FIELD OF THE INVENTIONS
This application is a continuation-in-part of International Application No. PCT/DE2003/003059, filed Sep. 15, 2003, which claims priority to German Patent Application DE 102 42 785.2 filed Sep. 14, 2002 and German Patent Application DE 103 05 872.9 filed Feb. 13, 2003.
- BACKGROUND OF THE INVENTIONS
The present invention relates to elastic, electrically conductive yarns, their use and methods for their manufacture.
Several methods are known for manufacturing electrically conductive yarns. For example, metal wires, wire mesh or metallized yarns have long been incorporated directly in fabrics to dissipate electrostatic charge. These fabrics are often difficult to produce on a loom and, due to the exposed wires, bear little optical resemblance to textiles and/or feel metallic to the touch.
Furthermore, methods for manufacturing so-called staple yarns are known. Essentially, they involve spinning short textile fibers together with short and very fine metal fibers into a yarn. Depending on the metal content, these yarns have more or less textile or metallic properties. Staple yarns with good electrical conductivity exhibit a metallic appearance and surface feel.
Methods are also known in which centrally carried metal wires are single- or double-wound with textile. Since it is substantially the wire that determines the tensile strength in these yarns, relatively thick wires with diameters greater than 0.1 mm are usually employed. Such yarns are comparatively rigid and thus unusable for textile applications.
EP 250 260 describes how also thin wires can be employed in the core of an enwound yarn by enwinding with wire and textile thread, fed in parallel. In this arrangement, the central textile thread provides for tensile strength, while the parallel thin wire produces the electrical conductivity of the yarn. However, such yarns are not particularly extensible.
CH 690 686 describes the manufacture of a composite yarn of textile roving and monofilament metal thread. During the yarn-spinning process on a ring spinner, a coated metal wire is added centrally to the roving. In the thermal treatment following the spinning process, the melting coating adheres the central wire to the spun textile sheathing. These yarns, too, do not exhibit good extensibility.
None of the above-described yarns can be appreciably elastically extended without loss of electrical conductivity, since the conductive threads either break or deform plastically.
The specifications of U.S. Pat. No. 4,776,160, U.S. Pat. No. 5,881,547 and U.S. Pat. No. 5,927,060 each describe yarns in which electrically conductive yarns are wound around centrally arranged textile threads. This arrangement facilitates in principle a certain elongation of the entire yarn unit without causing the yarn or the conductive wrapping to tear.
U.S. Pat. No. 5,881,547 teaches the production of a high-tensile-strength, electrically conducting yarn for employment in fencing wear. These yarns are composed of a non-electrically conductive core thread and a double, crossed wrapping with stainless steel wire. Due to the large diameter of the stainless steel wires used, in the range of 0.6 mm to 1.2 mm, they are very rigid, hardly extensible and by no means elastic.
Both U.S. Pat. No. 4,776,160 and U.S. Pat. No. 5,927,060 mention the use of flexible, extensible core threads for manufacturing conductive yarns with good textile properties. U.S. Pat. No. 4,776,160 mentions, as materials for the core thread, thermoplasts such as nylon, polyester, rayon, acrylic, PEEK, PBS, PBI, polyolefins (PE, PP) and liquid crystal polymers, polycarbonate, polyvinyl alcohol and aramid fibers. None of these materials possesses rubber elastic properties.
The preferably multifilament synthetic yarn described in U.S. Pat. No. 5,927,060 can bear elongation by about 5% without a change in the electrical conductivity. The textile core thread employed there possesses no rubber elastic properties whatsoever. Moreover, the weak wrapping with a mere 200 to 600 turns per meter allows only a little elongation under the given conditions before the sheathing wire breaks.
Also the last-described yarns possess no rubber elastic properties. Even if they can withstand minor elongations in the range of 3% to 5% without loss of electrical conductivity, considerable permanent elongations remain. The last-described yarns also cannot withstand elongations by more than 10% without a break or at least without loss of conductivity.
