Production of metal pattern containing fabric

Abstract

A flexible fibrous sheet material is provided, the component fiber units of which are electrically non-conductive and magnetically non-responsive, said material having discrete areas of electrically conductive or magnetically responsive patterns in which the fiber units from one surface through to the corresponding opposite surface of the material are coated with a film of electrically conductive or magnetically responsive metal. This material is useful by way of example only, for decorative purposes, as a flexible electrical circuit, as a magnetically responsive article such as one track or multi-track recording tape, as part of a capacitance circuit, as a convenient electrical contacting lead and circuit connecting part of a human body to a medical instrument such as an electrocardiac machine, and the like.

Parent Case Text

This is a division of application Ser. No. 28,912, filed Apr. 15, 1970, now abandoned.

Description

This invention relates to flexible fibrous sheet material provided with metallic electrically conductive or magnetically responsive elements, and to methods for producing same.

Fabrics of the aforementioned type are of course well known. Such fabrics can for example be prepared and are available which carry on one or both surfaces uniform or patterned layers of metal or metal-containing paint, varnish, lacquer or plastic and are decorative or useful as magnetic or electrical components such as a printed circuit or the like. Fabrics are also known which contain in the weave at intervals or in predetermined designs, metallic filaments or ribbons serving a particularly desired electrical function. These and similar products have however not been entirely satisfactory for a number of reasons including reduced flexibility inherent in their use of solid continuous metal ribbons, filaments and layers, filament to filament or yarn to yarn adhesion preventing free independent relative movement thereof, flaking or separation of metal or metal-containing layers from the surfaces of the base fabrics, accelerated breakdown of the metal ribbons, filaments and layers due to their relatively low fatigue strength under repeated bending and flexing conditions, inadequate recovery from deformative forces such as rolling, bending, creasing, squeezing, denting and crumpling, relatively high cost of making these products involved in special weaving requirements or large amounts of metal or the like, unduly high gross weight of these solid metal-containing products, and the like.

It is an object of this invention to provide a flexible fibrous sheet material provided with metallic electrically conductive or magnetically responsive elements which is not subject to one or more of the above disadvantages of defects. Another object of this invention is the provision of such a material which is substantially uniformly flexible regardless of the presence and/or location of the said metallic elements therein. Still another object is the provision of such a material which has a flexibility, drape, handle, feel, weight, and/or fatigue resistance substantially similar to the same material devoid of such metallic elements. A further object of this invention is the provision of such a material in which said metallic elements have improved properties with respect to permanence, resistance to fatigue, recovery from deformative forces, electrical conductivity, and/or magnetic response and the like. A still further object of this invention is the provision of such a material which is relatively economical and simple to make. Yet a further object is the provision of methods for preparing such material. Other objects and advantages will appear as the description proceeds.

The attainment of the above objects is made possible by this invention which includes the provision of flexible fibrous sheet material, the component fiber units of which are electrically non-conductive and magnetically non-responsive, said material having discrete areas or patterns in which the fiber units from one surface through to the corresponding opposite surface are coated with a film of electrically conductive or magnetically responsive metal. More particularly, the aforedescribed material of my invention possesses all or substantially all the characteristics referred to in the preceding paragraph as constituted the objects of such invention.

The component flexible fiber units of the fibrous sheet material employed in this invention may comprise, consist of, or be constituted by any fiber-forming or filament forming substance which is electrically non-conductive and magnetically non-responsive. The substance may be natural or synthetic, organic or inorganic monopolymeric, copolymeric (from two or more monomers), or mixtures of two or more prepolymerized monomers, admixed where desired with usual assistants, modifiers, softeners, plasticizers, colors, stabilizers, fillers, and the like. As examples of such fibrous substances, there may be mentioned silk, non-alkaline, boro-silicate and other silica glasses; filaments of synthetic organic polymers, copolymers and mixed polymers such as polyvinyl chloride, polyvinylidene chloride, vinyl chloridevinyl acetate copolymer, polyolefins such as polyethylene and polypropylene, polyacrylonitrile, modacrylics, acrylic and methacrylic acids and their methyl, ethyl esters, polyesters such as polyethylene terephthalate, polyurethanes such as spandex, linear superpolyamides such as nylon and polypyrrolidone, and mixtures and copolymers of the foregoing. A number of such fibers, filaments, and fabrics are commercially available as for example Vinyon, Saran, Velon, Dynel, Acrilan, Orlon, Dacron, and Terylene and the like.

