Stitch-bonded nonwoven fabric, composite material made from it and use of such a material

Abstract

Stitch-bonded nonwoven fabric structure with at least one mesh layer of staple fibers, wherein openings on the mesh layer are separated from each other by mesh bridges, characterized in that the mesh bridges have a layer of a carbon-based conductive material applied by printing, wherein the openings of the mesh layer remain essentially free of such material.

Description

The invention relates to a stitch-bonded non-woven fabric structure comprising at least one mesh layer of staple fibres, openings on the mesh layer being separated from one another by mesh webs, a composite material consisting of such a stitch-bonded non-woven fabric structure and a use of the above-mentioned materials according to the teaching of claims 1, 8 and 9, respectively.As is known, seat structures are used in vehicle construction which have the possibility of electric heating but also cooling, that is to say overall air conditioning.Usually, a metal frame is provided with a seat foam. Above this, a cover is arranged which is realized as a composite consisting of a top material laminated onto foam.As an alternative to the use of foam, it is possible to use bulky nonwoven fabrics, for example multiknit.In the side walls or headrests, mali fleece is also used as cushioning material.Seat heaters based on heating wires, or using metallized yarns, are prone to errors because of possible cable breaks. Hot spots or a general functional failure can occur here.Furthermore, the temperature distribution is not sufficiently homogeneous. Heating of subsurfaces is problematic.Because electrical seat heaters are arranged between the seat foam and the covering material, they are located relatively far from the surface to be heated. If the heating wire arrangements were to be arranged closer towards the surface, these will become visible or tactile, which is disadvantageous for the user.WO 2007 / 056557 A1 or WO 2014 / 202768 A1 disclose nonwoven-fabric-based surface heaters with a heating layer. It has also been proposed here to apply the heating layer directly to the decorative or carrier material in the automobile interior.In principle, however, a substrate with a homogeneous, closed and low absorbent surface is required.In the adhesive tape made of nonwoven fabric according to DE 199 23 399 A1, an adhesive is applied by means of screen printing or similar methods. This is only important for applying a sufficient amount of adhesive, it even being desired for the distribution of the adhesive on the adhesive tape to be uniform and intensive.DE 10 2015 220 253 A1 discloses an arrangement of cladding elements for a motor vehicle, for example a door, a roof lining or a steering wheel, wherein a conductive coating is applied to the rear side of the decorative ply or a carrier part. The coating can serve here simultaneously for forming an adhesive bond.According to DD 232 407 A3, printing of pile goods, for example carpets, is known. Printing is effected here on the pole side. The subsequently necessary process for removing superfluous printing ink together with drying makes such a solution very complicated and cost-intensive.With regard to the production of nonwoven or nonwoven pile fabrics, reference is made to DD 288 634 A5 and the prior art described therein.According to the stitch-bonded fabrics presented there, this is understood to mean puncturing one or more supplied media by needles operating in the same direction arranged in a row. The hooks present on the needles are temporarily closed. This serves the purpose of solidifying the corresponding medium to form a textile fabric or else of changing the surface character of an existing fabric. In this regard, the material of the punctured medium is meshed.The media supplied can be smoothly extended, formed yarn layers with longitudinal or transverse lay, fleeces or flat base webs. The needles with pointed and lockable hooks are referred to as so-called slide needles with separately driven closing wire.A nonwoven fabric is accordingly a nonwoven fabric consolidated by stitchforming from staple fibers, which can be used, for example, instead of a foam material in a motor vehicle seat.From the above it is the object of the invention to develop a stitch-bonded nonwoven structure with at least one mesh layer of staple fibers, which has openings on the mesh layer, which openings are separated by mesh webs, in such a way that at least partial sections are electrically conductive, have a defined electrical resistance and prove suitable, for example, for heating purposes, for example for motor vehicle seat heaters.The stitch-bonded non-woven structure is to be further developed to form a composite material.The object of the invention is achieved by a stitch-bonded non-woven fabric structure according to the combination of features according to claim 1, by a composite material according to claim 8 and by the use according to the invention of such a stitch-bonded non-woven fabric structure or composite material according to claim 9.As explained, a stitch-bonded non-woven fabric structure is used as the starting point, which comprises at least one mesh layer of staple fibers. Openings on the mesh layer are separated from one another by mesh webs, i.e. the openings form between the mesh webs.According to the invention, the mesh webs have a layer of a carbon-based conductive material applied by printing, wherein the openings of the mesh layer remain substantially free of a relevant conductive material.In one embodiment of the invention, only partial areas are provided with the layer of the conductive material, wherein the partial areas can be electrically connected.The nonwoven material can be a mali-nonwoven, kunit or multiknit nonwoven fabric.In a multiknit nonwoven fabric, at least one meshed surface side is provided with the layer of conductive material. Here, in particular, the more strongly meshed surface side is selected.According to the invention, the conductive material in the form of an aqueous ink comprises carbon nanotubes, i.e. so-called CNTs.The diameter of the CNT is substantially between 0.5 and 50 nm. The tubes themselves are elongated and, for example, open.The elongated structure of the carbon nanotubes may follow a deformation or stretching of the nonwoven fabric structure. This ensures the contact between the individual conductive particles of the coating. The conductivity changes only insignificantly.In contrast, in the case of spherical particles, the distance between the particles and thus the conductivity would change to an undesired extent.Further conductive particles can also be added to the CNT-based ink or printing ink. This may be, for example, conductive carbon black.A screen printing method is preferably used for forming the conductive layer, since larger application quantities can be realized in this case.Surprisingly, it has been found that the latching or the geometry of the printing stencil is not to be matched specifically to the surface structure of the nonwoven. Uniform layer formation on the mesh layer is achieved independently of the gridding of the stencil.Of course, however, alternative methods of printing or coating may also be used which do not impair the desired remaining open structure of the nonwoven fabric structure.For the electrical interconnection, conductor tracks can be provided which have a higher electrical conductivity than the printed heating surface. These electrical conductor tracks can be based on a wide variety of technologies, for example conductive yarns, metallic foils, but also printed regions. The application of the conductor tracks, which serve as electrodes for supplying current, can be carried out before or after the printing of the actual heating surface.As a particular advantage, it should be noted that the coating of conductive material obtained by printing is neither visible nor tactile when the correspondingly finished construction, for example of a vehicle seat, takes place. The material remains flexible, stretchable, elastic and breathable despite the printing. The resulting open material structure and the confinement of the conductive coating to the mesh ridges promotes the desired breathability with good moisture transport. Especially in vehicle seats which, in addition to the possibility of heating, are also ventilated and thus cooled, this is particularly expedient. This is also particularly true when the electrical conductor tracks are likewise printed.It is within the meaning of the invention to limit the coating with conductive material obtained by printing to individual actuatable segments or subareas in order to supply specific regions, for example of a vehicle seat or a headrest or similar components, with heating energy differently.Due to the conductive surfaces that are not full-surface but are nevertheless continuous, minor damage to the coating does not influence the functionality in contrast to conventional heating wires. The creation of hotspots or a total failure of the function is reliably avoided.Multiknit nonwovens usually have a more meshed and a less meshed side. In vehicle construction, the more strongly meshed side in the motor vehicle seat is oriented toward the decorative layer. For this reason, this more strongly meshed page is preferably printed. As a result, the heating surface reaches close to the surface.In addition, it is possible to print on the less meshed page as well.In the case of mali fleece or kunit materials, according to the invention only the mesh side is printed.Due to the further, known and advantageous properties of the nonwoven knits, for example good acoustic and thermal insulation, the surface heating that can be realized by means of the invention is also suitable for other fields of application. In the automobile construction, for example, the headliner or the door panels or in the home sector, the application for room dividers, wall panels, carpets or the like may be mentioned here.The invention will be explained in more detail below with reference to an exemplary embodiment and a figure.The figure shows a view of a multiknit material printed according to the invention over a part area, with recognizable openings free from the coating material and having mesh webs coated by printing.In the exemplary embodiment, a multiknit nonwoven fabric made of 100% polyester with a weight per unit area of 320 g / m 2, a thickness of 6.5 mm, a machine fineness of 18 needles / 25 mm and a stitch length of 2.5 mm is used as the starting point.On this multiknit nonwoven fabric, a conductive patch having a size of 5 × 5 cm 2 was printed by flat bed screen printing at a screen fineness of 30 mesh.An aqueous, CNT-based ink (GSB Wahl company) was used as the conductive material.Two opposite sides of the printed area were each provided with a strip of silver-based ink from DuPont, which serve as electrodes.After application of a DC voltage of 12 V, an average temperature of 80° C. was determined after 120 s by means of the thermographic measurement.Subsequently, a surface material (PES fabric) typical for motor vehicle seats was laminated onto the printed side.Lamination was carried out on a flat bed laminating unit. In this case, the two layers were bonded together by means of a polyester adhesive web, so that a polyester composite of the same type is obtained.After application of a DC voltage of 12 V, an average surface temperature of 60° C. was determined by means of thermographic measurement after 120 s. The converted electric power is about 800 W / m 2.

