JPS6313259B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method of manufacturing a magnetic recording medium, and more particularly to a method of manufacturing a magnetic recording medium with excellent orientation of magnetic particles in a magnetic layer. Generally, magnetic recording bodies are manufactured by providing a magnetic layer on a nonmagnetic support by plating or coating, and then applying a magnetic field to orient the magnetic particles in the magnetic layer. When providing a magnetic layer by coating, coating methods include air doctor coating, blade coating, air knife coating, squeeze coating, impregnation coating, reverse roll coating, transfer roll coating, gravure coating, cast coating, spray coating, kiss coating, etc. was commonly used. Magnetic recording and reproducing is performed on the magnetic recording body manufactured in this way using a magnetic head, but at that time, the lines of magnetic force from the magnetic head penetrate through the magnetic layer at an angle to the surface near the surface. On the other hand, in the deep part of the magnetic layer, that is, in the vicinity of the support, the particles penetrate almost parallel to the surface of the magnetic layer, and it is desirable that the magnetic particles are sufficiently oriented in the recording direction even in the deep part of the magnetic layer. In recent years, high-density recording has been promoted in video tapes, etc., but even in this case, if the orientation of the magnetic particles in the deep part of the magnetic layer is not sufficient, the output of audio signals, control signals, etc. is likely to be insufficient.
It is required that the magnetic particles be sufficiently oriented even deep in the magnetic layer. In addition, it is generally recognized that improved orientation improves audio sensitivity and reduces distortion, resulting in a significant increase in so-called dynamic range. It is necessary to improve. However, when the present inventors investigated the orientation distribution in the thickness direction of the magnetic recording body, it was found that the orientation in the deep part of the magnetic layer was low and insufficient. The reason for this is not necessarily clear, but in a wet coated magnetic layer, the fluidity of the liquid decreases in the deep part of the magnetic layer, that is, near the surface of the support, and the apparent viscosity increases. This is presumed to be due to the fact that it becomes difficult to fully orient the magnetic particles. However, as long as the above-mentioned coating method is used, which requires orientation after the magnetic layer is provided on the support, it seems difficult to improve the orientation in the deep part of the magnetic layer. In order to solve such conventional problems, the present inventors formed a free-falling curtain made of a magnetic coating liquid, and applied a magnetic field to the free-falling curtain portion while conveying the free-falling curtain across the free-falling curtain. We have discovered a method of applying the magnetic coating liquid onto the surface of a strip-shaped support, and have already filed a patent application.
This was clarified by the specification of application No. 51-96675. According to this method, it is now possible to manufacture magnetic recording materials by curtain coating, which was previously considered to be extremely difficult due to the instability of the curtain film. However, when the coating speed was extremely high, it was found that air was easily drawn in, causing air bubbles to form in the magnetic layer coating, and in severe cases, leaving uncoated areas. . The reason why such defects occur is that when the traveling speed of the strip support is increased to increase the coating speed, the line of intersection between the free falling curtain and the strip support (hereinafter referred to as the "wetted line") is This is thought to be because, as a result of being pulled by the belt-shaped support, the curtain deviates from a straight line in the running direction of the belt-shaped support, and the angle between the free-falling curtain and the belt-shaped support becomes an acute angle when viewed macroscopically. In order to prevent air from being drawn into the free-falling curtain, it has been proposed to provide an air shield upstream of the free-falling curtain (for example, Japanese Patent Publication No. 49-24133, Japanese Patent Publication No. 49-2413,
35447, etc.), it is extremely difficult to completely remove the entrained air flow only by using an air shield, and it is virtually impossible to effectively remove air entrainment, especially when coating at high speed. Moreover, due to the recent demand for improved production efficiency, the need for faster coating is increasing rapidly, and the problems associated with high-speed coating are now being recognized as extremely important issues. A quick solution was desired. An object of the present invention is to provide a novel method for manufacturing a magnetic recording medium. Another object of the present invention is to provide a method for manufacturing a magnetic recording medium with excellent orientation. Another object of the present invention is to provide a method for manufacturing a magnetic recording medium with excellent orientation throughout the entire layer. Another object of the present invention is to provide an excellent method for manufacturing an audio magnetic recording medium. Another object of the present invention is to provide a method for manufacturing a videotape with excellent audio output. Still another object of the present invention is to provide a method for manufacturing a magnetic recording medium that does not cause uneven coating. In order to achieve the above object, the present inventor has conducted intensive research and found that the above object can be achieved by applying a magnetic coating liquid so that the line of contact between the free-falling curtain and the strip-shaped support becomes substantially a straight line. I have discovered what can be achieved. Hereinafter, embodiments of the present invention will be described in detail based on the accompanying drawings. FIG. 1 is a schematic diagram of a magnetic coating liquid coating device showing a preferred embodiment of the present invention, and FIG. 2 is a schematic perspective view thereof. 1 and 2, the magnetic coating liquid is supplied to the coating head 3 through a nozzle 1 and a pipe 2, and then sent to a pocket 4 provided over almost the entire width of the coating head 3. The dynamic pressure of the liquid is eliminated, and the liquid is sent to a slit 5 provided over almost the entire width of the coating head 3 and flows down to form a free-falling curtain 6. Both ends of the free-falling curtain 6 are supported by guide rods 7a and 7b to prevent contractions and allow the free-falling curtain 6 to
Consideration has been given to further enhance the stability of the system.
