US3647661A - Electrodeposition of coating layers on subtrate structures - Google Patents

Abstract

A CURRENT IS PASSED THROUGH A CATHODE AND AN ARTICLE ADAPTED TO FUNCTION AS AN ANODE, THE CATHODE AND ANODE BEING DISPOSED IN AN ELECTROLYTIC VESSEL CONTAINING AN EMULSION PREPARED BY DISPERSING FINE PARTICLES OF A FILLER IN AN AQUEOUS SOLUTION HAVING AS ITS PRINCIPAL CONSTITUENT AN ANIONIC, POLYVALENT POLYELECTROLYTE CONSISTING OF A RESIN COMPONENT, WHEREBY A MIXTURE OF THE FINE PARTICLES AND RESIN COMPONENT IS ELECTRODEPOSITED ON THE ARTICLE. THE COATING LAYER IS THEN DRIED TO CAUSE POLYCONDENSATION OF THE RESIN COMPONENT TO FORM A FILM WHICH FUNCTIONS DIRECTLY AS A BINDER BETWEEN THE FINE PARTICLES.

Description

March 1972 AKIRA MATSUSHITA 3,647,651

ELECTRODEPOSITION OF COATING LAYERS ON SUBSTRATE STRUCTURES Filed Dec. 18, 1968 FIG. I(B) FIG. I(A) United States Patent O 3,647,661 ELECTRODEPOSITION OF COATING LAYERS ON SUBTRATE STRUCTURES Akira Matsushita, 99, 2-chome, Kosugigoten-cho, Kawasaki-shi, Japan Filed Dec. 18, 1968, Ser. No. 784,552 Claims priority, applizcatioiilgpan, Dec. 23, 1967,

Int. Cl. B01k 5/00; C23b 13/00 US. Cl. 204-181 12 Claims ABSTRACT OF THE DISCLOSURE BACKGROUND OF THE INVENTION This invention relates generally to the field of electrodeposition of materials and more particularly to improvements in techniques for causing electrodeposition on any selected substrate or base structure of at least one coating layer containing an additive capable of affecting electromagnetic, dielectric, optical, and/or mechanical properties of substances.

Heretofore, various methods such as painting, evaporation deposition, and electrodeposition by such techniques as electroplating have been known as techniques for causing coating layers as mentioned above to be deposited on and adhere to substrate structures. By these conventional methods, however, it has been extremely difiicult, it not impossible, in many cases to deposit truly uniform and fine-texture coating layers on substrate structures in a simple manner. Some of the reasons for this difiiculty are set forth below.

Among the numerous articles requiring coating layers, there are various kinds of magnetic recording mediums or materials, which are produced by various respective methods. For example, the process in the production of magnetic tapes used in magnetic sound recording and image transcription or video recording includes the steps of admixing a magnetic oxide such as 'y-Fe O or Fe O in powder form with a resin solvent to prepare a mixture of the consistency and form of paint and applying this mixture as uniformly as possible as a thin layer on the surface of a substrate or carrier structure in sheet form or tape form made of a material such as Mylar (a polyethylene terephthalate resin produced by E. I du Pont de Nemours & Co., Inc., U.S.A.) and cellulose acetate.

Sound recording wires are made by wire drawing magnetic alloys of magnetic substances such as iron, nickel, and cobalt or coating the surface of a non-magnetic wire with a thin film or magnetic alloy by a method such as electroplating, evaporation deposition, sputtering, or cladding.

In the memory devices such as magnetic drums and magnetic disks used in electronic computers, their magnetic recording mediums are also fabricated by methods similar in principle to the above mentioned conventional methods.

In the production of a magnetic recording medium by applying as a coating a known magnetic material ren- 'ice dered into a paint state as mentioned above, it is necessary, in order to increase the remanence (residual magnetism) by increasing of the degree of filling of the magnetic material, to use magnetic powder which has been rendered into extremely fine particles when preparing the magnetic paint and to carry out thorough mixing so as to obtain good dispersion of the powder in the binder resin and uniform surface finish. Moreover, the paint application also necessitates a complicated process requiring great care uch as spraying, use of a whirler, or electrostatic coating.