BRIEF DESCRIPTION OF THE DRAWINGS
Thus, there continues to be a need for yarns that, in addition to electrical conductivity, exhibit high elasticity and improved elongation properties.
DETAILED DESCRIPTION OF THE INVENTIONS
FIG. 1 depicts an electrically conductive yarn.
This is where the present invention applies. The object of the invention as characterized in the claims is to provide yarns that are electrically conductive, that can be elongated considerably, at least briefly, without loss of conductivity, and that exhibit improved elongation properties.
As illustrated in FIG. 1, the yarns 1 according to the present invention are made up of at least one elastic core thread 2, at least one electrically conductive thread 3 that is wound around the core thread, and at least one binding thread 4 that is wound around the core thread 2. The extensibility of the entire electrically conductive yarn is limited by the binding thread 4. A thread can comprise a strand, cord, filaments of natural or synthetic material, or multi-strand products such as other yarns.
The conductive yarn 1 possesses a number of improved properties. The yarn 1 exhibits elastic properties across a wide range of a tensile load. In contrast to the conductive yarns known from the background art, a tensile overload does not lead to a decrease in the conductivity of a yarn 1 according to the present invention. This is achieved through the limiting of the extensibility of the yarn 1 by the binding thread 4. By limiting the extensibility through the binding thread 4, it is additionally achieved that the yarn retains its elastic properties across its entire load range.
According to a preferred embodiment of the present invention, the restoring force of the thread 4 increases disproportionately above a certain tensile load. The reason for this disproportionate rise in the restoring force lies in the binding thread 4. That is to say, above a certain tensile load, said binding thread can no longer give way to this load by spreading its helical form to a smaller number of turns per unit of length of the core thread 2, but rather allows a further extension only through an elongation in the longitudinal direction. The transition from an expansion of the helical structure to an effective extension of the binding thread itself in its lengthwise direction leads to a strong rise in the restoring force, preventing a further elongation of the yarn. This disproportionate increase in the restoring force occurs at a tensile load at which the electrically conductive thread has not yet broken. The yarn 1 is thus still conductive.
The scope of the extensibility of the binding thread 4 depends primarily on the material properties and the number of turns of the binding thread 4 around the core thread 2. Greater extensibility is generally achieved through a greater number of turns. In addition, a higher elongation at break of the material leads to increased extensibility.
A material's elongation at break is understood to mean the elongation of the material through tensile load until it breaks. It serves to determine the strength of the stressed material. Thus, a material with a high elongation at break can be stretched by a large amount before it breaks.
According to the present invention, the extensibility of the entire electrically conductive yarn 1 is limited by the binding thread 4. In order to fulfill this property, the core thread 2, conductive thread 3 and binding thread 4 are expediently coordinated with respect to the material and the number of wraps of conductive thread 3 and binding thread 4 around the core thread 2. In addition, advantageously, some further parameters known to persons skilled in the art of yarn manufacturing are adjusted. That is to say, the extensibility further depends on the force with which the wrapping of the core thread occurs. Also, the various thread materials exhibit various coefficients of friction, making differing expenditures of force necessary in order to shift the individual threads against each other.
For persons skilled in the art of yarn manufacturing, such a selection is no problem. For the selection of suitable materials and manufacturing parameters, persons skilled in the art will usually present a certain core thread, wrap it with a thin wire and then specify the binding thread such that the yarn fulfills the stipulated properties.
It should be understood that the number of turns around the core thread in the resulting yarn is influenced not only by the number of turns actually executed, but also by the degree to which the core thread is pre-drawn. The higher the force with which the core thread is pre-drawn, the more dramatic is the rise in the number of turns present per unit of length of the core thread after alleviation of the load on the core thread.
