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You are an expert at summarizing long articles. Proceed to summarize the following text: 
BACKGROUND OF THE INVENTION 
     It is a familiar practice to also use roller curtains made from laths for sun protection. For this purpose, a user will let down the roller curtain a bit, so that the roller curtain casts an appropriate shadow. Relatively little light gets through the roller curtain itself. The ratio of slots to the overall surface is about 1.5%. As a result, the roller curtain generally cannot be let down entirely for sun protection purposes since the resulting darkness would be too deep. 
     Known roller curtains are made from individual laths with a bottom with an undercut channel and a hooked slat at the top. Extremely tiny slots, relative to the surface of the roller curtain, are situated in the area of the hooked slat. Thus, larger slots cannot be provided on the main body of the lath since it no longer would be possible to control the admission of light by rolling the roller curtain up or down. 
     Known laths have a roll shaped profile that is often packed with foam or provided with crosspieces running in the longitudinal direction of the lath in order to achieve the necessary strength. 
     BRIEF SUMMARY OF THE INVENTION 
     In view of the foregoing, a general object of the present invention is to create a new type of lath. 
     According to one aspect of the invention, a lath is provided which comprises a roll shaped part that does not require any further reinforcement measures on the inside. 
     According to another aspect of the invention, a lath is provided which affords good sun protection by preventing direct admission of sunlight when the sun is high in the sky while still allowing a lot of indirect light to get through the lath. 
     The roller shutter lath of the present invention can be made as a single piece from a strip of metal by a rolling shaping process. The roller shutter lath has a slat on its top side or upper edge that terminates in a channel that is open toward the bottom relative to the normal usage position. This arrangement produces a hook-like structure when viewed from the side that joins the roller shutter lath with another roller shutter lath located above it. The roller shutter lath also has a body on which the slat is formed as a single piece. At the lower side of the lath body there is a slot that is designed to receive the roller shutter lath located below. The roller shutter lath has a constant cross section across its length. 
     Since the new roller shutter lath can be made as a roll shaped part, any material suitable for rolling can be used including, for example, special steels, materials that otherwise would not be suitable for a roller shutter lath. Additionally, making the roller shutter lath as a roll shaped part allows the area of roller shutter body to be made relatively voluminous so that the final roller curtain has a large thickness and is therefore quite durable. 
     Because special steels can be used as the starting material, the roller shutter lath of the present invention is extremely weather-resistant and can be used in areas where aluminum would fail. For example, areas where a roller shutter lath of the present invention which is made of special steel materials can be used are the food industry or near sea water, even aboard ships or oceangoing containers. Moreover, because special steels can be used, the roller shutter lath of the present invention can be relatively resistant to forced entry, i.e., it takes a very long time to forcibly open the roller shutter curtain. According to one embodiment, the new roller shutter lath also can advantageously be made from coated aluminum. 
     Particularly favorable conditions result when the roller shutter lath has a continuous two-ply construction in terms of the cross section. With such a construction, one can employ a thin sheet metal for the rolling and forming while still producing a finished lath with a sufficient wall thickness. 
     Even though the roller shutter lath as a whole is has a two-ply construction, the individual segments could be single-ply or two-ply depending on the desired design. In particular, this can be the case for the slat, the area of the channel, the front side, the back side, or the bottom side. 
     For producing a particularly reliable locking together of the roller shutter laths and the facilitating mobility, the slot can be bounded by two parallel edges with at least one of the edges being curved upwards in the direction of the interior of the lath body. Such an arrangement produces a defined hanging edge for the channel on the hanging slat of the underneath lath. It can be particularly advantageous if the roller shutter lath has a double-ply construction in this area in order to easily support the weight of the entire roller curtain. 
     With the roller shutter lath of the present invention, the individual metal sheet layers can lie tightly and directly against each other except for in the root area of the slat. However, the layers can be separated from each other in the area of the front side so as to create a substantially enclosed chamber that can be packed with hard foam if so desired. 
     Advantages with respect to self-cleaning properties can be achieved if the lath is bounded on its front side by a surface that emerges from the slat, slants downward and then merges into a vertical surface. This slanting surface helps prevents areas where grime can build up. 
     If it is desired to allow light and/or air to still get in when the roller curtain is for the most part closed, elongated light slots can be located in the area of the slat between the roller shutter body and the molded-on channel. The height of these light slots can correspond to the height of the slat so that when the roller curtain is hanging down, the upper lath does not project into the light space profile of the light slot. 
