US2229985A - Electrically insulating composition - Google Patents

Description

Jan. 28, 1941. Pl' NOWAK ETAL 2,229,985

ELECTHICALLY INSULATING COMPOSITION vFiled Nov. 1e, 1937 r 4- CO/VVE'NT/O/VAL FIL LING MATER/0L ""Aknozep covfe//va Inventors:

Paul Nowak,v Walter Detlofc,

Their` Attorneg.

Patented Jan. 28, 1941 UNITED STATES PATENT OFFICE 2,229,985 vELEC'IRICALLY IN SULATING COMPOSITION of New York Application November 1s, 1937, serial No. 174,889

Germany November 21, 1936 s claims. (ci. :aso-s) The present invention relates to electrical cables. It is more particularly concerned with cables comprising a conductor insulated with a composition comprising vulcanized polymerized acrylic acid or its homologues, or vulcanized polymerized derivatives of acrylic acid or homologues thereof. Compositions and cables of this kind are described in the copending applications of Paul Nowak, Serial No. 749,476, filed October 22, 1934, now Patent No. 2,105,361, issued January 11, 1938, and of Paul Nowak and Hermann Hofmeier, Serial No. 33,898, tiled July 30, 1935, now Patent No. 2,105,362, also issued on January 11, 1938, both of which patents are assigned to the same assignee yas the present invention. In the following description of the invention and in the appended claims, the class of polymers above mentioned is designated, generally, as "polymerized acrylic acid derivative.

For certain cable purposes it is desirable lto provide an electrically insulating composition which retains more elastic properties over a wide temperature range than is possessed by compositions of the kind described in the aforementioned applications. It has been found in practice that in many cases an absolute resistance of the insulating or sheathing composition to oil is not required. Under such circumstances addition materials, which in themselves have relatively little or inferior resistance to oil, may be incorporated in the compositions.

In accordance with the present invention coml positions comprising vulcanized polymerized acrylic acid derivatives are made more resistant to the eiect of cold on their flexibility, and are given improved elastic properties at elevated temperatures, by incorporating therewith a small amount, for example, about 2 to 10 per cent by Weight of the whole of new (unused) or reclaimed (used) rubber.

In the accompanying drawing Figs. 1 and 2 represent cross-sectional views of single-conductor cables enclosed in a sheath of our improved insulating composition; and Fig. 3 shows a similar view of a multi-conductor cable comprising three single-conductor cables insulated as shown in Fig. 2.

The reference numeral l designates the metallic conductor; 2 conventional electrically insulating material such, for example, as paper, rubber, asbestos, spun glass, varnished cambric, etc.; 3 the insulating composition of the present invention; 4 conventional filling material, such as jute, asbestos or the like, for bringing a multiconductor cable to uniform cross-section; and 5 an armored covering. Like numerals designatev like parts in all figures.

In Fig. 1 the new insulating material is shown as being superposed directly on a metallic conducting core. In Fig. 2 conventional insulating l material is shown as being superposed directly on the conductor and the composition of this invention constitutes the external sheath. Fig. 3 shows three individual conductors insulated as shown in Fig. 2, and the whole surrounded by an 10 armored covering, with nlling material in the intervening space between the individual conductors and the armoredy covering.

The following speciiic examples illustrate how the new electrically insulating compositions of 15 this invention may be prepared:

Example 1 Parts by weight Polymerized ethyl ester of acrylic acid..--- 500 Powdered adsorbent (surface-active) ma- Preferably the polymerized ethyl acrylate is plasticized prior to mixing with the other ingredients, for example, by incorporating there- 30 with a suitable amount of dibutyl phthalate. The specified components may be kneaded togetherv at about to 90 C. in a suitable mixing apparatus, for exam-ple, a Banbury mixer,'followed by working on heated mixing rolls. A small amount, 35

for instance about 15 parts by weight, of an antioxidant such as beta-naphthol may be incorporated in the above-described mass during the kneading operation. In the foregoing formula active magnesium silicate is the preferred ad- 40 sorbent, although other adsorbents also may be used, for example, active carbon, silica gel, activate-d alumina, fullers earth, activated bleaching clays, activated bauxite, and the like. Talcum, French chalk or other powdered iilllng ma- 45 terials may be used. The rubber may be crude rubber of commerce, but mainly for purpose of economy the use of plasticized reclaimed rubber is preferred. If desired, the polyacrylate, ad-

sorbent and ller, with or without the sulfur, 50

may be separately mixed, after which the rubber or the rubber and the su1fur(if the sulfur Was not previously added) may be incorporated with the said mixed or reacted components. Under certain conditions it may be preferred to mix rst the polyacrylate and rubber, and then to incorporate therewith the adsorbent, inert ller and sulfur. When crude natural rubber is used and to effect complete vulcanization of the rubber, then sometimes it may be necessary to employ a little more sulfur than that specified in the formula'.

v Example 2 Parts by weight Polymerized ethyl ester of acrylic acid 318 Powdered adsorbent (surface-active) material- 195 Powdered, inert (non-active) inorganic lling material 467 Sulfur 2 Rubber 20 to 100 Example 3 Parts by Weight Polymerized ethyl ester of acrylic acid 30.50 Reclaimed rubber composition (70 per cent natural rubber) 9.00 Powdered talc 36.00 Active carbon 23.00 Anti-oxidant (for example,betanaphthol) 0.70 Plasticizer (for example, stearic acid) 0.80

The description given under Example 1 with respect to plasticizing the polyacrylate, and to methods and temperatures of mixing or combining the components, also applies to this example. Other adsorbents, inert lling materials, antioxidants and plasticlzers than those mentioned by way of example may be employed.