According to a preferred embodiment of the present invention, the core thread is composed of a rubber elastic material. The term “rubber elastic material” shall be understood to mean that, following deformation of the material and subsequent load alleviation, the original state of the material reappears. According to DIN 7724 (February 1972), there are two types of elasticity, namely energy elasticity (steel elasticity) and entropy elasticity (rubber elasticity). According to a preferred embodiment of the present invention, the elastic core thread exhibits an elongation at break of at least 50%, preferably of at least 100%, particularly preferably of at least 200%. Very particularly preferably, the core thread possesses an elongation at break of at least 300%, especially of at least 400%, and particularly preferably of at least 500%.
The elastic core thread(s) is/are responsible for the rubber elastic properties of the entire yarn unit. The market offers a variety of rubber elastic threads from which the material suited to the relevant application can be selected. These include natural and synthetic rubbers, the various types of polyester and polyether elastane, modified polyester, post-cross-linked thermoplasts, etc. Polyester-polyurethane elastomers and/or polyether-polyurethane elastomers are very particularly suited as materials for the rubber elastic core thread.
Following elongation, the yarns according to the present invention should, due to the rubber elastic properties of the core thread, recontract to at least almost the original length. According to a preferred embodiment of the present invention, following an elastic elongation by at least 15% in the lengthwise direction, the electrically conductive yarn exhibits a maximum permanent elongation of 5% without loss of its electrical conductivity. Particularly preferably, following an elastic elongation by at least 30% in the lengthwise direction, the electrically conductive yarn exhibits a maximum permanent elongation of 5% without loss of its electrical conductivity.
The core thread can be employed in a form that is suitable for the relevant application. To cite a few variants by way of example: monofilament, multifilament, segmented types and textured types. If required, multiple threads may also be employed in the core in parallel or twisted. Threads of the same kind or of different kinds may be employed side by side.
The elastic core of the composite yarn is furnished with at least one electrically conductive wrapping. The elastic core can be wound multiple times with conductive threads. These conductive wrappings can also be applied in differing wrapping directions and, if appropriate, they can be separated from one another by intermediate layers.
Metallic wires, wire cords or meshes, conductingly coated synthetic fibers, staple yarns with a metal portion, threads of conductive polymers and conductively filled synthetic fibers are especially suitable as conductive threads. The conductive threads can be employed singly or multiply, from a single grade or mixed. Monofilament metal wires used as conductive threads exhibit a diameter between about 0.01 and 0.1 mm, preferably between 0.02 and 0.06 mm, and particularly preferably between 0.03 and 0.05 mm.
Although, in principle, numerous metals and alloys, which may additionally be coated, anodized or etched, are suitable as conductive threads, copper wires, silver-coated copper wires and stainless steel wires are particularly preferred due to technical and economic factors. The use of coated or lacquered wire types improves the corrosion resistance and washability of the yarns according to the present invention. Not only are such yarns easily washable, but what is more, they even withstand dry-cleaning.
In addition to monofilament metal wires, multifilament stainless steel yarns are excellently suited for manufacturing the yarns according to the present invention. The thickness of a single stainless steel filament ranges between 0.002 mm and 0.02 mm. The number of individual filaments contained lies between 10 and 200.
The use of silver-coated synthetic yarns for the electrically conductive wrapping of the elastic core lends itself to numerous applications. Wash-resistant, silver-coated nylon threads are particularly suitable for manufacturing the yarns according to the present invention. The market offers both monofilament and multifilament yarns. Compared with monofilament fibers, higher surface coverage of the core can be achieved with multifilament yarns as the wrapping, with the same yarn diameter.
In addition to the electrically conductive wrapping, the yarn comprises a further wrapping. Such a wrapping can assume various functions. To cite a few by way of example: electrical insulation (outwardly, inwardly or between multiple conductive layers), mechanical abrasion protection, improvement of the working properties of the yarn on fast-running machines, color, luster, appearance, handle, surface feel, protection against overstretching, tensile strength, equalization of the internal torsional stress of the yarn after wrapping in one direction. It should be pointed out that this further binding thread will not usually be electrically conductive. However, the present invention also covers binding threads that exhibit electrical conductivity of any magnitude.
