US2523037A - Method of making an organopolysiloxane insulated copper conductor - Google Patents

Description

Sept. 19, 1950 MATHEs 2,523,037

METHOD OF MAKING AN ORGANOPOLYSILOXANE INSULATED COPPER CONDUCTOR Filed Aug. 5. 1946 I COPPER CONDUCTOR Z HYDRDCARBON -5UB5T/TUTED POLYSILOXANE RESIN 4 SYNTHETIC RESINOUS INSULATION e g.,A MfiD/F/ED POLYV/NYL ACE T'AL RES/Iv 5 AWN-CONDUCTING POWDER Irwvamborw Kehneth N. M abhas,

by M (EFL/J Patented Sept. 19, 1950 METHOD OF MAKING AN Ol tGANOPOLY- SILOXANE INSULATED COPPER CON- DUCTOR Kenneth N. Mathel, Schenectady, N. Y., assignor to General Electric Company, a corporation of x New York Application August 3, 1946, Serial No. 688,319

3 Claims. (Cl. 117-29) This invention relates to electrical conductors and to methods of making the same. More particularly, the invention i concerned with an insul'ated metallic electrical conductor comprising (1) a core of metal, e. g., copper, (2) an outer sheath comprising a synthetic resinous insulation material, (3) an inner sheath comprising an organopolysiloxane resin (for brevity hereinafter denoted as the polysiloxane resin"), for example, a curable hydrocarbon-substituted polysiloxane resin, and (4) a substantially nonconducting preferably a non-hygroscopic, pulverant material (or powder) disposed on the organopolysiloxane resin intermediate this resin and the synthetic resinous insulation of (2), i. e., contacting both the inner and outer sheaths.

One of the objects of this invention is to prepare an insulated metallic conductor (e. g., insulated copper wires, insulated copper bus bars, etc.), which has good heat-stability and, in addition, good abrasion resistance and chemical resistance.

Another object is to effect wetting of organetion sheath. Disposed on the polysiloxane resinous sheath is a substantially non-conducting powder 3 which is disposed upon the polysiloxane resin and which is intermediate this latter resin and the synthetic resinous insulation 4 positioned in the form of an outer sheath.

Organo-substituted polysiloxane resins, e. g., hydrocarbon-substituted polysiloxane resins, including the thermoplastic and potentially thermosetting or heat-hardenable resinous types, because of their outstanding heat resistance, are admirably suited for insulating electrical conductors which maybe used in electrical equipment ordinarily expected to operate at elevated temperatures. However, great diiliculty has been encountered in the use of the organo-substituted polysiloxane resins for insulation purposes due to the inferior abrasion resistance of the polysiloxane resin. Attempts have been made to apply other more abrasion-resistant organic synthetic resinous materials as outer protective sheaths for the polysiloxane resin sheath. However, these attempts have not been successful bepolysiloxane resins with other organic resinous materials and to improve the adhesion of a coating of a synthetic resinous insulation material to a coating of an organopolysiloxane resin previously applied to an electrical conductor.

A further object of this invention is to make a copper electrical conductor having an inner sheath of a heat-resistant organopolysiloxane resin, e. g., a hydrocarbon-substituted polysiloxane resin, and an outer sheath of a synthetic resinous insulation material, e. g., a modified or unmodified polyvinyl acetal resin, which is strongly adherent to the under-coating of the polysiloxane resin and which imparts good abrasion resistance to the conductor. In one of the more specific embodiments of my invention, the organo-substituted polysiloxane resin is disposed directly on the copper core.

The novel features of my invention are set forth in the appended claims. The invention itself, however, will be understood more readily from the following description when considered in connection with the accompanying drawing in which the two figures disclosed therein consist of a partly sectional longitudinal view (Figure .1) of an insulated electrical conductor embodying the invention and a cross-sectional view (Figure 2) of the same conductor. there is disclosed a copper conductor I on which is present a sheath of an organopolysiloxane resin, e. g., a hydrocarbon-substituted polysiloxane resin 2, acting as the heat-resistant insula- In these figures.

cause up until now it has not been possible to induce the usual organic resins with which it is desired to coat the pohrsiloxane resin, to "wet" the latter sufllciently to form a continuous, homogeneous, tightly adherent outer sheath.