Even when such care is exercised in the preparation and application of the magnetic paint, evaporation of the organic solvent and gelatinisation of the binder resin tend to occur during paint application step or the heating and drying step and give rise to a thickness reduction phenomenon. As a result, uniform dispersivity of the magnetic material, fineness of the magnetic material, and uniformity of the finished thickness are impaired.

Consequently, there is a lack of uniformity of the internal magnetic field within the magnetic layer at the time of recording, and impairment of high-density recording such as causing of nonuniformity of demagnetisation occurs. For this reason, it has been the common practice in the production of the magnetic materials to carry out several repeated cycles of the paint application step and the drying step with the aim of attaining the above men tioned uniformity.

Furthermore, in the case of known magnetic recording mediums coated with a ferromagnetic alloy film as mentioned above, when this film is made thin so that it has a thickness of the order of a number of microns or some thousands of angstroms with the aim of preventing eddy currents and demagnetising fields and of increasing the unit of magnetisation within a unit volume, the formation of such a magnetic alloy film in a uniform manner is accompanied by various technical difficulties in actual practice. Moreover, since the magnetic coating is a thin film, several problems such as those relating to the adhesivity with respect to the substrate, the mechanical strength, and wear resistance of the film still remain to be solved.

SUMMARY OF THE INVENTION It is an object of the present invention to overcome the above described difficulties and provide a method of electrodepositing on substrates coating layers of greater uniformity and finer texture than those which can be deposited by known methods.

Another object of the invention is to provide a method of the above stated character which can be practiced by an extremely simple and rapid process by means of relatively simple apparatus.

The foregoing objects and other objects and advantages as will presently become apparent have been achieved by the present invention which, briefly summarised, provides a method for electrodepositing layers on substrate structures which is characterised by the steps of preparing an emulsion electrolyte by dispersing fine powder particles of a coating material (filler) in an aqueous solution having an anionic, polyvalent polyelectrolyte consisting of a resin component as its principal constituent, adapting a substrate structure to function as the anode in the emulsion electrolyte, applying an electrical potential across the anode and cathode thereby to cause the resulting mixture of coating material particles and high-polymer resin to be electrodeposited on the substrate structure, and drying the coating layer thus electrodeposited thereby to cause polycondensation of the coating high-polymer resin, the resin component thereof providing a film to function as a binder between the fine particles of the coating layer.

3 While, in the practice of the invention, the use of direct current as the process current produces amply satisfactory results, it is possible to carry out particularly effective.

electrodeposition through the use of a combined current consisting of a direct current and a current varying with time, such as alternating current, pulse current, highfrequency current, and pulses, superimposed on the direct current for reasons and in the manner as described hereinafter in detail with respect to electrodeposition of magnetic recording material.

The nature, principle, utility, and details of the invention will become more clearly apparent from the following detailed description, beginning with general considerations and concluding with specific examples of preferred embodiment of the invention, when read in conjunction with the accompanying drawing, in which like parts are designated by like reference numerals and characters.

BRIEF DESCRIPTION OF THE DRAWING In the drawing:

FIG. 1(A) is a schematic diagram illustrating one example of an electrical circuit for the practice of the invention;

FIGS. 1(B) and 1(0) are schematic diagrams respectively showing examples of modifications of the circuit shown in FIG. 1(A);

FIGS. 2 and 3 are fragmentary perspective views, with parts cut away, respectively showing two examples of magnetic recording mediums in wire or rod form fabricated in accordance with'the method of the invention; and

FIGS. 4 and 5 are fragmentary perspective views, with parts cut away, respectively showing two examples of magnetic mediums in sheet or tape form fabricated in accordance with the method of the invention.

