Cable and method for producing the cable

Abstract

A cable is used, in particular, as an underwater cable and contains a central element, which is surrounded by a cable sheath. The cable sheath has an inner hydrophobic sheath layer made of a first plastic and an outer sheath layer applied to same and made of a different plastic to the inner sheath layer. A polyolefin-type plastic is used for the inner sheath layer and one of the sheath layers, in particular the inner sheath layer is chemically functionalized, and a sealed connection is formed between the two sheath layers.

Claims

1. A cable, comprising: a central element; and a cable sheath having an inner hydrophobic sheath ply formed from a first plastic and an outer sheath ply being applied to said inner hydrophobic sheath ply and formed from a plastic different from that of said inner hydrophobic sheath ply, wherein a polyolefinic plastic is used for said inner hydrophobic sheath ply, wherein one of said inner hydrophobic sheath ply or said outer sheath ply is chemically functionalized resulting in a chemically functionalized sheath ply, wherein said outer sheath ply is formed from a polyurethane, and wherein a fluid-tight connection is formed between said inner hydrophobic sheath ply and said outer sheath ply.

2. The cable according to claim 1, further comprising a medium-density polyethylene copolymerized with vinylsilane being used for forming said inner hydrophobic sheath ply; and wherein said polyurethane for forming said outer sheath ply has a catalyst.

3. The cable according to claim 1, further comprising a silane-modified polyolefinic plastic having silicon-functional groups being used for said chemically functionalized sheath ply.

4. The cable according to claim 3, wherein a fraction of silanes in said chemically functionalized sheath ply is in a range between 0.1-5.0 wt %.

5. The cable according to claim 1, further comprising a plastic having a reactive functional group is used for the chemical functionalization.

6. The cable according to claim 5, wherein a fraction of said reactive functional group in said chemically functionalized sheath ply is in a range between 0.01-3.0 wt %.

7. The cable according to claim 1, wherein a polyolefin with a blend partner is used for said chemically functionalized sheath ply.

8. The cable according to claim 7, wherein a fraction of said blend partner is in a range of 1-50 wt %.

9. A cable, comprising: a central element; a cable sheath having an inner hydrophobic sheath ply formed from a first plastic and an outer sheath ply being applied to said inner hydrophobic sheath ply and formed from a plastic different from that of said inner hydrophobic sheath ply, wherein a polyolefinic plastic is used for said inner hydrophobic sheath ply, wherein one of said inner hydrophobic sheath ply or said outer sheath ply is chemically functionalized resulting in a chemically functionalized sheath ply, and wherein a fluid-tight connection is formed between said inner hydrophobic sheath ply and said outer sheath ply; and a catalyst system being incorporated in one of said inner hydrophobic sheath ply and said outer sheath ply in order to form the fluid-tight connection between said inner hydrophobic sheath ply and said outer sheath ply.

10. The cable according to claim 9, further comprising a polyurethane being used for said outer sheath ply.

11. The cable according to claim 9, wherein said catalyst system has a Brnsted or a Lewis acid.

12. The cable according to claim 9, wherein said catalyst system has a sulfonic acid catalyst.

13. The cable according to claim 9, wherein said catalyst system has an organotin catalyst.

14. The cable according to claim 9, wherein a fraction of said catalyst system is in a range of 0.1-5.0 wt %.

15. The cable according to claim 1, wherein said inner hydrophobic sheath ply has a Shore hardness of 45D to 65D and/or said outer sheath ply has a Shore hardness of 70A to 70D.

16. The cable according to claim 1, wherein the cable has an overall diameter of between 5 mm to 45 mm.

17. The cable according to claim 1, wherein said inner hydrophobic sheath ply has an inner wall thickness which is between 0.1 mm for a small overall diameter to 1.5 mm for a large overall diameter.

18. The cable according to claim 1, wherein said outer sheath ply has an outer wall thickness which is between 0.2 mm for a small overall diameter to 2.0 mm for a large overall diameter.

