JPS61233415A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain the title magnetic recording medium having a magnetic layer whose surface roughness and vertical orientation are improved and having an excellent electromagnetic transducing characteristic by providing the magnetic layer contg. magnetic powder consisting of 20-70wt% plate magnetic powder having >=0.01 and <0.1mum mean particle diameter and 80-30wt% plate magnetic powder having 0.1-0.5mum means particle diameter and a binder on a carrier. CONSTITUTION:A magnetic layer contg. magnetic powder consisting of 20-70wt% plate magnetic powder having >=0.01 and <0.1mum mean particle deameter and 80-30wt% plate magnetic powder having 0.1-0.5mum mean particle diameter and a binder is formed on a carrier. The powder is closely packed because of the different mean particle diameters, a magnetic recording medium with improved surface roughness is obtained, the vertical orientation is improved and the electromagnetic transducing characteristic is also improved. The mag netic recording medium can be effectively used for a digital audio tape, a floppy disk, an 8-millimeter video tape, etc.

Description

[Detailed description of the invention]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium, and particularly to a magnetic recording medium capable of increasing density. Prior art and its problems In recent years, there has been a demand for higher recording density in magnetic recording media. However, in the conventionally widely used in-plane magnetic recording method in which the direction of magnetization is within the plane of the recording medium, the magnetizations repel each other, making it impossible to achieve high density in a fixed position. Therefore, perpendicular magnetic recording methods, in which the direction of magnetization is perpendicular to the surface of the recording medium and thus do not have repulsion of magnetization, are attracting attention. In this method, methods have been proposed in which a Co--Cr sputtered film is used as a recording film, and a method in which a coating type recording layer is formed using magnetic particles such as barium ferrite. When forming a coating-type recording layer, barium ferrite in the form of a hexagonal crystal plate is often used because it is easy to achieve vertical alignment. No. 57-212623, No. 58
-6526, 58-222446, 59-96
No. 532, etc. In such perpendicular magnetic recording methods, factors such as the size of the magnetic particles used, particle size distribution, and surface roughness of the coating film are deeply related to the characteristics of the magnetic recording medium, such as the degree of vertical orientation and noise during recording and reproduction. It is believed that this is the case, and various improvements have been attempted in the above-mentioned patent documents. However, it is still not sufficient, and further improvements in the magnetic layer including magnetic particles are desired. ■! OBJECTS OF THE INVENTION An object of the present invention is to provide a magnetic recording medium having a magnetic layer with improved surface roughness and perpendicular orientation and excellent electromagnetic conversion characteristics. ■ Disclosure of the Invention This purpose is an average of 20-70% by weight. A binder and magnetic powder containing plate-like magnetic powder with a particle size of 0, OI ILm or more and less than 0.1 Lm, and 80 to 30% by weight of plate-like magnetic powder with an average particle size of 0.17 tm or more and 0.51 Lm or less. This is achieved by a magnetic recording medium characterized in that it has a magnetic layer on a support. ■Specific structure of the invention The specific structure of the present invention will be explained in detail below. The magnetic recording medium of the present invention has a magnetic layer containing magnetic powder and a binder as described below. The surface roughness R20 of the surface of this magnetic layer is preferably 0.08JL11 or less, and particularly preferably R2o = 0.061L11 or less. This is because if R2O exceeds the o, oaIL intestine, the surface roughness deteriorates, head touch becomes poor, and the C/N ratio deteriorates. The magnetic powder is preferably hexagonal barium ferrite having a hexagonal plate shape, and has an average particle size of 0.01 to 0. The IJL layer is particularly preferably 0.02 to 0.08, and the average particle size is 0.1 to 0.5 JL11. Particularly preferably 0
．． It consists of 1 to 0.2 pots. and the former is 2
The content is preferably 0 to 70% by weight, especially 30 to 70% by weight, and the remaining 80 to 30% by weight, especially 70 to 3% by weight.