Since the free-falling curtain 6 of the magnetic coating liquid is generally unstable, it is desirable to provide guide rods 7a and 7b. An air-core solenoid coil 8 (not shown in FIG. 2) is provided adjacent to the free-falling curtain 6, and a magnetic field is applied in the falling direction of the free-falling curtain to orient it. On the other hand, a band-shaped support 9 is conveyed in the direction of the arrow so as to cross this free-falling curtain 6.
The magnetic coating liquid in the free-falling curtain 6 that has passed through the orienting magnetic field collides with the strip-shaped support 9, and coating is performed to form a magnetic layer 10. In this embodiment, the guide rods 7a and 7b are not installed vertically but inclined in the direction in which the belt-shaped support 9 moves. Therefore, the magnetic coating liquid falling as a free-falling curtain 6 is pulled downward by gravity, and the line in contact with the liquid moves upstream with respect to the traveling direction of the strip support 9, as shown in FIG. As shown, the wetted line is substantially straight. by the way,
When the guide rods 7a and 7b are installed vertically,
The line in contact with the liquid is stretched by the continuously running belt-shaped support 9 and forms a shape that bulges downstream at its center line, so by moving the line in contact with the liquid upstream in this way, it is possible to It becomes possible to maintain the liquid line substantially straight. Although it is not clear why the entrainment of air into the free-falling curtain 6 is reduced by straightening the liquid contact line in this way,
The entrainment of air increases as the deviation ratio of the line in contact with the liquid from the straight line (the ratio of the amount of deviation from the straight line at the center of the line in contact with the liquid to the width of the free-falling curtain 6) increases, and conversely, as the deviation ratio of the line in contact with the liquid from the straight line increases, the entrainment of air decreases as it decreases. It is recognized that The degree to which the guide rods 7a and 7b should be tilted depends on the degree of curvature of the curtain film, the physical properties such as the viscosity and surface tension of the magnetic coating liquid used, the falling speed of the magnetic coating liquid, and the running speed of the strip support. Since it depends not only on the coating conditions, but also on the width of the free-falling curtain 6 or the coating width, it is difficult to unconditionally discuss what level is appropriate, and it is appropriate to determine it experimentally. In order to further reduce the airflow reaching the free-falling curtain 6, the free-falling curtain 6
An air shield 11 is provided on the upstream side of the free-falling curtain 6 to improve the stability of the free-falling curtain 6. Furthermore, the conveyance path of the strip-shaped support 9 is also changed in direction immediately before the free-falling curtain 6 to prevent entrained airflow from impairing the stability of the free-falling curtain 6. Further, the free-falling curtain 6 is provided beyond the width of the strip-shaped support 9, and the widthwise end (hereinafter referred to as
It's called the "ear part." ), the aim is to prevent thick coating, which is generally thought to occur. The uncoated magnetic coating liquid is collected by a known collection device (not shown) and reused as necessary. The strip-like support 9 carrying the magnetic layer 10 thus provided is sent to a drying step while being supported by a backing roll 12. In order to further enhance the orientation effect, an auxiliary orientation magnet 13 may be provided here. It goes without saying that the present invention is not limited to the above-described embodiments, and that various modifications can be made. For example, in the embodiment described above, the liquid contact line is made substantially straight by tilting the guide rods 7a, 7b, but the guide rods 7a, 7b themselves are provided vertically, and the air-core solenoids 14 facing each other are arranged vertically.
