GB2197115A

GB2197115A - Electrical or optical cable

Info

Publication number: GB2197115A
Application number: GB08724629A
Authority: GB
Inventors: Heinz Eilentropp; Walter Steffes; Klaus Schwamborn
Original assignee: HEW Kabel Heinz Eilentropp KG
Current assignee: HEW Kabel Heinz Eilentropp KG
Priority date: 1986-10-28
Filing date: 1987-10-21
Publication date: 1988-05-11
Anticipated expiration: 2007-10-21
Also published as: JPS63170809A; FI91569C; FR2605791A1; GB2197115B; DE3636621C2; FI874404L; SE8704170L; ATA279887A; BE1003063A5; SE505160C2; CH673350A5; FI91569B; GB8724629D0; SE8704170D0; AT394282B; FR2605791B1; DE3636621A1; FI874404A0

Abstract

In a highly flexible cable with stretchable coverings (7; 10) made of insulating materials, at least the inner surface of a covering (10) is covered by a longitudinally-extending stretched and sintered film (11) made of a fluoropolymer e.g. PTFE. This improves the mobility and flexibility of the cable whilst reducing the stretchability of the covering. The film (11) is preferably stretched in one direction only up to 20 times its length before being sintered. This increases the porosity of the film which may be made more porous by perforating with needles. The outer conductor of the co-axial cable is made of wires (8) and glass-fibre threads (9). In another embodiment, a multiplicity of wires (1) are covered by a strip (2), netting (3), a sintered and stretched film of PTFE (5) and a cross-linked silicone rubber sheath (4). <IMAGE>

Description

SPECIFICATION Electrical cable or line The present invention relates to a highly flexible electrical cable or a corresponding line with stretchable coverings arranged in the cable structure, or line structure, and made of insulating materials.

Highly flexible cables and lines are primarily used as connection or supply lines wherever the consumer has to execute rotary or bending movements during operation. One particular province where such cables or lines are used is the medical sector, where it is necessary that measuring, control or treatment instruments supplied with electrical energy should be freely movable as possible. This requirement applies equally to single-wire, for example coaxial supply lines for surgical instruments, and to multi-wire data cables which are equipped, for example, with measuring heads at the ends and which serve for medical investigation.

It has not hitherto been possible to achieve substantially free mobility of such connection lines, among other things because, with an increase in mobility or flexibility, the tensile strength of the cable decreases, and consequently its operating reliability, for example, for the purposes mentioned, is impaired.

If the tensile strength of the cable is increased, for example, by means of appropriate high-tensile threads or fabrics inserted in the sheath, as has long been known, such a structure prevents the torsional movements which, for example, are transmitted to the connection line as a result of a rotary movement of a measuring head. This often results in cable breaks, in particular, at the end of the cable.

An object of the present invention is, therefore, to provide cables and lines of the type in question such that they allow the necessary mobility in any direction, but at the same time also have adequate tensile strength.

According to the invention, there is provided a highly-flexible electrical cable or corresponding line having at least one stretchable covering arranged in the cable or line structure and made of electrically insulating material, wherein at least the inner surface of a covering is covered by a stretched and sintered film of a fluoropolymer in the form of a strip with longitudinally-extending edges and fixed to the covering.

The use of such a strip results in virtually free rotatability of the particular covering over, for example, the cable core, the conductor, the insulation, and so on. Movements in the axial direction, with rotation taking place at the same time, are easily carried out by the cables or lines according to the invention. At the same time, the sheath, for example, of a cable according to the invention, which because of the necessary flexibility is produced from a rubber material and which is therefore itself stretchable, has increased tensile strength. These are properties which ensure that the cables or lines according to the invention can also be used advantageously, for example, in the field of handling devices (robots), with the long operating times customary here and the constantly changing cycle of movement.

A large proportion of the kinetic forces which, for example, are exerted axially or radially on the sheath of a cable according to the invention is absorbed directly by the latter, and the core or a sensitive conductor surrounded thereby is essentially freed from external forces. Moreover, the use of a film in accordance with the invention has further advantages. The use of a film made of a fluoropolymer, that is to say a material for use at relatively high temperatures, at the same time leads to increased protection of, for example, a sensitive core against the effect of external temperatures and against chemically aggressive media.This is especially important, for example, for connection lines in surgical medicine, where, after the instruments have been used, they, together with the connection lines, have to be sterilised at increased temperature, and are expected to be fully ready for service again afterwards. Lines used at the present time only meet all these requirements for a short time, or to a limited extent, since, for example, the sterilising operation repeatedly results in the bonding of adjacent individual elements in the laminated structure of the line, and because of this the mobility or flexibility necessary for the use of the line is considerably impaired.