DETAILED DESCRIPTION As a representative application of the present invention, one aspect thereof, that is, electrodeposition of magnetic layers of magnetic recording mediums on the substrates thereof is set forth in the following detailed description beginning with general considerations and concluding with specific examples of preferred embodiment of the invention.

The aforedescribed difiiculties encountered in the prior art can be overcome by the present invention providing, in one aspect thereof, a method which comprises preparing an emulsion by dispersing fine particles of a magnetic powder in an aqueous solution having an anionic polyvalent polyelectrolyte consisting of a resin component as its principal constituent, placing the substrate structure to be coated by electrodeposition as an anode in this emulsion, impressing a D-C voltage between the anode and the cathode thereby to electrodeposit on the substrate structure an electrically insulative mixture of the fine magnetic particles and the resin component, water washing the coating thus electrodeposited, subjecting the same to a drying process to cause the deposited resin component undergo polycondensation and solidification, and causing the resin component thereof to form directly a film as a binder between the fine magnetic particles.

In this manner, a magnetic electrodeposited layer of high uniformity and fine texture can be produced, whereby a magnetic recording medium having highly desirable characteristics can be obtained.

The above described method can be improved by superimposing a current to any desired magnitude which varies with time, such as an alternating current, a pulsating current, high-frequency current, or pulses, in addition to the electrophoretic energy of the anions toward the anode depending on the D-C potential gradient during the electrical power application for electrodeposition and carrying out the electrode-position while a component force for deflecting the electrophoretic direction of the anions or retarding the velocity thereof is applied. By this improved method, the process of depositing a uniform coating can be accomplished with further effectiveness.

By the method of the invention as described above for electrode-position of recording magnetic material, the resin component in the deposited coating can be polycondensed and solidified by merely drying the electrolytic emulsion after electrodeposition thereof on the substrate, and the resin component thereof directly undergoes complete gelation to form a solid film as a binder between the fine magnetic particles.

Accordingly, by introducing the coated substrate structure directly into a heat treatment vessel and drying the same or by pressing a heating jig with a mirror surface against the electrodeposited surface to cause it to form a solid film, it is possible to obtain in a very simple manner a smooth surface having uniform dispersivity and fineness of the magnetic material without carrying out, thereafter, surface finishing by a procedure such as lapping.

Furthermore, in the case wherein, for the electrodeposition current, a bias current which varies with time is superimposed on a direct current, the electrophoretic effect during electrodeposition is promoted, and the effectiveness in discharging and separating of substances such as cations, moisture, cationic impurities, and generated gases produced by the electrosmosis and electrodialysis effect and existing within the precipitated film is promoted, whereby effectiveness equal to or exceeding that of known applications such as repeated (secondary) painting and repeated electrodeposition is exhibited. Accordingly, the separated quantity per unit of electrical power can besubstantially increased to obtain an excellent coating film.

In the practice of the invention, moreover, by applying an external magnetic field on the anodic substrate on which the magnetic material is to be deposited and selecting the magnetic field direction so that a force component which draws the magnetic particles toward the anode side is created or so that the magnetic particles of the electrodeposited layer are magnetically orientated as desired, it is possible to promote the electrodeposition action or cause the electrodeposited magnetic layer to acquire magnetic axes as desired.

In this case, it is possible to impart the desired orientation in a smooth manner by further applying a deflecting magnetic field of a desired magnitude generated by an agency such as a current which varies with time to the external magnetic field which contributes to the principal orientation of the magnetic spin and imparting a starting moment to the magnetic spin. This method is, of course, similarly effective also in the succeeding drying step.

In the practice of this invention, the finer the magnetic particles to be mixed into the electrolyte are, the more effective they are in increasing the magnetisation unit number per unit volume of the finished magnetic layer, and an increase in the degree of filling of the magnetic particles in the magnetic layer causes an increase in the residual magnetism.

Heret-ofore, in the application of a magnetic layer as a coating on a substrate, the rapid evaporation of organic solvents has been considered to be a great problem. The deposited film formed in accordance with this invention, however, does not contain an organic solvent. Moreover, the solvent containing water as its principal constituent is separated out from this deposited film in the electrodeposition step, whereby the deposited layer is a so-called solid component of a resin component and filler in an unripened state.