The strength of the magnetic field acting on the free-falling curtain 6 is made larger on the upstream side of the strip support 9 than on the downstream side, and the free-falling curtain 6 is pulled upstream by magnetic force, and Air entrainment can also be prevented by inflating and thereby correcting the deviation of the wetted line from a straight line and making it substantially straight. According to such a method, since the orientation magnetic field has both the functions of orientation and prevention of air entrainment, it is possible to simply control the strength of the magnetic field on the upstream and downstream sides of the free-falling curtain 6. This has the advantage of preventing air entrainment. In addition, in the embodiment described above, an extrusion type coating head is used as the coating head, but other coating heads may also be used, such as those disclosed in Japanese Patent Publications No. 49-24133, Japanese Patent Publication No. 49-35447, etc. For example, a sliding type application head can also be used.
When only a sliding type coating head is used, it is necessary to take precautions to prevent the binder in the magnetic coating liquid from evaporating. Further, in the embodiment described above, the width of the free-falling curtain 6 is set larger than the width of the band-shaped support 9 to prevent thick coating on the ears, but it is not necessary to do so. It is also possible to apply the coating while keeping the width of 6 within the width of the strip-shaped support 9. In this case, thick coating tends to occur at the ears, so in order to prevent this, some bristles are attached to the lower ends of the guide rods 7a and 7b as disclosed in Japanese Patent Publication No. 49-35447. A brush made of a material, a strip made of a flexible elastic material, etc. may also be provided. Also, as for the method of applying the magnetic field, an air-core solenoid is preferable from the viewpoint of stability of the curtain film, but permanent magnets having opposing magnetic poles can also be used. In the present invention, the initial falling velocity of the magnetic coating liquid supplied to the free-falling curtain is approximately 20 cm/sec or less,
Preferably, it is about 15 cm/sec or less. If it is more than this, the stability of the curtain film will decrease, which is not preferable. Curtain film formation by gravity provides the desired results. In the present invention, the falling distance of the curtain membrane is approximately 3
It is desirable to set it in the range of cm to approximately 40 cm. Depending on the surface tension of the magnetic coating liquid, the falling distance is approximately 40
If it exceeds cm, the falling speed of the magnetic coating liquid becomes excessive as a result of acceleration due to gravity, and the thickness of the curtain film becomes too thin, making it easy to tear the curtain film in a sagging pattern. Also, about 5 cm or less, especially about 3 cm
If the diameter is less than cm, it will be difficult to arrange the magnet. In the present invention, the supply amount of the magnetic coating liquid is approximately 0.7 cc/sec or less per 1 cm width of the free-falling curtain.
In particular, it is required to be about 1 c.c./sec or more in order to form a stable curtain film. In the present invention, the viscosity of the magnetic coating liquid is approximately 15 cp.
It is desirable that the amount is about 100 cp or less. Approximately 15cp
If it is less than about 100 cp, the magnetic particles tend to be poorly dispersed, and if it exceeds about 100 cp, it becomes difficult to form a thin curtain film. The strength of the magnetic field applied in the present invention is also related to the coercive force of the magnetic particles, but is desirably 300 Oersted or more, preferably 500 Oersted or more. If it is less than this, the orientation will deteriorate. Further, it is desirable that at least 1/3 or more of the free fall length of the curtain film passes through the above magnetic field strength. If it is less than this, the orientation will be lowered and the stability of the curtain film will also be lowered. In the present invention, when the wetted line is made substantially straight only by the strength of the upstream and downstream magnetic fields, the strength of the upstream magnetic field is at least 50 It is desirable that it be larger than Oersted. Methods of creating a difference in the strength of the magnetic fields on the upstream and downstream sides include, for example, dropping a curtain at a position offset by the required distance from the center of the air-core solenoid, and changing the winding density between the upstream and downstream sides. How to use different air core solenoids,
