US2129157A - Insulated electric cable - Google Patents

Description

Sept. 6,1938. E. w. TROLANDER ET AL 2,129,157

INSULATED ELECTRIC CABLE Filed April 10, 1936 F/LM cam/v6 A/vc/m/w/vs" ZO/VE F/LM #vsumw/va COMP05/7/0/V 03W .9 diarnc y.

?atented Eept. 1%38 uru'rso STATES Z,i2s,157

.FFWE

son, Chicago, 111., assigncrs to Pyroxylin Prodnets, 1110., Chicago, Ill, a corporation of Illlnois Application April 1W,

12 Claims.

This invention relates to improved insulated electrical conductors and more specifically to high tension conductors such as those used in the ignition system of internal combustion engines.

One object of the invention is to provide an improved coating over a flexible insulation such as rubber and rubber substitutes, which coating is impervious .to water, oils, ozone, acids, etc. thus protecting the insulating composition from deterioration and injury by such injurious sub stances.

Another object is to provide an insulating structure that will retain its flexibility and remain intact over a wide range of temperature, so that it will withstand high temperatures without deterioration with resulting embrittiement, and will also not become stiff and brittle at low temperatures. A particular object is to provide an insulating sleeve that does not deteriorate so as to lose its insulating properties, or become weakened and break down in the presence of oils even when'exposed to such oils at relatively high temperatures.

A still further and specific object is to provide an insulated conductor having a flexible cellulose ether base outer coating, said coating being soft and pliable andat the same time free from stickiness or tackiness so that the coating does not adhere to itself when the insulated cable is wound on a spool or roll, and which will lurthcr= more have a surface which will be suiilciently slippery and tough to enable the conductors to be easily pulled through a conduit and permit the surfaces to be easily slipped over one another.

Other objects of the present invention center about the provision of a coating material having a cellulose ether base and modifying agents to render the same'capable of meeting the above conditions. Other and ancillary objects will be found in and be apparent from the following specifications and claims.

In our copending application Serial No. 534,612, filed May 2, 1931, nova Patent No. 2,061,528, issued November 17, 1936, we have described an electrical insulation that can be produced at a relatively low cost, which insulation is suitable for many purposes. However, the present type and design of automotive internal combustion engines, and especially those used on some of the newer models of trucks and buses. expose the ignition cable to extremely severe coriditions. The conductor should withstand temperatures as high as'240 F. to 300 F., or higher, for relatively long periods of time with no serious impairment of its protective properties. Also the 1936,, Serial No. @3393 (Q1. Nil-264) conductors may be covered with hot lubricatin oils, or it may be necessary to remove spark plugs and flex the cables at low temperatures. With high compression engines, higher voltages are used, which increase the rate of ozone generation. Under such severe conditions the conductors heretofore available will break down in a few weeks, and must be replaced. Automotive conductor cable calls for a high degree of elastlcity in a cable coating, in addition to flexibility, 1 and ordinary bases and fiexibilizing plasticizers are not suitable for cable.

Our invention provides a conductor capable of meeting these severe conditions, and provides a conductor having at least two or three'times the efllcient life oi conductors heretofore available.

it has long been lsnown to insulate a conductor with rubber insulation. The rubber insulation, however, rapidly breaks down under the severe exposure such as to hot oil, the ozone generated by the high tension cmrent, etc. One method of protecting the rubber is described in our aforementioned applicationseriall los534,612. Another method is to weave a braid over the rubbar, and coat the braid with a nitrocellulose base lacquer. Still another method is to wrap varnished carnbric over the rubber base insulation, place a braid over the varnished cambric, and finally a coating oi nitrocellulose base lacquer over the braid. In all or" these methods, the nitrocelluose coating may be exposed to temperatures above its decomposition point, so that the coating deteriorates rapidly, becoming still and brittle and finally cracking and exposing the rubber underneath. Cellulose ester coatings are not satisfactorily resistant to the more severe exposures in the automotive field.

Furthermore, cable which has covering, such as a cotton braid or a paper strip or cord winding, protected by cellulose esters, is subject to embrittlement and destruction of the cellulose itself, in spite of its protection. By use of the present invention, such cellulose material can be exposed without destruction, to temperatures which will destroy cellulose alone. or cellulose protected by cellulose esters. I

In the accompanying drawing there are shown several forms of cable embodying the present invention, the character of the coating being more 50 particularly set forth in the detailed explanation.

Fig. 1 shows a rubber insulated conductor cable coated with a film of cellulose ether base, anchored to the rubber bye. suitable priming coat.