The term "fiber unit" is intended to include the individual fibers and filaments, in addition to yarns, twisted and untwisted bundles of such fibers and filaments, all of which are used in forming the flexible fibrous sheet material employed herein. The sheet material may be fabricated in any desired manner as by weaving, knitting, and the like, and may of course include mixtures of fibers, filaments, yarns, and the like of differing polymeric basis as described above. The component fiber units may likewise comprise similar mixtures.

The fibers, filaments, component fiber units and sheet material containing which are employed in this invention are those well known and commercially available. Their structures, properties, chemical compositions, and the like are not critical and per se form no part of this invention. For example, the fibers and filaments may have any desired size and shape permitting the flexibility usual in such materials. They may have cross-sectional shapes which are symmetrical or unsymmetrical, circular, elliptical, flat, triangular, polygonal, multilobar, and the like, and range in thickness or diameter from about 0.5 denier or less to 10 denier or more, or from about 1 micron or less to 40 microns or more. They may be continuous filaments and the twisted or untwisted yarns or bundles containing them may comprise any number such as from 2 to 150 filaments or more in a cross-section, and range from 20 denier or less to 200 denier or more. Material fabricated from yarns and the like may have any desired knitted construction or weave such as plain, rip stop, twill, leno, and the like, and may have an open construction or relatively closed, dense construction, with a weight range for example of from about 0.1 oz. to 1 or more pounds per square yard, generally about 0.5 to 10 oz. per square yard, and preferably a relatively light weight close weave of about 1/2 to 3 oz. per square yard.

For most purposes contemplated herein, and for the desired properties of flexibility, durability, strength, weight, and metallization, woven fabrics made for continuous filament yarns having a basis of polyester, polyacrylonitrile, silk, glass, and optimally nylon, are preferred for use herein. In these fabrics, as in any of the other above described types of flexible fibrous sheet material employed herein, the component flexible fiber units are, as commonly available, substantially entirely unattached to, and free to move, roll or slide relative to the adjacent fiber units. Stated otherwise, the component fibers, filaments, yarns and the like in the material can move independently of each other, since they are not bonded or attached to each other by any means at their points of contact or intersection, being only constrained by the nature of the fiber unit structure or weave.

In accordance with this invention, the above-described flexible fibrous sheet material, the component fiber units of which are electrically non-conductive and magnetically non-responsive, is provided with discrete areas or patterns in which the fiber units from one surface through to the corresponding opposite surface of the material are coated with a film of electrically conductive or magnetically responsive metal. To retain the flexibility, feel, handle, and fatigue strength, and the like, of the product substantially uniform in both the coated and uncoated areas, the thickness of the continuous metal film is relatively small, such as from about 1 .times. 10.sup..sup.-6 to 40 .times. 10.sup..sup.-6 inches, preferably about 2 .times. 10.sup..sup.-6 to 6 .times. 10.sup..sup.-6 inches. Like the uncoated fiber units, the metal-coated fiber units are substantially entirely unattached to each other and are free to move, roll orslide independently of each other. The metal-containing patterns in the products of this invention are independent of the construction of the fibrous sheet material, i.e. whether it is knitted or woven, the direction, size or shape of the fiber units, etc. Otherwise stated, the lines of demarcation separating the metal-containing patterns or areas from the uncoated insulative portions of the material in substantially all instances cross fiber units whereby one segment or more of the crossed fiber, filament, yarn, etc. is coated with a film of the metal and lies within the metal-containing pattern, and the other segment of the same fiber unit is uncoated and lies outside said pattern and within the insulative portions.

