Abstract:
A power and/or telecommunication cable (Ia,Ib) includes one or several conductor elements ( 10,20,30 ) surrounded by an outer sheath, where the outer sheath ( 40,50 ) comprising a first layer ( 40   a,    40   b ) able to emit light radiation, and a second layer ( 50 ) made of a light transmitting thermoplastic polyurethane (TPU) material surrounding the first layer ( 40   a,    40   b ), so that h first layer ( 40   a,    40   b ) is visible through the second layer ( 50 ).

Description:
BACKGROUND 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a power and/or telecommunication cable comprising a layer able to emit light radiation. 
         [0003]    More particularly, the power and/or telecommunication cable is used in mines and similar applications such as severe abrasion and dark environment. 
         [0004]    2. Description of Related Art: 
         [0005]    A conventional power or telecommunication cable includes one or more conductor elements, especially insulated conductor elements, with a protective outer sheath. An electrical power cable is typically constructed with conductor elements formed of copper wire for efficiently conducting electrical power on whatever scale is desired. A telecommunication cable is typically constructed of relatively small wire conductor elements for conducting electrical signals and/or fiber-optic strands for conducting optical signals. 
         [0006]    Power and telecommunication cables are used in many environments. One of the harshest environments for cables is mining operations in dark environment, In particular, the cables used in mining operations tend to be subjected to severe abrasion due to equipment, traffic, and mining materials moving over or along the mining cable. In addition, the lack of cable visibility in said dark environment frequently produces cable crushing or abrasive wearing by the mining trucks and the shovel machines. 
         [0007]    Technical solutions already exist to visualize the cable so that the cable is less subjected to severe abrasion. In this respect, two variants are well-known 
         [0008]    The first variant consists in using an outer sheath such as an outer rubber sheath pigmented with a fluorescent pigment. However, said outer sheath presents low durability of the fluorescent pigments due to direct exposure to the ground, air, water and UV light. 
         [0009]    The second variant is to case a reflective tape helically wrapped over the outer sheath of the cable. However, said additional reflective tape risks to be easily destructed due to severe use in mining conditions. 
       Objects and Summary 
       [0010]    The present invention seeks to solve the above-mentioned problems of the prior art, and proposes a cable showing both high abrasion resistance and a good visibility in dark environment, more particularly in outdoor dark environment. 
         [0011]    To this end, an object of the present invention is to provide a poi power and/or telecommunication cable including one or several conductor elements surrounded by an outer sheath, wherein said outer sheath comprising :
       a first layer able to emit light radiation, and   a second layer made of a light transmitting thermoplastic polyurethane (TPU) material surrounding the first layer, so that the first layer is visible through the second layer, and preferably the second layer is the outer most layer of the cable.       
 
         [0014]    More particularly, the first layer can be visible through the second layer in dark environment in emitting light radiation. 
         [0015]    The first layer can typically be a tape wrapped helically around the conductor element (wrapped tape) a layer extruded around the conductor elements (extruded layer). 
         [0016]    One understands by the expression “a first layer able to emit light radiation”, a layer which can directly or indirectly emit light radiation, especially visible light radii on. The tern “directly” means that the radiation light is emitted from the first layer as such. The term “indirectly” means that the radiation light is emitted by the first layer, but from the intermediate of an external light radiation source. 
         [0017]    In a first embodiment, the first layer is made of a luminescent material. The luminescent material allows to directly emit light. Said light does not derive energy from the temperature of the emitting material. 
         [0018]    The luminescent material can be selected among a fluorescent material, a phosphorescent material, and a bioluminescent material, or a mixture thereof. 
         [0019]    Preferably a fluorescent material is used. The fluorescent material of the first layer absorbs light in order to emit light in dark environment. So, once the cable according to the invention is exposed with light, it able to emit light in dark environment. For example, positioning in outdoor environment, the cable can be energized with sunlight during the day and emit the absorbed light during the night. 
         [0020]    In a first example, when the first layer is a tape, the outer surface of the tape is coated with fluorescent ink. 
         [0021]    For example, the tape material as such is selected among cotton fabric, crosslinked acrylic compound on polyester/nylon substrate and other appropriate fabrics. 
         [0022]    In a second example, when the first layer is an extruded layer, the extruded layer is made of a thermoplastic polymer including fluorescent pigments. 