Fig. 2 represents an electric conductor heavily 55 insulated by a fiexible elastic composition protected with a cotton braid, which is coated with the essential protecting film.

In the drawing l0 illustrates a single wire conductor housed as usual in a rubber insulation sleeve II. The zone designated i! represents a bonding composition between the ultimate outside filmy sleeve or coat l3. and the rubber II, it being understood that the layer I 2 is not a distinct and separable layer, but an anchoring or merging layer between the composition of the coat I! and the rubber composition l I. Fig. 1 shows the cable wrapped about a mandrel ll, thus producing stretch in the rubber and its coating, at the part" designated l5. It is high elasticity at this point that is a rigid requirement, and the stretched film must remain stable and resistant to oil,"

, ozone, and heat, and the film must not break to expose the rubber beneath it to oil, air or ozone.

In Fig. 2 the conductor is shown as a flexible group 20 of fine wires, covered as usual with a sleeve of rubber composition 2|, and then protected with a braided sleeve 22 as of cotton threads. The sleeve is then covered and/or impregnated with film 23 of the present invention. Likewise a mandrel 24 is shown over which the cable may be bent, producing stretch at 25. The

stretched film may adhere to and must protect the braid, without breaking, so as not to allow oil, air or ozone, acids and the like to enter and affect the braid or the rubber.

We have discovered that these difiiculties may be avoided, and the insulation protected against the most severe conditions encountered in connection with internal combustion engines by the use of a cellulose ether base protective coating or film. A cellulose ether such as ethyl cellulose when used alone, however, is not satisfactory, and modifying agents must be used therewith as described herein below.

the cellulose ethers. Cellulose ethers so plasticised give protective coatings or films having new and unusual properties. For example we have found that ethyl cellulose and the glycerol ester of sebacic acid may be used to produce films, which are substantially oil-proof, which are unaffected by ozone, which are highly flexible and elastic at temperatures of 0 I". or below, which will remain flexible after exposure for along period of time at temperatures as high as 325' l, and which are relatively stable even at temperatures of 400 I". or higher.

The use of these polyhydric alcohol esters of the higher dibasic aliphatic acids alone with the cellulose ethers is, however, apt to produce films which will not readily slip over each other. This is objectionable in many instances, as for example, in pulling a conductor cable througha conduit in which there are other conductors, since the cables are apt to be damaged unless they have sufiicient "slip" over one another. Furthermore, the friction may be excessively high, resulting in excessive mechanical wear where thesurfamlrof two cables rub over each other during movements caused by vibration or otherwise. I We have discovered that this can be avoided by the addition of lubricating agents. While a conductor having a film with no lubricating agent may be surface lubricated, i. e. a lubricant simply wiped over the surface, we prefer to incorporate a suitable lubricant in the film itself, since surface lubricants tend to disappear in a short time. We have discovered that certain of the non-drying animal and. vegetable oils may be incorporated directly into the films without loss of the above-mentioned desirable properties. Mineral oils may also be used, but are not as satisfactory as the animal and vegetable oils.

The protective coating or film of our invention includes a cellulose ether and a polyhydric alcohol omega-omega dibasic higher aliphatic acid ester as the essential plasticizer, and with or without a lubricating agent incorporated therein. It is to be understood that we may substitute other plasticizers for the softening or flexibilizing functions of the essential plasticizer, retaining sufllcient polyhydric alcohol-dibasic acid ester for the elasticizing property.

Our protective film or coating may be conveniently applied by dissolving the aliphatic cellulose ether and plasticizing ester, and preferably the lubricating agent in a suitable solvent,

applying the solution tothe surface to be pro- I tected, and allowing the solvent to evaporate, whereby the fllm or coating is deposited on the said surface. While such protective films or coatings may be applied directly to the rubber insulation, we prefer to interpose a fabric such as a cotton braid between the rubber insulation and the protective coating, as shown in Fig. 2. When the film has a high percentage of the essential plasticizer itadheres well to the rubber, but in cases where adherence is poor, the rubber may be coated twice. The first layer ll, may be a thin layer of the plasticizing ester, or a layer of cellulose ether which is rich in the plasticizing agent to the point of being somewhat tacky when dry. Upon this anchoring layer, the final layer may be'applied. Intermediate layers are not excluded, but for practical purposes, are not necessary.

The following discussion relates to the final coats l3 and 23. The ratio of cellulose ether to total plasticizer may be varied within wide limits depending upon the degree of flexibility desired. However, the amount of elasticizlng plasticizing ester must be sufilcient, although variable, to secure the desired degree of elasticity. stability and resistance to breaking, oil, and ozone at the points II and 25, according to commercial specifications. The following examples are given by way of illustration, but it is to be understood that wide variations may be made both in the materials used and in the proportions thereof without departing from the spirit of the invention.

