Abstract:
This disclosure relates to a light-directing system, comprising a textile sheet material, which can be positioned in a light incidence region in front of a space and has a weft-thread layer composed of a plurality of weft threads, wherein the weft threads are extended substantially linearly and bound mesh openings of the sheet material. According to this disclosure, some or all weft threads have a non-circular thread cross-section bounded by a plurality of individual side parts and are arranged parallel to each other, the orientation of the side parts of the weft threads being uniform.

Description:
RELATED APPLICATIONS 
       [0001]    This application is a continuation of PCT/EP2014/072253, filed Oct. 16, 2014, which claims priority to EP 13189005.5, filed Oct. 16, 2013, both of which are hereby incorporated herein by reference in their entireties. 
     
    
     BACKGROUND 
       [0002]    The invention relates to a light-directing system, in particular for sunlight, having a textile sheet material which in a light-incidence region is positionable in front of a space to be shielded or to be illuminated, or in the use state is positioned in front thereof, and has a weft-thread layer which is formed from a multiplicity of weft threads, wherein the weft threads are stretched in a substantially linear manner and delimit mesh openings of the textile fabric. 
         [0003]    A weather-protection device having a textile fabric which forms a shield against weather influences as well as solar radiation is known from WO 2012/160115 A1, which textile fabric develops the protective functions thereof in that the warp threads and weft threads delimit elongate rectangular mesh openings, wherein the opening length is at least 10 times the opening width. It is achieved therewith that undesirable radiation and precipitation is repelled by the tight longitudinal delimitations. However, by virtue of the round thread cross-sections light reflections into the shielded region do also occur. 
       SUMMARY 
       [0004]    Proceeding therefrom, this disclosure is based on the object of further improving the devices known in the prior art and of achieving a two-dimensional structure for influencing in a targeted manner incident light above all of sunlight or daylight, respectively, in a region of a building. 
         [0005]    This disclosure proceeds from the concept of achieving a defined light-directing structure by adapting the topography of a woven fabric. Accordingly, it is proposed according to this disclosure that some or all weft threads have a non-circular thread cross-section which is delimited by a plurality of individual lateral portions or lateral areas, respectively, and said weft threads at uniform orientation of the lateral portions thereof are disposed as unidirectional threads so as to be mutually parallel. In this manner, targeted light-directing is made possible in that uniformly aligned lateral portions form an optical surface for direct (mirrored) reflection and/or refraction. As opposed to round cross-sections, ranges of incident angles which are determined by segmented thread profiles are effectively masked also with a view to multiple reflections, such that a type of “louver effect” is achievable by a thread structure. The degree of protection is thus substantially determined by the thread profile while suitable mesh openings may be kept free for viewing therethrough. 
         [0006]    In order for the light-directing range to be optimized both in terms of capture as well as reflection, it is advantageous when the lateral portions have at least one planar or concave region. 
         [0007]    Further improvement results from the lateral portions being mutually delimited by protrusions, clearances, or edges in the thread cross-section. 
         [0008]    It is particularly favorable in terms of angular orientation when the non-circular weft threads have a polygonal, in particular a triangular or trilobal cross-section. 
         [0009]    A further variant of this disclosure provides that the weft threads are disposed in weft-thread groups having thread diameters which vary in a groupwise manner, that is to say that thread diameters vary in every group, wherein the lateral portions of the weft-thread groups are uniformly oriented. By virtue of the various thread diameters in every group, said various thread diameters being repeated from one group to another, lateral portions which in relation to the group are likewise variably oriented result quasi as a sheathing end of the weft-thread group or of the repeat, respectively, such that the above-mentioned advantages are likewise achievable. The repeat forms the smallest self-repeating part of the weave, that is to say that the weft-thread groups are always placed on top of one another in the same manner. 
         [0010]    For targeted influencing of light radiation it is advantageous when at least one side portion which faces away from the space or faces the light-incidence region is impinged as a light-directing area with incident light. 
         [0011]    In order for effective shading to be enabled and for glare and unintended heat input to be avoided, it is advantageous when the weft-threads or weft thread groups, respectively, by way of at least one lateral portion form a reflector for reflecting incident light. Advantageously, the weft threads should run transversely to the plane of the radiation path. 
         [0012]    Further improvement of shading while at the same time providing good viewing therethrough is achieved in that the weft threads are provided with a light-reflecting or light-absorbing coating, and/or are dyed dark. 