Preferably, 0% by weight is the latter. The reason for this ratio is that the former (small particle size) is 2
If it is less than 0% by weight, the surface roughness will deteriorate, leading to a decrease in electromagnetic conversion characteristics, especially the C/N ratio, and if it exceeds 70% by weight, the particle size will become small.@inR
White 14 (() This is also a decrease in electromagnetic conversion characteristics,
This is because, in particular, this will lead to deterioration of the C/N ratio. In general, grains with small diameters, especially those with a platelet ratio (average particle size/average thickness) of less than 6, are difficult to orient. However, in the present invention, even if small grains with a platelet ratio of 6 or less are used, The degree of orientation and electromagnetic conversion characteristics are improved by combining particles with a large particle size (preferably those with a platelet ratio of 6 or more). Of course, these characteristics can also be improved by combining a small particle size with a platelet ratio of 6 or less with a large particle size with a platelet ratio of 6 or more. Here, the average particle size is the average of the measured values for each particle size obtained by observing, for example, about 50 cross sections of hexagonal barium ferrite particles using an electron micrograph (SEM). Further, the plate ratio can be calculated by dividing the average grain size by the average thickness determined in the same manner. As barium ferrite, hexagonal barium ferrite such as B a Fe 12019 and some of the Ba and Fe of barium ferrite are Ca,
Sr, Pb, Co, Ni, Ti, Cr, Zn, In,
Examples include those substituted with Mn, Cu, Ge, Nb, and other metals. These may be used in combination. Manufacturing methods for barium ferrite include ceramic method,
Co-precipitation-calcination method, hydrothermal synthesis method, flux method, glass crystallization method, alkoxide method, plasma jet method, etc.1
Any method may be used in the present invention. For details of these methods, reference may be made to "Ceramics 18 (1983) No. 1O" co-authored by Yoshiyasu Koike and Osamu Kubo. It is preferable to use a hardened radiation-curable compound as the binder. Specific examples of radiation-curable compounds include acrylic double bonds such as acrylic acid, methacrylic acid, or their ester compounds, which exhibit radically polymerizable unsaturated double bonds, and allylic double bonds such as diallylphthalate. It is a thermoplastic resin containing or introducing into its molecules a group that can be crosslinked or polymerized and dried by radiation irradiation, such as a double bond or an unsaturated bond such as maleic acid or a maleic acid derivative.
Any compound having an unsaturated double bond that undergoes cross-linking polymerization upon irradiation with radiation can be used. The following unsaturated polyester resins are examples of resins containing groups in the molecule of thermoplastic resins that can be crosslinked or polymerized and dried by radiation irradiation. Polyester compound containing radiation-curable unsaturated double bonds in the molecular chain 1 For example, in the following (2) saturated polyester resin consisting of an ester bond of a polybasic acid and a polyhydric alcohol, a part of the polybasic acid is replaced with maleic acid. Examples include unsaturated polyester resins containing radiation-curable unsaturated double bonds. The radiation-curable unsaturated polyester resin is prepared by adding maleic acid, fumaric acid, etc. to one or more polybasic acid components and one or more polyhydric alcohols ff in a conventional manner, that is, in the presence of a catalyst, at 180 to 200°C in a nitrogen atmosphere. After the dehydration or dealcoholization reaction, the product can be obtained by a condensation reaction at a temperature of 240 to 280° C. and under a reduced pressure of 0.5 to 1 Hg. The content of maleic acid, fumaric acid, etc. is 1 to 4 in the acid component due to crosslinking during manufacturing, radiation curability, etc.
0 mol%, preferably 10 to 30 mol%. Examples of thermoplastic resins that can be modified into radiation-curable resins include the following. (1) Vinyl chloride copolymer Vinyl chloride-vinyl acetate-vinyl alcohol copolymer, vinyl chloride-vinyl alcohol copolymer, vinyl chloride-vinyl alcohol-vinyl propionate copolymer, vinyl chloride-vinyl acetate-malein m
Co-x combination, vinyl chloride-vinyl acetate-vinyl alcohol-maleic acid copolymer, vinyl chloride-vinyl acetate-terminated OH @ chain alkyl group copolymer, such as VROH, VYNClVYEGX, VERR, VY manufactured by UCC
ES, YMCA. Examples include VAGH, to which acrylic double bonds, maleic acid double bonds, and allylic double bonds are introduced to perform radiation sensitivity modification. (2) Saturated polyester resin Saturated polybasic acids such as phthalic acid, isophthalic acid, terephthalic acid, succinic acid, adipic acid, and sebacic acid, and ethylene glycol, diethylene glycol, glycerin, trimethylolpropane, 1.2 propylene glycol,
1,3 butanediol, dipropylene glycol, l. Saturated polyester resins obtained by ester bonding with polyhydric alcohols such as 4-butanediol, 1,6-hexanediol, pentaerythritol, sorbitol, glycerin, neopentyl glycol xane dimetatool, or these polyester resins with SO3Na etc. Modified resin (
For example, Viron 53S) is cited as an example, and these also undergo radiation sensitivity modification. (3) Polyvinyl alcohol-based resin Polyvinyl alcohol, butyral resin, acetal resin, formal resin and copolymers of these components,
Radiation sensitivity modification is performed on the hydroxyl groups contained in these resins. (4) Epoxy resin, phonoxy resin Epoxy resin produced by the reaction of bisphenol A with epichlorohydrin or methyl epichlorohydrin, such as Shell Chemical Co., Ltd. (Epicoat 152.154, 828, 1001.100)
4.1007), manufactured by Dow Chemical (DE N431
, DER732, DER511, DER3
31), Dainippon Ink (Ebikuron 400, 800
), and phenoxy resins manufactured by UCC (PKHA, PKHC, PKHI ()), which are high polymerization degree resins of the above epoxies.
