Abstract:
A silicone article, such as a cable with a silicone outer jacket. Solid mica particles are introduced into the surface of the cable or other article. An intermediate product which has a silicone-type base material on the exterior is initially provided in a state that is not, or no more than partially, cross-linked. The solid material particles are subsequently pressed in, before the complete cross-linking takes place. The solid material particles are present only in the surface region.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation, under 35 U.S.C. §120, of copending international application No. PCT/EP2013/060807, filed May 24, 2013, which designated the United States; this application also claims the priority, under 35 U.S.C. §119, of German patent application No. DE 10 2012 208 871.7, filed May 25, 2012; the prior applications are herewith incorporated by reference in their entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The invention relates to a method for producing an element, particularly a cable, which has on the outside a silicone-type base material. The invention relates, furthermore, to such an element. 
     The element is, in particular, an electrical cable with a cable sheath made from silicone. However, the invention is not restricted to the field of use of electrical cables. 
     Electrical cables with a silicone sheath are employed, for example in medical technology, because of their special properties. To be precise, on the one hand, silicone as the material is distinguished by very high flexibility or elasticity, so that highly flexible elastic cables, for example with diameters ranging from 1 mm to 10 mm, can thereby be formed. At the same time, silicone also has a high continuous use temperature of about 180° C. Such cables are therefore suitable for medical applications in which the cables regularly have to be sterilized. This takes place usually with the aid of so-called steam sterilization at temperatures of about 140° C. to 150° C. 
     An electrode line for medical use is described in U.S. patent application publication No. US 2012/0022624 A1 and its counterpart European published patent application EP 2 409 725 A1. There, electrical conductors are introduced into an insulating hose and therefore to some extent lie loosely in the hose. The electrode line serves for use inside the body, for example for heart pacemaker electrode lines. To improve the abrasion resistance of the hose, particulate filling material is introduced into the base material of the hose. The base material is, for example, silicone, polyurethane, polyamide, PTFE, etc. To produce the insulating hose, the filler particles are admixed to an extrudate and are then extruded or injected to form the insulating hose. In a design variant, a two-layer insulating hose is formed by coextrusion, and in this only the outer layer is filled with the filler material. Alternatively to extrusion, a basic hose is dipped into a low-viscosity base material which is mixed with the film material in order to form the outer layer. 
     On account of the good temperature resistance of silicone, silicone is also adopted, in particular, for fire-resistant cables. To improve the fire resistance, as described, for instance in Japanese patent application publication JP 2001035267 the introduction of filler materials, to be precise mica particles, is likewise provided. 
     SUMMARY OF THE INVENTION 
     It is accordingly an object of the invention to provide a method and an article of manufacture which overcome the above-mentioned and other disadvantages of the heretofore-known devices and methods of this general type and which provides for a novel method for producing an element, such as a cable, and also an element, particularly a cable, which is preferably produced by the novel method and which is suitable, in particular, for a medical use environment and, while being simple to produce, makes it possible to have improved properties, as compared with prior art cables. 
     With the foregoing and other objects in view there is provided, in accordance with the invention, a method of producing an article or manufacture, in particular an electrical cable, with an exterior surface of a silicone-type material, the method comprising: 
     in a first step, fashioning an at least partially non-cross-linked base material into an intermediate product; 
     subsequently, in a second step, introducing solid mica particles into the surface by guiding the at least partially non-cross-linked intermediate product through a reservoir containing the solid mica particles therein, and exposing the reservoir to vibration or generating in the reservoir a vortex or an airstream to thereby mechanically press the solid mica particles into the surface and to cause the particles to be distributed over the surface, with a dot-shaped contact zone formed in each case, and wherein at least some of the solid mica particles project out of the surface as scales; and 
     subsequently, in a third step, cross-linking the at least partially non-cross-linked base material. 
     In other words, the objects of the invention are achieved by way of a method for producing an article, particularly a cable, which has on the outside a silicone-type base material. In a first step, the silicone-like base material is first fashioned into a non-cross-linked, at least not completely cross-linked intermediate product. Subsequently, in a second step, solid particles are introduced into the surface, and finally, in a third step, the non-cross-linked or only partially cross-linked base material is cross-linked up to the desired degree of cross-linking, in particular is cross-linked completely. 