A method may be considered in which the curtain is caused to fall through opposing magnets in which magnetic poles of magnets with different strengths are made to face each other, but the method is of course not limited to these methods. The thickness of the magnetic layer to be coated in the present invention is preferably 100 μm or less and 5 μm or more in an undried state. Further, the conveying speed of the belt-shaped support to be coated is determined by the desired coating amount (coating film thickness) and the supply amount of the magnetic coating liquid, and is preferably 50 cm/sec to 700 m/min. Regarding the manufacturing method of the magnetic coating liquid used in the present invention, Japanese Patent Publications No. 35-15, No. 39-26794, No. 43-186, No. 47-
No. 28043, No. 47-28045, No. 47-28046, No. 47-28048
No. 47-31445, No. 48-11162, No. 48-21331,
It is described in detail in publications such as No. 48-33683 and Soviet Patent Specification No. 308033. The magnetic coating liquid described in these documents includes ferromagnetic powder, binder,
The main component is a coating solvent, and may also contain additives such as a dispersant, a lubricant, an abrasive, and an antistatic agent. The ferromagnetic fine powder of the present invention includes ferromagnetic iron oxide,
Ferromagnetic chromium dioxide, ferromagnetic alloy powder, etc. can be used. The above ferromagnetic iron oxide is a ferromagnetic iron oxide whose x value is in the range of 1.33≦x≦1.50 when expressed by the general formula FeOx, that is, maghemite (γ-Fe ₂ O ₃ , x
= 1.33), magnetite (Fe ₃ O ₄ , x = 1.50) and their bertholide compounds (FeOx, 1.33<x
<1.50). The above x value is x = 1/2 x {2 x (atomic% of divalent iron) + 3
×(atomic% of trivalent iron)}×1/100. A divalent metal may be added to these ferromagnetic iron oxides. Divalent metals include Cr, Mn,
These include Co, Ni, Cu, Zn, etc., and are added in an amount of 0 to 10 atomic% relative to the iron oxide. The above ferromagnetic chromium dioxide includes CrO ₂ and its addition to Na, K, Ti, V, Mn, Fe, Co, Ni, Tc,
Metals such as Ru, Sn, Ce, Pb, semiconductors such as P, Sb, Te, or oxides of these metals from 0 to
20wt.% added _CrO2 is used. The acicular ratio of the above ferromagnetic iron oxide and ferromagnetic chromium dioxide is about 2/1 to 20/1, preferably 5/1.
1 or more, average length is about 0.2 to 2.0 μm, preferably
A range of 0.3 to 1.5 μm is effective. The above ferromagnetic alloy powder has a metal content of 75 wt.% or more, and 80 wt.% or more of the metal content is at least one ferromagnetic metal (i.e., Fe, Co,
Ni, Fe−Co, Fe−Ni, Co−Ni or Co−Ni−
Fe), with a metal content of 20wt.% or less,
Preferably 0.5-5wt.% is Al, Si, S, Sc, Ti,
V, Cr, Mn, Cu, Zn, Y, Mo, Rh, Pd,
Ag, Sn, Sb, Te, Ba, Ta, W, Re, Au,
It has a composition of Hy, Pb, Bi, La, Ce, Pr, Nd, B, P, etc., and may also contain a small amount of water, hydroxide, or oxide. Specifically, Special Publication No. 36-5515, No. 37-4825
No. 39-5009, No. 39-10307, No. 44-14090
No. 45-18372, No. 47-22062, No. 47-
No. 22513, No. 46-28466, No. 46-38755, No. 47
-4286, 47-12422, 47-17284, 47
-18509, 47-18573, 48-39639, US Patent No. 3026215; US Patent No. 3031341; US Patent No. 3100194;
No. 3242005; No. 3389014; British Patent No. 752659;
782762; 1007323; French patent 1107654
No.: West German Published Patent Application (OLS) No. 1281334, etc. As the binder for the magnetic coating liquid used in the present invention, conventionally known thermoplastic resins, thermosetting raw resins, reactive resins, and mixtures thereof are used. As a thermoplastic resin, the softening temperature is 150℃ or less, the average molecular weight is 10,000 to 200,000, and the degree of polymerization is approximately 200 to 2,000.
For example, vinyl chloride vinyl acetate copolymer, vinyl chloride vinylidene chloride copolymer, vinyl chloride acrylonitrile copolymer, acrylic ester acrylonitrile copolymer, acrylic ester vinylidene chloride copolymer, acrylic ester styrene. copolymer, methacrylic acid ester acrylonitrile copolymer, methacrylic acid ester vinylidene chloride copolymer, methacrylic acid ester styrene copolymer, urethane elastomer, polyvinyl fluoride, vinylidene chloride acrylonitrile copolymer, butadiene acrylonitrile copolymer,
Polyamide resin, polyvinyl butyral, cellulose derivatives (cellulose acetate butyrate,
Cellulose diacetate, cellulose triacetate, cellulose propionate, nitrocellulose, etc.), styrene-butadiene copolymers, polyester resins, amino resins, various synthetic rubber thermoplastic resins (polybutadiene, polychloroprene, polyisoprene, styrene-butadiene copolymers, etc.) polymers, etc.) and mixtures thereof. Examples of these resins are given in Japanese Patent Publication No. 37-6877, 39-
No. 12528, No. 39-19282, No. 40-5349, No. 40-20907
No. 41-9463, 41-14059, 41-16985, 42
-6428, 42-11621, 43-4623, 43-15206
No. 44-2889, No. 44-17947, No. 44-18232, 45
−14020, 45−14500, 47−18573, 47−
No. 22063, No. 47-22064, No. 47-22068, No. 47-22069
No. 47-22070, No. 48-27886, U.S. Pat.