     The new roller shutter lath has a lower side that extends horizontally or, if appropriate, slants upward from the front side in the direction of the slot. In this way, dripping water cannot get into the region of the slot and penetrate through the light slots. 
     The lath of the present invention can have a slat at its upper edge whose height is relatively large in comparison to the lath body. With such an arrangement, it is possible to form very large light/air slots in lath. The lath body can itself function as a sun canopy for the light slot of the lath located underneath. Thus, in an assembly of laths each of the laths can act like a small sun canopy that shades the light slot underneath from direct solar radiation. 
     A shutter curtain using the lath of the present invention divides the window surface into several light-transmitting strips situated one above another with each strip being formed by the respective light/air slot in the particular lath. Because of this division into strips, only relatively short projecting “sun canopies” are needed to accomplish the desired shading action for the light/air slots even when the sun is still relatively low in the sky. If there were no gap between the light-transmitting strips, a more protruding sun protection roof may be required. 
     With a division into spaced apart narrow strips, the spatial depth of the sun protection roof is reduced and can be accommodated within the thickness of a lath. 
     A curtain using the laths of the present invention lets through a great deal of indirect light while only shading incident sunlight. Accordingly, the shutter curtain can be let down entirely in the summer on a window outfitted with such a shutter curtain. The room with the window will remain bright, but the direct solar radiation will be blocked and unwanted heating of the room due to the direct solar radiation will be prevented. 
     The arrangement of the invention can operate in relatively narrow guide rails inside the room. In one embodiment, the thickness of the lath body viewed in the direction parallel to the normal line of the window surface is around 8-15 mm, while the height of the lath body varies between 8 and 15 mm (preferably, 10 mm). 
     Those skilled in the art will appreciate from the following figures and description of the illustrated embodiments that a number of changes can be made to the roller shutter lath based on the particular usage requirements or during the rolling and forming process. To present each individual modification would needlessly expand the description. The particular dimensions used will correspond to the particular requirements of a given application. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a highly schematic perspective view of an illustrative window or door shutter utilizing a shutter curtain including roller shutter laths according to the present invention. 
         FIG. 2  is a front view of a first exemplary embodiment of a roller shutter lath according to the invention. 
         FIG. 3  is a front view of an assembly of two roller shutter laths according to  FIG. 2 . 
         FIG. 4  is a side view of a second exemplary embodiment of a lath according to the present invention that has been fabricated as a rolled and formed part. 
         FIG. 5  is a side view of a third exemplary embodiment of a roller shutter lath according to the present invention that has been fabricated as a rolled and formed part. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to  FIG. 1  of the drawings, a roller shutter curtain  1  is shown such as is used for windows or roll down doors. A majority of the extent of the roller shutter curtain  1  is unwound from a winding shaft  2  to which the upper edge of the roller shutter curtain is fastened. The roller shutter curtain  1  includes a plurality of individual roller shutter laths  3 , each of which can move to a limited extent about an axis that lies parallel to the axis of the winding shaft  2 . 
     The cross sectional profile of each individual lath  3  is shown in  FIG. 2 . As shown in  FIG. 2 , the roller shutter lath  3  includes a base body  4  and a slat  5 . The slat is formed at the upper edge of the base body and is curved into a downward opening channel  6  at its free end away from the base body  4 . The lower side of the lath  3  contains an interengagement slot  7 . 
     The base body  4  defines a front wall including first and second front wall segments  8  and  9 . The first front wall segment  8  slopes downward at an angle of around 45° from the slat  5  in the state of use shown in  FIG. 2 . At its lower end, the first front wall segment  8  passes into the vertical second front wall segment  9  and is integral therewith. The lower free edge of the second front wall segment  9  is adjoined by a bottom side  10  that extends from a transitional edge  11  to a slot edge  12 . 
     At the upper end, the front slanting first wall segment  8  merges with the slat  5 , running at an angle of around 10° to the vertical. The upper free end of the slat  5  extends into the downward opening channel  6 . The position of the channel  6  should be chosen such that its highest point in a usage position lies on a vertical line above the slot edge  12 . The back side of the slat  5  is adjoined to a rear wall  14  via a bend piece  13  that extends roughly vertically when in a state of usage. The rear wall  14  terminates at an edge  15  that forms the other edge of the slot  7 . Accordingly, the edge  15  is offset from the edge  12  in the horizontal direction. As also shown in  FIG. 2 , the illustrated roller shutter lath  3  has a two-ply construction with respect to its profile. 
