US2483441A - Plastic composition for coating wire - Google Patents

Description

Patented Oct. 4, 1949 PLASTIC COMPOSITION FOR COATING WIRE Howard E. Smith, Brooklyn, N. Insl-X Corporation, Brooklyn,

tion of New Jersey No Drawing.

Y., assignor to N. Y., a corpora- Original application March 25, 1938, Serial N0. 198,016.

Divided and this application October 22, 1943, Serial No. 507,247 3 Claims. (Cl. 106-171) My invention relates to a plastic composition comprising in large part ethyl cellulose in combination with plasticizers and wax. The wire is coated with this plastic composition according to a specific method involving temperature control of the wire and temperature control of the plastic material within certain definite ranges, and specific controls with respect to the length of the extrusion die and the expansion of the plastic composition.

In the past, it has been customary to coat wire with rubber to produce an insulating and protective covering for the conductor. Because of the nature of rubber, however, rather bulky coating must be efiected to obtain sufi'icient dielectric strength and to obtain the necessary properties in the final wireor cable. In many instances, it is highly desirable that a wire with the maximum of conductor diameter and minimum of insulation covering be employed. This is particularly so in machine wiring.

It is highly desirable to have a thin insulating covering for wire with a high dielectric strength. Thus, in addition to conserving space, which in many instances is of great importance, the cost of shielding may be materially reduced when thin insulating coverings are employed.

When lead shields are employed as for mechanical protection or or grounding when multiple Wires'are employed within a single shield, less lead is necessary to cover a thinly covered wire than to cover a thickly covered wire. Since the cost of lead is a material factor in the cost of protective coverings, reduction in the amount of lead necessary is of great importance.

Therefore, because the plastic composition which I shall set forth may be used in the form of a much thinner covering than the customary rubber insulating covering, a saving is efiected first in the material costs because of the employment of the lesser quantity of insulating covering and secondly, in the lead or similar sheathing since less lead is necessary because such a thin insulating covering is used.

Whe large conductors are to be insulated, as for example bus bars, certain specific problems arise. "B 5 bars carry an extremely heavy load of high amperage. A great deal of heat is developed and it is important that such heat be dissipated as much as possible since the heat detrimentally afi'ects the current carrying capacity of the conductor. therefore, may be made hollow so that the heat may be dissipated internally to a certain degree.

Such conductors,

It is obviously of great advantage that the heat be dissipated externally also. If, however, a heavy insulating coating be employed, such dissipation of heat cannot be eiiected as rapidly as desired. For this reason, the thin highly dielectric insulating coverings of my invention are of great imDOI'tance in connection with the insulation of heavy conductors of this nature.

Further, it is desirable that the covering of the wire have an aesthetically attractive coloring, and it is well known that the ordinary rubber insulating is dull and black. I

Although it has been suggested that metallic conductors be coated with insulation materials comprising certain plastics, such attempts have been found lacking in producing satisfactory results according to the methods employed.

The plastic covering of my invention is resistant to alkalis such as are present in the soil, especially in the western half of the country. This resistance to alkalis is exceptional in the case of the ethyl cellulose insulating covering composition of my invention. It is of particular importance since such insulating coverings are often carried through the ground and are necessarily exposed to the efiect ofthe alkalis. In addition to soil alkalis, there are employed of course in many industrial chemical processes such as the manufacture of viscose and rayon alkali reagents. It is desirable that the-wiring in -machines used in connection with these reagents or adjacent these reagents be resistant and unafiected by such alkalis. This property has not been found in many plastic compositions which may have been suggested for this purpose. The plastic composition of my invention is found ,resistant to weak acids and oxidation. The ethyl cellulose composition is very stable and as shown herein is especialy adapted for insulating coverings for electric conductors- The prior art of coating conductors with plastic was deficient in that the plastic coatings lacked the necessary bend and crease properties, were not sufiiciently water and moisture vapor proof, and became hard and subject to rupture under low temperature conditions such as winter temperatures (serious difliculty). When a remedy for these deficiencies was attempted, the desirable high breakdown found in the present invention was not even approached.

I have found that by employing certain compositions to be hereinafter set forth and by employing certain controls in the coating process, I may coat a metal conductor with the plastic com- Composition:

positions of my invention and obtain a wire with Parts by weight Ethyl cellulose (45% ethoxy) 100 Chlorinated diphenyl 20 Dibutyl phthalate--- Parafilne wax 2 Castor oi 20 Triphenyl phosphate Solvent 1 to 5 The ethyl celiulosewhich I employ is preferably of a 43 to 45 per cent ethoxy content. Preferably, I employ a 45% ethoxy ethyl cellulose. The ethyl cellulose then has about two to two and one-quarter molecules of ethoxy to each cellulose molecule. The viscosity of the ethyl cellulose is preferably about 150 centipoises.