No. 3144352; No. 3419420; No. 3499789; No. 3499789;
Described in No. 3713887. The thermosetting resin or reactive resin has a molecular weight of 200,000 or less in the coating liquid state, but when added after coating and drying, the molecular weight becomes infinite due to reactions such as condensation and addition. Also, among these resins, those that do not soften or melt before the resin is thermally decomposed are preferred. Specifically, for example, phenol-formalin-novolak resin, phenol-formalin-resol resin, phenol-furfural resin, xylene-formaldehyde resin, urea resin, melamine resin, drying oil-modified alkyd resin, carbonic acid resin-modified alkyd resin, maleic acid resin. Modified alkyd resins, unsaturated polyester resins, epoxy resins and curing agents (polyamines, acid anhydrides, polyamide resins, etc.),
Terminal isocyanate polyester moisture curable resin, terminal isocyanate polyether moisture curable resin, polyisocyanate prepolymer (compound having 3 or more isocyanate groups in one molecule obtained by reacting diisocyanate and low molecular weight triol, diisocyanate) trimers and tetramers), polyisocyanate prepolymers and resins containing active hydrogen (polyester polyols, polyether polyols, acrylic acid copolymers, maleic acid copolymers, 2-hydroxyethyl methacrylate copolymers, para-hydroxystyrene copolymers) , others), and mixtures thereof. Examples of these resins are given in Japanese Patent Publication No. 39-8103, 40-
No. 9779, No. 41-7192, No. 41-8016, No. 41-14275,
No. 42-18179, No. 43-12081, No. 44-28023, 45-
No. 14501, No. 45-24902, No. 46-13103, No. 47-22065
No. 47-22066, No. 47-22067, No. 47-22072,
No. 47-22073, No. 47-28045, No. 47-28048, 47-
No. 28922, U.S. Patent No. 3144353; U.S. Patent No. 3320090;
No. 3437510; No. 3597273; No. 3781210; No. 3781210;
Described in No. 3781211. These binders may be used alone or in combination, and other additives may be added. The mixing ratio of ferromagnetic powder and binder is ferromagnetic powder by weight ratio.
The binder is used in an amount of 8 to 150 parts by weight, preferably 10 to 100 parts by weight, and more preferably 12 to 60 parts by weight per 100 parts by weight. In addition to the binder and ferromagnetic fine powder described above, additives such as a dispersant, a lubricant, an abrasive, and an antistatic agent may be added to the magnetic coating liquid. Dispersants include caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid, elaidic acid, linoleic acid,
Fatty acids with 12 to 18 carbon atoms such as linolenic acid and stearolic acid (R ₁ COOH, R ₁ is an alkyl or alkenyl group with 11 to 17 carbon atoms); Alkali metals of the above fatty acids (Li, Na, K, etc.) ) or alkaline earth metals (Mg, Ca, Ba); fluorine-containing compounds of the above fatty acid esters; amides of the above fatty acids; polyalkylene oxide alkyl phosphates; lecithin; Tetraammonium salts (alkyl having 1 to 5 carbon atoms, olefin being ethylene, propylene, etc.) are used. In addition, higher alcohols having 12 or more carbon atoms and sulfuric esters can also be used. These dispersants are used in amounts of 0.5 to 20 parts by weight per 100 parts by weight of binder.
It is added in a range of parts by weight. For these, please refer to Special Publication No. 39-28369, No. 44-17945, No. 48-7441.
No. 48-15001, No. 48-15002, No. 48-
No. 16363, No. 50-4121, U.S. Patent No. 3387993, U.S. Pat.