Accordingly, in the drying step, the rate of thickness reduction is small, as mentioned hereinbefore, and the fine and uniform dispersivity of the magnetic material is excellent. Therefore, a uniform recording layer of good homogeneity of the magnetisation characteristic within the magnetic layer and excellent recording resolution can be produced.

In the practice of the method of fabricating an electrodeposition layer of a magnetic recording medium, magnetic oxides such as 'y-Fe o Fe O CrO and ferrite or magnetic alloys of metals such as iron, nickel, and cobalt are used in the form of microgranular particles for the fine magnetic particles. For the electrolyte, a natural or synthetic, anionic, polyvalent polyelectrolyte having as its principal constituent at least one resin such as a watersoluble alkyd resin, a water-soluble phenolic resin, or an acrylic resin is used.

For the substrate to be used in accordance with the invention for electrodeposition thereon of the magnetic material, any material which has electroconductivity to function as the anode Within the electrolyte can be used. For example,'metallic conductors such as pure metals and metal alloys, carbon, and semiconductors such as silicon and germanium can be used in any desired form.

However, in the case where a substrate material which readily forms an oxide film on its exposed surface, such as aluminium or chromium, or a metal which has been subjected to chemical surface processing is to be used as the anodic substrate, the surface of the substrate may be cleaned beforehand by a mechanical or chemical process prior to the electrodeposition step, Alternatively, the electrodeposition procedure may be carried out with a high voltage such as to overcome the electrical resistance of the oxide film.

It is possible, furthermore, to use poor conductors such as synthetic resins, cellulose acetate, and ceramics as the anodic substrate by coating them with a metal thin film.

An electroconductive substrate is effective in preventing accumulation of electrostatic charge in mediums such as recording tapes. In this case, however, depending on the necessity the conductive film of the substrate to be coated with the magnetic mixture is oxidised in the subsequent drying step or is heat teated in a manner such that fine cracks are formed by a cause such as condensation of conductive particles thereby to transform the entire film into a non-conductive film, whereupon the recording tape thus fabricated can be caused to have characteristics equivalent to those of conventional magnetic soundrecording tapes in which electrically insulative substrates are used.

One example mode of practice of the invention is indicated in FIG. 1(A). 'First, the example will be considered with the assumption that the inductance L, the capacitance C, and the A-C power supply shown in FIG. 1(A) do not exist. Then, an emulsion electrolyte 1 prepared by dispersing microgranular magnetic powder in an aqueous solution having an anionic, polyvalent polyelectrolyte as its principal constituent as described hereinbefore is placed in an electrodeposition bath vessel 2, and an anode 3 and a cathode 4 are placed in opposed positions in the electrolyte 1.

The anode 3 comprises an electrically insulative structure such as a synthetic resin or a ceramic and a coating on the surface thereof of a metal thin film deposited by evaporation deposition or some other suitable process, whereby the surface is rendered conductive. The cathode 4 is or ordinary type.

When a D-C current I from 'a D-C electric power source S is passed through the cathode 4 and the anode 3, a magnetic film is uniformly and finely electrodeposited on the surface of the anode 3, whereby this anode structure can be used as an excellent magnetic recording medium.

Next, an inductance L for cutting off alternating current, a capacitance C for cutting off direct current, and an A-C power supply A are connected as shown in FIG. 1(A), and electrodeposition is carried out efiiciently by superimposing an A-C bias current I on the aforementioned D-C current I whereupon a magnetic layer is deposited with even higher uniformity and fineness.

Circuits of further examples of apparatus which differ from that in FIG. 1(A), and in which use is made of a superimposed current of a direct current and a current 6 varying with time, e.g., an alternating current, are illustrated in FIGS. 1(B) and 1(C), in which reference numerals and characters 1, 2, S, and A designate parts equivalent to those of the same designations in FIG. 1(A).