Claims

Stitch-bonded nonwoven fabric structure having at least one mesh layer of staple fibers, wherein openings on the mesh layer are separated from one another by mesh webs, characterized in that the mesh webs have a layer of a carbon-based conductive material applied by printing, wherein the openings of the mesh layer remain substantially free of a material in this respect.Stitch-bonded non-woven fabric structure according to claim 1, characterised in that only partial surfaces are provided with the layer of the conductive material, wherein the partial surfaces of the non-woven fabric structure are designed to be electrically connectable.Stitch-bonded non-woven fabric structure according to one of the preceding claims, characterized in that the non-woven fabric structure is formed from non-woven, conit or multiknit non-woven fabrics.Stitch-bonded non-woven fabric structure according to claim 3, characterised in that in a multiknit non-woven fabric at least one more strongly meshed surface side comprises the layer of conductive material.Stitch-bonded non-woven fabric structure according to one of the preceding claims, characterized in that the conductive material comprises carbon nanotubes (CNT).Stitch-bonded non-woven fabric structure according to one of the preceding claims, characterized in that the conductive material is applied by means of screen printing.Stitch-bonded non-woven fabric structure according to one of claims 2 to 6, characterised in that for the electrical interconnection, conductor tracks are provided which have a higher electrical conductivity than the printed carbon-based layer.Composite material, consisting of a stitch-bonded non-woven fabric structure according to one of the preceding claims and a decorative upper material laminated on the printed side.Use of a stitch-bonded non-woven fabric structure according to one of Claims 1 to 7 or of a composite material according to Claim 8 for heating surfaces, spaces or objects, in particular a vehicle interior or as a seat heater.