It is described in No. 3470021, etc. As lubricants, conductive fine powders such as carbon black, graphite, and carbon black graft polymers; inorganic fine powders such as molybdenum disulfide and tungsten disulfide; polyethylene, polypropylene, polyethylene vinyl chloride copolymers, polytetrafluoroethylene, etc. fine plastic powder; α-olefin polymer; unsaturated aliphatic hydrocarbon that is liquid at room temperature (a compound in which an n-olefin double bond is bonded to the terminal carbon, approximately 20 carbon atoms); carbon number
Fatty acid esters consisting of 12 to 20 monobasic fatty acids and monohydric alcohols having 3 to 12 carbon atoms can be used. These lubricants are added in an amount of 0.2 to 20 parts by weight per 100 parts by weight of the binder. Regarding these, Special Publications No. 41-18064, No. 43-23889,
No. 46-40461, No. 47-15621, No. 47-18482,
No. 47-28043, No. 47-32001, No. 50-5042,
US Patent No. 3470021; US Patent No. 3492235; US Patent No. 3497411
No. 3523086; No. 3625760; No. 3630772;
No. 3642539; “IBM Technical Disclosure
Bulletin” Vol. 9, No. 7, Page 779 (December 1966);
Described in “ELEKTRONIK” 1961, No. 12, Page 380, etc. Commonly used polishing materials include fused alumina, silicon carbide, chromium oxide, zircon (ZrSiO ₄ ), aluminum phosphate (AlPO ₄ ), cerium oxide (CeO ₂ ), boron carbide (B ₄ C), and boric acid. Aluminum (AlBO ₃ ), spinel (MgAl ₂ O ₄ ),
Rutile, anatase (all TiO ₂ ), diaspor (α-AlOOH), corundum, artificial corundum, diamond, artificial diamond, garnet, emery (main components: corundum and magnetite), etc. are used. These abrasives have a Mohs hardness of 5
Above, those having an average particle diameter of 0.05 to 5 μm are used, particularly preferably 0.1 to 2 μm. These abrasives are added in an amount of 0.5 to 20 parts by weight based on 100 parts by weight of the binder. Regarding these, Special Publication No. 47-18572, No. 48-15003,
No. 48-15004 (US Patent No. 3617378), No. 49-
No. 39402, No. 50-9401, U.S. Patent No. 3007807;
No. 3041196; No. 3293066; No. 3630910; No. 3630910;
No. 3687725; British Patent No. 1145349; West German Patent (DT-PS) No. 853211; British Patent No. 1101000. Antistatic agents include conductive fine powders such as carbon black, graphite, and carbon black graft polymer; natural surfactants such as saponin; nonionic surfactants such as alkylene oxide, glycerin, and glycidol; and higher alkyl amines. , quaternary ammonium salts, pyridine and other heterocycles, phosphonium or sulfonium, and other cationic surfactants; anionic surfactants containing acidic groups such as carboxylic acid, sulfonic acid, phosphoric acid, sulfuric ester groups, and phosphoric ester groups. ;
Ampholytic activators such as amino acids, aminosulfonic acids, sulfuric acid or phosphoric acid esters of amino alcohols, etc. are used. The above conductive fine powder is added in an amount of 0.2 to 20 parts by weight, and the surfactant is added in an amount of 0.1 to 10 parts by weight, based on 100 parts by weight of the binder. Some of the conductive fine powders and surfactant compounds that can be used as antistatic agents are
No. 22726, No. 47-24881, No. 47-26882, No. 48
-15440, 48-26761, U.S. Patent No. 2271623,
Same No. 2240472, No. 2288226, No. 2676122, Same No.
No. 2676924, No. 2676975, No. 2691566, No. 2676975, No. 2691566, No.
No. 2727860, No. 2730498, No. 2742379, No.
No. 2739891, No. 3068101, No. 3158484, No. 3158484, No.
No. 3201253, No. 3210191, No. 3294540, No.
No. 3415649, No. 3441413, No. 3442654, No. 3441413, No. 3442654, No.
