Abstract:
An improved method of manufacturing a light waveguide cable having a light waveguide bundle of at least one lead with the filling material received in an outer sheath characterized by the method including applying an outer sheath on the bundle with the filling material, said sheath being of a material at least partially light permeable and cross-linking the filling material by irradiating the sheath with light radiation, such as ultraviolet light, which will pass through the sheath to cross-link the filling material.

Description:
BACKGROUND OF THE INVENTION 
     The present invention is directed to a method for manufacturing a light waveguide lead or cable, wherein at least one light waveguide together with at least a partially cross-linkable filling compound are introduced into a sheath. 
     U.S. Pat. No. 4,641,916, whose disclosure is incorporated by reference and which was based on German Application No. 34 00 605, discloses a light waveguide provided with a cushion layer, which is accommodated inside of a sheath of hard material. A glide layer, that exhibits carrying properties and is preferably composed of a cross-linkable or thixotropic material, is provided between the hard sheath and the cushion layer. 
     When the cross-linkable filling compounds are used, an application of energy is usually needed for the implementation of the cross-linking process. For example, one can work under elevated outside temperature conditions in order to provide the required energy on the basis of the correspondingly high temperature. Otherwise, the production line must be established, for example, with long paths so that an adequate cross-linking can be achieved at lower temperatures, for example before the lead or cable is wound onto drums. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to provide a method in which the application of energy can be introduced for at least partially cross-linking the filling compound in an especially simple way. This object is accomplished in an improvement in the method for manufacturing the light waveguide cable or lead by providing at least one light waveguide, providing at least partially cross-linkable compound, introducing the light waveguide and the cross-linkabe compound together into a sheath. The improvements are that the sheath is formed of at least a partially light permeable material and the method further includes irradiating the sheath with light energy immediately following the assembly of the protective sheath with the light passing through the sheath to partially cross-link the filling compound. 
     The cross-linking can be executed after the application of the protective sheath on the basis of a suitable selection of the material of the sheath so that at least a partially light permeable material is used. In this condition, the filling compound no longer drips or runs off and the radiated means, moreover, can be introduced into the manufacturing sequence in a simple way without constraints. 
     Polyetherimide, polycarbonate, for example sold by Bayer AG under the tradename &#34;MAKROLON 3118&#34;, polyamide, for example sold by Emser Werke AG under the tradename &#34;GRILAMID TR 55&#34; and PEEK are preferably suited as materials for the protective sheath. 
     Other features and advantages of the present invention will be readily apparent from the following description of the preferred embodiments, the drawings and claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic illustration of a production line forming a light waveguide lead or cable in accordance with the present invention; and 
     FIG. 2 is a cross sectional view through a light waveguide lead or cable manufactured in accordance with the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The principles of the present invention are particularly useful for producing a light waveguide lead or cable, which is generally indicated LWA in FIG. 2. The light waveguide cable LWA has a hard outer protective sheath SH that is composed of an entirely or partially light permeable material. In the present example of FIG. 2, it is assumed that a single optical fiber LF, provided with a coating CT, is arranged on the inside of the light waveguide cable LWA as a light waveguide LW1. However, as indicated and discussed with regard to FIG. 1, the cable may have a bundle of a plurality of light waveguides LW1-LWn in the inside of a common protective sheath SH. The filling compound FC, which serves as a glide layer, is provided between the light waveguide LW1 and the sheat SH so that the light waveguide LW1 is displaceable or movable relative to the protective sheath, at least to a slight extent. Compensation events can be executed better in this way without damaging the sensitive optical fiber LF. 
     In order to prepare the cable LWA, a series of light waveguides or fibers LW1-LWn are provided on a series of reels SP1-SPn, as shown in broken lines in FIG. 1. These light waveguides are taken from the supply reels SP1-SPn and supplied to a coating means BF in which a filling compound FC is supplied via a corresponding pipe line, as indicated by the arrow. This filling compound FC, for example, can be applied to the light waveguide bundle as it is being conducted through the pipe in which the filling compound is being introduced from a side of the pipe. This light waveguide bundle, with the filling compound FC, leaves the device BF as a coated bundle LWF. This bundle enters into a bore of an extruder head EX1, whose output end extrudes a stretching cone SHR, which is later drawn to the desired diameter by a stretching process to such an extent that it forms a hard outer protective sheath SH, as shown in FIG. 2. 