In the above example the neats-foot oil acts as a lubricant. Such a composition gives a protective coating that is flexible, highly resistant to lubricating oils, substantially unaffected by clone,

and which is stable at any temperatures likely to be encountered when used in connection with internal combustion engines.

Example II Parts by weight Non-volatile:

In the above composition a part of the polyhydric alcohol dlcarboxylic aliphatic acid ester has been replaced with another plasticizer, namely butyl acetyl ricinoleate for the softening or flexibilizing function. The neats-foot oil is used as the lubricating agent, and it is to be understood that such agents may aid in softening or fiexibilizing to some degree.

In some cases, as for example-on airplane engines, an entirely flame-proof coating ishighly desirable. We are able to make such a coating using our composition with an added fire-proofing agent, as illustrated by the following example:

Emmple III Parts by weight Non-volatile:

Ethyl cellulose 55 Glycerol ester of sebacic acid 34 Chlorinated diphenyl (liquid product)" 3d Cocoanut oil 12 Volatile:

Anhydrous ethyl alcohol Toluol 220 The chlorinated diphenyl is a fire-proofing agent primarily, but to some extent may act as a plas-' ticizer. The cocoanut oil is a lubricating agent. Coatings made from the above composition will not support combustion, and are of great value for use in ignition cables where non-inflammability is desired.

Toluene Example V Parts by weight Non-volatile:

Methyl cellulose 4 Ethyl cellulose 35 Glycerol ester of sehacic acid 2'7 Butyl acetyl ricinoleate 5 Neats-foot oil 7 Volatile:

Water 16 Anhydrous ethyl alcohol 35 Butyl alcohol. 10 Toluol In the above formula the methyl cellulose is first dispersed to a. colloidal form as a sol or gel in water, and this dispersion used" in compounding with the other ingredients. This does not make an excellent film for the purpose of the invention, and the exampleonly illustrates the facts mentioned concerning methyl cellulose and mixtures of ethers.

For the sake of clearness and simplicity in the above compositions ethyl cellulose has been predominantly used as an example of the aliphatic ether of cellulose. It is presently preferred, be-

cause of its availability and'becsuse it is highly satisfactory for the purposes of the invention. We have found that other aliphatic cellulose ethers (excepting methyl cellulose) such as propyl cellulose, butyl cellulose, etc. may be used in place of the ethyl cellulose in the practice of our invention. Methyl cellulose.of the character now commercialy available is not useful as the sole cellulose ether base, but it is permissible as a diluent for the ultimate purposes of the invention. Methyl cellulose requires a different type of solvent than its higher homologs beginning with ethyl cellulose, and the aromatic celluiose ethers. Because it is too much affected by water, and furthermore requires solvents including water, it should not be used as the entire cellulose ether for this invention. Several cellulose ethers may be used together as the cellulose ether of this invention, and small amounts of; methyl cellulose ether may be tolerated in such mixtures.

The preferred cellulose ethers are the aliphatic ethers having two or more carbon atoms in the aliphatic radicle. While the aromatic cellulose others are useful in our protective coating, we have found they have a tendency to soften at higher temperatures. Cable covered with a film having aromatic cellulose ethers, and no aliphatic cellulose others are suitable for use where they are not exposed to melting or softening temperatures. We may, in general however, substitute an aromatic cellulose ether, as for example benzyl ccllulose, for a part of the preferred aliphatic cellulose ether. Thus we may use, for example, equal parts of benzyl cellulose and ethyl cellulose, or one part benzyl cellulose with three parts ethyl cellulose. Ingeneral, however, we have found that the best results are secured where ethyl cellulose is used as the major constituent of the cellulose ether content.

Likewise for the sake of clearness and simplicity in the above compositions we have shown the .glycerol ester of sebacic acid as the essential plasmore of the dicarboxylic acids may be used in our invention. The various esters may be mixed as well as being used alone.

It is also to be understood that other modifying agents such as coloring materials as for example dyes, pigments, finely divide metals such as the so-called aluminum or gsud bronzes may be added to give the desired color efiect. Example 11 shows carbon black as a coloring agent. Example III shows a fire-proofing agent. We may also add waxes to decrease the moisture vapor permeability, or for other purposes, also resins, as is well understood in the art.