3475174, 3545974, OLS 1942665, UK patent 1077317,
No. 1198450, etc., "Synthesis of surfactants and their applications" by Ryohei Oda et al. (Maki Shoten 1964 edition); AM
“Surf S Active Agents” by Schwarz & J.W. Peiri (Interscience)
Publication Incorporated (1958 edition); JP Sisley, Encyclopedia
It is described in books such as "Of Surf S Active Agents, Volume 2" (Chemical Publishing Company, 1964 edition); "Surfactant Handbook", 6th edition (Sangyo Tosho Co., Ltd., December 20, 1964). ing. These surfactants may be added alone or in combination. Although these are used as antistatic agents, they are sometimes applied for other purposes, such as dispersion, improving magnetic properties, improving lubricity, and as coating aids. Organic solvents used during coating include ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; alcohols such as methanol, ethanol, propanol, and butanol; methyl acetate, ethyl acetate, butyl acetate, ethyl lactate, and acetic acid. Ester systems such as glycol monoethyl ether; glycol ether systems such as ether, glycol dimethyl ether, glycol monoethyl ether, and dioxane; tar systems (aromatic hydrocarbons) such as benzene, toluene, and xylene; methylene chloride, ethylene chloride, and tetrachloride Carbon, chloroform, ethylene chlorohydrin, chlorinated hydrocarbons such as dichlorobenzene, etc. can be used. The magnetic coating liquid used in the present invention is prepared by kneading and dispersing ferromagnetic metal powder, a binder, a dispersant, a lubricant, an abrasive, an antistatic agent, a coating solvent, and the like. During kneading, the ferromagnetic metal powder and each of the above-mentioned components are fed into a kneader either simultaneously or individually one after another. For example, there is a method in which ferromagnetic metal powder is first added to a solvent containing a dispersant and kneaded for a predetermined period of time to form a magnetic coating liquid. Various kneaders are used to knead and disperse the magnetic coating liquid. For example, two-roll mill, three-roll mill, ball mill, pebble mill, tron mill, sand glider, Szegvari attritor,
These include high-speed impeller dispersion machines, high-speed stone mills, high-speed impact mills, dispers, kneaders, high-speed mixers, homogenizers, and ultrasonic dispersion machines. The technology related to kneading and dispersion is described in “Paint Flow and Pigment Dispersion” by TCPATTON (1964).
(published by John Wiley & Sons). It is also described in US Pat. No. 2,581,414 and US Pat. No. 2,855,156. Supports used in the present invention include polyethylene terephthalate, polyethylene-2,
Polyesters such as 6-naphthalate, polyolefins such as polypropylene, cellulose derivatives such as cellulose triacetate and cellulose diacetate, plastics such as polycarbonate, and non-magnetic metal foils such as Cu, Al, and Zn are used. The appropriate thickness of these supports is about 2 to 125 microns, preferably about 3 to 100 microns. The above support has a so-called backcoat on the side opposite to the side on which the magnetic layer is provided for the purpose of preventing static electricity, preventing transfer, preventing wow and flutter, etc.
(i.e., has a back layer). Regarding back coats, for example, the US patent
No. 2804401, No. 3293066, No. 3617378, No. 3617378, No. 3293066, No. 3617378, No.
No. 3062676, No. 3734772, No. 3476596, No.
No. 2643048, No. 2803556, No. 2887462, No. 2887462, No.
No. 2923642, No. 2997451, No. 3007892, No.
No. 3041196, No. 3115420, No. 3166688, No. 3115420, No. 3166688, No.
It is shown in No. 3761311 etc. The magnetic layer provided on the support according to the present invention is
It is sent to a drying process and dried by air flow. The drying temperature depends on the solvent used in the coating solution, but is generally about 50 to 120°C, preferably 70 to 100°C, particularly preferably 80 to 90°C. The flow rate of drying air is about 1 to 5 Kl/m ² , preferably about 2 to 3 Kl/m 2 .
m ² and the drying time is approximately 30 seconds to 10 minutes, preferably approximately 1 to 5 minutes. It is desirable that the dried magnetic layer is subjected to surface smoothing treatment. In general, the curtain coating method can form a coating film with excellent surface properties, but in the case of a magnetic coating liquid, due to its composition, it may not be possible to obtain sufficient smoothness by itself, and the surface of the magnetic recording medium is Since strict accuracy is required for the smoothness, it is desirable to further perform a smoothing process. The surface smoothing treatment is usually carried out by calendering or smoothing sheet after drying. In the case of calendering, it is preferable to carry out the supercalendering method in which the material is passed between two rolls such as a metal roll and a cotton roll or a synthetic resin (for example, nylon) roll. The conditions of supercalender are about 25-100Kg/cm, preferably 30-70Kg/cm of inter-roll pressure, about 35-100℃,
Preferably at a temperature of 40-80℃, 5-200m/min
It is preferable to carry out the processing at a processing speed of . Temperature and pressure above these upper limits have an adverse effect on the magnetic layer and non-magnetic support. Also, the processing speed is about 5m/
If it is less than min, the effect of surface smoothing cannot be obtained, and about
If the speed is more than 200m/min, processing operation becomes difficult. U.S. patents regarding these surface smoothing treatments
No. 2688567; No. 2998325; No. 3783023; West German Published Patent (DT-OS) No. 2405222; JP-A-49-53631
No. 50-10337, etc. The method using a smoothing sheet is a method in which a flexible sheet is brought into surface contact with the magnetic layer while the magnetic layer is in an undried and unsolidified state to smooth the magnetic layer. Examples will be given below in order to make the effects of the present invention more clear. In the examples, all parts are by weight. Example After kneading the composition shown in Table 1, it was put into a ball mill, and after being dispersed for 24 hours, polyisocyanate (3
Adduct of 1 mol of tolylene diisocyanate and 1 mol of trimethylolpropane. 75wt% ethyl acetate solution. NCO content approximately 13.3wt%. bayer
7 parts of "Desmodeur L-75" (manufactured by AG) were added and dispersed under high speed shearing for an hour, and filtered through a filter with an average pore size of 2 .mu.m to obtain a magnetic coating solution. The viscosity of this coating liquid was 35 cp.