     As soon as the stretching cone SHR for the protective sheath SH has been drawn down to the desired, ultimate diameter of the protective sheath, one or more illumination means UVL1 and UVL2, whose radiation preferably operates in an ultraviolet range, is directed onto the light waveguide cable LWA. Since the outer protective sheath SH is at least partially light permeable, the light also proceeds through the sheath into the inside and impinges on the filling compound FC, which serves as a glide layer. This will cause the filling compound to be cross-linked to the desired degree, and this is capable of being accomplished on the basis of the intensity of the radiation of the light sources UVL1 and UVL2 in a simple way in combination with the rate of travel. The cross-linking is, thereby, expediently carried out to such an extent that the initially, practically liquid filling compound is at least partially cross-linked. The viscosity of the filling compound FC, when filling, should be very low and should, preferably, lie between 10 m Pa s and 30,000 m Pa s. In the final or cross-linked condition, by contrast, the viscosity of the filling compound is substantially higher and, namely, lies in a range of between 10×10 3  m Pa s and 2×10 6  m Pa s (milli Pascal second). 
     When the filling compound is especially thin-bodied, it is recommended to replace the coating means BF in FIG. 1 and use a filling needle FN, which is illustrated in broken lines in the FIG. 1 and which extends into the extruder EX1. The outlet opening of this filling needle FN is shown, and is roughly in the region of the stretching cone SHR or shortly before the stretching cone. 
     UV-cross-linkable materials, preferably, come into consideration as the materials for the filling compound FC. In particular, an ultraviolet silicone resin that is sold and known under the order name &#34;RC 640&#34; by the Goldschmitt Company, will make up approximately 95% of the weight of the filling compound. The remaining 5% is formed by a photo initiator sold under the order name &#34;A2&#34; by the Goldschmitt Company. As needed, it is expedient to use an oil, particularly a silicone oil, in the mixture for changing the viscosity, and an example of such a silicone oil is sold under the tradename &#34;AK1000&#34; by Wacker Chemie. Other material that can be used as a filling compound FC and, thus a glide layer, are sold by Siemens AG under the order names &#34;CS24&#34; and &#34;C38&#34;. 
     Suitable materials for the protective sheath SH with adequately good light-transmitting properties are selectd from a group consisting of polyetherimide, polycarbonate, polyvinyl chloride and polyamide. Polyamides, polyvinyl chloride, polyetherimides and polycarbonates are suitable materials for the sheath SH. The wall thickness of the protective sheath SH should, therefore, be expediently selected between 0.1 mm and 2 mm. 
     The filling compound FC serves as a glide layer. It should have its properties modified by the cross-linking process so that the material obtained in the final result, i.e., after the cross-linking which is obtained by an illumination device UVL1 and UVL2 can still have its properties determined by a viscosity measurement but it should not be cross-linked to such a point that it becomes an elastomer. A complete cross-linking elastomer would too-firmly embed the sensitive light waveguide LW1, whereas an excessively liquid filling compound has a tendency to still drip out of exposed locations, such as splicing locations. 
     When a further protective sheath SHA, as indicated in broken lines in FIG. 2, is to be applied to the protective sheath SH, the light waveguide cable LWA passes through a second extruder EX2, which applies the second or additional outer sheath SHA in the form of a stretching cone SAR. After the second outer sheath SHA has been stretched down to the desired final outside diameter, the light waveguide lead or cable can transverse a cooling basin CL and is subsequently applied via conveyor means in the form of, for example, a caterpillar pull-of device AZ to a drum TR where the light waveguide cable or lead is wound. 
     When the two layers SH and SHA are applied, then the illumination means UVL1 and UVL2 are arranged before the second extruder EX2. In other words, the application of light is only carried out through the innermost protective sheath SH. Of course it is, thus, no longer necessary that the outer or second protective sheath SHA be composed of a light permeable material. 
     Although various minor modifications may be suggested by those versed in the art, it should be understood that we wish to embody within the scope of the patent granted hereon all such modifications as reasonably and properly come within the scope of our contribution to the art.