Compositions produced in a manner such as described under the foregoing illustrative examples are soft and yielding, and after the mixing operation readily may be extruded upon a metallic conducting core (for example, solid 0r stranded copper wire) at an elevated temperature, for instance at about 100 to 120 C. 'I'he insulated conductor ordinarily is given a vulcanizing heat treatment in order to effect or to complete vulcanization of the applied insulating composition and particularly vulcanization of the polymerized acrylic acid derivative in the composition. The advantage of vulcanizing polymerized acrylic acid derivative in the presence of surface active materials (adsorbents) as is done in making the compositions of this invention, is fully described in the aforementioned Nowak application Serial No. 749,476, now Patent No. 2,105,361.

The compositions used in making the insulated conductors or cables of the present invention preferably comprise vulcanized polymerized acrylic acid ethyl ester and new or reclaimed rubber in an amount by weight correponding tot from about 5 to 35 per cent that of such es er.

Specic examples of acrylic compounds that may be employed in practicing this invention are, for instance, polymerized acrylic acid, polymerized methyl, ethyl, propyl, butyl and higler alkyl esters of acrylic and methacrylic acids, polymerized acrylonitrile, or mixtures of two or more such substances.

The insulating compositions of this invention are elastic over a wide temperature range, and have adequate flexibility at temperatures as low as minus 15 C. They also show a greater resistance to flow (less tendency to soften) at elevated temperatures than compositions comprising vulcanized polymerized acrylic acid derivatives which have not been modified as herein described. These improvements in the physical properties of such polymerized acrylic acid derivatives are all the more surprising in that they are eiected by the additionof such relatively small proportions of rubber, more particularly (as hereinbefore pointed out) from 2 to 10 per cent by Weight of the Whole.- Further, these ends are attained without materially affecting the resistance of such compounds to water, ozone, aging and in ilammability.

Compositions comprising polymerized acrylic acid derivative. polymerized vinyl ether, and addition agents of the kind herein described with reference to polyacrylate compositions similarly are improved in their physical characteristics by incorporating rubber therewith as here- `inbefore set forth.

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

1. An electrically insulating composition comprising polymerized ethyl ester of acrylic acid,

plasticized used rubber in an amount by weight corresponding to from about 5 to 35 per cent that of the said ester, sulfur, a filler substantially free from surface activity and an adsorbent, said rubber constituting from 2 to 10 per cent by weight of the whole, the said ester and rubber-being conjointly reacted with the sulfur in the presence of the adsorbent, and the said composition being water-', ozoneand ageresisting, exible and elastic at temperatures as low as minus 15 C., and having a greater resistance to flow at elevated temperatures than a composition containing no rubber component but with all other components and proportions thereof substantially the same.

2. An electrically insulating composition comprising a filler substantially free from surface activity andthe reaction product of a vulcanizing agent with a mixture containing -rubber, polymerized acrylic acid derivative and polymerized vinyl ether in the presence of an adsorbent, said rubber constituting from 2 to 10 per cent by weight of the whole.

3. An insulating material adapted for insulating an electric cable, said material being water, ozoneand age-resisting and comprising a filler and the product of co-vulcanization of rubber and polymerized acrylic acid derivative with a vulcanizing agent in the presence of an adsorbent, said rubber" constituting from 2 to per cent by weight of the whole and increasing substantially the ilexibility and elasticity of said composition at temperatures as low-as minus C. and, also, the resistance to ow of the composition at elevated temperatures.

4. An insulating material adapted for insulating an electric cable, said. material being water, ozoneand age-resisting and comprising' a filler, plasticized used rubber and polymerized acrylic acid derivative coreacted with sulfur in the presence of an adsorbent, said rubber constituting from 2 to 10 per cent by weight of the whole and increasing substantially the flexibility and elasticity of said composition at temperatures as low as minus 15 VC. and, also, the resistance to flow of the composition at elevated temperatures.

5. An electrically insulating composition comprising a filler substantially free from surface activity and the product of co-vulcanization of rubber and polymerized ester of acrylic acid with a vulcanizing agent in the presence of an adsorbent,` said rubber constituting from 2 to 10 per cent by weight of the whole and increasing substantially the flexibility and elasticity of said composition at temperatures as 10W as minus 415 C. and, also, the resistance to iiow of the composition at elevated temperatures.

6. A Water, ozoneand age-resisting composition comprising the product of vulcanization of a mixture containing approximately Parts by weight Polymerized ethyl ester of acrylic acid 500 Powdered adsorbent material 200 Powdered inert inorganic filling material", 280 Sulfur 5 Rubber 20 to 100 PAUL NoWAK. WALTER DIETLOFF. l

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