[Table] The magnetic coating solution thus prepared was applied continuously to a polyethylene terephthalate film having a width of 300 mm, a thickness of 23 μ, and a surface roughness of 0.15 μ, which was continuously traveling at a traveling speed of 180 m/min. Coated. The initial velocity of the free-falling curtain is 5.
cm/sec, and the amount of coating liquid was controlled by changing the cap length of the nozzle. In addition, the falling distance of the free-falling curtain was set to 20 cm. The magnetic field was applied using the length of the air core (longitudinal direction) of 15 cm, width (web width direction) of 40 cm, and thickness (web length, edge of the air core in the running direction) of 5 cm.
The orientation direction was the free falling direction of the curtain (#1 to #3) or the longitudinal direction of the support (#4).

[Table] In Table 2, △l is the amount of inclination of the guide rod from the vertical, compared to when the guide rod is installed vertically.
It is shown by the distance traveled by the guide rod tip along the support surface. In #1 and #2, the liquid contact line during coating was substantially straight, and the curtain film was stable and stable coating was performed. In #3, partial fluctuations in the thickness of the curtain film were observed, air was sometimes entrained, and uncoated parts occurred here and there. The liquid contact line during coating was curved by 1.3 cm in the running direction at the center of the support. Stable coating was possible with #4. After coating and drying #1 to #3, a polyamide plastic roll is used as an elastic roll and a chromium-plated iron roll is used as a metal roll, and supercalendering is performed using a calendar that combines both rolls to smooth the surface of the magnetic layer. It became. The wide support provided with the magnetic layer was then cut into 1/2-inch pieces in the longitudinal direction to form a videotape. The electromagnetic conversion characteristics of the four types of videotapes thus obtained were measured using a unified type I VTR ("AV-8700" manufactured by Sony Corporation), and the results are shown in Table 3 along with the BH characteristics of each videotape.

[Table] According to Table 3, #1 to #3 made by the curtain coating method have a better squareness ratio than #4 made by the doctor coating method.
It was found that #2 had significantly better characteristics overall than #4.

[Brief explanation of the drawing]

1 and 2 are schematic diagrams of a curtain coating device showing an embodiment of the present invention. FIG. 3 is a diagram showing the magnetic field application position in the example. DESCRIPTION OF SYMBOLS 1... Nozzle, 2... Pipe, 3... Application head, 4... Pocket, 5... Slit, 6... Free falling curtain, 7a, 7b... Guide rod, 8...
...Air-core solenoid coil, 9...Strip support, 1
0...Magnetic layer, 11...Air shield, 12...
...Backing roll, 13...Orienting magnet.

Claims (1)

[Claims] 1. A free-falling curtain of a magnetic coating liquid consisting of at least ferromagnetic fine powder and a binder is formed between two guide rods, and a magnetic field is applied at the free-falling curtain section while the magnetic coating liquid is conveyed across the free-falling curtain. On the strip support surface that is
In the method for manufacturing a magnetic recording medium by applying the magnetic coating liquid, the guide bar is tilted toward the traveling direction of the strip-shaped support, or the strength of the magnetic field acting on the free-falling curtain portion is adjusted. 1. A method of manufacturing a magnetic recording medium, characterized in that the upstream side of the strip support is larger than the downstream side, so that the line in contact with liquid is substantially straight.