Method of insulating an electrical conductor
United States Patent 1191 1111 3,874,961 Steinert Apr. 1, 1975 [54] METHOD OF INSULATING AN 2,164,168 6/1939 Wertzheiser (it al. 174/120 C ELECTRICAL CONDUCTOR 2,298,748 10/1942 Bt&#39;O WI&#39;I 156/56 2,389,725 11/1945 GllllS et a1 156/54 175 Inventor: T or W- Stemert. e o M 2,5s0,050 12/1951 Sparks et&#39;al..... 156/53 2,697,675 12 1954 G 156 289 [73] Assgnee K&#39;mberly&#39;clark corporat&#39;on 2,786,757 3i1957 423/331 Neenahi 3,112,357 ll/l963 11111101,... 156/53 3,207,603 9/1965 Savit 117/154 [22] Filed Sept 1972 3,284,279 11/1966 Rumberger 117/152 [21] Appl. No.2 288,820  
  Related Application Data Primary Examiner-Char1es E. Van Horn [60] Continuation of Scr. No. 22,102, March 5, 1970, Assistant i1J L i abandoned, which is a division of Ser. No. 644,093, Anome, Agent or Firm Breitenfeld &amp; Levine June 7, 1967, abandoned.  
 152] US. Cl 156/53, 156/192, 156/289,  
  174/110 P, 174/120 C, 174/121 B [57] ABSTRACT [51] Int. Cl. H011) 3/52, H01b 13/08 1 1 Field 01 Search- 56, High density, high dielectric strength, wood pulp fiber 174/1 10 121 122 120 paper is provided with a surface coating ofa lubricant 423/327, 331 which produces a hard, dry, slippery film on the paper, thereby preventing breaking of the paper as it is 1561 Refere Ce C te wrapped around electrical conductors.  
 UNITED STATES PATENTS 2,029,546 2/1936 Schatzcl 174/122 5 Claims, N0 Drawings METHOD OF INSULATING AN ELECTRICAL CONDUCTOR This application is a continuation of copending application Ser. No. 22,102, filed Mar. 5, 1970, which was a division of copending application Ser. No. 644,093, filed June 7, 1967, both now abandoned.  
  This invention relates to a method of insulating wires which carry electric current.  
  Electric wire is, in practice, provided with a paper insulation wrapping in various ways, depending in part on the ultimate use to which the wire is put. For example, the insulated wire may be wound on a core in the manufacture of a transformer. In large power transformers, the insulation on each wire or conductor becomes all or part of the insulation between the turns of the windings. To aid in understanding this invention, reference will be made to its use in connection with the manufacture of electrical transformers. However, the invention obviously has broader scope and its usefulness is not limited to this particular environment.  
  Insulation of transformer wire is accomplished by drawing the wire through the center of a series of revolving taping heads. Continuous webs of paper are drawn from supply rolls of the paper mounted on the taping heads, the webs being fed over adjustable guides and finally wrapped in spiral fashion around the wire. Since a number of taping heads are employed, several layers of paper are applied to the wire, the layers being overlapped or butted to create a smooth surface. The insulated, or taped, conductors are subsequently wound around a core to produce the transformer.  
  For many years, paper made from used rope (Manila hemp) has been employed to insulate many types of electrical conductors, including those employed in the manufacture of transformers. Such paper is strong and stretchable, and these mechanical qualities permit the paper to be used on high speed taping machines without breaking. However, rope fiber paper has a low dielectric strength, and consequently the insulation thickness of the conductors must be relatively large.  
  It would be desirable, therefore, to employ high dielectric strength paper to insulate some types of electrical conductors. High dielectric strength paper, such as is conventionally employed in electrical capacitors, is more dense than rope fiber paper. Therefore, a smaller amount of thinner high dielectric strength paper could replace the thicker rope fiber paper, thus reducing the overall bulk of a transformer. High dielectric strength paper is made from wood pulp fibers, and in the past, attempts to use such paper to insulate wires have not been successful. If the taping machine is run at normal speeds, the wood pulp paper breaks. Addition of plasticizers to the paper, to increase its stretchiness, has not solved the problem. If the taping machine is run more slowly, the wood pulp paper can be used without breaking, but the speeds are so slow as to be uneconomical.  
