GB2113454A

GB2113454A - Electrically-insulated conductive wire

Info

Publication number: GB2113454A
Application number: GB08201410A
Authority: GB
Inventors: John Norman Macsween
Original assignee: WL Gore and Associates Inc
Current assignee: WL Gore and Associates Inc
Priority date: 1982-01-19
Filing date: 1982-01-19
Publication date: 1983-08-03

Abstract

Electrically-insulated electrically- conductive wire is produced by wrapping the wire helically with overlapping turns of tape formed of polyether ether- ketone film, an adhesive being applied between the turns which, upon the application of heat at or above the temperature at which the adhesive is fluid but below the heat-setting temperature of the film, seals the overlapping turns of the film.

Description

SPECIFICATION An improved electrically-insulated electrically conductive wire This invention relates to the production of electrically-insulated electrically-conductive wire (hereinafter referred to as insulated wire) in particular for aerospace use.

A requirement exists for an insulated wire having a lightweight high-temperature resistant insulating coating which also has high cut-through resistance.

Insulated wire is conventionally produced by extrusion, i.e. the wire is passed through an extrusion head to which insulation material in fluid form is supplied, the material forming a homogeneous coating around the wire as the wire passes out of the extrusion head. However, such extrusion technique has numerous disadvantages, in particular it does not produce a highly-concentric coating.

It is also known to coat wire with insulating material by wrapping it with a strip of insulating film, and such coating can be sealed with a suitable adhesive. However, such a wrapping technique has not yet produced an insulation having the present required properties.

According to the present invention there is provided an insulated wire having thereon a wrapped coating of polyether etherketone film.

The present invention also provides a method of forming an insulating coating on a wire which comprises wrapping the wire helically with overlapping turns of tape formed of polyether etherketone film, applying an adhesive between overlapping turns of the film, the adhesive being capable of bonding the film, and heating the coating at a temperature at which the adhesive is fluid but below the heat-setting temperature of the film to seal the overlapping turns of the film.

In accordance with the invention, electrically conductive wire is helically wrapped with overlapping turns of a film of polyether etherketone (hereinafter referred to as PEEK), a suitable adhesive having been applied to the film, and the wrapped coating is heated to a temperature at which the adhesive is fluid, but below the heat-setting temperature of the film.

In a preliminary step of the process, the film which is produced with a thickness of .001 to .010 inches is biaxially or uniaxially oriented by stretching in a ratio of 3:1.

The adhesive for bonding together the overlapping turns of the PEEK film can be a polyester, polyether sulphone, polysulphone or other resin which will flow at a temperature below the heat setting temperature of the film.

The adhesive dissolved, in a solvent, is coated on to one side of a wide sheet of film (e.g. 12 inches wide) by passing the film in contact with a contrarotating roller whose surface passes through a bath containing a solution of the adhesive and solvent.

The coating on the film is restricted to a predetermined thickness by passing the film under a doctor blade. The coating is then heated to evaporate the solvent. The wide band of film is subsequently slit to form films of suitable width for wrapping, e.g. 1/2 inch to 3/16 inch.

The wrapped and heat-sealed coating of PEEK has the advantage over an extruded coating of the same material, that is has high resistance to cut-through in relation to its thickness, a considerably higher tensile strength, and greaterflexibility. Moreover, by wrapping the film, a coating is formed which can be considerably thinner and hence lighter in weight, then an extruded coating of the same material and the thickness of the coating will be much more concentric and even than that of an extruded coating. Again, a wrapped coating does not extend into the interstices of a wire, e.g. a stranded wire, and accordingiy stripping of the coating is simplified.

As a further advantage, the dielectric strength of the oriented film is considerably higher than that of extruded insulation, and the wire produced by tape-wrapping the laminate will have considerably higher voltage rating per unit thickness of insulation than a wire having an extruded coating of equal wall thickness.

Since the film is applied in the cold state and is never heated during processing, above its melt point, there is no tendency for the film to stick to the wire. This makes stripping of the insulation predictable and consistent.

After heat sealing, the coating will have a solvent resistance considerably better than an extruded coating of the same composition.

Since the PEEK film is transparent, and the material itself is expensive to colour, adhesive of different colours can be used to give colour-coded wire.

If the PEEK materials were extruded on to the wire, the coating would need to be heat treated to ensure that sufficient crystallinity were induced in the resin to impart the insulative, mechanical, electrical and environmental resistance properties achieved by the present invention.

1. An insulated wire having thereon a wrapped coating of polyether etherketone film.

2. An insulated wire according to claim 1 wherein overlapping turns of the film wrapping have been heat sealed to each other.

3. An insulated wire according to claim 1 or claim 2 wherein the overlapping turns of the film are bonded to each other by an adhesive.

4. An insulated wire according to claim 3 wherein the adhesive is a polyester, polyether sulphone, polysulphone or other resin which will flow at a temperature below the heat-setting temperature of the film.