19. A cable comprising: a central element; a cable sheath having an inner hydrophobic sheath ply formed from a first plastic and an outer sheath ply being applied to said inner hydrophobic sheath ply and formed from a plastic different from that of said inner hydrophobic sheath ply, wherein a polyolefinic plastic is used for said inner hydrophobic sheath ply, wherein one of said inner hydrophobic sheath ply or said outer sheath ply is chemically functionalized resulting in a chemically functionalized sheath ply, and wherein a fluid-tight connection is formed between said inner hydrophobic sheath ply and said outer sheath ply; and the cable is pressure-resistant for several 10 bar and resistant to fluctuating pressure stresses.

20. The cable according to claim 1, wherein at least one of said inner hydrophobic sheath ply or said outer sheath ply has a flame-retardant plastics mixture as said first plastic or said plastic.

21. The cable according to claim 1, wherein further measures for ensuring the fluid-tightness, such as a separating ply between said inner hydrophobic sheath ply and said outer sheath ply, a swellable nonwoven, or fillers, are eschewed.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) The single FIGURE of the drawing shows a diagrammatic, cross-sectional view through a cable having a central element which is surrounded by a double-walled sheath according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

(2) Referring now to the single FIGURE of the drawing in detail, there is shown, in a simplified representation, a cross section through a cable 2 having a central element 4 which is surrounded by a double-walled sheath 6. The latter has an inner sheath ply 8, which is applied, in particular by extrusion, directly to the central element 4. The inner sheath ply 8 is surrounded directly by an outer sheath ply 10, which is applied, again preferably by extrusion, to the inner sheath ply 8. The sheath 6 has an overall thickness D which is in the range between 5 mm and 45 mm. The inner sheath ply 8 has an inner wall thickness d1 in the range from 0.1 mm to 1.5 mm. The outer sheath ply 10 has an outer wall thickness d2 in the range from 0.2 mm to 2 mm. The structure may be surrounded by a further exterior sheath, or two or more such cables 2, in particular in combination with other elements as well, form an assembly surrounded by a common exterior sheath. Preferably, however, the outer sheath ply 10 forms an exterior sheath.

(3) The central element 4 is more particularly a cable core made up of individual cable elements. Specifically, the cable 2 is a data cable having a plurality of data transmission wires which form the cable core 4. With preference, therefore, there are exclusively data transmission elements in the cable core 4. In principle, it is also possible for power elements to also be integrated as well as the data transmission elements. The data transmission elements more particularly are electrical lead wires which are arranged preferably in pairs for symmetrical data transmission. Each pair of wires in this case is twisted or untwisted and provided with or without pair shielding. In addition there may also be optical transmission elements integrated.

(4) In general, diffusion of water into the central element 4 is prevented or at least sufficiently reduced by the selection, as sheath material for the inner sheath ply 8, of a plastic which possesses a very low rate of diffusion and of saturation. Particularly suitable here are halogen-free, polyolefinic materials having hydrophobic qualities, such as polyethylene, polypropylene or polyolefinic elastomers (POEs), for example.

(5) Given the further requirement also for the cable on the one hand to be flexible and on the other hand to necessarily be amenable to effective, pressure-tight casting in plug connectors and housings by a polyurethane-based casting compound, a soft polyurethane is used for the outer sheath ply, this polyurethane preferably having a Shore hardness of between 64D and 95A.

(6) A fundamental physical quality of polyolefinic materials is that they possess low surface tension and therefore display a very low tendency to join with the polar polyurethane, which has a high surface tension.

(7) If the polyurethane is extruded onto a cable having a standard polyolefinic water-repellent layer, the two sheaths lie against one another with virtually no connection, and can be separated from one another without great peeling force. The connection is not positive and is also not pressure-tight in the longitudinal direction.

(8) This, however, would mean that water having diffused through the outer polyurethane sheath would flow onto the inner polyethylene or polypropylene sheath in the longitudinal direction and so would enter the plug connector or housing.