The metal coating or film may comprise any normally solid film-forming metal since substantially all such metals have electroconductive or magnetically responsive properties to some degree. Thus, the metal may for example be silver, gold, platinum, palladium, copper, aluminum, nickle, cobalt, iron, titanium, molybdenum, chromium, tungsten, lead, tin, zinc, cadmium, manganese, antimony, germanium, indium, rhenium, ruthenium, rhodium, selenium, rare metals, and the like, and mixtures and alloys of any two or more thereof. In general, iron, cobalt, and nickle, and mixtures and alloys thereof, are preferred for magnetic properties, and gold, platinum, palladium, aluminum, copper, and especially silver, and mixtures and alloys thereof, are preferred for electroconductivity.

Several methods may be employed for making the metallized pattern-containing flexible fibrous sheet material of the present invention. The preferred method herein comprises removing the metal film coating from fiber units in only certain portions of one surface through to the corresponding opposite surface of a flexible fibrous sheet material, the component fiber units of which are electrically non-conductive and magnetically non-responsive and are coated with a continuous film of electrically conductive or magnetically responsive metal.

The foregoing method involves the use as a starting material of a flexible fibrous sheet material corresponding overall to the desired discrete metallized areas or patterns, i.e. in which all the component electrically non-conductive, magnetically non-responsive fiber units are coated with a continuous film of electrically conductive or magnetically responsive metal as described above. Such starting material, having electrical resistive values of about 0.01 to 500 ohms per square, and preferably about 0.5 to 5 ohms per square for optimum electroconductive purposes, is well known and commercially available. It may be prepared by methods which are also well known and disclosed in a number of patents and other publications, generally involving metallization treatment in known manner of an electrically non-conductive, magnetically non-responsive flexible fibrous sheet material to deposit the desired continuous metal film on the individual fiber units, or similar treatment of the component fiber units followed by fabricating the resulting metal-coated fiber units into a flexible fibrous sheet material.

Illustratively, reference is made to U.S. Pats. Nos. 2,511,472, 2,867,552, 2,896,570, 2,897,091, and 3,043,769 for disclosures of such metallization treatments of electrically non-conductive, magnetically non-responsive fibers, filaments, yarns, and fabrics. The surface metallization treatments disclosed in U.S. Pat. Nos. 2,862,783 and 3,014,818 may also be employed, but only for metallizing electrically non-conductive, magnetically non-responsive fiber units, and not the metal-containing fiber units disclosed in these latter patents. In general, these metallization treatments involve reduction of one or a mixture of salts or other reducible compounds of the selected metal ormetals, as deposited from an aqueous or organic solution thereof, in situ on the surface of the fiber unit or "gas plating" in which one or a mixture of heat-decomposable gaseous compounds of the selected metal or metals is thermally decomposed in situ on the surface of the fiber unit.

The removal of the metal film from the fiber units in those portions of the sheet material intended to be insulative, i.e. those portions other than the discrete areas or patterns in which the fiber units are metal-coated, is carried out by selectively treating such portions with a fluid which is a solvent for the metal. The particular fluid solvent employed in any specific instance will of course depend mainly on the metal to be removed or dissolved. Such solvents or metal strippers are generally liquid and inorganic, optionally with additives which may be organic, and are well known and commercially available. Routine reference to standard texts and literature sources will establish those operative for the specific metal to be removed, as for example the metal strippers and procedures described in the chapter entitled "Stripping Metallic Coatings" pages 507 to 517 of "Metal Finishing Guide Book 1968" published by Metals and Plastics Publications, Westwood, New Jersey, which disclosure is incorporated herein by reference thereto. In general, acids are operative as such solvents but for obvious reasons must be selected according to the metal to be removed. Thus, dilute nitric acid dissolves silver, copper, cobalt, iron and nickle; hot or concentrated sulfuric acid dissolves silver, copper, cobalt, aluminum, and palladium; and aqua regia dissolves gold and platinum.

The duration and temperature of the metal solvent treatment will of course depend on the thickness of the metal film on the fiber units being treated. Generally, temperatures from room temperature to about 90.degree.C. may be employed, higher temperatures in this range generally serving to accelerate the solvation process. For practical purposes, the duration should not exceed about 30 minutes in any particular instance, but should for most purposes be stopped when all the metal in the insulative portions has been dissolved. This is particularly important where the solvent, after removal of the metal film, will then proceed to attack the freshly exposed surfaces of the fiber units themselves, unless of course such attack is unobjectionable or even desired to the point of total destruction for certain usages.

