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RELATED APPLICATIONS 
   The present patent document claims the benefit of the filing date of Provisional U.S. Patent Application Ser. No. 60/465,370 filed Apr. 25, 2003, which is hereby incorporated by reference. 

   BACKGROUND 
   The present invention pertains generally to industrial curtains and doors used as environmental closures for openings through which traffic can still pass. The curtains generally comprise a plurality of usually transparent strips that are suspended contiguously to each other from a hanger or support generally fixed adjacent to a top margin of the opening. Each of the strips usually consists of a length of flexible, generally transparent, material terminating adjacent to a lower margin of the opening. The present invention relates particularly to improvements that will provide enhanced margin visibility particularly in low light situations. 
   Strip curtains and doors are conventionally employed to provide closures between, for example, separate manufacturing areas within large buildings, warehouses and the like. Goods are often required to be transported from one area of a manufacturing or storage facility to another where one or the other of the areas is heated, air-conditioned or even refrigerated. On occasion, other environmental concerns need to be addressed such as dust, fumes, smoke, dirt, or even noise. Where the traffic is only occasional, conventional doors can be employed to close any doorway between the two areas. Where the traffic is considerable, the use of conventional doors gives way to suspended flexible screens or curtains, which inhibit the wholesale transfer of air from one area to the other yet still permit goods-transporting vehicles such as fork lifts to pass through with little effort. 
   The doors and curtains are generally made of elongated plastic strips that hang side-by-side from a support system mounted to extend across the top of the opening. For safety reasons, it is desirable that the curtain be sufficiently transparent that one operating a transporting vehicle be able to see any hazard or obstruction that might exist on an opposite side of a curtain before proceeding through. Persons on the opposite side of a curtain also desire to be able to see oncoming transport vehicles so appropriate evasive action can be taken. Thus, plastic materials, which were more or less transparent, such as polyvinyl chloride and polyethylene, were adopted as the preferred materials for forming such screens as shown, for example, in U.S. Pat. Nos. 4,095,642, 4,165,778, 4,232,725, 4,289,190, 4,607,678, 5,127,460, and 6,394,171. 
   U.S. Pat. No. 4,312,396 discloses that the strips forming such doors can be transparent, opaque, or in any desired color, depending on the expected use. As a practical matter, however, opaque strips running the full vertical length of a door inhibit the visibility needed by transportation vehicle operators and others as previously indicated. When used a doors, transportation equipment operators have found it desirable for some of the strips in strip curtain doors, such as the outer edge strips or a center divider strip, to be made of a contrasting or different color for delineating either the sides of the opening or the center of a passageway, or both as suggested by U.S. Pat. No. 4,257,471. This has typically been carried out by incorporation a tinting agent in the plastic forming the colored strips that only minimally reduces the transparency of the strips. 
   While such colored strips perform adequately in well lighted situations to identify the sides of a doorway opening, the differences in color become difficult to discern in low light situations. Further no attention has been paid to the overhead margin of the doorway opening, which can be quite important to vehicles that have a variable height requirement. 
   BRIEF SUMMARY OF INVENTION 
   Accordingly, the present invention is directed to an environmental curtain system for at least partially obstructing a passage that is defined by an upper margin and two lateral margins. The system includes a curtain-holding apparatus to be fixed adjacent to the upper margin of the passage for suspending a plurality of flexible transparent strips of the curtain in the passage. The curtain-holding apparatus can be any of a number of designs, including any of the designs disclosed in my earlier filed application PCT/US03/05964. Each of the flexible transparent strips has an upper end fixed to the curtain-holding apparatus and a lower end adjacent to a lower margin of the passage such as the floor. The curtain system also includes a margin highlighter fixed to the curtain-holding apparatus and positioned adjacent to one or more of the lateral or upper margins of the passage. 
   The margin highlighter can include a luminescent agent in sufficient concentration to provide a visible light emission in the event of lighting failure resulting in a significant reduction in overall visibility so that the margin of the passage remains apparent. The luminescent agent preferably has a color in the range of about 500 to 650 nm to enhance its visibility even in low light conditions. The luminescent strip can be formed as a matrix of plasticized PVC or other substantially transparent polymer and a phosphorescent pigment loading of from 0.5% to 30%. The incorporation of the phosphorescent pigment allows the margin highlighter to glow and become visible in reduced light or darkness. The phosphorescent pigments absorb light energy from daylight and artificial lighting, and release it in certain wavelengths in reduced light or darkness. 
   The margin highlighter can also include a fluorescent pigment that allows the highlighter to vividly stand out even in reduced light situations. The fluorescent margin highlighter can be formed as a matrix of plasticized PVC or other substantially transparent polymer and a fluorescent pigment loading of from 0.5% to 30%. While the light emission of a non-fluorescent colorant generally cannot exceed about 10% of its specific wavelength, when a fluorescent color is utilized, the light emission exceeds 10% and can be as much as 300% under certain lighting conditions. This higher light emission is definitely a safety enhancer when used margin highlighters of the present invention. 