         [0023]    In a second embodiment, e first layer is made of a reflective material. The reflective material allows to indirectly e it light. Indeed, the reflective material is a surface on which a light, coming from a external source (e.g. car light), is reflected on its surface. 
         [0024]    The reflective material is preferably a tape, chic h can be cased alone or wrapped helicoidally and alternatively with a colored binder tape well-known in the art, The reflective material can be a silvered reflective tape. 
         [0025]    This second embodiment is especially suited for indoor dark environments like underground mines. 
         [0026]    In a third embodiment, the first layer is made of a luminescent material and of a reflective material, both materials being already described previously 
         [0027]    More particularly, the first layer can comprise a tape of luminescent material wrapped helicoidally and alternatively around the conductor element with a tape of a reflective material. 
         [0028]    The light transmitting material is such that the first layer can be visually seen through the second layer as if there as substantially no intervening material. By way of example, a material which transmits light can be a translucent material or a transparent material. 
         [0029]    One understands that the second layer made of trans transmitting T material is a light transmitting layer. 
         [0030]    The second layer made of a light transmitting TPU material can be an extruded TPU layer, which is Obtained by an extrusion process well-known in the art. 
         [0031]    In a specific embodiment, the TPU material (i.e. second layer) can be crosslinked. Crosslinking processes are well-known in the art and one example can be to crosslink the TPU material in presence of X-radiation. 
         [0032]    The second layer can further comprise at least one flame retardant filler selected among triphenylphosphate, tertbutylphenyl diphenyl phosphate and tertbutylated diphenyl phosphate, or mixtures thereof, to obtain a flame retardant layer, and more particularly a halogen free flame retardant JIFF second layer. Said flame retardant filler does advantageously not affect transparency of said second layer. 
         [0033]    The obtained second layer can therefore be a transparent HFFR extra heavy duty thermoplastic polyurethane jacket. 
         [0034]    According to the invention, the first and the second layers of t le outer sheath allows advantageously to provide a very resistant outer sheath which is visible in dark environment. 
         [0035]    In addition, the cable according to the invention satisfies to the TCEA S-75-381-2008 standard concerning “Portable and power feeder cables for use in mines and similar applications”. 
         [0036]    In a first variant, the second layer cal be directly in contact with the first layer, or in other terms, there is no intermediate layer positioned between the first layer and the second layer. 
         [0037]    In a second variant, the cable further comprises an intermediate layer along the cable between the first layer and the second layer, so that the first layer is visible through the intermediate layer. 
         [0038]    In this respect, said intermediate layer can be a reinforcing open material and/or can be made from a light transmitting material. 
         [0039]    For example, the reinforcing open material can be an open mesh such as threads used as double serving. 
         [0040]    The light transmitting material can be a non-extruded layer covering the whole surface of the first layer, such as a tape, and more particularly a polyester tape, wrapped helically around the first layer. 
         [0041]    Said light transmitting material as intermediate layer is more particularly suitable when the first layer is a reflective tape, and more especially a silvered reflective tape. Indeed, the extrusion of TPU layer directly around a reflective tape aims at damaging the micro-crystal structure of the reflective tape since the applicant noticed that in this case, the reflective tape lost its reflectance properties. 
         [0042]    The thickness of the second layer as well as the nature and quantity of fillers in the material of second layer is such as the second layer keeps substantially a sufficient transparency to visualize the light radiation emitting material in dark environment, in this respect, the man skilled in the art is able to perform trials to find the optimum or workable second layer by routine experimentations. The same conditions apply to the intermediate layer when it is used. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0043]    The present invention will become more fully understood from the detailed description given herein below and from the accompanying drawings which are given by way of illustration only, and thus, which are not limits of the present invention, and wherein: 
           [0044]      FIG. 1  represents a schematic cross-sectional view of a first embodiment of a cable according to the invention. 
           [0045]      FIG. 2  represents a schematic cross-sectional view of a second embodiment of a cable according to the invention. 
       
    
    
       [0046]    These two embodiments are favorable for use in dark environment, especially as a mining cable. 
         [0047]    For reasons of clarity, the same elements are designed by identical references. Similarly, only those elements that are essential for understanding the invention are shown in diagrammatic manner, and scale is not complied with. 
       DETAILED DESCRIPTION 
       [0048]    Referring to  FIG. 1 , the cable Ia includes a plurality of conductor elements  10 , 20 , 30 , said plurality of elements being surrounded by an outer protective sheath  40   a,    50  according to the invention. Said cable schematically illustrates a SHD, shielded round three-conductor cables (5001 to 25000 Volts) according to ICEA S-75-381-2008 standard, part 3.10.3.2. 