Since for most purposes solvent attack on the fiber units per se is to avoided, and such attack on certain fibers by acids is often difficult to control, it is preferred to employ as the metal solvent or stripper an alkali metal, e.g. sodium or potassium, cyanide generally in the form of an aqueous solution ranging in concentration from about 0.5 to 10% by weight. Certain known assistants such as hydrogen peroxide, m-nitrobenzoic acid, sodium m-nitrobenzenesulfonate and the like, may also be added to the cyanide solution, generally in concentrations of about 0.1 to 10% by weight. The solvation process may be further expedited with respect to certain metals such as platinum and palladium by concurrent mild electrolytic action, as by connecting the portions of the metal coated fibrous material in contact with the solvent to a source of low voltage DC current, in a conductive, corrosion resistant metal tank connected also to the same source of low voltage DC current. It has been found that the above-described alkali metal cyanide metal stripping solutions are highly advantageous in expeditiously removing the metal film without undue deleterious effect on the fiber units per se under the usual solvent treatment conditions of temperature and duration.

Following are illustrative examples of some metal solvent or metal stripping solutions which may be employed in making the products of this invention as described above:

EXAMPLE A

NaCN or KCN -- 1 oz.

Water to make 1 gal.

Applied at 90.degree.-180.degree.F.

EXAMPLE B

NaCN or KCN -- 50 grams

Water to make 1 liter

Applied at 70.degree.-160.degree.F.

EXAMPLE C

NaCN or KCN -- 1 oz.

H.sub.2 o.sub.2 (30% conc.) -- 0.5% by volume

Water to make 1 gal.

Applied at 70.degree.-160.degree.F.

EXAMPLE D

NaCN or KCN -- 1 oz.

H.sub.2 o.sub.2 (30% conc.) -- 3% by volume

Water to make 1 gal.

Applied at room temperature to 70.degree.-160.degree.F.

EXAMPLE E

NaCN or KCN -- 50 grams

M-nitrobenzoic acid -- 50 grams

Water to make 1 liter

Applied at 50.degree.-70.degree.C.

EXAMPLE F

NaCN or KCN -- 50 grams

Sodium m-nitrobenzene sulfonate -- 50 grams

Water to make 1 liter

Applied at 50.degree.-70.degree.C.

The selective treatment of certain portions of the starting fibrous sheet material containing metal-coated fiber units with the metal stripping solvent so as to dissolve the metal only in such portions may be carried out in a number of ways, and by batch or continuous manner. For example, this objective may be accomplished by subjecting such portions to the action of a direct stream, jet or spray of the metal stripping solvent for a time sufficient to dissolve out the metal in said portions, preferably followed by a wash or rinse of such portions or of the entire material with water to remove all traces of metal compound, dissolved metal and metal stripping solvent. Complete removal can be established when such portions are determined by suitable electrical instruments or meters to be non-conductive.

According to another method, the treatment with the metal stripping solvent is confined to such certain portions by first providing the metal-coated fiber units in the remaining areas or patterns of the fibrous sheet material with a coating resistant to the action of said metal-stripping solvent, which latter coating is then preferably removed following said treatment.

The resistant protective coatings must be applied so as to coat the metal-coated fiber units in the areas or patterns desired to remain electrically conductive or magnetically responsive from one surface through to the corresponding opposite surface of the material. The metal stripping solvent can then be applied to the entire sheet material, as by dipping or the like, whereby the metal in the remaining unprotected portions of the material is dissolved and removed. If the metallized areas or patterns are required to be exposed, as in uses involving electrical contact with the surfaces thereof, the resistant protective coating is then removed as by treatment, by dipping or otherwise, with one or more volatile solvents.