The circuit shown in FIG. 1(B) is further provided with capacitors C for suppressing direct current, coils L for suppressing the AC component, and rectifiers 14 for selectively determining the direction of passage of the D-C component. The circuit shown in FIG. 1(C) is provided with a capacitor C having the function of waveform smoothing, resistances or impedances 16 and 17 for current adjustment, and rectifiers 15 for selectively determining the passage direction of the D-C component.

FIG. 1(A) illustrates an apparatus in which one anode and one cathode are used, but the same effect can be obtained by dividing each of these electrodes into two or more divisional electrodes. Examples in each of which two anodes 11 and 12 and a single cathode 13 are used are shown in FIGS. 1(B) and 1(C).

In order to indicate still more fully the nature and utility of the invention, the following examples of specific practice embodying the invention are set forth, it being understood that these examples are presented as illustrative only and that they are not intended to limit the scope of the invention.

Example 1 The apparatus illustrated in FIG. 1(B) was operated with an electrolyte prepared by mixing fine particles of 'y-Fe O a magnetic oxide, in a quantity of 15 percent by weight with a polyvalent polyelectrolyte of a watersoluble alkyd resin containing 10 percent of solids. Flat and smooth metal sheets each measuring 10 x 50 mm. and having a thickness of 0.25 mm. were used for the anodes 11 and 12 and placed in opposed positions spaced 40 mm. apart. The cathode 13 was disposed at a distance of 30 mm. from each of the anodes 11 and 12. With the above described apparatus and electrolyte and under the process conditions as set forth herebelow, the following results were obtained.

When electrodeposition was carried out by applying only a D-C voltage of 30 volts until completion of the electrodeposition on the anode surfaces, the layer thus deposited on each of the anodic substrates 11 and 12 had a film thickness of 10 microns.

Then, when a D-C voltage of 20 volts and an A-C voltage of 10 volts were similarly applied, the resulting layers had a film thickness of 13.5 microns. Furthermore, when a D-C voltage and an A-C voltage, each of 15 volts, were applied, a finished film of a l5-micron film thickness was obtained on each anode.

Thus, while each electrodeposition process is carried out with a total applied voltage of 30 volts, the electrodeposition efficiency in the case of superimposition of DC and A-C voltages is higher than that in the case where only a D-C voltage is applied. Moreover, by appropriately selecting the ratio of the A-C and D-C voltages, it is possible to produce an excellent finished film.

Example 2 The circuit indicated in FIG. 1(C) was operated with an electrodeposition bath vessel 2 provided with the same electrode organisation as that in example illustrated in FIG. 1(B) and with the same electrolyte as that specified in Example 1, that is, an electrolyte prepared by mixing 15 percent by weight of fine particles of 'y-Fe O with a polyvalent polyelectrolyte containing 10 percent of solids, the pH value of the electrolyte being approximately 7.

The operating conditions were as follows. A constant A-C voltage of 60 lvolts was applied continually by the power supply A. Then, by causing resistance 16 to be amply high relative to resistance 17 and suitably selecting the capacitance of capacitor C the ratio of the D-C component to the A-C component applied to substrate 11 or 12 which functions principally as the anode was caused to be 8:1, 4:1, 1:1, and 0.6:1, at each of which ratios the process current was passed for 10 minutes.

Each film thus electrodeposited on the substrates 11 and 12 was washed with water, dried, and heat treated to produce a finished film. The finished films thus produced with the above stated ratios had thicknesses of 20, 22, 30, and 40 microns, respectively. When the same applied potential was supplied by bnly an A-C component to carry out electrodeposition under conditions which were the same in all other respects as thoseset forth above, the thickness of the resulting film was only 11 microns.