, a copolymer of brominated bisphenol A and epichlorohydrin, manufactured by Dainippon Ink and Chemicals (Evicron 145° 152, 153, 1120), etc. These also include those containing a carboxylic acid group. Radiation sensitivity modification is performed using the epoxy groups contained in these resins. (5) Various cellulose derivatives are used, but particularly effective ones include nitrified cotton, cellulose acetobutyrate, ethyl cellulose, butyl cellulose, and acetyl cellulose. Perform sensory degeneration. Other resins that can be used for radiation sensitivity modification include polyfunctional polyester resins, polyether ester resins, polyvinylpyrrolidone resins and derivatives (PVP
Also effective are acrylic resins containing at least one of olefin copolymers), polyamide resins, polyimide resins, phenol resins, spiroacetal resins, hydroxyl group-containing acrylic esters, and methacrylic esters as polymerization components. Examples of elastomers or prepolymers are listed below. (1) The use of polyurethane elastomer or prepolymer polyurethane provides abrasion resistance and the base film,
For example, it is particularly effective in terms of good adhesion to PET film. Examples of urethane compounds include inocyanate, 2.4-toluene diisocyanate, 2.6-
Toluene diisocyanate, 1,3-xylene diisocyanate, 1.4-xylene diisocyanate, 1.5
- naphthalene diisocyanate, m-phenylene diisocyanate, p-phenylene diisocyanate, 3.3
'-Dimethyl-4,4'-diphenylmethane diisocyanate, 4,4'-diphenylmethane diisocyanate, 3,3'-dimethylbiphenylene diisocyanate,
4. Various polyvalent incyanates such as 4'-biphenylene diisocyanate, hexamethylene diisocyanate, infron diisocyanate, dicyclohexylmethane diisocyanate, Desmodur and Desmodur N, and linear saturated polyesters (ethylene glycol, diethylene glycol, glycerin, trimethylol) Polyhydric alcohols such as propane, 1,4-butanediol, 1,6-hexanediol, pentaerythritol, sorbitol, neopentyl glycol, 1,4-cyclohexanedimetatool, and phthalic acid, isophthalic acid, and terephthalic acid. , linear saturated polyethers (polyethylene glycol, polypropylene glycol, polytetramethylene glycol), caprolactam, hydroxyl-containing acrylic esters, Polyurethane elastomers and prepolymers made of polycondensates of various polyesters such as hydroxyl-containing methacrylic esters are effective. By reacting the terminal isocyanate group or hydroxyl group of these urethane elastomers with a monomer having an acrylic double bond or an allylic double bond,
Modification to radiosensitivity is very effective.
It also includes those containing OH, COOH, etc. as a polar group at the end. Furthermore, monomers having an unsaturated double bond that have an active hydrogen that reacts with an incyanate group and have radiation curability, such as mono- or diglycerides of long-chain fatty acids that have an unsaturated double bond, are also included. (2) Acrylonitrile-butadiene copolymer elastomer Elastomers such as an acrylonitrile-butadiene copolymer prepolymer with a terminal hydroxyl group commercially available as PolyBD Retired Resin manufactured by Sinclair Petrochemical Co., Ltd. or Hiker 1432 J manufactured by Nippon Zeon Co., Ltd. are elastomers such as 1, especially butadiene. The double bonds in the elastomer are suitable as elastomer components that can be crosslinked and polymerized by generating radicals when exposed to radiation. (3) Polybutadiene Elastomer A prepolymer having a low molecular weight terminal hydroxyl group, such as PolyBD Retired Resin R-15 manufactured by Sinclair Petrochemical Co., is particularly suitable in terms of compatibility with thermoplastic resins.
Since the R-15 prepolymer has a hydroxyl group at the molecular end, it is possible to increase the radiation sensitivity by adding an acrylic unsaturated double bond to the molecular end, making it more advantageous as a binder. In addition, polybutadiene cyclized product, CBR- manufactured by Japan Synthetic Rubber Co., Ltd.
M901 also has excellent properties when combined with thermoplastic resin. Other suitable thermoplastic elastomer and prepolymer systems include styrene-butadiene rubber, chlorinated rubber, acrylic rubber, imprene rubber, and its cyclized product (ClR701 manufactured by Nippon Synthetic Rubber Co., Ltd.), epoxy-modified rubber, internal plastic Elastomers such as saturated linear polyester (Toyobo Vylon #300) can also be effectively used by subjecting them to radiation-sensitive modification treatment. Compounds having a radiation-curable unsaturated double bond used as oligomers and hexamers in the present invention include styrene, ethyl acrylate, ethylene glycol diacrylate, ethylene glycol dimethacrylate, diethylene glycol diacrylate, diethylene glycol dimethacrylate, 1. 6-hexane glycol diacrylate, 1,6-hexane glycol diacrylate, N-vinylpyrrolidone, pentaerythritol tetraacrylate (methacrylate), pentaerythritol triacrylate (methacrylate), trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, polyester Functional oligoester acrylate (Aronix M-7100, M-5400, 550
0,5700, etc., Toagosei), acrylic modified products of urethane elastomer and Twinlan 4040), or those into which functional groups such as C0OH have been introduced, trimethylolpropane diacrylate (methacrylate)
, 7 acrylate of phenol ethylene oxide adduct (
methacrylate), an acrylic group (methacrylic group) or ε in the pentaerythritol condensed ring represented by the general formula below.