     In this method, therefore, the at least partially non-cross-linked state of the base material is utilized in order to introduce the solid particles into the surface of the base material. On account of the non-cross-linked state, this is possible in a simple way in terms of the process employed. As a result of the subsequent cross-linking operation, the solid particles are then incorporated firmly into the surface. The solid particles are applied loosely as such and are therefore not embedded in a carrier material. The solid particles are in the form of a powder. 
     The solid particles are therefore introduced from outside solely into the surface. There is no incorporation of the solid particles as filler material into the volume of the base material. By virtue of the chosen production method, the depth of penetration of the solid particles is therefore also usually limited at most to the extent of the solid particles. The solid particles are therefore not admixed to the base material during the production process. 
     This method is based on the recognition that elements, in particular cables with an silicone-type outer material, i.e., a material that is at least silicone-like or is composed of silicone, have a high coefficient of friction. This often leads to a downright “adhesion” of the element to surfaces, such as, for example, to an operating table or even to the human skin. 
     Proceeding from this, the invention is based on the idea of beneficially influencing the silicone-specific feel by the introduction of solid particles solely on the surface and, in particular, of markedly reducing the coefficient of friction at the surface, in order to avoid or at least reduce undesirable adhesion. By the solid particles being applied merely on the surface, the solid particles regularly project somewhat above the surface formed by the base material. Friction is therefore determined critically by the solid particles. On account of their nature and structure in comparison with silicone, friction is markedly reduced. Furthermore, the loose distribution of the solid particles over the surface has an advantageous effect, so that there is no full surface friction, but instead only a punctiform contact zone occurs in each case. 
     The terms silicone-type or silicone-like base material is understood in general to mean cross-linkable plastics which in the final cross-linked state have, in particular, a coefficient of friction comparable to silicone. Other such base materials in addition to silicones themselves are also polyurethanes, polyamides, polytetrafluoroethylene (PTFE), ethylenetetrafluoroethylene (ETFE), perfluoroethylenepropylene (FEP), perfluoroalkoxy (PFA), etc., and also copolymers of these. Preferably, however, silicone or a silicone-containing material (copolymer) is used for the base material. 
     In a preferred refinement, the solid particles are introduced into the surface of the intermediate product mechanically. In this case, in general, a mechanical force is exerted upon the particles. In the simplest instance, this may be the weight. Alternatively or as a backup to a mechanical application, there is also the possibility of electrostatic application of the solid particles. In this case, electro(static) forces are utilized instead of mechanical forces. The loosely present solid particles are in this case, in particular, charged electrostatically before application. 
     Preferably, for mechanical introduction, in the second step, the intermediate product is led through a reservoir having solid particles contained therein. Since the intermediate product usually has high adhesiveness because of its at least partially non-cross-linked state, the solid particles are automatically caught on the surface. 
     In order to assist this adhesion of the solid particles and in order to achieve as homogeneous a degree of coverage as possible, the reservoir is preferably exposed to vibration, so that the solid particles are virtually pressed mechanically into the surface. The reservoir is therefore designed as a vibrating container. In principle, the element itself could also be moved back and forth mechanically. 
     In an expedient development, the reservoir is designed in the manner of a hopper through which the intermediate product is led. This also makes it possible, in particular, for the intermediate product, formed particularly as a string, to be led vertically through the reservoir in a continuous process. Alternative forms of the reservoir are likewise possible. 
     Alternatively to this, the intermediate product is led through a cyclone container in which an airstream or a vortex as a carrier stream is formed for the solid particles, so that these are swirled around and are therefore caught on the outer surface of the intermediate product. 
     The intermediate product itself is expediently formed as a result of an extrusion process, the solid particles preferably being introduced immediately thereafter in a continuous process. For this purpose, in particular, the intermediate product formed as an endless string is led through the reservoir. 
     In a preferred development, excess solid particles are removed again in a cleaning stage. This takes place, in particular, after the third step of cross-linking, so that all the solid particles not incorporated into the surface are therefore removed again. This takes place preferably by means of a washing process. For this purpose, the element is expediently led through a cleaning bath which, for example, is additionally acted upon ultrasonically. 