         [0013]    In order for radiation regions to be influenced in particular in the case of sunlight incident from obliquely above, it is advantageous when the weft threads in a delimited angular range are uniformly coated so as to be reflective or absorbent. 
         [0014]    Further functionality in the sense of targeted utilization of light may be achieved in that the light-directing area forms a light-permeable surface, the weft threads being transparent, such that light is directed away from the light-incidence side and thus into the space to be illuminated. On account thereof, the brightness in interior rooms may be influenced without the employment of artificial lighting. 
         [0015]    Advantageously, the weft threads are formed from a monofilament thread material such that defined optical surfaces are achieved. In order for non-directed diffusion and thus also for glare protection to be optionally enabled, multifilament yarns may also be additionally employed. 
         [0016]    A particularly preferable structure provides that that the textile fabric has a dual-layer thread structure of warp threads forming a warp-thread layer, and of weft threads forming a weft-thread layer which is parallel with said warp-thread layer, wherein the warp threads and the weft threads are interconnected by binder threads and the weft threads bear on a single side of the warp-thread layer. 
         [0017]    The weft threads preferably run horizontally, the weft-thread layer extending vertically. 
         [0018]    In order to facilitate utilization, it is advantageous when the textile fabric is mounted so as to be two-dimensional in a mounting construction or is unrollable therefrom. It may also be advantageous here when the textile fabric is embedded in a transparent support plate or in a composite structure, respectively, for example in laminated glass. 
         [0019]    A further advantageous embodiment provides that the textile fabric is disposed or is positionable in a mounting construction on the external side of a building, in front of a building opening, the weft threads running horizontally. 
         [0020]    In order for targeted light-directing to be enabled, it is particularly advantageous when the weft threads, on the light-incidence side thereof that faces the light-incidence region or on the external side, respectively, are free from warp threads, and said weft threads across the length thereof are thus not continuously covered by warp threads. 
         [0021]    In order to achieve reflection or transmission which is angle-selective and thus dependent on the position of the sun, it is advantageous when the weft threads run horizontally and have a reflective area which points obliquely upward into the light-incidence region, and in that the weft threads are held so as to be mutually spaced apart, wherein the spacing is determined such that incident light from obliquely above, when above a given height-related critical angle, is reflected into the light-incidence region and, when therebelow, is passed between the weft threads through into the space that faces away from the light-incidence region. 
         [0022]    It is particularly favorable when the spacing of the weft threads has a defined uniform value between 0.05 mm and 0.1 mm. 
         [0023]    In order to provide a suitable transition from reflection of sunlight in the summer to permeability in winter, the height-related critical angle should be in the range between 40° and 50°. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0024]    The above-mentioned aspects of exemplary embodiments will become more apparent and will be better understood by reference to the following description of the embodiments taken in conjunction with the accompanying drawings, wherein: 
           [0025]      FIG. 1  shows a light-directing system having a textile fabric which is disposed in front of a building, in a schematic illustration; 
           [0026]      FIGS. 2 and 3  show the textile fabric which is configured as a dual-layer leno-woven fabric in a partial plan view onto the weft-thread side and onto the warp-thread side; 
           [0027]      FIG. 4  shows the textile fabric having triangular weft threads and light rays which are reflected thereon, in a fragmented vertical sectional view; 
           [0028]      FIG. 5  shows a further embodiment, having weft-thread groups of various diameters, in an illustration corresponding to that of  FIG. 4 ; 
           [0029]      FIGS. 6 and 7  show exemplary embodiments of the textile fabric, having an angle-selective transmission of light rays, in an illustration corresponding to those of  FIGS. 4 and 5 . 
       
    
    
     DETAILED DESCRIPTION 
       [0030]    The embodiments described below are not intended to be exhaustive or to limit the invention to the precise forms disclosed in the following description. Rather, the embodiments are chosen and described so that others skilled in the art may appreciate and understand the principles and practices of this disclosure. 
         [0031]    It should be understood that the terms “horizontal” and “vertical” are generally used herein to establish positions of individual components relative to one another rather than an absolute angular position in space. Further, regardless of the reference frame, in this disclosure terms such as “vertical,” “parallel,” “horizontal,” “right angle,” “rectangular” and the like are not used to connote exact mathematical orientations or geometries, unless explicitly stated, but are instead used as terms of approximation. With this understanding, the term “vertical,” for example, certainly includes a structure that is positioned exactly 90 degrees from horizontal, but should generally be understood as meaning positioned up and down rather than side to side. Other terms used herein to connote orientation, position or shape should be similarly interpreted. Further, it should be understood that various structural terms used throughout this disclosure and claims should not receive a singular interpretation unless it is made explicit herein. By way of non-limiting example, the terms “weft thread,” “warp thread,” “fabric,” to name just a few, should be interpreted when appearing in this disclosure and claims to mean “one or more” or “at least one.” All other terms used herein should be similarly interpreted unless it is made explicit that a singular interpretation is intended. 