The term "wetting as applied herein is intended to mean the ability of an organopolysiloxane resin-coated electrical conductor to be led through a bath containing, e. g. a solution of another synthetic resinous material (other than a polysiloxane resin), thereby to deposit on the organopolyslloxane coating an outer sheath of the other synthetic resinous material which is homogeneous, continuous, adherent and even. Ordinarily, polysiloxane coatings cannot be "wet" by other synthetic resinous materials because the latter, when in solution form or in molten form, drain from the surface of the polysiloxane resin leaving bare uncovered spots thereon.

I have now discovered that copper conductors provided with a sheath comprising a polysiloxane resin, (e. g. a curable polysiloxane resin: 1. e., a polysiloxane resin capable of being advanced to a greater degree 01' condensation by the application of heat or rendered substantially insoluble and infusible by said heat) can be further coated with organic varnishes containing other synthetic resinous insulation materials to yield surfaces having high mechanical toughness not obtained by the use of the polysiloxane resin alone as a sole insulation. I have also found that by means of my invention, the polysiloxane resin can be coated with the organic varnishes to yield films which act as though they actually "wet the polysiloxane resin to form a continuous, homogeneous even, adherent sheath around the inner polysiloxane resin sheath. In accordance with my invention I obtain the foregom desirable results by (1) coating the copper conductor with a polysiloxane resin, e. g., a hydrocarbon-substituted polysiloxane resin, (2) dusting or disposing a substantially non-conducting pulverant material on the said coated copper conductor to lay down a homogeneous layer of the pulverant material, and (3) applying an adherent Outer coating or sheath of a synthetic resinous insulation material to the dusted copper conductor. The presence of the powder on the polysiloxane resinous coating acts as an anchor for attaching the outer sheath of the other synthetic resinous insulation material.

Various non-conducting powdered materials may be used for dusting or disposition on the polysiloxane resinous sheath. These include for instance, siliceous powdered materials, e. g., ground mica, talc, flint, silica, powdered glass, etc. Although any finely divided or powdered non-conducting material may be employed, I prefer to use inorganic materials which are substantially insoluble in water, non-hygroscopic, and are substantially non-conducting electrically.

The outer sheath may comprise any of the usual synthetic resinous insulation materials ordinarily employed in the art for coating electrical conductors, especially those which are tough, abrasion-resistant, and flexible. Among these synthetic resinous insulation materials there may be mentioned, e. g., the thermoplastic types, for instance, polyvinyl acetal resins (modifled or unmodified), e. g., polyvinyl formal resins. polyvinyl butyral resins, etc. cellulose ethers and esters, e. g., ethyl cellulose, cellulose acetate, cellulose acetobutyrate, etc.; superpolyamide resins, commonly known as nylon; polyethylene, etc.; the potentially thermosetting or heat-hardenable resins, e. g., modified polyvinyl acetal resins, e. g.,

polyvinyl formal resins modified with heat-hardenable resins, e. g., heat-hardenable phenol-aldehyde or cresol-aldehyde condensation products, such modified resins being more specifically disclosed in Jackson and Hall U. 8. Patent 2,307,588, issued January 5, 1942; superpolyamide resins modified with heat-hardenable resins, e. g., heathardenable phenol-aldehyde and cresol-aldehyde condensation products, such modified resins adaptable for use in coating electrical conductors being more specifically disclosed in Smith and Jackson U. S. Patent 2,271,233, issued January 27, 1942, both of the two aforementioned patents being assigned to the same assignee as the present invention; phenol-aldehyde resins modified with unsaturated alkyd resins; phenol-aldehyde condensation products modified with various oils, e. g., drying oils, compatible therewith, for instance linseed oil, China-wood oil, etc.; modified melamine-aldehyde resins, e. g., alkyd-modified melamine-aldehyde resins, especially the alkydmodified melamine-aldehyde condensation products modified with drying or non-drying oils, etc.

The polysiloxane resins employed for the inner sheath of the copper conductor may generally be considered to fall into two categories: the thenmoplastic type and the potentially thermosetting or heat-convertible type. Itwill, of course, be appreciated by those skilled in the art that in many cases the line of demarcation between thermoplastic and potentially thermosetting resins 4 will often be quite indistinct since, by applying sufficient heat, it is possible to convert so-called thermoplastic polysiloxane resins to polysiloxane resins having the characteristics and properties similar to the heat-converted or thermoset polyslloxane resins.