         [0049]    The insulated conductor elements comprise three power insulated conductors  10 , one ground check insulated conductor  20  and two grounded uninsulated conductors  30 . A power insulated conductor  10  is for example composed of a plurality of stranded conductor wires  11  surrounded successively. 
         [0050]    by a first semiconductor layer  12 , a dielectric insulation  13 , a second semiconductor layer  14 , and a shield  15 . 
         [0051]    The outer protective sheath  40   a,    50  is a two-layer sheath according to the invention. 
         [0052]    The inner layer  40   a  is a fluorescent tape wrapped around the conductor elements  10 , 20 , 30 . An extruded outer layer  50  of light transmitting thermoplastic polyurethane surrounds said inner layer  40   a,  the outer layer  50  being directly in contact with the inner layer  40  in order to see visually the inner layer through the outer layer, especially in a dark environment. 
         [0053]    in addition, the cable according to the invention can comprise a reinforcing open material such as nylon threads (not represented) between the inner layer and the outer layer. 
         [0054]    The cable represented on  FIG. 1  is manufactured such as the power insulated conductors  10 , the ground check insulated conductor  20  and the grounding uninsulated conductors  30  are gathered to form an assembly. Then, the inner layer  40   a,  and eventually the reinforcing nylon threads, are applied over said assembly. Finally, a light transmitting thermoplastic polyurethane material is extruded around the fluorescent tape, or around the reinforcing nylon threads if existed, to form the outer layer  50  of the outer sheath. 
         [0055]    In this example, the fluorescent tape is commercialized by Loypos under the reference Fluorescent Tape, said tape having a thickness of about 0,20 mm. The light transmitting thermoplastic polyurethane material is commercialized by Lubrizol under the reference Estane ZHF 80AT3 NAT 021 or by AlphaGary under the reference Irogran A78P 4766NM, the extruded thermoplastic polyurethane layer having a thickness of about 7.5 mm. The reinforcing nylon threads are commercialized by Synthetic Thread Co Inc., under the reference Nylon 1050/3 Ply Preshrunk. The outer sheath according to the invention can be defined according to outer sheath thickness in the part 321.2 of ICEA S-75-381-2008 standard, and according to cable outside diameters in the part 3.22 of ICEA 5-75-381-2008 standard. The additional threads between the two layers of the outer sheath are provided according part 3.21.2 of ICEA 5-75-381-2008 standard. 
         [0056]      FIG. 2  represents a same type of cable as described in  FIG. 1 , except that the outer sheath is related to another embodiment of the invention. 
         [0057]    More particularly, the cable lb includes a plurality of conductor elements  10 , 20 , 30 , said plurality of elements being surrounded by an outer protective sheath  40   b , 40   c , 50  according to the invention. 
         [0058]    The outer protective sheath  40   b , 40   c , 50  is a three-layer sheath according to the invention. 
         [0059]    The inner layer  40   b  is a reflective tape wrapped around the conductor elements. An intermediate layer  40   c,  which is a light transmitting polyester tape, is wrapped around said inner layer  40   b , said intermediate layer  40   c  being directly in contact with said inner layer  40   b.    
         [0060]    An extruded outer layer  50  of light transmitting thermoplastic polyurethane surrounds said intermediate layer  40   c,  the outer layer  50  being directly in contact with the intermediate layer  40   c  so that the inner layer  40   b  is visible through the outer layer  50  and through the intermediate layer  40   c , especially in a dark environment. 
         [0061]    In this example, the reflective tape is commercialized by HUATP LIMITED under the reference H-F 0101, said tape having a thickness of about 0.20 mm. The intermediate tape is commercialized by Gareware polyester Limited under the reference ERE 36, said tape having a thickness of about 36 micrometer. The light transmitting thermoplastic polyurethane material is commercialized by Lubrizol under the reference Estane Ziff 80AT3 NAT 021 or by AlphaGary under the reference Irogran A78P 4766NM, the extruded thermoplastic polyurethane layer having a thickness of about 7.5 mm. 
         [0062]    The cables as represented by  FIGS. 1 and 2  illustrate cable haying a circular cross section. However, the circular cross section is given by way of illustration, and thus other forms can be considered such as for example a flat cross section.