         [0032]    The light-directing system  10  which is illustrated in the drawing comprises a textile fabric  12  which is disposed in a light-incidence region  13  in front of a space  14  which is to be shielded or to be illuminated, in the region of a building opening, on the external side of a building  16 . To this end, the textile fabric  12  is extendable in a web-shaped manner as a roller blind from a winding device  18 . The space  14  behind the textile fabric  12 , depending on the embodiment of the textile fabric  12 , is shaded against direct solar radiation or is illuminated therewith in a targeted manner, respectively. 
         [0033]    As is indicated (not to scale) in  FIG. 1 , the textile fabric  12  has weft threads  20  and warp threads  22  which are interconnected in a mesh-like manner. The warp threads  22 , at comparatively large mutual thread spacing, run in the vertical direction, while the horizontal weft threads  20 , while adhering to a comparatively tight mutual thread spacing, intersect the warp threads  22  at a right angle. In this manner, rectangular mesh openings  24  in the mesh-shaped textile fabric  12 , which to a certain degree allow viewing therethrough, are kept free. 
         [0034]    As is visualized in  FIGS. 2 and 3 , the textile fabric  12  has a two-dimensional dual-layer structure in which the weft threads  20  and warp threads  22  are stretched in a linear manner and in each case form a dedicated planar thread layer  26 ,  28 . The two thread layers  26 ,  28  in each case define a single separate plane. The weft-thread layer  26  thus on one side or on the external side, respectively, bears on the warp-thread layer  28 , wherein the warp-thread layer  28  forms exclusively the internal side of the fabric which faces the building space  14 , and the weft-thread layer  26  forms the external side of the fabric which is directed outward toward the light source or the sun, respectively. 
         [0035]    When viewed in the direction of the surface normal of the textile fabric  12 , unobstructed mesh openings  24  which on the longitudinal side are delimited by the weft threads  20  thus result. In order for the layers to be mutually fixed, the weft threads  20  and warp threads  22  are wrapped in the manner of a leno weave by comparatively thin binder threads  30 . The binder threads  30  run along the warp threads  22 . Said binder threads  30  thereby traverse the two thread layers  26 ,  28  of the warp and weft threads and encompass the external sides thereof that face away from one another. 
         [0036]    The warp threads, weft threads, and binder threads are expediently composed of a monofilament polymer thread material, for example of PET. The thread thicknesses of the weft threads and warp threads  20 ,  22  are in the range between 0.1 to 2.4 mm, while the thinner binder threads  30  have a thickness of 0.05 to 0.1 mm. In the case of non-round cross-sections, the maximum transverse dimension is determined as the thread thickness. The mesh openings  24  result from the spacings of 0.05 to 2 mm between adjacent weft threads  20 , and from the spacings of 0.6 to 5 mm between warp thread centers. 
         [0037]    In a first embodiment the weft threads  20  have a non-circular thread cross-section and are disposed so as to be mutually parallel, having uniform orientation. Uniform orientation may be obtained in that the weft threads  20  during weft insertion are drawn off tangentially and thus without twist from a supply package and are kept tensioned. 
         [0038]    As can best be seen from  FIG. 4 , the weft threads  20 , which are triangular in the cross-section, have three planar lateral faces or lateral portions  32 , respectively, which are mutually delimited by edges  34  which converge at an acute angle. By virtue of uniform orientation, all weft threads  20  by way of one side bear on the layer of warp threads  22 , while the lateral portions  32  which are inclined away from the warp threads  22  are impingeable as a light-directing area  32  with incident sunlight  38 . 
         [0039]    In the configuration which is visualized in  FIG. 4 , the weft threads  20  as micro-louvers form a reflector to reflect incident light  38 . Here, at least the light-directing area  36  is provided with a reflective coating  40  such that light is reflected in a mirrored manner. Such a segmented coating may be produced, for example, by directed vapor deposition of a metal layer on the weft threads  20 . In the case of a reflective coating across the full area on all lateral portions, multiple reflections may also lead to reflection of the light  38  and thus to effective shading of the space  14  behind the textile fabric  12 . 