     The roller shutter lath  3  is produced from an appropriately wide metal strip of a suitable material, such as coated aluminum sheeting or stainless steel (such as V2A or V4A steel) by a rolling process. One edge of the raw metal strip material, in this case the edge  17 , lies at the free end of the channel  6 . From that point, the formed material first follows the inner curvature of the channel  6  and then passes over to the outer layer of the slat  5 . As a result of the forming process, in the lower region of the slat  5  the metal strip produces the outer layer of the slanting first front wall segment  8  and then passes into the outer layer of the vertical second front wall segment  9 . Additionally, the metal strip adjoins the edge  11  in the outer layer of the bottom surface  10 . From there it extends to the slot edge  12 . At the slot edge  12 , the material is bent over onto itself and extends as the inner layer of the bottom surface  10  up to the edge  11 . Here, the material rises vertically upward and it lies closely against the outer layer of the second front wall segment  9 . The sheet metal material then continues as the inner layer of the slanting first front wall segment  8 , lying directly against its back or inner side, as far as the root of the slat  5 . Here, the formed metal strip provides a partly cylindrical curved surface  18  as the inner layer of the bend piece  13 . Adjoining this, the formed metal strip provides an interior layer of the rear wall  14 , and thus up to the slot edge  15 . Here, the metal strip is bent over onto itself by 180°, and from this point on it forms the outer layer of the rear wall  14 . The metal strip follows the rear wall  14  until roughly the apex of the concavely curved surface  18  or the bend piece  13 . 
     As shown in  FIG. 2 , after being formed the metal strip provides the layer of the slat  5  that lies toward the room or window side, as far as the channel  6 . Here, the formed metal strip runs along the outer side of the channel  6  and finally, after the last forming process, it encloses the free lengthwise edge  17  of the metal strip in a U-shape. The other edge  19  of the metal strip lies inside the channel  6 . This prevents any joint surfaces from being open to the outside. The joint surface is protected by the short wraparound  20  at the free end of the hook. With respect to the starting material, the two edges  17  and  19  are parallel to each other. The starting material is endless, as is usual with roller forming processes. 
     The roller bending forming process is carried out in such a way that, with the exception of a small triangular region at the root of the slat  5 , two layers that lie close against each other without any gaps are produced in all locations. The two lengthwise edges  17  and  19  of the strip like starting material lie in close proximity to each other in the region of the channel  6  which forms a hook. As further shown relative to the connection of the roller shutter laths  3 , the edges are thereby located in a protected region that helps prevent the possibility that the two layers might separate from each other at some place. 
     Due to the special configuration of the first and second front wall segments  8  and  9  in relation to the rear wall  14 , the lath body  4  forms a relatively large, approximately triangular cavity  21  which, apart from the ends of the lath  3 , is accessible only via the slot  7 . The sheet metal does not have any free edge in the area of the slot edges  12  and  15 . There, the material is turned over onto itself so as to provide good strength. The cavity  21  is free of slats or braces. 
     In order to allow light and air to pass when the roller shutter curtain  1  is hanging down, the illustrated slat  5  is provided with air or light slots  22 . These slots  22  extend longitudinally. In particular, the slots  22  extend with their major axis parallel to the lengthwise dimension of the roller shutter lath  3  and have a vertical height limited to the area from the upper edge  13  to beneath the channel  6 . 
       FIG. 3  illustrates how two neighboring laths  3  are joined together. The lath  3   b  located beneath the lath  3   a  hangs with its channel-shaped profile segment  6  over the slot edge  12 . So as to produce the most defined conditions possible, the illustrated lower wall  10  is bent upward at an angle of around 30° at a short distance from the slot edge  12 . This produces a bend  23  which ensures that the back side of the slat  5  does not touch the slot edge  15  when the roller shutter curtain  1  is hanging down. This enables the roller shutter curtain  1  to be rolled up easily with the back wall  14  facing the axis of the shutter shaft  2 . 
     The lower wall  10  extends horizontally or, starting at the slot  7 , slightly downward slanting manner to the edge  11  in order to serve as a drip edge when used outdoors that keeps water draining from the slanting first front wall segment  8  away from the slots  22 . The slanting first front wall segment  8  ensures that the lath  3  increases in volume in the thickness direction while preventing dirt deposits. Furthermore, incident light is reflected so that glare cannot get through the light slot  22  by virtue of multiple reflections at the lower wall  10 . 
     The width of the slot  7  is dimensioned so that the lath  3   b  suspended therein can swivel sufficiently about an axis (that is perpendicular to the plane of  FIG. 2 ) relative to the lath  3   a  situated above it. 