-Caprolactone-A compound with an acrylic group, where lm=1, a=2, b=4 (7) compound (hereinafter referred to as special pentaerythritol condensate A), m=1. A compound where a=3, b=3 (hereinafter referred to as special pentaerythritol condensate B), m=1. a=6, b=
oc7) compound (hereinafter referred to as special pentaerythritol condensate C). A compound where m=2, a=6, and b=0 (hereinafter referred to as special pentaerythritol condensate). and special acrylates represented by the general formula below. 1) (CH2=CHC00H2)3-CCH20
H (special acrylate A) 2) (CH2=CHC00H2)3-CCH20
H3 (special acrylate B) 3) (CH2=CH0C+0c3Ha)n-CC
H2) 3-CCH2CH3 (Special acrylate C) (Special acrylate D) (Special acrylate E) (Special acrylate F) 8) CH2=CHCOO-(CH2CH20)4-
COCH=CH2 (Special acrylate H) (Special acrylate I) (Special acrylate J) A-(X-”1-X-A A Niacrylic) 4. X: Polyhydric alcohol Y: Polybasic acid (Special acrylate) K ) Next, an example of synthesis of a radiation-sensitive binder will be explained. a) Synthesis of acrylic modified product (radiation-sensitive modified resin) of vinyl chloride vinyl acetate copolymer resin Partially saponified vinyl chloride vinyl acetate copolymer having OH group Coalescence (average degree of polymerization n=500
) 750 parts, toluene 1250 parts, cyclohexanone 5
Pour 00 parts into the fourth flask of No. 51, heat and dissolve,
Add 61.4 parts of ditolylene diisocyanate-hydroxyethyl methacrylate adduct* by increasing the temperature to 80°C.
Furthermore, tin octylate 0.012 parts, hydroquinone 0
．． 012 parts of the mixture were added and allowed to react at 80°C in a N2 stream until the NGO reaction rate reached 90%. After the reaction is completed, the mixture is cooled and diluted with 1250 minutes of methyl ethyl ketone.

[*Production of 2-hydroxyethyl methacrylate (2HEMA) adduct of tolylene diisocyanate (TDI) After heating 348 parts of TDI to 80°C in a fourth flask of 11 in a N2 stream, 260 parts of 2-ethylene methacrylate, octyl Tin acid 0.07 part, hydroquinone 0.05
After the dropwise addition was completed, the mixture was stirred at 80°C for 3 hours while controlling the cooling so that the temperature inside the reaction vessel was 80 to 85°C. Complete the reaction. After the reaction is completed, take it out and cool it to obtain a white paste-like TD.
2HEMA of I was obtained. b) Synthesis of Brachyl resin acrylic modified product (radiation-sensitive modified resin) Butyral Resin Building Block Chemical Co., Ltd. BM-5 100 parts Wotoluene 191.2 parts, Cyclohexanone 71.4 minutes and 51 parts
4 parts of 2HEMA adduct* of TDI were added after heating to 80°C, followed by 0.015 parts of tin octylate and 0.01 part of hydroquinone.
5 parts was added and the NCO reaction rate was 90% at 80°C in a N2 stream.
Let it react until it reaches the above level. After the reaction is completed, the mixture is cooled and diluted with methyl ethyl ketone. C) Synthesis of saturated polyester resin acrylic modified product J & (radiation sensitive modified resin) Saturated polyester resin (Toyobo Vylon RV-200)
, too part is 116 parts of toluene, 1 part of methyl ethyl ketone
After heating and dissolving 16 parts of TDI at 80°C, 2HEM of TDI
Add 3.55 parts of A adduct*, further add 0.007 parts of tin octylate and 0.007 parts of hydroquinone,
The reaction was allowed to proceed at 0° C. in a N2 stream until the NGO reaction rate reached 90% or more. d) Synthesis of O epoxy resin acrylic modified product (radiation sensitive modified resin) Epoxy resin (Epicoat 1007 manufactured by Shell Chemical Co., Ltd.) 40
After heating and dissolving 0 parts in 50 parts of toluene and 50 parts of methyl ethyl ketone, 0.006 parts of N,N-dimethylbenzylamine was dissolved.
1 part, 0.003 part of hydroquinone was added and the temperature was adjusted to 80°C,
69 parts of acrylic acid was added dropwise and reacted at 80° C. until the acid value reached 5 or less. ■Synthesis of acrylic modified phenoxy resin (radiation-sensitive modified resin) 600 parts of phenoxy resin with OH group (PKHH: manufactured by UCC, molecular weight 30,000), 1 part of methyl ethyl ketone
Pour 16 parts into a 31 quart flask, heat and dissolve,
After raising the temperature to 80°C, 6.0 parts of 2-hydroxyethyl methacrylate adduct of tolylene diisocyanate was added, followed by 0.012 part of tin octylate and 0.0 part of hydroquinone.