         [0040]    In order to avoid that reflected light radiation passes through the textile fabric  12  between the threads  20 ,  22 , radiation-absorbing additives may also be added to the thread material. Viewing therethrough from the inside to the outside may be improved in that the thread material is dyed dark. 
         [0041]    The degree of reflection of the textile fabric  12  may be adjusted by way of the weft-thread density and thus by way of the thread spacings and by way of the thread diameters. In principle, zonal variation of the thread densities and thread thicknesses is also possible. 
         [0042]    In a further variant the weft and warp threads  20 ,  22  are composed of a transparent thread material, wherein incident light for targeted illumination is directed into the space  14  by partial reflection and refraction at the light-directing areas  36 . Weft threads  20  having combinations of reflective and transmissive lateral portions  32  are also conceivable, for example in order to avoid direct solar radiation onto the floor of a space  14  but to otherwise enable illumination. 
         [0043]    In the embodiment shown in  FIG. 5 , same or similar parts as have been described here above are provided with the same reference signs. The substantial difference lies in that the weft threads  20  have a circular cross-section and are disposed in weft-thread groups  42  having various thread diameters per group. This means that a plurality of weft threads  20  which differ from one another in terms of their thread diameter are grouped in every weft-thread group  42 . The weft-thread groups  42  here are uniformly oriented, wherein lateral portions  32  are defined by the sheathing end  44  of the respective weft threads  20 . As shown in  FIG. 5 , the placement of the different size threads relative to one another is the same in each of the groups. Here too, an arrangement similar to that of a louver is implemented. 
         [0044]    Shading in a desired angular range may be influenced by suitably adapting the thread diameter. The lateral portion  32  which points obliquely downward may here be determined by a common tangent on the thread cross-sections. 
         [0045]      FIGS. 6 and 7  visualize the possibility of angle-selective shading or illumination of the space  14  depending on the position of the sun, respectively. This means that the textile fabric  12  in the case of a high position of the sun, and thus at a steep incident angle or impact angle, respectively, reflects as many of the sun rays  38  as possible. By contrast, in the case of a flat angle, as much as possible of the radiation  38 ′ is directed into the space  14 . In this manner, utilization of solar radiation that is adapted to the seasons may be achieved. 
         [0046]    In order for this property to be implemented in the textile fabric  12 , the horizontally running weft threads  20  should have a reflection area  46  which points obliquely upward into the light-incidence region  13 . Here, the mutual spacing of the weft threads in the woven fabric is adjusted such that light which is incident from obliquely above, when above a given height-related critical angle, is reflected into the light-incidence region  13  and, when therebelow, is passed through the thread gap between the weft threads  20 , into the space  14 . Here, multiple reflections may also occur, as is visualized in  FIG. 7  for the thread group  42 . There, the circumferential regions of the weft threads  20  that point obliquely upward act as a reflection area  46  for the primary angle selection, wherein by virtue of the reduction in terms of diameter the upper weft thread of each thread group is substantially selective for the return reflection into the incidence region  13 . The weft thread spacing should expediently be in the range between 0.05 mm and 0.1 mm. Adaption of the spacing may be determined by simple experiments or else by simple geometric considerations. 
         [0047]    In principle, instead of the half-cross leno weave described for producing a planar weft-thread layer  26 , it is also possible for a structure having stretched weft threads  20  to be implemented by warp-knitted fabric (warp-knitted and Raschel-knitted), a cross-laid structure, or a woven fabric in plain weave, for example. In the case of the warp-knitted fabric, the stretched weft threads are held in a stitch. In this case, the stitch wales replace the warp thread. In the case of the cross-laid structure, thread layers are deposited unidirectionally on top of one another. The structure is then fixed by interloping and stitching. In a plain weave, substantially linear weft threads may be implemented in that the diameter of the weft in comparison to the warp threads is significantly larger and the warp-thread tension during production is kept low. In this way, only the warp-thread system undulates while the weft lies stretched between the warp threads. Weft threads which are stretched in a substantially linear manner result in all cases, wherein the deviations from linearity are minor in comparison with the thread diameter. 
         [0048]    While exemplary embodiments have been disclosed hereinabove, the present invention is not limited to the disclosed embodiments. Instead, this application is intended to cover any variations, uses, or adaptations of this disclosure using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.