Electrical conductors made according to our process have the surprising property of protectproducts of 'thenitrocellulose lacquers heretofore used cause the braid to be rapidly weakened. Our protective coating not only does not decompose to liberate products which weaken the braid, but actual tests indicate that the braid is protected and its life prolonged by our coating. In certain types of busesand trucks the life of the ignition cable heretofore available has been very short. Cables made according to our process have a useful life many times longer than the ignition cables heretofore available.

Where the term rubber" is used in the specification and in the claims, it is intended to include ordinary rubber as it has long been known in composition form for insulation purposes, and also other substances or compositions used as substitutes for such rubber as insulation on electric conductors, alone or in mixtures. There are various such substitutes now known and used, such as "Duprene" made by'the Du Pont Company of Wilmington, Delaware, U. B. A.; Plioform made by the Goodyear Tire and Rubber Company of Akron, Ohio, U. S. A.; "Thiokol made by the Thiokol Corporation, Yardville, New Jersey. U. S. A.; "KoroseaY made by the Goodrich Rubber Company, Akron, Ohio, U. S. A.; balata, and other natural or synthetic rubbery products.

The fact that rubber in electric conductor cable is subject to injury from numerous sources makes it necessary to protect the same by housing it in some envelope such as the sleeve described. The film-type of sleeve covered by this invention provides the desired protection by reason of the essential combination of cellulose ether .as a base material and a modifying ester of polyhydric alcohol and omega-omega dicarboxylic alpihatic acid havingat least a six-carbon straight chain. The various forms of cable construction and variations in the protecting sleeve which are permitted by the invention are expressed in the appended claims.

Reference is made to applicants copending application Serial No. 73,797, filed April 10, 1936,

covering the coating composition per se.

We claim: I

l. A flexible insulated electrical conductor particularly useful as ignition cable for internal combustion engines and capable of attaining a temperature of 325 1'. without loss of its effective properties, comprising a conductor, a rubber base insulating sleeve housing said conductor, a cellulose covering over said rubber sleeve, and a protective film over said covering, said film comprising the essential combination of cellulose ether as a base containing ethyl cellulose as an essential ingredient, as a modifying agent an ester of a polyhydric alcohol and an omegaomega dicarboxylic acid having at least a six carbon straight chain, a lubricating agent, and a fire-proofing agent.

2. Flexible electric cord or cable which is particularly suitable to withstand use as ignition cable for internal combustion engines, comprising a flexible conductor, a flexible insulating sleeve of rubber-base material over said conductor which is subject to injury or destruction by oil or ozone, a flexible fabric cover over said sleeve of material normally subject to deterioration and destruction at elevated temperature, and a coating material over said fabric cover which coating I material when on the cable is capable of attaining a' temperature of 325 F. without loss of its effective protective properties or of the effective properties of the cord or cable as a whole upon attaining said temperature or thereafter at lower temperatures, said coating material comprising cellulose ether of which ethyl cellulose is an essential part, and as a modifying agent an ester of a polyhydric alcohol and an omega-omega dicarboxylic aliphatic acid having at least a sixcarbon straight chain.

3. Flexible electric cord or cable which is particularly suitable to withstand use as ignition cable for internal combustion engines, comprising a flexible conductor, an insulating sleeve of rubberbase material which is subject to injury or destruction by oil or ozone, and a coating material over said insulating sleeve which coating material on the cord or cable is capable of attaining a temperature of 325 F., without loss of its effective protective properties or of the effective properties of the cord or cable as a whole upon attaining said temperature or thereafter at lower temperatures, said coating material comprising cellulose ether of which ethyl cellulose is an essential part, and as a modifying agent an ester of a polyhydric alcohol and an omega-omega dicarboxylic aliphatic acid having at least a six-carbon straight chain.

4. Flexible electric cord or cable which is particularly suitable to withstand use as ignition cable for internal combustion engines, comprising a flexible conductor, a flexible insulating sleeve over said conductor, a flexible fabric cover over said sleeve of material normally subject to deterioration and destruction at elevated temperature, and a coating material over said fabric cover which coating material on the cord or cable is capable of attaining a temperature of 325 1",, without loss of its effective protective properties or of the effective properties of the cord or cable as a whole upon attaining said temperature or thereafter at lower temperatures, said coating material comprising cellulose ether of which ethyl cellulose is an essential part, and as a modifying agent an ester of a polyhydric alcohol and an omega-omega dicarboxylic aliphatic acid having at least a six-carbon straight chain.