As is apparent from the foregoing examples of practice, an appropriate selection of the D-C/A-C component ratio affords a remarkable increase in electrodeposition efiiciency per unit electrical quantity consumed relative to that attainable through the use of only a D-C power supply or an A-C power supply. Furthermore, in the case where there are additives dispersed in a high-polymer electrolyte, not only can the deposited coating quantity, i.e., the film thickness, be increased, but structural features such as external appearance and texture of the finished film can also be improved, and, moreover, higher adhesivity of the film with respect to the substrate and numerous other desirable features relating to electrical characteristics are afforded.

The method of the invention as described above can be carried out to produce various kinds of magnetic recording mediums, of which the most important are in the form of rods or wires and strips, sheets, or tapes as described below with reference to FIGS. 2, 3, 4, and 5.

In one example of such a recording medium as illustrated in FIG. 2, the substrate 5 is in the form of an electroconductive rod or wire completely sheathed therearound by a recording medium layer 6 in which a magnetic oxide is admixed, and which has been electrodeposited on the surface of the substrate 5 and dried. While this recording medium has an outer surface which is electrically insulative because of the high polymer functioning as a binder therein, it is also possible, in accordance with necessity, to apply a further protective coating layer 7 of an electrically insulative material.

In another example of a magnetic recording medium' fabricated by the method of the invention as illustrated in FIG. 3, at least one layer 8 (two layers in the example illustrated) of an Fe-Ni alloy is deposited by a suitable method on the surface of a non-magnetic, electroconductive substrate rod or wire 5. Then, on the outer surface of the outermost layer 8, a recording medium layer 6 having a magnetic oxide such as 'y-Fe O as its principal constituent is electrodeposited.

In this organization, a combination of a magnetic alloy core wire and a non-magnetic metal coating therearound can also be used as the substrate wire 5. In all cases, two or more composite laminations of magnetic materials having respectively different magnetisation characteristics are formed on and around the core wire 5. It is also possible to interpose or sandwich a non-magnetic metal layer in an intermediate position between these compound laminations.

The magnetisation characteristics of the composite magnetic laminations are so arranged that, for example, the intermediate layer or layers have characteristics similar to those of permalloys which have relative low values of coercive force H and a material of a magnetic characteristic with a high coercive force H is utilised in the outermost layer. In this manner, the magnetisation easy axes of the magnetic layers are all aligned beforehand in the same direction which is either in the Wire axial direction or the wire circumferential direction or are orientated in any desired angular direction. The coated wire thus produced can then be used as a wire memory constituting a non-destructive memory. (Reference: US. Ser. Nos. 471,589; 513,438; 515,310.)

The process of superposing a magnetic film of high coercive force in a composite manner on another magnetic film by only a procedure such as electroplating is accompanied in actualpractice by various difiiculties such as the necessity of high skill in adding a minute quantity of cobalt. By the method of the present invention, however, this process can be easily carried out. Furthermore, in this connection, an even greater effectiveness in improv ing magnetic orientation characteristic, that is the squareness (or square-loop property) of the 3-H characteristic curve of the finished electrodeposited layer can be attained by inscribing beforehand by a mechanical method fine scratches on the surface of the substrate structure in the desired magnetisation direction.

In the case of a conductive substrate structure in the form of a tape or sheet, fine particles of magnetic powder dispersed in a high-polymer resin can be electrodeposited as a magnetic recording material layer 6a on the surface on only one side of the substrate 5a as shown in FIG. 4. This may be accomplished by carrying out the electrodeposition with the other side (the side not coated) of the substrate covered by an electrically insulative layer 9.

In this electrodeposition step, it is possible, of course, to impart directivity to the magnetic characteristic of the electrodeposited material by causing the magnetic field due to the passage of the process current or an external magnetic field to act directly on the substrate. It will also be obvious that, in the case of a recording medium of a specific cross section, such as a wire or a tape, it is possible to form a closed magnetic circuit by electrodepositing a magnetic layer around the entire outer surface of the substrate structure.

When narrow tapes are to be produced, the electrodeposition may be carried out on a wide sheet, which can then be cut into narrow strips of the required width.