12 parts was added, and the NGO reaction rate was 9 at 80°C in a N2 stream.
Allow to react until it reaches 0%. The molecular weight of this phenoxy modified product is 35,000. There is one double bond per molecule. e) Synthesis of acrylic modified urethane elastomer (radiation curable elastomer) 250 parts of a terminal isocyanate diphenylmethane diisocyanate (MDI) based urethane prepolymer (Nitsuporan 3119 manufactured by Nippon Polyurethane), ZHEMA32.
Part 5, /
h engineering +1. Put 0009 parts of Yumi 000 into a reaction can, heat and melt at 80°C, then add 43.5 parts of TDI until the temperature inside the reaction can reaches 80°C.
It is added dropwise while cooling to ~90°C, and after the dropwise addition is completed, it is allowed to react at 80°C until the reaction rate is 95% or more. f) Synthesis of acrylic modified polyether-terminated urethane-modified elastomer (radiation-curable elastomer) Polyether PTG-500, 2 manufactured by Nippon Polyurethane Co., Ltd.
50 parts, 2HHMA 32.5 parts, hydroquinone 0.0
7 parts and 0°009 parts of tin octylate were placed in a reaction vessel, and 8
After heating and dissolving at 0°C, 43.5 parts of TDI is added dropwise while cooling the reaction vessel to a temperature of 80 to 90°C, and after the dropwise addition is completed, the reaction is allowed to occur at 80°C until the reaction rate reaches 95% or more. g) Synthesis of acrylic modified polybutadiene elastomer (radiation curable elastomer) Low molecular weight terminal acid co-polybutadiene polybutadiene resin R-15250 parts manufactured by Sinclair Petrochemical Co., Ltd., 32.5 parts of 2HEMA, 0.07 parts of hydroquinone, Tin octylate 0.00
Put 9 parts into a reaction vessel, heat and melt at 80"C, and then dissolve TDI4
3.5 parts were added dropwise while cooling the reaction vessel to a temperature of 80 to 90°C. After dropping, the reaction rate was 95 at 80°C.
% or more. It is known that some polymers disintegrate when irradiated with radiation, while others cause crosslinking between molecules. Examples of substances that cause crosslinking between molecules include pyriethylene, polypropylene, polystyrene, polyacrylic ester,
polyacrylamide, polyvinyl chloride, polyester,
These include polyvinylpyrrolidone rubber, polyvinyl alcohol, and polyacrolein. With such crosslinked polymers, the crosslinking reaction occurs even without special modification as described above, so in addition to the above-mentioned modified products, these resins can be used as they are for radiation crosslinking. Furthermore, according to this method, even a solvent-free resin that does not use a solvent can be cured in a short time, so such a resin can be used. By using such a radiation-curable resin, large diameter so-called jumbo rolls are free from tight winding, and the difference in electromagnetic conversion characteristics between the inside and outside of the jumbo rolls is eliminated and the characteristics are improved. Also, since it can be done online, productivity is improved. The weight ratio of magnetic powder/binder is preferably 1/1 to 9/1, particularly 2/1 to 8/1. The reason for using such a ratio is that if it is less than 1/l, the saturation magnetic flux density will be low, and if it exceeds 9/l, the surface roughness will deteriorate due to poor dispersion, and the coating film will become brittle, making it undesirable. In addition, various known thermoplastic resins and thermosetting resins can also be used as binders. In the present invention, a non-reactive solvent is used if necessary.
There are no particular restrictions on the solvent, but it is appropriately selected in consideration of the solubility and compatibility of the binder. For example, ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone, esters such as ethyl formate, ethyl acetate, and butyl acetate, alcohols such as methanol, ethanol, impropatol, butanol, and aromas such as toluene, xylene, and ethylbenzene. group hydrocarbons, ethers such as isopropyl ether, ethyl ether, dioxane, tetrahydrofuran,
Furfural and other furans are used as a single solvent or a mixture of these solvents. These solvents are 10 to 10,000w to the binder.
t%, especially 100 to 5000 wt%. The magnetic layer may contain an inorganic pigment. Examples of inorganic pigments include 1) conductive carbon black and graphite, and 2) 5i02.