When choosing the type of polysiloxane resin to be used for the inner insulation sheath, it is desirable that the polysiloxane resin have an average of from about 1 to 2, preferably 1.2 to 1.8, hydrocarbon groups present for each silicon atom. Stated alternatively, the organo-siliooniorganopolysiloxane) resins may be considered as organic derivatives of ortho silicic acid. The monomers may be considered as ortho silicic acids with one or more hydroxyl groups replaced by organic radicals such as alkyl, aryl, aralkyl, alkaryl, etc., and are prepared, e. g., by hydrolysis of organo-silicon halides. Upon dehydration of the so-called monomers, poly-condensation occurs which yields resins of varying degrees of hardness. These resins may cure under the influence of elevated temperatures with or without cure accelerators (catalysts) to produce insoluble, infusible products or thermoplastic, tough resinous products. More specific directions for the preparation of these resins may be found in Rochow U. S. Patents 2,258,218 to 2,258,222, all of which patents are assigned to the same assignee as the present invention.

In the preferred embodiments of this invention, considering the organopolysiloxane resin (organosilicon resin) as a derivative of ortho silicic acid, organo-silicon resins are employed in which an average of from about 1 to 2, preferably 1.2 to 1.8, hydrocarbon groups (e. g., methyl, ethyl, phenyl, benzyl, tolyl or total methyl and phenyl groups) have been substituted on the ortho silicic acid. If more than an average of 1.5 hydrocarbon groups are substituted on the ortho silicic acid, the resulting resins tend to be tougher and more thermoplastic than those having a smaller average number of substituents, whereas resins in which the average of hydrocarbon groups is less than 1.5, e. g., from about 0.5 to 1.3 or 1.4, may be cured to the substantially insoluble and infusible state.

Each insulation sheath, both inner and outer, may be applied by methods now well known in the art. For example, the polysiloxane resin may be dissolved in a suitable solvent, for instance, a hydrocarbon solvent, e. g., toluene, or a hydrocarbon and another solvent, e. g., toluene and n-butanol, and thereafter the copper conductor is passed through or dipped in the resinous solution containing the polysiloxane resin. .At this point the resinous film on the conductor may be rendered less tacky by passing the coated conductor for a short time'through a heated zone maintained at an elevated temperature of the order of, e. g., from about C. to a maximum of 450 C. This heat treatment which obviously advances partially the cure of the polysiloxane resin, drives off some of the residual solvent, allows better adhesion of the powdered substance to the polysiloxane resin, and enables the particles of powder to remain on the surface of the polysiloxane resin rather than permit the particles to sink too deeply into the polysiloxane coating.

After coating the conductor with the polysiloxane resin, the conductor may then be led into a pulverant material (powder) applicator of any desired type, or the powdered substance may be blown onto the coated conductor, e. g.,

asaaoa'r by suitable mechanical means, or may be applied with a cloth containing the pulverant material in dry powder form. The dusted polysiloxane resin-coated electrical conductor is then preferably passed through a heated zone (graduated, e. g., from about 50 C. to 400 C.) which drives off the remaining solvent and condenses (advances) the polysiloxane resin to the desired state, thereby firmly afilxing the pulverant material securely to the surface of the organopolysiloxane resinous sheath.

Thereafter, the conductor may be led into a tank containing a solution of the synthetic resinous insulation material to be used as the outer sheath. The constitution of the solution in this case will depend on such factors as the type ,pf synthetic resin employed, type of solvent, thickness of the film desired to be deposited on the coated and dusted conductor, etc. After this operation, the finally coated conductor is preferably passed through another heated zone, e. g., an oven heated at a temperature of, e. g., from about 100 C. to a maximum of about 350 C. By means of this final heat treatment, substantially all the last traces of residual solvent are driven from the resins comprising the inner and outer sheaths, and, in addition, the heat-convertible or potentially thermosetting resins are converted to the substantially infusible and insoluble state.