     The height of the slat  5  up to the lower edge of the channel  6  is around 30% to 60% of the height of the lath body  4 . The height of the light/air slot  22  is around 40% to 80% of the height of the slat  5 . When hanging down, the surface component of the light/air slots  22  is around 20% to 30% of the overall surface of the roller shutter curtain  1 . Due to this relatively large proportion, a large amount of diffuse, scattered light can get in via the light/air slots when the roller shutter curtain  1  is completely deployed and spread out in front of a window. On the other hand, the lower side  10  projecting out from the light/air slot acts as an awning or sun canopy casting a shadow on the light/air slot and prevents direct solar radiation from getting through the light/air slot. Depending on the relation between the height of the light/air slot  22  and the amount of projection, this shadowing effect occurs as the sun moves through the sky down to around 22° above the horizon. 
     The light/air slots  22  uniformly divide the window surface into light-transmitting strips, each strip having its own awning casting its own shadow. This reduces the size of the projection of the sun canopy as compared to an arrangement in which the light slots are joined to each other. Such an arrangement would require an “awning” that projects far out to cast the same shadow with the same angle of incidence. 
     With an arrangement according to the present invention, the roller shutter curtain  1  can be used on the inside of the window, since its overall thickness measured in the direction perpendicular to the window surface is around 8-15 mm. Moreover, a roller-type lath according to the invention allows roller shutter curtains  1  to be constructed which prevent direct solar radiation in the summer and thus reduce room heating, while still allowing sufficient daylight to reach the room. 
     The high proportion of transparent surface due to the large slots also significantly improves the subjective perception of transparency. A person in the room can see out better through a roller shutter curtain made from laths according to the present invention. There is no feeling of being “closed in.” A roller shutter lath of the present invention does not prevent visual contact with the outside world, as is the case with known roller shutter laths. 
     If the roller shutter curtain  1  is placed on the window sill and the roller shutter curtain  1  collapses on itself, the slat  4  at each roller shutter lath  3  disappears entirely in the lath body  4  so as to achieve a total darkening even for diffuse light. 
     A roller shutter curtain  1  made from the laths of  FIG. 2  or  FIG. 3  across the front wall segment  9  can be easily rolled up. Moreover, the roller shutter curtain could be wound up in the opposite direction, i.e. wherein the front side faces the winding shaft. 
     In the embodiment of  FIG. 2 , the channel  6  that serves as a hook and thus a form-fitting connection mechanism points downward with a component away from the front side of the roller shutter lath  3 . The embodiment of  FIG. 4  illustrates that is possible to reverse the orientation of the channel  6  that serves as a hook. In the embodiment of  FIG. 4 , the channel  6  again opens downward, but with a component away from a surface that is defined by the rear wall  14 . 
     In order to hook together the roller shutter laths  3  in the vertical direction of the roller shutter curtain  1 , the profile is slightly modified in the vicinity of the rear slot edge  15  in the embodiment of  FIG. 4 . The double-ply rear wall  14  passes into an upwardly open channel  25  at its lower end, so that the slot edge  15  is situated at the free edge of an upwardly pointing bend  26 . The slot edge  12  lies directly at the end of the lower wall  10 , which in this case is not bent upward. The roller shutter lath  3  located underneath hangs by its channel  6  over the slot edge  15 . 
     In the embodiments of  FIGS. 2 and 4 , the layers of the starting material lie closely against each other in all possible locations. An embodiment in which an additional chamber  27  is formed in the area of the slanting first front wall segment  8  and the vertical second front wall segment  9  is shown in  FIG. 5 . In this area, one segment  28  of the inner layer is displaced in the direction of the rear wall  14 . This produces a closed chamber  27 . This chamber  27  can be packed with hard foam from the side. The cavity  27  has a right trapezoidal cross-sectional shape. 
     A roller shutter lath is provided that consists of a profile that is formed from a flat metal strip by a rolling process. The roller shutter lath comprises, as a single piece, a shutter body with a slot contained at the bottom side and a hooked slat provided at the top edge. The proportion of slots in the overall surface of the roller shutter lath is around 20%.

Summary:
The invention relates to roller blind slats having a profile which is shaped by flat sheet metal in a rolling step. A single-pieced roller blind body is associated with the roller blind slats. The roller blind body is formed with a slot on the underside thereof and a hooked strip is provided on the top edge thereof. The slot part is approximately 20% on the total surface of the roller blind slats.