   The margin highlighter can take a variety of shapes. A margin highlighter for the upper margin can take the form of a plurality of elements extending downward from the curtain-holding apparatus by between about 3 cm and 30 cm. The upper margin highlighter can have the form of vertically arranged bands overlying the transparent strips of the curtain system. The upper margin highlighter can also have the form of a single horizontal band fixed to the strip holding portion of the curtain-holding apparatus. The upper margin highlighter can also have the form of discrete elements fixed to each of the strip holding elements of the curtain-holding apparatus. The upper margin highlighter can also have the form of the curtain-holding apparatus itself being made of, or coated with, a polymer having a luminescent agent and/or fluorescent agent. 
   A margin highlighter for a lateral margin of the passage can take the form of a geometric pattern of luminescent or fluorescent agent containing bodies fixed to an otherwise transparent strip, the pattern being selected to leave sufficient transparent portions of the strip to maintain sufficient visibility through the strip to observe therethrough any occurrence of movement. The geometric pattern can take the form of horizontal, diagonal or vertical stripes or waves, chevrons, checks, cross-hatches, as well as other pattern. The geometric pattern can be created by lamination, co-extrusion, or other well known processes. Preferably, the surface area of the luminescent agent portions is less than the surface area of the transparent portions of the strips forming the lateral margin highlighter. 
   Any of the embodiments can be made from suitable plastics incorporating visibility enhancing materials such as are disclosed in U.S. Pat. Nos. 5,674,437; 5,904,017; 6,123,871 and 6,375,864 as well as in the prior art therein identified and/or discussed. 
   Additional features and advantages of the present invention will become apparent to those skilled in the art from a consideration of the following discussion of preferred embodiments that referenced the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view of an environmental strip curtain system of the present invention. 
       FIG. 2  is a front elevation of a first curtain-holding apparatus and including an upper margin highlighter of the present invention. 
       FIG. 3  is a side elevation of the apparatus shown in  FIG. 2 . 
       FIG. 4  is a front elevation of a second curtain-holding apparatus including the upper margin highlighter of  FIG. 2 . 
       FIG. 5  is a side elevation of the apparatus shown in  FIG. 4 . 
       FIG. 6  is a detail view similar to  FIG. 3  showing movement of the transparent strips. 
       FIG. 7  is a front elevation view of a third curtain-holding apparatus including another upper margin highlighter embodiment. 
       FIG. 8  is a side elevation of the apparatus shown in  FIG. 7 . 
       FIG. 9  is a front elevation view of the apparatus shown in  FIG. 4  with another embodiment of an upper margin highlighter. 
       FIG. 10  is a side elevation of the apparatus shown in  FIG. 9 . 
       FIG. 11  is a front elevation view of the apparatus shown in  FIG. 4  with yet another embodiment of an upper margin highlighter. 
       FIG. 12  is a side elevation of the apparatus shown in  FIG. 11 . 
       FIG. 13  is a front elevation view of a lateral margin highlighter of the present invention. 
       FIG. 14  is a side elevation of the highlighter of  FIG. 13 . 
       FIG. 15  is a front elevation view of another curtain-holding apparatus constituting an upper margin highlighter embodiment. 
       FIG. 16  is a sectional view taken along line  16 — 16  of the apparatus shown in  FIG. 15 . 
       FIG. 17  is a front elevation view of another lateral margin highlighter of the present invention. 
       FIG. 18  is a sectional view of the highlighter of  FIG. 17  taken along line  18 — 18 . 
       FIG. 19  is an alternative sectional view of the highlighter of  FIG. 17  taken along line  18 — 18 . 
   

   DESCRIPTION OF PREFERRED EMBODIMENTS 
     FIG. 1  shows a perspective view of an environmental strip curtain system  20  that incorporates highlighting features  21  and  22  of the present invention. The curtain system  20  is fixed adjacent a passage  23  through a wall  24 , the passage being defined in part by lateral margins  25 . The strip curtain system  20  includes a strip curtain  26  comprising a plurality of flexible transparent strips  28 , each strip of width W and length L suspended on the curtain holding apparatus  27 , usually in an overlapping pattern. The curtain holding apparatus  27  is fixed adjacent to an overhead margin  29  of the passage  23 . The strips  28  are sufficiently flexible that transportation vehicles  30 , such as fork lifts, can move through the passage  23  in wall  24  by displacing the strips  28  as shown in  FIG. 1 . The general nature and use of such environmental curtain systems  20  are well known, and the present invention is directed at enhancing the visibility of the margins  25  and  29  using overhead highlighters  22  and lateral highlighters  21  as further described herein. 