     The solid particles introduced into the surface are expediently laminated silicates (mica particles), micro glass balls, metal soaps or talc particles. Investigations have shown that the desired effect of a reduction in friction is especially marked particularly in the case of mica particles. Talc particles have also turned out to be suitable. 
     Investigations have shown, furthermore, that the size of the solid particles has a decisive influence upon the desired friction-reducing property. The solid particles preferably have a size which corresponds to a mesh size in the region of 320+/−40. Mesh is in this case the mesh width of a screen for separating the desired particles. The solid particles therefore preferably have generally a maximum particle size preferably in the range of 35 μm to 55 μm. 
     With a view to an especially efficient and economical production method, the article, particularly the cable, is produced in a continuous fully automatic process, the following steps being carried out directly in succession: first, the intermediate product is generated as a continuous string preferably in an extrusion process, and solid particles are subsequently introduced into the surface of the extruded string before the base material is then cross-linked. Thereafter, the product thus obtained is cleaned of excess solid particles, and finally the product obtained is typically wound, for example, on a drum. 
     The article is preferably in general an electrical cable designed as a sheathed line, with at least one line conductor which is surrounded by an outer sheath made from the silicone-like base material. The cable is, in particular, a data or signal cable in which a plurality of insulated line conductors are surrounded by a common outer sheath. The line conductors typically have an electrical conductor which is itself surrounded by insulation. The electrical conductor may be a solid wire or preferably an ultrafine or fine wire strand. The entire cable has, for example, a diameter in the range of about 1 mm-5 mm, the sheath thickness of the silicone outer sheath, lying, for example, in the range of 0.5 mm to 3 mm. 
     With the above and other objects in view there is also provided, in accordance with the invention, an article, comprising: 
     an outside surface formed of a silicone-type base material; 
     solid particles embedded in the surface of the base material for reducing a coefficient of friction of the surface; 
     the solid particles being mica particles pressed into the surface and distributed over the surface so that merely a dot-shaped contact zone is formed in each case, and at least some of the solid particles projecting out of the surface in the manner of scales. 
     This element is characterized in that solid particles are embedded only in the surface of the base material. The solid particles are therefore present only in a near-surface region, the volume of the base material itself consequently being free of solid particles. The depth of penetration of the particles into the surface therefore preferably corresponds to no more than the particle size. 
     Furthermore, there is preferably provision whereby at least some of the solid particles project out of the surface in the manner of scales. The solid particles in this case also preferably have no preferential orientation, but instead are embedded haphazardously or randomly into the surface. The solid particles are, in particular, flaky elements, in particular mica particles, and have a size preferably in the range of 35 μm-55 μm (measured in the direction of the greatest extent). 
     Other features which are considered as characteristic for the invention are set forth in the appended claims. 
     Although the invention is illustrated and described herein as embodied in a method for producing an element, particularly a cable, from a silicone-like base material, comprising introduction of solid material particles into the surface of an intermediate product, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims. 
     The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
         FIG. 1A-C  show diagrams to illustrate the production method for producing a cable with a silicone outer sheath having solid particles introduced therein; 
         FIG. 2  shows a greatly simplified cross-section through a cable produced accordingly; and 
         FIG. 3  shows a microscopic photograph (micrograph) of the surface of a cable produced in this way. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the figures of the drawing in detail and first, particularly, to  FIGS. 1A, 1B, and 1C , to produce a cable  2  which is first in the form of continuous stock, various installations and components may be employed. For example, three variants in each case modified in relation to one another are illustrated in the mentioned  FIGS. 1A to 1C . 
     In all variants, a plurality of line conductors  6  are fed to an extruder  4  and within the framework of an extrusion process are surrounded with an outer sheath  8  made from a silicone-type base material. The outer sheath in this case surrounds the line conductors  8  directly. It therefore rests directly against the line conductors  6 . In addition to the line conductors  6 , if required, filler or hose elements or else strain relief threads may also be incorporated. 
     The base material used in the context is a silicone which, when it leaves the extruder  4 , is still in an at least partially non-cross-linked state. An intermediate product  10  therefore emerges from the extruder  4 . This intermediate product is subsequently guided in a continuous process through a reservoir  12  which is filled with solid particles  14 , in particular mica particles, present as loose bulk material, or into which at least the solid particles are introduced. 