According to a preferred method for the selective treatment of certain portions of the starting metallized fibrous material with the metal stripping solvent so as to dissolve the metal only in such portions, said treatment is applied to said starting material while it is compressed between solid plates provided with matching openings corresponding to such certain portions. The metal stripping solvent is thereby confined to, and can only contact, such portions of the material and is prevented by the plates from contacting the remaining areas or patterns required to remain metallized. The plates are preferably of rigid material resistant to the action of the metal stripping solvent such as steel, glass, plastic or the like, and provided with clamps or other means for tightly compressing the metallized fibrous material therebetween to minimize any possibility of seepage of said solvent edgewise into the portions of the compressed fibrous material adjacent the slots and outside edges of the plates. As further means for preventing such seepage, the inner surface of the plates contacting the compressed fibrous material are preferably resilient, as by being provided with thin layers of resilient synthetic rubber or closed foam plastic serving as gaskets. The entire assembly is then submerged in a bath of the metal stripping solvent, such as in Examples A-F above, until all the metal coating in the portions of the fibrous materiall exposed in the slots is dissolved. The assembly is then removed from the metal stripping bath, thoroughly washed with water and unclamped or dismantled.

The products of this invention are obviously useful for many electrical and magnetic purposes. Thus, the areas or patterns therein containing metal coated fiber units may define at least part of an electrically conductive circuit, or at least part of a capacitance circuit, or an antenna or dipole, or magnetically responsive elements or the like. Their peculiarly advantageous properties as described above render these products suitable for a number of novel uses. Thus, where the metallized pattern is in the form of an antenna of varying geometry such as a dipole or the like, the product can be invisibly incorporated into the lining of a curtain for location identification, or into the lining, label or other part of clothing apparel for discrete shoplifter identification as at the exits of clothing stores. The metallized patterns may be a series of separated 1 inch squares whereby the product can serve as part of a flexible invisible capacitance circuit. The product with a pattern in the form of a band or series of bands of electroconductive metal coated fiber units may constitute a convenient, confortable contact lead connecting part of a human body to a medical instrument such as an electrocardiac machine. Or it may serve as an electrical circuit incorporated into a performer's costume such as a dancer's skirt which could be electrified for low voltage lighting. Or it may serve as an electrical connection at the end of a flexible banner such as a fluttering, waving flag. Patterns in the form of parallel bands of magnetically responsive metal coating fiber units permit use as a novel type of multi-track recording tape.

The following examples are only illustrative of preferred embodiments of my invention and arenot to be regarded as limitative.

EXAMPLE I

A 3 1/2inch wide by 12 inch long sample of nylon cloth weighing 1 oz. per square yard and composed of 40 denier yarns of continuous filaments coated with a 2-5 .times. 10.sup..sup.-6 inch thick film of silver is tightly clamped between two 3 1/2 .times. 12 inch rigid steel plates each provided with three matching 1/2 inch wide by 11 1/2inch long slots or openings spaced equally across the width and length of the plates. The unslotted inside surfaces of the plates adjacent the compressed cloth are each provided with a 5 mil thick layer of neoprene rubber acting as a gasket preventing seepage of metal stripping solvent edgewise between the plates into the areas of compressed cloth adjacent the open slots and outer edges of the plates.

The entire clamped assembly is then submerged into a KCN metal stripping bath as in Example A above at about 120.degree. F. for about 4 minutes with agitation of the bath and/or assembly until all the silver coating in the portions of the cloth exposed in the slotted openings is removed by dissolution.

The assembly is then removed from the bath, thoroughly washed with watter and unclamped or dismantled. The product corresponds to the starting silvered cloth except for three equally spaced 1/2 inch wide by 11 1/2inch long desilvered electrically non-conductive bands corresponding to the slots in the plates. The 1/4 .times.3 1/2 inch strip of silvered cloth between the ends of the non-conductive bands and the edges at each end of the cloth is cut away, leaving a pattern of four parallel 1/2 inch wide silvered electrically conductive bands insulated from each other by the three desilvered bands. If desired, the plates could be so constructed as to directly produce the same banded article without requiring subsequent cutting away of the two ends.