More specific directions for passing a coated conductor, e. g., a coated copper wire, through a heated zone to remove residual solvent from the resin or to advance or further condense a resinous coating disposed on an electrical conductor may be found in the copending application of Edward J. Flynn, Serial No. 658,364, filed March 29, 1946, and assigned to the same assignee as the present invention. In addition, by utilizing my invention together with the concept disclosed and claimed in the aforesaid Flynn application of applying a metallic coating of cadmium or chromium to the copper core prior to coating the copper core with the polysiloxane resin, it is possible to obtain electrical conductors having outstanding heatstability, good abrasion-resistance, and capable of being used at elevated temperatures without danger of peeling or cracking of the insulation from the conducting core.

The type of substantially non-conducting, i. e., non-electrical conducting, powdered substance employed in the practice of my invention is not critical, although generally I prefer inorganic, siliceous powders. Insulated copper electrical conductors prepared according to my invention and using siliceous pulverant materials, preferably mica dust, have outstanding abrasion-resistance and good electrical properties. The surfaces of such conductors will not craze even when used at elevated temperatures for extended periods of time. The failure of the surface of the insulated conductors to craze for extended periods, when prepared according to my claimed invention, is believed to be due to the protection afforded the inner polysiloxane resinous sheath by the outer sheath, which protects the softer polysiloxane resin during its initial service use when curing or advancement of the polysiloxane resin may still be continuing. This leads to a further advantage derived from the practice of my invention, namely, it is possible to obtain more flexible conductors by advancing the cure or conversion of the polysiloxane resin to an intermediate or incomplete cure state in which the polysiloxane resin is not as hard as when it is in the finally cured state. Under the protection of the outer insulation sheath, which can be disposed on the polysiloxane resin as a result of my invention, the polysiloxane resin canbe allowed to cure slowly while it is in service without harmful effects. This enables handling of the conductor in a flexible condition, which condition may not be necessary once the conductor has been placed in its permanent position.

The thickness of the layer of powdered material disposed on the polysiloxane resin may be varied depending, for example, on such factors as the thickness of the individual particles contained in the pulverant material, etc. Usually I prefer to use a pulverant material which has been ground to pass through a 100 or 200 mesh screen. If applied properly, the thickness of the powdered coating will preferably be approximately one layer thick, i. e., the thickness will be equal essentially to the thickness of the powdered particles.

In order that those skilled in the art may better understand how the present invention may be practiced, the following examples are given by way of illustration and not by way of limitation. All parts are by weight.

Example 1 A thin strip of copper sheet about 0.005 inch in thickness was dipped in a per cent methyland phenyl-substituted polysiloxane resin solution (toluene solvent), there being present about 1.7 hydrocarbon groups (methyl and phenyl groups substituted on the silicon atom) per silicon atom. The copper strip was baked for a short time at about 275 C. to drive oif some of the solvent. The tacky strip was dusted with a cloth containing mica dust (200 mesh) loosely attached to the cloth. The dusted strip was then exposed to a current of air to remove excess mica dust, leaving behind a coating of the mica dust approximately one layer thick firmly adhering to the polysiloxane resin.

The dusted strip was coated with a thin film of a polyvinyl formal resin modified with a cresolformaldehyde condensation product by dipping the strip in a solution of this resinous material. The resin solution had the following formulation:

iN0rE.The above-described modified n iv 'im'l m'ctai res n was of the t ne di closed a d used in U. 9. Patent 2.307.568 (supra) fl making insulated electrical conductors] This coated strip, which contained the modified polyvinyl formal resin adhering to the polysiloxane resin in the form of a smooth, coherent, continuous sheet. was dried in a C. oven for about one-half hour and then for approximately 10 minutes at 200 C. This final heat-treatment removed substantially all the residual solvent and advanced the two resins (inner and outer sheaths) to a more advanced state of cure. This finally treated strip had a hard, tough surface, good abrasion-resistance and couldbe bent on itself without harmful effects. When a copper strip was coated with the same polysiloxane resin as employed above, and the mica dust treatment and the dipping in the modified polyvinyl formal resin solution were omitted, heating of the resulting strip at 200 C. for 10 minutes yielded a poorly abrasion-resistant surface as evidenced by the fact that it was possible to scrape off the polysiloxane coating with one's finger nail. Although it was possible to obtain a hard surface by baking at 300 C. for about eight hours, the sample would not tolerate any bending or creasing of itself without the occurrence of cracks in the polysiloxane coating. Without the use of the pulverant material, no resinous coating could be caused to adhere to the polysiloxane resin.