Another example of a magnetic recording medium of sheet or tape form according to the invention, as illustrated in FIG. 5, is fabricated by causing a metal thin film layer 10 to adhere by any suitable method to the surface of an electrically insulative substrate 5a such as a synthetic resin or a ceramic and, with this metal layer 10 as the anode, electrodepositing on only this layer 10 a magnetic film 6a.

In the case where a large number of separate magnetic tracks are to be formed on an article such as a drum or a flat plate in the electrodeposition of a magnetic recording material, the electrodeposition may be carried out with insulative layers deposited beforehand on the parts of the spaces between the magnetic tracks in accordance with the principal described above with reference to FIG. 5.

Furthermore, the method of the present invention can, of course, be applied to the fabrication of magnetic keepers in high-density memories. For example, electroconductive members in the form of wire or any other desired form may be provided beforehand between the bit storage points or between word storage parts, and then appropriate electrodeposition is carried out with respect to these members. Alternatively, magnetic layers may be formed by the method of the invention in the proximity of the required points on the upper surface or lower surface of all bit storage points forming the memory plane.

While the invention has been described above with respect to its application to principally electrodeposition of magnetic coating layers of magnetic recording medlums, the invention is not limited to this single application. The method of the invention can be similarly applied to accomplish effective electrodeposition of a wide range of coating layers containing fillers which have effects on electromagnetic, optical, and mechanical properties on materials or parts of various articles as, for example, automotive machines and equipment, electronic apparatus and devices, and components and parts thereof.

More specifically, examples of such fillers having effects on electromagnetic, optical, and mechanical properties are fine particles of such materials as electroconductors, magnetic materials, semiconductors, electrical insulators, dielectric materials, and luminous materials in photoelectric cells, photoconductive films, and EL luminescent materials. In particular, such luminous materials may comprise zinc sulfide and fluorescent material mixed with metal particles of, for example, aluminum and calcium. Fine particles of each of these fillers, or a mixture of fillers for a combination of characteristics, are dispersed in an aqueous solution having as its principal constituent an anionic polyvalent polyelectrolyte to form an emulsion.

With this emulsion as an electrolyte and the substrate article as the anode, a current is passed through the electrodes in the same manner as described herein above. This current is a direct current or a current resulting from the superimposition on a direct current of a current varying with time, such as an alternating current, a pulse, or a pulsive current. In this manner, a uniform and fine electrodeposited layer can be produced on the substrate article by the same principle as in the production of magnetic recording mediums.

Various applications are obviously possible for the above mentioned layers having combined characteristics. One example is a device fabricated by electrodepositing in accordance with the method of the invention a composite mixture layer of a dielectric material and a magnetic material on an electroconductive core wire. The dielectric material comprises, for example, barium titanate or titanium oxide, and the device including said composite mixture layer can be effectively utilised as a delay line element.

In the practice of this invention, the shape of the cathode is not limited to that of a fiat plate 'but may be any suitable form such as a net or lattice, a grid, or one or more bars. Furthermore, the cathode material may be one which is generally used in processes such as electrolysis and need not be limited to a specific material,

For the fine powder particles to be dispersed in the aqueous solution of the anionic, polyvalent polyelectrolyte, particles of any suitable material depending on the purpose of the electrodeposited layer can be used. For example, for electrodeposition coating of articles such as automotive equipment, a material of the water-soluble alkyd resins class or a material of the acrylic resin class used for this purpose, that is, for coating metal surfaces, is amply suitable. Furthermore, the particles to be added as a filler may also be a substance such as a colouring pigment generally used heretofore.

A further feature of this invention is that, in the practice thereof, it is also possible to move anodic substrate structures to be coated into and out of the electrolytic bath successively in a continuous manner 'by means of roller driving devices, winding and unwinding devices, and the like, or it is also possible to circulate the electrolyte. Furthermore, it is also possible, of course, to utilise the electrolytic bath vessel as the cathode.

