|Publication number||US2211584 A|
|Publication date||Aug 13, 1940|
|Filing date||Oct 9, 1937|
|Priority date||Oct 9, 1937|
|Publication number||US 2211584 A, US 2211584A, US-A-2211584, US2211584 A, US2211584A|
|Original Assignee||Ruben Samuel|
|Export Citation||BiBTeX, EndNote, RefMan|
|Referenced by (10), Classifications (10)|
|External Links: USPTO, USPTO Assignment, Espacenet|
Aug. 13, 1940. Y s. RUBEN 2,211,584
COAXIAL ELECTRICAL CONDUCTOR I 7 Filed Oct. 9, 1937 x g I 42 Condunlfwe coazfz g INVENTOR Jamaal Fam' ATTORNEY Patented Aug. 13, 1940 UNITED STATES PATENT OFFICE 9 Claims.
This invention relates to coaxial electrical conductors.
An object of the invention is to provide improved flexible coaxial conductors.
A further object is the provision of a unitary structure comprising an insulated conductor having a flexible conductive sheath over the insulating surface.
A further object is the provision of a coaxial ,cable having a central insulated conductor and 'a second conductor of finely divided metal bonded to the surface of the insulation.
Still another object is the provision of coaxial conductors in which one of the conductors comprises finely divided metal rendered conductive in place upon an insulated conductor. 1
Another object is the provision of a method for applying a conductive surface to an insulated wire.
Other objects will be apparent from the disclosure and from the drawing in which:
Fig. 1 illustrates a method and apparatus for providing a coaxial conductor on an insulated wire, and v Fig. 2 is a view in perspective, partially cut away, of a coaxial conductor showing the central conductor core, the insulation and a second convaporized metal is sputtered upon the insulator ductor over the insulation.
The invention comprises the use of a conductive base, such as a copper wire, an insulation on said wire, such as enamel, rubber, etc., and a coating of finely divided metal held on said insulation by a binder, the metal particles being normally non-' conductive, due to inter-particle contact resistance, and a method for eliminating the interparticle resistance and rendering the finely divided metal conductive over the entire surface. The
,metallic conductive coating produced thereby may be further improved by electro-plating or electrodepositing of additional metal thereon.
Heretofore several methods have been used to provide electrically conductive coatings on insulating or high resistance bases. By one method atomized metal is sprayed onto the insulator surface by a Schoop gun. By another method surface. Such methods are expensive inasmuch as they require the use of hydrogen, vacuum or inert atmospheres and the coatings produced are in a great many cases unsatisfactory due to rigidity and lack of uniformity. Another method,
much used, is to graphitize the non-conductive surface and electroplate a metal over the graphite. While for a number of uses this method is ffsatisfactory, the specific resistance of thecarbon or graphite is so high as to preclude the initial use of high current densities in the electro-plating process. In addition, as the graphite is not bonded to the insulator, peeling sometimes results with consequent dislodglng of the plated 5 metal film.
The coating produced by my present method results in a low resistance surface, the conductivity of which closely approximates that of metal foil.
In an endeavor to produce a coaxial cable utilizing an insulated wire and an auxiliary or second conductor over the insulation which would be free of the limitations heretofore encountered in the art, I have found the following:
If the insulated wire is coated with a thin layer of metal powder, such as copper bronze powder, even though a very small amount of binder is used, insufficient to completely surround the particle surfaces, the coating is practically non- 20 conductive, the resistance being of an unusably high value. This high resistance I have discovered is due to the additive effect or sum of the high contact resistance which exists between the particles. Further, I have discovered that the 25 non-conductivity or high resistance of these coatings of copper or copper alloys, such as bronze powder, is apparently due to a superficial layer of cuprous and other oxides on the surfaces of the particles and that if this oxide layer is re- 30 moved as by reducing and dissolving the cuprous oxide, the inter-particle contact resistance is eliminated and a highly conductive surface is obtained. One method is to coat the insulated wire with copper bronze powder to a thickness of 3 about mil, using a quick drying binder, such as a solution of 2 ounces of nitro cellulose in one gallon of amylacetate. This solution forms a porous skin between the particles and allows them to be treated. After the coated film is dried it is exposed to a strong solution of hydrochloric acid, then washed in hot water to remove excess acid or by-products and thereafter dried and heated to eliminate any absorbed moisture or 45 methacrylate, etc.
acid, other solutions may be used, for instance, mercurous chloride, mercurous nitrate, hydro- ,fiuoric acid or lactic acid. However, the hydrozchloric acid gives the best results and is preferred.
5 Where mereurous chloride or mercurous nitrate are used, a slight amalgamation takes place between the bronze and the mercury, in addition to the reducing or dissolving action effected.
I have also'found it possible to eliminate the metal powder interparticle resistance by exposing the coated wire to the vapors given off by warm hydrochloric acid. This is readilyaccomplished by passing the wire through a closed chamber above a vessel containing heated hydrochloric acid, the reducing or dissolving action being due to the hydrogen chloride gas derived from the acid. After the exposure which may be from one to five minutes, depending upon the temperature of the acid, the wire is heated to bring about a further reduction in resistance and drive off any surface absorbed gas or vapors.