5. In a flexible electric cord or cable which is particularly suitable to withstand use as ignition cable for internal combustion engines, having a flexible conductor, a flexible insulating sleeve and a flexible fabric cover over said sleeve which is normally subject to deterioration and destruction at elevated temperature, the combination with said fabric cover of a coating material thereon which coating material on the cord or cable is capable of attaining a temperature of 325 F., without loss of its effective protective properties or of the effective properties of the cord or cable as a whole upon attaining said temperature or thereafter at lower temperatures, said coating cellulose is an essential part, and as a modifying agent an ester of a polyhydrio alcohol and an omega-omega dicarboxylic aliphatic acid having at least a six-carbon straight chain.

6. In a flexible electric cord or cable whichis particularly suitable to withstand use as ignition cable for internal combustion engines, having a flexible conductor and a flexible insulating sleeve, the combination "with said sleeve of u flexible fabric cover over said sleeve of materiai which is normally subject .to deterioration and destruc-v tion at elevated temperature, and a coating material on said cover, which coating material on the. cord or cable is capable of attaining a temperature of 325 F., without loss oi its effective protective properties or of the effective properties of the cord or cable as a whole upon attaining said temperature or thereafter at lower temperatures, said coating material comprising cellulose ether of which ethyl cellulose is an essential part,

and as a modifying agent an ester of a polyhydric alcohol and an omega-omega dicarboxylic aliphatic acid having at least a six-carbon straight chain.

7. In a flexible electric cord or cable which is particularly suitable to withstand use as ignition cable. for internal combustion engines, having a flexible conductor and a flexible insulating sleeve, the combination with said sleeve of a flexible fabric cover over said sleeve of material which is normally subject to deterioration and destruction at elevated temperature, and protective coating material on the material of said fabric cover which coating material on the fabric on the cord or cable is capablcof attaining a temperature of 325 FL, without loss of its effective protective properties or of the efl'ective properties of the cord or cable as a whole upon attaining said temperature or thereafter at lowertemperatures, said coating material comprising cellulose ether of which ethyl cellulose is an essential part, and as a modifying agent an ester of a polyhydric alcohol and an omega-omega dicarboxylic aliphatic acid having at least six-carbon straight chain.

8. In a flexible electric cord or cable having a,

conductor, insulation on said conductor comprising a cellulosic material, and a protective coating material therefor which coating material on the cord or cable is capable of attaining a temperature of 325 F. without loss of its eiiective protective properties or of the efiectlve properties of the protected celluloslc material upon attaining said temperature orthereafter at lower ter'nperatures. said material comprising cellulose ether of which ethyl ccllulosc'is an essential part.- and as a modifying agent an ester of a polyhydric alcohol and an omega-omega dicarboxylicl aliphatic acid having at least a six-carbon straight chain. A

9. Flexible electric cord "or-cable which is particularly suitable to withstand use as ignition cable for internal combustion engines, comprising a flexible conductor, an insulating sleeve of rubber-base material which is subject to injury or destruction by oil or ozone, and a. coating material over said insulating sleeve which coating material on the cord or cable is capable of attaining a. temperature of 325 F., without loss of its effective protective properties crof the effective properties of the cord or cable as a whole upon attaining said temperature or thereafter at lower temperatures, said coating material comprising rial on the cord or cable is capable of attaining a temperature of 325 F., without loss of its eflective protective properties or of the effective.-

properties of the cord or cable as a whole upon attaining said temperature or thereafter at lower temperatures, saidcoating material comprising cellulose ether of which ethyl cellulose is an essential part, and as a modifying agent an ester of glycerol and an omega-omega. dicarboxylic aliphatic-acid having at least a six-carbon straight chain. l

11. Flexible electric cord or cable which is particularly suitable to withstand use as ignition cable for internal combustion engines,- comprisingva flexible conductor, an insulating sleeve of' rubber-base material which is subject to injury by destruction by oil or ozone, and a coating material over said insulating sleeve which coating material on the .cord or cable is capable of attalning a temperature of 325 F.,; without loss of its eifcctlve protective properties ;or oi the effective properties of the cord or cable as a whole upon attaining said temperature or thereafter at lower temperatures, said coating material comprising cellulose cther of which ethyl cellulose is an essential part. and as s modifying agent an ester of glycol and sebacic acid.

12. Flexible electric cord or cable which is particulsrly suitable to withstand use as ignition cable for internal combustion engines, comprising a flexible conductor, an insulating sleeve of rubber-base material which is subect to injury or destruction by oil or ozone, and a coating matcrisl over said insulating sleeve which coating material on the cord. or cable is capable of at.- taining a temperature of 825 1''., without loss of its elective protective properties or ofthe effectivc properties of the cord or cable as a whole.

prising cellulcsc other of which ethyl cellulose is Q an essential part. and as 's modifying agent on r ester of glycerol 'sndscbacic acid.

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