The use of a heat-convertible methyl polysiloxane resin (containing about 1.5 methyl groups per silicon atom) in place of the methyland phenyl-substituted polysiloxane resin employed above gave the same advantageous results. Tale, in finely divided form, could be substituted for the mica employed in the above example to effect the same adhesion of the polyvinyl formalmodified eresol-formaldehyde condensation product to the inner coating of the polysiloxane resin.

Example 2 A copper wire was dipped in a methyland phenyl-substituted polysiloxane resin solution identical with the one employed in Example 1. The coated copper strip was baked for about 18 hours at 160 C. and, while hot, was dusted with mica dust or powder (about 100 mesh particle size) in the same manner as was employed in the foregoing example. The mica-coated strip was dipped in a resin solution comprising a petroleum spirits solvent and a resinous material consisting of a linseed oil-modified tertiary-butylphenol formaldehyde condensation product. Without the presence of the mica dust disposed on the polysiloxane resin, no coherent, even, homo geneous coating of the oil-modified phenolic resin could be formed on the polysiloxane resin.

Example 3 A copper bar was wrapped with two turns of 0.005 inch thick glass tape. The bar was dipped in a methyl-substituted (containing about 1.5 methyl groups per silicon atom) polysiloxane resin solution. The coated conductor was placed in a 275 C. oven for a time sufiicient to cure the resin to the tacky stage. Mica dust was then blown against the coated bar until a thin homogeneous layer was disposed on the outer surface of the wire. The excess mica dust was removed by exposing the bar to a blast of air. The micacoated bar was then dipped in a China-wood oilmodified eresol-formaldehyde resinous solution.

The film deposited on the outer surface of the bar thus treated was uniform, even, homogeneous and adherent.

When an attempt was made to coat a bar with the abovementioned oil-modified eresol-formaldehyde resin, said bar having been prepared identically as this one with the exception that the mica coating was omitted, no even, continuous, uniform outer coating could be obtained. The former bar, i. e., the one containing the coating of mica dust, when heated at 160 C. for about one-half hour, yielded a strong, abrasion-resistant insulated bar having good heat-stability.

The coated bar, i. e., the mica-dust-containing insulated bar, sheathed by the homogeneous, adherent, continuous coating of the oil-modified eresol condensation product, was thereafter tested for abrasion resistance by exposing the surface of the coated bar to a cemented tungsten carbide abrading surface having a load of about one kilogram. The bar was rotated against the abrading surface at a uniform rate and the total number of turns were noted when the abrader wore through the inner and outer resinous coat- 8 ingsofthebartothebarecopper. l'oracontrol, a copper bar was dipped in the aboveidentifled polysiloxane resin and heated for about 16 hours at 200 C. The copper bar having the coating of mica dust and an outer coating of the oil-modified eresol-formaldehyde condensation product required 3850 turns of the abrader before the bare surface of the copper was reached, while the copper bar containing only the coating of the polysiloxane resin withstood only 1440 turns of the abrader before the abrader wore through to the bare copper surface.

It will be understood by those skilled in the art that my invention is not limited to the particular organo-substituted, e. g., hydrocarbonsubstituted, polysiloxane resin or the particular organic resins employed as the outer sheath for the copper conductor in the foregoing examples. Additional examples of the various other resins which may be employed in the practice of this invention have been more fully enumerated previously.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. The process which comprises (1) coating a copper conductor with a resinous solution comprising a heat-curable hydrocarbon-substituted polysiloxane dissolved in a solvent and containing an average of from 1.2 to 1.8 hydrocarbon groups per silicon atom, (2) passing the coated conductor through a heated zone maintained at a temperature of about to 450 C., for a time sumcient to remove residual solvent from the said polysiloxane solution and to advance partially the cure of the said polysiloxane resin, (3) disposing on the coated conductor a thin homogeneous layer of a non-conducting inorganic siliceous pulverant material, (4) passing the conductor through a heated zone to advance to a substantial degree of condensation the cure of the polysiloxane resin, (5) applying to the heat-treated conductor obtained in (4) a coating of a synthetic resinous insulation material comprising a eresol-aldehydemodiiled polyvinyl formal resin, and (6) heattreating the finally coated product to render the polysiloxane and the polyvinyl formal coatings substantially infusible and insoluble.