For numerous applications, a yarn construction with inward-lying elastic core, inner wrapping with conductive thread and textile outer wrapping executed in the opposite direction thereto is suitable. The external wrapping is structured such that, in the event of a strong elongation, it is completely stretched before the inward-lying conductive wrapping. In this way, the outer wrapping breakes an elongation before the conductive wrapping is damaged.
Further preferred embodiments of the yarn according to the present invention include the use of multifilament yarns as a non-conducting wrapping. When wrapping a core, multifilament yarns preferably arrange themselves laminarly on the core thread, such that they effect considerably greater surface coverage compared with a monofilament, with the same external diameter.
Depending on the application, all kinds of threads can be suitable for the described further wrapping. To cite some representatives for the possible materials by way of example: nylon, polyester, rayon, polyamide, linen, wool, silk, cotton, polypropylene, kevlar in its various embodiments, blended yarns of all kinds, and metallized yarns, such as silver-coated nylon.
The manufacture of the yarns according to the present invention can occur in various ways. The preferred method is traditional yarn winding. Here, the central elastic thread is drawn on drawing equipment. The drawn elastic core thread is passed through a rotating hollow spindle. On the hollow spindle sits the bobbin with the conductive thread or the binding thread. This thread is carried along by the elastic core thread that is taken up evenly, such that the conductive thread or the binding thread is wound around the core thread in the form of a spiral. When the drawn core thread relaxes again after winding, the individual turns lie substantially closer together than during winding.
Compared with inelastic yarns, rubber elastic yarns can be produced with high draft, which, under otherwise identical production conditions, leads to considerably tighter turns resulting from the described relaxation of the yarn after winding. With the cited method, elastic yarns can be wound more tightly than non-elastic yarns.
As a basic principle, the winding of the core thread with a further thread creates internal torsional forces that lead to the yarn in the relaxed state, that is, when unwinding from the bobbin, twisting about itself. Winding two threads around the core thread results in the possibility to eliminate these internal torsional forces. This is referred to as “equilibration” of the yarn. That is to say, if the second thread is wound around the core thread in the opposite direction to the first thread, torsional forces are yielded in opposing directions. Now, through simple experiments, the material and number of turns can be coordinated such that the magnitudes of the torsional forces are approximately equal, yielding a resulting torsional force of nearly zero. Consequently, it is ensured that the yarn in the relaxed state twists about itself very little, if at all.
Thus, according to a preferred embodiment of the present invention, the electrically conductive thread and the binding thread are wrapped in opposite directions around the elastic core thread. Thus, for example, if the electrically conductive thread is wound around the elastic core thread in the S-direction, then the binding thread is wrapped around the elastic core thread in the Z-direction. It is thus a crosswise wrapping.
The present invention also comprises the use of the yarns and fabrics according to the present invention for data transfer and power supply of electrical and electronic components. In addition, also comprised is the use of the yarns and fabrics according to the present invention as electrically conducting materials that, similar to a ribbon cable or a local-resolution-activatable two-dimensional matrix, can transport various electrical signals side by side with no appreciable mutual interference.
Furthermore, yarns according to the present invention or products produced therefrom can be employed for shielding electromagnetic fields or for dissipating static charges. A use of the yarns according to the present invention as a heating resistor in the context of electrical heating is possible.
The present invention also comprises the use of the yarns according to the present invention as electrical heat conductors, and the fabrics produced therewith as elastic, electrically heatable fabrics.
- Means of Executing the Invention
The present invention additionally comprises the use of the yarns according to the present invention as a sensor material, preferably as a humidity sensor or strain sensor.
- EXAMPLE 1
In the following, the invention will be explained in greater detail based on exemplary embodiments, but it is expressly pointed out that the invention is not intended to be limited to the specified examples.