(9) In order to avoid this problem, therefore, provision is made in accordance with the invention for chemical functionalization of the polymer of the inner sheath ply 8 and also for activation particularly of the surface of the inner sheath ply 8, specifically in such a way that the polyurethane layer, which is extruded in a further operation onto the inner polyethylene or polypropylene sheath, enters into a shape-tight and pressure-tight connection with the inner layer.

(10) The activation is accomplished preferably by corona exposure of the inner sheath ply consisting of the polyolefinic material having the water-repellent qualities. Alternatively, plasma exposure is provided. Here, oxidation radicals are formed and/or the surface is polarized.

(11) In further alternatives, an adhesion promoter or an adhesive is applied.

(12) For the chemical functionalization, the polyolefinic material is modified. According to a first variant, polyolefinic materials are used which have been grafted with maleic anhydride. According to a second variant, polyolefinic materials are used which have been copolymerized or grafted with reactive or functionalized or silicone-functional silanes (e.g. alkoxysilane compounds). Used especially is a medium-density polyethylene which has been grafted or has been copolymerized with vinylsilane, more particularly vinylalkosysilane.

(13) The formation of the fluidtight connection between the sheath plies 6 and 8 is supported additionally by a catalyst system which is incorporated into the outer sheath ply 8. The catalyst system incorporated into the material for the outer sheath ply 10 is, for example, an organotin compound, preferably a sulfonic acid.

(14) All in all there is a (chemical) reaction between the (corona-activated) polyolefinic MDPE sheath ply and the TPU sheath ply provided with the catalyst.

(15) It is conceivable, for example, for the corona-activated polyolefinic sheath ply to react with the amide groups of the urethane group and for this reaction to be accelerated by the catalyst which has been added to the polyurethane sheath.

(16) In a specimen fabrication, a cable 2 with a silane-modified inner sheath ply 8 with an outer TPU sheath ply 10 was produced using a sulfonic acid as catalyst system. The diameter of the central element (cable core 4) was 14 mm. The inner wall thickness d1 was about 1 mm. The corona electrodes were positioned so that they treated the entire cable circumference with overlap. With preference, 3 electrodes are used. The corona voltage was 7 kV. Corona treatment is carried out in-line subsequent to the extrusion of the inner sheath ply 8, i.e. immediately after the extrusion and continuously during the production. Subsequent to the corona treatment, the outer sheath ply was extruded on. The outer sheath ply 10 was extruded on with a (linear) velocity of 2.4 m/min. The outer wall thickness d2 was likewise approximately 1 mm.

(17) The cable 2 is in particular an underwater cable.

(18) The cable comprises at least one element possessing a defined impedance (Ethernet, Cat 6, Cat 7 with respective 100-ohm elements; Profibus, Profinet, Canbus with 120-ohm and/or 150-ohm elements; coaxial cable) and also, optionally, further elements as hybrid cables. An alternative possibility is to employ the principle for other underwater cable constructions, such as for optical waveguide cables, for example, but also signal cables and energy cables. Also possible is the use of the invention for all cables requiring enhanced protection from the penetration of water or moisture. It is conceivable as well for the proposed combination of materials and layer construction to be selected in order to achieve further combinations of qualities, such as, for example, better mechanical employability of the cable or an improvement in the abrasion resistance.

(19) Sheath materials which can be used are in principle flame-retardant and non-flame-retardant mixtures. The inner sheath ply 8 preferably comprises a PE material, for example HDPE (high-density PE), an LDPE (low-density PE), and in particular an MDPE (medium-density PE) with silane grafting, or a silane copolymer is used.

(20) Preferably, the inner sheath ply has in general a Shore hardness of 45 D to 65 D. For the outer sheath ply 10, a preferred material used is a polyurethane with Shore hardnesses of 80A to 64D.

(21) In investigations, the best properties were found when using a silane-modified, medium-density polyethylene in combination with a TPU admixed with a catalyst system, more particularly with a sulfonic acid. Used in particular were the copolymer available under the tradename Visico ME4425 for the inner sheath ply, and the TPU available under the tradename Elastollan 1185A10 and/or Elastollan 1185A10FHF, admixed with 6% to 10% of Ambicat, for the outer sheath ply.