The process which comprises (1) coating a copper conductor with a resinous solution comprising a heat-curable methyl-substituted polysiloxane dissolved in a solvent and containing an average of from 1.2 to 1.8 methyl groups per silicon atom, (2) passing the coated conductor through a heated zone maintained at a temperature of about 150 to 450 C. for a time sufficient to remove residual solvent from the said polysiloxane solution and to advance partially the cure of the said polysiloxane resin, (3) disposing on the coated conductor a thin homogeneous layer of powdered mica, (4) passing the conductor through a heated zone to advance to a substantial degree of condensation the cure of the polysiloxane resin, (5) applying to the heat-treated conductor obtained in (4) a coating of a synthetic resinous insulation material comprising a cresol-formaldehyde-modifled polyvinyl formal resin, and (6) heat treating the finally coated product to render the polysiloxane and the polyvinyl formal coatings substantially infusible and insoluble.

3. The process which comprises (1) coating a copper conductor with a resinous solution comprising a heat-curable methyland phenyl-substituted polysiloxane dissolved in a solvent and containing an average of from 1.2 to 1.8 total 9 methyl and phenyl groups persilicon atom, (2) passing the coated conductor through a heated zone maintained at a temperature of about 150 to 450 C. for a time sufficient to remove residual solvent from the said polysiloxane solution and to advance partially the cure of the said polysiloxane resin, (3) disposing on the coated conductor a thin homogeneous layer of powdered mica, (4) passing the conductor through a heated zone to advance to a substantial degree of condensation the cure of the polysiloxane resin, (5) applying to the heat-treated conductor obtained in (4) a coating of a synthetic resinous insulation material comprising a cresol-formaldehyde-modifled polyvinyl formal resin, and (6) heat treating the finally coated product to render the polysiloxane and the polyvinyl formal coatings substantially iniusible and insoluble.

HINNETH N. MATHES.

REFERENCES CITED tile 0! this patent:

UNITED STATES PATENTS Number Name Date 1,200,041 Speed Oct. 3, 1916 2,081,420 Bent et a1 May 25, 1937 2,085,995 Patnode et a1 July '6, 1937 2,258,218 Rochow Oct. '7, 1941 2,277,083 Dorough Nov. 24, 1942 2,307,588 Jackson et a1. Jan. 5, 1943 FOREIGN PATENTS Number Country Date Great Britain 1910

Claims (1)

1. THE PROCESS WHICH COMPRISES (1) COATING A COPPER CONDUCTOR WITH A RESINOUS SOLUTION COMPRISING A HEAT-CURABLE HYDROCARBON-SUBSTITUTED POLYSILOXANE DISSOLVED IN A SOLVENT AND CONTAINING AN AVERAGE OF FROM 1.2 TO 1.8 HYDROCARBON GROUPS PER SILICON ATOM, (2) PASSING THE COATED CONDUCTOR THROUGH A HEATED ZONE MAINTAINED AT A TEMPERATURE OF AOBUT 150* TO 450*C., FOR A TIME SUFFICIENT TO REMOVE RESIDUAL SOLVENT FROM THE SAID POLYSILOXANE SOLUTION AND TO ADVANCE PARTIALLY THE CURE OF THE SAID POLYSILOXANE RESIN, (3) DISPOSING ON THE COATED CONDUCTOR A THIN HOMOGENEOUS LAYER OF A NON-CONDUCTING INORGANIC SILICEOUS PULVERANT MATERIAL, (4) PASSING THE CONDUCTOR THROUGH A HEATED ZONE TO ADVANCE TO A SUBSTANTIAL DEGREE OF CONDENSATION THE CURE OF THE POLYSILOXANE RESIN, (5) APPLYING TO THE HEAT-TREATED CONDUCTOR OBTAINED IN (4) A COATING OF A SYNTHETIC RESINOUS INSULATION MATERIAL COMPRISING A CRESOL-ALDEHYDEMODIFIED POLYVINYL FORMAL RESIN, AND (6) HEATTREATING THE FINALLY COATED PRODUCT TO RENDER THE POLYSILOXANE AND THE POLYVINYL FORMAL COATINGS SUBSTANTIALLY INFUSIBLE AND INSOLUBLE.

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