An elastic thread of LYCRA® elastane yarn (dtex/type: 1880 dtex, Type T-163C) manufactured by DuPont® is pre-drawn on a yarn winding machine. The elongation at break of the thread is 500%, with a tear strength of 1300 cN. After elongation of 100%, the thread relaxes except for a permanent elongation of 2.4%.
The pre-drawn LYCRA® thread is passed through a hollow spindle. This hollow spindle carries a conical yarn spindle from which a 0.04 mm thick, hard silver-plated copper wire is drawn off overend by the LYCRA® thread. Silver/Copper Textile wire with TW-D coating manufactured by Elektro-Feindraht AG may be used. The diameter of this wire including its lacquer coating measures about 0.048 mm. The wire also exhibits an elongation at break of 21.3%.
The single-wire-enwound LYCRA® is passed through a second hollow spindle. This hollow spindle carries a commercially available multifilament polyamide (PA) yarn of PA66 with 78 dtex and 34 individual filaments. PA66 multifilament polyamide yarn having a product designation of RN01235 78/34/1S and manufactured by Radicifil S.p.A./Synfil GmbH with elongation at break of 28% may be used. The PA66 yarn is wrapped around the core counter to the wire. The machine parameters are selected such that an equilibrated yarn is created that is as free as possible from internal torsional stress.
- EXAMPLE 2
The outer PA66 yarn is wound around the core 3200 times per meter of yarn; the inner wire is wound around the core 3600 times per meter of yarn. The inward-lying wire is nearly completely covered by the outward-lying PA66 yarn, so that the yarn possesses a textile appearance and surface feel. The yarn possesses excellent electrical conductivity. If elongated by approximately 250%, the restoring force of the yarn becomes disproportionately stronger through complete extension of the PA66 yarn. Only when elongated approximately 300% does the yarn lose its electrical conductivity due to wire break.
- EXAMPLE 3
The elastic, electrically conducting composite yarn in example 1 is employed as the weft thread on a commercially available power loom. The warp beam is composed of 0.3 mm thick, single-twisted cotton threads combined in groups of 8 threads. When interwoven, a firm fabric is created that possesses excellent electrical conductivity in the weft direction, and that does not conduct the electric current in the direction of the warp. These electrical properties are retained even after elongation by more than 120% in the weft direction. If the poles of a direct current voltage source are connected, spaced apart in the warp direction, this voltage can be used, at a distance of one meter in the weft direction, to operate an electrical sink, such as a light-emitting diode. The fabric can be stretched in the weft direction with no impact on the power supply of the light-emitting diode.
The elastic, electrically conducting composite yarn in example 1 is employed as the weft thread on a commercially available power loom. The warp beam is composed of an electrically conducting but not rubber elastic composite yarn. To manufacture the warp thread, a commercially available polyester yarn with 100 dtex and 36 individual filaments is furnished with an inner wrapping of 0.041 mm thick, hard silver-plated copper wire and an outer wrapping of commercially available polyamide yarn (PA66) with 78 dtex and 34 individual filaments.
- EXAMPLE 4
When interwoven, a firm fabric is created that possesses excellent electrical conductivity in the weft direction and an electrical conductivity in the direction of the warp thread independent from the one in the weft direction. These electrical properties are retained even after elongation by more than 120% in the weft direction. This fabric, which is economical to produce, can, with suitable electronic activation, be employed as a matrix for spatially resolving signal capture, or for operating a spatially resolving output unit, such as a monitor.