The longitudinally extending strip-shaped film can be arranged on the inner surface of the particular covering in such a way that the strip edges butt flush against one another. However, it is especially advantageous if the longitudinally extending strip edges overlap one another. This affords additional safety in production and guarantees complete covering of the inner surface of a covering and consequently the certainty of free mobility.

Conveniently, the strip-shaped film used in the invention consists of a fluoropolymer, for example polytetrafluoroethylene, either alone, or as a copolymer, which is processed by paste extrusion and subsequent rolling.

To achieve the necessary tensile strength in 'the direction of the film extending iiongitudi- nally in the laminated structure of the cable or line, it has been found to be advantageous-to stretch the film up to 2000%, preferably between 300 and 1000%. Appropriate stretching can also be additionally carried out transversely to the strip direction, should it appear expedient for putting the invention into practice, for example in order to increase the porosity of the film and consequently to im prove the mechanical connection with the particular covering.

The specific gravity of the film used in the invention is advantageously 0.2 to 0.7 g/cm3 in the stretched and sintered state. If, as is particularly advantageous, stretching is carried out only in the strip direction, then the ratio of the tensile strengths in the stretching direction of the strip-shaped film and transversely to this is 10-15:1.

The thickness of the stretched and subsequently sintered strip-shaped film may be in the range of 15 to 250 microns, preferably 30 to 100 microns. In comparison with known elements for increasing the tensile strength, such as threads or fabrics, the film of the present invention is completely inconspicuous in the laminated structure of the cable or line.

Thus, for example, the requisite outer dimensions can be maintained without difficulty, whilst at the same time the operating properties are substantially improved.

Besides additional stretching in the transverse direction in order to increase the porosity, the film stretched in the strip direction and sintered can also be perforated, for example by guiding the film through a needle roller before it is inserted in the cable or line.

The strip-shaped film of the invention can be used at any location in the laminated structure of a cable or line, depending on the particular requirements. If, for example, the cable consists of a plurality of thin wires which are flexible per se, and if this core is covered by a stretchable sheath, the strip-shaped stretched and sintered film is advantageously arranged on the sheath surface facing towards the core. Not only does the film ensure that the sheath, which is itself stretchable and flexible, has the required tensile strength, but the presence of the film ensures that the sheath is substantially freely rotatable over the core.

If the line has a coaxial arrangement of an inner conductor and an outer conductor, the strip-shaped film can conveniently be arranged between the outer conductor and the enclosing insulation.

A suitable process for producing a cable or a line according to the invention has been found to be one in which, before the stretchable covering in question is applied, the stretched and sintered strip-shaped film is laid longitudinally round the respective substructure, which may be a cable core, a conductor or the like, and the insulating covering is formed directly on the film. Its material is substantially cross-linked, whereby the stripshaped film located on the inner face of the covering, is bonded or welded to the covering simultaneously with the formation of the covering and/or its subsequent cross-linking.

If, as with silicone rubber, the rubber material is applied cold to the strip-shaped film and only thereafter is a heat treatment carried out for cross-linking purposes, it can sometimes be advantageous to carry out pre-heating of the strip-shaped film already laid in place.

The invention will now be further described with reference to the drawings, in which: Figures 1 and 2 are similar schematic, perspective views of two respective embodiments of the invention.

Fig. 1 shows a multi-wire electrical cable, the stranded or bunched wires 1 of which are held together by a strip 2. Over this composite wire structure, there is arranged a netting 3, for example, as mechanical protection or for shielding purposes, when such a cable is to be used as a flexible connection line for a measuring or control instrument. A sheath 4 made, for example, of a cross-linked silicone rubber, is of corresponding form because of the necessary flexibility and is also basically stretchable in the direction of the wires. This stretchability of the sheath is a disadvantage as soon as the cable is exposed to tensile stresses during operation, since the core enclosed by the sheath is incapable of following its elongations.Although the stretchability of the sheath could be reduced by the appropriate addition of fillers to the mixture from which the sheath is formed, this measure would, however, also result in a change in other material properties which cannot be tolerated, for example, because of the high flexibility required.

The invention remedies this by arranging between the sheath 4 and the netting 3 a stretched and sintered film 5 which consists, for example, of a tetrafluorethylene polymer.

This film 5 acts as an excellent sliding or separating film, so that the sheath 4 is virtually freely rotatable over the netting 3; as a result of the mechanical connection of the film with the inner surface of the sheath 4, it at the same time performs the function of a tension element in the cable structure, and this represents a substantial restriction of the stretchability of the sheath 4. When the sheath 4 is attached, because of the film 5 the sheath material also cannot be pressed into the netting 3 which would have an adverse effect on the flexibility of the cable.