TiO2, A203, Cr203, SiC, Cab
, CaCO3, fermented zinc, goethite, γ-Fe203
．． Examples include talc, kaolin, CaSO4, boron nitride, graphite fluoride, molybdenum disulfide, and ZnS. In addition, the following fine particle pigments (aerosil type, colloidal type): 5i02, AlI303, T
iO2, ZrO2, Cr203, Y203, CeO
2, Fe304, Fe203, ZrS i04,
S b205 , S n02 and the like are also used. These fine particle pigments are, for example, 5i02. ■Ultrafine particle colloidal solution of silicic anhydride (Snowtex,
Examples include water-based, methanol silica sol, etc. (Hasan Kagaku), and (1) ultrafine particulate anhydrous silica produced by combustion of purified silicon tetrachloride (standard product 100 people) (Aerosil, Niki Aerosil Co., Ltd.). Further, the ultrafine particle colloidal solution of (1) above, ultrafine aluminum oxide produced by the same vapor phase method as (2), titanium oxide, and the above-mentioned fine particle pigment may be used. The appropriate amount of such inorganic pigments to be used is 1 to 30 parts by weight per 100 parts by weight of the binder for l), and 1 to 30 parts by weight for 2). It has the disadvantage that it becomes brittle and more likely to drop out. Regarding the diameter of the inorganic pigment, l) is 0,
I JL is preferably 11 or less, more preferably 0.057L or less, and regarding 2), 0,7 JLrx or less. Furthermore, a layer of 0.05 g or less is preferable. The magnetic layer may contain a dispersant. Organic titanium coupling agents, silane coupling agents and surfactants are used as dispersants, natural surfactants such as saponin are used as antistatic agents: nonionic surfactants such as alkylene oxide, glycerin, and glycidol: higher alkyl amines. cationic surfactants, such as quaternary ammonium salts, pyridine and other heterocycles, phosphonium or sulfonium; anionic surfactants containing acidic groups such as carboxylic acid, sulfonic acid, phosphoric acid, sulfuric acid ester groups, and phosphoric acid ester groups; Agents: Ampholytic activators such as amino acids, aminosulfonic acids, sulfuric acid or phosphoric acid esters of amino alcohols, etc. are used. The magnetic layer may contain a lubricant as an antistatic IF agent. As a lubricant, silicone oil is conventionally used as a lubricant for this type of magnetic recording medium. Although fluorine oil, fatty acids, fatty acid esters, nokurafuin, liquid paraffin, surfactants, etc. can be used, it is preferable to use fatty acids and/or fatty acid esters. Examples of fatty acids include fatty acids with 12 or more carbon atoms (RCO
OHlR is an alkyl group having 11 or more carbon atoms), and fatty acid esters include fatty acid esters consisting of a monobasic fatty acid having 12 to 16 carbon atoms and a monohydric alcohol having 3 to 12 carbon atoms, and 17 g1 carbon atoms. A fatty acid ester consisting of the above monobasic fatty acid and a monohydric alcohol having 21 to 23 carbon atoms in total, and an alkali metal or alkaline earth metal of the fatty acid is used. metal soap, lecithin, etc. are used. As the silicone, those made of fatty acid-modified silicones and those partially fluorine-modified are used. The alcohol used is one made of higher alcohol, and the fluorine used is one obtained by electrolytic substitution, telomerization, oligomerization, etc. Radiation curing type lubricants are also used.
In order to suppress the lotus-shaped transfer to the Okimarin V lid, it prevents dropouts, reduces the output difference depending on the inner and outer diameter when wound into a roll, and is also available online. It has the advantage that it is possible to manufacture Radiation-curable lubricants include compounds that have a molecular chain exhibiting lubricity and an acrylic double bond in their molecules, such as acrylic esters, methacrylic esters, vinyl acetate esters, acrylic amide compounds, and vinyl alcohol esters. , methyl vinyl alcohol ester, allyl alcohol ester, glyceride, etc. The structural formula of these lubricants is CH2= CH-CH2COOR. CH2= CHCON HCH20CORRCOOCI
(=C)(2, RCOOCH2-CH=CH2, etc., where R is a linear or branched saturated or unsaturated hydrocarbon group, and the number of carbon atoms is 7 or more, preferably 12 or more and 23 or less, These can also be fluorine-substituted products. As fluorine-substituted products, CnF -1CnF (CH2)m-2m+1
2n+1 (however, m=1 to 5)
, CnF502NCH2CH2. 2n+1 CnF CH2CH2NHCH2CH2-12n+
1 CnF 05 top 2(g)->-1 etc. Preferred specific examples of these radiation-curing lubricants include:
Stearic acid methacrylate (acrylate), stearyl alcohol methacrylate (acrylate),
Examples include glycerin methacrylate (acrylate), glycol methacrylate (acrylate), and silicone methacrylate (acrylate). The dispersant and lubricant are 0°1 to 20° relative to the binder.
Parts by weight may be included. As the support, various materials such as various resins such as polyester, polyamide, and polyimide, and various metals such as A resin can be used. In the magnetic recording medium of the present invention, magnetic layers may be provided on both sides of the support. Further, a bark coat and a top coat may be provided as necessary. Of these, the back coat is a binder. The composition preferably consists of a pigment and a lubricant. As the binder, the radiation-curable resin used in the magnetic layer described above can be used. For example, (A) has two or more unsaturated double bonds that are curable by radiation.