I claim:

1. A method for producing magnetic recording mediums which comprises: preparing an electrolyte by dispersing fine magnetic particles, selected from the group consisting of 'y-Fe O Fe O and CrO and ferrite or magnetic alloys of metals such as iron, nickel and cobalt, in an aqueous solution having as its principal constituent an anionic, polyvalent polyelectrolyte consisting of a resin component; placing a cathode and a substrate structure as an anode in said electrolyte; passing an electric current through said anode and cathode to cause simultaneous electrodeposition of a mixture of said particles and resin component as a coating layer on said substrate structure; and drying said coating layer to cause said resin component to undergo polycondensation and solidification and to convert said resin component to a film providing a binder between said particles.

2. A method for producing magnetic recording mediums which comprises: preparing an electrolyte by dispersing fine magnetic particles, selected from the group consisting of 'y-Fe O Fe 0 and CrO and ferrite or magnetic alloys of metals such as iron, nickel and cobalt, in an aqueous solution having as its principal constituent an anionic, polyvalent polyelectrolyte consisting of a resin component; placing a cathode and a substrate structure as an anode in said electrolyte; simultaneously passing an electric current through said anode and cathode and subjecting said anode to an external magnetic field to cause simultaneous electrodeposition of an electrically insulative mixture of said particles and resin component as a coating layer on said substrate structure; and drying said coating layer to cause said resin component to undergo polycondensation and solidification and to convert said resin component to a film providing a binder between the fine magnetic particles.

3. A method for producing magnetic recording mediums as claimed in claim 2 in which said external magnetic field is applied in the direction in which the fine magnetic particles within the electrolyte are attracted to the anode.

4. A method for producing magnetic recording mediums as claimed in claim 2 in which said external magnetic field is applied in a direction such that a magnetic orientation in a specific direction is imparted to the magnetic particles within said coating layer.

5. A method for producing magnetic recording mediums as claimed in claim 2 in which said electric current passed through the anode and cathode is applied as a direct current.

6. A method for producing magnetic recording mediums as claimed in claim 2 in which said electric current passed through the anode and cathode is applied as a combined current consisting of a direct current and a current which varies with time and is superimposed on said direct current.

7. A method for producing recording mediums as claimed in claim 2 in which said external magnetic field is applied to impart a starting force component to the magnetic spin thereby to facilitate deflection.

8. A method for producing magnetic recording mediums as claimed in claim 4 in which a second magnetic field is applied during said drying step to impart a starting force component to the magnetic spin to facilitate defiection.

9. A method for producing magnetic recording mediums as claimed in claim 2, comprising the step of preparing said substrate structure by electrodeposition of a conductive coating of a metal thin film on a substrate material selected from the group consisting of synthetic resins, cellulose acetate, and ceramics, and performing said drying step after said deposition of said coating layer to form oxidation only on said conductive coating to convert said conductive coating to a non-conductive coat- 10. A method for producing magnetic recording mediums as claimed in claim 2, comprising the step of preparing said substrate structure by electrodeposition of a conductive coating of a metal thin film on a substrate material selected from the group consisting of synthetic resins, cellulose acetate, and ceramics, and performing said drying step after said deposition of said coating layer to form cracks only on said conductive coating to convert said conductive coating to a non-conductive coat- 11. A method for producing magnetic recording mediums as claimed in claim 2, in which said substrate structure comprises a non-magnetic electroconductive substrate having an Fe-Ni alloy deposited thereon.

12. A method for producing magnetic recording mediums as claimed in claim 11, in which said Fe-Ni alloy has a coating of a non-magnetic metal layer.

(References on following page) 12 References Cited 3,362,899 1/1968 Gilchrist 204181 UNITED STATES PATENTS 3,525,679 8/1970 WilCOX 61; 3.1. 204181 6/1947 Robinson et al. 204-1s1 X DANIEL -WYMAN, Primary Examiner 3/1956 McBride 204-181 X 5 W. J. SHINE, Assistant Examiner 11/1959 Satriana et a1. 204-181 Us. cl X.R- 10/1967 Matkan et a1. 204-181 117 235 240

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