The film 5 was stretched before sintering or at the same time as this heat treatment. Apart from the high tensile strength achieved, such a film is therefore porous, thus providing a firm connection with the sheath when the sheath material is attached or when it is cross-linked under heat treatment. Moreover, since the film 5 extends over the entire inner surface of the sheath 4 and there is a plurality of bonding points distributed around the periphery of the cable, the connection between the sheath 4 and the film 5 is ensured, despite the stretchability of the sheath material used, considerable tensile forces can be absorbed by the film 5 supported on the sheath 4 in accordance with the invention, and consequently the cable core can be relieved of tension.In spite of the substantially free mobility of the sheath 4 over the netting 3, the positive connection between the sheath 4 and the core located beneath it is not lost.

Fig. 2 shows an electrical supply line of coaxial design. The inner conductor 6 is in the form of a bunched conductor and is surrounded by flexible insulation 7, on which wires 8 of the outer conductor and glassfibre threads 9, for example, for fixing them on the surface, are arranged, for example, alternately next to one another. A flexible sheath 10 is attached over this core as an outer covering and according to the invention, a film 11 again performs the function of a sliding or separating film between the sheath 10 and the outer conductor 8 and at the same time that of a tension element which is firmly connected mechanically over the entire periphery to the inner surface of the sheath.

The overlapping of the strip edges of the film 11 is indicated at 12. This is obtained because a strip having a width larger than the circumference of the line- at this point is selected for laying the longitudinally extending film round the outer conductor (8, 9), for example, by means of a conically-tapering tool.

In this particular use, the film 11 which is attached with the strip edges overlapping, also has the function of protecting the coaxial line structure against the effect of increased temperature which, for example, in the disinfection of medical instruments, can result in bonding of the outer conductor to the sheath and/or the insulation of the inner conductor and can thus destroy the flexibility and restorability of the line.

The electrical conductors shown in Figs. 1 and 2 may conveniently be bunched conductors made of metallic materials for reasons of flexibility. But light waveguides can also be used advantageously in cables or lines according to the invention. This is because the stretched and sintered film relieving the core of mechanical stresses affords an essential protection for the sensitive light waveguide.

Claims

1. A highly-flexible electrical cable or corresponding line having at least one stretchable covering arranged in the cable or line structure and made of electrically insulating material, wherein at least the inner surface of a covering is covered by a stretched and sintered film of a fluoropolymer in the form of a strip with longitudinally-extending edges and fixed to the covering.

2. A cable or line as claimed in Claim 1, wherein the longitudinally-extending edges of the strip overlap one another.

3. A cable or line as claimed in Claim 1 or Claim 2, wherein said film consists of a fluoropolymer alone as a copolymer and is processed by paste extrusion and subsequent rolling.

4. A cable or line as claimed in any one of Claims 1 to 3, wherein said film is stretched in the longitudinal direction of the strip.

5. A cable or line as claimed in Claim 4, wherein said film is streched up to 2000% in the longitudinal direction of the strip.

6. A cable or line as claimed in Claim 5, wherein said film is stretched by between 300 and 000% in the longitudinal direction of the strip.

7. A cable or line as claimed in any one of the preceding Claims, wherein said film is stretched both in the longitudinal direction of the strip and transversely thereto.

8. A cable or line as claimed in any one of the preceding Claims, wherein the specific gravity of said film is from 0.2 to 0.7 g/cm3 in the stretched and sintered state.

9. A cable or line as claimed in any one of the preceding Claims, wherein the ratio of the tensile strengths in the direction of stretching of the strip-shaped film and transversely to this is 10-15:1.

10. A cable or line as claimed in any one of the preceding Claims, wherein the thickness of said stretched and sintered film is 15 to 250 microns.

11. A cable or line as claimed in Claim 10, wherein the thickness of said stretched and sintered film is 30 to 100 microns.

12. A cable or line as claimed in any one of the preceding Claims, wherein said film is additionally perforated.

13. A cable or line as claimed in any one of the preceding Claims, comprising a plurality of wires combined to form a core and a stretchable sheath arranged over this core, said film being fixed on the sheath surface facing towards the core.

14. A cable or line as claimed in any one of the preceding Claims in the form of a coaxial structure with an inner conductor and an outer conductor, wherein the insulation of the outer conductor is provided with said stretched and sintered film fixed on its inner surface facing towards the outer conductor.

15. A process for producing a cable or a line as claimed in Claim 1, comprising the steps of fixing said stretched and sintered strip-shaped film longitudinally around the respective core/conductor substructure of the cable or line, before the application of said covering thereto and said covering is formed directly on said film, the material of said covering being subsequently cross-linked, the strip-shaped film located on the inner face of the covering being bonded or welded thereto, simultaneously with the application of the covering and/or the subsequent cross-linking.

16. A process as claimed in Claim 15, wherein said film is heated before the covering is applied.

17. A highly flexible electrical cable or corresponding line substantially as hereinbefore described with reference to and as shown in Fig. 1, or Fig. 2, of the drawing.