The co-axial conductors thus produced are suitable for many uses. However, in order to minimize abrasion effects, facilitate soldering and reduce the possibility of corrosion I prefer to electro-plate a film of metal over the coated bronze surface. This may be readily accomplished at a higher current density than is possible in the electro plating of metals upon graphitized or carbonized surfaces, the low resistance of the sprayed surface making the immediate use .of high currents practicable. In part, this superiority to the usual carbon or graphite surfaces heretofore used is due to the more intimate binding of the conductive particles to the insulation,
the water-proof character of the bronze coating and its lower resistance. Any of the commonly used plating metals may be employed, for instance, copper, chromium, tin, cadmium, lead,
49 etc. While I have found a solution of 2 ounces of nitro cellulose to one gallon of amylacetate to be a very satisfactory binder, other materials may be used, such as shellac, glyptal, meta The amount of binder used should be limited so as not to form a complete physical insulating layer around the particles, but sufficient to firmly hold the metal particles upon the insulation. In practice, I have used a 50 mixture consistingof 2 ounces of nitro cellulose -In order to more completely describe the inv vention, reference is made to the drawing.
In Fig. 1, enamel or rubber covered copper wire is passed into vessel 2, containing finely divided bronze suspended in asolution of nitro cellulose amylacetate 4. The bronze coated wire passes via pulley 3, up through heated dryer 5, via pulley 6, into vessel I, containing hydrochloric acid 8, which reduces the inter-particle resistance. The treated wire then passes via pulley 9, around pulley III, into vessel containing water I2, a fresh supply of water being continuallymaintained through inlet I4, and outlet IS. The washed wire then passes via pulley. l3, up
through heater and dryer l6, which drives out 1' any residual water or acid and thereafter passes via pulley II, into plating tank I8, containing cadmium plating solution I9, and cadmium electrode 20. The plating potential is supplied by battery 3|. The plated wire then passes via pulley 2| to metallic roller 22, which is connected to one side of battery 3|, and thereafter passes into vessel 23, containing water wash 24, a fresh supply of water being maintained through inlet 26 and outlet 21. After this final wash the wire \is passed up through heater and dryer 28, and over top roller 29, to be wound ready for use on mandrel 30,
In Fig. 2 copper wire I, is shown with enamel varnish insulation II, and top metal coating 42, corresponding to the condition of the wire as it is rolled on to mandrel 30.
It is apparent that rubber covered wires containing two or more insulating layers and two or more conductors in a single casing can also be produced by this method using the conductive sheath as a shield, ground or common return conductor for all of the enclosed wires.
The coating produced by the above method is highly conductive, flexible, adherent and well bonded to the insulation.
Having described my invention, what I claim as new and desire to secure by Letters Patent, is:
1. Coaxial electrical conductors comprising a conductor core, an insulated coating thereover and a conductive coating thereon of copper bronze metal particles bonded to said insulation by an organic binder, said particles having initially high resistance surface layers of superficial thickness so that said coating is substantially non-conductive along its length, said high resistance layers being chemically reduced in situ on said base insulation to a highly conductive state.
2. Coaxial electrical conductors comprising a conductor core, an insulating coating thereon and an electrically conductive surface bonded thereto comprising copper base metal particles and a waterproof organic binder, said surface being initially characterized by high inter-particle contact resistance at the particle interfaces so as to make said surface non-conductive along its length, said high contact resistance being eliminated by chemical reduction at the particle interfaces in situ on said base insulating coating, and a metal layer electroplated upon said particles.
3. The method of adding a conductive surface to an insulated wire which comprises coating said insulated wire with copper-bronze particles and a carrier therefor adapted to permanently bond said copper-bronze particles to said insulated wire, said copper-bronze particles having normally a high resistance layer of superficial thickness at the surfaces thereof, subjecting said coated insulated wire to the action of a reducing acid capable of reacting withcopper-bronze particles to convert said high resistance surfaces to a conductive state.
4. The method of adding a conductivesurface to an insulated wire which comprises coating said insulated wire with copper-bronze particles suspended in a carrier adapted to permanently bond said copper-bronze particles to said insulated wire, subjecting said coated insulated wire to the action of an acid in vapor form capable of reacting with said bronze particles to convert the initial high resistance surfaces of said bronze particles to a conductive state, heating said treated coated insulated wire to drive off acid vapor and moisture and thereafter electroplating another metal layer upon said coated insulated wire,
5. Themethodof adding a conductive surface to an insulated wire which comprises coating said I insulated wire with finely divided copper base particles and a permanent organic binder, drying said coating upon said insulated wire, said coating being characterized by high contact resistance at the particle interfaces, reacting hydrochlorlc acid with said interfaces to bring about high inter-particle conductivity.
6. The method of producing a conductive surface upon an insulated wire which comprises applying to an insulated wire a coating of finely divided copper bronze powder and a permanent organic binder therefor, said coating being substantially non-conductive along its length due to high resistance between the bronze particles, subjecting said coating to the action of hydrochloric acid in vapor form to reduce said inter-particle resistance and causing said coating to become conductive along its length.
7. The method of producing a conductive surface upon an insulated wire which consists in applying acoating of powdered copper bronze and a permanent organic binder to an insulated wire, said coating'at this stage being substantially non-conductive along its length, and thereafter subjecting said coating to the action of hydrochloric acid to cause said coating to become conductive along its length.
tion of a reducing acid to convert initial high resistance surfaces of said bronze particles to a conductive state.
9. An electrical conductor comprising a highly conductive metal core, an insulating coating and an electrically conductive surface bonded thereto comprising copper-base metal particles and a water-proof organic binder, said surface being initially characterized by high inter-particle resistance at the particle interfaces so as to make said surface nonconductive along its length, said high contact resistance being eliminated by chemical reduction at the particle interfaces in situ on said base insulating coating and a metal I layer electroplated on said particles.
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|U.S. Classification||174/102.00C, 205/917, 336/84.00R, 427/118, 205/138, 427/123|
|Cooperative Classification||Y10S205/917, H01B11/1817|