A plastic-like compound with a molecular weight of s, ooo to too, ooo, (B) having one or more unsaturated double bonds that are curable by radiation, or not curable by radiation;
A rubber-like compound with a molecular weight of 3.000 to 100 and OOO (C) a compound with a molecular weight of 200 to 3.000 that has one or more unsaturated double bonds that are curable by radiation; 70% by weight, (B) 20-80% by weight,
(C) A combination used in a proportion of 10 to 40% by weight is preferred. Thermoplastic resins and thermosetting resins can also be used, and these preferably have an average molecular weight of 200.000 or less. Particularly preferred is a thermosetting resin (using a curing agent) consisting of a combination of cellulose resin (nitrified cotton, etc.), vinyl chloride-vinyl acetate-vinyl alcohol copolymer, and urethane. As the pigment, the inorganic pigment used in the magnetic layer described above can be used. For 1), it is preferable to leave 20 to 300 parts by weight per 100 parts by weight of the binder, and for 2), it is preferable to leave an excess of 10 to 300 volumes of IIA.As the lubricant, the one used for the magnetic layer described above can be used. . Among these, it is preferable to use fatty acids and/or fatty acid esters. The magnetic recording medium of the present invention can be manufactured according to a conventional method. Magnetic powder is mixed and dispersed with a binder, an organic solvent, etc. to prepare a magnetic paint, and this magnetic paint is gravure coated on a substrate such as a polyester film. , reverse roll coating, air knife coating, air doctor coating, blade coating, kiss coating, spray coating, etc., and orientation treatment is applied so that the direction of easy magnetization of the magnetic powder is perpendicular to the magnetic layer. The film may be dried, preferably subjected to radiation curing according to a conventional method, and a back coat and a top coat may be applied as necessary. Orientation treatment follows a conventional method. In this case, the magnetic field for orientation treatment is 100 to 6000G, preferably the coercive force (H
It is preferable to set the magnetic field to about 2 to 4 times that of c). Typical orientation methods used are permanent magnets, DC magnets, and AC magnetic fields, and various combinations of these,
For example, a combination of vertical and horizontal, a combination of a permanent magnet or a DC magnetic field and an AC magnetic field, a mechanical orientation, or a combination of mechanical orientation and the above can be used. Then, the magnetic particles are dried in a magnetic field so that the orientation of the magnetic particles due to the demagnetizing field will not be disturbed due to the demagnetizing field and the orientation will deteriorate. It is necessary to dry it so that the magnetic powder does not move. ■ Specific effects of the invention According to the invention, the average particle size of 20 to 70% by weight is 0.01
= 0.1 JLs of plate-shaped magnetic powder, and the remainder average particle size of 0.1 JLs.
Since it has a magnetic layer containing magnetic powder made of plate-shaped magnetic powder of 1-0.5 μm and a binder, the magnetic recording material has a dense packing due to the different average particle diameters and improved surface roughness. A medium is obtained. The degree of vertical orientation is also improved. As a result, electromagnetic conversion characteristics also improve. Such magnetic recording media are effective for use in digital audio tapes, floppy disks, 8 mm video tapes, video floppies, hard disks, and the like. (2) Specific Examples of the Invention Hereinafter, specific examples of the present invention will be shown and the present invention will be explained in more detail. Example 1 Barium ferrite A with an average grain size of 0.071 Lm and a plate ratio of 3 (B a F e 12019 f) B a
Table 1 shows the barium ferrite (with a grain size of 0.1 SIL layer and a plate ratio of 1O synthesized using the hydrothermal synthesis method) with a partial substitution of F e). A magnetic paint was prepared in the following manner using magnetic powders mixed in the proportions shown. Barium ferrite A, 8 120 parts by weight α-Au2 o3 C0,51L powder) 2 parts by weight Carbon black (20mJL) 10 parts by weight Solvent (MEK/) Luene: 50150) 100 parts by weight The above composition was milled in a ball mill. The barium ferrite was soaked for a while and thoroughly moistened. Next, as a binder, vinyl chloride-vinyl acetate-vinyl alcohol copolymer (
Contains maleic acid; MW 40,000) 6 parts by weight (calculated as solid content! l!!), acrylic double bond-introduced vinyl chloride-vinyl acetate copolymer (
Contains maleic acid: MW20,000) 12 parts by weight (calculated as solid content), Acrylic - Way to the tongue,,+! +11-÷11. ^Shishiaki Noelastomer (MW40.000) 9 parts by weight (solid content equivalent), 3 parts by weight of pentaerythritol triacrylate, 200 parts by weight of solvent (MEK/) luene; 50150) 4 parts by weight of stearic acid, and stearin Two parts by weight of butyl acid were mixed and dissolved. This was placed in a ball mill containing the magnetic powder mixture and mixed and dispersed again for 42 hours. The thus obtained magnetic paint was gravure coated onto a 331L polyester film, vertically oriented while drying on a permanent magnet (3000G), and then the solvent was dried using a far-infrared lamp or hot air. After surface smoothing treatment,
Using an electrocurtain type electron beam accelerator manufactured by ESI, the acceleration voltage was 150 KeV, the electrode current was 20 mA, and the total irradiation amount was 5 Mr.