  It is an object of the present invention to provide a method of insulating electrical conductors with a high density, high dielectric strength, wood pulp paper capable of being used without breaking on conventional wire insulating equipment while the latter operates at normal speed, i.e., a speed comparable to that employed when insulating with rope fiber paper.  
  These objects are achieved, according to the present invention by providing high dielectric strength, wood fiber, paper with a surface coating of a lubricant. The surface lubrication apparently reduces the friction between the paper and the various metal surfaces over which it is drawn during the taping, or wire wrapping, process, and also reduces the friction between the layers of paper wrapped around the conductor. Paper lubricated according to the present invention, as well as identical paper without lubrication, have been used on several types of insulating machines which differ markedly in their mode of operation, and the surface lubrication has been found to be essential to satisfactory performance in all cases. For example, on one taping machine, having a normal taping speed of 35 feet per minute, paper without surface lubrication was found to break when the speed of the machine reached 22 feet per minute. In contrast, when lubricated paper according to this invention was employed, the machine taped successfully at 40 feet per minute.  
  Lubricants which have been found to work satisfactorily include refined paraffin wax, a zirconium wax complex, an ethylene oxide polymer, the alkali metal or alkaline earth soaps of stearic acid, a complex colloidal magnesium aluminum silicate product derived from a naturally-occurring mineral and sold by R. T. Vanderbilt Company, Inc. under the trademark Biltcote. Other materials believed useful for paper surface lubrication are unsaponified stearic acid, and other solid fatty acids or their soaps, and the vegetable waxes such as carnauba wax. On the other hand, products which have been tried unsuccessfully include talc and lubricating oils. It appears, therefore, that the lubricant used must be one which forms a hard, dry, slippery film on the paper surface.  
  The lubricant, as either a dispersion or a solution in an organic solvent or water, may be applied to the paper in any appropriate manner, such as by a simple roll coating technique. It has been found that as little as 0.001 pounds of lubricant per 1,000 square feet of treated paper surface yields successful results.  
  A laboratory test for determining the efficacy of any particular surface lubrication treatment is defined by ASTM D 202 which measures the surface friction of paper. According to this procedure, a sheet of paper is secured to an inclined plane, the angle of inclination of the plane being adjustable. Another sheet of the same paper is secured to a weighted block placed on the plane with the paper sheets in contact. The angle of inclination of the plane with respect to the horizontal, measured in degrees, at which the block slides freely on the plane is an indication of the relative slipperiness of the paper. In general, high density, high dielectric strength, wood pulp paper without treatment according to this invention, has been found to give angle-ofinclination readings of about 20 30. In contrast, the same paper after surface lubrication treatment gives readings of 10- 15.  
  Some specific examples of paper treatment according to this invention are set forth below:  
 EXAMPLE I A paper made from unbleached kraft softwood pulp, the paper having a thickness of 2 mils, a density of 1.0 grams per cubic centimeter, and a dielectric strength of 600 volts per mil, was treated with an aqueous dispersion of a refined paraffin wax having a melting point of 134F, and dried. The amount of wax applied to the sheet was 0.01 pounds per thousand square feet of sheet surface treated. The paper was treated by conventional size press application, without the surface treatment with wax, the paper had a surface friction angle of 27, as measured in accordance with ASTM D-202. After application of the surface lubricant, the friction angle was reduced to 8.  
 EXAMPLE II Instead of paraffin wax, the paper of Example I was treated with an aqueous dispersion of a zirconium-wax complex (a commercial water repellant treatment for textiles and paper, sold under the trademark Sunchem F H by Sun Chemical Company) and dried. The amount of this material applied was 0.003 pounds per thousand square feet of sheet surface. This treatment reduced the surface friction angle to 10.  
 EXAMPLE III Instead of paraffin wax, the paper of Example I was treated with an aqueous solution of an ethylene oxide polymer (sold under the trademark Polyox WSR 301 by Union Carbide Corporation). The amount of dry polymer deposited was 0.005 pounds per thousand.  
 square feet of sheet surface. The surface friction angle was reduced to 14 by this treatment.  
 EXAMPLE IV Instead of paraffin wax, the paper of Example I was treated with an aqueous dispersion of calcium stearate and dried. The amount of calcium stearate applied was 0.025 pounds per thousand square feet of sheet surface. The surface friction angle was reduced to 7.  