5. A method of forming an insulating coating on a wire which comprises wrapping the wire helically with overlapping turns of tape formed of polyether etherketone film, applying an adhesive between overlapping turns of the film, the adhesive being capable of bonding the film, and heating the adhesive at a temperature at or above the temperature at which the adhesive is fluid but below the heat

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION An improved electrically-insulated electrically conductive wire This invention relates to the production of electrically-insulated electrically-conductive wire (hereinafter referred to as insulated wire) in particular for aerospace use. A requirement exists for an insulated wire having a lightweight high-temperature resistant insulating coating which also has high cut-through resistance. Insulated wire is conventionally produced by extrusion, i.e. the wire is passed through an extrusion head to which insulation material in fluid form is supplied, the material forming a homogeneous coating around the wire as the wire passes out of the extrusion head. However, such extrusion technique has numerous disadvantages, in particular it does not produce a highly-concentric coating. It is also known to coat wire with insulating material by wrapping it with a strip of insulating film, and such coating can be sealed with a suitable adhesive. However, such a wrapping technique has not yet produced an insulation having the present required properties. According to the present invention there is provided an insulated wire having thereon a wrapped coating of polyether etherketone film. The present invention also provides a method of forming an insulating coating on a wire which comprises wrapping the wire helically with overlapping turns of tape formed of polyether etherketone film, applying an adhesive between overlapping turns of the film, the adhesive being capable of bonding the film, and heating the coating at a temperature at which the adhesive is fluid but below the heat-setting temperature of the film to seal the overlapping turns of the film. In accordance with the invention, electrically conductive wire is helically wrapped with overlapping turns of a film of polyether etherketone (hereinafter referred to as PEEK), a suitable adhesive having been applied to the film, and the wrapped coating is heated to a temperature at which the adhesive is fluid, but below the heat-setting temperature of the film. In a preliminary step of the process, the film which is produced with a thickness of .001 to .010 inches is biaxially or uniaxially oriented by stretching in a ratio of 3:1. The adhesive for bonding together the overlapping turns of the PEEK film can be a polyester, polyether sulphone, polysulphone or other resin which will flow at a temperature below the heat setting temperature of the film. The adhesive dissolved, in a solvent, is coated on to one side of a wide sheet of film (e.g. 12 inches wide) by passing the film in contact with a contrarotating roller whose surface passes through a bath containing a solution of the adhesive and solvent. The coating on the film is restricted to a predetermined thickness by passing the film under a doctor blade. The coating is then heated to evaporate the solvent. The wide band of film is subsequently slit to form films of suitable width for wrapping, e.g. 1/2 inch to 3/16 inch. The wrapped and heat-sealed coating of PEEK has the advantage over an extruded coating of the same material, that is has high resistance to cut-through in relation to its thickness, a considerably higher tensile strength, and greaterflexibility. Moreover, by wrapping the film, a coating is formed which can be considerably thinner and hence lighter in weight, then an extruded coating of the same material and the thickness of the coating will be much more concentric and even than that of an extruded coating. Again, a wrapped coating does not extend into the interstices of a wire, e.g. a stranded wire, and accordingiy stripping of the coating is simplified. As a further advantage, the dielectric strength of the oriented film is considerably higher than that of extruded insulation, and the wire produced by tape-wrapping the laminate will have considerably higher voltage rating per unit thickness of insulation than a wire having an extruded coating of equal wall thickness. Since the film is applied in the cold state and is never heated during processing, above its melt point, there is no tendency for the film to stick to the wire. This makes stripping of the insulation predictable and consistent. After heat sealing, the coating will have a solvent resistance considerably better than an extruded coating of the same composition. Since the PEEK film is transparent, and the material itself is expensive to colour, adhesive of different colours can be used to give colour-coded wire. If the PEEK materials were extruded on to the wire, the coating would need to be heat treated to ensure that sufficient crystallinity were induced in the resin to impart the insulative, mechanical, electrical and environmental resistance properties achieved by the present invention. CLAIMS

5. A method of forming an insulating coating on a wire which comprises wrapping the wire helically with overlapping turns of tape formed of polyether etherketone film, applying an adhesive between overlapping turns of the film, the adhesive being capable of bonding the film, and heating the adhesive at a temperature at or above the temperature at which the adhesive is fluid but below the heat setting temperature of the film to seal the overlapping turns of the film.

6. A method according to claim 5 which comprises es the initial step of biaxially or uniaxially orienting the film, the oriented film having a crystallinity of between 70 and 100%.

7. A method according to claim 6 wherein the adhesive is a polyester, polyether sulphone, polysulphone or other resin which will flow at a temperature below the heat-setting temperature of the film.

8. An insulated wire substantially as herein described.

9. A method of forming an insulated coating on a wire, which method is substantially as herein described.