     FIGS. 2 and 3  show a holding apparatus  27  that includes a plurality of forwardly projecting pegs  30  coupled to bar  31 . Each of the pegs includes an end cap  32  that is somewhat larger in size than the corresponding peg  30 . A fuller description of hardware of this type is to be found in my earlier international application PCT/US03/05964. A plurality of transparent strips  28  can form a strip curtain  26 . Each of the strips  28  can include a plurality of holes permitting the strips  26  to be impaled over the end caps  32  and onto pegs  30 . 
   An upper margin highlighter  22  of the present invention can take the form of a plurality of discrete discs  33 , each disc having a central opening permitting the disc  33  to be impaled over the end cap  32  and onto peg  30  after installation of the plurality of strips  28  forming the strip curtain  26 . The discs  33  can each have a diameter of about 3 cm or more. The discs  33  can include a luminescent agent and/or a fluorescent agent as identified previously. The discs  33  are preferably brightly colored so as to make the upper margin  29  of any passage  23  to which the holding apparatus  27  is mounted highly visible regardless of the lighting situation. 
     FIGS. 4 and 5  show an alternative embodiment for the holding apparatus  27  that includes plurality of threaded fasteners  34  with heads  35  permitting attachment of the threaded fasteners  34  to bar  31  with nuts  36  that can be fixed to a back surface of the bar  31 . The upper margin highlighter  22  can again be in the form of discs  33  containing a luminescent agent and/or a fluorescent agent as identified previously, which are placed onto the threaded fastener  34  adjacent to the head  35 . The threaded fastener  34  can then be pushed through the openings in the strips  28  of the strip curtain  26  and then engaged in threaded nuts  36  that are fixed to bar  31 . The visual effect of the discs  33  forming the upper margin highlighter  22  in the embodiment shown in  FIGS. 4 and 5  can be substantially identical to that shown in  FIGS. 2 and 3 . 
   As shown in  FIG. 6 , displacement of the strips  28  in the direction of arrow A due to movement of transportation vehicles  30  or other equipment through the curtain  26  can cause displacement of the strips  28  to the position shown in phantom. Even under extreme movement, the discs  33  forming the upper margin highlighter  22  can act as a buffer preventing direct interaction of the strips  28  with the back surface of the end cap  32  thus, reducing any tendency for damage to the strips  28  by virtue of such repeated displacement. 
     FIGS. 7 and 8  show an alternative embodiment for a holding apparatus  27  in which an upper portion  37  of the apparatus is intended to be secured to a vertical surface rather than a horizontal surface as in the embodiments shown in  FIGS. 2–6 . The holding apparatus  27  in  FIGS. 7 and 8  can include the threaded fasteners  34  with heads  35  as shown previously in connection with  FIGS. 4 and 5 . The upper margin highlighter  22  can take the form of a horizontally elongated bar  38  containing a luminescent agent and/or a fluorescent agent as identified previously and having a plurality of openings to receive the plurality of threaded fasteners  34 . The bar  38  can have a vertical dimension h of about 3 cm or more, and a horizontal dimension limited merely by the overall width of the strip curtain  26 . The bar  38  can be formed by an extrusion process and pre-punched at the desired spacing for the fasteners  34 . The extruded bar  38  can be rolled lengthwise to provide easy handling prior to installation. 
   A holding apparatus  27  similar to that shown in  FIGS. 4 and 5  is again shown in  FIGS. 9 and 10  together with plurality of strips  28  forming a strip curtain  26 . The upper margin highlighter  22  can take the form of a plurality of vertically elongated bars  39  containing a luminescent agent and/or a fluorescent agent as identified previously. The vertically elongated bars  39  can have an opening in an upper end  45  designed to receive one of the threaded fasteners  34 . The method of assembling of the upper margin highlighter  22  shown in  FIGS. 9 and 10  can be similar to that of the discs  33  shown in  FIGS. 4 and 5 . The vertically elongated bars  39  can have the advantage of extending downward by a distance sufficient to extend at least down to if not into the passage  23 . The vertical dimension of the vertically elongated bars  39  can be from at least 3 cm up to about 30 cm. 
     FIGS. 11 and 12  show a strip curtain holding apparatus  27  as described previously in connection with  FIGS. 9 and 10  with yet another embodiment of an upper margin highlighter  22 . In this embodiment, the upper margin highlighter  22  takes the form of rectangular pads  40  containing a luminescent agent and/or a fluorescent agent as identified previously and having a plurality of openings for receiving two or more fasteners  34 . Again, the vertical dimension of the rectangular pads can be up to 30 cm in length. Of course, it will be appreciated that in both of the embodiments shown in  FIGS. 9–12 , the vertical dimension of the upper margin highlighters  22  should not be greater than that necessary to alert machine operators to the presence of the upper margin of the passageway and should not be long enough to obstruct the view of the machine operator through the transparent strips  28 . 
