the non-magnetic support is provided alone, the pore volume V1 of the lower magnetic layer after calendering is 0.02.
ml/g or less, and when the upper magnetic layer is provided alone, the pore volume V2 of the upper magnetic layer after calendering is 0.03 to 0.07 ml/g, and the lower magnetic layer is The pore volume V3 of the magnetic layer consisting of the upper magnetic layer and the upper magnetic layer after calendering is 0.01 to 0.
．． 05 ml/g, and a relationship of V2 > V3 > V1. 2. The lower magnetic layer has a dry film thickness of 1.0 to 5.0 μm after calender treatment, and the upper magnetic layer has a dry film thickness of 1.0 to 3.5 μm after calender treatment. The magnetic recording medium according to claim 1, characterized in that: 3. A magnetic layer consisting of a lower magnetic layer and an upper magnetic layer is obtained by coating two kinds of magnetic paints containing ferromagnetic powder and a binder on a non-magnetic support, and after drying and orientation, calendering is performed. In the method for producing a magnetic recording medium, the amount of the binder in the magnetic paint used for the lower magnetic layer closer to the non-magnetic support is 10 to 30 parts by weight per 100 parts by weight of the ferromagnetic powder, and the lower magnetic layer When provided alone, the pore volume V1 is 0.02 ml/g or less after calendering, and the ferromagnetic powder of the magnetic coating used for the upper magnetic layer is
The amount of the binder is 15 to 50 parts by weight relative to 0 parts by weight, and when the upper magnetic layer is provided alone, the pore volume V2 after calendering is 0.03 to 0.07 ml.
/g, and the magnetic paints for the lower magnetic layer and the upper magnetic layer are applied simultaneously or sequentially by a wet coating method to obtain the magnetic layer consisting of the lower magnetic layer and the upper layer, dried, oriented, and then calendered. By doing so, the pore volume V3 of the entire magnetic layer after calendering is 0.01 to 0.05.
ml/g and a magnetic layer having the relationship of V2 > V3 > V1. 4. The lower magnetic layer has a dry film thickness of 1.0 to 5.0 after calender treatment, and the upper magnetic layer has a dry film thickness of 1.0 to 3.5 after calender treatment. A method for manufacturing a magnetic recording medium according to claim (3).