Irradiate with an electron beam under N2 atmosphere under the conditions of a and d,
The coating was cured. The samples thus prepared were referred to as samples 1 to 9 (Table 1), and the characteristics of these samples were investigated. The characteristics were evaluated as follows. (1) Surface roughness R20 It was determined by the 20-point average method from a chart obtained using Talystep (manufactured by TAYLOR-HOBSON). The cutoff was 0.17 mm, and the needle pressure was 0.1 x 2.5 bars. (2) Perpendicular orientation The squareness ratio B r /B m in the vertical direction of the magnetic tape was measured, and demagnetizing field correction was performed. (3) C/N-2 Indicates the C/N ratio (relative value) when recording and reproducing on a video floppy with a center frequency of 7 MHz and an RF signal. C/N-2 is 1. This is the measured value at a distance of OMHz. Rotation speed 360 rpm, relative speed 6.6 m/sec
And so. These results are shown in Table 1. From Table 1, it can be seen that the samples using the magnetic powder of the present invention had good surface roughness and good vertical orientation, and had excellent electromagnetic conversion characteristics. Example 2 Barium ferrite (B a F e12019 (7) B a, F e
IrF () and barium ferrite (B a Fe 1201 g (7) B a F e 1201 g (7) B a
, synthesized by co-precipitation method after partially converting F e) in a weight ratio of 6=4, 120 parts by weight, α
-A Bun 203 (0.51L powder) 2 parts by weight, dispersant (soybean oil unrefined lecithin) 3 parts by weight and solvent (MEK/cyclohexanone 0/30) 100 parts by weight in the same manner as in Example 1. A magnetic powder mixture was made. Next, as a binder, vinyl chloride-vinyl acetate-vinyl alcohol copolymer (
Contains maleic acid; MW 20,000) 6 parts by weight (in terms of solid content), acrylic modified phenoxy (MW 35,000) 6 parts by weight (in terms of solid content). Acrylic modified polyether urethane elastomer (MW
20,000) 18 parts by weight (in terms of solid content), 200 parts by weight of solvent (MEK/cyclohexanone 0/30). 3 parts by weight of higher fatty acid-modified silicone oil and 3 parts by weight of butyl silistate were mixed and dissolved. After that, sample A was prepared by the same operation as in Example 1,
We investigated the characteristics. However, the orientation treatment was performed using an alternating current magnetic field (3000G). The characteristics of this sample A are shown below. R200,04 pot layer orientation degree 0.80 C/N-2+1.5 Sample A was treated in the same manner except that the radiation-curable binder was replaced with a thermosetting binder. Namely, vinyl chloride-vinyl acetate-vinyl alcohol copolymer (containing maleic acid), acrylic modified phenoxy,
Acrylic modified polyether urethane elastomer total 30
Parts by weight were 15 parts by weight of vinyl chloride-vinyl acetate-vinyl alcohol copolymer (VAGH manufactured by Union Carbide Co., Ltd.) and urethane (Nipporan 302, manufactured by Nippon Polyurethane Co., Ltd.).
) Sample B was prepared in the same manner as Sample A except that the amount was changed to 15 parts by weight. However, in this case, an isocyanate compound (Coronate L manufactured by Nippon Polyurethane Co., Ltd.) is added to the magnetic paint after dispersion.
) was added in an amount of 5 parts by weight (calculated as solid content). Further, after the surface was smoothed, heat curing was performed at 80° C. for 48 hours. For Samples A and B, the C/N values were determined on the outside and inside of the jumbo roll when 5000 ma was cut onto an 8-inch diameter take-up roll. The results are shown below. C/N-2 Outside Inside Sample A (invention) +1.5 +1.5 Sample B (
Comparison) +1.3 +0.3 From this result, it can be seen that sample B had tight winding on the jumbo roll, and the C/N-2 decreased significantly on the inside. From the above, the effects of the present invention are clear.

Claims (4)

[Claims] (1) 20 to 70% by weight with an average particle size of 0.01 μm or more
．． Having on a support a magnetic layer containing a binder and magnetic powder containing plate-shaped magnetic powder of less than 1 μm and 80 to 30% by weight of plate-shaped magnetic powder with an average particle size of 0.1 μm or more and 0.5 μm or less. A magnetic recording medium characterized by: (2) Surface roughness R_2_0 of the magnetic layer surface is 0.08 μm
A magnetic recording medium according to claim 1 below. (3) The magnetic recording medium according to claim 1 or 2, wherein the binder is a cured radiation-curable compound. (4) The magnetic recording medium according to any one of claims 1 to 3, wherein the magnetic powder is hexagonal barium ferrite.