Fabric (woven – knitted – or nonwoven textile or cloth – etc.) – Coated or impregnated woven – knit – or nonwoven fabric which... – Coating or impregnation intended to function as an adhesive...
Reexamination Certificate
1993-04-27
2002-06-11
Zirker, Daniel (Department: 1771)
Fabric (woven, knitted, or nonwoven textile or cloth, etc.)
Coated or impregnated woven, knit, or nonwoven fabric which...
Coating or impregnation intended to function as an adhesive...
C442S150000, C442S180000, C174S12100B, C174S1210SR, C174S12200R
Reexamination Certificate
active
06403503
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to an improved electrical insulating tape and a method of forming same. The tape of this invention includes a woven fiberglass cloth component bonded to a thermoplastic resin component whereby one surface of the tape is woven fiberglass cloth, and the opposite surface is thermoplastic resin. Alternatively, the fiberglass cloth can be impregnated with the thermoplastic resin.
DESCRIPTION OF RELATED ART
One product which has been widely commercially used for a number of years as an insulation for magnet wire is a combination fiberglass-polyester yarn which is formed from a mixture of fiberglass strands and polyester strands. This insulation yarn is sold by Owens/Corning, and others. This material is widely used at present to insulate magnet wire, but it has several drawbacks which have been accepted by the industry due to the lack of a competing product which avoids these drawbacks while providing equivalent electrical insulating qualities at competitive cost. The problems with the polyester-fiberglass yarn insulation include the rate at which it can be wound onto a wire. This insulation yarn will typically be wound or wrapped onto the wire at a rate of about 15-20 feet per minute. This yarn creates only about a 10 mil width of coverage on the wire when wrapped thereon, thus the relatively slow rate at which it can be wound onto a wire. Another drawback relates to the fact that this insulation will bond to the wire, and is not easily strippable therefrom. In fact, it must be ground off of the wire, if the wire is to be stripped. The fibers are also susceptable to being bunched together, even when double wrapped, whereby gaps in the insulation can form. When single wrapped, gaps occur due to uneven distribution of yarn fibers. This problem requires double wrapping layers at different angles of wrap, about 90 degrees difference between overlying layers.
U.S. Pat. No. 2,691,694 granted Oct. 12, 1954 to H. R. Young discloses insulated electrical conductors in which a three layer insulation is used. The first layer wrapped directly onto the conductor is a polytetrafluoroethylene (PTFE) film tape. A PTFE powder is suspended in water and is then impregnated into a glass fiber tape which is then wrapped onto the conductor over the PTFE film. A final outer layer of glass yarn is either wrapped or braided onto the PTFE impregnated glass fabric layer. The composite is heated to high enough temperatures to fuse the PTFE. The PTFE will not fuse unless it is subjected to high temperatures (above 600 degrees F.), and high pressures concurrently. This insulated product is very time consuming to make, given the fact that there are three layers required, and that the last layer is a glass yarn layer which is wrapped or braided onto the conductor, the latter step being itself an extremely slow process. The resultant insulation does however include a resin film part, and a glass yarn or braid component.
The aforesaid patent to H. R. Young refers to U.S. Pat. No. 2,539,329, granted Jan. 23, 1951 to P. F. Sanders for instructions as to how the glass/PTFE insulation is produced. The Sanders patent describes a method for making an insulation tape having a woven fiberglass carrier part and a PTFE part layered onto the fiberglass carrier. A water/PTFE slurry is formed, and the fiberglass cloth is dipped Into the slurry to form a thick layer of PTFE powder. There are three dipping steps, and three intermediate water evaporation and calendering steps which result in a thick, crack-free layer of PTFE on the glass substrate. The sheet will then be heated to a temperature of 700 degrees F. to fuse the PTFE particles to form a coherent layer of PTFE. The fusing step can be performed either prior to, or subsequent to, a slitting of the cloth into tapes suitable to be wound on an electrical conductor wire. It will be appreciated that the Sanders teaching is merely a teaching of a method for forming PTFE insulation strips. The glass component is insignificant and is only used as a carrier for the PTFE since glass has the ability to withstand the fusing temperatures of the PTFE. The PTFE is present in at least a 5:1 ratio to glass. The Sanders process requires extremely high temperatures and numerous preparation steps simply to produce a PTFE insulation tape.
U.S. Pat. No. 3,867,758 granted Feb. 25, 1975 to D. B. Johnson relates to a method for making glass insulated electrical coils. A wide sheet of glass strands which are all parallel, with no crossing strands are united together by passing the strands through an enamel bath to coat all of the strands with enamel, which are then heated to bake the enamel so as to coherently form the parallel glass strands into a sheet of insulating material. Heat cured polyesters or other similar polymers may be used for the enamel. The sheet is then slit into tapes which are wrapped onto conductor wires. Coils are formed from the wrapped conductor wires, which coils are then impregnated with the enamel and thereafter baked to fuse the windings in the coils to each other. The result may be a polyester and glass insulated conductor.
U.S. Pat. No. 4,761,520, granted Aug. 2, 1988 to I. W. Wade, Jr. et al discloses an insulated magnet wire wherein the wire is first wrapped spirally with a fiberglass yarn, and then over wrapped with a polyester film tape. The tape has two layers of polyester, one being amorphous and being laid against the glass yarn layer, and the other being crystalline. The wrapped wire is then heated sufficiently to cause the amorphous layer to become crystalline and fuse to the glass yam layer. A glass yarn/polyethyleneterephthalate insulation is thus formed. The forming process is however slow since there are two winding steps, one of which involves winding a yam on the wire. The yarn winding step requires a very slow feeding of the wire during production.
U.S. Pat. No. 4,868,035 granted Sep. 19, 1989 to M. J. Weinberg et al discloses a glass/polymer insulation, and a conductor wrapped therewith. The polymer component is a PET film tape having one amorphous surface and one crystalline surface. In one embodiment, the crystalline surface has parallel fiberglass yarn strands adhered to it by an adhesive. The composite insulation may be wrapped onto a conductor with either side facing the conductor. A glass/PET insulation which is fusable to itself or to the conductor is thus disclosed.
It will be appreciated that all of these prior art glass/resin insulations which require multiple wrappings are undesirably slow to produce and expensive. When the multiple wrappings are performed on a single line with a plurality of in-line wrapping assemblies, the slowest wrapping operation will dictate the speed of the entire line. In the prior art procedures which include wrapping of single strand glass yarn, or glass/resin composite yarn layers, the wrapping operation is quite slow. When a heat curing resin is used as the resin component, there will always be required a final resin coat and a subsequent cure step before the wrapping will adhere to the conductor.
When only parallel glass strands are used, the problem of feeding and maintaining the parallelism of the strands is formidable, and if the parallel strands are to be adhered to the resin layer, the use of a separate adhesive can affect the performance of the insulation. When PTFE is used as the resin component, production of the insulation and the insulated conductors requires extremely high temperatures.
SUMMARY OF THE INVENTION
This invention relates to an improved and simplified electrical insulation, and to a method of forming the same into tapes from stock sheets of the insulation material. The insulation of this invention is a ribbon or tape which includes a woven fiberglass component and a thermoplastic resin component. The resin is coated or bonded onto one side of the woven fiberglass component so that one surface of the insulation tape is essentially woven fiberglass, and the opposite surface is essentially a solidified layer of thermoplastic resin. Use of an insul
Jones William W.
Zirker Daniel
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