 EXAMPLE V EXAMPLE VI Instead of paraffin wax, the paper of Example I was treated with an aqueous solution of sodium stearate and dried. The amount of dry material deposited was 0.01 pounds per thousand square feet of sheet surface. The surface friction angle was reduced to 13.  
 EXAMPLE VII Another proprietary wax complex water repellant sizing material (sold under the trademark Nalan HR by E. I. duPont de Nemours &amp; Co., Inc.) was substituted for the product (Sunchem FH) used in Example 11. The amount of dry product applied was 0.003 pounds per thousand square feet of sheet surface. The surface friction angle was reduced to 10.  
 EXAMPLE VIII Example VII was repeated with the level of treatment reduced to 0.0015 pounds per thousand square feet of sheet surface. The surface friction angle of the treated paper was 14.  
 EXAMPLE IX A paper made from unbleached kraft softwood pulp, the paper having a thickness of 2 mils, a density of 0.8 grams per cubic centimeter, and a dielectric strength of 425 volts per mil, was treated with an aqueous dispersion of a refined paraffin wax having a melting point of 134F, and dried. The amount of wax applied to the sheet was 0.007 pounds per thousand square feet of sheet surface treated. Without the surface treatment, the paper had a surface friction angle of 24. After application of the surface lubricant, the friction angle was reduced to 9.  
 EXAMPLE X A paper made from unbleached kraft softwood pulp, the paper having a thickness of 2 mils, a density of 1.0 grams per cubic centimeter, and a dielectric strength of 600 volts per mil, was treated with an aqueous dispersion of a refined paraffin wax having a melting point of 134F. and dried. The amount of lubricant applied was 0.007 pounds per thousand square feet of sheet surface treated. The paper was then supercalendered to a density of 1.1 grams per cubic centimeter. The final product had a surface friction angle of 7 and a dielectric strength of 725 volts per mil.  
  It will be noted that the paper employed in the present invention is wood pulp paper having a high dry dielectric strength exceeding 400 volts per mil. Equally important, the paper has a high density of at least 0.80  
 high density, the paper provides increased dielectric strength when impregnated with insulating liquids. For example, the kraft pulp paper described in Example I, after lubrication and impregnation with transformer oil had an impulse voltage breakdown strength of 4500 volts per mil. On the other hand, rope fiber paper having a density of only about 0.70 grams per cubic centimeter had an impulse voltage breakdown strength of about 2200 volts per mil after impregnation with transformer oil.  
  The paper may be treated according to this invention on only one side, where in use only one side of the paper frictionally contacts parts of the taping or wrapping machine. l-Iowever, in some circumstances, it may be necessary or desirable to treat both sides of the pa per. In any case, the values given herein concerning the amount of lubricant applied to the paper relate to the amount applied to each treated surface of the paper.  
  It may be pointed out that although the primary benefit of the present invention involves the solution of the problem of paper breaking during the taping of conductors, the invention also plays a part in the winding of the taped conductors. When the conductors were wrapped in wood pulp paper without surface lubrication treatment, it was difficult to properly position them on the core around which they are wound. This problem was, however, alleviated by the use of surface lubrication on the paper.  
  The invention has been shown and described in preferred form only, and by way of example, and many variations may be made in the invention which will still be comprised within its spirit. It is understood, therefore, that the invention is not limited to any specific form or embodiment except insofar as such limitations are included in the appended claims.  
 What is claimed is:  
  1. A method of insulating an electrical conductor comprising the steps of lubricating the surface of a paper web with a lubricant which forms a hard, dry, slippery film on the paper, the lubricant being applied to the paper in an amount between 0.001 and 0.025  
  6 pounds per thousand square feet of web surface, and cant is an ethylene oxide polymer. after said hard dry film has formed, wrapping the web 4. A method as defined in claim 1 wherein the lubriaround the conductor. cant is a soap of stearic acid.  
  2. A method as defined in claim 1 wherein the lubri- 5. A method as defined in claim 1 wherein the lubricant is a wax. 5 cant is a magnesium aluminum silicate complex.  
 3. A method as defined in claim 1 wherein the lubri-