- EXAMPLE 5
An elastic thread of LYCRA® 163C by DuPont with 1880 dtex is pre-drawn on a yarn winding machine. The pre-drawn elastic thread is passed through a hollow spindle. This hollow spindle carries a conical yarn spindle from which a conductive thread comprising silver-coated polyamide thread with 30 denier and 18 individual filaments (X-static, Life SRL, I-25015 Desenzano, Italy) is drawn off overend by the elastic thread. In this example, X-static® (a silver-coated fiber) manufactured by Life SRL is used. The elastic, single-enwound with the silver-coated fibers, is passed through a second hollow spindle. This hollow spindle carries a commercially available multifilament polyamide yarn of PA66 with 33 dtex and 10 individual filaments. The PA66 yarn is wrapped around the core counter to the silver-coated fibers. The machine parameters are selected such that an equilibrated yarn is created that is as free as possible from internal torsional stress. The outer PA66 yarn is wound around the core 3200 times per meter of yarn; the silver-coated thread is wound around the core 3600 times per meter of yarn. The inward-lying silver-coated thread is not completely covered by the outward-lying PA66 yarn. The yarn possesses excellent electrical conductivity. If elongated by approximately 250%, the restoring force of the yarn becomes disproportionately stronger through the complete extension of the PA66 yarn. Only when elongated approximately 320% do the yarns sheathing the LYCRA® core break.
The elastic, electrically conducting composite yarn in example 4 is employed as the weft thread on a commercially available power loom. The warp beam is comprised of an electrically conducting but not rubber elastic composite yarn. To manufacture the warp thread, a commercially available polyester yarn with 100 dtex and 36 individual filaments is furnished with an inner wrapping of a silver-coated polyamide thread with 30 denier and 18 individual filaments (X-static® by Life SRL) and an external wrapping of commercially available polyamide yarn (PA66) with 33 dtex and 10 individual filaments.
- EXAMPLE 6
When interwoven, a firm fabric is created that possesses excellent electrical conductivity. Due to the non-complete insulation of the silver-coated wrappings in both the warp and the weft thread, all electrically conducting yarns in the fabric are in electrical contact with one another. This direction-independent electrical conductivity is retained even after elongation by more than 100% in the weft direction. Such a fabric possesses excellent shielding properties against electromagnetic radiation, especially in the range of 1 to 2000 MHz.
The elastic, electrically conducting composite thread in example 1 is employed as the warp thread on a commercially available ribbon weaver. The warp beam is alternately composed of sequences of 8 identical threads each. The alternation occurs between bundles of eight of the yarns described in example 1 and yarns without a conductive portion. The threads without a conductive portion correspond largely completely to the yarns described in example 1 except for the fact that, instead of the wire, a multifilament polyamide yarn of PA66 with 78 dtex and 34 individual filaments is employed. A commercially available multifilament polyamide yarn is employed as the weft thread.
- EXAMPLE 7
The elastic ribbon manufactured in this way possesses coexisting conducting ribbons that are electrically insulated from one another. In order to preclude short circuits between the conducting ribbons even in damp environments, it is advantageous to use a plastic-coated wire to manufacture the yarn. A flat elastic cable described in this example is outstandingly suited to connecting electrical and electronic components in clothing. The ribbon can be extended in the warp direction without loss of electrical conductivity. The ribbon is not sensitive to the creases and folds that occur when clothing is worn.
The elastic, in weft direction electrically conducting fabric in example 2 is electrically contacted in the weft direction by means of commercially available flat cable connectors at a width of 1.1 cm and a length of 50 cm. After a direct current voltage is applied, electric current flows. Midway between the connection points, the temperature increase resulting from the current flow is determined by means of an NTC resistance. At a heat output of 5 W (1.4 A at 3.6 V), the temperature increase achieved measures 30° C. At a heat flow of 13 W (2 A at 6.5 V), the temperature increase measures 64.5° C.
The extensibility and the textile surface feel of the fabric makes it highly suitable for manufacturing elastic, electrically heatable textiles that come into direct contact with the body. Examples of applications include socks, joint warmers, back warmers, gloves, elastic bandages, etc.
Thus, while the preferred embodiments of the devices and methods have been described in reference to the environment in which they were developed, they are merely illustrative of the principles of the inventions. Other embodiments and configurations may be devised without departing from the spirit of the inventions and the scope of the appended claims.