In place of the ethyl ether of cellulose, I may employ the benzyl ether of cellulose. The benzyl ether of cellulose provides an insulating cover with a breakdown of 2200 volts: per mil while the ethyl ether has a breakdown of 1800 volts per mil. This ether cellulose composition such as.I have set forth has a great flexibility even below zero degrees centigrade. This is of great importance in view of the low temperatures to which such insulating coverings are commonly subjected. This low temperature flexibility is in marked contrast to other plastic compositions, notably cellulosic esters such as celloulose nitrate and cellulose acetate. My plastic composition further is relatively non-inflammable. This low inflammability is further decreased by the employment of suitable plasticizers such as the tri-cresyl and triphenyl phosphate.

I have found that if I preheat the wire and contact this preheated wire with heated plastic under pressure that a good union of plastic and metallic conductor is obtained. The plastic coated wire is drawn through a die. The length of the die which produces the best results is a length equal to about three times the diameter of the die opening. The wire with the plastic covering is drawn through a die at such a speed and under such pressure as will product about a twenty per cent expansion of the coating. when a metallic conductor is coated with an insulating compositlon as set forth, of a thickness of 30 mils, the insulation has a breakdown value of 1800 volts per mil.

The object of my invention is an insulating composition comprising ethyl cellulose, chlorinated diphenyl, wax, plasticizer and castor oil.

An important feature of my invention lies in the fact that a die is employed which has a length of approximately three times the diameter of the die opening. This particular length is critical and it has been found that the relation of the length of the die with respect to the diameter of the die opening as set forth produces exceptional results in the final product. The speed of the wire travelling as indicated is carefully regulated to product an expansion of approximately twenty per cent in the plastic coating as the wire and coating emerge from the die. This expansion of twenty per cent is the preferred expansion although the expansion may range from 10 to 25 per cent. Again. this speed of the wire with respect to the expansion obtained is critical in that the product produced according to this method is far superior to that produced when this control is neglected. When a coating of approximately 25 mils has been applied to the wire, an expansion of about five mils should be procured. The temperature ranges set forth for the wire and plastic material are not merely for the purpose of softening the plastic so that it can be molded about the wire but the specific ranges I have set forth ap pear to be critical in that if such ranges are neglected an inferior product is obtained.

In the composition I, the chlorinated diphenyl which I employ is a mixture of the diand trichlorinated diphenyl; the dlphenyl group may represent a mixture of diphenyl and di-tolyl. This compound imparts in addition to slow burning properties, a plasticizing effect upon the insulating composition that in the process set forth does not excessively soften the composition so as to obtain an undesired low-viscosity but at the same time has sufflcient plasticizing effect to obtain proper molding with respect to the conductor. In lieu of the castor oil which is employed in this composition, I may use more dibutyl phthalate, as for example five extra parts dibutyl phthalate. As a solvent for the composition indicated I employ a mix comprising approximately per cent of ethyl alcohol and twenty per cent of toluol. Another solvent composition which I may employ comprises fifty per cent of acetone and fifty per cent of benzol.

In the plastic insulating composition in which ethyl cellulose is a principal constituent, I preferably use 45 to 65 parts of plasticizer. This range has been found to produce entirely superior results.

When a wire is coated with the insulating plastic composition coating, such conductor has been found to have a breakdown of approximately 1800 volts per mil for a thirty mil thickness.

The plastic coated wire thus produced has a high insulating value as indicated. Further it is substantially non-inflammable and has remarkable resistance to water and moisture vapor. The coating has sufficient hardness for all ordinary uses and, at the same time, because of its plastic nature, can be subjected to flexing and indeed a bending of about 360 degrees without cracking the insulating coating.

,Further, only a relatively thin insulating coating is required in comparison to the coatings heretofore necessary. Because such thin coating can be used a marked saving is effected both in sheath material and because so little space is required for the insulated wire. This is of particular importance, as for example in machine and cable work.

This application is a division of my copending application Serial No. 198,016 for Method of coating wire with a plastic composition, filed March 25, 1938, now Patent No. 2,332,538.

I claim:

1. A composition comprising in substantially 7 2 An insulating coating composition consisting substantially of the following ingredients in the indicated proportions:

Parts by weight A cellulose ether 100 Chlorinated diphenyl 20 Dibutyl phthalate 10 Par'aflln wax 2 Castor oil 20 'I'riphenyl phosphate 15 Solvent 1 to 5 said cellulose ether being selected from the group consisting of benzyl cellulose and ethyl cellulose.

3. An insulating coating composition consisting substantially of the following ingredients in the indicated proportions:

HOWARD E. SMITH.

nnmnmcns crmn The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,188,376 Lilienfeld June 20, 1916 2,061,528 Trolander et al Nov. 17, 1936 2,064,292 Charch Dec. 15, 1936 2,065,792 Charch et a1. Dec. 29, 1936 2,098,539 Charch et a1 Nov. 9, 1937 2,105,489 Moss Jan. 18, 1938 2,129,156 Trolander Sept. 6, 1938 2,138,578 Hershberger Nov. 29, 1938 2,178,365 Brobst Oct. 31, 1939 2,205,428 Mitchell June 25, 1940 2,249,280 Koch July 15, 1941 2,257,104 Burrows et al Sept. 30, 1941 2,266,940 Traylor Dec. 23, 1941 2,287,947 Shoemaker June 30, 1942 OTHERI REFERENCES "Benzoyl Cellulose," Hercules Powder Company (1941), mes and 36.