The article as produced above may be employed as part of an electrical circuit, for example as a human contact lead connected to an electrocardiac or other medical instrument, or as a feed or control component of an electronic information storage or retrieval machine. In the above mentioned use as a human contact lead, the said article provides the warm, non-metallic feel of a soft, comfortable bandage as opposed to the cold, relatively rigid metal cable leads presently used. A similar article containing iron, nickel and/or cobalt instead of silver is useful as a flexible magnetic recording tape or other recording component of a magnetic memory device.

The foregoing description and working example are concerned with a generally preferred method of producing the metallized pattern-containing products of this invention involving selective removal of the metal film coating from certain portions of a fibrous sheet material in which all the fiber units are coated with a metal film. The reverse procedure may also be employed for making the products of my invention, involving direct metallization of discrete areas or patterns of an unmetallized fibrous sheet material.

More particularly, such direct metallizing method comprises coating, with a substantially continuous film of electrically conductive or magnetically responsive metal, the fiber units from one surface through to the corresponding opposite surface in discrete areas or patterns of a flexible fibrous sheet material, the component fiber units of which are electrically non-conductive and magnetically non-responsive. This method obviously avoids a metal stripping step as described above.

Confinement of the direct metallizing treatment to the desired discrete areas or patterns may preferably be accomplished along the lines illustrated in Example I above, for example by compressing a similar but unmetallized sample of nylon cloth between the same slotted plates, and then subjecting the entire assembly to any known metallization treatment as described above, such as by reduction of one or a mixture of salts or other reducible compounds of the selected metal ormetals on an aqueous or organic solution thereof, or preferably by "gas plating," i.e. by thermally decomposing one or a mixture of heat-decomposable gaseous compounds of the selected metal or metals in situ on the surfaces of the fiber units in the exposed slotted areas of the assembly.

References in the foregoing descriptions to the metal film coatings in the discrete areas or patterns of the products of this invention as continuous or substantially continuous will be understood as including coatings at least sufficient to provide an uninterrupted electrically conductive metal path along the length of the fiber unit. In most instances, the film forms a continuous coating on the entire surface of the fiber unit except for minute holes, cracks, etc. inherent in the metallization process. A relatively thin metal film is necessary to maintain flexibility and avoid the cracking, breaking and other permanent deformational effects to which thicker metal films and solid metal filaments (including wires) and layers are prone.

As illustrative of a further utility of products of the type produced in Example I above, such products can be adapted for use as and/or in place of electrically conductive components of pressure operable switches disclosed and claimed in U.S. Pat. Nos. 3,056,005 and 3,308,253.

This invention has been disclosed with respect to certain preferred embodiments and it will be understood that various modifications and variations thereof will become obvious to persons of ordinary skill in this art which are to be included within the spirit and purview of this application and the scope of the appended claims.

Claims

I claim:

1. A method comprising treating a flexible fabric woven with yarns composed of electrically non-conductive and magnetically non-responsive continuous filaments individually coated with a flexible, substantially uniform and continuous about 1 .times. 10.sup..sup.-6 to 40 .times. 10.sup..sup.-6 inch thick film of electrically conductive or magnetically responsive metal to remove the metal film coating from all the filaments in only certain portions of one surface through to the corresponding opposite surface of the fabric by treating said certain portions with a solvent for said metal film coating.

2. A method as defined in claim 1 wherein said treatment is applied to the metal-coated fabric while it is compressed between solid plates provided with openings corresponding to said certain portions whereby said solvent is prevented from contacting the remaining areas or patterns.

3. A method as defined in claim 2 wherein the surfaces of the solid plates facing and contacting the fabric are resilient.

4. A method as defined in claim 2 wherein said solvent is an aqueous alkali metal cyanide solution.

5. A method as defined in claim 4 wherein said filaments comprise nylon, polyethylene terephthalate, polyacrylonitrile, silk or or glass.

6. A method as defined in claim 5 wherein said metal is silver, gold or platinum.

7. A method as defined in claim 6 wherein the surface of the solid plates facing and contacting the fabric are resilient.

8. A method as defined in claim 4 wherein said filaments comprise nylon.

9. A method as defined in claim 8 wherein said metal is silver.

10. A method as defined in claim 9 wherein the surface of the solid plates facing and contacting the fabric are resilient.