     In the design variant according to  FIG. 1A , the reservoir  12  is preferably a vibrating hopper which can be set in vibration. The string-shaped intermediate product  10  runs through the reservoir  12  preferably in the vertical direction, selectively from the top downward ( FIG. 1A ) or from the bottom upward ( FIG. 1C ). Alternatively, a horizontal leadthrough through the reservoir is provided ( FIG. 1B ). The reservoir in  FIG. 1B  is in this case preferably designed in the manner of a cyclone container in which an airstream is generated, so that the solid particles  14  preferably stored in the reservoir  12  are swirled around. 
     Finally, in a non-illustrated further alternative, the solid particles  14  are applied with electrostatic backup. For this purpose, the solid particles  14  are first charged electrostatically and are subsequently brought into contact with the intermediate product  10 . This preferably takes place, in turn, with the aid of a container  12 , for example similar to that illustrated in  FIG. 1B , in that the solid particles  14  are led through an electrostatic charging module and are subsequently applied to the intermediate product  10  from above in the manner of a trickling installation. If required, in this case, there may be backup by an airstream for the generation of turbulence. 
     After the solid particles  14  have been applied to the surface  18  (cf.  FIG. 2 ), the intermediate product  10  is led through a cross-linking station  20  in order to cross-link, or completely cross-link the base material. Cross-linking takes place, for example, by thermal treatment or else by UV treatment etc. The intermediate product  10  may in each case be deflected via deflecting rollers  16 . These are preferably arranged downstream of the cross-linking station  20 , as illustrated in  FIG. 1C . In the embodiment according to  FIG. 1B , the deflecting rollers  16  are dispensed with entirely. 
     Finally, after the cross-linking station  20 , the cable  2  also runs through a cleaning stage  22 . In the exemplary embodiment, this is a cleaning container which is filled with a washing liquid. A drying stage may also be connected thereafter, before the finished cable  2  is then wound on a drum  24 . 
     A cable  2  produced in this way is illustrated, for example, in  FIG. 2 . It may be gathered from this that the individual solid particles  14  are embedded, distributed homogeneously, into the surface  18  of the outer sheath  8 , without penetrating into the inner volume. The surface  18  is in this case, in general, an outer surface, which may therefore come into contact with external objects. The individual line conductors  6  have in each case a central conductor  26  which is surrounded by conductor insulation  28 . The group of line conductors  6  is surrounded directly by the outer sheath  8 . 
     Still with reference to  FIG. 2 , the individual solid particles project somewhat out of the surface  18  in the manner of scales. They are formed, in particular, as flaky solid particles. The solid particles  14  are embedded solely in the surface  18  and penetrate into the surface  18  at most to about their particle size. 
     Finally,  FIG. 3  also shows a microscopic magnification of a surface produced in this way, in which the individual solid particles  14  can be recognized from the bright regions. By contrast, the dark regions show the matrix of silicone material in which the solid particles  14  are embedded. The largest solid particles  14  therefore have a size of no more than about 45 μm. 
     The method described here is not necessarily limited to the production of an electrical cable having a silicone cable sheath. In principle, the fundamental idea, to be precise that of introducing solid particles into the surface of a silicone element in order to improve the feel and, in particular, to reduce the coefficient of friction, can also be applied to other products which have a silicone-like base material on their surface. By means of the method described here, a silicone product with a pleasant feel and with a low coefficient of friction is provided in a simple way in terms of the process employed. The use of mica particles with a grain size in the range of 35 μm to 45 μm has turned out to be especially advantageous in this case. Silicone products of this type are suitable particularly for medical applications. Use in cables particularly for the medical sector is especially advantageous, since, as a result, handling is improved and disruptive adhesion to surfaces or even to the skin is avoided. 
     The following is a summary list of reference numerals and the corresponding structure used in the above description of the invention: 
       2  cable 
       4  extruder 
       6  line conductor 
       8  outer sheath 
       10  intermediate product 
       12  reservoir 
       14  solid particles 
       16  deflecting roller 
       18  surface 
       20  cross-linking station 
       22  cleaning stage 
       24  drum 
       26  conductor 
       28  conductor insulation.