     FIGS. 13 and 14  show a lateral margin highlighter  21  in the form of a vertical strip  41  including a series of openings  42  to permit engagement with one of the strip holding apparatus  27  previously described. The vertical strip  41  includes transparent portions  43  separated by more translucent or opaque portions  44  containing a luminescent agent and/or a fluorescent agent as identified previously. It will be noted that the transparent portions  43  can be larger in area than the portions  44  including the luminescent and or fluorescent agents, thereby ensuring a sufficient measure of transparency of the strip  41  to retain the ability to see motion through the strip. The luminescent and/or fluorescent agent containing portions  44  can be secured to a continuous strip of transparent material  43  a shown in  FIG. 14 . While  FIG. 13  shows the pattern of the luminescent containing portions  44  to constitute diagonal stripes, other patterns including horizontal or vertical stripes, waves, chevrons, checks, and crosshatches, etc. are possible. 
     FIGS. 15 and 16  show another form of an upper margin highlighter  22 . In this embodiment, the upper margin highlighter  22  takes the form of a strip curtain supporting structure  46  that is molded of a suitable engineering plastic such as a polyacetal, ABS, PEEK, polyamide, and others, containing a luminescent agent and/or a fluorescent agent as identified previously. The structural upper margin highlighter  46  can include a lower vertical portion  47  and an upper portion  48  which can be substantially continuous and horizontal, as shown in  FIG. 6  for corresponding upper portion  37 . The upper portion  48  of the structural highlighter  46  can also be substantially vertical as shown in  FIGS. 7 and 8  for corresponding upper portion  37 . The upper portion  48  can also be as shown in  FIGS. 15 and 16  as merely short segments  49  joined to the lower vertical portion  47 . Webs  50  can extend from the front surface  51  of the lower portion  47  to the lower surface  52  of the upper horizontal segments  49  to reinforce the angular relationship between the upper portion  48  and lower portion  47 . The pegs  53  can be similar in shape to pegs  30  shown in  FIGS. 2 and 3 . The pegs  53  can include a cap  54  having an outermost edge  55  that can be circular. The distal surface  56  of cap  54  can be essentially a truncated cone extending forward from the outermost edge  55  to a distal end portion  57 . The pegs  53  can be secured to the lower vertical portion  47  by various means disclosed in connection with pegs  30 , but are preferably formed as a single one-piece unitary molded structure with the remaining portions of the strip curtain supporting structure  46 . The use of a structural upper margin highlighter  46  in place of a standard curtain holding apparatus  27  eliminates the need for installation of any separate upper margin highlighter  22  such as is disclosed in connection with  FIGS. 2 through 12 , thus lowering material costs and lowering installation time. 
     FIGS. 17 through 19  show a lateral margin highlighter  21  in the form of a vertical strip  58  including a series of openings  59  to permit engagement with a strip holding apparatus  27  or  46  as previously described. The vertical strip  58  includes transparent portions  60  and translucent or opaque portions  61  and  62 , containing a luminescent agent or a fluorescent agent, respectively. The portions  60 ,  61  and  62  can be bonded laminated to each other or co-extruded in any order. That is, portion  61  can contain a luminescent agent while portion  62  contains a fluorescent agent. Alternatively, portion  62  can contain a luminescent agent while portion  61  contains a fluorescent agent. Further either portion  61  or  62  can contain both a luminescent agent and a fluorescent agent.  FIG. 18  is a cross-sectional view of a lateral margin highlighter  59  in which lateral edges  63  of the portions  60 ,  61  and  62  are bonded together or co-extruded so as to form a highlighter  59  of uniform cross-sectional thickness.  FIG. 19  is a cross-sectional view a lateral margin highlighter  59  in which the various portions  60 ,  61  and  62  are laminated face to face to form a layered structure. While the layered structure shown in  FIG. 19  might appear to require more material, and thus be more expensive, the support provided by portion  60  for the entire width of the highlighter  59  enables much thinner layers  61  and  62  to be used, which can result in a total lower cost, depending on the thickness of the various layers. The visual pattern of vertical stripes should appear to be similar if not identical in the structures of both  FIGS. 18 and 19 . 
   In all the forgoing embodiments, the luminescent and/or fluorescent agent should be present in an amount sufficient to render the margin highlighters  21  and/or  22  highly visible in even low-light situations. It should be understood that the foregoing detailed description should be regarded as illustrative rather than limiting, and the following claims, including all equivalents, define the spirit and scope of this invention.

Summary:
A margin highlighter is fixed to a strip curtain-holding apparatus and positioned adjacent to one of the lateral or upper margins. The margin highlighter including a luminescent agent in sufficient concentration to provide a visible light emission in the event of lighting failure, the luminescent agent having a color in the range of about 500 to 650 nm.